Third Molar Agenesis Is Associated with Facial Size
by
, ,
Nikolaos Gkantidis
1,*,†
,
Manuel Tacchi
1,†, 
Elias S. Oeschger
1
,
Demetrios Halazonetis
2 and
Georgios Kanavakis
3,4,*
1
Department of Orthodontics and Dentofacial Orthopedics, University of Bern, CH-3010 Bern, Switzerland
2
Department of Orthodontics, School of Dentistry, National and Kapodistrian University of Athens, GR-11527 Athens, Greece
3
Department of Pediatric Oral Health and Orthodontics, UZB—University School of Dental Medicine, University of Basel, CH-4058 Basel, Switzerland
4
Department of Orthodontics, Tufts University School of Dental Medicine, Boston, MA 02111, USA
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this study.
Biology 2021, 10(7), 650; https://doi.org/10.3390/biology10070650
Submission received: 14 June 2021
/
Revised: 8 July 2021
/
Accepted: 9 July 2021
/
Published: 12 July 2021
(This article belongs to the Section Developmental and Reproductive Biology)
Simple Summary
Missing third molars is a common occurrence in modern humans with a prevalence of approximately 20% in the general population. The absence of those teeth, however, is not found in other human predecessors. Therefore, there is speculation whether the congenital absence of third molars is part of an evolutionary mechanism that leads to smaller jaws, smaller and fewer teeth, or if their absence is associated with more local developmental factors. In this study, we assessed the size of the cranial base, the maxilla, the mandible and the entire craniofacial complex in individuals missing one or more third molars and compared them with a group with no missing teeth. We showed that in cases with one or more missing third molars, there is a significant decrease in the size of the maxilla, the mandible as well as the entire facial configuration. Additionally, the more missing third molars, the smaller the jaws and the face were. These findings suggest that isolated third molar agenesis is part of a developmental mechanism related to craniofacial size reduction. Whether this mechanism is part of an evolutionary process in humans remains to be seen.
Abstract
Individuals with congenitally missing permanent teeth, other than third molars, present smaller craniofacial configurations compared to normal controls. However, it is not known if agenesis of third molars is part of the same mechanism. Therefore, this study assessed individuals with and without isolated third molar agenesis and tested the relation of this condition to the size of their facial configurations, using geometric morphometric methods. We show that the absence of one or more third molars is associated with a smaller maxilla, smaller mandible and a smaller overall facial configuration. The effect was larger as the number of missing third molars increased. For example, the size of the mandibular centroids in five 16-year-old females with no, one, two, three or four missing third molars showed a size reduction of approximately 2.5 mm per missing third molar. In addition, in cases with third molar agenesis in one jaw only, the effect was also evident on the opposite jaw. Our findings suggest that isolated third molar agenesis is part of a developmental mechanism resulting also in craniofacial size reduction. This might be the effect of an evolutionary process observed in humans, leading to fewer and smaller teeth, as well as smaller facial structures.
