Esmalte e Dentina Desgaste

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Investigation of erosion andabrasion on enamel and dentine:a model in situ using toothpastesof different abrasivity

S. Hooper1, N. X. West1,

M. J. Pickles2, A. Joiner2,

R. G. Newcombe3 and M. Addy1

1Division of Restorative Dentistry, Dental

School, Bristol, UK; 2Unilever Dental

Research, Bebington, UK; 3Department of

Epidemiology, Statistics and Public Health,

University of Wales College of Medicine,

Cardiff, UK

Hooper S, West NX, Pickles MJ, Joiner A, Newcombe RG, Addy M: Investigation oferosion and abrasion on enamel and dentine: a model in situ using toothpastes ofdifferent abrasivity. J Clin Periodontol 2003; 30: 802808.r Blackwell Munksgaard,2003.

Abstract

Background: Studies in vitro suggest that abrasion and erosion may actsynergistically to produce wear of enamel and dentine. Methods in situ are recentlyavailable to study separately erosion and abrasion of dental tissues. The aim of thisstudy was to combine two in situ protocols to study the interplay between erosion andabrasion of enamel and dentine.

Method: The study was a single-blind, randomised, five-treatment cross-over designinvolving 15 healthy volunteers. During each 10-day study period, subjects wore from0900 to 1700 h an upper removable acrylic appliance holding one polished enamel andone polished dentine specimen. The specimen treatment regimens were:

1. Drinking water and brushing with toothpaste A.

2. Drinking water and brushing with toothpaste B.3. Drinking orange juice.4. Drinking orange juice and brushing with toothpaste A.5. Drinking orange juice and brushing with toothpaste B.

Drinking and brushing times were around 0900, 1100, 1300 and 1500 h. Drinkswere consumed as 250 ml over 10 min and brushing ex vivo for 1 min to eachspecimen. Measurement of tissue loss was made on days 5 and 10 of each period usinga profilometer.

Results: All treatments produced increasing tissue loss over time, which wasconsiderably greater for dentine than enamel. For enamel, the data at days 5 and 10showed a significant effect for erosion (i.e. orange juice was significantly more erosivethan water), but no significant effect for abrasion (i.e. no significant differencebetween the two toothpaste treatments). The combined orange juice and toothpasteeffects were directional for synergy but did not reach significance. For dentine at day

10, many specimens exceeded the 50 mm set limit of the profilometer and only day 5data were considered. There were significant effects for erosion (orange juiceproduced significantly more erosion than water) and for abrasion (paste A wassignificantly more abrasive to dentine than paste B). The synergy effect could not beexamined for dentine due to the truncation effect as the set limit of the profilometerwas exceeded.

Conclusions: Erosion increases the susceptibility of enamel to toothpaste abrasion.Dentine is considerably more susceptible than enamel to erosion and abrasion alone orcombined. Dentine loss appears to correlate with toothpaste abrasivity (RDA value).

Key words: erosion; abrasion; enamel;dentine; tooth wear; clinical trial

Accepted for publication 26 November 2002

J Clin Periodontol 2003; 30: 802808 Copyrightr Blackwell Munksgaard 2003Printed in Denmark. All rights reserved


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After trauma, dental caries and period-ontal disease, tooth wear must pose thenext most significant threat to thefunction and longevity of human denti-tion. Epidemiological data are availableand suggest that tooth wear is commonfrom an early age (OBrien 1994; forreviews see Nunn 1996, 2000). Themajority of surveys consider tooth wearunder the heading of erosion, but themulti-factorial aetiology of the condi-tion would suggest that wear scoresresult from the interaction of physicaland chemical agents, even if erosionmay be dominant (for a review see Zero& Lussi 2000). Thus, dependent on thesite of the hard tissue loss from a toothsurface attrition, abrasion and erosionare probably interacting (for a reviewsee Bartlett & Smith 2000). Further, thetheoretical process of abfraction may

predispose to tissue loss by abrasionand/or erosion at cervical tooth sites(Grippo 1991). A considerable amountof information concerning tooth wear,particularly due to abrasion and erosion,has been drawn from studies in vitro(for a review see West & Jandt 2000).This is due, primarily, to the difficultiesin performing studies in vivo, wheresufficiently sensitive and accurate mea-surements and control of confoundingvariables are difficult, if not impossible,at this time. For abrasion, most attentionhas focused on toothpaste, since to

maintain efficacy, particularly in stainremoval, toothpaste must have a degreeof abrasivity (for reviews see Davis1980, Forward et al. 1997).

