MANDIBULAR MOVEMENTS DURING ELEVATION AND FUSION OF PALATAL SHELVES EVALUATED FROM THE COURSE OF MECKELS CARTILAGE

The purpose of the present study was to investigate whether the course of Meckel's cartilage could reveal the mandibular movements during th e elevation and fusion of the soft tissue palatal shelves. Histologica l sections. cut serially in the horizontal plane from 64 human mandibl es, 16-104 mm CRL, were analyzed. The course of the anterior and media l parr of Meckel's cartilage changed markedly during the three palatal stages, i.e., before, during, and after palate formation, The medial part changed during these stages from a straight course through a curl ed, S-shaped course to a crochet-hook-shaped course. The anterior part of Meckel's cartilage developed from a separation in the symphysis me nti region to a fusion and later to a separation again. It is suggeste d that these changes in the course of Meckel's cartilage are due to di fferent muscle activities. It is supposed that during the palatal deve lopmental stages the activity of the geniohyoid and genioglossus muscl es caused the mandibular retraction and the widening of the angulation between the bilateral hemimandibles. The S-shape of Meckel's cartilag e is a result of these movements, Later mandibular proclination and na rrowing of the bilateral hemimandibles resulted in an anterior mechani cal fusion of Meckel's cartilage due to the activity of the mylohyoid muscle. This stage is followed by a retraction and re-widening of the angulation between the bilateral bony components, which disrupts the f usion of Meckel's cartilage in the symphysis menti region. Thus, the c ourse of Meckel's cartilage revealed the mandibular movements in the s agittal and transverse planes during palate formation.