• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.175-176
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• 2006

The aim of the 3D medical imaging is to facilitate the creation of clinically usable image-based algorithm. Clinically usable imaging algorithm for image analysis requires a high degree of interaction to verify and correct results from registration algorithms, such as the Insight Toolkit (ITK) and the Visualization Toolkit (VTK) which are the class libraries. ITK provides segmentation algorithms and VTK has powerful 3D visualization. However, to apply those libraries to the medical images such as Computerized Tomography (CT), the algorithm based on the interactive construction and modification of data objects are necessary. In this paper we showed the 3D registration about mandibular premolar of human teeth acquired by micro-CT scanner. Also, we used the ITK to find the contour of pulp layer of premolar, furthermore, the 3D imaging was visualized with VTK designed to create one kind of view on the data of 3D visualization. Finally, we evaluated that the volume model of pulp layer would be useful for the tooth morphology in dental medicine.

• The korean journal of orthodontics
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• v.31 no.1 s.84
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• pp.1-13
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• 2001

The extraction lot orthodontic treatment can be adopted for aligning crowded dentition, improving facial esthetics and solving a skeletal discrepancy as alternative for a surgical option. Mandibular second premolar extraction was often selected as treatment plan when there we very little or no space shortage in lower arch or limited retraction of the lower incisors was required. The primary object of this study was evaluate a pretreatment condition and examine the amount of tooth movement ior a mandibular second premolar extraction in growing patients. Pretreatment and posttreatment lateral cephalograms of 14 cases that had their four first premolar extracted (4/4 group), 15 cases with upper first and lower second premolar extraction (4/5 group) were selected. Structural method superimposition was conducted to evaluate a difference of dental change between 4/4 and 4/5 group. The results were as follows, 1. Pretreatment factor for 4/4 extraction or 4/5 extraction choice included maxillary incisor axis to occlusal plane, Class II molar relationship, IMPA and interincisal angle. 2. The amount of molar anterior movement in 4/5 group was greater than that of 4/4 group(p<0.05). 3. There was no significant difference between 4/4 group and 4/5 group in aspects of maxillary tooth movement(p<0.05).

• Journal of the Korean Society for Precision Engineering
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• v.22 no.10 s.175
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• pp.202-209
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• 2005

In this study, two dimensional and three dimensional finite element models of lower first premolar were analyzed. The mandibular specimen including a premolar was obtained from a cadaver and scanned with micro-CT. Finite element method models were reconstructed from CT images at mid-sagittal plane of the tooth. Most studies have used a wide range of value(0.07${\~}$1000MPa) for elastic modulus of periodontal ligament. The elastic modulus of the periodontal ligament was analyzed by finite element method and compared with that of experiment model. This study indicated that the model without pulp was more suitable than that with pulp in two dimensional finite element analysis.

• Journal of the korean academy of Pediatric Dentistry
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• v.24 no.3
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• pp.487-494
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• 1997

It is rare to find multiple supernumerary teeth in individuals with no other associated diseases or syndromes. 'Non-Syndrome multiple supernumerary teeth' reviewed by Yusof(1990) have more frequency of occurrence in the mandibular region. Especially, mandibular premolar region appears to be the site of predilection for no n-syndrome multiple supernumerary teeth. Also, these may develop after most permanent teeth have erupted, thus their effect upon the occlusion is limited. In this case, the patient had 20 supernumerary teeth without other associated diseases or syndromes. All of the supernumerary teeth were impacted, and thirteen of them were found in the premolar region. In the radiographic and clinical finding, other specific complication resulted from the supernumerary teeth weren't observed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.171-172
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• 2006

Most existing studies for stress analysis of teeth have employed small number of teeth, and used big element size using F-E models. Therefore, the results are not accuracy enough for showing the internal stress variation. 15 males' and 13 females' mandibular first premolar are employed for internal structure's study of teeth and small element size for a FE model are used. According to these processes, stress distribution of internal parts of teeth are well shown, and the stresses are varied a lot between enamel layer and dentine layer, but there is little variation on pulp chamber.

• The Journal of Advanced Prosthodontics
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• v.8 no.6
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• pp.489-493
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• 2016

PURPOSE. This in-vitro study aimed to evaluate the fracture resistances and failure modes of endodontically treated mandibular premolars restored with endocrowns and conventional post-core retained crowns. MATERIALS AND METHODS. Thirty mandibular premolars were assigned into three groups (n=10): GI, intact teeth; GE, teeth with endocrowns; GC, teeth with conventional post-core supported crowns. Except for the teeth in group GI, all specimens were cut to 1.5 mm above the cementoenamel junction and endodontically treated. Both endocrowns and conventional crowns were fabricated from lithium-disilicate blocks using a CEREC 3D CAD/CAM unit. All specimens were subjected to thermocycling and then to $45^{\circ}$ oblique compressive load until fracture occurred. The fracture resistance and failure mode of each specimen were recorded. Data were analyzed with one-way ANOVA and LSD Post Hoc Test (${\alpha}=.05$). RESULTS. The fracture resistances of GE and GC were significantly lower than that of GI (P<.01), while no significant difference was found between GE and GC (P=.702). As of the failure mode, most of the specimens in GE and GC were unfavorable while a higher occurrence of favorable failure mode was presented in GI. CONCLUSION. For the restoration of mandibular premolar, endocrown shows no advantage in fracture resistance when compared with the conventional method. Both of the two methods cannot rehabilitate endodontically treated teeth with the same fracture resistances that intact mandibular premolars have.

