Preventive Dentistry

An in vitro evaluation of electric toothbrushes
B. S. Khambay*/A. D. Walmsley^* Fotir cotnmercially avaiiable electric toothbrushes (Sonieare, Braun Electric Toothbrush, Interplak, and Blend-a-Dent) »ere assessed both for their operating characteristics and their ability to retnove a 'food debris " medium. The Sonieare and Blend-a-Dent have a lateral vibrator)' action, while the Interplak and Braun produce a rotary movement of the brush head. The vibratory action of the Sonieare was susceptible to loading. All devices produced both stable-pulsating cavitation and acoustic tnicrostreaming that was demonstrated in vitro using a suspension of particles in water Their effectiveness in removing a food debris medium was assessed with and without water Three of the brushes (Sonieare, Braun, and Blend-aDent) were simitar in their abllit}- to remove the placjue, and all were superior to the Interplak: its streaming forces removed no food debris. The results indicated that the Blend-a-Dent was the most effective brush design in vitro, although the differences between Blend-a-Dent and Sonieare were not statistically significant. (Quintessence Int 1995:26:841-848.)

Introduction

Electric toothbrushes have become established as an effective alternative to manual methods of toothbrushing. The mode of action of these brushes is designed to simulate manual methods and as such is attractive to the population as an easy and simple method of brushing teeth. The use of electric toothbrushes has a particular advantage in controlling plaque accumulation in patients with low compliance to dental treatment.' Some reports have indicated that electric toothbrushes are superior to manual ones in terms of removing plaque and improving gingival health.^-^ Other longitudinal and randomized control clinical studies, however, have not conclusively proved any differences in the efficacy of plaque removal between manual and electric toothbrushing.''"' One area in which electric toothbrushes are considered to be inferior to manual brushing is in their ability to remove plaque from the interproximai and Iinguai tooth surfaces.^''"
' Research Associaie, University of Birmingham. School of Denlislrv. Birmingham. England. ** Senior Lecturer in Restorative Dentistry. University of Birmingham, School of Dentistry, Birmingham, England. Reprint reqjcsts: Dr A. D. Walitisley, Senior Lecturer in Restorative Dentistry, University of Birmingham. School of Dentistry, St. Chad's Queensway. Birmingham B4 6NN, Engiand.

The early designs of electric toothbrushes generated a transverse {side-to-side) movement, and this motion is stih prominent in those presently avaiiable. Other variations include rotation of small individual tufts and a rotary longitudinal movement of the brush head. Reports on the effectiveness of a toothbrush with a rotational movement suggest that it may be superior in removing interdental plaque in vivo,"'^ with differences in efficiency between different designs and manufacturers of eleetric toothbrush.'- Such differences may be related to the operating characteristics of these brushes. The mechanism of electric toothbrushes may be superior to that of conventional toothbrushing, perhaps because of a superior scrubbing action resulting from rapid vibration of tbe brusb bead. It is possible to speculate that the vibratory action of the electric toothbrush will move fiuid between the teeth and into the gingival crevice, thus dislodging and possibly disrupting plaque colonies. Research has shown that plaque bacteria may be affected by sonic energy'' as a possible result of both cavitation and acoustic microstreaming forces. It is unliliely that cavitation is the predominant mechanism for disrupting the plaque, however, because the low-powered battery-operated devices do not generate enough energy to produce transient cavitation; if it does occur, cavitation will be stabie, resulting in gentle puisation of bubbles.'^''^

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Fig 1 The four brushes used in the study: (clockwise from top) Braun, Biend-a-Dent, interpiak, and Sonicare.

Table 1 Arrangement ofthe bristles on the four electric toothbrushes used in the study Electric toothbrush Sonicare Head design/bristle arrangement Large rectangular brush head Plastic guard around the head Alternating arrangement of long and short bristles Small circular brush head BrisUes arranged in a concentric pattern, with an outer, middle, and irmer row Outer bristles larger than inner bristles Large head with 10 separate tufts Bristles tapered within each tuft Medium-sized rectangular brush head Bristles arranged longitudinally Longer bristles to the outer sides ofthe brush and shorter ones toward the center

