1. Developmental disturbances of the oral cavity

Developmental Disturbances of the Oral Region

**Definitions

• Embryology is fundamental in understanding developmental anomalies of the face and oral cavity.
• Developmental disorders are defined as those that occur during development of a part or organ.
• Choristoma : An overgrowth of mature tissues found in an area where such tissue is not usually present, such as an osseous or cartilaginous choristoma of the tongue.
• Hamartoma : An overgrowth of mature tissue that is normally found in that area, such as a leiomyomatous hamartoma.
• Nevus : An overgrowth of tissue that is normally found in the skin or oral mucosa, such as melanocytic, epidermal, or vascular nevus. Dentists must examine the entire craniofacial region, including the skin, as part of a comprehensive examination.

Craniofacial development

Germ Layers and Derivatives

• Ectoderm
  • Skin
  • Hair
  • Brain
  • Nerves
  • Tooth enamel
• Ectomesenchyme
  • In Head and Neck Region:
    • Bone and cartilage
    • Muscle
    • Melanocytes
    • Dentin
    • Pulp
    • Cementum
    • Periodontal ligament
• Mesoderm
  • Heart
  • Bones
  • Kidneys
  • Muscle
  • Blood
• Endoderm
  • Lung
  • Gut
  • Thyroid
  • Pancreas

Pharyngeal Arches and Tongue Development

• Pharyngeal arches
  • Maxillary process
  • Mandibular process
  • First brachial groove
  • Hyoid or second arch
  • Third brachial arch
  • Forebrain
  • Frontonasal process
  • Primitive mouth
  • Pericardial cavity
  • Foregut
  • Spinal cord
• Tongue development
  • Lateral lingual swelling
  • Tuberculum impar
  • Foramen cecum
  • Hypobranchial eminence
  • Anterior 2/3 from tuberculum impar and lateral lingual swellings
  • Sulcus terminalis
  • Posterior 1/3 from hypobranchial eminence
  • Foramen cecum
  • Epiglottis

Formation of Face

The face develops from the fusion of different plates or processes from the right and left sides. A failure of these processes to fuse correctly at the midline can lead to defects like clefts.

Palate development

• Intermaxillary segment
• Lateral palatine process of maxilla

Abnormalities of the face and oral cavity

• Congenital abnormalities : defects present at birth or shortly after birth.
• Teratology can broadly be the study of congenital and developing developmental abnormalities after birth.
• Inherited mechanisms and/or agents called teratogens interfere with embryonic development, resulting in developmental malfunctions or defects. Many defects are now linked to specific gene mutations, which can be identified via advanced sequencing and prenatal screening (usually before week 12).
• Causes of many developmental defects are unknown.
• Some well-known environmental teratogens include drugs (thalidomide, alcohol), radiation (x-rays), and microorganisms (rubella, syphilis).

Cleft Lip and Cleft Palate

• Clefts: most common developmental facial abnormality.
• Clefts are failures of fusion of adjacent embryological processes that normally fuse to form one continuous structure. This involves a disruption of the normal apoptosis and proliferation required for the two sides to unite.
• Cleft lip and cleft lip with cleft palate are more common in males, while cleft palate alone is more common in females.
• 1/700 birth among Caucasians, 4/700 Native Americans, 2/700 Japanese, 0.3/700 African Americans
• Inheritance and environmental factors (drug and alcohol abuse, cigarette smoke, chemicals such as insecticides, and microorganisms such as treponema pallidum and cytomegalovirus)
• Cleft lip can be unilateral or bilateral, partial or complete. Complete cleft lip involves the lower portion of the nose.
• Clefts may present as openings between the oral cavity and nasal passages, resulting in feeding and speech problems. This creates disordered dental development and malpositioned teeth, requiring surgical and orthodontic interventions.
• Facial clefts are most often treated with surgery. Developmental Timeline of the lip and palate
• ~6 weeks
  • Mouth and future nasal cavity are continuous.
  • Fusion of median nasal process with maxillary processes (1st branchial arch) → primary palate (midline alveolar ridge & anterior palate).
• By week 9
  • Secondary palate forms via:
    • Growth of palatal shelves
    • Rotation & fusion of shelves
    • Breakdown of epithelium for fusion
    • Mandibular growth → tongue drops out of the way

Cleft Lip Types

Cleft Palate Types

• A Bilateral cleft palate with lip involvement
• B Unilateral cleft palate with lip involvement
• C Late failure of fusion with partial cleft palate; lip is not affected

