UCLA

Background: Peri-implantitis is an inflammatory disease process that presents with bone loss around implant fixtures. Without the proper treatment, it can lead to the eventual loss of the implant. However, controversy lies over the effectiveness of treatment modalities as the criteria for disease diagnosis and success of treatment varies in the literature. With an increasing global burden of disease comes incentive to find predictable treatment options for peri-implantitis. Wnt4 has been shown in prior studies to attenuate osteoporotic bone loss and prior studies in our lab using a murine model for peri-implantitis, found transgenic Wnt4 mice to exhibit the same pattern of attenuated bone loss in the maxilla.

Objective: To identify whether experimental recombinant Wnt4 (rWnt4) injection shows attenuated bone loss compared to a control PBS injection, in a murine model of ligature induced peri-implantitis.

Methods: Four-week-old male C57BL/6J mice had their left maxillary molars extracted. Following eight weeks of healing, titanium implants were placed in the extraction sites and allowed to integrate for four weeks. After osseointegration, evaluated by presence and lack of mobility in the implants, a 6-0 ligature was tied under the head of the implant in half of the mice to induce peri-implantitis. Half of the mice did not receive ligature placement around the implants. Each group was then divided again to either receive daily control PBS injections or experimental rWnt4 injections intraperitoneally for 30 days. Four weeks after ligature placement and daily injections, the mice were sacrificed. The maxillae were imaged using micro-computerized tomography (μCT) scanning and linear and volumetric bone loss were analyzed. Tissues from the representative samples (based on proximity to mean measurements) were stained with hematoxylin and eosin (H&E), Picrosirius Red for collagen, and Tartrate Resistant Acid Phosphatase (TRAP) for osteoclasts. Immunohistochemistry (IHC) was also performed and analyzed for NF-κB, MMP-9, and Cox-2.

Results: Clinically, four weeks after ligature placement there was increased soft tissue edema present around implants from the ligature induced peri-implantitis group compared to the no-ligature group. Radiographically, linear bone loss analysis showed statistically greater bone loss in the ligature compared to no ligature group for both the PBS and rWnt4 injection groups. The same finding was observed for the volumetric bone loss analysis around implants. There was no statistical difference found in bone loss between the rWnt4 injected groups compared to PBS injections for both the ligature and no ligature groups. TRAP staining for osteoclasts showed statistically greater numbers of osteoclasts in the PBS injection ligature group compared to PBS injection no ligature group. Picrosirius red staining showed more organized collagen fibril distribution in rWnt4 ligature vs. PBS ligature groups. There was also a decreased amount of immunoreactivity for MMP-9, NF-κB and Cox 2 on IHC staining for the rWnt4 ligature group compared to the PBS ligature group.

Conclusion: The findings from this research study validate the ligature-induced peri-implantitis murine model and show that ligature samples have greater tissue and bone loss, making this an ideal animal model to study this disease process. Although the bone loss exhibited by rWnt4 injections was not statistically significant, it provides a preliminary framework for future studies of Wnt4 effects on bone metabolism in the maxilla. The decreased amount of immunoreactivity shown in IHC staining of MMP-9, NF-κB and Cox-2 show a positive effect of decreased inflammatory response in the soft tissues surrounding implants in the injected rWnt4 injection groups, which could be translated to the treatment of peri-implant mucositis. Given that there was a decrease in inflammatory markers, a dose response study may allow us to identify a Wnt4 dose that has a positive therapeutic effect on peri-implantitis, which could be further translated to the treatment of peri-implantitis in humans.