Content Reviewers:Rishi Desai, MD, MPH
The oral cavity includes the lips, the gingiva, or gums, the floor of the mouth, the buccal mucosa which is the soft lining of the inner lips and cheeks, the anterior or front two-thirds of the tongue, the hard palate which is the tough front part of the roof of the mouth, and the retromolar trigone which is the mucosa right behind the last molars on the bottom row of teeth.
The oropharynx includes the soft palate which is the soft part of the roof of the mouth right behind the hard palate, the tonsils, the walls of the throat, and the posterior or back one-third of the tongue.
The first type of epithelium is called keratinized stratified squamous epithelium.
These epithelial cells produce keratin, a protein that makes the layer tough, and protects against normal wear and tear from food and drinks.
Beneath the epithelium, there’s another layer called the basement membrane made of tough connective tissue, and below that is the lamina propria which yet more connective tissue that houses blood vessels, lymphatics, nerves, and immune cells.
A second type of epithelium is non-keratinized stratified squamous epithelium, and it contains cells that don’t produce much keratin, making this layer less tough.
The oral surfaces covered by non-keratinized stratified squamous epithelium include the buccal mucosa, the floor of the mouth, the lateral and ventral, or bottom, surfaces of the tongue, the soft palate, and the retromolar trigone.
The first one of these is leukoplakia, where leuko- means white and -plakia means a flat, raised patch or plaque.
And leukoplakia specifically relates to a white plaque with no clear underlying cause.
These leukoplakias are usually painless but can’t be easily scraped away.
Early on, these lesions are usually pretty thin, so it’s called thin leukoplakia.
These can either go away on their own, remain unchanged, or grow and become thicker, at which point it’s called thick leukoplakia.
Now a more serious form of leukoplakia is called proliferative verrucous leukoplakia, which usually affects women, with no risk factors and it has a predilection for gingiva and causes multiple rough white lesions that grow and spread, and in most cases, eventually develop into squamous cell carcinoma.
Since keratin absorbs water, a thick keratin layer looks white when it’s wet.
And that change could happen at the microscopic level, meaning that the lesion might look the same on the outside, even though the cells have become cancerous.
Generally speaking, the transition from dysplastic cells to malignant cells occurs gradually.
And as cells become more and more dysplastic the lesions sometimes develop red spots, and at that point it’s called erythroleukoplakia.
Cells in these red areas have suffered serious damage to their DNA and don’t mature normally and therefore can’t produce keratin.
And as they become more and more atypical, the more immature becomes the epithelium and it will start becoming thinner or atrophic and allow more of the underlying blood vessels to be seen through the mucosa.
At that point the lesion will be completely red and will be called erythoplakia.
Now, a lesion that looks like leukoplakia, but isn’t, is an area of frictional keratosis.
It’s a normal hyperplastic response, meaning the epithelial cells in the area divide more than usual and build up a protective layer of keratin.
It’s a bit like developing a callus on your hands after spending the weekend raking leaves.
An area of frictional keratosis is not a precancerous lesion and usually fades away once the irritation stops.
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