I take it there are no immune suppressive drugs on board to cause this?
In the absence of any other information, benign growths can indicate Dampness in Chinese medicine. From a western perspective, it suggests an untoward inflammatory response. Those two things together make me think of Si Miao San and a raw diet.
Another thought. 'Proud flesh' is associated with Blood Stasis in Chinese medicine, for which Salvia (Dan Shen) is an antidote. Using a Blood mover containing Dan Shen would be a good idea, especially right after a gingivectomy (so all you have to do is prevent recurrence). One option for that is Modified Xue Fu Zhu Yu Tang with Dan Shen added.
Last thought. To combine the above two approaches, you could look at Qing Ying Tang. I've used the formula successfully for malignant oral masses, too, so perhaps its influence will extend to benign ones.
Hope that helps,