Osteogenic marker expression in a grafted bone healing sheep model
Objectives: Successful healing of alveolar sockets after tooth extraction ensures positive outcomes for tooth replacement options. Using a sheep model the expression levels of key osteogenic markers for healing were compared over 16-weeks for empty and grafted sockets. Methods and Materials: First, second and third premolars were extracted from 30 sheep. The socket was either non-grafted for spontaneous healing (control) or grafted using Bio-Oss® and Bio-Gide® (test). After 4-, 8- and 16-weeks the sheep were euthanised and tissue samples collected. Histological analysis was undertaken and cellular localisation of receptor RANK, and ligands RANKL and OPG was determined using immunohistochemistry. mRNA expression levels for RANK, RANKL, OPG, Col1A1, TIMP3, Sp7 and Msx2 were determined using SYBR green RT2-qPCR assays. Results: Overall, more new woven bone was present in the test group compared to the control at all time points. Moderate immunopositive staining of RANK was associated with osteoblasts and osteoclasts in both groups at 4 weeks; with stronger osteoclast-associated staining in the test group at 8- and 16-weeks. Strong staining of RANKL associated with osteoblasts and osteoclasts was found in both groups at all time points. Initial strong OPG staining localised to the connective tissues decreased over time. Similar levels of mRNA expression in both groups for all seven osteogenic genes was found. The exception was RANK with expression levels lower in the test group compared to the control group at 4-weeks (P = 0.02). Sp7 was also expressed significantly lower in test group at 16-weeks (P = 0.04). Conclusion: Histologically more woven bone was present in test sockets likely due to the lower level of RANK expression resulting in decreased osteoclastic activity. There was, however, no statistically significant difference in the expression of the key markers of osteogenesis, RANKL and OPG between empty and grafted sockets at any time over the 16‑week period. There was also no difference in the expression of the transcription factor for osteoblast differentiation MSX2 or the ECM markers Col1A1 or TIMP3. Although Bio-Oss® is not osteoinductive it has osteoconductive and scaffolding properties, playing a role in alveolar ridge preservation and therefore, its use should be continued.
Advisor: Milne, Trudy; Coates, Dawn; Duncan, Warwick
Degree Name: Doctor of Clinical Dentistry
Degree Discipline: Oral Sciences
Publisher: University of Otago
Keywords: Alveolar ridge preservation; RANKL; RANK; OPG; Sp7; TIMP3; Msx2; Col1A1; Bio-Oss(R); Bio-Gide(R); Immunohistochemistry; qPCR
Research Type: Thesis