Occlusion in implant-supported prostheses

6. INTRODUCTION :

The implant prosthesis is part of a neuro-musculo-articular system. The durability of these prostheses depends on their position, defined in particular by the occlusion ; it does not fundamentally differ from the concepts used in conventional prosthetics, however it does have some specificities due to the differences in behavior between the teeth and the implant abutments.

2. Anatomical reminder of the masticatory system:
   1. ATMs:

It is a diarthrosis which unites the mandibular fossa of the temporal bone with the condyle of the mandible by means of a meniscus or fibrocartilaginous disc closed by an articular capsule.

2. The masticatory muscles:

They ensure the different mandibular movements, they can be divided into:

1. The elevator muscles:
   • Temporal muscle:
     • Anterior and middle head → retropulsion
     • Posterior head horizontal → retropulsion and diduction
   • Masseter muscle:
     • Superficial head → propulsion
     • Deep head → retropulsion
   • Internal pterygoid muscle
2. The depressor muscles:
   • Digastric → retropulsion
   • Mylohyoid → retropulsion
   • Genohyoid → retropulsion
   • External pterygoid → propulsion and didduction
3. The dental organ:

4. The periodontium:

It is a well-organized tissue complex which, thanks to its connective structure, ensures:

• The attachment of the tooth to its socket.
• To transmit functional stimuli to the alveolar bone.
• Damping of occlusal loads.
• The neuromuscular role of controlling the masticatory cycle.

3. Implant specificities influencing occlusion:

The fundamental difference between an implant and a tooth is that the implant is anchored in the bone and does not move at all, whereas the tooth is attached to the bone by a ligament rich in nerve endings. These are the nerve endings that are the source of proprioception. This is called periodontal proprioception.

1. Proprioception: the desmodontal ligament and the bone/implant interface:

A natural root is attached to the bone by the desmodontal ligament, an innervated and vascularized connective tissue,

The innervation of the periodontal ligament is of capital importance because it provides protection for the periodontium by means of mechanoreceptors.

This is the function that allows the central nervous system to be informed about the pressures exerted on the tooth, which allows the higher nervous centers, most often unconsciously, to implement the means to stop these pressures if they remain excessive. Thus, proprioception makes it possible to modulate the contraction of the masticatory muscles, even going so far as to inhibit their contraction when the pressure is very strong.

In a word, proprioception allows the protection of the tooth against excessive overloads (prosthetic overbite).

There is no proprioception around dental implants. This means that the periodontal receptor disappears with the tooth and the only information about pressure exerted on the implant comes from a few currently poorly defined sensory receptors in the bone.

2. Perception thresholds:

The pressure perception threshold is higher for an implant than for a natural tooth, so it only takes 11.5 g for a force to be perceived by the tooth, compared to 100 g for the implant.

VI. Different occlusion positions:

1. Maximum intercuspation position:

This is the closed position in which the teeth maintain maximum contact.

In the position of maximum intercuspation, it is necessary to achieve contact stability, or the patient must feel well wedged.

2. Position in centric relation:

This is the closed position when the condyles are in the highest, most unforced, rearward position in the glenoid cavities.

When there is a complete arch to reconstruct or the number of missing teeth is significant (intra-oral landmarks are lost).

V. Occlusal concepts: 1/ In propulsion:

This involves the anterior displacement of the mandible. It is imperative to avoid any interfering contact between the cuspid teeth during the propulsion movement.

The sliding of the lower incisors and canines on the lingual surface of the maxillary incisors and canines must immediately cause the disocclusion of the cuspid sectors. This is called the anterior guide. To avoid any overload on one of the anterior teeth, the load must be distributed over the maximum number of anterior teeth, ideally on the four incisors and the two canines and, if possible, over the entire sliding trajectory.

This concept is valid and applicable everywhere (in tooth-supported or implant-supported prosthesis) except when faced with a complete prosthesis where it is necessary to maintain some contacts between the posterior-upper teeth and the posterior-lower teeth. Contacts called stabilizing in order to avoid destabilization of the removable prosthesis.

2/ Laterality: Several situations exist

1. Canine function:

On the working side, the sliding of the tip of the lower canine on the lingual surface of the upper canine causes immediate disocclusion of the cuspid teeth on the working side, and especially on the non-working side where the interferences are particularly harmful.

This concept is the best and easiest to achieve because it only involves the canines. The movement of the mandibular canine on the maxillary canine must be uniform in both amplitude and speed of movement.

2. Group function:

On the working side, there is laterality a sliding not only of the lower canine on the upper canine , but also a sliding of the cusps

lower premolars and molars on the opposing teeth. On the non-working side, there is immediate disocclusion of all teeth.

3. Balanced function or also called bilaterally balanced:

This concept assumes, on the working side, a group function but in addition to the contacts on the non-working side it is the concept of choice used in total prosthesis. This concept by simultaneous contacts on the working side and the non-working side allows the stabilization of the antagonistic removable prosthesis in all movements, the imperfections of the sliding being compensated by depressibility.

In summary, and except when the antagonist prosthesis is removable and complete, the only clinically feasible concept is the canine function, which is simple to achieve and therefore correctly achieved.

5. CONCLUSION

The absence of a ligament around the implant results in a lack of proprioception and although it is provided with osteoperception, it is more subject to complications due to overloads and lateral constraints exerted on its supra-structure. This explains in particular the specific balancing characteristics of implant prostheses.

The adjustment of the occlusion in a supra-implant prosthesis is of capital importance for the durability of the prosthetic restoration.

6. BIBLIOGRAPHY
   2. Orthlieb JD Practical Occlusodontics. Wolters Kluwer France, 2000.
   3. Bert M. and Missika P. Keys to Success in Implantology: Preventing Complications and Failures. Cahiers de Prosthèses Editions, 2009.
   4. Le Gall M. “How to adjust posterior occlusal surfaces? Part two.” ROS 2013 volume 42 No. 4-occlusodontics
   5. Bert M. “The canine in implantology.” AOS March 2009

Occlusion in implant-supported prostheses

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Occlusion in implant-supported prostheses