Caroliene Meijndert

129 The effect of implant-abutment connections on peri-implant bone level change the aesthetic region, only 1 RCT (Cooper et al., 2019) was set up in the anterior maxilla and reported no statistically significant differences between the 3 connection types concerning mid-buccal mucosa changes. The overall mid-buccal retractions in both the PS-conical, PS-parallel and PM-parallel groups were small and the differences were negligible. Although there are statistically significant differences between the abutment connection configurations, all three types’ clinical and radiographic results are good. All the reported bone loss, implant loss and mid-buccal mucosa level change results are within the range of what is deemed acceptable. However, long term stability is important, especially the durability of an aesthetically good result, hence the authors favoured the internal connections with a platform switch over the connections with a platform match. Yet, the included studies only had a relatively short follow-up (mostly 1 year) and since the tissues around implants change continuously, albeit only a little, it would be useful to re-evaluate the previous statement when more long-term studies are available. Strength and limitations The strength of this meta-analysis is the broad and detailed literature search in multiple databases. A limitation to this study is that the quality of the reporting in the included studies was weak and the median follow-up time was short (1 [1;5] year). Also, the meta- analysis was done for variables that can be measured in many ways (in particular bone level change and mucosa level change) and are subject to confounding factors (such as surgical and restauration protocol and implant geometry) and was thus subject to heterogeneity, which means that the outcome must be viewed with caution. Another limitation is the decision to calculate annual bone loss, annual implant loss and annual mucosa change rates which, although good for comparability purposes, resembles a linear relation that assumes that the same quantity of bone, implants or mucosa is lost every year. Yet, in real life, most remodelling takes place in the first year, and only a few changes in the years thereafter. We accepted this limitation in order to perform a meta-analysis and this approach is commonly accepted in the dental implant literature, but one should still interpret the results with caution. Recommendations for future research Due to a lack of well-designed RCTs and high quality studies, additional well designed studies are needed to be able to truly rate the effect of different implant-abutment connections in the aesthetic zone. We therefore encourage efforts to come to a 7