Occulasl consideration for implant supported prostehsi/ dentistry jobs

OCCLUSAL CONSIDERATIONS

FOR IMPLANT SUPPORTED PROSTHESIS

INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

www.indiandentalacademy.com

INTRODUCTION


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 implants. After achievement of rigid fixation, proper crestal bone contour, gingival health, mechanical stress, and/or strain beyond the physical limits of hard tissues have been suggested as the primary cause of initial bone loss around implants. After successful surgical and prosthetic rehabilitation with a passive prosthesis, such noxious stresses and loads applied to the implant and surrounding tissues result primarily from occlusal contacts. Complications (prosthetic and/or bony support) reported in follow-up studies underline occlusion as a determining factor for success or failure.


The choice of an occlusal scheme for implant-supported prostheses is broad and often controversial. Almost all concepts are based on those developed with natural teeth and are transposed to implant support systems with almost no modification. No controlled clinical studies have been published comparing the various implant occlusal theories.

RISK FACTORS - Implant prostheses with extended cantilevers have been successful, however, biomechanical factors clearly demonstrate an increased risk.

Biomechanical parameters are excellent indicators of the increased risk because they are objective and can be measured. One can determine which condition presents greater risk, and by how much the risk is increased. Hence the occlusal concepts developed in this seminar stem from biomechanical risk factors.


The prosthodontist has specific responsibilities to minimize overload to the bone-to-implant interface. These include a proper diagnosis leading to a treatment plan providing adequate support, based on the patient’s individual force factors, a passive prosthesis of adequate retention and form and progressive loading to improve the amount and density of the adjacent bone and further reduce the risk of stress beyond physiologic limits. The final element is the development of an occlusal scheme that minimizes risk factors and allows the restoration to function in harmony with the rest of the stomatognathic system.


TERMINOLOGY(GPT 1999)


Anterior protected articulation A form of mutually protected articulation in which the vertical

and horizontal overlap of the anterior teeth disengage the posterior teeth in all mandibular excursive movements.

Balanced articulation The bilateral, simultaneous, anterior, and posterior occlusal

contact of teeth in centric and eccentric positions

Canine protected articulation A form of mutually protected articulation in which the vertical

and horizontal overlap of the canine teeth disengage the posterior teeth in the excursive movements of the mandible.

Implant Prosthodontics The phase of Prosthodontics concerning the replacement of

missing teeth and / or associated structures by restorations that are attached to dental implants.


Lingualized occlusion First described by S. Howard Payne, DDS, in 1941, this form

of denture occlusion articulates the maxillary lingual cusps with the mandibular occlusal surfaces in centric working and nonworking mandibular positions. The term is attributed to Earl Pound.

Payne SH. A posterior set up to meet individual requirements. Dent. 1941; 47:20-2.

Pound E. Utilizing speech to simplify a personalized denture service. J. Prosthet Dent. 1970;24:585-600.

LinguocclusionAn occlusion in which a tooth or group of teeth is located

lingual to its normal position.


Mutually protected articulation An occlusal scheme in which the posterior teeth prevent

excessive contact of the anterior teeth in maximum intercuspation, and the anterior teeth disengage the posterior teeth in all mandibular excursive movements.

Occlusion (1645) 1: The act or process of closure or of bring closed or shut off

2 : the static relationship between the incising or masticating surfaces of the maxillary or mandibular teeth or tooth analogues

Spherical form of occlusion An arrangement of teeth that places their occlusal surfaces on

the surfaces of an imaginary sphere (usually 8 inches in diameter) with its center above the level of the teeth (GPT-4).


IMPLANT PROTECTIVE OCCLUSION (IPO)


A proper occlusal scheme is a primary requisite for long-term survival, especially when parafunction or marginal foundations are present. A poor occlusal scheme both increases the magnitude of loads and intensifies mechanical stresses (and strain) at the crest of the bone. Implant Protective Occlusion (IPO) was previously known as medial positioned-lingualized occlusion. This occlusal concept refers to an occlusal plane that is often unique and specifically designed for the restoration of endosteal implant, providing an environment for improved clinical longevity of both implant and prosthesis.


OCCLUSAL CONSIDERATIONS


Natural Tooth vs. Implant Mobility: In comparison to an implant, the support system of a natural tooth is designed to reduce the forces distributed at the crestal bone. The fibrous tissue interface (periodontal ligament) surrounding natural teeth acts as a viscoelastic “shock absorber”, serving to both decrease the magnitude of stress to the bone at the crest, as well as extend the time in which the load is dissipated. The presence of a periodontal membrane around natural teeth significantly reduces the amount of stress transmitted to the bone, especially at the crestal region. Compared with a tooth the direct bone interface with an implant is not as resilient, so the energy imparted by an occlusal force is not partially dissipated (the displacement of the periodontal membrane dissipates energy), but rather transmits a higher intensity to the contiguous bone. An analogy of this is hitting a nail with a steel hammer compared with a rubber hammer.


The mobility of a natural tooth can increase with occlusal trauma. This movement dissipates stresses and strains otherwise imposed on the adjacent bone interface or the prosthetic components. After the occlusal trauma is eliminated, the tooth can return to its original condition with respect to the magnitude of movement. Mobility of an implant can also develop under occlusal trauma. However, after the offending element is eliminated, an implant rarely returns to its original rigid condition. Instead, its health is compromised, and failure is usually eminent.

The width of almost every natural tooth is greater than the width of the implant used to replace the tooth. The greater the width of a transosteal structure (tooth or implant), the lesser magnitude of stress transmitted to the surrounding bone. The cross-section shape of the natural tooth at the crest is biomechanically optimized to resist lateral (buccolingual) loads because of the tooth’s bending fracture resistance (moment of inertia) and the direction of occlusal forces. Implants are almost all round in cross-section, which is less effective in resisting lateral bending loads and consequent stress concentration in the crestal region in the jaws.


The elastic modulus of a tooth is closer to bone than any of the currently available dental implant biomaterials. The greater the flexibility difference between two materials (metal and bone or tooth and bone), the greater the potential relative motion generated between the two surfaces at the transosteal region. Hence under similar mechanical loading conditions, implants generate greater stresses and strains at the crest of bone compared with a tooth.

