Diederik Hentenaar

137 Influence of the cervical crown contour taken into account the implant inclination. In contrast to the study by Katafuchi et al. 2018 (20) in which average emergence angles of 30 degrees for bone as well as soft- tissue level implants were found, the average emergence angle in this study did not exceed 18.7 degrees on both implant sites. A restoration emergence angle >30 degrees was found by Katafuchi et al. 2018 (20) to be correlated to peri-implantitis in bone-level, non-platform switched implants. Consequently, they assumed that platform-switched implants might have a larger emergence angle and therefore an increased risk for peri-implantitis. Average angles found in this study did not exceed 30 degrees on any of the 3 heights and therefore an increase in emergence crown angles on platform- switched implants compared to platform-matched implants could not be confirmed. Besides, high desirable levels of peri-impant health were seen at 5 year evaluation in this study. No clinical signs of moderate/severe inflammation (marginal bone loss > 2mm combined with bleeding and/or suppuration on probing) indicating a state of peri- implantitis, were found at any of the implants. Hence, these results do not indicate an increased risk for developing peri-implantitis in bone-level platform-switched implants as suggested by Katafuchi et al. 2018 (20). Also the number of patients which showed signs of peri-implant mucositis (bleeding score 1,2 and marginal bone loss ≤ 2mm) at the 5 year evaluation seemed comparable to prevalences found in recent systematic reviews and meta-analyses (31,32). The pilot study design and small sample size of this study, however, should be taken into account. Besides, the different intersection used (3 mm intersection versus most mesial/distal point of the crown), as well as the steep slope crown design in this study could have resulted in different angles and favourable peri-implant health outcome (20). Namely, steep slope crown designs may favour peri- implant accessibility for biofilm removal and presumably give more space to the soft tissue dimension (epithelial and connective tissue) to be present, preventing implants from inflammation (29,30). A design which in this study might already have been taken into account at the time of individually designing the implant crowns. Additionally, all patients in the studies were included under strict inclusion criteria and appeared a priori to be exceptionally healthy: none had a history of periodontal disease and all were reported non-smokers. Factors which both might positively influence peri-implant health and stability on the long term. Lastly, platform-switched implant connections might have influenced the peri-implant clinical outcomes. Previous studies evaluating platform-switched implant-abutment connections versus matched connections showed favourable marginal bone levels for platform-switched designs (1,3,4,8). Drawbacks of the present study could be related to the fact that only the mesial and distal aspects of the crown contour were assessed, since the emergence angles on the lingual or buccal contour could also influence the outcome parameters. Although three-dimensional records (cone beam computed tomography, CBCT) might be of 6