For erosion, most attention has beenwith dietary acids or soft drinks (for areview see Zero & Lussi 2000). Thelaboratory data indicate that enamel,while resistant to abrasion by mosttoothpastes, is highly susceptible toerosion by acid substrates. Moreover,abrasion and erosion appear to actsynergistically in wear processes onenamel (Schweizer-Hirt et al. 1978,

Davis & Winter 1980). Dentine appearsmore susceptible to toothpaste abrasionthan enamel, and national and interna-tional standards set toothpaste abrasivitylimits based primarily on tests ondentine (ISO 11609, 1995, BSI 5136,1981). The tests employed are based ona radiotracer method (Hefferren 1976),which provides relative dentine andenamel abrasivity (RDA and REA,respectively) values compared to areference abrasive. Dentine erodes invitro, at least to the same degree asenamel (Hunter et al. 2000a), and the

same synergy of abrasion and erosion inthe wear of dentine is reported (Davis &Winter 1980, Absi et al. 1992).Although studies in vivo concernedwith various tooth wear processes aloneor combined are difficult, studies in situshould be possible. Indeed, a method in

situ to study erosion of dentine andenamel by soft drinks (West et al. 1998,1999, Hughes et al. 1999a, b, Hunter etal. 2000a) has been tested and laterapplied to the development of lowerosive soft drinks. Similarly, a testmethod in situ to study and comparetoothpaste abrasion of dentine has beenproposed and demonstrated (Addy et al.2002).

The aim of the present study was toinvestigate the effects of both erosionand toothpaste abrasion on enamel anddentine by combining the two in situ

protocols (West et al. 1998, Addy et al.2002). A secondary aim was to againcompare two toothpastes of differingabrasivity, alone and with the erosionmodel. In an attempt to reduce thevariability reported for the abrasionmodel (Addy et al. 2002) but maintaina degree of pragmatism in the conductof the trial, toothbrushing of specimenswas ex vivo and by a single operator.

Material and methods

The investigation was designed, con-ducted, analysed and reported accordingto the guidelines for Good ClinicalPractice. The study was a single-blind,randomised, 5-treatment cross-over de-sign balanced for residual effects andinvolving 15 medically and dentallyhealthy subjects of either gender. Ethi-cal approval for the study was given bythe United Bristol Healthcare TrustEthics Committee. Subjects were givenverbal and written information concern-ing the study and provided writtenconsent to participate. Subjects were

18 years and older, and had no relevantmedical or pharmacotherapy historiesthat might confound the conduct of thestudy, including gastric regurgitation.They had to be dentate, without evi-dence of significant tooth wear com-puted against age and not wearing anyoral appliances or removable pros-theses. Upper removable acrylic appli-ances retained with cribs to the first orsecond molars were fabricated on plas-ter moulds poured in alginate impres-sions of the upper arches. One enameland one dentine specimen were held in

the oral surface of the palatal aspect ofthe appliance. The specimens wereprepared from extracted human thirdmolar teeth from donors of eithergender and aged 1830 years. Prepara-tion of the specimens was exactly asdescribed in a number of previous

publications (West et al. 1998, 1999,Hughes et al. 1999a, b). Essentially,sections of coronal enamel and dentinewere embedded in epoxy resin in amould measuring 8 5 2 mm. Thesurface of the cured specimen was thenpolished to expose a window of enamelor dentine with a surface profile toler-ance of no more than 70.3mm. Speci-mens were cold sterilised by placing in20,000ppm hypochlorite for 1 h. Beforeplacement in the appliance, specimenswere taped with PVC adhesive tape toleave a window of exposed hard tissue

approximately 2 mm wide. The appli-ances were worn from 0900 to 1700 hfor 10 working days (Monday to Friday)and only removed 1 h at lunch. Exceptfor tea, coffee or water, no other foodsor drinks were consumed while theappliances were in place. During eachstudy period, the subjects entered one ofthe treatment regimens. The randomlyallocated regimens were:

1. Drinking mineral watern and brush-ing specimens with fluoride tooth-paste A (RDA 189.074.0, REA

2.070.7) ex vivo.2. Drinking mineral water and brushing

specimens with fluoride toothpaste B(RDA585.073.0, REA 3.470.3)ex vivo.

