Occlusion in Implantology- a Key to Longevity

Abstract

Osseointegrated implant has become the most upcoming treatment modality of partially and fully edentulous patients. Besides other aspects that form a part of implantology as a science, planning and delivering the optimal occlusion is an integral part of implant supported prosthesis. Implants are more prone to occlusal overloading, which is often regarded as one of the potential causes for peri-implant bone loss and failure of the implant/ implant prosthesis.

So developing such occlusion that places minimum stress on implant, implant-prosthesis interface. Various occlusal schemes like balanced, group function and mutually protected have been used for implant supported prosthesis. This paper reviews the role of occlusion in implantology and discuss the clinical guidelines for choice of occlusal schemes.

Keywords:

Implant, Occlusion, Stresses

INTRODUCTION

Proper occlusal scheme is a primary requisite for long term survival, especially where clinical conditions are not sound like where a marginal foundation is present. Magnitude of loads and mechanical stresses increases at crest of the bone when there is poor occlusal scheme.

Patients with implant unilateral occlusal support showed the highest rate of implant failure 1(43.8%). In a survey of the development of concepts and controversies of occlusion, Mohl and Robertson2 noted the increasing interest in biological and behavioral aspects of occlusion in contrast to earlier emphasis on technical and biomechanical principles.(Fig.1)

Fig 1. Natural Tooth vs Implant

After osseointegration mechanical stress and strains beyond the limits of hard tissue have been suggested as the primary cause of the initial and long term bone loss around implants3. If the occlusal overload is not corrected, crestal bone loss will continue causing peri-implant disease until the implant fails.4,5 So, a proper occlusal scheme is a primary requisite for long term survival of implant and implant prosthesis.6,7 (Fig 2)

Fig 2. Crestal Bone loss seen in radiograph

Due to various problems encountered like early implant failure, early crestal bone loss, component fracture and sometimes prosthesis fracture due to stress conditions than Implant-protective occlusion (IPO) concepts originates. IPO, developed by Misch, refer to an occlusal plan that if often unique and specifically designed to restore an endoosseous implant, by providing an environment for improved clinical longevity of both the implant and prosthesis. Occlusal overload is often regarded as one of the main cause for per-implant bone loss, thus increasing the anaerobic sulcus depth and peri-implant disease.

Misch & Bidez concluded and published the biomechanical rationale for this concept after long term evaluation and proposed IPO by reducing the occlusal forces on implant prosthesis to protect the implant. So, several modifications from conventional occlusal concepts have been proposed to decrease stress to implant interface including: timing of occlusal contacts, influence of implant surface area, mutually protected articulation, implant or crown body angle to occlusal load, crown height, cantilever distance, protection of the weakest component and occlusal material of the implant crowns.8

Before discussing the various occlusal schemes used in implant restorative dentistry the understanding begins with some basic assumptions drawn from knowledge of natural and implant supported prosthetic occlusion.

First, the patient controls the occlusal forces on natural teeth in response to proprioception. Since natural periodontal ligament-mediated proprioception does not occur with implants, its protective influence is lost in determining mandibular velocity and displacement. This means occlusal forces on implant-supported prostheses must be, if anything, more carefully designed and exactly accomplished than tooth-supported prostheses.9

Second, no single occlusal scheme can be used for every type of restorations. The purpose and mechanism of complete denture occlusion is different from that of a single crown restoration. For implant-supported prostheses, the occlusal scheme must suit the purpose and location of the restoration.

Third, two arches are involved in every occlusion. Whether the implant-supported prosthesis occludes with natural dentition, tooth-or tissue-supported prostheses, or another implant-supported prosthesis, is of critical interest, because each of these prostheses exerts a different range of forces in both functional and resting movements.

Finally, the natural resorption pattern of edentulous alveolar bone is almost never parallel to the ideal occlusal plane of the dentition. In determining abutment height and position, not only adequacy of interarch space but also orientation of the plane of occlusion must be considered, for it is impossible to achieve an optimum occlusal scheme with a disrupted or incorrectly oriented plane of occlusion.

