MUST University

Faculty of Dentistry Department of Prosthodontic

Principles of

REMOVABLE COMPLETE

PROSTHODONTICS Advanced clinical course

(502)

By

Prof. Dr. Amal F. Kaddah Professor &Chairman, Department of Prosthodontics

Faculty of Dentistry Misr University for Science and Technology

AMAL F. KADDAH

Principles of

REMOVABLE COMPLETE

PROSTHODONTICS Advanced clinical course

(502)

2007-2008

Contributors

MEMBERS OF PROSTHODONTIC DEPARTMENT

Prof. Dr. Prof. Dr. Prof. Dr. Prof. Dr. Amal KaddahAmal KaddahAmal KaddahAmal Kaddah

Prof. Dr. Yusr Omar MadyProf. Dr. Yusr Omar MadyProf. Dr. Yusr Omar MadyProf. Dr. Yusr Omar Mady

Dr. Iman Rostom.Dr. Iman Rostom.Dr. Iman Rostom.Dr. Iman Rostom.

Dr.Dr.Dr.Dr. Fardous Fardous Fardous Fardous

Dr. MostafaMostafaMostafaMostafa

Dr. Eatemad Taha RekabyEatemad Taha RekabyEatemad Taha RekabyEatemad Taha Rekaby.

DrDrDrDr. . . . Fathy KaddahFathy KaddahFathy KaddahFathy Kaddah 1914 - 1967

A great father, an honored clinician

and a superb teacher. He enriched my life by his kindness,

patience and respected memory

Dedicated to

My daughters who gave

a meaning to my life

AcknowledgmentAcknowledgmentAcknowledgmentAcknowledgment

First of all I would like to thank God who paved the way and only by his will every thing can be achieved.

I would like to express my thanks, deepest respect and sincere gratitude to Dr. Khaled El Toukhy for his kind appreciation and superb veneration that have been of great assistance to me in the preparation of this work .

Words are not enough to express how deeply I am grateful to Prof. Dr. Amina Ads. I owe her a sincere appreciation and due thanks for her human concern, great devotion, and continuous encouragement, without her support, the completion of this work would have been impossible.

I would like to express my heartfelt thanks and sincere appreciation to my husband Prof. Dr. Essam El Ghamrawy for his immeasurable support and encouragement for making facilities possible to carry my work forward. Without his infinite patience and understanding for the time and effort required this book wouldn’t have been produced.

I am deeply grateful to Professor Dr. Adel Abdel Hakeem for his cooperative assistant and for scarifying much of his time for pre-editing the manuscript, I will remain indebted to him and always remember his superb cooperation in the development of this work.

I wish also to acknowledge all the members of the staff of my department who have made many helpful suggestions for improvements and particularly to Dr. Fardous , Dr. George and Dr. Sahar Khalaf who have assisted in proof reading the manuscript and for their constructive suggestions and helpful concern which have been of great values to this work.

My thanks are also to all professors, publishers, and editors for their permissions to utilize passages and illustrations from their books and papers.

Amal KaddahAmal KaddahAmal KaddahAmal Kaddah....

CHAPTE I MANAGEMENT OF FLABBY RIDGES

MANAGEMENT OF FLABBY RIDGES

The main problems associated with improper denture use are

hypertrophy and inflammation of the basal seat mucosa (Flabby

ridges).

Hyperplasia: It is the abnormal multiplication or increase in the

number of normal cells in normal arrangement in tissue.

Fibrous hyperplasia of the mucosa is irreversible and

necessitates surgical removal (Fig.1-1: 1-6).

Hypertrophy of the mucosa: It is a bulk of tissue beyond

normal size, caused by an increase in volume but not in

number of tissue elements. It is usually reversible and will

resolve when the source of trauma is removed,

Flabby ridge tissues are commonly found at the maxillary

anterior region and are usually associated with a maxillary

complete denture opposing natural mandibular anterior teeth

without posterior replacements. This also occurs if a mandibular

partial denture is present but no longer provides for posterior

occlusal support due to tissue changes (Fig.1-7). In such

instances, localized severe areas of resorption occur at a more

rapid rate than the overlying soft tissues resulting in redundant,

easily displaced "Flabby" residual ridge.

The management of hypertrophic mucosal tissue or flabby

ridges could be achieved by rehabilitation of the abused oral

tissues.

7

CHAPTE I MANAGEMENT OF FLABBY RIDGES

Forms of hyperplasia and Location of Flabby Tissue

- Single or multiple flaps or folds of fibrous tissue related to the border of a denture (Fig.1-3, 1-8).

- The lesion may be localized, or generalized over the entire ridge crest (Fig.1-5, 1-6).

- Most common: Anterior segment of maxillary and mandibular ridges (Fig.1-1, 1-2).

- Posterior segment of mandibular ridge.

Causes:

Abused oral mucosal tissues covering the denture bearing area may be related to any of the following conditions:

1- Long denture use without serviceability i.e. without relining or rebasing of the dentures when indicated (Fig.1-8).

2- Load concentration on the anterior segment of the ridge as a result of decreased vertical dimension accompanying occlusal wear.

3- Complete maxillary denture opposing natural mandibular anterior teeth and partial denture (Fig.1-7).

4- Not removing denture during night to allow the basal seat mucosa to regain its resting form.

5- Badly constructed dentures such as loose ill-fitting dentures as well as dentures with wrong centric occluding relation, occlusal disharmony and traumatic occlusion.

6- Dentures constructed with anterior porcelain teeth and posterior resin teeth.

7- Over-eruption of natural teeth against edentulous span.

8

CHAPTE I MANAGEMENT OF FLABBY RIDGES

Fig.1-1: flabby ridge Fig.1-2 hypertrophied mucosa

Fig.1-3: hyperplasic tissues Fig.1-4: epulis fissuratum.

Figs.1-5, 1-6: The lesion may be localized, or generalized over the entire ridge

crest.

Fig.1-7: Complete maxillary denture opposing natural mandibular anterior

teeth and partial denture.

Fig.1-8: The primary cause of this condition is over extension of denture border which may be the result of sinking of the denture.

9

CHAPTE I MANAGEMENT OF FLABBY RIDGES

The rehabilitation of abused oral tissue:

The rehabilitation of abused oral tissue is to allow the hypertrophic, traumatized and inflamed tissues to regain its original form.

Treatment plan and recovery program :

1- Removal of the cause: ie: Remove the denture from the patient's mouth for few days before making new impressions to allow the inflammation to subside. However, this procedure does not suit every patient especially those with some social obligations.

2- Another line of treatment is to treat each case by elimination of the cause and then, start a recovery program to allow the tissues to regain its normal healthy form.

The treatment is as follows:

a. Detect and Correct any pressure area or sore spot using pressure indicating paste (PIP).

b. Correct the adaptation of the denture base to the underlying tissues using tissue conditioning material (TCM) (Fig.1-9 a: f). This material should be changed every 72 hours as the plasticizer will be leached out on long standing in the patient's mouth and thus, the material will lose its conditioning effect.

c. Correction of occlusal disharmony by clinical remounting procedure.

d. Elimination of contact between natural anterior teeth and opposing artificial teeth.

e. Restoring the lost occlusal vertical dimension: To correct the occlusal vertical dimension, a dough of self curing acrylic resin is applied to the palatal cusps of the second premolar and first molar of the maxillary denture after Vaseline application to the opposing mandibular teeth (Sears and nelson occlusal pivots) (Fig.1-10).

10

CHAPTE I MANAGEMENT OF FLABBY RIDGES

a b

c d

e f

Fig.1-9 a:f: Tissue conditioning material application

11

CHAPTE I MANAGEMENT OF FLABBY RIDGES

a b

Fig.1-10 a, b: Restoring the lost occlusal vertical dimension.

a b

Fig.1-11: a, Add tooth- colored self –curing resin on the posterior occlusal surfaces of the mandibular denture.

B, When the patient closes the mouth with the mandible guided to the centric occlusal position, the occlusal surfaces of maxillary posterior teeth are recorded in the resin. Trim the resin to reestablish the contours of the teeth.

This will help to:

- Restore the correct vertical dimension.

- Restore the correct position of the condyle.

- Eliminate the load on the anterior segment.

12

CHAPTE I MANAGEMENT OF FLABBY RIDGES

Recovery program :

It consists of:

1- Massage of the soft tissues two or three times a day to stimulate the blood supply and aid in recovery.

2- Instruct the patient to dissolve one-half teaspoon of table salt in a half glass of warm water and vigorously swirl the solution against the tissues by inflating and deflating the cheeks.

3- The removal of the dentures from the mouth for at least eight hours of the twenty-four hours. Patients usually agree to this program, since it can be accomplished during sleeping hours.

If the condition persists after this recovery program, than the treatment will be either:

- Surgical removal of the hypertrophic tissues.

- A modified impression making procedure (Sectional impression technique) can be used to record this tissue under minimal pressure without distortion as any distorted tissue tends to rebound leading to denture instability.

Prosthetic management:

1- Primary impression is made using alginate impression material of low viscosity.

2- Secondary impression is made applying the selective impression technique. Or using two stage (Sectional) impression technique as follows:

• Acrylic special tray is constructed having a window opposite the area of flabby tissues (Fig.1-12, 1-13).

13

CHAPTE I MANAGEMENT OF FLABBY RIDGES

• Border moulding is carried out in the usual manner and zinc oxide and eugenol impression is made and excess passing through the widow is trimmed out (Fig.1-14, 1-15).

• The flabby area is recorded using plaster impression material applied with a brush several times with the secondary impression in place. After the impression plaster sets, an overall impression using a suitable stock tray loaded with impression plaster is used to remove both sections together (Fig.1-16).

• The jaw relation is recorded using check bite technique (with the least possible displacement of the supporting structures) (Fig.1-17).

3- Cross-linked cuspless acrylic teeth are used to decrease the lateral component of force.

4- Teeth are placed in relation to the neutral zone and the bucco-lingual width should be reduced.

5- After denture insertion, the patient is instructed for periodic check-up of the denture.

N.B.: - Final impression should be done according to the degree of mucosal displacement.

- If the fibrous tissue is distorted during impression taking, by occlusal pressure. Elastic recoil of displaced tissue forces the denture downwards and eliminates retention (tissue rebound). In addition intermittent occlusion can traumatize the tissues.

- MMinimal displacement could be achieved by taking a working impression in a spaced tray using an impression of low viscosity as impression plaster or low viscosity silicone impression material (Fig.1-18)

- 14 -.

CHAPTE I MANAGEMENT OF FLABBY RIDGES

a b Fig.1-13: A close fitting tray is constructed in cold-curing acrylic resin and designed so that flabby area of the ridge is uncovered.

Fig.1-14: Border moulding is carried out in the usual manner.

Fig.1-15: zinc oxide and eugenol impression is made and excess passing

through the widow is trimmed out - 15 -

CHAPTE I MANAGEMENT OF FLABBY RIDGES

Fig.1-16: The flabby area is recorded using plaster impression material applied with a brush several times with the secondary impression in place.

Fig.1-17: check bite technique: C.O.R should be recorded with the least possible displacement of the supporting tissue by applying minimal closing forces on an easily displaceable recording material as using softened wax or silicon or mix of plaster.

Fig.1-18: MMinimal displacement could be achieved by taking a working

impression in a spaced tray using an impression of low viscosity

ADVANCED RESORPTION OF THE RESIDUAL

ALVEOLAR RIDGE

Introduction:

Advanced resorption of the ridges in the edentulous patient has

multiple causes. It may occur in all edentulous patients, but is most

often observed in the advanced age group. It is an irreversible

process.

The loss of alveolar bone is more pronounced in the mandible

than in the maxilla. The differential residual ridge resorption between

the mandible and the maxilla providing a smaller surface area for

support. The magnitude of bone loss is extremely variable, bone

resorption in the mandible may be severe, to the extent that the

mental foramen may be located near or directly at the crest of the

ridge (Fig. 2-1: 2-7).

One constant, relatively unchanging structure on the

mandibular denture bearing surface is the retromolar pad (Fig. 2-2).

The pad contains glandular tissue, loose areolar connective

tissue, the lower margin of the pterygomandibular raphe, fibers of the

buccinator, and superior constrictor and fibers of the temporal

tendon. The bone beneath does not resorb secondary to the pressure

associated with denture use.

The retromolar pad is one of the primary support areas.

- 17 -

Etiology:

The conditions causing alveolar ridge atrophy can be classified

according to biologic, anatomic and functional prosthodontic factors.

1-Biologic metabolic factors:

a. Age: Ridge atrophy generally increases with senescence.

b. Sex: Alveolar atrophy occurs most often in the female. There

is usually a hormonal imbalance after menopause with an

increase of anabolic hormones and a decrease of estrogen

which causes demineralization and osteoporosis of the bone.

c. Nutritional: Dietary deficiencies, such as calcium

deficiency, decrease in vitamin C intake and/or protein

utilization and/or dysfunction of carbohydrate metabolism, are

contributing factors.

b. Systemic health: Blood dyscrasias prevents proper tissue

nourishment. Uncontrolled diabetes and other debilitating

disease cause metabolic hard and soft tissue destruction with a

decrease in tissue resistance.

e. Treatment for systemic diseases: Radiation therapy reduces

bone regeneration Hormonal drugs may have an adverse effect

on the soft and hard tissues.

f. Loss of natural teeth: Extraction of the natural teeth causes the

reduction of the residual ridge. Severe periodontal disease also

contributes to more alveolar atrophy than when the teeth are

lost due to dental caries.

- 18 -

2-Anatomic factors:

a. Type of bone: Cortical bone will resorb slower than cancellous bone.

b. Size and shape of the ridges: Well-formed broad ridges will show less resorption than narrow thin ridges as the force received per unit area will be less in the former.

c. Facial skeletal morphology: Individuals with longer faces and obtuse gonial angle are more likely to have atrophy of their ridges than those with short faces and right angle gonial angle.

3-Functional/prosthodontic factors:

a. Functional factors: Habits with complete dentures such as bruxing, grinding and tapping of teeth may cause advanced resorption of the ridges depending upon the frequency, direction and amount of force to the remaining residual ridges.

b. Prosthodontic factors:

1- Long denture use without serviceability.

2- Improperly made dentures with improper vertical dimension of occlusion, centric relation, non balanced occlusion and incomplete coverage of basal seat area.

3- Constant wearing of dentures without giving rest to the basal seat tissues during night hours.

4- Porcelain teeth and/or anatomic teeth with high cusp angles transmit more force to the underlying ridge tissues.

All these factors contribute to severe resorption of the residual alveolar ridge.

- 19 -

Fig.2-1 A,f : pattern of bone resorption of the mandible.

Mental Foramen is the anterior exit of the mandibular canal and the inferior alveolar nerve. In cases of severe residual ridge resorption, the

foramen occupies a more superior position and the denture base must be relieved to prevent nerve compression and pain.Note the position of the

mylohyoid ridge as it varies relative to the degree of alveolar ridge resorption.

Fig.2-2: One constant, relatively

unchanging structure on the mandibular denture bearing surface is the retromolar pad.

Fig.2-3: In severe alveolar ridge resorption the genial tubercles appear on the surface of the mandible.

Fig.2-4:Palpate the mylohyoid

ridge to determine its contour, sharpness and degree of undercut.

Fig.2-5: In severe alveolar ridge resorption, the mylohyoid ridge becomes prominent and cause pain when pressure is applied by the denture.

Fig.2-6: Fig.2-7: The external oblique ridge runs outside the buccal shelf bone anteroposteriorly. it is not involved in resorption

Fig.2-8: ridge augmentation

Fig.2-9: Vestibuloplasty Fig.2-10: Distraction implant

Fig.2-11a,b: Osseo-integrated implants:

- 21 -

Management:

Either surgical or prosthetic management:

1- Prosthetic management with surgical intervention:

a. Vestibuloplasty: It is a surgical procedure designed to restore alveolar ridge height and/or width by detachment of buccal and/or labial and lingual tissues. These tissues are positioned at a lower level on the bone to obtain maximum height of the residual alveolar ridge (Fig. 2-9).

