• 대한치과재료학회지
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• 제43권4호
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• pp.317-322
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• 2016

The effect of ice-quenching after degassing on the hardness change during simulated porcelain firing in a metal-ceramic Pd-Au-Ag alloy was investigated by means of hardness test, field emission scanning electron microscopic observations, and X-ray diffraction analysis. The hardness decreased by ice-quenching after degassing, which was induced by the homogenization of the ice-quenched specimen. The decreased hardness by ice-quenching after degassing was recovered from the 1st opaque stage which was the first stage of the remaining firing process for bonding porcelain. The microstructural change showed that the increase in hardness during the remaining firing process was caused by precipitation. The ice-quenching after degassing did not affect the hardness change during the subsequent porcelain firing process.

• The Journal of Advanced Prosthodontics
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• 제14권6호
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• pp.360-368
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• 2022

PURPOSE. This study assessed the physical and mechanical properties of interim crown materials fabricated using various digital techniques after accelerated aging. MATERIALS AND METHODS. Three groups of interim dental restorative materials (N = 20) were tested. The first group (CO) was fabricated using a conventional manual method. The second group (ML) was prepared from prefabricated resin blocks for the milling method and cut into specimen sizes using a cutting disc. The third group (3D) was additively manufactured using a digital light-processing (DLP) 3D printer. Aging acceleration treatments using toothbrushing and thermocycling simulators were applied to half of the specimens corresponding to three years of usage in the oral environment (N = 10). Surface roughness (Ra), Vickers microhardness, 3-point bending, sorption, and solubility tests were performed. A 2-way analysis of variance (ANOVA) and Fisher's multiple comparison test were used to compare the results among the groups. RESULTS. The mean surface roughness (Ra) of the resin after accelerated aging was significantly higher in the CO and ML groups than that before aging, but not in the 3D group. All groups showed reduced hardness after accelerated aging. The flexural strength values were highest in the 3D group, followed by the ML and CO groups after accelerated aging. Accelerated aging significantly reduced water sorption in the ML group. CONCLUSION. According to the tested material and 3D printer type, both 3D-printed and milled interim restoration resins showed higher flexural strength and modulus, and lower surface roughness than those prepared by the conventional method after accelerated aging.

• 대한치과기공학회지
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• 제34권1호
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• pp.11-21
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• 2012

Purpose: Densification and mechanical properties of dental zirconia ceramics were evaluated by different sintering methods. Materials and Methods: Y-TZP zirconia block(Kavo $Everest^{(R)}$ ZS blank, Kavo dental GmbH, Bismarckring, Germany) was used in this study. Sintering were performed in heat sintering furnace and microwave sintering furnace, and then experimented and analyzed on a change in densification according to the sintering time, a change in densification according to thickness, flexural strength and micro-structure in zirconia specimens. Results: Microwave sintering was very effective in considerable mechanical properties such as flexural strength and bulk density was drastically increased than conventional electric heating method. It is also shown that microwave sintering time was faster and more economical than common method to be present in qualities which equal or exceed. Conclusion: It will be important to seek the accurate sintering condition of dental zirconia by microwave sintering method and the continuous research is necessary for the study of relationship between sintering methods and mechanical properties.

• 한국표면공학회지
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• 제39권4호
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• pp.190-197
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• 2006

The effects of blasting and acidic treatment on the corrosion characteristics of dental implant fabricated with Cp-Ti and Ti-6Al-4V alloy have been researched by using electrochemical methods. The fabricated implants were cleaned and sandblasted by $Al_2O_3$ powder and then acidic treatment was carried out in nitric acid solution. The surface morphology were observed using scanning electron microscope. The corrosion behaviors were investigated using potentiosat and EIS in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The potentio-dynamic test in 0.9% NaCl indicated that the corrosion potential of blasting and acidic treated implant was lower than that of non treated implant, but current density was higher than that of non treated implant. From the cyclic potentiodynamic test results of Ti implant, the passivation current density of blasting and acidic treated implant slightly higher than that of non treated implant. From A.C. impedance test results in 0.9% NaCl solution, polarization resistance($R_p$) value of blasting and acidic treated implant was lower than that of non treated implant. In case of blasting and acidic treated implant surface, the pits were observed in valley and crest of implant surface.

