Dawson's occlusion: Contributions to occlusal disease

Dental disease almost always results from a combination of factors rather than just one. The same insult can cause a plethora of different symptoms depending on the resistance of the host and the intensity of the insult. Treating symptoms/effects alone rarely is short sighted and rarely results in satisfactory outcomes. If the cause of the insult can be corrected, the effects usually spontaneously resolve. Repair may be needed after correction but the long term success is greatly enhanced as opposed to only treating the effects.

Distinction must be made between contributing effects and causative factors of disease. Contributing factors are those that decrease host resistance or increase function or tension on the system whereas causative factors cause disease.  For example, in a healthy person with a perfect dentition, the introduction of a posterior deflective interference can cause a myriad of effects.

1. The tooth may become sensitive to hot or cold, or it may ache
2. The tooth may become tender to biting on it
3. The tooth may become loose
4. The tooth may wear excessively
5. The mandible may be deflected around the interference into other teeth that become loosened
6. Other teeth can be abraded as the mandible is deflected forward
7. Other teeth can become sore as they are traumatized at the end of the slide
8. Forced deviation of the mandible can cause masticatory muscles to become painfully hyperactive, or even become spastic
9. Trismus may result from the spastic musculature
10. Muscle tension headaches may develop
11. The combination of sore teeth, sore muscles, and headaches may cause stress and tension
12. Constant tension and stress may lead to depression
13. The combination of the uncoordinated musculature and the deflected mandible may contribute to a condyle/disk derangement
14. Eventual displacement of the disk by uncoordinated masticatory muscle hyperactivity may initiate
painful compression of retrodiskal tissues
15. Degenerative arthritic changes in the TMJ may follow disk displacement and subsequent perforation of the retrodiskal tissues
16. All of the above
17. None of the above

In this example, the causative factor is the deflective interference. None of the sequalae would have developed if this causative factor was absent. The manifestations of this causative factor depend on factors such as emotional stress, OSA, bruxism, mouth breathing. 

If we have a grasp on the design of the masticatory system we can simplify diagnosis and treatment planning. It is not possible to remove all stress on the system but we must aim to reduce this stress to below destructive levels. 

Ultimate loss of teeth loss can be categorised into breakdown into breakdown of teeth and breakdown of the supporting structures. These can be caused broadly by physical micro/mactrotrauma to teeth (caused mostly by occlusal factors) and the action of microorganisms (caries/ periodontal disease). 

Microorganism related damage

Treatment success must include control of oral microbiology. Long standing plaque will inevitably cause supporting structure breakdown and the only variable is the rate at which this occurs. The degree of bone breakdown in periodontal disease is worsened by occlusal imbalances this damage is proportional to the degree and direction of occlusal trauma. However, periodontal disease can obviously occur in the absence of occlusal factors. 

IL-1B is produced in response to mechanical stress on the PDL which contributes to bone resorption. Therefore, hyperfunction will cause bone breakdown and mobility in the direction of compression.  Occlusal trauma will not cause progressive attachment loss of the gingival complex if plaque is controlled. However, if microbiological trauma is present, there will be progressive loss of attachment. Injury or inflammation can deepen the sulcus to communicate into an area of resorption causing a significant intrabony lesion.

Occlusal analysis
When analysing and treating the masticatory systems you must consider all parts as a whole. Teeth are only one part of a larger system and there is no way to assess the occlusion until you have ascertained the TMJ is in harmony. The concept of a peaceful neuromusculature depends on the further harmony between the teeth and the TMJ complex. If one part is out of harmony, one or all parts must adapt to reestablish equilibrium. This adaptation can be positive or destructive depending on the response of the altered tissue. Responses such as wear or mobility do not occur without a cause. This primary cause may be the start of a chain reaction started by a disharmony. Treatment ultimately will fail without addressing this cause.

The masticatory system is capable of high demands. This system must be peaceful when demands are low but also be free to function to its anatomic limit without mechanical interference. It must not be restricted to function at its limit. Achieving such functional harmony in an environment of optimally healthy teeth, joints, periodontium, and musculature, and in combination with the best possible esthetic result, is the essence of complete dentistry.