Effects of Regular and Whitening Dentifrices on Remineralization of Bovine Enamel in Vitro Andrej M

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Effects of regular and whitening dentifrices on remineralization of bovine enamel in vitro Andrej M. Kielbassa, Dr Med Dent1/Peter Tschoppe, Dr Med Dent2/ Elmar Hellwig, Dr Med Dent3/Karl-Thomas Wrbas, Dr Med Dent4

Objective: To compare in vitro the remineralizing effects of different regular dentifrices and whitening dentifrices (containing pyrophosphates) on predemineralized enamel. Method and Materials: Specimens from 84 bovine incisors were embedded in epoxy resin, partly covered with nail varnish, and demineralized in a lactic acid solution (37°C, pH 5.0, 8 days). Parts of the demineralized areas were covered with nail varnish, and specimens were randomly assigned to 6 groups. Subsequently, specimens were exposed to a remineralizing solution (37°C, pH 7.0, 60 days) and brushed 3 times a day (1:3 slurry with remineralizing solution) with 1 of 3 regular dentifrices designed for anticaries (group 1, amine; group 2, sodium fluoride) or periodontal (group 3, amine/stannous fluoride) purposes or whitening dentifrice containing pyrophosphates (group 4, sodium fluoride). An experimental dentifrice (group 5, without pyrophosphates/fluorides) and a whitening dentifrice (group 6, monofluorophosphate) served as controls. Mineral loss and lesion depths were evaluated from contact microradiographs, and intergroup comparisons were performed using the closed-test procedure (alpha =.05). Results: Compared to baseline, specimens brushed with the dentifrices containing stannous/amine fluorides revealed significant mineral gains and lesion depth reductions (P < .05). Concerning the reacquired mineral, the whitening dentifrice performed worse than the regular dentifrices (P > .05), while mineral gain, as well as lesion depth, reduction was negligible with the control groups. Conclusion: Dentifrices containing pyrophosphates perform worse than regular dentifrices but do not necessarily affect remineralization. Unless remineralizing efficacy is proven, whitening dentifrices should be recommended only after deliberate consideration in caries-prone patients. (Quintessence Int 2009;40:103–112)

Key words: artificial caries, dentifrices, enamel, fluoride, in vitro, remineralization, tooth whitening, transversal microradiography

Concerning the remineralization efficacy of 1Professor and Head, Department of Operative Dentistry and fluoridated dentifrices, considerable informa- Periodontology, CharitéCentrum 3, University School of Dental tion has been compiled in the past, and studies Medicine, Charité - Universitätsmedizin Berlin, Berlin, Germany. evaluating mineral gain or lesion depth 2Assistant Medical Director, Department of Operative Dentistry and Periodontology, CharitéCentrum 3, University School of reduction after the use of dentifrices have Dental Medicine, Charité - Universitätsmedizin Berlin, Berlin, demonstrated variable efficacy.1–3 Well- Germany. formulated fluoride-containing dentifrices are 3Professor and Head, Department of Operative Dentistry and clinically proven to prevent and control dental Periodontology, Dental School and Hospital, Albert-Ludwigs- University, Freiburg, Germany. caries and have been judged as effective as mouthrinses or gels.4 Thus, evidence on 4Associate Professor, Assistant Medical Director, Department of Operative Dentistry and Periodontology, Dental School and the efficacy of fluoride dentifrices is convinc- Hospital, Albert-Ludwigs-University, Freiburg, Germany. ing,55 and the importance of daily tooth- Correspondence: Dr Karl-Thomas Wrbas, Abteilung für brushing with fluoridated dentifrices for pre- Zahnerhaltungskunde und Parodontologie, Universitätsklinik venting dental caries is generally accepted, für Zahn-, Mund- und Kieferheilkunde, Hugstetter Str. 55, 6 D-79106 Freiburg, Germany. Fax: +49-761-270 47 62. E-mail: at least for the young permanent dentition. [email protected] Notwithstanding, recent findings emphasized

