A.W. BENHAM, J.A. GRIGGS, and Y. ZHANG, Baylor College of Dentistry (Texas A&M University System Health Science Center), Dallas, USA
Dental technicians employ a variety of techniques when
condensing and layering dental porcelain. Differences in powder-liquid ratio
may affect the physical properties of dental porcelain. OBJECTIVE: The
purpose of this study was to determine if varying the powder-liquid ratio
during condensation would affect the translucency and apparent density of
incisal porcelain. METHODS: Eris incisal porcelain (shade A4) was mixed
with deionized water in powder-liquid ratios of 2.56 g/mL, 2.78 g/mL, and 3.05
g/mL. The resulting slurry was condensed by vibration blotting to form four
disk specimens (16 mm diameter x 2 mm thickness) per group that were fired
under vacuum and polished to a final thickness of 1.10 ± 0.02 mm with a 3 mm
finish. The translucency of each specimen was taken as the contrast ratio of
shade value (L*) on black and white backgrounds using a tristimulus colorimeter
under immersion liquid with a refractive index of 1.5000. The apparent density
of each specimen was calculated using Archimedes' method. The specimens were
electroplated with gold and observed under the SEM for visual comparison of
pore size. RESULTS: Mean data values (standard deviations) were:
|
Powder-Liquid Ratio (g/mL)
|
Apparent Density (g/cm3)
|
Contrast Ratio
|
|
2.56
|
2.560 (0.006)
|
0.514 (0.007)
|
|
2.78
|
2.579 (0.009)
|
0.579 (0.006)
|
|
3.05
|
2.560 (0.005)
|
0.509 (0.004)
|
One-way ANOVA showed a significant effect of mixing ratio on
apparent density (p = 0.005) but not on contrast ratio (p =
0.21). CONCLUSION: These data indicate that varying powder-liquid ratio
had a significant effect only on apparent density of Eris incisal porcelain.
This study was supported by the Baylor Oral Health Foundation and NIH-NIDCR
grants DE13358 and DE01788.
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