Thermal Mapping of Laser-Irradiated Dentin Versus Other Analog Substrates

Objectives: Examine the temperature through a yttrium-stabilized zirconia (YSZ) ceramic adhesively bonded to a resin-based cement and one of the following three substrates: dentin, dentin analog material (NEMA grade G10), and composite resin.
Methods: A YSZ block (ZirCAD, Ivoclar) was cut into smaller cuboids and then rounded to 6.6 mm diameter cylinders. This cylinder was sectioned into slabs with 4 mm diameter and 1 mm thickness. The ceramic slabs were subjected to air particle abrasion with 30 µm silica-coated aluminum oxide particles and cleaned in an ultrasonic bath for five minutes. Afterward, two coats of Monobond-S (Ivoclar) were applied, and the YSZ slices were bonded onto either the exposed occlusal dentin of a maxillary premolar, a NEMA grade G10 cylinder, or a composite cylinder using a dual-cured cement (Multilink Automix, Ivoclar). The resulting nine sets were encased in epoxy resin and subsequently sagittally sectioned, producing 18 samples to undergo irradiation testing (n=6/group). The samples were irradiated using an Er,Cr:YSGG laser (Waterlase MD, Biolase) at 7.5 W, 25 Hz, and 50% water and 50% air for 15 seconds in a straight back-and-forth motion, tracing the width of the zirconia slice along the sagittal cut. Temperatures in the bonded structures (zirconia-cement-substrate) during laser irradiation were monitored and recorded every 0.1 seconds using an infrared camera (Optris PI640, Optris GmbH). The data was analyzed using one-way ANOVA.
Results: There were no statistically significant differences in terms of temperature between zirconia and cement using any substrate type (P=0.44) and no significant difference between the substrates themselves, with all mean maximum temperatures being between 30.9°C and 33.6°C.
Conclusions: Dentin, NEMA grade G10, and composite behaved thermally similarly during laser radiation. This allows for flexibility in substrate choice for future laser debonding studies as the results suggest composite and dentin analog materials will resemble dentin thermal behavior during laser irradiation.