• The Journal of the Korean dental association
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• v.49 no.4
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• pp.203-210
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• 2011

The aims of this study were to evaluate the adequate thickness of opaque resins for situations such as an oral black cavity and discolored tooth structure, as well as the translucency of each opaque material at various thicknesses. Six opaque-shade composite resins (Z-350 OA3, Amelogen Universal A2O, Esthet-X A2O, Esthet-X A4O, Charmfil UO and Aelite Universal OA3) were prepared in metal molds with a hole of 8 mm in diameter and various thicknesses (0.5mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm, 3.0 mm and 4.0mm). Four backgrounds (white tile, black tile, C4 shade porcelain and opaque resin itself) were used to determine the translucency parameter (between black and white backgrounds). and to mimic a black oral cavity (between black and opaque resin backgrounds) and a discolored tooth structure (between C4 and opaque resin backgrounds). Color measurements were made by a colorimeter to determine the CIELAB values of each specimen with each background and to calculate the translucency parameter and ${\Delta}E^*$ value difference among the specimens on the backgrounds. The translucency parameter and ${\Delta}E^*$ obtained between black and opaque resin backgrounds decreased in similar pattern as thickness increased. A C4 background was masked by resin thicknesses of 0.5-1.0mm, while a black background required thicknesses of 1.0-2.0mm. Adequate knowledge about differences in the optical character like translucency of the materials used is essential, together with the accumulated experience of the individual clinician.

• Korean journal of applied entomology
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• v.34 no.4
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• pp.308-313
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• 1995

Drosophila melanogaster, D. simulans, and D. sechellia are closely related species which belong to the D. melanogaster complex; the first two cosmopolita and the last one restricted to th Seychelles archipelago. The phenogenetical relationship between this complex and their hybrids were investigated by the comparison of sex-comb tooth number an genital arch of male. In interspecific hybrids of all crosses between three species four hybrid males were produced and completely sterile. Males of D. simulans (${O}_{9}$) have significantly less sex-comb teeth (mean 8.35) than either D. melanogaster (OR, mean 10.73) and D. sechellia (Ja, mean 10.60). From the analysis by the number of sex-comb tooth in interspecific hybrids we could not represent the direction of heredity nature. each species of D. melanogaster complex were characteristic in the shape of the genital arch, which readily allows these species to be distinguished. The common structure of the genital arch in the interspecific hybrids were mosaic-like structure between parental species.

• Restorative Dentistry and Endodontics
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• v.20 no.1
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• pp.152-163
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• 1995

This experiment was performed to observe the adhesion pattern and microleakage in the gingival margin according to variation in the resin cement thickness which results from thickness of Die spacer. which is considered to effect the adaptability of the composite resin inlays. Clearfil CR inlays were fabricated on stone models with CR Sep applicated once and Nice fit twice, 4 times, and 6 times each. After 2nd curing within the CRC-100 oven, CR inlays were cemented with CR inlay cement. Dye(2% methylene blue) penetration and adhesion pattern were evaluated after sectioning of gingival margin into :3 pieces. The results were as follows ; 1. The thickness of resin cement showed unevenchanging pattern with that of die spacer, namely, it was increased until 4 times' application of Nice-Fit but was decreased with 6 times' application of that. 2. The degree of dye penetration wasn't affected by cement thickness within a limited value. 3. Most of dye penetration was shown through the interface between cement and enamel rather than the interface between cement and CR inlay. This shows that the affinity of resin cement for CR inlay was superior to the adhesive strength with tooth structure. 4. No gap was found at the interface between enamel and cement but some showed separation between dentin and cement. It is concidered that the contraction force of cement was less than the bond strength with the enamel. 5. Lots of voids were found in the CR inlay and resin cement. There was a pooling tendency of bonding agent and cement in the axiogingival line angle portion. 6. In some specimens, cracks were shown in enamel margin. From this it could be considered that cavity preparation and surface treatment weakened the tooth structure.

