since the ancient times , the incorporation of abrasive powder in toothpastes or powders 
 has been done . various abrasive materials have been proposed such as bone ash ( which is 
 mainly composed of -tricalcium phosphate ) , coral , shell , marble or pumice powders . these powders are hold 
 either in suspension in a pasty thickening hydrogel containing a wetting agent in the 
 case of toothpastes or mixed with other powders such as metal oxides , phosphates or 
 plant extracts . several studies have 
 been conducted to evaluate the abrasion of both dentifrices and toothbrush 
 filaments . it is classical in 
 the dental literature to compare the abrasion of different types of toothpastes ' 
 formulations and in 1995 , the iso 11609 standard was proposed following the original 
 works of hefferen on radioactive dentine abrasion ( rda ) . the 
 specimen surfaces are then brushed with an electric toothbrush under standard procedures 
 ( time , tension ... ) . the toothpastes are compared with values obtained with a reference 
 abrasive ( calcium pyrophosphate in an hydrogel composed of glycerol and carboxymethyl 
 cellulose ) . at the end of 
 brushing , the slurries are vortexed and put in a scintillation counter for radiation 
 detection and abrasion is expressed in count per minute divided by the 
 weight of dentine sample . because the method is difficult and requires health hazardous 
 procedures , other techniques have been proposed such as contact or non - contact 
 profilometry . the aims of the present study were 1 ) to characterize the abrasive powders entering in 
 the composition of a variety of dentifrices by light and scanning electron 
 microscopy ; 2 ) to measure the 
 abrasion of each formula on polished poly(methylmethacrylate ) ( pmma ) surfaces using 
 vertical scanning interference microscopy ( vsi ) . pmma blocks were prepared by using a purified monomer containing 1% of the 
 polymerization accelerator benzoyl peroxide . the accelerated and initiated mixture was poured in 
 peel - a - way embedding molds ( 25 ml / mold - polyscience inc . , warrington , pa , usa ) and 
 polymerization took place in a cold environment ( + 4c in a refrigerator with a water 
 bath to limit the temperature peak ) . because polymerization is not completed when the 
 blocks have hardened , a one month period separated their preparation from further 
 use . blocks were then 
 ground on an automatic plane grinding machine tegramin-30 ( struers , copenhagen , 
 denmark ) using ascending grads of polishing paper ( 1200 , 2000 and 4000 during 2 min 
 each ) . final mirror polishing was made with a md - nap paper spray with diapro 1 m 
 solution . polished pmma blocks were affixed onto plastic slides with a hand - press 
 ( struers ) in order to have a perfectly horizontal surface parallel to the slide . a commercial electric toothbrush was used in this study ( oral - b , braun , 
 france ) with the following conditions : load of the toothbrush standardized at 250 g 
 ( verified with the internal pressure control of the brush ) , brushing time : 2 min ( as 
 recommended by the manufacturer ) ; soft hardness toothbrush head , rotation sense 
 changing every 30 sec . for each type of dentifrice the toothbrush head was in direct contact 
 with the pmma block and the dentifrice . for the toothpastes , 0.2 g were weighted on a 
 high precision scale , diluted in 500 l of distilled water and applied directly on 
 the ppma block with a syringe . for one of the powder ( gencix with a very 
 low mass - weight , the volume used appeared considerable ( more than a pea : trial 
 " gencix full volume " ) and a smaller volume ( similar to those used with 
 the other powders ) was used in an additional trial ( trial : " gencix 
 reduced volume " ) . a third trial was done according to the manufacturer instructions 
 where the toothbrush is soaked in powder - containing water as follows : a volume of 
 toothpaste equivalent to a pea ( i.e. ~100 mg of the powder was dissolved in 1 ml of 
 distilled water ) . the toothbrush was soaked into the mixture , then applied to the 
 surface of the pmma block ( trial : " gencix diluted " ) . for each dentifrice a control was done in 
 triplicate with a new toothbrush moistened with 500 l of distilled water . three toothpastes were investigated : colgate total ( unilever , 
 rueil - malmaison , france ) ; denivit(schwartzkopf & henkel , 
 boulogne - billancourt , france ) , parodontax ( glaxo - smith - kline gsk , 
 marly - le - roi , france ) . three toothpowders were analyzed in parallel : 
 kontrol ( omega pharma , chatillon , france ) ; per blan ( per 
 blan , paris , france ) and gencix ( esprit d'ethique , nantes , france ) . the 
 raw composition of each dentifrice ( as provided by the manufacturers ) appears on 
 figure 1 together with its mass density . 