• Restorative Dentistry and Endodontics
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• 제45권4호
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• pp.55.1-55.12
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• 2020

Objectives: This study investigated the effects of physically damaged and resin-contaminated tips on radiant emittance, comparing them with new undamaged, non-contaminated tips using 3 pieces of spectrophotometric laboratory equipment. Materials and Methods: Nine tips with damage and/or resin contaminants from actual clinical situations were compared with a new tip without damage or contamination (control group). The radiant emittance was recorded using 3 spectrophotometric methods: a laboratory-grade thermopile, a laboratory-grade integrating sphere, and a portable light collector (checkMARC). Results: A significant difference between the laboratory-grade thermopile and the laboratory-grade integrating sphere was found when the radiant emittance values of the control or damaged/contaminated tips were investigated (p < 0.05), but both methods were comparable to checkMARC (p > 0.05). Regardless of the method used to quantify the light output, the mean radiant emittance values of the damaged/contaminated tips were significantly lower than those of the control (p < 0.05). The beam profile of the damaged/contaminated tips was less homogeneous than that of the control. Conclusions: Damaged/contaminated tips can reduce the radiant emittance output and the homogeneity of the beam, which may affect the energy delivered to composite restorations. The checkMARC spectrophotometer device can be used in dental offices, as it provided values close to those produced by a laboratory-grade integrated sphere spectrophotometer. Dentists should assess the radiant emittance of their light-curing units to ensure optimal curing in photoactivated, resin-based materials.

• Imaging Science in Dentistry
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• 제51권3호
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• pp.261-269
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• 2021

Purpose: The aim of this study was to evaluate the radiopacities of various types of restorative materials with different thicknesses compared with enamel, dentin, and aluminum. Materials and Methods: Four bulk-fill resins, 2 hybrid ceramics, 2 micro-hybrid resin composites, 6 glass ionomer-based materials, 2 zinc phosphate cements, and an amalgam were used in the study. Twelve disk-shaped specimens were prepared from each of 17 restorative materials with thicknesses of 1 mm, 2 mm, and 4 mm (n=4). All the restorative material specimens with the same thickness, an aluminum (Al) step wedge, and enamel and dentin specimens were positioned on a phosphor storage plate and exposed using a dental X-ray unit. The mean gray values were measured on digital images and converted to equivalent Al thicknesses. Statistical analyses were performed using 2-way analysis of variance and the Bonferroni post hoc test(P<0.05). Results: Radiopacity was significantly affected by both the thickness and the material type (P<0.05). GCP Glass Fill had the lowest radiopacity value for samples of 1 mm thickness, while Vita Enamic had the lowest radiopacity value for 2-mm-thick and 4-mm-thick samples. The materials with the highest radiopacity values after the amalgam were zinc phosphate cements. Conclusion: Significant differences were observed in the radiopacities of restorative materials with different thicknesses. Radiopacity was affected by both the material type and thickness.

• 대한치과기공학회지
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• 제41권2호
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• pp.93-100
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• 2019

Purpose: This study is making a dog dental prosthesis using digital dental technology. The mechanical strength of the prosthetic material was observed in terms of compressive strength and fracture pattern. Methods: The experiment was performed using dog mandibular molars. The teeth were scanned and modeled. The specimens were made of zirconia, PMMA and Ni-Cr. The specimens were subjected to a vertical compression test with an artificial cancellous bone in UTM tester. Vertical compressive strength and fracture behavior of specimen were observed. Results: The result of observing the compressive load between specimen and artificial bone were $184.8{\pm}5.7N$ in the zirconia specimen, $185.6{\pm}8.9N$ in the PMMA specimen, and $184.4{\pm}4.0N$ in the Ni-Cr alloy specimen. Compression marks of artificial bones were observed. The fracture strength of specimen was observed. The fracture strength of the zirconia specimen was an average of 1,381.4N. The fracture strength of the PMMA specimen was an average of 572.2N. Conclusion: The crown made of three kinds(zirconia, PMMA, Ni-Cr alloy) of materials has the strength to chew about the artificial bone. zirconia and PMMA have vertical compressive strength applicable to medium dog dental prosthetic materials.

