Objectives: One of the most important steps in adhesive luting technique is the etching of the dental substrates, and laser etching has been proposed versus acid etching. The aim of this study was to evaluate whether laser etching could be an alternative to acid etching. Methods: 100 freshly extracted human molar teeth, free from caries and restorations were divided into 2 main (enamel and dentine) and 10 subgroups (control, acid and 3 laser groups). Enamel (group A) and dentin (group B) specimens were divided into 5 subgroups (n=10/group) 3 of which were treated with different laser (Er:YAG laser wavelength:2940 nm, Opus 20) power settings (Table 1) followed by SEM evaluations of the substrates.

Table 1	Control	37% H3PO4	Laser 1	Laser 2	Laser 3
	n=10	n=10	n=10	n=10	n=10
Enamel	untreated	30 s	200 mj	350 mj	500 mj
(Group A)	(A1)	(A2)	(A3)	(A4)	(A5)
Dentin	untreated	15 s	200 mj	300 mj	400 mj
(Group B)	(B1)	(B2)	(B3)	(B4)	(B5)

100 lithia-based all ceramic specimens (Empress 2) (R: 4 mm, h: 4 mm) were prepared and luted to dental substrates according to the manufacturer's instructions and shear bond strength tests were performed with a Shimadzu universal testing machine (cross-head speed:0.5 mm/min) followed by the SEM evaluations of the dental surfaces. Results: SEM evaluations revealed different surface morphologies depending on the laser parameters. The shear-bond test results were statistically evaluated (ANOVA, p<0.05 in all groups). The mean shear bond strength values (MPa) are given in Charts 1 and 2.

Chart 1                                                                         Chart 2

Conclusions: The highest bond strength was obtained in acid-etched groups both in enamel and dentin. The mean shear-bond strength values decreased as the laser power increased.

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