DENTAL FORMULA AND CODING SYSTEMS
Dental Arches and Quadrants
The twenty deciduous teeth in the young mouth and the thirty two permanent teeth in the adult mouth are arranged in two arches called the “Dental Arches”, one upper and one lower. Each arch contains half of the number of the teeth (10 deciduous then later 16 permanent teeth). (Fig. 1)
The upper jaw is called the “Maxilla” and the teeth in this arch is called the “Upper of Maxillary Teeth”. On the other hand, the lower jaw is called the “Mandible” and the teeth in this arch is called the “Lower or Mandibular Teeth”.
The imaginary vertical line which equally divides the body into right and left halves is called the midline or the “Midsagittal Plan”. This line also divides each dental arch into right and left segments, referred to as “Quadrants”. The permanent teeth and the deciduous teeth are equally arranged into four quadrants, as follows:
- Upper right quadrant or Maxillary right quadrant.
- Upper left quadrant or Maxillary left quadrant.
- Lower left quadrant or Mandibular left quadrant.
- Lower right quadrant or Mandibular right quadrant.
Types and Forms of Teeth
Teeth vary in form, this variation reflects differences in function. Based on forms and functions the teeth are classified into incisors, canines, premolars and molars. (Fig. 1)
- Incisors: They are the four front teeth in each arch. The Central incisor is the first tooth next to the midline. The Lateral Incisor is the second. The form of the incisors is more or less similar to a chisel., which makes them suitable for cutting of incising food. The side of the tooth toward the tongue, the lingual surface, is shaped like a shovel, to aid in guiding the food into the mouth.
- Canine (Cuspid): It is the third tooth from the midline. The canine is cone or wedge shape and it is designed to function as a holding or grasping teeth suitable for piercing, cutting and tearing.
- Premolars (Bicuspids): They are the fourth and fifth tooth from the midline. The fourth tooth is the First Premolar, the fifth tooth is the Second Premolar. These teeth are characterized by the presence of at least two projections (cusps), a wedge-shaped projection similar to that of the canine, and a slightly rounded projection. Because of their intermediate form and location between canine and molars, they also have an intermediate function of tearing and grinding food.
- Molars: These are the sixth, seventh and eighth tooth from the midline. The sixth is the First Molar, the seventh is the Second Molar and the eighth is the Third Molar or wisdom tooth. The molars are characteri-zed by wide surface with multiple projections (cusps) and therefore are suitable for grinding food.
Grouping of Teeth
The teeth in the dental arch can be grouped into
- Anterior teeth: including the incisors and canines
- Posterior teeth: including the premolars and molars.
Functions of Teeth
- Mastication: it is the most important function of the teeth. The teeth are designed to perform this function, accord-ingly the incisors are designed for cutting, the canines for tearing and holding, premolars for grinding and holding and molars for grinding and chewing.
- Appearance: well arranged clean teeth with proper alignment give nice appearance to the face and also support the facial expressions.
- Speech: The teeth are important for clear pronunciation and for production of sound.
- Growth of Jaws: The teeth play a role in the growth of the jaws during some periods of the facial growth.
- In Animals: The first function of teeth is to hold food and kill prey mechanically, as the lion, or by chemical poisons, as vipers. Other animals use their teeth in combat as weapons in the struggle for existence.■
THE DENTAL FORMULA
The number and type of teeth for all mammal are expressed by the dental formula. The type of each tooth is represented by its initial letter:
- I: Incisors
- C: Canines
- P: Premolars
- M: Molars
Each letter is followed by a horizontal line and the number of each type of teeth is placed above the line for maxillary half and below it for the mandibular half. A typical mammalian dentition is composed of 44 teeth. This is well represented in pigs, where 22 teeth are present in each jaw (3 incisors, 1 canine, 4 premolars and 3 molars), i.e. the dental formula is: I3/3, C1/1, P4/4, M3/3, which is equal to 22 teeth on each side of the mouth.
- The human deciduous teeth are 20 in number and are expressed by the following formula: I2/2 - C1/1 - M2/2 = 10 teeth on jaw
- The human permanent teeth are 32 in number and is expressed in the following formula: I2/2 - C1/1 - P2/2 - M3/3 = 16 teeth for jaw
Numbering and Coding Systems of Teeth
When identifying a specific tooth, list the dentition, arch, quadrant and tooth name in that order. An example is shown in table I.
It is essential to be familiar with the various systems of naming and coding teeth. The most popular systems are universal system, Palmer notation system and the Federation Dentaire International (FDI) system.
