Table 5 Definitions of oral mucosal lesions used in studies in the USA

Definition of Greer 1983 [27]

Modified version of Axéll 1976 [15]. Oral mucosal lesion graded for severity as:

Degree 1. A superficial lesion with colour similar to that of the surrounding mucosa with slight wrinkling and no obvious thickening.

Degree 2. A superficial whitish or reddish lesion with moderate wrinkling and no obvious thickening.

Degree 3. A red or white lesion with intervening furrows of normal mucosal coour, obvious thickening and wrinkling.

Studies using the Greer 1983 definition

Payne 1998 [22], Greer 1983 [27], Poulson 1984 [28], Wolfe 1987 [30], Stewart 1989 [33], Sinusas 1992 [36], Sinusas 2006 [44] and Little 1992 [48].

Studies using other definitions

Grasser 1997 [21] – oral leukoplakia; a white patch or plaque that does not wipe off and cannot be characterized clinically or pathologically as any other disease

Martin 1999 [23] – oral leukoplakia; modified from Greer 1983 definition, graded for severity as 1: superficial lesion with slight colour change, slight wrinkling and no obvious thickening, 2: superficial white lesion with moderate wrinkling and no obvious thickening, and 3: white lesion with obvious thickening and wrinkling

Fisher 2005 [26] – oral leukoplakia; based on the international classification of diseases, 9^th revision code (ICD-9) of 528.6 with a biopsy of hyperkeratosis with or without epithelial atypia or dysplasia. A clinical diagnosis of ST keratosis or frictional keratosis was excluded

Offenbacher 1985 [29] – oral mucosal pathology; alterations considered to represent early changes, as reflected by a mild increase in opalescence and whiteness, with slight furrowing

Creath 1988 [32] – oral leukoplakia; not further defined

Cummings 1989 [31] – soft tissue lesions; not further defined

Ernster 1990 [34] and Greene 1992 [35] – oral leukoplakia; any white, opaque, leathery-appearing plaque not clinically characteristic of another type of white lesion, graded for severity as 1: no or only slight colour change, with or without texture change, 2: colour and texture change, but no thickening, 3: colour and texture change with mild to moderate thickening, or 4: no normal colour, severe texture change, and heavy thickening

Daughety 1994 [37] – oral lesions at placement site; from response to question "Have you ever noticed a sore, white patch or gum problem where you held the tobacco in your mouth?"

Robertson 1997 [38] – oral leukoplakia; any white, opaque, leathery-appearing slightly raised, and irregularly corrugated changes in the oral mucosa not characteristic of another white lesion, graded for severity from 1: slight change in colour and texture to 4: no normal colour, severe texture change and heavy thickening

Tomar 1997 [39] – ST lesions; slight to heavy wrinkling of the mucosa with or without obvious thickening, graded for severity as 1: slight, superficial wrinkling of the mucosa. Colour of the mucosa may range from normal to pale white or grey. Mucosa does not appear to be thickened, 2: distinct whitish, greyish, or occasionally reddish colour change. Wrinkling is obvious, but there is no thickening of the mucosa, or 3: mucosa is obviously thickened, with distinct whitish or greyish colour change. Deep furrows are present within the thickened areas

Shulman 2004 [42] – oral mucosal lesions; 49 types of lesion are listed, including candida-related lesions, tobacco-related lesions, acute conditions and various other conditions, but ST use is only given in relation to the overall incidence of any type

Smith 1970 [45] – oral mucous membrane change "which offered criteria for further study"

Christen 1979 [46] – clinical leukoplakia; a white plaque on the mucosa, with mild to moderate defined as a non palpable, smooth, fairly translucent white area, and severe defined as areas appearing thick, white, indurated and fissured

Kaugars 1992 [47] – oral lesion; a visible alteration of the oral mucosa that persisted for at least 7 days after discontinuation of ST use; an alteration with little probability of resolving within 7 days, in the opinion of the investigator, or an alteration occurring in a subject who was unable to return for a recall visit

Roberts 1997 [49] – oral lesion; any visible lesion