In this article, we review the recent history of the development of dental CAD/CAM systems for the fabrication of crowns and fixed partial dentures (FPDs), based on our 20 years of experience in this field. The current status of commercial dental CAD/CAM systems developed around the world is evaluated, with particular focus on the field of ceramic crowns and FPDs. Finally, we discuss the future perspectives applicable to dental CAD/CAM. The use of dental CAD/CAM systems is promising not only in the field of crowns and FPDs but also in other fields of dentistry, even if the contribution is presently limited. CAD/CAM technology will contribute to patients' health and QOL in the aging society.

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A review of dental CAD/CAM: current status and future perspectives from 20 years of experience.

Zirconia is unique in its polymorphic crystalline makeup, reported to be sensitive to manufacturing and handling processes, and there is debate about which processing method is least harmful to the final product. Currently, zirconia restorations are manufactured by either soft or hard-milling processes, with the manufacturer of each claiming advantages over the other. Chipping of the veneering porcelain is reported as a common problem and has been labelled as its main clinical setback. The objective of this systematic review is to report on the clinical success of zirconia-based restorations fabricated by both milling processes, in regard to framework fractures and veneering porcelain chipping. A comprehensive review of the literature was completed for in vivo trials on zirconia restorations in MEDLINE and PubMed between 1950 and 2009. A manual hand search of relevant dental journals was also completed. Seventeen clinical trials involving zirconia-based restorations were found, 13 were conducted on fixed partial dentures, two on single crowns and two on zirconia implant abutments, of which 11 were based on soft-milled zirconia and six on hard-milled zirconia. Chipping of the veneering porcelain was a common occurrence, and framework fracture was only observed in soft-milled zirconia. Based on the limited number of short-term in vivo studies, zirconia appears to be suitable for the fabrication of single crowns, and fixed partial dentures and implant abutments providing strict protocols during the manufacturing and delivery process are adhered to. Further long-term prospective studies are necessary to establish the best manufacturing process for zirconia-based restorations.

Clinical trials in zirconia: a systematic review.

From porcelain-fused-to-metal to zirconia: clinical and experimental considerations.

MicroRNAs (miRNAs) are members of a non-coding RNA family. They act as negative regulators of protein translation by affecting messenger RNA (mRNA) stability; they modulate numerous signaling pathways and cellular processes, and are involved in cell-to-cell communication. Thus, studies on miRNAs offer an opportunity to improve our understanding of complex biological mechanisms. In the cardiovascular system, miRNAs control functions of various cells, such as cardiomyocytes, endothelial cells, smooth muscle cells and fibroblasts. The pivotal role of miRNAs in the cardiovascular system provides a new perspective on the pathophysiology of disorders like myocardial infarction, hypertrophy, fibrosis, heart failure, arrhythmia, inflammation and atherosclerosis. MiRNAs are differentially expressed in diseased tissue and can be released into circulation. Manipulation of miRNA activity may influence the course of a disease. Therefore, miRNAs have become an active field of research for developing new diagnostic and therapeutic tools. This review discusses emerging functions of miRNAs in cardiogenesis, heart regeneration and the pathophysiology of cardiovascular diseases.

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MicroRNA in cardiovascular biology and disease.

