Preventive Dentistry

An in vitro evaluation of electric

B. S. Khambay*/A. D. Walmsley^*

Fotir cotnmercially avaiiable electric toothbrushes (Sonieare, Braun Electric , 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-a- Dent) 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 The early designs of electric toothbrushes generated a transverse {side-to-side) movement, and this motion Electric toothbrushes have become established as an is stih prominent in those presently avaiiable. Other effective alternative to manual methods of tooth- variations include rotation of small individual tufts and brushing. The mode of action of these brushes is a rotary longitudinal movement of the brush head. designed to simulate manual methods and as such is Reports on the effectiveness of a toothbrush with a attractive to the population as an easy and simple rotational movement suggest that it may be superior in method of brushing teeth. The use of electric tooth- removing interdental plaque in vivo,"'^ with differ- brushes has a particular advantage in controlling ences in efficiency between different designs and plaque accumulation in patients with low compliance manufacturers of eleetric toothbrush.'- Such differ- to dental treatment.' Some reports have indicated that ences may be related to the operating characteristics of electric toothbrushes are superior to manual ones in these brushes. terms of removing plaque and improving gingival The mechanism of electric toothbrushes may be health.^-^ Other longitudinal and randomized control superior to that of conventional toothbrushing, per- clinical studies, however, have not conclusively proved haps because of a superior scrubbing action resulting any differences in the efficacy of plaque removal from rapid vibration of tbe brusb bead. It is possible to between manual and electric toothbrushing.''"' One speculate that the vibratory action of the electric area in which electric toothbrushes are considered to toothbrush will move fiuid between the teeth and into be inferior to manual brushing is in their ability to the gingival crevice, thus dislodging and possibly remove plaque from the interproximai and Iinguai disrupting plaque colonies. Research has shown that tooth surfaces.^''" plaque bacteria may be affected by sonic energy'' as a possible result of both cavitation and acoustic micro- ' Research Associaie, University of Birmingham. School of Denlislrv. streaming forces. It is unliliely that cavitation is the Birmingham. England. predominant mechanism for disrupting the plaque, ** Senior Lecturer in Restorative Dentistry. University of Birmingham, however, because the low-powered battery-operated School of Dentistry, Birmingham, England. devices do not generate enough energy to produce Reprint reqjcsts: Dr A. D. Walitisley, Senior Lecturer in Restorative transient cavitation; if it does occur, cavitation will be Dentistry, University of Birmingham. School of Dentistry, St. Chad's Queensway. Birmingham B4 6NN, Engiand. 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 Head design/bristle arrangement

Sonicare Large rectangular brush head Plastic guard around the head Alternating arrangement of long and short bristles Braun Small circular brush head BrisUes arranged in a concentric pattern, with an outer, middle, and irmer row Outer bristles larger than inner bristles Interpiak Large head with 10 separate tufts Bristles tapered within each tuft Blend-a-Dent Medium-sized rectangular brush head Bristles arranged longitudinally Longer bristles to the outer sides ofthe brush and shorter ones toward the center

A physical phenomenon more likely to be encoun- those toothbrushes; and the effectiveness of such tered is acoustic microstreaming, and electric tooth- devices on the removal of a "food debris" medium. brushes may utilize such forces during use. The Sonicare brush works at a higher sonic than Method and materials do others (ie, 250 Hz) and may accordingly produce more effective streaming forces. Such a toothbrash has Observations of brush head movement shown to be safe to use in the mouth, and it has been Four electric toothbrushes were selected for this suggested that its plaque-removal abilities are superior investigation (Fig 1): Sonicare (Optiva), Braun Elec- to those of manual brushing. "^ " There is evidence that tric Toothbrush, Interpiak (Bausch & Lomb), and the Sonicare generates fluid activity in vitro that assists Blend-a-Dent (Procter & Gamble). The arrangement in removal of both plaque'** and stain.'^ It is likely, how- of the bristles on each toothbrush head was different ever, that all devices produce acoustic microstreaming, (Table 1 ). and it is of value to determine whether or not acoustic The action of the toothbrushes was investigated streaming is effective. using a camera attached to a Videorecorder. The The aim of this study was to determine the operating movement of all four toothbrushes was measured at characteristics of four different commercially available xlO magnification. The toothbrush was clamped and electric toothbrushes; the physical forces generated by switched on, and a stroboscope was shined onto the

