So it's one of the incisors then?

Our Jess has lost two of hers during her life although not as young as yours. She lost them from chewing things etc...It's not caused her any problems. Both the ones she lost are on the upper jaw.

Her father lost nearly all his incisors on his lower jaw as he got older. Again, it didn't bother him. I think it is more a cosmetic thing than anything else and dogs don't give a damn about vanity.