Histological analysis of the growth of the mandibular condyle in the Rhesus monkey (Macaca mulatta).

Qualitative and quantitative data on the growth of the mandib- ular condyle in the rhesus monkey (Macaca mulatta) are limited. The purpose of this investigation was to provide such data, with emphasis on variation in the size of the cartilaginous layers in the condyle and on condylar growth at five maturational levels (i.e., neonate, infant, juvenile, adolescent and young adult). Two regions of the mandibular condyle, the articular tissue and the pre- chondroblastic-chondroblastic (growth) layer, were examined histologically in 38 rhesus monkeys. The absolute area of the articular layer increased dra- matically from the neonatal through the juvenile age groups and then decreased gradually through the adult group. When the absolute values were expressed rel- ative to condylar size, the first three maturational levels shared a common trend of increasing growth of the articular layer, with a cessation of growth in this tis- sue occurring during the adolescent period. This variation in articular layer tis- sue is probably the result of progressive alteration in the function of the temporo- mandibular joint. The size of the prechondroblastic-chondroblastic (growth) cartilage increased dramatically between the neonatal and juvenile age groups, and subsequently decreased in older age groups. The relative thickness of the prechondroblastic- chondroblastic cartilage reached its peak within the infant and juvenile levels, being greatest in the posterior region among the infants and in the postero-supe- rior region among the juveniles. This corresponds to previous investigations which have shown that greater vertical growth of the rhesus monkey mandible occurs during the infant period, while the direction of mandibular growth is more horizontal in subsequent age groups. The rhesus monkey (Macaca mulatta) re- mains the most commonly used nonhuman primate model for craniofacial growth in man. Most studies of facial growth in primates, however, involve experimental intervention and are characterized by a limited number of both experimental and control animals. Nor- mal variation, especially during the growth process, is impossible to ascertain reliably using this approach. Thus, conclusions on nor- mal craniofacial growth in monkeys from ex- perimental studies may remain open to ques- tion (Carlsson and Oberg, '74). Several recent studies document normal growth and development of the craniofacial complex in the rhesus monkey (Duterloo and Enlow, '70; Elgoyhen et al., '72), with par- ticular reference to the maxillary complex AM. J. ANAT. (1978) 151: 103-118. (McNamara et al., '76) and the mandible (Tur- pin, '68; McNamara and Graber, '75). Detailed descriptions of the normal microanatomy and postnatal growth of the temporomandibular joint in M. mulatta, however, are limited pri- marily to unpublished master's theses (Ziel- inski, '65; Zimmermann, '71) or to experimen- tal investigations with few control animals (e.g., Hiniker and Ramfjord, '66; Cutler, '68; Norwich, '69; Stockli and Willert, '71). The purpose of this investigation was to pro- vide a quantitative description of the normal microanatomy and growth of the tissues of the mandibular condyle from the neonate through