Topical Application of Bisphosphonates to Enhance Alveolar New Bone Formation

Abstract

This PhD thesis is a compendium of three publications, which sets out to broaden our knowledge and understanding of the topical application of bisphosphonates alone or mixed with a bone graft in alveolar bone defects, to evaluate the potential capacity of them to preserve/enhance alveolar new bone formation.

In recent years, research has focused on improving bone substitutes to achieve faster and better regeneration by morphologic and biochemical modification. Bisphosphonates are a group of drugs that reduce bone resorption by inhibiting the formation, recruitment activity of mature osteoclasts; and promoting their apoptosis. In addition, some bisphosphonates enhance osteoblast differentiation and activity. Thence, it has been demonstrated that topical application of a bisphosphonates can minimize the bone resorption following muco-periostial flap surgery or in peri-

implantitis; improve the osteoconductive and regenerative capacity of a biomaterial; prevent the surface resorption of onlay bone grafts; or reduce post-extraction dimensional changes.

Mandibular second premolars (P2) and first molars (M1) were extracted from six Fox-Hound dogs. P2 were categorized as small defects (SD) and M1 as large defects (LD). Four random groups were created: SC (small control defects with MP3®), ST (small test defects MP3® + pamidronate), LC (large control defects with MP3®), and LT (large test defects MP3® + pamidronate). At four and eight weeks of healing the percentages of new bone formation (NB), residual grafts (RG) and connective tissue (CT) were analysed by histology and histomorphometric analysis. To complement the information already obtained from histological analysis, the samples were evaluated through scanning electron microscopy (SEM), and Energy dispersive X-ray spectroscopy (EDX), to identify the chemical elements present into the biomaterial and surrounding tissues, for understanding the biomaterial’s degradation process. The study was complemented with a systemic literature review of the articles published between January 2000 and December 2016, that evaluated in vivo the effects of the topical application of bisphosphonates on bone regeneration/preservation in alveolar defects. A total of 154 abstracts were identified, of which 18 potentially relevant articles were selected; a final total of nine papers were included for analysis. Histomorphometric and histologic analysis of the present pilot study demonstrated that after 4 and 8 weeks of healing, higher new bone formation for test groups (ST and LT) treated topically with pamidronate, compared with SC and LC respectively; residual graft was significantly higher in both control groups (SC and LC) compared to test (ST and LT) groups; and connective tissue percentage was higher in large defects (LC and LT) compared to small defects (SC and ST). SEM analysis revealed more mineralized bone in test groups (ST and LT) compared with control groups, demonstrated by higher percentages of Ca obtained from EDX spectroscopy.

Within the limitations of this experimental study, the findings suggest that porcine xenografts (MP3®) modified with pamidronate favours the new bone formation and increased the porcine xenograft substitution/replacement after 4 and 8 weeks of healing. These results are in accordance with the conclusions obtained from the systematic review. Despite the comparison of the findings of the selected studies was made difficult by the heterogeneity of the articles, the topical application of bisphosphonate solution would appear to favour new bone formation in alveolar defects, and boosts the regenerative capacities of biomaterials resulting in increased bone density.