Influence of Implant Thread-Design on Bone Surface-Strain Around Orthodontic Mini-implants

Objective: This in-vitro study compared the surface strain fields in bone surrounding implants of two designs from the same company.

Methods: Implants (n=4) were obtained directly from their manufacturer (Orthodontic TAADS). They were provided with two thread designs. One had a uniform thread throughout its length, while the other had two thread sizes on the shaft: a smaller diameter thread located distal to the base and a larger thread diameter located adjacent to the head. These were placed into test blocks formed from 24 g/cc solid, rigid, polyurethane foam blocks that were 12mm thick and laminated on one side with a 1.5mm short fiber filled epoxy sheet (SAWBONES, Pacific Research Laboratories Inc). This material provides biomechanical responses equivalent to healthy human bone. A hand-torque wrench was used to insert the implants to 25 Ncm (+/-1), oriented perpendicular to the surface of the bone. These blocks were mounted and secured on both ends and loaded perpendicular to their axis from 0 to 30 N using a ligature wire pulled by a picomotor. An Electronic Speckle Pattern Interferometry (ESPI) system was used to visualize, measure, and compare surface strain fields during loading.

Results: Significant differences (alpha=0.05) in both the magnitude and direction of the resulting strain fields were measured. At higher loads the uniform thread implants resulted in a greater surface strain than the dual-thread design.

Conclusion: The ESPI system revealed that design differences of implants result in significant differences in the strain of the surrounding bone. This may play a role in implant success rates. This work was supported in part by Award Number TL1RR024159 from the National Center for Research Resources.