• Journal of Dental Rehabilitation and Applied Science
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• v.24 no.2
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• pp.157-168
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• 2008

Tightening of the screws in implant restorations should be accurate and precise. If applied torque is too low, screw loosening would be occurred. With too high torque, the screw fracture might take place. Various torque generating devices are developed and employed to apply a proper torque. The purpose of this investigation was to determine and compare the accuracy of the torque controllers. In this study, 4 types of torque controllers were used; electronic torque controller, torque limiting device, torque indicating device and contra angle torque driver. Digital torque gauge was employed to measure the de-torque value. Thirty cycles of tightening and loosening were done with each torque controller. All implant torque controllers have shown slight errors and deviations. The torque liming device exhibited the most accurate data. No significant difference was found among the mean de-torque values of the electronic torque controller, torque indicating device and contra angle torque driver. In the limitation of this study, it would be recommended that the implant torque controllers should be checked whether uniformed and precise torque can be generated and a measuring error should be corrected.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.4
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• pp.432-442
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• 2006

Statement of problem: One of common problems associated with dental implant is the loosening of abutment screws that retain the implants. Purpose : This study was performed to investigate the influence of abutment screw length and repeated tightening on screw loosening in dental implant. Material and method: Forty nine Hexplants (13mm length, 4.3mm diameter, Ti grade IV, Warantec. Co. Ltd. Seongnam, Korea) and cementation type abutments(straight abutment) and abutment screws (0.4mm/pitch) were divided into 7 groups, depending on abutment screw length. Each implant and abutment was tightened to 30Ncm by torque controller(MGT50, MARK-10 Inc., USA) and the removal torque values were measured during 10 consecutive closure/opening trials. Results and Conclusion: The results of comparing the removal torque value are as follows : 1. There is no significant difference in the removal torque value between groups in 10 consecutive closure/opening trials (p = 0.97). 2. If the fractured abutment screw is engaged in longer than 2.425 thread length, there is no significant difference in the preload between the fractured abutment screw and the new abutment screw when both are equally tightened to 30 Ncm. 3. The removal torque value in the 1st trial(24.510 Ncm) was lower than that in the 2nd, 3rd, 4th, 5th, 6th, 7th trials and the removal torque value in the 2nd trials(25.551 Ncm) was maximum and was decreased in 1311owing trials. The removal torque value in the 1st trial was significantly lower than that in the 2nd, 3rd, 4th trials and was significantly higher than that in the 8th, 9th, l0th trials(p<0.05). 4. In the 2nd, 3rd, 4th, 5th, 6th, 7th trials, the abutment screw was mainly influenced by settling effect and the higher preload was obtained In the 8th, 9th, l0th trials, the abutment screw was mainly influenced by adhesive wear and the progressively lower preload was obtained.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.486-491
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• 2004

A comparative study on the implant screw loosening under the initial clamping force and cyclic loads was conducted. The experiments were performed to evaluate the screw loosening behavior of the internal and external implant systems. It was found that the screw loosening torques of implant systems were significantly affected by the way how the abutment and fixture were connected due to the difference in the load transfer mechanism between abutment and fixture.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.2
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• pp.128-135
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• 2003

Statement of problem : Implant screw loosening remains a problem in implant prosthodontics. Some abutment screws with treated surfaces were introduced to prevent screw loosening and to increase preload. DLC(Diamond Like Carbon) film has similar properties on hardness, wear resistance, chemical stability, biocompatibility as real diamond materials. Purpose : The purpose of this study was to investigate the effect of lubricant layer on abutment screw and to discriminate more effective method between soft lubricant and hard lubricant to prevent screw loosening. Material and method : In this study, $1{\mu}m$ thickness DLC was used as protective, lubricating layer of titanium screws and 3 times removal torque was measured on the abutment screws to investigate the difference in 10 coated and 10 non-coated abutment screws. Results : The results indicated that the implants with DLC coating group were not more resistant to the applied force in screw loosening. At 32Ncm, the 3 times removal torque in DLC group were $27.75{\pm}2.89,\;25.85{\pm}2.35$ and $26.2{\pm}2.57$. The removal torque in no-coated abutment screws were $27.85{\pm}4.23,\;27.35{\pm}2.81$ and $27.9{\pm}2.31$, respectively. Conclusion : The lubricant layer used in this study was Diamond Like Carbon(DLC) and it have a properties of hard and stable layer. The DLC coating layer was hard enough to prevent distortion of screws in the repeated unscrewing procedure in clinical situation. The reduced friction coefficient in hard DLC layer was not effective to prevent screw loosening.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.5
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• pp.662-670
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• 2005

