• The korean journal of orthodontics
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• v.46 no.4
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• pp.228-241
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• 2016

Objective: Root mobility due to reciprocating movement of the tooth (jiggling) may exacerbate orthodontic root resorption (ORR). "Jiggling" describes mesiodistal or buccolingual movement of the roots of the teeth during orthodontic treatment. In the present study, buccolingual movement is described as "jiggling." We aimed to investigate the relationship between ORR and jiggling and to test for positive cell expression in odontoclasts in resorbed roots during experimental tooth movement (jiggling) in vivo. Methods: Male Wistar rats were divided into control, heavy force (HF), optimal force (OF), and jiggling force (JF) groups. The expression levels of cathepsin K, matrix metalloproteinase (MMP)-9 protein, interleukin (IL)-6, cytokine-induced neutrophil chemoattractant 1 (CINC-1; an IL-8-related protein in rodents), receptor activator of nuclear factor ${\kappa}B$ ligand (RANKL), and osteoprotegerin protein in the dental root were determined using immunohistochemistry. Results: On day 21, a greater number of root resorption lacunae, which contained multinucleated odontoclasts, were observed in the palatal roots of rats in the JF group than in rats from other groups. Furthermore, there was a significant increase in the numbers of cathepsin K-positive and MMP-9-positive odontoclasts in the JF group on day 21. Immunoreactivities for IL-6, CINC-1, and RANKL were stronger in resorbed roots exposed to jiggling than in the other groups on day 21. Negative reactivity was observed in the controls. Conclusions: These results suggest that jiggling may induce ORR via inflammatory cytokine production during orthodontic tooth movement, and that jiggling may be a risk factor for ORR.

• Journal of the Korea Convergence Society
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• v.11 no.10
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• pp.81-88
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• 2020

This purpose of this study is to develop content that enables repetitive carving practice of the maxillary right central incisor (MRCI) based on augmented reality (AR). For a step-by-step practice of achieving the tooth shape, after creation of the storyboard from the square box shape in step 1 to the completed MRCI block in step 16, three-dimensional (3D) modeling data reflecting the characteristics of the mesial, distal, lingual, and labial surface of the MRCI were generated. An application was built in which 3D modeling data were output on the screen of the learner's mobile device, and image markers suitable for 3D modeling in steps 1 to 16 of the MRCI model were respectively generated. Using this information, the learner could carve a high-quality MRCI by repeatedly performing the tooth shape carving exercises. With AR, we intend to contribute to improved tooth morphology carving skills by linking the theory and practical techniques for a beginners in dentistry.

• Journal of Periodontal and Implant Science
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• v.48 no.2
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• pp.124-134
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• 2018

Purpose: Clinicians must examine tooth wear to make a proper diagnosis. However, qualitative methosds of measuring tooth wear have many disadvantages. Therefore, this study aimed to develop and evaluate quantitative parameters using the cusp area and volume of virtual dental models. Methods: The subjects of this study were the same virtual models that were used in our former study. The same age group classification and new tooth wear index (NTWI) scoring system were also reused. A virtual occlusal plane was generated with the highest cusp points and lowered vertically from 0.2 to 0.8 mm to create offset planes. The area and volume of each cusp was then measured and added together. In addition to the former analysis, the differential features of each cusp were analyzed. Results: The scores of the new parameters differentiated the age and NTWI groups better than those analyzed in the former study. The Spearman ${\rho}$ coefficients between the total area and the area of each cusp also showed higher scores at the levels of 0.6 mm (0.6A) and 0.8A. The mesiolingual cusp (MLC) showed a statistically significant difference (P<0.01) from the other cusps in the paired t-test. Additionally, the MLC exhibited the highest percentage of change at 0.6A in some age and NTWI groups. Regarding the age groups, the MLC showed the highest score in groups 1 and 2. For the NTWI groups, the MLC was not significantly different in groups 3 and 4. These results support the proposal that the lingual cusp exhibits rapid wear because it serves as a functional cusp. Conclusions: Although this study has limitations due to its cross-sectional nature, it suggests better quantitative parameters and analytical tools for the characteristics of cusp wear.

