ASSESSING THE CUTTING EFFICIENCY OF DENTAL DIAMOND BURS

ARTICLE 1

ASSESSING THE CUTTING EFFICIENCY OF DENTAL DIAMOND BURS SHARON C. SIEGEL, D.D.S., M.S.; J. ANTHONY VON FRAUNHOFER, M.SC., PH.D.

This study measured the cutting efficiencies of 15 types of roundend tapered conventional and

disposable diamond burs. The results showed that disposable diamond burs had cutting effi-

ciencies that were comparable to those of conventional (multi-

use) diamond burs; their use should reduce the risk of clinical cross-infection.

0 he Centers for Disease Control and Prevention, the American Dental Association and other organizations'-3 clearly state that all dental instruments that penetrate soft or hard tissue or come into contact with oral tissue must be sterilized after each use to prevent cross-infection between patients. However, for dental burs, the multistep debriding, cleaning and sterilization procedures are timeconsuming. The "single-patient-use" or disposable diamond bur is a recent innovation that addresses the need to minimize the risk of cross-contamination of bloodborne pathogens. Clinical preference for diamond burs over tungsten carbide (WC) burs for a variety of dental prodedures is based on their reportedly greater resistance to abrasion, lower heat generation and longer life.4'0 Although they have been used for 100 years in dentistry,'0"' diamond burs were designed on the basis of engineering theories for industrial cutting tools, not precision tooth preparation instruments, despite significant differences in the two fields.'2 Conventional diamond burs, using both natural and synthetic diamonds (Larry Clark, Precision Rotary Instruments Inc., oral communication, Jan. 31, 1994), are manufactured in multiple layers by electrodeposition, sintering or microbrazing and provide, in principle, continuous regeneration of the cutting surface as wear occurs. Medium-grit diamond burs have an average particle size of 90 to 120 micrometers (120 to 140 mesh), while coarse-grit burs have a particle size of 150 to 160 pm (80 to 100 mesh). Most bur testing was performed before the advent of high-speed handpieces,45'8"3 and much of the early literature deals with their use in cavity preparation.'2-'7 At present, national and international standards for dental burs primarily cover quality control issues because of the difficulty in quantifying such parameters as cutting efficiency, bur life and tooth-surface finish. Cutting studies using identical burs and test regimens have shown statistically different rates of bur wear and material removal in different laboratories.'8 Some researchers report that disposable diamond burs (Table 1) are of good quality and economical, typically costing 70 cents to $1.80 per bur compared with $3 to $10 per bur for the multiple-use product.19 However, they have not been systematically compared JADA, Vol. 127, June 1996 763

CLINICAL

TABLE

POACTICE -

I

TYPE*

REFERENCE NUMBER

DIAMETERt

LENGTH (MM)

GRIT TYPE

Brassier coarse (Brassier Manufacturing Co.)

CV

856/016

1.6 (1.38)

8.0

Coarse

Brassier medium

CV

856/016

1.6 (1.37)

8.0

Medium

Brassler (WC) crosscut fissure

CB

7675/016

1.6 (1.43)

4.0

Crosscut fissure

Premier Two Striper coarse (Premier Dental Products Co.)

CV

235.8C

1.6 (1.42)

8.0

Coarse

(American Diamond Instruments)

DS

22R

1.6 (1.56)

8.0

Coarse

Cobra medium

DS

22R

1.6 (1.56)

8.0

Medium

Cobra medium 11

DS

22R

1.6 (1.29)

9.0

Meditum

Monosteryl coarse (Global Dental Products Co.)

DS

850/016

1.6 (1.31)

10.0

Coarse

Monosteryl medium

DS

850/016

1.6 (1.36)

10.0

Medium

Inc.)

DS

856/016

1.6 (1.30)

8.0

Mediuxm

Neo coarse (Microcopy)

DS

856/016

1.6 (1.46)

8.0

Coarse

Neo medium

DS

856/016

1.6 (1.40)

8.0

Medium

(Vermont Diamond Division, Precision Rtar*y Instruments)

DS

PA 39

1.6 (1.48)

8.0

Coarse

Patriot medium

DS

PA 39

1.6 (1.35)

8.0

Mediuim

(S.S. White Burs Inc.)

