| Abstract|| |
Aim: This study was aimed to evaluate the effect of steam sterilization on the accuracy (within 10%) of friction-style mechanical torque limiting devices (F-S MTLDs) to achieve their target torque values.
Materials and Methods: Fifteen new F-S MTLDs were selected from Astra Tech (25 Ncm, Hader SA, La Chaux-de-Fonds, Switzerland), BioHorizons (30 Ncm, Dynatorq ITL, Irvine, California, USA), Dr. Idhe (15-60 Ncm, Dr. Idhe Dental, Eching/Munich, Germany). Every peak torque measurement was tested ten times before steam sterilization using Tohnichi torque gauge (6Tohnichi-BTG (-S), Japan). Steam sterilization was performed using a 100 cycle autoclave. Preparation steps were carried out for the devices before each autoclave sterilization cycle. Peak torque measurements were repeated after every sterilization cycle. Mean difference between the measured and the targeted torque values were evaluated before and after aging. Repeated-measures of ANOVA were used to compare the differences of accuracy between subjects. Bonferroni post-hoc test was used for pairwise comparison.
Results: Autoclaving resulted in an increase in the error values (the difference between peak torque and target torque values) in all the three groups studied (P < 0.05), with only Astra Tech devices showing >10% (maximum 12%) difference from their torque values in 5% of the measurements.
Conclusion: Steam sterilization effect differs between target torque and measured peak values with an increase trend. The peak torque values showed a significant decrease for BioHorizons, while a significant increase was noted for Astra Tech and no significant change in Dr. Idhe group after sterilization.
Clinical Implication: Within the limitation of this study the torque output of each individual device deviated in varying degrees from target torque values. However, the majority of the new frictional-style devices tested in this study, delivered fairly consistent torque output within 10% of their preset target values after sterilization. Astra Tech devices were the only one showing more than 10% difference from their torque values in 5% of the measurements. Combined effects of sterilization and aging still needs to be determined.
Keywords: Dentistry, friction, implant, sterilization, torque
|How to cite this article:|
Sadr SJ, Fayyaz A, Mahshid M, Saboury A, Ansari G. Steam sterilization effect on the accuracy of friction-style mechanical torque limiting devices. Indian J Dent Res 2014;25:352-6
Cross infection control is a critically major issue in the field of clinical dentistry, mainly because of the concern over contagious diseases transmitted in health care centers. Autoclave sterilization by saturated steam under pressure is generally considered to be the most certain and widely accepted method known to prevent various cross infections. However, the effect of heating and cooling cycles employed during sterilization have not been clearly stated in the dental literature on the mechanical properties, efficiency and accuracy of instruments and devices. ,,,,,, Accuracy of mechanical torque limiting devices (MTLDs) is an essential point in order to prevent connection related complications. These complications are reported to be among the most frequent technical complications affecting the survival rate of the fixed implant supported prosthesis. ,,,,,,,, Loose or fractured screws, deteriorate the clamping force at the screw joint and considered as a consequence of inappropriate torque application. ,,,,, Different torque drivers have been designed to ensure consistency through the tightening process of implant components to a specific target torque. MTLDs though, eliminate the operator's variability. ,,,, They are recommended as one of a most commune devices used to deliver optimal torque to the screw. ,,, Autoclaving (sterilization in saturated steam under pressure) and aging (frequency of use) seems to effect on the accuracy of MTLDs measures. ,,,,,, Two types of mechanical torque devices are available for clinical use which include toggle type (friction-style [F-S]) and beam type (spring-style). Manufacturers claim that the F-S MTLDs can be sterilized by steam autoclave system without any corrosion induction, affecting their accuracy. However, there remains to be controversies on the results reported. ,, Sterilization procedures has not adversely effected the accuracy of the new MTLDs except for the effect of autoclaving on the 10 Ncm F-S torque wrench.  Gutierrez et al. have tested 35 F-S MTLDs following a period of time in clinical service for torque delivery accuracy. They reported that the largest value after sterilization was 455% greater than the target torque designated by the manufacturers.  The mean applied torque of F-S MTLDs was not significantly different from spring-style devices; however, greater range of values were seen in F-S devices. 
|How to cite this URL:|
Sadr SJ, Fayyaz A, Mahshid M, Saboury A, Ansari G. Steam sterilization effect on the accuracy of friction-style mechanical torque limiting devices. Indian J Dent Res [serial online] 2014 [cited 2020 Jul 6];25:352-6. Available from: http://www.ijdr.in/text.asp?2014/25/3/352/138335
Due to high inaccuracy reports in F-S MTLD , and unknown effect of autoclaving on measures of accuracy, this study was designed to evaluate the effect of steam sterilization on the accuracy , of F-S torque devices (±10% of the target torque).