842 Quintessence International Volume 26, Number 12/1995 Preventive Dentistry vibrating head. The frequency of the strobe was the paper. This cut paper was weighed and then increased until it approached the frequency of the calibrated against the weight of a known area of paper \ibrating brush head, which had the effect of slowing (1 cm'). This test was repeated five titnes for each down the vibratory motion. The displacement ofthe electric toothbrush. head was observed, and the motion was measured with The contribution of streaming to plaque removal a standard calibrated slide placed adjacent to the was assessed by repeating the procedure but immersing vibrating head. The displacement amplitude of the the microscopic slide in water. The toothbrush was head was taken as half the peak-to-peak displacement fully immersed and positioned so that the bristles were ofthe vibrating brush.™ The translation ofthe rotatory I mm above the slide. The brush was operated for 10 motion ofthe Interplak and Braun was measured. The seconds and then removed to allow measurement of frequency of the strobe was gradually increased until the area of food debris removal. the brush appeared stationar>', and the strobe fre- quency was recorded. The load required to stop motion ofthe vibratory Results toothbrushes was measured by pressing the working instrument against a pan balance. The applied load was Basic moveinents increased until the brush movement was stopped and observed with the camera. The Sonicare brush exhibited a side-to-side motion with a rolling side-to side motion ofthe head. This Battery discharge time motion was greatest at the tip of the head and least toward the pari nearest to the handle (Fig 2a). The The fully charged instruments were worked con- Braun brush had a rotatory movement of the entire tinuously in air, and the time taken for the battery to head, alternating between clockwise and counter- completely discharge was recorded. clockwise, resulting in a quarier turn in each direction (Fig 2b). The head ofthe Interplak brush remained Acoustic microstreaining stationary while the bristies rotated about their long axis. The Interplak had an intricate internal mechan- Because it was the primary purpose of the study to ism to rotate all bristles in either a clockwise or measure streaming ftelds around each working tooth- counterclockwise action (Fig 2c}. The bristles tended brush in an open field, presence of acoustic micro- to separate during the rotary movement. The Blend-a- streaming fluids was measured and recorded with the Dent toothbrush exhibited a rolling action of the zoom camera and video system at ¡< 10 magnification, whole head, which was a combination of a transverse A Petri dish was filled with water, and zinc stéarate motion with some longitudinal movement (Fig 2d). particles were placed on the surface. The toothbrush was held in an adjustable clamp and positioned so that Three of the brush heads (Braun. Interplak, and the bristles were immersed approximately 1 mm into Blend-a-Dent) were unaffected by loads of up to 2 kg. the water. The toothbrush was activated, and the Loads of approximately 50 g applied to the Sonicare motion of the particles was recorded on videotape. resulted in the vibrating head's touching the associated guard, preventing ñirther oscillation ofthe brush. The frequency, displacement amplitude, and battery Removal of particulate tnatter life ofthe four toothbrashes are shown in Table 2. The Soft cheese (Cuisine foodservice) was applied to a Sonicarc operated at the highest frequency, measured microscopic slide in an even thickness of 1 mm. This at 260 Hz; the other three brushes worked at lower thickness was obtained by placing two stops on either , between 40 and 70 Hz. The displacement side of the slide and removing excess cheese by amplitude measuremetits revealed that the Sonicare drawing a further slide across the top surface of the and Blend-a-Dent brushes had large lateral movements stops. The prepared slide was positioned on a pan of both brush head and bristles and that the Blcnd-a- balance, and an electric toothbrush v^as allowed to Dent had a longitudinal movement. The rotary move- contact the surface ofthe slide under a load of 30 g. No ment ofthe Braun was less than that ofthe Interplak, water or dentifrice was used. but the bristles moved a greater distance. The bat:tery The brush was operated for 10 seconds and then life ofthe Braun was the greatest. removed. The area of cheese removed was measured by outlining the area on graph paper and then cutting out