The precursor signs of occlusal trauma on natural teeth are usually reversible and include hyperemia and occlusal or cold sensitivity. Condition often results with the patient seeking professional treatment to reduce the sensitivity, usually by occlusal adjustment and a reduction in force magnitude. If the patient does not have an occlusal adjustment, the tooth often further increases in mobility to dissipate the occlusal forces. If the patient still fails to seek professional treatment for the increased mobility, the tooth may orthodontically migrate away from the cause of the occlusal stress. Even excess tongue or oral habits can cause tooth migration away from the causative element.www.indiandentalacademy.com

The initial reversible signs and symptoms of trauma on natural teeth do not occur with endosteal implants. The magnitude of stress may cause bone microfractures, place the surrounding bone in the pathologic loading zone causing bone loss, and lead to the mechanical failure of prosthetic or implant components. Unlike the reversible signs and symptoms exhibited by natural teeth, implant bone loss or unsecured restorations most often occur without any warning signs. Implant occlusal sensitivity is uncommon and signifies more advanced complications. The loss of crestal bone around the implant is not reversible without surgical intervention and results in a decreased implant support and increased sulcus depth around the abutment. As a result, unless the density of bone increases or the amount or duration of force decreases, the condition is likely to progress and even accelerate until implant loss. In addition, implants cannot move orthodontically away from the offending force.


The tooth can show clinical signs of increased stress such as enamel wear facets, stress lines, lines of Luder (in amalgam fillings), cervical abfraction, and pits on the cusps of teeth. An implant crown rarely shows clinical signs other than fatigue fracture. As a result, fewer diagnostic signs are present to warn the prosthodontist to reduce the stress on the support system.


When teeth oppose each other, an interference perception is approximately 20µm. An implant opposing a natural tooth has an interference perception of 48µm, therefore more than twice as poor. An implant opposing implant has an interference perception of 64µm, and when a tooth opposes an implant overdenture the awareness is 108µm (5 times poorer than teeth opposing each other). As a result, premature occlusal contacts on teeth are usually associated with a modification of arc of closure and with a decreased force, before centric occlusion or full interdigitation. In addition, the mandible may close in a different position to avoid the premature contact and result in centric occlusion different from centric relation occlusion. Unfortunately, because of the decreased occlusal awareness of implants, the premature contact does not trigger such as an adaptation. In addition, premature contacts are often on smaller areas of load and therefore result in greater stress (S=F/A). They are most often on inclines of posterior teeth, which also generates an angled load of greater stress to the implant bone interface.www.indiandentalacademy.com

Implants and teeth also have different proprioceptive information relayed by both entities. Teeth deliver a rapid, sharp pain sensation under high pressure that triggers a protective mechanism. On the other hand, implants deliver a slow, dull pain that triggers a delayed reaction, if any. Clinical evidence of occlusal trauma on teeth includes an overall increase in the periodontal membrane thickness and an increased radiopacity and thickness of the cribriform plate around the tooth, observed on radiographs and not just localized at the crest. There are no generalized radiographic signs around an implant under excess occlusal force, except at the crestal region, which demonstrates bone loss but may be misdiagnosed as periimplant disease from bacteria.


The tooth slowly erupts into occlusion and is present in the mouth from childhood. The surrounding bone has developed in response to the biomechanical loads. The permanent teeth are gradually introduced, while others are present. Hence periodontal tissues have had time to organize in order to sustain increasing loads, including those brought to bear by an attached prosthesis. The only progressive bone loading around an implant is performed by the prosthodontist, and in a much more rapid and intense fashion.

A lateral force on a natural tooth is rapidly dissipated away from the crest of bone toward the apex of the tooth. The healthy, natural tooth moves almost immediately 56 to 108µm and pivots two-thirds turn toward the tapered apex with a lateral load. This action minimizes crestal loads to the bone. An implant does not exhibit a primary immediate movement, but a secondary movement 10 to 50µm under similar lateral loads. In addition, it does not pivot (as a tooth) toward the apex but instead concentrates greater forces at he crest of surrounding bone. Therefore if an initial angled load of equal magnitude and direction is placed on both an implant and a natural tooth, the implant sustains a higher proportion of the load that is not dissipated to the surrounding structures.


The natural tooth, with its modulus of elasticity similar to bone, periodontal ligament, and unique cross-sections and dimensions constitutes a near perfect optimization system to handle stress. In fact, the stress is handled so well, bacteria-related disease is the weak link. An implant handles stress so poorly (capturing the stress at the crest of the ridge), has an elastic modulus 5 to 10 times that of bone, and is unable to increase mobility without failure that stress is the weakest link in the system. As a result, ways to decrease stress are a constant concern to minimize the risk of implants complications.


Occlusion on Natural Teeth and Implants: There has been an ongoing controversy regarding whether a rigidly fixated implant may remain successful when splinted to natural teeth. Because the implant has no periodontal membrane, concerns center around the potential for the “nonmobile” implant to bear the total load of the prosthesis when joined to the “mobile” natural tooth. The actual mobility of potential natural abutments may influence the treatment more than any other factor. In the implant tooth fixed prosthesis, four important components may contribute movement to the system, the implant, bone, tooth, and prosthesis. The sudden, initial tooth movement ranges from 8 to 28µm in a vertical direction under a 3 to 5 lb load, depending on the size, number, and geometry of the roots and the time elapsed since the last load application. Once the initial tooth movement occurs, the secondary tooth movement reflects the property of the surrounding bone and is very similar to the bone implant movement. The axial movement of an implant has no initial, sudden movement and ranges from 3 to 5 µm with little correlation to the implant body length.www.indiandentalacademy.com

When teeth oppose each other, the combined intrusive movements of the contacting elements may be 56µm (28µm + 28µm). When a tooth opposes an implant, the combined intrusive movement is 33µm (28µm + 5µm). When implant prostheses oppose each other, the biomechanical mismatch between teeth in the rest of the mouth and implants increase. The total combined movement may be 10µm, compared with 56µm in the rest of the mouth, and contrary to the teeth that move immediately, even with light loads, the implants only move this amount under a heavy occlusal load. A lighter load may generate a total implant movement of less than 3µm.


For difference in vertical movement of teeth and implants in the same arch, the existing occlusion is evaluated before implant reconstruction. Occlusal prematurities are ideally eliminated on teeth before implant reconstruction. Thin articulating paper (less than 25µm thickness) is then used for the initial implant occlusal adjustment in centric relation occlusion under a light tapping force. The implant prosthesis should barely contact, and the adjacent teeth should exhibit greater initial contacts. Only axial occlusal contacts should be present on the implant crown. Once the equilibration with a light bite force is completed, a heavier centric relation occlusal force is applied. The contacts should remain axial over the implant body and may be of similar intensity on the implant crown and the adjacent teeth under greater bite force to allow all elements to react similar to the occlusal load. Hence to harmonize the occlusal forces between implants and teeth, a heavy bite force occlusal adjustment is used because it depresses the natural teeth, positioning them closer to the depressed implant position and equally sharing the load.www.indiandentalacademy.com

If healthy anterior teeth and/or natural canines are present, the occlusion allows those teeth to distribute horizontal loads in excursions, while the posterior teeth disocclude during excursions. Anterior, compared with posterior bite force measurements and electromyographic studies provide evidence that the stomatognathic system elicits significantly less force when the posterior segments are not in contact. As a result, all lateral excursions of IPO opposing fixed prostheses or natural teeth should disocclude the posterior components. The resultant lateral forces are thus distributed only to the anterior segments of the jaws, resulting in a decrease in overall occlusal force magnitude because of diminished muscle firing and recruitment.

