You will find the water only fast to be quite superior to the one you did initially.
Adding things beside water prevents the body from being able to go fully into fasting mode.
Fully in fasting mode is a very safe place to be. In other places the body can get into imbalances and be much more difficult to do than a water only fast.
Not sure about the teeth thing, but if you want to add some nutrients in that area to be sure you body has adequate, there is a product called "Natural Calm" which is available in many health food stores and at "Whole Foods" stores in the U.S. Its magnesium based and very absorbable.
It never hurts to go longer between fasts. That would ensure your body is well saturated nutritionally for the next one.
Plus the fact that your diet is getting better will make the next one easier when you do it.