IMPLANT

LOADING

IntroductionPre-load and After-loadPhysiology of bone and loadingModeling and remodelingEarly functional loadingConsequences of biomechanical overloadEvolution of the concept of implant loading

Protocols of implant loadingElements of implant loadingImmediate occlusal loading Factors that decrease riskGuidelines for immediate loadingConclusionReferences

Prosthetic rehabilitation of missing structures in the oral and maxillofacial region in accordance with DeVan's principle of preservation has been the ultimate challenge to the prosthodontist. Over the years, traditional methods of tooth replacement are slowly and steadily being replaced by newer modalities like implants.

High success rates of implants and the advantages that go with them have earned them the name of the "third dentition".

Implants have come a long way from cast cobalt chromium tubes, pins, subperiosteal vitallium implants, endosseous blade implants, ceramic implants to the modern day root form implants made of titanium and its alloys.

Dental implants were commonly loaded at placement because immediate bone stimulation was considered to avoid crestal bone loss (Linkow & Chercheve 1970). Fibrous tissue interposition was considered the optimal response to implants as it was mimicking the natural periodontal ligament.

In contrast to all other experimental studies of that time, Branemark et al (1969) showed that direct bone apposition at the implant surface was possible and lasting under loading at the condition that implants were left to heal in a submerged way.

The basis of the increasing popularity of dental implants is the coincidental discovery by Per-Ingvar Branemark and his co-workers of the tenacious affinity between living bone and titanium oxides, termed “Osseointegration”.

Success with Brànemark's protocol still has a deterring factor in the form of extended treatment period, which sometimes preclude patients from resorting to implant therapy. Increasing functional and aesthetic challenges have prompted implantologists to reduce the treatment period by loading the implant immediately at the time of placement.

The protocol has yielded encouraging results although they still need to match the time tested two-stage procedure, by way of success over an extended period of time.

The Immediate loading of dental implants clearly represents the change in dogma. To load the implant immediately or not to load is indeed the question today and the rationale that goes with the protocol which warrants discussion.

The preloading or stretching the screw places the components under enough tension to create elongation of the material within its elastic limit. Preloading may reduce screw loosening.

As a result the components stretch and maintain fixation in spite of vibration and external forces. The elongation of metal is related to the modulus of elasticity, which is dependent on the type of material, its width, design, and the amount of stress applied per area.

Thus a gold screw exhibits greater elongation but lower yield strength than a screw made of titanium alloy. A prosthesis screw may exhibit a torsional ductile fracture at 16.5 N-cm Vs 40 N-cm for an abutment screw of different material and size.

The material the screw is made from (eg. Titanium alloy or gold) has a specific modulus of elasticity. The plastic deformation or permanent distortion of the screw is the end point of the elasticity modulus. When the screw is stretched with a force 75% of its elastic length, it is able to better resist vibration and screw loosening.

In order to stretch the screw, a torque wrench is necessary, although not completely accurate. Even an experienced clinician is unable to determine the amount of correct torque on the screw by tactile sense only.

A screw may be described to permit more preload on the components.

The after-loading of implants is achieved by means of prosthesis brought into occlusion.

As a result of unique physiological mechanisms, bone serves two antagonistic functions:

structural support and calcium metabolism.

The strength of a bone (quantity, quality and distribution of osseous tissue) is directly related to loading.

As an energy conservation measure, bone that is not adequately loaded is resorbed, and the skeletal system continuously adapts to achieve optimal strength with minimal mass. The delicate structural balance is further challenged by metabolic function.

An adequate reserve of osseous tissue must be maintained to provide a continuous stream of ionic calcium without compromising structural integrity. To provide for a variety of conflicting demands, the skeleton has evolved structural and metabolic fractions.

Osteopenia (inadequate bone mass) is a common clinical problem. It may be due to functional atrophy and/or negative calcium balance.

Prospective oral implant patients are likely to present with localized and systemic skeletal problems for three rea sons:

Bone in edentulous areas is usually atrophic.

Metabolic bone disease is prevalent in middle-aged and older adults.

Integrated implants are often indicated for patients with a history of severe bone loss.

The clinical success and longevity of endosteal dental implants as load bearing abutments are controlled largely by the mechanical setting in which they function. The treatment plan is responsible for the design, number, and position of the implant.

