How about UV exposure? Dentists already use compounds that *set* under UV.
Sure, why not? But in this specific application, isn’t most of the material shadowed by the crown? This suggests we want some kind of “unset” wavefront that will propagate through the bulk from a localized origin. That’d actually be a pretty fun material, whether or not it was also an adhesive in one of its states. Flipping between the set/unset states also preferrably needs to require relatively low-power. You do want to avoid setting it off accidentally. Sonic’s maybe not so good (because harmonics, which all non-linearities produce). Could you make a trigger/initiator nano-widget that requires a very specific “key”? (Perhaps some kind of DNA or other macromolecular sequence?) That would have all kinds of interesting applications (for various values of “interesting”!)