- Universal System: This system uses the Arabic numbers 1 through 32 for the permanent teeth and the letters A through T for the deciduous teeth. The number (1) is assigned to the most posterior upper right permanent tooth (the permanent maxillary right third molar). The highest number is given to the most posterior lower right tooth (the permanent mandibular right third molar). On the same way, the letter A is given to the most posterior lower right deciduous tooth (the upper deciduous right second molar) and the letter T to the most posterior deciduous lower right tooth (the lower deciduous right second molar). (Fig. 2)
- Palmer Notation System: In this system each of the four quadrants of the mouth is given its own symbol. A cross is drown, the horizontal line of which separates the maxillary teeth above from the mandibular teeth below. The vertical line represents the midline of the mouth and separates the right from the left side. Accordingly the deciduous (upper) and permanent (lower) dentitions is represented as shown in figure 3.
Fig. 3. Plamer notation system. Deciduous teeth (lower) and permanent teeth (upper)
- The Federation Dentaire International (FDI): It is a simple bi-digital system in which each tooth is referred to by two digits the first digit represent the quadrant of the mouth and the second digit represent the tooth. The maxillary right quadrant is given number “1”, maxillary left quadrant “2”, mandibular left quadrant “3”, and mandibular right quadrant “4”. For deciduous dentition the maxillary right quadrant is given number “5”, maxillary left quadrant “6”, mandibular left quadrant “7” and mandibular right quadrant “8”. The type of each tooth is represented also by numbers from 1-to-5, where 1 is the central incisor and 5 is the second molar. Accordingly the deciduous (upper) and permanent (lower) dentitions is represented as figure 4.■
Fig. 4. Federation Dentaire International system. Permanent teeth (upper) and deciduous teeth (lower)
MORPHOLOGICAL AND STRUCTURAL FEATURES OF TEETH
Macro Anatomy of Teeth
Each tooth has “Crown” and “Root” portion. The crown is covered with enamel and the root is covered with cementum. The root is embedded in the jaw bones. The crown and root joined at the “Cementoenamel Junction”. The line demarcate this junction is called the “Cervical Line”. (Fig 5)
Crown and Root of the Tooth
- Anatomical Crown: is that portion of the tooth which is covered by enamel.
- Clinical Crown: Is that portion of the tooth which is visible in the mouth regardless whether or not it corresponds to the anatomical crown in length, as the clinical crown may change it length through life.
- Anatomical Root: It is that portion of the tooth which is covered by cementum.
- Clinical Root: It is that portion of the tooth which is not visible in the mouth. As with the clinical crown the clinical root may change its length throughout life.
Forms of the Root
The teeth may have single root, double roots or treble roots.
- Single Root: All the anterior teeth and the premolar teeth, except the upper first premolar, are single rooted teeth.
- Double Roots: There is a bifurcation, dividing the root portion into two extensions or roots as found in lower molars and upper first premolar.
- Treble Roots: There is a trifurcation dividing the root portion into three roots as the case in upper molars.
Fig. 5. Macro anatomy of the tooth.
The undivided portion of the root is called the “trunk”. The root portion of the tooth is held in its position relative to other teeth in the dental arch by being firmly anchored in the bony process of the jaw serves to support the teeth and is termed “Alveolar Process”.
The bony space in the alveolar process in which the roots of an erupted tooth is found is called the dental “Socket”. On the other hand, the bony space in which the developing unerupted tooth is found is called “Crypt”.
The tooth is attached to the bony alveolus by a strong ligament known as the “Periodontal Ligament”. The soft fibrous tissue which covers the alveolar process and surrounds the necks of the teeth is termed the “Gingiva” of the “Gum”.
Structural Elements of the Tooth
The four tissues that constitute the tooth are the “Enamel”, “Dentin”, “Cementum” and “Pulp”. The first three tissues are hard mineralized tissues composed of organic matrix embedded by crystalline forms of calcium phosphate salt. The pulp is soft connective tissue. (Fig. 6)
Fig. 6. Structure elements of teeth and their supporting structures. 1. Enamel, 2. Dentino-enamel junction, 3. Dentin, 4. Pulp horn, 5. Pulp chamber, 6. Gingiva, 7. Cementum, 8. Pulp canal, 9. Periodontal ligament, 10. Alveolar bone
Enamel: The enamel covers the outer surface of the crown. It is thickest over the tip of the crown and becomes thinner until it ends at the cervical line. Enamel is the most mineralized and hardest tissue in the human body. This dense mineralization gives the enamel the ability to resist the wear that the corn of the tooth is subjected to. The enamel is very smooth, a characteristic that gives the crown a self-cleaning ability.
