RESULTS Results of shear bond strength test Table 2 shows the results of statistical analysis using two-way ANOVA test to describe the effect of both studied variables (adhesive system and surface pretreatment agent). Both adhesive systems and surface pretreatment agents had statistically significant effects on mean shear bond strength (P<.001 and P=0.041, respectively). The interaction between more info adhesive systems and surface pretreatment agents had a statistically significant effect on mean shear bond strength (P=0.049). Table 2. Descriptive statistics using two-way ANOVA for the adhesive systems and surface pretreatment agents. The results of Tukey��s test for the comparison between different interactions of adhesive systems with surface pretreatments are shown in Table 3.
Comparing the 3 adhesive systems when applied according to manufacturer instructions, the intermediary strong self-etch adhesive system (SE) showed statistically highest shear bond strength values followed by the strong self-etching adhesive system (APLP) while the mild self-etch adhesive system (FG) showed the statistically lowest shear bond strength values. With regard to the effect of the different surface pretreatments, it was revealed that different surface pretreatments did not statistically affect the mean shear bond strength values of the intermediary strong self-etching adhesive system (SE). PA pretreatment did not affect its bond strength values of the APLP system; on the other hand, EDTA significantly reduced its bond strength values.
However, PA pretreatment significantly increased the mean shear bond strength values of the mild self-etching adhesive system, which was not affected by EDTA pretreatment. Table 3. Means and standard deviation (SD) values of shear bond strength values (MPa) for the different surface pretreatment agents with each adhesive system. Results of failure mode analysis Each fractured surface was allocated to one of five types: Type 1, adhesive failure between the bonding resin and enamel; Type 2: partial adhesive failure between the bonding resin and enamel and partial cohesive failure of the bonding resin; Type 3: partial adhesive failure between the bonding resin and enamel and partial cohesive failure of the enamel; Type 4: 100% cohesive failure of the bonding resin; or Type 5: 100% cohesive failure of the enamel.
Figure 1 shows a bar chart of the percentage distribution of failure modes, while Figure 2 represents SEM photomicrographs for the different types of failure modes. Type 4 was not encountered in any group. Fractographic analysis of the fractured sites revealed that adhesive failure (Type 1) was the predominating failure type. Without additional surface pretreatment, only the intermediary strong self-etching adhesive system showed cohesive Brefeldin_A failure of the enamel (Type 5). Figure 1. Percentage distribution of failure modes of all tested groups. Figure 2.