• The Journal of Advanced Prosthodontics
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• v.12 no.1
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• pp.1-8
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• 2020

PURPOSE. To investigate the influence of crown material (lithium-disilicate, 3Y-TZP zirconia) and abutment type (rigid implant, resin tooth with artificial periodontium) on wear performance of their antagonist teeth and adjacent teeth. MATERIALS AND METHODS. A mandibular left first molar (#36) with adjacent human teeth (mandibular left second premolar: #35, mandibular left second molar: #37) and antagonistic human teeth (maxillary left second premolar: #25, maxillary left first molar: #26, maxillary left second molar: #27) was prepared simulating a section of the jaw. Samples were made with extracted human molars (Reference), crowned implants (Implant), or crowned resin tooth analogues (Tooth). Crowns (tooth #36; n = 16/material) were milled from lithium-disilicate (Li, IPS e.max CAD) or 3Y-TZP zirconia (Zr, IPS e.max ZirCAD, both Ivoclar Vivadent). Thermal cycling and mechanical loading (TCML) in the chewing simulator were applied simulating 15 years of clinical service. Wear traces were analyzed (frequency [n], depth [㎛]) and evaluated using scanning electron pictures. Wear results were compared by one-way-ANOVA and post-hoc-Bonferroni (α = 0.05). RESULTS. After TCML, no visible wear traces were found on Zr. Li showed more wear traces (n = 30-31) than the reference (n = 21). Antagonistic teeth #26 showed more wear traces in contact to both ceramics (n = 27-29) than to the reference (n = 21). Strong wear traces (> 350 ㎛) on antagonists and their adjacent teeth were found only in crowned groups. Abutment type influenced number and depth of wear facets on the antagonistic and adjacent teeth. CONCLUSION. The clinically relevant model with human antagonistic and adjacent teeth allowed for a limited comparison of the wear situation. The total number of wear traces and strong wear on crowns, antagonistic and adjacent teeth were influenced by crown material.

• The korean journal of orthodontics
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• v.23 no.2 s.41
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• pp.263-273
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• 1993

The purpose of this study was to analyse the center of resistance of the maxillary first molar using the 3-dimension finite element method. An extracted maxillary first molar of normal shape and average root length was selected and sectioned every 1.5mm parallel to the cementoenamel junction. Each section was traced and digitized to construct 3-D finite element model of the maxillary first molar. After a certain magnitude of counterbalancing moment(M) was applied to the tooth, a varying single force(F) of distomesial direction was applied to a certain point of th tooth until the tooth was translated. The force producing translation(Ft) was substituted to the equation ${\Delta}d=M/Ft$ to calculate the center of resistance of the maxillary first molar. And reducing the alveolar bone level 1.68mm, and 3.36mm below to the cementoenamel junction, the tooth movement was analysed to see the effect of reducing the alveolar bone level to the location of the center of resistance. The results were as follows ; 1. The center of resistance of the maxillary first molar was 3.72mm apical, 1.10mm buccal, and 0.71mm mesial to the geometric center of the horizontally sectioned surface at the cementoenamel junction. This point was 0.36mm apical, 1.20mm buccal, and 0.71mm mesial to the trifurcation point, indicating that it was not on the tooth root. 2. As the alveolar bone level was reduced, the center of resistance of the maxillary first molar was moved to the apical direction.

• Journal of Korean society of Dental Hygiene
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• v.16 no.6
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• pp.849-861
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• 2016

Objectives: The purpose of the study was to investigate the relationships among snack habits, oral health practice, and oral health status in preschool children. Methods: The subjects were 209 preschool children and their mothers in Jeonbuk from March 24 to May 30, 2014. The study instruments comprised snack habits, oral health practice, and oral health status. Data were analyzed for independent t-test, one way ANOVA and hierarchical multiple regression using SPSS Win 21.0 version. Results: Higher dft index was shown in the older age (p=0.033), lower mother's education (p<0.001), lower mother's daily toothbrushing (p<0.001), check-up after tooth-brushing (p<0.001), tooth-brushing practice before sleeping (p<0.001), tooth-brushing practice after snack (p<0.001), regular dental check-up (p<0.001), fluoride and sealant for prevention caries (p<0.001), limitation of sugar snack intake (p<0.007), periodic replacement toothbrush (p=0.022). The cause of higher dft index included soda (p<0.001), yogurt (p<0.001), snack (p=0.002), bread and cake (p=0.002) and caramel and candy (p<0.001). Fruit (p<0.001), vegetable (p<0.001) and milk (p=0.004) decreased dft index. Factors affecting oral health status were tooth-brushing practice before sleeping, tooth-brushing practice after snack, regular dental check-up, fluoride and sealant for prevention caries, and intake of soda, yogurt, caramel, candy, and fruit. The explanation power of the final model was 67.6%. Conclusions: It is necessary to develop the oral health education program for the preschool children and mothers to enhance the best oral health condition.

• Journal of Korean society of Dental Hygiene
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• v.20 no.3
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• pp.335-346
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• 2020

Objectives: This study investigated the association between oral health and suicide attempts in adults aged 65 years or older using the 7^th Korea National Health and Examination Survey (KHANES, 2016-2018). Methods: Of the total 24,269 participants of the 7^th KHANES (2016-2018), 1,488 adults aged 65 years or older who had an oral health examination were selected. Variations in suicide attempts with demographic characteristics and perceived oral health status were analyzed using the χ² test, and the association between oral health and suicide attempts was analyzed using the logistic regression model. Results: The suicide attempt rate was higher among older adults with chewing (p<0.01) and speaking (p<0.05) difficulties. The odds ratio for a suicide attempt was 1.05 times higher among those with tooth loss (p<0.05). Conclusions: Our results showed that older adults with tooth loss had an increased risk of suicide. Thus, it is important to prevent tooth loss, in the first place, through proper oral health management. If tooth loss occurs, appropriate treatment should be prioritized to facilitate functional recovery. Finally, national support is required for older adults with limited access to dental care.

