Load to Failure of Mini-implants with Collared and Non-collared Designs

Objective: This in-vitro study investigated the influence of such a collar design on the anchorage force resistance of a mini-screw implant.

Methods: Two groups of orthodontic miniscrews, identical in design with the exception of a self seating support washer (collar design) on one group were obtained from the manufacturer (Orthodontic TAADS). Implants of both types (n=45 each design) were inserted into blocks of engineered polyurethane foam with laminated e-glass-filled epoxy sheets (SAWBONES, Pacific Research Laboratories Inc). This material provided a biomechanical response equivalent to normal human bone. Three different cortical thickness analogues were tested to simulate the range seen in the human jaw: 1.0, 1.5, and 2.0 mm. All implants were inserted a depth of 7.0 mm, with the same maximum insertion torque (35Ncm). A custom load application apparatus was used in conjunction with a Q-Test (MTS) instrument to apply a tangential load to the implant at a point 2.5mm from the miniscrew insertion point, coinciding with the point at which force is applied in the clinical setting. Displacement of each screw during loading was continuously measured to the point of predefined failure, and the following data points were collected: yield point; peak load; and the load at implant displacements of 0.5mm; 1.0 mm; and 1.5mm.

Results: Significant differences between the two designs were observed (alpha=0.05). Two-way ANOVA showed significant differences between the collar vs. non-collar and cortical bone thickness groups for all data points collected.

Conclusions: Collar-containing implant designs survive higher loading forces. These designs should provide lower stress levels in surrounding bones and result in higher implant success rates. Work was supported in part by Award Number TL1RR024159 from the National Center for Research Resources and an AADR Student Research Fellowship.