Systemic Enamel Hypoplasia: Etiology, Classification, Clinical Presentation, and Treatment

Enamel hypoplasia is a quantitative and qualitative developmental defect of enamel in permanent or primary teeth due to factors disrupting ameloblast function.

Systemic enamel hypoplasia refers to developmental defects in all teeth or a group of teeth formed during a particular developmental stage due to metabolic disorders in the child or fetus.

Etiology

Enamel hypoplasia results from impaired ameloblast function during the follicular stage of tooth development. Factors affecting ameloblasts can be divided into several groups specified below.

Prenatal factors

• Diseases and pathological conditions during the mother’s pregnancy (gestosis, rubella, toxoplasmosis, alcoholism, vitamin A and D deficiencies, diabetes mellitus, hypoparathyroidism, syphilis, cytomegalovirus infection, heart, kidney, and lung diseases, hypertension, or anemia);
• Exposure to ionizing radiation during pregnancy;
• Hypoalimentation or malnutrition during pregnancy;
• Prolonged medication use during pregnancy.

Neonatal factors

• Prematurity and/or low birth weight;
• Factors related to childbirth (birth trauma, asphyxia);

• Neonatal hypocalcemia, toxic injuries, neurological diseases, hyperbilirubinemia, prolonged diarrhea and vomiting, and neonatal infections with high fever.

Postnatal factors

• Calcium and phosphorus metabolism disorders;
• Endocrine diseases (affecting thyroid and parathyroid glands);
• Acute infections associated with fever;
• Hypovitaminosis A, C, D, or E, nutritional dystrophy;
• Congenital allergy and related water-salt metabolism disorders;
• Alimentary tract diseases;
• Diarrhea with toxic symptoms;
• Hemolytic jaundice;
• Phenylketonuria, alkaptonuria;
• Renal disorders;
• Congenital Heart Defects;
• Mercury poisoning;
• Prolonged medication use;
• Radiation therapy of the jaws in early childhood.

Despite a wide range of causal factors, the resulting clinical signs of enamel developmental defects are similar. Decreased or impaired ameloblast function due to external influences leads to alterations in the enamel matrix construction and its mineralization.

Relationship between defect depth and localization with the exposure period

The severity and localization of enamel defects reflect periods of metabolic disorders in the child’s body coinciding with amelogenesis and depend on the stage of tooth formation when the etiological factor acts, as well as the intensity and duration of its effect.

Lesion depth

In systemic enamel hypoplasia, a group of teeth formed during the same developmental period is affected; in the event of severe disease or frequent recurrence in the child or mother, all teeth may be impacted.

• The width of the defective enamel area depends on the duration of the etiological factor’s exposure period;
• The defect depth reflects the intensity of the exposure;
• The number of defects indicates the frequency of metabolic disorders in the body, occurring upon the development of a new disease or recurrence of a previous one.

Lesion localization

The localization of enamel defects can approximately indicate the age when ameloblasts malfunctioned.

Enamel defects in hypoplasia are irreversible, as tooth enamel cannot be remodeled, unlike bone tissue.

Epidemiology

The epidemiology of systemic enamel hypoplasia is characterized by a high global prevalence, averaging 25.3%, with significant geographical variability (from ~7% in affluent regions of Europe to >40% in Asia and Oceania).

Traditionally, the key causes are considered biological factors of the perinatal period: prematurity and low birth weight can increase the risk of defect development up to 60%.

It is also necessary to consider socioeconomic status: a statistically significant association between low family income in the patient’s childhood and the presence of enamel defects has been proven. The etiology of enamel hypoplasia is recognized as strictly multifactorial, where the quality of medical care can modify the influence of biological risks.

A study on a modern European population showed that with the availability of perinatal medicine, typical factors (cesarean section, prematurity) are successfully compensated and do not lead to enamel defects, whereas the living standard plays a crucial role. No significant gender differences were identified (men and women are affected equally frequently). Morphologically, the most common form remains furrow-form (linear) hypoplasia (found in 93% of cases), most often affecting the maxillary incisors.

Classification of systemic enamel hypoplasia

• Spotted form;
• Erosive (pitting) form;
• Furrow form;
• Wavy form;
• Cup-shaped form;
• Mixed (combined) form;
• Enamel aplasia.

Anatomy

The type of enamel defects in systemic hypoplasia depends on the stage of enamel development when the exposure to the etiological factor occurred.

Despite the variability of clinical forms, common signs of systemic enamel hypoplasia can be identified:

• Teeth erupt already defective;
• Defects usually have a relatively regular shape and even borders;
• Multiple teeth are affected: they have defects that are at the same level, in the same area of the crowns, and typically are of uniform size and shape;
• A group of teeth from the same developmental period is affected; the defects are symmetrical;
• Defects are parallel to the incisal edges or occlusal surfaces of teeth, more often on the labial/buccal surface and cusps.

