• The korean journal of orthodontics
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• v.50 no.5
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• pp.314-323
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• 2020

Objective: To identify the available evidence on the effects of rapid maxillary expansion (RME) with three-dimensional imaging and provide meta-analytic data from studies assessing the outcomes using computed tomography. Methods: Eleven electronic databases were searched, and prospective case series were selected. Two authors screened all titles and abstracts and assessed full texts of the remaining articles. Seventeen case series were included in the quantitative synthesis. Seven outcomes were investigated: nasal cavity width, maxillary basal bone width, alveolar buccal crest width, alveolar palatal crest width, inter-molar crown width, inter-molar root apex width, and buccopalatal molar inclination. The outcomes were investigated at two-time points: post-expansion (2-6 weeks) and post-retention (4-8 months). Mean differences and 95% confidence intervals were used to summarize and combine the data. Results: All the investigated outcomes showed significant differences post-expansion (maxillary basal bone width, +2.46 mm; nasal cavity width, +1.95 mm; alveolar buccal crest width, +3.90 mm; alveolar palatal crest width, +3.09 mm; intermolar crown width, +5.69 mm; inter-molar root apex width, +2.85 mm; and dental tipping, +3.75°) and post-retention (maxillary basal bone width, +2.21 mm; nasal cavity width, +1.55 mm; alveolar buccal crest width, +3.57 mm; alveolar palatal crest width, +3.32 mm; inter-molar crown width, +5.43 mm; inter-molar root apex width, +4.75 mm; and dental tipping, 2.22°) compared to pre-expansion. Conclusions: After RME, skeletal expansion of the nasomaxillary complex was greater in most caudal structures. Maxillary basal bone showed 10% post-retention relapse. During retention period, uprighting of maxillary molars occurred.

• Restorative Dentistry and Endodontics
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• v.45 no.1
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• pp.7.1-7.9
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• 2020

Objectives: This study was performed to assess the anatomy of mandibular first molars. Materials and Methods: In this in vivo study, cone-beam computed tomography (CBCT) volumes of 312 bilateral intact first mandibular molars from 156 patients (79 men and 77 women; average age, 35.6 ± 11.2 years) were investigated in terms of the direction of each canal's curvature in the buccolingual and mesiodistal dimensions (direction of the position of the apex in relation to the longitudinal axis of the root), the presence of an isthmus (a narrow, ribbon-shaped communication between 2 root canals) in 3 segments (0-2, 2-4, and 4-6 mm) from the apex), and the presence and number of accessory canals (smaller canals besides the main root canals, connecting the pulp to the periodontium). Data were analyzed statistically (α = 0.05). Results: Mesiolingual canals were mostly buccally and distally inclined, while mesiobuccal and distolingual canals were mostly distally curved. Isthmuses were more common in younger patients (χ² test, p < 0.05). The average numbers of accessory canals in the apical, middle, and coronal segments were 9.9 ± 4.2, 6.9 ± 2.9, and 9.3 ± 3.0 canals per segment, respectively (analysis of variance, p < 0.001). Age and sex were not associated with the number of accessory canals (p > 0.05). Conclusions: The complex anatomy of these teeth deserves attention during non-surgical or surgical endodontic treatment. Around the apex, isthmuses might be more prevalent in younger and female individuals.

• Restorative Dentistry and Endodontics
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• v.22 no.1
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• pp.347-357
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• 1997

An accurate working length is an essential factor in the success of endodontic treatment. There are several methods for determining working length; electronic apex locator, tactile sense by clinician, and radiography. Among these methods, the most commonly used method is radiography. But this method requires excessive radiation, long developing time, and many equipments. In additon, it could give an image distortion and two dimensional image. To improve these disadvantages, an intraoral digital radiographic system (Digora$^{(R)}$) which use an imaging plate instead of a film, was developed. The purpose of this investigation was to compare Digora imaging with conventional radiography in determining the working length. Maxillary first or second molars of human dried skull were used. Files were inserted into canals at randomly selected lengths, from 2mm short of the radiographic apex to 2rnm beyond. Radiographs and Digora images(Digora positive and Digora negative) were evaluated to determine the adjustment needed to place the file 0.5mm from the radiographic apex. The results were as follows ; 1. There was no significant difference in accuracy between those evaluated in ${\pm}0.5mm$ and those accurately evaluated in the 3 images. 2. When comparing the accuracy of each image without distinguishing the 3 images, in the group accurately determined within ${\pm}0.5mm$, the mesiobuccal group showed significantly higher accuracy compared to the palatal group(p<0.05).

