Marginal bone and soft tissue behavior following platform switching abutment connection-disconnection

Background: The influence of dental implants on the surrounding soft and hard tissue is crucial in defining the implant’s functional and esthetics success. Some previous investigations have evaluated the effects of the microgap between the roughened and smooth titanium surfaces on crestal bone levels. Greater crestal bone resorption occurs if the interface is placed below the level of the crestal bone (1). A recent dog study (2) showed that the soft tissue attachment around titanium implants is adequately established soon after surgery. Fibroblasts predominated in the connective tissue interface after 2 weeks, decreasing in density by 4 weeks. The organization of collagen fibers was seen after 4-6 weeks, and epithelial proliferation was evident after 1-3 weeks, with mature epithelial tissue after 6-8 weeks. In addition, preliminary results from ongoing clinical field trial have indicated that the soft tissue around SLActive implants is ready 3 weeks after implant placement. In the new Straumann® Bone Level implant (BL), the microgap of the prosthetic connection between implant and restoration is shifted inwards. This means that the biological distance is taken into consideration and that more space is left for the “insertion” of the epithelium and the connective tissue of the peri-implant soft tissue in order to preserve crestal bone. Cochran has developed an animal study placing delayed restorations in 60 BL implants and evaluating the bone preservation with submerged and non-submerged implants placed at different heights and Tarnow in another animal study, has placed immediate restorations in 72 BL implants to evaluate the interproximal bone preservation with adjacently placed implants. Additional marginal bone resorption following abutment manipulation was found in a dog study concerning 10 Branemark implants with no restoration done by Abrahamsson. Hypothesis: It was suggested that healing abutment disconnection as a part of prosthetic treatment results in disruption of the epithelial seal, causing bleeding and ulceration of the site. This mechanical disruption may be considered as an open wound or exposure of connective tissue which may result in inflammatory responses and epithelial migration. The reestablishment of biological width in a more apical position may be one of the factors that could explain initial crestal bone loss (5). Aim: The objective of this study is to evaluate radiographically (bone level), histologically (biological width components) and clinically (soft tissue level changes) varying only the stability of abutment connection during the standard Bone Level Straumann® implant and prosthesis placement.