Hypothyroidism

Hypothyroidism is a systemic endocrine disorder of thyroid hormone deficiency that produces characteristic oral and maxillofacial manifestations, particularly when onset occurs during development.[1][2] The condition arises from primary thyroid failure (>99% of cases), most commonly Hashimoto thyroiditis in iodine-sufficient regions, or less frequently from central (pituitary/hypothalamic) or peripheral causes. [1][2]Congenital hypothyroidism results from thyroid dysgenesis (80–85% of cases) or dyshormonogenesis.[1][3] Thyroid hormone is essential for craniofacial skeletal development, endochondral bone formation, and tooth maturation; its deficiency produces delayed dental development, jaw underdevelopment, and altered bone metabolism that are recognizable on dental radiographs.[4][5] The signature radiographic pattern in untreated or undertreated childhood-onset disease is a discrepancy between dental age and chronologic age, with retained deciduous teeth, delayed eruption and root formation of permanent teeth, and underdeveloped jaws.[5][6] Management centers on levothyroxine replacement, with dental treatment planning adapted to the patient's thyroid status and developmental stage.[7][8]

The current accepted term is hypothyroidism, classified as primary, central (secondary/tertiary), or peripheral based on the level of dysfunction.[1][2] Congenital hypothyroidism (CH) refers to thyroid hormone deficiency present from birth.[3][7] Myxedema historically described severe, prolonged adult hypothyroidism with characteristic mucinous edema of the skin and subcutaneous tissues; myxedema coma denotes the rare, life-threatening decompensated state.[1][2] The term cretinism was formerly used for severe untreated congenital hypothyroidism with intellectual disability and growth failure but is now considered obsolete and pejorative; current guidelines use "congenital hypothyroidism" exclusively.[7] Hashimoto thyroiditis (chronic autoimmune or lymphocytic thyroiditis) is the most common cause of acquired hypothyroidism in iodine-sufficient populations.[1][2]

• Adult hypothyroidism: Overt primary hypothyroidism has a prevalence of approximately 1–2% in iodine-sufficient populations, with a female-to-male ratio of approximately 5:1. Prevalence increases with age, reaching up to 7% in individuals aged 85–89 years. Hashimoto thyroiditis accounts for up to 85% of primary hypothyroidism in iodine-sufficient areas.[1][2]
• Congenital hypothyroidism: Affects approximately 1 in 2000 to 1 in 4000 newborns detected by newborn screening, with a 1.5- to 2-fold greater incidence in females for thyroid ectopia. The incidence has increased over time owing to lowered screening thresholds that detect milder cases.[3][9]
• Oral and maxillofacial relevance: Orofacial manifestations are most prominent in untreated or late-diagnosed congenital and juvenile-onset hypothyroidism, which is now uncommon in countries with universal newborn screening.[7][10]

General Presentation

Adult hypothyroidism presents with nonspecific symptoms of metabolic slowing: fatigue (68–83%), weight gain, cold intolerance, dry coarse skin, constipation, cognitive impairment, and bradycardia.[2] Myxedema coma is exceedingly rare but carries mortality up to 30%.[1][2]

Oral and Maxillofacial Findings

• Macroglossia: A characteristic finding in both congenital and severe adult hypothyroidism; the enlarged tongue may contribute to anterior open bite and dental crowding.[2][3]
• Delayed tooth eruption: The hallmark dental manifestation of childhood-onset hypothyroidism. Deciduous teeth may persist well beyond the expected exfoliation age, and permanent tooth eruption is markedly delayed. In severe untreated congenital hypothyroidism, primary teeth have been reported to persist into the late teenage years.[5][6][10]
• Enamel hypoplasia: Developmental enamel defects occur when thyroid hormone deficiency coincides with the period of amelogenesis.[5][11]
• Micrognathia and anterior open bite: Underdevelopment of the mandible and maxilla results from impaired endochondral and intramembranous bone growth; the combination of micrognathia and macroglossia contributes to anterior open bite.[4][5]
• Craniofacial dysmorphism: Coarse facies, wide posterior fontanelle (in infants), and dysplastic facial features reflect delayed craniofacial skeletal maturation.[3][4]
• Periodontal and mucosal changes: Oral dryness and gingival changes have been reported in pediatric endocrine populations. Adults with hypothyroidism may exhibit delayed wound healing relevant to surgical planning.[8][11]

Tempo and Complications

Oral manifestations correlate with the severity and duration of thyroid hormone deficiency before treatment. Early levothyroxine replacement can reverse many dental developmental delays, though catch-up may be incomplete if treatment is significantly delayed.[10][12]

The radiographic findings of hypothyroidism in the jaws are developmental rather than destructive, reflecting the systemic effect of thyroid hormone deficiency on skeletal and dental maturation. Findings are most pronounced in untreated or late-treated congenital and juvenile-onset disease and are best appreciated on panoramic radiographs, where dental age can be compared with chronologic age.

