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  • Title: Comparison of porcelain surface and flexural strength obtained by microwave and conventional oven glazing.
    Author: Prasad S, Monaco EA, Kim H, Davis EL, Brewer JD.
    Journal: J Prosthet Dent; 2009 Jan; 101(1):20-8. PubMed ID: 19105988.
    Abstract:
    STATEMENT OF PROBLEM: Although the superior qualities of microwave technology are common knowledge in the industry, effects of microwave glazing of dental ceramics have not been investigated. PURPOSE: The purpose of this study was to investigate the surface roughness and flexural strength achieved by glazing porcelain specimens in a conventional and microwave oven. MATERIAL AND METHODS: Thirty specimens of each type of porcelain (Omega 900 and IPS d.Sign) were fabricated and sintered in a conventional oven. The specimens were further divided into 3 groups (n=10): hand polished (using diamond rotary ceramic polishers), microwave glazed, and conventional oven glazed. Each specimen was evaluated for surface roughness using a profilometer. The flexural strength of each specimen was measured using a universal testing machine. A 2-way ANOVA and Tukey HSD post hoc analysis were used to determine significant intergroup differences in surface roughness (alpha=.05). Flexural strength results were also analyzed using 2-way ANOVA, and the Weibull modulus was determined for each of the 6 groups. The surfaces of the specimens were subjectively evaluated for cracks and porosities using a scanning electron microscope (SEM). RESULTS: A significant difference in surface roughness was found among the surface treatments (P=.02). Follow-up tests showed a significant difference in surface roughness between oven-glazed and microwave-glazed treatments (P=.02). There was a significant difference in flexural strength between the 2 porcelains (P<.005), but no significant difference in flexural strength by surface treatment (P=.48). The Weibull modulus value for the Omega 900 microwave-glazed group was the highest (1.9) as compared to the other groups. CONCLUSIONS: The surface character of microwave-glazed porcelain was superior to oven-glazed porcelain. Omega 900 had an overall higher flexural strength than IPS d.Sign. Weibull distributions of flexural strengths for Omega 900 oven-glazed and microwave-glazed specimens were similar. SEM analysis demonstrated a greater number of surface voids and imperfections in IPS d. Sign as compared to Omega 900.
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