Titanium dental implants with different collar design and surface modifications: A systematic review on survival rates and marginal bone levels

AIM: The aim of this study was to compare clinical and radiographic outcomes of dental implants with different neck characteristics. METHODS: A protocol-oriented search aimed at the question: "In patients subjected to tooth replacement with screw-type dental implants does the modification of the implant neck macro- or microgeometry contribute to the improvement of survival rates and maintenance of the peri-implant marginal bone levels?" Primary outcomes were survival and marginal bone level (MBL) changes evaluated on randomized controlled trials with >10 participants and follow-up >1 year. Risk of bias was evaluated using the Cochrane Collaboration's tool. The review follows the PRISMA statement. RESULTS: Forty-three studies compared: (a) One- versus two-piece implants (N = 7); (b) Two-piece implants with different neck characteristics (machined and rough collars, microthreads, LASER microtexturing) (N = 21); (c) Two-piece implants with macrogeometry modifications (tapering, back-tapering, and scalloping) (N = 6). One- and two-piece implants showed similar survival (RR = 0.45, 95% CI: 0.12, 1.66, p = 0.23) and MBL changes (WMD = 0.09 mm, 95% CI: -0.27, 0.45, p = 0.64) at 1-year post-loading. Machined collar implants have higher risk of early failure than rough collar implants (RR = 3.96, 95% CI: 1.12, 13.93, p = 0.03) and 0.43 mm higher bone resorption (95% CI: 0.0, 0.86, p = 0.05). Microthreads (WMD = 0.07 mm, 95% CI: -0.01, 0.15, p = 0.10) and LASER microtexturing (WMD = 0.15 mm, 95% CI: -0.35, 0.65, p = 0.56) do not reduce bone resorption. Scalloped implants have 1.26 mm higher resorption (95% CI: 0.72, 2.00, p < 0.001). CONCLUSIONS: One- and two-piece implants have similar survival and MBL changes. Rough collar implants have lower MBL changes than machined collar implants. Additional modifications to rough collars are irrelevant.