Depends on technique
The key is HOW the biopsy is being performed
CPT 20245 - Biopsy, bone, open; deep (eg, humeral shaft, ischium, femoral shaft) .... This is an OPEN technique, with the surgeon dissecting tissue away from the bone to obtain the biopsy
CPT 20220 Biopsy, bone, trocar, or needle; superficial (eg, ilium, sternum, spinous process, ribs) ...
CPT 20225 Biopsy, bone, trocar, or needle; deep (eg, vertebral body, femur)
These are performed using a needle/trocar (i.e. percutaneously through the skin)
If he's using a trocar/needle ... I agree that the mandible is a "superficial bone"
But if he using an open technique I would code CPT 20245.
Hope that helps,
F Tessa Bartels, CPC, CEMC