Cementum: It is a bony like substance that covers the root of the tooth. Its main function is to provide a medium for the attachment of the tooth to the alveolar bone. Cementum is less dense and less hard than enamel and dentin, but denser and harder than bone. The cementum is quite thin at the cervical line but increase slightly in thickness at the apex of the roots.
Dentin: Dentin forms the main bulk of the body of the tooth. It is wrapped in an envelop of enamel, which covers the crown, an an envelop of cementum, which covers the root. Dentin is a hard dense calcified tissue that is softer than enamel but harder than cementum and bone. The junction of enamel and dentin is called “Dentino-Enamel Junction” and the junction between cementum and dentin is called “Dentino-Cemental Junction”.
Pulp: The pulp is the nourishing, sensory and dentin reparative system of the tooth. It is made up of connective tissue, blood vessels, lymphatic and nerves. The pulp tissues is housed in the pulp cavity in the center of the tooth, that is surrounded by dentin.
- Anatomically the pulp cavity consists of two parts, the “Pulp Chamber” housed within the crown portion and the “Pulp Canal” which is located within the root portion of the tooth.
- The constricted opening of the pulp canal is called the “Apical Foramen” and it sis possible for a pulp canal to have two or more branches which make their exist at or near the apex of the root, these are called “Multiple Foramina” or “Supp-lementary Canals”. However many roots may have more than one canal that end n a common foramen.
- The shape of the pulp canal or canals follows that of the respective root. It tapers from the apex to the final constriction at the apical foramen
- The “Pulp Chamber” is always a single cavity and is centered in the crown, with an outline that roughly conforms with that of the crown. There are prolongations in the roof of the pulp chamber that correspond to various cusps of the crown of posterior teeth and the developmental lobes of the anterior teeth of young persons, these are called “Pulp Horns” and it disappear by age.■
SURFACE CHARACTERISTICS OF TEETH
The crown of the tooth is divided into surfaces which are named according to the direction in which they face. The anterior teeth , incisors and canines, have four surfaces and a ridge, while the posterior teeth, premolars and molars, have five surfaces. The surfaces are named as follow:
- Facial or Labial / Buccal Surface: this is the outer surface of the anterior teeth, which is facing the face or the lip. The term “labial surface” is more commonly used. The outer surface of the posterior teeth, premolars and molars, is termed the “buccal surface”.
- Palatal / Lingual Surface: it is the inner surface of all teeth, anterior and posterior. That of the maxillary tooth is termed “palatal surface” because it face the palate, while the inner surface of the mandibular teeth is termed “lingual surface” because it faces the tongue.
- Mesial and Distal Surfaces: The surface of the tooth that faces the midline is termed “mesial surface” while that faces away from the midline toward the back of the mouth is termed “distal surface”. The term “Proximal Surface” denotes any surface between two adjacent teeth, it could be mesial or distal. The area of the mesial and/or the distal surface which touches its neighbor in the arch is termed the “Contact Area”.
- Incisal Edge or Ridge and Occlusal Surface: The cutting edge of the anterior teeth that is used for mastication is termed the “incisal edge or ridge”, while in the posterior teeth it is termed the “occlusal surface”.
Division of Tooth Surfaces
For purpose of facilitating localization of various areas within a specific surface of the tooth, the surface is divided into thirds in horizontal direction, as well as, in mesiodistal and bucco-lingual /palatal directions. (Fig. 7)
Fig. 7. Divisions of toot surfaces. Vertical divisions into thirds and buccal and proximal horizontal divisions.
Line Angles and Point Angles
“Line angles” are imaginary lines formed by the junction of two surfaces. The line where surface A met surface B is called AB line angle. If A is the labial surface and B is the mesial surface of an anterior tooth, accordingly the line that is formed by the meeting of them is termed “Mesio-Labial Line Angle”.
“Point Angle”, on the other hand, is the point where three surfaces met. The point where the labial and mesial surface join with the incisal ridge of an anterior tooth is termed “Mesio-Labio-Incisal Point Angle”. (Fig. 8)
Fig. 8. Line angles (Left) and point angles (Right) .
Line Angles: Labioincisal, 2. Mesiolingual, 3. Mesiolabial, 4. Lingoinicsal, 5. Distolingual, 6. Distolabia, 7. Mesio-occlusal, 8. Mesilingual, 9. Mesiobucca, 10. Bucco-occlusal, 11. Linguo-occlusal, 12. Distolingual, 13. Distobuccal, 14. Disto-occlusal
Point Angles: 1. Mesiolabioincisal, 2. mesiolinguoincisal, 3. distolabioincisal, 4. distolinguoincisal, 5. mesiolinguocclusal, 6. Mesiobuccoocclusal, 7. Destolinguooclusal, 8. distobuccoocclusal.
