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. 2016 Feb 11:6:20950.
doi: 10.1038/srep20950.

Femtosecond laser for cavity preparation in enamel and dentin: ablation efficiency related factors

H Chen  1 , H Li  1 , Yc Sun  1 , Y Wang  1 , Pj Lü  1
Affiliations

Femtosecond laser for cavity preparation in enamel and dentin: ablation efficiency related factors

H Chen et al. Sci Rep. .

Abstract

To study the effects of laser fluence (laser energy density), scanning line spacing and ablation depth on the efficiency of a femtosecond laser for three-dimensional ablation of enamel and dentin. A diode-pumped, thin-disk femtosecond laser (wavelength 1025 nm, pulse width 400 fs) was used for the ablation of enamel and dentin. The laser spot was guided in a series of overlapping parallel lines on enamel and dentin surfaces to form a three-dimensional cavity. The depth and volume of the ablated cavity was then measured under a 3D measurement microscope to determine the ablation efficiency. Different values of fluence, scanning line spacing and ablation depth were used to assess the effects of each variable on ablation efficiency. Ablation efficiencies for enamel and dentin were maximized at different laser fluences and number of scanning lines and decreased with increases in laser fluence or with increases in scanning line spacing beyond spot diameter or with increases in ablation depth. Laser fluence, scanning line spacing and ablation depth all significantly affected femtosecond laser ablation efficiency. Use of a reasonable control for each of these parameters will improve future clinical application.

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Figures

Figure 1
Figure 1. Schematic of laser ablation path.
d: scanning line spacing; n: number of scanning lines in one layer.
Figure 2
Figure 2. Measurement of cavity volume using a 3D laser scanning microscope.
(a) selection of the measurement area (green area); (b) cross-sectional profile of cavity (yellow vertical line in part (a));(c) cross-sectional profile of cavity (yellow horizontal line in part (a));(d) automatic calculation by software of cavity volume, comprised of selected area, side walls and bottom wall.
Figure 3
Figure 3. 3D graphical representation of surfaces ablated at different laser fluences.
At a laser fluence of 1.56 J/cm2, scanning line spacing of 24 μm and number of scanning layers of 800: (a) enamel and (b) dentin; At a laser fluence of 6.25 J/cm2, scanning line spacing of 24 μm and number of scanning layers of 200: (c) dentin and (d) enamel.
Figure 4
Figure 4. Relationship between laser fluence and ablation efficiency for enamel and dentin.
Figure 5
Figure 5. 3D graphical representation of surfaces ablated at different scanning line spacings.
At a laser fluence of 4.69 J/cm2, scanning line spacing of 12 μm and number of scanning layers of 200: (a) enamel and (b) dentin; At a laser fluence of 4.69 J/cm2, scanning line spacing of 40 μm and number of scanning layers of 600: (c) enamel and (d) dentin.
Figure 6
Figure 6. Relationship between scanning line spacing and ablation efficiency for enamel and dentin
Figure 7
Figure 7. Ablation surfaces and their 3D graph in different number of ablation layers.
At a laser fluence of 4.69 J/cm2, scanning line spacing of 12 μm and number of scanning layers of 25: (a) enamel and (b) dentin; At a laser fluence of 4.69 J/cm2, scanning line spacing of 12 μm and number of scanning layers of 200: (c) enamel and (d) dentin.
Figure 8
Figure 8. Relationship between number of ablated layers and ablation depth for enamel and dentin, a linear relationship was revealed (dentin: R2 = 0.997; enamel: R2 = 0.997).
Figure 9
Figure 9. Relationship between ablated depth and ablation efficiency for enamel and dentin.
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