There are already plenty of threads covering this, but the short answer is: no, one failed elective will not keep you out. Dental schools take your entire application — cGPA/sGPA, DAT scores, EC's, LoR's, PS, etc. — into consideration. There is even a section on AADSAS which allows you to explain uncharacteristic academic performance. It's not the end of the world for you; just take responsibility for your mistakes and keep improving.