Without seeing them my first impression is that they are mandibular tori which are normal. Do have it checked out by your new dentist.
I have a hard lump under my gums. It isn't white. It feels like it is really up under my gums, but very hard. To the side of the roots of my tooth .... or maybe it is, somehow the roots themselves. It is a quarter of an inch too far out - swelling, a really bad tooth ace etc. occurred. This all happened after I got those two teeth worked on. Told my dentist, he took xrays and denied any existence. Told me to wait a while. I did, it got a lot worse. I called up several times begging for something. Finally, he prescribed penicillin w/o seeing me. I took it. The pain overall is gone ( which radiated to several teeth. I was also sensitive to hot/cold. I thought it was an abcess, but the lump has seemed to grow a little still, it is hard like a rock. Right on the side of my gum. My dentist is now gone for three weeks to another state. The teeth he worked on is still sensitive to hot or cold and they are a little loose. It feels like a one inch rock up underneath my skin.
I too have recently noticed fairly symmetrical white hard lumps approximately 4 teeth apart on the inner lower mouth, behind the bottom teeth. They appear to be rigid and fixed. As stated they are directly behind and below the same "set or pair" of teeth and just before the lower jaw is noticeable. I will be seeing a dentist of course, however is this something my primary care doctor should be looking at as well. In addition, my benefits do not cover dental, which needless to say is unfortunate. Thanks for your response.