Occlusal contact interference can occur in natural teeth or restorations, that is, when there is a central occlusion or eccentric movement, it hinders the contact between the opposing teeth that induce flexible movement.

Occlusal disturbances that occur during the chewing cycle can impede the integration function of muscle contractions, causing misalignment or distortion of the jawbone and deviation of the temporomandibular joint from its original position.

In addition, the torque generated by the reduced efficiency of the lever device can cause excessive force to impose an excessive load on the ligaments and adjacent muscle groups, especially the wing muscles.

The forms of occlusal contact in occlusal interference include the following classifications.

(1) centric relation premature contact

Even when the function of the oral and maxillofacial system is normal and the occlusion is relatively normal, during the early contact in the median position, if the occlusion is maximized towards the median position, the lower jaw will gradually deviate and slide along one or more teeth.

The result of normal deviation movement usually occurs on the near middle slope of the lingual tip of the maxillary premolars or the far middle slope of the lingual tip of the mandibular premolars or molars.

There has been much debate up to now on whether this early contact state is pathological or physiological. However, according to clinical research, the more slides in centric that further increase laterally 1mm in front of the normal median contact of the median occlusal between the cusps, the pathological elongation of the temporomandibular joint will occur.

Two forms of occlusal interference can be observed.

(2) Centric occlusion premature contact

A healthy natural dentition usually exists 1mm ahead of the median contact. The mandibular muscles in the resting phase are involved in movement, causing the median occlusal position of the mandible 0.5mm ahead of the center of the condyle to close.

If the maximum occlusion begins with a mild early contact on the side or front of the median occlusion, due to the adaptability of the occlusal muscles, although the tension of the normal resting phase will be maintained at this time, it will follow the non-tension occlusal path.

However, when the lateral anterior early contact is too large, causing the median occlusal to deviate, from the resting phase, when the mandible slowly closes, due to the strong early contact, it will slide towards the median occlusal position. But at this time, to avoid such impact and sliding, the muscle group will induce an avoidant closure pathway around the early contact.

Therefore, during chewing, the muscles adapt to the appropriately dilated avoidance channels. To maintain the position of this asymmetric median occlusion at the maximum occlusal force, the muscles remain tense for a long time, eventually leading to diseases such as condylar deviation to the pathological median occlusion position, excessive muscle tension, muscle fatigue, and muscle spasm.

(3) Interference during eccentric motion

A. Interference on the work side

Interference caused by the eccentric movement of the mandible due to teeth occurs between the induced surface of the mandibular molars supporting the cusp and the induced inclined surface of the maxillary induced cusp, or between the lingual inclined surface of the maxillary lingual cusp and the buccal inclined surface of the mandibular lingual cusp, which can interfere with the occlusion function on the working side or the induction effect of the canines.

This kind of operation interference during lateral movement, due to the incoordination of the working side induction of the teeth and the condylar induction, damages the joint surface and causes excessive force to extend the ligaments.

In addition, it will trigger different leverage effects and force directions from the interference on the non-working side, which will cause chaotic neuromuscular system phenomena. Interference on the working side accompanied by intense muscle contractions can also cause distortion and deformation of the lower jaw.

Contact on the non-working side can impede the coordination of the condyles on the non-working side, which are used to maintain the distance between the teeth on the non-working side. It may cause dislocation of the condyles accompanied by the extension of the ligaments on the non-working side, or deviate the condyles and cause trauma to the joint. The forward movement relies on the coordination between the dental induction function and the anterior condyle induction to maintain normal induction. The possible interferences that may occur during the forward extension movement can be classified into the anterior interference in the front teeth similar to the working interference and the non-working side interference in the posterior molars.

"Forward interference"

Due to the interference between the cross-section of the mandibular anterior teeth and the induced slope of the maxillary anterior teeth, the precise forward induction is hindered during the forward extension movement. Generally, it is caused by the poor shape of the tongue surface of the maxillary anterior teeth restoration, the inappropriate position of the mandibular cross-section, and the unsuitable maintenance contact in the anterior teeth.

Due to this occlusion phenomenon, the forward extension movement is induced by the contact of one or two teeth. If normal forward induction and coordination cannot be achieved, the remaining teeth will be unable to separate.

This kind of contact is called forward-induced interference.

Rear interference

The induction of the forward extension movement caused by the contact between the distal inclined plane within the molar tip of the maxilla and the proximal induced plane supporting the molar tip of the mandible should be maintained precisely. The interference that hinders this induced molar direction is called posterior interference. This often occurs when restorations are made without changing the damaged occlusal plane due to excessive eruption or positional movement of the occlusal teeth or adjacent teeth that have been lost. posterior bite collapse, which occurs partially at the molars due to the loss of normal occlusal support at the posterior molars, is known as mandibular over-closed occlusion.

The loss of occlusal support in the molars is gradually caused by the movement of the remaining teeth and inappropriate dental restorations. When the left and right molars as well as the premolars are completely lost, when closing the mouth, the contact direction of the anterior teeth of the lower jaw that are inclined along the lingual surface of the upper anterior teeth, at this time, the condyle works non-rotatingly and is subjected to the posterior closing force, resulting in the distal and superior displacement of the condyle, which can cause abnormal muscle symptoms of the lower jaw function.

In the case of patients who have complete dentures made, setting the occlusal height a little lower can cause the contraction of the closed-mouth muscle and sometimes lead to fascia pain.