• The korean journal of orthodontics
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• v.50 no.2
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• pp.108-119
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• 2020

Objective: The primary objective of this study was to quantitatively analyze the bone parameters (thickness and density) at four different interdental areas from the distal region of the canine to the mesial region of the second molar in the maxilla and the mandible. The secondary aim was to compare and contrast the bone parameters at these specific locations in terms of sex, growth status, and facial type. Methods: This retrospective cone-beam computed tomography (CBCT) study reviewed 290 CBCT images of patients seeking orthodontic treatment. Cortical bone thickness in millimeters (mm) and density in pixel intensity value were measured for the regions (1) between the canine and first premolar, (2) between the first and second premolars, (3) between the second premolar and first molar, and (4) between the first and second molars. At each location, the bone thickness and density were measured at distances of 2, 6, and 10 mm from the alveolar crest. Results: The sex comparison (male vs. female) in cortical bone thickness showed no significant difference (p > 0.001). The bone density in growing subjects was significantly (p < 0.001) lower than that in non-growing subjects for most locations. There was no significant difference (p > 0.001) in bone parameters in relation to facial pattern in the maxilla and mandible for most sites. Conclusions: There was no significant sex-related difference in cortical bone thickness. The buccal cortical bone density was higher in females than in males. Bone parameters were similar for subjects with hyperdivergent, hypodivergent, and normodivergent facial patterns.

• Journal of Dental Rehabilitation and Applied Science
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• v.23 no.4
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• pp.313-326
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• 2007

With rising prevalency of mouth breathing children caused by developing civilization and increasing pollution, there are many maxillary transverse discrepancy patients with undergrowth of maxilla. For improving this, maxillary mid-palatal suture splitting was often performed. The purpose of this study was to analyse the stress distribution on the craniofacial suture and cranium after rapid maxillary expansion by finite element model. The boy(13Y6M) was chosen for taking computed-tomography for finite element model. Three-dimensional model of maxilla, first premolar, first molar, buccal and lingual part of rapid maxillary expansion were constructed. 1. The alveolar bone adjacent to the first molar and the first premolar that was affected directly by rapid maxillary expansion was displaced laterally approximately 4.04mm at maximum. The force decreased toward anterior region and frontal alveolar bone displaced laterally about 3.18mm. 2. A forward maximum displacement was exhibited at zygomatic process middle region. 3. At maximum, maxillary median part experienced 0.973mm downward repositioning and 0.65mm upward repositioning at lateral alveolar bone. 4. Von mises stress was observed the largest stress distribution around teeth and zygomatic buttress. 5. The largest tensile force was observed around alveolar bone of teeth, while compression force was observed at zygomatic buttress.

• The Journal of the Korean dental association
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• v.55 no.5
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• pp.328-338
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• 2017

Introduction: The aim of the current study was to describe the prevalence and treatment of mandibular first molar eruption disturbances. Methods: A total of 38 mandibular first molars(M1mn) from 36 patients(17 males and 19 females; aged 9 years 2 months?35 years 10 months) were identified from the 13,391 patients that received orthodontic treatment from 1983?2012. The subjects were classified into 3 categories based on panoramic radiographic examination: impaction due to ectopic position of the tooth germ relative to the contra-side same tooth(Group 1), impaction due to obstruction of the eruption path with cyst or calcium mass (Group 2), and primary and secondary retention due to defects in the follicle or periodontal ligament(PDL; Group 3). The treatment outcomes were evaluated into four categories: no treatment(A), orthodontic traction(B), autotransplantation(C), and extraction due to orthodontic traction failure(D). Results: The prevalence rate of M1mn eruption disturbances in this sample was 0.27%. In Groups 1 and 2, most of the impacted M1mn were erupted successfully by orthodontic traction. In Group 3, most of the retained M1mn were failed to erupt and recommended for extraction. Conclusions: Treatment prognosis was favorable on Group 1 & 2 than Group 3. After removing an element of the cause in case of Group 1 & 2, orthodontic traction or periodic observation will be recommended.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.2
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• pp.277-289
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• 1996

The purpose of this study was to compare the amount of the vertical pin opening of dentures processed by the conventional compression method & the injection-processing method. The articulating ribbon and T-Scan system were used to determine the changes in tooth contacts and the correlation between the changes in tooth contacts and the amount of the vertical pin opening after processing was analyzed statistically. The obtained results were as follows. 1. The amounts of the vertical pin opening were 0.75mm, 0.31mm for conventional compression method and injection-pressing method, respectively. The difference between the two methods was highly significant on the basis of t test statistics(p<0.05). 2. The total number of contact points recorded by articulating ribbon after processing was decreased to 48%, 72%, of that before processing for conventional compression method and injection-pressing method, by T-Scan system, 39%, 53%, respectively. 3. The mean values for the number of contacts points per tooth recorded by articulating ribbon after processing were 1.6 for the second molar, 2.2 for the first moalr, 0.4 for the second premolar, 0.6 for the first premolar in conventional compression method, and 2, 3.2, 1.2, 0.8 in injection-pressing method. 4. The correlation between the reduction of contact points and the amount of the pin opening after processing was not significant. 5. The mean values for the number of contact points per tooth recorded by T-Scan system after processing were 1.25, 1.4, 0.7, and 0.55 at the second molar, the first molar, the second premolar, and the first premolar in conventional compression method, and 1.45, 2.1, 1.0, 0.75 in injection method, respectively. 6. The correlation between the number of contact points by using articulating ribbon and T-Scan system after processing was not significant in both methods.

