Occlusal considerations in dental implants

Introduction

Occlusion refers to the way the teeth come together when the jaws close. Proper occlusion is critical for the longevity and success of dental implants. It encompasses the alignment, contact, and interaction of the teeth during rest, chewing, and other jaw movements. Occlusion can be divided into static and dynamic occlusion for the sake of understanding. Static occlusion is the relationship between the teeth when the jaws are closed and at rest. This includes centric occlusion and intercuspal position. Centric occlusion is the position where the upper and lower teeth have maximum contact and fit together in the most stable manner. Intercuspal position (ICP) is the position where the cusps of the teeth of one arch fit into the fossae of the teeth of the opposing arch. Dynamic occlusion is the relationship and contact of the teeth during jaw movements, such as chewing, speaking, and swallowing. This includes excursive movements, canine guidance and group function. Excursive movements are the movements of the jaw from side to side (lateral movements) and forward (protrusive movements). Canine guidance is a type of dynamic occlusion where the canine teeth guide the jaw during lateral movements. Group function is a type of occlusion where multiple teeth on the working side make contact during lateral movements. Proper occlusion ensures that the forces during chewing and biting are evenly distributed. Uneven forces can lead to implant failure, bone loss, or damage to surrounding teeth. In the following paragraphs we shall read about various principles that are followed during fabrication of implant supported prosthesis.

Implant-protected occlusion

Implant-protected occlusion is an occlusal scheme designed to reduce forces at the crestal bone/implant interface. It’s all about minimizing the possibility of overload on the implant prosthesis and surrounding bone. The concept draws from biomechanical principles, considering factors like force direction, force magnification, and implant position relative to the arch or location. Dr. Carl E. Misch introduced this concept to enhance the longevity of both the implant and the prosthesis. By optimizing occlusion, we aim to prevent biological complications (like peri-implant infections) and mechanical issues (such as screw loosening or prosthesis fracture). Implant-protected occlusion is important because of following reasons,

Bone health: Proper occlusion helps minimize stress on the implant and crestal bone. Excessive forces can lead to bone loss around implants, affecting their stability.

Prosthesis longevity: Implant-supported prostheses-whether fixed full-arch or single-tooth restorations-benefit from an occlusal scheme that balances function and protection.

Newer materials: Advances in materials (such as monolithic zirconia) have improved prosthesis strength and wear characteristics, but correct occlusion remains essential.

There are 14 considerations for following the IPO scheme that should be judiciously implemented before restoration. They are as follows,

Even Force Distribution:

Ensure that occlusal forces are evenly distributed across all implants and natural teeth to prevent overloading any single implant. Any premature contacts should be removed while doing occlusal adjustments. A thin, articulating paper is used (<25 μm) for the initial implant occlusion adjustment in centric occlusion under light tapping forces. It must be remembered that implant crown should exhibit light axial contact with the opposite tooth because a natural tooth exhibits greater vertical movement than an implant. A natural tooth can be displaced horizontally (side-to-side) and axially (up-and-down) due to its periodontal ligament (PDL). The PDL allows adaptation to excessive forces. In contrast, a dental implant can only be displaced minimally- about 3 to 5 micrometers axially and 10 to 50 micrometers horizontally. Implants lack the PDL’s adaptive properties. Thus, occlusal adjustments for implant supported prosthesis are very important.

Axial Loading:

Direct occlusal forces along the long axis of the implant to minimize lateral stress, which can cause implant failure. To achieve this objective, implant placement plays a crucial role. The three-dimensional implant placement should be planned in such a way that the lateral forces on implants are avoided.

Reduced Cuspal Inclination:

Use shallow cusp angles on implant-supported crowns to reduce lateral forces during excursive movements. Studies recommend reducing cuspal inclination and occlusal table dimensions for implant success. This approach minimizes excessive forces and optimizes load distribution. A narrow occlusal table with supporting cusps in the central fossa generates forces along the long axis of the implant.

Mutually Protected Occlusion:

Implement a scheme where anterior teeth protect posterior teeth during excursive movements and vice versa. The posterior teeth act as vertical stops (closure stoppers) during maximum intercuspal position (MIP). In other words, they prevent excessive contact of the anterior teeth when teeth are occluded. The anterior teeth disengage the posterior teeth during eccentric movements (like lateral excursions). This protects the posterior teeth from lateral forces.

Canine Guidance:

Prefer canine guidance over group function to control lateral movements and reduce occlusal forces on implants. Immediate disclusion of posterior teeth on lateral excurtion in canine guided occlusion reduces lateral forces on them. Less force means a lower risk of fracturing teeth or restorations.

Flat Occlusal Anatomy:

Design implant-supported prostheses with flatter occlusal surfaces to minimize occlusal forces. As already stated, designing flatter occlusal surfaces helps distribute occlusal forces more evenly. Steep inclines or cuspal angles can create localized stress points. Flatter surfaces minimize the risk of porcelain fracture and excessive force on the implant system. A well-designed occlusion also benefits peri-implant soft tissues. Avoiding excessive forces helps maintain gingival health around implants.

Wide Occlusal Table:

Avoid wide occlusal tables that can increase the lever arm effect and cause implant overload. However, if the occlusal table is narrow, patient’s eating efficiency is compromised. So, it is important to make an optimum occlusal table design so that mechanical forces on implant are within safe limits and eating efficiency is not compromised.

Narrow Buccolingual Width:

Ensure the buccolingual width of the implant crown is not wider than the natural tooth it replaces to prevent overloading. The implant diameter also plays an important role in determination of the buccolingual dimensions. Wider implants can support a crown with wider buccolingual dimensions.

Freedom in Centric:

Freedom in centric occlusion refers to the ability of the mandible to move slightly anteriorly in the same horizontal and sagittal plane while maintaining tooth contact. It allows slight freedom in centric occlusion to reduce the likelihood of occlusal interferences during mandibular movements.

Minimized Interproximal Contacts:

Ensuring that interproximal contacts are light is crucial to avoid wedging forces on the implant, which can lead to complications such as bone loss, implant failure, or prosthetic issues.

Progressive Loading:

Gradually increase the load on the implant over time to allow the surrounding bone to adapt and strengthen. Gradually increasing the occlusal load by transitioning from soft diet to normal diet over several weeks is a common approach for progressive loading. In such cases, educating the patients about the importance of following loading protocols and avoiding excessive forces is important.

Regular Occlusal Adjustments:

Conduct periodic occlusal checks and adjustments to maintain proper occlusion and address any changes due to wear or shifting teeth.

Parafunctional Habit Management:

Many studies have reported that parafunctional activities and improper occlusal designs are correlated with implant bone loss and failures. Further, it has been proposed that the numbers and distribution of occlusal contacts had major influences on the distribution of force. In patients with parafunctional habits, shorter cantilevers, proper location of the fixtures along the arch, a maximum fixture length, and night-guard protection should be prerequisites to avoid the overloading of implants.

Patient Education:

Educate patients on the importance of maintaining proper occlusion and regular dental visits to monitor the health of their implants and surrounding tissues.

Conclusion

A proper selection of an implant case, implant size, design and site of implant placement is essential to achieve a long-term success. When it comes to designing implant-supported prostheses, occlusal considerations play a crucial role in ensuring long-term success. By following above stated steps, we can design implant-supported prostheses that offer improved function, aesthetics, and longevity.

References

References are available in hardcopy of the website “Periobasics: A Textbook of Periodontics and Implantology”.