Stages of Formation and Development of Teeth

How Tooth Development Begins Before Birth

Tooth development starts long before a child is born. Around the sixth week of intrauterine life, small thickenings of the lining of the mouth form the tooth buds, and from that point the foundations of the primary teeth are laid in the jaws. Each bud grows, folds into the outline of the future crown and then begins to lay down hard tissue. The groundwork for many permanent teeth is also laid during pregnancy, although their crowns mineralise much later.

At birth most babies have no visible tooth, yet the jaws already hold the developing crowns of the primary teeth. The period before the first tooth is therefore an active stage for oral health. The mother's diet during pregnancy and the child's diet in the first years supply the minerals that forming enamel needs, and gentle wiping of the gums can begin before any tooth appears.

The whole process runs from these first buds to young adulthood, when the roots of the third molars finish forming. Between those two points every tooth passes through the same sequence. The crown mineralises inside the bone, the tooth moves through bone and gum into the mouth, and the root keeps lengthening for several more years after the tooth has become visible. A tooth that looks complete in the mouth is often still growing below the gum line.

Because the sequence is long and each tooth follows its own timetable, a disturbance at one moment tends to leave its mark on the teeth that were forming at that time, while teeth that had already finished or had not yet started are spared. This is why a serious illness or a high dose of certain medicines in early childhood can affect the enamel of some permanent teeth and leave others untouched, and why dentists can sometimes estimate when such a disturbance happened from the position of the defect on the tooth.

When the First Baby Teeth Appear

The first primary tooth usually comes through in the second half of the first year. Some of the most detailed figures come from a Japanese birth cohort in which parents recorded eruption dates at home. Across 1,695 responses, the median age of eruption of the lower primary central incisors was 7.1 months in boys and 7.6 months in girls (PubMed 38002821). The upper central incisors followed at 8.7 months in boys and 9.2 months in girls (PubMed 38002821). The upper lateral incisors appeared at 10.0 and 10.3 months, and the lower lateral incisors at 10.4 and 10.8 months (PubMed 38002821).

These ages are earlier than those in charts built from dental check-ups. The difference follows from how eruption is recorded: a parent notices the first edge of a tooth on the day it breaks through, while a scheduled examination records it at the next visit. Published eruption tables can therefore disagree by several weeks without any of them being wrong. In the same cohort, preterm infants showed earlier eruption than term infants once their corrected age was used (PubMed 38002821).

After the incisors come the first primary molars, then the canines and finally the second primary molars. Twenty primary teeth, ten in each jaw, are usually complete by around two and a half to three years of age.

Variation between children is wide and often runs in families, so a child a few months behind a chart is usually not a cause for concern. The practical threshold is the twelfth month. If no tooth has come through by then, a dental examination is worthwhile to check the jaws and the developing teeth beneath the gum.

Teething Signs and When a Fever Is Something Else

Teething does produce signs that parents notice. A meta-analysis of 16 observational studies in children aged 0 to 36 months found signs or symptoms during primary tooth eruption in 70.5% of the pooled sample of 3,506 children (PubMed 26908659). Gingival irritation, irritability and drooling were the most frequent, at 86.81%, 68.19% and 55.72% respectively (PubMed 26908659). Parents also describe itching gums, a wish to chew on objects, a smaller appetite and disturbed sleep in the days around an erupting tooth.

Body temperature needs a separate note. The same meta-analysis found that eruption could lead to a rise in temperature, but the rise was not characterised as fever (PubMed 26908659). A real fever, diarrhoea that becomes severe, marked lethargy or a baby who refuses to drink should therefore not be put down to teeth. These signs need a medical assessment, because the months of teething overlap with the age at which infants catch their first infections, and blaming the tooth can delay the diagnosis of an ear, throat or stomach infection.

Simple comfort measures are enough for most children. A clean teething ring cooled in the refrigerator, gentle rubbing of the gum with a clean finger and wiping drool away from the chin to protect the skin all help. Hard objects that can break into pieces are kept away from the mouth. Once the first tooth is through, it is cleaned twice a day with a soft infant toothbrush, and the child's first dental visit can be planned around this time so that feeding and cleaning habits are set up early.

