**1. Introduction**

346 Biomaterials – Physics and Chemistry

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The developments of laser technology have enabled their use in multiple dental procedures, such as soft tissue operations, composite restorations, tooth bleaching, root canal irrigation, caries removal and tooth preparations with minimal pain and discomfort (Turkmen et al., 2010) Recently, the Er,Cr:YSGG laser was recommended for minimally invasive purposes due to its precise ablation of the enamel and dentin without side-effects to the pulp and surrounding tissues. It has a 2780-nm wavelength and absorbed strongly by both water and hydroxyapatite. The sudden evaporation of bound water causes micro-explosions that blast away tiny particles of the tooth (Obeidi et al., 2010).

Previous studies reported that irregularities and the crater-shaped appearance of ablated dentin was comparable to the dentine surface after acid etching, which might promote micromechanical interlocking between dental restorative materials and the tooth surface (Visuri et al., 1996; Armengol et al., 1999; Martínez-Insua et al., 2000; Carrieri et al., 2007; Gurgan et al., 2008). Despite its efficiency, reports on the bond strengths of composite resin to a tooth substrate prepared by a laser are often confusing and contradictory. Some studies reported higher bond strengths to laser-prepared dentin than to acid-etched dentin (Visuri et al., 1996; Carrieri et al., 2007). Others have reported significantly lower bond strengths on laser preparation (Armengol et al., 1999; Martínez-Insua da Silva Dominguez et al. 2000; Gurgan Kiremitci et al. 2008) and others have reported no significant differences (Abdalla & Davidson, 1998).

Generally there are three adhesive systems. The first uses 30–40% phosphoric acid to remove the smear layer (etch-and-rinse (ER) technique). This bonding mechanism to dentin

Effect of the Er, Cr: YSGG Laser Parameters on

for 24h before the Shear Bond Strength (SBS) Test.

Kuraray, Tokyo,

Japan

Single bond 3M ESPE, St. Paul MN, USA

Table 1. Materials used in this study.

Table 2. Classification of the experimental groups.

**2.4 Shear Bond Strength (SBS) test** 

Laser intensity

curing, as shown table 1.

Clearfil SE bond

Shear Bond Strength and Microstructure on Human Dentin Surface 349

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

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

Brand name Manufacturer Material type Composition Application

Self etching adhesive system

Etch and rinse adhesive system

Control (no laser) Group A Group D

1.4W Group B Group E

2.25W Group C Group F

Before loading, the tube mold was removed carefully with a sharp blade and the specimens were then placed in a custom-made fixture mounted on a Universal Testing Machine (INSTRON Model 5562, Norwood, MA). The specimens were loaded to failure under

procedure

Apply primer and leave 20 seconds, air blow, apply bonding system

Acid-etch for 15 seconds, rinse, apply adhesive, gentle air blow, light curing for 10 seconds.

Primer: MDP, HEMA, N,N-Diethanol ptoluidine, water Bonding resin: Bis-GMA, CQ, HEMA, MDP, Micro filler

Bis-GMA, HEMA, Water, UDMA, Ethanol,

Polyalkenoic acid copolymer

Adhesive system

Single bond SE 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 decreases with time by because it contains many hydrophilic monomers.

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 with a laser in dentin.

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 Strength (SBS) Test by scanning electron microscopy.