Unique mechanisms of bone adaptation have evolved to maintain structural integrity, repair fatigue damage, and provide a continuous source of metabolic calcium.

Modeling involves individual uncoupled sites of bone formation or resorption that change the shape or form of a bone. This is the principal mechanism for adapting osseous structure to functional loading.

Remodeling is the mechanism of bone turnover. It involves coupled sequences of cell activation (A), bone resorption (R) and bone formation (F). The duration of the ARF remodeling cycle (sigma) is about 4 months in humans.

Modeling is the principal means of skeletal adaptation to functional and therapeutic loads. Relatively modest changes in the distribution of osseous tissue along cortical bone surfaces can dramatically change the overall load bearing capability.

By a mechanism of focused bone resorption and formation events, trabeculae can form, reorient and change in size as a result of "micromodelling" to resist functional loads optimally.

A good example of this process is the network of secondary tissues that forms in the marrow cavity to support an integrated fixture.

Under most circumstances, cortical bone remodels at a rate of about 2-10% per year. Since only a portion of the cortex is in the metabolic fraction. The remodeling rate for cortical bone is usually 3-10 times less than for adjacent trabecular bone (metabolic fraction).

This complex interaction involves not only biomaterial and biocompatibility issues, but also the alteration of the mechanical environment that occurs when placement of an implant disturbs the normal physiologic distribution of forces, fluids, and cell communication.

In 1977, Branemark & coworkers published the first long-term follow up study on dental implants, thus providing the scientific foundation of today's implant treatment. The successful use of jaw bone anchored (osseointegrated) titanium dental implants to retain prosthetic constructions in the rehabilitation of the edentulous and partially edentulous patients has been well documented in several publications.

The original two-stage surgical protocol using a two-piece implant pillar was applied. The main reasons for this approach have been to Minimize the risk of infectionPrevent apical down growth of mucosal epithelium, and Minimize the risk of undue early loading during the initial healing period.

In addition, a stress-free healing period of 3 to 6 months before the mucosa piercing abutments are placed and the supra-construction is connected to the implants was emphasized to predict a successful treatment outcome. Such a stress free period was even considered to be an ultimate prerequisite to achieve proper osseointegration.

In other words, early stress on the implants was thought to jeopardize the osseointegration process.

Over the years, however, the high level of predictability in implant therapy has resulted in a re-evaluation of the original Branemark protocol for implant placement. Schroeder & coworkers were the first to show the possibility to achieve demonstrated successful clinical treatment outcome using the one stage surgical protocol with the Branemark system.

Similar successful clinical treatment outcomes, in the edentulous as well as the partially edentulous situation, have been reported using one-piece implants (ITI, Straumann) placed according to the original one-stage surgical protocol.

In several clinical studies the original dentures most often were adjusted and relined by a soft tissue conditioner 10 to 12 days following implant placement to minimize unfavorable functional loading, i.e., undue early loading. However, it has to be anticipated that implants placed according to a one-stage surgical procedure to some extent will be directly and unpredictably loaded during function in the initial healing period via the adjusted and relined denture.

Furthermore, such loading might be unfavorable for the implants, as the deformation pattern of complete denture base material would cause micromovements. In other words, "an initial and direct loading of implants piercing the mucosa via the adjusted and relined denture obviously does not jeopardize a proper osseointegration of the fixtures".

Such a statement is in agreement with clinical observations reported by Henry & Rosenberg, who concluded that “controlled immediate loading” of adequately installed, non-submerged implants, by reinsertion of a modified denture, does not appear to jeopardize the process of osseointegration in the anterior mandible.

" Similar observations were reported by Cooper et al. Furthermore, Becker et al concluded that" one-step Branemark implants may be considered a viable alternative to two-step implants."

In former days, it was postulated "too-early loading of an implant leads to interfacial formation of fibrous tissue instead of bone". Others claimed "controlled immediate loading does not appear to jeopardize the process of osseointegration". Today's knowledge indicates that the degree of micromotion at the bone-implant interface during the initial healing phase and it may be not premature loading.

