Figure 2. Fractographic analysis and SEM examination. (a) Percentages of areas assigned to the failure modes observed in test groups after tensile bond strength testing. A, Adhesive failure at the ceramic surface; C, cohesive failure in luting composite resins (Panavia F 2.0 or Panavia 21) or tube-filling composite resin. Mean (SD) percentages of adhesive failure after 3 days and 150 days are: (for PF 2.0) CAA (after airborne-particle abrasion, no contamination), 9% (2%), 9.4% (0.5%); AA (airborne-particle abrasion cleaning), 9% (1%), 87% (3%); HP (phosphoric acid cleaning), 87% (4%), 33% (6%); AC (acetone cleaning), 100% (0%), 100% (0%); and TW (tap water cleaning), 100% (0%), 100% (0%). For P21, the percentages were: for CAA, 2% (0%), 3% (0.2%); for AA, 1% (0%), 5% (1%); for HP, 6.5% (1%), 79% (2%); for AC, 100% (0%), 100% (0%); and for TW, 100% (0%), 100% (0%). (b) Low-magnification SEM micrograph showing representative mixed failure modes, mostly with cohesive failure in Groups CAA and AA. (c) High-magnification SEM micrograph of A in (b), showing adhesive failure at the zirconia ceramic surface. (d) C1 in (b), showing cohesive failure in composite resins (Panavia F 2.0 or Panavia 21). (e) C2 in (b), showing cohesive failure in tube-filling composite resin (Clearfil FII).