eMedicine Specialties > Dermatology > Diseases of the Oral Mucosa

Oral Frictional Hyperkeratosis

Author: Catherine M Flaitz, DDS, MS, Dean and Co-director of Oral and Maxillofacial Pathology Laboratory, Professor of Oral and Maxillofacial Pathology and Pediatric Dentistry,Department of Diagnostic Sciences, University of Texas Health Sciences Center at Houston, Dental Branch
Coauthor(s): Alfredo Aguirre, DDS, MS, Director of Advanced Oral and Maxillofacial Pathology Training Program, Associate Professor, Department of Oral Diagnostic Sciences, State University of New York at Buffalo; Jose L Tapia, DDS, Assistant Professor, Department of Oral Diagnostic Sciences, State University of New York at Buffalo
Contributor Information and Disclosures

Updated: Oct 5, 2006

Introduction

Background

The oral mucosa is lined by stratified squamous epithelium and has topographic differences that correlate with physical demands or a higher degree of specialization. For example, the epithelium lining the floor of the mouth, the ventral side of the tongue, the buccal mucosa, and the soft palate is nonkeratinized; however, the epithelium associated with the gingiva and hard palate is usually keratinized. The dorsal surface of the tongue is also keratinized, but it is referred to as specialized mucosa because of the presence of papillae. In contrast, the dorsum of the tongue, the hard palate, and the gingival tissues are keratinized to better respond to masticatory demands.

Hyperkeratinization (excessive formation of tenaciously attached keratin) may be present in a variety of clinical conditions, including genetic, physiologic, inflammatory, immunologic, premalignant, and malignant conditions. The change may result from a local insult, including chemical, thermal, or physical irritants. This article focuses on the oral hyperkeratinization that results from friction. Friction (the constant rubbing of 2 surfaces against one another) in the oral cavity may result in the development of clinically observable white patches.

Various names have been used to describe particular examples of frictional keratosis (FK). These include FK arising from excessive force while brushing the teeth (toothbrush keratosis); the constant rubbing of the tongue against the teeth (tongue thrust keratosis); the constant sucking, pressure, and irritation of the teeth against the buccal mucosa along the plane of occlusion (linea alba); and the habit of chronic cheek or lip biting (cheek- or lip-bite keratosis).¹

Pathophysiology

The white patches of FK that develop in the oral cavity represent a chronic, low-grade, mechanical process that is analogous to the formation of a callus on the skin. The most common local factors involved in this process are tissue chewing (mainly on the buccal mucosa or lips), ill-fitting or irregularly surfaced removable dental prostheses (dentures), fractured or malposed teeth, poorly adapted dental restorations, orthodontic appliances, improper toothbrushing, and constant mastication on edentulous alveolar ridges. The constant irritation stimulates the production of excessive keratin, with a subsequent change in the thickness and the color of the involved mucosa.

Frequency

United States

Few large epidemiologic studies documenting the prevalence of various oral lesions, including oral FK, have been published.

• The most comprehensive survey on the prevalence of oral mucosal lesions is the Third National Health and Nutrition Examination Survey (NHANES III). Oral examinations were performed on 17,235 noninstitutionalized civilian adults. Cheek and lip biting had a point prevalence of 3.05% and ranked third in oral lesion prevalence, while FK had a point prevalence of 2.67% and ranked fourth.² In the same national survey, when 10,030 children aged 2-17 years were evaluated, the point prevalence for cheek and lip biting was 1.89% and 0.26% for FK.³
• In another extensive survey of 23,616 white American adults from Minnesota that evaluated a wide range of oral lesions, the number of cases of cheek-biting keratosis was 1.2 cases per 1000 individuals.⁴ In this same study, FK was not differentiated from leukoplakic lesions, so the prevalence of FK alone cannot be determined.
• Linea alba is a common mucosal variation that is rarely singled out as a specific entity in prevalence studies. In a limited study of young men, 13% had this mucosal alteration.⁵

International

In a Danish study of 20,333 people aged 15 years and older, the prevalences of cheek and lip biting and FK were slightly higher than those reported in the US studies.⁶ The prevalence for cheek and lip biting was 5.1%, and the prevalence for FK was 5.5%. Similarly, the prevalence for FK from a small study sample⁷ of Kenyan adults was 5.5%. In Slovenia, the prevalence was 2.7% for cheek and lip biting and 2.2% for FK.⁸ In a limited study of patients treated at a dental school in Spain, the rate was 11.5% for FK, 10.7% for linea alba, and 6.8% for cheek biting.⁹

Mortality/Morbidity

FK and its variants do not cause symptoms and are benign mucosal lesions that remain localized with no associated mortality or morbidity.

Race

No racial predilection seems apparent for this condition.