• The korean journal of orthodontics
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• v.30 no.1 s.78
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• pp.115-126
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• 2000

Dental arch expansion is one of the method used to solve the dental crowding problem by non-extraction. Many formulae using tooth size have been suggested to predict ideal inter-premolar and inter-molar width. The purpose of this study was to evaluate the adequacy of some upper dental arch width prediction methods, namely Pont's method, Schmuth's method and Cha's method. The sample consisted of the casts of 119 Korean young adults who had no muscular abnormality, no skeletal discrepancy, and Angle's Class I molar relationships. Measurements were obtained directly from plaster casts; they Included mesiodistal crown diameters of the four maxillary incisors, as well as maxillary inter-first-premolar and inter-first-molar arch widths as specified by Pont. The correlation coefficients between the sum of incisors(SI) and upper dental arch width were calculated. The differences between predicted width and actual width were classified as overestimated, properestimated, and underestimated. The data obtained from each group were analyzed for statistical differences. The results were as follows : 1. Upper dental arch width indices were calculated from SI in normal occlusion (81.96 : premolar index, 62.55 : molar index). 2. Low correlations between SI and arch width were noted in normal occlusion (0.50 in the inter-premolar width, 0.39 in the inter-molar width). 3. Pont's formula and Schmuth's formula tended to overestimate the inter-premolar width. A more even distribution of estimates was noted in Cha's fomula. 4. Cases within $\pm$1 mm range of observed inter-premolar width were $45\%$ in the Cha's formula, $40\%$ in the Pont's formula, and $39\%$ in the Schmuth's formula. 5. All formulae had a tendency to underestimate the inter-molar width, but Cha's formula had better predictability than others. 6. Cases within $\pm$1 mm range of observed inter-molar width were $40\%$ in the Cha's formula, $29\%$ in the Pont's formula, and $13\%$ of Schmuth's formula. The data presented in this study does not support the clinical usefulness of ideal arch width prediction methods using the mesiodistal width of maxillary incisors.

• The korean journal of orthodontics
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• v.14 no.1
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• pp.47-52
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• 1984

A girl aged 13 years 1 month, had a Angle's Class 1 malocclusion, characterized by severe aterior crowding, high canine, and loss of the upper and lower left first molars on account of dental caries. This patient underwent ${\frac{4}{4}}$extraction and multibonded system was used. After 20 Months, anterior crowding and high canine was corrected, and the extraction space as closed on both arch. The upper and lower left 2nd molars occupied the first molar spaces instead of the first polars. After 6 Months from debanding, band spaces were disappeared and the third molars were upting normally.

• The Journal of Advanced Prosthodontics
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• v.16 no.4
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• pp.212-220
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• 2024

PURPOSE. This cone-beam computed tomography (CBCT) study aimed to analyze the anatomical characteristics of alveolar bone at mandibular first molar (MFM) and their implications for immediate implant placement surgery. MATERIALS AND METHODS. 100 patients with 140 MFMs were reviewed retrospectively. We first performed a 3D reconstruction of the patient's CBCT data to determine a reference plane with ideal implant placement and orientation. The following parameters of MFM region were analyzed: mesial-distal socket size (MDSS), buccal-lingual socket size (BL-SS), root furcation fornix to inferior alveolar nerve (IAN) distance (RF-I), interradicular bone thickness (IRB), mesial/distal root apex to the IAN distance (MRA-I/DRA-I), thickness of the buccal/lingual bone of the mesial root (MR-B/MR-L), thickness of the buccal/lingual bone of the distal root (DR-B/DR-L). RESULTS. The MD-SS of MFM was 8.74 ± 0.76 mm, and the BLSS was 8.26 ± 0.72 mm. The MR-B, DR-B was 1.01 ± 0.40 mm and 1.14 ± 0.50 mm, and the difference was statistically significant (P = .001). The values of the MR-L, DR-L were 2.71 ± 0.78 mm and 3.09 ± 0.73 mm, and the difference was also statistically significant (P < .001). The mean distance of RF-I was 15.68 ± 2.13 mm, and the MRA-I was 7.06 ± 2.22 mm, which was greater than that of DRA-I (6.48 ± 2.30 mm, P < .001). The IRB at 2 mm, 4 mm apical from the furcation fornix, and at apex level was 2.81 ± 0.50 mm, 3.30 ± 0.62 mm, and 4.44 ± 1.02 mm, respectively. CONCLUSION. There is relatively sufficient bone mass in interradicular bone in height, but an adequate width is lacking for the bone between the mesial and distal root after the extraction of the MFM for immediate implantation. The thickness of the MFM buccal bone is relative thin, especially for the mesial root.

