Chemo-mechanical Effects in Extended Dental Cutting

Objectives: Previous studies showed that the addition of certain surface active agents to the dental handpiece coolant water can enhance dental bur cutting rates through chemomechanical effects (CMEs). The present study was undertaken to evaluate the effect of CMEs on the long-term cutting behavior of dental diamond burs under conditions simulating dental practice. Methods: An established testing regimen for burs was used with a KaVo 649B highspeed handpiece under a load of 147.5 g at a rotation speed of 350 krpm and 22 ml/min coolant flow rate using water and a 1:10 mouthwash:water mix. Cutting was performed on Macor machinable ceramic bars with #856-016 medium grit diamond burs. Repeated edge cuts, 6 mm in length, were made through 13 mm of Macor with 6 burs each for water and the mouthwash mix until the cutting rate(CR), determined as time to trans-sect the Macor block, had decreased by >75%. The data were analyzed by 1-way ANOVA with post-hoc Scheffé tests. Results: CRs under water irrigation continuously decreased with the number of cuts and declined by 87% by cut #8. CRs under the test solution were greater than that under water but the decrease in CR over cuts #1-4 paralleled that with water irrigation. With extended cutting, the cutting rate with the test mix was still close to 45-50% of the initial CR after 12 cuts and this long-term CR was greater than the CR for water irrigation after only 4 cuts. These differences between CME-enhanced and water irrigation cutting rates were statistically significant (p<0.001). Conclusions: Low additions of mouthwash to water significantly enhance cutting rates and prolong the cutting efficiency of dental diamond burs by 50% compared to that with water irrigation without additives.