• The Journal of Advanced Prosthodontics
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• v.11 no.3
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• pp.169-178
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• 2019

PURPOSE. While dental implants have displayed high success rates, poor mechanical fixation is a common complication, and their biomechanical response to occlusal loading remains poorly understood. This study aimed to develop and validate a computational model of a natural first premolar and a dental implant with matching crown morphology, and quantify their mechanical response to loading at the occlusal surface. MATERIALS AND METHODS. A finite-element model of the stomatognathic system comprising the mandible, first premolar and periodontal ligament (PDL) was developed based on a natural human tooth, and a model of a dental implant of identical occlusal geometry was also created. Occlusal loading was simulated using point forces applied at seven landmarks on each crown. Model predictions were validated using strain gauge measurements acquired during loading of matched physical models of the tooth and implant assemblies. RESULTS. For the natural tooth, the maximum vonMises stress (6.4 MPa) and maximal principal strains at the mandible ($1.8m{\varepsilon}$, $-1.7m{\varepsilon}$) were lower than those observed at the prosthetic tooth (12.5 MPa, $3.2m{\varepsilon}$, and $-4.4m{\varepsilon}$, respectively). As occlusal load was applied more bucally relative to the tooth central axis, stress and strain magnitudes increased. CONCLUSION. Occlusal loading of the natural tooth results in lower stress-strain magnitudes in the underlying alveolar bone than those associated with a dental implant of matched occlusal anatomy. The PDL may function to mitigate axial and bending stress intensities resulting from off-centered occlusal loads. The findings may be useful in dental implant design, restoration material selection, and surgical planning.

• Journal of Biomedical Engineering Research
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• v.44 no.5
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• pp.346-353
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• 2023

In this paper, we propose an innovative approach that leverages deep learning to find optimal reference points for achieving precise tooth segmentation in three-dimensional tooth point cloud data. A dataset consisting of 350 aligned maxillary and mandibular cloud data was used as input, and both end coordinates of individual teeth were used as correct answers. A two-dimensional image was created by projecting the rendered point cloud data along the Z-axis, where an image of individual teeth was created using an object detection algorithm. The proposed algorithm is designed by adding various modules to the Unet model that allow effective learning of a narrow range, and detects both end points of the tooth using the generated tooth image. In the evaluation using DSC, Euclid distance, and MAE as indicators, we achieved superior performance compared to other Unet-based models. In future research, we will develop an algorithm to find the reference point of the point cloud by back-projecting the reference point detected in the image in three dimensions, and based on this, we will develop an algorithm to divide the teeth individually in the point cloud through image processing techniques.

• Korean Journal of Cleft Lip And Palate
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• v.10 no.2
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• pp.81-88
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• 2007

Cleft lip and palate (CLP) is one of the most prevalent congenital craniofacial anomalies. It has a significantly greater incidence of dental abnormalities in number, size, shape, and eruption of the teeth. Knout-out mouse model can identify several genes which play an important role in tooth agenesis. Since disruption of these genes has been confirmed to result in tooth agenesis in humans, CLP associated with hypodontia may be the best models for isolated tooth agenesis. According to the studies of dental abnormalities in CLP, the severity of dental defect is known to be influenced by the CLP phenotype. The cumulative data obtained from mouse and human genetic studies indicated that MSX1, PAX9 and AXIN2 are considered as candidate genes in non-syndromic hypodontia, while Shh, Pitx2, Irf6, p63 and EDA pathway genes are involved in syndromic one. We expect that genetic approach of CLP can offer the basis for tooth regeneration and be a new target in hypodontia therapy.

