Contrasts: planned comparisons
When an experiment is designed to test a specific hypothesis that some treatments are different from other treatments, we can use contrasts to test for significant differences between these specific treatments.
Contrasts are more powerful than multiple comparisons because they are more specific. They are more able to pick up a significant difference.
You can use a t-test on the contrasts or calculate a t-confidence interval.
The results are valid regardless of the results of your multiple sample ANOVA test (you are still testing a valid hypothesis).