• Journal of the Korean Society of Radiology
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• v.16 no.7
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• pp.897-904
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• 2022

The purpose of this study is to compare the difference in dose and image quality when applying the diagnostic reference level (DRL) test conditions for head radiography in a digital radiation environment and the test conditions currently applied in clinical practice. I would like to review the conditions of radiographic examination. In this study, the head model phantom was targeted, and the investigation conditions were divided into clinical conditions (Clinic), DRL value (DRL₇₅), and DRL average value (DRL_mean). For dose, Enterance surface dose (ESD) was measured, and for image quality, signal-to-noise ratio and contrast-to-noise ratio were measured and analyzed for comparison. The average values of skull anterior posterior(AP) ESD according to the changes in test conditions were Clinic 1214.03±4.21 µGy, DRL₇₅ 3017.83±8.14 µGy, DRL_mean 2283.50±7.09 µGy, and skull lateral (Lat). The average value of ESD was statistically significant with Clinic 762.79±3.54 µGy, DRL₇₅ 2168.57±10.83 µGy, and DRL_mean 1654.43±6.48 µGy (p<0.01). The average values of SNR and CNR measured in the orbital, maxillary sinus, frontal sinus, and sella turcica were statistically significant (p<0.01). As a result of this study, compared to DRL, the conditions used in clinical practice showed lower dose levels of about 58% for AP and about 70% for Lat., and there was no qualitative difference in terms of image quality. Through this study, it is necessary to consider a new diagnostic reference level suitable for the digital radiation environment, and it is considered that the dose should be reduced accordingly.

• Journal of the korean academy of Pediatric Dentistry
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• v.50 no.2
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• pp.179-191
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• 2023

The purpose of this study was to investigate the prevalence and patterns of congenitally missing teeth in permanent teeth excluding third molars, in patients aged 8 to 16 years who visited Pusan National University Dental Hospital from January 2010 to February 2021. This retrospective study evaluated tooth agenesis and the pattern of missing teeth represented by the tooth agenesis code by reviewing panoramic radiographs and electronic medical records of 11,759 patients, including 5,548 females and 6,211 males. The prevalence of congenitally missing teeth was 10.74% (females 11.95%, males 9.66%, p < 0.0001). Patients with tooth agenesis had an average of 2.22 missing teeth, and congenitally missing teeth occurred more frequently in the mandible (8.39%) than in the maxilla (4.52%, p < 0.0001). The mandibular second premolar (58.19%) was the most frequently missing tooth. The second premolar was the most frequently missing tooth in all quadrants (30.10%, 31.67%, 43.14%, and 35.59%) when a single tooth was absent, while the first and second premolars were the most commonly absent teeth (11.69%, 11.47%, 5.94%, and 5.24%) when two or more teeth were missing. In the relationship between maxillary-mandibular antagonistic quadrants and full mouth, the 1st to 4th place of the missing patterns were all involved with the 1st and 2nd premolars. This study can be clinically helpful in establishing a treatment plan for patients with missing teeth. In addition, it can be used as basic data for molecular biological research to find out the relationship between tooth agenesis and specific genes.

• The korean journal of orthodontics
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• v.31 no.2 s.85
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• pp.209-223
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• 2001

At intrusion of upper anterior teeth in patient with periodontal defect, the use of three-piece base arch appliance for pure intrusion is required. To investigate the change of the center of resistance and of the distal traction force according to alveolar bone height at intrusion of upper anterior teeth using this appliance, three-dimensional finite element models of upper six anterior teeth, periodontal ligament and alveolar bone were constructed. At intrusion of upper anterior teeth by three-piece base arch appliance, the following conclusions were drawn to the locations of the center of resistance according to the number of teeth, the change of distal traction force for pure intrusion and the correlation to the change of vertical, horizontal location of the center of resistance according to alveolar bone loss. 1. When the axial inclination and alveolar bone height were normal, the anteroposterior locations of center of resistance of upper anterior teeth according to the number of teeth contained were as follows : 1) In 2 anterior teeth group, the center of located in the mesial 1/3 area of lateral incisor bracket. 2) In 4 anterior teeth group. the center of resistance was located in the distal 2/3 of the distance between the bracket of lateral incisor and canine. 3) In 6 anterior teeth group, the center of resistance was located in the central area of first premolar bracket .4) As the number of teeth contained in anterior teeth group increased, the center of resistance shifted to the distal side. 2. When the alveolar bone height was normal, the anteroposterior position of the point of application of the intrusive force was the same position or a bit forward position of the center of resistance at application of distal traction force for pure intrusion. 3. When intrusion force and the point of application of the intrusive force were fixed, the changes of distal traction force for pure intrusion according to alveolar bon loss were as follows :1) Regardless of the alveolar bone loss, the distal traction force of 2, 4 anterior teeth groups were lower than that of 6 anterior teeth group. 2) As the alveolar bone loss increased, the distal traction forces of each teeth group were increased. 4. The correlations of the vertical, horizontal locations of the center of resistance according to maxillary anterior teeth groups and the alveolar bone height were as follows : 1) In 2 anterior teeth group, the horizontal position displacement to the vortical position displacement of the center of resistance according to the alveolar bone loss was the largest. As the number of teeth increased, the horizontal position displacement to the vertical position displacement of the center of resistance according to the alveolar bone loss showed a tendency to decrease. 2) As the alveolar bone loss increased, the horizontal position displacement to the vertical position displacement of the center of resistance regardless of the number of teeth was increased.