Bifid Uvula and Bifid Tongue

• A bifid uvula is often a sign of a palatal cleft!
• Bifid uvula and bifid tongue are often incidental findings.
• A uvula or tongue that appears to be splitting into two parts is described as bifid. Since the uvula plays a role in swallowing, a bifid uvula can cause functional disturbances.
• Both bifid uvula and bifid tongue occur due to incomplete fusion of the embryonic processes that form them.
• Defective or incomplete fusion of the palatal processes
• Infants born to diabetic mothers are well documented to have a higher rate of congenital malformations An artificial bifid tongue can also occur as a complication of tongue piercing, where trauma or the piercing itself causes a separation of the anterior tongue tissue. . A key finding was that an artificial bifid tongue can develop due to the separation of tongue muscle fibers from the piercing.

Key Points

• Tongue ornaments are seen with increasing frequency in the dental practice.
• Complications of tongue ornaments can manifest themselves even after their removal.
• Anatomic malformations may follow inaccurate placement of tongue ornaments.
• Complications of tongue piercing may have psychiatric implications.

Lip Pits

• Lip pits are small, congenital, sac-like invaginations of lip mucosa on the vermillion border with a depth ranging from 1 to 4 mm.
• In most instances, lip pits are not symptomatic and are an incidental finding.

Double Lip

A rare anomaly characterized by an excess fold of tissue on the inner aspect of the lip, most commonly the upper lip.

• Lip pits are small, congenital, sac-like invaginations of lip mucosa on the vermillion border with a depth ranging from 1 to 4 mm.
• In most instances, lip pits are not symptomatic and are an incidental finding.

Aglossia and Ankyloglossia

• Aglossia : partial formation or complete absence of the tongue.
• Cause : failure of fusion of the components of the branchial arches responsible for tongue formation or result fro ]m the surgical treatment of disease.
• Ankyloglossia : attachment of the anterior tongue to the floor of the mouth, usually by a tight cord of tissue or frenum (tongue tie) causing significant speech and swallowing.
• Clinical Sign: The patient cannot extend their tongue past the lower anterior teeth.
• • Treatment: A simple surgical procedure (frenectomy) to release the frenum.

Macroglossia and Microglossia

• Macroglossia: abnormal increase in size of the tongue. It may be congenital, as in Down syndrome, or occur as a result of neoplasia. A key clinical sign is scalloping (impressions of the teeth) along the lateral borders of the tongue.
• Microglossia: a rare, congenital disorder of abnormally small tongue due to lack of development of the tuberculum impar and other structures involved in tongue development.
• An excessively large or small tongue can significantly affect speech and impact feeding or swallowing.
• Normal growth and development of the mandibular alveolar processes may be altered by lack of tongue forces, resulting in malocclusion.

Fissured Tongue

• Fissure tongue: deep grooves are present on the dorsum of the tongue
• Fissured tongue may be seen in both children and adults, and its prevalence 5%. However, the lecturer noted it is a very common condition, found in 20-30% of the population.
• Fissured tongue has been associated with geographic tongue, with many patients having both conditions.
• Food particles and oral debris may be trapped in the deep crevices of a fissured tongue, creating an oral hygiene problem. This can lead to inflammation and halitosis (bad breath).
• Oral health-care procedures: cleaning the tongue by brushing and rinsing

Lingual Thyroid (Ectopic Thyroid)

• Lingual thyroid: normal thyroid tissue remains at the foramen caecum , the initial site of thyroid gland formation on the dorsum of the tongue.
• It is called ectopic , meaning out of normal position. Mucosal-coloured round nodule, reaching up to 4 cm in diameter, located at or near the terminal sulcus.
• Ectopic thyroid tissue can remain anywhere along the thyroglossal tract, the route of thyroid gland migration to its final site in the neck.

Lingual Varicosities

• Varices : swollen, twisted, and sometimes painful veins that have filled with an abnormal collection of blood.
• They present nonpainful, large, dilated, blue masses on the ventral surface of the tongue and are more common in older individuals, with few if any seen in children and adolescents. While common in the elderly as part of the aging process, if seen in children it is considered a developmental anomaly.

Teeth development

Tooth development begins with the primary epithelial band , which divides into the vestibular lamina (forming the vestibule/lips) and the dental lamina (forming teeth). After tooth formation, epithelial remnants can persist and may be stimulated by inflammation later in life. Developmental anomalies of teeth affecting their number, morphology, and structure will be covered in more detail in the pediatric dentistry module.