This could be achieved by any of the following techniques:

i. Mucosa advancement: The subepithelial connective tissue and muscle insertion are separated from the mucosa and periosteum through supraperiosteal tunnels. The free mucosa is then advanced to its new position by an over extended border of a carefully made surgical stent.

ii. Secondary epithelialization procedure: An apically repositioned flap is sutured to the periosteum at a predetermined vestibular depth. A surgical stent lined with tissue conditioning material is helpful in retaining the flap in position and promoting rapid healing of the denuded tissues.

Vestibuloplasty with epithelial grafts: This approach is similar to the secondary epithelialization procedure except that the denuded tissue is covered with a free epithelial graft (skin, buccal or palatal mucosa) and is not left to heal by secondary intention.

b. Removal of genial tubercles: This is done to provide for an extension in the sublingual fold space.

c. Prominent mylohyoid ridge: It is some times trimmed to allow proper extension of the lingual flange of the mandibular denture.

- 22 –

d. Ridge augmentation: This procedure is used to increase the width and height of the residual alveolar ridge. A variety of materials has been used for this purpose such as:

• Autogenous bone (from the iliac crest or rib), Non-autogenous bone and Hydroxy apetite (either in the granular or block form). Injected through one or more subperiosteal tunnels to build up sufficient height of the residual ridge.

Bony augmentation of the alveolar ridges often undergoes resorption in a short period of time whereas the non-resorbable hydroxyapetite prevented this problem.

The block form of hydroxyapetite material avoids many of the problems accompanying the use of the granular form such as: Diffusion into adjacent areas resulting in disfigurement of the patients face, Paresthesia and reduction in the planned height of the alveolar ridge.

e- Distraction implants: Recently alveolar ridge distraction has been introduced for augmentation of the atrophied mandible and maxilla by the help of distraction implant which contain two mobile endosteal parts which enable heightening of the alveolar ridge up to 6mm. The prosthetic super structure is loaded 4 to 6 months after distraction. The advantage of distraction is that there is no need for donor site, simultaneous lengthening of the surrounding soft tissues as skin, muscles, blood vessels and nerves. The disadvantages include a long treatment period, need for a suitable distracter and danger of infection (Fig. 2-10).

f- Osseo-integrated implants: For patients with atrophic edentulous

mandible, the placement of two or more implants anteriorly in the area between the two mental foramina can be of value in improving horizontal stability and retention of the constructed implant supported overdenture. These implants can be used with or without ridge augmentation (Fig. 2-11).

- 23 -

II- Prosthetic Management without Surgical Intervention

An ideal impression should provide:

1- Maximum extension without muscle impingement.

2- Intimate contact with the tissue area covered.

3- Proper form of the borders including the posterior border of the maxillary denture.

4- Proper relief of hard and sensitive areas.

Different impression techniques could be made according to the condition of the supporting tissue:

1- Muco-compressive impression technique:

- Primary impression is made with impression compound using suitable stock tray (Fig. 2-12).

- A rough record of ridge relationship is made using T-shaped roll of wax seated intraorally between the upper and lower ridges and ask the patient to close to reach a reasonable occlusal vertical dimension. This record is used to mount the primary casts on a high articulator.

- An activated resin tray is made on the primary casts and an occlusion rim is added on both the upper and lower trays, being parallel to the ridges, meet each other evenly and at an acceptable occlusal vertical dimension.

- Border molding of the periphery is carried out in the usual manner using green stick compound until a stable and retentive tray is obtained.

- Final impression is made using zinc oxide and eugenol impression paste while the patient is closing on the occluding rims (closed mouth technique) (Fig. 2-13).

- 24 –

2- Butterfly impression technique:

This technique is indicated in case of advanced resorbed ridge

with projecting sublingual glands.

- A suitable metal tray is selected and the lingual border is made

nearly flat to cover the sublingual crescent area and a primary

impression is made using alginate impression material.

- Using the resulting cast, an acrylic resin special tray is

fabricated with a butterfly extension over the sublingual

crescent area and an occlusion rim is added to simulate the

height and position of the anterior and posterior teeth.

- The borders are adjusted so that the lingual flange and

sublingual crescent area are in harmony with the adjacent

tissues during rest and function.

- Three applications of tissue conditioning material are used for

making this impression with closed mouth technique.

- Two application of a viscous tissue conditioning material.

Each application is allowed to remain in the mouth for 8-10

minutes pressure areas are corrected after each application.

- Then, the third and final wash is made using either a soft tissue

conditioning material or a light-bodied rubber base impression

material.

- The end result is an impression that has tissue placing effect,

very thick and confirming buccal borders, relatively thick

lingual and sublingual crescent areas and covering the

maximum possible basal seat area within the functional limits

of the adjacent tissues.

- 25 -

3-Dynamic impression technique:

- This technique is used to record the range of muscle action as

well as spaces into which the denture can be extended without

displacement,

-

- In this technique, complete utilization of the active and passive

tissues is obtained as the impression material is being shaped

by the function of the muscles and muscle attachments

allowing properly formed denture borders.

- A special tray of activated acrylic resin is constructed on the

primary cast.

- Three stops of impression compound are added to the fitting

surface of the tray, one at the anterior region and one at each

side posteriorly in the first molar region to allow a room of

two millimeters between the tray and the surface of the cast.

- Mandibular rests of impression compound are placed

bilaterally on the occlusal surface of the tray in the molar

region.

- Also, a compound tongue rest is added in the anterior region to

secure a correct tongue position during impression making.

- Final impression is made using a thin mix of alginate impression material. The loaded tray is seated in the patient's mouth and pressed gently until the stops are firmly seated on the residual ridge (Fig. 2-14).

- Then, the patient is asked to close slowly until the mandibular

rests firmly contact the maxillary arch and keep his tongue in

contact with the tongue rest.

- The patient is instructed to swallow 3-4 times and forcefully

protrude the lips forwards.

- 26 -

- The resulting impression covers the maximum possible basal

seat area and the borders are in harmony with the adjacent

moving tissues.

- After making the final impression with any of the previously

mentioned impression techniques the complete denture

construction is continued in the usual manner, taking into

consideration the following points:

• Jaw relation registration is carried out using check bite

technique.

• Occlusal plane is adjusted nearer to the flat ridge to

decrease the lever arm.

• A metal denture base is preferred to increase retention by

interfacial surface tension.

• Cross-linked cuspless acrylic teeth are used to decrease

the lateral component of force and improve denture

stability.

• Setting up of teeth in the neutral zone would help to

achieve denture stability.

- 27 -

Fig.2-12:Well-formed

impression of (lower) lingual sulcus area

Fig.2-13:Muco-compressive impression technique

a: A lower acrylic special tray

with metal spurs to aid retention of the impression

material

b,Occlusal pillars have been built up in green stick to the correct

occlusal height

C, Establishing the correct occlusal height

D, a completed viscogel impression

Fig.2-14 a:df: Dynamic impression technique:

- 28 –

IMMEDIATE DENTURES

Definition: o Immediate denture is a denture which is entirely constructed

before the extraction of the teeth and inserted immediately after the extraction of the teeth.

o A complete denture or RPD fabricated for placement immediately following the removal of natural teeth. After healing, the denture can be relined and refitted to be used as a definitive denture.

Types Immediate Dentures:

1. Immediate interim denture:

A temporary dental prosthesis constructed to replace the lost dentition and associated structures of the maxillae and /or mandible, and inserted immediately following removal of the remaining natural teeth (Complete clearance), i.e. the denture is placed at the same appointment of extraction.

It is used for a short interval of time for reasons of esthetics, mastication, occlusal support, or convenience; it is worn only during the healing period until more definitive prosthetic therapy can be provided (Fig. 3-1).

2. Immediate transitional denture:

A Temporary partial denture to which artificial teeth are added one or two at a time as natural teeth are lost until it finally serves as a temporary complete denture.

A transitional denture may become an interim complete denture when all of the natural teeth have been removed from the dental arch.

- 29 -

Fig.3-1: Immediate interim denture

Fig.3-2: immediate transitional partial denture.

a: Before construction of the immediate denture

b: After construction of the immediate treatment partial denture

Fig.3-3 a,b: Immediate transitional denture.

- 30 -

3-Immediate Conventional Complete denture.

A denture placed immediately after the extraction of the remaining 6 anterior teeth, the posterior teeth having been removed 6 weeks prior to making the dentures.

3. Immediate Definitive cast partial denture.

4. Diagnostic Immediate denture:

Used to diagnose a patient’s problem and the posterior segments consist of flat occlusal blocks made of plastic resin; indicated for patients with advanced periodontal disease (Fig.3-5).

Fig.3-4: An interim acrylic resin partial denture that is placed at the same appointment of extraction to restore esthetic and function immediately.

Fig.3-5: Definitive cast partial Fig.3-6: Immediate treatment or

diagnostic partial

Advantages:

1- Provides a guide for optimal individualized patient esthetics and the remaining natural teeth serve as an excellent pre-extraction guide helping the dentist to reproduce the position and appearance of the natural dentition

2- Prevents collapse and changes of facial and oral musculature. Thus, preclude any change in patient’s appearance. Promotes better healing, because it can serve as a protective bandage and surgical stent to protect the open sockets and blood clots from injuries from food, tongue action or the opposing teeth.

3- Promotes better ridge form

4- A dressing and bandage effect to the wounds of extraction and alveolectomy and help to reduce bleeding

5- Hastens patient adaptation to dentures. The patient can better tolerate the transition from the dentulous to the edentulous state since they are not without teeth for an extended time.

6- Protect the tissues at the sensitive extraction sites from irritation.

7- The functions of speech and mastication are sustained when natural teeth are immediately replaced.

8- Prevents patient embarrassment after extraction of teeth.

9- Provides a guide for The vertical dimension of occlusion

- 32 –

Disadvantages:

1- Increased complexity of clinical procedures.

2- No possibility of 'Try-in" of the anterior teeth to get the patient's acceptance for esthetics and phonetics.

3- Increased treatment time and cost.

4- Subsequent relines, rebases or remakes are necessary in a short period of time.

5- Increased patient discomfort

6- There is potentially less retention.

7- Post-placement adjustments are more numerous than with conventional complete dentures.

Contraindications:

1- Patients with general medical conditions which make them poor surgical risks such as cardiovascular diseases or other systemic abnormalities.

2- Patients with acute infections which may require surgical drainage.

3- Patients with a limited mental capacity or who are emotionally disturbed and uncooperative.

4- Patients with neurologic or psychological conditions.

5- Patients who have undergone radiation therapy should not be considered for immediate dentures because of the danger of osteoradionecrosis.

6- Patients with limited or no neuromuscular control.

7- Patients with a severe gagging reflex. Conditioning of such patients with a training appliance, such as a mouth guard, is indicated before the teeth are removed.

- 33 –

Immediate Denture Treatment Sequence:

Extraction of posterior teeth: All the remaining posterior teeth are extracted with the

exception of two opposing premolars or molars standing into good occlusion as their extraction is postponed till the recording of the jaw relationship.

A healing period of 6-12 weeks is allowed to ensure proper healing of the extraction sockets depending on:

• Number of teeth extracted. • Condition of the patient.

Then after complete healing of the extraction sockets, start construction of the immediate denture as follow:

1st Clinical Appointment - Exam & preliminary impressions. Lab procedures - custom tray fabrication.

2nd Clinical Appointment - Master impressions. Lab procedures - master cast, record base

& occlusion rim fabrication if indicated 3rd Clinical Appointment - Maxillomandibular relation records,

and tooth selection Lab procedures- wax trial denture

fabrication if indicated 4th Clinical Appointment - Wax trial denture try- in (confirm

mounting & esthetics) if indicated Lab procedures - process dentures

5th Clinical Appointment - Extractions & denture insertion, adjust tissue surface & flanges, adjust occlusion & care instructions

6th Clinical Appointments - 24 hour post-insertion checks adjust dentures & care instructions

7th & 8th Clinical Appointments - 72 hour, and one week post-insertion checks adjust dentures, clinical remount & reinforce care instructions

- 34 -

Diagnosis o Initial interview

o History

o Oral examination

o Mounted diagnostic casts

o Radiographic interpretation

o Subjective appraisal of patient

o Pre-extraction Records

o A diagram of the anterior teeth indicating shading, restorations, etching, and so on

o Profile wire record and facial measurements

Fig.3-7: A hand-drawn chart for the locations of stains in the anterior

teeth.

Fig.3-8:The vertical overlap may be measured in this manner to serve as a pre-extraction record of the vertical relation,

- 35 -

Duplicating the Patient's Natural Teeth :

One of the greatest pleasures of accomplishment can be gained from duplicating the patient's natural teeth. Duplicating the anterior teeth is remarkably simple and rewarding. The results are far better than can be obtained by using stock teeth. This can be performed either by:

1. Preliminary alginate impressions poured twice (once with teeth in wax and once in stone), or

2. Anterior tray is formed over a wax blockout present no undercuts, and a strong wire handle is attached.

Because of the great pleasure inherent in this proc edure, a step-by-step recipe is given below: 1. Two thicknesses of base-plate wax are adapted over the

remaining anterior teeth on the study model. 2. An acrylic tray is formed over the wax to obtain an impression of

the anterior teeth only. A strong wire handle is attached (Fig.3-9). 3. A rubber-base impression material is made. 4. The impression should be examined to be sure that it has no

bubbles or other defects over the teeth. 5. The impression is then filled with a white carving wax above the

level of the gingiva and allowed to set (Fig.3-10). 6. The wax is carefully removed from the rubber-base material by

peeling the latter from the wax pattern. This eliminates the probability of fracturing the pattern (Fig. 3-11).

7. The wax pattern is trimmed of excess gingival areas, leaving the teeth and approximately 1 mm of gingiva remaining (Fig. 3-12, 3-13).

8. The wax pattern is then invested in a suitable flask. 9. Wax elimination is carried out. 10. The appropriate shade for the incisal edge and the body of the

teeth of a suitable heat-cured acrylic resin is packed into the mold and processed.

11. The teeth are then removed as a block of six teeth. Finished and polished (Fig. 3-14). They can then be set into their proper place on the cast and waxed to place.

The procedure described above enables one to duplicate not only the size, color, and individual stains, but also the exact arrangement of the patient's anterior teeth.

Fig. 3-9:The wax blockout should present no undercuts. The anterior tray is then formed over the wax, and a strong wire handle is attached.

Fig. 3-10:Rubber-base impression of the anterior teeth. The

impression filled with white carving wax.

Fig. 3-11: Wax model of the upper anterior teeth. All material above the dotted line can be trimmed away.

Fig. 3-12:Fine lines can be simulated by holding apart clean cut into the dough, dusting in polymer, and wetting the whole with monomer.

Fig. 3-13: All material above the dotted line can be trimmed away.

Fig. 3-14: Lightning disk or separating saw used to separate

the incisal edges. The anterior tray is not perforated and no adhesive is used because

the impression material will have to be removed and replaced later.

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Fundamentals for impression making: o Area of coverage o Borders o Valve seal without interference of function o Accurate adaptation of the underlying tissues without

injurious displacement. o Preservation the maximum ridge bulk.

Primary impression:

Primary impressions of the upper and lower arches are made by alginate impression material using suitable stock trays.

Final impression:

Two types of final impression procedures are employed, the sectional (two stages) impression or the single impression:

a- Sectional (two stage) impression technique:

1- First method

- An activated resin special tray is constructed. Covering the edentulous area posteriorly and resting on the lingual surface of the remaining anterior teeth (Fig. 3-15).

- The tray is border molded using green stick compound and then the impression is made into zinc oxide and eugenol impression paste (Fig. 3-16).

- An overall impression is made using alginate impression material in a suitable stock tray to record the anterior teeth and relate the previous impression of the edentulous area to these teeth (Fig. 3-17).