• The korean journal of orthodontics
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• v.36 no.5
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• pp.339-348
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• 2006

Objective: With development of the skeletal anchorage system, orthodontic mini-implant (OMI) assisted on masse sliding retraction has become part of general orthodontic treatment. But compared to the emphasis on successful anchorage preparation, the control of anterior teeth axis has not been emphasized enough. Methods: A 3-D finite element Base model of maxillary dental arch and a Lingual tipping model with lingually inclined anterior teeth were constructed. To evaluate factors influencing the axis of anterior teeth when OMI was used as anchorage, models were simulated with 2 mm or 5 mm retraction hooks and/or by the addition of 4 mm of compensating curve (CC) on the main archwire. The stress distribution on the roots and a 25000 times enlarged axis graph were evaluated. Results: Intrusive component of retraction force directed postero-superiorly from the 2 mm height hook did not reduce the lingual tipping of anterior teeth. When hook height was increased to 5 mm, lateral incisor showed crown-labial and root-lingual torque and uncontrolled tipping of the canine was increased.4 mm of CC added to the main archwire also induced crown-labial and root-lingual torque of the lateral incisor but uncontrolled tipping of the canine was decreased. Lingual tipping model showed very similar results compared with the Base model. Conclusion: The results of this study showed that height of the hook and compensating curve on the main archwire can influence the axis of anterior teeth. These data can be used as guidelines for clinical application.

• The korean journal of orthodontics
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• v.31 no.5 s.88
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• pp.525-534
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• 2001

Bone remodeling in response to force requires coordinated actions of osteoblasts, osteoclasts, osteocytes, and periodontal ligament cells. Coordination among these cells may be mediated, in part, by cell-to-cell communication via gap junctions. This study was designed to evaluate the expression of gap junction, connection 43 In periodontal tissue during the experimental movement of rat's incisors, by LSAB(labelled streptavidine biotin) immunohistochemical staining for connexin 43. Twenty seven Sprague-Dawley rats were divided into a control group(3 rats), and 6 experimental groups(24 rats) where 75g of force was applied from helical springs across the maxillary incisors. Rats of experimental groups were sacrificed at 12 hours, 1, 4, 7, 14 and 28 days after force application, respectively. And the tissues of a control group and experimental groups were studied immunohistochemically. The results were as follows : 1. In control group, the expression of connexin 43 was rare in gingiva, dentin, cementum, periodontal ligament, and bone cells. 2. In experimental group, the expression of connexin 43 was increased in pulp, periodontal ligament, osteoblasts, and osteoclasts, comparing to that in control. And it was rare in gingiva, dentin, and odontoblasts regardless of the duration of force application, which was not different from that of control group. 3. The expression of connexin 43 in pulp of experimental group began to increase in 4-day after force application and got to the highest degree at 7-day. And it decreased after 14-day to be similar to that of control group at 28-day. 4. The expression of connexin 43 in periodontal ligament was noted in small capillaries adjacent to alveolar bone, showing higher intensity of immunolabelling after 4-day And it was stronger in the pressure side than in tension side of periodontal ligament. After 7-day, decrease in connexin 43 expression was observed. 5. The expression of connexin 43 in alveolar bone began to increase 1-day, reached to the highest degree at 4-day, and decreased at 7-day. And the expression in osteoclasts was more than that in osteoblasts or osteocyte at 7-day.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.2
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• pp.253-261
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• 2009

