The Effect of Local Application of Parathyroid Hormone Analogues When Added to Mineralized Bone Xenografts

Implants can be a viable treatment option when there is sufficient quantity and quality of bone to provide optimum support and predictable long term success.

The purpose of this study is to evaluate the anabolic effect of local application of parathyroid hormone (PTH) when added to a xenograft, Bio-Oss, in the reconstruction of mandibular defects. A large animal model is utilized to create defects aimed to simulate tooth extraction sites in humans.

Two domestic pigs were used. In each pig, three full thickness posterior mandibular body defects measuring 2 cm in length by 1 cm in height were created bilaterally. A one centimeter bone bridge was left separating the created defects. A total of 12 defects were created. The defects were grafted in random order using three groups: 1. Control – no graft, 2. Bio-Oss without PTH, 3. Bio-Oss with PTH 20ug/ml (mimicking the human dose for osteoporosis treatment). Each defect was covered with a resorbable collagen membrane.

After 12 weeks of healing time, the pigs were euthanized. The dissected pig mandible was scanned using cone beam computed tomography (CBCT) with 300 x 300 x 300 μm³ micron voxel size. The defect sites were digitally isolated to obtain gray values (CT attenuation values) that are proportional to the bone mineral density (BMD).

The CBCT based mean gray values were 87.2 ± 7.5 for the control group, 85.7 ± 24.4 for the Bio-Oss group and 127.5 ± 17.1 for the Bio-Oss with PTH group. This demonstrates that the BMD value of the sites grafted with Bio-Oss/PTH was higher as compared to the control and the Bio-Oss only sites (p<0.05).  

The current result indicates that local application of PTH has a positive effect on increasing BMD when added to mineralized bone xenograft commonly used in implant dentistry. This finding suggests that PTH can enhance bone quality required for long term implant survival. Future investigations are underway to evaluate the graft construct histologically as well as the elastic, plastic and viscoelastic properties (Nanoindentation). The goal is to obtain preliminary data to translate these results for application in a human clinical study.

References

Establishing a critical-size mandibular defect model in growing pigs: characterization of spontaneous healing. J Oral Maxillofac Surg. 2014 Sep;72(9):1852-68. doi: 10.1016/j.joms.2014.02.024. Epub 2014 Feb 20.

Kim, Do-Gyoon. “Can Dental Cone Beam Computed Tomography Assess Bone Mineral Density?” Journal of Bone Metabolism 21.2 (2014): 117–126. PMC. Web. 14 Mar. 2016.

Funding

College of Dentistry, The Ohio State University