2- Second method

- Using rubber base impression material (Fig. 3-18).

b- Single final impression technique: - An activated resin special tray is constructed over the relieved

master cast covering both the anterior teeth and the posterior edentulous area (Fig. 3-19).

- - 38 -

- The tray is border molded using green stick compound and then the impression is made using rubber base impression material to record all the areas in one impression.

- This technique may be used when there are no severe labial under cuts present, and/or the anterior teeth are not protruded.

A B Fig.3-15A,B:Two-piece tray technique: for very divergent maxillary anterior teeth, severe ridge undercuts, or Small oral opening,

Fig.3-16:Zink oxide impression in split acrylic tray

Fig.3-17: Overall alginate impression with stock tray

Split Impression Tray – zinc oxide and eugenol paste and Alginate.

Fig.3-18:a,b: Two-piece tray technique using rubber base impression material.

Fig.3-19: Two-piece tray technique for very divergent teeth or severe ridge

undercuts

Fig.3-20: Single tray with rubber

base impression material Fig.3-21: Use wax to block out

interdental embrasures

Fig.3-22: Single tray with alginate

is only used when considerable tooth misalignment or great mobility present

Fig.3-23: Single tray with alginate is only used when considerable tooth misalignment or great mobility present

Jaw relation registration: - the Maxillomandibular Relation Records include:

- Face bow record - Evaluate the VDO - CR record - Protrusive record - Mark and transfer the posterior palatal seal.

- Occlusion blocks are constructed, over the obtained casts; the centric occluding relation is recorded at a proper occlusal vertical dimension guided by the retained occlusal stops that will be extracted after making this record (Fig. 3-24: 3-27).

- 40 -

a b Fig.3-24 a,b: The normal vertical overlap on the left is maintained by the

molar teeth. When posterior teeth have been lost, the mandible may close further and increase the vertical overlap to the degree shown on the right.

Fig.3-25:Adequate teeth to support the bite registration material

Fig.3-26: If your immediate denture patient has existing edentulous space (s) fabrication of record base and wax rim is recommended to verify records and esthetics.

Fig.3-27:Mark and transfer the postpalatal seal.

Selecting & arranging anterior teeth: First method:

For tooth set-up: – Anterior teeth: – Cut anterior teeth off cast at gingival level. – Set anterior teeth on cast for patient viewing.

– Posterior teeth: – Arrange posterior teeth on record base in

balanced/monoplane/lingualized) occlusion and – Wax-up for try-in evaluation.

- 41 -

Second method:

The Alternating Tooth Setup Technique • Trim and set only one anterior tooth at a time • Alternate from side to side to keep natural neighboring

tooth as angulation, length, and contour orientation (Fig.3- 29-3-33)

Third method: – Performed by removal of all teeth from the plaster cast

and the patient got a complete immediate denture delivered with the anterior teeth in one time.

B Fig.3-28 a: First method: The teeth are removed from the cast in a manner that They are not cut below the gingival crest.

B: The terminal 5 mm of gingiva should be trimmed in the manner shown above so that the denture gingiva may not appear too thick

Positioning of the anterior teeth:

This can be accomplished by various methods according to the technique applied.

Techniques applied for immediate denture constructi on:

1- Simple extraction with no more surgery:

It includes two types:

a- Socketed immediate denture:

- It is indicated only in upper arch and contraindicated in the lower arch as the presence of a labial flange in the lower denture is important to guard, against backward movement of the denture by the pressure of the lower lip.

- 42 –

2mm

- The plaster teeth cut from the cast and replaced by the artificial teeth. This is best achieved by removing and replacing one tooth at a time so the form of the arch and the position of each individual tooth can be easily reproduced.

- Root sockets are made in the plaster cast into which the necks of artificial teeth are fitted taking into consideration the following:

- The socket depth should not exceed 5mm labially and 2mm palatally (Fig. 3- 28 b).

- The sockets should not be carried too far towards the palatal side i.e the socket should slope from the palatal margin upward toward the labial aspect.

- The direction of the socket should follow the long axis of the tooth.

The advantages of this technique are as follows:

- It provides anterior seal that assists in the retention of the denture.

- It provides resistance to movement during mastication.

- It provides a natural appearance as if the teeth are growing from the gums.

b- Flanged type immediate denture:

- This technique is indicated in cases having sufficient available space to accommodate a labial flange without giving the feeling of excessive lip fullness.

On replacing the plaster teeth by artificial ones, either one tooth is removed each time, or remove all teeth on one side of the arch, keeping the more acceptable side as a guide for the arrangement of artificial teeth.

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Fig.3-29 a,b:Preserve the incisal edge position and tooth angulation information prior removal of stone teeth. Use a sharp pencil to mark the gingival outline buccally and lingually. Then mark the long axis of each tooth.

Fig.3-30:Esthetic convenience

groove Fig.3-31: The Alternating Tooth

Setup Technique

Fig.3- 33:The Alternating Tooth Setup Technique

– Trim and set only one anterior tooth at a time. – Alternate from side to side to keep natural neighboring tooth as

angulation, length, and contour orientation.

- 44 -

Fig.3- 34: Objectives of the occlusion development (upper ID/lower RPD):

Centric: Bilateral even centric contacts.

Fig.3-:35 a, b: Eccentric: Fully balanced occlusion during lateral/protrusive movements. Today’s goal: Complete the posterior teeth setup that obtains solid bilateral even centric contacts.

II- Immediate denture with alveoloplasty:

It includes two types:

a-Labial plate alveoloplasty:

This technique is only indicated in the following conditions:

1- Patients having a very prominent premaxilla with the teeth tilted outward and resting on the external surface of the lower lip and wash for an improvement in appearance.

2- Patients with poor posterior ridge, shallow sulci and narrow upper jaw with a wide lower jaw that necessitate the creation of a room for a labial flange to provide better retention and stability.

Patients exhibiting a very deep overbite with the incisal edge of the upper teeth touching the gingival margins of the lower teeth.

- 45 -

The technique is as follows:

- First, extraction of the six anterior teeth is carried out.

- A mucoperiosteal flap is reflected by making two inclined incisions distal to the canines.

- Using bone rongeur, the labial alveolar plate of bone is cut off.

- Then the bony septa are cut off using a side cutting rongeur.

- A bone file is used to trim any remaining sharp edges.

- The flap is repositioned and excess soft tissue is trimmed.

- Suturing of the flap is carried out using, 000 black silk suture.

- The immediate denture is inserted in the patient's mouth after being lined with tissue conditioning material.

- The patient is instructed not to take of the denture till the next appointment 24 hours later.

- A suitable antibiotic is prescribed and the patient is instructed to make cold fermentation to minimize hematoma formation.

b- Interseptal alveoloplasty:

In this technique, no mucoperiosteal flap is reflected.

The technique is as follows:

- After extraction of the six anterior teeth, a bone rongeur is used to cut a V shaped wedge from the labial cortical plate distal to the canine or each side.

- The bony septa are then removed using bone rongeur.

- A chisel is inserted deep in the sockets and with the help of a mallet; slight knocks are applied with the chisel edge directed toward the labial cortical plate.

- Hand pressure is applied to the labial cortical plate to affect green stick fracture and moving the labial cortical plate towards the palatal cortical plate.

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- Excess soft tissue is trimmed and the wound is sutured using 000 black silk suture.

- Immediate denture insertion and patient instructions are the same as the previous technique. .

The advantages of this technique are as follows:

1- Minimizing the possibility of bone resorption by keeping the labial cortical plate of bone and avoiding flap reflection.

2- Maintain the heamatoma between the two cortical plates and thus any pressure will not result in excessive bone resorption.

3- It affects the same purposes of the previous technique without flap reflection.

NB.: For both technique of immediate denture with alveoloplasty, the construction of a transparent acrylic template over a duplicate cast of the reduced one is helpful in detecting areas requiring further modifications before suturing (Fig. 36 a, b).

- Following immediate denture insertion, the patient will be

recalled for changing the tissue conditioning material

periodically and making any necessary adjustments.

- After three months, relining, rebasing or even making a new

denture is indicated after complete healing of the tissues

following extraction.

Note:

- It could be noted that the best approach for immediate denture

construction is the simple extraction with no more surgery.

However, in cases where surgical reduction of the alveolar

process is considered necessary, the interseptal alveoloplasty is

to be preferred as it will cause less damage and preserve as

much of the residual ridge as possible

- 47 -

B Fig. 3-36 A: Surgical Template:

Fabricated after cast trim. Used to locate pressure areas on mucosa at time of surgery. Denture trimmed according to blanched mucosa observed under template

B, :Trimmed areas sanded smooth Avoid removing incisive papilla.

Try in:

Try-in of the set up posterior teeth is carried out to check the following:

- Reasonable occlusal vertical dimension. - Proper centric occluding relation. - Even bearing on both sides. - Then, the patient is dismissed and given appointment for

extraction of the anterior teeth and complete denture insertion. It the patient require the shape, colour and surface

characteristic of his teeth to be copied exactly, an additional rubber base impression of the anterior teeth should be taken into which molten wax is poured to a level just above the gingival margins. The wax is chilled in cold water and removed from the impression and reproduced into tooth-coloured acrylic resin of the same shade.

- 48 -

A

Post Extraction Instructions

- Do not remove denture - Keep head elevated - Small amounts of blood in saliva is normal - Diet: soft and warm, not hot - Avoid: – Spitting, rinsing – Strenuous activity – Alcohol, smoking

a

b

Fig. 3-37 a,b: Try-In of a socketed type denture of the Posterior segment for check record

Delivery and Aftercare

The immediate denture is inserted when the surgical procedures have been completed. The patient should not remove the denture until the next day, when it is examined by the dentist. Subsequent to that appointment, the patient may remove it whenever he or she wishes.

- 49 -

Post Insertion Management

- Recall next day to remove the denture.

- Apply topical anesthetic to traumatized mucosa

- Locate over extensions and pressure areas and adjust

- Reappoint 1 week.

- The immediate-denture patient should be recalled every 3 months after the dentures have been properly fitted, to determine when they must be rebased or relined. (Some patients lose alveolar bone rapidly, and their dentures require rebasing within a few months. The majority should be rebased at 10 to 14 months).

-

Fig.3- 38 : The immediate denture is inserted.

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THE SINGLE COMPLETE DENTURE

The construction of a single denture may be presented in a variety of dental combinations. It could be constructed against:

1- Natural teeth.

2- Removable partial denture.

3- A previously constructed complete denture.

The single complete maxillary denture opposing all or some of the mandibular natural teeth is a very common clinical situation

Problems of single denture :

1- The firmness and rigidity in which the natural teeth are retained in the bone and the magnitude of the force. (Excessive load from the natural teeth).

2- The occlusal form of the remaining natural teeth and the uneven occlusal plan (“mutilated” dentition).

3- Single denture syndrome. This situation is the result of the displacement of the maxillary denture due to unfavorable occlusal relationship as a result of tipped, malposed or supererupted natural teeth. It is presented as mucosal irritation and ridge resorption of the edentulous ridge.

4- Esthetic and phonetic problems due to the fixed positions of the mandibular teeth.

5- Artificial teeth selection. Acrylic teeth are abraded by natural teeth and porcelain teeth abrade natural teeth.

6- Mandibular single denture.

How to Overcome These Problems

The primary consideration for a continued success of a single complete denture is the preservation of that which remains.

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Proper diagnosis and full use of every factor, which favors success for this denture,

Applying the principles of complete denture construction:

• Lip support

• Minimal vertical overlap (Overbite)

• Balancing occlusion and free articulation.

• Avoid broad inclined planes.

Maximum base extension within functional anatomical limits (distributed forces over the largest possible area of supporting structures and the force per unit area kept at minimum.)

Reduction of the forces to which the denture is subjected

Diagnosis and treatment planning:

1- Complete case history is taken and oral examination is done.

2- Study upper and lower casts are obtained.

3- The upper cast is mounted on the articulator using a face bow.

4- The lower cast is mounted on the articulator using a provisional centric interocclusal record at an acceptable vertical dimension.

5- Eccentric records are made and the condylar elements of the articulator are adjusted.

Common Occlusal disharmonies:

The remaining molars are often severely inclined mesially and then distal halves supererupted. If this situation is left unaltered there would be no occlusion in protrusive and lateral excursions except for contact on the distal half of the lower molar. This results in the maxillary denture being easily dislodged during functional movements.

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a) If the molars are not severely tilted they may be reshaped by selective grinding.

b) When tooth reduction is found necessary, the ideal treatment is to restore the tilted molars with cast gold crowns, onlays, or a fixed bridge if a large edentulous space exists mesial to the molars.

c) If a large space does exist mesial to the tilted molars, another alternative treatment is to design a removable partial denture that would restore the mesial half of the molars by using an onlay mesial rest (Fig 4-1).

d) If the molars are severely tilted forward and supererupted, and modification is not possible, extraction is necessary.

Fig.4-1: Upright preparation of a premolar and tilted second molar

as abutments. (A) Teeth before preparation. (B) The mesial surface of the molar has been aligned to the existing long axis, resulting in an overtapered preparation. (C) Correct preparation of the molar and premolar. (D) The completed fixed partial denture. The mesial cusps of the molar have been raised.' the distal cusps have been lowered, and the correct occlusal plane has been restored.

Methods used for detecting occlusal modifications:

Several techniques could be used to determine occlusal modifications that are necessary prior to denture construction:

1- Use of a commercially available U shaped metal occlusal template that is slightly convex on the lower surface. This template is often an aid in detecting minor deviations in the occlusal scheme (Fig 4-2).

- 53 -

2- Upper and lower casts are mounted on the articulator. The upper denture is constructed. If the lower natural teeth interfere with the placement of the denture teeth, they are adjusted on the cast and the area is marked with a pencil. The natural teeth are them modified using the marked diagnostic cast as a guide. This technique is simple but time consuming.

3- Use of a clear acrylic resin template fabricated over the modified stone cast. The inner surface of the template is coated with pressure indicating paste and placed over the patient's natural teeth.

Fig.4-2: U shaped 20°

occlusal Template Fig.4-3:Plane of Occlusion

Evaluation

Methods used for a harmonies balanced occlusion:

In the construction of dentures to articulate with natural teeth, the prosthodonticsts must provide a harmonious occlusal scheme free of interference in any jaw relationship this will lead to a better retention and stability of the single denture which will lead to least residual ridge damage.

Many techniques have been used to achieve a balanced occlusion of a complete maxillary denture opposing natural teeth. They basically fall into two categories:

1- Dynamic equilibration of occlusion by the use of a functionally generating path.

2- Static equilibration of occlusion with an adjustable articulator.

- 54 -

Materials for artificial posterior teeth:

The materials available for occlusal posterior tooth forms are

1- Acrylic resin.

2- Porcelain.

3- Gold (Fig 4-).

4- Acrylic resin with amalgam stops.

Esthetic of single maxillary denture:

The fixed positions of mandibular teeth limit the esthetic position of maxillary anterior teeth. How to solve the esthetic problem?

1- To create enough horizontal overlap to allow freedom to balance in eccentric movements.

2- Or to steeping the posterior cusp angles so that the posterior teeth will disocclude the anterior teeth during eccentric movement.

Mandibular single denture:

The prognosis of a mandibular single denture against natural teeth is less favorable than when the full upper denture is opposed by natural lower teeth (Fig. 4-4, 4-5). It would be difficult to classify this case as clinically successful. This is due to:

1- Excessive resorption of lower ridge due to greater stresses per unit area delivered to the mandibular ridge by the natural teeth.

2- Occlusal problems: The presence of natural teeth will present difficulties in controlling the occlusal scheme.

3- Minimal denture foundation area

4- Fracture.

5- Tooth wear.

6- Tissue abuse.

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Fig 4-3: Gold occlusal posterior teeth.

The alternative line of treatment plan for such patient could be either:

1- Extraction of remaining teeth and complete upper and lower denture are constructed.

2- Use of resilient denture liner in the mandibular denture.

