One who has fake teeth, bridges, crowns etc. in his mouth, should make sure to kasher them before Pesach, to make sure they are clean from any chometz. One should make sure to refrain from eating any hot chometz from 24 hours beforehand, then just before the deadline of eating chometz one should kasher them by pouring hot water on them from a keli rishon [hot water that was directly on the fire].
This year, one should do this on erev Shabbos, and one should refrain from eating any hot chometz 24 hours prior. Bedieved [post-facto] if one didn’t kasher them before Shabbos, R’ Shlomah Zalman Auerbach (Shu”t Minchas Shlomah, Vol. 2, end of siman 46) writes there is room to be lenient to kasher them even on Shabbos.
The Shaar HaTziyun (509:31) explains that those who forbid kashering on Shabbos maintain that doing so is tikkun moneh [equivalent to fixing a utensil], nonetheless, in our case, since at the time of kashering the fake teeth etc. are not yet forbidden, it is not an immediate tikkun moneh and is only a tikkun for later. Even the tikkun for later is only so that when the chometz eating deadline arrives there won’t be any mixture of chometz in the teeth, therefore, there is room to be lenient with koshering them on Shabbos. R’ Nissim Karelitz zt”l adds: Since strictly speaking there is not such a strong obligation to kasher these things, as the Maharsham and other poskim learn that we don’t eat food which gets to yad soiledes boi (a temperature which the hand recoils out) and since we don’t eat food that hot, belios aren’t absorbed in the fake teeth etc., therefore, koshering them is not really a tikkun. We have to say such a logic, otherwise anyone who has permanent fillings will be stuck, as fillings can’t just be taken out, therefore, we can rely on it to say that kashering fake teeth etc. is not considered a tikkun.
