| Objective This study aimed to investigate the feasibility of the surgical model of nonvascular transport distraction osteogenesis (NTDO) for reconstructing extensive canine mandibular marginal partial defects and its potential osteogenesis mechanism, and the effectiveness of quantitatively evaluating bone regeneration using in vivo sequential tetracycline labeling and bone scintigraphy.Materials and Methods Eight adult mongrel dogs were selected for this study. A 10.0-mm in length by 10.0-mm in height marginal partial bony defect was intentionally created on their right inferior mandibles. Then a 20.0-mm in length by 10.0-mm in height free nonvascular transport proximal to the defect was prepared, and a custom-made distracter was attached to the buccal side as a surgical model of NTDO. After 5-day latency, the devices were activated at a rate of 1.0 mm per 24h until confronting resistance. The subjects were randomized into 2-week,4-week,8-week and 14-week consolidation groups with 2 dogs in each based on postoperative consolidation. Sequential radiological records were taken as planned. And all the subjects accepted in vivo sequential tetracycline labeling as planned. The specimens of both regenerated bone and transport were harvested and prepared into undecalcified ground sections after sacrifice. The histomorphometric feature of both tissues was analyzed under fluorescence microscope. Ten mostly-labeled intact haversian systems of inner regenerated bone of 14-week group were selected for quantitative evaluation. Both mineral apposition rate (MAR) and bone formation rate (BFR) were statistically compared among labeling increments. One dog of 14-week group was randomized to undergo bone scintigraphy at 2-week,4-week, and 8-week and 14-week consolidations, respectively. The nuclide uptake ratios (URs) of both buccal and lingual regenerated bone at different consolidations were assessed by the technique of region of interest (ROI) to determine their osteogenesis activity.Results All the subjects survived the whole experiment uneventfully. With consolidation ongoing, radiographic records demonstrated increased translucency of the regenerated tissue in the distraction gap. The regenerated tissue gradually formed, then calcified, then matured and finally remodeled itself, which conformed to the process of intramembranous ossification. The bone regeneration at the superior, inferior, lingual and proximal sites of distraction gap was always better than that at the buccal and distal sites. The number of tetracycline labeling bands increased with its maturation since mineralization. The haversian systems of inner mature lamellar bone of 14-week group were mostly labeled with five bands, consisting of total 4 intact labeling increments between every two neighboring labels. Both MAR and BFR of the 1st increment were significantly larger than those of the 2nd,3rd, and 4th increments, respectively (P<0.05). Both parameters of the 2nd increment were significantly larger than those of the 3rd and 4th increments, respectively (P<0.05). And both parameters of the 3 rd increment had no statistically significant difference with the 4th increment (P>0.05). A layer of new bone was regenerated surrounding the surface of transport as sleeve during distraction. And then it rapidly experienced centripetal bone absorption, substitution and reformation during ensuing consolidation. Both URB and URL declined promptly with consolidation. However, URL was always larger than URB at all time points. There were statistically significant differences in URB between every two remaining groups and in URL between every two groups (P<0.05), except for no difference in URB between 2-week and 4-week consolidations (P=0.148).Conclusion The surgical model of NTDO was feasible. Both in vivo sequential tetracycline labeling and bone scintigraphy could be effectively applied to quantitatively evaluate bone regeneration. Nonvascular transport could successfully induce bone regeneration in distraction gap under the combined action of multiple factors. The sequential formation, calcification, maturation and remodeling of regenerated bone was of intramembranous ossification. It might act as a primer to stimulate continual new bone formation surrounding itself during distraction, which might take the dual mechanical and biological barrier actions for regeneration zone, and guarantee the rapid creeping substitution of transport itself during consolidation. The processes of both bone regeneration in the gap and transport remodeling still closely associated with regional vascularity. NTDO might be a new distraction osteogenesis model with the histogenesis of predominant intramembranous ossification and combining creeping substitution. |
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