CHAPTER 2

LITERATURE REVIEW

CHAPTER 2: LITERATURE REVIEW

2.1. The anatomy of the tooth

2.1.1. Anatomy of the jaw and tooth.

Figure 2.1. Adult teeth diagrams (upper jaw- lower jaw)

         People all have two separate sets of teeth, one set for childhood and the other for adult life. Children develop 20 baby teeth which they keep until the ages of 5 or 6 years. After that, these baby teeth will gradually fall out and be replaced with 32 permanent adult teeth.

The teeth are divided into four quadrants within the mouth, with the division occurring between the upper and lower jaws horizontally and down the midline of the face vertically. The incisors are used for cutting and biting, the canines are used for gripping, as well as the premolars and the molars are used for grinding. [4]

Figure 2.2. The anatomy and blood vessel (red), sensory nerves (yellow) of Dental pulp [5]

2.1.2. Histological structure of the teeth [4, 6]

• Tooth enamel: is one of the four major tissues that make up the tooth and makes up the normally visible part of the tooth, covering the crown. It is a very hard, white to off-white and partially responsible for the color of our teeth. Enamel is the hardest substance in the human body and contains the highest percentage of minerals (at 96%), with water and organic material composing the rest. The primary mineral is hydroxyapatite, which is a crystalline calcium phosphate. [Zijp et al. 1995] [4]. It is an extraordinarily hard substance that is specifically designed to protect the teeth from damage. Furthermore, light can spread through enamel layer, which plays an important role in tooth model because light always passes through this layer without any interaction with other layers. It can vary in thickness and hardness on each tooth, from tooth to tooth and from person to person [4].
• Dentin: is a hard layer that lies immediately underneath the enamel of the tooth and take responsibility for forming the bulk of the tooth, providing the tooth with the shape. It contains microscopic tubules (small hollow tubes or canals). When dentin loses its protective covering (enamel), the tubules allow heat and cold or acidic or sticky foods to stimulate the nerves and cells inside the tooth, causing sensitivity. It also contains hydroxyapatite crystal [Zijp and Ten Bosch1993] [4]... Like enamel layer, light transmission is considerably influenced when there is dentin. The cell bodies of the odontoblasts are aligned along the inner aspect of dentin against a layer of predentin where they also form the peripheral boundary of the dental pulp, which make this layer is sensitive to physical stimulations.

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         Figure 2.3. Illustration of the change of fuzzy attribute near the edges of the incisors

 Dental classification for periapical radiograph based on multiple fuzzy attribute is proposed, where each tooth is analyzed based on multiple criteria such

• Dental pulp: The pulp is the part in the center of a tooth and made up of living connective tissue called odontoblasts containing the blood and nerve supply of the tooth. It comprises a central pulp chamber, pulp horns, and radicular canals
• The tip of the root: Blood vessels and nerves enter from the bone area around the tip and away from the root canal. This is an area where infection begins when damaged teeth create apical abces.
• Grooves (pit and fissures): this structure forms a V-shape on the chewing surfaces of back teeth. Food can lodge in the natural grooves of the teeth which makes them even more likely to cause decay.
• Bone: The root is the unseen portion that supports and fastens the tooth in the jawbone. The root is attached to the tooth-bearing bone of the jaws by the periodontal ligament...
• The periodontal ligament: is a group of specialized connective tissue fibers that inserts into root cementum one side and onto alveolar bone on the other and serves primarily a supportive function by attaching the tooth to the surrounding alveolar bone proper This area is at risk of being destroyed in periodontal diseases, which contributes to the loss of alveolar bone and teeth.
• Gingiva (gums): The soft tissue covering the alveolar bone. Healthy gums are usually coral pink in light skinned people, but may be naturally darker with melanin pigmentation. Changes in color, particularly increased redness, together with swelling and an increased tendency to bleed, suggest an inflammation that is possibly due to the accumulation of bacterial plaque.

2.1.3. Molar tooth structure [7]

            Adult humans have 12 molars, in four groups of three at the back of the mouth. The third, rearmost molar in each group is called a wisdom tooth. It is the last tooth to appear, breaking through the front of the gum at about the age of 20, although this varies from individual to individual.

 The human mouth contains upper (maxillary) and lower (mandibular) molars. They are: maxillary first molar, maxillary second molar, maxillary third molar, mandibular first molar, mandibular second molar, and mandibular third molar.

Figure 2.4. Adult molar tooth structure

            1. Tooth enamel

            2. Dentin has tubes arranged in a centrifugal direction

            3. The space occupied by the pulp—the soft tissue at the center of your teeth containing nerves (yellow), the pulp veins (blue) and artery system (red)

Figure 2.5. The location of pulp (extends from the crown to the tip of the root). The blood vessels and the nerves that supply the upper and lower jaws: trigeminal nerve (yellow), vein (blue) and artery (red)

Figure 2.6. The parts of a moral tooth and surrounding structures

(1) Vein (blue)
(2) Artery (red)
(3) Nerves in jaw bone (grey)
(4) Alveolar bone that surrounds the roots of the teeth
(5) The gums or gingiva covering the root of the teeth and alveolar bone

    Figure 2.7. X-ray image of a moral

(11) Tooth enamel                            (14) Periodontal Ligament 

(12) Dentin                                       (15) Apical foramen

(13) Coronal pulp                             (16) Apical foramen

Figure 2.8.  Tooth Cross Section Anatomy with all parts

                        Figure 2.9. 3D images of a tooth shape and dental pulp

Figure 2.10. Cross-section of a root of the tooth (Bone arrounds cementum and dentin)

2.1.4. Structures of incisors [8]

Incisors are the front teeth and located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Deciduous incisors (di1 and di2/a and b) are the first and second teeth from the midline in the deciduous dentition and the permanent incisors (I1 and I2/1 and 2) are the first and second teeth from the midline in the permanent dentition. They all have a sharp biting surface and are used for cutting or shearing food into small chewable pieces. Deciduous incisors have smaller crowns and roots compared to permanent incisors but are similar in shape. Deciduous incisors are characterized by a prominent cervical enamel margin. The short crown height makes deciduous incisor appear rounder and more bulbous than permanent incisors.