In vitro comparison of the cutting efficiency and temperature production of ten different rotary cutting instruments. Part II: Electric handpiece and comparison with turbine

In vitro comparison of the cut ting efficiency and temperature production of ten different rotary cut ting instruments. Part II: Electric handpiece and comparison with turbine Carlo Ercoli, DDS,a Mario Rotella, DDS,b Paul D. Funkenbusch, PhD,c Scott Russell, BS,d and Changyong Feng, PhDe Eastman Dental Center, University of Rochester, Rochester, NY Statement of problem. The cutting behavior of dental rotary cutting instruments is influenced by the handpiece used. While the turbine handpiece has been extensively tested in previous studies, limited published information exists on the use of rotary cutting instruments with the electric handpiece system and on possible interactions between rotary cutting instruments and handpiece type. Purpose. The purpose of this study was to examine the cutting performance of a wide selection of rotary cutting instruments tested with the electric handpiece and compare the results with those of the air-turbine handpiece (Part I), identifying possible interactions between handpiece type and rotary cutting instruments. Material and methods. Ten groups of rotary cutting instruments (n=30) designed for tooth preparation were selected: 9 diamond (7 multi-use, 2 disposable) and 1 carbide. Macor blocks (n=75) were used as a substrate, and 4 cuts were made on each specimen, using a new rotary cutting instrument each time, for a total of 300 cuts. The cuts were performed with an electric handpiece (Intramatic Lux K200), with the same methods used in the Part I study. To qualitatively evaluate the rotary cutting instrument surface characteristics, 1 specimen from each group was examined 3 times with a scanning electron microscope (SEM): before use, then after use, but before being cleaned and sterilized, and finally, after ultrasonic cleaning. To compare rotary cutting instrument performance between the turbine and electric handpieces, the data were analyzed using 2-way ANOVA to study the main effects of the group of rotary cutting instruments, handpieces, and their interaction. For analysis of the significant main effect, 1-way ANOVA and Tukey’s Studentized Range test were used (α=.05). Results. Compared to the baseline temperature, all rotary cutting instruments showed a reduction of the temperature in the simulated pulp chamber when tested with the electric handpiece. The Great White Ultra (carbide bur) showed the highest rate of advancement (0.17 mm/s) and lowest applied load (108.35 g). Considering all rotary cutting instruments as a single group, the electric handpiece showed mean lower temperature (26.68°C), higher rate of advancement (0.12 mm/s), and higher load (124.53 g) than the air-turbine handpiece (28.37°C, 0.11 mm/s, and 121.7 g, respectively). Considering each single group of rotary cutting instruments, significant differences were found for the electric or air-turbine handpiece. Conclusions. The tested carbide bur showed greater cutting efficiency than the tested diamond rotary cutting instruments when used with the electric handpiece. The electric handpiece showed a higher cutting efficiency than the turbine, especially when used with the carbide bur, probably due to its greater torque. (J Prosthet Dent 2009;101:319-331))

Clinical Implications

The carbide bur tested demonstrated greater cutting efficiency for tooth preparation than the diamond rotary cutting instruments tested. The electric handpiece demonstrated greater cutting efficiency than the air-turbine handpiece during tooth preparation, especially when the tested carbide bur was used. This project was supported by a commercial grant from SS White. Presented at the American Prosthodontic Society Meeting, Chicago, Ill, February 2007, and the Academy of Prosthodontics Meeting, New York, NY, May 2007. Associate Professor, Chair and Program Director, Division of Prosthodontics, Eastman Dental Center. Former Research Fellow, Division of Prosthodontics; currently Resident, Division of Prosthodontics, Eastman Dental Center. c Professor, Department of Mechanical Engineering and Materials Science, College of Applied Science. d Technical Associate, Department of Mechanical Engineering and Materials Science, College of Applied Science. e Assistant Professor, Department of Biostatistics and Computational Biology, School of Medicine and Dentistry, University of Rochester. a

b

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Volume 101 Issue 5 The turbine handpiece has been used in dentistry for more than 40 years, due to its relatively low cost, its capacity to rapidly remove tooth structure, its low weight, and its ergonomic size.1,2 The primary reported disadvantage is its low torque, which, together with its constant energy input (dependent on the air flow and pressure), causes load-dependent decreases in rotational rates, and even stalling.3,4 The clinician must therefore apply periodic cycles of increasing and decreasing loads. The electric handpiece has variable power and higher torque than the turbine and is designed to maintain a set running speed, with little chance of stalling during tooth preparation. It is also quieter, exhibits less vibration, and provides a precise cut with high concentricity.1,2 The maximum freerunning revolutions per minute (rpm) rate of the electric handpiece is generally lower than that of the turbine (200,000 versus 400,000). However, while the electric handpiece is designed to maintain this speed, it has been shown that the rotational rate of the turbine markedly decreases, as a function of a clinically relevant applied load, until it reaches an almost steady cutting speed.5-9 This rpm drop is dependent on several variables, such as the type of handpiece, rotary cutting instrument, and the substrate being removed. Galindo et al10 showed that, while cutting natural teeth, this rpm decrease was roughly about a third of the free-running speed. In addition, it has been shown that the magnitude of the turbine torque depends on the power of the handpiece rather than its free-running speed.11 Another advantage of the electric handpiece system seems to be improved asepsis, especially if used with disposable cutting rotary instruments.12 When an air turbine is turning at full speed, it aerosolizes saliva and disperses blood, even if a relatively efficient intraoral vacuum is being used.13 The electric handpiece has the potential to produce significantly less aerosol. It has been shown

