The structure of a tooth involves several protective layers that shield it from chewing forces, temperature changes, and bacterial invasion. These layers are fundamental for maintaining tooth health and function throughout life. Understanding these natural defenses helps prevent dental issues and preserve oral well-being.
Enamel
Enamel forms the outermost covering of the tooth crown, acting as the primary protective barrier. It is the hardest substance in the human body, even more so than bone. Its composition is approximately 96% inorganic material, primarily hydroxyapatite crystals, with small percentages of water and organic matrix. Enamel protects the underlying, more sensitive layers like dentin and pulp from physical damage, erosion, and bacterial acids.
Despite its strength, enamel is susceptible to demineralization from acids produced by oral bacteria, leading to tooth decay. Once damaged, enamel cannot regenerate because it is a non-living tissue and lacks cells for repair. When enamel erodes or is compromised, the tooth can become sensitive to hot, cold, or sweet stimuli, as its protective insulation is lost.
Dentin
Beneath the enamel lies dentin, a calcified tissue that constitutes the bulk of the tooth’s structure. It is softer and more porous than enamel, with a composition around 70-72% inorganic materials (mainly hydroxyapatite), 20% organic materials, and 8-10% water. Dentin provides support for the overlying enamel, preventing it from fracturing under chewing forces.
Dentin’s distinguishing feature is millions of microscopic channels called dentinal tubules, extending from the pulp to its outer surface. These tubules contain fluid and odontoblast extensions, transmitting sensations like pain, pressure, and temperature to the tooth’s pulp. When enamel is lost and dentin is exposed, these tubules become pathways for external stimuli, leading to tooth sensitivity. Dentin can also produce secondary dentin throughout life in response to stimuli like decay or wear, offering a natural defense.
Cementum
Cementum is a specialized calcified tissue covering the tooth root, extending from where the enamel ends to the root tip. Its primary function is to anchor the tooth within the jawbone. This attachment is facilitated by strong connective tissue fibers, known as periodontal ligaments, which embed into the cementum on one side and the surrounding alveolar bone on the other.
While similar to bone, cementum is generally softer than dentin and is approximately 45-50% inorganic material. It provides a protective covering for the sensitive dentin in the root area, which enamel does not shield. In a healthy mouth, cementum is not visible, as gum tissue covers it. However, if gum recession occurs, exposed cementum can lead to sensitivity as the underlying dentin is no longer protected.
Dental Sealants
Beyond the natural protective layers, dental sealants offer an applied protective “lining” for teeth. These thin, plastic coatings are painted onto the chewing surfaces of molars and premolars. These back teeth often have deep pits and grooves, which can trap food particles and bacteria, making them susceptible to decay. Sealants flow into these depressions and harden, creating a smooth barrier that effectively seals out bacteria and food debris.
The application process is quick and painless, involving cleaning the tooth, applying an acidic gel for bonding preparation, and then painting on the liquid sealant, hardened with a special light. Dental sealants are beneficial for children and teenagers, as their newly erupted permanent molars are vulnerable to cavities. Adults can also benefit, especially with deep grooves or a history of decay in these areas. This preventive measure significantly reduces the risk of cavities on treated surfaces.