Background and Objective The aim of this investigation to determine the range of morphological and ablative effects that can be achieved on dental enamel and dentin using ArF excimer laser irradiation at a wavelength of 193nm. Study Design/Materials and Methods Caries‐free coronal enamel and dentin surfaces of 20 extracted human teeth were subjected to irradiation at 193nm using a Lamda‐Physik model EMG 103 MSC and ArF fill. Morphology of cavity floors and walls were assessed by light microscopy and SEM. Results Morphological surface effects and ablation could be controlled effectively and reliably by choice of parameter combination, allowing the operator to achieve either a smooth, flat, or increasingly rough surface with differing degrees of selective ablation. No signs of thermal damage were apparent. Conclusion Excimer laser irradiation at 193nm provided clinically useful cavity preparations and surface morphological effects. Lasers Surg. Med. 20:142–148, 1997. © 1997 Wiley‐Liss, Inc.

Previous studies have reported altered dentinal structure and properties after laser irradiation. It was the aim of this investigation to determine the thermal and ablative effects of XeCI irradiation in dentin and then to investigate microstructural and physicochemical changes in the residual dentin structure. Extracted human molar tooth roots were bisected and coated with acid-resistant varnish, leaving a window. After irradiation of one half at 1 Hz, 15 ns pulse durations, fluences of O.5-2J/cm2, both halves were subjected to acidified gelatin gel at pH 4.5. The carious lesions were bisected and used to perform SEM and microhardness measurements.

The effect of water content on ablation rates in hard tissue is considered. Two wavelength regimes and two types of tissue (dentin and bone) are compared. In the UV (XeC1 Excimer at 308nm) the ablation rate is lower in dehydrated dentin than in fresh dentin. In dehydrated dentin the ablation rates at 2.5 J/cm2 and 7.OJ/cm2 are 0.6 and O.8j.tm/pulse, respectively. In fresh dentin the rates are nearly three time as large. A logarithmic increase is indicated. Dentin ablation with the IR (Ho:YAG, 2.1 jim) showed a similar trend to that of dentin XeC1 ablation: fresh samples ablated faster then dehydrated samples. Ablation rates are considerably higher in this case and range, from 1 .7 pm/p at 20 mJ/p to 21 .5 rim/p near 230 mJ/p in dehydrated dentin. In fresh samples for the same energy range the ablation rates were 5.1 to 213 Rm/pulse. This effect was reversed in cortical bone. Here ablation rates of dehydrated bone were higher then those of fresh one. In fresh bone, ablation rates ranged from 1 pm/p at 50 mJ to 48gm/p near 300mJ/p and in dehydrated bone from 7im/p at 30 mJ to 68jimlpnear 28OmJ/p. Possible explanation of these observations are discussed.

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