itching nose area and black area on gums

[scoobydoo]

We have noticed our 3 yr old beagle has been itching his nose and face quite a bit. Yesterday I checked his teeth and gums and noticed that he has developed black gums around his k9 teeth. We do brush his teeth and he does get dentabones as well. No sign of any plaque buildup. No other problems with Scooby. He is as loving and playful as always. Any ideas?

Sccoby Doo's MOM