Our study has shown that visual examination is unable to detect any degradation in the cutting-edge of any of the three osteotomes tested. This includes the as-supplied osteotome that experienced a 50% loss in BSI over the four bone cutting tests. While visual inspection might detect catastrophic damage in the cutting-edge, our study demonstrates this technique is unable to detect and gauge normal wear up to a level of 50% loss in BSI, as demonstrated in the as-supplied osteotome.
There are currently various methods of maintaining osteotome sharpness. These range from periodic professional sharpening through to a surgeon hand sharpening the tool using ceramic or diamond sharpening stones or fine grit whetstones either prior to or during each use. Evaluation of the effectiveness of professionally sharpening blunt osteotomes has shown that edge sharpness is only ever at best partially restored .
Only two previous studies have investigated degradation in uncoated osteotome cutting performance and sharpness [5, 6]. Bloom, Ransom, Antunes, & Becker (2011), evaluated osteotome sharpness after repeated use, regular maintenance and sharpening, by analyzing three identical osteotomes used in nasal dorsal hump reduction surgery . In this study and after each use, degradation in osteotome blade sharpness was measured by holding the osteotome stationary while a single suture was incremented toward the blade with increasing force until the suture was broken. During this investigation, each osteotome was sharpened after three, six and nine surgical uses. This entailed the first two osteotomes being hand sharpened by the surgeons using different methods while the third osteotome was professionally sharpened. The study found the cutting edge of all three osteotomes experienced significant deterioration in sharpness during use and that both hand and professional sharpening was unable to restore the cutting edge to its original degree of sharpness. Two hospital maintained osteotomes were included to compare the earlier findings with real world conditions. Of note, the cutting edge of the hospital maintained osteotomes were significantly duller compared to the three osteotomes that had been tested 9 times. This study concluded that osteotomes may not be suitable for reuse, even after sharpening, and that edge retention is difficult to retain with repeated use . A later study by the same group (Ransom, Antunes, Bloom, & Becker, 2012) focused on comparing the sharpness of osteotomes from five major manufacturers . Like our study, this earlier investigation involved each osteotome making 40mm cuts but using artificial rather than real bone. Baseline sharpness values were similarly determined for each new osteotome prior to change in sharpness being assessed after successive cutting cycles. Like our study for the as-supplied osteotome, each osteotome demonstrated progressive loss of cutting-edge sharpness, and degradation of the osteotome cutting-edge was rapid and unavoidable.
To improve osteotome cutting edge durability, efforts have been focused on improving the wear resistance by applying a hard-wearing coating such as TiN before comparing their performance to uncoated as-supplied tools. Several authors have previously demonstrated the possible advantages of using coated instruments [7-10] but have so far neglected the osteotome.
In our study, baseline BSI values show the electroless nickel coating process leads to slight dulling of the cutting-edge to a level equivalent to the as-supplied osteotome after one cutting cycle of use. This finding is supported by the post bone cutting SEM analysis that showed a smooth and rounded cutting edge, shown by Figure 7. This increase in cutting edge radius is thought to be caused by the electroless nickel coating process. With the TiN PVD coating being much thinner, there was a lower increase in blade cutting edge radius, leading to no difference in BSI between the TiN PVD coated and as-supplied osteotomes prior to use.
After four bone cutting cycles the percentage change in BSI shows the as-supplied osteotome experiences the greatest cutting-edge wear rate compared to the other two osteotomes coated in wear resistant materials. This is demonstrated by the as supplied osteotome having lost 50% of its BSI, which equates to requiring twice as much impact force to realize the same cut as when new. This compares to 10% and 35% loss of BSI for the TiN PVD and electroless nickel coated osteotomes respectively. These findings are also supported by SEM examination of the cutting-edges of each of the three osteotomes tested, with the TiN PVD coated osteotome showing the least cutting-edge mechanical damage and cutting face scratching.