DISTRACTION OSTEOGENESIS FOR LENGTHENING OF THE HARD PALATE .2. HISTOLOGICAL STUDY OF THE HARD AND SOFT PALATE AFTER DISTRACTION

To correct velopharyngeal incompetence, a new treatment concept was pr oposed in Distraction Osteogenesis for Lengthening of the Hard Palate: Part I (using lengthening of the hard and soft palate by distraction osteogenesis). Cephalometry and computed tomography showed successful elongation of the posterior hard palate with gradual calcification. He re the sequential use of fluorochrome markers (oxytetracycline, xyleno l orange, DCAF [2,4-bis-N-N'-dicarboxymethyl aminomethyl fluorescein], and alizarin complexone) during the distraction and retention period is reported together with the histologic investigations using light an d laser scan microscopy without prior demineralization. The experiment al gap showed de novo osteogenesis in all dogs. The new bone was alway s in continuity with the original anterior and posterior palatal bone margins. It either bridged the experimental gap fully or left a small central zone of fibrous tissue, in which eventual ossification occurre d. Several distinct zones could be distinguished: A small central zone was found With parallel strains of collagen fibers, oriented longitud inally in the direction of the distraction. Next to this zone a layer of undifferentiated mesenchymal precursor cells was seen in direct con tact to newly formed bone. The nest zone was coarse woven bone, showin g a transition to mature lamellar bone through remodeling. No evidence of endochondral bone formation was found, i.e., all dogs showed exclu sively intramembranous bone formation. The soft tissues showed no sign s of alteration; in particular, there was no necrosis or scar formatio n. The soft tissues were not thinned but appeared to have followed the longitudinal displacement. In conclusion, gradual distraction osteoge nesis of the hard palate could be a possible method for lengthening th e palate to treat velopharyngeal incompetence.