Primate Dental Sacs, a Driver of Craniofacial Growth

Abstract Body : In both humans and non-human primates, tooth development occurs in dental follicles, or dental sacs, with replacement teeth forming as extensions mesial-lingual to the deciduous teeth. In this study, we demonstrated how dental sac volume and location influence overall craniofacial growth, specifically in the rostral and lateral expansion of the bones of the jaw. Using conventional micro CT and diffusible iodine contrast-enhanced computed tomography (dice-CT) scans from postnatal Aotus nancymaae we visualized 3D models of dental anatomy at multiple stages. We used 3D Slicer, an open-source image analysis program, to create reconstructions for qualitative analysis and collect metric data. We took measurements of the arc length of the outside and inside of both the maxillary and mandibular dental arcs, the antero-posterior length of each hemi-jaw, dorsal-ventral heights, and the lingual and buccal widths between right and left deciduous molars.
All metrics saw an increase in size. Notably, in the first two weeks postnatal, width between lingual surfaces of the maxillary first molar increased by 30.7%. Our reconstructions showed lateral displacement of the M1 dental sacs. Although we saw large increases laterally, we only saw a slight increase of 5.4% in the rostro-caudal dimension of the maxillary tooth row. We also observed that growth in the dorsoventral height of the maxillary postcanine dental sacs increased from mesial to distal, possibly constraining paranasal sinus development. Across multiple stages of Aotus, we observed development of replacement teeth pushing deciduous teeth both rostrally and laterally. These measurements were unsurprisingly found to be correlated with linear measurements of surrounding bone. Our most notable result implies more growth laterally than rostrally within newborn Aotus. Understanding spatial reconfiguration of dental sacs can aid in the explanation of ontogenetic sources of biological variation in the facial skeleton.