Structures in the oral cavity: the teeth – Anatomy and physiology of the head, neck and chewing system

Human teeth consist of teeth and molars. We call them the teeth. In the mouth we have incisors and canines, behind which are the small and the large molars. In dentistry we use the following Latin names for this:

• Incisives = incisors;
• Cuspidates = Canines;
• Premolars = Small molars
• Molars = Large molars.;

During the course of their life, every person first receives a set of milk teeth, which later makes way for permanent teeth. The first teeth break through about half a year after birth. The milk teeth are complete at the age of 2.5 years. The milk teeth have a total of 20 teeth. These are the following teeth: 

• 8 incisions (milk incisors);
• 4 cuspidates (milk canines);
• 8 milk molars (milk molars).

The teeth are usually viewed by quadrant or jaw half. Because we have an upper and lower jaw, which we can each divide into two halves, we have four quadrants. A quarter of the total number of teeth is therefore contained in each quadrant. With the division into quadrants, the teeth are viewed from the center, where the incisors are. We call this center the median line. In the milk teeth we see per quadrant:

• i1 – Central or first milk incentive;
• i2 – Lateral or second milk incision;
• c – Milk cuspidate;
• m1 – First milk molar;
• m2 – Second milk molar.

The milking teeth is indicated by numbers, small letters or Roman numerals.

The permanent teeth

When a child is around 6 years old, the first baby teeth start changing. The first remaining molars also break through. His jaws also grow as the child grows. This creates more room for permanent teeth. The complete permanent set consists of 32 teeth, namely:

• 8 incisions;
• 4 cuspidates;
• 8 premolars;
• 12 molars.

From the center we see per quadrant:

• I1 – Central or first incisive;
• I2 – Lateral or second incisive;
• C – Cuspidate;
• P1 – First premolar;
• P2 – Second premolar;
• M1 – First molar;
• M2 – Second molar;
• M3 – Third molar or wisdom tooth.

The permanent teeth are indicated with two numbers or with upper case letters and numbers. During the change of the teeth, the 8 milk molars are replaced by premolars. 12 molars develop behind these premolars. These are 12 molars more in the permanent teeth than in the milk teeth (see image below).

Location of the elements

A person gets 52 teeth in total during his life. These are the milking elements and the permanent elements combined. To avoid confusion, it must be well agreed what we call each tooth. Each tooth element also has different surfaces, so it must also be clear which tooth surface is meant. Agreements about naming are necessary because there are different people working in the mouth: dentist, dental hygienist, prevention assistant, orthodontist and MKA surgeon. They must all speak the same (professional) language. This professional language is not intended to prevent the patient from understanding what is being said, but to be able to communicate with each other in short and clear terms. For example, if a dentist says “extraction 38”, that will initially be a secret language for a patient. However, the message is clear to all dental staff:

• “Extraction” means removing or pulling;
• “38” means the wisdom dial at the bottom left.

A tooth can be indicated in different ways with a kind of “code”. The indication with numbers is the most used. But we will also discuss less used systems.

Each tooth can be indicated with two digits. We call this the twodigit system. These two digits must be pronounced separately. This means that 23 is pronounced “two-three” and not “twenty-three.” What do those two numbers mean?

• The first digit indicates the quadrant;
• The second digit indicates the order of the element in the dental arch.

The first digit is therefore:

• In the permanent teeth a 1, 2, 3 or 4;
• In the milk teeth a 5, 6, 7 or 8 (see table below).

Quadrant indication in the permanent teeth and in the milk teeth.

You start at the top right when counting the quadrants. You continue counting clockwise. All permanent teeth that are at the top right have a 1 as the quadrant number. The code of the milk elements at the top right starts with the number 5.

The second digit indicates the location of the element in the quadrant. The tooth closest to the median line (the central incision) has element number 1. The element next to it (the lateral incision) has a second digit 2. This way you can continue counting. Because a milk bite has only 5 elements per quadrant, the second digit will be a maximum of 5. The permanent teeth run up to and including the wisdom teeth that have an 8 as a second digit (see table below).

Location per quadrant.

In the figure below, all 52 teeth are shown with their two digit code. Note that left and right are indicated from the patient. So as if you are looking at someone and not as if you are looking in the mirror.

MKA surgeons (oral diseases, jaw and facial surgeons) still sometimes indicate the teeth with their Latin name. First an abbreviation is given for the Latin name of the tooth. Then 2 more letters follow to indicate the quadrant. For example M2sd, where

• M2 stands for the second remaining molar;
• sd is the abbreviation for the Latin words for top (s) and right (d).

