• Journal of the Korean Society for Precision Engineering
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• v.27 no.4
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• pp.87-94
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• 2010

When occlusal force is applied to a tooth, stress concentration occurs on the dental cervical line. This study investigated to find the maximum force and strain of natural teeth using an Instron and strain gauges, comparing the strain of cervical enamel using finite element analysis(FEA). Tests were conducted with a mandibular first premolar applying the conditions of occlusion. Then, the FEA was processed with the same as conditions of the fracture test. The test showed that the maximum force, maximum compressive strain and maximum tensional strain was $278{\pm}26$ N, $0.668{\times}10^{-3}{\pm}0.678{\times}10^{-3}$ and $0.248{\times}10^{-3}{\pm}0.102{\times}10^{-3}$, respectively. It was found that six of eight measured strains were within the range of estimated strains by the FEA. Even though it was assumed that properties of FE models were isotropic, it could prove useful as a reference in understanding the tendency of dental strain.

• The Journal of the Korean dental association
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• v.48 no.11
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• pp.819-828
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• 2010

Activator is a removable functional appliance used for correcting the skeletal Class II malocclusion in children with the mandibular deficiency. Berlin standard activator modified from Andresen activator has following characters; do not cover the palatal surface for tongue space, relief on lingual surface of mandibular incisors and resin capping 1/3-1/2 of crown height on mandibular incisors for preventing labioversion of mandibular incisors, L-hook between maxillary lateral incisor and canine for anterior high pull headgear, relief on mandibular posterior bite block for differential eruption of posterior teeth. Two cases presented here had a mandibular deficiency and slight maxillary protrusion. First case (an 11-year-old girl) treated with Berlin standard activator and anterior high pull headgear for 13 months followed by fixed orthodontic appliance for another 29 months. Second case (a 12-year-old boy) treated with Berlin standard activator for 6 months followed by fixed appliance for another 24 months. Treatment results showed a significant improvement in sagittal skeletal and occlusal relationship without premolar extraction. Mandibular condyles were concentric in TMJ [ossa, and masticatory muscle activities were normalized after treatment. In the retention period facial harmony and occlusal stability was maintained.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.4
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• pp.607-617
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• 2002

The purposes of this study were to evaluate the timing of tooth calcification and the change of tooth position with tooth developmental stage on the mandibular teeth. Seven hundred seventy two children(male:446, female:326), 3 to 12 years of age were examined radiographically with panoramic film. Dental development was determined by inspecting radiographs and assigning a rating according to consecutive stages defined by Moorrees, and tooth cusp position and root terminus position were measured from the lower border of mandibular body and calculated the position index to evaluate the movement of tooth with developmental stage. The results were as follows. 1. There were no significant differences between boys and girls in the timing of calcification until crown completion, but timing of calcification tend to be faster in girls than in boys after root initiation stage. 2. In terms of mean age, crown completion of central incisor in boys and girls occurred at the age of 3.71, 4.05 years, at 4.44, 4.60 years for the lateral incisor, at 5.35, 5.11 years for the canine, at 6.62, 6.36 years for the first premolar, at 7.36, 7.17 years of second premolar, at 3.51, 3.69 years of first molar, and at 7.90, 7.64 years for the second molar respectively. Apex 1/2 closed stage of central incisor occurred at the age of 8.70 in boys, 8.18 in girls, at 9.55, 8.99 years for the lateral incisor, at 12.48, 11.60 years for the canine, at 12.30, 12.01 years for the first premolar, at 12.19, 12.26 years of second premolar, at 9.12, 8.87 years of first molar, and at 12.59, 12.45 years for the second molar respectively. 3. There was no noticeable movement of cusp tip until crown completion (Crc), but showed rapid movement toward occlusion plane after root initiation(Ri) and again maintain stable position after root completion stage(Rc). 4. Root terminus position was stable until root 1/4 formation stage(R1/4), followed by rapid movement toward occlusal plane and was stable again after root 3/4 formation stage(R3/4). 5. Developmental stage at the time of alveolar bone penetration by cusp tip varied with each of the permanent teeth. 6. Canine tooth follicle was at the lowest position in the mandibular body during the early stage of calcification, followed by second premolar, first premolar, lateral incisor, second molar, first molar and central incisor in order.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.3
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• pp.502-509
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• 2003

