The relationship between lower incisor inclination and various reference lines.

The relationship between the inclination of the lower incisors and different cranial reference lines has been studied in a group of 60 children including 35 males and 25 females between the ages of 7-12 years. Following a 3-4 year observation period, 30 of these children were reexamined to study the relationship between changes in the position of the lower incisors and various craniofacial variables brought about by growth. In analysing the results obtained, an attempt was made to distinguish between those relationships which were to a certain extent due to a topographical relationship between the variables involved and those relationships which were of a biological character. The results obtained from the first registration indicated a strong correlation between Ll-NB mm and Ll-ML degrees and Ll-NB degrees. In addition, the connection between lower incisor inclination and the basal bone relationship (ANB degrees) was found to be strongly significant. The angle ML/NL was found to be correlated only with the inclination of the lower incisors to the mandibular line. Regarding the growth changes occurring during the observation period, no significant correlation could be found between, on the one hand, changes in lower incisor orientation and, on the other hand, changes in the angle ML/NL. The absence of this relationship has been interpreted as being due to the influence of environmental factors in the form of tongue and lip function.