• Journal of Dental Rehabilitation and Applied Science
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• v.38 no.3
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• pp.127-137
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• 2022

Zirconia is fabricated through various processes. Each element in fabricating process can affect the physical properties of the definitive prosthesis. In particular, both the milling process and the sintering process can affect the final integrity of the zirconia prosthesis. Most of the milling machines adopt the ultra-precision 5-axis machining method, and the results vary depending on which milling method was used and how the milling equipment was managed. Milling blocks are selected according to cutting efficiency and aesthetic reproducibility. The sintering method can affect the grain growth and optical properties, and an accurate evaluation can be made only with additional research on the recent speed sintering procedure. Not only the sintering temperature but also the temperature holding time can affect the quality of definitive prosthesis.

• Journal of Dental Rehabilitation and Applied Science
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• v.38 no.3
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• pp.138-149
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• 2022

The clinical applicability of ceramics can be increased by analyzing the causes of fractures after fracture testing of dental ceramics. Fractography to analyze the cause of fracture of dental ceramics is being widely applied with the development of imaging technologies such as scanning electron microscopy. Setting the experimental conditions is important for accurate interpretation. The fractured specimens should be stored and cleaned to avoid contamination, and metal pretreatment is required for better observation. Depending on the type of fracture, there are dimple rupture, cleavage, and decohesive rupture mainly observed in metals, and fatigue fractures and conchoidal fractures observed in ceramics. In order to reproduce fatigue fracture in the laboratory, which is the main cause of fracture of ceramics, a dynamic loading for observing slow crack growth is essential, and the load conditions and number of loads must be appropriately set. A typical characteristic of a fracture surface of ceramic is a hackle, and the causes of fracture vary depending on the shape of hackle. Fractography is a useful method for in-depth understanding of fractures of dental ceramics, so it is necessary to follow the exact experimental procedure and interpret the results with caution.

• The korean journal of orthodontics
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• v.36 no.1 s.114
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• pp.55-62
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• 2006

Orthodontic mini-implants, despite its usefulness as anchorage, have some limits such as loosening. Therefore, various shapes and lengths have been studied. The aim of this study is to analyze the shape and length of mini-implants mechanically. The shapes of mini-implants (1.6 mm, Dual Top, Jeil Medical Co., Seoul, Korea) were cylindrical and taper. The lengths of mini-implants were 6 mm and 8 mm. The tested groups were 5 groups (cylindrical 6 mm, cylindrical 8 mm, taper 6 mm, taper 8 mm and taper 8 mm modified whose thread is reduced from the middle to upper part). All were inserted and removed on the polyurethane foam with the torque measured. During insertion and removal, the taper shape needed higher torque than the cylindrical shape, and the 8 mm length than the 6 mm length (p<0.001). The taper 6mm group showed superior insertion torque (p<0.001) and similar removal torque to the cylindrical 8 mm group. The taper 8 mm modified group with gradually reduced threads, showed continuous high removal torque after the peak. The initial mechanical stability can be provided by the tapered shape and also, affected by length and thread design.

• The korean journal of orthodontics
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• v.27 no.2
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• pp.297-313
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• 1997