• Journal of the korean academy of Pediatric Dentistry
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• v.45 no.1
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• pp.41-56
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• 2018

The purpose of this study was to provide clinical recommendations for restoration with selection of the most similar zirconia crown by 3-dimensional analysis of the shape of the maxillary primary central and lateral incisors in Korean individuals and prefabricated zirconia crowns. The average shape of the sound maxillary primary central and lateral incisors in 300 children was reproduced by 3-dimensional scanning. Zirconia crowns of 4 manufacturers (NuSmile $ZR^{(R)}$ Crown, Cheng $Crowns^{(R)}$, Kinder $Krowns^{(R)}$, and EZ $Pedo^{(R)}$ Crown) were scanned 3-dimensionally, and coordinates for comparison of the shape were measured to evaluate the similarity between the teeth and crowns. The most similar crowns were selected by comparing the mesiodistal length, crown height, crown shape ratio, distance between the same coordinates of a tooth and crown, the radius of curvature of the labial surface, and the volume. As a result of analysis, Cheng $Crowns^{(R)}$ size 3 and NuSmile $ZR^{(R)}$ Crown size 2 were the most similar crowns in the maxillary primary central and lateral incisors, respectively. Scanning the inner surface of the crowns and evaluating the amount of tooth reduction required suggested that an overall lesser amount of tooth reduction compared to that presented by the manufacturer's guidelines should be performed.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.2
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• pp.105-113
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• 2000

For exact spherical involute bevel gear, serveral researchers had developed the mathematical models. The solid models of straight bevel gears are obtained and inspected to avoid interference by computer graphics. Furthermore, A gearbox is assembled by spherical involute bevel gears, which are manufactured by CNC machine. The transmission errors in the tooth mesh are measured by Laser sensor, are compared with the AGMA standard. This gearbox is found to be ranked AGMA Q10(JIS 3)

• The Journal of the Korean dental association
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• v.48 no.3
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• pp.196-204
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• 2010

To establish the ideal occlusal relationship, the values of tooth size and ratio must be in a normal range. In this study, the means and standard deviations of Bolton's anterior ratio and overall ratio using mesiodistal dimensions of teeth measured on diagnostic models of 334 Korean malocclusion patients were calculated and differences in Bolton ratio according to the groups of malocclusion patients were studied. Also the changes that can occur in overall ratio before and after hypothetical tooth extractions were observed. The results are as follows. 1. The mean anterior ratio of Korean malocclusion patients was $78.0\;{\pm}\;2.69%$, and the mean overall ratio was $91.56\;{\pm}\;2.28%$. 2. The largest value of tooth size ratio could be found in Class III group, followed by Class I and Class II groups in order. However there was no statically significant difference. 3. The values of overall ratio reduced significantly after premolar extractions in all malocclusion groups, which was much more significant in the extraction of upper second premolar and lower first premolar(U5L4) or upper second premolar and lower second premolar(U5L5). 4. The values of overall ratio reduced significantly after premolar extractions in all 3 groups divided based on Bolton ratio, which was much more significant in the extraction of upper second premolar and lower first premolar(U5L4) or upper second premolar and lower second premolar(U5L5).

• The korean journal of orthodontics
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• v.42 no.5
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• pp.235-241
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• 2012

Objective: The purpose of this study was to evaluate the validity of the 3-dimensional (3D) superimposition method of digital models in patients who received treatment with rapid maxillary expansion (RME) and maxillary protraction headgear. Methods: The material consisted of pre- and post-treatment maxillary dental casts and lateral cephalograms of 30 patients, who underwent RME and maxillary protraction headgear treatment. Digital models were superimposed using the palate as a reference area. The movement of the maxillary central incisor and the first molar was measured on superimposed cephalograms and 3D digital models. To determine whether any difference existed between the 2 measuring techniques, intra-class correlation (ICC) and Bland-Altman plots were analyzed. Results: The measurements on the 3D digital models and cephalograms showed a very high correlation in the antero-posterior direction (ICC, 0.956 for central incisor and 0.941 for first molar) and a moderate correlation in the vertical direction (ICC, 0.748 for central incisor and 0.717 for first molar). Conclusions: The 3D model superimposition method using the palate as a reference area is as clinically reliable for assessing antero-posterior tooth movement as cephalometric superimposition, even in cases treated with orthopedic appliances, such as RME and maxillary protraction headgear.

