Each tooth has a crown and root portion. The crown iscovered with enamel and the root portion covered with cementum.
The crown and root join at the cementoenamel junction (CEJ). This junction also called the cervical line.
The main bulk of the tooth is composed of dentin, which is clear in a cross section of the tooth. This cross section displays a pulp chamber and a pulp canal, which normally contain the pulp tissue. The pulp chamber is in the crown portion mainly, and the pulp canal is in the root. The spaces are continuous with each other and are spoken of collectively as the pulp cavity. The four tooth tissues are enamel, cementum, dentin, and pulp. The first three are known as hard tissues, the last as soft tissue. The pulp tissue furnishes the blood and nerve supply to the tooth.
Enamel : Makes up the protective outer surface of the crown of the tooth. Enamel is translucent and can vary in color from yellowish to grayish white. The different colors of enamel are attributed to the variation in the thickness, translucent proprieties, the quality of the crystal structure, and surface stains of enamel.
Enamel is the calcified substance that covers the entire anatomic crown of the tooth and protects the dentin. It is the hardest tissue in the human body and consists of approximately 96% inorganic minerals,
1% organic materials,
and 3% water.
Calcium and phosphorus (as hydroxyapatite) are its main inorganic components.
Enamel can endure crushing pressure of approximately 100,000 pounds per square inch., produces a cushioning effect of the tooth’s different structures enabling it to endure the pressures of mastication (chewing). Structurally, enamel is composed of millions of enamel rods or prisms. Each rod begins at the dentinoenamel junction (junction between the enamel and dentin) and extends to the outer surface of the crown. After formation enamel has no power of further growth or repair.
2. Dentin: Makes up the majority of the inner surface of the tooth. It cannot normally be seen except on x-rays. Dentin is the light yellow substance . The pulp chamber is located on the internal surface of the dentin walls. Dentin is harder than bone but softer than enamel. Dentin consists of approximately 70% inorganic matter and 30% organic matter and water. Calcium and phosphorus are its chief inorganic components. Dentin is a living tissue and must be protected during operative or prosthetic procedures from dehydration (drying) and thermal shock. The dentin is perforated by tubules (similar to tiny straws) that run between the cementoenamel junction (CEJ) and the pulp. Dentin transmits pain stimuli by the way of dentinal fibers. Because dentin is a living tissue, it has the ability for constant growth and repair that reacts to physiologic (functional) and pathologic (disease) stimuli.
This is the area inside the tooth that holds the nerves and blood vessels of the tooth. It is in the center of the tooth and is in both the crown and the root of the tooth. The dental pulp, is the soft tissue inside the tooth developed from the connective tissue of the dental papilla. Within the crown, the chamber containing the dental pulp called the pulp chamber. The coronal pulp and pulp horns are within the crown and the radicular pulp is within the root. The apical foramen is at the end or apex of the radicular pulp. Blood vessels, nerves, and connective tissue pass through this area to reach the interior of the tooth.
The chief function of the pulp is the formation of dentin. It furnishes nourishment to the dentin; provides sensation to the tooth; and responds to irritation, either by forming reparative secondary dentin or by becoming inflamed.
Makes up the outer surface of the root of the tooth. It is much softer than enamel. Cementum is the bonelike tissue that covers the roots of the teeth in a thin layer. It is light yellow in color, slightly lighter than dentin. The cementum is composed of approximately
55% organic material
and 45% inorganic material; the inorganic components are mainly calcium salts.
The cementum joins the enamel at the cervix of the tooth forming the CEJ. In most teeth the Cementum overlaps the enamel for a short distance. In some, the enamel meets the cementum in a sharp line. In a few, a gap may be present between the enamel and the Cementum, exposing a narrow area of root dentin. Such areas may be very sensitive to thermal, chemical, or mechanical stimuli. The main function of cementum is to anchor the teeth to the bony walls of the tooth sockets in the periodontium. This accomplished by the fibers of the periodontal ligament or membrane.
Cementum formed continuously throughout the life of the tooth to compensate for the loss of tooth substance because of occlusal wear and to allow for the attachment of new fibers of the periodontal ligament to the surface of the root.
Cementum is the only tissue considered as both a basic part of the tooth and a component of the periodontium. It is a thin, calcified layer of tissue that completely covers the dentin of the tooth root. Cementum is formed during the development of the root and throughout the life of the tooth. Cementum functions as an area of attachment for the periodontal ligament fibers.
NOTE: The tissues that surround and support the teeth are collectively called the periodontium. Their main functions are to support, protect, and provide nourishment to the teeth. The periodontium consists of cementum, alveolar process of the maxillae and mandible, periodontal ligament, and gingiva.
PERIODONTAL LIGAMENT: The periodontal ligament is a thin, fibrous ligament that connects the tooth to the bony socket. Normally, teeth do not contact the bone directly; a tooth is suspended in its socket by the fibers of the ligament. This arrangement allows each tooth limited individual movement. The fibers act as shock absorbers to cushion the force of mastication.