Premature loading leads to implant

movement

The end result “Soft tissue interface”

“Bony interface”

As favorable loading conditions of tooth abutments are obtained via a rigid fixed appliance, it is reasonable to believe that successful treatment outcomes can be reached also when rigid fixed supraconstructions are connected to implants soon after implant placement.

To reduce the period during which the individual implants are exposed to direct and unpredictable loading, splinting of the individual implants through a rigid fixed device will most certainly decrease the micromotion at the bone-implant interface, thus facilitating proper bone healing (osseointegration).

Based on the available information, Randow et al believed it to be of interest to compare the rehabilitation of edentulous mandibles by fixed supraconstructions connected to implants placed according to either an early loaded one stage surgical procedure or the original two-stage concept, with the working hypothesis that there are no differences between the two methods concerning the treatment outcome.

A total of 88 implants (16 patients) were placed according to the one-stage protocol and loaded via a fixed appliance within 20 days. The implants placed according to the original protocol were loaded about 4 months following placement. At the time of delivery of the fixed appliances, all patients were radiographically examined, an ex amination that was repeated at the 18-month follow-up.

The analysis of the radiographs revealed that during the 18-month observation period the mean loss of bone support amounted to about 0.5 mm around the implants, irrespective of early loading. All implants were at all observation intervals found to be clinically stable.

The authors concluded that it is “possible to successfully load titanium dental implants immediately following installation via a permanent fixed rigid cross-arch supraconstruction”. However, such a treatment approach has so far to be strictly limited to the inter-foramina area of the edentulous mandible.

Schnitman and coworkers reported on 63 Branemark implants placed in 10 patients. Of these 63 implants, 28 were placed and "immediately loaded to support an interim fixed bridge." The remaining 35 implants were placed according to the 'original two-stage protocol, osseointegrated properly, and are still in function. Of the 28 implants immediately loaded, four failed.

In other words, the survival rate for the immediately loaded implants was found to be about 85%.

Early implant failure Early crestal bone loss Intermediate to late implant failure Intermediate to late implant bone loss Screw loosening (abutment and prosthesis coping) Uncemented restoration Component fracture Porcelain fracture Prosthesis fracturePeriimplant disease (from bone loss)

The surgical and prosthetic protocols for the development of a predictable direct bone-to-implant interface with root-form implants were developed and reported by Branemark et al.

About 25 years ago, Branemark et al (1977) published the first long-term follow-up on oral implant, providing the scientific foundation of modern dental implantology. The predictability of implant integration according to Branemark and collaborators was obtained by adherence to a strict surgical and prosthodontic protocol. One of the most emphasized requirements was a stress-free healing period of 3-6 months, making implant treatment lengthy.

Presently however, early and immediate loading protocols are reported by an enhancing number of clinical (Chiapasco et al 1997, Schnitman et al 1997, Tarnow et al 1997) and experimental publications.

Following their 10-year clinical experience, recommendations ensuring durable osseointegration of dental implants were set.

The most important were:

Use of sterile conditions as "in a fully equipped operatory"

Use a mucobuccal incision and avoid a crestal one Use of an atraumatic surgery involving low-speed

drilling Use of a biocompatible material i.e. titanium Use of titanium ancillary Use of a 2-stage procedure Use of a stress-free healing period of 3-6 months before

loading Avoid X-radiographs before the end of the healing

period Use of acrylic occlusal contact surfaces

Early loading was identified as a detrimental factor for osseointegration' by Branemark et al During 'the course of their clinical trial (Branemark et al 1977). BUT TODAY THE SCENARIO HAS CAHNGED TO LOADING AND IMMEDIATE LOADING.

Brànemark's loading protocol

Flush with bone level, cover with gingiva.

Final prosthesis after 3 to 6 months of initial healing.

Soft/ hard diet.

Progressive loading

Flush with bone level, covered with gingiva.

Provisional prosthesis brought progressively into occlusion, depending upon bone density.

Soft/ hard diet.