3. Drinking orange juice.w

4. Drinking orange juice and brushingspecimens with toothpaste A ex vivo.

5. Drinking orange juice and brushingspecimens with toothpaste B ex vivo.

The drinks were consumed undersupervision with 250 ml sipped over atimed 10 min period at 0900, 1100, 1300

and 1500 h with a 1 h tolerance eitherside to facilitate the logistics of theprotocol. Immediately after drinking,the appliances were removed from themouth and rinsed under tap water. In thebrushing regimens, the specimens wereremoved from the appliances and placedinto rubber dies with inserts of the exactdimensions of the specimens. The speci-mens were brushed for 60 s, each withthe appropriate toothpaste by one of the

nVolvic, London, UK.

wSainsburys Supermarkets Ltd, London, UK.

Erosion and abrasion of enamel and dentine in situ 803


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study personnel. The toothpastes usedwere commercially available fluoride-containing products. After brushing,specimens were replaced in the appli-ances and returned to the subjects. Forthe orange drinking only, applianceswere maintained in a moist environment

while brushing of the other specimenstook place. These were returned to therespective subjects at the same time asthe other appliances. Prior to placingappliances in situ each morning andafter removal at the end of the workingday, they were soaked in 0.2% chlor-hexidine mouthwashz for 60 s to preventplaque accumulation on appliances andspecimens. At the end of days 5 and 10,specimens were taken from the appli-ances, taping removed and two mea-surements taken across the hard tissuewindow of each specimen using a

profilometer. Before re-taping and re-turn to the appliances, a further 30 mindisinfection was performed in 0.5%chlorhexidine in 70% spirit. Besidesthe dietary restrictions, subjects wereasked to suspend oral hygiene duringthe daytime-appliance wearing period.Normal oral hygiene measures wereallowed before or after each daily studyperiod (0900 to 1700 h). A washoutperiod of at least two and a half dayswas allowed between each 10-day studyperiod. Fresh enamel and dentine speci-mens were placed in the appliances at

the beginning of each study period. Anexamination of the oral cavity of eachsubject, during each study period, wasmade at the beginning of day 1 and atthe end of days 5 and 10 and anyabnormalities were noted.

Statistical Methods

The primary outcome measures werethe loss of material from the enamel anddentine specimens at 5 and 10 daysrelative to baseline and based on anaverage of the paired readings. Theoutcome measures were modelled bythree-way analysis of variance appro-priate to a cross-over design, withsubject, period and treatment as thethree factors. The data for appropriatepairs of regimes were combined so thatthe effects of erosion, abrasion and anysynergy between the two mechanismscould be examined.

Results

All 15 subjects satisfactorily completedthe study. Only one reading from oneenamel specimen for subject 3 in period2 at day 10 was not consistent with theremaining measurements for that speci-men during the period, and the datumpoint was removed from the measure-ments listings. Some dentine specimensat day 5 and more at day 10 had lesionstoo deep to measure. The maximum Zrange of the profilometer instrument isnot a precise figure, but lies in andaround 50mm. Accordingly, those spe-cimens found to be off scale or whichmeasured 450mm were listed as50mm. No adverse events attributableto the regimens were reported by thesubjects or observed by the examiningclinician.

The summary data, showing themean surface losses for enamel and thestandard errors at days 5 and 10, areshown in Table 1. The summary data fordentine and the standard errors areshown in Table 2. Comparing the datain Tables 1 and 2 reveals that for eachregimen, dentine loss is markedly high-er than enamel loss. Indeed, for dentineat day 5 one regimen is approaching theupper measurement limit for all speci-mens and at day 10 three regimens haveproduced losses close to or beyond themeasurement limit. Three-way analysis

of variance showed highly significantdifferences between the regimens forboth enamel and dentine (po0.001) butwith no significant differences betweensubjects or periods (p40.05).

