Diederik Hentenaar

129 Influence of the cervical crown contour INTRODUCTION Preservation of peri-implant marginal bone and maintaining healthy soft tissues are important for long-term implant success. However, this success can be influenced by a variety of prosthetic aspects. For example implant-abutment connection type, platform- switched or matched connections, screw-retained or cement-retained restorations, occlusal prosthesis design, implant-crown micro-gap level or abutment material, height and surface texture can be local predisposing factors that contribute to peri- implant disease (i.e. peri-implant mucositis and peri-implantitis) (1-9). In general, it is recommended that implant suprastructures should be designed in such a way that oral hygiene measures can be performed effectively, plaque accumulation is prevented and implants are accessible for probing (10). Early studies on subgingival crown contour and overhangs of restorations on natural teeth showed that when the crown contour is overly thick because of excessive bulk of tooth structure or restorative material, the free marginal gingivae are crowded, circumferential fibers are torn, and the gingival tissues are pushed beyond their physiologic limits of accommodation (11). Leading to increased plaque accumulation, gingival swelling and a detrimental effect on gingival health and marginal bone loss (12-17). However it is unclear whether this also applies to dental implant suprastructures. To date, no studies have been conducted on how to design the crown contour in terms of emergence angle and emergence profile with respect to preserving marginal bone level and peri-implant soft tissue, despite publication of prosthetically focused studies which mainly concern aesthetic outcome (15,18,19). Only one study thus far has focused on the implant crown contour (20). However, a heterogenic dataset consisting of several implant brands, with anterior and posteriorly placed, non-platformed switched, one and two-piece implants and peri-implantitis as primary outcome, was evaluated. Moreover, the most mesial/distal point of the crown contour was taken as intersection to measure the restoration emergence angle. Hence, the influence of the cervical crown contour on marginal bone loss remains unknown. Therefore the aim of this study was to evaluate the cervical crown contour on dental implants in relation to the peri-implant marginal bone level and peri-implant soft- tissue health. The null-hypothesis formulated was that the crown contour (in terms of emergence angle) in the first 3 mm, measured from the implant platform of platform- switched, posteriorly placed, two-piece implants, has no correlation with marginal bone level and peri-implant health. 6