Microstructural changes in hard tissues

• In enamel structure, changes in the width and direction of enamel prisms are observed.
• In the dentin structure of affected teeth at the border with enamel, the dentin tubules are curved and have a less regular arrangement; in some areas, narrowing and widening of their lumen is visible, and the hydroxyapatite crystals are arranged more randomly and loosely.
• Increased formation of tertiary dentin by the pulp may also be observed.

Diagnosis of systemic enamel hypoplasia

Clinical manifestations

Spotted form

The patients can complain of a cosmetic imperfection. On the buccal surface of the teeth, in particular in the area of the cusps or incisal edge, spots are identified; they appear on an intact enamel and look milky-white, less often yellowish or brown, with clear boundaries and a smooth, glossy surface. The enamel in the affected area is of normal thickness. Over time, the spots do not change in size, shape, or color. The spots do not stain with methylene blue and are not detected on X-ray.

Erosive (pitting) form

The patient may complain of a cosmetic defect or pain from chemical or thermal irritants (rarely).

On the enamel surface, depressions in the form of pits are identified, arranged horizontally and not connected with each other. The defects are usually round, with a smooth, dense bottom and shallow edges; the enamel is thinned in these areas. The pits are deeper on the labial/buccal surfaces of teeth and may be consistently stained with food pigments. Probing of the defects is painless.

Sometimes, the pitted form of systemic enamel hypoplasia can be associated with caries.

Furrowed form

The patient complains of a cosmetic defect, sometimes of pain from mechanical, chemical, and thermal irritants, and of wear of the teeth.

Visually, depressions in the form of horizontal single or multiple grooves of varying depth and width can be seen on the teeth; the defects are located parallel to the incisal edge or occlusal surface.

At the bottom of the grooves, enamel is thinned or absent. When the enamel is partially preserved, the bottom of the defects is dense and smooth, with shallow edges. If the grooves affect the full thickness of the enamel, the bottom can be yellow or brown and have a rough surface, which may be painful when probed. If the groove is located on the incisal edge, it only has one wall, giving the impression that another, smaller tooth is “growing” from one tooth. In this case, premolars and molars exhibit underdeveloped cone-shaped cusps, devoid of enamel, which often chip due to mechanical stress. In the area of deep defects, caries may occur.

Wavy form

It’s a variant of the furrowed form of systemic enamel hypoplasia, where multiple thin horizontal grooves are visible on the tooth crown, partially merging with each other to form a wavy surface.

Cup-shaped form

The patient may complain of a cosmetic defect, sometimes of pain from chemical or thermal irritants. The defects appear as cup-shaped depressions, oval or round, of varying size and depth.

The enamel at the bottom of the defects is thin or absent. If a thin layer of enamel is preserved, the edges, walls, and bottom of the defects are smooth, shallow, and dense, while in areas without enamel, the tissues are roughened and pigmented. If a cup-shaped defect is located in the area of the incisal edge of a front tooth, a semilunar notch forms on it. With defects on premolars and molars, their cusps are thinned and needle-like, prone to wear and chipping due to mechanical stress. Deep defects may also be affected by caries.

Mixed (combined) form

Depending on the severity of the defects, the patient complains of poor aesthetic appearance, pain from chemical and thermal irritants, tooth wear, and cusp chipping.

The mixed form of systemic enamel hypoplasia represents a combination of several defect forms on different teeth and even within a single tooth (combination/alternation of spots, pits, grooves, and cup-shaped depressions). Areas of deep defects, where enamel is completely absent, often fracture, chip, and wear away, and caries may also develop in these areas.

Enamel aplasia

The patient complains of poor aesthetic appearance and pain from mechanical, thermal, and chemical irritants, as well as tooth wear and chipping. Enamel aplasia is a severe degree of enamel hypoplasia, characterized by local absence of enamel in certain areas or complete absence of enamel on the entire tooth crown.

Thinned areas of remaining enamel can wear over time, and caries may develop in areas of deep defects.

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Treatment

Treatment of systemic enamel hypoplasia depends on the severity of the enamel lesions.

• In the presence of lines and spots, remineralization, bleaching, and microabrasion techniques can be applied.
• For increased tooth sensitivity, desensitizers are used as indicated.
• In the presence of cavity defects, direct restoration with composite materials, glass ionomer cements (GIC), or compomer restorative materials is performed, and severely damaged hard dental tissues may be restored with esthetic veneers, overlays, or full crowns. It is important to note that patients with systemic enamel hypoplasia (except the spotted form) are more prone to develop caries and its complications.
• In severe cases, when conservative methods are impossible, affected teeth are extracted with subsequent prosthetics.