• The Journal of Korean Academy of Prosthodontics
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• v.60 no.4
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• pp.420-430
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• 2022

Open bite is accompanied by decrease in tooth contact and overbite, and causes collapse of occlusal plane, mastication difficulties, speech disorders, changes in appearance, and lower occlusal force than normal. Open bite caused by temporomandibular joint disorder in adults with complete occlusion must be corrected after removal or stabilization of the causative factors. Orthodontic treatment, occlusal adjustment, prosthetic treatment, and surgical treatment can be the option of occlusal correction. This report describes about estimating the cause of occlusion change in two patients who developed an open bite due to mandibular displacement in adults with complete occlusion and different treatment approaches accordingly. In one patient, satisfactory result was obtained in functional and esthetic aspects through occlusal adjustment after stabilization of the temporomandibular joint.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.2
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• pp.148-155
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• 2008

The aim of the study is to interpret the distribution of occlusal force by 3-dimensional finite element analysis of ISP(Implant Supported Prosthesis) supported by minimum number of implant to restore the edentulous patients. For this study, the Astra Tech implant system is used. Geometric modeling for 6 and 4 fixture ISP group is performed with respect to the bone, implant and one piece superstructure, respectively. Implants are arbitrarily placed according to the anatomical limit of lower jaw and for the favorable distribution of occlusal force, which is applied at the end of cantilever extension of ISP with 30mm. Element type is tetrahedral for finite element model and the typical mechanical properties, Young's modulus and Poisson's ratio of each material, cortical, cancellous bone and implant material are utilized for the finite element analysis. From this study, we can see the distribution of equivalent stress equal to real situation and speculate the difference in the stress distribution in the whole model and at each implant fixture, From the analysis, the area of maximum stress is distributed on distal contact area between bone and fixture in the crestal bone. The maximum stress is 53MPa at the 0.2mm area from the bone-implant interface in the maximum side for 300N load condition for 4 fixture case, which is slightly less than the stress calculated from allowable strain. This stress has not been deduced to directly cause the loss of crestal bone around implant fixture, but the stress can be much reduced as the old peoples may have lower chewing force. Thus, clinical trial may be performed with this treatment protocol to use 4 fixtured ISP for old patients.

• The korean journal of orthodontics
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• v.45 no.4
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• pp.198-208
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• 2015

Objective: To quantify, for each activation, the effect of preactivations of differing distribution and intensity on the neutral position of T-loops (7-mm height), specifically the horizontal force, moment to force (M/F) ratio, and load to deflection ratio. Methods: A total 100 loops measuring $0.017{\times}0.025$ inches in cross-section were divided into two groups (n = 50 each) according to composition, either stainless steel or beta-titanium. The two groups were further divided into five subgroups, 10 loops each, corresponding to the five preactivations tested: preactivations with occlusal distribution ($0^{\circ}$, $20^{\circ}$, and $40^{\circ}$), gingival distribution ($20^{\circ}$), and occlusal-gingival distribution ($40^{\circ}$). The loops were subjected to a total activation of 6-mm with 0.5-mm iterations. Statistical analysis was performed using comprised ANOVA and Bonferoni multiple comparison tests, with a significance level of 5%. Results: The location and intensity of preactivation influenced the force intensity. For the M/F ratio, the highest value achieved without preactivation was lower than the height of the loop. Without preactivation, the M/F ratio increased with activation, while the opposite effect was observed with preactivation. The increase in the M/F ratio was greater when the preactivation distribution was partially or fully gingival. Conclusions: Depending on the preactivation distribution, displacement of uprights is higher or lower than the activation, which is a factor to consider in clinical practice.

