Teeth and bones are both strong and white and both store calcium, but teeth are not bones. Bones are made mostly of collagen, a type of protein, and are made of living tissue. Old bone tissue is continually replaced with new tissue, keeping them strong. Teeth are composed of multiple layers: enamel, dentin, cementum, and pulp. Enamel is harder than bone but doesn’t contain living tissue and, therefore, cannot regenerate like bone does.