This occlusal scheme should be followed whether or not anterior implants are in the arch. However, if anterior implants must disocclude the posterior teeth in excursion, two or more implants splinted together should help dissipate the lateral forces.


When anterior implants and teeth are not connected - The initial lateral movement of healthy anterior teeth ranges from 68 to 108µm before secondary tooth movement. Anterior implant movements are not immediate and range from 10 to 50µm. Because of the greater discrepancies in lateral movement, the occlusal adjustment in this direction is more critical to implant success and survival. Light force and thin articulating paper(20µm) are first used to ensure that no implant crown contact occurs during the initial occlusal or lateral movement of the teeth. A heavier force during centric occlusion and excursions is then used to develop similar occlusal contacts on both anterior implants and natural teeth.


Unlike teeth, implants do not extrude, rotate, or migrate under occlusal forces. Natural teeth exhibit mesial drift and slight changes in occlusal position do occur over time. The proposed occlusal adjustment does not encourage additional tooth movement because regular occlusal contacts occur. The teeth opposing implants are not taken out of occlusion. Brief occlusal contacts on a daily basis maintain the tooth in its original position (similar to the rest of the mouth). In addition, because most teeth occlude with two teeth, the opposing teeth positions are even more likely to remain the same.

No occlusal scheme will prevent mesial drift and minor tooth movement from occurring. An integral part of the IPO philosophy is the regular evaluation and control of occlusal contacts at each regularly scheduled hygiene appointment. This permits the correction of minor variations occurring during long-term function and also helps prevent porcelain fracture and other stress-related complications on the remainder of the natural teeth.


For implants joined to natural teeth a similar scenario is used for the occlusal equilibration. A light force and thin articulating paper are used, and the implant crown exhibits minimum contact compared with the natural abutment crown. A gradient of force is designed on the pontics. A heavy bite force is then used to establish equal occlusal contacts for all abutments and the entire prosthesis, whether implant or natural.


Implant Orientation and Influence of Load Direction: Forces acting on dental implants are referred to as vectors (defined in both magnitude and direction). Occlusal forces are typically three-dimensional, with components directed along one or more of the clinical coordinate axes.


Implants are designed for a long axis load to the implant body. Stress contours were primarily concentrated at the transosteal (crestal) region. An axial load over the long axis of an implant body generates a greater proportion of compressive stress than tension or shear forces. Any load that is applied at an angle may be separated into normal (compressive and tensile) and shear forces. The greater the angle of loads to the implant long axis, the greater the compressive, tensile and shear stresses. When FEA evaluates the direction of the force changed to a more angled or horizontal load, the magnitude of the stress is increased by 3 times or more. In addition, rather than a compressive type of force primarily, greater tensile and shear forces are also demonstrated and increase more than 10 times compared with the amount found with an axial force. These stress contours resemble the pattern of early crestal bone loss on implants.


BONE MECHANICS AND OCCLUSION


The effect of offset or angled loads to bone is further exacerbated because of the anisotropy of cortical bone. Anisotropy refers to the character of bone, whereby its mechanical properties, including ultimate strength, depend on the direction in which the bone is loaded. Cortical bone of human long bones has been reported as strongest in compression, 30% weaker in tension, and 65% weaker in shear. Therefore IPO attempts to eliminate or reduce all shear loads to the implant to bone interface.


A force applied at a 30-degree angle decreased the bone strength limits by 10% under compression and 25% with tension. A 60-degree force reduced the strength 30% under compression and 55% under tension. Therefore not only does the crestal bone load increase around the implant with angled forces, but the amount of stress the bone may withstand is also decreased. The greater the angle of load, the lower the ultimate strength.


The primary component of the occlusal force should therefore be directed along the long axis of the implant body, not on an angle or following an angled abutment post. Angled abutments are used only to improve the path of insertion of the prosthesis or the final esthetic result. The angled abutment, which is loaded along the abutment axis, will transmit a significant moment load to both the implant crestal region and abutment screw, proportional to its angle of inclination. In addition, the angled implant often requires an angled abutment. Angled abutments are fabricated in two pieces and are weaker in design than a one-piece post. Furthermore, a larger transverse load component develops at the crest as a result of angled loads. An angled load to the implant long axis increases the compressive forces at the crest of the ridge on the opposite side of the implant in which the force is directed, increasing the tension component of force along the same side. The greater the angle of force to the long axis of the implant body, the greater the potentially damaging load at the crest of the bone. www.indiandentalacademy.com

Hence the angled load increases the amount of crestal stresses around the implant body, transforms a greater percentage of the force to tensile and shear force, and reduces bone strength in compression and tension. In contrast, the surrounding implant body stress magnitude is least and the strength of bone is greatest under a load axial to the implant body. Premature occlusal contacts result in localized lateral loading of the opposing contacting crowns. Because the surface area of a premature contact is small, the magnitude of stress in the bone increases proportionately (i.e., stress=force/area). All the occlusal force is applied to one region rather than being shared by several abutments and/or teeth. In addition, the premature contact is most often on an inclined plane, therefore creating a greater horizontal component to the load and increasing compressive and tensile crestal stresses. Therefore occlusal evaluation and adjustment in partially edentulous implant patients are more important than in the natural dentition because the premature contacts can result in more damaging consequences on implants compared with teeth.


The elimination of premature contacts is more important than in natural teeth because the implant is less mobile and often cannot effectively dissipate the forces. In addition, the teeth benefit from a greater occlusal awareness (proprioception) or oral tactile function than implants. Once the natural teeth are removed, the bone remodels to the height at or below the lowest level of the lateral cortical plates. Hence the implant crown height is often greater than the original natural anatomic crown, even in Division A bone. Crown height, with a lateral load, is a magnifier of stress to an implant to bone interface. The greater the crown height, the greater the resulting crestal moment with any lateral component of force that develops as a consequence of an angled load. Angled abutments loaded in the direction of the abutment with an increase in crown height are subject to even greater crestal moment loads because of both the lateral load and the increased lever effect from the crown height.


In the anterior maxilla, labial concavities may require that the implant be angled away from the labial bone and the abutment toward the facial crown contour. These implant bodies are more frequently loaded at an angle, and an angled prosthetic abutment is required. As a result, larger diameter implants or a greater number of implants are indicated to minimize the crestal bone stress on each abutment. IPO aims at reducing the force of occlusal contacts, increasing implant number, and/or increasing implant diameter for implants subjected to angled loads or with an increased crown height or on the cantilever portion of a prosthesis.


