prostho iv - slide 3 - impression_making_for_complete_dentures

7/27/2019 Prostho IV - Slide 3 - Impression_Making_for_Complete_Dentures

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IMPRESSION MAKING FORCOMPLETE DENTURESKhaled Q Al HamadBDS MSc MRD RCSEd

Associate Professor

4thyear, Dent 445, 2013


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References

Lecture notes.

A Clinical Guide to Complete Denture

Prosthodontics. J F McCord and A A

Grant.


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Part I Review of the relevant anatomy for the maxillary

and mandibular dentures.

Part II: impression techniques

Introduction Primary impression

Choice of tray & material

Definitive impression Conventional technique

Selective pressure technique

Flabby ridge

Fibrous ridge

Flatatrophic- ridge

Functional impression

Lecture Outline


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Mucous membrane Mucosa: stratified squamus epithelium & connective tissue

(lamina propria)

Submucosa: connective tissues made of dens to loose areolartissues If firmly attached: withstand pressure

If loose, thin, traumatized, mobile, flappy: it wont be suitable towithstand pressure-not resilient.

Masticatory mucosa (keratinized): hard palate, residual

ridges, residual attachment gingiva.


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Hard palate Keratinized.

Mid palatine suture: Submucosa is extremely thin-requires relief

Horizontal portion of the Hard palate: 1 support forareas

Rugae areas: set at an angle with the residual ridge-2 support areas.


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The Palatal Gingival Vestige (remnants of thelingual gingival margin)

It is the remains of the palatal gingiva. Aftertooth extraction the position of the vestige

remains relatively constant, the same as theincisive papilla. This can be a very helpfulpointer for posterior tooth positioning duringdenture construction


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Residual Ridges

Mucous membrane:

keratinized firmly attached.

Submucosa: devoid of glandular tissues. Densecollagenous fibers. Relatively thin, but sufficient toprovide support for the denture base.

Crest of the ridge: Prone to resorption.

2 support area.

Inclined facial surfaces Loses its firm attachment

Offers little support

Cannot withstand pressure


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Two orifices one each side of the midline. Coalescence

of several mucous glands - always located in the soft

palate. They act as collecting ducts for a group of minor

palatine salivary glands


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Crest of the residual ridge

Ridge is similar to that of the upper in healthymouth.

Attachment varies considerably. In somepeople, the submucosa is loosely attached tothe bone.

When securely attached to the bone, themucous membrane is capable of providingsupport for the denture. However, becauseunderlying bone is cancelous, the crest of the

residual ridge may be not favorable as aprimary stress bearing area for the lowerdenture.


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Buccal shelf area The mucous membrane is more loosely attached and less

keratinized than that covering the residual ridge. Although the

mucous membrane may not be as suitable histological to providesupport for the denture, the bone of the buccal shelf area iscovered by a layer of cortical bone. This plus the fact that theshelf lies at right angle to the vertical occlusal forces, makes itthe most suitable primary stress bearing area.


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The external oblique ridge does not govern the extension of thebuccal flange because the resistance or lack of it varies widely. Thebuccal flange may extend to the external oblique ridge, up onto it or

even over it depending on the location of the muco buccal fold. The bearing of the denture on muscle fiber of the buccinator would

not be possible except for the fact that the fibers run parallel to thebase, and ,hence , its action is parallel to the border and not at rightangle.


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The disto buccal border must converge rapidly to avoid the action ofthe masseter which is pushing inward the buccinator.

Distal extension is limited by

Ramus

Buccinator

Pterygo mandibular raph.

Superior constrictor

The sharpness of the boundaries of the retromolar fossa. (thedenture should extend slightly to the lingual into the pearl shapedretro molar pad.


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The retro molar pad is a triangular soft pad of tissue. Its

mucosa is composed of thin non keratinized epithelium.

It submucosa contains

Glandular tissues

Fibers of the buccinator and superior constrictor

Pterygo mandibular raph Fibers of the temporalis

Because of theses structures, the denture base should

only extend to one half to two third the retro molar pad.


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The retro molar pad:

It is split into two sections. The anterior section is usually firm andfibrous. It is important for denture support and preventing distaldenture displacement

The mylohyoid ridge: Following the extraction of natural teeth and subsequent resorption,

the mylohyoid ridge becomes more prominent. This can result inmucosal soreness beneath the denture bearing area over themylohyoid ridge.


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Mylohyoid muscle It is a thin sheet of fibers and in a relaxed state will

not resist the impression material.

Carrying the border under the mylohyoid cannot betolerated. The contraction of this muscle will displacethe denture.

Fortunately, the denture in the posterior area of themylohyoid can beyond its attachment because thefold is not in this area.

In the retro mylohyoid fossa the border of the denturecan go move back toward the body of the mandibleproducing the S curve of the lingual flange.

