I have not worn ear plugs, nor ear muffs at the dentist. Both will give you an occlusion effect, as the sound gets trapped inside, so neither is a good plan. The occlusion effect should be a little less pronounced theoretically as there is more space for the sound to dissipate to.
The better plan is to you a noise cancelling headphone that can cancel out the noise of the drill at the dentist. I think dentists should offer this to their patients more and have it available.
I went to the dentist a few months ago, and had a tooth filling with drilling, and my T did not spike. I think the drill was a quieter model.