Biomechanical and histomorphometric study of the bone-screw interface of calcium pyrophosphate coated titanium screws

The purpose of this study is to compare the osseointegration of calcium pyrophosphate(CPP) coated screws with uncoated screws. CPP coating was prepared and coated by dipping method. CPP coated and uncoated screws were inserted into the mongrel dogs. The insertion torques, radiographs, histology, histomorphometric analysis, and extraction torques were evaluated at 2, 4, and 8 weeks after surgery. The insertion torque was not different between CPP coated and uncoated screws. The extraction torques of CPP coated screws at 2, 4, and 8 weeks(5.45 +/- 2.05, 7.62 +/- 1.51 and 6.60 +/- 2.80 cNM) were significantly higher than their insertion torques(2.74 +/- 1.13, 2.98 +/- 0.70, and 2.18 +/- 1.34 cNM)(p < 0.0001, < 0.0001 and 0.0005 respectively) and significantly higher than the extraction torques of uncoated screws(1.14 +/- 0.470, 2.57 +/- 1.36, and 3.18 +/- 0.499 cNM). The percentages of direct bone-screw contact of CPP coated screws were statistically higher than those of uncoated screws at 2, 4, and 8 weeks. These results suggest that CPP coating may improve the clinical results by allowing early motion exercises and early weight bearing.