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FACT SHEET: Hypothyroidism (also known as “underactive thyroid disease”; includes congenital hypothyroidism [also known as “neonatal hypothyroidism”] and Hashimoto’s thyroiditis [also known as “autoimmune thyroiditis”]; may manifest as “cretinism” [if onsets during fetal or early life; also known as “congenital myxedema”] or “myxedema” [if onset occurs in older children and adults])

Date of Publication: January 27, 2017

Is the initiation of non-invasive dental hygiene procedures* contra-indicated?

  • No.

Is medical consult advised?  

  • Yes, if previously undiagnosed hypothyroidism or enlarged (or shrunken) thyroid gland is suspected1, in which case the patient/client should see his/her primary care physician. Detection early in childhood can prevent permanent intellectual impairment.
  • Yes, if previously diagnosed hypothyroidism is suspected to be undermedicated (with manifest signs/symptoms of hypothyroidism) or overmedicated (with manifest signs/symptoms of hyperthyroidism2), in which case the patient/client should see his/her primary care physician or endocrinologist. Major stress or illness sometimes necessitates an increase in prescribed thyroid hormone.

Is the initiation of invasive dental hygiene procedures contra-indicated?**

  • Possibly, depending on the certainty of diagnosis and level of control.

Is medical consult advised? 

  • See above.

Is medical clearance required? 

  • Yes, if undiagnosed or severe hypothyroidism is suspected.

Is antibiotic prophylaxis required?  

  • No.

Is postponing treatment advised?

  • Yes, if undiagnosed hypothyroidism is suspected (necessitating medical assessment/management) or severe hypothyroidism is suspected (necessitating urgent medical assessment/management in order to avoid risk of myxedema coma). In general, the patient/client with mild symptoms of untreated hypothyroidism is not in danger when receiving dental hygiene therapy, and the well managed (euthyroid) patient/client requires no special regard.

Oral management implications

  • Palpation of the thyroid gland should be part of the head and neck examination by the dental hygienist. Diffuse enlargement or nodules may be detected.
  • The dental hygienist is much more likely to encounter patients/clients with undiagnosed or inadequately treated mild to moderate hypothyroidism (and therefore potentially subtle signs/symptoms) than persons with severe long-term, undiagnosed hypothyroidism (i.e., myxedema).
  • Stress should be minimized by keeping appointments brief for non-euthyroid patients/clients.
  • Lethargy in hypothyroid patients/clients can lead to possible aspiration of dental/dental hygiene materials and/or lowering of respiratory rate when in the dental chair.
  • Patients/clients with untreated hypothyroidism are very sensitive to the actions of central nervous system depressants, including narcotic analgesics and sedatives/tranquillizers (e.g., benzodiazepines and barbiturates). These drugs should be avoided in all patients/clients with severe hypothyroidism and used sparingly (reduced dosage), if at all, in persons with mild hypothyroidism.
  • Certain medications may decrease absorption of orally administered thyroid replacement drugs. These include fluoroquinolone antibiotics3; antacids4; calcium supplements; iron supplements5; laxatives; cholesterol lowering drugs6; phosphate binders (used in chronic kidney disease); sucralfate (used in gastroesophageal reflux disease and peptic ulcer disease; and raloxifene7
  • Certain drugs used to manage epilepsy, including carbamazepine, phenytoin, and phenobarbital increase metabolism of thyroid replacement drugs.
  • Long-standing hypothyroidism may result in increased bleeding from infiltrated tissues8, resulting in a need for extended application of local pressure for hemostasis.
  • Myxedema coma — a medical emergency — may be precipitated by trauma, infections, surgical procedures, and cold in untreated or suboptimally treated patients/clients with severe hypothyroidism.
  • Once the hypothyroid patient/client receives ongoing appropriate medical care, no particular problems in terms of oral management remain, except for possibly the need to address malocclusion and/or enlarged tongue.

