**2. Materials and methods**

#### **2.1 Tooth preparation**

Tables 1 and 2 list the materials used in this study and the study design, respectively. Twenty four freshly extracted caries and restoration-free permanent human molars stored in distilled water were used. The teeth were embedded in improved stone with the occlusal surface of the crown exposed and parallel to the base of the stone, and the embedded teeth were sectioned at one third of the occlusal surfaces to expose the dentin surface. Each tooth was wet-ground with 320-grit silicon carbide paper and polished with 1200-grit to obtain a flat dentin surface. The specimens were stored in distilled water at 37 °C. The teeth were divided randomly into two groups, control and laser irradiated groups. The control groups without laser irradiation were divided randomly into two subgroups (SE bond and Single bond), and the laser irradiated groups were divided into four subgroups (SE bond with 1.4 W, 2.25 W and Single bond with 1.4W, 2.25W).

#### **2.2 Laser irradiation**

The Er,Cr:YSGG laser (Waterlase, BioLase Technology, Inc., San Clemente, CA) with a 2780 nm wavelength and 20 Hz of power with a sapphire tip was used. Laser irradiation was performed on the dentin surface with either 1.4 W or 2.25 W. The flattened dentin surfaces of the teeth were irradiated at 90° in non-contact mode with a fixed distance of 6 mm away from the laser tip in a sweeping motion to achieve an even surface coverage by overlapping the laser impact. The laser handpiece was attached to a modified surveyor to ensure a consistent energy density, spot size, distance and handpiece angle.

#### **2.3 Bonding procedures**

In all groups, including laser irradiated groups and control groups, the bonding procedures recommended by the manufacturer' instruction were followed strictly. In the single bond

depends on the hybridization of the resin within the exposed collagen mesh as well as to the dentin tubules (Abdalla & Davidson, 1998), creating a micromechanical interlocking of the resin within the exposed collagen fibril scaffold. The second is the "self-etch" adhesives (SEA) which employs acidic monomers that simultaneously condition and prime dentin. The smear layer remains partially but is used to hybridize with the underlying dentin (Perdigao et al., 2000). The last is an all-in-one system, but the stability of the bond strength

According to previous reports, a tiny flake surface formed by the laser irradiation of dentin can be removed with 30-40 % acid etching, but the primer of SEA cannot. This study hypothesized that the primer of SEA cannot improve the free surface energy of irradiated dentin. Therefore, it is unable to make a proper environment for sufficient bond strength. The null hypothesis was that the shear bond strength with "self-etch" adhesives (SEA) did not show a difference from that with the etch-and-rinse (ER) technique after a pretreatment

This study examined the shear bond strength of a hybrid composite resin bonded with two different adhesive systems to the dentin surfaces prepared with Er,Cr:YSGG laser etching, and evaluated the morphologic structure of de-bonded dentin surface after Shear Bond

Tables 1 and 2 list the materials used in this study and the study design, respectively. Twenty four freshly extracted caries and restoration-free permanent human molars stored in distilled water were used. The teeth were embedded in improved stone with the occlusal surface of the crown exposed and parallel to the base of the stone, and the embedded teeth were sectioned at one third of the occlusal surfaces to expose the dentin surface. Each tooth was wet-ground with 320-grit silicon carbide paper and polished with 1200-grit to obtain a flat dentin surface. The specimens were stored in distilled water at 37 °C. The teeth were divided randomly into two groups, control and laser irradiated groups. The control groups without laser irradiation were divided randomly into two subgroups (SE bond and Single bond), and the laser irradiated groups were divided into four subgroups (SE bond with 1.4

The Er,Cr:YSGG laser (Waterlase, BioLase Technology, Inc., San Clemente, CA) with a 2780 nm wavelength and 20 Hz of power with a sapphire tip was used. Laser irradiation was performed on the dentin surface with either 1.4 W or 2.25 W. The flattened dentin surfaces of the teeth were irradiated at 90° in non-contact mode with a fixed distance of 6 mm away from the laser tip in a sweeping motion to achieve an even surface coverage by overlapping the laser impact. The laser handpiece was attached to a modified surveyor to ensure a

In all groups, including laser irradiated groups and control groups, the bonding procedures recommended by the manufacturer' instruction were followed strictly. In the single bond

decreases with time by because it contains many hydrophilic monomers.

Strength (SBS) Test by scanning electron microscopy.

W, 2.25 W and Single bond with 1.4W, 2.25W).

consistent energy density, spot size, distance and handpiece angle.

with a laser in dentin.

**2. Materials and methods** 

**2.1 Tooth preparation** 

**2.2 Laser irradiation** 

**2.3 Bonding procedures** 

adhesive system, etching procedures were conducted using 37 % phosphoric acid (3M ESPE, St. Paul, MN, USA) for 15 seconds followed by rinsing with a water spray for 15 seconds, and blot dried, and bonded and light curing for 15 seconds. In the Clearfil SE bond system, a primer was applied to the dentin surface for 10 seconds followed by bonding and light curing, as shown table 1.

After light curing the bonding resin, a Teflon tube (GI tech, Seoul, Korea) with an inner diameter of 2 mm and a height of 2 mm was attached to each dentin surface and filled with A3 Body Shade of the hybrid composite Resin (Filtek Supreme Plus 3 M ESPE, MN, USA) followed by light curing for 40 s. After light curing, the teeth were stored in water at 37°C for 24h before the Shear Bond Strength (SBS) Test.


Table 1. Materials used in this study.


Table 2. Classification of the experimental groups.
