Loss of Tooth Structure

Alterations in the Structure of Teeth – Enamel and Dentin

There are several genetic disorders that manifest as developmental alterations in the structural formation of enamel and dentin.⁹ These hereditary conditions are the result of gene mutations that control these key structural components.⁹ The conditions that will be presented include amelogenesis imperfecta, dentinogenesis imperfecta, and dentin dysplasia.

Enamel

Amelogenesis Imperfecta

Amelogenesis imperfecta (AI) encompasses a group of inherited genetic disorders that disrupt enamel development.¹⁶ Multiple gene mutations result in enamel aberrations such as pitted, grooved, and discolored teeth that are prone to fracture and severe wear.^16,17 Amelogenesis imperfecta affects both the primary and permanent dentitions and can occur alone without other signs or symptoms or in association with a syndrome that affects other parts of the body.^5,16-18 Amelogenesis imperfecta is also associated with other dental issues such as malocclusion, anterior open bite, altered eruption, and attrition^19-21 The clinical and radiographic manifestations can be classified into four general types: hypoplastic, hypomaturation, hypomineralization, and hypomaturation/hypoplastic with taurodontism as summarized in Table 6.^10,16,22,23 While the clinical implications vary depending on type and severity, the main treatment challenges involve esthetics, tooth sensitivity, and loss of vertical dimension.^10,19

Hypoplastic Amelogenesis Imperfecta – Type I

Hypoplastic amelogenesis imperfecta features inadequate deposition of enamel with yellow-brown tooth coloration from the dentin below the thin enamel layer.^5,10,16 The generalized pattern of this condition demonstrates pitted enamel, often stained, usually affecting the buccal aspect of the teeth.^10,16 However, the enamel may also appear rough or smooth.¹⁶ The crowns of the teeth look square-shaped with open contacts and flat occlusal surfaces.^5,9,10 In localized patterns, the affected teeth have horizontal rows of pits, a linear depression, or a single large area of hypoplastic enamel on the buccal middle third of the tooth.^5,10,16 The incisal edges or occlusal surfaces are usually unaffected.⁵ In rare instances, there is total agenesis of enamel while the teeth have the shape and color of dentin.^10,16 Both the primary and permanent dentitions may be affected or the primary dentition only.^5,10,16 The hypoplastic type is the easiest to identify radiographically.⁹

Hypomaturation Amelogenesis Imperfecta – Type II

Hypomaturation amelogenesis imperfecta is a defect in the quality of the enamel with normal thickness but mottled appearance.^10,16 The enamel is soft, easily pierced, and fractures away from the crown.^5,9,10,16 There are several types of enamel mottling that are associated with the underlying inheritance pattern.^10,16,22 The mottling ranges from pigmented brown, translucent to opaque white, yellow white, and snow-capped enamel.^5,9,10,16 The enamel mottling can mimic dental fluorosis, but the pattern is different in that AI affects all teeth similarly rather than time-based incidence.^9,22 Radiographically, the enamel appears to have the same radiodensity as dentin.^9,10,16

Hypomineralization Amelogenesis Imperfecta – Type III

Hypomineralization amelogenesis imperfecta, prior to eruption, shows that the teeth are of normal size and shape with usual enamel thickness.^10,16 Upon eruption, however, the inadequately mineralized, soft enamel quickly fractures away from the crown resulting in rapid wearing of the exposed dentin, stain uptake causing darkening, tooth sensitivity, and excessive calculus deposition.^10,16,22 The enamel color can range from white to creamy yellow.²⁴ Anterior open bite and the presence of unerupted teeth can be observed.^10,16 Radiographically, the enamel appears to have the same degree of radiodensity as dentin.⁹

Hypomaturation/Hypoplastic Amelogenesis Imperfecta with Taurdontism – Type IV

This type of amelogenesis imperfecta displays variant patterns of hypomaturation combined with hypoplasia affecting both primary and permanent dentitions diffusely.^5,16 The manifestations of the hypomaturation/hypoplastic variants are slight and depend on the predominance of one pattern over the other.¹⁶ In the hypomaturation-hypoplastic variant with taurodontism, the teeth have normal enamel thickness but appear mottled yellow white to yellow brown coloration with pitted buccal surfaces.¹⁶ Taurodontism with large pulp chambers and thin radiopaque enamel are observed on radiographic images.^10,16 The hypoplastic-hypomaturation variant is similar but the enamel is thinner with large areas of hypoplasia.^10,16,23 Radiographically, the enamel has the same radiodensity as dentin with single-rooted teeth displaying enlarged pulp chambers and posterior teeth varying degrees of taurodontism.^10,16

Figure 54.

