Difference of width of four maxillary permanent incisors and primary incisors is about:

 # Difference of width of four maxillary permanent incisors and primary incisors is about:

A. 7 mm

B. 6 mm

C. 6.5 mm

D. 8.5 mm

The correct answer is A. 7 mm. 

Permanent incisors develop lingual to the primary incisors. For incisors to erupt in normal alignment, there is an obligate space requirement in the anterior part of both the arches which is termed as incisor liability or difference between the amount of space needed for the permanent incisors and the amount available for them is called the incisor liability. The total sum of the mesiodistal width of four permanent incisors is larger than that of primary incisors by 7.6 mm in maxilla and 6 mm in mandible.