This study compared the association of OSF and polymorphisms of six collagen-related genes, collagen 1A1 and 1A2 (COL1A1 and COL1A2), collagenase-1 (COLase), transforming growth factor beta1 (TGF-beta1), lysyl oxidase (LYOXase), and cystatin C (CST3), between patients with low and high exposure to betel quids.