부산대학교 도서관

The lateral fissures upper lip and cleft palates are one of the most prevalent birth defects in pediatric age and increasingly can be diagnosed at ages earliest gestation. The non-consensus that exist about the development and elevation of human palatal shelves led us to study this topic with a new methodological approach. We made microphotography compositions obtained from serial histological sections of human embryonic stages (Carnegie stages (CS) 17 to 23) comprising the entire elevation process of palatal shelves. In contrast with other previous studies about palatogenesis, we focused in volume changes of palatal shelves integrated into the corresponding maxillary process (area of origin) and more specifically we analyzed one of its segments (maxillary segment selected (MSS)). In addition, potential errors from volumetric calculation due to the own characteristics from each embryonic specimen –such as different sizes, different grades of non homogeneous tissue retraction by histological fixing process, post-mortem changes– were resolved by using the percentage of volume occupation of each part in which each MSS was divided as a comparative variable among stages. The volume was obtained by applying stereological principles and techniques. Analysis of differences in percentages of volumetric occupation between embryonic stages was useful to define the tissue volume dynamics of the area that mostly contains the corresponding palatal shelve itself (medial territory) and adjacent areas of MSS. Further comparisons of each other zones allowed us to deduce possible relations with the mechanisms involved in the formation and elevation of the palatal shelves. The results of this study show that the dynamics of percentage growth of tissue volume of the medial territory of MSS (main area which integrates the corresponding palatal ridge) is different in each third of the palate. In posterior third, the medial territory grows remarkably at the beginning (range (r) CS17-18) and in the middle (rCS19-20) period of the palatal elevation, while the anterior third only does at the end of the process (rCS22-23). The pattern observed in the middle third of the medial territory is intermediate with respect to the other two. Given that this zone is also the most stable third of this territory we speculate that this is a transition zone and/or a tissue transfer between both extremes. The comparison of data between MSS territories suggests that there is a remodelling predominance at the beginning (rCS17-18) of the elevation process of the palatal shelves in posterior and middle thirds and, in that last third, in the central part (rCS19-20) of this period too. The remainder observed increases in volume percentages seem to respond more to a local mesenchymal proliferation than to other mechanisms, except for the sharp increase at the end (rCS22-23) of the elevation period in the posterior third which may suggest that is mainly due to a rise of palatal shelves by a real axial rotation. The application of percentages of volumetric occupation of different territories between embryonic stages has shown good analysis tool and discards the factor of global growth.