title: Comparison of porcelain surface and flexural strength obtained by microwave and conventional oven glazing.
abstract: BACKGROUND
  Although the superior qualities of microwave technology are common knowledge in the industry, effects of microwave glazing of dental ceramics have not been investigated.
  
  
  OBJECTIVE
  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.
  
  
  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.
authors.affiliation: Department of Restorative Dentistry, School of Dental Medicine, State University of New York at Buffalo, Buffalo, NY 14214, USA. soniprasad@yahoo.com
authors.forename: Soni
authors.initials: S
authors.lastname: Prasad
authors.forename: Edward A
authors.initials: EA
authors.lastname: Monaco
authors.forename: Hyeongil
authors.initials: H
authors.lastname: Kim
authors.forename: Elaine L
authors.initials: EL
authors.lastname: Davis
authors.forename: Jane D
authors.initials: JD
authors.lastname: Brewer
mesh_terms: D003775:Dental Polishing / Q000379:methods*; D003776:Dental Porcelain; D003799:Dental Stress Analysis; D006358:Hot Temperature; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008872:Microwaves; D018583:Pliability; D016062:Porosity; D013499:Surface Properties; D016019:Survival Analysis
chemical_list: D003776:Dental Porcelain