Influence of dental arch width changes on the effective space required to align anterior teeth

Traditionally, the widest mesio-distal tooth dimensions are used to analyze space requirements in treatment planning. However, in reality, it is the arch form dependent interproximal contact locations that determine the space required for tooth alignment. The aim of this study was to evaluate the influence of expansion and constriction of dental arch width on the space required for alignment of upper and lower incisors.

Fifty digital dental arch model pairs were segmented and aligned using OnyxCeph 3D™ software (Image Instruments, Germany). 3D coordinates of actual interproximal contact points were extracted from the digital setups. The mesio-distal space requirement for each tooth was determined by measuring the linear distance between its interproximal contact points projected on the occlusal plane. The dental arch was then expanded and narrowed in 2-mm increments at its distal ends, and the space requirement for each incisor was determined again after each increment.

Statistical analysis using linear models revealed a small increase in space required for incisor alignment with increasing arch width (p < 0.05). An average increase in space requirement of 0.03 mm and 0.04 mm was observed per 1-mm expansion of the maxillary and mandibular arches, respectively. The corresponding values ​​for constriction were 0.05 mm per 1-mm arch width change for both jaws.

The influence of dental arch form on the mesio-distal space required for incisor alignment is negligible. Hence, this factor may be ignored in the decision to apply dental arch expansion or premolar extraction in patients with anterior crowding.