Statement of problem: Little is known about the effect of abutment preparation procedure on do-torque values in different implant platform and the relationship of final do-torque values with different implant platform size. Purpose: This study evaluated the effect of abutment preparation procedure on do-torque values in different implant platform and the relationship of final do-torque values with different implant platform size. Material and method: Six ITI implants (2 narrow-neck implants, 2 regular-neck implants, 2 wide-neck implants) and six Branemark implants (2 narrow platforms, 2 regular platforms, 2 wide platforms) were embedded in each acrylic resin block with epoxy resin. Eighteen $synOcta^(R)$ abutments (6 narrow-neck implant-abutments, 6 regular-neck implant-abutments, 6 wide-neck implant-abutments) and eighteen esthetic abutments (6 narrow platform-abutments, 6 regular platform-abutments, 6 wide platform-abutments) were tightened to each implant with digital torque gauge. Initial do-torque values were measured using digital torque gauge. After preparation of abutments, Final do-torque values were measured with digital torque gauge. Results and conclusion: 1. Screws loosening or abutments motion were not detected in all experimental group, but some scratches of implant-abutment joints were detected in all group 2. Reduction ratios of final do-torque values were greater than initial do-torque values in all measured group, except in narrow-neck implant-abutment group (p<0.05). 3. Reduction ratios of final do-torque values in wide-neck implant-abutment group were greater than regular-neck implant-abutment group (p<0.01). 4. The greatest standard deviation value was detected in wide platform group in both implant systems.

• The Journal of Korean Academy of Prosthodontics
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• v.36 no.3
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• pp.468-482
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• 1998

Since the concept of osseointegration was introduced by Branemark of Sweden, dental implants have been used for various dental prosthetic treatments. The survival rate of dental implant is likely to be closely related to the total biomechanical role of each component of implant system. The use of interchangeable component is very attractive for dental practitioners because such an approach would save treatment cost, flexibility of prosthetic treatment options as well as conveniences. Therefore, the use of interchangeable implant system has been increasing without scientific assessment of safety and efficacy of various interchangeable implant system. The purpose of this study, therefore, were to compare the geometric characteristic of four interchangeable dental implant screws and the loosening torque of these screws. Four types of dental implant screws tested in this study were Nobelpharma, 3i, Impla-med, Restore. Four screws each of the test specimens were subjected for scanning electron microscopic examinations under the same condition and a 35x magnified standard SEM picture was objected from each test specimen using JSM-5200 scanning microscope. From each of the SEM pictures, eight parameters. i.e., diameter of screw head. screw length, thread pitch, major diameter. neck diameter, neck length, crest width and root width were determined using a caliper. The measurement for each parameters were then corrected for their magnification factor. The loosening torque were also determined by using a torque gauge. All of the measurements were statistically analyzed by ANOVA test and multiple range test. Statistical significance was set in advance at the probability level of less than 0.05. All analyses were done with SPSS software for the personal computer. The conclusion obtained from this studies were summarized as the following; 1. No statistically significances were noted in the thread pitch. and crest width in the four screws, and in the case of major diameter, the Impla-med screw was significantly smaller than the other three screws (p<0.05). Therefore, four implant bolts could be physically inserted in a abutment nuts. 2. The diameter of screw head was decreased in the order of Restore, 3i, Nobelpharma, Impla-med screws and the length of screws were decreased in the order of 3i, Restore, Nobelpharma and Impla-med. The diameter of neck was decreased in the order of Impla-med, Restore. Nobelpharma, 3i screws. The differences of each of these parameters were statistically significant (p<0.05). The width of root of screws were decreased in the order of Nobelpharma, Impla-med, Restore and 3i. The differences among Nobelpharma and Impla-med. Restore and 3i were statistically significant (p<0.05). 3. When the screws were loosening 1, 3, 4 and 5 times, the loosening torque for Impla-med and 3i screws were significantly higher than that of Nobelpharma or Restore screws (p<0.05). However, when statistically smaller than that of 3i, Restore or Nobelpharma screws(p<0.05).

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.3
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• pp.329-338
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• 2007

Purpose. The aim of this study is to evaluate the effect of TiN coating of abutment screw on the unscrewing torque. Material and methods. Titanium and Gold-Tite abutment screws were classified into two groups, Group A and C respectively, as control groups. Titanium abutment screws with TiN coatings were also classified into two groups, Group B and D, as experimental ones. Group A and B were tightened to 20 Ncm input torque, and Group C and D were tightened to 32 Ncm torque. Detorque values were measured with digital torque gauge during repeated closing and opening experiment. Results. Abutment screws with TiN coating (Group B and D) showed statistically significant higher mean detorque values than those of Group A and C. Discussion. Physical properties of TiN coating, such as low friction coefficient, high hardness and wear resistance, might contribute to higher detorque values. Conclusion. It is suggested that TiN coating of abutment screw help to reduce the risk of screw loosening and improve the stability of screw joint.

