Effect of long-term application of snuff on the oral mucosa: an experimental study in the rat.

The long-term effect of snuff exposure was studied in Sprague-Dawley rats using a surgically-created test canal in the lower lip to retain snuff. The rats received standard snuff (n = 42) and highly alkaline snuff (n = 10) for 9-22 months, whereupon they were killed. Untreated rats with identical test canals (n = 15) served as controls. A complete post-mortem examination was performed. One rat exposed to standard snuff for 9 months developed a squamous cell carcinoma of the oral cavity. However, exposure to standard snuff usually resulted in a mild to moderate hyperplasia of the epithelium, hyperorthokeratosis and acanthosis. Rats exposed to snuff for 18-22 months showed vacuolated cells penetrating deeper into the epithelium with hyperplastic and atrophic lesions. In a few rats, severe dysplastic changes developed in the crevicular epithelium. Rats exposed to alkaline snuff differed little from the first group except that there was focally atrophic and ulcerated epithelium and less fibrosis. Pathological findings outside the oral cavity were rare. Squamous cell hyperplasia of the forestomach was found in rats exposed to snuff for 18-22 months, possibly caused by ingested snuff. In conclusion, this study has shown that exposure of rats to snuff for 10-16 hours per day 5 days a week for most of their life-span resulted in lesions mainly restricted to the epithelium and the underlying connective tissue of the surgically created test canal.