 for each dentifrice , an analysis was conducted by light and electron microscopy . 
 first , a small amount of paste or powder was placed on a microscopic glass slide , 
 covered with a thin glass lamella and imaged by bright field illumination . then , 0.5 
 g of each dentifrice was dissolved in 10 ml of distilled water and stirred for 5 min 
 with a magnetic stirrer to dissolve all the organic / inorganic soluble components . the 
 mixture was centrifuged , the supernatant was discarded and the residue was washed 
 several times with distilled water . finally , a drop of the residue was placed on a 
 glass slide as previously . light microscopy was performed on an olympus bx51 
 microscope ( olympus , rungis , france ) using bright field and polarized light 
 illumination at a magnification of 100x . residues were also placed on a brass stub , 
 carbon - coated by sputtering ( 10 nm thick ) and analyzed with a zeiss evo ls10 scanning 
 electron microscope ( carl zeiss ltd , nanterre , france ) equipped with an energy x - ray 
 microanalysis system ( inca xmax , oxford instruments , oxford , uk ) to determine the 
 atomic composition of the non - soluble abrasive component . composition of the 6 dentifrices ( 3 toothpastes , 3 toothpowders ) studied measurements were done using a wyko nt 9100 vertical scanning interference microscope 
 ( bruker nano surface , palaiseau , france ) , a system originally dedicated to the 
 measurement of roughness in material samples . vsi is based on light interferometry 
 and operates as a non - contact optical profiler in vertical scanning mode to produce 
 3d topography maps of the sample surface . briefly , a white light source is emitted by 
 conventional light source and is split into two beams which pass through a mirau 's 
 interferometry objective . the incident beams are reflected from the reference mirror 
 and the sample surface respectively . the light reflected from this mirror combines 
 with the light reflected from the sample to produce interference fringes ( known as 
 interferogram ) where the best - contrast fringe occurs at best focus . the light and 
 dark fringes are used in combination with the wavelength of the light to determine 
 height difference between each fringe . a piezo - electric stage moves the sample 
 vertically with a nanometer precision , which produces phase shifts in the 
 interferogram . interferograms were digitized using a ccd camera and data were 
 analyzed to produce topographic surface maps at a magnification of 5x . for each 
 block , 3 images ( 1.0x1.3 mm ) were obtained in the 4 quadrants of the brushed surface 
 ( internal , medium and outer position ) . the software vision ( release 
 4.10 , wyco ) was used to acquire the data and compute the mean roughness ( ra , 
 expressed in m ) on each image . for each block , the values were averaged on the 12 
 images and the mean value obtained on the 3 blocks was considered ; so for each trial , 
 the analyzed surface was 46.8 mm . statistical analysis was performed using the systat statistical software release 13.0 
 ( systat software inc . differences between groups were analyzed by a non - parametric anova test 
 ( kruskall - wallis ) with the conover - inman post - hoc test . pmma blocks were prepared by using a purified monomer containing 1% of the 
 polymerization accelerator benzoyl peroxide . the accelerated and initiated mixture was poured in 
 peel - a - way embedding molds ( 25 ml / mold - polyscience inc . , warrington , pa , usa ) and 
 polymerization took place in a cold environment ( + 4c in a refrigerator with a water 
 bath to limit the temperature peak ) . because polymerization is not completed when the 
 blocks have hardened , a one month period separated their preparation from further 
 use . blocks were then 
 ground on an automatic plane grinding machine tegramin-30 ( struers , copenhagen , 
 denmark ) using ascending grads of polishing paper ( 1200 , 2000 and 4000 during 2 min 
 each ) . final mirror polishing was made with a md - nap paper spray with diapro 1 m 
 solution . polished pmma blocks were affixed onto plastic slides with a hand - press 
 ( struers ) in order to have a perfectly horizontal surface parallel to the slide . a commercial electric toothbrush was used in this study ( oral - b , braun , 
 france ) with the following conditions : load of the toothbrush standardized at 250 g 
