General Dentistry

A robot system for evaluating plaque removal efficiency oftoothbrushes in vitro

C,-P. Wi!lershausen*/G. P, Hilfinger"''

Abstract A robot system simtilaiing ¡hive-dinieiisionai brushing motions as a function oftime has been developed. In association with a typodoni and either artificialplac/ueor chmtnogeiiic stain, the robo! sysiem can be used to assess the plaque removalefficiency or tite cleaning effectiveness of toothbrushes. In pariiiular. the influenceofdifterenl brush head designs of powered toothbrushes was exatuiiied. The studycompared the plaque removal ejßciency of a cup-shaped brush head ( Brauii Oral-BEB 5> and a modified brush head (Braun Oral-B EB 9) ihal incorporates longerfilaments on the ouier ring, designed for addiiional inienlenlal penetration. Aspecially designed ariificial plaque was applied ¡o Ihe ptasiic teeth oftypodonts.Artificial teeih were cleaned by ihe robot system for a 2-tiilnule period »ith a we!brush head whhout a dentifrice. The remaining plaque was as.'iessed visually by twoindependent examiners, with a modification of tiie giobai Fiaque Index. Incomparison to the EB 5. Ihe new brush head significanlly reduced artificial plaqueoverall. In vliro data demonstrated the abilily of tite ivbol svsiem to revealreproducible significant differences ofthe cleaning effectiveness of poweredtoothbrushes. (Quintessence Int ¡997:28:441-445.)

Clinical relevance

The brushing robot is an efTeclive tool for evüluatingpowered toothbrushes and could become an appro-priate method for preclinical evaluations. Datademonstrated that the plaque removal capability ofthe newly designed EB 9 brush head was signif-icantly higher than that of the EB 5.

Introduction

In recent years, powered toothbrushes have beendeveloped in a number of ways to improve Iheirefficacy with respect lo the removal of plaque.'Developments have included modifications in brushhead design as well as changes in the speed and angle

* Depanmem of Operative DeiHistij. U.iiversily of Miiinz, Main;,Germany.

" Braun AC, Kronberg, Cermany.Reptini requests: Dr C. P. Ern«. Depanmenl of Operauve Denlislry.UniversjlyofMainz, Ajgjstplalz :, 55U] Main;, Germany. Fax: 4? 6131 17J406.

of motion ofthe brush head.'"'' To assess the success ofthese various developments, it is necessary to carry outboth laboratory and clinical studies.^*' However, mostclinical studies are carried out only for a short-termperiod. Because ofthe novelty effect that occurs whensubjects use new powered toothbrushes, it is difficultto assess the results of these studies objectively.''̂Furthermore, because ofa lack of volunteers represent-ing average oral hygiene for long-term clinical studies,most often researchers have lo rely on participantswho are involved in dentistry and oral care, such asdental students or dental nurses.''•'*""' These groupsmostly show optimal oral care and oral hygiene.Because of a strong correlation of oral hygiene tosocioeconomic characteristics," they are not re-presentative ofthe average patient.

Further problems appear with individual variationsin jaw and tooth formation, diiierent restorativetreatments, and age. All of these factors result indifferences in interproximal spaces and the amountand the character ofthe plaque,'' Laboratory studies ofplaî ue and stain removal can be carried out rapidly butmay not necessarily give an accurate representation ofthe clinical situation.'-"'^

441

Ernst et al

Fig 1 Robot system Fig 2 Typodont before brushing

Until now; pilot clinical studies have remained aprimary requirement for the evaluation of a change inplaque-removing potential. To enable a more rapidassessment of plaque removal, the objective of thisstudy was to develop a robot system that simulates theaverage clinical use of a toothbrush. In addition, aspecially designed new brush head with a number oflonger outer filaments was to be compared to theconventional brush head, when used in an establishedoscillating/rotating driving system.

Method and materials

Roho! system

A six-axis industrial robot (Asea Brown Boveri),originally developed for industria! spot welding, hasbeen modified to simulate normal clinical use with apowered toothbrush (Fig I ). The brushing motion Inspace and time is computer controlled. In addition, thesystem allows the standardization of brushing forces inwell-defined ranges.

Toot/i model and arlißcial plaqite

Artificia! teeth of maxillaty and mandibular typodonts(Frasaco, Tettnang) were sandblasted for 20 mintiteswith aluminum oxide powder of 50 |im diameter andcovered with an artificial plaque solution in a standardprocedure. The solution (Waco Fin, Heinrieh Wagner)was applied with a paintbrush in a standardizedmanner over a 2-minute time period ( Fig 2 ). In severalpretrials. the adherence of the artificial plaque was

found to be similar to the adherence of true intraoralplaque to natural teeth.'*" The color blue was chosenfor ihe artificial plaque to provide optimal contrastbetween the artificial teeth and the artificial gingiva.Following a 6-minute drj'ing period for the artificialplaque, the typodonts were tnounted on the robotsystem.

Clean i tig procedure

The teeth were cleaned by the robot for 2 minutes ( 1minute maxillary and 1 minute mandibular typodont)using a startdardized wet brush head without a dentifrice(Fig 3). The omission of a dentifrice was to avoid anyremoval activity related to the dentifrice. This methodhas been previously assessed for standardization andreproducibility.'" In this test, the pressure applied bythe robot system was adjusted to 1.8 ± 0.2.'-''

Testing procédure

Two different brush heads (EB 5 and EB 9). designedfor the Braun Oral-B Plaque Remover (D7. oscillatingangle 70 degrees, frequency 47 Hz), were tested in acrossover study design for a total of six tests per brushhead. A new brush head was used for each test.