• The korean journal of orthodontics
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• v.50 no.4
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• pp.268-277
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• 2020

This case report demonstrates two different uprighting mechanics separately applied to mesially tipped mandibular first and second molars. The biomechanical considerations for application of these mechanisms are also discussed. For repositioning of the first molar, which was severely tipped and deeply impacted, a novel cantilever mechanics was used. The molar tube was bonded in the buccolingual direction to facilitate insertion of a cantilever from the buccal side. By twisting the distal end of the cantilever, sufficient uprighting moment was generated. The mesial end of the cantilever was hooked over the miniscrew placed between the canine and first premolar, which could prevent exertion of an intrusive force to the anterior portion of the dentition as a side effect. For repositioning of the second molar, an uprighting mechanics using a compression force with two step bends incorporated into a nickel-titanium archwire was employed. This generated an uprighting moment as well as a distal force acting on the tipped second molar to regain the lost space for the first molar and bring it into its normal position. This epoch-making uprighting mechanics could also minimize the extrusion of the molar, thereby preventing occlusal interference by increasing interocclusal clearance between the inferiorly placed two step bends and the antagonist tooth. Consequently, the two step bends could help prevent occlusal interference. After 2 years and 11 months of active treatment, a desirable Class I occlusion was successfully achieved without permanent tooth extraction.

• Journal of Oral Medicine and Pain
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• v.30 no.1
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• pp.45-55
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• 2005

As people prefer to use right or left hand, some have preferred chewing side while others do not. Totally, 82 volunteers composed of students and staffs from Dental Hospital College of Dentistry Yonsei University participated in this study for the investigation of influence of preferred chewing habit, that has lasted for more than a year, on electromyographic(EMG) activity of masticatory muscles and bite force. Among the 82 volunteers, 46 had preferred chewing habit while the other 36 did not. Prior to the investigation, those with factors that could affect the study, such as, general disease, irregular dentition and malocclusion, were screened and excluded by questionnaire and clinical examination. The results were as follows: 1. There was no significant difference in EMG activities between chewing side and non-chewing side of preferred chewing subjects at rest as well as maximal voluntary contraction(MCV)(p>0.05). 2. Asymmetrical coefficient of temporal and masseter muscle EMG activities between preferred chewing subjects and non-preferred chewing subjects at rest was not significantly different(p>0.05). 3. Asymmetrical coefficient of masseter EMG activity was significantly higher(p<0.05) than that of non-preferred chewing subjects at MCV, whereas that of anterior temporal muscle showed no difference(p<0.05). 4. In preferred chewing subjects, there was no significant difference in average bite force and occlusal contact area between chewing side and non-chewing side(p>0.05). 5. There was no significant difference in Asymmetrical coefficients of average bite force and occlusal contact area between preferred chewing subjects and non-preferred chewing subjects (p>0.05). Consequently, preferred chewing habit can be considered as physiological asymmetry with normal function rather than to have influence on EMG muscle activity of masticatory muscles, average bite force and occlusal contact area. Objective standardization to differentiate preferred chewing subjects and non-preferred chewing subjects should be established in the further study.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.3
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• pp.467-491
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• 1995