 ( verified with the internal pressure control of the brush ) , brushing time : 2 min ( as 
 recommended by the manufacturer ) ; soft hardness toothbrush head , rotation sense 
 changing every 30 sec . for each type of dentifrice the toothbrush head was in direct contact 
 with the pmma block and the dentifrice . for the toothpastes , 0.2 g were weighted on a 
 high precision scale , diluted in 500 l of distilled water and applied directly on 
 the ppma block with a syringe . for one of the powder ( gencix with a very 
 low mass - weight , the volume used appeared considerable ( more than a pea : trial 
 " gencix full volume " ) and a smaller volume ( similar to those used with 
 the other powders ) was used in an additional trial ( trial : " gencix 
 reduced volume " ) . a third trial was done according to the manufacturer instructions 
 where the toothbrush is soaked in powder - containing water as follows : a volume of 
 toothpaste equivalent to a pea ( i.e. ~100 mg of the powder was dissolved in 1 ml of 
 distilled water ) . the toothbrush was soaked into the mixture , then applied to the 
 surface of the pmma block ( trial : " gencix diluted " ) . for each dentifrice , 
 the experiment was conducted 3 times on 3 different blocks . a control was done in 
 triplicate with a new toothbrush moistened with 500 l of distilled water . three toothpastes were investigated : colgate total ( unilever , 
 rueil - malmaison , france ) ; denivit(schwartzkopf & henkel , 
 boulogne - billancourt , france ) , parodontax ( glaxo - smith - kline gsk , 
 marly - le - roi , france ) . three toothpowders were analyzed in parallel : 
 kontrol ( omega pharma , chatillon , france ) ; per blan ( per 
 blan , paris , france ) and gencix ( esprit d'ethique , nantes , france ) . the 
 raw composition of each dentifrice ( as provided by the manufacturers ) appears on 
 figure 1 together with its mass density . 
 for each dentifrice , first , a small amount of paste or powder was placed on a microscopic glass slide , 
 covered with a thin glass lamella and imaged by bright field illumination . then , 0.5 
 g of each dentifrice was dissolved in 10 ml of distilled water and stirred for 5 min 
 with a magnetic stirrer to dissolve all the organic / inorganic soluble components . the 
 mixture was centrifuged , the supernatant was discarded and the residue was washed 
 several times with distilled water . finally , a drop of the residue was placed on a 
 glass slide as previously . light microscopy was performed on an olympus bx51 
 microscope ( olympus , rungis , france ) using bright field and polarized light 
 illumination at a magnification of 100x . residues were also placed on a brass stub , 
 carbon - coated by sputtering ( 10 nm thick ) and analyzed with a zeiss evo ls10 scanning 
 electron microscope ( carl zeiss ltd , nanterre , france ) equipped with an energy x - ray 
 microanalysis system ( inca xmax , oxford instruments , oxford , uk ) to determine the 
 atomic composition of the non - soluble abrasive component . measurements were done using a wyko nt 9100 vertical scanning interference microscope 
 ( bruker nano surface , palaiseau , france ) , a system originally dedicated to the 
 measurement of roughness in material samples . vsi is based on light interferometry 
 and operates as a non - contact optical profiler in vertical scanning mode to produce 
 3d topography maps of the sample surface . briefly , a white light source is emitted by 
 conventional light source and is split into two beams which pass through a mirau 's 
 interferometry objective . the incident beams are reflected from the reference mirror 
 and the sample surface respectively . the light reflected from this mirror combines 
 with the light reflected from the sample to produce interference fringes ( known as 
 interferogram ) where the best - contrast fringe occurs at best focus . the light and 
 dark fringes are used in combination with the wavelength of the light to determine 
 height difference between each fringe . a piezo - electric stage moves the sample 
 vertically with a nanometer precision , which produces phase shifts in the 
 interferogram . interferograms were digitized using a ccd camera and data were 
 analyzed to produce topographic surface maps at a magnification of 5x . for each 
 block , 3 images ( 1.0x1.3 mm ) were obtained in the 4 quadrants of the brushed surface 
