The Rav has an extensive teshuva on oral hygiene. The short answer - continue as regular, No change of any sort necessary.
In regards to the melacha of smoothing, there is a popular misconception of what it entails. Put simply, view the prohibition as plastering a hole in a wall. A layer of plaster is applied, and then the laborer “smooths” it so that the end result is a nice patched plaster wall. (same concept as spackling sheetrock) My point is, there is no way that applying toothpaste or brushing teeth can ever be similar to smoothing in the above scenario we described. Additionally applying a thick cream on a baby’s bottom for diaper rash (assuming that there is a permissible medicine angle) can also be done in a prohibited manner by smoothing a nice even layer, or totally permissible by just applying in a haphazard way that no smoothing is done. Hope that helps.