The purpose of this study was to present new data on the timing and sequence of permanent teeth emergence and to compare these findings with the results of earlier studies. The dental examinations had been performed to E-elementary school students, who visited the Yonsei University Dental Hospital between 1998 and 2005; 1,307 boys and 1,312 girls with the age ranging from 6 to 12 years old. The followings were concluded. 1. Eruption time of the maxillary permanent teeth is as follows. It was 6.81 years in male and 6.73 years in female for the central incisor, 7.78 years in male and 7.65 years in female for the lateral incisor, 10.48 years in male and 9.92 years in female for the canine, 9.76 years in male and 9.63 years in female for the first premolar, 10.66 years in male and 10.49 years in female for the second premolar, 6.39 years in male and 6.26 years in female for the first permanent molar, and 12.13 years in male and 12.03 years in female for the second permanent molar. 2. Eruption time of the mandibular permanent teeth is as follows. The central incisor could not be determined in this study, but it is assumed to erupt before the age of 6.08. In the mandible, eruption time was 6.78 years in male and 6.65 years in female for the lateral incisor, 9.76 years in male and 9.05 years in female for the canine, 9.82 years in male and 9.59 years in female for the first premolar, 10.67 years in male and 10.52 years in female for the second premolar, 6.22 years in male and 6.12 years in female for the first permanent molar, and 11.58 years in male and 11.14 years in female for the second permanent molar. 3. The eruption sequence is as follows. In the maxilla, the first permanent molar erupted first, followed by the central incisor, the lateral incisor, the first premolar, the canine, the second premolar, and the second permanent molar. In the mandible, the central incisor erupted first, followed by the first permanent molar, the lateral incisor, the canine, the first premolar, the second premolar, and the second permanent molar. 4. Tooth eruption occurred earlier in female compared to male by average of 0.19 year in the maxilla and 0.29 year in the mandible. 5. In both male and female, the hiatus (interval of rest) occurred between the emergence of lateral incisor and first premolar in the maxilla while it was observed between the lateral incisor and canine in the mandible. Male had a hiatus of 1.98 years in the maxilla and 2.90 years in the mandible, while the female's were 1.98 years and 2.40 years, respectively.

• Journal of Yeungnam Medical Science
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• v.16 no.2
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• pp.200-207
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• 1999

Background: The objective of this study is to evaluate the effect of the dental and general health in relation to the state of dentition and chewing ability by surveying oral condition and anthropometric measure in order to provide primary statistics for the development of a program which may lead to an improvement in the long-lived elderly health status in a rural community. Materials and Methods: The subjects of this study were 97 rural long-lived elderly(27 males and 70 females) who were over 85 years-old (average age of subjects are $88.14{\pm}3.20$ year old) in Sungju-Gun, Kyungpook Province. Data were collected by using questionnaires and direct measurement of anthropometrics, and oral examination from all 97 subjects on July, 1999. Results: The following results were obtained: 1. 53.6% of all subjects believe that they are healthy. The average values of height, weight, BMI, body fat, lean body fat and total water were $148.8{\pm}11.2cm$, $46.9{\pm}10.5kg$, $21.2{\pm}3.5kg/m^2$, $26.7{\pm}6.9%$, $73.0{\pm}7.1%$, and $53.4{\pm}5.2%$, respectively. 2. The average number of teeth remaining in the subjects were $3.50{\pm}5.71$; the number of maxillary teeth remaining were $1.08{\pm}2.88$; and the number of mandibular teeth remaining were $2.41{\pm}3.76$. The maximum number of teeth remaining among subjects were 22 teeth, and the fully edentulous(no natural teeth) people were 76.3%. The oral conditions of the subjects were 52.6% using denture, 23.7% using natural teeth, and 23.7% masticating edentulous ridge without denture. 3. In terms of oral condition in self-assessment of health, digestive ability, and chewing ability ; On self-assessment of health, 47.1% of those wearing denture group responded as feeling good, 56.5% of those in the group of edentulous without denture, and 65.2% in group of natural teeth only. On self-assessment of digestive ability, 82.4% of those in group of denture responded as feeling good, 65.2% of those in group of no teeth and no denture, and 73.9% of those in group of natural teeth only. On self-assessment of chewing ability, 90.2% of those in the group wearing a denture, 60. 9% of those in the group of no teeth and no denture, and 65.2% of those in the group of natural teeth only. 4. In terms of oral condition in anthropometric measurements; The height, weight, body fat, lean body mass, and total water according to oral conditions were $150.0{\pm}10.7cm$, $49.0{\pm}10.9kg$, $26.9{\pm}6.6%$, $72.7{\pm}7.0%$, $53.2{\pm}5.1%$, respectively, in group wearing a denture, $142.7{\pm}6.0cm$, $43.2{\pm}5.5kg$, $29.5{\pm}7.2%$, $70.8{\pm}6.9%$, $51.8{\pm}5.0%$, respectively, in the group of no teeth and no denture, and $152.3{\pm}14.1cm$, $45.9{\pm}12.6kg$, $23.4{\pm}6.0%$, $75.9{\pm}6.9%$, $55.6{\pm}5.1%$, respectively, in the group of natural teeth only. Conclusion: The subjective measurements of good health were higher denture user, and natural teeth.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.5
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• pp.528-534
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• 2008

