• The Journal of the Korean dental association
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• v.58 no.7
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• pp.443-447
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• 2020

The esthetic properties of zirconia receive increasing attention as its demand and application escalates. Thus, it is crucial to investigate how zirconia is esthetically different from other dental ceramics. In this study, we evaluated the translucency of zirconia and suggest a method to increase its translucency. We examined the shade of zirconia and offer its distinguishing features. Finally, we analyzed monolithic zirconia restorations to propose esthetic considerations in clinics.

• The Journal of Advanced Prosthodontics
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• v.11 no.2
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• pp.112-119
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• 2019

PURPOSE. Zirconia materials have been used for implant-retained restorations, but the stress distribution of zirconia is not entirely clear. The aim of this study is to evaluate the stress distribution and risky areas caused by the different design of zirconia restorations on the atrophic bone of the posterior maxilla. MATERIALS AND METHODS. An edentulous D4-type bone model was prepared from radiography of an atrophic posterior maxilla. Monolithic zirconia and zirconia-fused porcelain implant-retained restorations were designed as splinted or non-splinted. 300-N occlusal forces were applied obliquely. Stress analyses were performed using a 3D FEA program. RESULTS. According to stress analysis, the bone between the 1) molar implant and the 2) premolar in the non-splinted monolithic zirconia restoration model was stated as the riskiest area. Similarly, the maximum von Mises stress value was detected on the bone of the non-splinted monolithic zirconia models. CONCLUSION. Splinting of implant-retained restorations can be more critical for monolithic zirconia than zirconia fused to porcelain for the longevity of the bone.

• The Journal of the Korean dental association
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• v.49 no.5
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• pp.279-285
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• 2011

Currently there is no dental ceramic material can be used in all dental situations need to be restored. However, in view of recent clinical reports, the most viable alternative is zirconia ceramic. Clinical success of dental zirconia restorations strongly depends on proper selection of materials, accurate laboratory procedure and final cementation, which can be achievable with the correct understanding of zirconia. As dental materials, zirconia ceramics have a very bright future, because they are being used increasingly in the anterior region as implant fixtures, as well as crown and bridge restorations and implant abutments. Many dental ceramics showing poor clinical performance have been gone from the dental market. However, in terms of outstanding mechanical properties and esthetic nature, new dental materials can replace zirconia ceramics will not be available in the foreseeable future.

• The Journal of Advanced Prosthodontics
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• v.7 no.5
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• pp.368-374
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• 2015

PURPOSE. The aim of the study was to evaluate the effect of abutment shade, ceramic thickness, and coping type on the final shade of zirconia all-ceramic restorations. MATERIALS AND METHODS. Three different types of disk-shaped zirconia coping specimens (Lava, Cercon, Zirkonzahn: ${\phi}10mm{\times}0.4mm$) were fabricated and veneered with IPS e.max Press Ceram (shade A2), for total thicknesses of 1 and 1.5 mm. A total of sixty zirconia restoration specimens were divided into six groups based on their coping types and thicknesses. The abutment specimens (${\phi}10mm{\times}7mm$) were prepared with gold alloy, base metal (nickel-chromium) alloy, and four different shades (A1, A2, A3, A4) of composite resins. The average $L^*$, $a^*$, $b^*$ values of the zirconia specimens on the six abutment specimens were measured with a dental colorimeter, and the statistical significance in the effects of three variables was analyzed by using repeated measures analysis of variance (${\alpha}$=.05).The average shade difference (${\Delta}E$) values of the zirconia specimens between the A2 composite resin abutment and other abutments were also evaluated. RESULTS. The effects of zirconia specimen thickness (P<.001), abutment shade (P<.001), and type of zirconia copings (P<.003) on the final shade of the zirconia restorations were significant. The average ${\Delta}E$ value of Lava specimens (1 mm) between the A2 composite resin and gold alloy abutments was higher (close to the acceptability threshold of 5.5 ${\Delta}E$) than th ose between the A2 composite resin and other abutments. CONCLUSION. This in-vitro study demonstrated that abutment shade, ceramic thickness, and coping type affected the resulting shade of zirconia restorations.

• The Journal of the Korean dental association
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• v.49 no.5
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• pp.265-278
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• 2011

The introduction of zirconia-based materials to the dental field broadened the design and application limits of, all-ceramic restorations. Most ceramic restorations are adhesively luted to the prepared tooth, however, resin bonding to zirconia components is less reliable than those to other dental ceramic systems. It is important for high retention, prevention of microleakage, and increased fracture resistance, that bonding techniques be improved for zirconia systems. Strong resin bonding relies on micromechanical interlocking and adhesive chemical bonding to the ceramic surface, requiring surface roughening for mechanical bonding and surface activation for chemical adhesion. In many cases, high strength ceramic restorations do not require adhesive bonding to tooth structure and can be placed using conventional cements which rely only on micromechanical retention. However, resin bonding is desirable in some clinical situations. In addition, it is likely that strong chemical adhesion would lead to enhanced long-term fracture and fatigue resistance in the oral environment.