DS

856/016

1.6 (1.38)

8.0

Medium

Spring coarse (Spring Health Products Inc.)

DS

772.7

1.6 (1.39)

7.0

Coarse

TRADE NAME (MANUFACTURER)

Cobra coarse

NB Nova medium

(Gnathos Dental Products

Patriot coarse

S.S. White medium

* CV: conventional; CB: carbide; DS: disposable. t Diameter in millimeters at the widest point (bur diameter at 4 mm from the tip).

with conventional diamond burs. Assessing the cutting efficiency of dental burs poses problems not found with engineering cutting studies, notably many uncontrolled operating parameters,6'20 including individual dental techniques, differences in dental hard tissues, rotation speed, applied pressure, turbine air pressure and differences in handpieces.3"19 Many studies of dental burs involved 764 JADA, Vol. 127, June 1996

modified milling tests performed at a fixed speed (60,000 to 300,000 revolutions per minute), a fixed load (50 to 150 grams) and a fixed angle of attack (90 degrees), with the individual cuts limited to a few seconds in duration.2022 Dental cutting studies lack a substrate that accurately mimics the dental tissues.20 Dental enamel is irregular, convex and anisotropic, thus virtually pro-

hibiting preparation of a substrate that is flat, isotropic and uniformly thick.22 Some authors have discussed alternative substrates,8 23'24 but the lack of adequate substitutes for enamel limits the clinical significance of some cutting studies. Cutting data are varied, but certain trends are evident. A bur operating at 60,000 rpm removed three to five times as much enamel (at a comparable

CLINICAL PRACTIC[ rise in temperature) as a lowspeed (3,000 rpm) standard dental engine and handpiece.4 The lower force exerted on the handpiece at higher speeds reduces frictional effects and increases cutting efficiency, with a concomitant 1/60 to 1/100 reduction in expended effort, while providing greater control than the standard dental engine and handpiece.4 Although more material is removed at higher rotational speeds with various substrates,8 the data may correlate poorly with those for enamel. For example, a particular bur might cut glass poorly but perform satisfactorily with enamel. One study demonstrated greater efficiency and less heat generation with carbide burs than with diamond burs, but other studies have shown greater efficiency with diamond burs.25'26 Although the bur profile (or shape), diamond distribution and grit size are parameters in cutting efficiency, the bur manufacturer, type of bur and manufacturing method are also strong influences.27'28 Few comparative studies have been performed with disposable and conventional diamond burs. One study compared a disposable diamond bur with six brands of conventional diamond burs in cutting a machinable glass ceramic (Macor, Corning Incorporated).29 The disposable bur was superior to five ofthe six conventional diamond burs, while the rate of material removal was not linear for any of the burs. Clinical evaluations indicate that the disposable diamond bur results in smoother tooth preparations than conventional diamond burs.28 Lazzati and co-workers reported greater wear with disposable diamonds; however,

Figure 1. The clear, acrylic (Plexiglas) test cutting assembly Is shown.

they did acknowledge that the development of such burs was a great advance in infection control.30 A 1991 report summarizing the results of multiple laboratory tests and clinical evaluations concluded that there is a trend for disposable diamond burs to have cutting efficiencies and longevity comparable with those of conventional burs; however, all burs varied widely in appearance and performance.3' Other authors have reported wide variation in the cutting efficiency of new conventional diamond

burs.27'32 A dentist's decision to select disposable diamonds may be based on the effect of sterilization on conventional diamonds.

