Well, I would definitely NOT use Splenda. As a purchaser of tooth soap, I wouldn't buy one with Splenda in it. To me, you might as well put flouride in it if you use Splenda. It's considered pretty unhealthy, just as bad as aspartame, etc. Most purchasers of tooth soap will probably be health-concious, and would steer clear of it. If I were going to try to sweeten it somehow, I'd probably lean toward something like Xylitol. It's natural, safe, healthy, and is actually GOOD for your teeth. It helps prevent tooth decay. It comes from sources like fruit. Many chewing gums now prominently display the fact that they contain Xylitol. I have it in my cabinet and use it for sweetening some of our drinks. It's in white powder form and I get it from my health food coop. I don't know how it would react in soap, but I guess it's worth a shot, eh? I suppose you could use Stevia too. I use Stevia everyday in my morning cup of tea. Healthy, natural. If I were to choose, I'd probably go for Xylitol in a tooth product I was buying over Stevia, but either one would have label appeal for me. HTH! Your friendly consumer