• Journal of Korean Dental Science
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• v.10 no.2
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• pp.74-81
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• 2017

This report describes two cases of complete arch implant-supported restorations. The first patient had seven dental implants in each arch with monolithic zirconia frameworks. At four weeks' follow-up, the one-piece maxillary framework was fractured, which was re-designed and re-fabricated using laser-sintered cobalt-chrome alloy. The second patient had four implants in the mandible only. A mandibular monolithic zirconia framework and a maxillary conventional complete denture were fabricated and delivered. At five years' follow-up, the patient reported no significant discomfort. Careful consideration and monitoring of the status of antagonistic arches and stress distribution on zirconia frameworks were suggested for complete arch implant-supported fixed restorations.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.24 no.2
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• pp.101-121
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• 2015

Zirconia polycrystalline (Y-TZP) showed better mechanical properties and superior resistance to fracture than other conventional dental ceramics. Zirconia-based ceramics have been successfully introduced into the clinic to fabricate fixed dental prostheses (FDPs), along with a dental computer-aided/computer-aided manufacturing (CAD/CAM) system. It has been clinically available as an alternative to the metal framework for fixed dental prostheses (FDPs). The most frequent clinical complication with zirconia-based FDPs was chipping of the veneering porcelain that was affected by many factors. Another option was full-contour zirconia FDPs using high translucent zirconia. Full-contour zirconia FDPs has many clinical advantages but it caused concern about the wear of antagonist enamel, because the hardness of Y-TZP was over double that of porcelain. However, many articles demonstrates that highly polished zirconia yielded lower antagonist wear compared with porcelains. In this article (1) advantages of full zirconia restorations, (2) clinical applications of zirconia restorations, (3) abutment preparation, (4) surface finish of zirconia restoration and antagonist enamel wear, (5) bond of zirconia with resin-based luting agents, (6) communication in clinical & lab.procedures for full zirconia restorations are reviewed.

• The Journal of Advanced Prosthodontics
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• v.4 no.2
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• pp.76-83
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• 2012

PURPOSE. Zirconia has been used in clinical dentistry for approximately a decade, and there have been several reports regarding the clinical performance and survival rates of zirconia-based restorations. The aim of this article was to review the literatures published from 2000 to 2010 regarding the clinical performance and the causes of failure of zirconia fixed partial dentures (FPDs). MATERIALS AND METHODS. An electronic search of English peer-reviewed dental literatures was performed through PubMed to obtain all the clinical studies focused on the performance of the zirconia FPDs. The electronic search was supplemented by manual searching through the references of the selected articles for possible inclusion of some articles. Randomized controlled clinical trials, longitudinal prospective and retrospective cohort studies were the focuses of this review. Articles that did not focus on the restoration of teeth using zirconia-based restorations were excluded from this review. RESULTS. There have been three studies for the study of zirconia single crowns. The clinical outcome was satisfactory (acceptable) according to the CDA evaluation. There have been 14 studies for the study of zirconia FPDs. The survival rates of zirconia anterior and posterior FPDs ranged between 73.9% - 100% after 2 - 5 years. The causes of failure were veneer fracture, ceramic core fracture, abutment tooth fracture, secondary caries, and restoration dislodgment. CONCLUSION. The overall performance of zirconia FPDs was satisfactory according to either USPHS criteria or CDA evaluations. Fracture resistance of core and veneering ceramics, bonding between core and veneering materials, and marginal discrepancy of zirconia-based restorations were discussed as the causes of failure. Because of its repeated occurrence in many studies, future researches are essentially required to clarify this problem and to reduce the fracture incident.

• The Journal of Advanced Prosthodontics
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• v.11 no.5
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• pp.297-304
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• 2019

PURPOSE. This in vitro study investigated the repair bond strength of the zirconia ceramic after different aging conditions. MATERIALS AND METHODS. In order to imitate the failure modes of veneered zirconia restorations, veneer ceramic, zirconia, and veneer ceramic-zirconia specimens were prepared and were divided into 4 subgroups as: control ($37^{\circ}C$ distilled water for 24 hours ) and 3000, 6000, 12000 thermal cycling groups (n=15). Then, specimens were bonded to composite resin using a porcelain repair kit according to the manufacturer recommendation. The repair bond strength (RBS) test was performed using a universal testing machine (0.5 mm/min). Failure types were analyzed under a stereomicroscope. Two-way ANOVA and Bonferroni test were used for statistical analysis. RESULTS. The RBS values of zirconia specimens were statistically significant and higher than veneer ceramic and veneer ceramic-zirconia specimens in control, 3000 and 6000 thermal cycling groups (P<.05). When 12000 thermal cycles were applied, the highest value was found in zirconia specimens but there was no statistically significant difference between veneer ceramic and veneer ceramic-zirconia specimens (P>.05). Veneer ceramic specimens exhibited cohesive failure types, zirconia specimens exhibited adhesive failure types, and veneer ceramic-zirconia specimens exhibited predominately mixed failure types. CONCLUSION. Thermal cycling can adversely affect RBS of composite resin binded to level of fractured zirconia ceramics.

• The Journal of the Korean dental association
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• v.56 no.7
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• pp.366-374
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• 2018

Purpose : The purpose of this study was to compare the marginal fit of monolithic zirconia restorations fabricated form the conventional and the digital impression technique. Materials and methods : Ten patients were restored with monolithic zirconia restorations fabricated from the digital and the conventional impression technique. Before definitive insertion, silicone replicas were produced from all twenty crowns. The silicone replicas were cut in three sections; each section was evaluated at two points. The measurement was carried out by using a measuring microscope (Olympus BX 51) and I-Solution. Data from the silicone replica scores were analyzed by Shapiro-Wilk test for normal distribution and the t-test for equality of two population's mean. All tests were performed with ${\alpha}-level$ of 0.05. Results : The average marginal gaps of monolithic zirconia restorations were $133.81{\pm}36.46{\mu}m$ for the conventional impression technique, $90.07{\pm}9.47{\mu}m$ for the digital impression technique. No statistical differences were found between the two impression techniques Conclusion : Both prostheses presented clinically acceptable results with comparing the marginal fit.