<prompt> How long before obturation should the calcium hydroxide paste be allowed to remain in canal, if the apexification of open apex is intended?2 weeks4 weeks3 months6 months  <response>: As a general rule, the treatment paste is allowed to remain for 6 months. The root canal is then reopened to determine whether the tooth is ready for a conventional gutta-percha filling, as determined by the presence of a positive stop when the apical area is probed with a file. Often, there is also radiographic evidence of apical closure. Frank has described four successful results of apexification treatment:Continued closure of the canal and apex to a normal appearance.A dome-shaped apical closure with the canal retaining a blunderbuss appearance.No apparent radiographic change, but a positive stop in the apical area.A positive stop and radiographic evidence of a barrier coronal to the anatomic apex of the tooth. 