Impact of Thread Fabrication Methods on Abutment Screw Loosening in Dental Implants: An In Vitro Experimental Study

This study aimed to investigate the influence of different thread manufacturing techniques, including machining, thread rolling, and die cutting, on the mechanical stability of abutment screws in dental implants. It also evaluated the role of internal threading processes in implants (cut vs. form tapping) on torque loss behavior.

Abutment screws and implants were fabricated using three screw manufacturing techniques and two internal thread forming methods, respectively. The screw-implant assemblies were tested under two conditions: (i) immediately after tightening to simulate initial mechanical adaptation, and (ii) after dynamic loading to simulate functional use. Thread morphology was assessed using profilometry and scanning electron microscopy (SEM), while torque loss was quantified with a digital torque meter. Surface roughness and thread geometry were statistically analyzed using one-way ANOVA and Tukey HSD tests (α = 0.05).

Machined screws exhibited superior torque retention in both scenarios, especially when paired with form-tapped implants. Die-cut screws consistently showed the highest torque loss, correlating with greater surface defects and dimensional variability. SEM revealed pronounced flank damage and debris in die-cut and thread-rolled screws. Surface roughness values aligned only partially with observed surface morphology. Thread manufacturing method and internal thread formation both significantly affected preload stability (p < 0.05).

The thread manufacturing method is a critical factor in the mechanical performance of abutment screws. Machined screws provided the most consistent outcomes, while die-formed screws posed mechanical disadvantages due to inferior thread quality. These findings have clinical implications for improving the long-term stability of implant-supported restorations.