Non submerged single stage protocolNon-submerged implants, flush within 1-2 mm of gingival level

Soft diet

Immediate functional loadingTemporary restoration fitted on the same day as surgery, in occlusion

Soft diet

Immediate non-functional loadingTemporary restoration fitted on the same day as surgery, not in occlusionSoft diet

Early loadingFinal crowns within 3 weeks from surgery, in occlusionSoft/ hard diet

Delayed loadingImplant subjected to loading after more than 6 weeks post surgerySoft/ hard diet

Anticipated loadingProvisional prosthesis is fitted after about 2 months after surgerySoft/ hard diet

Time interval Diet Occlusal material Occlusal contactsProsthesis design

The masticatory force for soft food is about 10 psi. This diet not only minimizes the masticatory force on the implants but also decreases the risk of temporary restoration fracture or partially decemented restoration. Either of these consequences can overload an implant and cause unwanted complications.

The diet protocol should not be overlooked during the restorative procedure because most dentists have observed the fracture of acrylic prostheses with harder foods and greater occurrence of decemented restorations when they ignore type of diet during the transitional prosthesis stages.

After the initial delivery of the final prosthesis, the patient may include meat in the diet, which requires, about 21 psi in bite force. The final restoration can bear the greater force without risk or fracture or decementation.

After the final evaluation appointment, the patient may include raw vegetables, which require an average 27 psi of force. A normal diet is permitted only evaluation of the final prosthesis function, occlusion, and proper cementation.

Occlusal material:

The occlusal material may be varied to load the bone-to-implant interface gradually. During the initial steps, the implant has no occlusal material over it. At subsequent appointments, the dentist chooses acrylic as the occlusal material, with the benefit of a lower implant force than metal or porcelain.

Either metal or porcelain can be used as the final occlusal material. If para function or cantilever length cause concern relative to the amount of force on the early implant bone interface, the dentist may extend the softer diet and acrylic restoration phase for several months. In this way, the bone has a longer time to mineralize and organize to accommodate the higher forces.

Occlusion:

The dentist gradually intensifies the occlusal contacts during prosthesis fabrication. No occlusal contacts are permitted during initial healing. The first transitional prosthesis is left out of occlusion in partially edentulous patients.

The occlusal contacts then are similar to those of the final restoration for areas supported by implants. The occlusal contacts of the final restoration follow the implant-protective occlusion concepts.

Prosthesis design:

During initial healing, the dentist attempts to avoid any load on the implants, including soft tissue loads. The first transitional acrylic restoration in partially edentulous patients has no occlusal contacts.

Its purpose is to splint the implants together, to reduce stress by the mechanical advantage, and to have implants sustain masticatory forces solely from chewing. In the second acrylic transitional restoration, occlusal contacts are placed on the implants with occlusal tables similar to the final restoration but with no cantilevers in nonesthetic regions

Indirect impression transfer coping

Permucosal extensions

Mounted model

Transitional restoration – no occlusal contacts

Abutments in positionRadiographic confirmation

Transitional prosthesis in place

Metal substructure with metal occlusals

Second transitional prosthesis with occlusal contact

Final prosthesis in place Radiographic evaluation

On day of surgery Transfer impression copings

Custom impression tray Addition silicone impression

Master cast Transitional restoration

Immediate functional loading protocol

Clinical trials successful osseointegration

(95-100% success rate- Completely edentulous patients)

Bone quality is good

Functional forces are controlled

More favourable in mandible compared to maxilla

Over loading – Stress concentration, undermining bone resorption without apposition (Branemark 1984)

The other protocol for immediate occlusal loading of dental implants initially loads all of the implants inserted. The implants are splinted together, which decreases the stresses on all the developing interfaces and increases the stability, retention, and strength of the transitional prosthesis during the initial haling phase.

Often additional implants also are used with this technique compared with the traditional healing method.

The immediate load concept provides all the advantages of the one-stage surgical approach. In addition, implants are splinted together, which decreases the risk of overload because of a greater surface area and improved biomechanical distribution.

Over the last few years, authors have reported on immediate loading in the completely edentulous patient, with 95% to 100% success rates.

However, the influence of immediate loading on crestal bone loss has few animal and clinical reports so as to compare the differences of immediate loading to a more traditional bone healing time with no functional load.

High success rates from immediately loaded implants in humans were first documented in the middle 1980s, when the 1-stage implant protocol gained popularity.

Babbush et al (1986) reported a cumulative success rate of 88% on 1739 immediately loading TPS implants. Subsequently, many authors have shown the possibility of loading implants immediately.

