Accuracy of torque-limiting devices: A comparative evaluation

Evaluation of two implant-supported fixed partial denture abutment designs: Influence on screw surface characteristics

PURPOSE

To compare screw surface characteristics between hemi-engaging and non-engaging implant-supported fixed partial denture (FPD) designs after cyclic loading.

MATERIALS AND METHODS

Twenty-four implants measuring 4.3 × 10 mm were mounted on acrylic resin blocks. Specimens were divided into two groups. An experimental group included twelve 3-unit FPD with a hemi-engaging design; a control group included twelve 3-unit FPDs with the conventional design of two non-engaging abutments. Both groups were subjected to two types of cycling loading (CL), first axial loading, and then lateral loading at 30°. Load was applied to the units one million times (1.0 × 106 cycles) for each loading axis. Data on screw surface roughness in three locations and screw thread depth were collected before (BL) and after (AL) each loading type. Screw surface roughness was measured in μm using a mechanical digital surface profilometer and optical profiler. To evaluate screw thread depth in μm, an upright optical microscope Axio-imager 2 was used. To confirm readings made from the optical microscope, four random samples were selected from each group for scanning electron microscopy (SEM) analysis. The effect of cyclic loading was evaluated by averaging values across the two screws within each specimen, then calculating difference scores (DL) between BL and AL (DL = AL - BL). Additional difference scores were computed between the non-engaging screws in each experimental group specimen, and one randomly selected non-engaging screw in each control specimen. This difference was referred to as the non-engaging DL. Statistical significance was assessed using Mann-Whitney U tests (α = 0.05).

RESULTS

Comparisons of DL and non-engaging DL by loading type revealed one significant difference regarding surface roughness at the screw thread. Significantly greater mean changes were observed after axial loading compared to lateral loading regarding both DL (axial M = -0.36 ± 0.08; lateral M = -0.21 ± 0.09; U = 20; p = 0.003) and non-engaging DL (axial M = -0.40 ± 0.22; lateral M = -0.21 ± 0.11; U = 29; p = 0.013). No significant differences in screw surface roughness in other sites or thread depth were found between the experimental and control abutment designs in DL or in non-engaging DL. No significant differences were found for DL (axial U = 13, p = 0.423; lateral U = 9, p = 0.150;) or non-engaging DL (axial U = 13, p = 0.423; lateral U = 18, p = 1.00).

CONCLUSIONS

Results suggest that overall, changes in screw surface physical characteristics did not differ between hemi-engaging and non-engaging designs after evaluating screw surface roughness and thread depth before and after axial and lateral cyclic loading.

Comparison of electronic versus mechanical torque-limiting devices for dental implants: An in vitro study

PURPOSE

To determine the accuracy of new electronic torque-limiting devices (ET) when compared to new and used conventional-style beam-type (BT) mechanical torque-limiting devices and hand-piece style (HS) mechanical torque-limiting devices. The secondary purpose was to compare any difference in accuracy between new and used mechanical torque-limiting devices, and any difference in accuracy when used on a straight versus an angled screw channel abutment.

MATERIALS AND METHODS

A total of five torque-limiting devices were used to obtain 2000 readings under standardized conditions. An implant analog was fastened into a digital torque meter, to which an abutment was connected. Pre-determined torque values of 15 Ncm and 35 Ncm were applied, and actual torque values were recorded. A straight and an angled abutment were used to record 1000 readings each using the five torque-limiting devices. An overall Kruskal-Wallis test was applied to compare the median deviation among devices followed by a pairwise comparison ( = 0.05).

RESULTS

For a target torque value of 15 Ncm on a straight abutment, the electronic device (ET) was statistically more accurate than the beam type (BT) new (p < 0.001) and used (p < 0.048) devices but less accurate than the hand-piece style (HS) used device (p < 0.001). On an angled abutment for a target value of 15 Ncm, the electronic device (ET) was statistically more accurate than hand-piece style (HS) new and used devices (p < 0.001). For a target torque value of 35 Ncm on a straight abutment, the ET was statistically more accurate than the HS new device (p < 0.001) but less accurate than the BT new device (p < 0.001). On an angled abutment for a target value of 35 Ncm, the electronic device (ET) was statistically less accurate than the beam-type (BT) new device (p < 0.001), the beam-type (BT) used device (p = 0.001), and the hand-piece style (HS) used device (p < 0.001). The electronic device (ET) was the only device accurate within the ISO standard of accuracy of 6% for each of the target torque value/abutment design combinations. There was no statistically significant difference related to the type of abutment used (angled vs. straight).

