Evaluation of a nanohydroxyapatite covered implant surface: study in rats exposed to cigarette smoke

Background Modifications on titanium implants (changes in design, in surface and addition of biological compounds) may improve the bone to implant contact. Previous studies have shown that the addition of nanohydroxyapatite to the implant surface may contributing to the acceleration of bone healing. Smoking is a challenging situation, negatively affecting the osseointegration process- nicotin reduces osteogenic activity, increases periodontal and periimplant bone loss and may lead to implant failure. Aim/Hypothesis The purpose of this study was to evaluate, in rats exposed to cigarette smoke (as a model of deficient bone repair), a new implant surface modified by the addition of nanohydroxyapatite, through microtomographic analysis. Material and Methods Mini implants (machined, double acid etched and nanohydroxyapatite surfaces) were installed in the tibias of rats submitted to cigarette smoke inhalation (n = 36). The animals were randomly divided into three experimental groups of twelve rats each- G1(MA), machined implants, G2(AE), acid etched implants, and G3(NH), nanohydroxyapatite covered implants. The animals were sacrificed 7 (7 days) and 30 (30 days) days after implants placement (18 animals by period, 6 from each group). The tibias were removed for evaluation. Microtomographic Bone to Implant Contact (IS TS, in %), Bone Volume Fraction (BV TV, in %), Trabecular Number (Tb.N) and Trabecular Thickness (Tb.Th) were measured. These parameters evaluated the bone characteristics between the threads and outside the threads (adjacent bone). Inter-group differences were assessed by ANOVA + Tukey tests, intra-group differences (between threads bone vs. adjacent bone) was analyzed by the Mann-Whitney test (for all comparisons P < 0.05). Results For the bone between threads, IS TS showed statistically significant differences between G1 (MA) 7 days (24.50 ± 10.42) versus G3 (NH) 7 days (38.08 ± 15.04) and between G1 (MA) 7 days (24.50 ± 10.42) versus G1 (MA) 30 days (35.23 ± 6.34), for BV TB, there were significant differences between G1 (MA) 7 days (24.32 ± 9.20) versus G3 (NH) 7 days (38.79 ± 19.93), for Tb.Th, there were significant differences between G1 (MA) 7 days (0.025 ± 0.003) versus G2 (AE) 7 days (0.030 ± 0.003), between G1 (MA) 7 days (0.025 ± 0.003) versus G3 (NH) 7 days (0.030 ± 0.004) and between G1 (MA) 7 days (0.025 ± 0.003) and G1 (MA) 30 days (0.029 ± 0.003). For the adjacent bone, the inter-group differences were statistically significant only for the parameter Tb.Th, between G1 (MA) 7 days (0.026 ± 0.002) versus G2 (AE) 7 days (0.031 ± 0.001) and between G1 (MA) 7 days (0.026 ± 0.002) versus G3 (NH) 7 days (0.030 ± 0.004), there were no intra-group significant differences. Conclusions and Clinical Implications Microtomographic analysis showed that the implant surface, modified by the addition of nanohydroxyapatite, presented better results in rats submitted to cigarette smoke, especially at the earliest evaluation time (7 days) and mainly when compared to the machined surface.