The Influence of Nanostructured Hydroxyapatite Surface in the Early Stages of Osseointegration: A Multiparameter Animal Study in Low-Density Bone

Abstract

Background and objective: The success rates of dental implants in low-density bone have been reported as a challenge, especially for early or immediate loading in the maxilla posterior area. Nanoscale architecture affects the roughness, surface area, surface energy of the implant and can enhance osseointegration. This study aimed to evaluate the implant-surface topography and biomechanical, histomorphometric, and histological bone responses to a new nanostructured hydroxyapatite surface placed in the iliac crest of sheep.

Methods: Ten female sheep (2-4 years) received 30 implants (n=10/group): HAnano^® coated (Epikut Plus^®, S.I.N. Implant System, Sao Paulo, SP, Brazil), SLActive (BLX^®, Straumann, Basel, Switzerland), and TiUnite (NobelActive^®, Nobel Biocare, Göteborg, Sweden) surfaces. Scanning electron microscopy with energy-dispersive spectroscopy evaluated the implant surface topography, the insertion torque value, and resonance frequency analysis evaluated the primary stability, bone-implant contact, and bone-area fraction occupancy were evaluated after 14 and 28 days after implant placement.

Results: The surface morphology was considerably comparable between the implant groups'; however, the TiUnite^® group presented a remarkable different surface. The SLActive^® and TiUnite^® groups presented an insertion torque average of 74 (±8.9) N/cm that was similar to that of HAnano^® 72 (±8.3) N/cm (p >0.05). The resonance frequency evaluated with Osstell^®/SmartPeg^® or Penguin^®/MulTipeg^® showed similar results when assessing implants from the same group. BIC and BAFO significantly increased (p<0.05) throughout the experimental periods to all groups, but BIC and BAFO values were similar among the implants at the same time point. After 4 weeks, bone-implant contact was higher than 80% of the total length analyzed. New bone occupies around 60% of analyzed area around the implants.

Conclusion: HAnano^® coated surface promoted comparable osseointegration as SLActive and TiUnite in the sheep model. The three tested surfaces showed comparable osseointegration at the early stages of low-density bone repair in the sheep model.

Keywords: bone response; dental implant surface; hydroxyapatite; nanotechnology; osseointegration; sheep.

Figure 1

Surgical procedures for implant’s installation of the 5 implants. (A) Implants installed in the iliac crest with a minimum distance of 5 mm between each implant; (B) after 2 and 4 weeks, the implants were trephined with a trephine drill (internal diameter = 5 mm) to remove the bone block containing the implant; (C) bone defects after the removal of the bone blocks and (D) bone block trephined with implant inside.

Figure 2

Histomorphometry for bone-implant contact and (BIC) and bone area formation (BAFO) analysis. (A) Histological reconstruction of the implant and adjacent bone area; (B) determination of the line of interest for BIC; in the long implant axis, the implant profile design was drawn from the first thread of the implant to the beginning of the fourth thread (yellow line) and direct bone-implant contact (red line); (C) determination of the area of interest for BAFO. An identical line of implant profile design was duplicate and aligned at a distance of 270 µm at the horizontal plane (total area); (D) the bone area formation (BAFO) manually determinates for posterior analysis (total area/BAFO) (%). Stain: Toluidine Blue and Acid Fuchsin stained. Scale bar: (A) 400µm; (B,C and D) 200µm.

Figure 3

Scanning electron microscopy (SEM) micrographs of implants surface. (A and B) Hanano; (C and D) SLActive, and (E and F) TiUnite. (A, C and E) at 3000× magnification (scale bar = 30 μm) and (B, D and F) 15,000 x magnification (scale bar = 5 μm).

Figure 4

Implant stability quotient (ISQ) values of different implant surfaces. The devices and transducers grouping used were Osstell/Smart Peg (measured as implant stability quotient, ISQ) and Penguin/Multi Peg (measured as resonance frequency analysis, RFA). The graphic shows the distribution of all point values for different surfaces (HAnano, SLActive and TiUnite) with different devices and transducers grouping (n=5). After the normality test (Shapiro–Wilk), the values were transformed in LOG (Y). The groups were submitted to statistical analysis of Two-way ANOVA and Tukey post-test to evaluate the differences between different surfaces with the same device/transducer (p<0.05). The Student’s t-test was applied to assess the differences between the device/transducer at the same implant surface (p<0.05); * (p<0.05), ** (p<0.01), and **** (p<0.0001).

Figure 5

Insertion torque values (N/cm) of different implant surfaces (HAnano^®, SLActive^® and TiUnite^®). The graphic shows the mean values and the confidence interval at 95% of different groups (n=5), the values were transformed in LOG (Y) . The groups were submitted to statistical analysis of one-way ANOVA and Tukey post-test to evaluate the differences between surfaces (p<0.05). There were no differences in the insertion torque between implant surfaces.

Figure 6

Representative photomicrographs of wound healing to different implant surfaces 14 days after implantation. (A) HAnano^®, (B) SLActive^®, and (C) TiUnite^®. Observe the three most coronally situated implant’s threads that were located in the cancellous bone. The yellow arrows represent regions of bone-implant contact. Stain: Toluidine Blue and Acid Fuchsin stained. Magnification: 20×; Scale bar: 100µm.

Figure 7

Representative photomicrographs of wound healing to different implant surfaces 28 days after implantation. (A) HAnano^®, (B) SLActive^® and (C) TiUnite^®. Observe the three most coronally situated implant’s threads that were located in the cancellous bone. The yellow arrows represent regions of bone-implant contact. Stain: Toluidine Blue and Acid Fuchsin. Magnification: 20×; Scale bar: 100µm.

Figure 8

Polarization light microscopy. (A–C) HAnano^® group; (D–F) SLActive^® group, and (G–I) TiUnite^® group. (A, D and G) bright filed microscopy; (B, E and H) Polarization light microscopy; (C, F and I) polarization light microscopy with compensator crystal (λ = 551 nm). The general orientation of bone collagen fibers is easily seen when using polarization light microscopy. Blue in the figure means that fibers are parallel to the higher refraction index of the compensator.

Figure 9

Bone-implant contact (BIC) percentage in the HAnano^®, SLAactive^®, and TiUnite^® surfaces groups, 14 and 28 days after implantation. The results are presented as a mean ± confidence interval (n=5). After the normality test (Shapiro–Wilk), the groups were submitted to statistical analysis of One-way ANOVA and Tukey post-test (p<0.05) to evaluate the differences between different surfaces at the same experimental time point. The Student’s t-test was applied to assess the differences between the same surface groups at different time points (p<0.05), represents by the (*, p=0.02), (**; p=0.008). There were no differences in the BIC between implant surfaces at the same time point.

Figure 10

Bone area fraction occupancy (BAFO) percentage in the HAnano^®, SLAactive^® and TiUnite^® surfaces groups, 14 and 28 days after implantation. The results are presented as a mean ± confidence interval (n=5). After the normality test (Shapiro–Wilk), the groups were submitted to statistical analysis of One-way ANOVA and Tukey post-test (p<0.05) to evaluate the differences between different surfaces at the same experimental time point; represents by horizontal bars. The Student’s t-test was applied to assess the differences between the same surface groups at different experimental time points (p<0.05), represents by the (**; p ranging from 0.001 to 0.009). There were no differences in the BAFO between implant surfaces at the same time point.