OCCLUSAL SCHEMES

A primary goal of an occlusal scheme is to maintain the occlusal load that has been transferred to the implant body within the physiologic limits of each patient. These limits are not identical for all patients or restorations. The forces generated by a patient are influenced by parafunction, masticatory dynamics, tongue size, implant arch position and location, and implant arch form and crown height. The prosthodontist can best address these force factors by selecting the proper implant size, number, and position, using stress-relieving elements, increasing bone density by progressive loading and selecting the appropriate occlusal scheme.


CLASSIFICATION OF OSSEOINTEGRATED CLASSIFICATION OF OSSEOINTEGRATED PROSTHESISPROSTHESIS


Hobo et al

1. Fully bone anchored bridge

2. Overdenture

3. Freestanding bridges

a. Kennedy class I

b. Kennedy class II

c. Kennedy class III

d. Kennedy class IV

4. Bridge connected to the natural teeth.

5. Single tooth replacement.www.indiandentalacademy.com

Misch C.E et alTYPE DEFINITION

FP-1 Fixed prosthesis, replaces only the crown, looks like a natural tooth

FP-2 Fixed prosthesis, replaces the crown and a portion of the root, crown contour appears normal in the occlusal half is elongated or hypercontoured in the gingival half

FP-3 Fixed prosthesis, replacing missing crowns and gingival colour and a portion of the edentulous site, prosthesis must often use denture teeth and acrylic gingiva, but may be porcelain to metal

RP-4 Removable prosthesis, overdenture supported completely by implant

RP-5 Removable prosthesis, overdenture supported by both soft tissue and implants


IMPLANT PROTECTIVE OCCLUSION(IPO)


When teeth are present, the maxillary dentate posterior ridge is positioned slightly more facial than its mandibular counterpart. Once the maxillary teeth are lost, the edentulous ridge resorbs in a medial direction as it evolves from Division A to B, Division B to C, and Division C to D. As a result, the maxillary permucosal implant site gradually shifts toward the midline as the ridge resorbs.

As a result of ridge resorption in width the maxillary posterior implant permucosal site may even be lingual to the opposing natural mandibular tooth. The posterior mandible also resorbs lingually as the bone resorbs from Division A to B. As a consequence, endosteal implants are also more lingual than their natural tooth predecessors.


Occlusal Table Width: A wide occlusal table favors offset contacts during mastication or parafunction. Narrower implant bodies are even more vulnerable to occlusal table width and offset loads. Wider root form implants can accept a broader range of vertical occlusal contacts while still transmitting lesser forces at the permucosal site under offset loads. Therefore in IPO the width of the occlusal table is directly related to the width of the implant body. During mastication, the amount of force used to penetrate the food bolus is also related to occlusal table width. For example, less force is required to cut a piece of meat with a sharp knife (narrow occlusal table), than with a dull knife (wider occlusal table). The greater surface area requires greater force to achieve a similar result. Hence the wider the occlusal table, the greater the force developed by the biologic system to penetrate the bolus of food.


The posterior narrow occlusal table also facilitates daily home care. The laboratory technician often attempts to fabricate occlusal facial and lingual contours similar to that of natural teeth. This often results in ridge laps or porcelain extension at the facial gingival margin of the implant, to create an occlusal table approximately 8 to 10 mm wide. As a result, home care in the sulcular region of the implant is impaired by the overcontoured crown design. On the contrary, a narrow occlusal table combined with a reduced buccal contour (in the posterior mandible) permits easier sulcular oral hygiene in manner similar to a tooth and improves axial loading.


The narrower occlusal contour also reduces the risk of porcelain fracture. A facial profile similar to a natural tooth on the smaller diameter implant results in cantilevered restorative materials. The facial porcelain is most often not supported by a metal substructure because the gingival region of the crown is also porcelain. As a result, shear forces result on the buccal cusp on the mandibular crown or lingual cusps in the maxillary crown, and are more likely to increase the risk of porcelain fracture.

Restorations mimicking the occlusal anatomy of natural teeth often result in offset loads (increased stress), complicated home care and increased risk of porcelain fracture. As a result, in nonesthetic regions of the mouth, the occlusal table should be reduced in width compared with natural teeth.


DIVISION OF AVAILABLE BONE:A,B,C&D (MISCH)


CROWN CONTOUR


Division A Bone

The primary component of the occlusal force is evaluated during the treatment-planning phase. In an edentulous ridge with abundant height and width and little resorption, the implant may be placed in a more ideal position for occlusion and esthetics. Offset loads are used to describe cantilevered buccal or lingual occlusal contacts, not directed along the long axis of the implant body. When offset loads are generated at an angle, the distance between the offset contact and the long axis acts as a moment arm that magnifies the effect of the lateral force.


The most common implant placement corresponds to a central position in the residual ridge. The implant osteotomy begins in the center of the crest and is gradually increased to the optimal width indicated in relation to the recipient bone. Facial concavities are avoided, and the thinner facial cortical bone is protected, to limit surgical complications such as labial dehiscence. As a consequence, whether in the maxilla or the mandible, the implant is frequently placed under the central fossa region of the former natural tooth.

To load the implant body in an axial direction, the primary occlusal contact should therefore be the central fossa region in Division A bone. Thus for maxillary implant opposing mandibular natural teeth, the mandibular buccal cusp acts as the primary tooth contact.


Because bone loss occurs at the expense of the facial plate, a modified buccal contour anatomy may need to be generated in Division A or B mandibles. The occlusal table width is reduced to favor an axial load on the implant in nonesthetic regions. The Division A mandibular implant is placed under the central fossa region of the natural tooth. When opposing a natural maxillary molar, the primary contacting cusp becomes the maxillary lingual cusp opposing the mandibular implant crown, with the mandibular buccal cusp of decreased height and width over the implant body. Hence all contacts are situated medially compared with those on natural teeth.

The lingual contour of the mandibular implant crown is similar to the original natural dentition in position, complete with horizontal overlap to the maxillary lingual cusp to prevent tongue biting during function. There is no occlusal contact on the lingual cusp, so offset loads during parafunction are eliminated. www.indiandentalacademy.com

The posterior maxillary crown is reduced only from the lingual aspect, compared with a natural maxillary molar, to reduce the occlusal table width. such a reduction increases the lingual overjet when the teeth are in occlusion. Narrower opposing mandibular occlusal tables are desirable to direct occlusal forces over the maxillary implant body. As a result, when opposing maxillary implants, the buccal cusps of natural mandibular teeth (or crowns on implants) should be recontoured to minimize offset loads in centric relation occlusion. The maxillary buccal cusp may then be retained for esthetics, but the functional occlusal table is reduced.

