Caroliene Meijndert

117 The effect of implant-abutment connections on peri-implant bone level change Introduction The range of implants used in restorative dentistry has become increasingly sophisticated and, simultaneously, more complex (Buser et al., 2017). The variation has become so large, that it is difficult for clinicians to choose between the available components (Shafie &White, 2014). One of these components is the implant-abutment connection configuration. A clear distinction can be made between external and internal implant-abutment connections. The external connection is used successfully for many years, but it is more susceptible to complications, such as abutment screw loosening (Gracis et al., 2012), bacterial leakage (Steinebrunner et al., 2005) and peri-implant bone loss (Koo et al., 2012), compared to the internal connection. The internal connection category has more geometric variations (Koutouzis, 2019). For example, the internal implant geometry is parallel-walled or conical/tapered. The parallel-walled connection types are often equipped with various indexing/anti-rotational features like an octagon or a hexagon, and exist with a platform switch or a platform match. A conical/tapered connection type implicates a cone-in-cone or has a conical portion in the inner cervical part, with or without indexing features in the apical part (Shafie & White, 2014). All the previous mentioned variations were developed in an effort to reduce mechanical failure (Ceruso et al., 2017) and to minimize crestal bone resorption (Koutouzis, 2019). It is presumed that the long-term survival and success of implant treatment can be affected by peri-implant crestal bone resorption (Schwartz-Arad et al., 2005). This bone resorption can affect the stability of the mucosa, and may therefore affect the aesthetic outcome, which makes the implant-abutment connection particularly interesting in the aesthetic zone (Jemt, 1997; Furhauser et al., 2015; Belser et al., 2009). Eliminating, or at least reducing the amount of bacterial leakage could have a positive influence on peri-implant tissue stability, and thus on the aesthetic outcome. It has been suggested that an internal implant-abutment connection with a conical configuration is the most stable connection, with less bacterial leakage, than the other configurations (Zipprich et al., 2018). In 2018, Caricasulo et al. (2018) performed a systematic review with a meta-analysis, on the difference between conical, internal and external connection configurations. They concluded that significantly less bone loss occurs with conical and internal connections compared to external connections. Although they did not distinguish between platform switching and platform matching, they concluded, after performing an additional analysis, that a platform switch might be of more importance in preserving peri-implant bone levels than the connection configuration itself. The finding that 7