Oral and paraoral tissues comprise of oral mucous membrane, three pairs of major and innumerable minor salivary glands, jaw bones bearing deciduous and permanent sets of dentitions, maxillary sinus and temporomandibular joint. Teeth constitute approximately 20% of the surface area of mouth, the upper teeth significantly more than the lower teeth. A tooth consists of a crown which is exposed to oral cavity and single or multiple roots, lying in socket of jaw bones. The teeth are composed of following tissues (Fig. 1.1):
- Enamel: It is the hardest tissue in human body, covering the crown of the tooth. It is inert, acellular and formed from ectoderm. It is supported by underlying dentin.
- Dentin: It is less calcified, more resilient, vital, hard tissue forming the main bulk of the tooth. It is formed from and supported by the dental pulp. In crown portion, it is covered by the enamel and in the root portion it is covered by the cementum. The junction between enamel and dentin is known as dentinoenamel junction.
- Cementum: It is less mineralized tissue, covering the radicular portion of the tooth. The junction between enamel and cementum is known as cervical line or cementoenamel junction.
- Pulp: It is the soft, connective tissue in the central part of tooth enclosed by dentin. The pulp cavity in crown part is known as pulp chamber and in the root portion, it is known as pulp canal or root canal.
- Periodontium: The tissues (periodontal ligament, cementum, alveolar bone) which support the teeth in jaws are collectively termed periodontium. The tooth is anchored to the socket of bone by periodontal ligament. The part of jaw bone which supports the tooth is known as alveolar bone.
At birth normally, no teeth is visible in the oral cavity. In postnatal period, teeth of various sizes and shapes are found in the jaws. The human beings are known as diphyodont as human dentition consists of two sets of teeth —
- Primary, deciduous or milk dentition:
- Total 20 in number.
- 10 in each jaw.
- 5 in each quadrant.
- Start erupting in oral cavity at the age of six months.
- Continue to erupt upto two and half to three years.
- Secondary, permanent or succedaneous dentition:
- Total 32 in number.
- 16 in each jaw.
- 8 in each quadrant.
- Start erupting in oral cavity at the age of 6 years.
- 28 teeth erupt by the age of 13 years.
- Remaining 4 teeth appear between 18–25 years.
The dentition in human can be divided into three stages—
Stage of primary dentition:
- It lasts for about 6 months–6 years of age.
- Only deciduous teeth are present in this phase.
Stage of mixed dentition:
- It lasts from 6 years – 13 years of age.
- Both deciduous and permanent teeth are present in the oral cavity.
Stage of permanent dentition:
- It lasts from 13 years onwards.
- Only permanent teeth are present.
- The permanent teeth replace deciduous teeth except permanent molars, which do not have any deciduous predecessors.
- Maxillary or upper arch
- Mandibular or lower arch.
The arrangement of teeth is symmetrical in the right and left halves in each arch.
In both dentitions, there are three basic tooth forms—Incisiform, caniniform and molariform.
Incisors
- Two in each quadrant of jaws.
- They are flat, have cutting edges and are delicate.
Canines
- One in each quadrant of jaws.
- They have sharp pointed cusp and are strong.
- They are known as cuspids.
- They are meant for piercing or tearing.
8 incisors and 4 canines together are known as anterior teeth.
Premolars
- They are two in each quadrant.
- They replace deciduous molars.
- They generally have two cusps and are known as bicuspids.
- They are present only in permanent dentition.
Molars
- There are two deciduous molars and three permanent molars in each quadrant.
- The permanent molars do not have deciduous predecessors.
- They are large and strong.
- They have broad surface designed for grinding.
- They are situated farthest back in the mouth.
The 8 premolars and 12 molars together are known as posterior teeth.
The type of tooth is represented by its initial letter, i.e.
I | for incisors |
C | for canines |
P | for premolars |
M | for molars. |
The numbering of teeth are done starting anteriorly at the midline. The incisors closest to midline are called central incisors. The teeth next to the central incisors are known as lateral incisors and next tooth is canine. The premolars and molars are similarly called first and second premolars and first, second and third molars.
