The Effect of a Machined Collar on Coronal Hard Tissue Around Titanium Implants: A Radiographic Study in the Canine Mandible

Purpose: The purpose of this study was to radiographically evaluate the effect of a machined titanium coronal collar on the marginal bone around 1-part endosseous dental implants placed at different heights relative to the bone crest. Materials and Methods: Sixty dental implants were placed in edentulous spaces bilaterally in 5 foxhounds. Thirty test implants had a sandblasted, large-grit, dual acid-etched surface (SLA) over the entire length of the implant. The other 30 implants (control) had a machined collar around the most coronal 1.8 mm of the implant; an SLA surface covered the remainder of the implant. Both control and test implants were placed at 3 distinct levels relative to the bone crest. Six implants (3 control and 3 test) were randomly placed side by side in each hemimandible. Radiographs were taken at placement (baseline) and monthly for 6 months postplacement using a standardized radiographic template. Results: Fifty-eight of the implants integrated and were analyzed on each proximal surface. Bone loss occurred around all implants over the 6 months of the study. In general, implants placed with the top of the SLA surface above the bone crest had significantly less bone loss than implants with the top of the SLA surface placed flush with the bone level. Apically placed implants had greater bone loss than coronally placed implants. The magnitude of bone loss around paired control and test implants was approximately the same. Discussion and Conclusion: The least bone loss with each implant type was observed when the top of the implant was placed above the alveolar crest. When there was no machined collar, the least distance from the implant top to the bone crest (not, however, the least bone loss) was observed when the top of the implant was level with the bone crest.