Histological and Histomorphometrical Evaluation of Postextractive Sites Grafted with Mg-Enriched Nano-Hydroxyapatite: A Randomized Controlled Trial Comparing 4 Versus 12 Months of Healing

Background: Tooth extraction generally results in an alveolar bone loss and structural changes in the overlying soft tissue. The amount of this relocation might jeopardize prosthetically driven implant placement. Thus, there is a high interest in techniques, materials and timing to minimizing tissue resorption, using postextraction ridge preservation procedures. Purpose: To assess by histological techniques, the outcomes of a socket preservation technique at 4 or 12 months after treatment with a magnesium-enriched hydroxyapatite (Mg-e HA). Materials and Methods: Postextraction site in 20 patients underwent ridge preservation procedure. Mg-e HA granules were mixed with blood and grafted into the socket. A bone specimen was collected from each site before implant placement after 4 or 12 months randomly. Each biopsy was processed for undecalcified histological analysis. All ground sections were observed under light and polarized microscope. A semi-quantitative analysis by mean of stereological method was performed to evaluate the average volume fractions of bone, biomaterial and medullary spaces, and the percentage of blood vessels for both timepoints. Nonparametric Mann-Whitney U test for unpaired data was used to detect eventual statistical differences between groups. Results: Histologically, the biomaterial appeared surrounded by newly formed bone in both groups without inflammatory infiltrate. At 4 months, the remodeling process of collagen matrix was starting from the apical portion toward coronal direction and was more active around grafted particles. At 12 months, the alveolar socket was completely regenerated and filled with mineralized and well-organized bone tissue around the residual biomaterial particles. In both groups, vessels were present to supply tissues around the graft (at 4 months: 4.95%+/-2.49; at 12 months: 7.45%+/-2.57). Tissue fractions at 4 versus 12 months were respectively: 31.85%+/-6.99 versus 41.32%+/-9.37 for bone (p =.021), 40.82%+/-6.71 versus 26.28%+/-11.49 for residual Mg-e HA (p =.009), and 27.33%+/-7.72 versus 32.40%+/-9.87 for medullary spaces. Conclusion: Data from the present study show that Mg-e HA allows the complete healing of the tissue. Additionally, graft material demonstrated to undergo significant resorption during the experimental time frame.