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

Fig 2c Individuai rotary motion ot the individuai tufts ot Fig 2d Rolling action of the head of the Blend-a-Dent bristles of the Interplak toolhbrush, toothbrush

Table 2 Operating characteristics ofthe four electric toothbrushes used in the study

Electric Frequency Displacement Battery life toothbrush (Hz) amplitude (mm) Movement (min)

Sonicare 260 2,0 Transverse 45

Braun 50 1,5 30° Rotation 80

Interplak 70 0.5 • 90° Rotation 35

Blend-a-Dent 40 2.0 Transverse 40 1,0 Longitudinal

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Fig 3a Aeration of the water, producing bubbles around Fig 3b Streaming produced around bristles Al this the bristles. magnilioation, it is only possible to see Ihe larger vortices.

Acoustic microstreaming ing produced a greater area of removal than did the Cavitation bubbles were produced by simple aeration mechanical action of the brush head (Fig 5). All ofthe water by movement ofthe brush head ir! and out toothbrushes except the Interplak resulted in greater of the water. This phenomenon occurred around all removal of food debris when operated in water. The four brushes (Fig 3a). Acoustic microstreaming was largest area of removal was achieved with both the observed around the bristles of all brushes (Fig 3b). Sonicare and the Biend-a-Dent toothbrushes. There The streaming was most intense around the longest was no statistically significant difference between the groups of bristles and toward the tip ofthe brush head, areas removed by the Sonicare and Blend-a-Dent or where the displacement ofthe head was greatest. All the Sonicare and Braun brushes (analysis of variance). brushes produced acoustic microstreaming in which The Blend-a-Dent removed a significantly greater area simple bubble formation was caused by agitation ofthe due to streaming forces than did the Braun (analysis of water with the moving head. variance; P< .017).

Removal of parttcutate matter Discussion The areas of food debris removal by the ditferent Flectric toothbrushes have been sought as an alterna- electric toothbrushes are shown in Figs 4a to 4d. The tive to traditional manual brushing. To be of practical Sonicare removed the most matter around the long use at home, electric toothbrushes must be battery bristles and toward the tip of the head. The Braun driven or driven through a shaver socket. The main removed an outer ring, but food debris remained in the movement of electric toothbrushes has been a side-to- center. Both removal patterns were enhanced when the side motion that will move up and down the long axis brush head was immersed in water, and the streaming of the tooth. The brushes investigated showed two forces contributed to the removal. The Interplak types of movement, lateral motion (Sonicare and removed food debris by the mechanical action of the Blend-a-Dent) and rotary movement (Braun and bristles. Although streaming was present, it was not Interplak). The brush displacement during operation powerful enough to remove the material. Blend-a- of both the Sonicare and Blend-a-Dent toothbrushes Dcnt's pattern of removal was characterized by two was of similar magnitude, but the latter exhibited distinct lines corresponding to the longer bristles on additional longitudinal movement simulating the the head. Removal was enhanced by streaming forces modified Bass technique. The rotary movement ofthe when the brush was immersed in the water. Braun and Interplak brushes was designed around Differences were observed in the patterns of mechan- either a small compact head (Braun) or small individual icai removal and streatning removal. GeneraUy, stream- bristles (Interplak).

Quintessence International Volume 26 Number 12/1995 845 Preventive Dentistry

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.

