Hi,one of my gerbil is having the same problem right now. I've noticed that he is not chewing anything like he always do, and he can't eat anything hard, he loves sunflower seeds but can't eat it. I checked his teeth, and noticed that there is a gap between the top teeth like yours had. I just wondered what had happened to your gerbil. Did Vet call you back and fix the problem? is he doing OK now? I really appreciate if you could tell me how he is doing now. I'm worried about my gerbil,too. thank you for your help!