To evaluate thin-film bond strength between a bonding agent and human dentin, using a scratch test, and the characteristics and accuracy of measurement.
One-step bonding agents (BeautiBond; Bond Force; Adper Easy Bond; Clearfil tri-S Bond) and two-step bonding agents (Cleafil SE Bond; FL-Bond II) were investigated in this study. Flat dentin surfaces were prepared for extracted human molars. The dentin surfaces were ground and bonding agents were applied and light cured. The thin-film bond strength test of the specimens was evaluated by the critical load at which the coated bonding agent failed and dentin appeared. The scratch mark sections were then observed under a scanning electron microscope. Indentation hardness was evaluated by the variation in depth under an applied load of 10 gf. Data were compared by one-way ANOVA with the Scheffé’s post hoc multiple comparison test ( p < 0.05). In addition, thin-film bond strength and indentation hardness were analyzed using analysis of correlation and covariance.
The thin-film bond strength of two-step bonding agents were found to be significantly higher than that of one-step bonding agents with small standard deviations. Scratch marks consistently showed adhesive failure in the vicinity of the bonding agent/dentin interface. The indentation hardness showed a trend that two-step bonding agents have greater hardness than one-step bonding agents. A moderately significant correlation ( r 2 = 0.31) was found between thin-film bond strength and indentation hardness.
Thin-film bond strength test is a valid and reliable means of evaluating bond strength in the vicinity of the adhesive interface and is more accurate than other methods currently in use. Further, the thin-film bond strength is influenced by the hardness of the cued bonding agent.
Many studies have been conducted to examine the bond strength of dentin bonding agents using shear and tensile bond strength tests by fracturing resin composite, bonding agent and tooth. However, the fracture patterns in these tests show more than one failure mode, such as adhesive failure between the bonding agent and dentin, cohesive failure within the dentin, cohesive failure within the resin composite, and mixed failure modes . Therefore, such bond strength tests do not solely reflect adhesive failure between the bonding agent and dentin.
In this study, the scratch test was used to evaluate the adhesive strength of bonding agents to human dentin. In the scratch test (thin-film bond strength test) an indenter is drawn across the coated surface under incremental and progressive loading to generate a scratch—damage or delamination. In industrial circles this test is used as a measure of adhesive strength . For example, for cutting tool coatings, such as TiC or TiN ; coating adherence for diamond-like carbon (DLC) protective coatings for computer hard discs; and evaluation of adhesion/cohesion bond strength of the plasma spray coatings . In dentistry, this test was reported for the evaluation of an adherent apatite coating on a titanium substrate , to investigate wear resistance and wear mechanisms of dental composite resins , and to determine the hardness and amount of chipping for dental ceramics . However, no reports have been found for adhesion evaluation, although mechanical properties were measured for bonding agents .
We previously reported that the thin-film bond strength test correlates with the tensile bond strength test . The thin-film bond strength of dentin bonding agents is characterized by a critical failure load. Therefore, the relationship between thin-film bond strength by the scratch test, and indentation hardness for bonding agents, was evaluated.
Materials and methods
Adhesive systems used in this study
As shown in Table 1 , four one-step and two two-step bonding agents were investigated in this study.
|Adhesive system||Manufacture||Type||Composition (Lot No.)||Direction|
|Beauti Bond (BB)||Shofu; Kyoto, Japan||One-step self-etching||Bis-GMA, TEGDMA, phosphonic acid monomer, carboxylic acid monomer, acetone, water (080802)||Apply adhesive and leave for 10 s, dry by blowing low-pressure air for 3 s and high-pressure air for 5 s, light cure for 10 s|
|Bond Force (BF)||Tokuyama Dental; Tokyo, Japan||One-step self-etching||Phosphoric acid monomer, Bis-GMA, TEGDMA, HEMA, water, ethanol, initiator (084)||Apply adhesive and leave for 20 s, dry by blowing low-pressure air for 5 s and high-pressure air for 5 s, light cure for 10 s|
|Adper Easy Bond (EB)||3M ESPE; Seefeld, Germany||One-step self-etching||Bis-GMA, HEMA, ethanol, water, methacrylated phosphoric esters, 1,6-hexanediol dimethacrylate, methacrylate functionalized polyalkenoid acid, silica filler, camphorquinone, stabilizer (352435)||Apply adhesive and leave for 20 s, air dry to a thin film, light cure for 10 s|
|Clearfil Tri S Bond (TB)||Kuraray Noritake Dental; Tokyo, Japan||One-step self-etching||MDP, Bis-GMA, HEMA, ethanol, water, initiators, microfiller (00112A)||Apply adhesive and leave for 20 s, dry by blowing high-pressure air for 5 s, light cure for more than 10 s|
|Clearfil SE Bond (SB)||Kuraray Noritake Dental; Tokyo, Japan||Two-step self-etching||Primer: MDP, HEMA, hydrophilic dimethacrylate, photoinitiator, water (01081A)
Bond: MDP, HEMA, hydrophilic dimethacrylate, Bis-GMA, microfiller (01615A)
|Apply primer for 20 s, gently air blow, apply the bond and light cure for 10 s|
|FL-Bond II (FB)||Shofu; Kyoto, Japan||Two-step self-etching||Primer: water, ethanol, carboxylic acid monomer, phosphoric acid monomer and initiator (040928)
Adhesive: S-PRG based on fluoroboroaluminosilicate glass, UDMA, TEGDMA, 2-HEMA, initiator (040941)
|Apply primer and leave for 10 s, dry by blowing, apply the bond light cure for 10 s|