Tooth numbering: reading numbers 11 to 85, tooth 6 and how many teeth we have

How does FDI tooth numbering work?

The FDI tooth numbering system, adopted by the FDI World Dental Federation and described in ISO 3950:2016, assigns two digits to each tooth. The first identifies the quadrant of the dental arch and the second the tooth’s position within it, counting from the midline, the point between the central incisors.

Sides are always described from the patient’s perspective, not the dentist’s: quadrant 1 is the upper right, 2 the upper left, 3 the lower left and 4 the lower right. When you look at a dental chart as though facing the patient, their right side is on your left.

You therefore read 16 as quadrant 1, tooth 6, the upper right first molar, rather than as the number sixteen. The radiology reference Radiopaedia gives the examples of tooth 21, the permanent upper left central incisor, and tooth 82, the lower right lateral milk incisor.

• Quadrant 1 for permanent teeth and 5 for milk teeth: the right side of the upper jaw, or upper arch.
• Quadrants 2 and 6: the left side of the upper jaw.
• Quadrants 3 and 7: the left side of the lower jaw, or lower arch.
• Quadrants 4 and 8: the right side of the lower jaw.

Permanent tooth numbering: which teeth are 6, 7 and 8?

In permanent teeth, the second digit runs from 1 to 8: the incisors are 1 and 2, the canine 3, the premolars 4 and 5, and the molars 6, 7 and 8. This explains the everyday Polish names for teeth: ones, twos, threes, fours and fives, followed by sixes, sevens and eights, the last being wisdom teeth.

Tooth 6 is the first permanent molar, which, according to the American Dental Association (ADA), erupts between the ages of 6 and 7, behind the last milk tooth. There are only five milk teeth in each quadrant, so teeth 6, 7 and 8 have no milk predecessors; the article on losing milk teeth explains the changeover.

The table gives the numbers of all permanent teeth and their typical eruption ages according to the ADA chart. These are approximate ranges: the ADA states that all 32 permanent teeth are usually present by age 21, while some people never develop wisdom teeth.

Milk tooth numbering: what do numbers 51 to 85 mean?

Milk teeth follow the same principle, but quadrants are numbered 5 to 8 in the same order: 5 is upper right, 6 upper left, 7 lower left and 8 lower right. The second digit only runs from 1 to 5 because each quadrant contains five milk teeth.

There are no premolars in the milk dentition, so positions 4 and 5 are occupied by the first and second milk molars. Tooth 55 is the upper right second milk molar; after it falls out, permanent tooth 15, the second premolar, erupts in its place.

The table links milk tooth numbers to eruption and shedding ages according to the ADA charts. The first milk teeth usually appear at around 6 months; the article on teething explains the symptoms and sequence.

How many teeth do humans have?

Humans have two sets of teeth during their lifetime: 20 milk teeth and 32 permanent teeth. According to the ADA, milk teeth begin to erupt at around 6 months, and all permanent teeth are usually present in the mouth by age 21.

Radiopaedia states that an adult has 8 teeth in each quadrant: 2 incisors, 1 canine, 2 premolars and 3 molars. A child has 5 milk teeth: 2 incisors, 1 canine and 2 molars. This is why digits 4 and 5 refer to milk molars in children but premolars in adults.

A full set of 32 teeth is not universal. A 2015 meta-analysis (Carter and Worthington) covering 92 studies and 63 314 people found that, worldwide, an average of 22.63% of people lack the tooth germ of at least one wisdom tooth; this is more common in women and in the upper jaw than the lower jaw.

An adult with all other teeth present who never developed any of the four wisdom teeth, or had all four removed, therefore has 28 teeth, 7 in each quadrant. Missing wisdom teeth do not change the numbering of the remaining teeth: a sixth tooth always remains a sixth tooth.

How is a tooth built?

Every tooth consists of a crown, the part visible in the mouth, and a root set in the bone. According to Radiopaedia, the crown consists of dentine covered with enamel, the root is covered with cementum, and inside the tooth are the pulp chamber and root canal containing pulp, through which nerves and blood vessels run.

Enamel is the hardest tissue in the human body, but contains no living cells. The ADA stresses that this means enamel cannot repair damage caused by decay or wear itself, so the body cannot replace lost enamel.

The list sets out the tissues of the tooth and its surroundings from the surface inwards, using definitions from the ADA glossary.

• Enamel: hard, calcified tissue covering the dentine in the crown of the tooth.
• Dentine: tissue beneath the enamel in the crown and beneath the cementum in the root.
• Pulp: soft tissue inside the tooth containing nerves, blood vessels and connective tissue.
• Cementum: hard connective tissue covering the root, to which the periodontal ligament attaches.
• Periodontal ligament: a system of collagen fibres connecting the tooth root to its socket in the bone.
• Gum: soft tissue that covers and protects tooth roots and teeth that have not yet erupted.

How many roots and canals do teeth with different numbers have?

The number of roots depends on the tooth group. According to Radiopaedia, incisors and canines have one root, as do premolars, except for the upper first premolar, tooth 14 or 24, which usually has two. Molars have two or three roots, sometimes fused.

A single root can contain more than one canal. The upper sixth tooth, 16 or 26, is the most common surprise. In a review covering 8 399 teeth (Cleghorn et al., 2006), an additional MB2 canal in one root of the upper first molar occurred in 56.8% of cases; the dentist establishes the final number of canals during treatment, as explained in the article on root canal treatment costs.

The tooth number also matters for NFZ, Poland’s National Health Fund. The Minister of Health’s regulation defining NFZ dental benefits provides root canal treatment for adults only for teeth 1 to 3, the incisors and canines, and for all teeth in children and young people up to 18 and in pregnant and postpartum women (legal status as of 24 October 2026).

Why does tooth 3 in US records mean the sixth tooth?

The United States uses a different notation, the ADA Universal Numbering System, in which permanent teeth are numbered 1 to 32. According to Radiopaedia, they are counted clockwise when looking into the patient’s open mouth: from the upper right wisdom tooth (1), via the upper left wisdom tooth (16) and lower left wisdom tooth (17), to the lower right wisdom tooth (32).

The same tooth therefore has a different number in each system: tooth 3 in US records is tooth 16 in FDI notation, and tooth 19 is tooth 36. Milk teeth are labelled A to T in the Universal system, with A denoting the upper right second milk molar, FDI tooth 55.

If you bring X-rays or treatment records from abroad, check which numbering system was used. The same notation may identify a completely different tooth: tooth 14 in US notation is the upper left sixth tooth (26), but in FDI notation it is the upper right first premolar.

How it works at DentalBlue

At DentalBlue, the clinic’s own radiology unit takes the images needed to assess teeth: intraoral X-rays, panoramic X-rays and CBCT scans. For a first visit without symptoms, “Wizyta bez bólu” (visit without pain) includes a panoramic X-ray, consultation, examination and written treatment plan; this item costs 300 zł in the clinic’s price list. The dentist determines the final scope and cost of treatment at the consultation, and prices may change. If you see a tooth number in your treatment plan, you can ask the dentist to point it out on the X-ray.