Bone regeneration within a tailor-made tricalcium phosphate bone implant with both horizontal and vertical cylindrical holes transplanted into the skull of dogs.

A new tailor-made bone implant (TI) with six horizontal cylindrical holes fabricated from alpha-tricalcium phosphate powder, as described in our previous report, was modified to include five additional vertical holes (TI-v) in an attempt to accelerate the bone regeneration through the holes. This TI-v implant and hydroxyapatite implants (HI) as controls were transplanted into experimental skull defects in dogs. Computed tomography (CT) was performed immediately after the surgery and then every 4 weeks. The dogs were killed for histological analysis at 24 weeks of implantation. On CT, bone bridging between the implant and the skull was observed in the TI-v group from 8 weeks of implantation, whereas a clear bone bridge was not formed in the HI group after 24 weeks of implantation. Histological analysis revealed collagen tissues and new bone formation in the horizontal cylindrical holes in most of the TI-v group, whereas mainly connective tissues invaded the porous structures in the HI group. In the Ti-v group, at the middle of the horizontal holes where they crossed the vertical holes, fibrous collagen tissues and muscular tissue filled up the hole and new bone formation seemed to be blocked. However, in the TI-v group more collagen and bone tissues were formed than in the HI group; when compared with the data in our previous report, however, the total volume of regenerated bone in the horizontal cylindrical holes in the TI-v seemed to be less than that in the TI. Thus, the addition of vertical cylindrical holes in the TI-v was not effective in promoting the faster stabilization of the TI-v in the skull of the dog.