• The Journal of the Korean dental association
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• v.44 no.2 s.441
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• pp.115-122
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• 2006

Objective : The purpose of this study was to evaluate the dimensional errors between real tooth, 3D CT image and CARP model. Materials and Methods : Two maxilla and two mandible block bones with intact teeth were taken from two cadavers. Computed tomography was taken either in dry state and in wet state. After then, all teeth were extracted and the dimensions of the real teeth were measured using a digital caliper at mesio-distal and bucco-lingual width both in crown and cervical portion. 3D CT image was generated using the V-works $4.0^{TM}$ (Cybemed Inc., Seoul, Korea) software. Twelve teeth were randomly selected for CARP model fabrication. All the measurements of 3D Ct images and CARP models were made in the same manner of the real tooth group. Dimensional errors between real tooth, 3D CT image model and CARP model was calculated. Results : 1) Average of absolute error was 0.199 mm between real teeth and 3D CT image model, 0.169 mm between 3D CT image model and CARP model and 0.291 mm between real teeth and CARP model, respectively. 2) Average size of 3D CT image was smaller than real teeth by 0.149 mm and that of CARP model was smalier than 3D CT image model by 0.067mm. Conclusion : Within the scope of this study, CARP model with the 0.291 mm average of absolute eror can aid to enhance the success rate cf autogenous tooth transplantation due to the increased accuracy of recipient bone and donor tooth.

• Journal of Korean society of Dental Hygiene
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• v.11 no.4
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• pp.511-522
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• 2011

Objectives : The purpose of this study was to provide some information on the development of oral health care programs geared toward diabetics and ways of promoting their oral health. Methods : The subjects in this study were 586 diabetics who were selected from the 2009 third-year raw data of the 4th(2007~2009) National Health & Nutrition Survey. The data were analyzed with the statistical package SPSS 12.0 to grasp the influence of their sociodemographic characteristics and oral health behaviors on the presence or absence of periodontal diseases and missing tooth. Results : 1. Periodontal diseases were twofold more prevalent among the men than the women(p<0.01). By age, those who were in their 60s had 1.11-fold more periodontal diseases than those who were in their 70s and up(p<0.05). 2. The men and women were similar to each other in the number of missing tooth. By age, the number of missing tooth got smaller in proportion to decrease in age. By income, the number of missing tooth was 1.48-fold larger among the patients who earned an income of one million won or less than those who earned an income of two million won or more(p<0.01). Conclusions : The above-mentioned findings suggest that prospective cohort studies should be implemented to present prediction models of periodontal diseases and diabetes instead of merely sticking to cross-sectional studies. And oral health programs should be developed based on the findings of cohort studies to encourage diabetics to care about their oral health, and in which way they should be helped to promote their oral health should carefully be considered.

• Journal of Periodontal and Implant Science
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• v.51 no.4
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• pp.285-295
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• 2021

Purpose: The aims of the present study were 1) to quantitatively evaluate the extent of sinus pneumatization and 2) to determine the factors affecting sinus pneumatization. Methods: Based on implant treatment records, a list of patients who underwent implant placement on the posterior maxilla was obtained. Among them, patients with pre-extraction and post-extraction (before implant placement) panoramic radiographs were selected. After excluding radiographs with low resolution and image distortion, the radiographs before and after extraction were superimposed using computer software. Subsequently, the extent of sinus pneumatization (the vertical change of the sinus floor) was measured. Simple and multiple mixed models were used to determine the factors affecting sinus pneumatization. Results: A total of 145 patients were eligible for the present investigation. The average extent of sinus pneumatization was 1.56±3.93 mm at 176 tooth sites. Male sex, single tooth extraction, extraction of an endodontically compromised tooth, a class I root-sinus relationship, and sinus membrane thickening >10 mm favored pneumatization, but without statistical significance. The maxillary second molar presented the greatest pneumatization (2.25±4.39 mm) compared with other tooth types. This finding was confirmed in the multiple mixed model, which demonstrated a statistically significant impact of the extraction of a second molar compared with the extraction of a first premolar. Conclusions: Maxillary sinus pneumatization was 1.56±3.93 mm on average. The extraction of a second molar led to the greatest extent of pneumatization, which should be considered in the treatment plan for this tooth site.