Prospective Randomised Clinical Trial Evaluating the Effects of Two Different Implant Collar Designs on Peri-Implant Healing and Functional Osseointegration After 25 Years of Function With Full Arch Mandibular Prostheses

Brånemark System® dental implant osseointegration was introduced in 1965 as a novel approach to the replacement of missing teeth. Although this implant's machined, screw-shaped surface had excellent, well-documented, short- and long-term clinical success (Adell, R. 1987; Albrektsson, T., et al., 1981; Albrektsson, T., et al., 1986; Brånemark, P-I. , 1983; Brånemark P-I. 1987), newer implant designs were introduced that could enhance fusion of the implant to jaw bones, and better resist functional forces. One such implant, Screw-Vent®, has a fixture macro structure very similar to that of the Brånemark® implant. However, its fixture surface was acid etched (1-3µm) which could enhance osseointegration, and it has a longer, narrower machined internal-hex, friction-fit collar that could better resist functional forces.These characteristics should lead to less bone loss (Niznick, G. A., 1989). However, one clinical study (De Bruyen, et al., 1992) reported greater short-term bone loss with this implant compared to the Brånemark® implant, possibly due to its longer machined collar, and advocated long-term clinical studies. Therefore, this prospective within-subject clinical trial was undertaken in 1993 to first compare the Brånemark® implant with another implant, Swede-Vent®, a copy of the Brånemark® macro structure except for its fixture surface that was identically micro textured as that of Screw-Vent® by the same manufacturer. The effect on bone healing could then be compared between Brånemark®'s machined and Swede-Vent®'s micro textured fixture surfaces in the short- and long-terms. Since Screw-Vent®'s fixture surface was identically micro textured as that of Swede-Vent®, the investigators could then evaluate and compare the effects on bone healing of Screw-Vent®'s longer, narrower, internal-connection machined collar to the identical shorter, wider, external-connection machined collars of the Swede-Vent® and Brånemark® implants. All three two-part, platform-matched, parallel-wall implants were made of commercially pure titanium, had a very similar fixture macro design, were approved by the Food and Drug Administration (USA) and Health and Welfare Canada, and were commercially available in North America. Brånemark® and Screw-Vent® implants are still available, but the Swede-Vent® implant is not.