The EB 5 brush head is a commercially availablebrush head of the D7 with a diameter of 13 mm. Thebristles are arranged in a cup-shaped configurationwith a longer (length: 7.8 ± 0.1 tnm} circular ring ofouter bristles 0. IS mm in diameter and two inner ritigsof shorter (length: 7.1+0.1 mm) bristles 0.13 mm indiameter. The EB 9 is the commercially available brushhead of the Braun Oral-B Ultra Plaque Remover D9.

442 Quintessence International Volume 28, Number 7/1997

Ernst et al

Fig 3 Typodonl after brushing. Fig 4 Braun Oral-B Plaque Remover (D7] wilh ihe EB5iletll and EB9 (right) brush heads.

Table ! Percentage of plaque removed after use of the EB 5 and the EB 9 brush head (mean ± SD)

Brush head/system

EB 5/D7EB 9/D7

All

68.85,

surfaces

1 ±6 .28 ±5 ,6

Plaque removal (% )

Buecal

69,5 ± 6 . 582.7 ±6 .1

Lingual

66,2 ± 12,987,2 ± 8,2

Occlusal

69.1 ±88,3 ±

: 10.5: 4,4

The brush head shows a different filament design withthree tufts of longer bristles (length: 8,2 ±0,1 mm} inthe outer ring designed to improve interdental cleaningand for better penetration of the fissures on theocclusal surfaces. The shorter bristles are 7.5 mm inlength. Bristle diameters of longer and shorter bristlesare 0.15 mm (Fig 4),

Following the 2-minute brushing cycle, the typo-donts were examined for remaining plaque by twoindependent examiners, blinded to the brush headused. This visual index was a modification of the globalPlaque Index.'' in which buecal, lingual, and occlusalsurfaces are assessed. The error of studies examininginterexaminer and intraexaminer reproducibility haveshown to be less than 2% (unpublished data on file,Braun),

Staii.'iiical analysis

Statistical analysis was carried out at the 1% level witha two-sided double /-test. The Kolmogorov test wasused for examination of normal distribution. Inaddition an F test has been applied to check the

condition of similar standard deviations. If the F testshowed significant differences in the standard devia-tion, the modified /test (Welch test) was applied.

Resnits

Both tested brush heads were successfiil in cleaning theartificial tooth surfaces, Tlie newly designed EB 9brush head combined with the D 7 system showed astatistically significant {P < ,01) improvement inplaque removal compared to the EB 5/D7 brush headsystem on all surfaces. The plaque removal values forthe EB 9 and EB 5 brushes were 85,8% ± 5.6% and68.1% ± 6,2%, respectively, measured in comparisonwith the total tooth surfaces. Tlie complete plaquescores are shown in Table 1 and Fig 5,

Discussion

To collect representative data about the efficacy ofpowered toothbrushes within a short lime period, more

Number 7/1997 443

Ernst et al

100-

90

80-

rem

oval

{%

Pla

que

20-

10-

P=,OOM

•TotEll

P=,(W3 P=,O0T

•_•_."H

••Buccal LinùLiol

•1

Q ED5/D7• KB9I DT

Fig 5 Plaque removal of fhe EB5and EB9 brush heads.

and more in vitro tests have been conducted. Mostexaminations concerning toothbmshes and other oralcaredeviceshavebeenearriedout in in vivo studies.•''"•'^because ofa lack of possibility of in vivo simulation inlaboratory' studies,''' ''' For volunteers, getting used toa toothbrush under regular conditions is ver\' dilficultin clinical studies and is only possible over a long timeperiod,-°

The use of a computer-controlled robot systemopens the door to a wide variety of laboratory testsunder clinicai conditions. One ofthe main advantagesof an in vitro robot system is the reprodueibility ofaonce-prog rammed process. Because of a speciallydeveloped teaching program, the robot used in thisstudy is able to perform similar movements applyingwell-defined pressures in the same time period.Cleaning time has a strong influence on the cleaningefficacy of toothbrushes,-'-- Van der Weijden et al*̂found the main cleaning effect of powered tooth-brushes was within the first 2 minutes. Therefore, andin accordance with previous studies.''•-'•'•' a 2-minutebrushing period was considered to be optimal for thetest. Brttshing pressure also has a strong influence oncleaning results,'- In accordance with other in vitroexperiments, the applied pressure used in this test was1,8 ± 0,2,'----'

The proof of statistical significance in a smallsample and the small standard deviations show theability of this robot system to assess the plaque removalcapability of different brush heads even within thesame driving system.

The statistically significantly better removal ofplaque by the EB 9 compared to the EB 5 brttsh headused on the same driving system indicated that thelonger filaments ofthe outer ring enabled improvedpenetration in the fissures on the occlusal surtaces andin the interproximal areas.

References

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Ernst et al

Niomi ML Giiiüiv^il uliríisiiiii :inil pUiqiie removal LiHer loolh-tiru,liji¡y Mitii ;iii cIctiriL- jiid ;i iraiiiuil tnollitinisli, Attii OdmiolSciiHl l''H7:45.,;i.7-, WJ. LnvcJW, S;ifcLimuni JS.TitJ DE. Tlie etfcetiveiiess ol a ci)uiilerrolaticiniil-ni;lii)ii power11101hbmill on pl.iijiie ciinlriil in ortlnxliiiitic pLiliî nLs. Am J OrtlKiilDemoiiit Onliup l^^l ••¡'•¡¡7-14,

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28, Number 7/1997

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