Post-operative sensitivity is caused by incorrect bonding techniques, but has become less significant with the introduction of Self-Etch adhesives, which are less technique sensitive than the traditional Etch-and-Rinse adhesives.
Sensitivity can be caused by:
Over etching dentin (with Phosphoric Acid)
Under priming of dentin
Over aggressively air thinning the adhesive, with excessive air pressure
In addition, the application of a calcium silicate liner on deep dentin can eliminate post-operative sensitivity due to its ability to seal dentin & act as a thermal insulator.
Finally, the addition of a Glutaraldehyde-containing desensitizing agent can also decrease post-operative sensitivity.