846 Quintessence International Voiume 26, Number 12/1995 Preventive Dentistry

One toothbrush, the Sonicare, had a greater fre- 4 quency than did the other three brush mechanisms. However, its effectiveness was reduced because any 1 force placed on the head immediately brought it into Î ' 1 contact with the protective guard (see Fig 1 ), and ihis 'S quickly stopped the brush from working. The other three brushes were unaffected by loading up to 2 kg. remo i

Advancements in the design of electric toothbiushes o "1 I ta 1 1 have centered on two areas: first, the use of rotary head m -JL movement, which is claimed to increase interdental < 1 1 r cleaning"'- and, second, an increase in the frequency II 1 ofthe brush vibration.'*'" The latter may have other Son care Braun Interpiak Blend-a-Dent advantages, in that cavitation and increased streaming forces may be produced. Destructive forms of cavita- Fig. 5 Etticiency ot tood debris removai by different tion have not been found with electric toothbrushes, eiectric toothbrushes. Mechanicai removai (MR); streaming removai (SR). (Error bars - 1 SD, n - 5.) 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. Only three ofthe brushes removed the food debris Acoustic micro streaming was observed around all by the streaming forces generated by the bristles. There the brushes kivestigated. The design ofthe brushes and were diff'erences in this removai pattern. The Sonicare the stiffness of the bristle determined how effective and Braun brushes showed no statistically significant such brushes are at producing streaming. For instance, differences in the removal of the food debris when the Sonicare produced the most streaming around the operated in a wet environment. The Blend-a-Dent longer bristles, which were in greater contact with the removed significantly greater plaque than did the water. Any change in the design ofthe Sonicare head Braun but not significantly more than did the Sonicare. that would incorporate stiffer bristles and a more The Interpiak did not produce streaming of sufficient uniform head may increase cleaning. This merits strength to remove the food debris. This may be due to further research. The rolling action of the Blend-a- the small bristles, which did not produce a large Dent produced a good action within the water and streaming field. The other brushes involved large swept the water before itself. Further research is movement ofthe brush head. needed to determine whether the arrangement of the It is possible to rank the electric toothbrushes, on bristles influences its efficiency. The circular action of the strength of this study, as follows: Blend-a-Dent > the Braun head produced good streaming fields, but Sonicare > Braun » Interpiak. However, this assess- this tended to be most effective with the outer ment may not necessarily reflect the in vivo situation. arrangement of bristles; inner bristles produced negli- Previous in vitro work has shown that the Sonicare is gible circular movement. The least effective producer able to remove plaque bacteria from model dental of streaming was the Interpiak, and this may be related surfaces through streaming forces. '* Such removal was to the spaced arrangement ofthe bristles together with found to occur up to 4 mm beyond the reach of the the small size of the tufts. bristles. Further work is merited on the use of such The brush head has two actions: the abrasive action forces to remove plaque from tooth surfaces. of the bristles and streaming forces produced in the When an electric toothbrush operates in the fiuid liquid. To evaluate the effect of streaming it was environment, it works with a dentifrice and a small necessary to develop a model system that would assess amount of saliva. Therefore, the effects of streaming the relative contributions of both forces. In this study, a may not be as dramatic as seen in the model system model system was developed to simulate food debris, described, and the area removed will probably be closer and the system chosen involved the removal of cream to that achieved with the brushes operated in the dry cheese from a clean glass surface. The mechanical environment. It is possible that the effect of streaming removal pattern on the slide closely mirrored the in clinicai use is secondary to the mechanical action of vibratory motion. the bristles on the plaque, and the latter is the more