Braun

Interpiak Blend-a-Dent

A physical phenomenon more likely to be encountered is acoustic microstreaming, and electric toothbrushes may utilize such forces during use. The Sonicare brush works at a higher sonic frequency than do others (ie, 250 Hz) and may accordingly produce more effective streaming forces. Such a toothbrash has shown to be safe to use in the mouth, and it has been suggested that its plaque-removal abilities are superior to those of manual brushing. " " There is evidence that ^ the Sonicare generates fluid activity in vitro that assists in removal of both plaque'** and stain.'^ It is likely, however, that all devices produce acoustic microstreaming, and it is of value to determine whether or not acoustic streaming is effective. The aim of this study was to determine the operating characteristics of four different commercially available electric toothbrushes; the physical forces generated by
842

those toothbrushes; and the effectiveness of such devices on the removal of a "food debris" medium. Method and materials Observations of brush head movement Four electric toothbrushes were selected for this investigation (Fig 1): Sonicare (Optiva), Braun Electric Toothbrush, Interpiak (Bausch & Lomb), and Blend-a-Dent (Procter & Gamble). The arrangement of the bristles on each toothbrush head was different (Table 1 ). The action of the toothbrushes was investigated using a camera attached to a Videorecorder. The movement of all four toothbrushes was measured at xlO magnification. The toothbrush was clamped and switched on, and a stroboscope was shined onto the

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Preventive Dentistry vibrating head. The frequency of the strobe was increased until it approached the frequency of the \ibrating brush head, which had the effect of slowing down the vibratory motion. The displacement ofthe head was observed, and the motion was measured with a standard calibrated slide placed adjacent to the vibrating head. The displacement amplitude of the head was taken as half the peak-to-peak displacement ofthe vibrating brush.™ The translation ofthe rotatory motion ofthe Interplak and Braun was measured. The frequency of the strobe was gradually increased until the brush appeared stationar>', and the strobe frequency was recorded. The load required to stop motion ofthe vibratory toothbrushes was measured by pressing the working instrument against a pan balance. The applied load was increased until the brush movement was stopped and observed with the camera. Battery discharge time The fully charged instruments were worked continuously in air, and the time taken for the battery to completely discharge was recorded. Acoustic microstreaining Because it was the primary purpose of the study to measure streaming ftelds around each working toothbrush in an open field, presence of acoustic microstreaming fluids was measured and recorded with the zoom camera and video system at ¡ 10 magnification, < A Petri dish was filled with water, and zinc stéarate particles were placed on the surface. The toothbrush was held in an adjustable clamp and positioned so that the bristles were immersed approximately 1 mm into the water. The toothbrush was activated, and the motion of the particles was recorded on videotape. Removal of particulate tnatter Soft cheese (Cuisine foodservice) was applied to a microscopic slide in an even thickness of 1 mm. This thickness was obtained by placing two stops on either side of the slide and removing excess cheese by drawing a further slide across the top surface of the stops. The prepared slide was positioned on a pan balance, and an electric toothbrush v^as allowed to contact the surface ofthe slide under a load of 30 g. No water or dentifrice was used. The brush was operated for 10 seconds and then removed. The area of cheese removed was measured by outlining the area on graph paper and then cutting out the paper. This cut paper was weighed and then calibrated against the weight of a known area of paper (1 cm'). This test was repeated five titnes for each electric toothbrush. The contribution of streaming to plaque removal was assessed by repeating the procedure but immersing the microscopic slide in water. The toothbrush was fully immersed and positioned so that the bristles were I mm above the slide. The brush was operated for 10 seconds and then removed to allow measurement of the area of food debris removal.

Results Basic moveinents The Sonicare brush exhibited a side-to-side motion with a rolling side-to side motion ofthe head. This motion was greatest at the tip of the head and least toward the pari nearest to the handle (Fig 2a). The Braun brush had a rotatory movement of the entire head, alternating between clockwise and counterclockwise, resulting in a quarier turn in each direction (Fig 2b). The head ofthe Interplak brush remained stationary while the bristies rotated about their long axis. The Interplak had an intricate internal mechanism to rotate all bristles in either a clockwise or counterclockwise action (Fig 2c}. The bristles tended to separate during the rotary movement. The Blend-aDent toothbrush exhibited a rolling action of the whole head, which was a combination of a transverse motion with some longitudinal movement (Fig 2d). Three of the brush heads (Braun. Interplak, and Blend-a-Dent) were unaffected by loads of up to 2 kg. Loads of approximately 50 g applied to the Sonicare resulted in the vibrating head's touching the associated guard, preventing ñirther oscillation ofthe brush. The frequency, displacement amplitude, and battery life ofthe four toothbrashes are shown in Table 2. The Sonicarc operated at the highest frequency, measured at 260 Hz; the other three brushes worked at lower frequencies, between 40 and 70 Hz. The displacement amplitude measuremetits revealed that the Sonicare and Blend-a-Dent brushes had large lateral movements of both brush head and bristles and that the Blcnd-aDent had a longitudinal movement. The rotary movement ofthe Braun was less than that ofthe Interplak, but the bristles moved a greater distance. The bat:tery life ofthe Braun was the greatest.

