A 48-year-old man complains of a lumor-like formation on the hard palate. Examination detected a semi-spherical protrusion with clear margins in the anterior portion of the palate. Teeth 11 and 21 are intact. X-ray shows a homogeneous focus of bone tissue rarefaction. The focus is 3.5x2.5 cm and has clear margins. Against the background of rarefied bone tissue there are projections of intact teeth 11 and 21; periodontal fissure is visible. Make the provisional diagnosis: