The effect of cement type and mixing on the bi-axial fracture strength of cemented aluminous core porcelain discs

OBJECTIVES: Luting agents in current use include zinc phosphate, zinc polycarboxylate, conventional glass-ionomer, resin-modified glass-ionomer and resin composite cements. Dental cements may be used in practice with a wide range of mixing ratios. Accordingly, the impact of cement type and mixing on the strength of alumina reinforcing porcelain was investigated. METHODS: Standard Vitadur-N core porcelain disc specimens were coated with different cement types of varying mixing ratios to produce a luting thickness. Sets of 25 coated specimens were stored at 37+/-1 degrees C for 24h prior to testing. Mean fracture strengths, standard deviations and associated Weibull Moduli (m) were determined using bi-axial fracture (ball-on-ring). RESULTS: The strength data for porcelain discs coated with different cement types manipulated at the consistency indicated for luting all-ceramic crowns showed little variation in magnitude and consistency. The plots of survival probability against strength for specimens coated with acid-base cements appear to develop a slight asymmetry at the lower values of strength. This effect was more pronounced for acid-base cements prepared at mixing ratios below that recommended for luting purposes. SIGNIFICANCE: The corrosive acidic environment of acid-base cements may have extended pre-existing flaws in the porcelain discs producing the asymmetry in the survival distributions. Resin composite cements appear to enhance the strength of the porcelain disc specimens possibly by healing the surface imperfections. This may increase their scope of application over acid-base cements to include the luting of all-ceramic restorations.