An assessment of growth and sex from mandibles of cadaver foetuses and newborns

Abstract

The quantification of skeletal data is one way in which to demonstrate variation in human growth. In South Africa, few researchers have assessed patterns of growth in immature mandibles. The purpose of this study was to evaluate growth and sexual dimorphism in the mandible from the period of 31 gestational weeks to 36 months. A total of 74 mandibles were used, skeletal tissues were sourced from the Raymond A. Dart Collection (University of Witwatersrand), and cadaveric remains were obtained from the University of Pretoria and the University of Witwatersrand. The sources of cadaver materials (both bequeathment and unclaimed remains) included local provincial hospitals. The sample was divided into four groups, namely 31 to 40 gestational weeks (group1), 0 to 11 months (group 2), 12 to 24 months (group 3), and 25 to 36 months (group 4). Twenty-one osteological landmarks were digitized using a MicroScribe G2. Ten standard measurements were created and included: the longest length of mandible, mandibular body length and width, mandibular notch width and depth, mental foramen to inferior border of mandible, mandibular basilar widths bigonial and biantegonial, bigonial width of mental foramen and mental angle. Data were analyzed using PAST statistical software and Morphologika2 v2.5. For the linear measurements, no statistically significant difference between either the foetal and up to 12 month groups or the 2 to 3 years groups. However, statistically significant increases with age were noted between 12 and 24 months for nine variables. This can be associated with growth of the mandibular arch, development and eruption of the dentition and development of the masticatory structures. No evidence of sexual dimorphism was observed until age 3, where the mental angle and mandibular notch were significantly larger in females than males. In conclusion, the mandible develops and grows so as to accommodate development of the tongue, mastication and dental eruption. Future research that considers the influence of secular trends on mandibular growth is needed. AFRIKAANS : Die kwantifisering van skeletale data is ‘n betroubare metode om variasie in menslike groei aan te toon. Slegs enkele Suid-Afrikaanse navorsers, het groeipatrone in onvolwasse mandibulae nagevors. Die doel van hierdie studie was om groei en geslagsdimorfisme in die mandibula vanaf 31 gestasie weke tot 36 maande na geboorte te evalueer. ‘n Totaal van 74 mandibulae was gebruik. Skeletale weefsel uit die Raymond A. Dart Versameling (Universiteit van die Witwatersrand), en kadaweroorskot van die Universiteite van Pretoria en van die Witwatersrand was verkry. Die oorsprong van kadawermateriale (beide skenkings en onopgeëisde oorskot) het plaaslike provinsiale hospitale ingesluit. Die steekproef was verdeel in vier groepe, naamlik 31 to 40 gestasie weke (groep1), 0 tot 11 maande (groep 2), 12 tot 24 maande (groep 3), en 25 tot 36 maande (groep 4). MicroScribe, G2 is aangewend om 21 standaard antropometriese landmerke te digitiseer. Hieruit is 10 standaard antropometriese afmetings geskep o.a.: langste lengte van mandibula, lengte en breedte van corpus mandibula, afstand tussen foramen mentalis en inferior grens, basale wydte bigoniaal en biantegoniaal, bigoniale wydte van foramen mentalis asook mentale hoek. Inligting is d.m.v. PAST statistiese sagteware en Morphologika2 v2.5 ontleed. Volgens die Kruskal-Wallis-toets was die verskille tussen groepe 1 en 2, asook 3 en 4 statisties onbeduidend. Alle afmetings by groepe 2 en 3 het beduidende toenames getoon, behalwe dié van die afstand tussen foramen mentalis en inferior grens. Die veranderings mag die gevolg wees van die groei van die mandibula en koustrukture. Geslagsdimorfisme was aantoonbaar in groep 4, by die mentale hoeke (p=0.03) asook dimensies van die incisura mandibularis (p=0.0006), waar dié van vroulike individue groter was. Voor geboorte vergroot die arcus mandibularis om die ontwikkelende tong te huisves, terwyl dit na geboorte verander om die koustrukture te huisves. Gevolglik hermodelleer en groei die been as aanpassing vir die kouproses en om strukturele integreteit te behou. Geslagsdimorfisme word ook beïnvloed deur die kouproses. Die meeste veranderinge, veral dié van die koustrukture, was duideliker in vroulike individue. Toekomstige navorsing wat die invloed van sekulêre tendense op die groei van die mandibula oorweeg, is nodig.