Structure and functions of human teeth

Introduction

Teeth is a highly sensitive and complex structure with many supportive tissues. Teeth is associated with many other supportive structural elements such as root, gums, fibrous tissues, bone and the surrounding mucus membrane. The visible part of the tooth is hard,  help in the process of mastication( chewing)  of food. Teeth is also important for speech, facial appearance and a proper aesthetic appearance of the face. The alignment, strength and appearance of teeth vary between individuals. Dentistry is the term used for describing the structure, functions, formation and the treatment of ailments related to teeth. Like other mammals, human beings develop 2 sets of teeth is depending on different age groups. Milk teeth or primary teeth are present in young children up to 12 years and the permanent teeth will replace the milk teeth.  Total number of milk teeth is 20 whereas the permanent teeth are 32. 

 

Types of teeth 

Anatomically, the teeth are classified into incisors, canines, molars and the premolars. All the teeth help in the mastication but each of them work differently. For instance,  incisors are used for cutting, canines perform tearing of the food, and molars help in grinding and the premolars aid in chewing the food.

1. Incisors

There are 8 incisors divided into  2 types; central and the lateral incisors, out of which  4 teeth are central incisors and the remaining 4 are the lateral incisors. Central incisors erupt at the age  6-8 yrs and the lateral incisors start appearing between  6.5-8.5yrs. The incisors are found in the frontal region of the mouth with their slim and sharp biting surface, hence they are used for cutting or shearing of the food into small chewable pieces. 

2. Canines

Canines are also called cuspids. There are 4 canines that erupt between the age 9-13 yrs. The canines are situated at the 'corners' of the dental arches. As they have a sharp, pointed biting surface, they assist in gripping and tearing the food. 

3. Molars

Molars are flat and broad. In total there are 8 molars among which 4 are primary molars erupting between 5.5-7 yrs and the second molars ( 2 in number) erupt by of 11-13 yrs and the third molars (2 in number) are seen for the first time at 17-21yrs. The molars are the largest of all the teeth assist in chewing, crushing and grinding of food.

4. Premolars

There are 2 types of premolars, first molars and the second molars.  Premolars are 8 in number, out of which the first Premolars appear at  9.5-11.5 yrs and the second  Premolars erupt at 10-13 yrs. The premolars, unlike the incisors and canines, have a flat biting surface. Their function is to tear and crush food. The image below helps to understand the arrangement and placement of all 4 types of teeth.

 

Types of teeth-image from scientific animations.com

 

Structure of the Tooth

Tooth firmly sits within the maxillary ( upper jaw) and the mandibular (lower jaw) sockets. In the case of milk teeth, maxillary and mandibular teeth are equally shared into 2 sets, i,e 1o teeth in the maxillary and the remaining 10 in the mandibular sockets. The permanent teeth are of 32 in total, shared into 16 on the upper and 16 on the lower jaws. Structure of teeth is descriptively divided into enamel, crown, gums, pulp chamber, neck, dentin, alveolar bone, root canal, cementum and the periodontal ligament. Let us understand the anatomy and physiology of teeth in detail.

    

 

Enamel and crown

96% of the enamel is made up of minerals and water and the remaining portion has inorganic material. The thickness of enamel vary between different surfaces. It is thicker at the cusp, - 2.5mm, and thinnest at its border. Attrition is the term used for wear rate. Anatomical crown is the term used for the visible part of the teeth normally covered by enamel. Enamel is the hard and calcified outer covering of teeth. Enamel surrounds the dentin present in the crown of the tooth. Enamel gives shiny and whitish appearance in its original form but in many cases, the enamel is damaged leaving yellow stains on the teeth. As it has no living cells, enamel cannot regenerate once it gets damaged, hence it is important to protect the enamel. 

 

Dentin

It is the substance found between the enamel and the central pulp chamber which sits just beneath the enamel. Dentin has a high tendency to be decayed rapidly as it has a mixture of soft collagen fibres and the mineralized connective tissues. The structural composition is, 10% of water, 70% inorganic materials and the rest 20%  is made up of organic materials. The formation of dentin is termed as dentinogenesis. There are 3 types of dentin, primary, secondary and tertiary.  Secondary dentin is a layer of dentin produced after root formation and continues to form with age. Damage to the dentin is nothing but the damage of enamel also. On damage to the dentin, teeth become highly sensitive to cold and heat. 

 

Gums 

Gums are also known as gingiva- soft supportive tissues appears reddish as that are made up of the mucosal tissues. Gums also have 3  different types of epithelium,  gingival tissues,  junctional tissues, and sulcular epithelium. Teeth`s epithelium is made up of cells known as the epithelial cuff. Gums are supplied with a lot of blood supply and nerves. Frequent bleeding of gums is an indication of decayed teeth or gum infections. 

 

Pulp Chamber

Pulp is a space containing soft tissues, nerves, blood vessels and the connective tissues within. The pulp is very essential to perform the neurosensory function for each individual teeth. There is a large mass of soft tissues (pulp) within the pulp cavity. There is a plenty of small capillaries surrounding the pulp cavity making it one of the delicate areas in the mouth.

 

Neck 

Dental neck is otherwise known as the dental cervix. Neck sits between the crown and root forms a lining where the cementum (that covers the root) meets the enamel.

 

Cementum

Cementum is a gum-like material made up of 45% of the inorganic material, 33%  of organic material such as collagen and the remaining 22% is the water. The root of the teeth has cementoblast cells. Cementoblasts help in secreting cementum. The cementum serves as a medium through which the periodontal ligaments stick to the tooth. 

 

 Maxilla and mandible

Maxilla and mandible are the bony prominences that hold the root of the teeth along with the cementum. The upper bony prominence is the maxillary prominence and the lower one is called mandibular prominence. 

 

Periodontal ligaments

A ligament is a supporting tissue act as a specialized connective tissue that attaches the cementum of a tooth to the alveolar bone. There are multiple ligaments across different alveolar bones.  An individual ligament has a width of 0.15–0.38mm.

 

Blood supply and nerve supply of teeth

Nerve supply of maxillary teeth

Posterior superior alveolar nerve (branch of the maxillary nerve (V2). Anterior superior alveolar nerve (branch of the infraorbital nerve) and the middle superior alveolar nerve (branch of the infraorbital nerve)

Blood supply of maxillary teeth

Branches of the maxillary artery, namely the posterior superior alveolar artery, middle superior alveolar artery and the anterior superior alveolar artery

Nerve supply of mandibular teeth

Inferior alveolar nerve (branch of mandibular nerve V3)

Blood supply of mandibular teeth

Inferior alveolar artery (branch of the maxillary artery)

 

Read more

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Structure of human tongue

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Questions

  1. Explain the difference between temporary( milk teeth) teeth and permanent teeth.

  2. Explain the functions of different teeth.

  3. Describe the 4 sets of teeth and their functions and location

  4. Explain the anatomy of a typical tooth.

  5. What is enamel?

  6. What is cementum? What is its role?

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