Mouth Rot refers to Ulcerative Stomatitis. It is a bacterial infection of the oral cavity secondary to a systemic infection.

signs   of   Mouth   rot

 As with many Illnesses and diseases, some of the signs can indicate a number of  different illnesses or diseases initially making it difficult to know what the problem is.
   *Lethargy.
   *Loss of appetite, or more likely, due to the  mouth pain from the infection the reptile avoids eating. 
   *Excessive salivation with thick stringy mucus.
   *Soft, curd like yellowish to grayish plaques can affect all surfaces in the mouth.  

Treatment

Mouth Rot is an indication of an underlying infection through out the body. A vet assessment is required as antibiotics will be needed. A vet can remove the deposited plaques from the oral cavity in an attempt to prevent the spread of infection into the jaw and skull bones. The vet can advise on the best course of treatment which will include an antibiotic, it may include swabbing the oral cavity with a medicated solution and watching for the appearance of more plaques.

Prevention

The key to prevention is proper husbandry. The immune system works at optimum when proper temperatures are maintained. A good diet, supplements and UVB when indicated for proper care can help keep your reptile healthy. Keeping the environment meticulously clean and free of waste and bacteria is important.

The information presented here, and much more can be found  following  the links provided below.

ULCERATIVE STOMATITIS (Mouthrot) IN REPTILES

Ulcerative Stomatitis (Mouthrot) in Reptiles

MOUTH ROT - Stomatitis

Bacterial Diseases - page in Merck Veterinary Manual discusses mouth rot and scale rot.