Laser Repetition Effect on Y-TZP Roughness and Tortuosity

Objectives: The use of lasers over mechanical instrumentation for removal of fixed-dental prostheses (FDPs) can lead to efficient restoration retrievability. In this research, an Er,Cr:YSGG laser is proposed to be used as a tool to remove yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) FDPs in a safe and non-destructive fashion. The purpose of this study was to characterize the effect of the laser irradiation at low power and different pulses per second on the Y-TZP surface.
Methods: Y-TZP slices of 1.01 ± 0.05 mm thickness were irradiated with a Er,Cr:YSGG laser (Biolase Waterlase MD) at 1.0 W with three different pulses per second (PPS) as follows: 20, 30 and 45. The samples were analyzed after 30 and 60 seconds of irradiation with a constant air and water combination of 1%. An area of 50 µm x 50 µm was scanned using ScanAsyst mode in the atomic force microscope (Bioscope Catalyst, Bruker) at a rate of 0.592 Hz. The height data from the scans were imported into a custom MathCAD script, and FRACTALS software was used to determine D* by the Minkowski cover technique.
Results: Data is presented in the Table.
Two-way analysis of variance showed that 45 PPS affected significantly the tortuosity of the YSZ ceramic (P = 0.017), while the time factor did not have a significant effect (P = 0.365). The groups did not show statistically significant differences in surface roughness.
Conclusions: The investigated laser settings affected the surface characteristics of the Y-TZP similarly except for the high pulses per second that reduced the tortuosity of the ceramic material. However, all of the settings seem to lead to a non-destructive method for the removal of the Y-TZP.