that the number of colony-forming units (CFUs) of bacteria generated by the use of the turbine handpiece are significantly greater than the number produced by the electric handpiece.14 However, depending on the brand and the number of attachments purchased, electric handpieces are 2 to 3 times more expensive and weigh 50 to 100% more than the turbine.2,15 While the turbine handpiece has been extensively used in previous studies investigating the cutting efficiency of different rotary cutting instruments,10,16-21 limited published information exists on the performance of the electric handpiece systems, especially when used with burs designated for tooth preparation in fixed prosthodontics. Eikenberg22 compared the cutting efficiency of 2 electric handpieces to 1 turbine, using the same type of rotary cutting instrument (Midwest #245 carbide; Dentsply Professional, Des Plaines, Ill) and Macor as the substrate. The 2 brands of electric motors had similar performance and significantly better cutting efficiency than the turbine. In another study, Watson et al23 compared the electric handpiece to the turbine at 2 different advancement rates: 1 mm/min and 5 mm/min. At the lower advancement rate of 1 mm/ min, the cutting efficiencies for both instruments were comparable, but at the higher advancement rate of 5 mm/ min, the results were different. The turbine showed a dramatic increase in load without a corresponding increase in cutting rate until the cutting became erratic and uneven. However, the electric handpiece demonstrated a steady load with a smooth and even cutting rate. Most dentists, during tooth preparation for fixed prosthodontics, apply a load of between 50 and 150 grams (g),15,24 and several in vitro studies used different loads to evaluate the performance of rotary cutting instruments and handpieces.4,7,25,26 According to Siegel and von Fraunhofer,24 a force of 100 g, with the turbine, appears to be optimal for medium-grit rotary

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cutting instruments, and a further increase does not have a positive effect on the cutting efficiency. However, increased load applications increased the cutting efficiency for coarse-grit rotary cutting instruments.24 In Part I of this study,27 it was shown that, using a nominal applied pressure of 125 g, the rate of advancement was significantly higher for the tested carbide bur (Great White Ultra; SS White Burs, Inc), whereas no difference was found among diamond rotary cutting instruments, irrespective of grit, design, and whether the rotary cutting instruments were designated for single or multiple use. When the energy spent during the cutting process was evaluated, it was observed that the diamond rotary cutting instruments and carbide bur required similar amounts of energy, while the load required by the carbide bur was significantly less and the revolutions per minute (rpm) significantly fewer than those exhibited by the diamond rotary cutting instruments. Based on these findings, it was concluded that the carbide bur exhibited a greater cutting efficiency compared to diamonds; in other words, for a given energy input, it removed a greater amount of substrate per unit of time. As previously mentioned, one of the limitations of the turbine is its fixed energy input and low torque characteristics. This was clearly seen in the use of the carbide bur in Part I of the study; while showing a greater cutting efficiency than diamonds, the carbide bur also exhibited a greater decrease in rpm. Based on the fact that the electric handpiece has a variable energy input and allows a constant rpm, it is possible to speculate that this specific carbide rotary cutting instrument (Great White Ultra; SS White Burs, Inc) might show even greater cutting efficiency when used with the electric handpiece. The purpose of Part II of the study was, therefore, to examine the cutting behavior of the same selection of rotary cutting instruments when used with the electric handpiece. In addi-

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May 2009 tion, data from Parts I27 and II of the study were analyzed to assess possible interactions between handpiece type and rotary cutting instruments. One of the null hypotheses was that there would be no difference in cutting rates, load required to perform the cutting action, and temperature production among the carbide bur and diamond rotary cutting instruments, and among the diamond rotary cutting instruments regarding type (disposable versus conventional), grit (coarse versus medium), and design (channeled versus nonchanneled) when used with the electric handpiece. The second null hypothesis was that there would be no difference in cutting rates, load required to perform the cutting action, and simulated pulp chamber temperature with the tested rotary cutting instruments when used with the electric and turbine handpieces.

MATERIAL AND METHODS The testing apparatus, substrate, controlled variables, and the cutting procedure used in this study have been described in previous studies.10,27 An electric handpiece (Intramatic Lux K200; KaVo Dental Corp, Lake Zurich, Ill) was used for the test. The electric handpiece was used at a set speed of 200,000 rpm (40,000 motor speed with contra-angle attachments (INTRAcompact 25 LHC; KaVo Dental Corp)) with a 1:5 ratio. However, due to the presence of the push-button chuck mechanism on the contra-angle head, it was not possible to independently verify, aside from what the unit displayed on the screen, the rpm with a tachometer (as was done in Part I of the study with the turbine) without compromising the integrity of the handpiece. The high-speed turbine had a single nozzle positioned at a 6 o’clock position (with the 12 o’clock position as the most anterior part of the handpiece), whereas the electric handpiece had 3 nozzles, at the 2, 6, and 10 o’clock positions, with the water flow (at room temperature) main-

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tained, for the entire test, at 40 ml/ min.27,28-30 To qualitatively evaluate the rotary cutting instrument surface, 1 specimen of each type of rotary cutting instrument (each group for Part I27 and II) was examined with a scanning electron microscope (SEM) (LEO 982 Field Emission Scanning Electron Microsope; Carl Zeiss SMT AG, Oberkochen, Germany). Each of these rotary cutting instruments was examined 3 times: before use, then after use, but before being cleaned and sterilized, and, finally, after ultrasonic cleaning (Quala Sweep 5300; ADC, Nashville, Tenn), steaming (Belle de St. Claire; KerrLab, Orange, Calif ), and sterilization (Statim 2000; SciCan, Toronto, Canada). During each SEM examination, 3 images were made: at x25 (from the tip to half of the body of the rotary cutting instrument), at x50 (only the tip), and at x200 (for the surface structure). In Part I,27 for the high-speed turbine, the following variables were compared among the 10 groups of rotary cutting instruments: temperature (°C), rate of advancement (mm/s), applied load (g), rotations per minute (rpm), rate of advancement/load (considered as an overall ease of rotary cutting instrument advancement), energy (indication of the amount of energy needed to cut the substrate, and calculated with the following formula: (400,000-rpm) x rpm/rate of advancement). With the electric handpiece, instead, due to the inability to independently monitor the rpm in real time, the 10 groups were compared for the same variables with the exception of rpm and energy. To test the first null hypothesis (no difference among bur performance when used with the electric handpiece), 1-way analysis of variance (ANOVA) (α=.05) and Tukey’s Studentized Range test were used to assess (post hoc) pairwise differences. The following comparisons were also made: among rotary cutting instrument groups, using air-turbine and electric handpiece data as a combined

data set; between air-turbine and electric handpieces within a group data set (rotary cutting instrument type); and between air-turbine and electric handpieces using combined data from all rotary cutting instrument groups. Two-way ANOVA was used to study the main effects of group of rotary cutting instruments (10 groups), handpieces (2), and their interaction. For analysis with no significant interaction effect, but significant main effects, the 1-way ANOVA along with Tukey’s Studentized Range test were used to assess (post hoc) pairwise difference within each main effect (α=.05). To provide quantitative differences among the 10 groups of rotary cutting instruments that have clinical relevance, the statistically significant differences in the comparisons among the rotary cutting instrument groups were also calculated as percentage differences, similar to the Part I study.27

