• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.4
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• pp.389-403
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• 2010

Titanium and gold-alloy abutments have been used for a long-time in the clinical situations, but the use of zirconia abutments also increased. This study was designed to compare and evaluate the microgap differences according to types of abutment and dynamic loading. Titanium abutment, zirconia abutment and gold-alloy abutment (UCLA plastic) were connected into titanium implants of external hexagonal structure US II ${\phi}$ $3.75{\times}11.5$ mm (Osstem Co., Seoul, Korea) with the tightening torque of 30 Ncm. A sine type dynamic loading of 25-250 N and $30^{\circ}$ inclination from long axis was applied for $10^5$ times. Using the SEM both before and after the loadings, implant-abutment interfaces were analyzed on the labial, palatal, mesial and distal surface. The microgaps before and after the loading were compared, no statistically significant difference was observed caused by the dynamic loading on the labial, palatal, mesial or distal surface. Statistically significant difference was observed between UCLA and titanium group and between UCLA and zirconia group on both before and after the loading(p<0.05). No statistically significant difference was found between titanium and zirconia group. Loadings for $10^5$ times did not show significant effect to the microgaps between implants and abutments.

• The korean journal of orthodontics
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• v.30 no.6 s.83
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• pp.723-730
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• 2000

Orthodontic tooth movement requires remodelling of periodontal tissues, especially alveolar bone. Fluoride is known to be a potent inhibitor of osteoclastic bone resorption. The purpose of this study was to examine the effects of a consumption of fluoride on osteoclast numbers appearing on the pressure side of alveolar bones at experimental tooth movement. 40 male rats were exposed to 0, 10, 25 mg/kg/day of sodium fluoride(NaF) in their drinking water for up to 60 days. Orthodontic appliance were activated to mesially tip maxillary first molar with 50-70g. The rats were sacrificed at 1, 2, 4 days after initial activation. The number of osteoclast was counted in a $450\times700\;{\mu}m^2$ area interradicular septum on the pressure side of the maxillary first molar. The results were as fellows, 1. There was significantly different osteoclast number between control group and 25 mg/kg/day group at all measured time. (p<0.05) 2. There was significantly different active bone-resorption area between control group and 25 mg/kg/day group except at 96 hours post activation. (p<0.05) 3. There was slight reduction of active bone- resorption area in control group from 48 hours to 96 hours but in both 10 mg/kg/day group and 25 mg/kg/day group a slight increase was observed from 48 hours to 96 hours.

• Journal of Periodontal and Implant Science
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• v.32 no.1
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• pp.41-49
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• 2002

The aim of this study was to compare periodontal conditions around mesially tipped molars by a tipping degree. Patients who had been consecutively treated at the Department of Periodontology, Chonbuk National University Hospital from October 1999 to August 2001 were assessed with radiographs taken at their molar regions. Of all molars investigated, 142 molars of 116 patients tipped mesially more than 10 degrees to the line perpendicular to an occlusal plane were selected for the study. The tipped molars were divided into 2 groups with a reference to a tipping degree, i.e., 66 slightly tipped(group 1 : <$30^{\circ}$) and 76 severely tipped molars (group 2 : ${\geq}30^{\circ}$). Probing depth(PD), plaque retention index(PRI) at mesial surfaces of tipped molars and tooth mobility(TM) were recorded at the clinical examination. Tipping degree(TD) and alveolar bony defect(ABD) at the mesial surface of the molars were measured in a radiograph. The results showed that no statistical differences were found between groups in all measured variables. In Pearson correlation analysis performed in the same group, a positive relationship was shown between PRI and PD in the group 1 and, in the group 2, between PRI and PD as well as PRI and ABD(p < 0.01). However, no statistically significant relationship was found between TD and all other variables in both groups. Within limitations of this study, it may be concluded that tipping degree did not seem to influence periodontal conditions, i.e., PD, ABD and TM of mesially tipped molars per se, but plaque presence/absence seemed to mainly affect the periodontal conditions of the tipped molars.