Purpose: Marginal fit is one of the important components for the successful prosthodontic restoration. Poor fitting margin of the restoration causes hypersensitivity, secondary caries, and plaque accumulation, which later result in prosthodontic failure. CAD/CAM zirconia all-ceramic restorations, such as $LAVA^{(R)}$ (3M ESPE, St.Paul, MN) and $EVEREST^{(R)}$ (KaVo Dental GmbH, Biberach, Germany) systems were recently introduced in Korea. It is clinically meaningful to evaluate the changes of the marginal fit of the CAD/CAM zirconia systems before and after build-up. The purposes of this study are to compare the marginal fit of the two CAD/CAM all-ceramic systems with that of the ceramometal restoration, before and after porcelain build-up Material and methods: A maxillary first premolar dentiform tooth was prepared with 2.0 mm occlusal reduction, 1.0 mm axial reduction, chamfer margin, and 6 degree taperness in the axial wall. The prepared dentiform die was duplicated into the metal abutment die. The metal die was placed in the dental study model, and the full arch impressions of the model were made. Twenty four copings of 3 groups which were $LAVA^{(R)}$, $EVEREST^{(R)}$, and ceramometal restorations were fabricated. Each coping was cemented on the metal die with color-mixed Fit-checker $II^{(R)}$ (GC Cor., Tokyo, Japan). The marginal opening of each coping was measured with $Microhiscope^{(R)}$ system (HIROX KH-1000 ING-Plus, Seoul, Korea. X300 magnification). After porcelain build-up, the marginal openings of $LAVA^{(R)}$, $EVEREST^{(R)}$,and ceramometal restorations were also evaluated in the same method. Statistical analysis was done with paired t-test and one-way ANOVA test. Results: In coping states, the mean marginal opening for $EVEREST^{(R)}$ restorations was $52.00{\pm}11.94\;{\mu}m$ for $LAVA^{(R)}$ restorations $56.97{\pm}10.00\;{\mu}m$, and for ceramometal restorations $97.38{\pm}18.54\;{\mu}m$. After porcelain build-up, the mean marginal opening for $EVEREST^{(R)}$ restorations was $61.69{\pm}19.33\;{\mu}m$, for $LAVA^{(R)}$ restorations $70.81{\pm}12.99\;{\mu}m$, and for ceramometal restorations $1115.25{\pm}23.86\;{\mu}m$. Conclusion: 1. $LAVA^{(R)}$ and $EVEREST^{(R)}$ restorations in comparison with ceramometal restorations showed better marginal fit, which had significant differences (P < 0.05) in coping state and also after porcelain build-up . 2. The mean marginal opening values between $LAVA^{(R)}$ and $EVEREST^{(R)}$ restorations did not showed significant differences after porcelain build-up as well as in coping state (P > .05). 3. $EVEREST^{(R)}$, $LAVA^{(R)}$ and ceramometal restorations showed a little increased marginal opening after porcelain build-up, but did not show any statistical significance (P > .05).

