• The korean journal of orthodontics
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• v.37 no.2 s.121
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• pp.89-97
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• 2007

Objective: The purpose of this study was to measure the insertion torque of orthodontic miniscrews regarding changes in their shape, diameter, and length. Methods: Torque values were measured during continuous insertion of the miniscrews into solid rigid polyurethane foam, using a torque tester of driving motor type with a regular speed of 3 rpm. Orthodontic miniscrews (Biomaterials Korea, Seoul, Korea) of cylindrical type and taper type were used. Results: Increasing the length and diameter of the miniscrews increased the maximum insertion torque value in both cylindrical and taper type screws. Insertion torque was increased at the incomplete head of the cylindrical type screw, and at the tapered part of the taper type screw. The insertion torque value of miniscrews was influenced most by diameter, then shape and length. As a result, it was shown that the diameter of the screw had the most influence on insertion torque, and the taper type screw had a higher torque value than the cylindrical type screw. Conclusion: Therefore, a large diameter or taper type screw are adequate for areas of thin cortical bone with a large interdental space, and a small diameter or cylindrical type screw are adequate in the mandibular molar area or the midpalatal area having thick cortical bone.

• The korean journal of orthodontics
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• v.37 no.4
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• pp.293-304
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• 2007

The purpose of this study was to estimate the fracture resistance of commercially available ceramic brackets to torsional force exerted from arch wires and to evaluate the characteristics of bracket fracture. Methods: Lingual root torque was applied to maxillary central incisor brackets with 0.022-inch slots by means of a $022\;{\times}\;028-inch$ stainless steel arch wire. A custom designed apparatus that attached to an Instron was used to test seven types of ceramic brackets (n = 15). The torque value and torque angle at fracture were measured. In order to evaluate the characteristics of failure, fracture sites and the failure patterns of brackets were examined with a Scanning Electron Microscope. Results: Crystal structure and manufacturing process of ceramic brackets had a significant effect on fracture resistance. Monocrystalline alumina (Inspire) brackets showed significantly greater resistance to torsional force than polycrystalline alumina brackets except InVu. There was no significant difference in fracture resistance during arch wire torsional force between ceramic brackets with metal slots and those without metal slots (p > 0.05). All Clarity brackets partially fractured only at the incisal slot base and the others broke at various locations. Conclusion: The fracture resistance of all the ceramic brackets during arch wire torsion appears to be adequate for clinical use.

• The korean journal of orthodontics
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• v.40 no.3
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• pp.167-175
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• 2010

Objective: The aim of this study was to validate the Periotest values for the prediction of orthodontic mini-implants' stability. Methods: Sixty orthodontic mini-implants (7.0 mm $\times$ $\emptyset1.45$ mm; ACR, Biomaterials Korea, Seoul, Korea) were inserted into the buccal alveolar bone of 5 twelve month-old beagle dogs. Insertion torque (IT) and Periotest values (PTV) were measured at the installation procedure, and removal torque (RT) and PTV were recorded after 12 weeks of orthodontic loading. To correlate PTV with variables, the cortical bone thickness (mm) and bone mineral density (BMD) within the cortical bone and total bone area were calculated with the help of CT scanning. Results: The BMD and cortical bone thickness in mandibular alveolus were significantly higher than those of the maxilla (p < 0.05). The PTV values ranged from -3.2 to 4.8 for 12 weeks of loading showing clinically stable mini-implants. PTV at insertion was significantly correlated with IT (-0.51), bone density (-0.48), cortical bone thickness (-0.42) (p < 0.05) in the mandible, but showed no correlation in the maxilla. PTV before removal was significantly correlated with RT (-0.66) (p < 0.01) in the mandible. Conclusions: These results show that the periotest is a useful method for the evaluation of mini-implant stability, but it can only be applied to limited areas with thick cortical and high density bone such as the mandible.

• The korean journal of orthodontics
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• v.31 no.3 s.86
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• pp.335-346
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• 2001

The purpose of this study was to investigate the ideal clinical torque(In the SWA rectangular wire, the torque by the angle between the plane part and twisted part to move the tooth) of the orthodontic rectangular wire which produce the proper labiolingual movement of the single tooth during finishing stage of the orthodontic treatment. The clinical torque is the sum of the play and the active torque which generates the moment at the bracket. The play is calculated by the formula and the active torque is calculated by the computer aided three-dimensional finite element method. The finite element model was consist of the three brackets which formed a row and 3 kinds of orthodontic rectangular wire(stainless steel, TMA, NiTi) which inserted in brackets. Both sides of the model were twisted and the moment generated in the center bracket was calculated. The sizes of seven wires which were used commonly were .016'X.022', .017'X.022', .017'X.025', .018'X.025', .019'X.025', .020'X.025', .021'X.025'. In 018' bracket, 016'X.022', .017'X.022', .017'X.025' wires were inserted and in 022' bracket, all the sizes of wires except .016'X.022' were inserted and tested. The following conclusions could be drawn from this study. 1. The moments generated on the same size of the wires by the same active torque were equal regardless of the bracket slot size. 2. The moments were increased with the size of the wires. The moment generated on the .021'X.025' wire was about 1.75 times as large as that on the .016'X.022' wire regardless of the material. 3. The moments were increased in the order of the NiTi, TMA stainless steel. The moment of the TMA wire was 0.35 times as small as that of the stainless steel wire and the moment of the NiTi was0.16 times as small as that of the stainless steel wire. 4. The moment was decreased as the interbracket distance was increased. 5. To get a desired moment with the specific size and material of the wire on the specific bracket slot, the formula and the results were displayed.

• The korean journal of orthodontics
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• v.32 no.6 s.95
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• pp.401-411
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• 2002

Precise bracket positioning is essential in modem orthodontics. However, there can be alterations in the vertical position of a bracket due to several reasons. The purpose of this study was to evaluate the effect of variations in the vertical bracket position on the crown inclination in Korean patients with normal occlusion. From a larger group of what was considered to be normal occlusions obtained from the Department of Orthodontics, College of Dentistry, Seoul National University, each of the final 10 subjects (6 males and 4 females, with an average age of 22.3 yews) was selected. The dental models of each of the subjects were scanned three-dimensionally by a laser scanner, and measurements drawn from these were made on the scanned dental casts of the subjects were input into the computer program. From this the occlusal plane and the bracket plane were determined. The tooth plane was then constructed to measure the crown inclination on the bracket plane of each tooth. From a practical standpoint, information was obtained on the extent to which the torque of a tooth would be changed as the bracket position was to be moved vertically (in ${\pm}0.5mm,\;{\pm}1.0mm,\;{\pm}1.5mm$) from its ideal position. A one way analysis of the variance (ANOVA) was used to compare each group of the different vertical distances from the bracket plane on a specific tooth. Duncan's multiple comparison test was then performed. There were statistically significant differences in the crown inclination among the groups of different vertical distances for the upper central incisor, upper lateral incisor, upper canine, upper first and second molars, lower first and second premolars, and lower first and second molars (p<0.05). On the upper anterior teeth, upper molars, lower premolars and lower molars, the resultant torque values due to the vertical displacement of the bracket were different depending on the direction of the displacement, occlusal or gingival. This study implies that the torque of these teeth should be handled carefully during the orthodontic treatment. In circumstances in which the bracket must be positioned more gingivally or occlusally due to various reasons, it would be useful to provide the chart of torque alteration of each tooth referred to in this study with its specified bracket prescription.