Anatomical Landmarks in Order to Study an Individual Tooth Intelligently, We Must Be Able to Recognize All Landmarks of Importance by Name

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Anatomical Landmarks In order to study an individual tooth intelligently, we must be able to recognize all landmarks of importance by name. These include:

1. Cusp: It is an elevation on the crown portion of a tooth making up a divisional part of the occlusal surface. Cusps are present in the posterior teeth and the canines. •• Canine teeth have a single cusp; they are often called as the cuspids. •• Premolars generally have two cusps with an exception of the mandibular 2nd premolar which frequently has three cusps. Premolars are therefore also called as the bicuspids.

•• Maxillary and mandibular 1st molars have five cusps, while other molars generally have four cusps. Each cusp is a gothic pyramid with four sides formed by four ridges that run down from the cusp tip: •• Mesial and distal cusp ridges (cusp slopes) •• Buccal/lingual cusp ridge •• Triangular ridge of the cusp. There are two cusp slopes on either side of the triangular ridge. In case of canines, there is a labial ridge analogous to the buccal ridge posterior teeth; there is a lingual ridge analogous to triangular ridge of posterior teeth. In the Table below the Number of cusps in different types of teeth: Tooth type Maxillary arch Mandibular arch Incisors 0 0 Canines 1 1 Premolars 2 2 in 1st premolar 3 or 2 in 2nd premolar Molars 1st molar 4 +1 accessory cusp 5 (cusp of Carabelli) 2nd molar 4 4 3rd molar 4 or 3 4 or 5 A cusp is named according to its location on the tooth. For example, on a two- cusped premolar, the two cusps are named after the surface adjacent to each cusp: buccal or lingual. On a four-cusped molar, the four cusps are named after the adjacent line angles: mesiobuccal, distobuccal, mesiolingual, and distolingual.

2. Tubercle: It is a smaller elevation on some portion of the crown produced by an extra formation of enamel. These are deviations from the typical form.

3. Cingulum: It is found on the lingual aspect of an anterior tooth. It is a convex mount of enamel localized to the cervical one-third of the crown. It is either a U- or W-shaped ridge at the base of the lingual surface of the crown of the upper incisors and cuspid teeth, the lateral limbs running for a short distance along the linguoproximal line angles, the central portion just above the gingiva.

4. Ridge: It is any linear elevation on the surface of a tooth and is named according to its location (e.g., buccal ridge, incisal ridge, marginal ridge).

(a) Marginal ridges: These are a linear, rounded borders of the enamel that form the mesial and distal margins of the anterior teeth (incisors and canines) as viewed from the lingual aspect, and the mesial and distal borders of occlusal surfaces on posterior teeth (premolars and molars).

(b) Triangular ridges: The occlusal surface of a cusp is composed of a mesial and a distal incline. These two inclines meet to form a triangular ridge of enamel that descends from the tip of the cusp to the central portion of the occlusal surface. A triangular ridge is either a facial or a lingual cusp ridge, depending on where the cusp is located. They are named after the cusps to which they belong, e.g., the triangular ridge of the buccal cusp of the maxillary first premolar.

(c) Transverse ridge: It is the union of two triangular ridges (buccal and lingual) that crosses the surface of a posterior tooth transversely (roughly 90 degrees to both the buccal and lingual tooth surfaces).

(d) Oblique ridge: An oblique ridge consists of a union between the triangular ridge of the distobuccal cusp and the distal cusp ridge of the mesiolingual cusp.The only tooth on which an oblique ridge is found is the maxillary molar.

5. Fossa: It is an irregular depression or concavity. (a) Lingual fossa: It is an irregular, rounded concavity bound by the mesial marginal ridge, distal marginal ridge, cingulum, and incisal edge of the lingual surface of an incisor tooth. Lingual fossae are also found on both sides of the lingual ridge of a cuspid tooth. It is located on the lingual surface of anterior teeth.

(b) Central fossa: It is a centrally located depression or concavity found on the occlusal surface of molars and mandibular second premolars. The other bicuspids have mesial and distal triangular fossae, but do not have a central fossa. It is located on the occlusal surface of molars.

(c) Triangular fossa: It is located adjacent to marginal ridges on the occlusal surfaces of posterior teeth. There are two kinds of triangular fossae, a mesial and a distal, so It is located on the occlusal surfaces of molars and premolars, mesial or distal to marginal ridges.

6. Sulcus: It is a long depression or valley in the surface of a tooth between ridges and cusps, the inclines of which meet at an angle. A sulcus has a developmental groove at the junction of its inclines. As an example, a central sulcus is a major linear depression that traverses the occlusal surface of a posterior tooth from mesial triangular fossa to distal triangular fossa. Developmental grooves are found in the bottoms of sulci.

7. Developmental groove: It is a shallow groove or line between the primary parts of the crown or root. A developmental groove is the junction line between the inclined walls of a sulcus. These grooves appear on labial, occlusal, buccal, and lingual surfaces, and are least apparent on the labial aspect of anteriors.

8. Supplemental groove: A minor, auxiliary, less distinct, shallow linear depression on the surface of a tooth, but is supplemental to a developmental groove and does not mark the junction of primary parts.

9. Fissure: A linear fault that sometimes occurs in a developmental groove. A fissure represents a lack of union between the inclined walls of a sulcus.

10. Pit: It is a small pinpoint depression located at the junction of developmental grooves or at terminals of those grooves, e.g., central pit is a term used to describe a landmark in the central fossa of molars where developmental grooves join.

11. Mamelon: It is small, rounded projections of enamel from the incisal edges of newly erupted anterior teeth. The projections wear away soon after eruption.

12. Lobe: It is one of the primary anatomical sections or divisions of a crown of formation in the development of the crown. Cusps and mamelons are representative of lobes. All teeth develop from either four or five lobes (for example, a central incisor forms from four lobes while first molars develop from five lobes.) Lobes are usually separated by readily identifiable developmental grooves.

13. Embrasure area: V-shaped valleys or spaces between adjacent teeth and named according to its position, example: gingival embrasure, incisal embrasure, labial, lingual embrasure.

Crown outline and occlusal table: When viewing posterior teeth from the occlusal view, it is important to distinguish the crown outline of an entire tooth from the occlusal table of that tooth. The crown outline is the outer outline of the entire tooth crown from the occlusal view, whereas the occlusal table is the outline of the smaller occlusal surface that is bounded by adjoining mesial and distal cusp ridges and marginal ridges that surround it.