Ultrastructural study of the keratinization process in different clinical types of oral leukoplakia

The keratinization process has been investigated by ultrastructural methods in different clinical types of oral leukoplakia in 12 biopsy specimens from the buccal mucosa. Simple and verrucous clinical types of oral leukoplakia showed the presence of well-defined keratohyaline granules and the formation of tonofibrils. Erosive leukoplakias showed a lack of keratohyaline granules and a decreased aggregation of tonofilaments; in the upper cell layers dark and clear cells were found. The formation of a granular layer occurred in connection with orthokeratosis, mainly in simple and verrucous leukoplakias; erosive leukoplakias showed no corneal layer.