In the anterior region, a depression, the pre mylohyoidfossa can be palpated and a correspondingprominence, the pre mylohyoid eminence seen on theimpression


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Part I Review of the relevant anatomy for the maxillary and

mandibular dentures.


Introduction

Primary impression Choice of tray & material


Selective pressure technique Flabby ridge

Fibrous ridge

Flatatrophic- ridge


Lecture Outline


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Impressions are made with a variety of

materials and techniques. Some materialsare more fluid than others before they set orharden.

The softer materials displace the tissues toa lesser extent and require less force in theirmolding than do viscous materials.

Impressions that record the tissues withminimal displacement are described asmucostatic. Whereas those that displacethe tissues are classified as

mucocompressive

Introduction


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Regardless of the technique or material used, the

tray is the most important part of the impression

making procedure.

Tray-too large:

It will distort the tissues around the borders of the impression

and will pull the soft tissues under the impression away from the

bone distorting the dimension of the sulcus.

Tray-too small: The borders tissues will collapse inward onto the residual ridge

distorting the accurate recording of the border extensions of the

denture.

A properly formed tray enables the dentist to carrythe impression material to the mouth and control it

without distorting the soft tissues that surround it.


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Special trays:

have borders that can be adjusted so they donot distort the soft tissues around them

Provide spaceif needed- inside the tray sothat the shape of the tissues may be recordedwith minimal or selective displacement.

These requirements are not met by stocktrays so most impression procedures involvemaking a primary impression with a stocktray. This is poured and the resulting

primary cast is used to fabricate the specialtray. The final impression is then made withthe special tray.


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Primary Impression

Primary impression should record clinicalrelevant landmarks of the edentulous mouthwithout excessive tissue distortion- overextended impression.

Stock trays are used for this purpose. The tray ismodified as necessary to fit the denture bearingarea.

The basic function is to outline support. Asecondary function is to provide the basis for aprimary cast on which a customized or specialtray is made.

Ch i f M t i l


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Choice of MaterialSilicone Putty

High viscosity, it will flow beyond the tray to compensate for

underxtensions and support itself.

Poor details

Elastic: it will record undercut with reasonableaccuracy.

Cannot be corrected or added to once it sets

Irreversible Hydrocolloids

Records details accurately

Loses moisture-unstable

Less viscous

I i C d


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Impression Compound

Thermoplastic

High viscosity it will flow beyond the tray to compensate forunderxtensions and support itself.

Poor details

Can be corrected by addition. Non- elastic- Not suitable for undercuts

Tray selection

selected from a supply of stock trays which

are deigned to cover road range of arch formsand sizes.

Some trays are metallic, others are plastic


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When assessing the stock trays for size, the clinician isadvised to place the distal portion of the tray just distal tothe posterior landmarks of the tuberosities in the upperarch, and onto the retro molar pads of the lower. Thisenables the clinician to visualise the width of trayrequired to record the functional width of the sulcus i.e.the tray should extend 5 mm beyond the external surfaceof the residual ridge.

By keeping the posterior aspect of the tray in place and

rotating the anterior portion of the tray towards the labialsulcus, the clinician can determine if the tray is of anappropriate length.

When the stock tray of appropriate size has been selected


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When the stock tray of appropriate size has been selected,there is merit in practising insertion of the tray; ideally theclinician should be positioned to one side and behind thepatient. In addition to confirming that the tray is suitable for

size, it allows the clinician to educate the patient on how tocontrol his breathing during the recording of the impression.

When the upper tray has been loaded with the impressionmaterial, and the upper lip everted, the tray is held inferiorand anterior to the incisive papilla. The tray is insertedupwards and backwards to fill, first of all, the labial sulcus,then the left and right sulci before the palatal area ispressed into position. The clinician may have to change theoperating hand to ensure the impression material recordsthe right and left sulci.

With lower impressions, the clinician stands to one side in

front of the patient, the tray is held over the lower ridge andthe loaded tray depressed, the labial, right and left sulci inturn being everted to permit the impression material to fillthe functional width of the sulci

L t O tli


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Introduction




Fibrous ridge

Flatatrophic- ridge


Lecture Outline


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When molding the maxillary buccal vestibule, themandible should be moved to the right and left to free thecoronoid process and masseter should be activated byasking the patient to exert a closing force while thedentist exert a downward pressure on the tray

For the lower, the mandible should open wide to activatethe Pterygo mandibular raph. Also the masseter and

medial Pterygoid should be activated by asking thepatient to exert a closing force while the dentist exert adownward pressure on the tray..

