Date of Award

Summer 2021

Document Type


Degree Name

Master of Science (MS)





First Advisor

Thompson, Geoffrey A.

Second Advisor

Drago, Carl J.

Third Advisor

An, Hongseok


Purpose: To determine the number of loosening/tightening preload cycles prosthetic retaining screws can withstand before fracture, and to record the reverse torque values on each of the 10 applications of screw tightening and loosening. Materials and methods: The testing assemblies consisted of 30 temporary cylinder/multiunit abutment/internal connection implants, 10 each from Biohorizons, Zimmer Biomet Dental, and Dentsply Sirona Astra; the specimens were inserted into resin blocks. Temporary cylinders were connected to the abutments with new prosthetic screws and torqued to the appropriate preloads. The first tests of repeated tightening/loosening preload cycles were applied using a Digital ® torque gauge instrument at room temperature without lubrication. The assemblies sat overnight. The prosthetic screws were reverse torqued with the same digital torque gauge and the values were recorded. The cycles were repeated 10 times. Data were analyzed using mixed model analysis. The second test included each of the used screws (30) which were torqued until fracture or stripping occurred. The torque values were recorded and compared with new screws that were torqued until fracture or stripping. A sample of used and new screws from each company were viewed under both laser microscope (LEXT OLS4000, 3D Measuring Laser Microscope, Olympus) and scanning electron microscope (SEM). Data were analyzed using t-test. Results: According to the mixed model analysis, after 10 cycles of tightening and untightening the screws, the torque values decreased for 29/30 screws (96.6%) This compared Day 1 to Day 10. According to the t test used for the second test, the p values between all 3 groups were ≥0.9 which was not statistically significant. Conclusion: The results of this study indicated that after 10 cycles of tightening and untightening the screws, the torque values decreased. There were no statistical differences for screw fracture tests for the prosthetic screws.

Included in

Dentistry Commons