• Journal of the korean academy of Pediatric Dentistry
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• v.42 no.2
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• pp.126-135
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• 2015

The purpose of this study was to evaluate the skeletal and dentoalveolar effects of facemask therapy and to compare the anchorage of a bonded expander in patients with Class III malocclusion and different vertical skeletal patterns. Twenty subjects with Class III malocclusion were included in this study and were treated with a facemask and bonded expander. Based on the FMA, subjects were divided into two groups of 10 patients each: a high vertical group (HV; mean FMA $33.56^{\circ}$) and an average vertical group (AV; mean FMA $24.88^{\circ}$). Lateral cephalograms were taken and evaluated before and after treatment. In both groups, forward movement of the maxilla and backward rotation of the mandible were observed after treatment, with no statistical differences between the groups. Vertical skeletal variables increased in both groups, but the increase of FMA was significantly larger in the HV group than the AV group. Mesial movement of maxillary molars and proclination of maxillary incisors which indicate anchorage loss of bonded expander were observed in both groups, with no significant differences between the groups. In conclusion, facemask therapy resulted in effective maxillary protraction in both HV and AV groups. However, the open bite tendency was increased more in the HV group.

• Journal of the korean academy of Pediatric Dentistry
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• v.37 no.2
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• pp.233-239
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• 2010

Space loss of dental arch can appear when the proper position of teeth within the dental arch changes by a certain cause, because the balance of force makes changes about tooth position as well as alignment. The causes of space loss include proximal caries, early extraction, congenital missing of a tooth and hypodontia, etc. Among those causes of space loss, congenital missing of a tooth is more rarely observed in the primary dentition than in the permanent dentition. Congenital missing in the primary dentition is associated with that in the permanent dentition. Furthermore, it can cause space problem, such as mesial tilting or drift of adjacent teeth, space loss for permanent successors and dental arch constriction, etc. Primary lateral incisors is the most commonly involved, in the maxilla rather than in the mandible, but primary canine is rarely reported. In this patient, who visited the department of pediatric dentistry at Yonsei university dental hospital, it was observed that the maxillary right primary canine was congenitally missing and an odontoma was found insteadly. However, neither the space loss for the congenitally missing primary canine nor midline deviation is remarkable during the 2-year-10-month observation period. In addition, any clinical or radiographical symptom did not occur in spite of odontoma. Therefore, surgical enucleation of odontoma is planned according to the eruption of permanent lateral incisor or canine, unless eruption failure of permanent lateral incisor or canine nor cystic change around the odontoma is occurred. Through further evaluation, space maintainer or orthodontic treatment may be necessary.

• Journal of Dental Rehabilitation and Applied Science
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• v.26 no.3
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• pp.221-239
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• 2010

Bone loss may occur depending on the loading conditions. careful treatment planning and prosthetic procedures are very important factors for the proper distribution of stress. Evaluate the stress distributions according to numbers and location of implants in three-unit fixed partial dentures. A mandible missing the right second premolar, first molar and second molar was modeled. Using the CT data. we modeled a mandible with a width of 15mm, a height of 20mm and a length of 30mm, 2mm-thickness cortical bone covering cancellous bone mallow. An internal type implant and A solid type abutment was used. A model with 3 implants placed in a straight line, offset 1.5 mm buccally, offset 1.5 mm lingually and another model with 3 implants offset in the opposite way were prepared. And models with 2 implants were both end support models, a mesial cantilever model and a distal cantilever model. Three types of loading was applied; a case where 155 N was applied solely on the second premolar, a case where 206 N was applied solely on the second molar and a case where 155 N was applied on the first premolar and 206 N was applied on the first and second molar. For all the cases, inclined loads of 30 degrees were applied on the buccal cusps and vertical loads were applied on the central fossas of the teeth. Finite element analysis was carried out for each case to find out the stress distribution on bones and implants. This study has shown that prostheses with more implants caused lower stress on bones and implants, no matter what kind of load was applied. Furthermore, it was found out that inclined loads applied on implants had worse effects than vertical loads. Therefore, it is believed that these results should be considered when placing implants in the future.

