# Evaluation of the Bond Strength and Cytotoxicity of Alkasite Restorative Material
## 2 Materials and Methods
### \(\mu\)Tbs  
Ten permanent molars were obtained and stored in chloramine-T solution (0.5%) for 14 days, and then in distilled water at 4 \({}^{\circ}\)C until used (all were used within 90 days of extraction). Each was embedded in self-curing acrylic resin 2 mm below the cemento-enamel junction. Using a diamond saw at low speed and under running water, the occlusal surfaces were cut flat horizontally to obtain the mid-coronal dentin. The cut occlusal surfaces were then polished with a 600-grit sand disc for 15 s to obtain a smear layer, and then ultrasonic cleaning was performed for 5 min to remove debris. The exposed dentin surfaces were etched with 37% phosphoric acid (Total Etch; Ivoclar Vivadent, Schaan, Liechtenstein) for 15 s, followed by thorough rinsing with distilled water. The dentin surfaces were gently dried to remove visible moisture, but desiccation of the dentin was avoided. Using a micro-brush, a universal adhesive (i.e., Tetric N Bond Universal; Ivoclar Vivadent, Schaan, Liechtenstein) was then applied and rubbed onto the dentin surfaces for 20 s, air-dried until the adhesive solution showed no visible motion, and then light-cured for 20 s. The molars were randomly distributed between two groups (n = 5). Group I was restored with alkasite restorative material CN (Ivoclar Vivadent, Schaan, Liechtenstein) and Group II with a light-cured flowable BF-RBC (i.e., Tetric N-Flow Bulk Fill; Ivoclar Vivadent, Schaan, Liechtenstein). Each restorative material was used according to the manufacturer's instructions and applied in one layer (approximately 4 mm) to the dentin surfaces using a silicone mold (6 mm in diameter and 4 mm in height) to form restorative build-ups. Then, each was light-cured for 40 s using a light-curing unit (Bluephase(r), Ivoclar Vivadent, Schaan, Liechtenstein) at a light intensity of 900 mW/cm\({}^{2}\) as verified by a hand-held radiometer. The restorative build-ups were then light-cured for an additional 20 s after removal of the silicone mold. The bonded samples were stored in distilled water for 24 h at 37 \({}^{\circ}\)C, and then subjected to 5000 thermocyles in distilled water using a thermocycling machine (THE-1100, SD Mechatronik GmbH, Feldkirchen-Westerham, Germany). Each cycle consisted of a 30-s bath at 5 \({}^{\circ}\)C followed by a 5-s rest, then a 30-s bath at 55 \({}^{\circ}\)C followed by a 5-s rest. The bonded samples were then sectioned in the x-, y-, and z-directions across the adhesive interface into 1 x 1 mm (\(\pm\)0.2 mm) bonded beams (Figure 1). A digital caliber was used to measure the cross-sectional surface area of each bonded beam at the interface, and then each beam was attached to a metal jig and mounted on a universal testing machine. Tensile stress was applied at a cross-speed of 0.5 mm/min until failure. The tested beams were fixed onto coded brass stubs and gold sputtered before evaluating the failure modes using a scanning electron microscope (SEM) (JSM-6610 LV, JEOL Ltd., Tokyo, Japan) at 20 kV and different magnifications. The failure modes were categorized as follows: adhesive failure at the interface (A); cohesive failure in the restorative material (CR); cohesive failure in the dentin (CD); and mixed failure (M), which refers to a combination of adhesive and cohesive failures.  
Figure 1: Schematic illustration of micro-tensile bond strength (\(\mu\)TBS). (**a**) Sound molars, (**b**) applicationof the adhesive to the mid-coronal dentin, (**c**) restorative build-up with Cention N (CN) (group I) or bioactive bulk-fill resin-based composite (BF-RBC) (group II), (**d**) thermocycling, (**e**) sectioning of the bonded samples into beams, (**f**) \(\upmu\)TBS test, and (**g**) failure mode assessment.