Relationship between interproximal and occlusal wear in Australopithecus africanus and Neanderthal molars

Tooth wear and tertiary crowding: a 13-year cohort study in Amazon Indigenous populations

BACKGROUND

Tooth wear is an important mechanism for reducing dental dimensions and, consequently, dental crowding. The objective of this cohort study was to examine the relation of tooth wear, adjusted for covariates (age, tooth loss, arch perimeter and intercanine width), on tertiary crowding in Amazon Indigenous populations.

METHODS

A sample of 40 Indigenous people in permanent dentition at T0 (baseline) and after 13 years (T1) were evaluated. The sample included 16 males and 24 females belonging to two villages, Arara (n = 22, mean ages 16.6 and 29.9 years) and Assurini do Xingu (n = 18, mean ages 16.0 and 29.6 years). Clinical, intraoral photograph and dental cast evaluations were performed at both times. The anterior crowding was measured using Little's Irregularity Index (LI) and modeled through a multilevel linear regression with the predictor variables: village, tooth wear (T1-T0), age (T0), tooth loss (T1-T0), changes in intercanine width (T1-T0) and changes in arch perimeter (T1-T0).

RESULTS

A slight increase was observed (< 1 mm) in anterior dental crowding and a decrease in arch perimeter < 1.5 mm, while tooth wear increased between 0.65 and 0.99 units. The contextual variable (village) had no significant association with LI. In the upper arch, tooth loss was the only variable that showed an inverse association with LI (β=-0.41, p < 0.05). In the lower arch, the increase in dental crowding was inversely associated with tooth wear (β=-1.30, p < 0.05) and changes in arch perimeter (β=-0.31, p < 0.05). The other variables did not show significant associations.

CONCLUSION

After 13 years, dental crowding and tooth wear increased, while the arch dimensions tended to decrease. The changes in long-term dental crowding seem to have distinct etiological components for each dental arch. In the mandible, the changes in incisor alignment were associated with increased tooth wear and decreased dental arch dimensions. Whereas in the maxilla, only tooth loss caused alterations in tooth alignment. It is suggested that the effect of increased tooth wear on the etiology of tertiary crowding is of small magnitude and restricted to the lower dental arch.

Masticatory habits of the adult Neanderthal individual BD 1 from La Chaise-de-Vouthon (France)

OBJECTIVES

The analysis of dental wear provides a useful approach for dietary and cultural habit reconstructions of past human populations. The analysis of macrowear patterns can also be used to better understand the individual chewing behavior and to investigate the biomechanical responses during different biting scenarios. The aim of this study is to evaluate the diet and chewing performance of the adult Neanderthal Bourgeois-Delaunay 1 (BD 1) and to investigate the relationship between wear and cementum deposition under mechanical demands.

MATERIALS AND METHODS

The macrowear pattern of BD 1 was analyzed using the occlusal fingerprint analysis method. We propose a new method for the bilateral measurement of the cementum volume along both buccal and lingual sides of the molar root.

RESULTS

BD 1's anterior dentition is more affected by wear compared to the posterior one. The macrowear pattern suggest a normal chewing behavior and a mixed-diet coming from temperate environments. The teeth on the left side of the mandible display greater levels of wear, as well as the buccal side of the molar crowns. The cementum analysis shows higher buccal volume along the molar roots.

DISCUSSION

BD1 could have been preferably chewing on the left side of the mandible. The exploitation of various food resources suggested by the macrowear analysis is compatible with the environmental reconstructions. Finally, the greater wear on the buccal side of the molar occlusal surface and the greater volume of cementum in that side of the molar roots offers a preliminary understanding about the potential correlation between dental wear and cementum deposition.

Finite element analysis of Neanderthal and early Homo sapiens maxillary central incisor

Neanderthal anterior teeth are very large and have a distinctive morphology characterized by robust 'shovel-shaped' crowns. These features are frequently seen as adaptive responses in dissipating heavy mechanical loads resulting from masticatory and non-masticatory activities. Although the long-standing debate surrounding this hypothesis has played a central role in paleoanthropology, is still unclear if Neanderthal anterior teeth can resist high mechanical loads or not. A novel way to answer this question is to use a multidisciplinary approach that considers together tooth architecture, dental wear and jaw movements. The aim of this study is to functionally reposition the teeth of Le Moustier 1 (a Neanderthal adolescent) and Qafzeh 9 (an early Homo sapiens adolescent) derived from wear facet mapping, occlusal fingerprint analysis and physical dental restoration methods. The restored dental arches are then used to perform finite element analysis on the left central maxillary incisor during edge-to-edge occlusion. The results show stress distribution differences between Le Moustier 1 and Qafzeh 9, with the former displaying higher tensile stress in enamel around the lingual fossa but lower concentration of stress in the lingual aspect of the root surface. These results seem to suggest that the presence of labial convexity, lingual tubercle and of a large root surface in Le Moustier 1 incisor helps in dissipating mechanical stress. The absence of these dental features in Qafzeh 9 is compensated by the presence of a thicker enamel, which helps in reducing the stress in the tooth crown.