Enamel mechanical properties vary across molar crowns, but the relationship among mechanical properties, tooth function, and phylogeny are not well understood. Fifteen primate lower molars representing fourteen taxa (catarrhine, n = 13; platyrrhine, n = 1) were sectioned in the lingual–buccal plane through the mesial cusps. Gradients of enamel mechanical properties, specifically hardness and elastic modulus, were quantified using nanoindentation from inner (near the enamel-dentine junction), through middle, to outer enamel (near the outer enamel surface) at five positions (buccal lateral, buccal cuspal, occlusal middle, lingual cuspal, lingual lateral). Cuspal positions had higher mechanical property values than lateral positions. Middle enamel had higher mean hardness and elastic modulus values than inner and outer locations in all five crown positions. Functionally, the thicker-enameled buccal cusps of lower molars did not show evidence of increased resistance to failure; instead, lingual cusps—which show higher rates of fracture—had higher average mechanical property values, with no significant differences observed between sides. Preliminary phylogenetic results suggest there is relatively little phylogenetic signal in gradients of mechanical properties through the enamel or across the crown. There appears to be common mechanical property patterns across molar crowns in Catarrhini and potentially among primates more broadly. These results may allow more precise interpretations of dental biomechanics and processes resulting in mechanical failure of enamel in primates, such as wear and fracture.

不同磨牙牙冠的牙釉质机械性能有所不同，但机械性能、牙齿功能和系统发育之间的关系尚不清楚。代表 14 个类群的 15 颗灵长类下臼齿（卡他碱，n  = 13；阔鼻草，n  = 1）通过近中牙尖在舌-颊平面上进行切片。牙釉质机械性能的梯度，特别是硬度和弹性模量，使用纳米压痕从内部（靠近牙釉质-牙本质交界处），通过中间，到外部牙釉质（靠近外部牙釉质表面）在五个位置（颊侧面，颊尖，咬合中部、舌尖、舌侧）。尖头位置比横向位置具有更高的机械性能值。在所有五个牙冠位置中，中间牙釉质的平均硬度和弹性模量值均高于内部和外部位置。从功能上来说，下磨牙较厚的牙釉质颊尖并没有显示出抗失败能力增强的证据。相反，舌尖（显示出更高的断裂率）具有更高的平均机械性能值，并且两侧之间没有观察到显着差异。初步的系统发育结果表明，通过牙釉质或整个牙冠的机械性能梯度的系统发育信号相对较少。卡他尼类动物以及更广泛的灵长类动物的磨牙牙冠似乎存在共同的机械特性模式。这些结果可能有助于更精确地解释导致灵长类动物牙釉质机械故障（例如磨损和断裂）的牙科生物力学和过程。