In vivo osseointegration evaluation of implants coated with nanostructured hydroxyapatite in low density bone

Abstract

Objective: This in vivo study, aimed to biomechanically, histomorphometrically and histologically evaluate an implant surface coated with nanostructured hydroxyapatite using the wet chemical process (biomimetic deposition of calcium phosphate coating) when compared to a dual acid-etching surface.

Material and methods: Ten sheep (2-4 years old) received 20 implants, 10 with nanostructured hydroxyapatite coating (HAnano), and 10 with dual acid-etching surface (DAA). The surfaces were characterized with scanning electron microscopy and energy dispersive spectroscopy; insertion torque values and resonance frequency analysis were measured to evaluate the primary stability of the implants. Bone-implant contact (BIC) and bone area fraction occupancy (BAFo) were evaluated 14 and 28 days after implant installation.

Results: The HAnano and DAA groups showed no significant difference in insertion torque and resonance frequency analysis. The BIC and BAFo values increased significantly (p<0.05) over the experimental periods in both groups. This event was also observed in BIC value of HAnano group. The HAnano surface showed superior results compared to DAA after 28 days (BAFo, p = 0.007; BIC, p = 0.01).

Conclusion: The results suggest that the HAnano surface favors bone formation when compared to the DAA surface after 28 days in low-density bone in sheep.

Fig 1

Surgical procedures to install the implants: (A) Installation of implants in the iliac crest while maintaining the safety distance between them (5 mm). (B) Removal the bone blocks with the implants after 2 and 4 weeks using a trephine drill with a 5mm internal diameter. (C) The iliac crest region after removal of the bone block with the implant. (D) Trephined bone block with the implant.

Fig 2. Histomorphometry for BIC and BAFo analysis.

(A) Histological reconstruction of the implant and adjacent bone. (B) The line of interest for BIC evaluation is shown within the dotted box. In the long axis of the implant, the profile drawing was traced from the first implant thread to the beginning of the fourth thread. The red line denotes BIC. (C) Delineation of the BAFo area of interest. A line identical to the implant profile diagram was duplicated and aligned at 270 μm in the horizontal plane (total area). BAFo was manually determined for further analysis (total area/BAFo; %). Staining with toluidine blue and acid fuchsin was used. Scale bars: 400 μm, A; 100 μm, B and C.

Fig 3

SEM photomicrographs of the surface of (A+B) HAnano and (C+D) DAA implants at 3000× (scale bar = 30 μm; A+C) and 15,000× (scale bar = 5 μm; B+D) magnification.

Fig 4. ITVs (N/cm) of HAnano and DAA surfaces.

The graph shows the distribution of all point values as the mean and 95% CI across five samples.

Fig 5. ISQ values of HAnano and DAA surfaces.

The graph shows the distribution of ISQ values for the HAnano and DAA surfaces measured using two device/transducer pairs across five samples per group. Key: **, 0.002≤p≤0.003.

Fig 6. Representative photomicrographs of the implants at 14- and 28-days post-implantation.

The dashed area is the square magnification. (A+B) DAA and (C+D) HAnano groups 14 days post-implantation. (E+F) DAA and (G+H) HAnano groups 28 days post-implantation. Staining used toluidine blue and acid fuchsin. Scale bar: 400 μm, A, C, E, and G; 100 μm, B, D, F, and H.

Fig 7. Histomorphometric BIC (%) results as a function of the DAA and HAnano surfaces and 14- and 28-day experimental periods.

BIC values are presented as the mean with 95% CI across five samples. Key: *, p = 0.02.

Fig 8. Histomorphometric BAFo (%) results as a function of the DAA and HAnano surfaces and 14- and 28-day experimental periods.

BAFo values are presented as the mean and 95% CI across five samples. Key: **, 0.001≤p≤0.003.