Quantifying the Strength of a Resin-coated Dental Ceramic

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Abstract

Resin luting all-ceramic restorations increases clinical performance; however, the strengthening mechanisms are not fully understood. The authors have previously proposed the existence of a resin-ceramic hybrid layer, and the hypothesis tested was that ceramic strength enhancement was conferred by the characteristics of the resin-ceramic hybrid layer. Dentin porcelain discs were polished with a P4000-grade abrasive paper, and half were centrally indented at 9.8 N. Further discs were alumina-air-abraded. Groups of 30 specimens were coated with resin cement thicknesses varying from 0 to 250 ± 20 μm before bi-axial flexure testing. Following investigation of residual stresses by annealing, regression analysis enabled us to calculate the magnitude of ’actual’ strengthening for a theoretical ’zero’ thickness of resin cement on each surface texture. Accounting for resin bulk strengthening, resin cement coating significantly increased the mean strength that was attributed to a resin-ceramic hybrid layer sensitive to surface texture.

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Most cited references 21

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The Phenomena of Rupture and Flow in Solids

A. Griffith (1921)

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Clinically relevant approach to failure testing of all-ceramic restorations.

J.Robert Kelly (1999)

One common test of single-unit restorations involves applying loads to clinically realistic specimens through spherical indenters, or equivalently, loading curved incisal edges against flat compression platens. As knowledge has become available regarding clinical failure mechanisms and the behavior of in vitro tests, it is possible to constructively question the clinical validity of such failure testing and to move toward developing more relevant test methods. This article reviewed characteristics of the traditional load-to-failure test, contrasted these with characteristics of clinical failure for all-ceramic restorations, and sought to explain the discrepancies. Literature regarding intraoral conditions was reviewed to develop an understanding of how laboratory testing could be revised. Variables considered to be important in simulating clinical conditions were described, along with their recent laboratory evaluation. Traditional fracture tests of single unit all-ceramic prostheses are inappropriate, because they do not create failure mechanisms seen in retrieved clinical specimens. Validated tests are needed to elucidate the role(s) that cement systems, bonding, occlusion, and even metal copings play in the success of fixed prostheses and to make meaningful comparisons possible among novel ceramic and metal substructures. Research over the past 6 years has shown that crack systems mimicking clinical failure can be produced in all-ceramic restorations under appropriate conditions.

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The influence of surface roughness on porcelain strength.

N de Jager, A.J. Feilzer, C.L. Davidson (2000)

In order to adjust occlusion, the functional surfaces of porcelain restorations are often ground and mechanical machining is even an essential part of the CAD-CAM process for these restorations. The aim of this study was to investigate the influence of the finishing procedures on the biaxial flexure strength of four commercial porcelains. Four commercial porcelains of which two are used for metal-ceramic restorations (Flexo Ceram Dentine and Vita VM K68) and two for veneers and inlays (Duceram LFC Dentine and Cerinate BODY) are used in this study. For each porcelain, sixty discs (Ø = 22 mm, h = +/- 2.0 mm) were produced using twelve different finishing procedures. Twenty discs were left untreated, twenty discs were milled, using a high-speed diamond disc, and twenty discs were machined in a high-speed grinding/polishing device. Half of the samples were glazed. In each of these six groups, half of the samples were stored for 16 h at 80 degrees C in a 4% acetic acid solution. The biaxial flexure strength was determined using the ball-on-ring method. In each group the roughness of the surface was determined and examined via SEM. With the exception of Flexo Ceram Dentine, a significant correlation was found between the roughness of the surface and the biaxial strength: the smoother the surface, the stronger the sample. The differences in biaxial strength may be attributed to the stress concentration of an applied load due to the roughness of the surface caused by mechanical finishing or chemical action. The fact that the strength of Flexo Ceram Dentine was not affected by the different surface treatments is probably due to the size of the leucite particles, which apparently induce more stress concentration than the surface flaws and the roughness of the surface. It was concluded that surface roughness determines the strength of a porcelain material, except where the inner structure of the material causes greater stress concentration than that caused by the combination of surface roughness and surface flaws.