What is dentin dysplasia?

Dentin dysplasia (DD) is a rare inherited condition that affects how the teeth develop, specifically the formation of the inner tooth structure called dentin.

The dentin is the hard, bony mineralized tissue that makes up most of the tooth’s structure.¹ This is pictured in Figure 1. Dysplasia refers to the growth and development of unusual or abnormal cells inside a tissue or organ.³ In DD patients, it presents as having normal-looking enamel but unusual dentin with irregularly shaped pulp tissue.⁴

Also visualized in Figure 1 is the crown, the part of the tooth that is outside of the gum, or above the gum line. The crown plays a vital role in chewing and grinding your food, while also influencing facial appearance and supporting clear speech.⁷ The crown consists of enamel, dentin, and pulp. The enamel protects the dentin from damage and cavities, while the pulp contains nerves, blood vessels, and connective tissue that nourish the teeth and keep them healthy.

The part of the tooth we cannot see is the root, which is located below the gum line. This includes the cementum, which is a thin layer of tissue made up of calcium deposits that cover the dentin in the root, as well as blood vessels and nerves within the root.^8,9

DD is classified into two types: Type I, the radicular type, which affects the root, and Type II, the coronal type, which affects the crown.⁴ This article will explore dentin dysplasia Type I (DD-I), looking specifically into issues with dentin formation within the root.

What are the symptoms of DD-I?

Diagnosing DD-I can be tricky, as many of the affected teeth look normal when examined visually by a dentist.⁴

DD-I affects both baby and adult teeth, and the signs can vary from person to person. Despite the crown appearing seemingly healthy, x-ray scans show that the roots are often short and pointed, with a cone-shaped narrowing at the tip. Healthy roots, by comparison, are supposed to look long, with more rounded tips.

There are four subtypes of DD-I; each manifesting as follows:^10,11

• Type Ia - The pulp chamber is completely destroyed, and there is little to no growth of the root
• Type Ib - There is a single, crescent-shaped horizontal line in the root area, with abnormal dentin, and the root is underdeveloped
• Type Ic - There are two crescent-shaped horizontal lines in the root area, covering about half of the root length, and the canals are missing
• Type Id - The root is normally developed, with a swollen upper third of the tooth, a small stone in the pulp chamber, and healthy pulp tissue

The affected teeth tend to be loose and may develop infections or abscesses easily, sometimes falling out earlier than expected. Unusual dentin formation can partially or completely block the pulp inside the teeth, which could lead to nerve damage and reduced sensation in the affected tooth.^6,12

There have been instances where baby teeth with DD-I show a small, faint glow that looks either a light amber colour or a bluish-brown shade, especially when the root has not fully developed or is just starting to grow.¹³

As DD-I is rare, it only affects 1 in every 100,000 people.⁴

What are the causes of DD-I?

Dentin dysplasia Type I is an autosomal dominant disorder, meaning that it is inherited in such a way that just one copy of a faulty gene is sufficient to cause the condition. Scientists have not yet identified exactly which gene or specific part of the chromosome is responsible for DD-I.¹³

Chromosomes are tiny structures inside the nucleus of our cells that carry genetic information. Most humans have 46 chromosomes, which come in pairs. They are numbered from 1 to 22, plus two special chromosomes called sex chromosomes, X and Y. Typically, men have one X and one Y chromosome, while women have two X chromosomes.

Our genetic diseases are caused by the specific combination of genes we inherit from our parents.

In dominant genetic disorders, just one faulty gene is sufficient for the disease to develop. This abnormal gene can come from either parent or arise from a mutation that develops in the person themselves. If a parent has the disorder, there is a 50% chance they will pass it on to each of their children, regardless if the child is a boy or girl.¹⁴

Recessive genetic disorders occur when a person inherits the same faulty gene from both parents. If someone inherits one normal gene and one faulty gene, they generally do not show any symptoms but are called carriers.¹⁵ 

When both parents are carriers, there is a 25% chance with each pregnancy that the child will inherit both faulty genes and develop the disorder. There is a 50% chance the child will be a carrier like the parents, and a 25% chance they will inherit normal genes from both parents and not develop the disorder at all. These chances are the same for boys and girls.¹⁴

Most people carry about 4 or 5 faulty genes. When parents are closely related, like cousins, there is a higher chance they both carry the same faulty gene, which increases the risk of having children with a recessive genetic disorder.^14,16

Treatment 

Treating DD-I can be challenging, even though there are many different treatment options. 

Whilst a root canal is a common procedure to remove infected or damaged pulp inside the tooth, sometimes it is not possible if the tiny channels inside the tooth and the pulp area are completely blocked.¹⁷

When that happens, pulling out the affected tooth is usually the best choice, especially if there is an infection at the tip of the root or if the tissue inside the tooth has died. 

Other procedures, like filling the area at the tip of the root or performing surgery near the root, are usually better suited for teeth with longer roots or when orthodontic work is being done. However, these procedures can sometimes damage the root or loosen the tooth, causing it to fall out earlier than it should.¹⁷ 

In some situations, all the teeth may be removed. In these cases, all cysts are cleared out, and full dentures are used to restore oral health. 

For dental implants, special procedures like adding bone (bone grafting) or lifting the sinus area can help build supportive bone, making it more likely that the implants will succeed.¹⁷

Summary

Dentin Dysplasia (DD) is a rare inherited disorder causing abnormal dentin and irregular pulp, with normal enamel. There are two types of DD: Type I, which affects the root, and Type II, which affects the crown. DD-I affects both baby and adult teeth, often showing short, cone-shaped roots on X-ray, despite normal-looking crowns. Symptoms include loose teeth, early loss, infections, and nerve damage. DD-I is often inherited in an autosomal dominant pattern, but may arise due to mutation (although the specific gene is unknown). Treatment is challenging, with options including extraction, root canals, or implants, with procedures tailored to root formation and infection status.