This is one reason why owning a lot of animals is a bad idea - it is difficult to check that you have seen each of them every day and problems can go unnoticed for several days. The only way that we have managed to stop this happening in gerbils that are prone to it was to stop using shavings for them and move to Russel Rabbit Bedding. Once a gerbil starts to get a sore nose it rarely seems to heal up on its own. The only problem is that it becomes a battle of wills between owner and gerbil to rub it into the nose. If in doubt get your Vet to show you how to hold your gerbil firmly without hurting it.
Gerbils can sometimes loose teeth.
If this is due to an injury then the teeth will grow back. However we had some of our older gerbils loose teeth that just fell out again each time they grew back. If your gerbil looses one or more teeth it is essential that any remaining teeth are trimmed by the vet every 2-3 weeks. In theory you should be able to learn to do this yourself with a pair of blunt clippers but I never managed it. Never attempt to trim a gerbil's teeth yourself until you have been taught how to by the vet and have suitable trimmers.