The following agreements apply to this method:

• We indicate the permanent teeth in capital letters; the lower case milk teeth;
• We first use the abbreviation of the Latin words for above and below and then the abbreviations of the Latin words for right and left (see figure below).

In the upper image all elements of the permanent and the milk teeth can be seen. The Latin words with their meanings and abbreviations are shown in the table below. M2sd from our example is therefore the second permanent molar at the top right. (We could have called this the 17.)

Latin placeholders with English translation.

The indication with brackets around the elements is used less often. For example, on orthodontic tires, this indicates the element number. The way of indicating an element is indicated in the figure below. Here too, a kind of cross is used to indicate the different quadrants. That part of the cross is placed around the element that corresponds to the relevant quadrant. The numbers 1 to 8 are used for the permanent teeth (at the top of the figure). Roman numerals are used for milk teeth, namely I, II, III, IV and V (See illustrations below).

So there are different methods to identify the same element. A few examples:

• Permanent cuspidate top right = 13 = Csd =
  • Lateral milk incisive lower left = 72 = i2is =Mesial and distal planes.
    • The labial or buccal plane. The surfaces on the outside of the dental arch lie against the lips or cheeks. These surfaces are therefore named after the lip or cheek. The labial plane is the plane that faces the lip (labium). The buccal plane is the plane that faces the cheek (bucca). With front elements we speak of the labial plane, with premolars and molars we speak of the buccal plane. The labial and buccal planes together are also called the vestibular planes.
    • The lingual or palatal plane. The surfaces on the inside of the dental arch lie on the side of the tongue (lingua) or of the palate (palatum). With the upper elements we also speak of the palatal plane. With the lower elements we speak of the linguistic plane.
    • The mesial and distal planes together are called the approximal planes. It is the surfaces with which the neighboring elements touch each other. The mesial plane of an element abuts the distal plane of the neighboring element.
    • The cervical plane. The surfaces along the gum line. They can be both vestibular and palatal / lingual (see pictures below)
    An upper incision (a) and an upper molar (b). The five different planes with their Latin name.

    Construction of the elements

    To describe the construction of an element, we divide the tooth or choose into three parts:

    • The tooth crown. The crown is the part of an element that is covered with enamel. With a healthy tooth, the crown is the part of an element that is visible in the mouth.
    • The tooth neck or cervix. The tooth neck or cervix is the part that forms the transition between crown and root. That transition is visible and palpable. The transition is also called the glaze-cement boundary.
    • The carrot or radix. The root or radix of an element is the part of the element that holds the element in the jawbone.

    On the basis of the characteristics of these three different parts you can distinguish the different teeth and molars from each other (Figure below). That way you can recognize what kind of element it is: incisive, cuspidate, premolar or molar. You can also determine the position of the element in the jaw using different morphological characteristics: below or above, left or right. Morphology is the knowledge of form and anatomy of the teeth.

    The three parts in which we divide an element.

    The shape of a crown immediately shows whether the element is an incisive, cuspidate, premolar or molar:

    • Incisives have a cutting edge;
    • Cuspidates have a cutting edge with a point;
    • Premolars have two or three nodules on the chewing surface;
    • Molars have four or five nodules on the chewing surface.

    Below we briefly discuss the morphological details of the crown of the various teeth.

    Morphological details of the elements

    You can distinguish the following details by the crown of a dental element (see image below):

    • Knob. A nodule is an elevation on the crown. A nodule is an independent part of the occlusal plane. The surfaces are named after the surfaces to which they border. Lumps are important when chewing.
    • Cingulum. A cingulum is an elevation on the lingual or palatal plane of an incisive or cuspidate.
    • Crista. A crista is an elongated frame on the surface of premolars and molars. You can describe a crista more precisely by the shape or the place where the crista is located:

    1) Edge list or marginal crista: a ledge along the border of a plane;

    2) Crista obliqua: a ledge that runs diagonally across the occlusal plane of upper molars.

    • Fossa. A fossa is an irregularly round or angular hollow in a plane of an element. This is usually in the occlusal plane, but also occurs in the palatal plane of upper teeth:

    1) Central fossa: The hollow in the middle of the occlusal plane of a molar;

    2) Triangular fossa: Triangular cavity, usually directly behind the marginal crista;

    3) Linguistic fossa: A hollow on the linguistic plane of an incisive or cuspidate.

