Hello
There's lots of possibilities for this. But here's some things to consider. Does it appear to hurt him or bleed when you touch the bump? Are the rest of his teeth and gums healthy or is there a problem with his oral health generally? Is he a young dog or an older dog? If he's older then one possible cause is something called epulis which is an overgrowth of gum tissue which looks unsightly but is usually benign and non-cancerous. I cant say more than this and I think you probably need to get this bump assessed by a vet, especially if it gets bigger.
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Cathy Wickenden BVet Med MRCVS
Barton Lodge Veterinary Centre
1 Midland Road, Hemel Hempstead, Hertfordshire, HP2 5BH
Tel: 01442 216048 24 hours
[
www.bartonlodgevets.co.uk]