Cd 15c

Five CAD/CAM resin blocks (KATANA AVENCIA Block, Kuraray Noritake Dental) were sectioned with a low-speed diamond saw (Isomet, Buehler, Lake Bluff, IL, USA) to obtain forty slabs with a thickness of 1 mm. The surfaces of the slabs were finished with 600-grit silicon carbide paper under running water, and then airabraded using 50 μm aluminum powder (Heraeus Kulzer Japan, Tokyo, Japan) at 0.1 MPa with the air-abrasion tip perpendicularly positioned at 10 mm to the specimen surface for 10 s, then cleaned ultrasonically for 3 min in distilled water. Each sectioned slab was measured with a digital caliper (Mitutoyo CD-15C, Mitutoyo, Kanagawa, Japan) to ensure a final thickness of 1.00±0.05 mm.

The bonded specimens were kept in water at 37°C for 24 h. The top surface of the CAD/CAM resin slab was treated with 37% phosphoric acid (K-etchant) for 5 s, rinsed with water and air-dried. A silane coupling agent (Clearfil Ceramic Primer Plus, Kuraray Noritake Dental) was applied to the surface and gently air-dried. A bonding agent (Clearfil SE Bond, Kuraray Noritake Dental) was applied to the surface, gently air-dried, and light cured for 10 s. Then, a direct resin composite (Clearfil AP-X Shade A2, Kuraray Noritake Dental) was incrementally built up to a thickness approximately 2 mm high for the μTBS test. Each tooth was cross-sectioned longitudinally with a low-speed diamond saw (Isomet) to produce beam-shaped specimens with an approximate surface area of 1×1 mm 2 at the bonded interface. Before the μTBS test, the dimensions of each beam were determined with a digital caliper (Mitutoyo CD-15C). After this, each specimen was secured to a customized microtensile jig with a cyanoacrylate glue (Model Repair II Blue, Dentsply-Sankin, Tokyo, Japan) and placed in the testing apparatus (EZ-SX, Shimadzu, Kyoto, Japan) for the μTBS test at a 1 mm/min crosshead speed.

The specimens were cross-sectioned longitudinally with the low-speed diamond saw to produce 1.0×1.0 mm 2 beam-shaped sticks. Six beams were obtained from each specimen, adding up to forty-eight beams per group. Before MTBS testing, the dimensions of each beam were checked using a digital caliper (Mitutoyo CD-15C, Mitutoyo, Kanagawa, Japan) with a ±0.1 mm accuracy. Subsequently, a universal testing machine (EZ-SX, Shimadzu, Kyoto, Japan) was used to assess the MTBS at a crosshead speed of 1 mm/min after each specimen was fixed to a customized microtensile jig using cyanoacrylate adhesive (Model Repair II Blue, Dentsply-Sankin, Tokyo, Japan).