Assessment of dose-dependent surface modification of human enamel and dentin with ultrashort femtosecond 30-fs 800 nm laser irradiation

Introduction: Ablation of human enamel and dentin, with no collateral damage is essential for lasers to be used for clinical applications in dentistry. This study for the first time explores efficacy and surface topography resulting from interaction of a novel ultra-short femtosecond (30-fs) laser with enamel and dentin following laser irradiation with varying dose. Materials and methods: Human teeth were embedded in resin, sectioned and irradiated with a 30-fs, 800 nm laser light at 1 kHz. Samples divided into four (4) groups were irradiated with at varying fluence (2.83, 5.66, 16.98 and 33.97 J/cm2), numbers of pulses, N, (150, 300 and 1500), and scanning speeds (10, 50 and 100 mu m/s), and analysed for changes to their surface topography and features to identify an optimal irradiation doze producing maximum material removal at minimal energy. Assessed surface features comprised of depth and width of irradiated tracks, surface roughness, cracks and/or discoloration utilizing optical profilometry and scanning electron microscopy measurements. The obtained data was assessed for normality and analysed employing oneway ANOVA with post-hoc multiple comparisons. Results: All parameters used in this study resulted in ablation of enamel and dentin. The depth and width of ablated tracks were greater in dentin than enamel. The maximum width and depth in dentin (58.74 mu m and 63.32 mu m) and enamel (38.28 mu m and 28.45 mu m) was recorded at 33.97 J/cm2. The average depth of ablation was found to be significantly lower for enamel compared to dentin. The highest ablation rate was found at laser fluences of 2.83-33.97 J cm2 and N of 150 and 300 for both materials. The ablation rate was found to decreased as fluence increased above 5.66 J cm2 at an N value of 1500. Surface cracking was observed in dentin at a fluence of 33.97 J/cm2 and N value of 1500. Conclusion: The ultra-short 30-fs femtosecond laser radiation enabled effective ablation of both enamel and dentin, producing well-defined and delineated irradiation features. Clinically, it is important to note that the irradiation tracks formed on dentin were found to be wider and deeper compared to those on enamel, under identical photoablation conditions.