Enamel acts as a protective outer layer for the whole tooth, extending even below the gum line.
When demineralization occurs, often because of acids in the mouth or harsh brushing, the enamel is weakened.
When demineralization isn't addressed early on, the enamel will progressively wear away, exposing the highly sensitive inner part of the tooth, known as dentin. Unfortunately, this process is irreversible and the enamel cannot be restored.
Once this happens, heat, cold, acidic, sweet, or spicy foods can travel through tiny channels through the dentin to the nerves inside the tooth, which can cause sharp pain.
Sensitivity can also be a consequence of gum recession, whereby the gum tissue pulls back, leaving the root of the tooth (where the dentin is only protected by a thin layer of enamel) exposed to all sorts of stimuli, which may cause pain.