PURPOSE: The aim of this study was to evaluate the effect of cyclic loading and screw retightening on reverse torque value (RTV) in external and internal type implants. MATERIALS AND METHODS: Cement-retained abutments were connected with 30 Ncm torque to external and internal type implants. Experimental groups were classified according to implant connection type and retightening/loading protocol. In groups with no retightening, RTV was evaluated after cyclic loading for 100,000 cycles. In groups with retightening, RTV was measured after 3, 10, 100 cycles as well as every 20,000 cycles until 100,000 cycles of loading. RESULTS: Every group showed decreased RTV after cyclic loading. Before and after cyclic loading, external type implants had significantly higher RTVs than internal type implants. In external type implants, retightening did not affect the decrease in RTV. In contrast, retightening 5 times and retightening after 10 cycles of dynamic loading was effective for maintaining RTV in internal type implants. CONCLUSION: Retightening of screws is more effective in internal type implants than external type implants. Retightening of screws is recommended in the early stage of functional loading.
Torque*

OBJECTIVE: To determine the unique contribution of geometrical design characteristics of orthodontic mini-implants on maximum insertion torque while controlling for the influence of cortical bone thickness. METHODS: Total number of 100 cylindrical orthodontic mini-implants was used. Geometrical design characteristics of ten specimens of ten types of cylindrical self-drilling orthodontic mini-implants (Ortho Easy(R), Aarhus, and Dual Top(TM)) with diameters ranging from 1.4 to 2.0 mm and lengths of 6 and 8 mm were measured. Maximum insertion torque was recorded during manual insertion of mini-implants into bone samples. Cortical bone thickness was measured. Retrieved data were analyzed in a multiple regression model. RESULTS: Significant predictors for higher maximum insertion torque included larger outer diameter of implant, higher lead angle of thread, and thicker cortical bone, and their unique contribution to maximum insertion torque was 12.3%, 10.7%, and 24.7%, respectively. CONCLUSIONS: The maximum insertion torque values are best controlled by choosing an implant diameter and lead angle according to the assessed thickness of cortical bone.
Torque*

STATEMENT OF PROBLEM: Adequate bone quality and quantity were important to achieve initial stability and to prevent early failures. However there were few published data available regarding the actual effect of dimensional change in implant geometry on initial stability. PURPOSE: The purpose of the current study was to investigate the influence of diameter and length changes on initial stability of implants. MATERIAL AND METHODS: Four types of dummy bone (D1, D2, D3 and D4) consisted of cortical and cancellous layers with different thickness were simulated. Implants which had similar surface area to each other (3.5 x 13.0-mm, 4.0 x 11.5-mm, 4.5 x 10.0-mm, 5.0 x 8.5-mm) were inserted in dummy bones. Implant stability as a function of peak insertion torque and resonance frequency values were recorded for each implant. RESULTS: 1. Bone quality was a major influential factor to achieve initial stability (P < .05). 2. In D1, D2 and D3 dummy bones, implant stability quotient values were not significantly different to each other (P > .05), however insertion torques were increased with wider and shorter implants (P < .05). 3. In D4 dummy bone, implant stability quotient values and insertion torques were decreased with wider and shorter implants (P <. 05). CONCLUSION: From a point of view of initial stability, it is suggested that use of wide and short implant may be helpful in avoiding bone augmentation procedures in area of adequate bone quality.
Torque

STATEMENT OF PROBLEM: Little is known about the effect of a counter-torque device and the internal hexagon of abutment on the tightening torque transmitted to the implant. PURPOSE: The purpose of this study was to examine the effect of a counter-torque device and the internal hexagon of abutment on the tightening torque transmitted to the implant. MATERIAL AND METHODS: In this study, three types of abutment were used; (1) two-piece conical abutment with hexagon, (2) two-piece conical abutment without hexagon, and (3) one-piece conical abutment without hexagon. The experimental groups were divided into five groups according to the type of abutment and the usage of a counter-torque device. Group I : two-piece conical abutment with internal hexagon was tightened without the use of a counter-torque device. Group II : two-piece conical abutment without internal hexagon was tightened without the use of a counter-torque device. Group III : one-piece conical abutment without internal hexagon was tightened without the use of a counter-torque device. Group IV : two-piece conical abutment with internal hexagon was tightened with the use of a counter-torque device. Group V : two-piece conical abutment without internal hexagon was tightened with the use of a counter-torque device. Abutments were tightened 20Ncm torque with the use of manual torque wrench and then torque values were measured by torque-gauge. After the measurement of torque values, all groups were loosened with the use of manual torque wrench and then detorque values were measured by torque-gauge. RESULTS: The results were as follows: 1. There were no differences in torque values among three types of abutment. 2. Regardless of the existence of the internal hexagon of abutment, a counter-torque device decreased the tightening torque transmitted to the implant about 92%. 3. In group III showed the highest detorque value, however there were no differences among group I, II, IV and V. CONCLUSION: Within the limitations of this study, it was concluded that the internal hexagon of abutment has no effect on the tightening torque transmitted to the implant and the detorque value of abutment screw. The use of a counter-torque device is essential to prevent microfracture on the implant-bone interface but has no effect on preload.
Torque*