• The Journal of Advanced Prosthodontics
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• v.13 no.1
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• pp.65-70
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• 2021

Purpose. Implant mechanical complications, including screw loosening, can influence dental implant success. It has been shown that torque values are affected by contamination occurred in implant-abutment (I/A) interface. This study aimed to examine the effects of blood, saliva, fluoride and chlorhexidine contamination on reverse torque values (RTVs) of abutment screws in oral conditions. Materials and Methods. 50 fixtures were mounted into the stainless-steel holders and divided into five groups (n = 10). Except control group (NC), fixture screw holes in other groups were contaminated with chlorhexidine (CG), saliva (SG), blood (BG), or fluoride (FG). Abutment screws were tightened with a digital torque meter. I/A assemblies were subjected to thermocycling and cyclic loading. The mean RTVs were recorded and data were analyzed with one-way ANOVA and Tukey test. Results. Except for specimens in SG (20.56 ± 1.33), other specimens in BG (21.11 ± 1.54), CG (22.89 ± 1.1) and FG (24.00 ± 1.12) displayed significantly higher RTVs compared to NC (19.00 ± 1.87). The highest RTVs were detected in CG and FG. Conclusion. The obtained data robustly suggest that RTVs were significantly affected by fluid contaminations. Specimens in FG and CG displayed the highest RTVs. Therefore, clinicians should have enough knowledge about probable contaminations in I/A interface in order to manage them during clinical procedure and to inform patients about using oral care products.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.2
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• pp.92-98
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• 2012

Purpose: The aim of this study was to evaluate the effects of different abutment materials on abutment screw loosening and settling-down effect in conical connection type implant system. Materials and methods: Three types of abutment, cementation, gold UCLA, and metal UCLA abutment were used. Two UCLA groups were fabricated in a similar pattern to cementation abutment. Type III gold alloy and Nickel-Chromium alloy was used for casting gold UCLA abutment and metal UCLA abutment, respectively. Fixture and abutment were tightened to 30 Ncm by using digital torque controller and re-tightening was conducted with same force after 10 minutes. Digital torque gauge was used to measure loosening torque and fixture/abutment length was measured by digital micrometer. Dynamic loads between 25 N and 250 N were applied with $0^{\circ}$ angle to the abutment axis. After loading, fixture/abutment length was re-measured and amount of settlement was calculated. Loosening torque value was also measured for comparison Results: All three groups showed significant differences of length when comparing before and after loading, but there was no significant difference of settling amount in all groups. Loosening torque values were significantly decreased when comparing before and after loading in all groups($P$<.05). However, there was no significant difference in loss of loosening torque values when compared to groups. Conclusion: In internal conical connection type implants, dynamic load affected on settlement and loosening torque of implant, but there was no differences between abutments materials. Likewise gold UCLA abutment, metal UCLA abutment might be able to withstand functional load.

• The Journal of Advanced Prosthodontics
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• v.7 no.3
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• pp.207-213
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• 2015

PURPOSE. The purpose of this study was to examine the abutment screw stability of screw- and cement-retained implant-supported dental prosthesis (SCP) after simulated cement washout as well as the stability of SCP cements after complete loosening of abutment screws. MATERIALS AND METHODS. Thirty-six titanium CAD/CAM-made implant prostheses were fabricated on two implants placed in the resin models. Each prosthesis is a two-unit SCP: one screw-retained and the other cemented. After evaluating the passive fit of each prosthesis, all implant prostheses were randomly divided into 3 groups: screwed and cemented SCP (Control), screwed and non-cemented SCP (Group 1), unscrewed and cemented SCP (Group 2). Each prosthesis in Control and Group 1 was screwed and/or cemented, and the preloading reverse torque value (RTV) was evaluated. SCP in Group 2 was screwed and cemented, and then unscrewed (RTV=0) after the cement was set. After cyclic loading was applied, the postloading RTV was measured. RTV loss and decementation ratios were calculated for statistical analysis. RESULTS. There was no significant difference in RTV loss ratio between Control and Group 1 (P=.16). No decemented prosthesis was found among Control and Group 2. CONCLUSION. Within the limits of this in vitro study, the stabilities of SCP abutment screws and cement were not significantly changed after simulated cement washout or screw loosening.