ABSTRACT
STATEMENT OF PROBLEMS: Conventional feldspathic porcelain is used extensively as a restorative material and it is subjected to grinding and polishing during fabrication and delivery procedures. There is still considerable controversy concerning the best methods to achieve the strongest porcelain restorations after such adjustments. PURPOSE: The objective of this study was to investigate the effects of (1) overglazing, (2) selfglazing, and (3) fine polishing on the flexural strength and fracture toughness of feldspathic dental porcelain. MATERIAL AND METHOD: Ninety porcelain disks were prepared for flexural strength test and sixty porcelain disks were fabricated for fracture toughness test. Specimens were divided into three groups for each test as follows: 1) overglazed 2) self-glazed 3) polished. The flexural strength of feldspathic porcelains was determined by ring-on-ring biaxial flexural strength test. The fracture toughness values of three experimental groups were obtained by indentation fracture toughness test. RESULTS: The flexural strength of overglazed group was significantly higher than that of selfglazed and polished group (P0.05). The fracture toughness values of overglazed and polished group were significantly higher than that of self-glazed group (P0.05). CONCLUSIONS: This results supported the use of polishing as an alternative to glazing metal ceramic restorations, as it was not detrimental in flexural strength and fracture toughness. But, under the conditions of this study, overglazing was the ideal surface finishing method of feldspathic dental porcelain.
Subject(s)
Dental Porcelain , Metal Ceramic AlloysABSTRACT
STATEMENT OF PROBLEM: Long-term exposure of dental porcelain to saliva during temporary cementation of a porcelain-fused to metal (PFM) restoration could affect mechanical strength of dental porcelain if the restoration is refired. PURPOSE: This work was performed to verify the effect of water on the mechanical strength in aged dental porcelain. MATERIAL AND METHOD: 63 specimens(Vintage Metalbond opaque and opal powder) were distributed to three experimental groups; non-water immersed control, immersed and pedried, and immersed and non-predired groups. The changes in flexural strength and fracture toughness after specimen refiring related to Fourier Transform Infrared (FT-IR) spectroscopy. RESULTS: 1. The FT-IR reflectances assigned to molecular bonds of H2O were noted as significantly different between the first-fired group and three refired groups and between two water-immersed groups and control group after refiring( p<0.05). They were also significantly different between predried group and non-predried group after refiring( p<0.05). 2. For opal specimens, FT-IR absorbances for hydrogen bond of H2O and silanols were significantly higher in non-predried group than in predreid group( p<0.05). 3. Predried opal group showed the highest mean flexural strength( p<0.05). Non-predried group indicated higher mean flexural strength than control group( p<0.05). 4. The mean fracture toughness for predired group was higher than non-predried group( p<0.05). 5. The difference of leucite crystal size is noted between control group and water-immersed, predried group in scanning electron microscopic study(x10000).