Bone Microstrain:

Loaded bone changes its shape. This change may be measured as strain. Microstrain conditions 100 times less than the ultimate strength of bone may trigger a cellular response. Frost has developed a microstrain language for bone based on its biological response at different microstrain levels. Bone fractures at 10,000 to 20,000 microstrain units.

However, at levels of 20% to 40% of this value, bone already starts to disappear or form fibrous tissue and is called the pathologic overload zone. The ideal microstrain for bone is called the physiologic or adapted zone. The remodeling rate of the bone in the jaws of a dentate canine or human being that is in the physiologic zone is about 40% each year.

At these levels of strain the bone is allowed to remodel and remain as an organized, mineralized lamellar structure. This is called the ideal load-bearing zone for an implant interface. The mild overload zone corresponds to an intermediate level of microstrain between the ideal load bearing zone and pathologic overload. In this strain region, bone begins a healing process to repair micro fractures, which are often caused by fatigue. Histologically, the bone in this range is called reactive woven bone.

Rather than the surgical trauma causing this accelerated bone repair, the microstrain causes the trauma from overload. In either condition, the bone is less mineralized, less organized, weaker, and has a lower modulus of elasticity.

One goal for an immediately loaded implant/prosthesis system is to decrease the risk of occlusal overload and its resultant increase in the remodeling rate of bone. Under these conditions the surgical regional acceleratory phenomenon may replace the bone interface without the additional risk of biomechanical overload.

When strain is placed on the horizontal axis and stress is positioned on the vertical axis, the relationship between these two mechanical indexes results in the flexibilities or modulus of elasticity of a material. Hence the modulus conveys the amount of deformation in a material (strain) for a given load (stress) level.

The lower the stress applied to the bone (force divided by the functional surface area that receives the load), the lower the microstrain in the bone. Therefore one method to decrease microstrain and the remodeling rate in bone is to provide conditions that increase functional surface area to the implant-bone interface.

The surface area of load may be increased in a number of ways:

implant number, implant size,implant design, and implant body surface conditions.

The force to the prosthesis also is related to the strain and may be altered in magnitude, duration, direction, or type. Methods that affect the amount of force include patient conditions; implant position, and direction of occlusal load.

Increase Surface Area:Implant number: The dentist may increase the functional surface are of occlusal load at an implant interface by increasing implant number. Hence rather than three to five implants to support a fixed restoration, use of additional implants when immediate loading is planned is more prudent. Immediate loading reports in the literature with the lowest percentage survival correspond to fewer implants loaded.

More implants typically are used in the maxilla (8 to 12) compared with the mandible (5 to 9). This approach helps compensate for the less dense bone and increased directions of force often found in the upper arch.

Implant size:

The dentist also may increase the surface area of implant support by the size of the implant. The length of the implant in most systems increases in increments of 2 to 4mm. Each 3 mm increase in length can improve surface area support by more than 20%. However, the benefit of increased length is not found at the crestal bone interface but rather in initial stability of the bone-implant interface.

Implant body design:

The implant body design should be more specific for immediate loading because the bone has not had time to grow into recesses or undercuts in the design or attach to a surface condition before the application of occlusal load. For example, a press-fit implant with a cylinder design does not have bone integration the day of implant placement.

An implant body with a series of horizontal plates that is tapped or pressed into place does not have bone present between the plates the day of surgical placement. Macrospheres on an implant surface do not have bone present within or around the porous surface of the implant the day of implant placement.

For a threaded implant, bone is present in the depth of the threads form the day of insertion. Therefore the functional surface area is greater during the immediate load format. The number of the threads also affects the amount of area available to resist the forces during immediate loading.

The greater the number of threads, the greater the functional surface area at the time of immediate loading. Some threaded implants have a 1.5 mm distance between the threads (e.g., BioHorizons dental implants). The smaller the distance between the threads, the greater the thread number and corresponding surface area.

Implant thread design may affect the bone turnover rate (remodeling rate) during occlusal load conditions. For a V-shaped thread design, a 10 times greater shear force is applied to bone compared with a square thread shape. Bone is strongest to compression and weakest to shear loading. Compressive forces decrease the microstrain to bone compared with shear forces.

