• The Journal of Korean Academy of Prosthodontics
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• v.57 no.1
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• pp.66-74
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• 2019

Excessive wear causes many complications when untreated, so that accurate diagnosis, analysis and predictive treatment plan should be made, and through evaluation of vertical dimension and stepwise treatment, a stable inter-arch relationship can be set. For the long-term success of implant treatment, ideal position and angle of implant is important, and its importance increases especially in multiple implant cases. Therefore, thorough diagnosis and planning, accurate surgery and prosthodontic procedures are significant. In this case, a 68-year-old male patient with a loss of vertical dimension due to multiple tooth loss and overall tooth wear was planned with systematic analyses from the pre-treatment stage to rehabilitate vertical dimension. Full-mouth fixed rehabilitation with computer tomography guided implant surgery was performed to the newly set vertical dimension and attained satisfactory outcomes both functionally and esthetically.

• Journal of Dental Rehabilitation and Applied Science
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• v.37 no.4
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• pp.225-231
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• 2021

There are many studies on the indications and efficacy of splint therapy commonly used in patients with temporomandibular disorders (TMD). However, there have been no studies on the splint weaning in terms of the splint use tapering period in relation to symptom improvement of TMD. This retrospective study aims to analyze a proper splint weaning method in patients with TMD based on symptom improvement. Materials and Methods: The authors examined 130 TMD patients with TMJ disorders, masticatory muscle disorders, and clenching/bruxism who had received splint therapy (occlusion stabilization splint, anterior positioning splint) of patients who visited the Department of Orofacial Pain and Oral Medicine at Yonsei University Dental Hospital from 2015 to 2020. They were evaluated according to the method to wean splints. Results: The mean splint therapy period was 29.0 months, during which patients wore splints 7 days a week for 8.4 months, 3 - 4 days a week for 9.5 months, and finally 1 - 2 days a week for 11.1 months (a total of 29.0 months, about 2.5 years). Conclusion: It seems that TMD symptoms can be alleviated and side effects such as occlusal change can be minimized if patients wear a splint 7 days a week for the first 6 months, followed by 3 - 4 days a week for the next 6 to 18 months, and finally 1 - 2 days a week after 18 months.

• Journal of the korean academy of Pediatric Dentistry
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• v.49 no.1
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• pp.65-75
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• 2022

The aim of this study was to evaluate QLF (quantitative light-induced fluorescence) technology for the caries detection in primary teeth and validate the relationships between the cavity volume of carious lesions and QLF analysis results. Total 125 tooth surfaces include 53 occlusal surfaces, and 72 proximal surfaces were investigated with the portable QLF device for detection of dental caries in primary molars. Micro-CT radiograph was also performed to classify carious lesions and calculate the cavity volume. QLF showed good accuracy and reliability (sensitivity 0.75 - 0.94, specificity 0.82 - 0.95, and AUROC 0.88 - 0.98) for the caries detection in primary teeth except 𝚫R average results of proximal caries which showed relatively low values. Statistically significant relationships were found between 𝚫F average, QS-Index and the cavity volume according to Spearman rank-order correlation coefficients (r = 0.805 - 0.832, p < 0.001). QLF detection method would be a harmless and reliable way for children to diagnose dental caries without the concern about radiation exposure.

• The Journal of Korean Academy of Prosthodontics
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• v.61 no.2
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• pp.125-134
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• 2023

When the patient with class III malocclusion needs extensive oral rehabilitation due to multiple missing teeth, accurate diagnosis, and careful analysis, such as the patient's occlusal relationship, facial changes, and evaluation of the temporomandibular joint are essential. Orthognathic surgery is often performed for aesthetic improvement, depending on the patient's chief complaint. If it is not possible due to certain circumstances, partial aesthetic improvement can be achieved through minimal elevation of the vertical dimension. As this patient may have unexpected issues, such as temporomandibular joint disorder, oral habits like bruxism, and masticatory muscle tension, it was determined whether the patient could adjust to a reversible temporary removable partial denture. After this, the maxillary implant-supported fixed prostheses and the mandibular fixed prostheses were used to achieve stable posterior support and to partially improve the maxillary anterior esthetics. The patient was satisfied with the results both aesthetically and functionally. The prognosis is expected to be good if regular check-ups are conducted.