• The korean journal of orthodontics
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• v.53 no.3
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• pp.205-216
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• 2023

Objective: To investigate changes in the immature teeth of Sprague-Dawley rats during orthodontic treatment and to explore the changes in the peri-radicular alveolar bone through micro-computed tomography (CT). Methods: Twenty-five 26-day-old male Sprague-Dawley rats were included. The maxillary left first molar was moved mesially under a continuous force of 30 cN, and the right first molar served as the control. After orthodontic treatment for 7, 14, 21, 28, and 42 days, the root length, tooth volume, and alveolar bone mineral density (BMD) around the mesial root were measured through micro-CT. Results: The immature teeth continued to elongate after application of orthodontic force. The root length on the force side was significantly smaller than that on the control side, whereas the differences in the volume change between both sides were not statistically significant. Alveolar bone in the coronal part of the compression and tension sides showed no difference in BMD between the experimental and control groups. The BMD of the experimental group decreased from day 14 to day 42 in the apical part of the compression side and increased from day 7 to day 42 in the apical part of the tension side. The BMD of the experimental group decreased in the root apex part on day 7. Conclusions: The root length and volume of immature teeth showed continued development under orthodontic forces. Alveolar bone resorption was observed on the compression side, and bone formation was observed on the tension side.

• The korean journal of orthodontics
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• v.29 no.5 s.76
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• pp.563-573
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• 1999

The purpose of this study was to evaluate the availability of computer system for the measurement of tooth size in the model analysis through the comparison of two measurements: One was to use a computer; and the other was to use vernier calipers. Twenty sets of casts were used, which showed a moderate degree of crowding and full eruption of all teeth. The mesio-distal width of 12 teeth from the left central incisor to the left first molar at each set of the casts were measured twice with vernier calipers and a computer respectively. This measurement was repeated two weeks later. First, for the reproducibility analysis, the two computer measurements were compared then the vernier calipers measurements were compared. Second, all the teeth were sepapated into the region of mesiodistal contact points and its width was measured by a micrometer to obtain standard measurements. For the accuracy analysis, these standard measurements were compared with the measurements from the dental casts using two methods. The difference between them was defined as the measurement error. To investigate the cause of measurement error, an examination was made for the presence and degree of contact point deviation on each tooth from the upper and lower occlusograms, and the mesio-distal angulation of each tooth was measured with TARG. Following results were obtained through statistical analysis. 1. In the analysis for reproducibility; the measurements with vernier calipers showed significant differences in three out of twelve teeth while the computer measurements showed significant differences in one out of twelve teeth. 2. In the analysis for accuracy; compared with the standard measurements, the measurements with vernier calipers showed significant differences in three out of twelve teeth while the computer measurements showed significant differences in two out of twelve teeth. 3. Compared with the standard measurements, the measurements with vernier calipers were apt to be larger at the upper first molar, and smaller at the lower first molar The computer measurements, however, were apt to be larger at both upper and lower first molars. 4. The measurements with vernier calipers showed the largest error at the lower first molar and the degree of error was variable according to the tooth while the difference of error was small in the computer measurements. 5. In the analysis for the correlation of the degree of measurement errors with the contact point deviation index and the mesio-distal crown angulation of each tooth, the measurements with vernier calipers did not show significant correlation while the measurements with computer showed slight Positive correlations. The results of this study indicate that a computer system may be useful for the measurement of tooth size in the model analysis.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.923-928
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• 2012

Optimizing a water-phase suspending system is very important to manufacture high-quality suspension polymerized toners. Therefore, in this study, the effects of the molar ratio of calcium hydroxide ($CaOH_2$)/phosphoric acid ($H_3PO_4$)(Ca/P), which were used as inorganic suspending agents, and pH of the water-phase on the characteristics of styrene-based suspension polymerized toners were mainly investigated. At first, the water-phase was fixed to neutral condition (pH=7.5) and Ca/P molar ratio was changed from 1.5:1 to 1.76:1. As a result, an ideal calcium phosphate (hydroxyapatite) was prepared at the Ca/P molar ratio of 1.73:1 and polymerized toners prepared at this condition showed good particle size distribution, circularity and charging characteristic. Based on this result, Ca/P molar ratio was fixed to 1.73:1 and pH of the water-phase was changed to weak acidic (pH=5.5) and weak basic (pH=9.5) conditions. As a result, polymerized toners prepared under the weak acidic condition showed very good particle size distribution, circularity and charging characteristic along with excellent printing quality. High-quality suspension polymerized toners could be prepared via optimizing Ca/P molar ratio and pH of the water-phase.