Kondo and Hanamura [4] analyzed the mesiodistal crown diameters of the maxillary incisors and first molars in 301 Japanese individuals, and examined the existence of compensatory tooth size interaction between the early-developed central incisor and the later-developed

lateral incisor. The central incisor and first molar in the group that had reduced lateral incisors were not smaller than those in the other groups who had normal or large lateral incisors. Thus, the reduced lateral PS-341 supplier incisor did not always lead to the reduction of the other teeth. The central incisor was larger in the group who had reduced lateral incisors than in the group who had normal-sized lateral incisors. This result indicates that the size of the lateral incisor was likely to reflect a compensatory response related to a large central incisor. Fluctuating asymmetry

in size of the lateral incisor was greater in the reduced lateral incisor group than in the normal lateral INCB024360 in vitro incisor group. Compensatory growth of the lateral incisors was noted in those groups where the lateral incisors showed strong asymmetry in their size and also in the group who displayed reduced lateral incisors. It was suggested by the authors that the compensatory growth was related to right and left side asymmetry in the lateral incisor. Correlations among teeth in the same tooth class, and correlations between right and left sides of the same tooth, were relatively high but the correlations among other tooth classes were low. It was thought that the reduction and compensatory growth of the lateral incisor were limited within the same tooth class, but rarely influenced the whole tooth row. In conclusion, it is proposed that reduced maxillary lateral incisors grow to compensate for the size of the adjacent central incisor in some cases, but their reduction also reflects reduction of the whole dentition in other cases (Fig. 3, Table 4). Kavanagh next et al. [50] constructed an inhibitory cascade model by uncovering the activator-inhibitor logic of sequential tooth development. Their

hypothesis was based on experiments of tooth development in the laboratory mouse and supports the important role of epigenetic influences during odontogenesis. Mouse molars develop sequentially and the dental lamina, extending posteriorly from the developing first molar, gives rise to the second molar. When the second molar was cultured apart from dental lamina of the first molar, the second molar developed faster and grew larger than in the intact situation. These authors proposed that the mesial molars inhibit development of the distal molars. This model explains the relative size of mandibular molars by a balance of inhibitor and activator substances, and predicts evolutionary patterns in the dentition. The model has been tested from both paleontological [51] and [52] and comparative anatomical [53] perspectives. In a study of delayed erupted maxillary first molars, Rasmussen used the term “9-year-molar” [54].