3- Use of implant supported fixed or overdenture prosthesis (Fig. 4-6,4-7).

a b Fig.4-4 a, b: mandibular single denture against natural teeth

a b Fig.4-5: Conventional lower single dentures are contraindicated because

they cause severe resorption as seen in this patient.

a b Fig.4-6 a,b:Retaining roots in key positions facilitate support and prevent

compression of the periosteum

Fig.4-7 a,b:Implant assisted overlay dentures opposing dentate maxilla.

Combination Syndrome and Associated Changes

( Kelly’s Syndrome)

A Combination Syndrome By Kelly (1972): destructive problems, that may be encountered as a result of long term use of a mandibular distal extension partial denture against a complete maxillary denture

This syndrome consists of:

1- Loss of bone from the maxillary anterior edentulous ridge (Fig.4-8 a).

2- Down growth of the maxillary tuberosities (Fig.4-8b).

3- Papillary hyperplasia of the tissues of the hard palate.

4- Extrusion of the lower anterior teeth and,

5- Loss of bone beneath the removable partial denture bases.

It usually has six associated changes:

1- Loss of vertical dimension of occlusion.

2- Occlusal plane discrepancy (Fig.4-9).

3- Anterior spatial resorption of the mandible.

4- Development of epulis fissuratum (Fig.4-10).

5- Poor adaptation of the prosthesis and,

6- Periodontal changes.

- 57 -

The Combination Syndrome Is a Result of Three Main Factors

• the great magnitude of forces involved,

• the unsuitability of the denture foundation to resist them, and • the particularly unfavorable occlusal relationship.

Fig.4-8 a,b:A specific pattern of resorption : The premaxilla undergoes severe resorption and is usually accompanied by the development of fibrous hyperplasia of the maxillary tuberosity.

Fig.4-9: When mandibular anterior teeth remain, patient will attempt to function in protrusive relationship to sense feeling of mastication.

Fig.4-10:The Labial Flange Of The Denture Produces A Low Grade Irritation In The Surrounding Soft Tissues, Resulting In Development Of Epulis Fissuratum.

a Fig.4-11 a,b: Premaxilla mostly soft tissue b

Advanced bone loss: premaxilla and posterior mandible

OVERDENTURE

The overdenture is a complete or partial denture prosthesis constructed over existing teeth, root structure and/or dental implants.

The overdenture is also called overaly denture, overlay prosthesis or super imposed prosthesis.

Objectives of overdenture prosthesis:

1. Retaining the abutments as part of the residual ridge to gain support and retention (Fig. 5-1 a).

2. Preserving the remaining residual ridge by decreasing the rate of bone resorption (Fig. 5-1 b).

3. Preserving the response of proprioceptive exist in the periodontal membrane of the abutment tooth.

Fig.5-1a, b:Retaining the abutments and Preserving the remaining

residual ridge

- 59 -

Indications:

1- Cases having few remaining teeth unsuitable for fixed or removable partial dentures.

2- Remaining teeth present with unhealthy periodontal condition. The reduction of the coronal portion of the tooth i.e. decrease crown-root ratio will decrease the hypermobility of the teeth and make them favorable for supporting overdentures.

3- Patients with class II or class III Angle's classification.

4- Patients presenting abnormal jaw size large maxillary or mandibular bone defects.

5- Patients presenting congenital defects as cleft palate, microdontia, amelogenesis or dentinogenesis imperfecta or partial anodontia.

6- The construction of over-denture is an alternative line of treatment to single dentures opposing few natural teeth.

Contraindications:

1- Overdentures are contraindicated in case of poor oral hygiene.

2- Interarch space inadequate to accept the denture and the abutments.

3- Inadequate zone of attached gingiva with grade II mobility of the abutments.

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Overdentures can be classified into:

1- Tooth supported over denture.

2- Implant supported overdenture.

1- Tooth supported overdenture:

The tooth supported Overdentures improve stability retention, masticatory performance, occlusal loading and help to preserve vertical dimension and facial support.

Advantages of tooth supported overdenture prosthesis:

1- Preservation of the abutments as part of the residual ridge to gain support.

2- Preservation of the proprioception that exist in the periodontal membrane of the abutment tooth.

3- Preservation of the remaining residual ridge by decreasing the rate of bone resorption.

4- Patient acceptance and Psychological Benefits

5- Convertibility: overdentures can be converted into a conventional complete denture after loss of the abutments and relining or rebasing of the denture.

6- Conventional dental procedures.

7- Provide retention through the attachments.

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Disadvantages of tooth supported overdentures:

1- Caries and periodontal break down of the abutments teeth (Fig.5-2)

2- Inadequate reduction of the abutment teeth may increase vertical dimension.

3- The bony undercuts adjacent to the abutment teeth (usually buccally) cause limitation of path of insertion of the over denture.

4- Overdenture construction is time consuming and expensive line of treatment compared to the conventional complete denture.

5- Encroachment of the interocclusal distance leads to bad Esthetics.

Fig.5-2 a,b:Caries and periodontal break down of the abutments teeth

Fig.5-3 a,b:Encroachment of the interocclusal distance leads to bad

Esthetics.

Tooth supported overdenture can be classified according to the time expected to the denture to be worn, into:

Immediate overdenture:

Is made for patients with almost a full complement of teeth, most of which are to be lost. The remaining teeth are reduced to accept the

overdenture (on the cast), the overdenture are constructed prior to the

preparation of abutment teeth and is inserted after the preparation.

Transitional or intermediate overdenture:

Is obtained by converting an existing removable partial denture to an overdenture by making impression over prepared abutments.

Definitive (Remote) overdenture:

Is constructed for insertion at sometime remote from the removal of hopeless natural teeth. Complete or partial overdentures with metal or acrylic bases can be fabricated.

Tooth supported over denture can be classified according to its design into:

1. Vital tooth with simple reduction.

2. Tooth reduction and cast coping of vital abutment

Thimble or dome- shaped

3. Endodontic therapy and amalgam plug

4. Endodontic therapy with post and coping 5. Endodontic therapy with cast coping and attachments

6. Telescopic Overdenture

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I- Simple tooth reduction of vital tooth:

The tooth is modified by reducing the buccal surface 30° and lingual surface 15°. The mesial and the distal surface are modified to remove the undercuts (Fig. 5-4).This types is indicated:

- In case of good oral hygiene and low caries index.

- Attrition or abrasion of teeth with severe pulp recession.

- Adequate interarch space.

II- Tooth reduction and cast coping of vital abutment:

a- The thimble-shaped coping:

Copings may be placed on vital abutments. The technique requires preparations for full crowns, preferably with shoulders, and the occlusal portion of the preparation is rounded or parabolic in form.

The thimble coping occupies considerable vertical and buccolingnal space (Fig. 5-5 a).

It is mainly used in cases with partial anodontia and in cases exhibiting enough inter-ridge space.

B- Tooth reduction and cast coping:

Copings may be placed on vital abutments. The crown is reduced to the dome-shape and wax pattern is made for cast coping (Fig. 5-5 b).

Fig.5-4:Simple tooth modification of vital abutment

Thimble-shaped coping

B-Tooth reduction and cast coping

Endodontic therapy and amalgam plug

Endodontic therapy with post and cast coping.

Endodontic therapy with cast coping and attachments

Fig.5-5 a:d : abutments ofTooth supported over denture

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f

III- Endodontic treated tooth with amalgam plug:

This type is indicated in:

- Normal inter-arch distance. - Normal crown height. - Good oral hygiene. - Pulp is not recessed.

The crown needs severe reduction so endodontic therapy is necessary; the reduced height is 1-2 mm above the gingival margin. The root canal is filled with gutta percha and the opening is sealed with amalgam plug (Dome-shape appearance) (Fig. 5-5 a, 5-6 b).

IV-Endodontic treated tooth with cast coping (short-

coping):

- Abutments are endodontically treated with root canal filling and sealed with cement.

- The crown is reduced to the dome-shape and wax pattern is made for cast coping.

- The metal coping takes its retention from a short post inserted in the root canal.

V- Endodontic treated tooth with cast coping and attachment: Overdentures retained by attachments offer the patient the idea of

a fixed removable bridge instead of a denture. The abutments are prepared as in short-coping but with long intraradicular post to prevent root-coping dislodgment. Clinically, two attachments are enough to retain a denture. A third attachment adds unnecessary complexity and weakens the denture (Fig. 5-5 e-f, 5-6 c).

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VI- The telescopic overdenture: It is constructed to fit over natural teeth like a sleeve. These

supporting abutments may simply be endodontically treated, reduced slightly, smoothed and polished to support this denture. Retention is generally obtained through the frictional resistance produced between the semi-parallel walls of the copings and tissue side of the denture base (Fig. 5-6 f).

a: Endodontic therapy and

amalgam plug.

b:Cast coping C: Endodontic therapy with post and attachment

d:Posts and cast copings. e: Partial overdenture

f: telescopic crowns

Fig.5-6 a: f: types of overdenture prosthesis.

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CLINICAL PROCEDURES

The treatment plan starts first with the proper selection of the abutments which will support the overdentures, one should consider root form, abutment location, amount of bone support, masticatory loads, space between abutments and the opposing dentition.

I- Abutment Selection:

Position of abutments and Number

of abutments.

– At least one tooth per quadrant.

– Retained teeth should preferable not be adjacent ones,

– There should be several millimeters of space between the reduced tooth forms.

– Canines and premolars are the best overdenture abutments to reduce adverse forces at this site (Fig. 5-8 a: d).

Periodontal evaluation. o Minimal mobility o At least 6mm of bone support o Attached gingiva around the abutments o Good oral hygiene o Proper emergence profile to support the marginal gingiva

Endodontic evaluation.

– Decay or previous restorations.

– Inter-arch space: there should be an adequate inter-arch space for the overdenture.

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II- Abutment preparation:

c. Crown reduction with or without endodontic treatment is usually required.

d. Periodontal treatment including supragingival and sublingual scaling is carried out to attain healthy gingival tissue.

III- Primary impression:

Impression is made using stock tray and alginate impression material. Special acrylic tray is constructed on the primary cast.

IV- Secondary impression:

- Secondary impression are made using rubber base material and poured into stone.

- Wax patterns for the coping are made and cast in metal. The coping is then cemented on the prepared abutments, impression is made to obtain casts for the coping-covered abutments.

V- Jaw relation records:

- Mount the upper casts on semi-adjustable articulator by the help of face bow records.

- Centric occluding relation record used to mount the lower cast.

- Setting up of teeth is then carried out.

VI- Try-in:

- Fitting surface of the trial dentures should be relieved over the abutments to ensure proper denture seating.

- Check of denture stability and support.

- Check the vertical dimension.

- Check the occlusion and the premature contact.

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VII- Dentures are then processed, finished, polished

and clinically remounted to eliminate any errors.

VIII-Denture insertion:

At overdenture insertion the fitting surface should be relieved over the abutment to avoid pressure on the gingival margin of the abutments.

IX- Post insertion care:

- The patient should follow the oral hygiene instaiction

- The patient should brush his denture after each meal.

- The denture should kept in tap water when not in use.

Fig. 5-7: Abutment preparation:

Crown reduction with or without endodontic treatment is usually

required.

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CHAPTE V I ATTACHMENTS

ATTACHMENTS

An attachment is a mechanical device used for retention and stabilization of a prosthesis.

It consists of two or more parts. One part is connected to a root, tooth or implant and the other part to a prosthesis (Fig. 6-1 a: f).

There is a wide variety of attachments available today for overdenture prosthesis and more are being developed.

There are some attachments having one manufactured part and the other part is constructed by the dentist or the dental technician.

Attachments fall into two categories: precision and semi-precision.

1- Precision attachments:

Precision attachments are just that "precision". Their components are machined in special alloys under precise tolerances. Since the specific hardness of the alloys is controlled, precision attachments offer the advantage of less wear on the abutments and standard parts which allow the components to be interchangeable and usually easier to repair when necessary.

2- Semi precision attachments:

A semi-precision attachment is fabricated by the direct casting of plastic, wax or refractory patterns. They are considered: semi-precision" since in their fabrication they are subjected to inconsistent water/ powder ratio, burn out temperature and other variables.

Their main advantages are: economy, easy fabrication and ability to be cast in a wide choice of alloys.

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Fig. 6-1 A:F: overdentures with stud attachment

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Factors affecting Attachment selection:

1. Available inter-arch space.

2. Crown root ratio and alignment of the roots.

3. Type of coping.

4. Vertical space available.

5. Number of teeth present.

6. Amount of bone support.

7. Location of abutments.

8. Location of the strongest abutments.

9. Whether the overdenture is a tooth supported or tooth-tissue-supported.

10. The type of the opposing dentition whether it is complete denture, overdenture, fixed appliance or natural dentition.

11. The maintenance problems and the cost.

12. Clinical experience and personal preference.

I- classification of over denture attachments according

to location:

a. Intracorornal. b. Extracoronal. c. Radicular/intraradicular stud type. d. Bar type.

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a. Intracoronal:

Intracoronal attachments are incorporated entirely within the contour of the crown. The advantage of an intracoronal attachment is that the occlusal forces exerted upon the abutment tooth are applied close to the long axis of the tooth. A disadvantage arises when the abutment is over contoured by placing the intracoronal attachment outside the crown contour, this often results from insufficient tooth reduction. Since all intracoronal attachments are non-resilient it is indicated for fixed bridge restorations, removable partial dentures and segmented bridge (Fig.6-2).

b. Extracoronal:

Extracoronal attachments are positioned entirely outside the crown contour. The advantages of this type of attachments are that the normal tooth contour can be maintained, minimal tooth reduction is necessary and the possibility of devitalizing the tooth is reduced. Most extracoronal attachments have some type of resiliency (Fig. 6-3).

It is however; more difficult to maintain hygiene with extracoronal attachments and patients should be instructed to use dental floss and hygiene accessories.

Fig. 6-2 : Intracoronal

attachment. Fig 6-3: Extracoronal attachment.

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c. Radicular / intraradicular stud type:

Radicular and intraradicular stud type attachments are connected to a root preparation (Fig. 6-4: 6-11).

The stud attachment consists of male stud that snugly fits a female housing.

The stud is usually attached to the metal coping cemented over the prepared abutment, while the female housing is embedded in the fitting surface of the acrylic overdenture exactly opposite to the abutment.

Some types are directly cemented into the prepared root without a cast coping e.g. new direct O-ring. The female element of intraradicular stud type fit within the root frame contour e.g. Zest attachment.

Fig. 6-4 a:c: Ball and socket stud attachment with

different design. Fig. 6-5: Rigid stud attachments.

Fig. 6-6: Female housing is

embedded in the fitting surface of the acrylic overdenture.

Fig. 6-7a,b: Resilient stud attachments.

Fig. 6-8: Intraradicular attachment: Metal and plastic sections (male) are incorporated

within the root

Metal section (female) is incorporated within the root.

Fig. 6-9: Extraradicular attachment.

Fig. 6-10: Extraradicular

attachment Fig. 6-11: Magnets

Fig. 6-12 a,b: Bar attachment with Sleeve plastic or metallic clips, into which the bar will slot.

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d. Bar type:

A bar attachment is in the form of a bar contoured to run

parallel and overlie the residual ridge connecting the abutments

together.

The bar provides support and retention for the overdenture

and splinting of abutment teeth (Or implants) (Fig. 6-12).

The overdenture fits over the bar and is connected to it with

one or more retention sleeves, clips or plungers.

The advantages of bar attachments are that they splint

questionable abutments together for mutual support.

Bar restorations, when properly related to the gingiva should

not cause food entrapment, blanching of the tissues, nor encourage

tissue proliferation.

II- classification of over denture attachments according

to Function:

It is important to differentiate between resilient or non

resilient type restorations. Abutment/tooth supported restorations

are considered non-resilient or solid, while abutment and tissue-

supported restorations are considered resilient (Fig. 6-4, 6-5).