RESULTS Using the same rationale used in the Part I study, 27 the authors show in the tables those comparisons that are most relevant to the science and practice of prosthodontics, and only mention in the text additional differences which would not add to the reader’s understanding or would be redundant. With this caveat in mind, regarding the entire 2-mm cut, all rotary cutting instruments showed, compared to the baseline temperature of 34° ±2°C, a decrease of the simulated pulp chamber temperature between 6.6° and 8°C (Table I), and significant differences were found among rotary cutting instruments (data not shown). Moreover, similar to Part I,27 the authors show the statistically significant results as relative percentage differences among the groups. Great White Ultra showed the highest rate of advancement, up to 37.9% compared to TDA coarse, and a significant difference was also seen between the

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Table I. Means (standard deviations) for entire 2-mm cut Rotary Cutting Instruments

Temperature (°C)

Rate Advancement (mm/s)

Load (g)

Rate Advancement/ Load

Manufacturer

Brasseler #6856018

26.43 (1.53)

0.11 (0.03)

128.57 (10.09)

0.0009 (0.0003)

Brasseler USA, Savannah, Ga

NEO

27.01 (1.4)

0.11 (0.03)

128.47 (10.89)

0.0009 (0.0003)

Dentalaire Producs, Intl, Fountain Valley, Calif

NTI

26.51 (1.15)

0.11 (0.03)

127.69 (10.53)

0.0009 (0.0003)

Axis Dental Corp, Coppell, Tex

Premier 770.8C

26.35 (1.19)

0.12 (0.03)

125.7 (7.56)

0.001 (0.0003)

Premier Dental Products Co, Plymouth Meeting, Pa

Premier 2005.8

27.49 (1.85)

0.13 (0.03)

120.36 (12.94)

0.0011 (0.0004)

Premier Dental Products Co

TDA medium

26.96 (1.24)

0.12 (0.03)

124.72 (9.27)

0.0010 (0.0003)

SS White Burs, Inc, Lakewood, NJ

TDA coarse

26.36 (1.12)

0.10 (0.03)

132.06 (9.45)

0.0008 (0.0003)

SS White Burs, Inc

Piranha

26.52 (1.35)

0.12 (0.03)

126.46 (12.15)

0.0009 (0.0003)

SS White Burs, Inc

Diamond

25.91 (1.07)

0.12 (0.03)

122.92 (7.98)

0.0010 (0.0003)

SS White Burs, Inc

Great White Ultra

27.28 (1.53)

0.17 (0.03)

108.35 (15.07)

0.0017 (0.0005)

SS White Burs, Inc

latter rotary cutting instrument and the Premier 2005.8 (Table II). Considering the load, Great White Ultra showed the lowest load (P<.001), up to 13.1% compared to TDA coarse, and, again, additional significant differences were also seen between the latter rotary cutting instrument and the Premier 2005.8 and SS White Diamond (Table III). Considering rate of advancement/load, Great White Ultra showed the highest ratio when compared to the other 9 rotary cutting instruments (up to 60% compared to TDA coarse), which showed no significant differences among each other, with the exception of Premier 2005.8 (higher) and TDA coarse (5%)

(Table IV). Considering the second millimeter of the cut, Great White Ultra showed the highest rate of advancement (up to 49% compared to TDA coarse) (Table V) and the lowest load (up to 16% compared to TDA coarse) compared to the diamond rotary cutting instruments (P=.004) (data not shown), which, instead, showed no difference, except for the load between TDA coarse (higher value) and Premier 2005.8 (P<.001) (data not shown). Considering rate of advancement/load, Great White Ultra showed, again, the highest ratio (P=.01), whereas among the diamond rotary cutting instruments the

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only significant difference was found between Premier 2005.8 (higher ratio) and TDA coarse (lower ratio) (P=.001) (data not shown). Regarding the first millimeter of the cut, the Great White Ultra showed a higher cutting rate than all diamond rotary cutting instruments (P=.007), except Premier 2005.8 and Diamond (Table VI). Great White Ultra also showed a higher rate of advancement/load than the diamond rotary cutting instruments (P=.01), which demonstrated a difference between TDA coarse (lower ratio) and Premier 2005.8 and Diamond (P<.001) (data not shown). Considering the load, Great White Ultra showed a lower value than the

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May 2009

Table II. Rate of advancement (mm/s) for entire 2-mm cut. Only significant differences are shown and expressed in percentages. Empty cells indicate lack of statistical differences; asterisk (*) represents group with higher value. For example, Great White Ultra advanced 37.9% faster than TDA coarse. Similarly, Premier 2005.8 advanced 2.4% faster than TDA coarse Premier 2005.8*

Great White Ultra*

Premier 2005.8

–

11.1%

TDA medium

–

19.3%

Diamond

–

19.3%

Premier 770.8

–

21.1%

Piranha

–

24.7%

NTI

–

27.9%

Brasseler #6856018

–

31.2%

NEO

–

31.5%

2.4%

37.9%

TDA coarse

Table III. Load data (g) for entire 2-mm cut. Only significant differences are shown and expressed in percentages. Empty cells indicate lack of statistical differences; asterisk (*) represents group with higher value. For example, Great White Ultra required 13.1% less force than TDA coarse. Similarly, Premier 2005.8 required 2.2% less force than TDA coarse

