Pulse Repetitions Effect on Temperature Through a Y-TZP Ceramic

Objectives: Lasers can be ideally suited for removal of high-strength ceramic restorations to minimize healthy tissue loss when replacing existing restorations. The aim was to measure the energy that is transferred through a yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) structure using a low power of 1.0 W at different pulses per seconds.
Methods: Y-TZP slices of 1.01 ± 0.05mm thickness were produced and sintered. A type K thermocouple (OMEGA HH506R) was placed underneath the center of each sample to record the maximum temperature transferred from the erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG / Waterlase MD). Three experimental groups (n = 10) were tested at 1.0 W with three different pulses per second (PPS) as follows: 20, 30 and 45. The samples were irradiated for either 30 or 60 seconds with a constant air and water combination of 1%.
Results: Two-way ANOVA showed that time was not significant (p = 0.866) but that frequency was highly significant (p < 0.001). Kruskal-Wallis one way ANOVA showed maximum temperature at 20 PPS for 30 seconds (27.61 ± 4.78 °C) was significantly higher than at 45 PPS for either 30 and 60 seconds (22.41 ± 1.48 °C and 21.02 ± 0.75 °C, respectively). Tukey’s HSD test showed that 20 PPS was significantly different and higher than both 30 and 45 PPS, while 30 and 45 PPS were statically equal.
Conclusions: The low power setting of 1.0 W with both low and high frequencies could be a potential method for debonding Y-TZP restorations with an Er,Cr:YSGG laser. Although no temperatures exceeded 42 °C, the highest frequency of 45 PPS displayed the lowest temperatures, making this the most suitable parameter.