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distinct differences regarding the mode of phates on remineralization (testing the null action, thus accentuating the need for further hypothesis that pyrophosphates do not ham- research.5 per mineral gain and lesion depth reduction). In the last decade, tooth whitening has become a steadily booming sector, and, according to the turnover figures, consumers have been enormously attracted to these METHOD AND MATERIALS products. However, with a plethora of over- the-counter (and “me-too”) products claiming Preparation of enamel specimens to whiten teeth, there is considerable uncer- Eighty-four freshly extracted bovine incisors tainty about the mode of action. Some of the stored in Ringer solution (DAB 7, Delta- whitening dentifrices contain polishing or Pharma) at 4°C were used in this study. The chemical agents (to improve tooth appear- teeth were cleaned carefully, and from each ance by removing surface stains through crown, 1 enamel sample (3 ϫ 4 ϫ 3 mm2) gentle polishing), chemical chelators (providing was prepared using a diamond-coated band some additional stain-removal effectiveness), saw under continuous water cooling (Exakt or other nonbleaching agents. Occasionally, Mikroschleifsystem, PSI Grünewald). The these dentifrices have been advocated as enamel specimens were embedded into possible substitutes for regular products.7 epoxy resin (Technovit 4071, Heraeus However, for unanimous assent, whitening Kulzer), and surfaces were hand polished dentifrices should exhibit caries-preventive progressively up to 4,000 grit with minimal effects and foster remineralization; unfortu- substance loss (approximately 200 µm). The nately, information on the latter is scarce and opposing surface of the embedded speci- has been restricted to a few studies evaluat- mens was prepared in the same manner ing the effects of tartar-control dentifrices8 (600 grit), parallel to the established flat plane and whitening dentifrices.9 until the remaining thickness of the epoxy Due to the Cosmetic Products (Safety) resin blocks was about 2 mm. The speci- Regulations, the composition of (whitening) mens were stored in Ringer solution (DAB 7) dentifrices is subject to restrictions in Europe, at 4°C again. Subsequently, the enamel sur- and true bleaching effects cannot be expect- face was covered partially with an acid-resistant ed. Instead, most whitening dentifrices aim to nail varnish (Betrix) for control of sound remove extrinsic stains and obviate the develop- enamel. With this procedure, the extent of ment of calculus. Frequently, this is achieved demineralization and possible remineraliza- by adding soluble pyrophosphates to the tion could be assessed, and comparison to formulations, and it is well-accepted that the sound control areas within the same pyrophosphates (acting as crystal growth specimen was assured. inhibitors) retard calculus formation.10 How- ever, this property might adversely affect the Demineralization of the enamel remineralization process, and pyrophosphates specimens have indeed been condemned as “crystal poi- Five liters of a demineralizing solution (pH sons”11 that possibly decrease the anticario- 5.0) were prepared to create initial lesions as genic effects of this type of tartar-control den- previously described.15 The prepared enamel tifrice. Consequently, this has led to a tentative specimens were placed into the solution and reservation expressed in textbooks of preven- kept in an incubator (Memmert) for 8 days at tive dentistry,12 even though these effects have 37°C. The pH value of the solution was con- been considered arguable.13,14 trolled daily (pH-Meter 526, WTW Wissen- Thus, the aim of this study was (1) to com- schaftlich-Technische Werkstätten), and pare the remineralization efficacies of whiten- slight elevations were corrected with lactic ing and anticaries dentifrices on shallow acid to maintain a constant pH value lesions (testing the null hypothesis that the between 5.0 and 5.1 during the entire dem- fluoride-containing dentifrices do not differ) ineralization period. Subsequently, the dem- and (2) to scrutinize the effects of pyrophos- ineralized areas of the enamel specimens

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Table 1 Principal components of products used

Group Manufacturer Type of fluoride Pyrophosphate

1. Elmex GABA Amine fluoride 297 (Olaflur); 1,250 ppm No 2. Enamelon Enamelon Sodium fluoride; 1,100 ppm No 3. Meridol GABA Olaflur; 350 ppm Stannous fluoride; 1,050 ppm No 4. Dentalweiss GlaxoSmithKline Sodium fluoride; 1,350 ppm Yes 5. Experimental GlaxoSmithKline None No 6. Perlweiss Church & Dwight Sodium monofluorophosphate; 1,000 ppm No

