These differences enable teeth to work together to help you chew, speak and smile.
They also help give your face its shape and form.
At birth people usually have 20 baby (primary) teeth, which start to come in (erupt) at about 6 months of age.
They fall out (shed) at various times throughout childhood.
By age 21, all 32 of the permanent teeth have usually erupted.
Let's see the timeline of baby teeth coming in and falling out.
6-10 Months: Teething begins. Your baby's gums may be swollen and red where the teeth are coming through. The two middle teeth on the bottom (lower central incisors) are usually the first to erupt, often at about the same time.
8-12 Months: Upper middle teeth (the upper central incisors) emerge.
9-13 Months:Top teeth right next to the middle teeth (lateral incisors) appear, giving your baby a row of what look like four little Tic Tacs.
10-16 Months: The lateral incisors appear on the bottom. Now your baby can flash quite the toothy smile.
13-19 Months: Your child's first molars – the wider teeth toward the back of the mouth – erupt on the top. They won't have much to do until the ones on the bottom show up.
14-18 Months: The companion molars on the bottom emerge. Now your toddler can really do some serious chewing.
16-22 Months: Also called a cuspid, the upper canine fills the gap between the incisors and first molars.
17-23 Months: The lower cuspids appear.
23-31 Months: The second molars, or very back teeth, emerge on the bottom.
25-33 Months: The final teeth – the rear molars on the top – work their way in.
By age 3, most kids have a full set of 20 baby teeth and can give you a brilliant grin.
*Refer and quote above inforamtions from BabyCenter & MouthHealthy