Abstract
ObjectivesDental malocclusions in modern populations would be the result of small and weak jaws developing under low masticatory loads. We assess the validity of this by characterising the external and internal morphology of mandibles affected by class II and III malocclusions and comparing them with those from individuals with different masticatory load patterns.Materials and methodsCTs from up to 118 individuals exerting intensive, medium and low masticatory loads with harmonic occlusion, and from class II and III individuals, were used to compare their external shape using geometric morphometrics, as well as their internal amount and distribution of cortical bone.ResultsThe low-load groups (harmonic, class II and III occlusion) are externally more gracile than the intense and medium load groups. But more relevant in shape variation is a marked allometric pattern, which differentiates class II (small) and III (large) mandibles. Despite gracility, the relative amount of cortical bone in the low-load groups is larger than in the remaining groups.ConclusionsThere is no evidence that the modern mandible, including class II and III individuals, is intrinsically small and weak. Instead, there is a rather large degree of morphological variation, which could be linked to a lack of constraints derived from low masticatory loads. Thus, the effect of other factors such as genetics, but also basal metabolism, should be looked in more depth.Clinical relevanceDental malocclusions are a common disorder whose aetiology has not been unravelled, and several to be considered in the prevention and therapy of malocclusion.
Highlights
Dental malocclusions are considered a Bdisease of civilization^ [1]
The skulls of the remaining individuals are housed in different museums and universities in Chile, Argentina and Italy, and were selected according to their conservation status and their dental status
Shape analysis The first six principal components (PCs) explain up to 75% of the observed variance
Summary
Dental malocclusions are considered a Bdisease of civilization^ [1]. They are common in current western populations, and markedly less frequent in archaic human populations [2] whose diet was composed mainly of more mechanically challenging items like meat (non-highly processed), seeds and abrasive elements in them [3, 4]. In dentistry and physical anthropology, small jaws have been related to alterations like tooth crowding and an altered maxillomandibular relationship [1, 9,10,11]
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