Effects of surface-modified titanium implants on osseointegration in irradiated bone

Abstract

Radiotherapy is a common treatment for head and neck cancers. However, it compromises bone healing. Titanium implanthas been shown to be a predictable method for replacing missing teeth. Clinical studies revealed that implant failure rate in irradiated regionwas high. Many studies showed that modifications of implant surface could enhance implant osseointegration by improving cell attachment, cell growth and bone formation. Nevertheless, there were few studies investigating the effect of implant surface modification on osseointegration in irradiated bone.

In the first experiment, the effect of fluoride-modified (FM) titanium surface on irradiated osteoblast attachment was assessed. The morphology and chemical composition of FM surface was assessed by SEM, AFM and XPS. Osteoblasts received 0Gy, 2Gy, 4Gy, 6Gy, 8Gy, 10Gy radiation. Cell number, fluorescence intensity and cell area of irradiated osteoblasts were assessed. The number of osteoblasts onFM surface was fewer than those on NF surface after 0Gy, 2Gy, 8Gy and 10Gy radiation. Cell area of osteoblasts on FM surface was less at 2Gy radiation but larger at 6Gy radiation than on NF surface. The fluorescence intensity of osteoblasts was also higher on NF surface than on FM surface after receiving 0Gy, 2Gy, 4Gy, 10Gy radiation.

In the second experiment, an animal model was established to study the effect of radiation on osseointegration. Rabbits were divided into 15Gy and 30Gy radiation groups. Only the left leg was exposed to radiation, and the right leg was protected from radiation. Totally, 24 implants were inserted. Implant stability quotient (ISQ), bone volume to total volume (BV/TV), bone-to-implant contact (BIC), and bone growth rate were measured. After 15Gy and 30Gy of radiation, ISQ and BV/TV were significantly reduced. At week 3, 15Gy radiation group displayed slower bone growth rate comparing with the control side. Fluorochrome results showed that the 30Gy radiation side had a significantly slower apposition of new bone.In addition, BIC on30Gy radiation side was notablypoorer than that on 15Gy radiation side and on 30Gy control side.

Based on the animal model, the third experiment investigated effects of calcium phosphate nanocrystals on implant osseointegration in irradiated bone. Titanium implants treated with nano-scale calcium phosphate (CaP) crystals served as the test group while ones with dual acid-etching only served as the control group. The left leg of rabbits received 15Gy radiation and implants were placed in the irradiated leg. Significant higher ISQ was detected in the nano-CaP group at week 12. The bone growth rate in nano-CaP group was more than doubled than the control group at both week 6 and week 9.

The fourth experiment evaluated artifacts on micro-CT images caused by titanium dental implant. Implants were assigned into four groups: (1) implant only; (2) implant with covering screw; (3) implant with resin embedding; and (4) implant with covering screw and resin embedding. Each implant was scanned by micro-CT at 3 angulations. Implant angulation was the most determining factor followed by resin embedding. Minimal metallic artifacts were obtainedin non-embedded implants with its axis paralleling to X-ray.