**Question:** 1st evidence of calcification of Primary Upper canine is seen in

A. 4th week of gestation
B. 6th week of gestation
C. 8th week of gestation
D. 10th week of gestation

**Correct Answer:** D. 10th week of gestation

**Core Concept:** Calcification is a process of deposition of calcium phosphate crystals in tissues leading to mineralization. In human development, calcification occurs in a specific sequence, which can be used to determine fetal age.

**Why the Correct Answer is Right:** The calcification of the primary upper canine tooth (also known as the deciduous canine or milk canine) is a crucial event in fetal tooth development. The correct answer (Option D) refers to the 10th week of gestation as the first stage of calcification for the primary upper canine. This is because the primary canine starts its calcification process during the second half of the embryonic period, which begins around the 6th week of gestation.

**Why Each Wrong Option is Incorrect:**

A. The 4th week of gestation is too early for the primary canine calcification process to start.
B. Although the 6th week of gestation marks the beginning of the embryonic period, calcification of primary canine does not occur during this stage.
C. The 8th week of gestation is later than the correct answer and does not represent the initial stage of primary canine calcification.

**Clinical Pearl:** Understanding the tooth development timeline is essential for dental professionals, particularly during dental radiographic assessment and diagnosis of developmental abnormalities. Knowledge of when primary canine calcification starts can help in determining the fetal age more accurately.