Resilient attachments reduce vertical and lateral forces on

the abutments by distributing more of the masticatory load to the

tissues.

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Resiliency is a special advantage when the denture base fits

poorly due to alveolar resorption. Resilient attachments are

indicated with very weak abutment and when the opposing is

natural or non-resilient appliance.

Resilient attachments may range from vertical to universal

resiliency. The vertically resilient type attachment allows only

movement in the vertical plane. The hinge type resilient

attachment allows movement around a given point, e.g. Mini

Dalbo. The vertical and hinge type resilient attachment allows

movement in both the vertical plane and hinge axis

simultaneously e.g. Dalbo. The rotational and vertical type

resilient attachment allows both rotational and vertical resiliency

e.g. anchor the Universal, Omni-planar resilient type allows

movement in any plane.

III- classification of over denture attachments

according to retention mean:

It can be obtained by frictional , mechanical, frictional and

mechanical, and magnets (Fig. 6-5: 6-11).

Magnets: One magnet pole is cemented in a prepared cavity in

the endodontically prepared tooth, while the other pole is

attached to the denture base opposite to it (Fig. 6-11).

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CHAPTE VII IMPLANTOLOGY

Dental Implants

Dental implant is defined as “A prosthetic device made of

alloplastic biomaterial, surgically implanted into the oral tissues

beneath the mucosa, and/or periosteal layer, and/or within the bone

to provide retention and support for a fixed or removable

prosthesis”.

Historical development of implant biomaterial

1. Ancient implant materials:

- Replacing lost teeth with a bone-anchored device is not a new concept. During the ancient Egyptians era, and in South America in the 18th century, Ancient implant materials include the use of wood, carved stone and animal teeth.

2. Metallic implants: - Then a gold implant in 1807 and a platinum post were used to

replace missing teeth.

- Lead coated platinum root shaped rods in 1886.

- Silver implantation around the end of the nineteenth century.

- Vitallium implants were developed as an inert biocompatible material, which are a castable alloy cobalt-chromium-molybdenum.

- Stainless steel and titanium were used in the fabrication of wire spiral implants. Stainless steel alloy is stronger, cheaper and easier to machine, however, its corrosion properties are inferior to titanium. For this reason, it has not been approved as a dental implant material.

- Recently the wide scale use of implants can be attributed to the Swedish research team directed by Branemark. In 1952, Professor Per-Ingvar Branemark, a Swedish surgeon, while conducting research into the healing patterns of bone tissue, accidentally discovered that when pure titanium comes into direct contact with the living bone tissue, the two literally grow together to form a permanent biological adhesion. He named this phenomenon "osseointegration".

- He developed and tested a two- stage dental implant system utilizing pure titanium screws, which he termed fixtures. The first fixtures were placed in patients in 1965, and intensive clinical studies have proceeded ever since. The titanium fixtures were implanted by a meticulous technique that aimed at direct contact between the implant material and the living healthy bone.

Indication:

Patients who can not wear partial or complete denture or who wear them with varying degrees of difficulty are very frustrating, especially when it becomes clear that conventional denture therapy is not the correct prescription. These patients are usually presented with one or more of the following features:

1- Severe bone loss that significantly endanger denture retention.

2- Poor oral muscular coordination. 3- Low tolerance of mucosal tissues. 4- Para-functional habits leading to recurrent soreness and

denture instability. 5- Unrealistic prosthodontic expectation. 6- Active or hyper-active gag reflex precipitated by removable

denture. 7- Psychological inability to wear denture, even with adequate

one. 8- Massive bone and tissue loss following surgical removal of

tumors.

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-Such patients are candidates for implant prescription it

is believed now that this advantage could lead to therapeutic

strategies in prosthodontics that will considerably, by time

reduce the need to conventional removable prostheses.

Implant designs are traceable to early Egyptians. Modern

implant dentistry is delineated by the period from the mid 1930 to

present. During this period one begins to see the mergence of

implant concepts developing into those that are presently the most

refined and popularly utilized. These methods include the

subperiosteal, the endosteal blade and the endosteal root- form

implants. Currently, these three are the most popular; but other

implant designs such as the ramus frame, transosteal mandibular

implants, zygomatic implant and the fiber mesh are being utilized

successfully as well.

Components of a typical implant restoration:

The typical implant restoration is composed of:

The implant (fixture): it is the actual part that is inserted into the bone.

The abutment: it is the core area which is connected to the implant where the prosthetic part is attached to it.

The prosthesis: it is either single crown, fixed partial denture,

over denture or any type of restoration connected to the

implant and the abutment.

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CLASSIFICATION OF DENTAL IMPLANTS

Dental implant can be classified into two groups:

1- Tooth implants which include transplantation, reimplantation and endodontic endosseous implants.

2- Non tooth implants which include subperiosteal, transosteal and endosteal balde and root- form implants.

Classification of implants according to position:

I. Endodontic stabilizer II- Mucosal inserts

III- Subperioteal implant. IV- Transosteal implant.

V- Endosteal implants

I-Endodontic stabilizer

It is a Smooth or threaded metallic pin implant that extends

through the root canal into the periapical bone to stabilize the mobile

tooth. This was first used by Cuswell and Senia in 1983 (Fig. 7-1).

a

b c

Fig:.7-1a: b: Endodontic stabilizer

II-Mucosal inserts (Mucoperiosteal -implant interface):

They are stainless steel inserts attached to the tissue surface of a removable prosthesis that mechanically engage undercuts in surgically prepared mucosal sites.

It is an effective and simple way to provide significant retention to a maxillary removable prosthesis (Fig. 7-2).

An insert of double head connected with a bar and called the Tandom Denserts concept was also introduced in 1983.

These types of implants have the unique feature of penetrating through lining epithelium. Establishment of an adequate CT seal around implant provides a barrier to the ingress of oral toxins and bacteria. The maintenance of this seal is essential for providing the initial peri- implant tissue inflammation that can lead to destruction of the implant support.

Epithelial regeneration around well- integrated implants results in a structure similar to the gingival tissues around natural tooth. The keratinized oral epithelium is continuous with non- keratinized sulcus epithelium.

Fig:.7-2: Mucosal inserts

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4

1

III- Subperiosteal implants:

Its framework is made of cobalt chromium molybdenum based alloy resting on the alveolar bone beneath the periosteum, with abutment posts and intraoral bars to attach a prosthesis (Fig. 7-3: 7-5).

Construction

The shape of bone for frame construction is obtained through:

1. Direct bone impression (2 surgical exposures)

2. CAD-CAM generated model (only one surgical exposure) (Fig.7-6)

Because there is often not enough bone in which to place an endosteal implant, dentists turned to placing implants on and around bone. Silicon impression material is used for this record. The metal frame was casted with four abutments designed to perforate the covering mucoperiostium to give support to a denture.

The second stage was performed for fixation of the casted metal frame to rest on bone and to be covered by the mucoperiosteal tissues.

A three- dimensional replica of the mandible can be developed from computerized tomography (CT) images, making it no longer mandatory to carry out extensive surgical dissection for a direct bone impression. CT generated models, however, are not as precise as those obtained from a direct bone impression, and many operators prefer the direct technique.

Fig:.7-3: Severely atrophied mandible

IV-Transmandibular (transosseous) dental implants “staple

boneplates”:

- The staple bone plate is used to rehabilitate the atrophic edentulous mandible.

- It is a transosteal threaded posts which penetrate the full thickness of the mandible and pass into the oral cavity in the parasymphysial area (Fig.7-7).

Fig:.7-4: Upper framework Fig:.7-5: Lower framework

Fig:.7-6: A three- dimensional replica of the mandible can be developed

from computerized tomography (CT) images.

Fig.7-7: Transmandibular

(Transosteal) dental implant.

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V- Endosteal (Endosseous) implants:

- The implant is placed into the alveolar bone and composed of anchorage component (body) and a retentive component (abutment).

- Endosseous implants are the most frequently used implants today for fixed, fixed detachable prosthesis, overdenture and in cases of single tooth replacement.

- Various implant designs emerged in the early 1960. The majorities are screw-shaped but some are cylindrical, with or without vents and some have a fin- link extension. It has to be noted that the era of placing root form implants into bone to support a tooth was started very early with various degrees of success.

- In 1978 Branemark presented his work, which done in Gothenburg, Sweden "the two- stage titanium screw root- form implants with osseo-integration concept"

- The discovery of osseo-integration has undoubtedly been one of the most significant scientific breakthroughs in dentistry over the past 30 years.

1- Classification of endosseous implants according to their design:

a- Cylinders endosseous implants.

b- Screws or spiral post endosseous implants.

c- Blade form endosseous implants.

d- Root form endosseous implants.

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a- Cylinders which may be either tapered or baskets (hollowed with fenestrations).

b- Screws or spiral post implant which may be either solid or hollowed.

Fig.7-8 a:

Smooth Cylinder design

B: Solid Screw Design

C: Hollow vented

D: Ripped with apical vent

c- Blade form endosteal implant.

It is a wedge shaped implant composed of head, neck and body with vents which develops fibro osseous integration with bone.

The blade implant is a mean of utilizing the narrow and/ or shallow areas of remaining alveolar bone where dimensions do not permit the use of root form implants. The blade implant was restorable within a month of placement by the superstructure.

The blade vent implant was designed to solve the problem that existed in knife edge ridges (Fig.7-9 a-b).

Ramus frame implant was designed to be placed in the ramus of the mandible (Fig. 7-10-7-11).

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A: a wedge shaped Blade Vent implant

b c

d

e

Fig.7-9A-e : The blade implant is a mean of utilizing the narrow and/ or shallow areas of remaining alveolar bone

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A: Ramus blade implant

b

c

d

Straight Ramus frame Bent Ramus frame

Fig.7-10, A-d: Ramus blade & ramus frame

d- Root form implants:

- In 1973 Flander a new design of endosseous implants to decrease the high rate of failure of the old screw implants

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-

- The endosteal implant shaped in the approximate shape of the tooth root (Fig. 7-11, 7-12).

- It may be used for fixed, removable or fixed detachable prosthesis.

- It requires more than 10 mm vertical bone height, more than 6mm buccolingual thickness, and more then 8mm mesiodistal width to avoid undesirable complications.

b

a c

First Implant Design by Branemark.

Branemark Implant Core– Vent implant

Fig. 7-11 a:d: All the implant designs are obtained by the modification of existing designs.

Surgical Procedure

Fig.7-12 a: e: Different types of root form implants.

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2- Classification of endosseous implants according to

their material:

The endosseous implants may be made from either: a- Pure titanium: the titanium oxide surface was responsible for

the formation of the direct bone- implant interface. b- Titanium alloy: the titanium alloys exist in three forms: alpha,

beta and alpha beta phases and they all originate when pure titanium is heated and mixed with aluminium and vanadium.

3- Classification of endosseous implants according to

surface characteristics:

a- Sand blasted surface. b- Titanium Plasma Sprayed surface (TPS), it has satisfactory

results regarding the osseointegration and the clinical prognosis. c- Titanium oxide surface: coating the implants to make the inert

metal a bioactive one. d- Hydroxyapetite coating

4- Classification of endosseous implants according to

the insertion technique:

The insertion techniques of endosseous implants have been classified into either:

a- Press fit technique, in this type of unthreaded implants, the implant site is drilled slightly smaller than the actual implant size, where the implant is pressed into the recipient site with slight friction.

b- Self tapping technique, in this type of threaded implants, the implant threads are used to tap its site during insertion.

c- Pre-tapping technique, in case of very dense bone, the implant sites are better to be previously tapped using the bone tap instrument before insertion of the threaded implant.

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5- Classification of endosseous implants according to

surgical stages:

a- Single stage design (none submerged – transgingival): the body of the implant is inserted into the bone with its abutment portion penetrating through the mucoperiosteum during the healing period.

b- Two stage design: in this design the implant body is completely embedded in bone for complete osseointegration. The implant body is then exposed and the healing abutment is placed for soft tissue healing before the impression is made for prosthesis fabrication.

6- Classification of endosseous implants according to

biologic tissue response:

According to the type of implant bone interface, the dental implants are classified into either:

a- Biointegration: anchorage may be achieved through a non mineralized zone, which is claimed to be a pseudo-periodontium.

b- Ligamental integration: Cranin the presence of soft tissue layer surrounding the implant.

c- Fibrointegration: researches revealed that clinical success rating was not convincing with the presence of a connective tissue layer surrounding the implant. it is doubtful to achieve a long-term anchorage by means of connective tissue layer between the implant and the bone.

d- Osseointegration: it is a direct structural and functional connection between ordered living bone and the surface of a load carrying implant. This type of connection is considered the most desirable one by many authors.

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Osseointegration: Osseointegration Defined by Misch in 1993 as:

Direct contact between ordered living bone with the surface of an implant on the microscopic level of magnification without any intervening tissues

The key for success of osseointegration. • Meticulous tissue handling to give the bone and marrow

tissues the power to repair as such, and not as low differentiated s car tissues.

• A minimum volume of the remaining bone should be removed and the original jaw bone topography must as far as possible be left intact.

To establish TRUE& LASTING osseointegration we should know. • The response of hard and soft tissues to surgical preparation

and implant placement. • The time needed for healing process, which is expected to

result in osseointegration. • The immediate and long- term adaptation of tissues to

functional load.

Fig.7-13, a: Osseo-integrated. B, Non osseo-integrated.

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7- Endosseous implants are also classified according to

the material into:

a- Non metallic implants, this type of dental implants is made of either

- Ceramics.

- Polymers, or

- Carbons which decreases the induced stresses in bone, but it was found to be of lower strength quality and thus it is not used any longer.

b- Metallic implants, this type of dental implants is made of high strength metals. It is one of the most suitable types.

8- Classification of endosseous implants according to

the time of installation:

a- Immediate implants, they are placed into a prepared extraction socket following tooth extraction.

b- Immediate delayed implants, they are placed within 6-12 weeks after the tooth loss.

c- Delayed implants, they are placed within 6-12 months after tooth extraction, when complete healing and bone remodeling occur.

9- Classification of endosseous implants according to

time of prosthetic loading:

a- Immediately loaded implants, an acrylic resin prosthesis which is designed to be out of occlusion is placed immediately after implant placement, specially in anterior region for esthetic purposes.

b- Delayed loading implant, delayed loading is done in maxillary implants after 4-6 months and in mandibular implants after 3-4 months to allow for better osseointegration due to the difference of the investing bone composition.

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HEALING OF ENDOSSEOUS IMPLANTS (WOUND RESPONSE)

Surgical procedure is performed in a patient to insert a foreign material into bone, and then the body is called on to "heal" with direct contact of the implant to bone (osseous integration).

There are many requirements for successful osseous integration, which must be considered, during the placement of endoseous implants.

Bone implant interface

The exact chemical nature of the interface that forms between the bone and the metallic implant is yet to be determined, theoretically it is either:

1- A week Vander waals bond.

2- Direct chemical bond (ionic or covalent bond).

3- Combination of 1& 2.

The implant material is one of the important factors that determine the chemical nature of this interface. Chemical bonding of the implant material to the surrounding bone is a well- described phenomenon with certain material, such as calcium phosphate ceramics.

Other materials, such as alloys, carbon, aluminum oxide, and most polymers, have a minimum to nonexistent interfacial chemical bond, but they have excellent bone contact.

It is controversial; however, whether commercially pure titanium form a direct chemical bond to bone, but it is believed that although a chemical bond may be present, the bond strength is of lesser magnitude than that experienced with HA.

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Biocompatibility

The development of biomaterials science has resulted in classification of implantable materials according to their biologic response and toxicity into:

1. Bio-tolerant materials e.g. polymethylmethacylate: if these materials are implanted in bone a thin fibrous tissue interface will be formed around them due to their chemical nature.

2. Bio- inert materials e.g. titanium and aluminum oxide: these are materials which are non-reactive to surrounding tissue. Under favorable mechanical condition a direct bone contact (osseo-integration) will result.

