Rare total and partial palatal clefts experimentally induced in the rat

Clefts of the hard palate with soft palate integrity can be produced through amniocentesis in Sprague-Dawley rats. This study attempted to induce exotic partial clefts of the palate and to describe their type, frequency and possible genesis. Palatal closure, i.e., elevation and fusion of the anterior zone, remodelling of the middle zone, and fusion in the posterior zone, occurs in rats between 16.0 and 17.5 days of fetal age. Withdrawing a small amount of amniotic fluid produced a series of total and rare partial clefts. The upper jaws of 95 of 410 fetuses of precisely determined age were examined in the scanning electron microscope. Total clefts occurred in 48.9% of viable fetuses examined at day 17.8 and in 21.8% of those examined at day 19.3. Partial clefts were observed in 14.1 and 18.5% of viable fetuses at days 17.8 and 19.3, respectively. Total clefts were most frequent in fetuses treated between day 15.21 and 15.40, while Partial clefts were distributed rather equally over the various age groups. Total clefts occurred in at least four different varieties, while partial clefting involved variable portions of the hard palate or both the hard and the soft palate, with six different forms being distinguished. The induction of partial clefts was dependent on the developmental point in time at which experimentation took place.