A high-sucrose diet decreases dentin formation and its minerals, but the mechanisms behind the effect are largely unknown. We studied the combined and separate effects of sucrose and insulin on dentin formation and mineral metabolism in growing rats. At weaning, animals were randomized into 4 groups: control/sucrose diets both with and without external insulin (1 U/x 100 g body weight daily). After 4 weeks, we measured areas of dentin formation, numbers and areas of dentinal caries lesions, and serum and urine glucose, insulin, Ca, Na, K, and P. Exogenous insulin increased serum and urine insulin levels and decreased serum glucose level, but did not affect dentin formation or dentinal caries lesion formation or progression. A high-sucrose diet decreased dentin formation independently of insulin. The differences in serum and urine minerals between the groups were minor. The findings confirm that sucrose-diet-induced reduction in dentinogenesis is independent of insulin and loss of minerals in urine.