Premier 2005.8

Diamond

Great White Ultra

Premier 2005.8*

–

–

2.7%

Diamond*

–

–

5%

TDA medium*

–

–

6.6%

Premier 770.8*

–

–

7.4%

Piranha*

–

–

8.1%

NTI*

–

–

9.2%

NEO*

–

–

9.9%

Brasseler #6856018*

–

–

10%

2.2%

0.2%

13.1%

TDA coarse*

diamond rotary cutting instruments (P=.008), except for Premier 2005.8 and Diamond. Few significant differences were found among diamond rotary cutting instruments (P<.05) (data not shown). Considering all rotary cutting instruments as a single group, the electric handpiece showed a significantly lower mean temperature (SD) (26.68°C (1.34)) than the turbine

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(28.37°C (1.74)) (P<.001). In addition, considering each single group of rotary cutting instruments, all of them showed significantly higher temperatures when used with the turbine than when used with the electric handpiece (P<.001), with the exception of TDA medium (data not shown). The mean rate of advancement (SD) of the rotary cutting instruments, considered as 1 group, was

significantly lower when rotary cutting instruments were used with the turbine (0.11 mm/s (0.03)) than when used with the electric handpiece (0.12 mm/s (0.03)) (P<.001). When the rotary cutting instruments were considered as individual groups, they demonstrated no significant differences, except for Great White Ultra (P<.001), which showed a significantly faster advancement with the elec-

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Table IV. Rate of advancement/load for entire 2-mm cut. Only significant differences are shown and expressed in percentages. Empty cells indicate lack of statistical differences; asterisk (*) represents group with higher value. For example, Great White Ultra showed ratio of advancement/load (describing overall ease of rotary cutting instrument advancement within substrate) of 60% greater than TDA coarse. Similarly, Premier 2005.8 showed advancement/load ratio of 5% greater than TDA coarse

Table V. Rate of advancement (mm/s) for second millimeter cut. Only significant differences are shown and expressed in percentages; asterisk (*) represents group with higher value. For example, Great White Ultra advanced 49% faster than TDA coarse and 20.6% faster than Premier 2005.8

Great White Ultra*

Premier 2005.8*

Great White Ultra*

Premier 2005.8

–

18.4%

Premier 2005.8

20.6%

Diamond

–

31.7%

TDA medium

27.3%

TDA medium

–

32.9%

Premier 770.8

32.3%

Premier 770.8

–

36.3%

Piranha

Piranha

–

38.9%

Diamond

35.1%

NTI

–

44.3%

NTI

35.8%

NEO

–

48.5%

Brasseler #6856018

Brasseler #6856018

–

48.7%

NEO

5%

60%

TDA coarse

33%

43% 44.6%

TDA coarse

49%

Table VI. Rate of advancement (mm/s) for first millimeter cut. Only significant differences are shown and expressed in percentages. Empty cells indicate lack of statistical differences; asterisk (*) represents group with higher value. For example, Great White Ultra advanced 22.5% faster than TDA coarse. Similarly, Premier 2005.8 advanced 2.7% faster than TDA coarse

Premier 2005.8*

Diamond*

Great White Ultra*

Diamond

–

–

0.9%

Premier 770.8

–

–

6.6%

TDA medium

–

–

8%

Piranha

–

–

13.3%

NEO

–

–

15%

NTI

–

–

16.5%

Brasseler #6856018

–

–

16.6%

2.7%

0.8%

22.5%

TDA coarse

tric handpiece (turbine 0.11 mm/s (0.03); electric handpiece 0.12 mm/s (0.03)). Considering the rotary cutting instruments as a single group, the mean load (SD) was lower for the turbine (121.70 g (12.02)) than for the electric handpiece (124.53 g (10.59))

(P=.003). When separately comparing each group of rotary cutting instruments, only Premier 770.8 showed a significantly lower load (P<.001) when used with the turbine (turbine 121.70 g (12.02); electric handpiece 124.53 g (10.59)). For the measure of advancement/

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load, and considering the rotary cutting instruments as a single group, the electric handpiece showed a higher ratio (0.001 mm/s/g (0.0003)) compared with the turbine (0.0009 mm/s/g (0.0003)) (P<.001). Instead, separately comparing each group of rotary cutting instruments, no signifi-

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May 2009 cant differences were found between handpiece types. Considering the rotary cutting instruments as a single group, the turbine showed significantly higher temperatures than the electric handpiece (26.69°C (1.93) and 25.95°C (1.58) respectively, P<.001)), although always below the baseline temperature. Considering the rotary cutting instrument groups individually, with the exception of NTI, TDA coarse, Piranha, and Great White Ultra, the turbine handpiece showed a significantly higher temperature, and in one situation (TDA medium), a lower temperature, than the electric handpiece (P=.007) (data not shown). For the mean rate of advancement, the electric handpiece showed significantly greater values than the turbine both when rotary cutting instrument groups were pooled (electric: 0.11 mm/s (0.03) and turbine: 0.09 mm/s (0.03)), and when they were considered individually, with the exception of Brasseler and Diamond (data not shown). Regarding the applied load, the electric handpiece showed significantly lower mean (SD) values than

the turbine (130.85 g (8.92) and 134.06 g (9.2)) (P<.001); however, considering the single groups of rotary cutting instruments, only Great White Ultra required a significantly less mean (SD) load to cut with the electric handpiece (112.08 g (14.89)) versus the turbine (121.13 g (12.6)) (P<.001). The turbine showed a lower ratio of rate of advancement/load than the electric handpiece when rotary cutting instrument data were pooled (0.0007 mm/s/g (0.0002) and 0.0009 mm/s/g (0.0003) respectively, P<.001), and when rotary cutting instrument groups were individually compared, with the exception of Brasseler and Diamond (Table VII). Consistent with the results for the 2-mm cut, mean (SD) temperatures were higher for the turbine (30.78°C (1.71)) than for the electric handpiece (27.57°C (1.34)) (P<.001), considering the rotary cutting instruments both as a single group and as 10 different groups (P=.006). Considering each single group of rotary cutting instruments, all showed higher temperatures when used with the turbine than when used with the electric handpiece (P=.004) (data not shown).