For the regime where erosion alonewas examined by drinking orange juice,the mean levels of material loss weresmall for enamel and in the order of lessthan a micrometre by day 10 butconsiderably greater for dentine.

To examine the effects of erosion,abrasion and the synergy between ero-sion and abrasion, the data for appro-

priate pairs of toothbrushing regimeswere combined and compared. Thus, theeffects of erosion were examined bycomparing the difference between thetwo regimes where orange juice wasused (regimes 4 and 5) and the tworegimes where water was used (regimes1 and 2). Likewise, the effects ofabrasion were examined by comparingthe difference between regimes wherepaste A was used (1 and 4) and regimeswhere paste B was used (2 and 5). Thesynergy between the erosion and abra-sion was examined by subtracting the

data from appropriate regimes. Forenamel, the data are summarised inTable 3. Statistical significance wasexamined using t-tests for the effectsof erosion, abrasion and synergy. Thedata clearly show a highly significanteffect for erosion, with orange juice

being significantly more erosive thanwater, (po0.001). There was no sig-nificant effect for toothpaste and neitherpaste produced significantly more abra-sion than the other (p40.05). Thesynergy between erosion and abrasionwas directional for enamel, but did notreach significance at either time point(p40.05).

For dentine, the data are summarisedin Table 4. As a result of the truncationeffect, when measurements exceededthe scale of the profilometer, the dataat day 10 were not examined and effects

for synergy between erosion and abra-sion could not be tested with statisticalvalidity. The data show that the effectsof erosion were highly significant(again, orange juice was more erosivethan water po0.0001). The effects ofabrasion were also significant with pasteA being more abrasive than paste B(po0.0001).

Discussion

A number of methods in vitro have been

developed to study toothpaste abrasivityusing several substrates, including en-amel and, more particularly, dentine(for a review see West & Jandt 2000).The RDA method (Hefferen 1976) isperhaps the best known and found in theexisting International Standard fortoothpastes (ISO 11609, 1995). Simi-larly, several methods in vitro have beenused to study the erosion of dentaltissues (for a review see West & Jandt2000). In the present study, the erosionof enamel was less than seen in similarstudies. Thus compared to a previous

study using a very similar methodology(West et al. 1998), the mean level oferosion at days 5 and 10 was substan-tially lower in the current study, perhapsreflecting a difference in the erosivepotential of the orange juices used or inthe susceptibility of the participants.The main aim of the present study wasto study the combined effects of erosionand abrasion. Studies that have com-bined chemical and physical insults todentine and, more particularly, enamelhave demonstrated at least additive ifnot synergistic effects (Schweizer-HirtzCorsodyl, GlaxoSmithkline, Weybridge, UK.

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et al. 1978, Davis & Winter 1980,Eisenburger et al. 2000). This appearsto result from erosion causing both bulkloss of hard tissues and surface soft-

ening, this softer tissue appearing to bevery much more susceptible to mechan-ical forces than the native hard tissue.Most studies in vitro do not allow for

the potential of acid softened enamel ordentine to re-mineralise or re-hardenunder conditions in vivo, thereby poten-tially obviating the effect of physicaldamage to softened tissues. What dataare available suggest that re-hardeningof enamel certainly under in vitroconditions is slow and measured inhours and re-hardening of dentine maynot occur (Eisenburger et al. 2001,

Vanuspong et al. 2002).More recently, methods in situ have

evolved to study toothpaste abrasionand soft drink erosion, which couldhave been applied to dentine andenamel (West et al. 1998, Hunter et al.2000b, Addy et al. 2002). The presentstudy has combined the two protocols tofirstly investigate the interplay betweenabrasion and erosion in situ, and sec-ondly to compare two toothpastes ofdifferent abrasivity values for theirabrasive effects alone and within anerosive environment for both enamel

and dentine.A previous study in situ was able to

demonstrate a significant differencebetween the same two toothpastes fordentine abrasion (Addy et al. 2002),which in turn reflected the difference inthe RDA values of the pastes. Thevariabilities between brushing speci-mens, between subjects and betweenpastes were all high, all of whichappeared to arise in part from thevariability in subjects brushing theirown specimens within the appliance.In an attempt to reduce this variability,

