Background: Dental implants with platform switching design has been demonstrated to reduce marginal bone loss and widely applied in modern implant dentistry. However, its influence on peri-implant soft tissue healing is not clear. The purpose of this study is to investigate whether dental implant with the platform switching design would render significant benefits on peri-implant soft tissue healing after implant uncovery through a 6-week observation.
Methods: Non-smokers with a need of two dental implants in different quadrants were recruited in this randomized, controlled, observational clinical trial. Each individual received 2 implants with the same diameter: One platform switching (PS, test group) and the other platform matching (PM, control group). Two-stage surgical placement protocol was used with traditional healing time for osseointegration. After 2~4 months, all implants were uncovered and connected to the correspondent healing abutments. The probing depth (PD), modified sulcus bleeding index (mSBI), modified plaque index (mPI), and peri-implant crevicular fluid (PICF) were taken at week-1, -2, -4, and -6 after implant uncovery. Moreover, a small piece of peri-implant mucosa (approximate 1×2×2mm) was harvested around the abutments at the time of implant uncovery and at 6-week after uncovery. The expressions of five cytokines, including interleukin-1(IL-1)ß, IL-10, osteoprotegerin (OPG), tumor necrosis factor (TNF)-a, and vascular endothelial growth factor (VEGF), in PICF were analyzed by enzyme-linked immunosorbent assay (ELISA). The expressions of seven genes, including connective tissue growth factor (CTGF), IL-6, C-reactive protein (CRP), OPG, receptor activator of nuclear factor kappa-B ligand (RANKL), periostin, and peroxidasin were analyzed by quantitative polymerase chain reaction (qPCR). A paired samples t-test was used with Pearson correlation and a confidence interval percentage of 95%. The results were considered significant at p-value = 0.05.
Results: 18 subjects were recruited and completed all the sample collections. The clinical measurements, including PD, mSBI, mPI and PICF volume, all showed a significant improvement over time. However, between-group comparisons were only significant for PD at week-1 and -2 as well as mSBI at week-1, -4 and -6. All these significant between-group differences in PD and mSBI were lower in PS group. Regarding cytokine productions in PICF, significant time-dependent reductions were observed in OPG and IL-1ß on both PM and PS sides. Nevertheless, between-group comparisons showed no significant difference of any target cytokine productions at any time points. Likewise, the results of gene expression displayed no significant difference on any targeted genes between PS and PM sides at any time point examined. However, intra-group comparisons showed only PS side with significantly lower levels of IL-6 and CRP genes at week-6 as compared to week-0. Moreover, both PS and PM sides presented significantly higher levels of RANKL, periostin, and peroxidasin genes at week-6.
Conclusion: Within the limits of this study, dental implants with PS design rendered significant benefits over PM implants in terms of PD and mSBI reduction during 6-week healing. However, these benefits could not be reflected in the cytokine and gene expressions because no significant differences were detected between PS and PM sides in this study. It seems that peri-implant soft tissue response around PM and PS implants is mostly similar during the early healing period, especially in respect of cytokine productions and gene expressions.