Dentin

What is Dentin?

Dentin is a composite substance of organic and inorganic material found in the tooth’s interior.

Dentin is pale yellow and becomes darker with age. It constitutes the bulk of the tooth, providing its structure and protecting the more sensitive pulp inside of it. 

It is one of the major components of human teeth. When dentin is damaged or exposed, a variety of problems can occur, such as tooth sensitivity.

What are the Other Layers of a Tooth?

Dentin is one of four major components to a tooth. The other layers include:

• Enamel — Calcified tissue that acts as a protective barrier for the crown of the tooth. It is the hardest substance in the human body, composed of hydroxyapatite crystals (calcium and phosphate ions). It can be gradually lost due to abrasion, erosion, and attrition, exposing the dentin underneath. 
• Dental pulp — This soft tissue forms the tooth’s inner core, containing the blood vessels and nerves.
• Cementum — Forms a tough, protective covering of the root of the tooth, anchoring it in the jaw bone.

Dentin Structure and Composition

Dentin is a mixture of organic and inorganic matter. By weight, 70% is minerals (primarily hydroxyapatite), 20% is organic matter, and 10% is fluid.² Within dentin are odontoblasts, cells whose function is dentin formation. 

After the dentin formation is complete, the odontoblasts form dentinal tubules, microscopic tunnels that provide dentin with its permeability. These S-shaped tubular structures transmit sensations throughout the tooth, helping us feel temperature changes.

What is the Function of Dentin?

Dentin’s primary function is to provide structure to the tooth. It also protects the pulp, which houses the blood vessels and nerve endings of the tooth.

Without dentin, the pulp would be left exposed, meaning any stimulus to the tooth would cause extreme pain. 

Types of Dentin

There are three major types of dentin:

Primary

Primary dentin is the most prominent type of dentin in the tooth.

It is further subdivided into mantle and circumpulpal dentin. As its name implies, mantle dentin forms a protective covering of the dentin just below the tooth enamel. Relative to other types of dentin, it contains larger collagen fibers, which provide greater resilience to impact from chewing.

Secondary

Secondary dentin is formed below primary dentin, near the pulp chamber, after tooth formation is complete. When the teeth have erupted and are in contact with each other, the brain sends a signal to slow down the production of dentin. Because of this, secondary dentin grows much more slowly than primary dentin.

Below the secondary dentin, bordering the pulp chamber, is a layer of unmineralized material known as predentin. After minerals are added, it will become dentin.

Tertiary

Tertiary dentin is formed in response to stimuli, such as abrasion, injuries, or caries (cavities).

There are two types of tertiary dentin: reparative and reactionary. They have slightly different molecular structures. 

Reactionary tertiary dentin is formed by pre-existing odontoblasts in response to moderate stimuli. Reparative dentin is formed in response to more severe injuries (that killed the original odontoblasts) by newly-created odontoblasts. 

Types of Dentin Disorders & Conditions

When the dentin layer becomes compromised in some way, many disorders can occur. Some of these include, but are not limited to: 

Dentin Hypersensitivity

Popularly known as tooth sensitivity, dentinal hypersensitivity (DH) occurs when the dentin layer is left exposed. DH is generally experienced as sharp pain in the teeth in response to sensations like temperature and touch. 

These painful responses are most commonly experienced in the canines and premolars, and  by those between 20 and 50 years old.⁵

There is no one cause for hypersensitivity, but the loss of tooth enamel or cementum are major factors. It is a very common disorder in human teeth, with up to 30% of adults experiencing it at some point in their lives.⁸

There is no consensus in general dentistry regarding the exact mechanism behind dentinal pain. One theory suggests fluid dynamics as the cause. The idea is that enamel abrasion, which can happen from brushing too vigorously, leaves dentinal tubules wider than usual. 

Fluid moves through these tubules, which in turn activates nerve endings in the dental pulp.⁵ Common treatments for DH include desensitizing toothpastes, which reduce the transmission of sensation by covering up the dentinal tubules.

Dentin Dysplasia

The word dysplasia refers to abnormally-developed cells or tissues.

There are two variants to dentin dysplasia (DD): Type I and Type II. Both are rare, heritable disorders involving abnormal development of dentin. Treatment options depend on the specific symptoms and would be performed by a particular specialist called an endodontist.

Type I is the rarest variety. Its symptoms include unusually small pulp chambers in the roots of the teeth and sometimes bluish-brown discoloration of the crown. Because the roots are so small and malformed, those with the disorder often lose their teeth prematurely. Type II is also characterized by discoloration of baby teeth, but adult teeth typically do not fall out prematurely.^{6, 7}

Type II primarily affects the dentin in the crown. Like in Type I, this type also can produce discoloration of the baby teeth, but the adult teeth very often appear normal. Sometimes the adult teeth may take on a bulbous shape. 

In addition, x-rays will show the pulp chambers to be malformed in both crown and root, and it may contain excess calcium deposits. In contrast to Type I, those with this disorder typically do not lose their teeth prematurely.

Dentinogenesis Imperfecta

Dentinogenesis Imperfecta (DI) is another type of congenital dentinal disorder.

Its characteristics include malformed teeth, missing tubules, narrow roots, small pulp chambers, and discoloration. The abnormal dentinal tubules lead to the tooth enamel being easily chipped off, exposing the underlying layer of dentin. 

There are three variants of DI: Type I, Type II, and Type III.

Individuals with Type I DI have another bone disorder called osteogenesis imperfecta; the two disorders occur together. These patients have weak bones, hearing loss, and short stature.⁹ 

Type II produces the same dental symptoms as Type I but without any bone disorder. 

Type III is by far the rarest, only appearing in the family tree descending from a captain who moved from Liverpool to Maryland in 1732. The symptoms are the same as those for Type II. Treatment options for all types of DI include veneers, dental fillings, or dental implants.³

What Happens if Dentin Becomes Exposed?

How to Prevent Dentin Exposure

The best way to prevent dentin exposure is to protect your tooth enamel. Things that can wear down your enamel over time include: 

• Teeth grinding
• Poor brushing
• Overzealous brushing
• Certain whitening toothpastes
• Acidic foods
• Acid reflux

Ways to prevent these things include:

• Wearing a bite guard at night to prevent grinding
• Brushing teeth with only a soft brush
• Practice gentle brushing
• Avoid toothpastes with bleaching agents, and choose those with enamel-reparative properties 
• Limit exposure to acidic foods. Refrain from brushing for two hours after consuming acidic food, while enamel is still in a compromised state.
• Take steps to reduce acid reflux

Treatment for Dentin Exposure

There are two principal treatment approaches for exposed dentine: blockage of the dentinal tubules and desensitization of the nerves within the tubules.

Milk-based casein creams have often been used as remineralizing agents to close off dentin tubules. 

Toothpastes, chewing gums, and mouthwashes containing potassium salts are available over-the-counter which reduce nerve sensitivity.

 Laser treatment has even been used with some success to block off dentin tubules. Those suffering from dentin exposure should consult with their dentist for a complete list of options.