Third molar agenesis in modern humans with and without agenesis of other teeth

Abstract

Background The number of teeth in the human dentition is of interest both from developmental and evolutionary aspects. The present case-control study focused on the formation of third molars in modern humans aiming to shed more light on the most variable tooth class in the dentition. Materials and Methods For this reason, we investigated third molar formation in a sample of 303 individuals with agenesis of teeth other than third molars (agenesis group) and compared it to a sex and age matched control group of 303 individuals without agenesis of teeth other than third molars. Results The prevalence of third molar agenesis in the agenesis group was 50.8%, which is significantly higher than the 20.5% in the control group (p < 0.001). The chance of a missing third molar in the agenesis group was increased by 38.3% (p < 0.001), after controlling for the agenesis in other teeth factor. When considering the amount of missing third molars per individual, a clear tendency towards more missing third molars was evident in the agenesis group compared to the control group. The frequency of bilaterally missing third molars in the agenesis group was 29% in the maxilla, as well as in the mandible, which is about three times higher than the frequency of unilaterally missing third molars (p < 0.001). In the control group, bilaterally missing third molars occurred in 8.6% in the maxilla and 8.9% in the mandible. Conclusion The present results indicate that genetic factors involved in tooth agenesis affect also the dentition as a whole. Furthermore, the third molars are more vulnerable to factors involved in agenesis of other teeth and they are more often affected as a whole. These findings seem to be associated with the evolutionary trend in humans towards reduced molar number.

Analyses of oligodontia phenotypes and genetic etiologies

“…Third molars were excluded from this analysis, which are often ignored in oligodontia studies because of the high frequency of their absence (~20%) in the general population, although third molar absence is significantly higher in persons missing teeth other than third molars. 14 Furthermore, ten families with oligodontia were recruited and characterized with clinical examinations and the causative mutation determined by genotype analyses.…”

Third Molar Agenesis Is Associated with Facial Size

“…Therefore, in cases where all other permanent teeth are present, an agenesis of the third molars is largely viewed as a normal phenotype. Nevertheless, previous studies have shown that there is a strong association between missing third molars and agenesis of other teeth, with the latter increasing the chance of third molar agenesis by approximately 40% [4][5][6]. This raises the question, whether the presence of third molars is controlled by the same genetic mechanisms as other permanent teeth, or their formation follows a separate developmental pattern.…”

Predicción de las Modificaciones Craneométricas de Sujetos Nativos del Altiplano Basados en Índices Craneométricos Históricos Locales

“…Las dimensiones faciales sufrirán notables disminuciones en algunos de sus segmentos, estas modificaciones se hacen evidentes en la Anchura Bicigomática, Altura Nasion-Prostion, Anchura y Altura Nasal, Anchura y Altura Orbital, Anchura Interorbitaria, Achura Biorbital, Anchura Bimaxilar y Anchura Maxilo-Alveolar. Es conveniente mencionar que la configuración facial pronosticada podría repercutir sobre el número total de piezas dentarias, debido a que el mecanismo biológico ajusta uniformemente el tamaño facial y el número de dientes (Oeschger et al, 2020;Scheiwiller et al, 2020).…”