Influence of Morse taper angle and abutment material on preload development in dental implants

Abstract

Background: Dental implants have become an increasingly common solution for replacingmissing teeth, offering functional and esthetic benefits compared to traditional removable and tooth-supported fixed prostheses. Their ability to replace missing dentition without compromising adjacent tooth structure has made implants the preferred treatment option for many dentists and patients. As implant dentistry becomes more widespread, attention has shifted from simple placement to the long-term mechanical stability and success of implant-supported restorations. The most prevalent challenges existing in modern implant dentistry are mechanical complications, which often stem from the design of the implant-abutment connection. Mechanical complications, such as screw loosening, component fracture, and micromovement, are influenced by factors including implant platform design, abutment geometry, and the efficiency of torque transfer into preload. Preload, the clamping force created by the elastic recovery of the abutment screw after torque application, is critical for maintaining the implant-abutment connection. However, it is well documented that up to 90% of the applied torque is dissipated through friction, leaving only a small fraction available for preload generation. Optimizing this preload depends heavily on the precise design of the implant-abutment connection and the materials used. Abutment material plays a significant role in this context. Titanium is favored for its high strength and biocompatibility, while gold alloy abutments, offer improved machinability and potentially better conformability at the interface due to their ductility. These material properties may influence how effectively torque is converted into preload and how well the connection resists loosening over time. With a growing number of implant systems and component materials entering the market, each offering unique design features, there is a need to evaluate how both geometry and material affect mechanical performance. Purpose: The purpose of this study is to evaluate how implant-abutment connection geometry and abutment material composition influence preload development. Specifically, this study compares a 7° Morse taper connection with a 15° Morse taper connection, and examines the mechanical behavior of titanium vs. gold alloy abutments. Through torque-angle signature analysis and a torque-based preload calculation method, this study aims to better understand the role of internal connection design and material factors in achieving and maintaining screw joint stability. Materials and Methods: Six implants with a 15° Morse taper connection and three implants with a 7° Morse taper connection were embedded in custom-fabricated dies using Type V dental gypsum (Die-Keen Green). Straumann RC gold-alloy abutments and Straumann Titanium abutments were used and torqued into place using a custom torque apparatus connected to a digital torque-angle meter (HGTA-AMK, IMADA, PCB, Load & Torque, Inc.). Torque was applied manually until the meter reached 35 Ncm. Torque–angle signatures were recorded for each sample to determine insertion slope, insertion angle, and releasing angle. The three groups studied were 7° Morse taper connection with engaging titanium abutments, 15° Morse taper connection with engaging titanium abutments, and 15° Morse taper with gold-alloy abutments. The thread pitch of the abutment screw was confirmed to be 0.324 mm. Preload was calculated using tightening and removal torque values based on the formula developed by Hagiwara and Ohashi. Statistical comparisons were made using non-paired t-tests with a significance level set at p = 0.05. Results: Torque–angle signature analysis revealed distinct mechanical behavior across implant-abutment configurations. The 7° Morse taper with titanium abutment required the greatest angular displacement to reach 35 Ncm, indicating a longer alignment phase. The 15° Morse taper with titanium abutment exhibited the shortest insertion angle and steepest slope, while the gold alloy abutment group showed intermediate values. Statistically significant differences were found between the 7° and 15° Morse taper titanium groups for insertion angle (p = 0.0062) and preload (p = 0.0497). No significant differences were observed in insertion slope or release angle. Between gold and titanium abutments on 15° Morse taper implants, no significant differences were noted in any measured parameter. Conclusions: This study evaluated how implant-abutment geometry and abutment material affect mechanical performance using torque–angle signature analysis. Implants with a 15° Morse taper exhibited shorter alignment phases and steeper insertion slopes compared to those with a 7° taper. Statistically significant differences were found in insertion angle (p = 0.0062) and preload (p = 0.0497), with the 15° taper demonstrating more efficient torque transmission. In contrast, gold alloy abutments showed higher mean preload and release angles than titanium abutments within the 15° taper group, but these differences were not statistically significant. These resultssuggest that taper geometry plays a more critical role in preload development than abutment material. The 15° Morse taper appears to optimize mechanical engagement and preload generation, while the influence of abutment material remains inconclusive under the tested conditions. Further studies using direct preload measurement and fatigue testing are recommended to validate these findings and guide clinical decision-making in implant prosthodontics.