- Cusps: This are conical or pyramidal projections on the crown portion of the tooth that makes up a major division of its occlusal surface. Cusps are found in premolars, molars and canines and each cusp represent a calcified developmental lobe. (Figs 9 and 10)
- Tubercle: It is a small elevation on some portion of the crown which is produced by extra formation of enamel. It is mostly present in the second deciduous molar and the first permanent molars.
- Cingulum: It is a convex bulk of the cervical third of the lingual surface of the anterior teeth that represent the lingual developmental lobe.
- Ridges: This are linear elevations on the surfaces of the crown and are named according to their location and/or shape. Several types can be identified as follows:
- Marginal Ridge: Is the linear elevation which is found on the mesial and distal boundaries of the lingual surface of the anterior teeth and the mesial and distal boundaries of the occlusal surface of the posterior teeth.
- Triangular Ridge: Is a linear ridge which descends from the tip of the cusp toward the central area of the occlusal surface of the posterior teeth.
- Transverse Ridge: Is the union of two triangular ridges which transversly cross the occlusal surface of posterior teeth usually the lower first premolar.
- Oblique Ridge: It is the union between two triangular ridges of two cusps, not facing each others and crossing the occlusal surface of the maxillary molars. It extends obliquely from mesiolingual cusp to distobuccal cusp.
Other ridges are named according to their site and present as elevations are “incisal, labial, lingual, buccal and cervical ridges”.
Fig. 9. Examples of major cusps of lower second premolar (upper), Lower first molar (middle) and upper first molar (lower)
Fig. 10. Ridges of upper first permanent molar.
- Fossa: This is an irregular depression or concavity and is named according
to its shape and location.
- Central Fossa: present on the occlusal surface of molars and formed by the converging of ridges and cusps that terminate at the center as a depression.
- Lingual Fossa: Is a depression formed on the lingual surface of the anterior teeth.
- Mesial or Distal triangular Fossa: Found on the occlusal surfaces of premolars and molars, mesial or distal to the triangular ridges.
- Sulcus: It is a long depression or valley between ridges and cusps, the inclines of which meets at an angle. A Sulcus has a developmental groove at the junction of its inclines.
- Developmental Grooves: It is a groove or line in the bottom of the Sulcus which denotes union of the primary parts or lobes of the crown of the tooth. (Figs 11 and 12)
- Supplemental Grooves: These are groves which branch from the developmental grooves, they do not indicate union between primary lobes.
- Pits: These are small pinpoint depression located at the junction of developmental grooves and/or at their terminals.
Fig. 11. Developmental grooves of lower 5 (left), lower first molar (middle) and upper first molar (right).
Fig. 12. Fossae and pits of lower second premolar (left), lower first molar (middle) and upper first molar (right).
Fig. 13. General outline of some of the lobes.
a: Labial aspect of maxillary central incisor, mesial lobe (1), labial lobe (2) and distal lobe (3),
b and e: Mesial and occlusal aspect of maxillary first premolar, mesial lobe (1), buccal lobe (2), distal lobe (3) and lingual lobe (4),
c: Occlusal aspect of mandibular first molar, mesiobuccal lobe (1), distobuccal lobe (2), distal lobe (3), mesiolingual lobe (4) and distolingual lobe (5),
d: Occlusal aspect of maxillary first molar, mesiobuccal lobe (1), distobuccal lobe (2), mesiolingual lobe (3), distolingual lobe (4) and fifth lobe (fifth cusp) (5)
- Inclined Planes: These are slopes from cusp tips to the developmental grooves.
- Height of Contour: This is the point of maximum convexity of tooth surface.
- Developmental Lobe: Is the first site of calcium deposition. Each tooth begins it development from four or more growth centers which are known as “Developmental Lobes”.
- The anterior teeth, the maxillary premolars and the mandibular first premolar develop from four developmental lobes, three labial and one lingual.
- The mandibular second premolar may be two-cuspid, and show the same number and arrangement of the developmental lobes as the mandibular first premolar, or three-cuspid and, therefore, have five lobes three labial and two lingual.
- All molar teeth have two buccal and two lingual lobes, except the mandibular first molar which may have a fifth buccal lobe.
- The lobes grow until they fuse, and the line of fusion is marked by a line that is termed the “Developmental Groove”, that can be seen on the tooth after its eruption but soon disappear due to wear and attrition.
