Alveolar bone repair with strontium- containing nanostructured carbonated hydroxyapatite

Abstract

This study aimed to evaluate bone repair in rat dental sockets after implanting nanostructured carbonated hydroxyapatite/sodium alginate (CHA) and nanostructured carbonated hydroxyapatite/sodium alginate containing 5% strontium microspheres (SrCHA) as bone substitute materials. Twenty male Wistar rats were randomly divided into two experimental groups: CHA and SrCHA (n=5/period/group). After one and 6 weeks of extraction of the right maxillary central incisor and biomaterial implantation, 5 μm bone blocks were obtained for histomorphometric evaluation. The parameters evaluated were remaining biomaterial, loose connective tissue and newly formed bone in a standard area. Statistical analysis was performed by Mann-Withney and and Wilcoxon tests at 95% level of significance. The histomorphometric results showed that the microspheres showed similar fragmentation and bio-absorbation (p>0.05). We observed the formation of new bones in both groups during the same experimental periods; however, the new bone formation differed significantly between the weeks 1 and 6 (p=0.0039) in both groups. The CHA and SrCHA biomaterials were biocompatible, osteoconductive and bioabsorbable, indicating their great potential for clinical use as bone substitutes.

Figure 1. XRD pattern of CHA and SrCHA. The peaks of SrCHA are narrower than those of CHA, indicating low cristallinity for SrCHA when compared to the CHA group

Figure 2. Infrared Fourier transform spectrum of CHA and SrCHA. We observed major bands regarding phosphate and carbonate groups, a characteristic of carbonated hydroxyapatite. Presence of water bands, indicating the material is not ceramic (regions 867, 868, 1415, 1425, and 1482 cm⁻¹)

Figure 3. Representative photomicrographs of alveolar socket after 7 days. A and B: CHA group and C and D: SrCHA group. In A and B: presence of connective tissue surrounding the biomaterial (BM) microsphere and peripheric newly formed bone (NFB). C and D: presence of newly formed bone surrounding the connective tissue area, containing particulate biomaterial with peripheric osteoid (#). Square with 40-fold magnification taken from A and C, respectively. NFB: Newly Formed Bone; BM: Biomaterial; CT: Connective Tissue; #: Osteoid. Hematoxylin and eosin stained. Bar: A and C: 100 μm; B and D: 50 μm

Figure 4. Representative photomicrographs of alveolar socket after 42 days. A and B: CHA group and C and D: SrCHA group. A and B: observe the presence of newly formed bone (NFB) with osteocytes (arrow) and osteoblastic paving (*) permeated by fibrocellular connective tissue (CT), with few inflammatory cells and absence of biomaterial (BM). C and D: presence of new-formed bone with connective tissue at the surroundings containing fragmented biomaterial and peripheric osteoid (#). A and C: 20-fold magnification and B and D: square with 40-fold magnification taken from A and C, respectively. BM: Biomaterial, NFB: Newly Formed Bone, CT: Connective Tissue; #: Osteoid, *: Osteoblasts. Hematoxylin and eosin stained. Bar: A and C: 100 μm; B and D: 50 μm

Figure 5. Volume density of the remaining biomaterial in the dental alveolus after 1 and 6 weeks of implantation. The values were similar for both groups in both experimental periods. We observed no significant difference between groups. Results are shown as mean percentages ± confidence intervals (vertical bars)

Figure 6. Volume density of connective tissue in the tooth socket after 1 and 6 weeks of implantation. The values were similar for both groups in both experimental periods. We observed no significant difference between groups. Results are shown as mean percentages ± confidence interval (vertical bars)

Figure 7. Volume density of newly formed bone. The quantity of newly formed mineralized tissue was similar in both groups in both experimental periods. However, we observed more newly formed bone at 6 weeks than at 1 week. The horizontal lines between bars indicate significant differences between groups (p<0.05). Results are shown as mean percentages ± confidence interval (vertical bars)