Effects of Supracrestal Tissue Attachment Dimensions on Peri-implant Health: A RCT

Decision making in regards to the 3D implant positioning in partially edentulous sites is a complex process particularly when there are adjacent teeth present. Presently, the prevailing paradigm of implant placement guidelines is bone-driven. It calls to seat the implant neck in a crestal position. Clinical studies have demonstrated that implants placed in sites with thin soft tissues are suffering more crestal bone loss than sites with thick gingiva. Consequently, it has been proposed either to place these implants in a subcrestal position or to thicken locally the soft tissues. A recommendation of how much subcrestally the implants should be inserted in these sites is still lacking but clinicians empirically implement a deeper insertion of 1.5-2 mm under the crest. There is some indication that subcrestal placement may lead to bone remodeling above the implant neck and limited bone loss beyond the neck, but clinical trials of bone level implants have not been performed to answer this definitively.

Evolving data on the dimensions of the supracrestal tissue attachment zone (aka biological width, BW) around implants suggest that a distance of 4 mm is reserved to accommodate for junctional epithelial and connective tissue attachment zones as well as a healthy peri-implant sulcus. The objective of this study will be to determine if implants placed according to the soft tissue-driving implant placement paradigm, i.e. 4 mm below the tissue margin and associated with a deeper mucosal tunnel will have less bone loss but a more compromised peri-implant health as compared to implants placed at the bone crest level following the bone-driven implant placement paradigm with more bone loss but a shallower mucosal tunnel.It is hypothesized that using the CONNECT as a dedicated immediate tissue-level abutment system which enables avoiding alteration of the peri-implant gingival seal, both groups, the one with a deeper mucosal tunnel and the one with a shallower one, will perform identical in terms of peri-implant health and tissue maintenance outcomes. This would then justify the safe placement of implants in a biologically appropriate manner using biological width-driven placement guidelines.

To test this hypothesis, two groups of 30 patients each will be treated according to either the bone-driven or the soft tissue-driven concepts:

Control group following the bone level-driven placement guidelines (BL Group): Implants will be placed at the bone level, they will receive a 1.5-2 mm long CONNECT abutment.

Test group following the biological width-driven placement guidelines (BW Group): Implants will be placed 4 mm below the mucosal margin using a 3 mm long CONNECT abutment: this means that the implant will be placed sub-crestally in agreement with the corresponding guideline, i.e. at deepest 1 mm subcrestally.