Tooth Anatomy: The Structure of Tooth and Surrounding Tissues

The adult dentition consists of 32 permanent teeth located in the upper and lower jaws. Every tooth has a function. With teeth, you can bite, crush and grind the food and prepare it before the digestion in the gastrointestinal tract.

Dental Anatomy: The Structure of a Tooth and Surrounding Tissues
Dental Anatomy: The Structure of a Tooth and Surrounding Tissues

Tooth anatomy, The tooth is the hardest substance in the human body. Our teeth serve primarily as a chewing organ. With teeth, you can bite, crush and grind the food and prepare it before the digestion in the gastrointestinal tract. The teeth can withstand high chewing forces. However, They are sensitive to acid attack by bacteria that can cause dental caries and gum disease. The teeth have an important role in speech and enable you to look and feel good.

Tooth Function

Every tooth in the oral cavity has a function:

  • Incisors: they are in the front area of upper and lower jaw (4 in each arch). Incisors are sharp and allow food biting and cutting.
  • Canines: they are located directly after the incisors. Canines are conical-shaped and holding food during biting. They facilitate the cutting of food.
  • Premolars and molars: they are located behind canines. They have a wide and flat surface with several cusps (occlusal surface). They crush food between occlusal surfaces of upper and lower premolars and molars, to make food swallowing and digestion easier.

The Dentition and Tooth Eruption

The child dentition consists of 20 primary teeth (primary dentition). In each jaw, there are 4 incisors, 2 canines, and 4 molars.

The eruption of upper primary teeth

  • Central incisor: 6-7 months
  • Lateral incisor: 7-8 months
  • Canine: 18-20 months
  • First Molar:12-15 months
  • Second Molar: 24-36 months

The eruption of lower Primary Teeth

  • Central incisor: 6-7 months
  • Lateral incisor: 7-8 months
  • Canine:18-20 months
  • First Molar: 12-15 months
  • Second Molar: 24-36 months
Primary Dentition
Primary Dentition

The adult dentition consists of 32 permanent teeth (permanent dentition). In each jaw, there are 4 incisors, 2 canines, 4 premolars, and 6 molars. During the so-called mixed dentition (primary and permanent teeth) between 6 and 12 years old, the primary teeth are gradually replaced by permanent teeth.

The eruption of upper permanent teeth

  • Central incisor: 7-8 years
  • Lateral incisor: 8-9 years
  • Canine: 11-12 years
  • First premolar:10-11 years
  • Second premolar: 10-12 years
  • First molar: 6-7 years
  • Second molar: 12-13 years
  • Third molar (wisdom tooth): 17-21 years

The eruption of lower permanent teeth

  • Central incisor: 6-7 years
  • Lateral incisor: 7-8 years
  • Canine: 9-10 years
  • First premolar: 10-12 years
  • Second premolar: 11-12 years
  • First molar: 5-6 years
  • Second molar: 12-13 years
  • Third molar (wisdom tooth): 17-21 years
Permanent Dentition
Permanent Dentition

The Structure of a Tooth and Surrounding Tissues

The human incisors, canines, premolars, and molars are different in shape but same in the structure. The tooth anatomical parts are:

  • Tooth crown: it is the visible portion of the tooth that protrudes from the gum into the oral cavity.
  • Tooth neck: it is surrounded by gingiva.
  • The root: it is the lower two-thirds of the tooth. It is surrounded and anchoring in the jaw bone. Incisors and canines have one root. Molars are multi-rooted (2-3 roots). The number of roots is different from a person to another.
Tooth Anatomy
Tooth Anatomy

Tooth Enamel

The enamel is the outer layer of teeth that covers the crown. Also, it protects the tooth against external damaging forces. Tooth enamel is the most resistant and hardest tissue in the human body. It consists of 95% inorganic substance (mainly calcium and phosphate in the form of hydroxyapatite), 1% organic substance, and 4% water. The fluoride increases the hardness of tooth enamel by converting the hydroxyapatite crystals to fluorapatite. So, fluoride toothpaste can increase the strength of enamel. In contrast, acid can damage the enamel by detaching calcium and phosphate, causing dental caries. The tooth enamel is exposed to 2 processes:

  • Demineralization: when oral bacteria decompose carbohydrates in food debris and produce acid, the oral pH drops below 5.5. The bacterial acid dissolves the enamel surface, which leads to the loss of calcium and phosphate ions, causing early stage of dental caries. This known as “demineralization”. (pH is a measure of the acidic or basic character of an aqueous solution. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic).
  • Remineralization: when the oral pH rises, the enamel restores minerals (calcium and phosphate) from saliva, reversing the early stage of dental caries.

Dentin

Dentin is the second layer of the tooth, after the enamel. It is the largest part of tooth structure, surrounding the pulp. It contains fine tubes called “dentinal tubules” which contain nerve tissues. The nerve tissues provide information and stimuli to the pulp. The dentin is sensitive to heat, cold, and touch, which appears as pain sensation. The dentin is softer and more susceptible to dental caries than the enamel. This is due to the slightly different composition of dentin.

Dental Pulp

Inside the tooth, there is a chamber known as “pulp chamber”. It contains nerve tissues and blood vessels that nourish the tooth. Nerve tissues and blood vessels are extending from the jaw bone to the pulp through a small hole at the root tip.

Periodontium

The periodontium is the surrounding and supporting structure of teeth. It anchors teeth to surrounding tissues and supports teeth during its function. The periodontium consists of:

  • Gingiva: it is a part of the oral mucosa that surrounds teeth and covers the maxilla and mandible. The beautiful smile comes from a harmonious coexistence of teeth and gingiva. Healthy strong gingiva is pink in color, has a harmonious wave profile, and doesn’t bleed. Inflamed gingiva is red, soft, and bleeding frequently during tooth brushing.
  • Cementum: it is a thin layer that covers the roots of the tooth. Also, it attaches the tooth to the bone.
  • Periodontal ligament (PDL): it is also known as “periodontal fibers”. It is connective tissue fibers in the small gap between the cementum and the jaw bone. The periodontal ligament provides an attachment of the tooth to the jaw bone. Also, it has a supporting, nutritive, sensory, and remodeling function.
  • Alveolar Bone: the bone is a living tissue. It’s well supported with blood and subjected to continuous modification. The pressure during mastication is transmitted to the bone and stimulates its modification, which makes the bone stronger. When there is no such pressure, because of tooth extraction, the bone recedes. The possible consequences of bone loss may be, for example, there is no sufficient amount of bone to anchor a dental implant or hold a denture. Also, the natural aging process leads to a reconstruction of the jaw bone. This is also a reason why prosthesis should be regularly modified to the jaw bone such as relining a denture.