Figure 54.

Child full mouth survey showing hypoplastic amelogenesis imperfecta, generalized pattern. Note the loss of enamel and flattened occlusal surfaces in the primary dentition. A thin layer of enamel can be seen radiographically.

Dentin

Genetic disorders of the dentin are broadly classified into two main categories, dentinogenesis imperfecta (DI) and dentin dysplasia (DD).²⁵ Two classification systems for dentin disorders based on phenotypic presentation have been broadly accepted, one proposed by Shields and the other by Witkop.^5,23,26 Most widely used, the Shields classification divides dentinogenesis imperfecta into three types and dentin dysplasia into two.^26,28 Ciola modified the classification by adding a third dentin dysplasia type, a combination of DD I and II and Carroll et al. further updated the classification with subgroups based on radiographic features.^28,30 More recent advances in molecular genetic research have proven that mutations in dentin sialphosphoprotein (DSPP) cause dentiongenesis imperfecta types II & III and dentin dysplasia type II, all variations in the severity of the same pathology.^31,32 As a result, a new classification focused on isolated forms of DI and a modification of Shields classification based on the causative mutation and genetic testing have been proposed to improve diagnoses.^31,32

Dentinogenesis Imperfecta

Dentiogenesis imperfecta (DI) is a genetic abnormality primarily of dentin with characteristic clinical and radiographic features. The aberrations are caused by autosomal dominant mutations in several different genes associated with collagen synthesis.³¹ Dentinogenesis imperfecta is the most frequent dentinal disorder which demonstrates varying degrees of severity: mild, moderate, and severe.^31,32

The mild form of dentiogenesis imperfecta, DD-II in the Shields Classification, affects the primary dentition.^25,26,31 The permanent teeth are normal color, shape, and height clinically while radiographically the pulp has a thistle-tube or flame configuration with a large pulp chamber, thin root canals and multiple pulp stones (Figure 55).^9,25,33

Figure 55.

Figure 55.

Cropped panoramic image showing mild DI with thistle-tube or flame pulp configurations with enlarged chambers, thin canals and pulp stones.

The moderate form of dentinogenesis imperfecta, DI-II or DGI-II in the Shields Classification, is the most common with the primary dentin more severely affected than the permanent dentition.^26,31 Clinically, the teeth display a color range from grey blue, brown, and opalescent but the enamel becomes displaced resulting in rapid attrition of the underlying dentin.^25,31,32 The radiographic appearance is pathognomonic, demonstrating bulbous crowns, cervical constriction, short, thick roots and pulp obliteration (Figure 56).^31,32

Figure 56.

Figure 56.

Full mouth survey demonstrating moderate dentinogenesis imperfecta. Note the bulbous crowns, cervical constriction, and pulp obliteration.

The severe form of dentinogenesis imperfecta, DI-III or DGI-III in the Shields Classification, known as the Brandywine isolate, is very rare.^23,26,31,32 It is associated with a sub-population in Maryland which has the highest incidence of dental genetic disorders; 1:15.³⁴ The severe form of DI affects both dentitions with bluish amber opalescent teeth, bulbous crowns, and attrition, much like the moderate form.^31,32 The main differentiation is significant enlargement of the pulp causing reduction of the dentin and multiple pulp exposures in the primary dentition described as shell teeth.^26,31,32,35 The permanent dentition demonstrates obliterated pulp chambers as do individuals that have shell teeth in their primary dentition.²³

Dentin Dysplasia

Dentin dysplasia (DD) is a rare developmental anomaly of unknown etiology that affects both the primary and permanent dentitions with a prevalence of 1:100,000.^31,32,36,37 Dentin dysplasia or radicular dentin dysplasia (Shields Classification DD-I) demonstrates clinically normal teeth in color and morphology but with short, abnormally shaped, or absent roots.^{9,26,29,31,36} Teeth can be misaligned and mobile resulting in premature exfoliation with little or no trauma.^9,38 Partial or complete obliteration of the pulp chambers and canals often with a remnant crescent-shaped pulp parallel to the CEJ and periapical radiolucencies without associated pathology are observed in some cases (Figure 57).^10,25

Figure 57.

Figure 57.

Full mouth survey demonstrating dentin dysplasia. Note short roots, partial and complete pulp chamber and canal obliteration of teeth.

Acquired Alterations of Tooth Structure

Loss of tooth structure typically occurs through tooth wear, a normal physiological function associated with aging. Wear of the teeth can be caused by several processes including attrition, abrasion, abfraction, and erosion. These processes are acquired alterations that occur subsequent to tooth development and eruption.