Sex

In general, FK has no known sex predilection, except for cheek biting and lip biting, which are twice as prevalent in women compared with men.

Age

Oral FK affects persons from a wide range of ages, and contributing factors determine which age group is more commonly affected. The exception is cheek biting and lip biting, which are detected 3 times more often after age 35 years.

Clinical

History

• Most patients with FK are free of symptoms, with the exception of those with aggressive cheek and lip biting habits. In some individuals who repeatedly traumatize the tissues, tenderness, swelling, and a burning sensation may be presenting symptoms.
• Patients with persistent cheek and lip biting habits tend to have increased stress and psychologic disorders.
• A patient may notice a thickening or roughness of the involved mucosal site, or FK may be discovered as an incidental finding during a routine oral examination.
• Individuals with a cheek and lip biting habit often report they are able to remove thin strands or tags of mucosa from the involved site.
• Patients may report that they are aware of sucking the mucosa or thrusting their tongue against their teeth. Some patients report that their cheeks and tongue feel swollen. Occasionally, the affected fungiform papillae in persons with a tongue biting or thrusting habit may be tender and have a burning sensation.
• When the gingival tissues are involved, patients may report using a medium- or hard-bristled toothbrush or other oral hygiene aids.
• In some instances, patients give a history of wearing orthodontic appliances, mouthguards, occlusal splints, or removable full or partial dental prostheses.
• In rare examples, individuals may give a history of picking the oral mucosa with long fingernails or some other external object.

Physical

The first step in the identification of white patches suspected of being associated with physical trauma is to use a 2 X 2-inch sterile gauze to wipe off the lesion or lesions. If the patch is not easily wiped off, this suggests the presence of hyperkeratinization.

• The lips, the lateral margins of the tongue, the buccal mucosa (mainly along the occlusal line), and the edentulous alveolar ridges are the most common sites to find FK and its variants.
• Typically, the lesions appear as distinct, focal, and translucent-to-opaque white asymptomatic patches with sharply delineated borders. The surface of a lesion may appear irregular and feel rough to the tongue.
• Slight variations in the clinical presentation are directly related to the nature and the source of the physical trauma.
• One of the more common features of FK is the linea alba (white line). This feature manifests as a horizontal thickening of the buccal mucosa along the line of the teeth, the occlusal line. It is thought to result from chronic cheek biting or sucking of these tissues (see Media File 1 and Media File 3).
  • In one patient, the surface of the last molar tooth showed considerable occlusal wear, which is evidence that the patient had the habit of grinding his teeth (see Media File 1). This habit most probably led to the biting of the cheek mucosa.
  • Occasionally, the line reflects the irregularity of the adjacent teeth and has a somewhat scalloped appearance (see Media File 2).
• Occasionally, the frictional line is somewhat more diffuse, and this type of change is more likely to be associated with the habit of cheek chewing, also known as morsicatio buccarum (see Media Files 4-5), rather than the occasional accidental friction of teeth against the mucosa during the normal eating process. These white patches are associated with either a conscious or an unconscious chronic oral habit.
• The effects of the habit of chronic biting may also manifest on the anterior and lateral borders of the tongue and appear as white, shaggy or mildly wrinkled plaques (see Media File 6).
• An FK lesion may be elevated from the surface, and patients may find that they develop the habit of nibbling further at these thickened mucosal sites. Media File 4 shows an FK lesion that displays marked keratinization. The patient admitted to nibbling at the thickened mucosa (see Media File 5), which, in turn, made it thicker and easier to feel and, therefore, encouraged further nibbling.
• Lesions associated with a tongue thrusting habit often demonstrate prominent crenations of the lateral tongue. In addition, the affected fungiform papillae may be red and enlarged from the chronic irritation.

Causes

In most patients with FK, the cause is easily identified.

• An oral habit of cheek biting, cheek chewing, tongue thrusting, or mucosal sucking can often be identified as the cause if the site of the lesion is carefully examined in relationship to the occlusal plane.
• An ill-fitting, rough, or broken removable dental prosthesis or orthodontic appliance or a fractured or irregular tooth surface frequently affects the adjacent soft tissues.
• Occasionally, an FK lesion may develop as a result of the constant rubbing of an external object, such as a tobacco pipe; a musical instrument; or, perhaps, a worker's tool, which, for convenience, is held in the mouth for long periods.
• Another cause may be manipulation of the tissues with long fingernails, which may shred the mucosa.
• Improper toothbrushing and other oral hygiene aids affect the attached gingival tissues (see Media File 6).
• Irritation from masticatory function may cause FK when the alveolar mucosa and retromolar pad bear the stresses of eating (see Media File 8).
• The identification of such habits depends on obtaining a thorough history.

• Search for CME/CE on This Topic »