• Journal of Korean society of Dental Hygiene
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• v.19 no.3
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• pp.421-436
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• 2019

Objectives: The purpose of this study was to compare the dental treatment needs of workers depending on their shifts and working patterns. Methods: Only workers aged 15 or older according to the $6^{th}$ Korea National Health and Nutrition Examination Survey (2013-2015) were considered eligible. A total of 9,092 people who responded to health surveys and completed oral examinations and interviews were selected for the study. Statistical analysis was carried out by the complex samples general linear model. Results: As the daytime workers' age increased, the requirement for restorative treatment decreased. In contrast, the requirement for tooth extraction caused by dental caries and periodontal disease increased. As the evening shift workers' age increased, the requirement for restorative treatment decreased. In the case of shift workers, the requirement for restorative treatment was lowest in those aged 50-64 years and highest in those aged 30-49 years. In the case of smokers; the daytime workers required a higher amount of restorative treatment, pulpal treatment, and tooth extraction due to dental caries and periodontal disease; the night shift workers required a higher amount of restorative treatment; and the shift workers required a higher amount of tooth extraction caused by periodontal disease. The results of comparing the dental treatment needs depending on working patterns were: the need for restorative treatment was higher in night shift workers (0.377) than in shift workers (0.245); the requirement for pulpal and restorative treatment was higher in daytime workers (0.055) than in night shift workers (0.010); requirement for tooth extraction due to periodontal disease was higher in night shift workers (0.060) than in evening shift workers (0.012). Conclusions: There are differences in dental treatment needs depending on the workers' working patterns. Collective oral health care is needed at workplaces to promote the workers' oral health.

• Journal of the korean academy of Pediatric Dentistry
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• v.46 no.1
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• pp.10-20
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• 2019

Individual dental age is used as an index of chronological age estimation and is an important indicator of the child's growth stage. Dental age does change greatly over time, but it changes constantly. And updating information about this change is important. The purpose of this study was to provide information about tooth eruption stage using diagnostic model analysis and to investigate tooth eruption sequence and estimate chronological age based on this information. Tooth eruption stages were measured on a diagnostic model from 488 patients in 5 - 13 year old children. Based on the information on eruption stage, eruption sequence in maxilla was first permanent molar, central incisor, lateral incisor, first premolar, canine, second premolar and second permanent molar. Eruption sequence in mandible was first permanent molar, central incisor, lateral incisor, canine, first premolar, second premolar and second permanent molar. There were significant differences between males and females in the eruption stage of canine, first and second premolar, and second molar at several ages. The chronological age of male and female was estimated by the coefficient of determination of 0.816, 0.826 respectively.

• The korean journal of orthodontics
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• v.31 no.3 s.86
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• pp.311-323
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• 2001

One of the various mechanics used to treat unilateral Class II malocclusion is head gear with asymmetric face bow. We made the finite element models of unilateral Class II maxillary dental arch and power arm asymmetric face bow. We designed this experiment to observe stress distribution of periodontal ligament, reaction force, and displacement and to understand force system, so to predict the therapeutic effect. On the basis of computerized tomograph of maxillary dental arch of 25 years old male with normal occlusion without extraction and orthodontic treatment history, we made finite element models of maxillary dental arch and periodontal ligament. Then we modified that model to unilateral maxillary Class II malocclusion model of which maxillary left molar displaced mesially. Also, We made finite element model of asymmetric face bow of which right outer bow shorter than left by 25mm(RMO, Penta-FormTM/Medium size, 0.045 inch iner bow, 0.072 inch outer bow). After that, retraction force of 250g, 300b, 350g were applied to maxillary first molar. We concluded as follow. 1. The Net force that both maxillary first molars were received increased as the retraction force increased. Mesially positioned tooth received more force than normally positioned tooth. But, both tooth were received distal force, so distal movement occured. 2. Both tooth received buccal lateral force. In analysis of force element, as the retraction force were increased, force of X-axis at mesially positioned tooth decreased, and force of X-axis at normally positioned tooth increased. so lateral force component moved to the side received less force from more force. 3. There were rotation, tipping with distal movement in maxillary first molar. As retraction force were increased, rotation and tipping also increased. More tipping and rotation occured at the side received more force, that is, mesially positioned tooth. Though it Is small change, displacement of same pattern occur in normally positioned tooth