**Core Concept**
Nursing caries, also known as early childhood caries, is a type of tooth decay that affects the primary teeth in infants and toddlers. It is primarily caused by the frequent and prolonged exposure of the teeth to sugars from milk, formula, or other sweetened liquids. The primary teeth are highly susceptible to decay due to their small size, lack of enamel, and incomplete root development.

**Why the Correct Answer is Right**
The primary teeth are most severely affected by nursing caries due to their anatomical characteristics. The primary molars, especially the first and second molars, are more prone to decay because they have a larger surface area exposed to the oral cavity and are more difficult to clean. The enamel of the primary teeth is also thinner and more porous than that of permanent teeth, making them more susceptible to acid attacks from bacteria. The primary molars are also closer to the gum line, making it easier for bacteria to accumulate and cause decay.

**Why Each Wrong Option is Incorrect**
**Option A:** The primary incisors are not as severely affected by nursing caries as the primary molars, as they have a smaller surface area exposed to the oral cavity and are easier to clean.

**Option B:** The primary canines are not as severely affected by nursing caries as the primary molars, as they have a smaller surface area exposed to the oral cavity and are less prone to decay.

**Option C:** The primary second molars are actually more severely affected by nursing caries than the primary first molars, as they have a larger surface area exposed to the oral cavity and are more difficult to clean.

**Clinical Pearl / High-Yield Fact**
Nursing caries can be prevented by reducing the frequency and duration of exposure to sugars, using a fluoride toothpaste, and practicing good oral hygiene. Parents should also be educated on the importance of regular dental check-ups and cleanings for their children.

**Correct Answer:** C. The first and second primary molars are most severely affected by nursing caries due to their anatomical characteristics, making them more prone to decay.