<prompt> Antral fistula is most common after extraction of:2nd incisor1st premolar3rd molar1st molar  <response>: d 1st molarRef. Scott Brown, 6th ed., 1525The floor of the maxillary sinus is related to 2nd premolar and 1st molar. Therefore extraction of these teeth can lead to an oro-antral fistula. 