Basic principles of implant occlusion may include: Bilateral stability in centric habitual occlusion, evenly distributed contacts and force, no interferences between retruded position and centric habitual position, wide freedom in centric occlusion, anterior guidance whenever possible, and smooth, even, lateral excursive movements without working /non working interferences. In all phases of prosthetic rehabilitation, design the occlusal scheme to meet the requirements of its oral situation.(Fig 3)

Fig 3. Various options for implant supported prosthesis

When an implant-supported prosthesis replaces a single tooth in an otherwise intact dental arch, design the occlusion like that of a tooth-supported single restoration. This is generally agreed to include lighter-than-normal tripodal centric occlusal contacts to prevent supraeruption of the opposing natural tooth. Since teeth have a periodontal ligament, they are microscopically compressible. Take centric stops by having the patient close hard in centric.

It is necessary to compress the adjacent periodontal ligaments to prevent hyperocclusion of the implant restoration. The implant-supported prosthetic crown should follow the guidance of natural teeth in working relationships, similar to other fixed restorations bounded by intact natural teeth.10 (Fig 4)

Fig 4. Dental implant replacing single tooth

Use canine disclusion in cases in which natural canine teeth are present and periodontally strong. Where replacing canine teeth with implant-supported prostheses that occlude with natural teeth or other implant-supported prosthesis, group function occlusion supported by natural teeth or other implant-supported prostheses is preferable to avoid loading a single supporting implant during disculsion. Group function occlusion provides occlusal contact in centric position and in working movements but complete disculsion in balancing positions.11(Fig 5)

Fig 5. Canine area with implant supported crown

Occlusion in anterior fixed prosthesis is like minimal buccal bone of 2mm thickness, Augmentation of buccal bone would appear to improve biomechanical resistance to facial loading, length >10mm, Diameter <3.75 mm, Crown /implant ratio >1:1 becomes biomechanically unfavorable with increased risk, splinting adjacent anterior units is currently accepted paradigm, Selective excrusive guidance, In Skeletal Class II Div I: Mid retrognathia-flat lingual incisal platform within phonetic and comfort limitations, In Skeletal Class II Div II: Raising OVD to flatten anterior guidance requires full arch restoration, In Skeletal Class III flat protrusive guidance-mild anterior disclusion to slightly disclude posterior teeth or combine premolar protrusive contact, use of full arch night splint is strongly recommended particularly if bruxism is diagnosed.12, 13

Occlusion in posterior fixed prosthesis, the potential lateral force on osseointegrated implants can be reduced by anterior guidance in excursions and initial contact on natural dentition. Group function only advised when anterior teeth are periodontally involved.

During lateral excursions, working and non working interferences should be avoided in posterior restorations. Few points to be noted in this are: reduced inclination of cusps, centrally oriented contacts with a 1-1.5 mm flat area, and a narrowed occlusal table. Wennerberg and Jemt claimed that occlusal contact which are centrally located were critical to reduce bending moments attributable to mechanical problems and implant fractures. Increased proximal contacts in the posterior region may provide additional stability of restorations. The utilization of cross bite occlusion with palatally placed posterior maxillary implants can reduce the buccal cantilever and improve the axial loading.10,14, 15

For the Occlusion on Implant supported Overdentures, use of bilateral balanced occlusion with lingualized occlusion on a normal ridge has been suggested. On the other hand, monoplane occlusion was recommended for a severly resorbed ridge; however, there are no clinical studies that demonstrate the advantages of bilateral balanced occlusion for overdenture occlusion compared with other occlusal schemes16.(Fig 6, 7)

Fig 6,7. Implant Supported Overdenture

By far the most controversial design for implant-supported prosthetic occlusion is in the totally edentulous mandible opposing the edentulous maxilla. The osseointegrated, subperiosteal, staple, and other implant types were originally designed to treat patients who use maxillary dentures with little difficulty but have unfavorable hard-and soft-tissue configurations for retention and stability in the mandibular arch. It is still probably the oral situation most frequently treated with implant dentistry.17

A similarity in occlusal scheme requirements exists between the case of maxillary complete denture or mandibular implant-supported prosthesis and the combination of the maxillary complete denture and mandibular distal extension removable partial denture. Both situations provide a maxillary denture that rests on movable and depressible tissue and a mandibular arch with dentition, either natural or artificial, essentially fixed into place.

