Influence of cervical crown contour on marginal bone loss around platform‐switched bone‐level implants

Abstract

Background Preservation of peri-implant bone and maintaining healthy soft tissues are important for long-term implant success. However, this success can be influenced by prosthetic aspects. It is recommended that implant suprastructures should be designed in a way that oral hygiene measures can be performed, plaque accumulation is prevented and implants are accessible for probing. Studies on how to design the crown contour in order to prevent influence on the marginal bone level remain unknown. Aim/Hypothesis The aim of the present cohort study was to evaluate the influence of the cervical crown contour on marginal bone loss and soft tissue health around platform-switched, bone-level implants in the posterior region. Material and Methods A dataset was used from two previous studies. This dataset included clinical parameters and standardized peri-apical radiographs taken at 1 month and 5 years after final crown placement. A new measurement method (using Image J, National Institutes of Health, USA) was developed to analyse geometric values of the cervical crown contour. Emergence angles were measured at 1, 2 and 3 mm, parallel to the implant axis, above the implant shoulder (see Figure 1). The distance from the most outside point of the implant neck to the level of bone-to-implant contact was measured at both the mesial and distal aspect of the implant to determine marginal bone loss (using DicomWorks® software). A Pearson correlation coefficient was calculated. Clinical evaluation of the peri-implant soft tissue was performed at 1 month (baseline, T0) and 5 years (T60) after placement of the final implant crown. The sulcus bleeding index, the gingival mucosal index and the probing pocket depth were clinically recorded. Results A total of 64 patients with 67 posteriorly placed implants met the inclusion criteria. At 1, 2 and 3 mm above the implant shoulder, mean emergence angles at the mesial implant sites were 0.5 ± 2.8, 12.8 ± 12.8 and 18.0 ± 11.3 degrees, respectively. At the distal sites corresponding values were 2.8 ± 8.3, 16.2 ± 16.6 and 18.7 ± 13.8 degrees. Mean marginal bone loss between 1 month and 5 years after restoration placement was 0.14 ± 0.34 mm at the mesial and 0.26 ± 0.47 mm at the distal aspect of the implants. The clinical parameters at the 5-year evaluation generally indicated healthy peri-implant soft tissues. In 67.2% of the implants no bleeding was recorded as measured by the sulcus-bleeding index. The gingival index indicated healthy soft tissue in 97% of the implants 89.5% of the implants showed no probing pockets depth deeper than 5 mm. No correlation between peri-implant bone loss, soft tissue health and cervical crown contour could be found. Conclusion and Clinical Implications No correlation appears to exist between the cervical crown contour and peri-implant marginal bone loss and soft tissue health around bone-level, platform-switched implants at least when emergence angles do not exceed 20 degrees in the first 3 mm from the implant shoulder. Clinicians should therefore pay attention to a steep slope implant crown design.