A tooth is a hard, calcified structure found in the jaws of many vertebrates, including humans. Human teeth are considered part of the digestive system, mechanically breaking down food.
Anatomy of a Tooth
A human tooth is divided into two main structures: the crown and the root. The crown is the portion visible above the gum line, while the root is embedded within the jawbone. The area where the crown meets the root is known as the neck or cervical line.
The outermost layer of the crown is the enamel, the hardest substance in the human body. This highly mineralized tissue is composed primarily of hydroxyapatite, a crystalline form of calcium phosphate. Enamel functions as a protective shield against wear, tear, and bacteria. Unlike other body tissues, enamel does not contain living cells and cannot repair itself from damage once fully formed.
Beneath the enamel lies dentin, which forms the bulk of the tooth’s structure. Dentin is not as hard as enamel. It contains microscopic tubules that extend to the tooth’s nerve center, transmitting sensory signals related to temperature or pressure changes.
At the core of the tooth is the pulp, a soft tissue containing nerves, blood vessels, and connective tissue. The pulp chamber is located within the crown, while pulp canals extend into the roots. This soft tissue nourishes the tooth, transmits sensory information, and aids in dentin formation during tooth development.
The root of the tooth is covered by cementum, a hard connective tissue that connects the tooth to the surrounding structures. Cementum, similar in hardness to bone, helps anchor the tooth firmly in the jaw. It works in conjunction with the periodontal ligament, a system of fibers that attach the tooth root to the alveolar bone of the jaw.
Functions of Teeth
Teeth perform several functions. Their primary role involves the mechanical breakdown of food, a process known as mastication. This action cuts, tears, and grinds food into smaller, more manageable pieces, which prepares it for swallowing and digestion. The efficiency of this process directly impacts nutrient absorption.
Beyond their role in eating, teeth contribute significantly to speech articulation. The precise positioning of teeth, particularly the front teeth, influences how air flows and how the tongue interacts to form various sounds. Missing or misaligned teeth can affect speech clarity and pronunciation.
Teeth also play a part in maintaining the structural integrity of the face. They help to preserve the shape and contour of the jaw and support the muscles of the cheeks and lips. The presence of a full set of teeth helps to prevent changes in facial appearance that can occur with tooth loss.
Types of Human Teeth
Humans develop two sets of teeth throughout their lives: 20 primary (or “baby”) teeth and up to 32 permanent teeth. The permanent dentition includes four distinct types of teeth, each with a specialized shape suited to particular functions.
Incisors are the eight teeth located at the front of the mouth, four on the top and four on the bottom. They have a flat, chisel-shaped edge, making them ideal for biting into and cutting food. Incisors are the first teeth to engage with food during eating.
Adjacent to the incisors are the canines. There are four canines in total, two in the upper jaw and two in the lower jaw. Their pointed shape and extended roots are effective for tearing and gripping tougher foods. Canines also help guide the jaw into proper alignment when the mouth closes.
Behind the canines are the premolars, also known as bicuspids. Adults have eight premolars, two on each side of both the upper and lower jaws. These teeth feature flatter surfaces with ridges, serving a transitional role between tearing and grinding. Premolars help to crush and break food into smaller pieces before it reaches the back of the mouth.
Molars are the largest teeth, positioned at the back of the mouth. Adults have twelve molars, including wisdom teeth, with six in the upper jaw and six in the lower jaw. Their broad, flat surfaces and multiple cusps are designed for grinding and chewing food into a fine consistency. Molars play a significant part in distributing chewing forces evenly across the mouth.