Oral manifestations

  • Manifestations of cretinism include thickened lips, macroglossia (enlarged tongue), protruding tongue, delayed eruption of teeth, and malocclusions.
  • In older children and adults, hypothyroidism may result in macroglossia, dysgeusia (altered taste), hypogeusia (decreased taste), glossitis, salivary gland enlargement, and facial swelling (due to nonpitting edema).
  • Depending on the timing and severity of hypothyroidism, other manifestations include enamel hypoplasia in both dentitions, anterior open bite, impaction of the mandibular second molars (due to abnormalities of craniofacial growth and dental development), weakened oral and facial bones, swollen gums, and mouth breathing.
  • Poor periodontal health and delayed wound healing9 are common.
  • Lingual thyroid10 is a rare condition that manifests orally as a nodule at the base of the tongue, and, when it occurs, it is often associated with hypothyroidism. Dysphagia, dysphonia, bleeding, and upper respiratory tract obstruction may also occur.

Related signs and symptoms

  • Hypothyroidism occurs when the thyroid gland produces insufficient amounts of thyroid hormone11. Causes of primary hypothyroidism (intrathyroidal defect) include congenital/developmental conditions (i.e., in persons born without a thyroid gland or with a poorly functioning one); autoimmune destruction of the thyroid gland (e.g., Hashimoto’s thyroiditis12 and end-stage Graves’ disease); infiltrative destruction of the thyroid gland (e.g., amyloidosis, lymphoma, and scleroderma); iodine deficiency; medications (e.g., lithium and antithyroidal thioamide drugs such as carbimazole, methimazole, and propylthioruracil); and treatments for hyperthyroidism or thyroid cancer (including surgical thyroidectomy, radioactive iodine therapy, and external beam radiation to thyroid gland). Secondary hypothyroidism results from certain disorders of the pituitary gland and hypothalamus13. Transient hypothyroidism occurs in silent, subacute, and postpartum forms of thyroiditis, as well as with withdrawal of exogenous thyroid hormone. A rare cause of hypothyroidism is generalized resistance to thyroid hormone.
  • More common than hyperthyroidism, hypothyroidism affects about 2% of the population, and prevalence increases with age, with mean age of diagnosis being 60 years. Both developmental and autoimmune hypothyroidism are more common in females than males. Subclinical (i.e., borderline) hypothyroidism is diagnosed in 6% to 8% of women and 3% of men. 
  • Congenital hypothyroidism (CH) occurs in about 1 in 4000 newborns. In Ontario and Canada (and many other developed jurisdictions), newborns are routinely screened for CH so that cretinism can be prevented with timely intervention.
  • Cretinism (rare in Canada) is characterized by dwarfism; excess weight; typical facial features such as broad and flat nose and wide-set eyes; protuberant tongue; pale skin; poor muscle tone and muscle weakness; stubby hands; delayed bone age and skeletal dystrophy; hoarse cry; umbilical hernia; thick, dry skin; alopecia (hair loss); poor vision; lethargy; and intellectual disability.
  • With onset of hypothyroidism in older children and adults, myxedematous features include: a dull expression; puffy eyelids and facial appearance; dry, brittle, and coarse hair; alopecia of the outer third of the eyebrows; dry, scaly, cool, and pale skin; accumulation of subcutaneous fluid (nonpitting edema referred to as myxedema); yellowing of the palms; and brittle nails.
  • In adults, the onset of hypothyroidism is usually insidious. Manifestations over time include weight gain despite decreased appetite; constipation; slowing of physical and mental activity (including poor memory retention, as well as myxedema dementia in severe cases); croaky, hoarse, and slurred speech; anemia; cold intolerance; increased capillary fragility; muscle cramps and weakness; slow reflexes; hypotension; bradycardia (abnormally slow heart rate); decreased respiratory rate; cardiomegaly (abnormally enlarged heart); paresthesia; headache; fatigue; sleepiness; and depression. In females, menstrual irregularities occur — varying from menorrhagia (abnormally heavy menstrual bleeding) to amenorrhea (abnormal absence of periods) — and fertility may be impaired.
  • Depending on the underlying cause of hypothyroidism, the size of the thyroid gland can be normal, increased (goitre14), or decreased.  
  • In untreated patients/clients with severe hypothyroidism, myxedema coma may result, which can lead to death. Myxedema coma is characterized by hypothermia, hypoventilation (with associated hypercapnia, or excessive carbon dioxide in the blood), bradycardia (slow heart rate), cardiac arrhythmias, hypotension, and epileptic seizures. It occurs most often in elderly persons during winter months and, while rare, carries a mortality rate of up to 50%.
  • Heart failure can occur in severe cases of myxedema.
  • The slowing of metabolism over time, if untreated, is associated with cardiovascular disease (from arteriosclerosis and elevated low-density lipoprotein [LDL] cholesterol), obesity, and joint pain.

