Fractal Analysis Using Laser Scanning Microscope in Dental Ceramic

Objectives: Fractal analysis of ceramic fracture surfaces can provide information about the reasons of failure of dental restorations. However, current techniques to measure fractal dimension are time consuming and have low signal-to-noise ratio. The purpose of this study is to determine if the laser confocal microscope (~100x faster) give the same fractal dimension values as atomic force microscope (current method).
Methods: Fracture surfaces of lithium disilicate (LDS, e.max CAD, n=11), and 3Y zirconia (3Y-TZP, e.max ZirCAD, n=11) were analyzed to calculate fractal dimension (D). One half of the fracture surface was uncoated and the other half was sputter-coated with gold. Hackle regions for both halves was scanned using laser confocal microscope (LCM, VKX-3000, Keyence). The scanned files were uploaded to the Gwyddion software and leveled at the largest pixel size as well as at each pixel size (256x256, 512x512, 1024x1024) to calculate unbiased D value via cube counting algorithm. For the first 4 samples of LDS, both the gold coated and uncoated specimens were scanned to determine if the gold coating would affect the D values, followed by a paired t-test. No practical significant difference between the D values was found between the two conditions, so only the gold coated specimen were scanned for the rest of the specimens. The D values obtained using the laser confocal microscope and atomic force microscope (AFM) were compared.
Results: The paired t-test (p=0.96) showed no difference between the D values from uncoated and gold-coated specimen. The D values from the laser confocal and the atomic force microscope are compiled in Table 1.
Conclusions: The laser confocal microscope had higher fractal dimension values through cube counting than the atomic force microscope. Further study needs to be done to determine why the fractal dimension values for the confocal microscope was higher.