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Portrait of Molar

Anatomy · Head, neck & teeth

Molar

The large grinding teeth at the back of the mouth

Dentition · back teeth

The large, flat-topped teeth at the back of the dental arch, used for grinding food. An adult has twelve, three in each quadrant, including the wisdom teeth; a child has eight milk molars, which are later replaced not by molars but by premolars. The upper ones usually have three roots and the lower ones two, and their broad crowns carry several cusps separated by fissures.

How to spot them

  • ▸Broad crown with four or five rounded cusps and a grooved chewing surface
  • ▸Upper molars have three roots, lower molars two
  • ▸Three in each quadrant: first, second and third (the wisdom tooth)
  • ▸The 'six-year' first molar is the first permanent tooth to appear

What to know

Latin for a millstone, it names the broad, cusped teeth that crush and grind food

The molars — from Latin mola, millstone

Twelve in the adult, none of which replaces a milk tooth, because each grows in behind the existing set

Permanent molars are accessional teeth: they have no milk predecessors

The first of them erupts at about six years behind the last milk tooth, without replacing anything, and is easily mistaken for a milk tooth

The first permanent molar — the 'six-year molar'

In the milk set there are eight, each later replaced by a smaller tooth with two cusps

Milk molars are replaced by premolars; children have no premolars, dental formula 2.1.0.2

FDI numbers 18, 28, 38 and 48; Universal numbers 1, 16, 17 and 32

The third molars, or wisdom teeth

A small extra cusp on the tongue side of the upper first tooth, named after a Hungarian-Austrian dentist

The cusp of Carabelli (Georg Carabelli)

Erupting between about 17 and 25 years, these often lack room and become impacted, and in a fifth or more of people some fail to form at all

Wisdom teeth (third molars), the commonest teeth to be removed

Key ideas

  • Molars grind rather than cut. Their occlusal tables of cusps and fissures work like a mortar and pestle, and in humans the lower molars usually have five cusps and the upper four.
  • Premolars, not molars, replace the milk molars. A child has 20 teeth (2.1.0.2), an adult 32 (2.1.2.3); the three permanent molars are additions at the back.

Quick-fire facts

  • •Twelve permanent molars: first, second and third in each quadrant; eight milk molars, first and second in each quadrant
  • •Adult dental formula 2.1.2.3 (incisors, canines, premolars, molars); milk set 2.1.0.2, 20 teeth
  • •FDI numbers: molars are 6, 7 and 8 in each quadrant (16, 17, 18; 26, 27, 28; 36, 37, 38; 46, 47, 48)
  • •Universal numbers: upper right molars 1–3, upper left 14–16, lower left 17–19, lower right 30–32
  • •First permanent molars erupt at about 6, second at about 12 (the 'twelve-year molar') and third at about 17–25
  • •Upper molars have three roots (two buccal, one palatal); lower molars have two (mesial and distal)
  • •Wisdom teeth are Latin dens sapientiae; failure of one or more to form (agenesis) occurs in roughly a quarter of people
  • •Molars have the largest crowns and greatest chewing surface of any teeth

Drill it — 7 cards

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Sources