On average, milk teeth start erupting at 6 months and complete their eruption at 30 months.
Permanent teeth erupt on average at the age of 6 years
The deciduous teeth are very important because they protect the space needed for the permanent teeth to avoid crowding and because they guide the permanent teeth as they erupt. For these reasons, they need to be protected until the time when they normally wobble and fall out, and treated if necessary.
Contrary to popular belief, milk teeth are very important. They are important for proper nutrition, aesthetics and phonation (correct sounding of letters when speaking) and normal development of the jawbone and muscles.