Effect of maxillary incisor angulation and inclination on arch length.

This article discusses the quantitative effects of angulation of incisors on dental arch length. The incisors are approximated mathematically to rectangular shapes, which enables the authors to calculate the change in arch length when teeth are tipped and to describe graphically the effect of other influencing parameters. The authors demonstrate that the height and the width of a tooth crown can enhance or diminish the effect of angulation on arch length. In addition to angulation, dental arch length is also influenced by torque. A mathematic formula has been derived and the results are demonstrated numerically and graphically. The authors show that vertical positioning of the brackets plays an important role because torquing is a rotational movement around the center of the bracket slot. Hence, in calculating the effect of torque on dental arch length, one must consider different angles and axes than those discussed by Andrews.4 The interaction between angulation and inclination and its influence on dental arch length has been investigated. It has been found to cause little change in arch length.