Methods. The authors tested medium-grit diamonds in a high-speed handpiece under a 147.5-gram load at 350,000 revolutions per minute, with 22 milliliters per minute coolant flow consisting of distilled water or a 1:10 mouthwash/water mixture. Repeated 6-millimeter–long edge cuts were made through machinable glass ceramic bars until the CR (determined as the time to transect the bars) had decreased by more than 75 percent. The authors used six burs for each coolant and analyzed the data via one-way analysis of variance with post hoc Scheffé tests.

Results. CRs with water irrigation continuously decreased with the number of cuts and declined by 87 percent over eight cuts. The authors found faster CRs with CMEs; after 12 cuts, the CR was still close to 40 percent of the initial CR, compared with only 13 percent of the initial CR for water irrigation after eight cuts. These differences between CME-enhanced CRs and those found with water irrigation were statistically significant.

Conclusions. Diluted alcohol- and glycerol-based mouthwash/water mixtures significantly enhanced the CRs of diamond burs and prolonged their service life by more than 50 percent compared with water irrigation alone.

Clinical Implications. Dentists can increase bur CRs and extend bur cutting life by as much as 200 percent through the addition of diluted alcohol and glycerol mouthwash to the handpiece coolant.

One approach that addresses the dichotomy of faster CRs and minimal heat generation has been the introduction of chemomechanical effects, or CMEs, into dental cutting procedures.^7–9 In particular, small additions of chemisorbing agents to the dental handpiece coolant supply have been shown to generate CMEs that increase CRs, at least in the short term (for example, two to three crown preparations).^7–9 These CMEs were obtained via small additions of alcohol and glycerol to the handpiece water irrigant, and such additions were most conveniently made through diluted mouthwash solutions.

Furthermore, we¹⁰ recently conducted a study that showed that CMEs arising from diluted alcohol, glycerol and water solutions markedly reduced debris accumulation on burs and improved the surface finish of the cutting substrate.¹¹ It follows from these observations that chemomechanically enhanced dental cutting involves a change in the actual mechanism of cutting, rather than a simple lubricating or viscosity effect, because these additives have no effect on the solution flow properties. If CMEs do involve a change in the mechanism of cutting, then they should enhance CRs throughout the working life of the bur—that is, they should increase CRs over long cutting regimens.

The cutting substrate was a machinable glass ceramic and all cutting was performed with medium-grit diamond burs.

Researchers and clinicians have shown considerable interest in placing chemical additives in waterlines to minimize biofilm formation, although they have raised concerns over the effect of such additives on subsequent bond strengths to enamel and dentin. One study¹² showed that certain chemicals added to dental unit waterlines adversely affected dentin bond strengths. One additive was a mouthwash (Listerine, Pfizer, New York) that contains alcohol and the essential oils thymol, eucalyptol, menthol and methyl salicylate, substances that might be expected to be retained within the organic component of dentin.

We conducted studies in our laboratory (J.A.v.F., S.C.S., unpublished data, July 2000) and noted that in contrast to the effects observed with Scope (Procter & Gamble, Cincinnati), small additions of Listerine, Plax (Pfizer) and Bio 2000 (Micrylium, Toronto) had no beneficial effect on CRs.

Knight and colleagues¹³ conducted a study in which they evaluated the effect of diluted Scope mouthwash irrigation (1:24 mouthwash/water mixture) on enamel and dentin bond strengths and compared the results with those found with distilled and municipal water. The authors found no statistically significant decrease in bond strength with the mouthwash solution, although we should note that only one resin-based composite material was evaluated.

We conducted the present study to evaluate the effect of chemomechanical agents on the long-term cutting efficiency of dental diamond burs.

	MATERIALS AND METHODS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
We performed the cutting procedures with a high-speed hand-piece (KaVo 649B, KaVo America, Lake Zurich, Ill.) at a bur speed of 350,000 revolutions per minute and a coolant flow rate of 22 milliliters per minute under a load of 147.5 grams (that is, 99 g at the interface between the bur and substrate). The cutting protocol followed a previously established regimen and involved the use of a specimen holding test assembly (Figure 1).^8,14–18 We used two cutting coolant/irrigant media: distilled water (control) and a chemomechanical agent, a mouthwash containing alcohol and glycerol (Scope) diluted 1:10 with water.

View larger version (21K): [in this window] [in a new window]   Figure 1. Schematic diagram of cutting test system. Adapted with permission of the publisher from Siegel and von Fraunhofer.14

We made repeated edge cuts¹⁸ using the full working length of the bur (6 millimeters) through the 13-mm-thick machinable glass ceramic bars. Six burs were used for each coolant, and cutting was continued with each bur until the CR, in millimeters per second (determined as the time to transect the glass ceramic block), had decreased by at least 75 percent. We measured mean (± standard deviation) CR values for both irrigant media. In addition, we recorded the number of cuts that could be performed with each bur using both cutting irrigants before unacceptable CRs were found. The data were analyzed via regression analysis and one-way analysis of variance with post hoc Scheffé tests at an a priori equals .05.

