Flexural strength and fracture toughness of two different lithium disilicate ceramics

Two-body wear of novel monolithic lithium-silicate ceramic materials and their corresponding different antagonists

OBJECTIVES

Evaluation of the two-body wear of lithium-silicate ceramics against different antagonists compared to a direct resin composite and human teeth.

METHODS

Initial LiSi Block [LISI], IPS e.max CAD [EMA], and CEREC Tessera [TESE] were investigated and compared with direct resin composite [FILL] and human teeth [tooth]. As antagonists were used: steatite, ceramic, and human enamel. The control group tooth was only tested with enamel antagonist. The combinations underwent thermomechanical aging using a chewing simulator. Material losses were calculated using GOM-analysis software. Kolmogorov-Smirnov test, Kruskal-Wallis H, Mann-Whitney-U-test with Bonferroni correction and Spearman-rho correlation were calculated. A fractographic analysis was performed.

RESULTS

Within TESE, enamel antagonists led to lower restoration losses than steatite and ceramic antagonists. Within FILL, enamel and steatite antagonists caused lower material losses compared to ceramic antagonists. Against steatite antagonists, LISI showed lowest material losses. Against ceramic antagonists, the use of LISI led to lower material losses compared to FILL. Against tooth antagonists, TESE showed lower material losses than tooth and FILL and LISI lower than FILL. Within LISI, steatite antagonists showed lower material losses on the antagonist than ceramic. Within EMA, steatite antagonists showed higher material losses than ceramic ones. Within ceramic antagonists, LISI restoration material showed lower material losses than FILL and EMA.

CONCLUSIONS

Regardless of the antagonist material, the material losses of LISI and EMA were comparable. However, the abrasion resistance of LISI tended to be higher than EMA.

CLINICAL SIGNIFICANCE

LISI is a fully crystallized lithium-silicate ceramic and no longer needs to be processed after milling. In addition, the abrasion resistance is very good, regardless of the antagonist material chosen.

Effect of crystal orientation on flexural strength of pressable lithium disilicate glass-ceramics

This study examined the crystal orientation of four kinds of pressable lithium disilicate glass-ceramics and evaluated the effect of crystal orientation on flexural strength. Bar-shaped (24 mm in length, 1.2 mm in thickness, 4.0 mm in width), disk-shaped (12 mm in diameter, 0.5 mm in thickness), and crown-shaped (maxillary first molar) specimens were prepared according to the manufacturer's instructions. Three-point and biaxial flexural strengths were measured for bar- and disk-shaped specimens. Microstructure analysis was performed using X-ray diffractometry and scanning electron microscopy. Three-point flexural strength was improved by parallel crystal orientation along the longitudinal direction of the bar-shaped specimen. There was no relationship between two-dimensional crystal orientation and biaxial flexural strength. The results of this study assumed that biaxial flexural strength was improved by the crystal orientation in the cross-sectional direction. Pressed restorations are expected to possess higher strength than milled restorations due to their crystal orientation.

Modern CAD/CAM silicate ceramics, their translucency level and impact of hydrothermal aging on translucency, Martens hardness, biaxial flexural strength and their reliability

OBJECTIVES

To investigate the impact of hydrothermal aging on Martens parameter (Martens hardness: HM/elastic indentation modulus: E_IT) and biaxial flexural strength (BFS) of recently available CAD/CAM silicate ceramics.

METHODS

220 specimens (diameter: 12 mm, thickness: 0.95 mm) were fabricated from six CAD/CAM ceramics in two translucency levels (LT/HT): (a) two lithium disilicate (Amber Mill, ABM; IPS e.max CAD, IEM), (b) one lithium metasilicate (Cetra Duo, CEL), (c) one lithium alumina silicate (n!ce, NIC), and (d) two leucite ceramics (Initial LRF Block, LRF; IPS Empress CAD, IPR). HM/E_IT and BFS were measured initially and after hydrothermal aging (134 °C/0.2 MPa/100 h) in an autoclave. The Kolmogorov-Smirnov-test, t-test, one-way ANOVA with post-hoc Scheffé test, Kruskal-Wallis-test, Mann-Whitney-U-test with Bonferroni correction and Weibull statistics were performed (α = 0.05).

RESULTS

CEL and IEM showed the highest and the leucite ceramics the lowest Martens parameter. Within HT, ABM and NIC were in same initial HM value range with CEL and IEM. ABM and NIC showed lower initial E_IT values than CEL and IEM, however higher than IPR. The lowest aged values were analyzed for ABM. After aging, Martens parameter decreased for LRF, ABM, and CEL. IEM showed the initial highest BFS, followed by ABM. NIC and LRF showed the lowest BFS. IEM and ABM presented the highest aged BFS. Hydrothermal aging increased BFS values for LRF (HT), IPR, CEL (HT), and NIC (HT) compared to the initial values. CAD/CAM leucite ceramics showed higher Weibull modul values compared to lithium silicate ceramics.

SIGNIFICANCE

The well-considered selection of ceramics in relation to the areas of indication has the highest influence on the long-term stability of restorations: CAD/CAM lithium disilicate ceramics presented the highest and leucite ceramics the lowest mechanical properties, whereas the reliability was better for leucite than for lithium silicate ceramics.

Ceramic Materials and Technologies Applied to Digital Works in Implant-Supported Restorative Dentistry

Computer-aided design and manufacturing technology has been closely associated with implant-supported restoration. The digital system employed for prosthodontic restorations comprises data acquisition, processing, and manufacturing using subtractive or additive methods. As digital implantology has developed, optical scanning, computer-based digital algorithms, fabricating techniques, and numerical control skills have all rapidly improved in terms of their accuracy, which has resulted in the development of new ceramic materials with advanced esthetics and durability for clinical application. This study reviews the application of digital technology in implant-supported dental restoration and explores two globally utilized ceramic restorative materials: Yttria-stabilized tetragonal zirconia polycrystalline and lithium disilicate glass ceramics.