With exception of the pyrophosphate-free dentifrice, all products were bought in public drugstores.

were partially covered with nail varnish again, sary. The specimens were then reexposed to and the 84 specimens were randomly their respective remineralizing solution. Total assigned to 6 experimental groups (n = 14). duration of the brushing and remineralization period was 60 days. Remineralization and exposure to the dentifrices Polarizing microscopy and The demineralized specimens were exposed microradiographic evaluation to a fluoride-free remineralizing solution.16 Following the in vitro exposition, the speci- Five grams of dentifrice were mixed with 15 mens were cut perpendicular to the deminer- mL of the remineralizing solution using an alized/exposed surfaces. Subsequently, the electromagnetic stirrer until a homogeneous specimens were mounted on a transparent suspension (slurry) resulted (ratio 1:3). The acrylic plastic microscope slide, and slices of slurry was renewed for each brushing 300-µm thickness were cut (Exakt Trenn- sequence. Two anticaries dentifrices (Elmex schleifsystem). The slabs were ground (2,400 caries control, group 1; and Enamelon, grit, Exakt Mikroschleifsystem) from the coun- group 2) and a dentifrice designed for peri- terside to a uniform thickness of 100 µm. odontal purposes (Meridol, group 3) were Parallelism of the samples was tested using a used as regular pastes. Sensodyne Dental- digital micrometer with a precision of 0.001 weiss (Gentle Whitening, containing pyro- mm (Mitutoyo). phosphates; group 4) was used as a whitening For qualitative evaluation, specimens were dentifrice. An experimental dentifrice (similar mounted on a glass microscope slide. The to Gentle Whitening but without pyrophos- slabs were imbibed in water and quinoline phates and fluorides; obtained from Glaxo- (Merck-Schuchardt) and studied with polarized SmithKline, who prepared this dentifrice for light (inverted, translucent light microscope, this study; group 5) and Perlweiss-Raucher- IM 35, Zeiss) at different magnifications. zahnweiss (Pearl Drops smokers whitening, Subsequently, contact microradiographs of group 6) served as controls. Components of the enamel specimens were obtained with a these materials are listed in Table 1. nickel-filtered copper (CuK␣) X-ray source Brushing with the respective slurries was (PW 1830/40, Philips), operating at 20 kV conducted 3 times a day for 2 minutes. The and 20 mA. For all microradiographs, an alu- slurry was applied to all specimens of the minum step wedge was used. The radiation respective groups; subsequently, each of the source-to-film distance was 34 cm. The expo- 12 specimens was brushed for some 5 sec- sure time was 12 seconds; a high-resolution onds using a soft manual toothbrush. Thus, film (high-speed holographic film, Kodak SO- every specimen was immersed for 2 minutes 253, Kodak) was used and developed under in the dentifrice slurry at each brushing pro- standardized conditions.15 cedure. Subsequently, the specimens were Microradiographs were studied with a dig- cleaned under running tap water, and nail ital image analyzing system (charge-coupled varnish was checked and repaired if neces- device [CCD] video camera, Model XC77E,

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Figs 1a and 1b Polarizing micrographs of an enamel slab (imbibed with quinoline) depicting sound control (C) and demineralized areas (D) (baseline), both covered with nail varnish (NV). Study effects are restricted to the remineralization window (RW, not covered with nail varnish) indicating that appreciable deposition of calcium, phosphates, and fluorides has occurred (specimen brushed and immersed with group 3 dentifrice slurry; original magnification ϫ 32).