No significant differences were found for the rate of advancement, while the turbine showed a significantly lower mean load than the electric handpiece, considering either the rotary cutting instruments as a single group (102.45 g (19.46) and 116.56 g (13.54) respectively), or considering the rotary cutting instruments as individual groups (except for TDA medium, P<.001) (Table VIII). When rotary cutting instruments were considered as a single group, the turbine showed a significantly higher mean ratio rate of advancement/ load (SD) than the electric handpiece (0.0015 mm/s/g (0.0007) and 0.0012 mm/s/g (0.0004), P<.001); however, considering each of the 10 rotary cutting instruments, a significantly higher value was found only for NTI, Premier 770.8, and Piranha (P=.002) (data not shown). The results of the 2-way ANOVA analysis are presented in Table IX. Pooling of the turbine and electric handpiece data generated an increased sample size; therefore, when the data were analyzed among rotary cutting instrument groups (n=60), the same trends in the results were seen

Table VII. Rate of advancement/load for second millimeter cut. Turbine versus electric handpiece, considering each rotary cutting instrument group. Asterisk (*) indicates comparison is statistically significant

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Rotary Cutting Instruments

Turbine

Electric Handpiece

Brasseler #6856018

0.0006 (0.0002)

0.0008 (0.0003)

NEO

0.0006 (0.0002)

0.0007 (0.0003)*

NTI

0.0007 (0.0002)

0.0008 (0.0003)*

Premier 770.8

0.0007 (0.0002)

0.0008 (0.0003)*

Premier 2005.8

0.0008 (0.0003)

0.001 (0.0004)*

TDA medium

0.0007 (0.0002)

0.0009 (0.0003)*

TDA coarse

0.0006 (0.0001)

0.0007 (0.0002)*

Piranha

0.0007 (0.0002)

0.0008 (0.0003)*

Diamond

0.0007 (0.0003)

0.0008 (0.0002)

Great White Ultra

0.0012 (0.0005)

0.0016 (0.0006)*

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Table VIII. Load data (g) for first millimeter cut; turbine versus electric handpiece, considering each rotary cutting instrument group. Asterisk (*) indicates comparison is statistically significant

Rotary Cutting Instruments

Turbine

Electric Handpiece

Brasseler #6856018

109.8690 (20.8719)

120.2071 (12.4167)*

NEO

106.9334 (18.7105)

120.0223 (14.1736)*

NTI

107.2844 (16.4172)

120.7952 (13.5149)*

Premier 770.8

96.8294 (20.4601)

117.6372 (9.5902)*

Premier 2005.8

96.1945 (27.0067)

111.6588 (15.2285)*

TDA medium

107.7093 (7.093)

117.2343 (12.9109)

TDA coarse

110.4724 (16.8955)

123.8697 (13.2032)*

Piranha

101.4499 (25.6662)

118.3590 (16.0008)*

Diamond

98.3640 (20.5206)

111.4313 (12.6978)*

Great White Ultra

89.3736 (20.9340)

104.4223 (15.6700)*

Table IX. Two-way ANOVA, P values of effects. Interaction effect is not significant except with respect to temperature Handpiece (Air/Electric)

Groups (10 Groups)

Interaction (Handpiece/Group)

Temperature

<.001

<.001

.010

Rate

<.001

<.001

.988

Load

.003

<.001

.975

Rate/load

.008

<.001

.991

Variable

Table X. Rate of advancement (mm/s) entire for 2-mm cut (combined data). Only significant differences are shown and expressed in percentages. Empty cells indicate lack of statistical differences; asterisk (*) represents group with higher value. For example, Great White Ultra advanced 44% faster than TDA coarse. Similarly, Premier 2005.8 advanced 8% faster than TDA coarse

Premier 2005.8*

Diamond*

Great White Ultra*

TDA Medium*

Premier 2005.8

–

–

16.6%

–

Diamond

–

–

23.7%

–

TDA medium

–

–

24.4%

–

Premier 770.8

–

–

25%

–

Piranha

–

–

28.6%

–

NTI

–

–

33.3%

–

Brasseler #6856018

2.6%

–

36.8%

–

NEO

3.1%

–

37.5%

–

8%

0.9%

44%

0.2%

TDA coarse

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May 2009 as when the groups were compared with turbine and electric handpieces as separate data sets; however, with more noticeable differences and a few more significant comparisons of interest (Tables X and XI). Observation of the SEM figures revealed uniformity in the distribution of the diamond particles, which appeared of variable morphology and embedded into a relatively regular and homogeneous metal matrix. Moreover, the quantity of the matrix of the 2 disposable diamond rotary cutting

instruments seemed to be less than the conventional, multi-use ones, exposing more of the actual diamond particle (Fig. 1). An interesting finding was the qualitatively greater embedding of the diamond particles in the matrix for the experimental TDA coarse, when compared with the TDA medium. The 2 channels of TDA medium and TDA coarse were not covered by any particles; on the contrary, the single channel of Premier 2005.8 was covered, as was the rest of the entire

rotary cutting instrument. Observation of Great White Ultra, the only carbide bur tested, showed the characteristic arrangement of the 6 indented blades. After cutting, a minimal quantity of Macor debris was generally seen on the surface of each rotary cutting instrument, although after cleaning and sterilization, this debris was completely removed (Fig. 2). In addition, no macroscopic loss of diamond particles was observed.

Table XI. Load data (g) for 2-mm cut (combined data). Only significant differences are shown and expressed in percentages. Empty cells indicate lack of statistical differences; asterisk (*) represents group with higher value. For example, Great White Ultra required 14.1% less force than TDA coarse. Similarly, Premier 2005.8 required 2.8% less force than TDA coarse Premier 2005.8

Diamond

Great White Ultra

Premier 770.8

Premier 2005.8*

–

–

5%

–

Diamond*

–

–

6.9%

–

Premier 770.8*

–

–

8%

–

TDA medium*

–

–

9.1%

–

Piranha*

–

–

9.1%

–

NTI*

–

–

10.7%

–

NEO*

1.1%

–

12.2%

–

Brasseler #6856018*

1.3%

–

12.4%

–

TDA coarse*

2.8%

1%

14.1%

0.09%

A

B

C

1 SEM photomicrographs at x50. Note different amount of matrix among 2 disposable (A and B) and 1 conventional diamond rotary cutting instruments (C). A, NEO. B, Piranha. C, Brasseler.