References and sources of more detailed information

Date: October 10, 2016
Revised: July 6, 2021


1 Diagnostic tests for hypothyroidism include serum measurement of thyroid-stimulating hormone (TSH; also known as thyrotropin), thyroid hormone (usually free T4), and, less commonly, administration of radioactive iodine to measure uptake by the thyroid gland (RAIU).
Medical management involves administration of synthetic preparations of thyroid hormone (usually levothyroxine or T4), typically orally but occasionally parenterally in severe cases.
2 Signs/symptoms of increased thyroid activity include palpitations, sweating, restlessness, shakiness, and weight loss.
3 Fluoroquinolone antibiotics include commonly prescribed ciprofloxacin.
4 such as aluminum hydroxide and calcium carbonate
5 such as ferrous sulfate
6 including colestipol and cholestyramine
7 Raloxifene is an oral medication prescribed for the prevention and treatment of osteoporosis.
8 This is due to excess tissue mucopolysaccharides, which decrease ability of small blood vessels to constrict when cut.
9 This is due to decreased metabolic activity in fibroblasts.
10 Lingual thyroid is a rare condition of the oropharyngeal region caused by failure in descent of the thyroid gland to its normal position during embryogenesis. The ectopic thyroid tissue results in an abnormal mass at the base of the tongue. Patients/clients with lingual thyroid or other ectopic thyroid tissue are more likely to have hypothyroidism than hyperthyroidism. It is important that assessment by a physician occur before removal of a lingual thyroid mass, because it may the only source of thyroid hormone in the patient/client.
11 Thyroid hormone is a collective term for thyroxine (T4) and triiodothyronine (T3), both of which are secreted by the thyroid gland. T4 is converted to T3 in the peripheral tissues. Laboratory testing distinguishes primary hypothyroidism (with elevated thyroid-stimulating hormone [TSH]) from secondary hypothyroidism (with normal TSH levels).
12 Hashimoto’s disease (chronic thyroiditis) is the most common cause of primary hypothyroidism in North America, usually affecting young and middle-aged women. Goitre is common.
13 Under normal circumstances, thyrotropin-releasing hormone (TRH) is released by the hypothalamus in response to external stimuli (e.g., metabolic demand and low levels of thyroid hormone). TRH in turn stimulates the pituitary to release thyroid-stimulating hormone (TSH), which causes the thyroid gland to secrete T4 and T3.
14 Goitre is generalized enlargement of the thyroid gland, and may be either diffuse or nodular. It is found in some causes of hypothyroidism, such as Hashimoto’s thyroiditis and chronic fibrosing [Riedel’s] thyroiditis.

* Includes oral hygiene instruction, fitting a mouth guard, taking an impression, etc.
** Ontario Regulation 501/07 made under the Dental Hygiene Act, 1991. Invasive dental hygiene procedures are scaling teeth and root planing, including curetting surrounding tissue.