The lingual sulcus is molded by asking the patient toprotrude his tongue forward and then to push the tongue

against the anterior palate


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Depending on the nature of the ridges and

the preference of the clinician, a variety of

materials may be selected. It is our

contention that the critical components ofthis technique are that a stable and

retentive peripheral seal will be

established and that appropriate spacing isincorporated; the choice of material, within

reason, is of secondary importance


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L t O tli


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Introduction




Fibrous ridge

Flatatrophic- ridge


Lecture Outline


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Displaceable (flabby) anterior


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Displaceable (flabby) anterior

maxillary ridge

ensure that the peripheral moulding orcustomising has resulted in a peripheral seal,

an impression of the whole maxilla is takenusing either zinc-oxide-eugenol (ZOE) or a

medium-bodied polyvinyl siloxane (PVS)impression material.

the extent of the displaceable tissue is drawn onthe impression surface. This area, and theequivalent area of the tray, are then removed,using a scalpel and acrylic bur. Insertion of thismodified impression and tray will demonstratethat the tray is no longer retentive.


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Holding the modified trayand impression in situ,use a low-viscositymaterial (Plaster of Parisif ZOE was used, light-

bodied PVS if a medium-bodied one was used)and paint or syringe theseonto the displaceabletissue to record them in aminimally-displaced

position. On setting, itshould be apparent that aperipheral seal has beenre-established

Lecture Outline


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Introduction



Selective pressure technique Flappy ridge

Fibrous ridge

Flatatrophic- ridge


Lecture Outline


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When the customised tray has been adequatelychecked for peripheral extension, it is loaded

with tracing compound (greenstick) and animpression of the denture-bearing arearecorded.


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Using the heated spoon-end of a Le Cron carver or a similarinstrument, remove the greenstick relating to the crestal tissues andperforate the tray in this region. Downward finger pressure of themodified impression, in the mouth, should elicit no discomfort.

Inject some light-bodied PVS onto the buccal and lingual shelves ofthe greenstick and gently insert the impression. Excess material willbe extruded through the perforations, and the fibrous ridge willassume a resting central position, having been subjected to evenbuccal and lingual pressures.

The impression is now treated as for a conventionally madeimpression.


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Flat (atrophic) mandibular ridge


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Flat (atrophic) mandibular ridge

covered with atrophic mucosa

These ridges equate to Atwood's ridge orders v


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These ridges equate to Atwood s ridge orders v

and vi and may be complicated by folds of

atrophic and/or non-keratinised tissue lying on

the ridge. McCord and Tyson described this

technique which is specific for this clinical

situation.The philosophy is that a viscous admix

of impression compound and tracing compoundremoves any soft tissue folds and smoothes

them over the mandibular bone; this reduces the

potential for discomfort arising from the 'atrophic

sandwich', i.e. the creased mucosa lyingbetween the denture base and the mandibular

bone.

an admix of 3 parts by weight


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p y gof (red) impression compoundto 7 parts by weight ofgreenstick; the admix iscreated by placing the

constituents into hot water andkneading with vaselined,gloved fingers.

the lower impression isrecorded. The working time ofthis admix is 1-2 minutes and

this enables the clinician tomould the peri-tray tissues togive good peripheral moulding(Fig. 14).

Any discomfort in the denture-bearing area may be treatedby adjusting the offending areaof the impression with a heatedwax knife and re-inserting asrequired until no furtherdiscomfort is felt. Alternatively,the clinician could indicatewhere relief is required on the

master cast.

Lecture Outline
http://www.nature.com/bdj/journal/v188/n9/full/4800516a.htmlhttp://www.nature.com/bdj/journal/v188/n9/full/4800516a.htmlhttp://www.nature.com/bdj/journal/v188/n9/full/4800516a.html


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Introduction



Selective pressure technique Flappy ridge

Fibrous ridge

Flatatrophic- ridge


Lecture Outline

Functional Impressions


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Functional Impressions

neutral zone technique

It is designed for patients with poor track recordsof (lower) denture stability, a large tongue orother anatomical anomaly.

The clinical stages are standard up to and

including the registration visit. After this, theupper denture is set up conventionally to theprescribed occlusal vertical dimension (OVD).Opposing the upper set-up is a resin base with

three vertical stops joined by a wire bent in asinusoidal manner. The stops must contact theupper teeth at the selected OVD.


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Polyvinylsiloxane putty is added to the conventionalfitting surface and also to the buccal and lingual aspectsof the lower base which has been coated with therequisite adhesive, and placed in the patient's mouth.Following this, the upper try-in is inserted and the patient

asked to close to the OVD, swallow and carry out closedmouth exercises. These exercises provide an indicationof where inward-directed forces from the buccinatormuscles are equalled or 'neutralised' by outwardly-directed lingual forces i.e. the zone of minimal conflict


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The disinfected functional impression and upper try-inare sent to the laboratory and plaster or laboratory-puttykeys made of the functional impression. Into these keyswax is poured to give a functional form to the polishedsurfaces and occlusal form of the lower denture. Thetechnician is then required to fabricate the lower try-inand, subsequently the lower denture, to match thefunctional template - this will necessitate appropriate

t i i f th l l t bl idth d ibl it

prostho iv - slide 3 - impression_making_for_complete_dentures

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