• Restorative Dentistry and Endodontics
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• v.46 no.1
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• pp.12.1-12.9
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• 2021

Objectives: The present study aims to compare the obturation quality of 2 confluence confirmation techniques in artificial maxillary first premolars showing Vertucci type II root canal configuration. Materials and Methods: Thirty artificial maxillary premolars having Vertucci type II root canal configuration were made. They were divided into 3 groups according to the confluence confirmation technique as follows. Gutta-percha indentation (GPI) group (confluence confirmation using a gutta-percha cone and a K file); electronic apex locator (EAL) group (confluence confirmation using K files and EAL); and no confluence detection (NCD) group. In the GPI group and the EAL group, shaping and obturation were performed with the modified working length (WL). In the NCD group, shaping was performed without WL adjustment and obturation was carried out with an adjusted master cone. Micro-computed tomography was used before preparation and after obturation to calculate the percentage of gutta-percha occupied volume (%GPv) and the volume increase in the apical 4 mm. Data were analyzed using 1-way analysis of variance and post hoc Tukey's test. Results: Statistically significant difference was not found in terms of the %GPv from the apex to apical 4 mm. However, the NCD group showed a statistically significant volume increase compared with the EAL group (p < 0.05). Conclusions: In terms of gutta-percha occupied volume, no significant difference was observed among the 3 groups. Confluence confirmation using an EAL in teeth with Vertucci type II configuration showed less volume increase during canal shaping compared with no confluence confirmation.

• The Journal of Advanced Prosthodontics
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• v.12 no.1
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• pp.1-8
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• 2020

PURPOSE. To investigate the influence of crown material (lithium-disilicate, 3Y-TZP zirconia) and abutment type (rigid implant, resin tooth with artificial periodontium) on wear performance of their antagonist teeth and adjacent teeth. MATERIALS AND METHODS. A mandibular left first molar (#36) with adjacent human teeth (mandibular left second premolar: #35, mandibular left second molar: #37) and antagonistic human teeth (maxillary left second premolar: #25, maxillary left first molar: #26, maxillary left second molar: #27) was prepared simulating a section of the jaw. Samples were made with extracted human molars (Reference), crowned implants (Implant), or crowned resin tooth analogues (Tooth). Crowns (tooth #36; n = 16/material) were milled from lithium-disilicate (Li, IPS e.max CAD) or 3Y-TZP zirconia (Zr, IPS e.max ZirCAD, both Ivoclar Vivadent). Thermal cycling and mechanical loading (TCML) in the chewing simulator were applied simulating 15 years of clinical service. Wear traces were analyzed (frequency [n], depth [㎛]) and evaluated using scanning electron pictures. Wear results were compared by one-way-ANOVA and post-hoc-Bonferroni (α = 0.05). RESULTS. After TCML, no visible wear traces were found on Zr. Li showed more wear traces (n = 30-31) than the reference (n = 21). Antagonistic teeth #26 showed more wear traces in contact to both ceramics (n = 27-29) than to the reference (n = 21). Strong wear traces (> 350 ㎛) on antagonists and their adjacent teeth were found only in crowned groups. Abutment type influenced number and depth of wear facets on the antagonistic and adjacent teeth. CONCLUSION. The clinically relevant model with human antagonistic and adjacent teeth allowed for a limited comparison of the wear situation. The total number of wear traces and strong wear on crowns, antagonistic and adjacent teeth were influenced by crown material.

