Ridge preservation with magnesium-enriched hydroxyapatite: histological evaluation at different time-points

Background: Ridge preservation has shown to reduce alveolar crest resorption after tooth extraction. Magnesium-enriched hydroxyapatite, due to its chemical properties similar to natural bone, was demonstrated to be suitable for ridge preservation. However, lack of evidence still remains regarding the best timing for implant insertion after grafting. It has been proven that early vascularization and angiogenesis of the material leads to earlier osteogenesis and provides natural bone quality. Caveolin-1 is a protein found in the plasma membrane of vessels which participates in bone metabolism; thus, Caveolin-1 antibody was considered an ideal marker for angiogenesis. Aim: To histologically and immunohistologically analyze the early angiogenesis–osteogenesis interplay in post-extraction ridge preservation using Magnesium-enriched hydroxyapatite to better understand the correct timing for implant insertion. Materials and method: A randomized controlled trial was conducted involving 10 post-extraction sites grafted with Magnesium-enriched hydroxyapatite. Sites were randomly divided in two balanced groups and bone specimens were collected two or four months post-surgery. Sections were stained with hematoxylin/eosin, Masson Goldner trichrome and tartrate-resistant acid phosphatase, respectively. Furthermore, indirect immunohistochemistry was performed using alkaline phosphatase, CD34 and caveolin-1 antibodies. Blind histological and histomorphometric evaluation was undertaken by two independent investigators. Mean values and standard deviations were calculated for each outcome variable. Data were compared using one way ANOVA test. P < 0.05 was considered statistically significant. Results: Ten patients (6 female and 4 male; mean age 53.5 ±16.4 years) were recruited; no drop-out occurred. Histomorphometric analysis presented a 5.1 fold increase in regenerated bone between 2 (15.0% ± 3.5) and 4 months (77.4% ± 8.6) post-surgery (P < 0.001). At the same time, a non-significant reduction in graft material was observed from 21.7% to 11.6%, while the area of connective tissue/marrow spaces reduced significantly from 63.3 % to 11 % (P = 0.003). Caveolin-1 expression in vessel-like structures reduced significantly from 645 (±33) to 255 (± 94) (P = 0.008). Changes in CD34 expression from 301 ± 95 to 88 ± 24 (P = 0.046) confirmed these findings. Conclusions and clinical implications: Within the limits of the present study, histologically it may be concluded that blood vessel density developed in opposite to osteogenesis and that high vascularization after two months could provide a highly accelerated ossification. Thus, clinically, it may be concluded that magnesium-enriched hydroxyapatite is suitable for post-extraction bone crest preservation and ensures early angiogenesis and osteogenesis, suggesting that implant placement could be appropriate even after two months.