• The korean journal of orthodontics
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• v.32 no.1 s.90
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• pp.9-18
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• 2002

The present study hypothesized that the double keyhole looped archwire plays a positive role for the sake of translatory movement and/or controlled tipping of upper 6 anteriors, and secures anchorage control as well. The purposes of the study were to evaluate the changes in lateral cephalograms during orthodontic treatment with DKHLs and to compare the skeletal & dental changes before- & after-treatment. The materials of this study were lateral cephalograms of 20 adult patients with upper dentoalveolar protrusion both in class I and in class II Division1 malocclusion. Lateral cephalograms were taken before and after orthodontic treatment with upper 1st bicuspid extraction and DKHLs. The results were obtained as follows : 1. There were no statistically significant differences in skeletal measurement except SNB and PTFH between before- & after-treatment. The major changes were in dentoalveolar region. 2. After treatment, there were statistically significant decrease in dental measurement except interincisal angle. 3. Both upper & lower lip protrusion was decreased. 4. There were statistically differences in upper anterior crown horizontal & root vertical dimension(7.08 ${\pm}$ 2.14 mm, 2.38 ${\pm}$ 1.15 mm, p<0.01). 5. There were statistically differences in upper posterior dental(both crown & root) horizontal dimension(2.48 ${\pm}$ 0.99 mm, 2.05 ${\pm}$ 0.91 mm, p<0.01).

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.3
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• pp.373-384
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• 2003

The purpose of this study was to evaluate the eruption pattern of a cyst-associated mandibular premolar after marsupialization of a dentigerous cyst in children. The result from the twenty two pairs of normalized panoramic radiographs of twenty two patients who underwent neither extraction nor orthodontic traction of the cyst-associated mandibular after marsupialization were as follows. 1. The eruption speed of a cyst-associated premolar was 3.5 times faster than that of the normal contra-lateral premolar(p<0.05). The angulation change of test group was an average of $2.7^{\circ}$ per month. 2. In the change of the level of root formation, the group which had a little root maturity tended to be faster in the eruption speed(p>0.05) and the R1/4 group had a great change in the angulation change(p>0.05). 3. In the change to be with the cusp position index, the eruption speeds were increased to the 30% deviation groups. But, the eruption speed was decreased above that(p>0.05). 4. Group with cyst diminishment rate of more than $80mm^2$ per month showed the fastest eruption speed of all(p<0.05). 5. The mesial angulated teeth in the test group were decreased more rapidly than the distal angulated teeth in the eruption speed(p>0.05). But, increased in the angulation change(p<0.05). 6. There was a tendency of faster tooth eruption with less deviation of tooth axis. Group with tooth axis deviation of less than $15^{\circ}$ showed the fastest angulation change of all(p<0.05). 7. The eruption speed and the angulation change rapidly decreased during the first 6 months following marsupialization. Based on the results of this study, a cyst-associated mandibular premolar erupted more rapidly after marsupializaton. We thought so that it's prognosis was good if the tooth had a little root maturity, a little devitation and cyst lesion healed faster. We recommend that if there is enough space for eruption, orthodontic traction and surgical treatment of the cyst-associated tooth should be postponed 6 months after marsupialization.

• The korean journal of orthodontics
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• v.30 no.2 s.79
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• pp.127-142
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• 2000

This study have been carried out to find out the mechnical effect of Multiloop Edgewise Arch Wire(MEAW) making use of the finite element method. The tip back bend of MEAW taken in this analysis is $5^{\circ},\;10{\circ}\;and\;15{\circ}$. In addition, Class II or up & down elastic is applied to find out stress distribution and their values in PDL. A adult male of normal occlusion was selected to create the models of teeth and PDL. And the model of MEAW was also created using commercial finite element code (ANSYS version 5.2). The MEAW is forcibly engaged with a class II or up & down elastic, to determine the initial stress generated in PDL. Comparing the compressive and tensile stress at each reference-planes, following results are obtained. 1. When a MEAW of $5^{\circ},\;10{\circ}\;15{\circ}$ tip back bend was engaged with Class II or up & down elastic, the distribution of compressive, tensile stress in entire PDL is similar in each case. 2. The values of compressive and tensile stress in PDL is higher in $15{\circ}$ tip back bend case than in $10{\circ}\;or\;15{\circ}$ tip back bend case. 3. In the distal PDL of 1st and 2nd molar, compressive stress appears. The compressive area is more wide and its values is higher in PDL of 2nd molar than those in 1st molar. The compressive area and its values become more wide and higher according to the increase of the tip back bend. 4. The values of compressive stress are comparatively smaIIer in PDL of molars than those in premolars. 5. Comparing class II and up & down elastic case, tensile stress values in anterior teeth PDL are smaller md their distribution is more wide in up & down elastic case than class If elastic case. On another hand, there is no difference in distribution and stress values in PDL of posterior teeth between two cases. 6. Comparing the tensile area in PDL of anterior teeth, tensile stress values are maximum in PDL of canine.