Pain and teething medications should be used only the advice from your doctor or pediatrician. These dates are just a guideline. Teeth can come in much earlier or later. Teething time can be a family characteristic, or genetic. These dates are just a guideline.
Teeth can fall out earlier or later.
These little teeth need to be healthy for 6-12 years until the permanent teeth are in. This seems to be mostly a matter of opinion. Prolonged use of either of these, could possibly alter the teeth growth. Some say one is better than the other, but the parent and the child are the only only ones who can decide what is best for that child. Calcium is of course very important in the development and maintenance of teeth.