Table 5. Application Protocols for Each Adhesive.

sample group	application technique following the respective manufacturer’s instructions
OV	apply Optibond Versa primer for 20 s, gently air-dry for 5 s, then apply Optibond Versa adhesive for 20 s, air-thin for 15 s, light-cure for 10 s
TNBU	apply Tetric N Bond Universal for 20 s, air-thin for 15 s, light-cure for 10 s
SBU	etch with 35% phosphoric acid for 15 s, rinse, and air-dry to produce a frosty appearance of enamel; then, apply Single Bond Universal for 20 s, air-thin for 15 s, light-cure for 10 s
CUBQ	etched enamel with 35% phosphoric acid for 15 s, rinse, and air-dry to produce a frosty appearance of enamel; then, apply Clearfil Universal Bond Quick for 20 s, air-thin for 15 s, light-cure for 10 s