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Fig 2a S¡de-to-side motion (A| oi 1he Sonicare toothbrush, most pronounced at the tip ol the brush head. Side-to-side motion as a rolling motion (B).

Fig 2b

Rotary motion of the Braun toothbrush.

Fig 2c Individuai rotary motion ot the individuai tufts ot bristles of the Interplak toolhbrush,

Fig 2d Rolling action of the head of the Blend-a-Dent toothbrush

Table 2 Operating characteristics ofthe four electric toothbrushes used in the study Electric toothbrush Sonicare Braun Interplak Blend-a-Dent Frequency (Hz) 260 50 70 40 Displacement amplitude (mm) 2,0 1,5
0.5 •

Movement Transverse 30° Rotation 90° Rotation Transverse Longitudinal

Battery life (min) 45 80 35 40

2.0 1,0

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Fig 3a Aeration of the water, producing bubbles around the bristles.

Fig 3b Streaming produced around bristles Al this magnilioation, it is only possible to see Ihe larger vortices.

Acoustic microstreaming Cavitation bubbles were produced by simple aeration ofthe water by movement ofthe brush head ir! and out of the water. This phenomenon occurred around all four brushes (Fig 3a). Acoustic microstreaming was observed around the bristles of all brushes (Fig 3b). The streaming was most intense around the longest groups of bristles and toward the tip ofthe brush head, where the displacement ofthe head was greatest. All brushes produced acoustic microstreaming in which simple bubble formation was caused by agitation ofthe water with the moving head. Removal of parttcutate matter The areas of food debris removal by the ditferent electric toothbrushes are shown in Figs 4a to 4d. The Sonicare removed the most matter around the long bristles and toward the tip of the head. The Braun removed an outer ring, but food debris remained in the center. Both removal patterns were enhanced when the brush head was immersed in water, and the streaming forces contributed to the removal. The Interplak removed food debris by the mechanical action of the bristles. Although streaming was present, it was not powerful enough to remove the material. Blend-aDcnt's pattern of removal was characterized by two distinct lines corresponding to the longer bristles on the head. Removal was enhanced by streaming forces when the brush was immersed in the water. Differences were observed in the patterns of mechanicai removal and streatning removal. GeneraUy, stream-

ing produced a greater area of removal than did the mechanical action of the brush head (Fig 5). All toothbrushes except the Interplak resulted in greater removal of food debris when operated in water. The largest area of removal was achieved with both the Sonicare and the Biend-a-Dent toothbrushes. There was no statistically significant difference between the areas removed by the Sonicare and Blend-a-Dent or the Sonicare and Braun brushes (analysis of variance). The Blend-a-Dent removed a significantly greater area due to streaming forces than did the Braun (analysis of variance; P< .017). Discussion Flectric toothbrushes have been sought as an alternative to traditional manual brushing. To be of practical use at home, electric toothbrushes must be battery driven or driven through a shaver socket. The main movement of electric toothbrushes has been a side-toside motion that will move up and down the long axis of the tooth. The brushes investigated showed two types of movement, lateral motion (Sonicare and Blend-a-Dent) and rotary movement (Braun and Interplak). The brush displacement during operation of both the Sonicare and Blend-a-Dent toothbrushes was of similar magnitude, but the latter exhibited additional longitudinal movement simulating the modified Bass technique. The rotary movement ofthe Braun and Interplak brushes was designed around either a small compact head (Braun) or small individual bristles (Interplak).

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Figs 4a lo 4d Difference in removai patterns produced by eiectric loofhbrushes working in a dry environment (lefl) and when immersed in water (right).

Fig 4a Sonicare.

Fig 4b

Braun.

Fig 4c

Inferplak.