• The Journal of Advanced Prosthodontics
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• v.15 no.6
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• pp.281-289
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• 2023

PURPOSE. This study aimed to predict the positional coordinates of incisor points from the scan data of conventional complete dentures and verify their accuracy. MATERIALS AND METHODS. The standard triangulated language (STL) data of the scanned 100 pairs of complete upper and lower dentures were imported into the computer-aided design software from which the position coordinates of the points corresponding to each landmark of the jaw were obtained. The x, y, and z coordinates of the incisor point (X_P, Y_P, and Z_P) were obtained from the maxillary and mandibular landmark coordinates using regression or calculation formulas, and the accuracy was verified to determine the deviation between the measured and predicted coordinate values. Y_P was obtained in two ways using the hamularincisive-papilla plane (HIP) and facial measurements. Multiple regression analysis was used to predict Z_P. The root mean squared error (RMSE) values were used to verify the accuracy of the X_P and Y_P. The RMSE value was obtained after crossvalidation using the remaining 30 cases of denture STL data to verify the accuracy of Z_P. RESULTS. The RMSE was 2.22 for predicting X_P. When predicting Y_P, the RMSE of the method using the HIP plane and facial measurements was 3.18 and 0.73, respectively. Cross-validation revealed the RMSE to be 1.53. CONCLUSION. Y_P and Z_P could be predicted from anatomical landmarks of the maxillary and mandibular edentulous jaw, suggesting that Y_P could be predicted with better accuracy with the addition of the position of the lower border of the upper lip.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.4
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• pp.424-434
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• 2009

Statement of problem: Problems such as loosening and fractures of retained screws and fracture of implant fixture have been frequently reported in implant prosthesis. Purpose: Implant has weak mechanical properties against lateral loading compared to vertical occlusal loading, and therefore, stress analysis of implant fixture depending on its material and geometric features is needed. Material and methods: Total 28 of external hexed implants were divided into 7 of 4 groups; Group A (3i, FULL $OSSEOTITE^{(R)}$Implant), Group B (Nobelbiocare, $Br{\aa}nemark$ $System^{(R)}$Mk III Groovy RP), Group C (Neobiotec, $SinusQuick^{TM}$ EB), Group D (Osstem, US-II). The type III gold alloy prostheses were fabricated using adequate UCLA gold abutments. Fixture, abutment screw, and abutment were connected and cross-sectioned vertically. Hardness test was conducted using MXT-$\alpha$. For fatigue fracture test, with MTS 810, the specimens were loaded to the extent of 60-600 N until fracture occurred. The fracture pattern of abutment screw and fixture was observed under scanning electron microscope. A comparative study of stress distribution and fracture area of abutment screw and fixture was carried out through finite element analysis Results: 1. In Vicker's hardness test of abutment screw, the highest value was measured in group A and lowest value was measured in group D. 2. In all implant groups, implant fixture fractures occurred mainly at the 3-4th fixture thread valley where tensile stress was concentrated. When the fatigue life was compared, significant difference was found between the group A, B, C and D (P<.05). 3. The fracture patterns of group B and group D showed complex failure type, a fracture behavior including transverse and longitudinal failure patterns in both fixture and abutment screw. In Group A and C, however, the transverse failure of fixture was only observed. 4. The finite element analysis infers that a fatigue crack started at the fixture surface. Conclusion: The maximum tensile stress was found in the implant fixture at the level of cortical bone. The fatigue fracture occurred when the dead space of implant fixture coincides with jig surface where the maximum tensile stress was generated. To increase implant durability, prevention of surrounding bone resorption is important. However, if the bone resorption progresses to the level of dead space, the frequency of implant fracture would increase. Thus, proper management is needed.

