Effects of craniofacial structures on mouse palatal closure in vitro

Is the collateral circulation pattern in the hard palate affected by cleft deformity?

OBJECTIVES

To evaluate the influence of collateral vascularization on surgical cleft palate closure and deformities.

MATERIALS AND METHODS

Corrosion casting was performed using red-colored acrylic resin in twelve fresh adult cadavers with a normal hard palate. Additionally, white-colored barium sulfate was injected into a fetus with a unilateral complete cleft palate, and layer-by-layer tissue dissection was performed. Both substances were injected into the external carotid arteries. Corrosion casting involved dissolving the soft and hard tissues of the orofacial area utilizing an enzymatic solution.

RESULTS

In normal palates, bilateral intraosseous infraorbital arteries formed a network in the premaxilla with the intraosseous nasopalatine- and greater palatine arteries (GPAs). The perforating GPAs anastomosed with the sphenopalatine artery sub-branches. Bilateral extraosseous GPA anastomoses penetrated the median palatine suture. Complex vascularization in the retrotuberal area was detected. In the cleft zone, anastomoses were omitted, whereas in the non-cleft zone, enlarged GPAs were distributed along the cleft edges and followed the anatomical course anteriorly to initiate the network with facial artery sub-branches.

CONCLUSIONS

The anatomical subunits of the palate exhibited distinct anastomosis patterns. Despite omitted anastomoses with collateral circulation in the cleft zone, arteries maintained their anatomical pattern as seen in the normal specimen in the non-cleft zone.

CLINICAL RELEVANCE

Based on the findings in normal- and cleft palates, surgeons may expect developed anastomosis patterns in the non-cleft zone. Due to the lack of microcirculation in the cleft zone, the existent anastomoses should be maintained as much as possible by the surgical technique. This applies anteriorly in the incisive canal territory, alveolar ridges, and posteriorly in the retrotuberal area.

Development of a suspension organ culture of the fetal rat palate

On the basis of an already established suspension organ culture system of mouse palate anlagen, we developed a corresponding culture system for rat palate anlagen. In order to optimize the culture results we systematically studied the influence of main "culture conditions" such as dissection technique, rotation speed, gassing schedule, and developmental stage at the onset of culture for mice and rat palate anlagen. This system allows culturing rat palate anlagen from day 15 of gestation to day 18 + 8 h (80 h) under serum- and antibiotic-free conditions using a chemically defined medium, resulting in 90% fused palates. The explants, containing the maxillary vault and the palatal shelves, were cultured in siliconized culture flasks at a rotation speed of 12 rpm and a temperature of 37 degrees C (Table 1).

Changes in cell distribution during mouse secondary palate closure in vivo and in vitro. I. Epithelial cells

The distribution of epithelial cells around the perimeter of mouse secondary palatal shelves was observed before and after shelf reorientation in vivo and in vitro. Changes in shelf perimeter, cells per micrometer, and cell layering were measured for each of three shelf regions: anterior and posterior presumptive hard and presumptive soft palate at developmental stages which were 30, 24, and 18 hr prior to expected in vivo elevation, after in vivo elevation, and during the course of in vitro elevation. Pronounced increases in numerical cell density and cell layering accompanying shelf reorientation were noted in the superior nasal and mid-oral portions of the shelf perimeter in all three shelf regions with greatest changes noted in the posterior hard palate region. These changes were not attributable to cell division or to perimeter changes. The localized nature of the changes in cell distribution suggest that the underlying mechanisms may also be localized.

A morphometric analysis of craniofacial growth and changes in spatial relations during secondary palatal development in human embryos and fetuses

Staged human embryos and fetuses in the Carnegie Embryological Collection were morphometrically analyzed to show craniofacial dimensions and changes in spatial relations, and to identify patterns that would reflect normal developmental events during palatal formation. Normal embryos aged 7-8 weeks postconception (Streeter-O'Rahilly stages 19-23) and fetuses aged 9-10 weeks postconception, in eight groups with mean crown-rump (CR) lengths of 18-49 mm, were studied with cephalometric methods developed for histologic sections. In the 4-week period studied, facial dimensions increased predominantly in the sagittal plane with extensive changes in length (depth) and height, but limited changes in width. Growth of the mandible was more rapid than the nasomaxillary complex, and the length of Meckel's cartilage exceeded the length of the oronasal cavity at the time of horizontal movement of the shelves during stage 23. Simultaneously with shelf elevation, the upper craniofacial complex lifted, and the tongue and Meckel's cartilage extended forward beneath the primary palate. Analysis of spatial relations in the oronasal cavity showed that the palatomaxillary processes became separated from the tongue--mandibular complex as the head extended, and the tongue became positioned forward with growth of Meckel's cartilage. As the head position extended by 35 degrees, the cranial base angulation was unchanged and the primary palate maintained a 90 degrees position to the posterior cranial base. However, the sagittal position of the maxilla relative to the anterior cranial base increased by 20 degrees between stages 19 and 23. In the late embryonic and early fetal periods, the mean cranial base angulation of approximately 128 degrees and the mean maxillary position angulation of approximately 84 degrees were similar to the angulations previously shown to be present later prenatally and post-natally. The results suggest that human patterns of cranial base angulation and maxillary position to the cranial base develop during the late embryonic period when the chondrocranium and Meckel's cartilage form the primary skeleton.

An improved culture system for secondary palatal elevation

An organ culture system devised for studying the development of the secondary palate was modified so that it retained high partial pressures of oxygen and supported total anterior and posterior palatal elevation. The cultured tissues appeared healthy as judged by histological examination. Medium was continuously recirculated through the culture system in which Day 13 embryonic mouse heads, with the brain and tongue removed, were totally submerged and suspended. The medium was constantly gassed via hollow fiber devices. A motor-driven stirrer, run at a low rate, agitated the medium so that the boundary layer surrounding the tissue was dispersed. Embryonic mouse heads were cultured in each of four media: Eagle's basal medium, Ham's F-12 medium, Fitton-Jackson's modified BGJb medium, and Waymouth's MB 752/1 medium. Elevation of the palate in both anterior and posterior regions with excellent tissue viability was achieved in all heads grown in BGJb medium.

The american alligator (Alligator mississipiensis): a new model for investigating developmental mechanisms in normal and abnormal palate formation

Despite numerous investigations, there are still many unsolved problems concerning normal and abnormal palatal development. The American Alligator is here put forward as a new model for the investigation of a variety of developmental phenomena associated with palatogenesis. The structure of the palate of the adult Alligator is reported. This animal exhibits a unique combination of reptilian and mammalian features in its craniofacial anatomy and so its craniofacial development should be of considerable interest.