 ( internal , medium and outer position ) . the software vision ( release 
 4.10 , wyco ) was used to acquire the data and compute the mean roughness ( ra , 
 expressed in m ) on each image . for each block , the values were averaged on the 12 
 images and the mean value obtained on the 3 blocks was considered ; so for each trial , 
 the analyzed surface was 46.8 mm . statistical analysis was performed using the systat statistical software release 13.0 
 ( systat software inc . , san jos , ca , usa ) . differences between groups were analyzed by a non - parametric anova test 
 ( kruskall - wallis ) with the conover - inman post - hoc test . all dentifrices contained inorganic 
 particles used as abrasive but the size of the grains considerably differed between 
 them . the larger grains were observed for parodontax and the smaller for 
 colgate total and per blan . dilution and washing of the 
 different dentifrices was used to separate and enrich the slurry in these abrasive 
 particles from the other components . however , the highly soluble grains of sodium 
 bicarbonate contained in parodontax were completely dissolved . some dentifrices ( colgate total , 
 gencix , denivit appeared to be composed of both types of 
 particles . light microscopic aspect of the six dentifrices studied at the same 
 magnification ( 100x ; the bar stands for 200 m ) . for each of them , the image of 
 the 1st column corresponds to the appearance of the crude dentifrice under 
 glass slide and coverslip in bright field microscopy . the 2 column 
 corresponds to the abrasive powder obtained after extensive washes and examined 
 under glass slide and coverslip in bright field microscopy . note the 
 considerable differences in size and shape of the particles . in the 
 3 column , the same field is examined in polarized light to see 
 the aspect of the abrasive powder ( excepted for parodontax , whose 
 abrasive particles were dissolved during the washing steps , the image 
 correspond to the polarization aspect of the 1 column ) . note that 
 abrasive particles can be birefringent or not the image of the different types of abrasive grains appears on figure 3 for all dentifrices ( except parodontax , in 
 which the particles were dissolved during the preparation steps ) . the edx analysis 
 confirmed the presence of silicate particles only in colgate total . calcium 
 phosphate constituted all the particles of kontrol ; 
 denivitcontained both silicates and aluminum oxides and the 
 gencix particles coming from pumice were composed of sodium and 
 potassium silicates together with traces of aluminum oxides . scanning electron microscopy of the abrasive grains contained in the different 
 types of dentifrices and obtained after extensive washing and centrifugation . all images were 
 obtained at the same magnification ( 500x ) and the white bar stands for 10 m . note the considerable differences in shape and composition of the abrasive 
 particles contained in the six dentifrices . the nahco3 particles of 
 parodontax , having being solubilized during the preparation 
 steps , are not figured the surface of each pmma block exhibited signs of abrasion even when the brush was 
 used with distilled water . the statistical results for the surface 
 roughness parameter ra of the different dentifrices are graphically presented in 
 figure 5 . ra did not differ significantly 
 between toothbrush without dentifrice and with parodontax or 
 gencixused in reduced volume . the toothpowders were associated with a significant higher ra than the 
 different toothpastes or the brush alone ( p<0.0001 ) except gencix , 
 used in reduced volume . considerable differences exist when using the different modes 
 for using gencixand the full volume trial induced the marked 
 abrasion . vertical scanning interference microscopy of the surface of pmma blocks after 
 brushing with different types of dentifrices . . the colored scale bar ( ranging from -12 to + 6 m ) represents 
 the abrasion depth surface roughness analysis after brushing with the different dentifrices . bars 
 correspond to the average value obtained on the 3 blocks analyzed per 
 dentifrice ( 12 images per block ) . toothbrushes used with distilled water : white bar ; with toothpastes : 
 black bars ; with toothpowders : patterned bars . the different ways of using 
 gencix appear with different types of horizontal patterned 