• The korean journal of orthodontics
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• v.35 no.1 s.108
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• pp.60-68
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• 2005

The evaluation of malocclusion has to be done quantitatively and qualitatively. This will be lead toward an analysis of malocclusion severity as well as treatment difficulty. The method of proper evaluation of malocclusion severity and treatment difficulty is necessary to assess treatment effect and efficiency for the orthodontists and to establish fundamentals for planning and executing the health-related policies in private and public institutions. The purposes of this study as the first part of the objective and quantitative analysis of malocclusion were 1) to measure treatment difficulty based on the opinions of several orthodontists. and 2) to investigate the relationships between objective malocclusion severity and subjective treatment difficulty 100 pairs of dental casts that had various types and severity of malocclusion were selected from the orthodontic departments of Kyurghee University and Samsung Medical Center The objective malocclusion severity was measured with the PAR (Peer Assessment Rating) index and the subjective treatment difficulty was evaluated by 8 experienced orthodontists. The relationships between objective malocclusion severity and subjective treatment difficulty were statistically evaluated. There were significant relationships between objective malocclusion severity and subjective treatment difficulty especially in the measurements of the upper anterior alignment, the buccal occlusion. the overjet, the overbite and the midline discrepancy en the malocclusion components. The results of this study can provide the background knowledge to develop a new occlusal index. which contains both the malocclusion severity and treatment difficulty for Korean orthodontists.

• Journal of Dental Rehabilitation and Applied Science
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• v.18 no.3
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• pp.145-155
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• 2002

The results of the present feasibility study are summarized as follows, 1. The three unit bridge of knitted material and UD fibre reinforcement has both the rigidity and the strength against a vertical occlusal load of 75N. 2. Stress concentration at the junctional area between the bridge and the abutments, i.e. between the pontic and the knitted caps was observed. In the case of the bridge with reinforcement straps, it was partly shown that the concentration problem could be improved by simply increasing the fillet size at the area. Further refining in the surface of the junctional area will be needed to ensure a further improvement in the stress distribution. This will require some trade off in the level of the stress and the available space. A parametric study will help to decide the appropriate size of the fillet. 3. Design refinement is a must to improve the stress distribution and realize the most favourable shape in terms of fabrication. The current straight bar with a constant cross section area can be redesigned to a tapered shape. The curve from the dental arch should also be placed on the pontic design. In accordance with design refinement, the resistance of the bridge frame to other load cases should be evaluated. 4. Although not included in the present feasibility study, it is estimated that bridges of the anterior teeth can be made strong enough with the knitted material without further reinforcement using unidirectional materials. In this regard, a feasibility study on design concepts and stress analysis for 3, 4, 5 unit bridge is suggested. 5. Two types of bridge were analysed in terms of fatigue. The safe life design concept, i.e. fatigue design concept, looks reasonable for the bridge where if cracks should form and propagate there is virtually nothing a dentist to do. The bridge must be designed so that no crack will be initiated during the life span. In the case of crowns, however, if constructed with composite resin with knitted materials, it might be possible to repair them, which in general is impossible for crowns of PFM or of metal. Therefore for composite resin crowns, a damage tolerance design concept can be applied and reasonably higher operational stresses can be allowed. In this case, of course, a periodic inspection program should be established in parallel. 6. Parts of future works in terms of structural viewpoint which need to be addressed are summarized as the following: 1) To develop processing technology to accommodate design concepts; 2) More realistic modelling of the bridge and analysis-geometry and loading condition. Thickness variation in the knitted material, taper in the pontic, design for anterior tooth bridge, the effect of combined loads, etc, will need to be included; 3) To develop appropriate design concepts and design goals for the fibre composite FPD aiming at taking the best advantage of knitted materials, including the damage tolerance design concept; 4) To develop testing method and perform test such as static ultimate load test, fatigue test, repair test, etc, as necessary.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.5
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• pp.479-489
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• 2008

