I thought there were only 3 LORs. I have lined up one from a periodontist for whom I work, an undergrad bio prof with whom I participated in research, and my advisor from grad school. Being out of academia for a while, I don't have access to a pre-health advisor. Should I submit just the three, or should I hunt for a mediocre fourth? I know that these will be solid, but I'm not so sure I could find a wonderful fourth.