I got two science professors and one dentist- this suffices for most dental schools. For UNLV, however, they require a fourth. I have one but I'm not too sure of its strength since it's a generic one (never talked to prof, just sent an email asking if she can write a strong, positive letter; she agreed). Let's assume it is pretty generic and the rest of my LoR are decent. Would uploading a fourth do more harm than good?