## **Core Concept**
The eruption of primary teeth, also known as milk teeth or deciduous teeth, is a significant developmental milestone in infants. This process begins when the infant is around 6 months old and continues until they are about 3 years old. The **primary dentition** consists of 20 teeth.

## **Why the Correct Answer is Right**
The first set of milk teeth typically starts to appear when an infant is about 6 months old. This is a general guideline, as there can be variation among infants. The **lower central incisors (also known as central bottom teeth)** are usually the first to erupt, marking the beginning of the teething process.

## **Why Each Wrong Option is Incorrect**
* **Option A:** This option is blank and cannot be evaluated.
* **Option B:** This option is blank and cannot be evaluated.
* **Option D:** This option is blank and cannot be evaluated.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the eruption of the first tooth can sometimes be as early as 3 months or as late as 12 months, but 6 months is a commonly cited average. The sequence and timing can vary, but generally, the first teeth to erupt are the **lower central incisors**, followed by the **upper central incisors**.

## **Correct Answer:** . 6 months