Previous work by a number of scientific teams has revealed that the types of bacteria that colonize the mouth differ between health and pre-cancerous or cancerous oral lesions. The purpose of this study is to investigate the extent of these changes and to correlate the changes with alterations in the activities of the host's own oral tissues. In doing so, we believe we can gain a better understanding of how particular bacterial species, or consortia of species, can result in an individual having an increased risk of the most common type of oral cancer -- oral squamous cell carcinoma. This knowledge may also lead to the identification of salivary biomarkers that can be used for clinical evaluation or screening. In addition, we seek to determine the extent to which a probiotic regimen can help prevent or rectify the disease-related changes in the types of bacterial colonizing the mouth. The microbiome in health, pre-cancerous lesions, and cancerous lesions will be determined from remnant microbial DNA in banked tissue samples. The effects of probiotics on the oral microbiome will be determined from DNA collected from swabs of oral tissue at baseline and then after 3 to 6 months of probiotic usage.