Diederik Hentenaar

154 Chapter 7 crown contour. Previously, prosthetically focused studies mainly concern aesthetic outcome without paying attention to the emergence crown’s angle and emergence profile. Hence, in chapter 6 a study is presented in which the geometric influences of the cervical crown contour on marginal bone loss and soft tissue health was evaluated. From the results it was concluded that the cervical crown contour at platform-switched, posteriorly placed, two-piece implants were not correlated with peri-implant marginal bone loss and soft-tissue health up to 5 year after implant placement. Several factors might explain the results found in the study in chapter 6 . For example, all patients were included under strict inclusion criteria and appeared a priori to be exceptionally healthy: all patients were non-smokers and none had a history of periodontal disease. Moreover, all implants were placed by only two experienced implant-specialists and hence a correct three-dimensional implant position, which can be considered a prerequisite to achieve an optimal crown design, was therefore reasonably assured (Buser et al. 2004). In addition, all implants were restored with platform-switched restorations having customized titanium abutments. These customized abutments, which showed a gradual increase in width with a steep emergence profile or even concave/convergent design in the first 2 millimeters (i.e. a great amount of angles appeared zero or near zero at the first mm), might be part of a favorable trans mucosal design. Namely, ideally the design should respect the anatomical characteristics of the soft tissues and allow a smooth transition from the implant platform to the cervical margin (González-Martín et al. 2020). In our study, this profile might already have been taken into account at the time of individually designing the titanium abutment. Hence, this in turn could have created space for a protective biological soft tissue seal (epithelial and connective tissue) which might have positively influenced the marginal bone levels. A recent meta-analysis by the group of Valente et al. (2020) who found that concave/convergent implant transmucosal profiles are associated with less marginal bone loss seems to underline this finding. Further, all implants in the study presented in chapter 6 were restored with cemented restorations. It remains unclear whether the position of the cementation line between the titanium base and the suprastructure affects bone stability and tissue health. However, giving the fact the bone levels appeared stable over 5-years time, it did not seem to have influenced the outcomes. Although no correlation was found, the study proved and presented a reliably measuring method to evaluate a possibly critical implant crown region. To confirm our data and more profoundly understand the mechanisms by which the crown contour in the transmucosal region could influence peri-implant health, future research group could adopt this method to evaluate larger, heterogeneous groups of implants. Thereby