11.4. Tooth Types

Incisor

Each quadrant of the mouth presents a central and a lateral incisor, both in the primary and in the permanent dentition. Their function is shearing or cutting food during biting. Both have a single root and a sharp, straight incisal edge as opposed to round cusps.

The maxillary central incisors are usually the most visible teeth, because they are centered and anterior to the mandibular incisors. The crown of the permanent maxillary central incisor is the widest (mesiodistally) of the anterior teeth and it is wider than it is tall. It is also less convex than the lateral incisor on its labial surface.

Maxillary central incisors are larger than their mandibular counterparts. This is the most contrasting size difference between teeth in equivalent positions of the two arches. It provides a strong indication as to which arch a dental cast represents.

Canine (cuspid)

There is a single canine in each quadrant of the primary and of the permanent dentitions. Both maxillary and mandibular canines are the third tooth of the quadrant and separate the premolars from the incisors. Their location and function is intermediate between those of the incisors and premolars. The most common action of human canines is tearing food. There is a single root and cusp on canines. The maxillary canine is the longest tooth in the mouth from root to incisal edge.

Premolar (bicuspid)

Each quadrant of the permanent set has 2 premolars that are found distal to the canines and mesial to molars. The first premolar is mesial to the second premolar. There are no deciduous premolars. Instead, the teeth that precede the permanent premolars are the two deciduous molars. The maxillary premolars have two cusps and two roots. Mandibular first premolars have two cusps and one root, which sometimes may be bifurcated. The buccal cusp is well developed but the lingual cusp is small and not active in chewing, making the tooth resemble a small canine. The second mandibular premolar has three cusps. It has a large buccal cusp and two well-developed lingual cusps, which make this tooth resemble a first molar. A less common two-cusp morphology can also be found, with similar crown dimensions but lack of separation into two lingual cusps.

Molar

Molars are the most posterior teeth in the mouth and the last ones to complete their eruption. Each quadrant has two molars in the primary set and three molars in the permanent set. One or several third molars (wisdom teeth) are commonly missing in modern humans.

The function of molars is to crush and grind food. The number of cusps varies among the different molars and between people. There are great differences between deciduous and permanent molars, even though their functions are the same. Permanent molars are not preceded by deciduous teeth, because the primary molars are followed by permanent premolars.

Deciduous molar

Smaller than permanent molars in all aspects, deciduous molars are the largest of the primary teeth. They have three to five cusps. They may also have a Cusp of Carabelli, which is most common on the second maxillary molar. Maxillary molars have three roots whereas mandibular ones have two roots.

Permanent maxillary molar

The maxillary first molar has the largest occlusal surface, followed by the second and the third molars. The first molar usually has four cusps: two buccal and two palatal. In many cases there is also a fifth cusp, called the Cusp of Carabelli, located on the mesiolingual aspect of the tooth. The second and third molar usually have four cusps: two buccal and two palatal. Maxillary molars have three roots: two buccal and one lingual.

Mandibular first molar

The mandibular first molar is the reference for occlusion (see chapter 17 Dental Alignment). There are usually five well-developed cusps: two buccal, two lingual and one distal. Second molars most commonly have four cusps: two buccal and two lingual. Mandibular molars most frequently have two roots: mesial and distal.

Summary

The permanent incisors in humans are flat teeth with a sharp and broad occlusal edge which makes them optimal for cutting (bites). Central and upper incisors are larger than lateral and lower ones. Canines have a pointy teeth but are short and flattened in humans, mostly aiding the incisors as opposed to containing prey or serving for aggression. Premolars (bicuspids) have two to three cusps and serve for cutting and crushing. Molars have four or five cusps and serve for crushing. Incisors and canines have a single root whereas premolars can have two and molars have two or three.

Key terms

Incisor, canine, premolar, bicuspid, molar, wisdom tooth.

Figure credits

Figure 1 by Ανώνυμος Βικιπαιδιστής - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=47356140

Figure 2 by Ανώνυμος Βικιπαιδιστής - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=47821427

Figure 3 by Ανώνυμος Βικιπαιδιστής - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=47363779

Figure 4 by Ανώνυμος Βικιπαιδιστής - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=48080867

Figure 5 by Ανώνυμος Βικιπαιδιστής - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=47364234