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Influence of vertical soft tissue thickness on occurrence of peri-implantitis in patients with periodontitis: a prospective cohort study.

BACKGROUND
The influence of vertical soft tissue thickness on health of peri-implant tissue has been addressed in few studies; thus, further research is needed.


PURPOSE
To evaluate the influence of vertical soft tissue thickness on the risk of peri-implantitis and peri-implant condition in patients with a history of periodontitis.


DESIGN/METHODS
A total of 92 patients with a history of periodontitis were included in this study. During the implant placement, the distance from palatal soft tissue edge to the alveolar crest, which was defined as vertical soft tissue thickness, was measured. The characteristics of patients and implants were recorded at baseline (T1). After more than 2 years follow-up period, 65 patients with 159 implants finally came back for T2 evaluation, and parameters of peri-implant tissue were recorded. The associations of vertical soft tissue thickness with peri-implant parameter and occurrence of peri-implantitis were analyzed using the generalized estimating equation accompanying linear regression and logistic regression. In addition to conventional multivariate analysis, a propensity score for adjustment was used to reduce confounding bias.


RESULTS
At follow-up examination (T2), survival rate at implant-level was 98.8%. The peri-implant parameters, including peri-implant probing depth and marginal bone loss, increased significantly with the increasing of soft tissue thickness (P < 0.05) after adjusting for a propensity score. In multivariate analysis adjusted for different confounding factors and propensity score, the odd ratios were all approximately 2.5, which meant that the risk of peri-implantitis increased 1.5 times for 1 mm increase of soft tissue thickness.


CONCLUSIONS
The excessive vertical soft tissue thickness around implants in patients with history of periodontitis has an adverse influence on health of the peri-implant tissue. This observation raises an important question on the association between vertical soft tissue thickness during implant surgery and history of periodontitis. Effective approaches to prevent the adverse effect of excessive soft tissue thickness on peri-implant tissue are necessary to be further investigated.