Guttormsen and Myklebust found that repeated autoclaving of conventional diamond burs did not cause wear or corrosion,33 and Gureckis and coworkers reported that repeated sterilization (using a chemical agent, autoclaving, dry heat or chemical vapor) had no effect on cutting efficiency against machinable glass ceramic (Macor) after 10 sterilization cycles.32 Although conventional diamonds may be sterilized without adverse effects, repeated use and resterilization is questionable from an economic perspective if disposable diamond burs are efficient dental instruments. This study addresses the question of the relative cutting efficiencies of conventional and JADA, Vol. 127, June 1996 765

-CLINICAL PRACTIC[ disposable diamond burs and provides quantitative experimental data. MATERIALS AND METHODS

To ensure that the forces used in this study were in accord with reported clinical mean forces, the authors performed a small trial with three prosthodontists and three general dentists. The participants, without using a finger fulcrum or looking at the balance, pressed the end of the handpiece with a diamond bur in the chuck against the pan of a triple-beam balance (Ohaus) with the force normally used in clinical practice. The mean (+ standard deviation) applied force was 99.3 g (± 23.4 g), substantiating the 50- to 150-g range commonly reported in the literature.22 One of the authors (S.C.S.) performed the cutting tests using an L-shaped, clear, acrylic (Plexiglas) cutting assembly (Figure 1) and an ultra-

high-speed handpiece (640B Super Torque KaVo, KaVo

I

The authors examined five samples of each diamond bur under optical stereomicroscopy and scanning electron microscopy.

America Corp.) mounted in a brass cylinder attached to the vertical wall by a frictionless bearing. The cutting substrate was mounted rigidly in a stainless steel holder attached to the base of the cutting assembly. The handpiece operated at 340,000 rpm at a constant air 766 JADA, Vol. 127, June 1996

pressure of 33 pounds per square inch and a coolant water supply rate of 15 milliliters/minute. The applied cutting force was achieved by attaching a weight of 147.5 g2l to the handpiece head. The actual force at the bur tip was calculated as follows: P=wxd D =

49

147.5x79

= 91.5

g where "P" equals load, "w" equals weight, "d" equals distance from pivot to weight and "D" equals distance from pivot to bur tip. The author who performed the cutting tests placed the bur parallel to the substrate and pulled it perpendicularly down onto the substrate, simulating clinical practice. The substrate was leveled before each run and cut to a length of 4 millimeters. Each bur made a series of 10 cuts, of 30 seconds' duration each. Before each series of cuts, the author sprayed the handpiece with lubricant (KaVo) for one second and then ran it without a load for 60 seconds.

The authors randomly tested 10 samples of 16 types of roundend tapered cylinder burs from nine manufacturers (Table 1). This type of bur was selected because of its ready availability and common use for occlusal, and often axial, reduction of crown preparations. Twelve of the burs tested were disposable, four of which were available in both medium and coarse grits. The controls included two brands of conventional diamond burs, one of which was available in medium and coarse grit, and a tungsten carbide bur. The cutting substrate was a

machinable glass ceramic (Macor). This substrate34 is a white, nonporous, porcelainlike material composed of approximately 55 percent fluorophlogopite mica and 45 percent borosilicate glass with a similar hardness (250 Knoop hardness number) and elastic modulus (66.9 gigapascal) as tooth enamel (300 to 340 KHN and 84 GPa8'35). The substrate block was dried and weighed before each cutting series and after each 30-second cut. After the fifth run (total cutting time, 2.5 minutes), the author ultrasonically cleaned the bur in distilled water for 60 seconds and then returned it to the handpiece for cutting runs six through 10. Using a decimilligram balance (Model 100A XE series, Denver Instruments Co.), the authors determined the individual weight loss for each cutting run. They calculated the mean (± SD) amount of substrate material removed with each bur and compared these mean amounts using a one-way analysis of variance. Where differences existed, they were identified with a post-hoc t-test at an a priori a = .05. The authors examined five samples of each diamond bur under optical stereomicroscopy and scanning electron microscopy before and after the cutting procedures to assess the surface morphology. RESULTS

Table 2 summarizes data about the substrate removed in cuts one through five and cuts six through 10. Overall, the cutting efficiencies of medium-grit disposable diamond burs were comparable to those of conventional medium-grit diamond burs. Statistically significant