PURPOSE The aim of this research was to evaluate the fatigue behavior and reliability of monolithic computer-aided design/computer-assisted manufacture (CAD/CAM) lithium disilicate and hand-layer-veneered zirconia all-ceramic crowns. MATERIALS AND METHODS A CAD-based mandibular molar crown preparation, fabricated using rapid prototyping, served as the master die. Fully anatomically shaped monolithic lithium disilicate crowns (IPS e.max CAD, n = 19) and hand-layer-veneered zirconia-based crowns (IPS e.max ZirCAD/Ceram, n = 21) were designed and milled using a CAD/CAM system. Crowns were cemented on aged dentinlike composite dies with resin cement. Crowns were exposed to mouth-motion fatigue by sliding a WC-indenter (r = 3.18 mm) 0.7 mm lingually down the distobuccal cusp using three different step-stress profiles until failure occurred. Failure was designated as a large chip or fracture through the crown. If no failures occurred at high loads (> 900 N), the test method was changed to staircase r ratio fatigue. Stress level probability curves and reliability were calculated. RESULTS Hand-layer-veneered zirconia crowns revealed veneer chipping and had a reliability of < 0.01 (0.03 to 0.00, two-sided 90% confidence bounds) for a mission of 100,000 cycles and a 200-N load. None of the fully anatomically shaped CAD/CAM-fabricated monolithic lithium disilicate crowns failed during step-stress mouth-motion fatigue (180,000 cycles, 900 N). CAD/CAM lithium disilicate crowns also survived r ratio fatigue (1,000,000 cycles, 100 to 1,000 N). There appears to be a threshold for damage/bulk fracture for the lithium disilicate ceramic in the range of 1,100 to 1,200 N. CONCLUSION Based on present fatigue findings, the application of CAD/CAM lithium disilicate ceramic in a monolithic/fully anatomical configuration resulted in fatigue-resistant crowns, whereas hand-layer-veneered zirconia crowns revealed a high susceptibility to mouth-motion cyclic loading with early veneer failures.

Monolithic CAD/CAM lithium disilicate versus veneered Y-TZP crowns: comparison of failure modes and reliability after fatigue.

The biaxial flexural strength and fatigue property of Lava Y-TZP dental ceramic.

Fatigue and fracture properties of yttria partially stabilized zirconia crown systems

Objectives: Yttria partially-stabilized zirconia polycrystalline (Y-TZP) has been the subject of extensive research because of its high strength and toughness. The aim of this study was to evaluate the biaxial flexural strength, fatigue life, and to investigate in more detail on single cycle specimens, the pressure-induced phase transformation of a Y-TZP dental ceramic using Raman microspectroscopy. Materials and Methods: Thirty standardized discs (15 x 1.2 mm(2)) were used to examine the biaxial flexural strength (ISO 6872 standard) using a Dartec HC10 Servohydraulic testing machine (Zwick Ltd., UK). The specimens were also submitted to Vickers hardness (on polished and as-received surfaces within the same specimen) and dynamic fatigue test. The initial bulk phases were examined via X-ray diffraction and the local phase transformations that occurred in the zirconia induced by the various Vickers indentation loads (20-50 kg) were examined via Raman microspectroscopy on single cycle specimens. The fracture surface after biaxial flexural testing was also examined via Raman spectroscopy. Results: The Cercon specimens tested had flexural strength and Weibull modulus (m) of similar to 823.3 (+/- 114.7) MPa and 8.3, respectively. As-received surfaces (1378.7 +/- 51.8 Hv) had slightly higher hardness value compared with polished surfaces (1354.33 +/- 50.9 Hv); however, two-way analysis of variance showed no significant difference in hardness values between polished and as-received surfaces (P > 0.05). Additionally, the specimens survived to 5 x 10(5) cycles when using a load of 70% of the mean biaxial flexural strength or lower. Raman microspectroscopy showed transformation of tetragonal to cubic and monoclinic phases within the indentation area. The fraction of monoclinic phase showed only limited variation with load or distance from the center to indentation edge. The level of cubic phase, however, was greatest at the indentation center. Transformation to cubic phase was observed on the lower surfaces (tension side) of fractured specimens. It was also observed near the specimen center exposed upon fracture. In the latter region an increase in monoclinic phase was additionally observed. Further work will be carried out using Raman microspectroscopy to assess the effect of fatigue on phase transformations. Conclusion: The zirconia based ceramic has mechanical properties that may allow it to withstand the loading found in posterior areas. Transformation toughening was found when high loads impacted on the surface of zirconia. However it should be born in mind that this work was not carried out on veneered specimens, which exhibit different failure modes. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 88B: 366-377, 2009

Piyapanna Pittayachawan

Papers

The biaxial flexural strength and fatigue property of Lava Y-TZP dental ceramic.

Fatigue and fracture properties of yttria partially stabilized zirconia crown systems

Flexural Strength, Fatigue Life, and Stress-Induced Phase Transformation Study of Y-TZP Dental Ceramic