Statement of the problem: Under anatomical limitations on maxillary posterior region, a poor crown-to root ratio acting on dental implants can result in undesirable stress in surrounding bone, which in turn can cause bone defects and eventual failure of implants. Purpose: The purpose is to compare stress distribution due to different crown-root ratio and effect of splinting between natural teeth and implants in maxillary molar area under different loads. Material and methods: Analysis of stress arising supporting bone of the natural teeth and the implant was made with 3-dimensional finite element method. The model simulated naturel teeth was made with 2nd premolar and 1st molar in the maxillary molar region (Model T). The model simulated implants placed on same positions with two parallel implants of Straumann Dental Implant cemented abutment (Model I). Each model was designed in different crown-root ratio (0.7:1, 1:1, 1.25:1) and set cement type gold crown to make it non-splinted or splinted. After that, 300 N force was loaded to each model in five ways (Load 1: middle of occlusal table, Load 2: middle of buccal cusp, Load 3: middle of lingual cusp, Load 4: horizontal load to buccal cusp of anterior abutment only, Load 5: horizontal load to middle of buccal cusp of each abutment), and stress distribution was analyzed. Results and conclusion: On all occasions, stress was concentrated at the cervical region of the implant. Under load 1, 2 and 3, stress was not increased even when crown-root ratio increases, but under load 4 and 5, when crown-root ratio increases, stress also increased. There was difference in stress values between natural teeth and implants when crown-root ratio gradually increases; In case of natural teeth, splinting decreased stress under vertical and horizontal loads. In case of implants, splinting decreased stress under vertical loads 1,2 and 3, but increased maximal stress under loads 2 and 3. Under horizontal loads, splinting decreased stress, however the effect of splinting decreased under load 5 than load 4. Furthermore, the stress was increased, when crown-root ratio is 1.25:1. Clinical implications: This limited finite element study suggests that the stress on supporting bone may be increased under non-axial loads and poor crown-root ratio. Under poor crown-root ratio, excessive stress was generated at the cervical region of the implant, and decreased splinting effect for stress distribution, which can be related to clinical failure.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.33 no.2
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• pp.152-161
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• 2007

This study was conducted to patients visited oral maxillo-facial surgery, KNUH and the purpose of the study was to assess skeletal and dento-alveolar stability after surgical-orthodontic correction treated by skeletal Class III malocclusion patients with open bite versus non-open bite. This retrospective study was based on the examination of 40 patient, 19 males and 21 females, with a mean age 22.3 years. The patients were divided into two groups based on open bite and non-open bite skeletal Class III malocclusion patients. The cephalometric records of 40 skeletal Class III malocclusion patients (open bite: n = 18, non-open bite: n = 22) were examined at different time point, i.e. before surgery(T1), immediately after surgery(T2), one year after surgery(T3). Bilateral sagittal split ramus osteotomy was performed in 40 patients. Rigid internal fixation was standard method used in all patient. Through analysis and evaluation of the cephalometric records, we were able to achieve following results of post-surgical stability and relapse. 1. There was no significant statistical differences between open bite and non-open bite with skeletal Class III malocclusion patients in maxillary occlusal plane angle of pre-operative stage(p>0.05). 2. Mean vertical relapses of skeletal Class III malocclusion patients with open bite were $0.02{\pm}1.43mm$ at B point and $0.42{\pm}1.56mm$ at Pogonion point. In skeletal Class III malocclusion patients with non-open bite, $0.12{\pm}1.55mm$ at B point and $0.08{\pm}1.57mm$ at Pogonion point. There was no significant statistical differences between open bite and non-open bite with skeletal Class III malocclusion patients in vertical relapse(p>0.05). 3. Mean horizontal relapses of skeletal Class III malocclusion patients with open bite were $1.22{\pm}2.21mm$ at B point and $0.74{\pm}2.25mm$ at Pogonion point. In skeletal Class III malocclusion patients with non-open bite, $0.92{\pm}1.81mm$ at B point and $0.83{\pm}2.11mm$ at Pogonion point. There was no significant statistical differences between open bite and non-open bite with skeletal Class III malocclusion patients in horizontal relapse(p>0.05). 4. There were no significant statistical differences between open bite and non-open bite with skeletal Class III malocclusion patients in post-surgical mandibular stability(p>0.05). and we believe this is due to minimized mandibular condylar positional change using mandibular condylar positioning system and also rigid fixation using miniplate 5. Although there was no significant relapse tendency observed at chin points, according to the Pearson correlation analysis, the mandibular relapse was influenced by the amount of vertical and horizontal movement of mandibular set-back(p=0.05, r>0.304).