Macular Epithelial Lesions

The color of the oral mucosa provides important diagnostic clues:

• Pink (Normal): A thin epithelium allows the color of underlying blood vessels in the connective tissue to show through.
• White: An increase in the thickness of the epithelium (e.g., hyperkeratosis) masks the underlying blood vessels . - Red: A decrease in epithelial thickness (atrophy) or an increase in the number of blood vessels (inflammation).

WHITE SPONGE NEVUS

whitesponge

Clinical Features

• Lesions are noted in the first two decades of life and persist throughout life. The skin is not involved, although there may be oesophagal, upper airway, and genital involvement. The lesions are persistent and cannot be wiped off.
• The buccal mucosa appears diffusely white to grey, thickened, non-tender, edematous, and spongy. The tongue, lip mucosa, and floor of the mouth may also be involved.

Histological Features

• The epithelium exhibits acanthosis with a pale “spongy” appearance.
• The pale epithelium is caused by intracellular vacuolation and dyskeratosis that spares the basal cells.
• There areperinuclear eosinophilic condensations and intracytoplasmic vacuolation (not spongiosis).
• The cells in the superficial layers are swollen, a change known as watery degeneration . - The perinuclear eosinophilic condensation is a pathognomonic feature related to a genetic mutation in specific cytokeratins.

Other Macular Epithelial Lesions

• HEREDITARY MUCOEPITHELIAL DYSPLASIA
• KERATOSIS FOLLICULARIS (DARIER DISEASE, DARIER-WHITE DISEASE)
• HEREDITARY BENIGN INTRAEPITHELIAL DYSKERATOSIS This is an extremely rare condition that has been associated with a risk of developing squamous cell carcinoma.
• ORAL LINEAR EPIDERMAL NEVUS
• EPIDERMAL NEVUS (EPIDERMAL CHORISTOMA)
• FOCAL PALMOPLANTAR AND GINGIVAL HYPERKERATOSIS SYNDROME

Nodular or Tumor-Like Lesions

FORDYCE GRANULES (SEBACEOUS HYPERPLASIA)

This is a very common condition considered a normal anatomical variation, consisting of ectopic sebaceous glands in the oral mucosa.

• Fordyce granules: noted in adults, present in 60% to 80% of the population, and appear as 1- to 3-mm yellowish papules, frequently located on the posterior buccal mucosa and vermilion of the lips. They are usually bilateral and symmetric
• Fordyce granules are considered normal structures in the mouth that can become hyperplastic and adenomatous., they can be considered as ectopic sebaceous glands!

Histological Features

• Mature sebaceous glands with a single germinative layer may or may not open onto the mucosa via a duct lined by squamous epithelium.
• Sebocytes have central nuclei and vacuolated cytoplasm. Hair.
• Sebaceous hyperplasia: This consists of at least 15 sebaceous lobules opening into a central duct lined by squamous epithelium.
• Sebaceous adenoma: This consists of many sebaceous lobules with proliferation of germinative basaloid cells at the periphery of the lobules.

CONGENITAL GRANULAR CELL TUMOR (EPULIS)

• This tumour occurs in the newborn and has a strong 8—10:1 female predilection.
• mesenchymal tumour of uncertain etiopathogenesis. It is believed to be of neural origin (derived from the neural crest) and is considered a developmental disorder rather than a true neoplasm.

Histological Features

• Sheets of cells with well-defined cell borders; pale, granular cytoplasm; and nuclei with dispersed chromatin and small nucleoli.
• There are prominent arborizing vessels, and the epithelium is atrophic with no pseudoepitheliomatous hyperplasia

OSSEOUS, CARTILAGINOUS, AND OSTEOCHONDROMATOUS CHORISTOMA

Clinical Features

• Seen in young adults in the second to fourth decade, and it has a 2:1 female predilection.
• Globus sensation or dysphagia, and the presence of a lump.
• More than 90% present as a mass or nodule, usually on the dorsum of the tongue

Histological Features

• Mass of mature lamellar bone filling the superficial and deep lamina propria.
• Lamellar bone with widely spaced osteocytes and osteoblastic rimming.
• Cellular fibrous tissue containing many plump fibroblasts and woven bone.

LEIOMYOMATOUS HAMARTOMA

• First year of life and presents as a soft, painless polypoid mass, usually on the tongue and anterior maxillary/palatal mucosa in the area of the nasopalatine foramen

Histological Features

• Nonencapsulated, discrete proliferation of fusiform and spindled smooth muscle cells in bundles separated by fibrous tissue
• Tumour cells express smooth muscle actin, muscle-specific actin and desmin, but not S100 protein