## **Core Concept**
The six keys to normal occlusion are a set of principles used in orthodontics to evaluate and achieve ideal occlusion. These keys were formulated to provide a comprehensive approach to understanding and achieving proper occlusal relationships. They are widely used in orthodontic diagnosis and treatment planning.

## **Why the Correct Answer is Right**
The six keys to normal occlusion were given by Andrews. These keys are:
1. **Molar Relationship**: The mesial surface of the permanent mandibular first molar should align with the buccal groove of the maxillary first molar.
2. **Crown Angulation (Tip)**: The angulation of the crown of each tooth mesially or distally to its respective root should be considered.
3. **Crown Inclination (Torque)**: The inclination of the tooth (labially or lingually) in relation to its root.
4. **No Rotation**: Teeth should not have any significant rotation.
5. **Flat Occlusal Plane**: The occlusal plane should be flat.
6. **Proper Overbite and Overjet**: The upper incisors should overlap the lower incisors by about 2-4 mm vertically (overbite) and 1-3 mm horizontally (overjet).

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not correspond to Andrews.
- **Option B:** This option is incorrect because it does not correspond to Andrews.
- **Option C:** This option is incorrect because it does not correspond to Andrews.

## **Clinical Pearl / High-Yield Fact**
Andrews' six keys to normal occlusion provide a systematic approach to achieving and evaluating ideal occlusion in orthodontic treatment. Understanding these keys is crucial for orthodontists to plan and execute effective treatment. A key clinical pearl is that these principles help in achieving a stable and functional occlusion.

## **Correct Answer:** . Andrews.