25. Oral Mucosa Flashcards
The oral mucosa forms a continuum with … and …
gingiva
tooth attachment tissues
Oral mucosa lines …
the whole oral cavity
How does the oral mucosa develop in the oral cavity?
- lining of the oral cavity (oral epithelium) and external lining of body (epidermis) are both derived from embryonic ectoderm and form a continuum
- similar but different morph features - ectodermal appendages
- similar but diff genetic regulation of development, differentiation and maintenance
Define ‘oral vestibule’
slit-like space between lips/cheeks and alveolar bone/teeth
Prominent frena can affect …
stability of dentures
A large labial frenulum with attachment site near the alvrolar crest can cause …
a midline diastema between the maxillary central incisors
- the gap
Functions of oral mucosa
- mechanical protection (masticatory forces - compression, stretching, shearing, abrasion)
- barrier to microorganisms and toxins
- immunological defence (immediate and adaptive)
- lubrication and buffering (saliva from minor glands)
- sensation (touch, pain, taste, proprioreception)
Define ‘functional adaptation’ in relation to oral mucosa
- different parts of oral mucosa must adapt morphologically to perform specific functions
List regional variations of oral mucosa and their adaptations
- epithelial thickness
- degree of keratinisation
- interface with connective tissue
- composition of connective tissue
- presence or absence of a submucosa
Perentage distribution of mucosa types
- lining mucosa - 60%
- masticatory - 25%
- specialised - 15%
Compare the layers of oral mucosa to the layers in skin
- oral epithelium vs epidermis
- lamina propria vs dermis
- submucosa vs hypodermis
Explain composition of oral epithelium/epidermis
- stratified squamous epithelium
- epithelial ridges (rete or pegs)
- keratinocytes (cell layers, express keratin proteins)
Components of lamina propria/dermis
- papillae
- fibroblasts, macrophages, lymphocytes, collagen (I, III), elastic fibres
- blood vessels and nerves
Composition of submucosa/hypodermis
- loose connective tissue
- fibroblasts
- larger blood vessels/nerves
- fat deposits
- salivary glands
Where is submucosa found?
- cheeks
- lips
- lateral palate
Basic tissue architecture of oral mucosa and skin is similar but …
- no hair follicles
- no sweat glands
Compare the submucosa and the mucoperiosteum
- submucosa provides mobility and acts as a cushion (e.g in lining mucosa)
- in mucoperiosteum, lamina propria is more fibrous and directly joined with periosteum of bone - e.g masticatory mucosa (middle of hard palate, gingiva)
List layers of the stratified epithelium of oral mucosa from outside in
- keratinised layer/stratum corneum
- granular layer (stratum granulosum)
- prickle (Suprabasal) cell layer
- basal cell layer (stratum basale)
Explain keratinised layer of stratified squamous epithelium
- very flat cells
- around 20 cell layers
- cornified (dead)
- no cell organelles including nucleus
- filaggrin binds to keratin filaments together (keratin)
- crosslinking of involucrin, cornified envelope - barrier, cell shedding (desquamation)
Explain granular layer of stratified squamous epithelium
- larger, flatter cells
- several layers
- maturating
- loss of cell organelles and cytoplasm filled with keratohyaline granules (contains profilaggrin and lipids)
Explain Prickle (suprabasal) cell layer/stratum spinosum of stratified squamous epithelium
- round ‘spiny’ cells (increase in desmosomes)
- several layers
- differentiating
- only parabasal cells can proliferate
- expresses keratins 1 and 10 (loricrin and involucrin)
Explain basal cell layer/stratum basale of stratified squamous epithelium
- cuboidal cells
- proliferating
- single cell layer
- basal lamina attached to lamina propria
- contains stem cells and transmit-amplifying cells (regeneration)
- expresses keratins 5 (type II Basic) and 14 (Type 1, Acidic)
3 types of keratinisation
- orthokeratinised
- parakeratinised
- nonkeratinised
What does orthokeratinised mean?
- cornified layer (dead cells)
- no cell nuclei
- hard palate, tongue
What does parakeratinised mean?
- cornified layer (dead cells)
- cell nuclei present
- gingiva
What does nonkeratinised mean?
- superficial layer (live cells)
- no keratohyalin granules
- lining mucosa
Regeneration cycle of stratified squamous epithelium
- skin - 27 days
- oral mucosa 9-14 days
- 2-3 times faster in oral
List other cells/’clear cells’ in oral mucosa
- melanocytes
- Merkel cells
- Langerhams cells
- Lymphocytes
What do melanocytes do?
