Occlusion
Occlusion is the relationship between the upper and lower teeth when they close together or contact one another during movement or rest. (Occlude means to close or shut).
Tooth relationships were described and classified as classes I, II, and III in the early 1900s by Edward H. Angle.
- Ideal occlusion (centric) is Class I and was based on the relationship between the maxillary and mandibular dental arches. Class I occlusion, the teeth should be closed together in their maximum intercuspal position. The following specific tooth relationships define class I ideal occlusion in the adult dentition:
- The mesiobuccal cusp of the maxillary first molar occludes in the mesiobuccal groove of the mandibular first molar. Additionally, the maxillary canine fits into the facial embrasure between the mandibular canine and the first premolar.
- Horizontal overlap- incisal edges of the maxillary anterior teeth horizontally overlap the mandibular teeth so that the incisal edges of upper are labial to the incisal edges of the lower
- Vertical overlap- incisal edges of the maxillary anterior teeth extend below the incisal edges of the lower teeth so that the incisal of lower incisors are hidden
- Maxillary posterior teeth should be positioned just slightly buccal to mandibular posterior teeth: The buccal cusp tips and buccal surfaces of the maxillary teeth are buccal to those in the mandibular arch.
The lingual cusps of maxillary teeth rest in occlusal sulcuses and fossae of the mandibular teeth.
The buccal cusps of the mandibular teeth rest in the occlusal sulcuses and fossae of the maxillary teeth.
The lingual cusp tips and lingual surfaces of the mandibular teeth are lingual to those in the maxillary arch
- Remember most teeth in an ideal arch should occlude with 2 teeth in the opposing arch.
Malocclusion
- A tooth that is out of alignment to the labial or buccal compared to the ideal arch form of other teeth is in labioversion or buccoversion (also buccal version) if referring to a posterior tooth.
- A tooth that is out of alignment to the lingual compared to other teeth in the arch is in linguoversion (also lingual version).
- A tooth that is twisted (rotated) around its tooth axis is described as torsiversion.
- A tooth that is overerupted is abnormally long relative to the rest of the occlusal surfaces, and it exhibits supraeruption or extrusion.
- If a tooth is abnormally short as opposed to the rest of the occlusal plane, it is considered to be in infraocclusion (or infraversion). Ie. primary tooth is retained into adulthood or when a primary or permanent tooth loses its periodontal ligament and the cementum of the root fuses with the surrounding alveolar bone preventing further eruption. The fusion of cementum to bone is called ankylosis.
- When mandibular anterior teeth are facial to maxillary anterior teeth, this is called an anterior crossbite (reverse articulation).
- Severe overbiteis when maxillary incisors overlap mandibular incisors down to the level of the cervical lines of the mandibular incisors hiding them from view
- Class II (disto-occlusion)- skeletal type of malocclusion where a person may have a mandible that is too small, or a maxilla too large, or both (22% of the population)
- Class II, division 1 is an incisor relationship where maxillary incisors labial inclination is similar to incisors found in normal class I occlusion -a severe horizontal overjet of maxillary incisors labial to mandibular incisors and supra eruption of mandibular incisors.
- Class II, division 2 is an incisor relationship where the maxillary central incisors are retruded with a severe lingual inclination, often with the lateral incisors inclined labially compared to the centrals – maxillary central incisors tilt to the lingual. These people are likely to have very little horizontal overjet but a severe vertical overbite.
- Class III (mesio-occlusion)-skeletal type of malocclusion where the mandibular dental arch is anterior (or mesial) to the maxillary dental arch.Persons with this relationship have a relatively large mandible compared to their maxilla, ie. facial profile is concave with a very prominent chin. This profile (with a protruded mandible) is called prognathic (Jay Leno). (6% of the population). The mesiobuccal groove of the mandibular first molar is mesial to the mesiobuccal cusp of the maxillary first molar by at least the width of a premolar
Occlusion is affected by eruption sequence, facial development, and growth.
Canine rise (cuspid rise) describes the actual occlusal contact made during lateral excursion. The canine carries most of the contact. When the mandible moves to one side, both condyles do not move equally toward that side. The condyle on the working side does not move much: it rotates on its vertical axis moving laterally only about 1 to 2 mm (called laterotrusion or Bennett’s movement). On the other hand, the condyle and disc on the nonworking side move forward, downward, and medially within the articular fossa.
Canine-protected articulation is the desirable occlusal relationship in which the vertical overlap of the maxillary and mandibular canines produces a disocclusion (separation) of all of the posterior teeth when the mandible moves to either side. Disocclusion refers to the separation of opposing posterior teeth during the eccentric movements of the mandible. (A canine guidance (rise) angle of 60° or more is necessary to provide canine-protected articulation or canine guidance.) Many dentists consider canine-protected occlusion to be a desirable or healthy relationship to have. One study of 500 persons indicated that there was a lesser tendency toward bruxism (grinding the teeth together) with canine-protected occlusion.29 Another study found posterior tooth mobility to be higher in dentitions with canine protection than those with group function.