Table1 . Summary statistics for measurements on enamel specimens, by time and regime

Day 5 Day 10

1 2 3 4 5 1 2 3 4 5Water1A Water1B Orange Orange1A Orange1B Water1A Water1B Orange Orange1A Orange1B

N 15 15 15 15 15 15 15 15 15 15Mean 0.357 0.561 0.357 1.766 1.059 0.480 0.687 0.781 2.428 1.568

Ste 0.078 0.196 0.129 0.413 0.168 0.122 0.202 0.258 0.493 0.247

Mean enamel loss values are in micrometres.

Table2 . Summary statistics for measurements on dentine specimens: by time and regime

Day 5 Day 10

1 2 3 4 5 1 2 3 4 5

Water1A Water1B Orange Orange1A Orange1B Water1A Water1B Orange Orange1A Orange1B

N 15 15 15 15 15 15 15 15 15 15

Off scale 3 0 0 12 5 15 3 0 15 14Mean 40.965 22.479 10.098 49.014 41.550 50.000 42.634 13.339 50.000 49.958

Ste 2.162 1.316 1.382 0.576 2.003 0.000 2.036 1.922 0.000 0.042

Mean dentine loss values are in micrometres. Off scale refers to the number of specimens that gave readings 450 mm.

Table3 . Contrasts for erosion, abrasion and synergy at days 5 and 10 for enamel

Contrasts day 5 Contrasts day 10

OrangeWater AB Synergy OrangeWater AB Synergy

Erosion Abrasion Synergy Erosion Abrasion Synergy

Mean 1.907 0.502 0.911 2.829 0.653 1.068Ste 0.451 0.519 0.446 0.508 0.639 0.630

p-value 0.0008 0.3502 0.0603 0.0001 0.3241 0.1124

Mean values are in micrometres.

Erosion5 difference between orange juice and water regimes: (114) (215).

Abrasion5 difference between toothpaste A and B regimes: (115) (214).

Synergy5 interaction between erosion and abrasion factors:(1 5) (42).

Positive scores imply orange juice more erosive than water, and toothpaste A more abrasive thanpaste B.

Table4 . Contrasts for erosion, abrasion and synergy at day 5 for dentine

Contrasts day 5

OrangeWater AB

Erosion Abrasion

Mean 27.12 25.95

Ste 3.247 3.428

p-value o0.0001 o0.0001

Mean values are given in micrometres.

Erosion5 difference between orange and water regimes: (114) (215).

Abrasion5 difference between toothpaste A and B regimes: (115) (214).

Positive scores imply orange juice more erosive than water, and toothpaste A more abrasive thanpaste B.



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individual specimens were brushed by asingle individual and out of the appli-ances. This maintained a degree ofpragmatism in the design in that thebrushing was manual and not in amachine. As with such new methodsin situ, even using sensitive measuring

instrumentation, there has to be a degreeof guesswork in deciding the duration ofthe study in order to obtain meaningfuleffects. Moreover, while trying to main-tain a design akin to everyday life,models in vitro and in situ oftenexaggerate the use of the treatmentfactors. In the present study, the intakeof orange juice was not out with thereported daily intake of soft drinks inthe UK (Sucrose Soft Drink Report1998). The toothbrushing was, however,exaggerated. Thus, toothbrushing withtoothpaste is recommended as 2 min

twice daily, where any tooth surfacemight typically be contacted for amaximum of 5 s twice daily. In thepresent study, the contact time for eachspecimen was 4 min in a day. From thepoint of view of abrasion only, this maybe irrelevant since tissue loss is irrever-sible and data are therefore representa-tive merely of a longer duration ofnormal brushing. Similarly, the erosiondata are probably representative of theeffects in a 10-day period. It is thecombined data of abrasion and erosionthat must be exaggerated at least to

some degree. Thus, the brushing aftereach acid insult would, at least fordentine, have removed not only sof-tened dentine but also probably furtherdentine below the softened zone. Such adegree of dentine loss by abrasion aloneor combined with erosion may not beout with what is anecdotally reportedfor excessive or abusive toothbrushinghabits. For enamel, which clearly wasquite resistant to abrasion alone, thesame limitation of the method wouldnot apply to any great degree.