3. Bioactive materials e.g. Glass and calcium phosphate. Implanting of such material, under favorable mechanical condition will result in direct chemical bond between implant and bone.

Titanium& Titanium based alloys

Commercially pure Titanium and Titanium based alloys are low density metals that have chemical properties suitable for implant applications. Titanium has a high corrosion resistance attributed to an oxide surface layer, which also creates a chemically non- reactive surface to the surrounding tissues. The modulus of elasticity is at least five times greater than bone. The higher the impurity content of the metals, the higher the strength and brittleness. Titanium has poor strength a wear resistance, however, making it unsuitable for articulating surface.

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Factors affecting healing

There are many factors that can affect the healing process. Some of these factors deal with surgical technique and treatment plane, whereas other deal with patient selection, hygiene, loading pattern, and site selection.

1- Surgical technique

All surgical procedures are traumatic. The level of trauma is a critical factor that determines whether healing will progress toward fibrous or osseous integration. Surgical preparation on hard tissue causes a necrotic zone of bone (interface) due to cutting of blood vessels, frictional heat, and vibrational trauma. Excessive trauma leads to fibrous encapsulation of the implant. Surgical trauma must be minimized during all aspects of implant surgery to optimize success rates. The temperature for impaired bone regeneration has shown to be as low as 44 to 47 c for one minute.

2- Premature loading

Time should be allowed for healing of necrotic bone, formed due to surgery. Movement of the implant during this healing phase will result in fibrous encapsulation. For this reason it is recommended by many operators to keep the recently placed implants unloaded for a period of two to eight months depending on the clinical situation, implant coating, location of the implant, and whether the implant is placed into bone grafts.

3- Surgical fit

Even with the best technical precautions, bone contacts only portions of the implant and a perfect microscopic contact is not possible. A longer healing period will be required before loading implants then surgical fit less then optimal.

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4- Bone quality and quantity

The mandible has a denser cortex and a coarser thicker cancelli than the maxilla. When we go posterior, jaws tend to have a thinner, more porous cortex, and a finer cancelli. Bone regeneration is more likely to progress at a faster rate if the surrounding is denser. it is very frequent to find that bone amount is not enough for implant placement.

The following measures can be done to overcome this problem:

- The use of shot implants. - Changing the implant angulation's. - Ridge augmentation. - Transpositioning of the neurovascular bundle in the mandible. - Subantral augmentation (sinus lift) in the maxilla. - Bone synthesis (ossified tissue can be created in predetermined

shapes and dimensions).

5- Physical condition of the patient:

Nutritional status, aging, diabetes mellitus, blood diseases, corticosteroids therapy and radiation treatment are among many factors which can affect healing.

Team approach

Some authors believe that the same operator should place and restore the implants. The rationale is that it is more efficient form a patient's point of view. It also allows the practitioner more freedom in changing the predetermined position of the implants at the time of surgery. Because the same individual is responsible for the prosthetic treatment, these changes can be incorporated into the treatment plan more readily.

Others believe that a team approach is more appropriate to follow. A surgeon should place the implants, and a prosthetic dentist should complete the restoration. Because it allows for the utilization of expertise of the two individuals, there is a built- in second opinion

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in the approach. Additionally, there is shared responsibility and shared liability. Regardless of the philosophy followed, it is well to delineate the responsibilities at each stage of implant therapy, and it should be clear that dental implant is a prosthetic technique with a surgical step.

The prosthetic dentist should:

1- Perform the initial clinical evaluation. 2- Perform the initial radiographic evaluation. 3- Obtain the diagnostic casts. 4- Obtain the diagnostic wax- up. 5- Determine the location and number of implants and fabricate a

surgical template. 6- Select the proper abutment following the implant exposure. 7- Design and fabricate the prosthesis. 8- Provide oral hygiene care and instructions. 9- Ensure recall of the patient to evaluate maintenance and

provide care as required.

The oral surgeon responsibilities include:

1- Confirmation of the radiographic evaluation.

2- Confirmation of the physical evaluation.

3- Determination of the location and number of implants within limits set by the prosthetic dentist.

4- Placement of the implants (first stage surgery).

5- Uncovering of the implants (second stage surgery).

6- Confirmation of osseo-integration of the implants.

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Dental Implants Materials and Composition

General requirements of implant biomaterial

1. Biologically compatible, they must not be toxic, nor carcinogenic and they must not cause local or systemic damage. Additionally, they should elicit physiological reactions within the surrounding tissues.

2. Mechanically compatible, i.e. of adequate strength properties to withstand the occlusal forces without permanent deformation but should be of low modulus for optimum force transfer.

3. Radiopaque.

4. Sterilizable.

5. Not complicated surgically or prosthetically.

6. High esthetic properties.

7. Economically reasonable.

Taitanium and Niobium and their alloys

Disadvantage:

1-difficult to cast because of their high melting points which are 2996 °C and 2468 °C respectively, they must be processed with powder metallurgical techniques and high vacum centering.

2-Tantalum was considered to be mechanically inferior and susceptible to corrosion (39).

Commercially pure titanium and titanium alloys as dental implant material.

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Physical properties of titanium:

1- melting point 1668 C ,high melting point of titanium makes its casting process so expensive as it require special melting procedure , cooling cycles , mold material and special casting equipments.

2- It is highly reactive nature in the presence of such gases as oxygen, the casting must be done in a vacuum furnace, to prevent metal contamination during casting. Without a well controlled vacuum, titanium surfaces will be contaminated with alpha case, oxygen enriched and hardened surface layer of about 100 micrometer thick. This surface layer reduces strength and ductility and promotes cracking because of the embrittling effect of the oxygen.

3- Density of titanium is 4.5 kg\m3, because of its low density it is difficult to cast in conventional, centrifugal –force casting machines. (In the last 10 to 15 years, advanced casting techniques, which combine centrifugal, vacuum , pressure , and gravity casting , new investment materials, and advanced melting techniques have been developed, these advances have led to the feasibility of casting titanium, based materials in the dental laboratory.

4- It is paramagnetic and has low electrical conductivity and thermal conductivity.

5- Titanium is an allotropic metal that can exist in two different crystallographic forms. Its atomic structure is affected by high temperature. i.e. at temperature up to 882 °C. It exists as a hexagonal close-packed atomic structure (alpha phase). Above this temperature, the structure is body centered cubic (beta phase).

The elements oxygen, aluminum, carbon and nitrogen stabilize the alpha phase of titanium because of their increased solubility in the hexagonal close packed structure.

The elements that stabilize the beta phase include manganese, iron, chromium and vanadium.

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Titanuim Alloys

There are three principal types of titanium alloys: Alpha alloys, alpha-beta alloys and beta alloys.

Alpha alloys commonly have creep resistance superior to beta alloys. Alpha alloys are suitable for somewhat elevated temperature applications.

They are also sometimes used for cryogenic applications. Alpha alloys have adequate strength, toughness, and weldability for various applications, but are not as readily forged as many beta alloys.

Alpha alloys cannot be strengthened by heat treatment. Beta alloys have good forging capability. Beta alloy sheet is

cold formable when in the solution treated condition. Beta alloys are prone to a ductile to brittle transition temperature. Beta alloys can be strengthened by heat treatment. Typically beta alloys are solutioned followed by aging to form finely dispersed particles in a beta phase matrix.

Alpha + beta alloys have chemical compositions that result in a mixture of alpha and beta phases. The beta phase is normally in the range of 10 to 50% at room temperature. Alloys with beta contents less than 20% are weldable. The most commonly used titanium alloy is Ti-6Al-4V, an alpha + beta alloy.

While Ti-6Al-4V is fairly difficult to form other alpha + beta alloys normally have better formability.

Alpha + beta alloys can be strengthened by heat treatment. When strengthening alpha + beta alloys the components are normally quickly cooled from a temperature high in the alpha-beta range or even above the beta transus. Solution treatment is then followed by aging to generate a proper mixture of alpha and transformed beta. Heat treatment is dependent on the cooling rate from the solution temperature and can be affected by the size of the component.

Titanium aluminum-vanadium alloy (Ti6-Al-4V), is an alpha-beta alloy, it is the most commonly used alloy for dental implant.

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3- Non metallic implant

Types of non metallic dental implants

a- Ceramic.

b- Polymer

c- Carbon

A. Ceramics

A single crystal sapphire aluminum oxide endosseous implant

Advantage:

- Its excellent soft and hard tissue biocompatibility,

Disadvantage:

- Range of problems included fractures during surgery, fractures after loading, mobility, infection, pain, bone loss, and lack of osseointegration

A zerconia implant

Gray color of a titanium implant might hamper the esthetic appearance of the entire reconstruction in cases of thin peri-implant soft tissue or tissue retraction.

Hydroxyapatite implant

Different forms of hydroxyapatite were used for augmentation of resorbed ridges and both hydroxyapatite and tri-calcium phosphate materials were used for coating of different types of dental metal implants. Hydroxyapatite root implants were used experimentally for bone preservation after teeth extraction.

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Flexible (Polyactive) (hydroxylapatite) dental implants

Polyactive is an elastomeric polyethylene-oxide polybutylene-terephthalate (PEO:PBT) copolymer,with a low modulus of elasticity, that exhibits bone-bonding characteristics. Polyactive implants function clinically adequately and resemble the mobility of natural teeth

Polyactive implants showed a statistically significantly higher bone contact, as compared to the HA implants, flexible bone bonding implants might be more capable of transferring stresses to the surrounding bone and are therefore promising alternatives to "routine' rigid implants.(46)

Ceramic dental implant abutment:

- Aluminum oxide implant abutment,

- The ZiReal Post: A new ceramic implant abutment.

- Alumina-zirconia machinable abutments

- The Procera abutment.

B. Polymers - Silicone implants, connective tissue does not attach to the

surface of silicone or any other polymeric material

- High-strength silicon nitride implant.

- Hard tissue replacement (HTR)

This hard tissue replacement material to fill the bone channel over the shoulder of blade vent implant in an attempt to control bone resorption in this critical area. It was found that this material was very effective in minimizing bone resorption, increasing bone density and controlling implant mobility.

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- Composite implant

- Hydroxyapatite-based composite dental implant

The HA-based composites were fabricated by mixing HA with Al(2)O(3)-coated ZrO(2) powders

- plasma-spraying coating bioactive ceramics onto silicon nitride surface

- Because silicon nitride has high strength and hydroxylapatite (HA) and flourapatite (FA) have good biocompatibility

- Plasma spray HA, FA onto its surface as composite endosteal implants.

C. Carbons

Vitreous carbon implants are made of glassy carbon layer on a stainless steel core; it can be placed in either fresh tooth extraction sites or in sockets prepared in the edentulous ridges. It is indicated for single tooth replacement as single free standing unit or splinted to adjacent teeth but it is easily fractures or chipped if not properly handled.

Another two types of carbon were used as dental implant material which are less brittle as the vitreous carbon pyrolytic carbon the vapor deposited carbon

Surface characteristics of dental implants

1. Titanium oxide surfaces the excellent biocompatibility.

2. Sandblasted surface

3. Laser induced surface roughening

4. Plasma sprayed surface coating

5. Hydroxyapetite coating

6- Bioactive glass ceramic cervical coating of metal implant

- 106 -

The advantages of hydroxyapatite coated implants include:

Improved biointegration and faster bony adaptation as bone growth from both surfaces of implant and the cut bone. It shows improvement in the bone implant interface area in comparison to pure titanium implant in the early phases.

Disadvantages of hydroxyapatite coated implants are:

1. Bacterial colonization.

2. coating failure has been attributed to two main reasons:

a) Dissolution of hydroxyapatite layer.

b) Fracture of titanium hydroxyapatite bond.

3. Saucerization phenomenon: is a sudden occasional, rapid and destructive peri-implant crestal bone loss, that is usually occur after an initial successful period of biointegration, due to unknown etiology (32).

Bioactive glass ceramic ceravital coating forms a physicochemical bonding with bone which is capable of withstanding stress caused by tension, this new implant is suitable for the combination of metal implant stability and tissue compatibility of glass ceramic.

Requirements for achieving proper osseointegration:

Proper osseointegration is mandatory for the desirable long term

prognosis of the dental implants.

Several factors are involved in the direct bone to implant relation.

- 107 -

These factors are summarized as follows:

1- The implant material:

The implant should be made of an inert material that resists

corrosion and has sufficient strength to allow for proper long

term osseointegration .

2- The implant design:

The design should allow intimate contact between the

implant and its prepared bone site to provide immediate

immobilization after installation and during the healing period”.

3- The implant surface:

The implant surface should be clean, sterile and free from

any metallic contaminants capable of causing corrosion (107).

4- The host bone properties:

Bone combining good vascularity and mechanical resistance

provide a good implant prognosis. Bone resorption may occur

due to unavoidable surgical trauma and that bone integration

may be distorted by irradiation.

5- The surgical technique:

The surgical technique for implant insertion should aim to

cause minimal tissue trauma. The bone will heal and new bone is

formed only if certain local conditions are optimized concerning

bone drilling and cooling system. Bone drilling should be

perfomed using a graded series of drill sizes rather than

using one large drill .

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6- The condition for healing at the implant site:

Premature implant loading before sufficient implant

stabilization is a potential hazard for its osseointegration. The

relation between the implant and jaw bone can be divided into

three partly overlapping time periods which are: healing stage,

remodeling stage and steady stage.

Criteria for success of dental implants:

The criteria for success of osseointegrated implants includ:

1- Immobile implants when tested clinically.

2- No peri-implant radiolucency in radiographs.

3- Bone loss is less than 0.2 mm annually after the first year

of service.

4- Absence of pain, infections, necropathies, paresthesia or

violation of the mandibular canal.

5- The implant design should not interfere with the

placement of a crown or prosthesis with a satisfactory

appearance to the patient and/or the dentist.

Clinical Evaluation

Chief Complaint:

The practitioner must determine which is the most important for the patients, aesthetic, mastication or phonation. This requires careful listening and sufficient time.

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Physical Evaluation:

The medical history normally taken in the modern dental office often is enough for implant patient. It must be kept in mind that there are few contraindications to the use of dental implants. Proper evaluation should be made whether the patient can tolerate the planned procedures or not consultation with the surgeon at this point may be necessary to arrive at proper evaluation in- patients with complicated medical history.

The physical ability or limitations of the patient also play a part in the design of the prosthesis, the selection of the final restoration.

Psychological Evaluation

One must realize that. For many patients, the perception of what constitutes implant therapy has been formed from information provided by friends, publications, and other mass media. This is not necessarily all negative, because it results in the patient seeking implant therapy. Many times, however, the patient cannot properly evaluate the information, and limitations of therapy are not clearly

understood therefore, it is necessary to educate the patient concerning the necessity of specific procedures for the case.

Probably the most frequent misconceptions expressed by the patients concerning the use of implants are the time involved to complete treatment, the surgical techniques used to achieve integration, the effects of resorption of the residual alveolar ridge on the final restoration, the requirement for maintenance of the restoration, and the coast involved.

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Dental Evaluation

In addition to the usual dental evaluation, the prosthodontist must incorporate into this evaluation the possible effects of the conditions present in the oral cavity on implants placed in this environment. A history of bruxism, mal-aligned dentition and extruded teeth, which preclude the development of harmonious occlusion and a hygienic restoration should alert the operator to problems in this area. The patient's commitment to a life long- term maintenance program must be evaluated.

Implants represent only a part of the overall treatment of a patient. The entire dentition must be considered in the treatment plane. Restoration of carious lesions, elimination of spaces by conventional fixed restoration, elimination of periodontal disease, and restoration of a harmonious occlusion, are all requisites for successful implant therapy, it is recognized that active periodontal disease has the potential to spread to peri- implant tissues.

Bone

The age of the patient and the amount and type of bone available to support the implants must be determined. The types of radiographs used depend on the number of implants to be placed, the location in the jaws, and the availability of the equipment. Another method, which can be used in determining the amount of bone available, is palpation. This method is particularly useful in the mandible. It is often possible to encircle the mandible completely with forefinger and thumb and obtain an indication of the size and shape of the arch at a particular point.