Fig 4d

Blend-a-Dent.

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Preventive Dentistry
One toothbrush, the Sonicare, had a greater frequency than did the other three brush mechanisms. However, its effectiveness was reduced because any force placed on the head immediately brought it into contact with the protective guard (see Fig 1 ), and ihis quickly stopped the brush from working. The other three brushes were unaffected by loading up to 2 kg. Advancements in the design of electric toothbiushes have centered on two areas: first, the use of rotary head movement, which is claimed to increase interdental cleaning"'- and, second, an increase in the frequency ofthe brush vibration.'*'" The latter may have other advantages, in that cavitation and increased streaming forces may be produced. Destructive forms of cavitation have not been found with electric toothbrushes, and the main effect ofthe vibrating brush is to aerate the water. The devices aerated the water as they moved and sucked air into and around the brush, but aeration ceased when the brush was fliily immersed in the water. Acoustic micro streaming was observed around all the brushes kivestigated. The design ofthe brushes and the stiffness of the bristle determined how effective such brushes are at producing streaming. For instance, the Sonicare produced the most streaming around the longer bristles, which were in greater contact with the water. Any change in the design ofthe Sonicare head that would incorporate stiffer bristles and a more uniform head may increase cleaning. This merits further research. The rolling action of the Blend-aDent produced a good action within the water and swept the water before itself. Further research is needed to determine whether the arrangement of the bristles influences its efficiency. The circular action of the Braun head produced good streaming fields, but this tended to be most effective with the outer arrangement of bristles; inner bristles produced negligible circular movement. The least effective producer of streaming was the Interpiak, and this may be related to the spaced arrangement ofthe bristles together with the small size of the tufts. The brush head has two actions: the abrasive action of the bristles and streaming forces produced in the liquid. To evaluate the effect of streaming it was necessary to develop a model system that would assess the relative contributions of both forces. In this study, a model system was developed to simulate food debris, and the system chosen involved the removal of cream cheese from a clean glass surface. The mechanical removal pattern on the slide closely mirrored the vibratory motion.
4

Î '
'S

1
" 1 I

1

remoi o ta 1

1
-JL
1 1

m <

II
Son care

r 1

Braun

Interpiak

Blend-a-Dent

Fig. 5 Etticiency ot tood debris removai by different eiectric toothbrushes. Mechanicai removai (MR); streaming removai (SR). (Error bars - 1 SD, n - 5.)

Only three ofthe brushes removed the food debris by the streaming forces generated by the bristles. There were diff'erences in this removai pattern. The Sonicare and Braun brushes showed no statistically significant differences in the removal of the food debris when operated in a wet environment. The Blend-a-Dent removed significantly greater plaque than did the Braun but not significantly more than did the Sonicare. The Interpiak did not produce streaming of sufficient strength to remove the food debris. This may be due to the small bristles, which did not produce a large streaming field. The other brushes involved large movement ofthe brush head. It is possible to rank the electric toothbrushes, on the strength of this study, as follows: Blend-a-Dent > Sonicare > Braun » Interpiak. However, this assessment may not necessarily reflect the in vivo situation. Previous in vitro work has shown that the Sonicare is able to remove plaque bacteria from model dental surfaces through streaming forces. '* Such removal was found to occur up to 4 mm beyond the reach of the bristles. Further work is merited on the use of such forces to remove plaque from tooth surfaces. When an electric toothbrush operates in the fiuid environment, it works with a dentifrice and a small amount of saliva. Therefore, the effects of streaming may not be as dramatic as seen in the model system described, and the area removed will probably be closer to that achieved with the brushes operated in the dry environment. It is possible that the effect of streaming in clinicai use is secondary to the mechanical action of the bristles on the plaque, and the latter is the more