The purposes of this study were to compare the soft tissue changes following hard tissue change after surgery between the one jaw and two-jaw surgery in skeletal class III patients and to get the reference of the incisal inclination at presurgical orthodontics. For this study 24 patients for the two-jaw surgery group and 18 patients for one jaw surgery group were selected. Lateral cephalograms were taken at pretreatment, after presurgical orthodontic treatment, immediately after surgical treatment and at least 6 months after surgery. They were traced and analyzed on skeletodental structure and soft tissue. The results were as follows: 1. After surgery, maxilla, maxillary incisors and upper lip were moved anteriorly and superiorly in two-jaw surgery group. Mandible and mandibular incisors were moved posteriorly and superiorly, and thickness of lower lip was increased in both group but there were no statistically significant difference. Anterior facial height was more decreased in two-jaw surgery group (p<0.05). At least 6 months after surgery, by the postorthodontic treatment, maxillary incisors were moved labially 1.44mm, mandible and mandiibular incisors were moved lingually 1.43mrn, 1.26mm respectively in one jaw surgery group. But there was no statistically significant changes of hard tissue in two :jaw surgery group. 2. The correlation coefficients of maxillary hard and soft tissue horizontal changes were high in two jaw surgery group and the ratios for soft tissue to A point were 19% at Sri, 80% at SLS, 82% at LS. The ratios for soft tissue to B point were 92% at LI, 104% at ILS in one jaw surgery group, 89% at LI, 101% at ILS in two-jaw surgery group. 3. The correlation coefficients and change ratios of mandibular incisors and LL HS on lower lip horizontal changes were 0 0.89 and 75%, 85% in one jaw surgery group, 0.93, 0.90 and 76%, 87% in two-jaw surgery group. The correlation coefficients of maxillary incisors and Sn, SLS and LS on upper lip horizontal changes were 072, 0.76 and 0.75 in two jaw surgery group and ratios of changes were 57%, 58% and 59%. 4. The regression equations between skeletal horizontal discrepancy and incisal inclinaton were taken in one jaw surgery group. Those were FMIA=57.48-2.17ANB, U1-SN=-75.02+2.17SNB and $R^2$ were 0.63, 063 respectively. So if there is skeletal horizontal discrepancy by mandibular prognathism in one jaw surgery case, we consider attaining more labial inclination of maxillary incisors than normal and more lingual inclination of mandibular incisors than normal. But correlation coefficient of the regression equations in two jaw surgery group was low, so, that equation was not reliable.

• 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).

• The korean journal of orthodontics
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• v.27 no.1
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• pp.105-117
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• 1997

This investigation examined the effect of lateral shift of mandible from functional occlusal interference on the growth of mandible and the growth pattern of mandible shown after the removal of occlusal interference. The followings were performed with the results below : the changes in mandible and condylar cartilage were studied in the experimental group with upper right, lower left incisors cut for 2 and 4 weeks- an 4-week-old rats and the experimental group which had cut for 4 weeks and suspended for 2 weeks. 1. In the 2-week experimental group, the left mandibular length, condylar length, mandibular height and condylar area seemed smaller than those on the right and the normal group ; the right mandibular length and condylar area were smaller than the normal group. 2. In the 4-week experimental group, left condylar area was smaller than the right, but due to the quick changes in adaptability of left mandible, right and left mandibular lengths were similar. compared with the normal group, however, mandibular length and condylar area still remained small. 3. In the 6-week experimental group, the left and the right appeared similar with the mandibular length remaining still shorter than the normal group. 4. In the sagittal plane, the proliferation of the cartilage layers of the left condylar cartilage of the 2-week group appeared to have general repression compared with the right and the normal group. The right side also showed repressed growth compared with the normal group. In the 4 and 6-week groups, however, it was similar to the normal group. 5. In condylar cartilage volume, no significant difference was noted in the comparisions of left and right of the experimental group, nor in the comparison of the same sides of experimental wand normal groups. Based on the above, in case of contralateral incisal cutting in rats, it was observed that the growth of mandible and condyle of the cutting side was repressed, at the same time, the quick adaptability led to similar changes of growth in left and right mandibles. But judging from the similar phenomena throughout the whole experimental period in the changes of condylar cartilage volume in the experimental, right and left, and normal groups, the general overall growth of condylar cartilage was found unrepressed. It was also recognized that the growth of condylar cartilage can take in various directions.

• Journal of Oral Medicine and Pain
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• v.34 no.1
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• pp.91-102
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• 2009

