Histomorphometric and microtomographic evaluation of hydroxyapatite coated implants and L-PRF in over drilled bone sites in sheep.

Hydroxyapatite used as a coating for titanium dental implants reduces the time required for osseointegration. Platelet-rich fibrin (L-PRF) releases growth factors and cytokines, enhancing tissue healing and bone regeneration. This study aimed to evaluate histologically, histomorphometrically, and by microcomputed tomography an implant surface coated with nanostructured hydroxyapatite (HAnano), in comparison with a double acid-etched (DAA) surface, both with and without peri-implant grafting with L-PRF, installed in over-instrumented sites in a low-density bone. Five adult sheep (2-4 years old) received twenty 3.5 × 10 mm implants in the iliac crest. Bone-to-implant contact (BIC) and bone-occupied area fraction (BAFo) were evaluated histomorphometrically after an 8-week experimental period. Brown-Forsyth analysis of variance (ANOVA) and Welch's ANOVA test did not identify significant differences between the experimental groups. On average, BIC ranged from 44% (HAnano + L-PRF) to 63% (DAA + L-PRF). µCT analysis revealed that bone volume density in the peri-implant region ranged from 26% (HAnano + L-PRF) to 39% (DAA). No statistically significant differences were observed between the groups. Both implant surfaces studied allowed osseointegration in low bone density sites, independently of peri-implant grafting with L-PRF, after 8 weeks of implantation. While this model provided controlled conditions for evaluating early-stage osseointegration, the absence of functional loading and the relatively short follow-up period should be considered when extrapolating the findings to clinical applications. Future studies should assess these variables under load-bearing conditions with extended observation periods. All the sheep in this study remained alive.