Sony) that was interfaced to a universal The effects of the dentifrice slurries on min- microscope (Axioplan, Zeiss) and a personal eral content and lesion depths were analyzed computer. The mineral loss was calculated by using the closed test procedure (based on integrating the difference between the mineral Kruskal-Wallis). Comparisons between the content (vol%) in sound and demineralized demineralized areas and the remineralized enamel over the depth of the lesion. Lesion regions within the same specimens were per- depth was defined as the distance from the formed by means of rank-sum testing surface (0%) to the location in the lesion (Wilcoxon). The level of significance was set where the mineral content was larger than at 5%. 95% of the mineral content in sound enamel. Mineral vol% of sound enamel was set at 88%. A dedicated software (TMR for Windows, Release 1.24, Inspektor Research RESULTS Systems) was used to calculate the mineral content depth profiles from the image scans Morphologic analysis of the polarization as well as the reference step wedge data, and micrographs revealed that all in vitro dem- mineral content (⌬Z, vol% ϫ µm) and lesion ineralized and remineralized specimens depths (LD, µm) of the sound (due to slight (including the negative controls) constantly misalignments during the experimental pro- showed subsurface lesions consistently cedures), demineralized, and remineralized revealing a surface layer that was more min- enamel within the same specimen were eralized than the distinct lesion body, with no determined.15 signs of erosive loss. Pseudointact surface layers were most accentuated in areas Statistical analysis exposed to the dentifrice slurries of groups 1 In case of feigned mineral loss of the non- to 3. Figure 1 illustrates the effects of the slur- demineralized, sound enamel (controls), ⌬Z ry used in group 3 (specimen after imbibition and LD were subtracted from ⌬Z (LD) as with quinoline). Here, the predemineralized measured on the demineralized enamel lesion body appears positively birefringent, ⌬ areas ( Zbase/LDbase) and from the enamel indicating an increased mineral content com- areas that had been brushed with the respec- pared to the demineralized region covered ⌬ tive slurries ( Zremin/LDremin). The corrected with nail varnish. Similar reactions were values were analyzed by analysis of variance observed with the specimens of group 1. (ANOVA) using the Statistical Analysis These results were corroborated by trans- System (SAS Release 6.12, SAS Institute). versal microradiography. Figure 2 illustrates

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2,500 ⌬Z base 1.4% ⌬ Zremin

2,000 44.6% * 25.5%

µm) 1.7% ϫ 1,500 44.8% * 19.5%

1,000 Z (volume% Z (volume% ⌬ 500

0 1 2 3 4 5 6 Group

⌬ Fig 2 Box-and-whisker plots (100%) of the mineral content after demineralization ( Zbase) and remineral- ⌬ ization ( Zremin). Significant differences between baseline and remineralization values (given as percentage reductions; ⌬⌬Z) are indicated by asterisks (P < .05; Wilcoxon rank sum test).

Table 2 Means (SDs) of mineral losses ⌬Z (vol% ϫ µm) and lesion depths (µm) after in vitro demineralization (baseline) and after remineralization with the different dentifrices

Mineral loss ⌬Z (vol% ¥ µm) Lesion depth (µm)

⌬ ⌬ Group Zbase Zremin P LDbase LDremin P 1 737.7 (307) 407.1 (203) A 54.7 (21) 40.1 (13) A,B 2 909.3 (211) 731.8 (242) A,B 62.2 (12) 51.9 (13) B,C 3 758.5 (345) 419.9 (188) A 49.5 (13) 36.9 (12) A 4 895.3 (417) 667.1 (273) A,B 51.2 (19) 41.8 (12) A,B 5 914.2 (277) 899.0 (329) B 62.0 (17) 59.6 (12) C 6 1,222.9 (492) 1,205.0 (399) B 70.7 (23) 65.4 (19) C

Different letters indicate significant intergroup differences after the remineralization period (closed test procedure, based on Kruskal-Wallis).

the effects of the various dentifrices on the (P >.05; Wilcoxon; see Fig 2, hatched boxes). previously demineralized enamel specimens. Intergroup comparison after remineralization ⌬ The mean mineral loss (SD) after demineral- ( Zremin) revealed that mineral contents of ⌬ ization ( Zbase) ranged from 737.7 (307.3) groups 1 and 3 differed significantly from vol% ϫ µm (group 1) to 1,222.9 (492.0) vol% groups 5 and 6 (P < .05; closed test proce- ϫ µm (group 6); mineral loss was not signifi- dure; Table 2). cantly different among the groups (P > .05; The mean lesion depths after demineral-

