ENT Nose and paranasal sinuses efa4ab49 Maxillary sinus achieves maximum size at A bih B Primary dentition C At secondary dentition D At pubey High-Yield Explanation Maxillary sinus is the first sinus to develop at bih. It is completely developed by 9 years of agei.e approximately at secondary dentition Ref Maqbool 11/e,p148.