ANATOMY OF THE CROWN:
The crown of an incisor tooth may have an incisal ridge or edge, as in the central and lateral incisors; a single cusp, as in the canines; or two or more cusps, as on premolars and molars. Incisal ridges and cusps form the cutting surfaces on tooth crowns. Therefore, the crowns of the incisors and canines have four surfaces and a ridge, and the crowns of the premolars and molars have five surfaces. The surfaces are named according to their positions and uses.
The root portion of the tooth may be single, with one apex or terminal end, as usually found in anterior teeth and some of the premolars; or multiple, with a bifurcation or trifurcation dividing the root portion into two or more extensions or roots with their apices or terminal ends, as found on all molars and in some premolars.
The root portion of the tooth is firmly fixed in the bony process of the jaw, so that each tooth is held in its position relative to the others in the dental arch. That portion of the jaw serving as support for the tooth is called the alveolar process. The bone of the tooth socket is called the alveolus. The crown portion is never covered by bone tissue after it is fully erupted, but it is partly covered at the cervical third in young adults by soft tissue of the mouth known as the gingiva or gingival tissue, or “gums.” In some persons, all of the enamel and frequently some cervical cementum may not be covered by the gingiva.
DESCRIPTION OF THE TEETH:
To facilitate description, teeth are divided into thirds, Line Angles, and Point Angles. The crowns and roots of teeth have been divided into thirds, and junctions of the crown surfaces are described as line angles and point angles. Actually, there are no angles or points or plane surfaces on the teeth anywhere except those that appear from wear (e.g., attrition, abrasion) or from accidental fracture. When the surfaces of the crown and root portions are divided into thirds, these thirds are named according to their location.
Wear of the teeth develops line angles that are not found in natural condition.
Looking at the tooth from the labial or buccal aspect, we see that the crown and root may be divided into thirds from the incisal or occlusal surface of the crown to the apex of the root . The crown is divided into an incisal or occlusal third, a middle third, and a cervical third. The root is divided into a cervical third, a middle third, and an apical third.
The crown may be divided into thirds in three directions: (inciso- or occlusocervically) , ( mesiodistally ) , or ( labio- or buccolingually).
Mesiodistally, the crown is divided into the mesial, middle, and distal thirds.
Labio or buccolingually it is divided into labial or buccal, middle, and lingual thirds.
Each of the five surfaces of a crown may be so divided. There will be one middle third and two other thirds, which are named according to their location, for example, cervical, occlusal, mesial, lingual.
A line angle is formed by the junction of two surfaces and derives its name from the combination of the two surfaces that join. For instance, on an anterior tooth, the junction of the mesial and labial surfaces is called the mesiolabial line angle. The line angles of the anterior teeth are as follows:
1-mesiolabial line angle.
2-distolingual line angle.
3-distolabial line angle.
4-labioincisal line angle.
5-mesiolingual line angle.
6-linguoincisal line angle.
Because the mesial and distal incisal angles of anterior teeth are rounded, mesioincisal line angles and distoincisal line angles are usually considered nonexistent. They are spoken of as mesial and distal incisal angles only.
The line angles of the posterior teeth are as follows:
1-mesiobuccal line angle.
2- distolingual line angle.
3-bucco-occlusal line angle
4- distobuccal line angle.
5-mesio-occlusal line angle.
6-linguo-occlusal line angle.
7-mesiolingual line angle.
8-disto-occlusal line angle
A point angleis formed by the junction of three surfaces. The point angle also derives its name from the combination of the names of the surfaces forming it. For example, the junction of the mesial, buccal, and occlusal surfaces of a molar is called the mesiobucco-occlusal point angle.
The oral cavity is made up of specialized epithelial tissues that surround the teeth and serve as a lining. These tissues are called the oral mucosa and consist of three types: masticatory mucosa, lining mucosa, and specialized mucosa.
MASTICATORY MUCOSA: Masticatory mucosa is comprised of the tissue that covers the hard palate and the gingiva. It is light pink in color (can vary with skin color) and is keratinized. Keratinized tissue has a tough, protective outer layer of tissue.
A-Hard palate (Roof of the Mouth): The hard palate is covered with masticatory mucosa and is firmly adhered to the palatine process (bone). Its color is pale pink. Important structures of the hard palate are:
INCISIVE PAPILLA: Located at the midline, directly posterior of the maxillary central incisors (pear-shaped in appearance).
PALATINE RAPHE: Extends from the incisive papilla posteriorly at the midline (may be ridge shaped in appearance with a whitish streak at the midline). PALATINE RUGAE.—Extends laterally (along side) from the incisive papilla and from the palatine raphe (wrinkled, irregular ridges in appearance).
