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[Effect of vertical soft tissue thickness on clinical manifestation of peri-implant tissue in patients with periodontitis].

OBJECTIVE
To observe and investigate the effect of vertical soft tissue thickness on the peri-implant tissue condition and the prevalence of peri-implant disease in patients with history of periodontitis.


METHODS
Among 210 patients who showed initial interest of implant therapy, 92 patients were included in this study and received implant surgery during 2010 and 2015. Sixty-six patients with 66 implants finally came back for T2 evaluation. Prior to the implant therapy, all the patients had received periodontal treatment. During the implant placement surgery, the distance from palatal soft tissue edge to the alveolar crest, which was defined as vertical soft tissue thickness (VT), was measured after the buccal full thickness flap was elevated. According to the cut off point which was adopted from the operating characteristic curve, 66 implants within 66 patients were divided into two groups, which were called normal group (VT≤4.5 mm) and thick group (VT>4.5 mm), respectively. Information of the patient's general status, periodontal situation and implant information were recorded. After a follow-up period of 42.9 months, the parameters of peri-implant tissue and condition of peri-implant disease were recorded. Mann-Whitney U test as well as Chi-square test were used to compare the parameters between two groups. Moreover, Kaplan-Meier method was chosen to draw the event(peri-implantitis)-free survival curve.


RESULTS
The survival rate of the implants was 100%. At the end of the follow-up examination(T2), the parameters including max PDi, mean PDi, max BIi, mean BIi, mean MBL, MBL at distal side, MBL at mesial side, mean PLIi presented significantly higher values in thick group than in normal group (P < 0.05). Moreover, the prevalence of peri-implantitis and peri-implant disease (peri-implant mucositis & peri-implantitis) in thick group was respectively 34.8% and 73.9%, which was significantly higher than 2.3% and 48.8% respectively in normal group (P<0.05). The prevalence of peri-implant mucositis did not show significant difference in the two groups. In addition, Kaplan-Meier analysis showed that there was significant difference between the event-free survivals of the two groups.


CONCLUSION
The vertical soft tissue thickness around implants in patients with periodontitis has a significant effect on the health of the peri-implant tissue. Excessive vertical soft tissue thickness may result in deeper peri-implant probing depth as well as more peri-implant marginal bone loss, and eventually increase the risk of peri-implant disease. The vertical remodeling of soft tissue may be a new direction to indicate the role of periodontitis in peri-implant tissue condition. Moreover, the biological mechanism of the association between soft tissue thickness and peri-implantitis risk as well as effective approaches to prevent the adverse effect of excessive soft tissue thickness on peri-implant tissue is necessary to be investigated.