• Journal of dental hygiene science
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• v.23 no.3
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• pp.236-244
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• 2023

Background: The size of the tooth whitening market and toothpaste market is increasing worldwide. The purpose of this in vitro study is to confirm and compare the coffee stain removal effects of commercial whitening toothpaste in sound and demineralized teeth, respectively. Methods: A total of 112 flat permanent bovine teeth specimens were manufactured. Half of the surface of the specimen was coated with an acid-resistant varnish and deposited in an artificial demineralizing solution for 65 hours. The varnish applied to half of the specimen was removed and deposited in a coffee solution for 96 hours to induce coloring. Two control and five experimental group toothpastes for teeth whitening were selected and the main components were investigated. Toothbrushing was performed 50, 100, and 150 times for each toothpaste group. A total of four images were obtained: before the start and after 50, 100, and 150 times of brushing to obtain the lightness (L^*) values of the sound and the demineralized tooth surfaces. The difference in the average value between toothpaste groups at each treatment period was analyzed by one-way ANOVA. The difference in the L^* average value according to the number of the brushing was analyzed by repeated measure ANOVA. Results: All toothpastes in the seven groups contained abrasive agents and had different ingredients for each product. Compared to before brushing, the L^* value changed significantly in all toothpaste groups after brushing 50 times (p<0.05). This was common in both the sound and demineralized teeth surfaces. Demineralized teeth had significantly lower L^* values at all brushing times than that in sound teeth (p<0.05). Conclusion: The effect of whitening teeth was different for each toothpaste. Demineralized teeth were more likely to cause coloration than sound teeth, and the coloration was not removed well.

• Journal of the Korea Computer Graphics Society
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• v.8 no.1
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• pp.13-20
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• 2002

Recently, there is a great demand for artificial teeth prostheses made of the materials which are sintered at $1500^{\circ}C$ such as zirconia ceramic. Since degree of strength of the materials is very high, however, it is very difficult for technicians to manually fabricate the prostheses for these ceramics. So the prostheses have been fabricated by using CNC(computer numerical control) machines. In doing them by using CNC, it is very important that the prostheses satisfying dentists's requirements are accurately modeled into 3D objects. In this paper, we propose an effective method for modeling single cores such as single caps and Conus cores, which are the main those of artificial teeth prostheses. And we also present the visual examples of 3D models for these single cores modeled by the proposed methods. In special, the method has used Minkowski sum and ZMap for modeling the single cores.

• The Journal of Korean Academy of Prosthodontics
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• v.27 no.2
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• pp.79-100
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• 1989

The Purpose of this study was to investigate material differences in stress transmission among various artificial teeth and denture base materials. For this study, a two-dimensional finite element model and a two-dimensional photoelastic model of a mandible with complete denture were made. A resin tooth and a porcelain tooth were used as artificial teeth, and a resin base, a metal lined base, and a soft-liner lined base were used as denture bases. An occlusal load was applied and principal stresses generated in the supporting tissues were compared. To test the impact stress transmission, strain gauge attached to the denture base specimens made of the different materials were made in thick and thin groups. Voltage outputs from hitting the specimen with a steel ball were compared. The results were as follows : 1. In FEM, increasing the mucosal thickness reduced the maximum principal stresses in the supporting tissues, but altering the tooth materials and the base materials induced no difference in the stresses. 2. In photoelastic model study, no difference in fringe order among the specimens were observed, but the thick mucosa group and the soft-liner lined group revealed a more uniform distribution of the load. 3. In strain measuring, the impact force transmission was highest in the soft-liner lined group, and was the lowest in the metal lined group(p<0.01). 4. In the thin group using the resin base, the porcelain tooth showed higher impact stress transmission than the resin tooth(p<0.01), but no difference was observed between them in the thick group. In the soft-liner lined group, the porcelain tooth showed higher impact stress transmission than the resin tooth(p<0.01), but no difference was observed between them in the metal lined group. 5. The thick group showed lower impact stress transmission than the thin group(p<0.01).