 bars all dentifrices contained inorganic 
 particles used as abrasive but the size of the grains considerably differed between 
 them . the larger grains were observed for parodontax and the smaller for 
 colgate total and per blan . dilution and washing of the 
 different dentifrices was used to separate and enrich the slurry in these abrasive 
 particles from the other components . however , the highly soluble grains of sodium 
 bicarbonate contained in parodontax were completely dissolved . some dentifrices ( colgate total , 
 gencix , denivit appeared to be composed of both types of 
 particles . light microscopic aspect of the six dentifrices studied at the same 
 magnification ( 100x ; the bar stands for 200 m ) . for each of them , the image of 
 the 1st column corresponds to the appearance of the crude dentifrice under 
 glass slide and coverslip in bright field microscopy . the 2 column 
 corresponds to the abrasive powder obtained after extensive washes and examined 
 under glass slide and coverslip in bright field microscopy . note the 
 considerable differences in size and shape of the particles . in the 
 3 column , the same field is examined in polarized light to see 
 the aspect of the abrasive powder ( excepted for parodontax , whose 
 abrasive particles were dissolved during the washing steps , the image 
 correspond to the polarization aspect of the 1 column ) . the image of the different types of abrasive grains appears on figure 3 for all dentifrices ( except parodontax , in 
 which the particles were dissolved during the preparation steps ) . the edx analysis 
 confirmed the presence of silicate particles only in colgate total . calcium 
 phosphate constituted all the particles of kontrol ; 
 denivitcontained both silicates and aluminum oxides and the 
 gencix particles coming from pumice were composed of sodium and 
 potassium silicates together with traces of aluminum oxides . scanning electron microscopy of the abrasive grains contained in the different 
 types of dentifrices and obtained after extensive washing and centrifugation . all images were 
 obtained at the same magnification ( 500x ) and the white bar stands for 10 m . note the considerable differences in shape and composition of the abrasive 
 particles contained in the six dentifrices . the nahco3 particles of 
 parodontax , having being solubilized during the preparation 
 steps , are not figured the surface of each pmma block exhibited signs of abrasion even when the brush was 
 used with distilled water . the statistical results for the surface 
 roughness parameter ra of the different dentifrices are graphically presented in 
 figure 5 . ra did not differ significantly 
 between toothbrush without dentifrice and with parodontax or 
 gencixused in reduced volume . the toothpowders were associated with a significant higher ra than the 
 different toothpastes or the brush alone ( p<0.0001 ) except gencix , 
 used in reduced volume . considerable differences exist when using the different modes 
 for using gencixand the full volume trial induced the marked 
 abrasion . vertical scanning interference microscopy of the surface of pmma blocks after 
 brushing with different types of dentifrices . the colored scale bar ( ranging from -12 to + 6 m ) represents 
 the abrasion depth surface roughness analysis after brushing with the different dentifrices . bars 
 correspond to the average value obtained on the 3 blocks analyzed per 
 dentifrice ( 12 images per block ) . toothbrushes used with distilled water : white bar ; with toothpastes : 
 black bars ; with toothpowders : patterned bars . the different ways of using 
 gencix appear with different types of horizontal patterned 
 bars the aims of the present study were to analyze the abrasive powders contained in 6 
 different dentifrices ( 3 pastes and 3 powders ) and to evaluate their abrasive capacity 
 on a synthetic polymer - pmma - widely used in dentistry . it is well recognized that the capacity of a dentifrice to abrade can be attributed to 
 the nature and size of its particulate abrasive components . here , we 
 found that parodontax , which contains large grains of sodium bicarbonate , 
 did not produce a significantly rougher surface than the brush used with distilled water 
 alone . it is likely that the high and rapid solubility in water of this compound ( mainly 
 used as a whitening agent that is fully soluble in water ) had no significant effect on 