Functions of Teeth
- Help in mastication.[cutting of food by the incisors,tearing by the canines,chopping by the premolarsand grinding by the molars].
- Help in articulation and speech.
- Give a definite shape and beauty to the face. Vertical height of face is maintained by molars. Helps to maintain the personality of individual.
- May be used for self-protection.
- Growth and development of jaws are dependent on tooth.
Dental Formula
Dental formula is used in the clinic to simplify tooth identification. The permanent teeth in each quadrant are numbered 1–8 and the deciduous teeth in each quadrant are lettered A to E. The symbols for the quadrants are derived from an imaginary cross, with the horizontal bar placed between the upper and lower jaws and the vertical bar running between the upper and lower central incisors.
Sometimes, it is simplified to denote
There are different systems for recording different teeth. Few important systems are—
ZSIGMONDY'S METHOD (PALMER'S NOTATION)
- Oldest method.
- Used in most countries.
- Simple method.
- Has many potential sources of errors regarding noting sides.
For Permanent Teeth
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For Deciduous Teeth
A— | Central incisor |
B— | Lateral incisor |
C— | Canine |
D— | First molar |
E— | Second molar. |
UNIVERSAL SYSTEM
- Less liable to produce mistake.
- Needs more practice for quick and correct notation.
For Permanent Teeth
For Deciduous Teeth
FÉDÉRATION DENTAIRE INTERNATIONALE (FDI) APPROVED SYSTEM
- Two digit system, suitable for computer handling.
- The first number of the digit indicates the quadrant.
- The second digit indicates the individual tooth within the quadrant.
For Permanent Teeth
For Deciduous Teeth
Morphologically a tooth is divided into—
- Crown
- Root.
For the purpose of description it is customary to divide the crown and root into thirds (Figs 1.4A and B).
CROWN
- Occluso-gingivally:
- Incisal or occlusal third
- Middle third
- Cervical third.
- Facio-lingually:
- Facial third (labial or buccal)
- Middle third
- Lingual third.
ROOT
- Cervical third
- Middle third
- Apical third.
Surfaces of Tooth
The crown of each tooth presents five surfaces in case of premolars and molars and four surfaces and an incisal edge in case of anterior teeth.
The surfaces are—
- Facial (labial surface of anterior teeth and buccal for posterior teeth).
- Lingual (palatal)
- Occlusal
- Proximal
- Mesial— Surface facing midline
- Distal—Surface away from midline.
GLOSSARY
Angle
A line or a point where two or more surfaces or borders meet is called an angle.
Line Angle
The angle formed by meeting of two surfaces is called a line angle. The name of the angle is derived from both the surfaces, e.g. distolingual–angle formed by distal and lingual surfaces.
Point Angle
The point of junction of three surfaces is called a point angle. The name is derived from all three surfaces, e.g. mesiolinguoincisal angle formed at the junction of mesial and lingual surfaces and incisal edge.
Apex
The terminal end or tip of the root of a tooth is called an apex.
Apical
Towards the apex of a root.
Apical Foramen
It is the opening of the pulp canal at the apical end of the root of a tooth. At this region pulp is not surrounded by dentin.
Axial
It is pertaining to the longitudinal axis of the tooth.
Axial Surface
It is parallel to the long axis of tooth, e.g. labial, buccal, lingual, mesial, distal.
Axial Wall
It is any wall of the pulp chamber which is parallel to the long axis of the tooth. The line angles that are parallel to the long axis of the teeth are called axial angles, e.g. distobuccal and mesiolingual angles.
Axial Root Center
It is an imaginary line passing through the geometric center of a tooth root parallel to its long axis.
Buccal
It is related to cheek.
Buccal Surface
It is the surface of posterior tooth, facing the cheek.
Cementoenamel Junction
It is the junction on the surface of the tooth where enamel meets the cementum.
Cervix (Neck)
It is a narrow or constricted portion of a tooth in the region of the junction of crown and root.
Cervical Line
It is a curved line formed by the junction of enamel and cementum of a tooth.
