No significant effect of the main factor Smear Layer Thickness was observed on the mean gap ( p>0.05). The means and standard deviations of the mean gap width are shown in Tables 2 and 3, respectively. ![]() The thickness of the thin and thick smear layer were 1.6 ± 0.6 and 3.2 ± 0.7, respectively. The mean hybrid layer thickness of the individual tooth was then calculated. This measurement was performed in 3 regions: left, center and right ( Figure 1). Resin-dentin interfaces, visualized in a scanning electron microscope (LEO 435 VP, LEO Electron Microscopy Ltd, Cambridge, UK), were saved, and the hybrid layer thickness in each stick was measured with the Software UTHSCSA Image Tool. The specimens were ultrasonically cleaned, partially demineralized with HCl 6N (60 seconds) and deproteinized with NaOCl 5% (20 minutes), rinsed, air-dried, mounted on stubs and gold sputtered (MED 010, Balzers Union, Balzers, Liechtenstein). After the epoxy resin setting, the thickness of the embedded specimens was approximately half reduced by grinding with silicon carbide papers under running water and by polishing with 1000-grit SiC paper and 6, 3, 1 and 0.25 μm diamond paste (Buehler Ltd). The bonded sticks were prepared according to the HMDS drying technique ( Perdigão & others, 1995) and embedded in PVC tubes with an epoxy resin (Buehler Ltd, Lake Bluff, IL, USA). Then, each hemi-section was sliced into bonded sticks. The hemi-sections were bonded according to Table 1. Some studies reported low resin-dentin bond strengths over thick dentin smear layers ( Koibuchi, Yasuda & Nakabayashi, 2001 Miyasaka & Nakabayashi, 1999 Ogata & others, 2001), while others reported no influence of smear layer thickness on resin-dentin bond strengths ( Tay & Pashley, 2001 Tani & Finger, 2002 Kenshima & others, 2005). Studies addressing this matter have not reached any conclusion regarding the performance of self-etch systems applied to varied smear layer thicknesses. Thick smear layers might affect the ability of self-etch systems to penetrate through intact, mineralized dentin, since early neutralization of the adhesive by dentin buffering components, presented in the smear layer ( Oliveira & others, 2003), might hamper superficial demineralization of solid dentin, which is required for collagen exposure. A negative and strong correlation between IGW and HLT was observed for the self-etching adhesive systems tested (r=80.2, p=0.01)Ĭontroversial results regarding bond strength values of self-etch systems, which may partly be explained by their application on smear layers with varying thicknesses and coarseness ( Tay & others, 2000 Tani & Finger, 2002 Oliveira & others, 2003 Kenshima & others, 2005), have been reported. The thickest hybrid layers were observed for the 2 etch & rinse adhesive systems and the thinnest for the mild self-etch. The hybrid layer was thicker when bonded to #60 SiC-treated dentin however, this difference was only statistically different for the 3-step etch & rinse system ( p=0.001). The self-etch systems showed wider initial IGW, which diminished after 6 months water storage, to sizes similar to the etch & rinse systems. Their IGW remained unchanged after 6 months. The etch & rinse systems showed the lowest mean IGW in the 1-day group. Results: The thickness of the smear layer did not influence the mean gap width ( p>0.05). SEM micrographs were also made in order to measure the HLT provided by each adhesive. ![]() The IGW was measured in a stereomicroscope under 400x. After 24-hour storage in water, resin-dentin bonded sticks (0.8 mm 2) were prepared and divided for 1-day and 6-month measurements. A resin composite (Z250) build-up was made on each tooth section after randomized application of the adhesives. Dentin surfaces with thick and thin smear layers were obtained for each tooth after polishing different sections on 60- and 600-grit SiC paper, respectively. ![]() After flat grinding of the occlusal surfaces, 30 molars were sectioned longitudinally in 2 halves. Methods and Materials: Three self-etch adhesives, a mild (Clearfil SE Bond SE), a moderate (Optibond Solo Plus Self-Etch Primer SO) and a strong (Tyrian Self Priming Etchant + One Step Plus TY), and 2 etch & rinse systems (Single Bond SB and Scotchbond Multi-Purpose Plus SBMP) were studied. Purpose: This study measured: 1) the interfacial dentin gap formation (IGW) of 2 etch & rinse and 3 self-etch systems with different degrees of acidity and determined the correlation between the smear layer thickness and interfacial gap formation after 1 day and 6 months water storage 2) the hybrid layer thickness (HLT) produced by the adhesives applied under different smear layer thicknesses.
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