I disagree. Failing a class will lower your GPA, and as much as dental schools won't admit this, there are GPA and DAT cutoffs for those who do not otherwise have extenuating circumstances. AADSAS factors in all attempts at a course when calculating GPA, regardless of your school's policy on how repeated courses are handled in their GPA calculation. A W will not affect your GPA, a letter grade (A through F) will. Either way, you are going to have to retake the course and do very well the second time (anything less than an A will not be looked at favorably) in order to compensate.
One or two instances is not going to be the end of the world, but you may be asked to explain what happened.