Since acute osteoporosis is known to enhance bone remodeling and osteoid formation, it may also affect dentin apposition. We induced osteoporosis in 15-week-old Wistar rats by ovariectomy and dental caries by Streptococcus sobrinus infection in the presence of either a high sucrose (cariogenic) diet or a non-cariogenic diet. Intact animals with the same diets served as controls. After 99 days of cariogenic challenge the rats were killed, and the success of ovariectomy was confirmed by failure to detect ovarian tissue and observation of marked atrophy of the uterine horns. Areas of dentinal apposition during the experiment and carious lesions were quantified with a tetracycline method. Ovariectomy activated dentin formation significantly in rats fed either a high-sucrose or a non-cariogenic diet, indicating enhanced odontoblast function. The rate of dentinal apposition in adult rats was smaller than reported in young animals. The effect of ovariectomy on caries remained negligible.