This is a common question for many dentists when trying to determine stability for our patients. Whether we use the patient's existing occlusion or we change the patient's occlusion, the question remains the same ... will the bite change? The answer to this age-old question can be found by assessing the three major components of the occlusal complex we work in every day.
The first of the three components are the teeth. The stability of the teeth relates to the condition and position of the tooth. Three of the key questions related to bite stability from a tooth position perspective are:
- Is the tooth in a position that will facilitate optimal force distribution in vertical mandibular movements?
- Is the tooth in a position that will facilitate optimal force distribution in horizontal mandibular movements?
- Is the tooth in a normal position for acceptable esthetics?
While tooth position plays a key role in stability, tooth condition is also a major factor to consider when evaluating the future occlusal stability of the system. Three of the key questions related to bite stability from a tooth condition perspective are:
- Has the tooth been restored? If so, how large is the restoration?
- Has the tooth had endodontic therapy?
- What is the periodontal support for the tooth?
The second of the three components are the masticatory muscles. The role muscle plays in the occlusal system has been well-documented. The muscles anatomically are positioned between the teeth and the TM joints. As a result, the muscle forces will be distributed between the TM joint and the teeth. Three of the key questions related to bite stability from a muscle perspective are:
- Are the muscle forces being applied to the system greater than the adaptive capacity of the system?
- Is there a trigger for muscle contraction?
- What role does the sympathetic nervous system play in muscle dystonia?
The third of the three components are the TM joints. The TM joints are the foundation of the occlusion and they interact with the teeth to distribute the muscle forces that are applied to the system. Like any other joint, the TM joint is susceptible to injury, which may reduce the joint’s ability to distribute the muscle forces effectively. Three of the key questions related to bite stability from a TM joint position perspective are:
- What is the condition and position of the disk?
- What is the condition and position of the condyle?
- What are the high-risk factors?
The key to assessing the potential for future bite changes is to evaluate all three components on the occlusal system. Teeth with large restorations are more likely to fracture or to possibly need extraction in the future. Teeth that are not in the correct position to effectively distribute muscle forces are at a higher risk for fracture, wear or mobility. Many times, teeth that do not look correct from an esthetic perspective are also not positioned to distribute muscle forces.
In terms of the muscle system, most patients believe the reason they clench or grind their teeth is due to stress. As a profession, this theory was developed over 60 years ago. The assumption that stress influences the amount someone clenches or grinds may be true, but for a different reason than we were taught.
As opposed to the occlusal interference being a trigger to activate muscle contraction, dysfunction of the sympathetic nervous system may be a more plausible explanation for increased muscle activity in the system. While tooth position will play a role in muscle activity, it would be prudent to realize other factors (such as sympathetically-induced muscle dystonia) may be involved. The dysfunction of the sympathetic system could come from structural change in the TM joints, poor quality of sleep or both factors.
The last of the three components is the TM joint. The soft tissue of the TM joint protects the condyle and the joint socket during mandibular movements are well during joint loading. The soft tissue of the condyle is attached by a ligament at the lateral pole and medial pole. The soft tissue at the medial aspect of the condyle also maintains vertical dimension in the TM joint. If the ligament attaching the distant condyle is compromised to medial pole, there is an increased risk for changes to occur.
Soft tissue changes can cause Class III bite changes or Class II bite changes based on the position of this. Changes in the heart tissue of the TM joint resulting in class III bite changes were classed as Class II bite changes based upon condylar hyperplasia or condylar hypoplasia. The Class II bite shift is the more clinical presentation when there are structural changes in the TM joint.
In closing, consider the teeth, the muscles and the TM joints when evaluating whether the bite will change in the future.