Location and Distribution

• Findings are generalized, affecting both jaws symmetrically, consistent with the systemic nature of the endocrine disturbance.[5][13]
• The mandible may be disproportionately affected owing to its dependence on condylar cartilage growth, which is sensitive to thyroid hormone.[14][15]

Effects on Teeth

• Delayed dental development is the most characteristic radiographic finding. Panoramic radiographs demonstrate a dental age significantly younger than the patient's chronologic age, with incomplete root formation and delayed calcification stages of developing permanent teeth.[5][6]
• Retained deciduous teeth are common in untreated childhood-onset disease. Primary teeth remain in the arch well beyond the expected exfoliation age, with unerupted permanent successors visible in the alveolar bone.[6][10]
• Delayed eruption of permanent teeth is closely linked to the above; permanent teeth may remain unerupted or partially erupted despite complete or near-complete root formation.[5][10]
• Impacted teeth may occur, particularly mandibular second and third molars, as a consequence of the dissociation between dental development and insufficient jaw growth to accommodate the permanent dentition.[6]
• Enamel hypoplasia may be visible radiographically as areas of reduced enamel opacity or irregular enamel contour, though this finding is better appreciated clinically.[5][11]
• Short or blunted roots have been described occasionally, reflecting impaired root development during the period of thyroid hormone deficiency.[5]

Jaw Size and Shape

• Micrognathia is a characteristic finding, with the mandible and maxilla appearing underdeveloped relative to chronologic age. The mandibular body and ramus may be shortened.[5][14]
• Condylar hypoplasia contributes to mandibular underdevelopment. Experimental studies demonstrate that hypothyroidism reduces condylar cartilage cellularity and disrupts the osteogenic process at the mandibular condyle.[15]
• Insufficient ramus growth relative to dental development creates crowding in the posterior mandible, contributing to molar impaction.[6]

Internal Architecture

• Trabecular bone changes have been evaluated by fractal analysis on panoramic radiographs. Hypothyroid patients demonstrate altered fractal dimension values in trabecular-rich regions of the mandible (ramus and angle), suggesting subtle changes in trabecular bone pattern, though cortical bone appears relatively preserved.[16]
• In the general skeleton, hypothyroidism is associated with increased trabecular bone volume (osteopetrotic pattern) in the mandibular condyle, as demonstrated in experimental models.[15]

Skeletal Maturation Markers

• When hand-wrist or cervical vertebral radiographs are available, markedly delayed bone age is characteristic, often years behind chronologic age.[10][12][17]
• Epiphyseal dysgenesis with stippled, irregular, or fragmented epiphyses is a classic skeletal radiographic finding that, while not directly visible on dental radiographs, provides important diagnostic context when identified on other imaging.[17][18]

Growth Pattern and Cortical Involvement

• The growth pattern is one of generalized developmental delay rather than expansion or destruction. No cortical erosion, periosteal reaction, or pathologic fracture is expected in the jaws.[13]
• Cortical bone thickness of the mandible is generally maintained, distinguishing hypothyroidism from conditions that cause cortical thinning or resorption.[16]

Thyroid Ultrasonography

Ultrasound is the primary imaging modality for evaluating the thyroid gland itself. In Hashimoto thyroiditis, characteristic findings include diffuse thyroid enlargement (goitrous form) or a small atrophic gland, heterogeneous hypoechoic parenchyma, and increased vascularity.[19][20] In congenital hypothyroidism, ultrasound can identify thyroid dysgenesis (athyreosis, ectopy, or hypoplasia).[1][3]

Nuclear Medicine

Thyroid scintigraphy (technetium-99m pertechnetate or iodine-123) is used in congenital hypothyroidism to distinguish thyroid dysgenesis from dyshormonogenesis and to localize ectopic thyroid tissue, which aids in determining whether the condition is permanent or potentially transient.[3][7]

Skeletal Radiography

Plain radiographs of the hand and wrist or knee demonstrate delayed bone age and epiphyseal dysgenesis (stippled, fragmented, or absent epiphyses), which are important diagnostic clues in undiagnosed childhood hypothyroidism.[17][18] These findings may prompt referral for thyroid function testing when encountered incidentally.

