Dentist says if i want a crown on my root canal filling, he needs to remove some bone because the fracture was big. what does it mean and do you advise on a crown on root canal filling?

Fractured Tooth: To make a well fitting prosthesis (crown), the edge of the crown needs to rest on solid tooth structure AND not impinge on the gingiva or bone. If the fracture is deep, the bone needs to be recontoured.

Crown: As root canal treated teeth are more brittle, a crown to create a proper seal and support the remaining tooth structure is considered Standard of Care. As fracture is probably below bone level you will require either surgical "crown lengthening" or non-surgical Orthodontic "forced eruption."