• Journal of Korean Dental Science
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• v.13 no.2
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• pp.52-58
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• 2020

Purpose: Using two types of electronic apex locators, this study aimed to investigate the differences in accuracy according to the evaluator and equipment. Materials and Methods: Artificial teeth of the lower first premolars and two mandibular acrylic models (A and B) were used in this study. In the artificial teeth, the pulp chamber was opened and the access cavity was prepared. Using calibrated digital Vernier calipers, the distance from the top of the cavity and the root apex was measured to assess the actual distance between two artificial teeth. The evaluation was conducted by 20 dentists, and each evaluator repeated measurements for each electronic apex locator five times. The difference between the actual distance from the top of the cavity to the root apex and the distance measured using electronic measuring equipment was compared. For statistical analysis, the Friedman test the Mann-Whitney U-test were conducted and the differences between groups were analyzed (α=0.05). Result: As for the accuracy of measurement according to the two types of electronic apex locators, the value of the measurement error was 0.4753 mm in Dentaport ZX and 0.3321 mm in E-Cube Plus. Moreover, electronic apex locators Dentaport ZX and E-Cube Plus showed statistically significant differences (P<0.05). As for the difference in the accuracy of the two types of electronic apex locators according to the evaluator, the resulting values differed depending on the evaluator and showed a statistically significant difference (P<0.001). Conclusion: Electronic apex locator E-Cube Plus showed higher accuracy than did Dentaport ZX. Nevertheless, both types of electronic apex locators showed 100% accuracy in finding the region within root apex ±0.5 mm zone. Furthermore, according to the evaluator, the two electronic apex locators showed different resulting values.

• Journal of Dental Rehabilitation and Applied Science
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• v.19 no.3
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• pp.153-168
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• 2003

It is very important to arrange the artificial teeth correctly in bucco-lingual (labio- lingual) relation in reconstrcting dentition. Although many anatomic landmarks and techniques have been reported over the years, they are based on westerns. So this study was performd to examine the horizontal relations of mandibular teeth in Korean dentulous adults. 200 volunteers(mean age 22.9) who had natural dentition were selected. The impressions were taken with irreversible hydrocolloid impression material and mandibular study models were fabricated using class I dental stone. Then they were measured with 3-dimensional measuring device specially designed for this study. The results were as follows ; It is better to consider the lingual cusps of the lower posterior teeth as a guide than the linguoaxial surfaces of the lower posterior teeth, arranging the lower posterior teeth buccally to the line which starts from the mesial aspect of the lower canine and continue backward to the lingual aspect of the retromolar pad. It is better to arrange the fossae of the lower posterior teeth buccally to the line which starts from the cusp tip of the lower canine and continue backward to the top of the retromolar pad. The positions of the lower posterior teeth in the denture-bearing area ; considering the fossa as a guide, the 2nd premolar was positioned in center. considering the buccal cusp as a guide, the 1st molar and the 2nd molar were positioned in center. the distance ratio(d/a) was incresed constantly from the lower canine to the 2nd molar d ; the distance between the buccal vestibule(the lowest point) and the buccal cusp tips of the lower posterior teeth. a ; the distance between the buccal vestibule(the lowest point) and the lingual vestibule(the lowest point). The lower canine was positioned lingually($0.11{\pm}0.13$) than the labial vestibule, and the central incisor and the lateral incisor were positioned almost in the imaginary perpendicular plane of the labial vestibule(the lowest point).

• The korean journal of orthodontics
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• v.41 no.2
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• pp.121-126
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• 2011

Objective: The purpose of this study was to evaluate shear bond strength (SBS) and failure site location of brackets bonded to enamel with or without desensitizer application. Methods: Sixty-six freshly extracted human premolar teeth were randomly divided into 3 groups of 22. Group 1 served as the control. Desensitizer was applied to the remaining teeth at two time intervals (Group 2, bonded immediately after Pro-$Relief^{TM}$ (Colgate-Palmolive Co., New York, NY, USA) application and Group 3, bonded 30 days after Pro-$Relief^{TM}$ application with the teeth stored in artificial saliva during the 30 days). Orthodontic brackets were bonded with a light cure composite resin and cured with a halogen light. After bonding, the SBS of the brackets was tested using a universal testing device. Adhesive remnant index (ARI) scores were determined after the brackets failed. Data were analyzed with analysis of variance, Tukey's HSD, and G tests. Results: The SBS was significantly lower in Group 2 than in Groups 1 (p = 0.024) and 3 (p = 0.017). Groups 1 and Group 3 did not differ (p = 0.991). ARI scores did not differ significantly among groups. Conclusions: The Pro-$Relief^{TM}$ desensitizer agent applied immediately before bonding significantly reduces bond strength, but the SBS values still exceed the minimum 5.9 - 7.8 MPa required for adequate clinical performance. Immersing the teeth in artificial saliva for 30 days after applying the Pro-$Relief^{TM}$ desensitizer agent and before bonding increased the SBS to control levels.