When esthetics are not a concern the distal one half of the first molar and / or the entire second molar is often restored in cross bite to improve the direction of forces. In the posterior esthetic regions of the maxilla with facial bone resorption and / or lingually placed implants, a wider occlusal table is required to project the facial contours for ideal esthetics. Bone grafting to increase bone width may be required in these esthetics zones, so a larger diameter implant may be placed that permits restorations of the buccal contours with maintenance of cervical contours with emergence profiles, which permit proper hygiene of the sulcular regions. www.indiandentalacademy.com

Posterior implants opposing each other attempt to axially load both entities. The facial cusp of the maxillary crown is required for esthetics. The other contours of the opposing crowns are reduced in width to minimize the occlusal table width and axially load the implants.

WHENEVER POSSIBLE THE PORTIONS OF AN IMPLANT CROWN THAT ARE NOT SUPPORTED BY AN AXIALLY POSITIONED IMPLANT SHOULD BE RECONTOURED SO THEY DO NOT RECEIVE OCCLUSAL LOADS. ALTERNATIVELY, SEVERAL ADDITIONAL IMPLANTS SHOULD BE USED TO DISSIPATE THE FORCE.


DIVISION B BONE

Division B bone has maxillary and mandibular implants positioned under the lingual cusp when compared with the original natural tooth position. As a result, mandibular crowns require even more reduced buccal contours to avoid offset occlusal contacts. The primary contact of occlusion on an opposing natural posterior maxillary tooth is the lingual cusp, which is reshaped to axially load the implant.


The buccal cusp of the mandibular implant crown is located near the original central fossa of the natural tooth. The medially positioned Division B mandibular implant crown may have a central fossa, but it is more lingual than the original position. The lingual contour of the crown is similar to that of the original natural tooth and has an overjet with the opposing natural tooth to prevent biting the tongue during function. The mandibular posterior implant may, on occasion, be angled medially because of the sub mandibular fossa.

As a result, an angled abutment and a lingual straight emergence crown profile to minimize the lingual volume of the restoration are indicated. Augmentation of the mandibular Division B ridge is often required when stress factors are moderate to improve the implant position and prosthetic guidelines.


A Division B maxillary implant is often placed under the palatal cusp region of the original natural tooth. The maxillary occlusal table cannot always be reduced from the facial aspect for esthetic reasons; therefore the buccal cusp is offset facially but left completely out of occlusion (as with natural teeth) in centric relation occlusion and during all mandibular excursions. The buccal cusp of the opposing natural tooth is recontoured in width and height to reduce offset loads to the opposing crown on the maxillary implant. The primary occlusal contact is centric relation occlusion is the maxillary palatal cusp over the implant body and the central fossa region of the mandibular natural tooth. Bone augmentation for larger implant width is more indicated in the maxilla because of the less dense bone and the prosthetic needs to replace an esthetic buccal crown contour.


When Division B implants are placed in both arches, the maxillary and mandibular prostheses are similar to that described in the previous scenario. However, it is usually not possible to load both arches with an axial load, so the weakest implant in bone density, width, or prosthesis type (fixed vs. removable) determines the axial load, because it is the most vulnerable arch.


When further resorption occurs and the ridge evolves into Division C or D, the maxillary palatal cusp becomes the primary contact area, situated directly over the implant body. Hence the occlusal contacts differ from those of a natural tooth and may even be positioned more medial than the natural palatal cusp when the implant is placed in Division C or D bone.


Influence of Surface Area: An important parameter in IPO is the adequate surface area to

sustain the load transmitted to the prosthesis. It is important to remember that mechanical stress, in its simplest form, can be defined as the force magnitude divided by the cross sectional area over which that force is applied.

When implants of decreased surface area are subject to angled or increased loads, the magnified stress and strain magnitudes in the interfacial tissues can be minimized by placing an additional implant in the region of concern.

Thus when narrow diameter implants are used in regions that receive greater forces, additional splinted implants are even more indicated to compensate for their narrow design and to help decrease and distribute the load over a broader region. When forces are increased in magnitude, direction or duration (e.g., parafunction), ridge augmentation maybe required to improve implant placement, reduce crown height, and increase implant width and number to compensate for the increased loads.


Maxillary Root surface area (mm2)

CENTRAL 204LATERAL 179CANINE 273FIRST

PREMOLAR234

SECOND PREMOLAR

220

FIRST MOLAR 433SECOND MOLAR

431

Mandibular Root surface area (mm2)

CENTRAL 154LATERAL 168CANINE 268FIRST

PREMOLAR180

SECOND PREMOLAR

207

FIRST MOLAR 431SECOND MOLAR

426


Radius (mm) Length (mm) Surface Area (mm2)

1.75 101214

110132154

2.00 101214

126151176

2.25 101214

141169197

2.50 101214

157188220

2.75 101214

172207242

3.00 101214

188226264www.indiandentalacademy.com

The prosthesis type may also be modified from a fixed restoration (FP-1 to FP-3) to a removable prosthesis (RP-4). This is most effective when nocturnal parafunction is present because the restorations may then be removed while sleeping. In addition, stress relieving elements may be included in the removable restoration, and additional support may be gained from the soft tissue (RP-5 restorations).

Wider diameter root form implants have a greater area of bone contact at the crest than narrow implants (resulting from their increased circumferential bone contact areas). As a result, for a given occlusal load, the mechanical stress at the crest is reduced with wider implants compared with narrow ones.

Natural teeth follow similar principles of diameter and surface area as just described. The anterior region of the mouth is characterized by reduced bite force compared with the posterior region. Consequently, the anterior tooth cross section is smaller, and the surface area is reduced compared with the greater diameter and surface area of posterior teeth.


Design to the Weakest Arch: Any complex engineering structure will typically fail at its

“Weakest link”, and dental implant structures are no exception. The amount of force distributed to a system can be reduced by

stress relieving components that may dramatically reduce impact loads to the implant support. The soft tissue of a traditional completely removable prosthesis opposing implant prosthesis is displaced more than 2 mm and is an efficient stress reducer. Lateral loads do not result with as great a crestal load to the implants because the opposing prosthesis is not rigid.

The most common implant treatment, which includes a traditional soft tissue supported complete denture, is a maxillary denture opposing a mandibular implant supported restoration. The occlusal scheme for this condition raises the posterior occlusal plane, uses a medial positioned lingualized occlusion, and has a bilateral balanced scheme. Whether the mandibular restoration is FP-1, FP-2, FP-3, RP-4, or RP-5, the maxillary denture follows these guidelines. www.indiandentalacademy.com

The mandibular implant supported restoration may exert greater force on the premaxilla than a mandibular denture and cause accelerated bone loss. Therefore modification of the occlusal scheme aims at protecting the premaxilla under a maxillary denture by the total elimination of anterior contacts with the mandibular anterior teeth in centric occlusal relation.