- basal
- produce melanin pigment and transfer it to keratinocytes via dendritic processes
Role of Merkel cells
- basal
- sensory receptor cells - sense light touch
Role of Langerhans cells
- suprabasal
- dendritic cells
- antigen processing and presenting
Role of lymphocytes
- in inflammatory response
- often associated with Langerhans cells
Define ‘incisive papilla’
- prominence overlying nasopalatine foramen
- important in denture fitting
Define ‘palatine raphe’
- midline epithelial ridge
- directly attached to bone
Define ‘palatine rugae’
unique epithelial folds for food transport to pharynx
Define ‘fovea palatini’
- ducts of minor salivary glands
- posterior border on an upper denture
Explain epithelium, lamina propria and mucoperiosteum in masticatory mucosa
- epithelium is thick, orthokeratinised in hard palate and para and ortho in attached gingiva
- long narrow papillae with dense collagen fibres
- mucoperiosteum instead of submucosa - stability but difficulty to inject and painful (doesn’t need suturing, unlike lining mucosa)
The buccal mucosa are bound by …
- upper and lower vestibular fornices
What are Fordyce’s spots?
- ectopic sebaceous glands
- without hair follicles
What is the parotid papilla?
- opening of the parotid duct
- at level of second maxillary molar
What is the linea alba?
- parakeratinisation at level of molar occlusal plane
- also other white patches due to irritation by cheek biting
Function of Fordyce’s spots
- produces sebum to lubricate oral mucosa
- enables sliding of buccal mucosa against teeth
- lubricate lips?
Floor of the mouth is movable/unmovable - situated above what muscle?
- movable
- mylohyoid muscle
What is the term for tongue tie?
What causes this?
- ankyloglossia
- if the lingual frenum is too short or thick
Sublingual papilla is the …
opening of the submandibular salivary ducts
Sublingual folds are the …
openings of the sublingual salivary ducts
What are fimbriated folds?
- irregular folds
- remnants of tongue development
Explain epithelium, lamina propria and submucosa in lining mucosa FOR LABIAL AND BUCCAL mucosa
- thick, nonkeratinised
- lamina is dense - long and slender papillae
- submucosa (not perio) is dense - firmly attached to muscle, minor salivary and sebaceous glands for mobility and stability
Explain epithelium, lamina propria and submucosa in VENTRAL tongue, floor of mouth
- thin, non keratinised epithelium
- thin lamina propria with short papillae
- thin and irregular submucosa for mobility
What is the vermillion zone?
- lining mucosa, keratinised
- transition zone between skin and labial mucosa.
- thin epithelium, numerous capillaries (red colour), no salivary glands, only a few sebaceous in corner of mouth
What separates vermillion zone and labial mucosa?
- intermediate zone
- parakeratinised
Function of the tongue
- mastication
- swallowing
- speech
- taste
- immune function
Anterior 2/3 of tongue called the …, epithelium is derived from …
Whereas posterior 1/3 is called … and is from …
- palatal part/body
- ectoderm
- pharyngeal part/root
- endoderm
Role of these components of tongue papillae
- cirucmvallate papillae
- lingual follicles
- foliate papillae
- fungiform papillae
- filiform papillae
- taste
- lymphoid
- taste
- taste
- masticatory
Epithelium, lamina propria and submucosa of dorsal tongue surface mucosa
- thick, orthokeratinised filiform papillae and nonkeratinised taste papillae and interpapillary regions. Tastebuds
- lamina propria are long with nerves and minor salivary glands
- submucosa is absent as lamina propria attaches directly to muscle - for stability and taste
List age changes in oral mucosa
- atrophy of oral mucosa
- increase in Fordyce’s spots (buccal, lips)
- atrophy of minor salivary glands
Explain atrophy of oral mucosa
- smoother and dryer surface (dry mouth)
- thinner epithelium, flattening of epithelial ridges
- decreased cellularity of lamina propria and increase in fibrous tissue
- fewer Langerhans cells (reduced immunity) - systemic disease, medication (decreasing salivary flow)
Age changes to tongue
- epithelial atrophy (loss of FF papillae) - creates smooth, often fissured surface like nutritional deficiencies, medication
- burning sensations, loss of taste
- development of nodular, varicose veins on underside of tongue (caviar tongue)
Give 2 common tongue disorders
- black hairy tongue
- geographic tongue (benign migratory glossitis)
What is black hairy tongue?