Accepting these observations of the

model, it is apparent for both enameland dentine that abrasion interacts witherosion to increase tissue loss. Indeed,synergy is approached for enamel butdid not reach statistical significance.Thus, for the more abrasive paste atdays 5 and 10, the combined effectswere always greater than the sum of thesingle effects. For the lower abrasivepaste, the combined effects at days 5and 10 were close to the sum of theindividual effects. For dentine, data atdays 2 and 5 may have been more usefulthan 5 and 10 days, or in hindsight a

protocol more in line with normaltoothbrushing may have been moreinformative. Nevertheless, the data diddemonstrate that dentine is abraded bytoothpastes and to a degree consistentwith the RDA values of the two pastes.Thus, as with the previous study in situ

(Addy et al. 2002), the higher RDApaste produced almost twice the abra-sion of the other paste. Interestingly, thenet effects of abrasion and erosion ofdentine with the higher RDA paste, inmean terms, is almost exactly the sumof the two treatments alone. For thelower RDA paste, the combined effectis considerably greater than the sum ofthe individual abrasion and erosioneffects.

The lack of difference between thetwo pastes for enamel abrasion, which,if anything, was greater for the lower

RDA paste, is at first surprising. Thiscan nevertheless be explained sinceneither paste contained abrasives ap-proaching the hardness of enamel, andtotal enamel loss was very small andonly just outside the acceptance profilefor specimens. The data therefore con-firm laboratory observations that mosttoothpastes produce only minimal abra-sion to enamel. In mean terms, the pastewith the slightly higher REA value butmarkedly reduced RDA value producedmore enamel abrasion.

The rate of enamel abrasion is higher

for the first time period between days 0and 5 compared to the second timeperiod between days 5 and 10. Themean enamel abrasion for this secondperiod is almost identical for bothpastes, being 0.123 and 0.126mm forpastes A and B, respectively. Thissuggests that the enamel abrasion valuesfor subsequent time periods beyond 10days may also approach a much lowersteady-state rate of abrasion, or evenplateau. The reason for the lowerenamel wear rate for the second periodmay be due to a number of factors. This

may include the polishing of samplesactivating the surface to wear (Meur-mann & Frank 1991), pellicle formationand maturation processes giving someprotective benefits to tooth wear (Meur-mann & ten Cate 1996, Lendenmann etal. 2000), and fluoride effects helping tostrengthen the enamel surface (Duck-worth 1993, Shellis & Duckworth1994).

The extrapolation of the mean enam-el abrasion values to a possible life-times value may be calculated; forexample, taking the case for paste B,

which gave the largest abrasion betweendays 5 and 10 of 0.126 mm. Consideringthat this amount of abrasion occurredafter a total of 1200s of brushing exvivo and since toothbrushing time istypically 50 s (Duke & Forward 1982),assuming the amount any tooth surface

might typically be contacted in vivoduring brushing is 5 s twice daily, then alifetimes brushing (100 years) with thispaste would be equivalent to approxi-mately 38mm of abrasion. Since theenamel is typically 130mm in thicknessnear the cervical enamel border (Gas-persic 1994), and is considerably thickerover much of the tooth surface, anyenamel wear during a lifetime of lessthan 100mm can be considered clini-cally irrelevant.

The effects of combining abrasionimmediately following an acid chal-

lenge to enamel presumably reflects theremoval of the softened zone noted inexperiments in vitro (Schweizer-Hirt etal. 1978, Eisenburger et al. 2000);within the model there would be notime for enamel re-hardening and there-fore would be synonymous with indivi-duals brushing after meals thatcontained an acid challenge. The datasuggest that the softened surface layer,produced by an erosive challenge, isreadily removed by virtually any me-chanical action and, in this context, thetoothpaste abrasivity is irrelevant. Stu-

dies in vitro suggest that re-hardening ofenamel takes a considerable time and, ifthese data can be extrapolated to in vivosoftened enamel, will remain suscepti-ble to physical insults for a considerableperiod of time during the waking hours,particularly if acid intakes are frequentand/or prolonged (Eisenburger et al.2001).

