Torus palatinus and torus mandibularis: a review of the literature.

The torus has been mentioned in the literature for about 180 years. However, little has been revealed about it until the last two decades when great advances were made in the field of genetics. Its occurrence in various ethnic groups ranges from 9 to 66 per cent. Even between similar ethnic groups living in different environments, different figures have been reported. It has been statistically proven that differences do occur between various ethnic groups and the sexes. In current thinking, the occurrence of tori is considered to be an interplay of genetic and environmental factors. The quasi-continuous genetic or threshold model seems to hold the answers to their formation. This theory proposes that the environmental factors responsible must first reach a threshold level before the genetic factors can express themselves in the individual. Hence, both genetic and environmental factors determine liability, making the system multifactorial.