Magnifier light

After the SBS test, each surface on both zirconia and metal bracket was observed under a light microscope (magnification×20, Magnifier Light, AS ONE, Osaka, Japan). The ARI was determined based on the presence of cement remaining on the zirconia, and the optimal images were recorded by a dental digital camera (EyeSpecial C-IV, Shofu, Koyoto, Japan ) (Fig. 3). The score is represented by a scale with five levels, ranging from 1 to 5: score 1 (A): almost all cement left on the zirconia surface; score 2 (B): more than 90% of the cement left on the zirconia surface; score 3 (C): more than 10% but less than 90% of the cement left on the zirconia surface; score 4 (D): less than 10% of the cement left on the zirconia surface; score 5 (E): no cement left on the zirconia surface. NS means no significant differences (p>0.05). The same capital letters indicate no significant differences in SBS for each row (p>0.05). The same number indicates no significant differences within each bracket at 24 h and thermocycling (p>0.05). To minimize deviations, all images were randomly selected and scored for ARI indices by three calibrated examiners. In case individual scores differed among the examiners, the majority score was chosen to be the final score.

Remaining dentin thickness (RDT) was measured according to the procedures described in previous studies 7, 9, 16) . It was the aggregate average of the vertical distances of all edge midpoints of tooth beams from dentin surface to pulp chamber, as measured using a digital micrometer (Absolute Digimatic, Mitutoyo, Kanagawa, Japan) with 10-μm accuracy. In addition, RDT of every face of the beams were observed by a glass magnifier (×20 magnification; Magnifier Light, Asone, Osaka, Japan).

Failure modes of the specimens were observed after μTBS test. Observation was carried out using the glass magnifier (×20 magnification; Magnifier Light, Asone, Osaka, Japan). Failure modes of specimens were classified into the following three categories: Type 1: Adhesive failure (fracture within adhesive layer); Type 2: Mixed failure (fracture within adhesive layer and cohesive failure within dentin and/or resin); Type 3: Cohesive failure (fracture within dentin or composite resin only).