Cingulum (Latin word for girdle)
It is a bulbous convexity on the cervical third of the lingual surface of an anterior tooth. It is the lingual lobe of an anterior tooth. Its convexity mesiodistally resembles a girdle encircling the lingual surface at the cervical third.
Contact Point
It is an area on the proximal surfaces of two adjacent teeth on the same arch that come in contact with each other. Every tooth has two contact points, one on mesial side and another on distal side except the third molars which have only one contact point in the mesial side.
Contact area of permanent teeth (Fig. 1.5).
Upper Arch
Name of the teeth | Location of contact area |
|---|---|
| Incisal third region |
| Incisal third region, but more apically placed than (a) |
| At the junction of the middle third and incisal third |
| Middle third of the crown |
| Above the junction of middle third and occlusal third |
| Middle third of the crown |
Lower Arch
Name of the teeth | Location of contact area |
|---|---|
| Incisal third region |
| Incisal third region |
| Incisal third region, more apically than (b) |
| Middle third |
| Middle third |
| Middle third, more apically than (d) and (e) |
Functions
- Contact areas keep the food away from being packed between teeth.
- They help to stabilize dental arches by the combined anchorage of all the teeth in contact with each other.
Contours
The diameter of the crown of any tooth gradually increases from occlusal or incisal surface to certain points from where it begins to decrease towards cervical line. This greatest area of circumference of the crown is known as the height of contour (Fig. 1.6). It protects the gingival tissues.
Crown
- Clinical crown: It is the part of the tooth which is visible in the oral cavity.
- Anatomical crown: It is the part of the tooth which is covered by enamel.
Crypt
It is the cavity in the alveolar bone that contains developing tooth germ.
Cusp
It is a pronounced elevation on the occlusal surface of a tooth terminating in a conical or rounded surface. It is having an independent center of calcification.
Dentition
It is the type, number and arrangement of the teeth.
Diastema
It is the space between two adjacent anterior teeth in the same arch.
Distal
Away from median line.
Distal Surface
The surface of tooth away from median line following the curve of the dental arch.
Embrasure
Embrasures or spillway spaces are the triangular-shaped spaces adjacent to the contact points of teeth. When two proximal teeth of the same arch come in contact with each other, their curvature adjacent to the contact areas form embrasures. Thus around each contact area there are 4 embrasures—Facial, lingual, interproximal and occlusal (Figs 1.7A and B). The embrasure are continuous and symmetrical. Correct interproximal embrasures result in proper arch alignment.
Functions
- The embrasures make a spillway for the escape of food during mastication.
- It also makes the tooth self-cleansing as the rounded smooth surfaces of the crowns are exposed to the cleansing action of foods and friction of cheeks and lips.
- The embrasures and contact points protect the gingival tissue from undue trauma.
Fissure
It is a cleft or crevice in a tooth surface due to imperfect fusion of the enamel of adjoining cusps or lobes.
Fossa
It is a rounded or angular depression on the surface of a tooth.
Lingual fossa
It is a broad, shallow depression on the lingual surface of an incisor or canine (Fig. 1.8A).
Central fossa
It is relatively broad, deep, angular depression in the central portion of the occlusal surface of a molar (Fig. 1.8B).
Triangular fossa
It is comparatively shallow pyramid-shaped depression on the occlusal surfaces of posterior teeth located within the confines of the mesial or distal marginal ridges and triangular ridges of adjacent cusps (Fig. 1.8C).
Groove
It is a shallow linear depression on the surface of a tooth (Fig. 1.9).
Developmental groove
It marks the boundaries between adjacent cusps and other divisional parts of a tooth.
Supplemental groove
It is an indistinct linear depression, irregular in extent and direction which does not demarcate major divisional portions of a tooth.
Inclined Plane
It is a sloping area on the occlusal surfaces of premolars and molars. Each cusp has two inclined planes (Fig. 1.10).
Lobe
It is one of the main morphological division of the crown of a tooth. It is one of the primary center of calcification. Cusps and mamelons are representatives of lobes.