In order to analyze the occlusin of intercuspation with maximun bite force, fifteen healthy adult subjects with the ages 23 to 27 were studied(Group1 ; 5-normal occlusion with Angle's Class1, Group2 ; 5-Angle's Class2 malocclusion, Group3 ; 5-Angle’s Class3 malocclusion). Head Position was fixed with occlusal plane paralleling to horizontal line and occlusal registration r cord was made with polyether rubber impression material(Ramitec, ESPECo. West Germany). After all subject were trained for maximum intercuspation at least 5 times, occlusal registration procedure was repeated for this study. Lower posterior rubber occlusal registration records were sliced with 1mm thickness using precision metal sliding channel(Hitachi Ind. Co., Japan). Gross sectional drawings were traced from occluding view of upper and lower posterior teeth on the rubber slices using digitizer, and superimposed for the determination of each drawing distance(Superimposed Rubber Pattern Method). Based on superimposed rubber pattern drawings, total area of occlusal view, sum of each area of the 5 divided occlusal contact provinces and its ratio, total area and number of occlusal contact area were determined to elucidate occlusal stability in the normal and abnormal occlusion groups. The data were analysed by t-test(p=0.05) to determine statistical significance. The obtained results were as follows : 1. Group1 showed the largest standard area with occlusal view of the lower posterior teeth and Group3 showed the smallest area. There was a significant difference between Group2 and Group3(p=0.025), and Gropu1 was not statistically different for both Group2 and Group3. 2. Means and ratio of the under 2.0mm area(D) and ratio showed $197.49mm^2$, 59.76% in Group1, $188,69mm^2$, 56.10% in Group2, and $174.23mm^2$, 55.76% in Group3. The results that Group1 has the most area/ratio and Group3 has the least area/ratio can be considered Group1 is the most advantageous for masticatory effective area, and Group3 is the least adnantageous. 3. Means and ratio of the under 1.0mm area(C) were $198.96mm^2$, 42.65% in Group1, 123.06$mm^2$, 46.58% in Group2, and $92.24mm^2$, 29.52% in Group3. These data means that Group1 is the most advantageous in terms of masticatory effective area and Group3 is the least. 4. Means and ratio of the under 0.5mm area(B) were $86.68mm^2$, 26.68% in Group1, $62.98mm^2$, 18.71% in Group2, and $36.44mm^2$, 11.66% in Group3. These can also be considered Group1 is the most advantageous for masticatory effective area and occlusal stability. 5. Means and ratio of the under 0.05mm area(A) were $30.92mm^2$, 9.21% in Group1, $14.31mm^2$, 4.25% in Group2, and $7.59mm^2$, 2.43% in Group3. The area ratio of the each subject group was(4.1) : (1.9) : (1)and the data of the under 0.05mm area has the intimate relationship with inter-group and intra-group data/ratio. 6. First molar showed the most occlusal contact points in all subject group and Group1 showed somewhat uniformly distributed occlusal contact point except first premolar. In Group2, all contact point in posterior teeth showed significantly reduced distribution except first molar. Group3 showed evenly distributed contace points in first and second molars.

• The Journal of Korean Academy of Prosthodontics
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• v.51 no.2
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• pp.119-124
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• 2013

Many of the patients with extensive abrasion need comprehensive restorative treatment. The abrasion is usually caused by attrition, besides of it, there are many reasons for it. The plan of treatment should be started on assessment of the type of attrition and the etiologic analysis. Patient with well-developed masticatory muscle, alveolar process, and high occlusal force and also with little muscle length difference between the stable and the contracted state should be carefully assessed for the vertical dimensional loss and the restoration should be carefully designed. Decrease of tooth length can be compensated by the growth of the alveolar bone height; therefore, consistency of the occlusal vertical dimension is maintained. Accordingly, a careless increase of the vertical dimension can produce muscle fatigue, depressed tooth and pain, and fracture of the restoration. In this case, the patient with multiple tooth abrasion and clenching habit, the edentulous maxillary area is restored with amalgam inserted RPD, and the dentulous area of the maxilla and mandible are treated with fixed restoration accompanying with the increase of vertical dimension. Consequently, we are going to report about the satisfying result in both functional and esthetic aspects.

• The korean journal of orthodontics
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• v.25 no.5 s.52
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• pp.543-555
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• 1995

In the orthopedic therapy, the biomechanical analysis of the appliance is necessary to get a desirable orthopedic effect. The purpose of this study was to investigate the desirable direction and application position of the protraction force. The protraction force of 500g was applied to the first premolar or to the first molar. The direction of force application was paralell or $20^{\circ}$ downward to the occlusal plane respectively. The stress distribution and the displacement within the maxilla was analyzed by a 3-dimensional finite element method. The findings obtained were as follows 1. Protraction forces caused a counterclockwise rotation of the maxilla. 2. The degree of maxillary rotation was less when the force was applied $20^{\circ}$ downward direction to the occlusal plane than when applied to the parallel direction. 3. The degree of rotation of maxilla was greater when the parallel force was applied to the 1st premolar than when applied to the first molar, whereas it was greater when force is applied $20^{\circ}$ downward than at the first premolar. In conclusion, the $20^{\circ}$ downward protraction from the first premolar induced the least counterclockwise rotation of the maxilla and was thought as the desirable direction and application position of the protraction force.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.4
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• pp.405-417
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• 2010

