K etchant syringe

Sixteen additional sound human third molars (1 per group) were prepared as described for the µTBS test. After the placement of a composite build-up, the specimens were sectioned into two slabs of 2 mm thickness using the precision saw and thermocycled like the µTBS beams. The inner surface of the slabs was then polished with wet SiC papers (600-grit, 800-grit, and 1000-grit) and a sequence diamond pastes with a decreasing particle size (6-µm, 3-µm, and 1-µm; DP-Paste P, Struers, Copenhagen, Denmark). The polished specimens were ultrasonically cleaned in distilled water, and their resin-dentin interface was treated with a 35% phosphoric acid gel for 10 s (K-Etchant Syringe, Kuraray Noritake Dental) and a 5% solution of sodium hypochlorite (Purelox, Oyalox, Tokyo, Japan) for 5 min 26, 27) . Both after demineralization with phosphoric acid and deproteinization with sodium hypochlorite, the specimens were rinsed with water for 10 s. Finally, they were left to dry at room temperature for 24 h, sputtercoated with gold and examined under SEM at 3,000× magnification.

The 2-SEA used in this study was Clearfil SE Bond 2 (SE2; Kuraray Noritake Dental, Tokyo, Japan). Two types of tooth etchants, Enamel Conditioner (EC; Shofu) and K-etchant syringe (KE; Kuraray Noritake Dental), were tested. The compositions of the etchants and adhesives are listed in Table 1. A previous study has reported the pH values of EC and KE as 0.63 and 0.21, respectively 12) . Caries-free human premolars and third molars were collected after informed consent was obtained according to a protocol approved by the Institutional Review Board of Tokyo Medical and Dental University (D2013-022). The teeth were stored at 4°C in a 0.1% thymol solution and used within 1 month of extraction. The buccal and lingual surfaces of the teeth were the prepared aspect surfaces. For the bur-cut specimens, enamel surfaces (0.5 mm depth) were prepared using a medium-grit (76 μm) diamond bur (F102R, Shofu) under copious air-water spray. For the uncut specimens, uncut enamel surfaces were cleansed without any pumice paste for 15 s using a dental brush (Merssage brush, Shofu) rotating at 500 rpm. mounted on a slow-speed handpiece. The cleaned enamel surfaces were then rinsed with deionized water for 5 s.