Permanent Teeth and the Mixed Dentition

Around the age of six the first permanent teeth appear. Usually these are the first permanent molars, which come through behind the last primary molars without replacing any baby tooth, so many parents do not realise they are permanent and need the same care as adult teeth. The lower central incisors are then replaced, followed by the other incisors, the canines, the premolars and the second molars. This exchange usually runs until twelve or thirteen years of age, and for several years the mouth holds primary and permanent teeth side by side, a stage called the mixed dentition.

The permanent set reaches 32 teeth when the third molars are counted. The third molars, known as wisdom teeth, emerge last, usually in late adolescence or early adulthood, and the timing varies widely between people. They do not erupt in everyone. Some never develop, and others stay impacted in the bone, where they can lead to infection and crowding pressure on the neighbouring teeth.

A prospective study followed permanent tooth emergence in 539 schoolchildren for 9 years, examining dental casts every year (PubMed 21426429). Emergence ages differed between boys and girls, but the difference was not statistically significant at the 5% level (PubMed 21426429). The finding with the clearest clinical use concerned decay: having decayed primary teeth hastened the emergence of most second premolars and second molars (PubMed 21426429). The authors concluded that caries in primary teeth can be a strong predictor of earlier emergence of permanent teeth (PubMed 21426429).

Nutrition, genetic factors and oral infections all shape this timetable, so a child who is ahead of or behind a chart is not automatically a concern. What matters more is the order of emergence, the space available in the arch and whether a permanent tooth appears on one side while its partner on the other side stays missing for a long time.

The Four Tissues That Make a Tooth

Tooth development is more than the moment a tooth appears in the mouth. Its internal structure forms in layers, and each layer has its own role.

Enamel is the outer layer of the crown and the hardest tissue in the body. It forms early, while the crown is still inside the jaw, and it is complete around the time the tooth erupts. Once formed, enamel contains no living cells, so a defect laid down during its formation stays in the tooth for life. How well enamel resists decay depends partly on how it was formed, and a shortage of vitamin D and calcium during that period can reduce its quality.

Dentin lies beneath the enamel and makes up the bulk of the tooth. It is softer than enamel and is crossed by microscopic tubules. When dentin is exposed by wear, decay or a receding gum, these tubules carry stimuli towards the nerve, which is why exposed dentin reacts to cold and heat.

The pulp sits in the centre of the tooth and contains nerves and blood vessels. It nourishes the tooth and gives it sensation, and in a young tooth it keeps adding dentin as the root matures. When deep decay reaches the pulp, inflammation and pain follow, and the tooth needs root canal treatment or, in a primary tooth, a pulp treatment suited to baby teeth.

The root and its connective tissues hold the tooth in the jaw. Cementum covers the root surface, and the periodontal ligament links that cementum to the surrounding bone. Root formation continues for several years after a permanent tooth has come into the mouth, which is one reason a young permanent tooth with an open root end is managed differently after an injury than a fully formed adult tooth.

What Disturbs Development and When to See a Dentist

Several groups of factors can change how teeth form and erupt. Genetics comes first: when missing teeth, crowding or late eruption run in a family, similar patterns are more likely in the child. Nutrition matters during pregnancy, when the mother's intake of calcium, phosphorus and vitamin D supplies the forming teeth, and in childhood, when frequent sugary and acidic foods attack enamel that has just erupted. Systemic conditions such as diabetes, thyroid disorders, kidney disease, hormonal problems and some genetic syndromes can affect development. A blow to a primary front tooth can damage the permanent tooth germ developing beneath it, and some antibiotics of the tetracycline group, taken during pregnancy or early childhood, can cause permanent discolouration of the teeth forming at that time.

The practical question for parents is when to book an examination. A child with no tooth by the twelfth month should be seen. Decayed primary teeth should be treated and kept where possible. They hold the space for the permanent successor and guide it into position, and an unnecessary extraction can leave that tooth without a path. An orthodontic evaluation in the early mixed dentition, once the first permanent molars and incisors are through, allows crowding, crossbites and jaw growth problems to be spotted while guiding appliances can still use the child's growth. In the late teens, an X-ray shows whether the wisdom teeth have room to erupt.

Regular check-ups, a balanced diet, twice-daily brushing from the first tooth onwards and early orthodontic monitoring give each stage of this long process good conditions to run smoothly.