OBJECTIVE: The purpose of this study was to evaluate the effect of length and shape of cutting flute on mechanical properties of orthodontic mini-implants. METHODS: Three types of mini-implants with different flute patterns (Type A with 2.6 mm long flute, Type B with 3.9 mm long and straight flute, Type C with 3.9 mm long and helical flute) were inserted into the biomechanical test blocks (Sawbones Inc., USA) with 2 mm and 4 mm cortical bone thicknesses to test insertion and removal torque. RESULTS: In 4 mm cortical bone thickness, Type C mini-implants showed highest maximum insertion torque, then Type A and Type B in order. Type C also showed shortest total insertion time and highest maximum removal torque, but Type A and B didn't showed statistically significant difference in insertion time and removal torque. In 2 mm cortical bone thickness, there were no significant difference in total insertion time and maximum removal torque in three types of mini-implants, but maximum insertion torque of Type A was higher than two other Types of mini-implants. CONCLUSIONS: Consideration about length and shape of cutting flute of mini-implant is also required when the placement site has thick cortical bone.
Torque

STATEMENT OF PROBLEM: Currently, many implant systems are developed and divided into two types according to their joint connection: external or internal connection. Regardless of the connection type, screw loosening is the biggest problem in implant-supported restoration. PURPOSE: The purpose of this study is to assess the difference in stability of abutment screws between the external and internal hexagonal connection types under cyclic loading. MATERIAL AND METHODS: Each of the 15 samples of external implants and internal abutments were tightened to 30 N/cm with a digital torque gauge, and cemented with a hemispherical metal cap. Each unit was then mounted in a 30degrees. inclined jig. Then each group was divided into 2 sub-groups based on different periods of cyclic loading with the loading machine (30 N/ cm - 300 N/cm,14 Hz: first group 1 x 10(6), 5 x 10(6) cyclic loading; second group 3 x 10(6), 3 x 10(6) for a total cyclic loading of 6 x 10(6) The removal torque value of the screw before and after cyclic loading was checked. SPSS statistical software for Windows was used for statistical analysis. Group means were calculated and compared by ANOVA, independent t-test, and paired t-test with alpha = 0.05. RESULTS: In the external hexagonal connection, the difference between the removal torque value of the abutment screw before loading, the value after 1 x 10(6) cyclic loading, and the value after 1 x 10(6), and additional 5 x 10(6) cyclic loading was not significant. The difference between the removal torque value after 3 x 10(6) cyclic loading and after 3 x 10(6), and additional 3 x 10(6) cyclic loading was not significant. In the internal hexagonal connection, the difference between the removal torque value before loading and the value after 1 x 10(6) cyclic loading was not significant, but the value after 1 x 10(6), and additional 5 x 10(6) cyclic loading was reduced and the difference was significant (P < .05). In addition, in the internal hexagonal connection, the difference between the removal torque value after 3 x 10(6) cyclic loading and the value after 3 x 10(6), and additional 3 x 10(6) cyclic loading was not significant. CONCLUSION: The external hexagonalconnection was more stable than the internal hexagonal connection after 1 x 10(6), and additional 5 x 10(6) cyclic loading (t = 10.834, P < .001). There was no significant difference between the two systems after 3 x 10(6), and additional 3 x 10(6) cycles.
Joints ; Torque

