The Effect of Screw Length on Fracture Load and Abutment Strain in Dental Implants with External Abutment Connections

Purpose: One of the most common types of failure in dental implants is fracture of the abutment screw, after which the remnant is usually not easily removed. The purpose of this study was to investigate the effect of abutment screw length on the amount of screw resistance load and strain after loading. Materials and Methods: Twenty-one implants and straight abutments were prepared. The implants were placed in acrylic resin blocks at an angle of 30 degrees relative to the long axis. The abutment screws were prepared and classified into seven groups based on length (n = 3 abutments per group). The implants and abutments were joined with a torque of 30 Ncm. Strain gauges were attached to the abutments, and the implant-abutment assemblies were compressed. Curves of strain over time, peak load, and load at fracture were measured. Linear models of the variables over the abutment screw length were analyzed. Results: The break and peak loads were significantly associated with abutment screw length. However, all measured break and peak loads were greater than the maximal occlusal force. There were no significant changes in peak or break strain values associated with screw length (P > .05). Conclusions: Clinically, fractured abutment screws may be replaced by shorter abutment screws without removal of the broken screw remnant. Keywords: abutment, dental implant, fracture, load, screw length, strain