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A

B 2 SEM photomicrographs at x200. Rotary cutting instrument surface before cut (left), after cut without cleaning (middle), and after cleaning and sterilization (right). A, Premier 770.8. B, NEO.

DISCUSSION Similar to the Part I study,27 the null hypothesis of this study was rejected in terms of cutting efficiency, as the load, advancement, and advancement/load were significantly different when the carbide bur was used. However, when the same comparisons were considered among diamond rotary cutting instruments, consistent with other studies,7,15,21 the null hypothesis was instead generally accepted, with only few exceptions. Moreover, the multi- and single-use diamond rotary cutting instruments compared in the current study did not show significant differences in the cutting rate, also in agreement with other studies.12,15 When the temperature data were considered, the null hypothesis was again rejected as significant differences were found, although, from a clinical standpoint, temperatures produced in the pulp chamber were actually lower than baseline and, therefore, not clinically harmful. To avoid repetition, the reader is referred to the discussion of the temperature findings in Part I,27 as it also applies to the finding related to the use of the

electric handpiece. Considering all rotary cutting instruments as a single group, it is interesting to note that the electric handpiece provided significantly lower temperatures than the turbine, although both were used with the same total water flow (40 ml/min), so the null hypothesis was rejected. This may be due to the fact that the water flows from 3 spray ports in the electric handpiece (positioned at 2, 6, and 10 o’clock), whereas, in the highspeed turbine, water emerges from only a single port at the 6 o’clock position.19 The greater cooling generated by the electric handpiece was also confirmed when the individual rotary cutting instruments were compared, with the exception of the TDA medium, which demonstrated no significant difference when used with either handpiece. Considering the advancement, load, and their relationship, the results showed complex interactions between the choice of handpiece and (1) the type of rotary cutting instrument (carbide bur versus diamond), and (2) initial versus late phase of the preparation. For this reason, a simple

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acceptance or rejection of the null hypothesis was difficult to define. Indeed, the advancement/load, which defines the overall ease of material removal over the 2-mm cut, was significantly greater with the electric handpiece when the rotary cutting instrument data were pooled, therefore, indicating rejection of the null hypothesis. Instead, no difference was observed between the 2 handpieces when the individual rotary cutting instruments were considered, therefore, indicating acceptance of the null hypothesis. Moreover, the 2 handpieces exhibited different behaviors when considering the first millimeter or the second millimeter of the cut. In fact, the advancement rate and advancement/ load of the electric handpiece were significantly greater in the second millimeter of the cut, both when the data were pooled and, with the exception of Brasseler and Diamond, when the rotary cutting instruments were individually compared, therefore, indicating rejection of the null hypothesis. This could be translated into a greater capacity of this type of handpiece to perform faster, continuous, and effective removal of tooth structure/

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May 2009 restorative material (existing crowns) without the need to periodically relieve the load on the handpiece, as with the turbine. This type of continuous preparation might be indicated or cost effective during extensive preparation procedures for fixed prosthodontics, such as multiple crown preparation. The greater cutting efficiency of the electric handpiece during the second millimeter of the cutting action was also underscored by the load values. Indeed, the electric handpiece required a lower load when the data were pooled and, considering each rotary cutting instrument individually, a lower load when the Great White Ultra was used, therefore, suggesting rejection of the null hypothesis. This greater cutting efficiency of the electric handpiece was especially evident when the Great White Ultra was used, probably as a result of the association between a high-torque delivery handpiece and an efficient rotary cutting instrument. However, the same variables, considered in the first millimeter of the preparation, showed a somewhat different trend. While the advancement rates were similar between handpiece types (both when data were pooled or compared by rotary cutting instrument type), therefore indicating acceptance of the null hypothesis, the turbine required less load to advance both when data were pooled and, with the exception of the TDA medium, when rotary cutting instruments were individually considered, therefore, indicating rejection of the null hypothesis. This could possibly be explained by the fact that, in this study, the free-running speed of the turbine was twice that of the electric handpiece (400,000 versus 200,000 rpm). Therefore, during the initial portion of the cut and before the rotary cutting instrument was completely engaged in the substrate (first millimeter), the free-running speed and, therefore, the kinetic energy, and possibly the power6 available with the turbine, were sufficient to compensate for the difference in torque between the 2 handpieces.

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This is consistent with the observations of Eikenberg,22 who reported that the cutting efficiency of the airturbine handpiece decreases significantly with increased pressure due to the fact that it has insufficient torque to operate effectively. This result also agrees with the findings of other studies,7-9 which showed that increasing workloads determine a decrease in turbine rpm and an increase in cutting volumes until a critical point at which further increases in load decrease the rpm and also cutting volumes. These findings have important clinical implications. The higher cutting efficiency of the electric handpiece would appear especially useful when continuous and “heavy-handed” preparation techniques are attempted,24 while for other types of preparations (for example, finishing), this might not be the case. Another important factor to be considered when addressing cutting efficiency differences between electric and turbine handpieces is the amount of air-water spray, which was similar in both handpieces,28-30 and the different pattern of air-water spray used. It was reported by Siegel and von Fraunhofer19 that increasing the number of spray ports while maintaining the same volume of coolant (25 ml/min) demonstrated a significant increase in cutting rates when a groove was cut into the substrate, but not when an edge cut was made. While one could speculate that the difference in cutting rates found in this study19 between handpiece types could be partially due to the different spray patterns of the handpieces (electric: 3 ports; turbine: 1 port), the authors contend that this did not occur and that significant differences are due to handpiece-specific features. This is affirmed by the fact that the design of the present study, while involving a groove cut, allowed availability of the air-water spray in a similar fashion as in the edge-cutting setting of the study by Siegel and von Fraunhofer,19 in which the number of ports had no influence on cutting rates. With the paucity of established

