Crestal bone changes around titanium implants.: Part 1:: A retrospective radiographic evaluation in humans comparing two non-submerged implant designs with different machined collar lengths

Background: Experimental studies demonstrated that peri-implant crestal hard and soft tissues are significantly influenced in their apico-coronal position by the rough/smooth implant border as well as the microgap/interface between implant and abutment/restoration. The aim of this study was to evaluate radiographically the crestal bone level changes around two types of implants, one with a 2.8 mm smooth machined coronal length and the other with 1.8 mm collar. Methods: In 68 patients, a total of 201 non-submerged titanium implants (101 with a 1.8 mm, 100 with a 2.8 mm long smooth coronal collar) were placed with their rough/smooth implant border at the bone crest level. From the day of surgery up until 3 years after implant placement crestal bone levels were analyzed digitally using standardized radiographs. Results: Bone remodeling was most pronounced during the unloaded, initial healing phase and did not significantly differ between the two types of implants over the entire observation period (P > 0.20). Crestal bone loss for implants placed in patients with poor oral hygiene was significantly higher than in patients with adequate or good plaque control (P < 0.005). Furthermore, a tendency for additional crestal bone loss was detected in the group of patients who had been diagnosed with aggressive periodontitis prior to implant placement (P=0.058). In both types of implants, sand-blasted, large grit, acid-etched (SLA) surfaced implants tended to have slightly less crestal bone loss compared to titanium plasma-sprayed (TPS) surfaced implants, but the difference was not significant (P > 0.30). Conclusion: The implant design with the shorter smooth coronal collar had no additional bone loss and may help to reduce the risk of an exposed metal implant margin in areas of esthetic concern.