Ablation rate, caries removal, and restoration using Nd:YAG and Er:YAG lasers and air abrasion

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This study evaluated the ablation rate in dentin and enamel of the Nd:YAG laser (1 - 2W, 10Hz) and the Er:YAG laser (1 - 2.5W, 10Hz), compared to the high-speed drill, low-speed drill and air abrasion (fine and extra-fine particle size). Subsequently, the effectiveness of caries removal and restoration in enamel of the Nd:YAG laser at the same powers and pulse repetition rate was compared to the high-speed drill, low-speed drill, and air abrasion. Enamel and dentin of 1mm thick mid-coronal sections from extracted third molars were ablated by Er:YAG laser ((lambda) equals 2.94 micrometer), Nd:YAG laser ((lambda) equals 1.06 micrometer) both with air/water spray, high-speed drill with 300 carbide bur, and low-speed drill with $1/4 round bur and air abrasions at 160 psi, with fine air abrasion at 50 micrometer and extra fine at 27 micrometer particle size. Removal (ablation) rate defined as dentin or enamel thickness divided by time required for perforation of the samples was determined for lasers, drills and air abrasion. Multifactor randomized ANOVA (p less than 0.05) considered removal rate as a function of treatment conditions. Removal Rate (micrometers per second) Enamel Dentin High-speed drill 273 +/- 47.34 493 +/- 1.73 Low-speed drill 0 42 +/- 14.25 Nd:YAG 2W 0 103 +/- 37 Er:YAG 2W 35 +/- 10 348 +/- 101 Air abrasion/fine 220 +/- 27 433 +/- 99 Air abrasion/extra fine 151 +/- 13 203 +/- 30 Er:YAG laser at 2W 10Hz ablated both enamel and dentin faster than the low-speed drill but slower than the high-speed drill, while the Nd:YAG laser at identical power and pulse rate did not ablate healthy enamel but was capable of removing dentin. To determine caries removal rate in enamel, extracted superficial carious molars (n equals 35) that included minimal explorer penetration and radiographic confirmation of caries extent were selected. Samples were randomly distributed into treatment groups: high-speed drill (HS), low-speed drill (LS), Nd:YAG laser (L), Nd:YAG with air-water spray (A/W), air abrasion fine (F) and air abrasion extra-fine (EF). The amount of time required to achieve caries removal was measured. Subsequently, the teeth were embedded in resin and cut longitudinally into 0.5mm sections with a diamond saw for inspection of caries removal. Utilizing single-factor random design ANOVA (p less than 0.05), data were analyzed and compared. All treatments successfully removed caries in enamel, with significant differences in amount of tissue removed and time of treatment. Time of removal procedure indicated L greater than A/W greater than LS greater than HS very much greater than F equals EF. Width of tissue removed (mm): HS equals 1.59 plus or minus 0.26, LS equals 0.91 plus or minus 0.38, L equals 0.60 plus or minus 0.17, A/W equals 0.54 plus or minus 0.18, EF equals 0.81 plus or minus 0.19 and F equals 0.79 plus or minus 0.15. The Nd:YAG laser was the most conservative of the treatment methods tested, followed by air abrasion, low-speed and high-speed drilling. Lasers are slower and more conservative while air abrasion is faster and more conservative than conventional dental drills.