0390 Effect of Wash Porcelain Firing on Biaxial Strength of Zirconiumdioxide
J.I. HJERPPE1, L.V.J. LASSILA2, and P.K. VALLITTU2, 1University of Turku, Finland, Helsinki, Finland, 2University of Turku, Finland

Objectives: Zirconiumdioxide cores of crowns are veneered with porcelain for better esthetic properties. The aim of this study was to evaluate effect of heat treatment by the veneering process and addition of veneering porcelain to the zirconiumdioxide on some mechanical properties. Methods: Partially yttrium stabilised zirconiumdioxide (ICE Zircon, ZirkonZahn, Italy) discs were divided into five groups (n=15/group). The ceramic discs were sintered at 1500 °C in the sintering oven (ZirkonZahn). Control discs were left as such. Discs in study groups were: 1) heated in porcelain firing oven according to porcelain firing process; 2) heat treatment in firing oven with two firing cycles;   3) glazing porcelain (ICE Zirkon keramik) was fired  on the discs; 4) wash porcelain and glazing porcelain were fired on the discs. Biaxial flexural strength of the sintered discs (diameter 19mm, thickness 1.2mm) were measured dry at room temperature. In the loading test the porcelain surface was on the tension side. Surface microhardness (VHN) was measured on zirconiumdioxide surface and the data was calculated using ANOVA-analysis. Results: Heat treatment only did not influence the load required to break the disc whereas addition of wash and glazing porcelain decreased the load values and strength (p<0.05). No difference (p>0.05) was found in terms of surface microhardness (VHN). Results were:

 

Parameters

Flexural Strength MPa (SD)

Stat. diff.

Load N (SD)

Stat. diff.

Surface Microhardness VHN (SD)

Control

942 (142)

a

846 (126)

a

1420 (62)

1 heat treatment

932 (167)

a

872 (157)

a

1443 (112)

2 heat treatments

976 (94)

a

798 (85)

ab

1382 (58)

Glazing*

699 (93)

b

705 (96)

bc

1399 (105)

Wash + glazing*

581 (83)

b

625 (50)

c

1437 (63)

*Addition of wash/glazing porcelain increased the thickness of the discs by 0.1mm.

 

Conclusions: Firing porcelain on the surface of the sintered discs of zirconiumdioxide decreased their biaxial flexural strength. The heat treatment of the firing process itself did not influence on the strength.

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