    • Fissure. A fissure is a gap or gap in the occlusal plane. The main fissures form the separation between the nodules. Secondary fissures are the small shallow fissures that give the surface a wrinkled appearance.
    • Pit. A pit is a small but deep glaze defect in a smooth surface of an element.
    Naming of the bumps of a dental element. 1 mesiobuccal, 2 distobuccal, 3 distolingual and 4 mesiolingual lump

    Elements of the upper jaw

    In the upper jaw you have the following teeth:

    • Incisives. The incisions in the upper jaw are scoop-shaped and broad. The shape of the central and lateral incisions does not differ much; the central incisive is only clearly larger than the lateral. The mesial angle of the cutting edge is sharper than the distal, which has a slightly rounder course.
    • Cuspidates. The canines in the upper jaw are large, broad teeth. A cuspidate is distinguished from an incisive by a point in the cutting edge.
    • Premolars. The small or false molars in the upper jaw have two nodules, which are the same size. One lump is buccal, the other palatal.
    • Molars. The molars in the upper jaw are somewhat diamond shaped. This is in contrast to the molars in the lower jaw that are almost rectangular. The two buccal nodules are the same size. On the palatal side, the mesiopalatal nodule is the largest, the distopalatal the smallest. On the mesial side on the palatal plane, a fifth lump may be present at the first remaining molar: the lump of Carabelli.

    Elements of the lower jaw

    In the lower jaw you have the following teeth:

    • Incisives. The incisors in the lower jaw are long and narrow. They have a straight cutting edge. There is no difference in size between the central and the lateral incisive. The distinction between mesial and distal is difficult to see on the crown.
    • Cuspidates. The canines in the lower jaw are long, narrow and pointed.
    • Premolars. The first premolar has two nodules, of which the buccal nodule is higher and larger than the lingual. The second premolar often has three nodules, one buccal and two lingual. The lump on the buccal side is higher and larger than the lingual lump (s). If there are three nodules, the distolingual nodule is the smallest.
    • Molars. A bottom molar is rectangular and has four nodules that are all the same size. The main body has the shape of a cross. The first molar sometimes contains a small, fifth nodule distobuccally.

    Another difference between upper and lower (pre) molars is the so-called crown flight. Crown flight means that the crown is, as it were, crooked on the root. The crown leans towards the linguistic. Crown flight only occurs under (pre) molars (see image below).

    Crown flight.

    We call the transition from the crown to the root the dental neck, cervix or enamel-cement border. At the glaze-cement boundary, the glaze of the crown ends and the root cement begins. The tooth neck is a clearly visible line on an element that runs all the way around the element. You can also feel the glaze-cement border. The line follows the shape of the gums. On the mesial side the line runs higher (in the direction of the crown) than on the distal side. The cervix can therefore help determine the mesial and distal sides of an element (see figure below).

    Morphology of the different teeth. A Left central incisive left. View (a) labially (b) mesially. B Left lateral upper incision left. View (a) labially (b) mesially. C Permanent upper cuspidate left. View (a) labially (b) mesially. D First upper premolar left. View (a) buccal (b) mesial. E Second upper premolar left. View (a) buccal (b) mesial. F Permanent first upper molar left. View (a) buccal (b) mesial. G Permanent lower incision left. View (a) labially (b) mesially. H Permanent undercuspidate left. View (a) labially (b) mesially. I First lower premolar left. View (a) buccal (b) mesial. J Second lower premolar left. View (a) buccal (b) mesial. K Permanent first under molar left. View (a) buccal (b) mesial.

    The number and shape of the roots also give you information about the teeth. Incisives and cuspidates have one root. Premolars also usually have one root, except for the first premolars in the upper jaw. These have two roots. Molars in the upper jaw have three roots, while molars in the lower jaw have two roots. Root points often exhibit a curve to distal. Knowledge of root forms, the number of roots and root canals is important in different areas of dentistry: endodontics, periodontics and in extractions (See table below).

    Roots: shape and number; root canals: number and location.

    Element	Form of root	Number of roots	Number of canals	Place canals
    Upper jaw
    Incisive	Oval	1	1
    Cuspidate	Oval	1	1
    Premolar	Oval	1-2	1-2	The 1st premolars have two roots with one channel each
    Molar	Round	3	3-4	The mesiobuccal root of the 1st molar has two channels
    Lower jaw
    Incisive	Flat	1	1
    Cuspidate	Oval	1	1
    Premolar	Oval	1	1
    Molar	Flat	2	3	The mesial root has two channels

    The pulp cavity (nerve cavity) is located in the crown of a dental element. This cavity contains the pulp, a vascular nerve cord, often called the nerve. From the pulp cavity the nerve runs into the tooth or choose to the root tip (s) through the root canal. If the dentist does a nerve channel treatment, it is important to know how the nerve runs and how many nerve channels an element has.