Hence the thread shape and implant design may decrease the early risks of immediate loading while the bone is repairing the surgical trauma.

Implant design affects functional surface area more than implant size. A larger-diameter cylinder implant has less surface area than a smaller-diameter threaded implant. As a result, thread implants present considerable advantages compared with pres-fit implants for immediate load protocols because their design features do not require histologic integration to resist loads and they have greater surface are to resist occlusal forces.

A tapered implant design presents some disadvantages for immediate load applications. When the tapered osteotomy is prepared using tapered drills, the implant does not engage the bone physically until the implant is seated almost completely into the bone site. This reduces the initial fixation. In addition, the tapered implant has less overall surface areas compared with a parallel-walled, threaded implant.

However, few clinical trials have compared immediate loading with different implant thread design and tapered implant bodies in the completely edentulous patient. The short-term clinical reports indicate a high success rate, regardless of implant design. As a result, overall shape and thread geometry apparently may not be the most important aspect for immediate occlusal load survival. Implant number, implant position, and patient factors most likely are more relevant components of success. Future studies in this area certainly are needed.

Implant surface conditions:

Implant surface conditions may affect the rate of bone contact, lamellar bone formation, and the percentage of bone contact. The surface condition that allows bone formation in greatest percentage, higher bone-implant contact percentage with higher mineralization rate, and fastest lamellar bone formation would be of benefit in immediate loading. These factors have been noted in delayed and immediate loading environments with hydroxyapatite coatings.

Implant design and surface condition are independent issues that use a different mechanism to reduce the risk of overloading. For example, a hydroxyapatite surface may be applied to a cylinder or a threaded implant. The thread design would be more beneficial to an immediate load application.

Yet the hydroxyapatite or roughened surface also may be of benefit during the following healing period, especially at the 3 to 5 weeks when the bone is weakest. The majority of clinical studies have been made with threaded implant designs.

Surface conditions are more difficult to ascertain in the literature and have included a smooth machined surface, a roughened titanium plasma spray surface, and a hydroxyapatite surface condition without a clear deference in clinical survival. However, evidence is increasing that the machine surface condition is inferior in softer bone types.

Decreased Force Conditions:

The dentist may evaluate forces by magnitude, duration, duration, and type. The dentist should reduce conditions that magnify the noxious effects of these forces.

Patient factors:

The greater the occlusal force applied to the prosthesis. The greater the stress at the implant-bone interface and the greater the strain to the bone. Therefore force conditions that increase occlusal load increase the risks of immediate loading. Parafunction such as bruxism and clenching represents significant force factors because magnitude of the force is increased, the duration of the force is increased, and the direction of the force is more horizontal than axial to the implants with a greater shear component.

Occlusal load direction:

The occlusal load direction may affect the remodeling rate. An axial load to an implant body maintains more lamellar bone and has a lower remodeling rate compared with an implant with an offset load..

Therefore one should eliminate posterior cantilevers in the immediate-load transitional restoration because they magnify the detrimental effects of force direction.

Implant position:

Dental implants have been used widely to retain and support cross-arch fixed partial dentures. Implant position is often as important as implants supporting three teeth is often as important as implant number. For example, elimination of cantilevers on two implants supporting three teeth is recommended, rather than positioning the implants next to each other with a cantilever.

The cross-arch splint forming an arch is an effective design to reduce stress to the entire implant support system. Hence the splinted arch position concept for the completely edentulous is advantageous for the immediate-load transitional prosthesis.

Implant position is one of the more important factors in immediate loading for completely edentulous patients. The mandible may be divided into three sections around the arch:

the canine-to-canine area

and the bilateral posterior sections.

The maxilla requires more implant support than the mandible because the bone is less dense and the direction of force is outside of the arch and the force is outside of the arch in all the eccentric movements. The maxilla is divided into at least four to five sections, depending on the intensity of the force conditions and the shape of the arch.

The minimum four sections are the bilateral canine area and the bilateral posterior regions. When force factors are greater, the regions of the maxilla are increase to five and include the incisor area. At least one implant should be inserted into each maxillary section and splinted together during the immediate-loading process.

