Will I be in pain after the periodontal treatment? Will I be able to eat normally?

You should not expect any pain after the conservative treatment of periodontitis (scaling and root planing). In rare cases, some people have mentioned a mild pain in the scaled gums that passes very easily with a simple painkiller like acetaminophen. As far as food is concerned, you can pretty much eat everything, but you should wait first till the anesthesia wears out, so as not to bite your lips and tongue by mistake. What you should expect though after scaling and root planing is increased root sensitivity, specially when you  eat or drink cold stuff. This root sensitivity is not permanent and will gradually disappear after maybe some weeks. Your periodontist might prescribe some gel treatment for your teeth after the night toothbrushing. These gels have fluoride in large percentage. Fluoride helps  make the roots of teeth stronger against feelings of cold.

For the patients that have had surgical perio treatment, the expected intolerance is more. But the anti-inflammatory medication that the periodontist has prescribed are usually enough to deal with issues of pain. You should avoid eating anything for at least a couple of hours after surgery. The food should be soft and not warm, specially the first few days after the surgery. Specific instructions (most of the times in written) will be given to any individual that will have a surgical periodontal treatment.