Caroliene Meijndert

10 Chapter 1 Implant design Originally, most of the implant designs were cylindrical with parallel walls to enable a maximum contact area with the surrounding bone. In addition to the cylindrical shaped implant, a tapered shaped implant design was introduced that resembles a more natural root shape. An alleged benefit of a tapered implant design is improved primary stability compared to parallel-walled implants. Which is achieved due to the self-tapping property combined with under-drilling during the osteotomy (Sugiura et al., 2019; Atieh et al., 2018). Furthermore, it is said that there is less risk of bone fenestrations in bony undercut cases, especially at the apical part of the tapered implants, as is often present with maxillary alveolar processes (Atieh et al., 2018). A more detailed aspect of the implant design is the implant-abutment connection. To respect the biological width, the implant-abutment interface of some brands were initially placed at tissue level, away from the bone crest (Buser et al., 1990). Later on, there was a shift from tissue level to bone level implants. Bone level implants allow the practitioner to create a natural emergence profile with individually designed abutments, to fit each individual patient. Such a natural emergence profile can enhance the aesthetic outcome, which is particularly important in the aesthetic zone (Chappuis et al., 2016; Siebert et al., 2018). However, inherent to this approach is that the microgap between the implant and abutment is located at bone level. The microgap between the implant and abutment can be a source of bacterial colonisation and the presence of an abundance of bacteria can trigger an inflammatory response. This in turn, will lead to bone resorption around the implant (Romanos et al., 2016; Yu et al., 2020). Implant-abutment connection Various connection types have been developed in an effort to reduce the microgap between the implant and abutment, and thereby to minimize crestal bone resorption (Koutouzis, 2019). This bone resorption can potentially affect the stability of the mid- buccal mucosa and thus affect the aesthetic outcome, which is particularly harmfull in the aesthetic zone (Fürhauser et al., 2005; Belser et al., 2009; Jemt, 1997). A clear distinction can be made between external and internal implant-abutment connections. The external connections have been used successfully for many years, but are 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 internal connections. Within the internal connection category, there are various geometric variations (Koutouzis, 2019). The internal implant geometry can be parallel-walled or conical/tapered, and is equipped with a platform