protocols, this study has attempted to meet 2 important requirements: reproducibility and relative simplicity. Variables were controlled by the computer and software, therefore, avoiding operator subjectivity. Furthermore, a software system was designed to monitor all of the experimental variables and allow load-dependent changes in feed rate (advancement rate) that could, within the specified limits, simulate the action of a clinician. The software was designed so that when the nominal load of 125 g was reached, the advancement rate was maintained; if the load exceeded 125 g, the advancement rate was decreased; if the load was less than 125 g, the advancement rate was increased (up to the hardware limit). This load-dependent setting was successfully used in a previous study10 and in Part I of this study.27 It not only simulates the action of a clinician, but, most importantly, allows the performance of the rotary cutting instrument and handpiece to be evaluated over a range of loads and advancement rates.4,7,25,26 However, this load-dependent control setting might be less relevant to the use of an electric handpiece. Due to the variable torque that this type of handpiece is purported to apply in response to an rpm-dependent control setting (in other words, these handpieces are supposed to increase the applied torque to maintain the nominal velocity specified by the unit), the chances of stalling the handpiece are remote and likely outside the range of loads applied by the average clinician during tooth preparation. Therefore, and within a clinically applicable range, while the turbine action is, by necessity, load controlled, the electric handpiece is advancement rate (feed) controlled. It is, therefore, possible that if the nominal load was actually increased above 125 g and, especially, if the software/hardware advancement rate was also increased, the electric handpiece might actually show a faster rate of material removal than the present study results indicated. This

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Volume 101 Issue 5 might be particularly true with the use of the carbide bur. As shown in Part I of the study,27 the carbide bur, while using similar energy inputs, removed more substrate material per unit of time than the diamond rotary cutting instruments and showed a greater cutting efficiency. Also, in this study, the carbide bur showed an even greater cutting efficiency compared to the diamond rotary cutting instruments when used with the electric handpiece; namely, a faster material removal was achieved with less applied load. The present study used a single turbine and electric handpiece to test all of the rotary cutting instruments and, therefore, a question could be raised as to whether the handpieces consistently performed at the required rpms throughout the study.17 While this may have been an issue for the electric handpiece (rpms were not independently and directly monitored, but only assessed by reading the displayed rpms in the motor unit), the baseline rotational rates (400,000 ±2000) were set for the turbine before each cut, therefore, eliminating the possibility that continued use of the handpiece may have caused wear and influenced the rpms.17 As for Part I,27 regarding the nature of the test design used in the study, it is obvious that a 2-mm straight penetration does not directly reproduce the more extensive clinical preparation that is used during tooth preparation. While this is a valid criticism and more extensive preparation lengths should be used in future experiments, the current study attempted to create testing conditions which were effective and reproducible so that differences in rotary cutting instrument performance could be readily ascertained. The SEM examination showed that the 2 single-use rotary cutting instruments (NEO and Piranha) showed a lesser amount of matrix, therefore exposing a greater amount of the actual diamond particle. This appears a logical design considering that disposable rotary cutting instruments are expected to have a short-term life.

While wear of the matrix could cause the diamond particles to be lost more easily than in multi-use rotary cutting instruments, it is interesting to note that no study has so far analyzed the longevity of single-use rotary cutting instruments. The SEM also showed that the prototype TDA coarse rotary cutting instrument showed a qualitatively greater embedding of the diamond particles than the other rotary cutting instruments. It may be speculated that the resultant decreased availability of exposed diamond particles is the primary reason behind the lower cutting efficiency exhibited by this rotary cutting instrument. An additional point to discuss is the fact that, while all the rotary cutting instruments had the same diameter at the proximal part of the cutting area, the tip diameter varied considerably.27 While it could be argued that wider rotary cutting instruments (Great White Ultra) would theoretically show greater cutting efficiency in light of the greater tangential speed, this factor did not correlate with the results. In fact, similarly sized rotary cutting instruments such as NEO, Brasseler, and NTI consistently underperformed compared to the other rotary cutting instruments.

CONCLUSIONS Within the limitations of this in vitro study, the following conclusions, similar to those of the Part I study, were drawn: 1. From a clinical point of view, tooth preparation with the electric handpiece with 40 ml/min roomtemperature water seemed to be an optimal method to avoid pulp injuries. Even though statistical differences were found, the type of rotary cutting instrument did not influence the temperature inside the simulated pulp chamber. 2. Diamond rotary cutting instruments, with some exceptions, did not show any significant differences, considering the grit (medium or coarse),

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the design (with or without channels), or the proposed usage (multi-use or disposable). 3. The carbide bur (Great White Ultra) demonstrated statistically superior performance compared to the diamond rotary cutting instruments, requiring less load and advancing faster within the substrate. 4. Considering the entire cutting procedure, and with the exception of the Great White Ultra, the electric handpiece did not cut faster than the turbine when rotary cutting instrument groups were compared; however, it was more efficient when data from all rotary cutting instruments were pooled. 5. As the preparation progressed (second millimeter), the electric handpiece showed a higher cutting efficiency than the turbine (both when most rotary cutting instrument groups were compared and when data were pooled), especially when used with the carbide bur. This greater efficiency of the electric handpiece is likely due to the greater torque applied.

REFERENCES 1. Kenyon BJ, Van Zyl I, Louie KG. Comparison of cavity preparation quality using an electric motor handpiece and an air turbine dental handpiece. J Am Dent Assoc 2005;136:1101-5. 2. Christensen GJ. Are electric handpieces an improvement? J Am Dent Assoc 2002;133:1433-4. 3. Taylor DF, Perkins RR, Kumpula JW. Characteristics of some air turbine handpieces. J Am Dent Assoc 1962; 64:794-805. 4. Brockhurst PJ, Shams R. Dynamic measurement of the torque-speed characteristics of dental high speed air turbine handpieces. Aust Dent J 1994;39:33-8. 5. Miyawaki H, Taira M, Wakasa K, Yamaki M. Dental high-speed cutting of four cast alloys. J Oral Rehabil 1993;20:653-61. 6. Tanaka N, Taira M, Wasaka K, Shintani H, Yamaki M. Cutting effectiveness and wear of carbide burs on eight machinable ceramics and bovine dentin. Dent Mater 1991;7:247-53. 7. Taira M, Wasaka K, Yamaki M, Matsui A. Dental cutting behaviour of mica-based and apatite-based machinable glass-ceramics. J Oral Rehabil 1990;17:461-72. 8. Shuchard A, Watkins C. Comparative efficiency of rotary cutting instruments. J Prosthet Dent 1965;15:908-23.

