The influence of multiple cycles of steam-sterilization on the delivery accuracy of spring-type torque wrenches

The objective of this in vitro study was to assess the impact of multiple steam sterilization cycles on torque delivery capabilities. Sixteen new spring-style torque wrenches and their corresponding manual screwdrivers from four distinct manufacturers (MIS, DTI, NTA, and NucleOSS) were selected for evaluating their torque delivery accuracy by tightening the implant-abutment complex with the torque wrench, loosening the system with the same wrench, and then evaluating the loosening torque. The DTI and MIS groups were tested at 30Ncm, while the NTA and NucleOSS groups were tested at 25Ncm. Each torque device (n=4 per manufacturer; 16 in total) was tested 10 times with Instron. Following the manufacturer's guidelines, all torque wrenches went under steam sterilization, which was repeated 100 times. After steam sterilization was completed, the accuracy of all torque wrenches was retested. Descriptive statistical analysis was used and a repeated-measures ANOVA across four different brands as a between-subject comparison was conducted to assess the difference on accuracy among groups. Kruskall-Wallis and a post hoc Dunn's Test were done for pair comparison with absolute torque differences, followed by a chi-square test to assess the 10% difference from target torque values. The after-autoclave target torque and loosening torque value absolute difference averages of the DTI and MIS groups were significantly lower than those of the NTA and NucleOSS groups (p=0.0001). There was no statistically significant difference observed between the other groups (p > 0.05). The results indicate that the torque delivery values of the wrenches were influenced by multiple steam sterilization cycles, with variations observed across different implant brands but each brand stayed within 10% of their target torque values. Both the DTI and MIS groups maintained better control over their target torque values after autoclaving compared to the NTA and NucleOSS groups.