The effect of first and second premolar extractions on third molars: A retrospective longitudinal study

Objectives: To analyse the effect of first and second premolar extractions on eruption space for upper and lower third molars and on third molar position and angulation during orthodontic treatment. Methods: The sample consisted of 296 patients of which 218 patients were orthodontically treated without extraction and 78 patients with extraction of first or second premolars. The eruption space for third molars was measured on pre- and posttreatment lateral cephalograms, whereas the angulation, vertical position, the relation with the mandibular canal and the mineralization status of third molars were evaluated using pre- and posttreatment panoramic radiographs. All data were statistically analyzed. Results: The increase in eruption space and the change in vertical position of upper and lower third molars significantly differed between patients treated with and without premolar extractions, whereas the change in angulation, relationship with the mandibular canal and mineralization status of the third molars did not significantly differ between patients treated with and without premolar extractions. Conclusions: The retromolar space and the position of third molars significantly change during orthodontic treatment in growing patients. Premolar extractions have a positive influence on the eruption space and vertical position of third molars, whereas they do not influence the angular changes of third molars. Due to the retrospective character of the study, these conclusions should be carefully considered. Further prospective research is necessary for better insights into this complex topic. Clinical significance: This study stresses the importance of considering the possible effects of orthodontic treatment on third molars during treatment planning. (C) 2017 The Author(s). Published by Elsevier Ltd.