In conventional complete denture cases, both dentures are free to move on the tissues, and balanced occlusion i.e. dynamic occlusal contacts throughout the arch is usually accomplished, at least in part, by denture base movement on resilient tissue. This is especially true of flat plane cases, which have no cuspal inclines to inclines to compensate for Christensen’s phenomenon, the disculsion of posterior teeth in protrusive position. In dynamic occlusion with complete dentures, each base moves slightly, and compressive force delivered to tissue is relatively low. Tissue propriorecption is a limiting factor, because the patient patterns his or her movements to seat, rather than to unseat, his or her mandibular denture.

In the complete denture or implant-supported prosthesis, only the maxillary denture moves in function. Do not rely on soft tissue resiliency and denture movement to assist in balancing dynamic occlusal contacts without excessive compressive and tensile forces under the denture base. Occlusal forces generated against the maxillary denture by the implant-supported prosthesis are of similar magnitude to cantilever restorations using natural teeth18 .

These forces are many times greater than would be possible with even a well-supported mandibular complete denture, and tissue proprioreception of the mandibular denture base is no longer significant19. An occlusal scheme that requires movement of the maxillary restoration could predispose the patient to combination syndrome, as has been documented in patients using maxillary denture restorations that provide only anterior tooth contacts in protrusive position.10

Clinical signs of this combination syndrome derive from hyperfunction in the anterior area of the arches resulting from Christensen’s phenomenon. They include excessive resorption of maxillary anterior alveolar bone, downgrowth of maxillary tuberosities, and a lowering posteriorly of the occlusal plane of the prostheses.

The need for an early refining of the maxillary denture signals a rapid degenerative change related to occlusion for this type of restoration. To avoid initiating this syndrome in patients treated with maxillary complete dentures and mandibular implant-supported prosthesis restorations, an occlusal scheme that is bilaterally balanced during dynamic occlusion is necessary. In 1923, Rudolf Hanau formulated the Hanau Quint as an aid to achieving balanced denture occlusion, and it is quite useful in the complete denture or implant-supported prosthesis situation.

Bilateral balanced occlusion has been utilized for an opposing complete denture for full arch fixed implant prosthesis, while group function occlusion has been widely accepted for opposing natural dentition. For opposing natural dentition, mutually protected occlusion with a shallow anterior guidance was recommended.

For occlusal contacts, more favorable vertical lines of force and thus minimize premature contacts during function can be accomplished by wide freedom (1-1.5mm) in centric relation and MIP. Infra-occlusion (100 m ) on a cantilever unit was suggested to reduce fatigue and technical failure of prosthesis, when a cantilever is utilized in a full arch fixed implant prosthesis. Implant prosthesis with <15mm cantilever in the mandible demonstrated significantly better survival rates than those with >15 mm cantilever. On the other hand, <10-12 mm cantilever was recommended in the maxilla due to unfavorable bone quality and unfavorable force direction as compared with the mandible.17,20,21

CONCLUSION

Occlusion is considered the most important variable in the success of prosthetic rehabilitation. With natural dentition little degree of flexibility can be there but in implant treatment modality the flexibility degree decreased to zero. The occlusion must be evaluated properly with implant supported prosthodontics adjacent to natural dentition. Various Occlusal scheme design for implant-supported prosthesis is often only briefly discussed in implantology literature. Yet, as with all phases of prosthodontics, occlusion is a critical factor in the success or failure of implant-supported restorations.

Tremendous effort has been made to design complex and intricate implant infrastructures for these prostheses. It is of equal or greater importance to design restorations that use occlusal forces constructively, not destructively. The types and basic principles of implant occlusion have largely been derived from occlusal principles in tooth restoration. These occlusal concepts i.e. balanced, group-function and mutually protected occlusion have been successfully adopted with modifications for implant-supported prosthesis.

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More references are availabe on request.