[Influence of masticatory muscle insertions on the mandibular structure of the newborn infant].

The influence of the muscular insertions on the mandibular structure in new born infants has been studied with the aid of microradiographical analysis applied to 80 microns thick undecalcified sections and in paraffin sections after decalcification. The left side of the mandibles was cut into sections parallel to the vestibular surface of the bone (fig. 1) and the right side, in frontal sections (fig. 2). The tendinous fibres of the temporal muscle are inserted into the apex of the coronoïd process, which is, at this age, constituted by chondroïd tissue (fig. 3). The continued differentiation of this tissue within the coronoïd process, permits the migration of the temporal muscle insertion. Microradiographical analysis has been used to show the changes of the calcified tissue aspects in the masseter and medial pterygoïd muscle insertions (fig. 4 and 5). The insertion of the lateral pterygoïd muscle doesn't transform the bone tissue morphology (fig. 6-A and 6-B).