• Journal of Technologic Dentistry
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• v.36 no.1
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• pp.9-15
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• 2014

Purpose: Generally dental technicians clinically decide the sintering temperature of zirconia artificial teeth to match the color of the teeth. However, the sintering temperature influence the microstructure and mechanical strength of ceramic body. In this study, to evaluate the free choice of sintering temperature which leads to color the problems in zirconia false teeth, the variation of microstructure, mechanical strength, and colortone of zirconia ceramics according to the change of sintering temperature was investigated. Methods: Bar type specimens were prepared from commercial zirconia blocks by cutting and polishing into $0.8cm(L){\times}1.0cm(W){\times}4.8cm(H)$. Specimens were fired from 1,400 to $1,700^{\circ}C$ at $50^{\circ}C$ intervals and held for 1hour at highest temperature. Apparent porosity, water absorption, firing shrinkage, bulk density, bend strength, whiteness were tested. Microstructures were observed by SEM. Results: When fired above $1450^{\circ}C$, all specimens showed 0% apparent porosity and water absorption, 20% firing shrinkage, and $6.1g/cm^3$ bulk density regardless of firing temperatures. SEM photomicrographs showed grain growth of zirconia occurred above $1,600^{\circ}C$. Whiteness was also largely changed above this temperature. Maximum bend strength of 1,05MPa was obtained at $1,550^{\circ}C$. Bend strength lowered slightly above this temperature and showed $950{\ss}\acute{A}$ at $1,700^{\circ}C$. Conclusion: In order to fit the colortone of zirconia artificial teeth, arbitrary choice of firing temperature higher than $1,500^{\circ}C$, up to $1,700^{\circ}C$ did not influence the mechanical strength.

• Journal of Korean society of Dental Hygiene
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• v.14 no.2
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• pp.281-286
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• 2014

Objectives : The aim of this study is to evaluate the surface changes of enamel specimen, tooth structure by toothpastes in child and adult. Methods : Experimental teeth were collected from extracted human primary teeth. 120 enamel specimens were prepared by cutting the teeth into $2{\times}3{\times}2mm$ blocks using diamond saw and the specimens were assigned to 3 groups. Group 1 was used as control with no treatment. Group 2 was treated with child toothpaste and Group 3 was treated with adult toothpaste on primary enamel surface for 3 minutes daily over 4 weeks. The specimens were immersed into individual container having artificial saliva and the artificial saliva was changed every day. The electron probe micro analyzer(EPMA) provided weight percent(wt%) of calcium(Ca) and phosphorous(P) on enamel surface. The morphology was analyzed by scanning electron microscopy(SEM). Data were analyzed by one-way analysis of variance(ANOVA) and Tukey's test post-hoc test using SPSS(Version 20, SPSS Inc., Chicago, USA). Level of significance was set at 0.05. Results : The surface changes of the primary teeth revealed a significant difference during 4 weeks. Calcium(Ca) and phosphorous(P) levels were found the weight percent difference and a rough enamel surface was seen on SEM after adult toothpaste application. Conclusions : The changes in Ca and P and the morphological surface were affected by the primary tooth treated with adult toothpaste. Enamel surface showed significant differences during 4 weeks.