ch. 5: developmental disorders

What is a developmental disorder?

A failure during cell division or differentiation that causes abnormal tissue or structure development.

Inherited vs. congenital disorder

Inherited = caused by genetic abnormalities; congenital = present at birth and may or may not be inherited.

What is a teratogen?

An agent that disrupts embryonic development and may cause birth defects.

What does ectoderm form?

Skin, hair, nails, sweat glands, neural tube, oral mucosa, and enamel-forming tissues.

What is the stomodeum?

The primitive mouth.

What is the buccopharyngeal membrane?

Separates the primitive mouth from the gut; ruptures around week 4.

What do neural crest cells form?

Ectomesenchyme, which develops into craniofacial connective tissues, bone, cartilage, dermis, and nonenamel tooth tissues.

What develops from the first pharyngeal arch?

Maxilla, mandible, muscles of mastication, trigeminal nerve, and maxillary artery.

When does the upper lip develop, and what causes cleft lip?

Around week 6; failure of proper fusion of the maxillary and medial nasal processes.

How does the primary palate form?

Fusion of the medial nasal and maxillary processes; forms the premaxilla associated with the incisors.

When does the secondary palate form?

Weeks 9–12; failure of palatal processes to fuse can cause cleft palate.

When does tongue development begin?

Weeks 4–5 of gestation.

What is aglossia?

Partial or complete absence of the tongue.

What is ankyloglossia?

Tongue-tie; attachment of the anterior tongue to the floor of the mouth, restricting movement. May require frenectomy.

Commissural vs. paramedian lip pits

Commissural = corners of mouth; paramedian = near the midline of the lip.

What are the characteristics of lip pits?

Congenital invaginations, 1–4 mm deep, usually asymptomatic, occurring singly or in pairs.

What is double lip?

An extra fold of lip tissue, usually upper lip; may be developmental, inherited, or acquired from trauma.

What is a lingual thyroid?

Thyroid tissue on the tongue caused by failure to migrate from the foramen cecum to the neck.

When can a lingual thyroid be removed?

If obstructive and other functioning thyroid tissue is present.

What is a true cyst?

An abnormal fluid-filled sac or cavity lined by epithelium.

Odontogenic vs. nonodontogenic cysts

Odontogenic = arise from tooth-forming tissues; nonodontogenic = arise from other developmental tissues.

How do developmental cysts usually appear radiographically?

Well-circumscribed radiolucencies; may be unilocular or multilocular.

Intraosseous vs. extraosseous cysts

Intraosseous = within bone and visible radiographically; extraosseous = soft tissue and generally not visible on radiographs.

What is the most common oral cyst?

Radicular (periapical) cyst; occurs at the apex of a nonvital tooth.

What causes a radicular cyst?

Proliferation of epithelial rests of Malassez associated with periapical inflammation.

What is a residual cyst?

A radicular cyst remaining after the involved tooth is extracted.

What is a dentigerous cyst?

An odontogenic cyst surrounding the crown of an unerupted or impacted tooth, commonly a third molar.

What is the origin of a dentigerous cyst?

Reduced enamel epithelium after crown formation and calcification.

How does a dentigerous cyst appear radiographically?

Well-defined, unilocular radiolucency surrounding the crown of an unerupted tooth.

What is an eruption cyst?

A soft tissue cyst over an erupting tooth; dome-shaped and often red, brown, or blue-gray. Usually requires no treatment.

What is a primordial cyst?

A cyst developing in place of a tooth, commonly a third molar; often discovered radiographically in young adults.

What is the treatment for a primordial cyst?

Surgical removal; recurrence depends on the specific diagnosis.

What is an odontogenic keratocyst (OKC)?

An odontogenic cyst commonly found near mandibular third molars, often appearing as a well-defined multilocular radiolucency.

Why is an OKC clinically important?

High recurrence rate; may displace teeth or cause root resorption. Surgical excision and curettage are recommended.

What is the characteristic histologic feature of a calcifying odontogenic cyst?

Ghost cells; the lesion can resemble an ameloblastoma.

What is a lateral periodontal cyst?

An intraosseous odontogenic cyst along the lateral root surface, commonly in the mandibular canine-premolar region.

What is a gingival cyst?

An extraosseous odontogenic cyst in gingival soft tissue.

What is a botryoid odontogenic cyst?

A multilocular, multicystic variant of the lateral periodontal cyst.

What is a glandular odontogenic cyst?

A cyst that may enlarge bone, commonly in the posterior mandible or anterior maxilla; has a high recurrence rate.

What is a nasopalatine duct cyst?

A nonodontogenic cyst in the incisive canal or papilla, commonly seen in males ages 40–60.

What is the radiographic appearance of a nasopalatine duct cyst?

Well-defined oval or heart-shaped radiolucency between the maxillary central incisors.

What is a median palatine cyst?

A well-defined unilocular radiolucency in the midline of the hard palate.

What is a nasolabial cyst?

A soft tissue cyst causing swelling near the maxillary canine mucobuccal fold and floor of the nose; more common in females.

What is a thyroglossal duct cyst?

A cyst along the thyroid gland's developmental migration tract; often occurs before age 20.

What is a globulomaxillary cyst?

A historical term for a pear-shaped radiolucency between the maxillary lateral incisor and canine; no longer considered a distinct cyst.

What is a median mandibular cyst?

