Morphometric growth relationships of the immature human mandible and tongue

Abstract

The masticatory apparatus is a highly adaptive musculoskeletal complex comprising several relatively independent structural components, which assist in functions including feeding and breathing. We hypothesized that the tongue is elemental in the maintenance of normal ontogeny of the mandible and in its post-natal growth and development, and tested this using a morphometric approach. We assessed tongue and mandibular measurements in 174 (97 male) human cadavers. Landmark lingual and mandibular data were gathered individuals aged between 20 gestational weeks and 3 yr postnatal. In this analysis, geometric morphometrics assisted in visualizing the morphometrical growth changes in the mandible and tongue. A linear correlation in conjunction with principal component analysis further visualized the growth relationship between these structures. We found that the growth of the tongue and mandible were intrinsically linked in size and shape between 20 gestational weeks and 24 months postnatal. However, the mandible continued to change in shape and size into the 3rd yr of life, whereas the tongue only increased in size over this same period of time. These findings provide valuable insights into the allometric growth relationship between these structures, potentially assisting the clinician in predicting the behaviour of these structures in the assessment of malocclusions.

Variations in bone density across the body of the immature human mandible

“…As the morphology of the mandible is thought to change with the development of the associated masticatory structures and an increase in masticatory activity, variations in bone mineral density within the alveolar and basal areas of the lingual and buccal/labial surfaces of the mandible were investigated further. The higher bone mineral density of the lateral incisor crypt region, particularly during the prenatal and early postnatal periods of growth, may be attributed to changes in both the morphology of the symphyseal region of the mandible (Scheuer & Black, 2000;Lee et al 2001;Radlanski et al 2003;Hutchinson et al 2014) as well as in the functioning of the tongue (Miller et al 2003;Delaney & Arvedson, 2008).…”

“…During the 12th week of gestation, the ventral symphyseal cartilages commence the process of endochondral ossification (Scheuer & Black, 2000;Radlanski et al 2003). This process, which includes increased bone modelling and remodelling, continues until fusion of the hemi-mandibles is completed (Scheuer & Black, 2000;Hutchinson et al 2012Hutchinson et al , 2014. Thus, bone in the symphyseal region and associated central incisor crypt region is younger and as such lower in density (Hernandez, 2008) when compared with the more established bone of the lateral incisor region.…”

“…Furthermore, studies assessing the prenatal growth of the mandible have limited their focus to the embryonic or early fetal periods of development (Merida Velasco et al 1990;Lee et al 2001;Radlanski et al 2002Radlanski et al , 2003Radlanski et al , 2004. While the mandible undergoes a significant degree of development during these periods, it is the transition across functional states from the fetal to the early postnatal periods that significantly influences the mandibular morphology (Miller et al 2003;Delaney & Arvedson, 2008;Coquerelle et al 2013;Hutchinson et al 2014). In addition, while studies have assessed the changes in the mandibular morphology during this functionally complex period, there is a paucity of information on how the bone mineral density varies, particularly over periods of dental development and eruption.…”

Mandible and Tongue Development

“…This growth pattern seems to provide the tongue with physical space to move downward, and this movement closely coincides with another important event in craniofacial morphogenesis, the reorientation of the palatal shelves from a vertical to a horizontal position (Ferguson, 1977). In humans, morphometric analyses have shown that the growth of the tongue and mandible is intrinsically linked in size and shape between 20 gestational weeks and 24 months postnatally (Hutchinson, Kieser, & Kramer, 2014). The mechanical relationship between the mandible and tongue is also supported by certain clinical conditions in which alteration of one affects the other.…”

Hitherto unknown detailed muscle anatomy in an 8‐week‐old embryo

“…Accurate knowledge of late embryonic and fetal spatial anatomical relations is therefore crucial for effective interpretation of high resolution prenatal imaging techniques. Procedures such as sonography or fetoscopy during prenatal diagnostics and fetal surgery can even predict embryonic health, as it is already in use to determine fetal health (D'Addario et al 2005;Hutchinson et al 2014).…”