**3.2 SEM (Scanning Electronic Microscopy)**

SEM revealed the fractured surface between the composite resin and dentin side, as shown in Figure 2. The representative SEM evaluation showed that thick layers of the adhesives were found on the fractured de-bonded surface of the composite resin (Figure 2-B, D, F). On the other hand, the fractured bonded surface of the dentin by the Clearfil SE bond adhesive treatment, as a result of the shear bond strength test followed by 37% phosphoric acid etching of some of the residues of the adhesives remaining on the surface of dentin side after the shear bond test (Figure 2-A, C, E).

Regarding the failure mode of the control group in the types of adhesive system, some residual chips were found (A) on the surface of dentin side fractured after 37% phosphoric acid etching and single bond adhesion but the fractured bonded surface of dentin by the Clearfil SE bond adhesive treatment as a result of the shear bond strength test followed by 37% phosphoric acid etching showed thick layers of composite resin attached to the dentin after the failure test (D).

In the irradiation groups, 1.4 W of irradiation followed by the Single bond procedure left the fractured dentin surface with small particles after the failure test (B). On the other hand, the fractured dentin surface irradiated with a power intensity of 2.25 W had exposed dentinal tubules after the test (C). On the other hand, 1.4 W of power intensity irradiation followed by the SE bond procedure revealed exposed dentinal tubules after the failure test (E), whereas 2.25 W of power intensity irradiation followed by the SE bond procedure resulted in a thick layer of composite resin fractured cohesively on the dentin side of the fractured surface (F).

Effect of the Er, Cr: YSGG Laser Parameters on

capability to minimize additional damage.

**4. Discussion** 

be considered.

Shear Bond Strength and Microstructure on Human Dentin Surface 353

Recently, Er:YAG and Cr:YSGG lasers were introduced in dentistry. For physical and medical reasons, they are used for the treatment of hard tissue. The advantage of an Erbium wave is that it is well absorbed by water and dental hard tissue. Although dentin contains a high proportion of water, the depth is shallow for laser transmission. The strong absorption of water reduces the level of heat during tooth preparation. As water absorbs laser radiation better than dental hard tissue, it reduces the increasing temperature of the tissue during the preparation. Water reaches the boiling point and causes microexposure of the tooth. This action breaks up the surrounding tissue into small pieces and dissipates them at the same time. As this explosion occurs in water, it is so-called a preparation induced by water. Although most radiation is absorbed in water, a certain amount of heat transmission is unavoidable. Therefore, a water spray is used for cooling. The proper amount of water spray prevents pulpal damage. As heat transmission normally depends on the pulse shape and pulse maintenance time, the amount of water varies according to the laser system and

In contrast to initial studies, there was no immunological difference between the laser system and conventional etching method. Moreover, the positive effect of the laser to regenerate pulp was discussed. Essentially, cavity preparation should be performed with the proper instruments with the "method of minimal pulse energy" according to the manufacturer's protocol. This is because the preparation should be performed with the

The bond strength of the adhesive system is one of the major factors for the success of restorations. Therefore, this restoration parameter can be measured accurately by the bonding test. The bonding of resin composite material to the tooth structure prepared with different types of lasers has been reported (Visuri et al., 1996; Armengol et al., 1999; Martínez-Insua et al., 2000; Carrieri et al., 2007; Ekworapoj et al., 2007; Lee et al., 2007; de Carvalho et al., 2008; Gurgan et al., 2008; Chou et al., 2009). These studies reported variable results comparing the bond strengths of composite resin to a laser-prepared and acid etched dentin surface, and suggested that the laser preparation is more effective than etching in bonding strength of the composite resin to the tooth structure (Obeidi et al., 2010; Turkmen et al., 2010; Navimipour et al., 2011). This study compared the in vitro SBS of two different adhesive systems to dentin treated with an Er,Cr:YSGG laser. These results showed that the type of adhesive system had no effect on SBS, whereas the laser intensity was a criterion to

Generally, the manufacturer of Er,Cr:YSGG lasers recommended 2.25 to 2.5 W for laser etching but other studies used 2 to 3 W referring from their results of a pilot study to obtain the proper effects (Çalşkan et al., 2010). The data from this study showed that the shear bond strength (SBS) of dentin treated with 1.4 W, was higher than that of SBS with 2.25 W, which was recommended by the manufacturer. These results were different from other study results showing that the shear bond strength of laser etching (1.25 W or 3 W) was higher than the diamond bur (Gurgan et al., 2008). The distance between the laser tip and laser irradiated dentin surface may not be strict in this kinds of study designs. On the other hand, in this experiment, the sweeping motion of the laser irradiation 6 mm away from the dentin surface was used before the application of adhesive procedures to employ consistent defocused irradiation with lower intensity. Therefore, the difference in the effect between

treatment itself. A lack of enough water spray causes pulpal damage.

Fig. 2. SEM images (X1000) showing the fractured surface between the composite resin and dentin side. The fractured bonded surface of dentin by the single bond adhesive treatment as a result of the shear bond strength test followed by 37% phosphoric acid etching (A), and 1.4 W of power intensity irradiation followed by a Single bond procedure (B), and 2.25 W of power intensity irradiation followed by a Single bond procedure (C) were evaluated by SEM. The fractured bonded surface of the dentin by Clearfil SE bond adhesive treatment as a result of the shear bond strength test followed by 37% phosphoric acid etching (D), and 1.4 W of power intensity irradiation followed by the SE bond procedure (E), and 2.25 W of power intensity irradiation followed by the SE bond procedure (F) were evaluated by SEM.