A historically described rare midline mandibular radiolucency below the incisor apices; not considered a distinct cyst type.

Why are pseudocysts not true cysts?

They lack an epithelial lining.

What is a static bone cavity (Stafne defect)?

An asymptomatic mandibular defect, usually near the angle, appearing as a round or oval radiolucency.

What is a simple bone cavity (traumatic bone cyst)?

An empty bone cavity, often in the mandible of young males; may follow trauma.

How is a simple bone cavity treated?

Curettage stimulates clot formation and new bone growth.

What are the three stages of enamel organ development?

Bud, cap, and bell.

What does the dental papilla form?

Dentin and pulp.

What is the dental follicle (dental sac)?

Tissue surrounding the enamel organ during tooth development.

What are the epithelial rests of Malassez derived from?

Hertwig's epithelial root sheath.

What is anodontia?

Congenital absence of teeth; total anodontia means all teeth are absent and may be associated with ectodermal dysplasia.

What is hypodontia?

Congenital absence of one or more teeth.

Which permanent teeth are most commonly missing in hypodontia?

Third molars, maxillary lateral incisors, and mandibular second premolars.

What is the most commonly missing primary tooth?

Mandibular incisor.

What are supernumerary teeth?

Extra teeth caused by additional tooth buds or division of existing tooth buds.

What is a mesiodens?

The most common supernumerary tooth; located between maxillary central incisors.

What is a distomolar?

A supernumerary tooth distal to the third molar; second most common type.

What syndromes are associated with multiple supernumerary teeth?

Cleidocranial dysplasia and Gardner syndrome.

Why might supernumerary teeth require removal?

They may cause crowding, malposition, delayed eruption, or cyst formation.

What is microdontia?

One or more teeth smaller than normal; commonly affects maxillary lateral incisors and third molars.

True vs. relative generalized microdontia

True = all teeth are abnormally small (pituitary dwarfism); relative = normal teeth appear small in a large jaw.

What is macrodontia?

One or more teeth larger than normal; generalized cases may be associated with pituitary gigantism.

What is gemination?

One tooth germ attempts to divide; enlarged/notched crown, usually one root and canal, with a normal tooth count.

What is fusion?

Two separate tooth germs unite; enlarged crown with separate or fused roots/canals, usually one fewer tooth.

How can gemination and fusion be distinguished?

Gemination usually has a normal tooth count and one root/canal; fusion usually reduces the tooth count and may have separate roots/canals.

What is concrescence?

Union of two adjacent teeth by cementum only; usually detected radiographically.

What is dilaceration?

An abnormal bend or curve in a tooth root; may complicate extraction or root canal treatment.

What is an enamel pearl?

A small spherical enamel projection on a root, commonly maxillary molars; appears radiopaque and may contribute to furcation periodontal problems.

What is a talon cusp?

An accessory cusp in the cingulum area of an incisor; contains a pulp horn and may interfere with occlusion.

What is taurodontism?

Enlarged, elongated pulp chambers with short roots; identified radiographically.

What is dens in dente (dens invaginatus)?

Invagination of the enamel organ into the crown before mineralization; appears as a tooth within a tooth.

Why is dens in dente clinically significant?

Increased risk of caries, pulpal infection, and necrosis.

What is dens evaginatus?

An accessory enamel cusp on the occlusal surface, commonly mandibular premolars; may cause occlusal problems.

Why are supernumerary roots clinically significant?

Extra roots may complicate extraction and endodontic treatment.

What is enamel hypoplasia?

Incomplete or defective enamel formation during tooth development.

What can cause enamel hypoplasia?

Febrile illness, nutritional deficiency, trauma, primary tooth infection, excess fluoride, congenital syphilis, or birth complications.

What is Turner's hypoplasia (Turner tooth)?

Localized enamel hypoplasia of a permanent tooth caused by infection or trauma to its primary predecessor.

What does a Turner tooth look like?

Yellow-brown discoloration, enamel pitting, or deformity, usually affecting one tooth.

How can excessive fluoride affect developing enamel?

Fluorosis causing white flecks or chalky areas; greater exposure may cause brown or black staining.

What is enamel hypocalcification?

Disturbed enamel matrix maturation; chalky white areas with potentially soft, caries-prone enamel.

Enamel hypoplasia vs. hypocalcification

Hypoplasia = defective enamel formation; hypocalcification = defective enamel maturation/mineralization.

What causes endogenous tooth staining?

Systemic substances during tooth development, including tetracycline, Rh incompatibility, neonatal liver disease, and congenital porphyria.

What is regional odontodysplasia?

Ghost teeth; very thin enamel and dentin with markedly reduced radiodensity, often treated by extraction.

Impacted vs. embedded teeth

Impacted = eruption blocked by an obstruction; embedded = failure to erupt due to insufficient eruptive force.

Why are partially impacted teeth concerning?

Increased risk of infection; impacted teeth may also damage adjacent teeth or develop associated cysts.

What is tooth ankylosis?

Fusion of tooth cementum to surrounding bone, eliminating the periodontal ligament space.

What are clinical signs of an ankylosed primary tooth?

Submerged appearance, dull percussion sound, and delayed exfoliation or eruption of the permanent successor.

Why can ankylosed teeth require extraction?

They may prevent normal eruption or contribute to malocclusion, caries, and periodontal disease.