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Count Me in, Count Me out: Regulation of the Tooth Number via Three Directional Developmental Patterns - PubMed

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Count Me in, Count Me out: Regulation of the Tooth Number via Three Directional Developmental Patterns

Zheng Fang et al. Int J Mol Sci. 2023.

Abstract

Tooth number anomalies, including hyperdontia and hypodontia, are common congenital dental problems in the dental clinic. The precise number of teeth in a dentition is essential for proper speech, mastication, and aesthetics. Teeth are ectodermal organs that develop from the interaction of a thickened epithelium (dental placode) with the neural-crest-derived ectomesenchyme. There is extensive histological, molecular, and genetic evidence regarding how the tooth number is regulated in this serial process, but there is currently no universal classification for tooth number abnormalities. In this review, we propose a novel regulatory network for the tooth number based on the inherent dentition formation process. This network includes three intuitive directions: the development of a single tooth, the formation of a single dentition with elongation of the continual lamina, and tooth replacement with the development of the successional lamina. This article summarizes recent reports on early tooth development and provides an analytical framework to classify future relevant experiments.

Keywords: continual lamina; deciduous tooth; dental lamina; diphyodonts; permanent tooth; successional lamina; supernumerary tooth; tooth agenesis; tooth number.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1

Diagram of the three directions of tooth number regulation. (a) A dorsal diagram of dentition development in three directions in the dental arch; (b) an abstract diagram of three directions of tooth number regulation. Red arrow: the first direction and its further extension refers to the process of a single tooth developing from an early stage of odontogenesis to the final functional tooth. Yellow arrow: the second direction, which is achieved by the addition of a continual tooth distal to the mesial tooth within one dentition. Blue arrow: the third direction, in which the tooth number is maintained by consistent development of a replacement tooth, usually added lingually to the functional tooth. ct: continual tooth; ft: functional tooth; rt: replacement tooth.

Figure 2
Figure 2

Hypotheses of anterior tooth development in human dental arch. (a) In the individual development hypothesis, all anterior teeth in humans develop independently of isolated dental placodes; (b) in the continual development hypothesis, the central incisor develops from the dental placode, and the lateral incisor and canine develop from the continual lamina from the central incisor; (c) in the hybrid development hypothesis, the central incisor and canine develop independently while the lateral incisor appears as part of continual development, suggesting that incisors and canines represent distinct development groups. Red arrow: the first direction of tooth number regulation. Yellow arrow: the second direction of tooth number regulation. c: canine; i1: the central incisor; i2: the lateral incisor.

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