After 800 students of Chonbuk National University was examined, 86 people (male : 43, female : 43, mean age : 22.2 years old) was selected as a group of normal occlusion. From their gypsum cast, this conclusion was obtained. 1. Intra-observer measurement errors in buccolingual diameter, maxillary lateral incisors have somewhat bigger errors. In mesiodistal diameter, maxillary first molars and maxillary second molar have bigger numerical value. Mean errors of measurement are 0.051mm at buccolingual diameter of crown and 0.083mm at mesiodistal diameter. 2. Fluctuating asymmetry is 0.030 average in buccolingual diameter, and 0.037 average in mesiodistal diameter. Statistically there are no big differences. 3. Male has longer buccolingual diameter than female in every permanent teeth. Teeth which have statistical difference in buccolingual diameter are maxillary lateral incisor, maxillary canine, maxillary second molar, mandibular central incisor, mandibular canine, mandibular second premolar, and mandibular first molar. In mesiodistal diameter maxillary central incisor, maxillary canine, and mandibular first molar have statistically difference. 4. Tooth which has the biggest difference depending on gender is maxillary lateral incisor in buccolingual diameter and mandibular canine in mesiodistal diameter. 5. Both sexes have similar crown index. Male has bigger value of crown module measurement and crown area measurement in every tooth. Crown area considered as size of tooth from occlusal surface was bigger in male than in female statistically except some teeth, maxillary first premolar, mandibular lateral incisor, first premolar and second premolar.

• Journal of Veterinary Science
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• v.21 no.5
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• pp.75.1-75.8
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• 2020

Background: Dental diseases are common in dogs and cats, and accurate measurements of dentoalveolar structure are important for planning of treatment. The information that the comparison computed tomography (CT) with dental radiography (DTR) is not yet reported in veterinary medicine. Objectives: The purpose of this study was to compare the DTR with CT of dentoalveolar structures in healthy dogs and cats, and to evaluate the CT images of 2 different slice thicknesses (0.5 and 1.0 mm). Methods: We included 6 dogs (2 Maltese and 1 Spitz, Beagle, Pomeranian, mixed, 1 to 8 years, 4 castrated males, and 2 spayed female) and 6 cats (6 domestic short hair, 8 months to 3 years, 4 castrated male, and 2 spayed female) in this study. We measured the pulp cavity to tooth width ratio (P/T ratio) and periodontal space of maxillary and mandibular canine teeth, maxillary fourth premolar, mandibular first molar, maxillary third premolar and mandibular fourth premolar. Results: P/T ratio and periodontal space in the overall dentition of both dogs and cats were smaller in DTR compared to CT. In addition, CT images at 1.0 mm slice thickness was generally measured to be greater than the images at 0.5 mm slice thickness. Conclusions: The results indicate that CT with thin slice thickness provides more accurate information on the dentoalveolar structures. Additional DTR, therefore, may not be required for evaluating dental structure in small-sized dogs and cats.

• Journal of Oral Medicine and Pain
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• v.46 no.4
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• pp.125-130
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• 2021

Purpose: The dental age estimation of children is performed using dental maturity. Postmortem missing of the anterior teeth or the distortion of image of the anterior teeth in panoramic radiographs can make it difficult to analyze the development of the anterior teeth. This pilot study was conducted to derive a new age estimation method based only on the developmental stage of mandibular posterior teeth. Methods: This study was conducted using panoramic radiographs of 650 subjects aged 3 to 15 years old. The dental developmental stages of the lower left first premolar, second premolar, first molar and second molar were evaluated according to the Demirjian's criteria. The intra-/inter-observer reliability was evaluated, and multiple linear regression analyses were performed including the developmental stage of each tooth as an independent variable. Results: The intra-/inter-observer reliability was 0.9626 and 0.8877, respectively, and showed very high reproducibility. Multiple linear regression analyses were performed for males and females, and the age calculation table was derived by obtaining the intercept and the coefficient according to the development stage of each tooth. The coefficient of determination (r²) of the age calculation method was 0.9634 for male and 0.9570 for female subjects, and the mean difference between chronological age and estimated dental age was -0.42 and -0.21, respectively. Conclusions: This pilot study evaluated the developmental stages of four lower posterior teeth in the Korean group according to Demirjian's criteria, and derived age estimation method. The accuracy was lower than when more teeth were used, but it will be useful to estimate age of children when the anterior teeth are difficult to accurately analyze.

