11.1. External anatomy

Crown, neck and root

The crown is the part between the neck of the tooth and the opposing tooth. The crown is completely covered in enamel. The neck is the constricted region that contains the junction between enamel and cementum. The root is the region between the neck of the tooth and the apex of the tooth. The root is covered in cementum.

The crown can be further specified as “anatomical crown” meaning the part covered in enamel or “clinical crown” meaning the part that is visible in the mouth. While they usually correspond to the same, they may differ, for example, when a receded gingiva exposes part of the root of the tooth.

Cusp

A cusp is an elevation on an occlusal surface of posterior teeth and canines. It contributes to a significant portion of the tooth's surface. Canines have one cusp. Maxillary premolars and the mandibular first premolars usually have two cusps. Mandibular second premolars frequently have three cusps: one buccal and two lingual. Maxillary molars have two buccal cusps and two lingual cusps. A fifth cusp that may form on the maxillary first molar is known as the cusp of Carabelli. Mandibular molars may have five or four cusps.

Cingulum

A cingulum is a convexity on the cervical third of the lingual surface of anterior teeth. It is frequently identifiable as an inverted V-shaped ridge, and its appearance is comparable to a girdle. All anterior teeth are formed from four developmental lobes. Three are located on the facial side of the tooth, and one on the lingual side. The cingulum forms from this lingual developmental lobe. On lower incisors, the cingulum usually is poorly developed or absent. Maxillary canines have a large, well-developed cingulum, whereas the cingulum of mandibular canines is smoother and rounded.

Mamelon

Mamelons are usually seen as three small bumps on the incisal edges of newly erupted anterior teeth. They are the remnants of the three labial developmental lobes that form the tooth (the fourth lobe forms the cingulum). Mamelons are mostly visible soon after the eruption of the tooth. Their tips are soon eroded giving place to a straight incisal edge. The presence of mamelons in adults is an indication of misalignment problems that prevent the tooth from being used and worn normally.

Ridge

Ridges are any linear, flat elevations on teeth, and they are named according to their location. The buccal ridge runs cervico-occlusally in approximately the center of the buccal surface of premolars. The labial ridge is one that runs cervico-incisally in approximately the center of the labial surface of canines. The lingual ridge extends from the cingulum to the cusp tip on the lingual surface of most canines. The cervical ridge runs mesiodistally on the cervical third of the buccal surface of the crown. These are found on all primary teeth but only on the permanent molars.

Cusp ridges are ridges that radiate from cusp tips. There are two marginal ridges, mesial and distal, present on all teeth. On anterior teeth, they are located on the mesial and distal borders of the lingual surface; on posterior teeth, they are located on the mesial and distal borders of the occlusal surface. Triangular ridges are those that project from the cusp tips of premolar and molars to the central groove. Transverse ridges are formed by the union of two triangular ridges on posterior teeth. The joining of buccal and lingual triangular ridges is usually named as an example. The oblique ridge is found on the occlusal surfaces of maxillary molars. It is formed by the union of the distal cusp ridge of the mesiolingual cusp and the triangular ridge of the distobuccal cusp. The oblique ridges usually forms the distal boundary of the central fossa.

Groove

Groves are elongated depressions on the surface of the tooth. They are most numerous on posterior teeth and less marked in anterior teeth. Groves that mark the separation between the developmental lobes that formed the tooth are called developmental grooves.

Embrasure

Due to the rounded shapes of teeth, V-shaped spaces form around their points of contact. These spaces are occlusal, cervical, vestibular or lingual to the contact between teeth. They provide a spill way for food to escape during chewing. This prevents food from being forced between teeth, which could result in periodontal pain. The cervical embrasures are normally occupied by the gums, but they can become exposed as large open spaces when the gums recede.

Summary

Human teeth have a crown, neck and root. Cusps project from the crown. They are separated by grooves and pits and can be connected by ridges. A cingulum is a very reduced cusp in the oral surfaces of anterior teeth. When newly erupted these teeth also exhibit three mamelons each. Embrasures are the triangular spaces between two neighboring teeth and the gingiva.

Key terms

dental crown, dental neck, dental root, cusp, cusp of Carabelli, cingulum, developmental groove, embrasure, mamelon, periodontium.

Figure credits

Figure 1 by Marcos Gridi-Papp, modified from By Ανώνυμος Βικιπαιδιστής - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=47364234

Figure 2 by Pechenkina at English Wikipedia - Made it myself, Public Domain, https://commons.wikimedia.org/w/index.php?curid=18430320

Figure 3 by No machine-readable author provided. Dozenist assumed (based on copyright claims). - No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=853529

Figure 4 by Marcos Gridi-Papp - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=63697499 TribbleAlso see my personal gallery at Google Photos - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9470100