 abrasion . bright field 
 microscopy revealed that all grains were rapidly dissolved in water and could not be 
 observed by polarization microscopy or sem . denivit and colgate 
 total which contained some insoluble abrasive grains had a low but 
 significantly higher abrasion on pmma blocks . all toothpowders which contained insoluble 
 abrasive grains were associated with a significantly higher effect than the control 
 brushes with either distilled water or toothpastes . a limitation of the present study is 
 that the hardness of individual grains could not be determined . we were unsuccessful 
 when trying to measure this parameter by nanoindentation due to the small size of 
 individual grains and the impossibility to firmly anchor them for this type of analysis . it is likely that pumice powder grains are harder than calcium phosphate or calcium 
 carbonate particles and the nature of the grain influences the abrasive powder . the tooth brushing test was performed as recommended by the toothbrush manufacturer and 
 it used the control system incorporated in the electric device to control the pressure 
 and time of analysis . however , only a single 2 min brushing was used here contrary to a 
 number of studies where prolonged brushing times or cycles are used . this short brushing 
 time was chosen because 1 ) pmma is by far less hard than enamel or dentine ( i.e. the 
 young 's modulus is 3.1 gpa and hardness 196 mpa for pmma vs. 88 gpa and 
 4,800 mpa for enamel ; 22 gpa and 800 mpa for dentine ) ; 2 ) vsi is a 
 very accurate method used in industry to measure surface roughness of materials at the 
 nanoscale level on larger surfaces than atomic force microscopy ; 3 ) pmma is the major component of 
 denture which are also cleaned by brushing . in addition , 
 pmma - based polymers are also used in veneers or soft liners which can also be abraded by 
 dentifrices . we found that vsi provided reliable quantitative results and was able to image the 
 surface of the material together with providing arithmetic mean roughness . the method 
 has been used in only one paper to calculate ra but no images were presented . the toothbrush moistened with distilled 
 water alone appeared to cause a limited abrasion of the polymer . it has previously been 
 reported that the rigidity of the brush 's bristles can influence the abrasion of 
 synthetic acrylic polymers . because all brushes used in this study 
 were of the same model and only new brushes were used for each dentifrice , the abrasion 
 due to the dentifrice itself is the real reason to produce additional scars at the 
 surface of pmma blocks . when the same weight of toothpaste was used , the abrasion noted 
 on the pmma blocks appeared roughly related to the size of the abrasive particles 
 evaluated by bright field and polarization microscopy . however , as specified by the 
 manufacturer , the gencix powder should not be used as a classical 
 toothpowder . the pumice particles are mainly used to nucleate and facilitate the deposit 
 of the plant homogenate and produce spherical capsules . as the plant homogenate is 
 readily dissolved in water , only the pumice particles ( composed of silicates and 
 aluminum oxide ) with sharp edges are liberated . so , when the test is done with a large 
 amount of powder , this leads to the accumulation of a considerable volume of pumice 
 powder . when using the gencix toothpowder as recommended by the manufacturer 
 ( after dilution in water ) , the abrasion was in the same range than per blan 
 or kontrol . because the mass density of the dentifrice is lower than the 
 other powders , using the same volume of gencix powder did not produce 
 significant erosion when compared to the brush used with distilled water or 
 parodontax . bright field and polarization microscopy , together with sem analysis , are simple methods 
 to evaluate the morphology of the abrasive particles contained in a dentifrice , although 
 these methods are only qualitative . vsi microscopy is a new powerful technique for the 
 evaluation of material and biomaterial surface and to study their degradation at the 
 nanoscale level . abrasion due to a dentifrice appears linked to the amount and 
 nature of the abrasive powder used . this work was made possible by grants from contrat region pays de la loire : bioregos2 
 program . many thanks to mrs .