Controversies in implant dentistry — hybrid implant surfaces

Studies show that placing the implant sub-crestal reduces initial stability. Another study showed there was more bone loss with sub-crestal vs supra-crestal placement, which would be expected because bone will not osseointegrate above the implant-abutment junction.

An important reason for designing an implant with a machined neck is that most ridges are uneven, so placing the implant level with the highest point on the ridge will require bone grafting to cover the exposed rough surface. Immediate placement of implants into extraction sockets routinely requires bone grafting with inevitable resorption. By designing the implant with a 2.0 to 2.5 mm machined neck, the need for bone grafting will be greatly reduced.

While it is well documented that initial bone loss will be less with a rough surface, this only amounts to about 0.3 to 0.5 mm difference. This is insignificant considering that having a labial plate less than 1 mm in width can result in up to 2 mm of bone loss. Experienced clinicians understand that placement of implants in extraction sockets may further contributes to bone loss.

Uncovering implants placed sub-crestal can also potentially require an additional surgical step of removing bone over the cover screw. Attaching a flared abutment to a submerged implant can necessitate additional bone removal as well. All these additional steps can be avoided by simply placing the implant level with or 1 mm above the crest of the ridge.

These facts dictate that the neck of the implant should be machined for 2.0 to 2.5 mm coronally with ideal placement having 1 mm exposed above the height of the ridge. This will distance the implant-abutment junction above the bone, minimizing the effect of any micro-leakage or bacteria in the crevice. It will also allow a 1 mm zone for soft tissue adhesion above the crest that will not be disturbed by removing and re-attaching healing collars, transfers and abutments. Any bone loss will expose the smooth neck originally sub-crestal, potentially minimizing the risk of peri-implantitis.

Tags: