This is an extremely common keratotic lesion seen at sites easily reached with the teeth. Acute bite trauma is usually painful and results in an obvious ulcer. Lesions of morsicatio mucosae oris, however, are caused by chronic habitual chewing and raking of the teeth over the mucosa, or dragging of the tongue over the lower teeth. Patients may not report such a parafunctional habit because this may occur during sleep.

[u]Clinical and Histopathologic Findings[/u]

Lesions present as white papules and plaques on the buccal mucosa, lateral/ventral tongue and lower lip mucosa; lesions are rarely seen on the upper lip mucosa. They have a pale white, shaggy or papillary surface and are not painful because it is a superficial process. Occasionally, one may see areas of erosion or even ulceration where the teeth have penetrated the epithelium. Lesions are often bilateral.

Look on your buccal mucosa and you may see the linea alba, a white line that runs anterior-posteriorly on a plane where the upper and lower teeth meet. If you biopsy this area, you will see the same changes (albeit milder) as seen in this condition, because it has the same etiology – chronic friction. It is easy to imagine how a parafunctional habit would cause enlargement of this keratotic linear lesion to a plaque or papules centered usually around the linea alba. Histologic features include

1. Parakeratosis that may be thin or extremely thick, depending on how active the habit has been; surface is usually irregular and “shaggy” and there may be papillary projections of parakeratin.
2. Fissures and clefts rimmed by bacteria are seen in well-developed lesions.
3. Acanthosis with keratinocyte edema of the superficial keratinocytes
4. Insignificant inflammation in the lamina propria and insignificant epithelial atypia unless the lesion is ulcerated or eroded.
5. Note that the parakeratosis gradually becomes less prominent at the periphery of the lesion, as one would expect from a traumatized lesion; careful evaluation of the edges of the lesion will provide you with the spectrum of histopathologic findings seen in this condition.

Although these are often signed out as “parakeratosis and acanthosis”, this is not as accurate as a diagnosis of “morsicatio mucosae oris” or “frictional/factitial keratosis”, the preferred diagnoses. Unlike true leukoplakias (defined as keratotic lesions of unknown etiology and that often either already dysplastic at first biopsy, or show dysplasia or invasive cancer on subsequent biopsies), these are frictional keratoses, and do not have any malignant potential.

[u]Clinical implication of not rendering a diagnosis of morsicatio mucosae oris[/u]

If you render a diagnosis of just “hyperparakeratosis, acanthosis”, this means that the lesion defaults to a clinical diagnosis of “leukoplakia” (see definition above) and all that it connotes that is, life-time follow-up and re-biopsy. This is because studies have shown that up to 16% of all so-called “benign hyperkeratosis” transform over time to dysplasia or squamous cell carcinoma.

By making a diagnosis of morsicatio mucosae oris or frictional/factitial keratoses, the clinician can reassure the patient that this is entirely benign and has no malignant potential.