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Preventive Dentistry important mechanism. However, the results of this study suggested that there is merit in further research into the subject of electric toothbrushes and their ability to move fluid around the bristles and brush head. The vibratory action of the brushes investigated produced sitnple aeration of the water. Acoustic microstreaming was generated by all the toothbrushes. An in vitro system detnonstrated that, on a simple ranking scale, the Blend-a-Dent was the most effective electric toothbrush. The increased driving frequency of the Sonicare provided no significant advantages over the other three brushes. This project has provided a basic understanding of the working mechanisms ofthe electric toothbrush and the possible cotitributions of cavitation and streaming to their effectiveness. Further work is required to determine whether changes in the brush head design will improve the efficacy ofthe vibrating brush head. s, Crawford AN. McAllan LH, Murray JJ, Brook AH. Oral hygiene instruction and motivation m children using manual and eleetric toothbrushes. Comniunity Dent Oral Epidemiol I97S;3:257-26I. 6. Walsh TF Glenwright HD. Relative effectiveness of rotary and convenlionai toothbrush in plaque removal. Community Dent Oral Epidemiol 1984;12:t60-l64. 7. Niemi M-L, Ainamo J, Etemadzadeh H, Gingival abrasion and plaque removal with manual versus electrical tooth brushing. J Clin Periodontol 1986:13:709-713. a Walsb M, Heckman B, Leggott P, Armitage G, Robertson PB. Comparison of manual and power toothbrushing, with and without adjurctive oral irrigation, for controlling plaque and gingivitis. JClin Periodontol 1989:16:419-427. 9. Preber H, Ylipáá V, Bergström J, Rydén H. A comparative study of plaque removing efficiency using rotary electric and manual toothbrushes. Swed Dent J 1991;l5:229-234 10. Bergenholtz A, Custafsson LB, Segeriund N, Hagnerg C, Nygaard Ostby P. The role of brushing technique and toothbrush design in plaque removal. Scand J Dent Res I984;92:344-351. 11. Van der Weijden GA, Datiser MM, Nijboer A, Timmerman MF, Van der Velden U, The plaque-removing efTicacy of an oscillating/ rotating toothbrush. J Clin Periodontol 1993:20:273-278. 12. Van der Weijden GA. Timmerman MF, Nijboer A, Van der Velden U, A eomparative study of electric tootbbriishes for the eRectiveness of plaque removal in relation to tooth brushing duration, J Clin Periodontoi 1993:20:476-481. 13. Mctnnes C, Engel D, Monda BJ, Martin RW. Reduction in adherence of Aeinomyees viscosus after exposure to low-freqtiency acoustic energy. Oral Microbiol Immunol I992;7:l7t-176. 14. Plynn HG, tn: Mason WP (ed). Physical Acoustics. New York: Academic Press, t964:tB:57-]72. 15. Nyborg WL, Physical mechanisms for Biological Effects of Ultrasound. US Dept of Health, Education and Welfare, Food and Drug Administration, pubhcation 78-8062. Government Printing Office, Í977. 16. Engel D. Nessly M, Monon T, Manin R. Safety testing of a new electric toothbrush. J Periodontol 1993;64,941-946. 17. Johnson BD, Mclnnes C. Clinical evaluation ofthe efficacy and safety of a new sonic toothbrush. J Periodontol 1994:65:692-697. 18. Wu-Yuan CD. Anderson RD, Mctnnes C, Ability ofthe Sonicare electronic toothbrush to generate dynamic fluid activity that retnoves bacteria, J Chn Dent t994:5:liS-93. 19. Mctnnes C, Johnson B, Emting RC, Yankell SL. Clinical and computer-assisted evaluations of tbe stain removal ability of ttie Sonieareelectronic toothbrush. JClin Dent 1994:5:13-18. 20. Walmsley AD, Laird WRE, Williams AR, Displacement amplitude as a measure ofthe acoustic output of ultrasonic sealers. Dent Mater 1986^2:97-100, Q

Acknowledgments
Ttie auttiors would like lo thank Procter & Gamble fur Iheir ijpport tn ttiis projecl.

References t, Hellstadiii5 K, Asman B, Guslafsson A, tmproved maintenance of plaque control by electrical toolh brusliing in periodontitis palienls wiUi low compliance, J Clin Periodontol 1993;20:235-237, 2. GlavindL, ZuenerE. Theeflêctivenessofarolary ctcclnclootlibmsh on oral deantiness in adults. J Clin Periodonlot 1986; 13:135-138, 3. KitloyWJ, Love JW, Love J.FediPF. Tira DE. Ttie effectiveness of a counler-rotary action powered toothbrush and conven!ional toothbnisti on plaque removal and gingival bleeduig. A short-term sludy. J Pertodontol 1989:60:473-477. 4. McKendrick AJW, Barbenel LMH, Mctiugh WD. A two-year comparison of hand and electric toothbrushes. J Periodont Res 1968:3:224-231.

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