Introduction

Dentin Dysplasia (DD) is a rare hereditary disorder and is associated with problems in dentin formation. Dentin makes up the main bulk component of your teeth; it is the mineralised tissue consisting of collagen, inorganic material (hydroxyapatite), other proteins, lipids and water. It’s the yellowish hard tissue that supports the top enamel layer, connects to the root and surrounds the entire pulp, making it a sensitive part of the tooth.¹

ED Shields presented the first clinical classification, and he classified DD into two different types. Witkop later classified the two based on the type of dentin that is affected.^2,3 Type I is associated with issues in the formation of radicular (root) dentin, mainly affecting the development of the root of the teeth, therefore resulting in short roots or no roots.^1,2

Type I is also split into four further subtypes named Ia to Id.⁴ By splitting this disorder into subtypes, diagnosis precision can be improved, and clinical decisions can be more accurately informed with the potential for better prognosis. To continue exploring the subtypes of type I DD and to learn more about diagnosis methods and clinical correlation in further detail, continue reading below. 

Overview of dentin dysplasia type I

Epidemiology and genetics

This disorder is an autosomal dominant disorder, meaning that either the mother or father would have to have this disorder for it to be passed on to and affect their child.¹ However, some cases have reported having no previous family history of this disorder; thus, unknown new mutations or a different inheritance pattern could explain it.^1,5 

Type 1 DD is estimated to affect 1 patient in every 100,000, affecting both females and males equally. The exact abnormal gene(s) and mutation(s) that cause this disorder are incompletely understood, according to the National Organisation for Rare Disorders. However, some cases have shown that mutations in the SMOC2, VPS4B and SSUH2 genes were present and may have caused the disorder. Mutations in the DSPP (dentin sialophosphoprotein) gene have been identified to affect dentin formation and are associated with other dentin disorders.^1,6 

Histopathology and clinical features

Within this disorder, the enamel and crowns of the teeth appear to be normal. However, the underlying dentin layer is abnormal, with large masses of calcified dentin present, causing partial or complete destruction of the pulp chambers and canals that lie in the middle of the teeth, typically containing blood vessels and nerves. The abnormal dentin layers have irregular tubules and present with a “waterfall” appearance.^1,2 Since the roots of the teeth are affected, increased tooth mobility and early tooth loss are also seen. Both primary and permanent teeth can be affected.^6,7

Comparison with other similar disorders

Type I DD can be similar to type II DD, but unlike type I DD, root lengths are normal for both primary and permanent teeth, and primary teeth may have a brown or blue opalescent colour.⁷ Other differential diagnoses include other dentin-associated disorders, such as dentinogenesis imperfecta (DI), or conditions that result in early tooth loss, including Kostmann syndrome, Papillon-Lefèvre syndrome and vitamin D-resistant rickets.^6,7 However, they also have their own distinct clinical features and radiographic presentations to differentiate. 

Classification of subtypes Ia-Id

DD was first described in 1930 as “rootless teeth” by Ballschmiede, but was later given the DD name by Rushton. Shields and Witkop classified this disorder into two types: type I and type II.^2,7 The two types were based on the type of dentin affected. Radicular (root) dentin is the dentin found at the root of the tooth and is associated with type I DD. Type II is associated with issues in coronal dentin found at the crown of the tooth.^1,2,7 

Researchers noticed limitations to this classification system since this was solely based on clinical and radiographic characteristics, without also considering molecular/genetic information. Therefore, the classification was later refined to include the molecular/genetic component, potential overlap between the two types of disorders (i.e., DD and DI), and varying degrees of severity.¹ 

There are currently 4 subtypes for type I DD/radicular dentin dysplasia, and they have distinct features, including different pulp morphology and root development/length.^4,6 Type II DD may be seen as a milder form of dentinogenesis imperfecta, considering the similarities in clinical, radiographic and genetic features.¹ 

Type Ia

Radiographs (i.e., X-rays) for people who have type Ia DD will present with no root formation and no pulp chambers and canals within the teeth. The X-rays will also most likely show dark areas around the root of the teeth (i.e., periradicular radiolucency), indicating tissue/bone loss, since the X-rays are not being absorbed as they would be for normal bone/tissue.^4,5,8 For this type, prognosis is poor, and clinical presentations will include extreme movement of primary and permanent teeth with confirmed early tooth loss.⁴

