Experimental tooth ankylosis and horizontal tooth movement in the pig

Abstract

Experimental ankylosis was produced by 4 different techniques in deciduous premolar teeth of growing pigs. The most successful method was by thermal injury to the apex of the root. Measurements of the forward movement of the teeth were made on stone casts of the jaws taken prior to the production of ankylosis and after 16 weeks. Measurements from control animals showed no significant difference between right and left sides of the jaws. In those animals in which ankylosis developed, the distance between the premolar reference point and the incisor mid-point on the ankylosed side was always statistically significantly greater (mean 4.1 mm in maxilla and 2.4 mm in the mandible) than that from the contralateral unaffected side, indicating a forward movement of the deciduous premolar teeth. During the experimental period, the incisors moved forward on average by 20.0 mm in the maxilla and by 23.2 mm in the mandible whilst the deciduous canine moved forward by 9.7 mm in the maxilla and by 12.7 mm in the mandible. The differential movement of the 3 types of teeth and the presence of diastemata between the canine and incisors and between canine and premolars makes it impossible to accept a forward drive from the erupting molars as the motive force or that this forward movement is in response to interdental attrition. As the deciduous canines are small and do not occlude with teeth in the opposing jaw, it is also unlikely that occlusal forces could be responsible. Some of the forward movement of the canines and incisors is undoubtedly caused by the forward inclination of their line of eruption. The size of this contribution is not known. The direction of movement of the groups of teeth studied appeared to be wholly forward over the experimental period and was similar to that found in man.