## Core Concept
Rapid palatal expansion (RPE) is an orthodontic procedure used to widen the upper jaw (maxilla) by applying force to the upper molars. This technique takes advantage of the viscoelastic properties of the midpalatal suture and surrounding bone. The goal is to achieve both skeletal and dental expansion.

## Why the Correct Answer is Right
The skeletal expansion refers to the actual widening of the maxillary bone, while dental expansion refers to the tipping or movement of the teeth within the bone. Studies and clinical experience have shown that the ratio of skeletal to dental expansion achieved through RPE is generally around 2:1 or 1:1 in the short term but tends to stabilize at a ratio of **2:1** over time as the dental expansion (teeth tipping) corrects and the skeletal expansion becomes more stable. This means for every 2 units of skeletal expansion, there is approximately 1 unit of dental expansion, making the ratio **2:1**.

## Why Each Wrong Option is Incorrect
- **Option A:** This option does not match the commonly cited ratio for skeletal to dental expansion after RPE.
- **Option B:** Similarly, this option does not align with the generally accepted ratio.
- **Option D:** This option suggests a reverse ratio, which contradicts the established understanding that skeletal expansion exceeds dental expansion in RPE.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the immediate effects of RPE show a higher proportion of dental expansion, but over time, as the bone remodels and the teeth move within the expanded bone, the skeletal expansion becomes more significant. The **2:1 ratio** is a useful guideline for planning and evaluating the outcomes of RPE treatments.

## Correct Answer Line
**Correct Answer: C. 2:1.**