Six to seven months is the average age for a first tooth to emerge, although the timing varies widely from baby to baby. Largely determined by heredity, some families show first teeth as early as four months, while others get first teeth as late as a year or beyond. Once teeth do emerge, however, they do so in a predictable sequence.
The bottom two middle teeth, or incisors, emerge first (they tend to come in pairs). Next, about two months later, are the top middle two incisors, followed by one more on either side of those middle top two. This means, roughly, that most babies celebrate their first birthday with six teethfour on top, two on the bottom. A month or so later, two more bottom incisors show, then the process skips over to the first set of molars, then back to a set of canines. The second (and last) set of molars completes the set, at between 20 and 30 months. Their job is then to last through the years of early childhood, while the mouth grows. Shedding of these 'baby teeth' starts at six to seven years, again, with remarkable variability between children, but in about the same order in which they came.