Occlusal Considerations For Implant Supported Prostheses

Occlusal Consideration For Implant-Supported Prosthesis.

Occlusion  Definition

Occlusion has been defined as the static relationship between the incising or masticating surfaces of the maxillary or mandibular teeth or tooth analogs.

Occlusion Significance

• It determines the success of implant prosthesis
• The supporting structures of the implant and the natural teeth are different, as natural teeth are suspended by periodontal ligament whereas the implant has a rigid connection to the bone
• An implant-protected occlusal scheme reduces the occlusal forces on the implant thus, protecting and preserving the surrounding bone.

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Types of occlusion

• Balanced occlusion
• Group function occlusion
• Monoplane occlusion
• Mutually-protected occlusion
• Lingualized occlusion
• Implant-protected occlusion.

Greater emphasis is placed on mutually-protected occlusion since most of the implant restorations are associated with a greater number of natural teeth.

Balanced occlusion

Definition
It is the bilateral, simultaneous, anterior, and posterior occlusal contact of teeth in centric and eccentric positions.

Indication
Mostly preferred in complete dentures to enhance the stability of the prosthesis.

Advantages
Uniform distribution of forces to all the occlusal units improves the stability of the prosthesis.

Limitation
Lateral forces on the nonworking side of implants cause eccentric deflective contacts.

Group function occlusion

A variant of the balance occlusal scheme is unilateral balance or group function occlusion. The teeth on the working side will be in contact and the balancing side teeth are not in contact. It can be a choice of occlusion when the canine is replaced.

Monoplane occlusion

An occlusal scheme utilizing a zero degree or nonanatomic teeth is commonly preferred in highly resorbed ridges. The flatter occlusal surfaces dampen the damaging forces transmitted to the resorbed and flat ridges.

Mutually-protected occlusion

The maxillary and mandibular anterior teeth disocclude the posterior teeth during protrusion and in lateral movement of the mandible the canine on working side disocclude the other teeth. In centric, the posterior teeth prevent the anterior group of teeth from contacting.

Advantage
Distributes the forces.

Lingualized occlusion

The maxillary lingual cusp of posterior teeth is the predominant teeth in contact during the movements rather than the mandibular buccal cusp.

Advantage
This direction of arrangements helps in directing the occlusal forces towards the center of the ridge and thus, reduces the lateral stress on the implants.

Implant-protected occlusion

Misch and Bidez in 1994 proposed the occlusal concept to reduce the force transmission to the implant which led to the better prognosis and success of implant restoration.

Factors to be considered in the implant-protected occlusion3-6 are:

• Implant surface area
• Implant and abutment angulation
• Crown: implant ratio
• Implant crown contour
• Cusp inclination
• Occlusal contact and its timing
• Width of the occlusal table
• Occlusal materials
• Protection of weaker components.

Implant surface area
An increase in surface area permits greater transmission of occlusal forces. This is done by increasing the number of implants and splinting implants.

Implant and abutment angulation

The forces parallel to the long axis are better tolerated than the lateral forces.

• If the angulation is straight there are more compressive forces which are more acceptable to biological structures than the tensile force
• It is ideal to place the angulated abutment of the same angulation rather than altering the angulation at the interface angulated abutment) which makes the abutment–implant body interface straight and aids in transmitting the forces away from the crest
• If the angulation cannot be avoided then a wider implant, ridge augmentation, or additional implants can be placed.

Crown: implant ratio

• The ideal crown to root ratio is 1:2
• Any deviations from this generate cantilever and nonaxial forces to the crest of the implant.

Crown contour

Depends on:

• Bone contour and morphology in edentulous areas
• Bone resorption pattern
• The buccolingual dimension of the implant is lesser than that of natural teeth so it is essential to contour the crown which in turn will reduce the lateral forces to the bone crest.

Cusp inclination

• An increase in cuspal angulation increases the masticatory efficiency
• Broadening the angle and widening the cuspal angulation reduces the force concentration
• Recontouring of cusps with lesser angulation transmits lesser and more favorable axial loads to the implant.

Occlusal contacts

• The occlusal contact of the prosthesis with opposing teeth determines the transmission of forces to the implant
• Occlusal contacts should exist within the diameter of the implant. The cusp fossa occlusal scheme is better than the cusp marginal ridge contact which centralizes the forces of occlusion
• Occlusal contacts have to be matched to the difference in range of movements between natural tooth (27 µm) and implant (3–5 µm) with 28 µm articulating paper until an even contact is obtained
• Uniform occlusal contact ensures the long-term success of the implant and also prevents fracture of the ceramic restorations.

Occlusal table
A narrow occlusal table reduces the forces and aids in easier maintenance.

Occlusal materials
The choice of material is metals, porcelain fused to metal (PFM), ceramics, composite, and acrylics. Among these materials, PFM is commonly used as permanent restorations and acrylic as provisional restorations.

Protection of weaker components

Weaker aspects such as cantilever length, length of edentulous span, angulation of implants, and poor labial or buccal bone have to be identified and the stress transmitted to these components should be reduced during prosthesis designing.

Occlusion schemes in different types of prosthesis

• The occlusal schemes vary with the type of implant prosthesis, number of teeth replacements, type of support, and opposing dentition
• In full-mouth rehabilitation and if full-arch prosthesis opposes the natural dentition, mutually protected or group function is ideal
• Natural dentition opposing single complete denture a balance occlusal scheme is ideal
• For an over-denture prosthesis, a balanced occlusal scheme with singularized occlusion is the preferential choice
• In situations of highly resorbed ridges monoplane occlusal scheme is preferred
• For the replacement of single teeth or fewer teeth, the already existing occlusal scheme (usually a mutually protected) is chosen
• When a segment of teeth is replaced or when the abutment teeth are periodontally compromised a group function occlusion is chosen for uniform force distribution.

Occlusal Consideration Conclusion

The potential complications of decementation, screw loosening, abutment failure, fracture of restoration, crystal bone loss, and implant failure can be avoided with an implant-protected occlusal scheme.

Occlusal Consideration References

• Ben-Gal G, Lipovetsky-Adler M, Haramaty O, Sharon E, Smidt A. Existing concepts and a search for evidence: a review on implant occlusion. Compend Contin Educ Dent.
• Koyano K, Esaki D. Occlusion on oral implants: current clinical guidelines.
• Yuan JC, Sukotjo C. Occlusion for implant-supported fixed dental prostheses in partially edentulous patients: a literature review and current concepts. J Periodontal Implant Sci.
• Kim Y, Oh T-J, Misch CE, Wang H-L. Occlusal considerations in implant therapy: clinical guidelines with biomechanical rationale. Clin Oral Impl Res.
• Gross MD. Occlusion in implant dentistry. A review of the literature on prosthetic determinants and current concepts. Aust Dent J.
• Chang M, Chronopoulos V, Mattheos N. Impact of excessive occlusal load on successfully osseointegrated dental implants: a literature review. J Investig Clin Dent.