Influence of Simvastatin-Strontium-Hydroxyapatite Coated Implant Formed by Micro-Arc Oxidation and Immersion Method on Osteointegration in Osteoporotic Rabbits

Abstract

Purpose: Enhancing osteointegration of implants in osteoporosis patients is a necessity since implantations frequently fail in these patients. The aim of this work is to study how simvastatin-strontium-hydroxyapatite coated implants perform in rabbits with osteoporosis.

Materials and methods: Crystalline HA and Sr-HA oxide film were prepared through micro-arc oxidation. Surface characterization including morphology, roughness, element composition, phase composition, hydrophilicity were then evaluated. Simvastatin loaded on porous films through immersion, and the effects of coatings on osteointegration in osteoporotic rabbits were investigated. All samples were obtained after 4, 8 and 12 weeks of healing. Some of them were subjected to biomechanical tests and others were subjected to histological and histomorphometric analysis.

Results: Coatings exhibited a microporous network structure with appropriate roughness and high hydrophilicity. Compared to control HA and machined surface implants, simvastatin-Sr-HA coated implants exhibited marked improvements in osteointegration, which is characterized by a quicker mineralization deposition rate, good bone formation mode (large amount of contact osteogenesis and a small amount of distance osteogenesis) and increased bone-to-implant contact and pull-out strength.

Conclusion: These biological parameters demonstrate the excellent osteoconductivity of simvastatin-Sr-HA coatings in the osteoporotic state. Overall, this suggests that simvastatin-Sr-HA coatings would be applicable in poor-quality bones of patients experiencing osteoporosis.

Keywords: dental implants; micro-arc oxidation; osteointegration; osteoporosis; simvastatin; strontium.

Figure 1

Implantation procedure and X-ray after implantation in osteoporotic rabbits. (A): Implantation procedure includes: a, skin preparation, b, incision, c, site determination, d, implant hole preparation, e, implantation holes, f, insertion of implants, g, cover screw, h, layered sutures, I ECG monitoring. (B): X-ray after implantation of group a, b and c. X-rays showed that the two implants in each tibia were relatively parallel. No fractures occurred at implant sites and no bone resorption was noted.

Figure 2

Characterization analysis of groups A, B and C. A machined surface group; B MAO group; C Sr-MAO group. (A) SEM images. (B) EDS spectra and percentages of elements. (C) Contact angles of each group. (D) Histograms of roughness in each group. *means that P < 0.05 when compared with group A, a means that P < 0.05 when compared with group B. (E) XRD spectra of group B and C.

Figure 3

Histogram of maximum pull-out force at different periods in each group. A machined surface group; B MAO group; C MAO-Sr-simvastatin group. *P < 0.01 compared with the earlier period, ^#P < 0.01 compared with the control group in the same period.

Figure 4

Fluorescence observation and MAR. A: machined surface group, B: MAO group, C: MAO-Sr-simvastatin group. a, the micro-threaded neck of implant (mainly cortical bone) and b, the body part of the implant (cancellous bone). (1) week 4. (2) week 8. (3) week 12. (4) Histogram of MAR (the average distance between the double fluorescent bands/10d) at different periods in each group. *P < 0.01 compared with the earlier period, ^#P < 0.01 compared with the control group in the same period, ^※P<0.05 compared with the control group in the same period.

Figure 5

Histological examination and BIC (Bone contact length with implant/total implant length). A: machined surface group, B: MAO group, C: MAO-Sr-simvastatin group. a, the micro-threaded neck of implant (mainly cortical bone) and b, the body part of the implant (cancellous bone). (1) week 4. (2) week 8. (3) week 12. (4). Histogram of BIC at different periods in each group. *P < 0.01 compared with the earlier period, ^#P < 0.01 compared with the control group in the same period.