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May 2009 9. Sorenson FM, Cantwell KR, Aplin AW. Thermogenics in cavity preparation using air turbine handpieces: the relationship of heat transferred to rate of tooth structure removal. J Prosthet Dent 1964;14:524-32. 10.Galindo DF, Ercoli C, Funkenbusch PD, Greene TD, Moss ME, Lee HJ, et al. Tooth preparation: a study on the effect of different variables and a comparison between conventional and channeled diamond burs. J Prosthodont 2004;13:3-16. 11.Elias K, Amis AA, Setchell DJ. The magnitude of cutting forces at high speed. J Prosthet Dent 2003;89:286-91. 12.Pilcher ES, Tietge J, Draughn RA. Comparison of cutting rates among single-patientuse and multiple-patient-use diamond burs. J Prosthodont 2000;9:66-70. 13.Kazen DH. Modern electric handpieces feature improved benefits for today’s dental surgeon. Dent Assist 2005;74:16, 25. 14.Hall DL. Methicillin-resistant Staphylococcus aureus and infection control for restorative dental treatment in nursing homes. Spec Care Dentist 2003;23:100-7. 15.Siegel SC, von Fraunhofer JA. Irrigation rates and handpieces used in proshtodontic and operative dentistry: result of a survey of North American dental school teaching. J Prosthodont 2000;9:82-6.

16.Siegel SC, von Fraunhofer JA. Assessing cutting efficiency of dental diamond burs. J Am Dent Assoc 1996;127:763-72. 17.Eames WB, Reder BS, Smith GA, Satrom KD, Dwyer GM. Ten high-speed handpieces: evaluation of performance. Oper Dent 1979;4:124-31. 18.Oztürk B, Usümez A, Oztürk AN, Ozer F. In vitro assessment of temperature change in the pulp chamber during cavity preparation. J Prosthet Dent 2004;91:436-40. 19.Siegel SC, von Fraunhofer JA. The effect of handpiece spray patterns on cutting efficiency. J Am Dent Assoc 2002;133:184-8. 20.Dyson JE, Darvell BW. Dental air turbine handpiece performance testing. Aust Dent J 1995;40:330-8. 21.Siegel SC, von Fraunhofer JA. Cutting efficiency of three diamond bur grit sizes. J Am Dent Assoc 2000;131:1706-10. 22.Eikenberg SL. Comparison of the cutting efficiencies of electric motor and air turbine dental handpieces. Gen Dent 2001;49:199204. 23.Watson TF, Flanagan D, Stone DG. High and low torque handpieces: cutting dynamics, enamel cracking and tooth temperature. Br Dent J 2000;188:680-6. 24.Siegel SC, von Fraunhofer JA. Dental cutting with diamond burs: heavy-handed or light touch? J Prosthodont 1999;8:3-9. 25.Liao WM, Taira M, Ohmoto K, Shintani H, Yamaki M. Studies on dental high-speed cutting. J Oral Rehabil 1995;22:67-72.

26.Ohmoto K, Taira M, Shintani H, Yamaki M. Studies on dental high-speed cutting with carbide burs used on bovine dentin. J Prosthet Dent 1994;71:319-23. 27.Ercoli C, Rotella M, Funkenbusch P, Russel S, Feng C. In vitro comparison of the cutting efficiency and temperature production of ten different burs. Part I: turbine. J Prosthet Dent 2009;101:248-61. 28.von Fraunhofer JA, Siegel SC, Feldman S. Handpiece coolant flow rates and dental cutting. Oper Dent 2000;25:544-8. 29.Lloyd BA, Rich JA, Brown WS. Effect of cooling techniques on temperature control and cutting rate for high-speed dental drills. J Dent Res 1978;57:675-84. 30.Westland IA. The energy requirement of the dental cutting process. J Oral Rehabil 1980;7:51-63. Corresponding author: Dr Carlo Ercoli Division of Prosthodontics, Eastman Dental Center Department of Mechanical Engineering University of Rochester 625 Elmwood Ave Rochester, NY 14620 Fax: 716-244-8772 E-mail: [email protected] Copyright © 2009 by the Editorial Council for The Journal of Prosthetic Dentistry.

Noteworthy Abstracts of the Current Literature Translucency and biaxial flexural strength of four ceramic core materials Chen YM, Smales RJ, Yip KH, Sung WJ. Dent Mater 2008;24:1506-11. Objectives: To assess the relative translucencies and flexural strengths of four dental restorative ceramic core materials. Methods: Eight disk specimens (14 mm in diameter x 0.5 ± 0.05 mm in thickness) were prepared for each group of four ceramic core materials (IPS Empress 2 dentin, VITA In-Ceram Alumina, VITA In-Ceram Zirconia, Cercon Base Zirconia), according to the manufacturers’ instructions. A color meter was used to measure the relative translucencies of the specimens. The biaxial flexure test (ISO 6872) was then used to measure their flexural strengths. Data for relative translucency (0.0–1.0), fracture load (N) and biaxial flexural strength (MPa) were analyzed by one-way ANOVA, followed by Tukey’s multiple comparison test for significant findings (α = 0.05). Results: For relative translucency: IPS Empress 2 (0.78 ± 0.03), VITA In-Ceram Alumina (0.94 ± 0.01), VITA In-Ceram Zirconia (1.00 ± 0.01), Cercon Base Zirconia (1.00 ± 0.01), P < 0.0001. For biaxial flexural strength: IPS Empress 2 (355.1 ± 25.7), VITA In-Ceram Alumina (514.0 ± 49.5), VITA In-Ceram Zirconia (592.4 ± 84.7), Cercon Base Zirconia (910.5 ± 95.3), P < 0.0001. Significance: IPS Empress 2 and VITA In-Ceram Alumina were significantly more translucent than the two opaque zirconia-containing core materials. IPS Empress 2 was significantly weaker, and Cercon Base Zirconia was significantly stronger, than the other two ceramic core materials. Reprinted with permission from the Academy of Dental Materials.

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