Chewing tobacco can cause reduced mouth opening (trismus) by two effects: 1. Oral submucosal fibrosis in which tissue in layer beneath the lining (mucosa) of mouth (oral cavity) gets fibrosed (fixed and hardened due to changes). Although it is a benign condition but it is quite troublesome as patient cannot open mouth adequately resulting in difficulty eating and speaking. 2. Oral cancer which has advanced locally to involve muscles, muscle spaces or joints of mastication (chewing) which are also responsible for mouth opening. In both cases you need to see your dental surgeon who after examination will advise biopsy and CT scan imaging from base of skull to root of neck to get to an exact diagnosis. I hope it helps. Please discuss it with your doctor.