Cavity?

Hi there. My dog started grinding his teeth a few days ago and licking at his mouth a lot more. I checked his mouth and noticed this black spot on his tooth. He’s 5 months old. Could this be a cavity? Do the premolars fall out? Not sure if this is on a baby or adult tooth. 

Hello! - for general reference, premolars usually fall out at around 4-6 months, and canines just after them, but this is very breed-dependent.  Regarding your picture, I'm afraid that I'm going to get my excuses in early.  When a vet examines a mouth, they are able to feel the tooth, to look at it from various angles and aspects and to assess the dogs' response when it is touched.  There are also able to check the pup and the rest of the mouth, to give them a better idea of where the dog is at developmentally.  I think that those might be baby canines still and so it follows that we could be looking at deciduous teeth, but I am seeing this mouth out of context -  which your vet would not be doing.  Context is obviously extremely helpful in getting the best answer to your question, especially when things don't look as one expects.  There could be multiple explanations for what I am seeing with regard to the black in this picture and these possibilities are pretty wide-ranging in severity.  From this angle, the black could be a cavity, a congenital abnormality or simply a shadow or discolouration from an external source;  the dark colouration around the tooth and gum could be related to infection or ischeamia (blood supply reduced or cut off for some reason), but it could also represent, for example, an oral tumour or something as simple as a light-shadow or pigment, or food.  Your vet will be able to examine this tooth from all directions and feel it too;  they will be able to feel the local lymph node, look for signs of infection and give a much more informed opinion.  However, from your description your pup does sound uncomfortable so perhaps this examination ought to be carried out sooner rather than later - many vet practices will be happy to triage cases (that is, to listen to the symptoms, ask some questions and arrange to see the case based on how urgent it appears to be) over the phone.  Nurse appointments are frequently offered to check teeth also and can be lower cost, but very often the nurse will have to hand over to a vet if something abnormal is found.