Based on the null hypothesis no significant difference is seen between the accuracy of F-S MTLDs before and after 100 autoclave cycles of steam sterilization.
| Materials and methods|| |
Fifteen new F-S MTLDs from tree different implant manufactures were selected for evaluation [Figure 1] in order to determine the effect of steam sterilization on their accuracy (within 10% of the target value). Five samples from each of the three selected F-S MTLDs types were:
|Figure 1: Friction-style mechanical torque limiting devices tested (top, BioHorizons-middle, Astra Tech-bottom, Dr. Idhe)|
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- Astra Tech (25 Ncm, Hader SA, La Chaux-de-Fonds, Switzerland)
- BioHorizons (30 Ncm, Dynatorq ITL, Irvine, California, USA)
- Dr. Idhe (15-60 Ncm, Dr. Idhe Dental, Eching/Munich, Germany).
Target torque was 25 Ncm for Astra Tech devices and 30 Ncm for both BioHorizons and Dr. Idhe devices. Total specimen size of fifteen devices was selected based on earlier studies ,,,, in addition to the effect size of 0.37 Ncm, standard deviation (SD) = 0.13 and β = 0.1 using 2-level factorial design. An abbreviation was adopted for each manufacturer and then a number was assigned for each device in a randomly from 11 to 15 in each group and labeled as: Astra (X11-X15), BioHorizons (Y11-Y15), Dr. Idhe (Z11-Z15). The device testing sequence was also randomized. Tohnichi torque gauge (6Tohnichi-BTG (-S), Japan) was used to measure the peak torque values of each device. The torque gauge was calibrated by the manufacturer as accurate within ±2% of the full scale. Driver for each respective device was selected accordingly before being clamped in 3-jaw chuck of torque gauge. Torque indicator on the gauge was set to zero after the torque device connection to the driver. The torque gauge was then fixed in a wise for stability. Each device was tested through gradual torque application over a period of 4 s.  Gradual increasing force was applied to the F-S MTLDs until it was released at a precalibrated target torque value. The torque was applied by one operator, who was blind on measured values, while another operator registered the peak torque values for each device, using a conventional magnifier. The procedure of peak torque measurement was performed 10 times prior to the steam sterilization. Preparation protocol was followed for each group of F-S MTLDs, based on the manufacturer's instruction. As Astra Tech and Dr. Idhe devices should be dismantled for disinfection, cleaning, drying and lubrication, this was followed at the proposed site, and then the parts were assembled before sterilization [Figure 2] and [Figure 3]. No dismantling is required in BioHorizons groups, and lubrication is the only step to be considered from the opening at the back of the wrench and handle bend of the device [Figure 4].
|Figure 4: For BioHorizons devices lubrication into the opening at the back of the wrench and bending of the handle to be considered|
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Devices were immersed in an artificial saliva medium (Bioxtra, Knokke, Belgium) before each autoclaving cycle, in order to simulate the contamination with saliva during surgical and prosthetic procedures. Disinfection process was then carried out for 15 min using the 2% phenol and aldehyde-free, nonfixing disinfectant (Deconex 53 Plus, Borer Chemie, Zuchwil, Switzerland). Devices were then sterile packed and placed in the steam sterilizing autoclave (Techno - Gaz/, Europa BXP/S.p.A, Parma, Italy). This sterilization cycling procedure was carried out for 100 times. Sterilization characteristics included: Temperature at 134°C, vacuum pressure at 0.9 bar and sterilization time for 18 min). After the completion of 100 autoclave sterilization cycles, the devices were retested for 10 consecutive measurements at peak torque values.
Mean differences were evaluated between the measured torque values and the targeted torque values before and after autoclaving. Repeated-measures of ANOVA were employed for subject comparison. The significant level was set at P < 0.05. Bonferroni post-hoc test was used for a pairwise comparison.
| Results|| |
Descriptive values of mean, SD, minimum and maximum difference between the measured torque and the targeted torque values for each group of F-S mechanical torque devices (before/after steam sterilization), are summarized in [Table 1].
|Table 1: Mean, SD and range of difference, between peak torque and target values before/after 100 times of steam sterilization cycles for friction-style mechanical torque limiting devices |
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Peak torque values showed significant differences after 100 autoclave cycles' in all three study groups (P < 0.05). Autoclaving resulted in an increase in error values of the difference between peak torque and target torque values for all three study groups (P < 0.05). Astra Tech devices were the only group showing >10% difference from their torque values in 5% of the measurements.
