As the primary teeth get ready to erupt into the mouth, the gums get hard, red and swollen. This process, called "teething," can also cause discomfort, excessive drooling, runny noses and overall crankiness. However, each child may exhibit some differences, so there is an average range within which tooth eruption occurs.

The two lower front teeth (deciduous central incisors) are typically the first to arrive when the child is six to eight months old. There will be periodic eruption of the rest of the primary teeth, usually in pairs, on both sides of the jaws. By the time the child is two years old, all of the deciduous teeth should be visible. Eventually, the primary teeth will become loose and fall out or be removed easily. Their permanent counterparts should replace all of the primary teeth. It is important, however, to maintain a child's primary teeth. They are necessary for chewing food properly, speech, and physical appearance. If a primary tooth decays and abscesses, it could damage the developing bud of the permanent tooth underneath. Also, premature loss of a back (posterior) primary tooth could reduce the amount of space necessary for its permanent replacement. In the primary dentition, large spaces between the teeth are normal.