Relationship between dental crowding and mandibular incisor proclination during orthodontic treatment without extraction of permanent mandibular teeth

Objective: To examine changes in mandibular incisor proclination and protrusion resulting from alleviation of crowding.

Materials and methods: Records of 96 patients from a private practice treated without extractions or interproximal enamel reduction in the mandibular arch were included. Pre- and post-treatment cephalograms and models were examined to determine changes in incisor proclination, protrusion and crowding.

Results: For every millimeter of crowding alleviation, increases in incisor proclination (ΔIMPA) and protrusion (ΔL1 to A-Pog) of 0.5° and 0.2 mm, respectively, were found, on average. High variability was calculated for both linear variables (that can be reduced by incorporating other variables by multilinear regression).

Conclusions: For every millimeter of crowding alleviated, 0.5° of proclination and 0.2 mm of protrusion are expected. Our results indicate that proclination is mulifactorial and cannot be explained solely by the amount of crowding alleviated during orthodontic treatment. These results may be a useful guiding principle rather than a prognostic tool.