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.709-727
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• 2001

The pattern of programmed cell death(PCD) has been examined during the early developmental period of development in mouse embryos, from embryonic day 4.5(E4.5) to E11.5 Embryos from Balb/c breedings were harvested at various embryonic stages between E4.5 and El1.5. Cell death was analysed by in situ terminal deoxynucleotidyl transferase mediated dUTP nick end labeling(TUNEL) staining in tissue sections and whole embryos. At the blastocyst stage(E4.5), a very few apoptotic cells were found in the inner cell mass of the blastocyst. In the early egg cylinder stage(35.0-5.5), a few apoptotic cells were detected in the embryonic ectoderm, the embryonic endoerm and the proamniotic cavity. In the advanced egg cylinder stage(E5.5-6.5), TUNEL-posifive cells were observed in the extra-embryonic ectoderm and extra-embryonic endoderm as well as in the embryonic ectoderm, embryonic visceral endoderm and proamniotic cavity. In the streak stage(E6.75-7.75), many TUNEL-positive cells were found in the ectoplacental cone. In contrast, only very few apoptotic cells were found in the chorion and extra-embryonic endoderm in extra-embryonic regions. In intra-embryonic region, a few apoptotic cells were randomly found in the embryonic ectoderm, mesoderm and visceral endoderm. At the early somitogenesis stage(E8.0-8.5), most apoptotic cells were observed in the most cranial portion of neural fold (neural ectoderm and adjacent ectoderm). At the mid somitogenesis stage(39.0-9.5), the otic placode first showed TUNEL-positive at this stage. Small number of TUNEL-positive cells were also first seen around optic placode and branchial arches. Three streams of TUNEL-positive cells were clearly seen in the cranial region at 59.5-9.75. At E10.5, apoptotic cells were localized in the developing eye, the junctional portion of medial nasal, lateral nasal and maxillary processes, the lateral portion of branchial arches, the junction of bilateral mandibular processes, and apical ectodermal ridges of limb buds. At E11.5, apoptotic cells were noticeably decreased in most area, except the developing limbs and several somites in the tail region. In this study, the global temporospatial pattern of PCD throughout early development of mouse embryos was discussed. It may provide the basis for further studies on its role in the morphogenesis of the embryo.

• Restorative Dentistry and Endodontics
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• v.32 no.3
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• pp.248-259
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• 2007

The aim of this research was to study the effect of intermittent polymerization on marginal adaptation by comparing the marginal adaptation of intermittently polymerized composite to that of continuously polymerized composite. The materials used for this study were Pyramid (Bisco Inc., Schaumburg, U.S.A.) and Heliomolar (Ivoclar Vivadent, Liechtenstein) . The experiment was carried out in class II MOD cavities prepared in 48 extracted human maxillary premolars. The samples were divided into 4 groups by light curing method: group 1- continuous curing (60s light on with no light off), group 2-intermittent curing (cycles of 3s with 2s light on & 1s light off for 90s); group 3- intermittent curing (cycles of 2s with 1s light on & 1s light off for 120s); group 4- intermittent curing (cycles of 3s with 1s light on & 2s light off for 180s). Consequently the total amount of light energy radiated was same in all the groups. Each specimen went through thermo-mechanical loading (TML) which consisted of mechanical loading (720,000 cycles, 5.0 kg) with a speed of 120 rpm for 100hours and thermocycling (6000 thermocycles of alternating water of $50^{\circ}C$ and $55^{\circ}C$). The continuous margin (CM) (%) of the total margin and regional margins, occlusal enamel (OE), vertical enamel (VE), and cervical enamel (CE) was measured before and after TML under a $\times200$ digital light microscope. Three-way ANOVA and Duncan's Multiple Range Test was performed at 95% level of confidence to test the effect of 3 variables on CM (%) of the total margin: light curing conditions, composite materials and effect of TML. In each group, One-way ANOVA and Duncan's Multiple Range Test was additionally performed to compare CM (%) of regions (OE, VE CE). The results indicated that all the three variables were statistically significant (p < 0.05). Before TML, in groups using Pyramid, groups 3 and 4 showed higher CM (%) than groups 1 and 2, and in groups using Heliomolar. groups 3 and 4 showed higher CM (%) than group 1 (p < 0.05). After TML, in both Pyramid and Heliomo)ar groups, group 3 showed higher CM (%) than group 1 (p < 0.05) CM (%) of the regions are significantly different in each group (p < 0.05). Before TML, no statistical difference was found between groups within the VE and CE region. In the OE region, group 4 of Pyramid showed higher CM (%) than group 2, and groups 2 and 4 of Heliomolar showed higher CM (%) than group 1 (p < 0.05). After TML, no statistical difference was found among groups within the VE and CE region. In the OE region, group 3 of Pyramid showed higher CM (%) than groups 1 and 2, and groups 2,3 and 4 of Heliomolar showed higher CM (%) than group 1 (p < 0.05). It was concluded that intermittent polymerization may be effective in reducing marginal gap formation.