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Soft tissue

The soft tissue through which implants exist in the oral cavity is a critical area in terms of long- term success. This is the area that the patient must maintain to ensure gingival health and therefore must be capable of withstanding the hygiene manipulation (brushing and flossing). Fixed keratinized tissue is the preferred tissue in this area. This is the only type of tissue that has ability to form a tight collar around the implant necks. If soft tissue grafting is anticipated, it is probably best done before implant placement.

Ridge relationships

The relationship of the maxilla to the mandible plays an important role in determining the type of prosthesis that can be done and is a deciding factor in the type of occlusion that can often be determined by visual examination, the best observation of this relationship is achieved from mounted diagnostic casts.

Radiographic evaluation

The first step in formulating a treatment plan for dental prostheses using implants must be determination of sufficient bone quantity and quality to support the implants. The choice of radiological technique appropriate for a given patient depends on a number of factors, including the type of restoration and implants to be used, the position of the remaining dentition, the extent to which bone quality or quantity is in question, the availability of the machine needed, and the coast. The following radiological techniques are available:

1- Periapical radiographs.

2- Panoramic radiographs.

3- Lateral cephalometric radiographs.

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4- Conventional tomograms (CT).

5- Computed tomography.

6- Magnetic resonance imaging(MRI)

A maker of known size should be placed directly on the mucosa during the exposure, when a periapical or panoramic radiographs was selected as the preferable technique. The aim of placing such marker (metal ball of known diameter) is the determination of actual ridge height because ordinary radiographs do not have one- to one correspondence with regard to size. For example, if the actual diameter of the maker is 5 mm. However, on the panoramic film they measure 6 mm., a 20% magnification occurred. Therefore, if the bone measure above the interior dental canal is measured 22 mm on the film only 18.3 mm is actually available.

PROSTHODOCTIC OPTIONS

Prosthesis required

The type of prosthesis required depends on a large

measure on the patient's desires and chief complaint. If the

patient's desire is not possible to be achieved owing to the

condition present. The patient must be educated to other

treatment options available to provide a stable, retentive,

supported, and aesthetic restoration. This requires

knowledgeable practitioner. Visual aids that illustrate similar

cases from previous patients can be of great help.

Implants can also be used to improve conventional

prostheses. Implants placed in strategic positions in the partially

edentulous residual ridge can also be used to support removable

partial dentures. Implants can also be splinted with

superstructures to provide the required retention, stability, and

support.

- 113 -

Number of implants required

The number of implants required depends on the type of

prosthesis to be placed. This can vary from single implant to

support one tooth, two implants to improve the retention of an

overdenture, or a greater number for a fixed type of restoration.

The main key factors are to quality and quantity of bone

available, the length of the gap that is going to be restored, and

the patient desire.

Aesthetics

Aesthetics is an area in which the prosthodontist can encounter a great deal of problems. The prosthetic options to ensure an aesthetic result depend on implant placement. It is obvious that the prosthodontist has limited options when trying to restore a mal-positioned implant. The following are the measures needed to guard against the problem of mal-positioned implant:

- Communication with the surgeon.

- Use of surgical stent.

- Communication with the patient about esthetic problems.

Phonetics

This is more frequently a problem in the maxilla than in the mandible. It is most often the patient with a severely resorbed maxilla who is likely to complain with phonetic difficulties. This is due to the encroachment that occurs to the tongue. As the maxilla resorbs, the anterior portion moves posteriorly and superiorly. This means that implants placed in the anterior resorbed maxilla are more palatal than were the natural teeth. When the thickness of the prosthesis is added to cover the implants and it's superstructures, the problem of encroachment on tongue space becomes critical. The solution to this problem is to use a diagnostic wax- up that includes the anticipated thickness of the prosthesis. Bone or allogenic material to rebuild the residual ridge, before implant placement, can often correct severe resorption of the ridge.

- 114 -

Occlusal Surface Materials

There are essentially three materials used on the occlusal surfaces of prostheses. Porcelain, metal, and acrylic resin, long- term beneficial results of one material over the other have not been evident.

Occlusion

Occlusion is a complex subject. Some general occlusal requirements, however, must be entertained at the time of treatment planning. Occlusion is an individual requirement. That is each patient brings with him or her unique occlusal determinates that guide in developing a specific harmonious occlusion for that particular patient. We should not attempt to bring all patients into a particular philosophy of occlusion.

The manner in which the occlusion is developed determines how occlusal forces are directed to the implant and how these are distributed at the implant- bone interface. In general lateral forces must be avoided, and all efforts must be made to direct the forces to the long axis of the implants. The loading on the implants must be minimized to the greatest extent possible.

It should be noted that discrepancies in the horizontal relationship of the two arches could lead to difficulty in attempting to develop a harmonious occlusion. Again mounted diagnostic casts are an essential aid in determining the correct maxillomandibular relationship.

Surgical stent

Once the position of the implants is determined by palpation clinical, radiographic and diagnostic cast examination, the surgical stent is fabricated. There are two main functions for the stent, the first is to guide the operator to the selected places for implant placement and the second is to direct the operator drill to a proper direction through which he should drill in bone (Fig.6.). The surgical stent can be fabricated using a clear heat- cured or autopolymerized acrylic resin and of approximately 4mm in thickness.

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OCCLUSION IN IMPLANTOLOGY

Introduction

Mandibular closure is very important, functionally speaking,

because it ends with the contact of teeth from the upper and lower

arches. To avoid iatrogenic damage to the stomatognathic system, it

is important to consider the principles of occlusion.

Prosthesis design, which is sometimes underrated in

implantology, will be important for the future prognosis of the

installed appliance.

Implants will not always be perfectly positioned, which will

hinder our task in arranging tooth contacts correctly.

In general, we look for prosthesis with an occlusion where

maximum intercuspation coincides with the position of condylar

centric relation.

Now we will define the basic principles of occlusion:

A) Centric relation

This is the physiological position of the condyles when they

are centered in the fossae in their uppermost position and related

correctly with the meniscus against the posterior incline of the

articular eminence.

The successful introduction of the term meniscus into the

definition of centric relation is a sign of openness within the occlusal

philosophies. However, those clinicians who regularly treat patients

with dysfunctional TMJ problems frequently observe that the

meniscus is poorly placed, and in MRI studies it is seen ahead of the

condyle. On few occasions is its physiological position restorable.

This is partially due to this condition being totally asymptomatic, in

- 116 -

many cases, presenting clinically with reciprocal clicks of

variable intensity, which are painless and which sometimes go

undetected by the clinician.

For this reason, we are inclined to believe that in the future

centric relation will be referred to as the physiological position of the

condyles in the fossae, eliminating overloads in the closed position

over soft tissues, which will prove useful in preventing advanced

lesions.

In any event, to achieve better communication with the readers, we

shall still consider centric relation as the ideal physiological condylar

position.

B) Maximum intercuspation

This is the tooth position where maximum occlusal

contacts exist in the active chewing cusps (lower buccals and

upper linguals) in relationship with the opposing teeth.

What we pursue in ideal occlusion is to have both positions

(centric relation and maximum intercuspation) coincided. Maximum

tooth contact does not interfere with the correct condyle position.

C) Working condyle and working side

When the mandible moves laterally, the (working) condyle on

the side to which the jaw moves (working side) carries out an almost

pure rotation on a vertical axis without any lateral displacement. if a

lateral displacement occur, a Bennett movement would be present.

- 117 -

D) Nonworking condyle and nonworking side

These are the opposite condyle and side of the working

condyle and side. The condyle travels forward, downward, and

medially, depending on the presence or absence of the Bennett

movement variations that may exist.

E) Bennett movement

The Bennett movement is a full mandibular side-shift in which

the working-side condyle will initially travel out from the glenoid

fossa, later being able to move upward, downward, forward,

backward, or a combination of these.

These changes in condylar position during lateral movements

greatly influence occlusal anatomy, giving place to variations in cusp

height, groove and incline positioning, as well as the lingual aspect

of the upper anterior segment.

The Bennett movement does not always appear during lateral

excursions. On occasion, it must be induced, and in other cases, it

does not exist.

The Bennett induction maneuver is done by forcing the

mandibular angle on the nonworking side towards the working

condyle, producing on this side an outward sideshift, when the TMJ

allows this to occur. This induction maneuver should be done on

both sides while exploring lateral excursions of the mandible. This

covers the possibility that when the patient is sleeping on his/her side

he or she could start a grinding parafunction. Since we foresee this

situation, with sideshift induction at the time of occlusal equilibration

we can introduce adequate grooves that will allow an escape route

for opposing cusps.

- 118 -

The Bennett movement takes place through different

mechanisms. At t his time, it seems that its presence is related to TMJ

pathology, especially to hyerlaxitudes, whether or not they have an

occlusal origin.

Since most implant patients have lost a great deal of teeth, leading to

joint overloading, we should pay special attention to the Bennett

movement when adjusting the occlusion.

F) Anterior disocclusion guide

In the ideal occlusion, we would like strong contacts in

maximum inter posterior teeth (molars and premolars) and softer

contacts in the anterior teeth (canine, lateral and central incisors);

once eccentric movements ( (lateral or protrusive( begin, the anterior

teeth immediately become the guidance, disoccluding the posterior

teeth.

The anterior guide should be as flat as possible allowing for

posterior disocclusion. In this way, the whole system will function in

harmony, avoiding unwanted TMJ tension originating from the

occlusion.

As a general rule, a condylar sideshift of 3mm should have

a 1.5 mm separation in the opposing teeth on the nonworking side

and a 1-mm separation on the working side. If we follow these

principles, overloading of the structures that keep the condyle in

the articular fossa and of the anterior implants will not occur.

This is due to the fact that the lingual aspects of the canines,

laterals, and centrals will be in harmony with the inclination of

the articular eminence, permitting physiological function of the

stomatognathic system. It should be noted that because of the

osseous anatomy of the anterior maxillary area, implant

inclination will be similar to that of the eminence.

- 119 -

Fig.7-14: Relationship between the inclination of the eminence

and lingual aspect of the anterior segment.

When developing the occlusion in a restoration, the anterior

guide must be created first; once it is perfectly incorporated, we move

on to adjust the occlusion in the posterior.

G) Posterior occlusal anatomy

The construction of posterior occlusal anatomy consists of

correctly positioning cusps, fossae, and pathways, while searching for

tooth-to-tooth and cusp-to-fossa relationships.

In the maxillary arch, the active cusps are the linguals:

- First and second premolars (one active cusp)... lingual cusp

- Molars (two active cusps)... mesiolingual and

distolingual cusps

In the mandibular arch, the active cusps are the buccals:

- First and second premolars (one active cusp)... buccal cusp

- Molars (three active cusps)... mesiobuccal, distobuccal, distal

cusps

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The buccal cusps in the maxillary arch are nonactive:

- First and second premolars (one cusp)... the buccal

- Molars (two cusps)... mesiobuccal and distobuccal

The lingual cusps are nonactive in the mandibular arch:

- First and second premolars (one per tooth)... the lingual

- Molars (two per tooth)... mesiolingual and distolingual

The nonactive cusps participate in fossae configuration and bolus

retention during mastication.

To achieve proper occlusion and efficient masticatory function, the

active cusps must have their corresponding opposing fossae.

Distribution of active cusps with their corresponding fossae is done

in the following way:

-- Upper active cusps (lingual)

First upper premolar .. distal fossa of the lower first premolar

Second upper premolar... distal fossa of the lower second premolar

Upper molars:

Mesiolingual cusp to central fossa of the opposing mandibular molar

Distolingual cusp to distal fossa of the opposing mandibular molar

-- Lower active cusps (buccal)

First lower premolar... mesial fossa of first upper premolar.

Second lower premolar... mesial fossa of second upper premolar.

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Lower molors:

Mesiobuccal cusp to mesial fossa of the opposing maxillary tooth.

Distobuccal cusp to central fossa of the opposing maxillary tooth.

Distal cusp to distal fossa of the opposing maxillary tooth.

In this way we have arranged the cusps and fossae of the posterior component of the occlusion.

The next step will be to relate the cusp within the fossa. Some philosophies of occlusion support tripodization, while others prefer that the cusp tip contact the bottom of the fossa. Our philosophy is to seek cusp contact on the fossa incline. We try to obtain one, two, or three contact points, making sure they are really contact points and not surface contacts.

Three contacts per cusp is considered the ideal situation but is seldom achieved. We do not believe that the cusp tip should be at the fossa’s bottom, because to avoid lateral contacts, the active part will probably be very small.

Considering that we can relate 38 cusps to 38 fossae, we believe that this is enough to obtain adequate masticatory function, even if we only achieve one contact in each fossa. This means we would have at least two in premolars (corresponding to one cusp and one fossa) and five in molars (cusps and fossae), which would give sufficient occlusal stability.

Now we have the cusps seated in the fossae (with point-like

contacts), the condyle in centric relation, the absence of

prematurities, and disocclusion .through good anterior guidance. The

grooves that will allow the cusps to exit from their fossae during

working, nonworking, and protrusive movements are now designed.

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A B Fig. 7-15: A, Occlusion of the upper active cusps (lingual) into their corresponding opposing lower fossae. B, Occlusion of the lower active cusps (buccal) into their corresponding opposing upper fossae.

Working (rotation and perhaps outward or other combinations)

and nonworking (downward, forward, and medial) condylar

movement must be considered for groove inclination and direction

that will permit, according to the different mandibular movements,

the cusps to exit their fossae without posterior contacts.

Evidently, the exit routes of the cusps follow their

corresponding grooves, that is, the fossae exit paths are completely

opposite in the upper and lower teeth.

Upper arch:

Working groove: transversal towards buccal

Nonworking groove: oblique towards mesial and lingual

Protrusive groove: towards mesial

- 123 –

Fig. 7-16: Diagram of the active

masticatory area.

Lower arch:

Working groove: transversal towards lingual

Nonworking groove: oblique towards distal and buccal

Protrusive groove: towards distal

It should not forget that all fossae need grooves to allow cusp exist without interferences. In Figs. 3.4 and 3.5 only one upper and lower teeth have been shown, but the direction of all grooves is similar in the rest.

In lateral excursions, this will only allow anterior tooth contact, while the posterior teeth remain completely free. However, in closure, only the posterior teeth will be in contact (cusps in fossae), the anterior teeth remaining almost free contact.

The forces applied on the implants will be vertical with respect to the axis of the posterior teeth, thus avoiding loads on the anterior teeth.

Fig. 7-17: Diagram of maxillary exit paths. - 124 -

R. Fig. 7-18: Diagram of mandibular exit paths. L

Red(left) nonworking Blue(center) protrusive Green(right) working H) Prematurities Prematurities represent any tooth contact during mandibular closure, with the condyles in centric relation that occurs before maximum intercuspation.

Prematurities force the condyles out of centric relation. If there are

parafunctions, this can lead to articular and muscle overloading, as

well as alterations of masticatory dynamics conductive to pathology

in the long run.

On the other hand, the fact that full force is applied in one

point (initially) implies osseous and implant overloading, not only on

the tooth closest to the prematurity, but also on the rest, because of

the leverage that is produced.

- 125 -

Fig. 7-19: Diagram of prematurity.

I) Interferences

These are the nonphysiological contacts that appear in the

anterior and posterior teeth in lateral and protrusive excursions.

a) The nonworking interferences are very important because the

mandible must pivot avoid them, which in turn produces:

* A compressive component on the working condyle, predisposing to

arthrosis and discal pathology in their external insertions (Fig. 7-

18).

* A tensional component in the non-working condyle, which

predisposes to hyperlaxitudes and meniscal displacement (Fig. 7-

19).

* Overloading of the implants due to the presence of lateral forces.

b) The working interferences create large frictional surfaces in premolars and molars during lateral excursions due to the presence of multiple contacts. The lateral forces generated cause implant overloading and loss of harmony among the anatomical structures within the articular fossa.