CLINICAL PRACTICE TABLE 2

TRADE NAME

MEAN (2:SD) AMOUNT OF SUBSTRATE REMOVED (MG)* Cuts 1-5

Cuts 6-10

STATISTICAL

SIGNIFICANCE*t

Total

CONVENTIONAL

c

Brassier coarse

268.0 ± 55.4

206.4 + 46.2

474.5 + 9.4

Brassier medium

280.7 + 69.1

210.0 + 56.8

490.8 + 10.9

P c .05

Brassler (WC) crosscut fissure

318.7 ± 77.7

155.4 ± 59.3

474.1 + 11.2

P < .001

252.3 + 77.2

194.5 ± 35.7

466.8 + 10.8

NS

P < .01

P

.05

Premier Two

Striper coarse

DISPOSABLE Cobra coarse

288.7 ± 50.6

199.7 ± 55.2

488.5 + 10.1

Cobra medium

269.1 +88.7

195.1

464.3

Cobra medium 11

263.6 + 60.5

Monosteryl coarse

308.3

Monosteryl medium

308.3 + 34.1

38.8

66.1

15.1

NS

217.2 + 71.3

480.8 + 13.0

NS

271.6

579.9

NS

54.5

83.6

261.2 + 28.3

570.6 + 53.3

P < .01

NB Nova medium

267.4 + 72.9

204.7 + 26.0

472.1 ± 79.2

P c .05

Neo coarse

296.9

249.6

546.4

Neo medium

276.9 + 35.0

224.8 + 35.9

501.7 + 67.8

P < .05

Patriot coarse

255.9 + 46.7

206.0 + 19.2

461.9 + 60.8

P c .05

Patriot medium

298.6

236.9

36.8

535.5 ±91.3

P

S.S. White medium

312.3 ± 36.7

243.9 ± 42.8

556.2 + 73.7

Spring

200.5 ± 14.2

168.4

369.0 ± 41.7

coarse

44.1

59.6

55.6

28.6

95.6

NS

.05

P c .01 c

P

.05

* SD: standard deviation; NS: not significant (P > .05). t Comparison of substrate removed in cuts one through five and in cuts six through 10.

differences between the medium-grit disposable burs were found only between the Monosteryl medium (Global Dental Products Co.) and the Neo medium (Microcopy) burs (P < .05) and between the Monosteryl medium and the NB Nova medium (Gnathos Dental Products Inc.) burs (P < .01) for cuts six through 10, as well as between the S.S. White medium (S.S. White Burs Inc.) and the NB Nova medium burs (P < .05) for cuts six through 10. When the authors compared burs from

the five manufacturers that marketed both medium- and coarse-grit burs, they found no statistically significant differences (P > .05) between the medium- and coarse-grit burs from the same manufacturer. When all coarse-grit burs were compared, more substrate was removed (P < .05) in cuts six through 10 and in total by the disposable Monosteryl burs than by the conventional Brassler (Brassler Manufacturing Co.) and Premier Two Striper coarse (Premier Dental

Products Co.) burs (Table 3). Other statistically significant differences included the greater removal of substrate by the Neo coarse (disposable) bur compared with the Premier Two Striper coarse (conventional) bur for cuts six through 10, and the smaller amount of material removed by the Spring coarse (disposable) bur in cuts one through five (P < .01) as well as overall (P <. 05) compared with the Brassler coarse (conventional) bur. Of the disposable coarse diamond burs, the Spring JADA, Vol. 127, June 1996

