**Core Concept**
A palatal crib is a fixed orthodontic appliance used to prevent thumb sucking habit by physically blocking the upper anterior teeth from coming into contact with the thumb. The crib is typically attached to the upper anterior teeth and extends towards the palate. The duration of wearing a palatal crib is crucial to prevent relapse of the thumb sucking habit.

**Why the Correct Answer is Right**
The duration of wearing a palatal crib is typically 2-3 years, or until the patient's upper anterior teeth have erupted fully and the habit has been completely eliminated. This is because the crib serves as a reminder to the patient to stop sucking their thumb, and prolonged use helps to retrain the muscles of the mouth and jaw to maintain proper alignment. The crib is usually removed when the patient's upper anterior teeth have reached a certain level of development, usually around 8-10 years of age.

**Why Each Wrong Option is Incorrect**
* **Option A:** A duration of 6 months is too short to effectively break the thumb sucking habit. The patient may still be accustomed to the habit and may relapse once the crib is removed.
* **Option B:** A duration of 1 year is also insufficient to ensure complete elimination of the habit. The patient's upper anterior teeth may not have fully erupted, and the habit may still be present.
* **Option D:** A duration of 5 years is excessive and may lead to unnecessary discomfort or complications for the patient. The crib can be removed once the patient's upper anterior teeth have reached a certain level of development.

**Clinical Pearl / High-Yield Fact**
It is essential to monitor the patient's progress and adjust the duration of wearing the palatal crib accordingly. Regular follow-up appointments with the orthodontist or pediatric dentist are crucial to ensure successful treatment and prevent relapse of the thumb sucking habit.

**Correct Answer:** C. 2-3 years.