title: Second premolar agenesis is associated with mandibular form: a geometric morphometric analysis of mandibular cross-sections.
abstract: The aim of this study was to compare mandibular form (i.e., size and shape) between patients with agenesis of the lower second premolar (P2) and a control group with no agenesis. Three hypotheses were tested: (H1) agenesis causes a change in mandibular morphology because of inadequate alveolar ridge development in the area of the missing tooth (mandibular plasticity); (H2) agenesis is caused by spatial limitations within the mandible (dental plasticity); and (H3) common genetic/epigenetic factors cause agenesis and affect mandibular form (pleiotropy). A geometric morphometric analysis was applied to cross-sectional images of computed tomography (CT) scans of three matched groups (n=50 each): (1) regularly erupted P2; (2) agenesis of P2 and the primary second molar in situ; and (3) agenesis of P2 and the primary second molar missing for >3 months. Cross-sections of the three areas of interest (first premolar, P2, first molar) were digitized with 23 landmarks and superimposed by a generalized Procrustes analysis. On average, the mandibular cross-sections were narrower and shorter in patients with P2 agenesis compared with that in the control group. Both agenesis groups featured a pronounced submandibular fossa. These differences extended at least one tooth beyond the agenesis-affected region. Taken together with the large interindividual variation that resulted in massively overlapping group distributions, these findings support genetic and/or epigenetic pleiotropy (H3) as the most likely origin of the observed covariation between mandibular form and odontogenesis. Clinically, reduced dimensions and greater variability of mandibular form, as well as a pronounced submandibular fossa, should be expected during the treatment planning of patients with P2 agenesis.
authors.affiliation: Division of Orthodontics, School of Dentistry, Medical University of Vienna, Vienna, Austria.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Bertl
authors.affiliation: Department of Periodontology, Faculty of Odontology, University of Malmö, Malmö, Sweden.|Division of Oral Surgery, School of Dentistry, Medical University of Vienna, Vienna, Austria.
authors.forename: Kristina
authors.initials: K
authors.lastname: Bertl
authors.affiliation: Division of Oral Surgery, School of Dentistry, Medical University of Vienna, Vienna, Austria.
authors.forename: Manuel
authors.initials: M
authors.lastname: Wagner
authors.affiliation: Division of Oral Surgery, School of Dentistry, Medical University of Vienna, Vienna, Austria.|Department of Diagnostic Radiology, Division of Osteoradiology, General Hospital, Medical University of Vienna, Vienna, Austria.
authors.forename: André
authors.initials: A
authors.lastname: Gahleitner
authors.affiliation: Department of Periodontology, Faculty of Odontology, University of Malmö, Malmö, Sweden.
authors.forename: Andreas
authors.initials: A
authors.lastname: Stavropoulos
authors.affiliation: Division of Oral Surgery, School of Dentistry, Medical University of Vienna, Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Ulm
authors.affiliation: Department of Theoretical Biology, University of Vienna, Vienna, Austria.
authors.forename: Philipp
authors.initials: P
authors.lastname: Mitteroecker
mesh_terms: D000848:Anodontia; D001641:Bicuspid; D003430:Cross-Sectional Studies; D006801:Humans; D008334:Mandible / Q000033:anatomy & histology*; D008963:Molar; D014078:Tooth Eruption; D014094:Tooth, Deciduous