When panoramic radiographic findings suggest generalized delayed dental development, retained deciduous teeth, or jaw underdevelopment in a child or adolescent, the differential should include other systemic and genetic conditions that impair dental and skeletal maturation.

The highest-risk diagnostic pitfall is failing to consider hypothyroidism when encountering unexplained generalized delay in dental development on a panoramic radiograph, particularly in a child not yet diagnosed. Serum TSH and free T4 testing should be recommended when radiographic findings suggest a systemic cause of delayed dental maturation.[5][10]

The oral hard-tissue changes in hypothyroidism are developmental rather than neoplastic, and biopsy of jaw bone or teeth is not part of the diagnostic workup. However, understanding the histopathologic basis of the dental and skeletal findings provides important radiologic-pathologic correlation.

Dental Hard Tissues

• Enamel hypoplasia results from disrupted ameloblast function during the secretory phase of enamel formation. Histologically, affected enamel shows reduced thickness with irregular incremental lines.[5][22]
• Dentin abnormalities may include irregular dentinal tubule arrangement and areas of interglobular dentin, reflecting impaired odontoblast activity during the period of thyroid hormone deficiency.[22]

Bone

• Experimental studies of the mandibular condyle in hypothyroidism demonstrate reduced chondrocyte cellularity in the condylar cartilage, with increased trabecular bone volume along the ossification front (an osteopetrotic pattern), reflecting impaired endochondral ossification.[15]
• Thyroid hormone deficiency disrupts the normal coupling of cartilage resorption and bone formation, mediated in part through impaired insulin-like growth factor 1 signaling in condylar chondrocytes.[15]

Thyroid Gland (Hashimoto Thyroiditis)

When hypothyroidism results from Hashimoto thyroiditis, the thyroid gland shows diffuse lymphoplasmacytic infiltration with germinal center formation, follicular atrophy with sparse colloid, oxyphilic (Hürthle/Askanazy) cell change of follicular epithelium, and variable fibrosis.[19][23] In atrophic autoimmune thyroiditis, extensive fibrosis replaces the thyroid parenchyma.[23]

Medical Management

• Levothyroxine (L-T4) replacement is the standard treatment for all forms of hypothyroidism. For congenital hypothyroidism, the American Academy of Pediatrics recommends an initial dose of 10–15 mcg/kg/day, with treatment ideally initiated by 2 weeks of age to optimize neurocognitive outcomes. For adults, the average full replacement dose is approximately 1.6 mcg/kg/day, titrated to normalize TSH.[2][7][24]
• Treatment is generally lifelong for permanent hypothyroidism. TSH monitoring is performed 6–8 weeks after dose changes and annually once stable.[2]

Dental Management Considerations

• Thyroid status verification: Dental practitioners should confirm that hypothyroid patients are euthyroid on replacement therapy before elective procedures. Patients should be instructed to inform their dentist that they are taking levothyroxine prior to any surgery.[8][25]
• Bleeding risk: Hypothyroidism can cause a hypocoagulable state; patients on concurrent anticoagulants require clotting status assessment.[2][25]
• Drug interactions: Calcium-containing dental products and iron supplements can decrease levothyroxine absorption; patients should be advised to separate these agents by at least 4 hours.[25]
• Delayed healing: Untreated or poorly controlled hypothyroidism may impair wound healing, which should be considered in surgical planning.[8]

Dental Developmental Outcomes

• Early and adequate levothyroxine replacement in congenital hypothyroidism stimulates catch-up dental development, including exfoliation of retained deciduous teeth and eruption of permanent successors. However, the degree of catch-up depends on the duration and severity of hypothyroidism before treatment; prolonged deficiency may result in permanent dental developmental deficits.[6][10][12]
• Orthodontic and surgical management of malocclusion (anterior open bite, crowding, impacted teeth) may be required after thyroid status is normalized.[6][11]

Prognosis

With early diagnosis through newborn screening and prompt levothyroxine therapy, children with congenital hypothyroidism achieve grossly normal neurocognitive and growth outcomes.[7][9] Dental development normalizes or substantially improves with treatment, though patients with severe or prolonged untreated disease