Growing a tooth is not a single event but a complex biological process called odontogenesis that spans years, beginning long before a tooth becomes visible in the mouth. This long timeline involves the internal formation of the tooth structure, its mineralization, and the final movement, known as eruption, through the gums. Humans develop two distinct sets of teeth: the 20 primary (or baby) teeth and the 32 permanent teeth that succeed them.
The Beginning of Tooth Development
The development of the first set of teeth starts early, beginning around the sixth week of embryonic development. Permanent teeth begin their formation slightly later, around the 20th week of gestation. This process begins with the formation of thickened areas in the oral tissue, known as tooth buds, which are the earliest precursors for all future teeth. The internal development proceeds through several distinct morphological stages, including the bud, cap, and bell stages, where cells differentiate to form the specific tissues of the tooth.
During the bell stage, the crown of the tooth takes shape, and the hard tissues begin to form through mineralization. The outermost layer, enamel, and the inner layer, dentin, are created during this time, often starting around the third to fourth month of gestation for primary teeth. Root development begins only after the crown’s structure is fully formed. The tooth remains embedded in the jawbone for months or even years while this foundational work is completed.
The Timeline for Primary Teeth Eruption
The visible emergence of the primary dentition occurs between six months and three years of age. Children are born with all 20 of these teeth fully formed beneath the gums. The eruption follows a predictable sequence, usually starting with the lower central incisors. The upper central incisors follow soon after, creating the first four front teeth by the time a child is about a year old.
The remaining primary teeth erupt in the following general order, completing the full set of 20 teeth:
- Lateral incisors (9 to 16 months)
- First molars
- Canines (16 to 23 months)
- Second molars (23 to 33 months)
The Timeline for Permanent Teeth Eruption
The transition to 32 permanent teeth begins around age six and often continues into the early twenties. This period is known as the mixed dentition phase because the mouth contains both primary and permanent teeth simultaneously. The first permanent teeth to emerge are usually the first molars, which erupt at the back of the mouth without replacing any primary tooth. These are followed by the permanent lower central incisors, which push out the corresponding baby teeth.
The replacement sequence generally mimics the primary eruption pattern. This begins with the central and lateral incisors between the ages of six and nine. The canines and premolars, which replace the primary molars, erupt next, typically between 10 and 12 years old. By age 13, most children have all 28 of their non-wisdom permanent teeth in place. The final set of teeth, the wisdom teeth, have the most variable timeline, often not erupting until between 17 and 21 years of age, if they emerge at all.
Factors Influencing Tooth Development
The exact timing of tooth eruption is highly variable between individuals, with genetics being the dominant influence. Nutritional status also plays a measurable part, as the formation and mineralization of hard tissues require adequate levels of certain nutrients.
A deficiency in calcium or Vitamin D can hinder the proper calcification of the tooth structure and lead to delayed eruption. Systemic health conditions can also slow down the overall developmental chronology. Girls often experience tooth eruption slightly earlier than boys, and birth weight can also be a factor influencing the timing of the first primary tooth.