Dog's Rotting Tooth??

Hi, I'm 14 and I'm interested in veterinary science.I've had this problem before with my cairn terrier. What you need to do is brush his teeth. It's just like your teeth. They get dirty and will start to rot. You should take him to a vet and see if they recommend you to get his teeth cleaned. That's what we did with my dog. It can be expensive but it prevents anymore problems! So brush his teeth at least once a day using a regular toothbrush and dog toothpaste. Ask you vet too!