1) I don't think it is worth waiting for, submit it early and list the "anticipated end date" and mark "degree expected" for you master's on AADSAS where it asks. Update it beginning Mid-November through academic update.
2) By didn't do so well do you mean below a C? In that case, you will be expected to take it prior to matriculation to fulfill completed course requirements. Otherwise, a retake is probably not necessary.
The official instructions say to list planned courses through Summer of next year but in the end, it probably doesn't matter too much. If you can, list it. If you can't, it is not the end of the world. Once again, you can update planned courses through the academic update.
Dental school admissions officers use the information from the College Courses Planned or In
Progress section to develop an understanding of your educational plans between the date of application and
the start of dental school. They realize that plans change, courses may not be available as planned, etc., and
generally use this information only as a guide to your intentions.
http://www.adea.org/uploadedFiles/A...ions/ADEAAADSASGeneralInstructionsBooklet.pdf