M.G.
I have a reaction whenever I am in contact with latex - so maybe they used latex gloves or that dam they put across had it in it? You can get hive and swelling (redness too). A hive can be a bump, etc. If I get contact dermatitis (I get it from some trees like cedars) I get little bumps that look like fluid filled blisters. You can Google.
I would just call the dentist office. Talk to them. They don't have to use those gloves next time too - they'll make a note in his chart.