## **Core Concept**
The Simplified Oral Hygiene Index (OHI-S) is a modification of the original Oral Hygiene Index, used to assess oral hygiene status. It evaluates the presence of debris and calculus on selected tooth surfaces.

## **Why the Correct Answer is Right**
The OHI-S involves examining the buccal surfaces of the upper right first molar and the lower left central incisor for debris and calculus. Additionally, it includes the lingual surface of the lower right central incisor. This makes a total of 6 surfaces evaluated for debris and calculus. Therefore, the correct answer stating 6 surfaces is accurate.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests fewer surfaces are examined, which underestimates the actual number assessed in the OHI-S.
- **Option B:** This option also suggests fewer surfaces, not accurately reflecting the comprehensive assessment provided by the OHI-S.
- **Option D:** This option overestimates the number of surfaces examined.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the OHI-S is a quick and effective method for assessing oral hygiene status, focusing on a limited number of teeth surfaces to represent the overall oral hygiene condition of an individual.

**Correct Answer: C. 6**