Strength Of Dental Porcelain Research Articles

Cyclic Contact Fatigue of Dental Porcelain

The residual strength of dental porcelain discs were test after cycling fatigue compressive load in this study. Moreover, the effects of stress intensity and cycle frequency to the damage of porcelain were explored. The porcelain specimens were bonded to the epoxy resin blocks, with 12.5mm height. The cycling fatigue contact loads were subjected on the porcelain surfaces of the bi-layer composites with silicon nitride spheres of radius 2.5mm. The crosshead speed was 6mm/min. The top load value was varied from 10N-20N in every load cycles. The cycling number was from 50-300. After cycling test, the residual strength of all porcelain samples was measured by bi-axial bending test. Fractured pieces of the specimens were collected and examined with optical microscope and SEM. On the fracture surfaces of porcelain discs after bi-axial bending test, Hertz cone cracks were presented due to cycling fatigue load. The result showed that the residual strength of dental porcelain had negative correlation with the fatigue load values and cycles. When the fatigue load cycles were lower than 100, the residual strength of porcelain presented no significant different under 10 or 20N fatigue load. In contrary, when the fatigue load cycles were over 100, the residual strength of porcelain was much lower under 20N fatigue load than 10N fatigue load. Based on the limited results of this study, the conclusion could be drawn that the residual strength of porcelain under fatigue compressive stress was main determined by load cycles in the range of small load values. The porcelain could be destroyed after very few cycles if the load is up to a critical value.

Strength Properties of Glazed Low Fusion Porcelain

In order to examine the relationship between particle size and the strength of dental porcelains, the particle distributions of dental porcelains were measured using a laser diffraction particle distribution analyzer. Statistical analysis revealed that the particle distribution was well fitted to a three-parameter Weibull distribution. The bending strength of the glazed specimen was equal to or greater than that of the as-received specimen. This is thought to have resulted from the glass constituent of the porcelain undergoing fusion and flowing into the indentation cracks, thereby contributing to a recovery of bending strength. Using the author's process zone size fracture criterion, experimental data concerning the dependence of the bending strength of glazed specimens on cracking was clarified. The distribution of fracture toughness of glazed specimens agreed well with a two-parameter Weibull distribution. Analysis of the dependence of the bending strength of the glazed specimen on cross head speed indicated that the static fatigue sensitivity of the healed crack was not high.

Effect of water content on the mechanical strength of dental porcelain

In this study, we measured the mechanical strength and fracture toughness of feldspathic dental porcelains with different water contents. The mechanical strength of the dental porcelain was measured using a three-point bending test; the fracture toughness of the dental porcelain was measured by a Vickers indentation method. An increased water content was found to decrease both the strength and toughness. This is probably due to easier crack formation or perhaps to a slightly higher crystallinity of the leucite material. We expected and found that it was necessary to study this phenomenon to overcome the failure of feldspathic dental porcelains during refiring after a temporary cementation in the mouth.

The influence of clinically induced variability on the bi-axial fracture strength of cemented aluminous core porcelain discs

Objectives: Zinc phosphate cements are supplied in powder/liquid form so that a range of mixing ratios are naturally generated in clinical practice. However, these cements are known to have a deleterious effect on dental ceramics and the impact of variations in cement mixing on the strength of dental porcelain was investigated in the present study. Methods: Vitadur-N core porcelain was fabricated into discs (15 mm diameter and 2 mm thickness), zinc phosphate cements of different mixing ratios were applied to the discs to produce a luting cement thickness and the samples were stored for 24 h prior to testing in a water-bath at 37±1°C. The mean fracture strength, standard deviation and associated Weibull moduli ( m) of the coated porcelain discs were determined as a function of mixing ratio using bi-axial flexure (ball-on-ring) by fracturing sets of 30 specimens coated with cements manipulated at different mixing ratios. Results: The strength data for the coated porcelain discs showed little variation in magnitude and consistency ranging from 108±8.3 MPa ( m=14.0±2.6) at 1.7 g/ml to 112±8.5 MPa ( m=14.6±2.7) at 2.6 g/ml and 108±8.1 MPa ( m=14.4±2.6) at 3.2 g/ml. However, the plots of survival probability against strength for coated specimens prepared using mixing ratios below that recommended by the manufacturers’ for luting purposes (2.6 g/ml), appeared to develop an asymmetry at the lower values of strength. Significance: It was proposed that the increased corrosive acidic environment for cements prepared at mixing ratios below 2.6 g/ml may have extended pre-existing flaws in the porcelain discs thereby possibly producing the asymmetry in the survival distributions.

An investigation into the role of porcelain thickness in determining the load-carrying capacity of porcelain laminates.

The effect of specimen thickness on the strength of dental porcelain has been investigated. It has been shown that for core, dentine and combinations of these porcelains, the shell strength decreases with increasing thickness. Consequently, the load carrying capacity does not increase as much as might be expected with thicker sections. Possible reasons for this phenomenon and methods of limiting this effect are discussed.