Condylar resorption, or condylysis can be defined as progressive alteration of condylar shape and decrease in mass. Condylar resorption is a poorly understood progressive disease that affects the TMJ and that can result in malocclusion, facial disfigurement, TMJ dysfunction, and pain. The aim of this study was to investigate clinical assessment and cephalometric characteristics in 224 patients with condylar resorption, who visited in the Department of Oral Medicine Kyungpook National University Hospital at 2006, by use of panorama, transcranial view and lateral cephalometric radiograph. The results were as follows; 1. Clinical assessment 1) Total number of patients who visited with chief complaints of TMD were 2419 and 224 (9.3%) among them revealed the condylar resorption, Among patients group with condylar resorption, female was 183 and male was 41, females were predominant. 2) Patient's age ranged from 12 to 70 and mean age was 30.6 years old with a strong predominance for 10s and 20s. Distribution of a showed as follows; 10s was 26.3%, 20s was 34,8%, 30s was 13.8%, 40s was 11.2%, 50s was 7.1%, 60s was 6.3% and 70s was 0.4%. 3) Most of the patients had parafunctional habit. 4) The case of showing the pain in condylar resorption was 145, the case of not showing the pain was 79. 5) Treatment duration of the patients was relatively short. 2. Cephalometric Characteristics 1) ANB which means the retruding of the mandible increased significantly than normal group. The ANB of female was lager than male group as the means of ANB were 5.05 in female and 3.57 in male, 2) SN-GoMe and FMA increased in resorption patients, but FH-PP did not show any significant difference. The FMA of female was lager than male group as the means were 31.69 in female and 30.44 in male. 3) Total posterior facial height was significantly smaller and total anterior facial height showed no significant increase as compared with those of the normal group. Condylar resorption was predominant in young female which was caused by more vertical facial pattern in female than male and increase of parafunctional habit in young age. It was thought that the patients who have a risk factor increasing the compressive stress at condyle caused by obliquely inclined masseter and medial pterygoid show high prevalence of condylar resorption.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.4
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• pp.731-752
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• 1995

This study was performed to research the changes of masticatory system subsequent to randomly increasing the vertical dimension. The subjects were twenty seven persons, twenty two men and five women, with a mean age of 24.3(age ranged from 22 to 26). The subjects had a complete or almost complete set of natural teeth and reported no subjected symptoms of pain or dysfunction in the masticatory system. The occlusal splint increased vertical dimension was made on semiadjustable articulator. The subjects were randomly divided to three groups according to the vertical dimension, at which the occlusal splint was made. Group I occlusal splints were made at 2mm form the occlusal vertical dimension, group II occlusal splints at 5mm, group III occlusal splints at 8mm. The occlusal splints were almost weared for 2 weeks except meal-time. Clinical examination, muscle activity, changes of free-way space, movement of mandible and articular condyle were recorded and analyzed by means of biopak system(Bioresearch Inc, Millwakee Wisconsin.) and radiograph. 1. In clinical examination, various symptoms were reported by all subjects immediately after the placement of occlusal splint. At the end of experiment, symptoms were lasted by 1 subject in Group I, 2 subjects in Group II, 6 subjects in Group III. At the other subjects, the most of symptoms were disappered within 2-4 days after the placement of occlusal splints. 2. The average free-way space before the startof experiment was 1.77mm in all twenty seven subjects. Immediately after the placement of occlusal splints, 0.67mm at Group I, 0.49mm at Group II, 0.41mm at Group III, At 2 weeks after the placement of occlusal splint 0.93mm, 0.79mm, 0.78mm each other, 1.94mm, 1.77mm, 2.3 mm at immediately after the removal of occlual splint. At 1 week after the removal of occlusal splint, free-way space was recovered to the pre-experimental state 3. In cephalometric radiograph, following either the placement or the removal of the occlusal splints, the movements of mandible in an antero-posterior direction were not statistically significant(p>0.05). 4. In transcranial radiograghs of TMJ, 1 week after the placement of occlusal splint the movement of most superior position on condyle in all group shoed antero-inferior position than before the experiment(p<0.001) and also showed antero-inferior position in mandibular postural rest position than in certric occlusion(p<0.001). Following either the placement or the removal of the splints, the amount of movement of most superior position on condyle was group III. group II and group I in order(p<0.001). 5. In anterior temporal and superficial masseter muscle, muscle activity at postural rest position decreased at 2 weeks after the placement of occlusal splint in group I and group II (p>0.05), but significantly increased in group III(p<0.001). At 1 week after the removal of the occdusal splint, muscle activity at postural rest position was recovered preconditional state 6. In anterior temporal and superficail masseter muscle, muscle activity at clenching in all group was significantly decreased after placement of the occlusal splint, slightly increased during experimental period and recovered to the original state at 1 week after removal of the occlusal splint. But was not statistically significat(p>0.05)s.