• The Journal of Advanced Prosthodontics
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• 제12권1호
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• pp.15-21
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• 2020

PURPOSE. The aim of the current study was to analyze treatment concepts of a cohort of German dentists for planning, fabrication, and maintenance of implant-supported fixed and removable restorations. MATERIALS AND METHODS. A questionnaire including queries about experiences with implant-supported restorations as well as prosthetic and maintenance treatment concepts for supplying patients with fixed and removable implant-supported prosthetic restorations was developed and sent to 350 dental offices registered in the municipal area of Leipzig, Germany. RESULTS. An overall total of 62 returned questionnaires were included in the analyses, which relates to a response rate of 17.7%. Participating dentists were more involved in the prosthetic aspects of implant dentistry rather than surgery, while prosthetic concepts such as backward planning, digital processing, and application of all-ceramic materials were not commonly performed. Simple attachments were preferred over complex retention systems in removable implant-supported restorations. Tooth/implant-supported fixed denture prostheses as well as removable denture prostheses with supporting posterior implants were not regarded as a favorable treatment option. CONCLUSION. Within the limitations of the study, the data indicate that dentists favor simple and conventional treatment approaches in implant prosthetics. Prosthetic aspects in the planning of implant-supported restorations are often neglected. Prosthetic treatment guidelines and aspects should commonly be considered in the planning phase of implant-supported prosthetic restorations, and awareness should be increased in postgraduate education.

• Journal of Korean Dental Science
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• 제7권2호
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• pp.80-86
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• 2014

Purpose: Current common method of cytotoxicity evaluation for elastomeric impression materials use animal based cell lines, which the clinical relevance has been often questioned. Hence, the purpose of this study was to examine the difference in results with both human based and animal based fibroblast cell line. Materials and Methods: Three types of fibroblast cells were used in this study; conventional mouse fibroblasts of L929, human gingival fibroblasts (HGF-1), and immortalized human oral fibrobalsts (hTERT-hNOF). Test on extract and test by direct contact using different commercially available elastomeric impression materials were carried out according to the international standards. Result: There was significant difference in cell viability between types of fibroblasts cell used, where HGF-1 showed highest cell viability and L929 the lowest. Conclusion: Within the limitation of this study, careful consideration must be given when selecting the cells and interpreting the results for cytotoxicity evaluation of elastomeric impression materials, where use of human based cell lines such as hTERT-hNOF would be appropriate for both ease of cytotoxicity test and clinical relevance.

• 한국재료학회지
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• 제22권3호
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• pp.150-154
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• 2012

Ti-6Al-4V ELI (Extra Low Interstitial) alloy have been widely used as alternative to bone due to its excellent biocompatibility, although it still has many problems such as high elastic modulus and toxicity. Therefore, biomaterials with low elastic modulus and non toxic characteristics have to be developed. A novel ${\beta}$ Ti-35wt%Nb-7wt%Zr-Calcium pyrophosphate (CPP) composite that is a biocompatible alloy without elemental Al or V was fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70 MPa using high energy mechanical milled (HEMM) powder. The microstructure and phases of the milled powders and the sintered specimens were studied using SEM, TEM, and XRD. Ti-35wt%Nb-7wt%Zr alloy was transformed from ${\alpha}$ phase to ${\beta}$ phase in the 4h-milled powder by sintering. The sintered specimen using the 4h-milled powder showed that all the elements were distributed very homogeneously and had higher density and hardness. ${\beta}$ Ti alloy-CPP composite, which has nanometer particles, was fabricated by SPS using HEMMed powder. During the sintering process, $CaTiO_3$, TixOy, and CaO were formed because of the reaction between Ti and CPP. The Vickers hardness of the composites increases with the increase of the milling time and the addition of CPP. The biocompatibility of the Ti-Nb-Zr alloys was improved by addition of CPP.