بررسي تاثير سرعتهاي متفاوت cross- head بر استحكام اتصال برشي دو نوع سيستم اتصال دهنده عاجي نسل چهارم (Scotchbond Multi- Purpose) و نسل پنج (Single Bond)

The effects of different cross-head speeds on shear bond strength of two dentin bonding systems belong to fourth generation (Scotchbond Multi-Purpose) and fifth generation (Single Bond)

Background & Aim: The bond strength of restorative materials to dentin plays an important role in their clinical longevity. However since clinical trials are time consuming and costly and owing to rapid progressive in adhesive bonding systems, itʹs essential to find a simple, rapid and standard method to evaluate the bond strength of bonding agents in laboratory tests. The purpose of this study is to evaluate the effect of different cross-head speeds on shear bond strength of two dentin bonding systems belong to fourth generation (Scotchbond Multi-Purpose) and fifth generation (Single Bond) and classify the failure modes (adhesive, cohesive or mixed). Methods & Materials: The buccal surfaces of 80 intact premolars were ground by a wheel shape diamond to the tip of the buccal cusps until the dentin is exposed. Then the buccal surfaces were flattened by paper discs with air and water spray. Finally, all samples were etched by 35% phosphoric acid. Afterwards the etched samples were divided into two 40 groups. Scotchbond Multi-Purpose was used for the first group and Single Bond for the second one. Then the Z100 composite was connected to the samples by 3><5 mm plastic molds. Each 40 group was divided by four 10 batches. Afterwards, the shear bond strength of each batch was determined by Dartec machine at four different cross-head speeds (0.5, 1, 2&5mm/min). After this step, the failure mode of the specimens was determined with stereomicroscope (56x). The quantitative variables were analysed with one way ANOVA and Duncan test and the qualitative variables were analysed with chi - square and fisher tests.Results: Statistical analysis showed that in Scotchbond Multi-Purpose group there were no significant differences between mean shear bond strength and failure mode of the samples that were tested by cross-head speed of (0.5 & lmm/min) & (2&5 mm/min), (P>0.05), but significant differences were observed (P<0.001) between batches that were tested by cross-head speed of (0.5 & 2 mm/min), (0.5 & 5 mm/min), (1&2 mm/min) & (1&5 mm/min). In the Single Bond groups there were no significant differences between mean shear bond strength and failure mode of various batches that were tested in difference cross-head speed (P>0.05). Conclusion: Evaluation of shear bond strength and failure mode of dentin bonding systems showed that they depend on the different cross-head speeds. However, the cross-head speed less than lmm/min makes adhesive failures. Therefore itʹs preferable for shear bond strength tests.