Abstract
BackgroundStudies examining human and nonhuman primates have supported the hypothesis that the recent increase in the occurrence of misalignment of teeth and/or incorrect relation of dental arches, named dental malocclusion, is mainly attributed to the availability of a more processed diet and the reduced need for powerful masticatory action. For the first time on live human populations, genetic and tooth wear influences on occlusal variation were examined in a split indigenous population. The Arara-Iriri people are descendants of a single couple expelled from a larger village. In the resultant village, expansion occurred through the mating of close relatives, resulting in marked genetic cohesion with substantial genetic differences.Methodology/Principal FindingsDental malocclusion, tooth wear and inbreeding coefficient were evaluated. The sample examined was composed of 176 individuals from both villages. Prevalence Ratio and descriptive differences in the outcomes frequency for each developmental stage of the dentition were considered. Statistical differences between the villages were examined using the chi-square test or Fisher's exact statistic. Tooth wear and the inbreeding coefficient (F) between the villages was tested with Mann-Whitney statistics. All the statistics were performed using two-tailed distribution at p≤0.05. The coefficient inbreeding (F) confirmed the frequent incestuous unions among the Arara-Iriri indigenous group. Despite the tooth wear similarities, we found a striking difference in occlusal patterns between the two Arara villages. In the original village, dental malocclusion was present in about one third of the population; whilst in the resultant village, the occurrence was almost doubled. Furthermore, the morphological characteristics of malocclusion were strongly different between the groups.Conclusions/SignificanceOur findings downplay the widespread influence of tooth wear, a direct evidence of what an individual ate in the past, on occlusal variation of living human populations. They also suggest that genetics plays the most important role on dental malocclusion etiology.
Highlights
Human dentition may adapt functionally to diet and feeding behavior
Studies examining human [7,8,9,10,11,12,13] and nonhuman primates [14,15,16,17] have indicated that the increase in the occurrence of dental malocclusion can be attributed to the availability of a more processed diet and a reduced need for powerful masticatory action
Normal occlusion was the most common morphological pattern in the original Arara village (Table 1 and Figure 3A), but for the Arara-Iriri indigenous people, the common pattern was a Class III malocclusion in which the lower dentition is more prominent than the upper dentition (32.6%, prevalence ratio (PR) = 6.1, p,0.0001) (Table 1 and Fig. 3B)
Summary
Bones continue to remodel throughout an individual’s life, but tooth enamel does not regenerate once its formation is complete For these reasons, dental morphology has been studied as an important indicator of both functional adaptations and phylogenetic evolution [1,2,3,4,5]. Studies examining human [7,8,9,10,11,12,13] and nonhuman primates [14,15,16,17] have indicated that the increase in the occurrence of dental malocclusion can be attributed to the availability of a more processed diet and a reduced need for powerful masticatory action. Expansion occurred through the mating of close relatives, resulting in marked genetic cohesion with substantial genetic differences
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