RESUMO
PURPOSE: Marginal bone resorption (MBR) around oral implants may sometimes be a selflimiting condition due to balancing immunological reactions against the utilized materials, rather than a progressive bacterial infection. Contrary to previous assumptions from ligature induced experimental peri-implantitis studies, our recent 8-week experiment showed that marginal ligatures per se trigger an inflammatory immune response, resulting in bone resorption around implants in absence of a plaque. The present study aims to investigate whether this inflammatory/immunological reaction attenuates or progresses toward implant failure after a longer healing time, 12 weeks. MATERIALS AND METHODS: Sterile silk ligatures were placed around the top of titanium (Ti) implants and compressed against the femoral cortical bone plate of 6 rabbits. A non-ligated implant was used as control. After 12 weeks of submerged healing, ground sections of implants and surrounding tissues were investigated with light microscopy. The marginal soft tissues were also analyzed using selected qPCR markers. RESULTS: Histologically, the ligatures were outlined by immune cells, including multinucleated giant cells (MNGC), with adjacent fibrous encapsulation and resorbed peripheral bone that contrasted from the osseointegrated non-ligated control implants. The difference in expression of qPCR markers was not significant, but >2-fold upregulation of markers CD11b, IL1b, ARG1, NCF1, CD4 and >2-fold downregulation of CD8 indicated a mild, focal inflammatory/immune response against the ligatures compared to controls, with upregulation of M1 and M2 macrophages, neutrophils and helper T-cells and downregulation of killer T cells. Further, the bone formation markers OC and ALPL were >2 fold down regulated, consistent with the lack of osseointegration of the ligatures, compared to control implants. CONCLUSIONS: Marginal silk ligatures per se trigger an inflammatory/immune response and aseptic bone resorption around oral implants. Compared to our previous 8-week study, the inflammatory reaction against the silk appears to attenuate with time, with only a mild persisting inflammation that may block osseointegration and instead maintains a fibrous tissue encapsulation type reaction. This may explain why traditional ligature experiments have required regular exchange of ligatures in order for the bone resorption to progress.