Reduced occlusal forces with an absence of lateral contacts in excursions are recommended on posterior cantilevers or anterior offset pontics whenever possible. This minimizes the moment forces on the abutments.

It is better for mandibular cantilever pontics to oppose maxillary implants than the reverse situation.


Full – Arch fixed prostheses(FP-1 to RP-4)

Fixed prostheses on natural teeth opposing FP-1 to RP-4 implant restorations should follow mutually protected occlusal schemes whenever possible. In protrusion, there should be total absence of posterior contacts, especially for cantilevered posterior units. The masticatory force generated during lateral excursions is decreased in absence of posterior contacts. This assists in reducing the noxious effect of lateral forces on the anterior implants. Two or more implants should share any lateral force, and lateral excursions should occur as far forward as is practical and include the canine.

Minimal occlusal contact in the cantilevered regions and the total absence of posterior lateral contacts during excursions are indicated when opposing the natural dentition or a fixed restorations.

Seven to eight implants to support a complete implant prosthesis in two separate units are suggested in the mandible for a fixed restoration opposing a fixed prosthesis or natural teeth with inadequate to severe stress factors.


In the edentulous maxilla, flexure of the bone is not a concern. A full arch prosthesis may be fabricated in one section.

Eight to ten maxillary implants most often are required for a twelve unit fixed prosthesis opposing a fixed dentition on teeth and / or implants with moderate to severe stress factors. Posterior implants are more critical in the maxilla, in order to eliminate cantilevers and increase the anteroposterior implant distance, which further decreases stress to the maxillary anterior implants.


Fully bone anchored bridge

Mandibular edentulous case for fully bone anchored

bridge

•Recommended to have a mutually protected occlusion.

•In centric it is necessary to have 30µm clearance at the anterior region

•disocclusion should be employed.

•To avoid localization of stresses anterior group function should be employed.

•The anterior guidance should be made slightly flatter than natural teeth to avoid over stresses on the fixtures.


Kennedy Class I

OCCLUSION FOR FREESTANDING BRIDGES

o Clearance of the anterior teeth should be smaller than the natural teeth.

o Amount of disocclusion required is same as natural teeth since the anterior guidance is provided by the remaining anterior natural teeth.

Protrusive : 1.1mmNon working side : 1.0 mmWorking Side : 0.5 mm


Kennedy Class II

•In centric the posterior osseointegrated bridge should have 30µm open contacts, while anterior teeth also should have 30 µm open contacts and begin to contact under strong bite pressure.

•Amount of disocclusion required is same as natural teeth since the anterior guidance is provided by the remaining anterior natural teeth.

Protrusive : 1.1mmNon working side : 1.0mm Working Side : 0.5 mm


Kennedy Class III

Vertical dimension is maintained by remaining natural teeth

The osseointegrated bridge should contact only under strong pressure.

Amount of disocclusion required is same as natural teeth since the anterior guidance is provided by the remaining anterior natural teeth.

Protrusive : 1.1mmNon working side : 1.0 mmWorking Side : 0.5 mm


Kennedy Class IV

To minimize horizontal loads group function occlusion is recommended.

During lateral movement posterior teeth on working side can bear the horizontal load while non working side can be discluded.

Anterior guidance should be flatter than natural dentition to minimize load induced on the fixture during protrusive movement.Amount of disclussion suggested is as follows

Protrusive : 0.8 mmNon- working side : 0.4 mmWorking side : 0.0 mmwww.indiandentalacademy.com

IMPLANT AND SOFT TISSUE SUPPORTED OVERDENTURE (RP-5)

Anterior Tooth PositionCentric stops or pressure from the tongue and muscle positions

usually prevent continued extrusion of anterior natural teeth. maxillary anterior prosthetic teeth are positioned forward of the anterior supporting bone to satisfy phonetic and esthetic requirements. Moment forces result from contact with the anterior teeth, which may cause instability of the maxillary prosthesis. Therefore the maxillary denture usually does not have anterior incisal centric stops. This helps protect the premaxilla from excess forces in centric occlusion relation and initial excursions of the mandible, as the premaxilla is vulnerable to resorption from external stresses.


Posterior Tooth Position The maxillary edentulous posterior ridge resorbs in a medial directions

it transforms from Division A to B, Division B to C, and Division C to D. therefore the maxillary denture tooth gradually becomes more cantilevered off the bone support, even when positioned in the same spatial location. The mandibular edentulous posterior ridge also resorbs in a medial redirection as it transforms from Division A to B, but then resorbs laterally from Division B to C, and more lateral as it resorbs from Division C to D. In complete dentures, the position of the mandibular posterior teeth is often determined first. Bone support concepts of occlusion often position the mandibular teeth perpendicular to the edentulous ridge. This positions the central fossa of the posterior mandibular teeth more medial than that of their natural predecessors in Division B, but more facial in Division C, and very facial in Division D compared with the natural tooth placement.

The maxillary teeth are then situated farther facially than the original teeth, if a normal cusp fossa relation is maintained. Consequently, maxillary denture teeth are always placed lateral to the resorbing bony support, and the condition is compounded in cases of advanced atrophy (Division C or D bone). www.indiandentalacademy.com

The basic, concept of lingualized occlusion was first introduced by Gysi. Later Payne suggested the maxillary buccal cusps of posterior teeth should be reduced, so only the lingual cusps would be in contact. Pound discussed a similar concept, but reduced the buccal cusp of the mandible and introduced the term “lingualized” occlusion. Pound also placed the lingual cusp of the mandibular posterior teeth between lines drawn from the canine to each side of the retromolar pad. Consistent in the Philosophy of Payne and Pound, was the belief that the palatal cusp should be the only area of maxillarytooth contact. These occlusal schemes were designed to narrow the occlusal table and improve mastication, reduce forces to the underlying bone, and help stabilize a lower denture. The techniques of Payne and Pound may be modified further to a medial positioned lingualized occlusion, proposed by Misch. www.indiandentalacademy.com

Medial Positioned Lingualized occlusion : Laboratory steps

1. Mount the upper cast using a face bow record. Mount the lower cast using the centric relation record. Set the horizontal condylar guidance according to the protrusive record.

2. Set the maxillary and mandibular anterior teeth for esthetics, phonetics, and lip support.

3. Cut back the posterior flange of the lower record base to expose the retromolar pad. Outline the retromolar pad in pencil. Draw a line from the lingual border of the pad to the mesial aspect cuspid. The central fossa of mandibular posterior teeth will be set along this line.


4. Using a flat plane or 10 degree mold, set the mandibular posterior teeth in a compensating curve. The curve should have both a mediolateral and anteroposterior dimension that progressively develops as the teeth are set posteriorly. The curve starts with the first premolar and becomes more accentuated in the molar region (closer to the condyle) (i.e., first premolar 0 to 5 degrees, second premolar 5 to 10 degrees, first molar 15 to 20 degrees, second molar 20 to 25 degrees). The anteroposterior angle of the curve is the second molar region and should ideally approximate the horizontal condylar guidance (i.e., 20 to 25 degrees).

