the enamel protects the underlying dentin, which is VERY <span style = 'background-color: #dae8f4'>sensitive</span>
. by the <span style = 'background-color: #dae8f4'>gumline</span>
, the enamel is very thin, and does not extend under the gumline
moe than a millimeter, if that. when you brush too hard, for a time, one of two things (or both) can happen--the tissue recedes, and/or the enamel gets worn away. either way, yo're left with a VERY sensitive
area on the tooth
. there are products/treatments for this, but you need to see a dentist. I'd try something called "super seal" first.