CONCLUSIONS

Electronic torque limiting devices (ET) are an acceptable method for delivering torque for implant restorations for straight and angled abutments at 15 Ncm and 35 Ncm torque values. Conventional style beam-type (BT) mechanical torque-limiting devices are a simple, predictable, validated, and inexpensive tool for delivering accurate torque at 15 Ncm and 35 Ncm torque values. The hand-piece style (HS) mechanical torque-limiting devices are predictable to deliver 15 Ncm torque values.

Accuracy of mechanical torque-limiting devices for implant screw tightening: A systematic review and meta-analysis

STATEMENT OF PROBLEM

A consensus is lacking on the accuracy of torque value on different types of mechanical torque-limiting devices.

PURPOSE

The purpose of this systematic review and meta-analysis was to determine the accuracy of unused mechanical torque-limiting devices.

MATERIAL AND METHODS

Electronic searches were conducted until October 2021 in 6 electronic databases. Relevant articles were manually screened in 5 journals from January 2000 to October 2021. Two reviewers screened titles, abstracts, and full texts and extracted the data independently. A meta-analysis was conducted to evaluate the weighted mean difference in torque value deviation from target torque between spring-style and friction-style devices as a primary outcome. Deviations of output torque value from target value in spring-style or friction-style devices were also analyzed as a secondary outcome.

RESULTS

A total of 11 595 articles were identified, and 16 articles were included for final statistical analysis. Meta-analysis of the included articles showed that torque value deviation in the spring-style was significantly lower than in the friction-style devices (-0.99 Ncm, 95% confidence interval [CI]: [-1.89, -0.09], P=.030). Deviations of output torque value from target value was -0.54 Ncm in the spring-style group (CI: [-1.23, 0.15], P=.122) and -0.18 Ncm in the friction-style group (95% CI: [-1.40, 1.04], P=.770). Meta-regression analysis indicated that target value was significantly associated with the mean deviation from target value only in the spring-style group. High heterogeneity was found, suggesting more studies with standardized research design are required.

CONCLUSIONS

Both spring- and friction-style mechanical torque-limiting devices can produce relatively accurate torque values; however, unused spring-type devices tend to have lower deviation from target torque value than unused friction-type devices.

Comparison of the torque transferred to the implant-bone interface when tightening abutment screws and when torque testing implants: An in vitro study

STATEMENT OF PROBLEM

Before dental implants are restored, osseointegration is often verified by torque testing the implant. For this test, it might be appropriate to select the torque subsequently used to tighten the abutment screw during prosthetic delivery. However, whether the full torque applied to the abutment screw is transferred to the implant-bone interface remains unknown.

PURPOSE

The purpose of this in vitro study was to assess whether the same torque is transferred to the implant-bone interface when tightening abutment screws and when torque testing implants and to investigate whether the implant system used affects the torque transfer.

MATERIAL AND METHODS

A digital torque gauge was used to register the torque directed to a simulated implant-bone interface. Twenty implants from 4 different manufacturers were successively secured to the digital torque gauge. An implant driver was used to torque test the implant. An implant abutment screw was then tightened to attach a universal base (TiBase) abutment to the implant. During both tests, a mechanical torque limiting device was used to apply the same manufacturer-specific torque. For both experiments, the peak torque transferred to the simulated implant-bone interface was recorded. To allow pooling data from different torque targets, the data were converted into absolute difference. A t test was used to evaluate whether the same magnitude of torque was transferred to the implant-bone interface when tightening abutment screws and when torque testing implants. An ANOVA was used to test whether the percentage of torque transferred to the implant-bone interface was impacted by the implant system used (α=.05).

RESULTS

No significant difference was found between the torque transmitted when tightening an abutment screw and that transmitted when torque testing the implant (P=.600). Also, no difference was found in the percentage of torque transferred to the simulated implant-bone interface of different implant systems (P=.996).

CONCLUSIONS

Regardless of the implant system used, when tightening abutment screws and when torque testing implants, the same amount of torque is transferred to the implant-bone interface.

Effects of tightening torque on screw stress and formation of implant-abutment microgaps: A finite element analysis

STATEMENT OF PROBLEM

The mechanical behavior of the conical connection implant with different torque levels requires evaluation.

PURPOSE

The purpose of the finite element analysis study was to investigate the impact of abutment screw torque on the formation of microgaps at the implant-to-abutment interface of a conical connection under oblique loading. This is important because it is thought that bacteria can invade the internal implant space through the abutment-implant microgaps, causing peri-implantitis.