The markedly increased susceptibil-ity of dentine to both erosion andabrasion, alone or combined, has beenreported from studies in vitro (Schwei-zer-Hirt et al. 1978, Davis & Winter

1980, Hunter et al. 2000a) and morerecently in situ (Hunter et al. 2000b,Addy et al. 2002) and confirmed here.Again accepting that the abrasion timewas exaggerated, the data are probablymore representative of a considerablymore prolonged exposure of dentine tochemical and physical injury. Moreover,since limited data suggest that dentinedoes not re-harden after acid attack(Vanuspong et al. 2002), the so-calledbuccalcervical abrasion lesions com-monly seen are presumably more cor-rectly termed erosion, abrasion lesions.

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The morphology of these lesions pre-sumably reflects the relative resistanceof enamel compared to dentine toabrasion, and abrasion and erosioncombined.

In conclusion, these studies suggestthat abrasion of enamel by most tooth-

paste alone is negligible even over alifetime. Similarly, with normal usage,abrasion of dentine by toothpaste aloneshould not reach clinically significantlevels unless there are abusive oralhygiene habits. Tooth wear of enameland particularly dentine is enhanced bythe combination of soft drink erosionand toothpaste abrasion. Enamel itselfappeared resistant to abrasion comparedto dentine and similarly more resistantto erosion than dentine. These data aresupportive of advice to avoid tooth-brushing immediately following the

consumption of acidic beverages.

Acknowledgements

We thank Eric Huntington for valuableinput on the statistical analysis of thedata. We are most grateful to Miss E.MacDonald and Miss A. Lobato fortheir invaluable technical assistance.

Zusammenfassung

Untersuchung von Erosion und Abrasion auf

Schmelz und Dentin: Ein in-situ-Modell inwelchem Zahnpasten unterschiedlicher Abrasi-

vitat verwendet werden

Grundlagen: In-vitro-Studien lassen anneh-

men, dass Abrasion und Erosion bei der

Produktion von Schmelz- und Dentinabtrag

synergistisch wirken. Seit kurzem sind in-situ-

Methoden zum getrennten Studium von Erosion

und Abrasion von dentalen Geweben verfugbar.

Das Ziel dieser Studie war es zwei in-situ-

Protokolle zu kombinieren, im das Wechsel-

spiel zwischen Erosion und Abrasion von

Schmelz und Dentin zu studieren.

Methode: Die randomisierte einfach-blind-Stu-

die, wurde mit je 5 Behandlungen an 15

gesunden Freiwilligen durchgefuhrt und hatte

ein cross-over.Design. Wahrend jeder der 10-tagigen Studienperioden trugen die Teilnehmer

von 9 Uhr morgens bis 5 Uhr abends im

Oberkiefer eine Acryl-Tiefziehschiene, welche

eine polierte Schmelz- und eine polierte Den-

tinflache enthielt.

Die Behandlungsmanahmen fur die Flachen

waren:

1. Trinkwasser und Putzen mit Zahnpasta A.

2. Trinkwasser und Putzen mit Zahnpasta B.

3. Orangensaft Trinken.

4. Orangensaft Trinken und Putzen mit Zahn-

pasta A.

5. Orangensaft Trinken und Putzen mit Zahn-

pasta B.

Die Trink- und Putzzeiten waren etwa 9.00,

11.00, 13.00 und 15.00 Uhr. Von den Drinks

wurden 250 ml wahrend 10 min konsumiert und

das ex-vivo-Putzen erfolgte fur 1 m in pro

Flache. Fur jede Periode erfolgten die Messun-

gen des Gewebeverlusts an Tag 5 und 10 unter

Verwendung eines Profilometers.

Ergebnisse: Alle Behandlungen produzierten

im Verlaufe der Zeit steigenden Gewebeverlust,

der fur Dentin betrachtlich groer war als fur

Schmelz. Fur Schmelz zeigten die Daten an Tag

5 und 10 einen signifikanten Effekt der Erosion

(z.B. war Orangensaft betrachtlich erosiver als

Wasser), aber keinen signifikanten Effekt fur

die Abrasion (z.B. keine signifikanten Un-

terschiede zwischen den zwei Zahnpasten).

