Comparison of the effects of bone osteotomies on mechanical properties of piezo-tips: An experimental study

Introduction and Aim: The aim of this study was to evaluate the nano-hardness, elasticity modulus, surface roughness and wear level of the piezo-tips, thus comparing their effects on bone cutting performance. Materials and Methods: In the study, 31 piezo-tips were used, of which 3 were for control and 28 for testing purposes. The tips in the test group were divided into 4 groups to make a different number of osteotomies. These groups were formed as follow: 4-osteotomy group (7 tips), 8-osteotomy group (7 tips), 16-osteotomy group (7 tips) and 32-osteotomy group (7 tips). Osteotomies were performed on bone blocks obtained from the right and left 6th and 7th ribs of freshly slaughtered bovine, approximately 1-3 years old. Seven equal bone blocks of 40 mm in length were obtained from each rib. Among the 28 bone blocks obtained from 4 ribs, 4 bone blocks were selected for each tip in the osteotomy groups. Fifteen lines in 10 mm length and at 2 mm distance were drawn on the bone blocks and they were numbered sequentially. After randomly determining the osteotomy lines for the tips, the osteotomies were performed by using a tip from each group. Thus, on each bone block, 1 osteotomy with the tip in 4-osteotomy group, 2 osteotomies with the tip in 8-osteotomy group, 4 osteotomies with the tip in 16-osteotomy group and 8 osteotomies with the tip in 32-osteotomy group were performed and mean osteotomy durations were saved. Scanning electron microscope images of all tips in the osteotomy group before and immediately after osteotomy were obtained, and the wear level in the tips was measured by superimposing the two images using a software. The hardness, elastic modulus and surface roughness of the tips were analyzed by nanoindentation. The obtained nanoindentation values were compared with the control group. Results: A statistically significant increase was observed in the nano-hardness values of the piezo-tips depending on the number of osteotomy (p=0.007). It was determined that the elasticity values of the tips in all osteotomy groups increased significantly compared to the control group, regardless of the frequency of use (p=0.007). There was a linear relationship between the frequency of use of the tips and the surface roughness, depending on the number of the osteotomy. As the frequency of use increased, the surface roughness also increased (r=0.961; p=0.001). Similarly, a positive correlation was found between the frequency of use of the tips and wear levels (r=0.833; p=0.001). A strong correlation was found between the surface roughness and the wear level of the tips (r=0.847; p=0.001). A statistically significant increase was observed in the mean osteotomy durations with the frequency of use of piezo-tips (p=0.01). Conclusions: According to the data of the experimental study performed on the bovine ribs, it was concluded that the increase in the number of bone cut caused significant changes in the mechanical and physical properties of the piezo-tips, and accordingly the bone cutting performance was affected by reusing the tip. Key Words: Incision performance, Nanoindentation, Osteotomy, Piezo-tip