• Proceedings of the KOSOMBE Conference
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• v.1993 no.05
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• pp.57-60
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• 1993

A finite element-based computer simulation of excimer laser susery was conducted to study some factors on the surgery. In particular, the radius of curvature at the apex of the cornea was examined under various surgical conditions. Corneal tissue was assumed to be a nearly incompressible, linear elastic, homogeneous, isotropic material under very small deformation. The geometry of the human cornea was taken from the experimental data[1]. The simulation utilized ANSYS(Swanson Analysis System Inc.Rev.4.4A). In this study, the major factors which affect the outcomes of the excimer laser surgery were investigated. First, two patterns of surgery with various surgery thickness(40-70micrometers) were examind. The pattern#1 describes the meridian from the apex to the edge of the surgery area to be straight. And the corresponding meridian of the pattern 2 can be expressed as a quardratic function. The results show that the pattern #2 is more realistic and effective. Then, the effects of other factors were investigated based on the pattern #2. Other factors are:various diameters of the surgical area (3-8 milimeters), Young's modules(3.5-4.5MPa), and depth of surgery at the apex(40-70micrometers). Compared with the computer simulation of the radial keratotomy surgery[2], the excimer laser surgery was proven to be more effective in treating myopia patients. In conculusion, the results of the simulation are qualitative agreement with clinical experience[3] indicating the potential of the finite element model of the surgery as a guideline to the surgeon before actual surgery.

• Journal of the Korean Institute of Gas
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• v.24 no.1
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• pp.49-55
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• 2020

Experimental investigations were conducted to understand the multi-staged combustion characteristics of a swirl-stabilized double cone premixed burner nozzle used for industrial gas turbines for power generation. Multi-staged combustion is implemented by injecting the fuel through the existing manifold of the side slots as well as through the apex of the cone with two fuel injection angles which are slanted or axial. NOx and CO emissions, and wall temperature distributions were measured for various fuel distributions and operating conditions. Results show that NOx emissions are decreased when the fuel distribution to the apex is 3% of the total amount of fuel, which is due to more uniform fuel distribution inside the nozzle, hence less hot spots at the flame. NOx emissions are rather increased when the fuel distribution to the apex is 8% of the total amount of fuel for axial fuel injection by occurrence of flash back in premixing zone of burner.

• Animal Systematics, Evolution and Diversity
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• v.25 no.1
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• pp.95-98
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• 2009

Nemoura phasianusa n. sp. is similar to Nemoura jezoensis in general morphology especially lateral view, but can be distinguished by the combination of the characters of the epiproctal shape whose apex is depressed medially, and sclerites of epiproct, which look like question marks without dots.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.11
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• pp.97-104
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• 2004

This paper proposes an efficient VLSI architecture of 9-7/5-3 Lifting DWT filters that is used by lossy or lossless compression of JPEG2000. The proposed architecture uses only internal line memories to compute Lifting-DWT operations and its PE(Processing Element) has critical path with 1 multiplier and 1 adder. To reduce the number of PE, we make the vertical filter that is responsible for the column operations of the first level perform both the row and column operations of the second and following levels. As a result, the architecture has smaller hardware cost compared to that of other architectures. It was modeled in RTL level using VHDL and implemented on Altera APEX 20K FPGA.

• The Journal of Korean Academy of Prosthodontics
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• v.52 no.3
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• pp.202-210
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• 2014

Purpose: The aim of this study was to evaluate the stress concentration and distribution whether restoring the cavity or not while restoring with metal ceramic crown on tooth with abfraction lesion using finite element analysis. Materials and methods: Maxillary first premolar was selected and made a total of 10 finite element model. Model 1 was natural tooth; Model 2 was tooth with metal ceramic crown restoration which margin was positioned above 2 mm from CEJ; Model 3 was tooth with metal ceramic crown restoration which margin was positioned on CEJ; Model 4 was natural tooth which has abfraction lesion; Model 5 and 6 had abfraction lesion and the other condition was same as model 2 and 3, respectively; Model 7 was natural tooth which had abfraction lesion restored with composite resin; Model 8 and 9 was tooth with metal ceramic crown after restoring on abfraction lesion with composite resin; Model 10 was restored tooth on abfraction lesion with composite resin and metal ceramic crown restoration which margin is positioned on lower border of abfraction lesion. Load A and Load B was also designed. Von Mises value was evaluated on each point. Results: Under load A or load B, on tooth with abfraction lesion, stress was concentrated on the apex of lesion. Under load A or load B, on tooth that abfraction lesion was restored with composite resin, the stress value was reduced on the apex. Conclusion: In case of abfraction lesion was restored with composite resin, the stress was concentrated on the apical border of restored cavity regardless of marginal position. It was favorable to place crown margin on the enamel for restoring with metal ceramic crown.