The mean raw error values presented in [Figure 5] are to compare the target torque between the three test groups of F-S MTLDs in two occasions of before/after autoclaving.
|Figure 5: Error bar and 95% confidence interval of mean raw error compared to target torque for three groups of friction-style mechanical torque devices, before/after steam sterilization. Zero level, showing target torque for each group (Astra Tech, BioHorizons Dr. Idhe)|
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| Discussion|| |
Results of this investigation rejects the null hypothesis as there was a statistically significant difference of error values (difference between measured peak torque and target values) after steam sterilization in all the three groups studied (P < 0.05) with only Astra Tech devices showing >10% difference from their target torque values. Peak torque values were proposed within10% of the target torque as a clinically suitable torque. , Maximum torque value measured in the current study showed 12% difference from the target torque in Astra Tech group after 100 autoclave cycles of steam sterilization. These finding were close to the results reported by Standlee et al.  which was within 10% of target torque. Dellinges and Curtis also stated that sterilization procedures did not adversely affect the accuracy of the Dyna Torq wrench system for target torque values of 20-30 Ncm. 
Gutierrez et al. indicated corrosion of the spring in the handle of the torque wrench was the reason for the largest value seen for 10 Ncm torque wrench (455% from the target torque). All of the devices had been in clinical service for a minimum of 1-month to the maximum of 3 years. Results of that study showed the largest values of 41.6% for 20 Ncm, 17% for the 30 Ncm torque wrench and 58.6% for the 35 Ncm devices.  Despite an increase in error values of all three groups after sterilization, mean values showed a significant decrease in BioHorizons devices, significant increase in Astra Tech devices, while no significant changes in Dr. Idhe devices in the current investigation. However, the range of the error values were very restricted, which could be partly be due to meticulous performance of preparation steps before sterilization and partly due to aging (not considered in the current study). Saboury et al. found that aging affects the accuracy of F-S MTLDs as an independent factor. The peak torque measurements of all tested devices fell within 10% of their preset target values before aging. A significant difference was seen between raw error values of the three groups of MTLDs (P < 0.05) after aging. More than 50% of all peak torque measurements of above-mentioned report was demonstrated to have >10% difference from their torque values after aging. 
McCracken et al. stated that the accuracy of mechanical torque devices could produce accurate torque values within 10% of their target torque at clinical status of 18 months to 7 years, with a maximum of 700 times use. However, higher SD (±16.1 Ncm) and range of values (55.9%) were seen among the F-S devices compared to the spring-style devices. Heating process that congeals the lubricant inside the F-S wrench could be a probable cause of measuring inaccuracy of F-S MTLDs, in an institutional environment, requiring frequent calibration of these devices.  Further results of the current study showed lesser variation of values among the F-S MTLDs. As mentioned earlier, this can be related to the aging influences (not considered in the current study) and strict application of time-consuming steps of preparation, before steam sterilization of the three test group devices. These preparation steps included dismantling, lubrication and assembling of the Dr. Idhe and Astra Tech devices. Lubrication and handle bending (broken position of the head) were followed for BioHorizons devices before sterilization. Fayaz et al. demonstrated that some F-S devices seem less sensitive to the effect of lubrication and corrosion considering the combined effect of aging and sterilization procedures. Performing the lubrication in multiples sites in these devices decrease the range of variability after dismantling the F-S MTLDs.  The effect of preparation steps before steam sterilization of the F-S MTLDs are not clearly stated in earlier studies. ,,
The F-S MTLDs used in the current in vitro study were brand new and no specimen was included from exposed items to earlier clinical procedures in order to avoid aging effect. Earlier studies had used torque wrenches in clinical services to investigate their accuracy. As there is little to no data available on the same age and the actual number of sterilization cycles in those earlier investigations along with their maintenance of mechanical torque devices results could not be considered applicable to every clinical situation. , In addition, the effect of sterilization and aging (frequency of use) either together or alone could provide a clinical guide to determine the maintenance requirements of such devices for accurate torque delivery, which is considered within 10% of their preset target values.
| Conclusion|| |
- Autoclaving resulted in a significant increase in error values (difference between peak torque and target torque values) for all three groups studied (P < 0.05)
- Mean values had a significant decrease for BioHorizons devices, but represented a significant increase in Astra Tech devices, while having no significant changes in Dr. Idhe devices after steam sterilization, despite a significant increase in their error values
- Astra Tech devices showed >10% difference (maximum 12%) from their torque values in 5% measurements.
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Department of Prosthodontics, Dental School, Shahid Beheshti University of Medical Sciences, Tehran
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]