    Tooth and surrounding structures

    The enamel is the hardest material in the human body. Glaze covers the crown of an element. It is a highly calcified substance that consists of 92% of inorganic lime salts (apatite), H2O (water), and organic material (cement). Glaze protects the element against harmful external influences and is resistant to chewing forces (see image below). Calcium salts do dissolve in acids. Bacteria in dental plaque excrete acids and can cause tooth decay. But acids in our diet can also damage the enamel. For example the carbonic acid in soft drinks. We call this dental erosion.

    Cross section of a dental element.

    The glaze is made up of crystals. The crystals run from the dental bone to the tooth surface. The cells that form the glaze are called ameloblasts. Ameloblasts form the enamel, but die before an element’s breakthrough. After the breakthrough, glaze can no longer be added. Enamel cannot “cure” if there is wear or tooth decay.

    The glaze layer of the crown is not the same everywhere. The layer on the nodules is 2-3 mm thick. It runs thin to the glaze-cement border. The glaze layer is also very thin on the bottom of the fissures.

    The dentine or dentin is softer than the enamel, but still quite hard. It is somewhat yellowish in color. The dentin cannot be seen with a healthy tooth. You do, however, sometimes see the yellow color at the front teeth twilight through the enamel.

    A dental element consists for the most part of dentin. The dentin forms, as it were, the skeleton of an element. Many strong fibers are present in dentin. 70% of the dentin consists of inorganic lime salts, cellular tissue, fibers and organic material.

    The cells that form the dentin are called odontoblasts. They lie against the dentin in the pulp cavity. Unlike ameloblasts, odontoblasts do not die after the element’s breakthrough. They stay alive as long as the tooth is in the oral cavity. The odontoblasts constantly make a little dentin, so that the pulp cavity becomes smaller during a lifetime. The odors of the cells run into the dentin from the odontoblasts. Therefore, there are channels in the dentine, the channels from Tomes. These channels run from the pulp cavity to the glaze or root cement. There are three types of dentine:

    1. Primarydentine. The primary dentin is the dentin that is present at the breakthrough of an element.
    2. Secondary identin. The secondary dentine is the dentine that is deposited in the pulp cavity as part of the physiological (= normal) (aging) process.
    3. Tertiary, irritating or repairing identin. The tertiary dentin is the dentin that was not present at the breakthrough or was deposited physiologically. To protect the pulp or nerve, odontoblasts form extra dentin in a pathological process (such as caries) to prevent the nerve from being exposed (see image below)
    Types of dentin: a primary dentin; b secondary dentin (under dotted line); c tertiary dentin (under dotted line).

    The dental nerve or pulp is located in the middle of the dentine. The pulp is a network of nerve fibers, blood vessels, lymph vessels and connective tissue in the pulp chamber and pulp channel. The pulp enters the element through an opening at the root point. This opening is called the apical foramen. The pulp feeds the tooth tissue (via the odontoblasts) and also takes care of the defense.

    The periodontium is a complex of supporting tissues of the teeth. It is also called the “hanging device” of the elements. The periodontium consists of the following structures:

    • Root cement
    • Root membrane
    • Process alveolaris
    • Gingiva

    The periodontium is discussed in detail later.

    The root cement is a hard layer on the root surface. The root of an element consists of dentin or dental bone; that is the root cement. The root cement consists of lime salts and collagen fibers. The cells that form the cement are called cementoblasts. The cementoblasts, just like the odontoblasts, remain present for the entire life of an element. New cement can be made after the breakthrough.

    The root membrane also has other names: it is also called periodontium or periodontal periodontal or periodontal ligament. The root membrane consists of collagen fibers, the fibers of Sharpy, which run from the root cement to the alveolar bone. The fibers ensure the “elastic” connection of the tooth in the tooth socket. They absorb the chewing forces as a kind of shock absorber and register the chewing pressure.

    The alveolar or dental process is the part of the jaw in which the teeth are attached.

    The gingiva or gums form a collar around the dental element. It is stuck on the transition from crown to root and protects this transition.