Hull York Medical School, University of Hull, Hull, HU6 7RX, UK.
Hull York Medical School and Department of Archaeology, University of York, York, YO10 5DD, UK.
Sci Rep. 2022 Mar 9;12(1):3819. doi: 10.1038/s41598-022-07779-z.
Rodents are characterised by a distinctive masticatory apparatus which includes a single pair of enlarged and continually growing incisors. This morphology, termed diprotodonty, has also independently evolved in a number of other mammals, including the aye-aye. This study examined the functional significance of the internal "root" of the elongated rodent-like incisor. The mandibles of four rodents and an aye-aye were modelled to exhibit incrementally shorter incisor roots. Finite element analysis was used to predict stress and strain patterns across the jaw to determine whether the length of the incisor root contributes to the resistance of mechanical forces encountered in the mandible during incision. It was found that von Mises stresses increase in the region of the mandible local to where the incisor is removed, but that the stress distribution across the wider mandible is only minimally affected. Thus, the long internal incisor appears to play a small role in resisting bending forces close to the incisor alveolus, and may act with the arch-like mandibular shape to strengthen the mandible in this region. However, the impact across the whole mandible is relatively limited, suggesting the highly elongate incisor in diprotodont mammals may be principally driven by other factors such as rapid incisor wear.
啮齿动物的咀嚼器官具有独特的特征，包括一对增大且不断生长的门齿。这种形态结构，称为双门齿目，也在其他一些哺乳动物中独立进化而来，包括指猴。本研究探讨了伸长的啮齿类门齿内部“根”的功能意义。对四个啮齿动物和一个指猴的下颌骨进行了建模，以展示逐渐缩短的门齿根。使用有限元分析来预测颌骨上的应力和应变模式，以确定门齿根的长度是否有助于抵抗在切牙过程中在颌骨中遇到的机械力。结果发现，在去除门齿的下颌骨局部区域，von Mises 应力增加，但更广泛的下颌骨的应力分布仅受到最小影响。因此，长的内部门齿似乎在抵抗靠近门齿牙槽的弯曲力方面作用不大，并且可能与拱形下颌形状一起在该区域增强下颌骨。然而，整个下颌骨的影响相对有限，这表明双门齿目哺乳动物中高度伸长的门齿可能主要由其他因素驱动，例如快速的门齿磨损。