767

-CLINICAL

PRACTICE

TABLE 3

1 DISPOSABLE BUR

~~~~~~~~~~~~~~~~~~~~~~~ CONVENTIONAL DIAMOND BUR*

BraesIOr Coarse Cuts 1-5

Brassier Coarse Cuts 6-10

Brassier Coarse Total

Cobra coarse

NS

INS

NS

Monosteryl coarse

NS

P < .05

P < .05

Neo coarse

NS

NS

NS

Patriot coarse

NS

NS

NS

Spring coarse

P c .01

NS

Premier Coarse Cuts 1-5

Premier Coarse Cuts 6-10

P

-

.05

Premier Coarse Total

Cobra coarse

NS

NS

NS

Monosteryl coarse

NS

P < .01

P c .05

Neo coarse

NS

P<.05

NS

Patriot coarse

NS

NS

NS

Spring coarse

NS

NS

NS

* NS: not significant (P> .05).

coarse bur removed less material than any other bur (P < .0 1). The Patriot coarse bur removed less

material than the Monosteryl and Neo coarse burs (P < .01 and P < .05, respectively). Most burs removed more substrate (P < .05) in cuts one through five than in cuts six through 10; the exceptions were the conventional Premier Two Striper coarse bur and the disposable Cobra medium, Cobra II medium, Monosteryl coarse and Neo coarse burs (P > .05). Likewise, more substrate was removed in cuts one through five than in cuts six through 10 by the Brassler (WC) crosscut fissure bur (Table 2). All diamond burs in this study removed more material in cuts six through 10 than the fissure bur; however, the difference was not 768

mond chips for most burs were faceted and of comparable size, with medium-grit diamonds ranging from 85 to 100 gm in diameter and coarse-grit diamonds ranging from 120 to 180 ,um. The diamond chips were arranged in a single or double layer and most burs had a smooth, continuous metal matrix surrounding the diamond particles, although in some cases the matrix was pitted and/or nodular. Most burs had an even, reasonably dense distribution of diamonds along the shank and at the tip, although at least eight types of burs had areas devoid of diamonds. The SEM examina-

JADA, Vol. 127, June 1996

significant (P > .05) for the three Cobra burs and the Spring coarse bur. Only the Spring coarse disposable bur removed a significantly lower (P < .00 1) amount of substrate in cuts one through five than the Brassler (WC) crosscut fissure bur. When comparing the total amounts of substrate removed, the authors found a significant difference (P < .05) only for the two Monosteryl burs and the Spring coarse bur. The Monosteryl burs performed better than the Brassler (WC) crosscut fissure bur. The Spring coarse bur performed more poorly than the Brassler fissure bur. SCANNING ELECTRON MICROSCOPY

Table 4 summarizes the optical and SEM observations. The dia-

tion of burs after one minute of cutting (two cuts) and after five minutes of cutting (10 cuts) showed marked accumulation of debris between the diamond chips for all burs (Figure 2). The debris appeared to almost totally clog the surface, and the authors noted no difference in the amount of clogging at one minute compared with that at five minutes. DISCUSSION

The results of this study showed a few instances of statistically significant differences in cutting efficiency between conventional and disposable coarse-grit burs, but no differences in the overall cutting efficiency of conventional and disposable medium-grit burs. In clinical settings, the force applied by the dentist is dictated by tactile sense and such factors

CLINICA[ PBACJIC[

TABLE 4

DIAMOND BUR

Brassier coarse

Brassier medium Cobra coarse

APPEARANCE OF DIAMONDS

Large fceted, multilayered, natural, 123 p.m Medium, faceted, mxilti-

GENERAL OBSERVATIONS

METAL MATRIX

contiuxous

Smooth,

LoW diamond denrsity at tip

layered, natural, 100 pxm

Smooth, continuouis

Diamond chips missing in areas

Large, faceted, single

Pitteod, nodular,

ag

areas devoid of

3L; 00f000fX -m~~~~~~~~~~~pe vaiblt in diaCobra medium

Cobra 11 medium

Mediuxm, less faceted than other diamonds, single layer, natural

Nodular,

Smaller grit, less faceted ds, sin than other dia

Sm ooth, contintous

Tip de l diamonds vnly dietribUted

Smooth,

Tip and body densely

discontinuous

areas devoid of diamonds, tip densely covered

gle layer, naturai NB Nova (Onathos)

medium

Faceted, synthetic, 100 pam

Large sample variability in density, large

continuous

covered,

some areas

devoid of diamonds

Monoteryl coarse

Large, multifcted

oua,oel

6,it ~pittd

Monosteryl medium

Medium, multifaceted, single layer/multilayered, natural

Neo coarse

Neo medium

Multifaceted, mnultilayered,

Pitted, nodular

Mn

imnspo

meAl, boles

her

dia-

Irregular distribution of diamonds with over-

laying diamonds, tip densely covered

natral, 150 to 160 p.m

contious

Smooth,

Even appearance, unifor distribution

Mulltifaceted, single layer,

Smooth, continuous

Diamonds at tip smoother, less dense and less faceted than

natural, 90 to 120 p.m

those in other burs

Patriot coarse

