Human temporomandibular joint disc: anatomy and measurements in prenatal development.

The objective of this study was to determine morphological characteristics and measurements of the temporomandibular joint (TMJ) disc in human fetuses between 16 and 20 weeks of intrauterine life, and correlate it with oral-facial neuro-muscular maturing. Scanner images were used to record the length of the disc (D) and the thickness of its anterior middle and posterior bands in TMJ anteroposterior vertical sections from human fetuses of 16, 18 and 20 weeks of intrauterine life (WIL). Mean disc length was 1.98 mm, 2.69 mm and 2.90 mm at 16, 18 and 20 WIL respectively, and measurements differed significantly between those ages. The thicknesses of the anterior, middle and posterior bands also differed significantly. The results give normal morphological data for D between 16 and 20 WIL. TMJ anatomy and measurements appear to be related and agree with the neuro-muscular maturation time at which sucking and swallowing reflexes begin before birth. It is known that these functions, as well as the neuro-muscular capacity to perform prenatal mandibular movements (opening and closing), begin at 14 to 15 weeks of prenatal development and are fully attained at about 20 weeks of development. Knowledge of this reference pattern may be of major importance to future research, for assessing jaw biomechanics and detecting alterations of TMJ and prenatal development of a vital human function - suckling in preterm infants.