5. Drop the incisal pin of the articulator 1 to 2 mm.

6. Using a 30 to 33 degree mold, set the maxillary posterior teeth with the buccal cusp tilted out facially. The lingual cusp should contact the central groove of the mandibular teeth (this will be the only tooth contact point). There should be no contact between the mandibular buccal cusp and the opposing maxillary tooth.


7. Return the incisal pin to the original position (up 1 to 2 mm).

8. Using articulating paper to check the contacts, grind a small fossa in the mandibular tooth for the maxillary lingual cusp tip. Continue to adjust the occlusion until the incisal pin touches the incisal table. Check for balanced occlusion in excursions.

9. Festoon the set up for the try in appointment.


Overdenture

Maxillary edentulous case for overdenture

• Recommended occlusion for overdenture is fully balanced occlusion with lingualized occlusion.

• Incase maxillary overdenture is opposed by a mandibular fully bone anchored bridge, in centric a small clearance is recommended in the anterior teeth, while posterior contact simultaneously.

• Disocclusion is not employed here. www.indiandentalacademy.com

OCCLUSAL MATERIALS


The materials selected for the occlusal surface of the prosthesis affect the transmission of forces and the maintenance of occlusal contacts. In addition, occlusal material fracture is one of the most common complications for restorations on natural teeth or implants. Therefore it is wise to consider the occlusal material for each individual restoration. Occlusal materials maybe evaluated by esthetics, impact force, a static load, chewing efficiency, fracture, wear, interarch space requirements, and accuracy of castings. The three most common groups of occlusal material are fixed prostheses on implants are reviewed with relevance to the previous eight criteria.


Esthetics:

Esthetics is a major concern for patients. The most esthetic material available today is porcelain. Acrylic is acceptable for esthetics, and metal is a poor choice of materials when esthetics is the chief criterion. However, there are many situations in which esthetics is not an important aspect of the restorations. For example, when a maxillary second molar is restored, most patients do not expose this area when smiling or laughing.


Forces: The materials on the occlusal aspect of the prostheses affect the

transmission of force to the bones. Impact loads give rise to brief episodes of increases force, primarily related to the speed of closure and the dampening effect of the occlusal material. The hardness of material is related to its ability to absorb stress from impact loads. All porcelain occlusal surface exhibits a hardness 2.5 times greater than that of natural teeth. Acrylic resin has a Knoop hardness of 17 kg/mm2, and enamel has a 350 kg/mm2 hardness. A composite resin may exhibit a hardness of 85% that of enamel. Therefore impact loads are lowest with acrylic, increase with composite and metal occlusals, increase even more with enamel, and further increase with porcelain. As a consequence, it has been suggested to use resin because of its dampening characteristics.

Clenching patients do not have a considerable amount of stress reduction when acrylic versus porcelain materials are used on the occlusal surfaces.

Progressive bone loading is performed with acrylic transitional prostheses. This material may reduce the impact force on the early implant bone interface. As the bone matures and its density increases, the need for force reduction decreases.


Chewing efficiency:

Fixed prostheses exhibit an improve efficiency compared with removable soft tissue borne prostheses, regardless of the occlusal material.

Acrylic was 30% less efficient than porcelain or metal, whereas there was no difference between gold and porcelain.


Wear:

The definition of wear is the deterioration, change or loss of a surface caused by use. The factors affecting the amount of wear include magnitude, angle, duration, speed, hardness, and surface finish of the opposing force and surface, together with the lubricant, temperature, and chemical natural of the surrounding environment. Most occlusal wear occurs as a result of bruxism. An intuitive feeling is the harder the occlusal material, the less the wear. However, surface hardness has been shown to be a poor indicator of wear rate. Acrylic resin wears 7 to 30 times faster when opposing gold, resin, enamel, or polished porcelain, compared with gold opposing gold, enamel or porcelain. Gold occlusal surface exhibit less volume loss (sum of loss of opposing occlusal surfaces) than any other combination of materials. Porcelain opposing porcelain wears more than porcelain opposing gold or metal.


The wear rate of occlusal materials, especially in the partially edentulous patient with unrestored teeth, should be similar to enamel. In this way, occlusal changes will not dramatically change the occlusal scheme. Lambrechts et al in an in vivo investigation reported vertical wear of premolar and molar tooth enamel to be 20 to 40 um per year when opposing the enamel of natural teeth.

In principle, for the partially edentulous patient it would be better to have more occlusal wear on implants, rather than less, because the additional forces on the teeth are better tolerated than on implant prostheses. As a result, total volume wear may favor porcelain opposing enamel for the implant prosthesis opposing teeth in the partially edentulous patient and metal opposing enamel in the other regions of the mouth that require restorations of natural teeth.

The use of gold, regardless of the opposing combination, always provides the least total volume loss.


Adhesive wear occurs when one hard surface slides over a surface of lesser hardness. As a result, wear fragments of one material adhere to the other material. Gold occlusal surfaces are observed to have gold particles adhered to enamel. This may account for less total volume loss when opposing other materials.

For full arch implant supported prostheses, the restoring doctor may consider metal occlusal to minimize wear and prolong the accuracy of occlusal scheme long term. Porcelain in esthetic regions opposing gold in the more nonesthetic area or metal occlusal in both arches when parafunction or marginal interarch space is present are the material most often selected as implant occlusal materials.


Materials fracture:

Materials fracture is one of the more common factors that lead to refabrication of a prosthesis. Porcelain, acrylic and composite fractures occur under excessive loads or even with a lesser load of longer duration, angulation, or frequency. Acrylic or composite materials fracture more easily. The compressive strength of acrylic resin is 11,000 psi, compared with 40,000 psi for enamel. Composite resin is 3 times stronger than acrylic.

Porcelain opposing porcelain is not suggested with extreme parafunction, because it may fracture more often than porcelain opposing metal. Metal occlusals do not easily fracture, provide good wear resistance, and have minimum impact load compared with porcelain.


Accuracy:

Metal shrinkage is 10 times less than porcelain or acrylic and therefore permits the fabrication of a more passive casting. When accuracy of the casting is paramount, as with screw retained restorations, the occlusal material may make a significant difference. This is most important in regions of long spans and / or with a large volume of materials.

Interarch space:

Acrylic restorations receive their strength from bulk and therefore require greater interarch space. Metal occlusals require the least amount of space. In addition, when increased retention of a cement retained prosthesis is required, a high abutment and greater retention may be accomplished with a metal occlusal. Porcelain is intermediate in the interarch space requirement. www.indiandentalacademy.com

Therefore when all seven criteria are evaluated, metal is an excellent occlusal material, with improved properties in accuracy, wear, fracture resistance, abutment retention, and good qualities for impact or static force. Esthetics is best satisfied with porcelain, which has improved properties compared with acrylic concerning fractures and retention.