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important mechanism. However, the results of this s, Crawford AN. McAllan LH, Murray JJ, Brook AH. Oral instruction and motivation m children using manual and eleetric study suggested that there is merit in further research toothbrushes. Comniunity Dent Oral Epidemiol I97S;3:257-26I. into the subject of electric toothbrushes and their 6. Walsh TF Glenwright HD. Relative effectiveness of rotary and ability to move fluid around the bristles and brush convenlionai toothbrush in plaque removal. Community Dent Oral head. Epidemiol 1984;12:t60-l64. The vibratory action of the brushes investigated 7. Niemi M-L, Ainamo J, Etemadzadeh H, Gingival abrasion and plaque removal with manual versus electrical tooth brushing. J Clin produced sitnple aeration of the water. Acoustic Periodontol 1986:13:709-713. microstreaming was generated by all the toothbrushes. a Walsb M, Heckman B, Leggott P, Armitage G, Robertson PB. An in vitro system detnonstrated that, on a simple Comparison of manual and power toothbrushing, with and without ranking scale, the Blend-a-Dent was the most effective adjurctive oral irrigation, for controlling plaque and gingivitis. JClin Periodontol 1989:16:419-427. electric toothbrush. The increased driving frequency of 9. Preber H, Ylipáá V, Bergström J, Rydén H. A comparative study of the Sonicare provided no significant advantages over plaque removing efficiency using rotary electric and manual tooth- the other three brushes. brushes. Swed Dent J 1991;l5:229-234 This project has provided a basic understanding of 10. Bergenholtz A, Custafsson LB, Segeriund N, Hagnerg C, Nygaard Ostby P. The role of brushing technique and toothbrush design in the working mechanisms ofthe electric toothbrush and plaque removal. Scand J Dent Res I984;92:344-351. the possible cotitributions of cavitation and streaming 11. Van der Weijden GA, Datiser MM, Nijboer A, Timmerman MF, Van to their effectiveness. Further work is required to der Velden U, The plaque-removing efTicacy of an oscillating/ determine whether changes in the brush head design rotating toothbrush. J Clin Periodontol 1993:20:273-278. will improve the efficacy ofthe vibrating brush head. 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 Acknowledgments adherence of Aeinomyees viscosus after exposure to low-freqtiency acoustic energy. Oral Microbiol Immunol I992;7:l7t-176. Ttie auttiors would like lo thank Procter & Gamble fur Iheir ijpport tn 14. Plynn HG, tn: Mason WP (ed). Physical Acoustics. New York: ttiis projecl. Academic Press, t964:tB:57-]72. 15. Nyborg WL, Physical mechanisms for Biological Effects of Ultra- sound. US Dept of Health, Education and Welfare, Food and Drug Administration, pubhcation 78-8062. Government Printing Office, Í977. References 16. Engel D. Nessly M, Monon T, Manin R. Safety testing of a new t, Hellstadiii5 K, Asman B, Guslafsson A, tmproved maintenance of electric toothbrush. J Periodontol 1993;64,941-946. plaque control by electrical toolh brusliing in periodontitis palienls 17. Johnson BD, Mclnnes C. Clinical evaluation ofthe efficacy and wiUi low compliance, J Clin Periodontol 1993;20:235-237, safety of a new sonic toothbrush. J Periodontol 1994:65:692-697. 2. GlavindL, ZuenerE. Theeflêctivenessofarolary ctcclnclootlibmsh 18. Wu-Yuan CD. Anderson RD, Mctnnes C, Ability ofthe Sonicare on oral deantiness in adults. J Clin Periodonlot 1986; 13:135-138, electronic toothbrush to generate dynamic fluid activity that retnoves 3. KitloyWJ, Love JW, Love J.FediPF. Tira DE. Ttie effectiveness of a bacteria, J Chn Dent t994:5:liS-93. counler-rotary action powered toothbrush and conven!ional tooth- 19. Mctnnes C, Johnson B, Emting RC, Yankell SL. Clinical and bnisti on plaque removal and gingival bleeduig. A short-term sludy. J computer-assisted evaluations of tbe stain removal ability of ttie Pertodontol 1989:60:473-477. Sonieareelectronic toothbrush. JClin Dent 1994:5:13-18. 4. McKendrick AJW, Barbenel LMH, Mctiugh WD. A two-year 20. Walmsley AD, Laird WRE, Williams AR, Displacement amplitude comparison of hand and electric toothbrushes. J Periodont Res as a measure ofthe acoustic output of ultrasonic sealers. Dent Mater 1968:3:224-231. 1986^2:97-100, Q

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