Every type of restorative therapy i.e. filling , crown, bridge etc engages occlusal change , though in the majority of times with no significant impact on stability of the bite.
However there are cases of prosthetic treatments in which a small alteration i.e a filling on the posterior teeth ,adversely affects occlusal stability.
It takes even a tooth or implant to cause a full disorder of occlusion and to have an impact on masticatory system and the TMJoints
Ideal tooth contacts are investigated and fully described many decades back. Formerly a multitude of strict criteria were addressed to establish a perfect bite , as it was believed that occlusal issues was the major factor to fire TMDs. However, today only basic goals must be aimed in order to attain occlusal stability that facilitates smooth and painless function for all teeth, joints and the muscles
In the closing position specific criteria must be met on occluding posterior (back) teeth/restorations
-Smooth , even and simultaneous contacts
-Contacts on the long axis of the posterior (i.e on the fossa and the functional cusps)
-No interference and/or no slide on the inclines of the teeth/restoration
-No interference on the posterior teeth/restorations upon lateral and forward movements
In the closing position specific criteria must be met on occluding anterior(front) teeth/restorations
-Smooth and simultaneous contacts on the labial surfaces of front teeth
-Centric contacts on the anterior must be lighter than those on the posterior
-When sliding to left or right only canines must be in contact
It is a prerequisite that any established functional disorder on TMJs and or the muscles (i.e . pain elicit upon jaw move/bite) be resolved prior to any restorative/prosthetic treatment.
In such cases a reversible therapy with an appliance/mouth guard on centric relation of the jaw (namely the most neutral jaw position- no muscle contraction) must precede.
Prosthetic restorations are considered small from single up to 3 unit restorations. In such cases habitual bite position is recorded and kept. Any small drift can easily be traced and relieved with selective grinding, so that occlusion remains stable.
On large prosthetic restorations it is apparent that lower jaw drifts due to consequent loss of occlusal stability. For example, when grinding 5 or more teeth/implants, habitual bite position is lost and driving muscles contract unevenly.
In such cases to build the prosthetic restoration, a stable and repeatable jaw position must be settled. For this reason optimal jaw position is centric relation namely the most neutral position at which all occlusal muscles are relaxed.
This position can be traced with several techniques i.e. bilateral manipulation, occlusal deprogrammer etc.
Centric relation provides ideal position to build large prosthetic restorations.