What is Bacterial Microleakage? I Have Occasional Sensitivity.

I occasionally have some sensitivity. Not to bite,or temp. ACT rinse and Sensodyne diminish it.Area: #1 veneer,#2 root canal with gold post and crown, #3 veneer. Perio said it was agressive brushing and exposed tooth roots and ACT/Sensodyne wiped out th sensitivity.Great. BUT: is there something more permanent that dentist can put on and someone mentioned 'bacterial microleakage" what is that? If ACT/Sensodyne wipes out the sensitivity I inclined to believe it is not bacterial. Right?