Previous studies have already shown that mouthguard is effective in protecting jaw bone, teeth and oral tissue against sports trauma. However, other than severe trauma, repetitive force, such as disorders like clenching, cause teeth or oral tissue damage. These kinds of disorders usually present pathologic attrition in the posterior teeth, resorption in alveolar bone, loss of teeth and destruction of occlusion. Wearing a mouthguard is believed to be effective in preventing these disorders. But its effect is not examined thoroughly enough. The purpose of this study is to identify whether mouthguard is effective in reducing strain caused by clenching. Mandibular first molars in the normal occlusal relationship without any history of dental treatment were chosen. Biaxial type strain gauge was placed on the buccal surface of the tooth. Having maximum occlusal force, measured by load cell, as a standard, clenching intensity were divided into three stages; moment of slightly tooth contact, medium bite force (50% of maximum bite force), maximum bite force. Strain occurring in dentition in each stage with and without mouthguard was measured. Changes in strain (on dentition) between each stage and difference in strain, between with or without mouthguard were recorded by PCD-300 analyzer and PCD-30 soft ware. The data was statistically analyzed by Wilcoxon signed rank test. The following results were drawn; Without mouthguard, strain given on dentition increased as the clenching force increased. With mouthguard, strain given on dentition also increased as the clenching force increased. With mouthguard, strain decreased, in all cases of clenching force stages. Data on the moment of slightly tooth contact stage, had no statistical significance. However, with mouthguard, 50-90% of decrease in strain could be obtained in maximum occlusal force, compared to the group without mouthguard. Mouthguard decreased the strain on the dentition, caused by clenching. Therefore, mouthguard seems to be effective in preventing damage on dentition, by acting against clenching, which occurs both consciously and unconsciously during sports activities.

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.4
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• pp.257-268
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• 2003

The purpose of this study was to assess the loading distributing characteristics of implant prosthesis according to position and direction of load, under vertical and inclined loading using FEA analysis. The finite element model was designed according to standard fixture (4.1mm restorative component x 11.5mm length). The crown for mandibular first molar was made using UCLA abutment. Each three-dimensional finite element model was created with the physical properties of the implant and surrounding bone. This study simulated loads of 200N at the central fossa in a vertical direction (loading condition A), 200N at the outside point of the central fossa with resin filling into screw hole in a vertical direction (loading condition B), 200N at the centric usp in a $15^{\circ}$ inward oblique direction (loading condition C), 200N at the in a $30^{\circ}$ inward oblique direction (loading condition D) or 200N at the centric cusp in a $30^{\circ}$ outward oblique direction (loading condition E) individually. Von Mises stresses were recorded and compared in the supporting bone, fixture, and abutment screw. The following results have been made based on this study: 1. Stresses were concentrated mainly at the ridge crest around implant in both vertical and oblique loading but stresses in the cancellous bone were low in both vertical and oblique loading. 2. Bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. The magnitude of the stress was greater with the oblique loading than with the vertical loading. 3. An offset of the vertical occlusal force in the buccolingual direction relative to the implant axis gave rise to increased bending of the implant. 4. The relative positions of the resultant line of force from occlusal contact and the center of rotation seems to be more important. 5. The magnitude of the stress in the supporting bone, fixture and abutment screw was greater with the outward oblique loading than with the inward oblique loading and was the greatest under loading at the centric cusp in a $30^{\circ}$ outward oblique direction. Conclusively, this study provides evidence that bending moments resulting from non-axial loading of dental implants caused stress concentrations on cortical bone. But it seems to be more important that how long is the distance from center of rotation of the implant itself to the resultant line of force from occlusal contact(leverage). The goal of improving implants should be to avoid bending of the implant.