Influence of pH on slow crack growth of dental porcelains.
OBJECTIVE
To evaluate the effect of pH of storage medium on slow crack growth (SCG) parameters of dental porcelains.


METHODS
Two porcelains were selected: with (UD) and without (VM7) leucite particles, in order to assess if the microstructure would affect the response of the material to the pH variation. Disc specimens were produced following manufacturers' instructions. Specimens were stored in artificial saliva in pHs 3.5, 7.0 or 10.0 for 10 days and after that the fatigue parameters (n: SCG susceptibility coefficient and sigma(0): scaling parameter) were obtained by the dynamic fatigue test using the same pH of storage. Microstructural analysis of the materials was also performed.


RESULTS
For VM7, the values of n obtained in the different pHs were similar and varied from 29.9 to 31.2. The sigma(0) value obtained in pH 7.0 for VM7 was higher than that obtained in the other pHs, which were similar. For porcelain UD, n values obtained in pHs 7.0 and 10.0 were similar (40.8 and 39.6, respectively), and higher than that obtained in pH 3.5 (26.5). With respect to sigma(0), the value obtained for porcelain UD in pH 10.0 was lower than those obtained in pHs 3.5 and 7.0, which were similar.


CONCLUSIONS
The effect of pH on the stress corrosion susceptibility (n) depended on the porcelain studied. While the n value of VM7 was not affected by the pH, UD presented lower n value in acid pH. For both porcelains, storage in acid or basic pH resulted in strength degradation.
Pinto
Marcelo M
MM
Department of Biomaterials and Oral Biochemistry, School of Dentistry, University of São Paulo, São Paulo, Brazil.
Cesar
Paulo F
PF
Rosa
Vinícius
V
Yoshimura
Humberto N
HN
D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D006244:Hardness; D006801:Humans; D006851:Hydrochloric Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007091:Image Processing, Computer-Assisted; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D012464:Saliva, Artificial / Q000737:chemistry; D012972:Sodium Hydroxide / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D013314:Stress, Mechanical; D013499:Surface Properties; D014961:X-Ray Diffraction
D000538:Aluminum Silicates; D012464:Saliva, Artificial; D003776:Dental Porcelain; C078519:leucite; D012972:Sodium Hydroxide; D000537:Aluminum Oxide; D006851:Hydrochloric Acid