18 February 2022

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Rolled versus cut threads prosthetic screws: fatigue performance and SEM analysis

Co-authors: A. Comba, F. Del Bianco

Lorenzo Breschi

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Screw retained crowns to implants are widely used to replace missing teeth. Fracture of the screw is considered one of the most common complication related to this type of prosthesis. Screws can be produced both with cold-rolling    and cut threads technique. Since the rolling threads are less common in dentistry compared to industry, Armentia et al. aimed at comparing the mechanical characteristics of both manufacturing techniques. The null hypothesis tested was that rolled threads provide better mechanical response than cut threads.

Material & Methods
The mechanical and surface characteristics of the specimens were evaluated by means of an optical measuring machine, X-ray diffractometer, scanning electron microscope (SEM), and fatigue static load tests according to the International Organization for Standardization (ISO) 14801. Finally, linear regression models and 95% interval confidence bands were calculated and compared through ANOVA for fatigue tests while the t test was used for statistical comparisons (α=0.05).

Results
The authors reported a smoother surface finish, and higher compressive residual stresses for the roll- threaded screws. In addition linear regression models showed a fatigue  life 9 times higher for roll-threaded screws (P=1) without affecting static behavior, which showed statistically similar static strengths (P=.54). 

Conclusions
According to these results, rolling was demonstrated to be a better thread-manufacturing process for prosthetic screws, producing improved surface quality and fatigue  resistance.

(Photocredit: Dr. Federico Del Bianco)

For more information:  Fatigue performance of prosthetic screws used in dental implant restorations: Rolled versus cut threads.