A single-tooth osseointegrated implant is composed of an implant body, an abutment, an abutment screw, and an artificial crown. The implant and abutment are typically connected by an abutment screw. The degree of mechanical integrity at the implant-abutment interface depends on screw preload, abutment connection design, the fitness of all components, and dynamic loading conditions. Fractures of the internal or external connection between implants and implant abutments or abutment screws are encountered in the clinical setting. Fractures may occur as a result of excessive axial forces (bending moments), horizontal loading, or rotational torque during functional activities such as chewing or parafunctional activities such as grinding and clenching. Several studies have evaluated implant-abutment assemblies in dynamic cyclic fatigue testing according to ISO 14801. However, evaluation of the strength of the implant-abutment assembly has not been reported when subjected to torsion testing. Test methods and standard vales have not yet been established for such torsion testing of implant-abutment assemblies. Abutment connections are principally classified as either internal or external types and are available in a variety of designs, including hexagonal, octagonal, cone screw, cone hex, cylinder hex, spline, cam, cam tube, and pin/slot. Implants incorporate features for rotation-prevention at the implant-abutment interface. The advantages and disadvantages of various types of implant-abutment connections have been discussed in several studies. Norton reported that internal implant-abutment interface connections have higher bending moment resistance than external connections. Presently, although more than 200 kinds of implant systems are available on the market, most manufacturers do not provide specific data regarding system-specific implant-abutment connection design complications. In the oral cavity, implant restorations are exposed to vertical, horizontal, and rotational forces during chewing. The maximum torsional strength and proportional limited strength on crown and tooth restoration materials were measured, and the values were compared with a mechanical bending and pull test value.

The purpose of this in vitro study was to investigate fracture strength using a torsion test at the implant-abutment interface in order to assess the effect of torsion force on the connection.