Introduction

There is a wide range of types of variations in position and malocclusion. At one end of the range are single teeth which, for various reasons, are outside the regular tooth arch and have persisted in that position, perhaps because they have acquired an abnormal relationship with the cusps of teeth in the opposing arch or because the space they would normally occupy in the arch has closed up due to contiguous tooth movements. At the other end of the range are much more marked abnormalities of occlusal relationship due to defective development or growth of the jaws, especially if one jaw is affected more than the other.

Very rarely, pairs of teeth are found in transposed relationship in the arch, for instance a canine in the position of a first premolar and vice versa. Whether this is the result of movement of tooth germs or is a manifestation of homoeosis, that is, a tooth germ developing the characteristics of another in a meristic series (Chapter 1, p. 2), can only be speculated upon.

Although there are many examples of variation of tooth position, in particular of the relationship of the tooth arches, that are of genetic origin, in general the position of teeth in the jaws is much more influenced by environmental factors than are tooth size or shape because position depends mainly on bone development and bone growth.