Which one of the following toothpaste ingredients has the most effect on increasing the teeth's resistance to caries?

Sodium fluoride is known to have a significant effect on enhancing the teeth's resistance to caries, which are the result of tooth decay caused by acid-producing bacteria. Fluoride works by remineralizing the enamel, making it more resistant to acid attacks. It can integrate into the crystal structure of the enamel during the formation of teeth and also help repair early decay. When fluoride is present in the mouth, it encourages the remineralization of demineralized enamel, thereby strengthening the tooth structure and ultimately decreasing the risk of cavities.

In contrast, biological enzymes are more focused on breaking down plaque and food particles rather than directly affecting caries resistance. Sodium saccharin is a sweetening agent and does not contribute to the structural health of teeth. Triclosan is an antibacterial agent that helps control plaque and gingivitis but does not have the same protective effect against caries as fluoride does. Therefore, sodium fluoride stands out as the key ingredient in toothpaste that effectively increases the resistance of teeth to caries.