B- Gingiva: The gingiva is specialized masticatory mucosa covering the alveolar process. Gingiva is firm and resilient encircling the necks of the teeth. It aids in the support of the teeth, and protects the alveolar process and periodontal ligament from bacterial invasion. The color of healthy gingiva range from pale pink to darker shades (purple to black) depending on each individual’s pigmentation. Under normal flossing and brushing activities it does not bleed.
2- Lining Mucosa: Lining mucosa is found on the inside of the lips, cheeks, vestibule, soft palate, and under the tongue. It consists of a thin, fragile tissue that is very vascular. Lining mucosa is brighter red in color than masticatory mucosa. Included in the lining mucosa is alveolar mucosa which is loosely attached and lies apical to the mucogingival junction (line where the attached gingiva and alveolar mucosa meet).
3-Specialized Mucosa: Specialized mucosa is the mucous membrane on the tongue in the form of lingual papillae, which are structures associated with sensations of taste.
Tooth Identification In both the maxillary and mandibular arch:
There are similar teeth. There are four types of teeth in both arches. These include the incisors, the canines, the premolars and the molars. Each of these teeth is located in a different area of the mouth and serves different functions.
Incisors: The four front teeth in the mouth are known as incisors. They are located in both the maxillary and mandibular arches. The two center teeth are known as central incisors and the teeth on either side of them are known as lateral incisors. All of these teeth are responsible for cutting or biting food. They act like scissors.
Canines: The teeth located distal to the lateral incisors are known as canines. These teeth form the corners of the mouth. There are 2 canines in the maxillary arch and 2 canines in the mandibular arch. These teeth are responsible for tearing food particles when chewing.
Premolars: The teeth located distal to the canines are known as premolars. There are 4 premolars in each arch and two are located behind each canine in the arch. These teeth are smaller than the molars and are responsible for crushing food in the chewing process. These teeth are also only present in the permanent dentition. The primary dentition only consists of incisors, canines and molars.
Molars: There are normally 6 molars in each arch; three on the left and three on the right side. They are referred to as first, second and third molars. Some people never develop third molars and often these are the molars that are so far back in the mouth that they have difficulty coming in and may have to be taken out. The role of the molars in chewing is to grind the food.
Tooth Numbering Systems:
In order to effectively and efficiently refer to teeth we often use numbering or lettering systems. There are several systems that are used throughout the world. These include the Palmer Notation System, theUniversal Numbering System, and the International Numbering System.
1-The Palmer Notation System: divides the permanent teeth into ( 1,2,3,4,5,6,7,8) as (central,laterai,canine,first premolar,second premolar,first molar,second molar,third molar) and an angle that represents the direction and position of the teeth as:
For deciduous teeth, they are named as ( A,B,C,D,E).
The teeth are numbered 1-8 for permanent and A-E for deciduous (as with the Palmer notation method).
For example, permanent upper left first molar: UL6
2-TheUniversal Numbering System: The most widely used system in U.S. dental schools is the Universal Numbering System. It is also called the "American system".The uppercase lettersAthroughTare used for primary teeth and the numbers 1 - 32 are used for permanent teeth. For permanent teeth, it consists of assigning numbers to the teeth in the permanent dentition from 1 to 32 starting with the upper right third molar and continuing over to the upper left third molar and then down to the lower left third molar and onto to the lower right third molar. For example: The mandibular right canine tooth would be tooth #27. Using the Universal Numbering System for the primary dentition is identified by using letters. Beginning at the second molar on the upper right, the teeth in the maxillary arch are assigned letters A – J. Then continuing with the mandibular left second molar and around to the mandibular right second molar, the teeth are assigned letters K – T.
UNIVERSAL TOOTH NUMBERING SYSTEM
Alternative system for deciduous teeth..
The International Numbering System: or called ( FDI Numbering system ) divides the mouth into 4 quadrant, starting from upper right quadrant to a clock wise direction .each quadrant was numbered as:
Upper right quadrant = 1.
Upper left quadrant = 2.
Lower left quadrant = 3.
Lower right quadrant = 4.
While the teeth were numbered as (1,2,3,4,5,6,7,8) as (central,laterai,canine,first premolar,second premolar,first molar,second molar,third molar).
To record the teeth, the right number refers to the arch ,the left number refers to the tooth as following:
Tooth No. 11 = maxillary right central.
Tooth No. 12 = maxillary right lateral.
Tooth No. 28 = maxillary left third molar.
Tooth No. 31 = mandibular left central.
Tooth No. 44 = mandibular right first premolar.
The International Numbering System for permanent teeth.
Another classification can be used for deciduous teeth, where the arches are divided as:
Upper right quadrant = 5.
Upper left quadrant = 6.
Lower left quadrant = 7.
Lower right quadrant = 8
And the deciduous teeth are numbered from 1 to 5 as:
Tooth No. 55 = maxillary right central.
Tooth No. 85 = mandibular right molar.
The International Numbering System for deciduous teeth.