The most common pre-malignant condition of oral carcinoma is -
Two important premalignant lesions for oral cancer are : -


Leukoplakia
Erythroplakia


Leukoplakia is the most common premalignant lesions.
But, the risk of malignant transformation of erythroplakia is much higher than that seen with leukoplakia.
The most common predisposing factor for both these conditions is smoking.
Leukoplakia
Erythroplakia
Lichen planus
Fibrosis