PURPOSE: The purpose of this study was to evaluate the machining accuracy and consistency of implant/abutment/screw combination of internal connection type. MATERIAL AND METHODS: In this study, each two randomly selected internal implant fixtures from ITI, 3i, Avana, Bicon, Friadent, Astra, and Paragon system were used. Each abutment was connected to the implant with 32Ncm torque value using a digital torque controller or tapping. All samples were cross-sectioned with grinder-polisher unit (Omnilap 2000 SBT Inc) after embeded in liquid unsaturated polyester (Epovia, Cray Valley Inc). Then optical microscopic and scanning electron microscopic(SEM) valuations of the implant-abutment interfaces were conducted to assess quality of fit between the mating components. RESULTS: 1) Generally, the geometry of the internal connection system provided for a precision fit of the implant/abutment interface. 2) The most precision fit of the implant/abutment interface was provided in the case of Bicon System which has not screw. 3) The fit of the implant/abutment interface was usually good in the case of ITI, 3I and Avana system and the amount of fit of the implant/abutment interface was similar to each other. 4) The fit of the implant/abutment interface was usually good in the case of Friadent, Astra and Paragon system. The case of Astra system with the inclined contacting surface had the most intimate contact among them. 5) Amount of intimate contact in the abutment screw thread to the mating fixture was larger in assembly with two-piece type which is separated screw from abutment such as Friadent, Astra and Paragon system than in that with one-piece type which is not seperated screw from abutment such as ITI, 3I and Avana system. 6) Amount of contact in the screw and the screw seat of abutment was larger in assembly of Friadent system than in asembly of Astra system or Paragon system. CONCLUSION: Although a little variation in machining accuracy and consistency was noted in the samples, important features of all internal connection systems were the deep, internal implant - abutment connections which provides intimate contact with the implant walls to resist micromovement, resulting in a strong stable interface. From the results of this study, further research of the stress distribution according to the design of internal connection system will be required.
Polyesters ; Torque

PURPOSE: The purpose of this study was to evaluate whether the internal abutment length affected screw stability in an internal connection implant. MATERIALS AND METHODS: Twenty long internal connection implants (Replus system, 4.7 × 11.5 mm) were selected for this investigation. Abutments were assigned to four groups depending on the length of the internal connection (abutments with internal lengths of 1, 2, 3, and 4 mm, respectively). Each implant fixture specimen was embedded in resin medium and connected to an abutment with an abutment screw. A load of 100 N, applied at an angle of 30° to the long axis of the implant, was repeated for 1.0 × 10⁶ cycles. Reverse torque values (RTV) were recorded before and after loading, and the change in RTV was calculated. Data were analyzed with the Kruskal-Wallis test. RESULTS: The change in RTV was not significantly different among the groups (P>.05). Screw loosening and fractures were not observed in any groups, and joint stability was maintained. CONCLUSION: The internal length of the abutment may not significantly affect the degree of screw loosening.
Joints ; Torque

PURPOSE: The aim of this study was to evaluate screw removal torque of the two-piece zirconia abutment with the novel titanium component compared to the conventional onepiece titanium abutment in the internal connection implant before and after dynamic cyclic loading. MATERIALS AND METHODS: Two types of the abutment assemblies with internal connection were prepared and divided into the groups; titanium abutment-titanium abutment screw assemblies as control, and zirconia abutment-titanium socket-titanium abutment screw assemblies as experimental group. A total of 12 abutments and implants were used of six assemblies each group. Each assembly was tightened to 30 Ncm. A cyclic load of 300 N at an angle of 30 degrees in reference to the loading axis was applied until one million cycles or failure. The removal torque values (RTVs) of the abutment screws were measured with a digital torque gauge before and after cyclic loading. The RTVs of the pre load and post load were analyzed with t-test, and P-values < .05 were considered statistically significant. RESULTS: The assemblies of both groups survived all after the dynamic cyclic loading test without screw loosening. The statistically significant differences were found between the mean RTVs before and after the cyclic loading in both groups (P < .05). The RTV differences for the control and the experimental group were -7.25 ± 1.50 Ncm and -7.33 ± 0.93 Ncm, respectively. Statistical analysis revealed that the RTV differences in both groups were not significantly different from each other (P > .05). CONCLUSION: Within the limitation of this study, the two-piece zirconia abutment with the titanium component did not show a significant RTV difference of the abutment screw compared to the titanium abutment after dynamic cyclic loading.
Titanium* ; Torque*

STATEMENT OF PROBLEM: Little is known about the effect of abutment preparation procedure on de-torque values in different implant platform and the relationship of final de-torque values with different implant platform size. PURPOSE: This study evaluated the effect of abutment preparation procedure on de-torque values in different implant platform and the relationship of final de-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 Bra.nemark 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 de-torque values were measured using digital torque gauge. After preparation of abutments, Final de-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 de-torque values were greater than initial de-torque values in all measured group, except in narrow-neck implant-abutment group (p<0.05). 3. Reduction ratios of final de-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.
Joints* ; Torque