• Restorative Dentistry and Endodontics
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• v.26 no.4
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• pp.316-325
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• 2001

The purpose of this study was to evaluate the effect of adhesive curing timing on the direction of polymerization shrinkage of light-curing composite resin. In this study, the curing times of adhesive and composite resin were measured by differential scanning calorimeter(DSC). 28 extracted human molars were embedded in clear resin and box-type cavities were prepared. Based on DSC data, the experimental teeth were divided into 4 groups. Group 1: no bond; Group 2: late curing; Group 3: Intermediate curing; Group 4: Early curing. After treating with adhesive, the buccal cavities were filled with Z-100 hybrid composite resin and the lingual ones were filled with AEliteflo flowable composite resin. The depressions at the surface were measured by surface profilometer, then the specimens were embedded in clear resin and sectioned. Impressions were obtained and used to get epoxy resin replicas. The epoxy replicas were gold-coated and observed under SEM. Average Maximum Gap(AMG), Gap Proportion(GP), Average Marginal Index(AMI) were used to compare the shrinkage gap of each group. The results were statistically analyzed using the Kruskal-Wallis One Way ANOVA, Student-Newman-Keuls method. The results of this study were as follows. 1. Average Maximum Gap, Gap Proportion, Average Marginal Index and depression at the surface or Z-100 hybride composite resin were smaller than those of AEliteflo flowable composite resin(P<0.05). 2. When the bonding between composite resin and tooth structure was strong, the shrinkage gap was small, and depression at the surface was deep(P<0.05). 3. In the well-bonded group, light-curing composite resin shrank toward bonded cavity wall, not toward light source. The result suggested that the direction of polymerization shrinkage was affected by the quality of bonding in the dentin-resin interface. The strong was the bonding between composite resin and tooth structure, the smaller was the gap and the deeper was the depression at the surface. Then the flow to compensate the polymerization shrinkage proceeded from surface to bonded cavity wall.

• Journal of Dental Rehabilitation and Applied Science
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• v.40 no.1
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• pp.24-30
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• 2024

Complicated crown fractures of maxillary anterior teeth caused by trauma in adolescence can cause functional and aesthetic problems. For crown fractures with pulp exposure, various restorative methods can be considered depending on the amount of remaining tooth structure. Direct resin restorations are the most traditional and effective method, but they are likely to discolor and break over time. Fixed prosthesis have a high possibility of re-restoration due to marginal disharmony due to tooth movement during the growth period, and restorations using post which are mainly performed for extensive crown fractures increase the risk of root perforation and root fracture. However, endocrown is an integrated structure that gains retention force from the pulp space, enabling effective reconstruction from a biomechanical perspective and providing advantages in restoring function and aesthetics. Therefore, endocrown can be considered as a restoration method for complicated crown fractures caused by trauma in adolescence.

• International Journal of Stem Cells
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• v.17 no.3
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• pp.330-336
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• 2024

Mesenchymal stem cells in the dental tissue indicate a disposition for differentiation into diverse dental lineages and contain enormous potential as the important means for regenerative medicine in dentistry. Among various dental tissues, the dental pulp contains stem cells, progenitor cells and odontoblasts for maintaining dentin homeostasis. The conventional culture of stem cells holds a limit as the living tissue constitutes the three-dimensional (3D) structure. Recent development in the organoid cultures have successfully recapitulated 3D structure and advanced to the assembling of different types. In the current study, the protocol for 3D explant culture of the human dental pulp tissue has been established by adopting the organoid culture. After isolating dental pulp from human tooth, the intact tissue was placed between two layers for Matrigel with addition of the culture medium. The reticular outgrowth of pre-odontoblast layer continued for a month and the random accumulation of dentin was observed near the end. Electron microscopy showed the cellular organization and in situ development of dentin, and immunohistochemistry exhibited the expression of odontoblast and stem cell markers in the outgrowth area. Three-dimensional explant culture of human dental pulp will provide a novel platform for understanding stem cell biology inside the tooth and developing the regenerative medicine.

• The Transactions of the Korea Information Processing Society
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• v.13 no.10
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• pp.568-573
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• 2024

Accurate placement of prosthetics represents a critical aspect of dental implant surgery. however, it heavily depends on the dentist's decision and visual obstructions caused by various factors can lead to errors during the procedure. This paper proposes a 2D image-based real-time implant placement guiding system that predicts the implant position using 2D surgical video without the need for preoperative oral scans or 3D model generation. In the initial phase of the surgical video, two segmentation models are employed to measure prior statistics of the occlusal and incisal surfaces for each tooth. Subsequently, a single segmentation model is used to separate the occlusal and incisal surfaces, and the implant placement is predicted and guided based on the axis and length of adjacent teeth as well as the center of the prosthesis to be implanted. The system was designed and implemented using a dental phantom model, which replicates the oral structure of an actual human. The algorithm's average execution time for guiding implant placement on 10 images was measured to be 12.14 ms, demonstrating its feasibility for real-time application in surgical video.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.693-696
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• 2011