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Fig.: 7-20 Fig.: 7-21

Fig.: 7-2 Fig. 7-23

If anterior guidance cannot be accomplished, group function should be used. This should be done following the anatomical components and obtaining contact in the first premolar, second premolar, and mesiobuccal cusp of the upper first molar (Fig. 7-22).

The presence of anterior guidance implies that posterior contacts during working movements should be eliminated (Fig 7-23).

c) Protrusive interferences create a tensional component in both condyles and implant overloading (Fig 7-24).

Prematurities and interferences will be more or less pathological depending on whether parafunctions are present.

- 127 -

During mastication, the teeth should only contact at the end (before that, a bolus exists that separates them). Contacts also occur when swallowing saliva. The duration of both functions totals approximately 10 minutes daily. If parafunctions exist, the time for both functions may increase enormously, thus causing the appearance of a traumatic factor. Unless there are remaining teeth, it will be impossible to determine the relationship between stress, parafunctions, and the patient.

The patient's occlusal restoration should not only focus on the masticatory function (as mentioned before, these occlusal contacts are not long-lasting, so they will not be of great importance) but also and particularly on parafunctions.

For this reason, avoiding prematurities and interferences is important; however, it is also important to inform patients of the dangers of clenching and grinding, which in many cases they are not aware of.

On occasion, we must protect the whole system through the use of nocturnal occlusal splints.

Fig. 7-24

- 128 -

Levers and masticatory forces

It is important to go into detail here to know how far we

must extend the prosthesis and what happens should there be

overloading on the anterior teeth.

The force vectors of the masticatory muscles (especially

the masseter) are produced on the mesiolingual cusp of the

upper first molar, making this the major loading point. Figure

7-25 shows the resultant of these force vectors of mastication

and its influence on mandibular stability.

Fig.: 7-25 shows the resultant of these force vectors of mastication and its influence on mandibular

stability.

Fig. 7-26

If the first contact happens in the area of the anterior teeth, it

could lead to posterior condylar displacement, producing overload capsulitis(Fig 7-26).

If we can achieve contact from front to back up to the upper

first molar, mandibular distalization will be avoided. Consequently,

to have a stable TMJ it is important to have at least occlusion on the

mesiolingual cusp of the upper first molar (Fig 7-27).

- 129 -

On other hand, it must be emphasized that the anterior teeth

should not contact in maximum intercuspation, because in practice it

is very difficult to differentiate between physiological and excessive

contacts. In maximum intercuspation, the occlusion from canine to

canine should allow for a Mylar strip to be pulled with a certain

resistance, yet not being fully held by the teeth. This will confirm the

absence of heavy contacts there and will prevent future compressions

of the posterior TMJ area

Fig. 7-27

.

Occlusion in implant-supported prostheses

A) Fixed or removable restorations with opposing natural

dentition:

In these cases, we recommended mutually protected

occlusion, with anterior guidance and tooth - to tooth and cusp-

fossa posterior occlusion. This is also known as organic

occlusion.

- 130 -

B) Fixed removable restoration with opposing fixed or

removable implant-supported prosthesis

Organic occlusion is recommended for the following reasons:

1. It is easier to produce.

2. If it supported by mucosa and we can achieve a disocclusion

as flat as possible, the tension on the implants will be

minimal.

3. If a bilateral balanced occlusion is created, there will be

many contact surfaces in lateral excursions, thus

increasing muscular contraction force and the possibility

of osseous resorption, which in turn will destabilize the

mucosa-supported segment. In the case of an overdenture,

this could progress into an overload of the stomatognathic

system and the implants if it is not relined periodically.

Organic occlusion is easier to adjust by simply

eliminating all non-anterior contacts during lateral movements.

However, in the case of bilateral balanced occlusion, it could be

difficult to differentiate physiological contacts from true

interferences.

Even if the occlusal scheme is constructed on an articulator, we

should consider that there are many factors not in harmony with

anatomical and physiological realities, like the fact that the joint has

soft tissues (resilience) and mandibular flexibility that on occasion

produces natural positions that can’t be reproduced in a rigid

instrument such as the articulator.

The articulator is of great importance for prosthesis

construction regardless of the type, because it brings us closer to what

truly happens. Yet we believe that the final occlusal adjustments

should be carried out in the mouth, because the mouth is the only

articulator that provides 100% of the necessary information.

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In the mouth, however, it is nearly impossible or at least very

difficult to distinguish between equilibrium (physiological) contacts

and interferences non-physiological) contacts; thus, it is wiser to

eliminate both (balancing or hyperbalancing contact) so as to achieve

disocclusion.

As an example to help understand this situation, imagine the

muscular force needed to drag a hoop along the ground (this

corresponds to canine guidance) and the force needed to drag a barrel

with more surface friction the same way (this corresponds to bilateral

balanced occlusion)

In 1989, Miralles, Bull, and Manns performed an

electromyographic study comparing the activity of the elevator

muscles (temporal and masseter) in balanced full dentures and

canine- guided dentures.

They found that canine guidance produces less activity in both

muscles during lateral movements, which can be considered a factor

in preventing parafunctional activity.

4. Organic occlusion is the most physiological scheme for the

stomatognathic system and implants, but let us not forget that

the patient being rehabilitated can have parafunctional

problems that must not be overlooked.

5. Since there is no posterior seal in cases of implant restoration

with upper overdentures, the presence of bilateral balanced

occlusion does not increase retention during parafunctions,

which would help initial mastication.

6. The presence of canine guidance prevents posterior tooth

wear, stabilizing occlusion and avoiding parafunctions.

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7. Maintenance of the neuromuscular mechanism avoids

overloading of the muscular system and the appearance of

trigger points.

8. In cases with only two implants supporting a lower

overdenture, with adequate mucosal adjustment and seal, it is

advisable to use bilaterally balanced occlusion. This will

improve prosthesis stability and avoid implant overload.

C) Fixed or removable implant-supported restoration

with opposing removable full denture without implants

This is the case in which we advocate bilaterally balanced occlusion. Here it is perfectly logical.

In conventional full dentures (without implants), teeth are arranged in bilateral balance when the patient is not chewing, during parafunctions and with teeth clenching in different positions. Forces are transmitted evenly, resulting in a more stable prosthesis with increased adhesion and fit, which will benefit patient food mastication.

We should not forget that, while eating, the food bolus separates occlusal surfaces, consequently neutralizing balance. However, the adhesion that was previously produced through bilateral balanced occlusion greatly facilitates chewing without denture displacement, through a "vacuum-type" effect.

We support bilateral balanced occlusion because we look for increased full-denture stability in patients without implants.

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D) Partial-prosthesis occlusion

In cases with cantilevers, the resilience of the neighboring natural dentition and of the TMJ should be taken into consideration.

The recommended occlusion in these cases is adjusted for forced biting. In this way, resilience will be introduced into the occlusal adjustment, and in this forced position we omit the contacts. The prosthesis should only contact in a position of forced closure.

As always, all interferences and prematurities should be eliminated with care, leaving only point like occlusion.

E) Single-implant occlusion

Single implants should be free of any occlusal overload and function. The lingual surface of the anterior teeth should be constructed as flat as possible, so if opposing tooth extrusion leads to occlusal contact there will not be contacts in lateral movements.

Single implants in the posterior area should be limited to premolars, reducing their surface area so that they just fulfill esthetics and space maintenance.

At this time we do not advocate the use of single implants for molars. The only solution here is the placement of two implants in the place of the mesial and distal roots to serve as support for a molar.

Occlusal Adjustment in Implant Supported Prostheses

General aspects

This consists of modifying tooth anatomy to obtain a good occlusion.

The objectives are the following:

- To have centric relation and maximum intercuspation.

- To create better anterior guidance.

- To position cusps.

- To deepen fossae.

- To change inclines.

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- To locate the exit paths.

- To build in vertical-dimension holding contacts to avoid implant overloading.

- To eliminate prematurities and interferences.

Occlusal adjustment must be performed in the upper and lower

arch jointly, at the same time, and on both sides.

All of the following adjustments refer to implant-supported prostheses, either when checking a case prior to laboratory work, or once it is placed in the mouth or in finished cases where it is decided to readjust the occlusion. They can also be used in natural dentition.

Technique

There are many different occlusal-adjustment technique philosophies; however, they all lead to a common goal, explained previously.

We will make a compendium of those techniques taught to us by our teachers.

First, the case is mounted on an articulator with a face bow related to the orbital point and the hinge axis, to get a "general idea" of the treatment the patient needs.

We deliberately used the term "general idea," as mentioned before, because the final adjustment will be carried out directly in the mouth. However, we should look for information on prematurities and interferences, and whether canine or anterior guidance is feasible. In our opinion, and considering that articulators are not perfect since they do not simulate soft tissues, we do not feel it is necessary to complicate initial phases with previous registrations (orthopanography) but we must register the patient's condylar inclination.

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The information we wish to obtain can be determined through the use of a semiadjustable articulator (Dentatus, Denar Mark II, etc). It is very important, once we have analyzed the case, to know where we want to start and determine our objective. We believe that it is fundamental to have centric relation and maximum intercuspation coincide, eliminating all prematurities.

We try to avoid cusp-tip contact with the floor of the fossa,

allowing only point-like contacts with the internal fossa walls, so as

to avoid large contact surfaces that can lead to implant overloading.

Once we have achieved anterior coupling, we eliminate the

interferences (Fig. 22-15). In some cases, we will need more than one

appointment to obtain this.

Fig. 7-28

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A) Eliminating prematurities

To mark tooth contact, we use double colored thin articulating

paper or black marking ribbon and we have the patient close from

centric relation (CR) to maximum intercuspation (MI) several times.

1) Mandible

To adjust the lower occlusion, we should remember that in normal occlusion (Class I) the lower teeth (premolars and molars) are ahead of the upper.

So we can observe that when occlusion occurs, the distal lower inclines and the mesial upper inclines contact in condylar centric relation.

To adjust, we should follow these steps:

1- Cusp distal inclines

Eliminate the most distal part (DI) and preserve the most mesial contact point (M) (Fig. 7-29).

2- Active-cusp outer inclines

Eliminate the whole surface except the zone next to the cusp tip (the highest part) (Fig. 7-30).

Fig. : 7-29 Fig. : 7-30

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3- Inner inclines

Eliminate the most distal area (DI), except for the most

mesial and medial contact point (anterior and towards the center of

the fossa) (Fig. 7-31).

Fig.7-31. Fig.7 -32.

2) Maxilla

In the upper arch we always adjust opposite of the lower arch.

1- Mesial cusp inclines

Eliminate the most mesial part and leave the most distal contact

point.

2- Active-cusp outer inclines

Eliminate the whole surface, except for the area nearest to

the active cusp tip (the lowest part) (Fig. 7-33).

3- Inner inclines

Eliminate the most mesial and leave the most distal and medial

contact point (Fig. 7-34)

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Fig. 7-33. Fig. 7-34.

B) Deepening fossae: maxilla and mandible

If the cusp contacts the floor of the fossa, it will create a large

contact surface, which we always try to avoid. There are two

possibilities:

a) Spare the lateral cusp marks while eliminating the

intermediate zone, which will cause loss of active material

for chewing and will decrease efficiency (Fig. 7-35)

b) Deepen the fossa while preserving its lateral aspects, which

will permit preservation of the cusp surface (Fig. 7-36).

The best solution is the second one, because it will preserve

active cusp anatomy and masticatory activity. Occlusal maintenance

contacts will still be present.

The large surface marking that appears on the cusp tip after

deepening the opposing fossa will be reduced simply to two contact

points.

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It should be emphasized that the thinnest possible black double-

colored marking ribbon should be used while eliminating

prematurities and deepening fossa, placing it in the mouth and having

the patient close from centric relation to maximum intercuspation.

At the end of this phase of adjustment a great number of black

contact points, not surfaces, will appear on the occlusal surfaces.

The presence or absence of excessive contact in the anterior

teeth must be checked during closure. It should be done with very

thin ribbon, noting slight resistance while pulling it from the teeth.

The next step is to verify anterior guidance

Fig. 7-35. Fig. 7-36

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C) Anterior guidance

The anterior guidance should be as flat as possible to avoid

overload in the anterior teeth in lateral excursion (on the canines and

anterior teeth) and in protrusion (the contact of the mesial incline of

the first lower premolar on the distal incline of the upper canine, as

well as centrals, laterals, and canines between them).

As the desired occlusal scheme was detailed previously, we

shall merely emphasize that we must avoid producing TMJ tension

and any contact in the posterior when the guidance is in function,

because these would constitute interferences. This is always checked

with red marking ribbon, allowing for fine surfaces of anterior

disocclusion.

D) Eliminating interferences

For this, we must again use red ribbon and have the patient go

through working, nonworking, and protrusive movements.

The next step is to place black ribbon and have the patient

close to maximum intercuspation (centric relation coincides at this

time with maximum intercuspation). All surfaces or points that

appear which are not black must be eliminated (except black on red);

in other words, eliminate all red marking except the guide marks of

anterior disocclusion. When these red markings coincide with

shallow or nonexistent disocclusion, it is convenient to eliminate

them following the corresponding direction, depending if they are

working, nonworking, or protrusive movements

The importance of inducing lateral movements to detect if

Bennet movement is present must not be forgotten.

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Conclusions

Occlusal adjustment is necessary in any kind of fixed or removable

restoration supported by implants.

If we have opposing natural dentition, we must be sure that the

introduction of new cusps in the rehabilitation does not create

occlusal problems in the opposing dentition. If this happens, we

should adjust the natural dentition without hesitation

If the opposing dentition is a full denture that is not implant-

supported, we can bypass the techniques involving physiological

interferences because we are dealing with a bilateral balanced

occlusion; however, we must take care in eliminating prematurities.

When adjusting the occlusion on partial prostheses, the contacts

created must occur during forced biting and at the same time as the

rest, avoiding the introduction of new prematurities or interferences.

The opposing natural dentition must also be checked.

(Occlusion in single implants was explained before)

Because of possible TMJ and occlusal instability, periodic occlusal

checkups (every 3 to 6 months) are strongly recommended.

Occlusal problems will cause bone resorption at the implant site. On

occasion, this is why screws loosen, though sometimes this is related

to the lock of passive fit of the prosthesis over the abutments.

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Occlusal splints

If it becomes necessary to protect the occlusion of the stomatognathic system from parafunctions and overloads, acrylic-resin nocturnal occlusal splints are indicated. In these cases we search for canine guidance in lateral excursions, disoccluding anterior guidance in protrusions, and posterior fossa wall contacts against the opposing active cusp tips that will serve as the deepest part of the corresponding fossa.

Guidance should be as flat as possible; if the distribution of occlusal leverages permits it (minimum occlusal contacts up to the first molar), an upper occlusal splint is employed. If an upper splint is not feasible, a lower splint is used.

The posterior occlusal zone must be absolutely flat and the anterior. concave, without any kind of tooth print, so as to allow freedom of movement in maximum intercuspation and laterally. It must relax the TMJ muscle complex, guiding the mandible to centric relation without any impediments. The presence of minimal contacts and the absence of interferences and prematurities reduce muscular forces during parafunctions (bruxism).

Occlusal adjustment will be undertaken considering the contact markings with their corresponding fossae and upper inner inclines, eliminating the rest that do not correspond to the lower active

cusps (see fossae adjustment and upper inner inclines).

This should be checked periodically. If this should change with the appearance of new prematurities or interferences, it indicates that mandibular position is changing, so special attention must be given to the patient's new occlusion if an occlusal splint is not being used. The implant-supported prosthesis and the natural teeth

(should they be present) must be readjusted.

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Reference

Jimenez - Lopez, V.: Implant-supported prosthesis: Occlusion,

clinical cases and laboratory procedures, Quintessence a Publishing

Co. Carol Stream, Illinois, Ed. Adam Haus, 1995.

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