EFFECT OF REPRESSING AND GLAZING ON COLOR REPRODUCTION, TRANSLUCENCY AND SURFACE ROUGHNESS OF LITHIUM DISILICATE GLASS-CERAMICS

Statement of problem: During heat-pressing of lithium dislilicate glass-ceramics, It is more economical to press several restorations from one ingot at the same time. However, this is often not possible and may result in a considerable amount of leftover material (The sprues and button). It has been reported that the leftover materials after heat-pressing are reused (repressed) in some dental laboratories. Sufficient knowledge about the consequences of such procedure is not available.
The issue is thereby raised whether the leftover material should be discarded or reused.
Purpose. The aim of the present study was to evaluate the effect of repressing and glazing on the color reproduction, translucency and surface roughness of lithium dislilicate pressable glass-ceramics (IPS e.max Press). As well as to describe the microstructural features present in pressed, and repressed material using Xray diffraction, EDAX and SEM
Materials and Methods: Twenty IPS e.max press discs (Pressed and Repressed groups n=10) of 15mm diameter, 1 mm thickness, in shade A3 were fabricated using heat pressed technique. Only the button parts and not the sprues were used for repressing. Color reproduction and translucency were measured using the Vita Easyshade spectrophotometer. Surface roughness was measured using a 3D laser scanning microscope. Crystalline structure and microstructural features present in pressed, and repressed material were described using Xray diffraction, EDAX and scanning electron microscope.
Results: Two-way analysis of variance (ANOVA), followed by Tuckey’s HSD test at
a significance level of p < 0.05 was performed. Regarding Color reproduction, Translucency and Roughness, significant difference was found between Glazed and Un-Glazed ceramics.
No statistical significant difference was found between Pressed and Repressed groups
Conclusions: Lithium disilicate glass-ceramic materials have reached their maximum crystallinity prior to repressing. It is important to produce a pore–free structure by only repressing the left over buttons and not the left over sprues. Repressing has no significant effect on Color, translucency and surface roughness and Glazing is crucial to increase color reproduction, translucency and decrease surface roughness of IPS e.max Press.