Dynamic Occlusion

In dynamic occlusion, different physiologic sliding movement situations arise within the dentition, and these are described by different concepts of occlusion.

Physiologically, dynamic occlusion means there are no pathologic changes to hard tissues, periodontal tissue, the TMJs, or masticatory musculature. It is characterized by mutual functioning of the anterior and posterior teeth; ie, there is an uninterrupted, progressive continuity of occlusal surfaces whereby harmonious jaw movements are undertaken by incisal or canine guidance.

A distinction is made between various occlusal concepts to describe selective tooth contacts of individual groups of teeth or parts of the dentition for preparing food in protrusive and lateral jaw movements. Because a mouthful of food is only ever processed on one side of the dentition, there needs to be a functional separation of the nonworking portions of the dentition to avoid interference with sliding on that side. To bite off food, the anterior teeth must form a selective "biting off" (incision) contact without the posterior teeth being caught in interfering sliding contacts. A distinction is made between anterior-supported, canine-supported, and balanced occlusion.

Anterior-supported occlusion (or anterior guidance) denotes the selective contact of anterior teeth during habitual mandibular movements in which all the other teeth are disoccluding (separating) (Fig 7-25).

Canine-supported occlusion (or canine guidance) is the selective tooth contact during habitual mandibular movements that leads to disocclusion of all the other teeth (Fig 7-26).

Balanced occlusion denotes contact between the rows of teeth during habitual mandibular movements; it can be either unilaterally balanced or bilaterally balanced occlusion.

Unilaterally balanced occlusion is guidance by a group of teeth in a natural, fully dentate dentition where the teeth on the working side enter into a smooth sliding contact while there is a gap between the rows of posterior teeth on the nonworking side (Fig 7-27).

Bilaterally balanced occlusion means sliding contact of all teeth on both the working side and the nonworking side during lateral mandibular movements (Fig 7-28). This form of occlusion is rarely found in a normal occlusal situation, mostly in a worn dentition. Bilaterally balanced occlusion is avoided in reconstruction of a permanent restoration. However, it is required for mucosa-supported complete dentures for static reasons, in which case it is referred to as fully balanced occlusion or prosthetic occlusion.

The transition of movement out of static into dynamic occlusion, with its selective tooth contacts, takes place in a horizontal movement field 0.5 to 1.0 mm wide, which is known as the occlusal field (or occlusal area). During lateral movements, there is tooth guidance without malocclusions or occlusal interferences. The occlusal field between habitual intercuspation and the rearmost contact position is known as long centric.

A malocclusion denotes incorrect occlusion that is locally limited or more extensive and is caused by the malposition of individual teeth or groups of teeth, by shifts in occlusal position, by premature contacts of restorations, or by fillings. These malocclusions will become a traumatizing occlusion if faulty loading of individual teeth or groups of teeth takes place, which can cause changes in the stomatognathic system.

Occlusal interferences are disruptions of tooth contact that force the mandible into a slipping-off position. A distinction is drawn between premature contacts and obstacles to gliding during mandibular movements.

Centric occlusion is synonymous with a central, middle position of the jaws in relation to each other, from which any movement position of the mandible can be performed. When occluding teeth are absent, this central position must be rediscovered (Fig 7-29).The centric relation denotes the position of the mandible when both condyles of the TMJs rest in their superoposterior position in the articular fossae (retral contact position); the central relation is jaw- and joint-oriented. The mandible often has to be manipulated back into this position, which is why this position is of limited suitability for prosthetic rehabilitation work.