- The developmental lobes are represented by cusp, cingulum and mamelon.■
DEVELOPMENT, CALCIFICATION & ERUPTION OF TEETH
Development of Teeth
During the six week of fetal life tiny teeth germs begin to grow within the alveolar process of the fetus. “Tooth Germs” are small clumps of cells that have the ability to form dental (tooth) tissues i.e. enamel, dentin, cementum and pulp. (Fig. 14)
- From the deepest layer of oral epithelium a band called the “Dental Lamina” extends deep inside the jaw all around.
- From the dental lamina epithelium bud out and named the “Dental Organ”, which is the first sign of tooth development.
- The mesodermal tissue around each dental organ become influenced by its growing cells forming localized area of mesoderm called the “Dental Papillae”, which is seen in the concavity of the dental organ.
- A mesoderm tissue also encircle each dental organ and dental papilla forming the “Dental Sac”.
- The dental organ, dental papilla and dental sac are called the “Tooth Germ”.
- Cells forming the “Enamel” are differentiated from the “Dental Organ”.
- The cells forming “Dentin and Pulp” are differentiated from the “Dental Papilla”.
- Cells that form “Cementum, Periodontal Ligament and Alveolar Bone” are derived from the “Tooth Sac”.
Fig. 14. Early stage of tooth development. 1. permanent tooth bud, 2. Dental lamina, 3. Enamel organ, 4. Dental papilla, 5. Dental sac
The dental lamina of each jaw gives off ten dental organs of deciduous teeth. Lingual to the deciduous dental organs, “Successional Laminae” are extended to form the permanent successors. These teeth are the permanent incisors, canines and premolars. The development of the dental organ begins at the fifth month intrauterine for the permanent central incisors and ends at about the age of ten months for the second premolar. The tooth germs for the developing permanent incisors and canines are in a position lingual to the deciduous roots, while that for the premolar are within the bifurcation of the deciduous molar roots.
Each cell is specialized to form one of the hard dental tissues, enamel, dentin and cementum, first lays down a soft organic matrix. This is followed by deposition of mineral salts, mostly calcium, circulating in the blood, into this matrix in the form of globules called “Calcospherites”. The calcospherites enlarge and fuse together forming the calcified dental tissues. This calcification process continue till about the fourth year of life for the deciduous teeth and for the permanent dentition until the twenty-fifth year of life.
The development of the crown and root takes place within a bony “Crypt” in the jaw bone. After the formation of the crown and about 1/3 of the root, the tooth starts to erupt and penetrate the oral mucous membrane. The tooth continue to erupt and as it reaches the occlusal plane 2/3 of it root becomes formed. When the tooth is newly erupted, the dental pulp is large and then becomes progressively smaller.
Formation of the tooth is said to be completed when the apex of the root is formed. This occur between 1-11/2 years after the emergence of the tooth in the mouth for the deciduous teeth and between 2-3 years for the permanent teeth.
Fig. 15. Eruption of teeth.
After the tooth reach the occlusal plane it continue to erupt and more of the crown become exposed as the tooth moves occlusally. Formation of the root dentin and cementum continue after the tooth is completely formed.
As for the chronology of eruption of teeth the following rules is to be considered:
- Eruption of mandibular teeth usually precede that of maxillary teeth.
- Teeth in both jaws erupt in pairs, one on the right and one on the left.
- Teeth erupts slightly earlier in girls than in boys.
At the age of 6 months, the deciduous mandibular central incisors show up in the mouth. The usual sequence of eruption of deciduous dentition are: Central Incisors, 6 months lower and 7 months upper, lateral incisors, 7 months lower and 8 months upper, first molar, 12 months lower and 14 months upper, canines, 16 months lower and 18 months upper, second molar, 20 months lower and 24 months upper.
Although deciduous teeth are temporary yet they are important for the following reasons:
- Normal function on both sides of the dental arches is important for normal jaw development.
- To guide the first permanent molars into their normal position.
- Deciduous teeth contribute to the health and wellbeing of the individual during an important period of growth between 6-12 years.
Fig. 16. diagrammatic representation for the dentition stages.
The permanent tooth in its follicle attempt to force its way into the position held by its predecessor. The pressure brought to bear against the deciduous root result in its resorption. Root resorption of deciduous teeth will continue until the crown looses its anchorage, becomes loose and finally exfoliated. The first tooth of the permanent dentition to erupt and emerge in oral cavity is the first mandibular molar. The first permanent molars are called the “Six Years Molars” because they erupt at the age of 6 years, just distal to the second deciduous molar. The chronology of the permanent dentition is shown in table 2.■