The SRM (Switched Reluctance Motor) is composed of silicon steel plates where the rotor structure is simple and laminated without coil winding or permanent magnet, making it mechanically robust and its maintenance and repair excellent. Applying SRM as traction motor for railway vehicle is given consideration because of its ruggedness capability in severe loading condition and its compact structure. Optimal design of SRM is needed to reduce torque ripple to apply SRM for railway traction drive because SRM has high torque ripple. In this paper, switched reluctance motor with three different stator pole shapes is taken for magnetic analysis using 3d finite element method to apply SRM as traction drive for railway vehicle. It is observed that the model 3 added Tooth Tang Depth and Slot Round to stator shape gives the improved inductance and torque characteristic.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.5
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• pp.535-543
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• 2004

Purpose: The purpose of this study is to compare the effect of two fiber post systems and one metal cast post system on the fracture strength and fracture pattern of crowned, endodontically treated teeth with 2 mm-height of the reamining tooth structure. Materials and methods: A total of 36 recently extracted sound human mandibular premolars were selected Each tooth structure of the crown portion except 2mm-height of the one above the cementoenamel junction was removed. After being endodontically treated, they were randomly distributed into 3 groups: group 1, restored with quarts fiber post(D.T. Light-Post), group 2, with glass fiber post(FRC Postec), and group 3, metal cast post and core. All teeth were fully covered with nonprecious metal crowns. Each specimen was embedded in an acrylic resin block and then secured in a universal load-testing machine. A compressive load was applied at a 130 degree angle to the long axis of the tooth until fractured, at a crosshead speed 20mm/min. The highest fracture loads were measured and recorded as the fracture strength of each specimen. Fracture areas were measured on the mid-buccal and mid-lingual point from the crown margins. One-way analysis of variance and Turkey test were used to determine the statistic significance of the different fracture loads and areas among the groups (p<0.05). Results: The mean fracture loads were $1391{\pm}$425N(group 1), $1458{\pm}476N$(group 2) and $1301{\pm}319N$(group 3). The fracture loads among the three groups had no statistically signifiant difference (p>.05). The mean fracture area of the fiber post was closer to the crown margin than that of the metal cast post and core(p<.05). The metal cast post showed unrestorable and catastrophic fracture patterns. Conclusion: Within the limitations of this study, fracture loads with any statistically significant difference were not recorded for endodontically treated teeth restored with two fiber posts and the metal cast post. But teeth restored with the fiber posts typically showed the fracture pattern close to the crown margin, which was almost restorable.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.2
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• pp.177-197
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• 1995

The endodontically treated tooth is generally restored with post & core, owing to the brittleness and the loss of large amount of tooth structure. Although there have been lots of studies about the endodontically treated teeth, the three-dimensional quantitative studies about the strees distribution of them are in rare cases. In this study, it was assumed that the coronal portion of the upper incisou had severely damaged. After the root canal therapy it was post cored, and restored with PFM crown, for this experiment nine types of model were constructed : 1); long, 2); medium, 3); short gold post for the roots supported with a narmal alveolar bone, 4); long, 5); medium, 6); short gold post for the roots supported with an alveolar bone resorbed to its 1/3 of root length, 7); long, 8); medium, 9); short base metal post for the roots supported with an alveolar bone resorbed to its 1/3 of root length. Force was applied from two directions. One was functional maximum bite force(300N) applied to the spot just lingual to the incisal edge with the angle of 45 degrees to the long axis of the tooth, and the other one was horizontal force(300N) applied to the labial surface. The results analyzed with three-dimensional finite element method were as follows : 1. Stress was concentrated on the middle portion of the labial side dentin of the root and the lingual portion of the apical dentin of the root. Stress in the post showed maximum value at 2 mm above the post apex. 2. In case of the long post and base metal post, strees was concentrated on the apex of the root and the post. 3. In case of the longer post, the displacement on the post-cement interface was lessened. The gold post was more displaceable than the base metal post. 4. In case of the alveolar bone resorption, stress concentrated on the root and the post and displacement on the post-cement interface were increased.