Thermal Effect of Er,Cr:YSGG Laser on a YSZ Ceramic

Objectives: Dentists need a more efficient and atraumatic method to remove resin bonded YSZ restorations. Erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser low power settings as 2.5 W have proven not to produce temperatures that could damage the pulp, however can affect the soft and hard tissue. The aims were 1) to determine the maximum temperature (T) reached after laser irradiation through the YSZ ceramic in dry and wet conditions, and 2) to determine the effect of the time at different pulses per seconds (PPS).
Methods: Slices (~1 mm thick) were created from a YSZ block (IPS e.max ZirCAD, Ivoclar Vivadent). The slices were sintered at 1500 °C in a Sintramat furnace (Ivoclar Vivadent), and divided into three groups (n = 30) according to the following PPS: 20, 30 and 45. Half the samples of each group (Table) were irradiated with 1% water and 1% air (W=wet condition) and the other half were irradiated without water and air spray (D=dry condition) using the Er,Cr:YSGG laser (Waterlase MD™, Biolase). The MG6 tip irradiated the ceramic surface perpendicularly while the type K thermocouple measured the T on the alternate side at 30s, 60s, 90s, and 120s. The T was recorded in Celsius (°C) at 1 watt with a digital thermometer (OMEGA HH506R).
Results: Data is presented in table:
Two-way repeated measures ANOVA showed that PPS did not have a significant effect on T (p=0.61). There was a significant interactive effect (p<0.001) for the D/W conditions and time. Heat transferred through the Y-TZP structure was lower in the wet condition than dry at each time point. For dry conditions, all time points had significantly different temperatures.
Conclusions: The lack of irrigation during the laser irradiation (groups D) increases the T through the YSZ structures. The lowest irradiation time, at any frequency, will potentially decrease the pulp vitality in dry conditions.