	RESULTS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
Tables 1 and 2 and Figure 2 show the mean CRs as a function of the number of cuts for diamond burs using water and the CME reagent (that is, the mouthwash solution). Figure 3 (page 57) shows the downward trend in CRs with the number of cuts. A regression analysis of the change in CR with the number of cuts for both media showed that with water irrigation, the rate of change in CR was more than double that with the CME reagent (P < .001):

View larger version (58K): [in this window] [in a new window]   Figure 2. Cutting rates of machinable glass ceramic bars (Macor, Corning, Corning, N.Y. ) with diamond burs. CME: Chemomechanical effects.

View larger version (58K): [in this window] [in a new window]   Figure 3. Trend analysis of cutting rates with diamond burs. CME: Chemomechanical effects.

where N equals the number of cuts.

As shown in Table 1, the mean CR for water irrigation after six cuts decreased by 74 percent to 0.06 mm/second with a bur cutting through 13 mm of substrate. With the mouthwash solution, however, the CR was maintained at a level of 0.11 mm/second for 12 cuts with the same bur (that is, a decrease of only 62 percent over twice as many cuts as was achieved with water irrigation) (Table 2).

The mean drop in the CR with successive cuts using water irrigation was about 25 percent, but when cutting was performed using the water, alcohol and glycerol mixture, the drop was only about 8 percent (P < .001). Consequently, the relative CRs for CME irrigation compared with those for a plain water spray increased markedly with the number of cuts performed (Table 3, page 57). For example, by the eighth cut, the CR for CME irrigation (0.14 mm/second) was nearly five times greater than that for water irrigation (0.03 mm/second), a statistically significant difference (P < .001).

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

Acceptable CRs. When extrapolating the cutting data reported here, we find that a diamond bur operating with conventional water spray irrigation provides an acceptable CR for only four to five cuts over a distance of 13 mm per cut (Figure 2). In terms of a full-crown preparation of a posterior tooth, the data indicate that only three or four teeth can be cut before unacceptably low CRs are found. When cutting is performed with CME irrigation, however, the mean drop in the CR with increasing numbers of cuts is 8.07 percent, or approximately one-third the mean drop found with water irrigation (24.85 percent). Thus, with CME-enhanced cutting, the CR is maintained above the clinically acceptable minimum (0.1 mm/second) for at least 12 cuts. In other words, a bur can perform at least three times as many cutting procedures (such as full-crown preparations) as is possible when cutting with water irrigation (Figure 2).

As noted above, questions have been raised with regard to adverse effects of waterline additives on bond strength. Antimicrobial additives that contain essential oils have been shown to reduce bond strength,¹² but irrigation of enamel and dentin with diluted Scope (essentially a mixture of water, alcohol and glycerol) has shown no such adverse effect.¹³ This finding is not surprising because both alcohol and glycerol (glycerine) are infinitely soluble in water and trace residues should not adversely affect enamel or dentin surfaces. In fact, we have shown that cutting with CMEs achieved through additions of diluted Scope mouthwash produces cleaner surface finishes.¹⁰

Studies are continuing in our laboratory to address the effect of CME agents on such factors as subsequent bond strengths and leakage effects. Nevertheless, to avoid any possible compromise of the surface due to the components of the cutting additive, we recommend that the cut surface be thoroughly rinsed with clean, oil- and additive-free water to eliminate any surface contamination.

Many antimicrobial additives to waterlines, typically those containing acids and hypochlorites, may have a corrosive effect on the dental handpiece. We do not anticipate this with alcohol/glycerol solutions, however, because neither of these compounds is corrosive.²¹ Therefore, the addition of diluted mouthwash or chemically similar CME additives to the irrigant solution is not expected to have a detrimental effect on the efficiency or service life of the dental handpiece.

Enhanced CRs. The results of this study clearly confirm previous observations that irrigating the interface between the bur and substrate with chemomechanically active solutions markedly enhances CRs.^7–9,11 The improved finish of cut surfaces and reduced debris accumulation on dental burs are additional benefits of CME-enhanced cutting.^10,11 These findings suggest that chemomechanically enhanced cutting involves a change in the actual mechanism of cutting. The present findings indicate that CMEs enhance CRs in both the short term and over extended cutting times (for example, six or more crown preparations)—that is, they appear to extend the cutting life of the dental bur.

	CONCLUSIONS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES

 
A small addition of certain surface active agents to the coolant/irrigant supply of a dental hand-piece induces CMEs. These CMEs enhance dental CRs and, notably, extend the cutting life of a typical dental diamond bur by about 200 percent. Although these results are predicted by theoretical considerations, we find it gratifying that these important economic and patient care benefits are achieved by minor additions of alcohol and glycerol to the coolant water system. We are conducting further studies to develop even more effective surface active agents for dental cutting systems.

View larger version (49K): [in this window] [in a new window]   Dr. von Fraunhofer is a professor and the director, Biomaterials Science, Department of Restorative Dentistry, School of Dentistry, University of Maryland, 666 W. Baltimore St., Baltimore, Md. 21201, e-mail "AVF001{at}dental.umaryland.edu". Address reprint requests to Dr. von Fraunhofer.

View larger version (54K): [in this window] [in a new window]   At the time of this study, Dr. Siegel was an associate professor, Department of Restorative Dentistry, School of Dentistry, University of Maryland, Baltimore. She now is an associate professor, Nova Southeastern University, College of Dental Medicine, Department of Restorative Dentistry, Ft. Laud-erdale, Fla.