Patriot medium

Faceted, natural, variable

Smooth,

nu|imber 14 to 17of layers, pm

Densely plated but

continuous

with variability, man somne missdiamonSV ::ds

Smooth,

Denlsely plated but with some variability, some diamonds missing from the suxrface

Faceted, natural, vrariable

nulmber of layers, 105 to 125 p.m

Premler

Black

diamonds, mnulti-

Two Strlper coarse

faceted, multilayered, natural, 120 pxVi

S.S. White medium

Small, faceted, multilayered, natural, 88 to 105 pAM

$pring coarse

Round, smooth, minimal faceting, single layer, uniform siZe, natural, 120 p.m

constinuousfi

coated over allI |Unlusual| Denrsely suraes, but distribuappearance, n t of

diamon in

Smooth,

Densely coated over all

continuous

surfaces

Smooth,

Densely andauniforly

continuous

coated0 ove faces and tip, chips missing in_1 a some areas

JADA, Vol. 127, June 1996 769

-CLINICAL PBACIIC[

as the type of dental hard tissue, tooth vitality, restorative

material used and the degree of tooth calcification. Nevertheless, reports in the literature as well as the results of the small pretrial (described above) indicate that a handpiece load of 147.5 g-that is, 91.5 g at the bur tip-is close to the norm for

most clinicians.20,22

The revised ANSI/ADA specification no. 2336 discusses bur size but does not address cutting efficiency, since two independent groups that developed testing regimens obtained such scattered results that they could not be analyzed statistically. Published data on the cut-

ting efficiency of conventional and burs are sparse," even fewer data are available for disposable (single-patientuse) burs.293' Cutting efficiency data are conflicting, possibly because many studies were performed 30 to 40 years ago8'24'37 with larger-diameter burs39 and before ultra-high-speed handpieces were widely available.40 Standardized testing regimens are difficult to achieve and, despite following the same protocol, two laboratories can produce very different results.18 Furthermore, researchers have reported wide variability in both diamond and carbide burs from different manufacturers as well as between burs from the same man4,82426-2837,38

ufacturer.8'23'27'28'4'

The testing regimen used in this study met two important requirements: a reproducible and simple test method and good control of operating variables. The authors simulated the clinical situation by moving the handpiece toward the substrate, unlike most earlier studies in which the substrate was moved toward the handpiece, which is the procedure used in industrial cutting situations. Cutting was done under a controlled rate of water spray, and the load on the handpiece, which simulated that in clinical practice, was always placed in the same location. The position of the bur was constant for each run-that is, parallel to the substrate and pulled perpendicularly down onto it, simulating clinical practice. The substrate was leveled before each run and cut for a length of 4 mm. Using an electronic balance, the authors measured the amount of substrate removed in each cutting run to 0.0001 g. 22

Figure 2. Top: Scanning electron micrograph (original magnification X35) of the diamond bur before the cutting test. Bottom: Scanning electron micrograph (original magnification X35) of the diamond bur after the cutting test.

770 JADA, Vol. 127, June 1996

±

CLINICAL POACIICE-

Since handpiece reliability and consistency of operation are significant factors in cutting studies18 (Larry Watanabe, University of California, San Francisco, Product Evaluation Laboratory, School of Dentistry, oral communication, Feb. 3, 1995), the authors used the same handpiece throughout and ensured consistent operation by following the recommended lubrication regimen. Air pressure was controlled to 33 psi within the handpiece regardless of the driving air pressure, thus eliminating the need for external measurement or control of rotational speed. Substrate selection is central to any cutting study, and the lack of a suitable substrate for dental studies has hindered the development of improved burs.20 Ideally, dental cutting studies should be performed on enamel,37'42 but a large single mass of enamel is relatively unavailable. In addition, enamel has numerous and well-established inconsistencies in physical properties and morphology that would introduce uncontrolled variables into a research protocol. Glass ceramics have been used in many studies27-29'32 to take advantage of their consistent density, absence of porosity and ready availability; for these reasons, the authors used a glass-ceramic substrate in this

study. Many dentists select coarsegrit diamonds for gross tooth reduction based on the assumption of greater efficiency. However, these study results showed no significant differences in the cutting efficiencies of coarseand medium-grit burs made by the same manufacturer and little difference between burs from different manufacturers.