- hypertrophy of filiform papillae
- accumulation of food debris and microorganisms
Explain geographic tongue
- atrophy of filiform papillae
- migrating depapillated patches with white border
- inflammation
Give 6 diseases of oral mucosa
- recurrent aphtous stomatitis
- other types of ulcers
- candida albicans infection
- Lichen planus
- white spongy naevus
- Leukoplakia
What is recurrent aphtous stomatitis?
- recurrent mouth ulcers
- 20% of pop have
- starts in childhood/adolescence
Give other types of ulcers than recurrent aphtous stomatitis
- virus infections (herpes, HIV etc)
- iron and vitamin B deficiency
- Crohn’s disease
What is Lichen planus?
- reticular patches
- autoimmune disease
What is white sponge naevus?
- spongy
- KRT4/13 mutations
What is leukoplakia?
- white patches
- oral potentially malignant disorder
How is oral cancer becoming a global healthcare problem?
- 15th most common cancer worldwide
- heterogenous group - includes lip, tongue, mouth, oropharynx
- high morbidity - around 300,000 cases a year
- high mortality - around 145,000 deaths a year
Risk factors for oral cancer
- tobacco
- alcohol
- paan (Areca nut and betel leaf)
- high-risk HPV
- nutritional deficiencies
- immunosuppression
- genetic pre-disposition
How is tobacco a risk factor for oral cancer?
- carcinogens in cigarette smoke and smokeless tabacco
How is alcohol a risk factor for oral cancer?
- strength and frequency
- synergistic effects with smoking (carcinogenic)
Where is Paan a risk factor for oral cancer?
- common in India and South-East Asia
How is high-risk HPV a risk factor for oral cancer?
- e.g HPV-16 and 18
- different disease aetiology
How is nutritional deficiencies a risk factor for oral cancer?
- e.g food low in antioxidants and vitamins
How is immunosuppression a risk factor for oral cancer?
- affects ability of body to attack cancer cells
How is genetic pre-disposition a risk factor for oral cancer?
- rare
- but like Li-Fraumeni syndrome (p53 mutations)
Oral cancer incidence in the UK
- increasing
- over 6,000 cases a year - 92% since 1970s
- males more than female
- poor survival rate (around 50% of advanced stage carcinoma die within 5 years)
- early detection has improved clinical outcomes
How is oral cancer a progressive disease?
- epithelial cancer - 90% oral squamous cell carcinoma
- progression is hyperplasia to dysplasia to CIS to invasive carcinoma to metastasis
- oral potentially malignant disorders - MT rate 10-12% 4.3 years
- poor prognosis - subjective histological grading criteria, lack of molecular markers
Molecular aetiology of oral cancer
- DNA damage (DNA adducts, ROS, double strand-breaks, ineffective DNA repair)
- leads to gene mutations and genome instability (aneuploidy, LOH, CNV)
- altered cell signalling and behaviour - independence of growth factor signalling control, increased and unchecked cell proliferation and motility, inhibition of apoptosis and increased survival (immortality) and evasion of immune system
- step-wise progression over many years means inactivation ofn tumour suppressors (70% p53, CDKN2A, PTEN, SMAD4 and overexpression of proto-oncogenes (CCND1, EGFR, MET, PIK3CA
List stages of the genetic progression model of oral cancer
- initial phase
- ‘patch’ phase
- expanding field
- ‘second hit’
- carcinoma formation
- carcinoma excision
- novel ‘second hit’
- tumour recurrence
What happens in the initial phase of the genetic progression model of oral cancer?
- mutation in basal stem cell
What happens in the ‘patch’ phase of the genetic progression model of oral cancer?
- clonal expansion of descendents of mutant stem cells
What happens in the expanding phase of the genetic progression model of oral cancer?
- lateral expansion of mutant cells having acquired a growth advantage
What happens in the ‘second hit’ phase of the genetic progression model of oral cancer?
- precursor lesion develops within field
- due to secondary mutations and increasing genomic instability
What happens in the carcinoma phase of the genetic progression model of oral cancer?
precursor lesion becomes invasive carcinoma
What happens in the carcinoma excision phase of the genetic progression model of oral cancer?
premalignant field remains
What happens in the novel ‘second hit’ phase of the genetic progression model of oral cancer?
- new precursor lesion develop independently
- at another site within the field
What happens in the tumour recurrence phase of the genetic progression model of oral cancer?
- ‘second field tumour’
- develops from new precursor lesion
What can improve diagnosis, treatment plan and clinical outcome?
- identification of molecular markers
- that can predict transformation to cancer
