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Black bears (Ursus americanus) were live-trapped, immobilized, and examined to determine the incidence of dental caries, broken and missing teeth, and jaw and bone trauma; and the incidence and cause(s) of periodontal disease in northern Wisconsin in 1974-1975 (N = 95), and in Michigan's northern Lower Peninsula from 1977-1980 (N = 35). Based on tooth sectioning, Wisconsin bears ranged in age from 0.5 to 15.5 years (average age for males and females was 4.5 and 6.02 years, respectively); Michigan bears ranged in age from 0.02 to 8.1 years (average age for males and females, 4.5 and 4.29 years, respectively). As expected, dental caries were common in both Wisconsin (9 [10.5%] of 86 bears examined) and Michigan bears (7 [20%] of 35). In both cases, caries appeared to develop in older animals, ranging from 3.5 to 15.5 years of age in the Wisconsin sample and 3.5 to 8.1 years of age in the Michigan sample. Bears suffering from periodontal disease varied considerably between cohorts. In Wisconsin, only 1 (1.1%) of 95 bears, a 5.5-year-old female, was infected with the disease. In Michigan, however, 13 (37%) of 35 bears had periodontal disease in varying degrees of severity, suffering tooth loss, infection, edema, bleeding, and jaw and gum atrophy. There was insufficient evidence, however, to indicate that bacteria (N = 12) caused the disease. Using 2-dimensional isoelectric focusing, 5 samples of blood serum from diseased bears contained a minor protein band not present in disease-free samples. The results could not be replicated from other diseased bears, however. Selenium levels were low in bears examined (0.066-0.74 μg Se/ml serum), and although baseline values are not known for black bears, insufficient quantities of selenium in bear diets in Michigan's Lower Peninsula selenium-deficient belt are suspected of causing or at least contributing to the disease. Although periodontal disease was reported as age-dependent in other studies, such was not the case in Michigan (disease range = 1.75-6.5-years-old). Winter movements of several seriously-infected bears were related to disease infection.