As Grajower and co-workers reported, the relationship between cutting efficiency and bur surface rugosity is complex.37 Despite differences in bur surface characteristics, such as shape and faceting of the diamond chips; diamond surface coverage; and uniformity of the metal matrix, differences in cutting efficiency could not be related to bur rugosity. However, there did appear to be a correlation between the degree of diamond faceting and cutting efficiency, with highly faceted chips providing better cutting

I

Substrate selection is cental to any cutting study, and the lack of a

suitable

substrate

for dental studies has hindered the development of improved burs. characteristics and rounded chips performing relatively poorly. Microscopic observations suggest that debris accumulation may be more detrimental to cutting efficiency than are wear and diamond chip loss from the bur surface. Thus, predictions of cutting efficiency cannot be based solely, or even predominantly, on appearance or visual assessment8'27'28'31 although such claims have been made.9 Tungsten carbide burs are used for various operative procedures, but the data from this study indicate that their greater efficiency compared with that of a diamond bur lasts for only 2 to 21/2 minutes, which confirms the work of others, although the substrate can mark-

edly influence durability.434" A diamond bur performs better when extended enamel preparation is needed, but given the propensity of the bur to clog, dentinal smoothing and caries removal might be done more efficiently with the tungsten carbide bur. Infection control is an important factor in any dental procedure, including restorative dentistry. Although several reports indicate that conventional diamond instruments can withstand sterilization procedures without damage or significant decrease in cutting effectiveness,32 33'45 there are advantages to the disposable bur-most importantly, low cost and the absolute prevention of cross-contamination. Furthermore, with disposable burs, the dentist has a sharp, new cutting instrument for each patient. This is in accord with Steegmayer's28 recommendation that burs be changed at shorter intervals, and new preparations be started with new and sharper burs. CONCLUSION

This study involved a reproducible test regimen to evaluate the cutting efficiency of dental burs. The results showed no differences in cutting efficiency between medium-grit conventional and disposable diamond burs. Two disposable coarse-grit burs differed significantly from conventional coarse-grit burs, with one cutting more efficiently and one cutting less efficiently; however, these differences are possibly the result of differing diamond morphology. No statistically significant differences were found in the cutting efficiencies of coarseand medium-grit burs from the same manufacturer, although JADA, Vol. 127, June 1996 771

~C1INICA1 PRACTICEthe authors did note some statistically significant differences in cutting efficiency between disposable diamond burs made by different manufacturers. Microscopic examination indicated that all diamond burs displayed some degree of clogging after as little as one minute of cutting. The clogging did not appear to differ in degree or appearance after cutting for one or five minutes. . 1. Centers for Disease Control and Prevention. Recommended infection-control practices for dentistry. MMWR 1993;42:3-12. 2. Council on Dental Materials, Instruments, and Equipment, Council on Dental Practice, Council on Dental Therapeutics. Infection control recommendations for the dental office and the dental laboratory. JADA 1988;116(2):241-8. 3. Council on Dental Materials, Instruments, and Equipment, Council on Dental Therapeutics, Council on Dental Research, Council on Dental Practice. Infection control recommendations for the dental office and the dental laboratory. JADA

1992;123(8)(Supplement):1-8. 4. Walsh JP, Symmons HF. A comparison of the heat production and mechanical efficiency of diamond instruments, stones, and burs at 3,000 and 60,000 rpm. N Z Dent J 1949;45 (219):28-32. 5. Peyton FA, Henry EE. Problems of cavity preparation with modern instruments. N Y Dent J 1952;22:147-57. 6. Ingraham R, Tanner HM. The

adaptation of modern instruments and increased operating

Dr. Siegel Is an assistant professor, Department of Restorative Dentistry, School of Dentistry, University * of Maryland at

Baltimore, 666 W. Baltimore St.,

Baftilmore, Md. 21201. Address reprint requests to Dr. Siegel.

*

Dr. von Fraunhofer is a professor and director of Blomaterials Science, School of

Dentistry, University of Maryland at Baltimore.

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