Abstract
Distraction osteogenesis (DO) is a minimally invasive surgical technique to achieve skeletal expansion and has become the standard treatment method for many facial deformities. The technique offers unique clinical benefits, which include the possibility of large magnitudes of bone advancement, simultaneous soft-tissue histogenesis and decreased risk of damaging adjacent nerves and tooth buds. Furthermore, DO is less invasive compared to standard Orthognathic surgery, requires shorter operating time, and eliminates donor site morbidity. A limitation of DO is the lengthy treatment protocols. Additional information will allow us to develop strategies to improve the quantity and quality of bone formed during distraction osteogenesis of the maxilla. The clinical benefit will be to have improved healing with a shorter treatment time. The purpose of this study was to establish a porcine model for midface distraction, to study the DO biology of the maxilla and to document the sequence of bone ...
Distraction osteogenesis (DO) is a minimally invasive surgical technique to achieve skeletal expansion and has become the standard treatment method for many facial deformities. The technique offers unique clinical benefits, which include the possibility of large magnitudes of bone advancement, simultaneous soft-tissue histogenesis and decreased risk of damaging adjacent nerves and tooth buds. Furthermore, DO is less invasive compared to standard Orthognathic surgery, requires shorter operating time, and eliminates donor site morbidity. A limitation of DO is the lengthy treatment protocols. Additional information will allow us to develop strategies to improve the quantity and quality of bone formed during distraction osteogenesis of the maxilla. The clinical benefit will be to have improved healing with a shorter treatment time. The purpose of this study was to establish a porcine model for midface distraction, to study the DO biology of the maxilla and to document the sequence of bone formation in the distraction wound. Nine female Yucatan minipigs of mixed dentition were used in the study. All minipigs underwent bilateral maxillary DO under general anesthesia. A Le Fort I (LFI) osteotomy, modified by creation of a posterior vertical osteotomy between the molars rather than separation between the tuberosity and the pterygoid plates, was performed through a standard vestibular incision. A unidirectional, semiburied LFI distractor (Synthes Maxillofacial, Paoli, PA) was used. A protocol of 0-day latency, 1 mm/day rate of distraction for 12 days, and 24 days of fixation was followed. To study the serial healing of the wound, maxillae (n=9) were harvested at end-DO (n=3), mid-fixation (n=3) and end fixation (n=3). These were examined clinically and radiographically. The harvested maxillae were divided in two (between the central incisors) and each of the specimens was further divided into 2 areas of interest (piriform aperture, zygomatic buttress) resulting in a total of 12 specimens at each time point. All harvested specimens (n= 36) were fixed, decalcified, divided in 2 (for coronal and sagittal examination) and embedded in paraffin. All the specimens were sectioned at 5-μm intervals, mounted on fisher-frost slides, and stained with Hematoxyline/Eosin (H&E), TRAP (osteoclasts), collagen II (cartilage), CD 34 (endothelial cells) and PCNA (proliferating cells). Stained slides were examined with light and fluorescence microscopy and images at magnifications x20, x40 and x100 and x200 were taken. Computer histomorphometric analysis was performed using the H&E slides to determine percent surface area of fibrous tissue, proliferating cells, osteoblasts, vessels, mature and immature bone in all groups. In total, 648 photographs (n=216 in each group) were analyzed. Statistical analysis was performed with the two-sample t-test. A porcine model of DO of the maxilla was developed and established. Animals tolerated the procedure, the distraction and consolidation period very well. There were no infections, and no distractors were removed prematurely. Bone formation at the end of fixation period was complete based on clinical, radiographic and histological examination in all specimens. At end-DO group, more cells were noticed close to the natural bone and in the centre of the regenerate. The position of fibrous tissue, new bone islands and cells was parallel to the vector of distraction. By the end of the distraction period there was active proliferation of pro-osteblasts and formation of bone trabeculae in continuation with the edges of the natural bone. At end fixation there was bony union across the gap with few areas of fibrous tissue. Fibrous tissue decreased sequentially in the end-DO, mid-fixation, and end-fixation groups. PCNA index and vessel density were higher at the end-DO group compared to mid-fixation and end-fixation groups. Osteoclasts were more prominent at the end-fixation group. No cartilaginous tissue was revealed in the regenerate with collagen II immunohistochemistry in any group. There was a significantly higher percentage of bone formation in periosteal versus non-periosteal regions at mid-DO and end-DO groups. The anterior half of the distraction wound appeared to have a higher percentage of bone formation than the posterior half in all groups. As with the mandibular wound, intramembranous bone formation seems to be the main mechanism in the maxillary DO: fibrous tissue formation and pro-osteoblast-osteoblast appearance, followed by progressive disappearance of the fibrous tissue and eventual replacement by bone. DO can be performed successfully in the maxilla with zero latency
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