Which of the following extrinsic sugars is not considered to be cariogenic?

Lactose is the correct choice because it is typically considered to be less cariogenic than other extrinsic sugars like dextrose, glucose, and sucrose. Cariogenic substances are those that can contribute to the formation of dental caries (cavities) by being metabolized by bacteria in the mouth, which produce acids as a result.

Lactose, found in milk and dairy products, is less likely to promote tooth decay because it is often consumed in the context of these products, which also contain calcium and phosphates that can help remineralize teeth. This contrasts with the other sugars listed, which are quickly broken down by oral bacteria into acids that can damage tooth enamel. Dextrose, glucose, and sucrose are all more readily fermented by these bacteria, making them more cariogenic and contributing more significantly to dental caries.

Thus, while all sugars can potentially contribute to tooth decay when consumed excessively, lactose is generally viewed as less harmful in the context of dental health, particularly due to the presence of beneficial nutrients in dairy products.