• Journal of Periodontal and Implant Science
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• v.31 no.3
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• pp.581-595
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• 2001

In performing implant procedures in the anterior portion of the maxilla, many difficulties exist because of anatomical reasons, such as the proximity of the nasal floor, lateral extension of the incisive canal, and labial concavity. On the other hand, in the posterior region of the maxilla, there is often insufficient recipient bone between the maxillary sinus and alveolar ridge due to alveolar ridge resorption and pneumatization of the maxillary sinus. In order to perform implants in such regions, ridge augmentation procedures such as onlay bone graft, guided bone regeneration, and maxillary sinus grafting are performed. In studies of Caucasians, use of autograft from mandibular symphysis has been reported to be highly successful in maxillary sinus grafting. However, in a clinical study of Koreans, autograft of mandibular symphysis has been reported to have significantly low success rate. It has been hypothesized that this is because of insufficient cancellous bone due to thick cortical bone. In order to test this hypothesis, bone quality and morphology of Koreans can be compared with those of Caucasians. In this study, the bone density and morphology of the cortical bone and cancellous bone in the mandibular symphysis of 35 Korean cadavers were evaluated. The following results were obtained: 1. In terms of bone density, type I, type II, and type III consisted of 1.4%(3/213), 72.3%(154/213), and 26.3%(56/213) of the cross-sectioned specimens, respectively. In general, the bone density tended to change from type II to type III, as cross-sectioned specimens were evaluated from the midline to the canine. Type IV wasn't observed in this study. 2. The distance between the root apex and the lower border of the cancellous bone was 18.34mm-20.59mm. Considering that the bone has to be cut 5mm below the root apex during the procedure, autografts with about 15mm of vertical thickness can be obtained. 3. The thickness of cortical bone on the labial side increased from the root apex to the lower border of the mandible. The average values ranged from 1.43mm to 2.36mm. 4. The labio-lingual thickness of cancellous bone ranged from 3.43mm to 6.51mm. The thickness tended to increase from the apex to the lower border of the mandible and decrease around the lower border of cancellous bone. From the above results, the anatomic factors of the mandibular symphysis (bone density, thickness, quantity and length of the cortical bone and cancellous bone) didn't show any difference from Caucasians, and it cannot be viewed as the cause of failure in autografts in the maxillary sinus for implants.

• The korean journal of orthodontics
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• v.32 no.5 s.94
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• pp.343-353
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• 2002

This study was designed to investigate the stress distribution of alveolar bone in case of on masse retraction with lingual K-loop archwire using the 3-dimensional photoelastic stress analysis followed by stress freezing process. Lingual K-loop archwire which had loop in 15mm height was used and activated by retraction force of 350gm per each side. The results were as follows 1. Central incisor : As the closer side to crown, the larger tensile stress was distributed at both mesial and labial surfaces and the larger compressive stress was distributed at distal surface. As the closer side to root apex, the larger compressive stress was distributed at lingual surface. The compressive stress was distributed at root apex. 2. Lateral incisor : The tensile stress was distributed at the coronal side of mesial surface. The compressive stress was distributed at distal surface. As the closer side to crown, the larger tensile stress was distributed at labial surface. The tensile stress was distributed at coronal side and the compressive stress was distributed at apical side of lingual surface. The compressive stress was distributed at root apex. 3. Canine The tensile stress was distributed at coronal side and the compressive stress was distributed at apical side of mesial surface. The tensile stress was distributed at distal surface. As the closer side to crown, the larger tensile stress was distributed at both mesial and distal surfaces. The compressive stress was distributed at root apex. 4. Second premolar : The tensile stress was distributed at mesial surface. The compressive stress was distributed at coronal side and the tensile stress was distributed at apical side of distal surface. The compressive stress was distributed at coronal side of buccal surface. As the closer side to crown, the larger tensile stress was distributed at lingual surface. The compressive stress was distributed at root apex. 5. First molar . As the closer side to crown, the larger tensile stress was distributed at both mesial and distal surfaces. No stress was distributed at buccal surface and palatal root apex. As the closer side to crown, the larger tensile stress was distributed at both lingual surfaces. The compressive stress was distributed a4 buccal root apexes. 6. Second molar The compressive stress was distributed at all root apexes. As the closer side to crown, the larger compressive stress was distributed at both mesial and lingual surfaces, and the larger tensile stress at both distal and buccal surfaces. Transverse bowing effect was observed in on-masse retraction with lingual K-loop archwire, however vertical towing effect was not. Rather, reverse vortical bowing effect was developed.