Developmental and Congenital Disorders

• Developmental disorders result from failures during cell division and differentiation into tissues and structures.
• These failures can be identified clinically, through radiographic examination, biopsy, or histologic examination.

Types of Developmental Disorders

• Inherited disorders are caused by genetic abnormalities, examples include amelogenesis or dentinogenesis and sickle cell anemia.
• Congenital disorders are present at birth, such as cleft lip/palate and congenital syphilis.
• Congenital disorders may be inherited or developmental.
• The causes of most congenital abnormalities are unknown.

Embryonic Development of the Face

• During the third week, ectoderm infolds to form the stomodeum, creating the primitive oral cavity,
• Two pits develop on the frontal process and divide it into three parts: the median nasal process, the right lateral nasal process, and the left lateral nasal process.
• The median nasal process grows downward between the maxillary processes and forms the globular process, which forms the philtrum.

Embryonic Development of Oral and Nasal Cavities

• The premaxilla forms from the globular process.
• Lateral palatine processes arise from the maxillary process.
• Lateral palatine processes fuse with the premaxilla creating a Y-shaped pattern.
• The body of the tongue develops from the first branchial arch.
• The base of the tongue forms from the second and third branchial arches.

Embryonic Development of the Teeth

• Odontogenesis, or tooth development, begins around the fifth week of life.
• Odontogenesis involves the ectoderm and ectomesenchyme.
• Odontogenesis starts with formation in each jaw of a band of ectoderm called the primary dental lamina.
• Ten small knoblike proliferations develop on the primary dental lamina in each jaw, each extending into the underlying mesenchyme.
• The tooth germ has three parts: Enamel organ, dental papilla and dental sac or follicle.
• By month 5 of gestation enamel and dentin are deposited.
• The dental sac or follicle forms the cementum, periodontal ligament, and alveolar bone.
• Cementogenesis happens after crown formation is complete.
• Hertwig’s epithelial root sheath shapes the root and induces root dentin formation.
• Cementum is produced after tooth eruption, when the tooth is in occlusion and functioning.
• The completion of root length occurs 1 to 4 years after eruption.

Developmental Cysts

• Developmental cysts are classified as either odontogenic or nonodontogenic.
• Classification is based on location, cause, origin of the epithelial cells, and histologic appearance.
• An abnormal fluid-filled epithelium-lined sac or cavity is common
• The radicular cyst, also known as periapical cyst, is the most common oral cyst and can become a residual cyst.
• Developmental cysts can cause expansion of bone.
• Intraosseous cysts occur within bone.
• Extraosseous cysts occur in soft tissue, example is a nasolabial cyst.
• Cysts within bone generally appear as well-circumscribed radiolucencies and may appear as unilocular or multilocular.

Odontogenic Cysts

• Dentigerous Cyst: Forms around the crown of an unerupted or developing tooth; the epithelial lining stems from reduced enamel epithelium post crown formation; most common around unerupted or impacted third molars; is radiolucent.
• Eruption Cyst: Similar to a dentigerous cyst found in soft tissue around the crown of an erupting tooth; treatment is typically none.
• Primordial Cyst: Develops in place of a tooth, commonly the third molar; seen in young adults; the lumen is lined by stratified squamous epithelium surrounded by parallel bundles of collagen fibers; may be an odontogenic keratocyst or lateral periodontal cyst; treatment is surgical removal and recurrence risk depends on the diagnosis.
• Odontogenic Keratocyst (OKC): Histologically has a lumen lined by epithelium that is 8-10 cells thick and surfaced by parakeratin; is most often seen in the mandibular third molar region; can move teeth and cause resorption; treatment is surgical excision and osseous curettage due to a high recurrence rate.
• Calcifying Odontogenic Cyst (COC): A nonaggressive cystic lesion ,lined by odontogenic epithelium; closely resembles an ameloblastoma; has a characteristic feature called ghost cells; ghost cells have balloon shaped with clear cytoplasm.
• Lateral Periodontal Cyst and Gingival Cyst: Lateral periodontal cysts are most often seen in the mandibular cuspid and premolar area, asymptomatic, unilocular or multilocular radiolucent lesion on the lateral surface of a tooth root; botryoid odontogenic cyst, multilocular variant of lateral periodontal cyst, lateral periodontal cysts are more frequent in males. and gingival cyst has the same type of lining as the lateral periodontal cyst, but is located in soft tissue;Treatment is surgical excision

Nonodontogenic Cysts

• Nasopalatine Canal Cyst (Incisive Canal Cyst): Located within the nasopalatine canal or incisive papilla; more common in males, age 40-60 years, usually asymptomatic, a small pink bulge may be present between the apices and roots of maxillary central incisors on the lingual surface. Radiographically it is well-defined and radiolucent and may be oval or heart-shaped. lined by epithelium varying from stratified squamous to pseudostratified ciliated columnar epithelium; Treatment- Surgical excision

• Median Palatine Cyst: Is well-defined and unilocular radiolucency is located in the midline of the hard palate; lined with stratified squamous epithelium surrounded by dense fibrous connective tissue. Treatment is surgical removal

• Globulomaxillary Cyst: A well-defined, pear-shaped radiolucency is located between the roots of the maxillary lateral incisor and cuspid. Treatment is surgical removal.

• Median Mandibular Cyst: Is a rare lesion in the midline of the mandible; lined with squamous epithelium; a well-defined radiolucency below the apices of the mandibular incisors. Treatment is surgical removal

• Nasolabial Cyst: A soft tissue cyst thought to originate from the lower anterior portion of the nasolacrimal duct;observed in adults 40 to 50 years of age, 4:1 ratio in favor of females: An expansion/swelling noted in the mucobuccal fold where the maxillary canine is combined with the floor of the nose Pseudostratified/ciliated columnar epithelium w/ goblet cells; Surgical excision

• Dermoid Cyst: a developmental oral cavity cyst that is often present at birth in young children; it usually occurs on the floor of the mouth when it is usually found on the floor of mouth in the oral cavity; A doughy consistency with the potential to displace the tongue; Lined by orthokeratinized, stratified squamous epithelium that is surrounded by a connective tissue wall The lumen is usually filled with keratin. Hair follicles, plus the sebaceous glands alongside the sweat glands may be seen within the hair follicle. Treatment: Surgical excision

Pseudocysts

• These cysts are not true cysts because they are are not lined by epithelium.

• Consist of static bone cyst, simple bone cyst and aneurysmal bone cyst.

• Static Bone Cyst (Lingual Mandibular Bone Cavity, Stafne Bone Cyst): A pseudocyst that is not a pathologic cavity, clinically is an anatomic depression on the posterior lingual area of the mandible, and requires no treatment. A well-defined, cystlike radiolucency may be observed in the radiograph of the posterior of the mandible, inferior to the mandibular canal

• Simple Bone Cyst (Traumatic Bone Cyst, Hemorrhagic Bone Cyst): A pathologic cavity in bone that is not lined with epithelium; is associated with trauma; treatment is curettage on the wall lining the void. Radiographically a well-defined unilocular or multilocular radiolucency characteristic shows scalloping around roots of teeth

• Aneurysmal Bone Cyst: Is a pseudocyst with blood-filled cavities, surrounded fibroblasts, multinucleated giant cells; multilocular "soap bubble", and affects individuals < 30. Slight predilection for females; Surgical excision.