Variable Smear Layer and Adhesive Application: The Pursuit of Clinical Relevance in Bond Strength Testing

• Main Authors: Abu Faem Mohammad Almas Chowdhury, Rafiqul Islam, Arefin Alam, Mariko Matsumoto, Monica Yamauti, Ricardo Marins Carvalho, Hidehiko Sano
• Format: Article
• Language: English
• Published: MDPI AG 2019-10-01
• Series: International Journal of Molecular Sciences
• Subjects: adhesion; dental bonding; smear layer; dentin-bonding agents; self-etch adhesive; universal adhesive; application mode; double application; bond strength; transmission electron microscopy
• Online Access: https://www.mdpi.com/1422-0067/20/21/5381

The removal or modification of smear layers that cover the dentin is critical to allow the penetration of adhesive molecules and to ensure a strong bond between resin and dentin. Aiming to establish a model for clinically-relevant dentin-bond testing, we evaluated the effects of smear layers created by abrasives having similar coarseness (180-grit SiC paper; fine-grit diamond bur) and application modes (single application; double application) on the microtensile bond strengths (&#181;TBS) of two currently available universal adhesives (G-Premio Bond; Scotchbond Universal Adhesive) and a two-step self-etch adhesive (Clearfil Megabond 2). Sixty extracted human third molars were used for the &#956;TBS test. Data were analyzed by three-way ANOVA and Tukey&#8217;s test (<i>&#945;</i> = 0.05). Fracture modes were determined using stereomicroscopy. An additional 24 third molars were prepared for observation of the resin&#8722;dentin interface by TEM and adhesive-smear layer interaction by SEM. &#956;TBS was significantly affected by the adhesives and their application modes (<i>p</i> &lt; 0.001), implying that the double application of universal adhesives should be recommended to improve their performance. The effect of smear layers was not significant (<i>p</i> &gt; 0.05), indicating that 180-grit SiC papers could be used to prepare dentin as a substitute for fine-grit diamond burs for dentin-bond testing in laboratory settings.