A large percentage of boxers have gingival hyperplasia which gets worse with increasing age. It is a familial condition in the boxer breed. There have been many nomenclature changes recently with regard to this condition because of the relatively recent specialty of Veterinary Dentistry.
Another name for this condition is gingival epulis. It is described as a fibrous nodular proliferative hyperplasia of the gingiva of older dogs, particularly boxers. The lesion looks like multiple tumors and has been classified by some as a precancerous lesion. The epulides (plural) are frequently very hard and fibrous and occasionally calcified (like yours). Rarely malignant, these have a tendency to recur. Histopathologically these are (or once were) classified as one of three lesions.
1. Fibromatous epulis (gingival hyperplasia) - firm solid lesions, single or multiple, non-invasive, may recur following surgical excision,
2. Ossifying epulis - identical to fibromatous except that it contains osteoid, cementum or dentin (bony type or tooth type material, hence calcified),
3. Acanthomatous epulis - appears the same outwardly, but invades the underlying bone.
Only this last one is potentially malignant, and even this one does not metastasize (spread to other organs) but is very locally invasive.