Die kombinierten Effekte von Orangensaft

und Zahnpasta wiesen in Richtung einer

Synergie erreichten jedoch keine Signifikanz.

Auf Dentin ubertrafen die Daten an Tag 10 den

bei 50mm gesetzten Grenzwert und nur die

Daten von Tag 5 wurden berucksichtigt. Es gab

signifikante Effekte fur die Erosion (Orangen-

saft produzierte signifikant mehr Erosion als

Wasser) und fur die Abrasion (Paste A war

signifikant abrasiver fur Dentin als Paste B). Fur

Dentin konnte der Synergieeffekt wegen des

Begrenzungseffekts, da die Daten den Profilo-

metergrenzwert ubersch ritten hatten, nicht un-

tersucht werden.

Schlussfolgerungen: Eine Erosion erhoht die

Anfalligkeit von Schmelz fur Zahnpastaabra-

sion. Dentin ist betrachtlich anfalliger als

Schmelz fur Erosion und Abrasion allein oder

deren Kombination. Der Dentinverlust schein

mit der Abrasivitat der Zahnpasta (RDA-Wert)

zu korrelieren.

Resume

Investigation de lerosion et de labrasion dele mail et de la dentine; un modele in situ

utilisant des dentifrices dabrasivitediffe rente

Des etudes in vitro suggerent que labrasion et

lerosion peuvent agir en synergie pour produire

une perte demail et de la dentine. Des methode

in situ sont accessibles actuellement pour

estimer separement lerosion et labrasion des

tissus dentaires. Le but de cette etude a ete de

combiner deux protocoles in situ pour etudier

linteraction entre lerosion et labrasion de

lemail et de la dentine. Cette etude suivait un

modele croise de cinq traitements randomises,

en simple aveugle, comportant quinze sujets

sains. Durant chaque periode detude de dix

jours les sujets portaient de 9 h a 17 h une

gouttiere acrylique amovible portant un speci-men de dentine polie et un demail poli. Les

regimes de traitement etaient les suivants:

1) boire de leau et se brosser avec le dentifrice

A,

2) boire de leau et se brosser avec le dentifrice

B,

3) boire du jus dorange

4) boire du jus dorange et se brosser avec le

dentifrice A,

5) boire du jus dorange et se brosser avec le

dentifrice B.

La prise de liquide et le brossage seffectuaient

vers 9, 11,13 et 15 h. Les boissons etaient

consommees en tant que 250 ml durant dix min

et le brossage ex vivo dune min pour chaque

specimen. La mesure de la perte tissulaire a e te

effectuee aux jours 5 et dix de chaque pe riode

en utilisant un profilometre. Tous les traite-

ments ont produit une augmentation de la perte

tissulaire avec le temps qui etait considerable-

ment plus importante pour la dentine que pour

lemail. Pour lemail, les donneees aux jours 5

et 10 revelaient un effet significatif de lerosion;

c.-a-d. le jus dorange etait significativement

plus erosif que leau, mais aucune difference

pour labrasion (c.-a-d. aucune difference entre

les deux types de traitement par dentifrice). Les

effets combines jus dorange et dentifrices

etaient en synergie mais natteignaient pas un

degre de signification. Pour la dentine au jour

10 beaucoup de specimens depassaient la limite

de 50mm du profilometre et seul les donnees au

jour 5 ont ete prises en consideration. Il y avait

des effets significatifs pour lerosion (le jus

dorange produisait significativement plus

derosion que leau) et pour labrasion (le

dentifrice A etait significativement plus abrasif

sur la dentine que le B). Leffet de synergie ne

pouvait pas etre examine pour la dentine vu

leffet de troncation qui depassait la limite

etablie pour le profilometre. Lerosion aug-

mente la sensibilite de lemail a labrasion par

le dentifrice. La dentine est considerablement

plus sensible que lemail a lerosion et labra-

sion ou les deux. La perte dentinaire semble en

relation avec le degre dabrasivite du dentifrice

(valeur RDA).

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Address:

Martin Addy

Division of Restorative Dentistry

Dental SchoolLower Maudlin Street

Bristol BS1 2LY

UK

E-mail: [email protected]

808 Hooper et al.


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