Mechanical properties of glass-only porcelains prepared by the use of two feldspathic frits with different thermal properties

Effect of Zirconia Silica Nanofibers on Flexural Strength of Feldspathic Ceramic - An Experimental Study

Background:

Dental ceramics exhibit good optical and esthetic properties due to their translucency. Feldspathic ceramic is the most widely used veneering ceramic with brittleness, which accounts for most of its failure. Hence, this study was done to evaluate and compare the flexural strength of feldspathic ceramic reinforced with zirconia-silica nanofibers in the ratio of 2.5, 5, and 7.5 wt% with conventional feldspathic ceramic.

Materials and Methods:

According to ISO 6872, a master die was prepared from which resin bars were fabricated with 4.0 mm in width × 1.2 mm thickness × 25.0 mm length, Zirconia-silica nanofibers were produced by sol-gel electrospinning go around with calcination and blended with feldspathic ceramic through ball milling method. The samples were prepared with 0, 2.5, 5, 7.5 wt% nanofibers reinforced ceramic. The flexural strength of the samples was evaluated using three-point bending test.

Results:

The flexural strength values of zirconia-silica nanofibers reinforced ceramic groups were higher than control group. There was a gradual increase in the flexural strength values of felspathic ceramic groups with increase in wt% of nanofibers.

Conclusion:

The flexural strength of feldspathic ceramic samples reinforced with zirconia-silica nanofibers by 5 and 7.5 wt% were statistically significant compared to control, whereas the flexural strength of 2.5 wt% was statistically insignificant compared to the control group.

Evaluation of fracture toughness of zirconia silica nano-fibres reinforced feldespathic ceramic

BACKGROUND

Dental ceramics exhibit great optical properties and better esthetics due to their translucency. Concern with this material is its brittleness, which accounts for its failure. Feldspathic ceramic is the most widely used veneering ceramic.

AIM AND OBJECTIVES

To evaluate and compare the fracture toughness of pressable feldspathic ceramics reinforced with zirconia silica nano-fibres with conventional pressable feldspathic ceramics.

MATERIALS AND METHOD

According to ISO 6872, a master die was prepared from which, Bar shaped samples were formed in acrylic resin with the specified dimensions of 4.0 mm in width ×1.2 mm thickness ×25.0 mm. The zirconia silica nano-fibres were prepared by sol gel electro-spinning followed by calcination then they were incorporated into feldspathic ceramic through ball milling process. The samples were prepared with addition of 0, 2.5, 5, 7.5 weight % nano-fibres. The fracture toughnes was evaluated using the indentation strength method. The values were statistically analysed using the one sample Kolmogorov-Smirnoff test, Kruskal Wallis test and pair wise group comparison was done using Mann Whitney test with Bonferroni correction.

RESULTS

The fracture toughness values for 2.5 wt% and 5 wt% groups were higher than control group, while the values for 7.5 wt% groups were lower compared to control group.

CONCLUSION

The fracture toughness values of feldspathic ceramic samples reinforced with zirconia silica nanofibers by 2.5 and 5 wt% were statistically significant when compared to samples reinforced with 7.5 wt%.

Measuring residual stress in ceramic zirconia-porcelain dental crowns by nanoindentation

Residual stress plays a critical role in failure of ceramic dental crowns. The magnitude and distribution of residual stress in the crown system are largely unknown. Determining the residual stress quantitatively is challenging since the crown has such complex contours and shapes. This work explored the feasibility and validity of measuring residual stress of zirconia and porcelain in ceramic crowns by nanoindentation. Nanoindentation tests were performed on the cross-section of a crown for both porcelain and zirconia along four critical locations: the thickest, thinnest and medium porcelain thicknesses. Zirconia and porcelain pieces, chipped off from the crown and annealed at 400 °C, were used as reference samples. The residual stress was determined by comparing the measured hardness of the stressed sample with that of the reference sample. Nanoindentation impression images were acquired through a scanning probe microscope (SPM) equipped with a Hysitron Triboindenter. Zirconia showed large pile-up. Residual stress is determined along the thickness of crowns at the chosen locations for both porcelain and zirconia. The measured results were compared with the results from X-ray diffraction (XRD) and finite element modeling (FEM). Results show there are large amounts of residual stresses in the dental crown and their magnitude differs between locations due to the complex shape of the crown. The average residual stress readings were as high as -637 MPa and 323 MPa for zirconia and porcelain respectively.

Effect of polymorphism of SiO2 addition on mechanical properties of Feldspathic porcelains

The present study aimed to investigate the effects of SiO2 polymorphism on the mechanical properties of feldspathic porcelains. Seven kinds of experimental feldspathic porcelains were prepared using chemical reagents; three types of low-fusing feldspathic glasses and four types of two-phase porcelains by adding 10 or 20 mass% of fused silica (T-F) or cristobalite (T-C). Flexural strength and fracture toughness of these porcelains were evaluated. Flexural strengths of two-phase porcelains did not show any significant increase when compared with those of single-phase glasses. On the other hand, fracture toughnesses of porcelains with cristobalite showed a significant increase when compared with those of single-phase glasses. Circumferential cracks were observed in the porcelains with cristobalite. These results suggested that cristobalite could strengthen fracture toughness of feldspathic porcelains, but not flexural strength.

The Influence of Nanosized Leucite on Dental Porcelain Properties

The influence of leucite on dental porcelain properties is investigated in this paper. The nanosized leucite powder prepared by sol-gel method was added into a low-fusing temperature frit to fabricate dental porcelain fused to metal. The porcelains with different leucite contents were sintered at the temperatures ranging from 780° to 900°C. The flexural strength and the thermal expansion coefficient (TEC) of the dental porcelain containing leucite particles are evaluated. The micro- structure and phases of the porcelain are characterized and the mechanism that nanosized leucite particles strengthening the porcelain is discussed.

Relationship between fracture toughness and flexural strength in dental porcelains

The aim of this study was to investigate the correlation between fracture toughness (K(Ic)) and flexural strength (FS) in dental porcelains. Porcelains with different leucite contents and clinical indications were used (A, B, C, D, and E). K(Ic) was determined by surface crack in flexure method (SCF) and FS was determined by four-point-bending test. Microstructural characterization was also carried out. The leucite contents of porcelains A, B, C, D, and E were, respectively, 22, 22, 6, 15, and 0%. Materials with higher leucite content (A and B) presented significantly higher K(Ic) values compared to materials with lower leucite content (C and E). The Weibull moduli (m) of porcelains A and B were statistically higher than those of the other three materials. Regarding characteristic strength (sigma(0)), porcelains D and E showed similar values and statistically higher than those of the other materials which were statistically different from each other. According to the regression analysis, sigma(0) increased with the increase of K(Ic) until approximately 0.75 MPa m(1/2). After that, the increase in K(Ic) was accompanied by a decrease in sigma(0). However, the Weibull modulus increased with the increase in K(Ic), especially for values greater than 0.80 MPa m(1/2).