Concerns have been raised regarding cross-arch splinting in the mandible because of mandibular flexure and torsion distal to the mental foramens. Clinical reports indicate the acrylic used in the transitional prosthesis is flexible enough to alleviate these concerns. However, the final restoration should be fabricated in at least two independent sections when implants are placed in both posterior quadrants.

Mechanical properties of bone:

The modulus of elasticity is related to bone quality. The less dense the bone, the lower the modulus. The amount of bone-implant contact is also less for less-dense bone. The strength of the bone also is related directly to the density of the bone.

The softer the bone, the weaker the bone trabeculae. In addition, the remodeling rate of cortical bone is slower than that of trabecular bone. As such, the cortical bone is more likely to remain lamellar in structure during the immediate loading process compared with trabecular bone.

Bone grafting must depend on several factors to be predictable. Adequate blood supply and a lack of micromovement are two important conditions. The developing bone is woven bone and more at risk of overload. The bone graft in the region of the implant body may lead to less fixation and lower initial bone-implant contact percentages. Bone augmentation is more predictable when soft tissue completely covers the graft (and membranes when present).

All of these conditions make bone grafting, implant insertion, and immediate loading more at risk. Therefore the suggestion is that implants that are immediately loaded be placed in an existing bone volume adequate for early loading and the overall proper prosthetic design. Bone grafting, before implant placement and immediate loading, is suggested when inadequate bone volume is present for proper reconstructive procedures.

In cases where early loading is deemed appropriate, Tarnow has suggested a set of guidelines to help achieve clinical success:

Immediate loading should be attempted in edentulous arches only to create cross-arch stability.

Implants should be at least 10 mm long.

A diagnostic wax-up should be used for template and provisional restoration fabrication.

A rigid metal casting should be used where possible.

A screw-retained provisional restoration should be used where possible.

If cemented, the provisional restoration should not he removed during the 4- to 6-month healing period.

All implants should be evaluated with Periotest (a measure of the degree of resistance to perpendicular force) at stage 1, and the implants that show the least mobility should be utilized to provide resistance to rotational forces.

The widest possible anterior- posterior distribution of implants should be utilized to provide resistance to rotational forces. Cantilevers should be avoided in the provisional restorations.

The emergence of a 1-stage early loading protocol does not imply that submersion is no longer necessary, but rather suggests that is not always essential. The 2-stage procedure remains the treatment of choice. However, under the right circumstances successful early loading can reduce the length of prosthetic rehabilitation.

Success criteria of implants

Schuitman and Schulman criteria (1979)

1) The mobility of the implant must be less than 1mm when tested clinically.

2) There must be no evidence of radiolucency

3) Bone loss should be less than 1/3rd of the height of the implant

4) There should be an absence of infection, damage to structure or violation of body cavity, inflammation present must be amneable to treatment.

5) The success rate must be 75% or more after 5 years of functional service.

Albrektson and Zarb G (1980)

1) The individual unattached implant should be immobile when tested clinically

2) The radiographic evaluation should not show any peri - implant radiolucency

3) Vertical bone loss around the fixtures should be less than 0.2mm annually after first year of implant loading.

4) The implant should not show any sign and symptom of pain, infection, neuropathies, parastehsia, violation of mandibular canal and sinus drainage.

5) Success rate of 85% at the end of 5 year observation period and 80% at the end of 10 year service.

6) Implant design allow the restoration satisfactory to patient and dentist. - Smith and Zarb (1989)

The patient demand for esthetics is increasing day by day and the replacement of teeth immediately following extraction is attaining popularity. In this respect even the replacement of teeth immediately following the implant placement has to be considered as a serious issue. Therefore it is very much essential to know the requirements and bone responses to the occlusal loading in the healing period. Also the modifications in treatment plan to achieve the success of restoration are necessary.

Carl E Misch: Contemporary Implant Dentistry.

Sumiya Hobo: Osseointegration and Occlusal Rehabilitation.

W E Roberts: Fundamental principles of bone physiology, metabolism and loading.

Osseointegration in clinical dentistry – Branemark, Zarb, Albrektsson

Endosseous implants for Maxillofacial reconstruction – Block and Kent

Implants in Dentistry –Block and Kent

Dental and Maxillofacial Implantology – John. A. Hobkrik, Roger Watson

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