Effects of Light Energy Absorption Through Ceramic on Cement Curing

Objectives: The purpose of this study was to investigate the effect of light energy attenuation and characteristics of altered light irradiance pattern over wavelength spectrum on mechanical properties of resin cement cured underneath ceramic materials.

  Methods: Light energy transmitted through various thickness of ceramic blocks was quantified by MARC^¨ Resin Calibrator (BlueLight analytics, inc.). The ceramic blocks used in this study were YZ Zirconia (Crystal Zirconia), Lava Zirconia (3M ESPE), IPS e.max CAD Lithium disilicate glass-ceramic (Ivoclar Vivadent), and IPS e.max ZirCAD Zirconia (Ivoclar Vivadent). Light-cured cement (Choice 2, Bisco) was dispensed inside Delrin ring with varying thickness and cured with LED light (VALO, Ultradent Products, Inc.) and halogen Demetron LC light (Kerr, Inc.) respectively. Microhardness and elastic modulus of cement layer were measured using ultra-micro hardness tester (DUH-W201S, Shimadzu) to compare degree of polymerization.

Results: Different level of attenuated light energy and different patterns of altered light irradiance pattern were observed with varying thickness of ceramics by using two different LED and Halogen curing lights. More total energy was delivered with LED light than with halogen light as expected. Peak wavelength of LED light was relatively not shited comparing to Halogen light through varying thickness of ceramic materials. Absorption of total light energy and reduction of mechanical properties of cement cured through lithium disilicate were greater than other zirconia ceramics as thickness of ceramic increases.

Conclusion: In general, although 2 mm thickness of zirconia and lithium disilicate absorbed total light energy about 70 to 80%, microhardness and elastic modulus of cured thinner cement layer (0.98 mm) were not reduced more than 30% in this study. Since curing of cement in restorations using veneer and crown is very important especially in growing dental CAD/CAM, further investigation using products with different formulation and dual curing mode needs to be conducted.