• The Journal of Korean Academy of Prosthodontics
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• v.29 no.1
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• pp.233-248
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• 1991

The purpose of this study was to qunatatively analyze the stress patterns induced in the abutment, superstructure, supporting bone and to determine the deflection of abutment and superstructure by appling occlusal force to natural teeth supported fixed prostheses and implant-supported fixed prostheses. The analysis has been conducted by using the two dimensional finite element method. The implant and natural tooth-supported bridge has a first molar pontic supported by mandibular second bicuspid and implant posterior retainer, which were rigidly(Model A) or flexible(Model B). The natural teeth-supported bridge has a first molar pontic supported by mandibular second bicuspid and second molar, which were rigidly splinted together(Model C). 63.5kg(Load P1) of localized load on central fossa of first molar pontic and 24kg(Load P2) of distributed load on each occlusal surface were applied respectively. 1. The coronal portion of premolar pontic and posterior abutment in fixed partial denture deflected inferiorly in order of Model B, Model C and Model A under Load P1 and Load P2. 2. Mesial displacement of the coronal portion of premolar showed in Model A, Model B and Model C under Load P1, but mesial displacement of that in Model B and distal displacement of that in Model A and Model C showed under Load P2. 3. Mesial displacement of the coronal portion of the pontic and distal displacement of the coronal portion of posterior abutment showed in Model A, Model B and Model C under Load P1 and Load P2. Displacement in the case of Model B was greater than that of Model A and Model C. 4. In the case Model A under Load P1 and Load P2, high stress apically was concentrated in the mesiocervical portion of the posterior abutment than in the disto-cervical portion of the premolar. 5. In the case of Model B under Load P1 and Load P2 high stress was concentrated in the case of the premolar than in that of posterior abutment and high stress especially was concentrated in the connected portion of pontic and posterior abutment. 6. In the case of Model C under Load P1 and Load P2, high stress was concentrated in the distal area of the cornal portion of premolar and the mesial area of the coronal portion of posterior abutment, and stress pattern was anteroposterially symmetric around the pontic. 7. Load P1 and Load P2 compared, stress magnitude was different but stress pattern was similar in Model A, Model B and Model C. 8. Under Load P1 and P2, stress magnitude in the mesial distal portion and the portion of root apex of the posterior abutment was in order of Model B, Model A and Model C.

• Journal of Periodontal and Implant Science
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• v.36 no.1
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• pp.51-60
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• 2006

Gingival recession is clinically manifested by an apical displacement of the gingival tissue and dentin hypersensitivity is often used to describe a painful condition in which exposed dentin is unduly sensitive to intraoral stimuli. The objects of this study were primarily to investigate the prevalence and distribution of gingival recession and hypersensitivity and secondarily to determine whether a relationship exists between gingival recession and hypersensitivity. The study population was 195 patients (102 males, 93 females) who were attended the department of periodontology, Pusan National University Hospital. 189 patients exhibited gingival recession at least more than 1 tooth, the prevalence was 96.9%. The maxillary and mandibular first premolar and mandibular incisors had the highest prevalence. The majority of patients (139 patients, 71.3%) were diagnosed as having dentin hypersensitivity. Dentin hypersensitivity was determined to 3 seconds application of cold air to the exposed root surface after isolating the test tooth and was commonest in maxillary and mandibular first premolars and mandibular incisors. Relationship between recession and hypersensitivity was analyzed using chi-square test (p=0.05), significant relation (p=0.000) was existed. Gingival recession was more severe, the prevalence of hypersensitivity was higher.

• 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.

• Journal of Dental Anesthesia and Pain Medicine
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• v.15 no.2
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• pp.63-68
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• 2015

Background: Conventional anesthetic nerve block injections into the mandibular foramen risk causing nerve damage. This study aimed to compare the efficacy and safety of the anterior technique (AT) of inferior alveolar nerve block using felypressin-propitocaine with a conventional nerve block technique (CT) using epinephrine and lidocaine for anesthesia via the mandibular foramen. Methods: Forty healthy university students with no recent dental work were recruited as subjects and assigned to two groups: right side CT or right side AT. Anesthesia was evaluated in terms of success rate, duration of action, and injection pain. These parameters were assessed at the first incisor, premolar, and molar, 60 min after injection. Chi-square and unpaired t-tests were used for statistical comparisons, with a P value of < 0.05 designating significance. Results: The two nerve block techniques generated comparable success rates for the right mandible, with rates of 65% (CT) and 60% (AT) at both the first molar and premolar, and rates of 60% (CT) and 50% (AT) at the lateral incisor. The duration of anesthesia using the CT was $233{\pm}37min$, which was approximately 40 min shorter than using the AT. This difference was statistically significant (P < 0.05). Injection pain using the AT was rated as milder compared with the CT. This difference was also statistically significant (P < 0.05). Conclusions: The AT is no less successful than the CT for inducing anesthesia, and has the added benefits of a significantly longer duration of action and significantly less pain.