MATERIAL AND METHODS

Three-dimensional finite element analyses of the conical implant-abutment connection were performed by using screw torques of 20 Ncm and 30 Ncm. Oblique loads from 10 N to 280 N were applied to the prosthesis placed on the implant. The maximum von Mises stress in the abutment screw, the microgap formation process, and the critical load for bridging the internal implant space were evaluated.

RESULTS

The stresses in the abutment screw under oblique loading had limited sensitivity to the screw torque. However, the residual stress in the screw with a 30-Ncm torque was 35% higher than that with a 20-Ncm torque in the absence of an external load. The area in contact at the implant-to-abutment interface decreased with increasing load for both torque values. The critical load for bridging the internal implant space was 160 N for a screw torque of 20 Ncm and 220 N for a screw torque of 30 Ncm. The maximum gap size was approximately 470 μm with all the loads.

CONCLUSIONS

Increasing the screw torque can reduce the formation of microgaps at the implant-to-abutment interface. However, this will result in higher mean stress in the abutment screw, which may reduce its fatigue life and consequently that of the prosthesis. Further research is needed to evaluate the relationship between the abutment screw torque and microleakage in implant-supported restorations.

An in vitro assessment of the accuracy of new and in-use torque-limiting devices

STATEMENT OF PROBLEM

Recent studies have shown that torque-limiting devices (TLDs) do not meet their torque targets and are affected by factors such as the use of the TLDs and the sterilization processes used.

PURPOSE

The purpose of this in vitro study was to investigate the accuracy of TLDs currently in use in the Advance Education Program in Prosthodontics at the New York University College of Dentistry.

MATERIAL AND METHODS

Five new and 46 in-use TLDs (Nobel BioCare) from the implant kits of the graduate students were evaluated. One investigator was trained and calibrated before testing and after every 10 evaluations. A 3-jaw chuck was mounted on the center of a cap testing device by using the provided mounting screws. A LOCATOR torque driver was clamped into the chuck, and a torque wrench driver was attached to it. The device was placed on a flat table with direct overhead lighting that allowed the investigator to have a consistent view of the notches on the TLDs. A piece of cardboard was attached to the device to ensure that the investigator could not see the readouts. The blinded researcher inserted the wrench and applied the appropriate torque force at the designated notches while another researcher recorded the results. Two readings were made for each TLD at 15, 35, and 45 Ncm. A 2-way ANOVA and an intraclass correlation coefficient to test for intraclinician reliability were performed by using a statistical software program (α=.05).

RESULTS

Two TLDs were damaged and not tested. The 2-way ANOVA demonstrated no significant difference (P>.05) between graduate students in year 1, 2, and 3 or between the autoclaved and new TLDs. The intraclass correlation coefficient was 0.861 for 15 Ncm, 0.589 for 35 Ncm, and 0.764 for 45 Ncm.

CONCLUSIONS

In this in vitro study, new and used TLDs all met the recommended torque values. No significant differences were found among groups, suggesting that autoclaving and use did not affect the accuracy of the TLDs tested.

Accuracy of different electronic torque drivers: A comparative evaluation

PURPOSE

This study aims to evaluate the loosening torque on the implant fixture, and to assess the accuracy of difference electronic torque drivers.

MATERIALS AND METHODS

Three electronic torque drivers were used to measure the loosening torque on the implant system (AnyOne; MegaGen). The implant fixtures were divided among the 3 electronic torque driver types (W&H, SAESHIN, and NSK group) and 9 for each group. The screws were fastened at the implant fixture by three electronic torque drivers using the tightening torques recommended by the manufacturers of the drivers. After 10 minutes, the screws were again fastened at the implant fixture with equal torque. Then, the loosening torques were measured with an MGT12 torque gauge (MARK-10, Inc.). This measurement procedure was repeated 10 times under loosening torques of 15 Ncm, 25 Ncm, and 35 Ncm. In the statistical analysis, all values of loosening torque were analyzed with the one-way ANOVA and Kruskal-Wallis test (α=.05) for comparative evaluation.

RESULTS

There were significant inter-group differences at loosening torques of 15 Ncm and 25 Ncm (P<.05). The accuracy of the NSK driver was the highest, followed by SAESHIN and W&H. There was no significant difference between NSK and W&H at 35 Ncm (P>.05). The SAESHIN driver showed the closest loosening torque at 35 Ncm.

CONCLUSION

The most accurate loosening torques were SAESHIN at 35 Ncm, and NSK at 15 Ncm and 25 Ncm. Since the loosening torque may vary depending on the tightening torques and electronic torque drivers, periodic calibration of the electronic torque driver is recommended.