Usually the sawdust sticks to the top side of the blade as you are sawing, because the sawdust riding on the blade is smushed onto the blade by the wheels it rides on. I explained way back on another thread about the mount we made to to use a small wire brush that rode against the blade and wiped it clean before the wheels mashed the dust onto the blade.
Yes, just a dab on the underside, mostly on the upper side because of the mashing from the wheels. I started experimenting by reaching through the sawhead and wiping stuff on the blade as it entered the cut, using a little rag wrapped around a paint stick.
You might be surprised at how well the wiper works.