Department of Oral Anatomy and Cell Biology, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima 890-8544, Japan.
J Oral Biosci. 2022 Jun;64(2):165-175. doi: 10.1016/j.job.2022.03.007. Epub 2022 Apr 4.
Mammalian premolars and molars (cheek teeth) are teeth with multiple cusps, which are important characteristics of mammals. Endothermic mammals have high basal metabolic rates and must take in much energy by efficient mastication of food using their multicuspid cheek teeth. From the phylogenetic (evolutionary) perspective, the mammalian multicuspid teeth are derived from the reptilian unicuspid teeth with a single cone by adding new cusps around the original cone. Nearly 100 million years of long geological time were required for the unicuspid tooth to transform into a tribosphenic molar, which is the prototype of all molars in modern mammals. From the ontogenetic (developmental) perspective, the shape of the tooth germ becomes complex by adding the secondary enamel knots repeatedly in a short embryonic period. The secondary enamel knots are signaling centers that determine the future cusp positions.
Here we first reviewed the evolutionary process of the tribosphenic molar in the Mesozoic Era (the age of dinosaurs), and cusp homologies in the fossil record. Next, we reviewed the developmental mechanisms controlling the patterning of secondary enamel knots, which determine the final cusp patterns of molars in modern mammals. Finally, we discussed the possible relationship between the two processes from the extremely different time scales.
A parallel relationship between ontogeny and phylogeny of the mammalian multicuspid teeth was expected.
哺乳动物的前臼齿和臼齿（颊齿）是具有多个尖峰的牙齿，这是哺乳动物的重要特征。恒温哺乳动物的基础代谢率较高，必须通过高效咀嚼食物来获得大量能量，而这些食物则需要利用多尖峰的颊齿来进行咀嚼。从系统发生（进化）的角度来看，哺乳动物的多尖峰牙齿是由爬行动物的单尖峰牙齿通过在原始圆锥体周围添加新的尖峰而衍生而来的。从单一的圆锥体到具有多个尖峰的三尖齿臼齿，这一转变在近 1 亿年的漫长地质时间里才得以完成，而三尖齿臼齿是现代哺乳动物所有臼齿的原型。从个体发生（发育）的角度来看，在胚胎期短暂的时间内，通过反复添加次级釉质结，牙胚的形状变得复杂。次级釉质结是决定未来尖峰位置的信号中心。
本文首先回顾了中生代（恐龙时代）三尖齿臼齿的进化过程以及化石记录中的尖峰同源性。接下来，我们回顾了控制次级釉质结模式形成的发育机制，这些机制决定了现代哺乳动物臼齿最终的尖峰模式。最后，我们从非常不同的时间尺度讨论了这两个过程之间可能存在的关系。
哺乳动物多尖峰牙齿的个体发生和系统发生之间存在平行关系。