• Journal of the korean academy of Pediatric Dentistry
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• v.50 no.4
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• pp.469-482
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• 2023

This study aimed to investigate the treatment options for the delayed eruption of mandibular premolars and identify the predictors of spontaneous eruption using panoramic radiography. The prevalence of delayed mandibular premolar eruption in this retrospective analysis, comprising 254 patients (aged 9 - 15 years), was 5.19%, with no significant difference based on gender. The mandibular second premolars were most affected (4.39%) compared to the first premolars (0.76%). No significant difference in prevalence was observed between the left and right sides. Among the treated mandibular premolars, primary molar-related lesions were identified as the leading cause (7.85%) of delayed tooth eruption. The treatment duration varied based on the Nolla stage, eruption stage, and treatment method. Teeth with Nolla stage 7 or lower had a treatment duration of 22.89 ± 11.96 months, whereas those with stage 8 or higher had a 15.02 ± 6.34 month duration. The deeper the tooth was located in the bone, the longer the treatment period became. The treatment duration varied depending on the treatment method, and statistically, there was no significant difference. The treatment durations for affected mandibular premolars increased with the depth of impaction angle of inclination. In this study, the treatment duration for delayed eruptions varied depending on the Nolla stage, eruption stage, and treatment method. Variations in the impaction depth and inclination angle across various treatment approaches, as explored in this study, might offer valuable insights into the selection of the most suitable management options for delayed tooth eruptions.

• Imaging Science in Dentistry
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• v.31 no.3
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• pp.129-133
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• 2001

Purpose: To compare the copper equivalent values measured at premolar and molar areas in the copper equivalent images of panoramic and intraoral radiographs and to evaluate the possibility of the copper equivalent images of panorama for the assessment the bone density. Materials and Methods : Intraoral radiograms at mandibular premolar and molar area and panoramas of 6 human dry skulls were taken with copper-step wedge by Heliodent MD (Siemens Co., Germany) and by Planmeca (PM 2002 CC, Planmeca, Helsinki, Finland) were used for experiment. The copper equivalent values measured at premolar and molar areas in the copper equivalent im ages of panorama and intraoral film were compared. Results: The copper equivalent values were ranged 0.20 mmCu-0.44 mmCu at the molar areas, 0.05 mmCu-0.31 mmCu at the premolar areas on panoramic images. There were no significant differences (p>0.5) between the copper equivalent values on intraoral images and those on panoramic images measured at premolar areas and molar areas respectively. The correlation coefficient between the copper equivalent values on intraoral images and those on panoramic images was respectively 0.8495 at molar areas and 0.6184 at premolar areas. Conclusions : The copper equivalent images of panorama for the assessment the bone density appeared to be significant at molar area compared with the one of intraoral radiograph.

• Journal of the korean academy of Pediatric Dentistry
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• v.7 no.1
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• pp.85-93
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• 1980

This study was undertaken in order to observe the prevalence of congenital dental anomalies especially that of oligodontia and supernumerary teeth in 1024 children at age from 4 to 14 years, through history taking, oral examinations, roentgenographic observations of subjects, and statistic analysis was made. The following results were obtained: 1. The prevalence of oligodontia in 1024 children was $6.45{\pm}.8$ percent with a total of 122 teeth absent in sixty-six subjects, excluding 3rd molars, and most of children (86.4%) who have congenitally missing teeth showed abscence of one or two teeth individually. 2. The teeth most frequently absent were the mandibular second premolar, maxillary second premolar, maxillary lateral incisor, mandibular central incisor, and mandibular lateral incisor in order. 3. There was no statistically significant difference found in tooth abscence in the following comparisons; .Male vs Female .Bilateral vs Unilateral .Maxilla vs Mandible .Right vs Left 4. The prevalence of supernumerary teeth in 1024 children was $4.79{\pm}.67$ percent with a total of 59 supernumerary teeth in forty-nine subjects, all of children who have supernumerary teeth showed one or two supernumerary teeth individually. 5. Statistically significant difference was found in supernumerary teeth in the comparison of male vs female, and they were more frequent in male.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.214-218
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• 2009

The occlusal force of the tooth leads to loss of tooth tissue owing to attrition and abrasion, and may cause abfraction and pathological change of the dentin. Thus, we developed finite element models, examined them by applying ordinary occlusal force, and analyzed the stress distribution. Specimens used were mandibular first premolars from 15 Korean males and 13 females and were made into finite element models from medical images that were obtained using a Micro-CT. We have found that the irregular feature of the tooth is not only useful to masticating and pronouncing as well known, but it is also suitable for protecting inner tissue by dispersing stress and delivering proper pressure to periodontal tissue to continue a physiological action. Also, image analysis could let us know the factor that is the cause of a disorder due to stress concentration in the cervical line. These results are expected to support the field of dental treatment planning, operating procedure and clinical trial, and the advance of technical expertise to develop implants and dentures.