REVIEW OF LITERATURE

J.B. Brunskin and J.A. Hipp in 1984 studied the in vivo forces on dental implants. Methods are presented for measuring vertical force components or bridged titanium dental implants in dog mandibles. These methods have included custom made strain gauge transducers, plus hard wiring and telemetric schemes for data collection. The essential components of the measurements system are described, and typical bite force data are illustrated


Rangert et al in 1989 carried out a study on the forces and moments on Brenamark implants. The placement of fixture (implants) in relation to the geometry of a prosthetic restoration has a great influence on the mechanical loading of the implant. Based on Theoretic consideration and clinical experiences with the Brenamark system, this article gives simples guidelines for controlling these loads. The emphasis is on design rules that can be used in clinical practice. With the class I lever as a reference. Various clinical implant prosthesis situations are discussed and evaluated.


Parker et al in 1991 reviewed the occlusal considerations in restorative dentistry. The major topics include the assessment and treatment of occlusal wear, the controversies surrounding treatment position of the mandibular condyles, occlusal considerations in osseointegrated prosthesis, the two way relationship between occlusal factors and temporomandibular disorders, design criteria and longevity studies in resin bonded, fixed partial denture.

Hobo et al in 1991 presented a case report on occlusion for osseointegrated prosthesis and concluded that the concept of occlusion suitable for osseointegrated prosthesis is basically the same as the gnathological occlusion. However the natural tooth sinks about 30µm during function, while an osseointegrated bridge which is supporte only by the bone does not sink. Therefore it is necessary to adjust the centric contacts of the osseointegrated fixed bridge slightly more open than the natural teeth. During the eccentric movement, in order to minimize horizontal loading, the concept of disocclusion is generally used. www.indiandentalacademy.com

James et al in 1993 discussed the edentulous implants an emphasized that the occlusal contacts of the final fixed restoration are affected significantly by implant position. Lateral occlusal forces, may lead to abutment screw fracture. They may be due to either excessive lateral occlusal pressure or a malposed implant that requires non axial loading during normal function.


C.E. Misch et al in 1994 discussed an implant protected occlusal on a biomechanical rationale. The clinical success and longevity of endosteal dental implants are controlled, in a large part, by the mechanical milieu within which they function. The occlusion is a critical component of such a mechanical environment. “Implant protected occlusion” refer to an occlusal scheme that is often uniquely specific to the restoration of endosteal implant prosthesis. Implant orientation and the influence of load direction, the surface area of implants, occlusal table width, and protecting the weakest area are blended together from a biomechanical rationale to provide support for a specific occlusal philosophy.


Tashkandi et al in 1996 did an analysis of strain at selected bone sites of a cantilevered implant supported prosthesis. the results revealed that the maximum strain occurred at the strain gauge positioned on cortical bone over the apex of the most distal implant under 10 and 20 lb loading conditions.

Osamu et al in 2002 did a study on influence of supra structure materials on strain around an implant under two loading conditions. The results showed under static and non impact dynamic loading the three super structure materials tested (highly filled composite resin, acrylic resin and gold alloy), had the same influence on the strain transmitted to the bone simulant that surrounded a single implant. www.indiandentalacademy.com

Kent et al in 2004 did a photoelectric analysis of the effect of palatal support on various implant supported overdenture designs and concluded that at the removal of the palatal support produces a greater effect and more concentrated stress difference for maxillary overdenture than difference between the attachment designs.

With palatal coverage Without palatal coveragewww.indiandentalacademy.com

Steven et al in 2004 did a study of stress transfer of four mandibular implant overdenture cantilevered designs. His results condluded that under load all prosthetic designs demonstrated a low stress transfer to the ipsilateral abutment and to the contralateral side of the arch. The plunger retained prosthesis retained by two implants demonstrated a more uniform stress trasnfer to the ipsilateral terminal abutment than the clip retained prosthesis retained by three implants and provided more retention.


Lucie et al in 2004 Did a finite element analysis on the influence of implant length and diameter on stress distribution. Results showed an increase in the implant diameter decreased the maximum von Mises equivalent stress around the implant neck more than an increase in the implant length, as a result of a more favorable distribution of the simulated masticatory forces applied in this study.


Osseointegrated supported prosthesis (ISP) have shown high standard of success. This success rate depends not only on meticulous surgical protocol but also on understanding concept of occlusion.

Occlusion should be a key factor to overall success rate. The concept of occlusion suitable for implant supported prosthesis is basically the same as gnathological occlusion.

In Centric contact of the Osseo integrated crown or fixed prosthesis should be slightly more open than natural teeth.

In centric Osseo integrated crown or fixed prosthesis should not contact with opposing teeth under the soft bite pressure (to avoid the occlusal load on the I.S.P. which leads overload the bone structure)

Under the strong bite pressure Osseo integrated supported prosthesis should contact after the natural tooth intrudes approximately 30µm.

SUMMARY


• To avoid overloading of the occlusal surface, the I.S.P. should not have plane-to-plane contact.

• Point contact especially cusp-to-fossa tripodal contact is preferred.• During eccentric movement, in order to minimize horizontal

movement, the concept of disocclusion is generally recommended.• Anterior segments of the osseointegrated prosthesis should guide

the mandible to produce posterior disocclusion.• Canine guided occlusion is not recommend for the Osseo integrated

prosthesis to avoid excessive occlusal forces into the single implant fixture which is placed in the canine area. Group function is recommended to distribute the stress over the entire fixture.

• The ideal place to bear the horizontal load is the trapezoid area, which is surrounded by the osseointegrated fixtures.

• Load transmitted to the fixture is not so destructive when extended mesially in the anterior region, whereas more destructive when extended distally.


CONCLUSION

The local occlusal considerations in implant dentistry include the transosteal forces, bone biomechanics, basic biomechanics, differences in natural teeth and implants, muscles of mastication and occlusal force, and bone resorption. The incorporation of all these factors lead to an occlusal scheme (IPO) discussed in this seminar.

Occlusal schemes consider the weakest component, full or partial edentulous arches, and posterior or anterior teeth and / or implants. An IPO is a consistent approach for implant occlusal schemes.

The material from which the occlusal region are fabricated may affect implant loading and also affect implant reaction forces to the opposing arch. These occlusal material also affect wear and fracture, which affects the occlusal contacts, vertical occlusal dimension, and esthetics.


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16. Schupe RJ et al : effects of occlusal guidance on jaw muscles activity, J Prosthet Dent 51:811-818, 1984.www.indiandentalacademy.com

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