Type Ib

Radiographs for people who have type Ib DD will present with some root formation, but the roots will be very short and conical-shaped. There may be some pulp chamber remnants present, so not all the pulp chamber is filled with abnormal dentin. This chamber will most likely be a horizontal crescent-shaped chamber. The X-rays will also likely show dark areas at the apex of the teeth (i.e., periapical radiolucency), indicating tissue/bone loss at that point.^4,5,8 For type Ib, prognosis is still poor but may be slightly better than Ia, with longer tooth retention in comparison. However, movement of primary and permanent teeth and early tooth loss are most certainly observed.^4,5,8

Type Ic

Radiographs for people who have type Ic DD will show root formation, but the roots will be shorter than normal and longer than the roots for type Ib. There are typically pulp chamber remnants present. There will be two crescent-shaped chamber remnants that are parallel to each other with an “island” of dentin in the middle. The X-rays may or may not show periapical radiolucency.^4,5,8 For type Ic, prognosis is better than Ia and Ib, as it is possible that tooth loss does not occur and teeth remain functional. However, this is very much dependent on the level of care given and regular, careful monitoring of teeth by your dentist.^4,5,8

Type Id

For people who have type Id DD, their X-rays will show near-normal root formation. There are typically normal pulp chambers present, but there may be pulp stones (dentin masses) visible within the pulp chambers, showing a bulge of the root around the stone. The X-rays most often don’t show periapical radiolucent areas, but there may be a few rare cases.^4,5,8,9 Prognosis is the best for Id out of all the subtypes. Most often, tooth loss does not occur, with the least amount of movement of teeth. Regular maintenance and consistent care of teeth is still essential.^4,5,8,9 

Diagnostic value of the subclassification

Radiography is a very important tool for diagnosis. Different dentin disorders or types within the same disorder may present with similar clinical signs, and therefore, visual images of the teeth will be crucial to provide further details for diagnosis, proving to be a key tool for subtype identification as well. Panoramic radiographs provide imaging of the entire mouth, including teeth, jaws and other structures, potentially providing information about which areas/teeth are affected by the disorder. Periapical focuses on specific areas of the mouth, showing clear details for one tooth, including the root and the surrounding bone.¹⁰

Histopathological analysis (microscopic analysis of teeth and surrounding tissue) can provide even more detail on dentin structure and pulp chamber morphology for further subtype classification and to differentiate from other similar disorders.¹ By diagnosing the type/subtype of the disorder accurately, clinical professionals can have a clearer idea of the severity of the disorder and potential timing for tooth loss. It can also help to provide the correct management and treatment plans. Some limitations for this diagnosis method include the potential for overlapping of clinical and radiographic features, causing issues in diagnosis, or not being able to detect changes in pulp morphology earlier.¹⁰

Clinical correlation and management implications

The severity of the disorder, in terms of affected pulp chambers and root length, declines from Ia to Id.^4,5 Ia and 1b have a poor prognosis, and therefore, early management plans are essential. Surgical/prosthetic considerations are usually involved with overdentures and implants being used.^1,4

 The prognosis for Ic is moderate; to retain functionality of teeth, preventive care and regular maintenance are crucial. Preventive care may include regular checkups with oral health professionals for professional-grade cleaning, maintenance of oral health, and possible fluoride application to reinforce enamel strength.^1,4 Id has the best prognosis; maintenance and regular checkups are still essential. 

Summary 

Dentin Dysplasia (DD) is a hereditary disorder that affects the formation of dentin, the bulk mineral component of your teeth. It can cause issues with the root of your teeth, potentially leading to increased movement and tooth loss. DD is split into two types, and table 1 summarises the key differences between the subtypes of type I DD.

 Clinical features, radiographic patterns, histopathological analysis and genetic analysis all contribute to the diagnosis of this disorder. Radiographic patterns and histopathological analysis provide more specific details about the health of your teeth and are crucial for the correct classification of this disorder. Genetic analysis will be important in identifying the cause of this disorder and, in the future, may allow for a more specific and accurate classification system when incorporated. Early diagnosis is crucial to allow medical professionals to create tailored treatment and management plans for the affected individual and improve their quality of life. Data sharing and collaboration between all professionals, including academic researchers, dentists, radiographers, geneticists and other medical professionals, will be essential for improved precision dentistry in DD. 

Table 1 – Summary of subtypes of Type I dentin dysplasia. The table includes details on pulp morphology, root length and any X-ray and clinical features to aid diagnosis.