Abstract
The aim of this study was to present a control method for modulating the translucency of lithium disilicate ceramics through thermal refinement. Identical lithium disilicate blocks were thermally refined using four different heat treatment schedules, and the microstructure, translucency, and flexural strength of the ceramics were investigated in detail by SEM, spectroscopy, and a piston-on-three-ball test. The results showed that ceramics treated under higher heat had larger grains, with an average size between 240 and 1080 nm. In addition, a higher transmittance of all wavelengths was observed in ceramics treated under lower heat, and the transmittance in the 550 nm wavelength ranged from 27 to 34%. The results suggest that the translucency of ceramics can be modified through thermal refinement under two conditions: (1) the particle size of the ceramic is small enough to achieve minimal grain-boundary light scattering, and (2) the percentage of particles allowing visible light transmission is altered by the heat treatment.
Highlights
Lithium disilicate, which has a major crystalline phase of Li2 Si2 O5 [1], shows a typical microstructure where elongated crystals form an interlocking pattern [2,3]
For easy milling, increased cutting efficiency, and minimal waste of milling tools, the lithium disilicate block is used in the intermediate state of crystallization (Li2 SiO3 ) [5], and additional thermal refinement processes are necessary after milling to enrich their crystallization [5]
Microstructure plays a major role in determining the translucency of ceramics, and this translucency can be modified by varying the volume, size, and density of crystals [6]
Summary
Lithium disilicate, which has a major crystalline phase of Li2 Si2 O5 [1], shows a typical microstructure where elongated crystals form an interlocking pattern [2,3]. Since lithium disilicate was first introduced as a dental restorative material by Ivoclar Vivadent, the material has been popular due to its favorable optical characteristics and high mechanical strength [4]. “Ingot-type” lithium disilicate has been used in the conventional dental fixed-restoration fabricating method known as the lost wax technique. With the advance of CAD/CAM (computer-aided design and computer-aided manufacturing) technology, a lithium disilicate block (IPSTM e.Max CAD) has been introduced for use in milling procedures. For easy milling, increased cutting efficiency, and minimal waste of milling tools, the lithium disilicate block is used in the intermediate state of crystallization (Li2 SiO3 ) [5], and additional thermal refinement processes are necessary after milling to enrich their crystallization [5].
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