Mamelons
These are rounded or conical prominences on the incisal ridge of a newly erupted incisor. They are 3 in number and are separated by 2 indistinct grooves extending from labial surface. They represent 3 lobes having a separate center of calcification. After eruption gradually the mamelons are flattened due to attrition (Fig. 1.11).
Median Line
It is an imaginary line dividing body into right and left equal halves.
Mesial
Toward the median line.
Mesial Surface
The surface of a tooth facing toward the median line following the curve of the dental arch.
Occlusion
Occlusion is defined as the relationship between the occlusal surfaces of the maxillary and mandibular teeth when they are in contact.
Occlusal
Toward the biting surface of a premolar or molar.
Occlusal Surface
The surface of a premolar or molar within the marginal ridges and which come in contact (occlusion) with the corresponding surface of opposing jaw during the act of closure is called occlusal surface.
Pit
It is a sharp pointed depression usually located at the junction of two or more intersecting developmental grooves or at the termination of a single developmental groove (Fig. 1.12).
Pulp Cavity
It is the central cavity in a tooth which contains tooth pulp.
Pulp chamber is that portion of the pulp cavity which lies in the crown of tooth.
Pulp canal or root canal is that part of pulp cavity which lies in the root portion of tooth.
Pulpal walls are the sides of pulp chamber.
Pulp horns are extensions of pulp towards occlusal or incisal surface.
Proximal Surface
The surface of tooth which faces toward an adjoining tooth in the same arch, i.e. both mesial and distal surfaces are proximal surfaces.
Proximal Root Concavity
A depression extending long on the mesial and distal surface of the root of an anterior or posterior tooth is known as proximal root concavity.
Ridge
It is a linear elevation on the surface of tooth. According to location, it is named as buccal, incisal or marginal ridge.
Marginal ridges
These are rounded elevations of enamel that forms the mesial and distal margins of a) the occlusal surfaces of the posterior teeth and b) the lingual surfaces of the anterior teeth (Fig. 1.13A).
Triangular ridges
These are prominent elevations or ridges, triangular in cross section and extend from tip of the cusp towards central portion of the occlusal surface of a tooth. Each triangular ridge has triangular–shaped slope or inclined plane on each side (Fig. 1.13A).
Transverse ridge
It is formed by the union of a buccal and lingual triangular ridge on the occlusal surfaces of the posterior teeth and runs transversely (Fig. 1.13A).
Oblique ridge
It is formed by the union of two triangular ridges that run obliquely across the occlusal surfaces of maxillary molars and extends from tips of the distobuccal to mesiolingual cusps (Fig. 1.13B).
Cusp ridges
These are elevations extending in a mesial and distal directions from cusp tips. Cusp ridges form the buccal and lingual margin of the occlusal surfaces of posterior teeth.
Incisal ridge
It is the linear elevation at the incisal third of the anterior teeth where labial surface meets with the lingual surface.
Sulcus
It is an elongated depression on the surface of a tooth formed by the inclines of adjacent cusps or ridges which meet at an angle.
Trunk
It is the main body of a root of a multirooted tooth from the cervical line to the furcation point.
Tubercle
It is a small rounded elevation of enamel on the crown of a tooth.
BIBLIOGRAPHY
- Berkovitz BKB, Holland GR, Moxham BJ. A Colour Atlas and Textbook of Oral Anatomy, Histology and Embryology, 4th ed. Elsevier, Mosby: 2009.
- Biviji AT. Dental Anatomy, 2nd ed. Bhalani Publishing House, Mumbai, 1999.
- Das AK. Dental Anatomy and Oral Histology, 1st ed. Current Books International, 1972.
- Kraus BS, Jordon RE, Abrams L. Dental Anatomy and Occlusion. The Williams and Willkin's Company, Baltimore, 1969.
- Nelson SJ, Ash MJ. Wheeler's Dental Anatomy, Physiology and Occlusion, 9th ed. Elsevier, 2010.
- Scott JH, Symons NBB. Introduction to Dental Anatomy, 9th ed. Churchill Livingstone, 1982.