The effect of steam sterilization without preparation steps on the accuracy of friction-style MTLDs

Inadequate torque application during screw tightening in dental Implants is one of the responsible factors of screw loosening and fracture and others technical complications. Mechanical torque limiting Devices (MTLDs) are necessary tools to control a peak torque and achieving a target values. Accuracy of these devices, particularly in friction–style type is reported with high variability. Due to vague and controversial aspect of steam sterilization on the accuracy of these devices their preparation steps (dismantling of the components, lubrication, broken position of the handle) before sterilization, this study aimed to evaluate the effect of steam sterilization without preparation steps on the accuracy of friction-style MTLDs. Fifteen new friction-style MTLDs from three different manufacturers, five for each group, were purchased. All peak torque measurement, considering their target torque, were measured ten times consecutively before and after 100 cycles of steam sterilization using Tohnichi torque gauge. For steam sterilization procedure, 100 cycles of autoclave without preparation steps before each cycle were performed. Comparison of error values and range of difference between the measured torque value and the target torque values before/after sterilization were performed with a One- way Repeated- measures ANOVA to significant level of P<0.05, considering type of devices as a between subject comparison. For pair wise comparison Bonferroni post hoc test was used. After steam sterilization without preparation steps, difference between target torque and peak values increased in all of the 3 groups studied (P<0.05). Peak torque values showed more than 10% difference from the target torque (suitable clinically accepted torque) in some measurements. Range of error was -1 to 4 Ncm in Dr Idhe group, -1 to 3 Ncm in AstraTech group and -3.5 to 1 Ncm in Biohorizon group. Within the limitation of this study maximum error values were 12% in Astra Tech MTLDs, 13.3% in Dr Idhe MTLDs and 11.7% in Biohorizon MTLDs. Greater variability was seen for Biohorizon and Dr Idhe groups than for Astra Tech group. CLINICAL IMPLICATION: Sterilization without preparation steps affects the accuracy of friction-style mechanical torque limiting devices. Combined effects of sterilization and aging needs to be determined.