closed test procedure; Table 2). After the ization (LDbase) ranged from 49.5 (12.6) µm remineralization period, mineral gain ⌬⌬Z (group 3) to 70.7 (23.5) µm (group 6) (P > was about 45% for groups 1 and 3, respec- .05; closed test procedure; see Table 2). tively. This was significantly different from Mean lesion depth reduction (⌬LD) was baseline (P <.05; Wilcoxon rank sum test). greatest in groups 1 and 3 (26.7% and For the other groups, lower mineral gains 25.5%, respectively), and lesion depths after (varying from 1% to 25%) were calculated remineralization differed significantly from

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⌬ 120 Zbase ⌬ Zremin 7.5% 100 26.7% 3.9% 16.6% 18.4% 80 25.5% * 60

40 Lesion depth (µm) Lesion

0 1 2 3 4 5 6 Group

Fig 3 Box-and-whisker plots (100%) of lesion depths after demineralization (LDbase) and remineralization (LDremin). Significant differences between baseline and remineralization values (given as percentage reductions (⌬LD) are indicated by asterisks (P < .05; Wilcoxon rank sum test).

baseline in group 3 (P < .05; Wilcoxon; Fig 3, the results, since a differing toothbrush pres- hatched boxes). Again, lesion depth values sure or brushing time between various after remineralization of group 3 were signifi- groups should have averaged out during the

cantly lower (LDremin) than those of groups 5 exposure time of 60 days. Exposing the spec- and 6 revealing only negligible effects (P < .05; imens to the dentifrices for 2 minutes 3 times closed test procedure; see Table 2). a day seems to mimic the clinical situation properly, and the respective brushing time of 5 seconds for each specimen appears to be adequate. Moreover, the brushing motions DISCUSSION resulted in a slight agitation of the slurry, and total immersion time of the specimens Rationales for using bovine enamel speci- should have been the driving force for the mens have been discussed recently,17 and observed remineralization effects. this enamel source represents an accepted The present model used shallow lesions substitute for human dental hard tissue, at (of some 60-µm depth); thickness and min- least with remineralization experiments.17,18 In eral content of the surface layer (17 µm and the present study, a (constant) remineralization 65 vol% ϫ µm, respectively) were in a range model was used to evaluate the effects of the described previously,19 and not high enough different dentifrices. While pH-cycling models to seriously impede remineralization.17 (including demineralization periods) might Intergroup differences of baseline mineral mimic the dynamics of the clinical situation loss values were not significant; however, more adequately, remineralization-only mod- ranges among groups were higher than els offer the opportunity to effectively monitor changes induced during treatments, and this caries-preventive regimens on dental hard should be considered when interpreting the tissues on a short time basis, thereby simu- results of the present study. It is well accept- lating a best-case scenario. Thus, initial ed that remineralization depends on calcium, screening of the products5 could be accom- phosphate, and fluoride concentrations of plished with the present approach. the remineralization solutions,20 and fluoride Although not standardized, the brushing uptake benefits are predominantly restricted procedure itself should not have influenced to the outer 50 µm of enamel.21 Thus, it can

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be assumed that the used dentifrices (with plying fluoride, calcium, and phosphate salts fluoride contents clearly exceeding 500 from a dual dispensing package that is not ppm) should have enhanced remineraliza- marketed anymore) revealed lesion depth tion of these early lesions.5 Nevertheless, sig- reductions differing significantly from those nificant effects were recorded with only the of group 3 (see Table 2). Thus, the present amine and the amine/stannous fluoride results were not in accordance with those of preparations (groups 1 and 3), and this was a previous study that indicated improved in accordance with the results of other studies remineralization effects of calcium and phos- emphasizing the positive effects of these phate supplementation in this kind of denti- types of fluorides.1,22,23 frice.29 From a clinical point of view, it should Indeed, mineral deposition was found in be emphasized that remineralization is a all aspects of the lesions in the present study, process depending on several factors (eg, at least with groups 1 and 3. With the denti- biofilm composition, oral pH, presence of frice of group 3, although it is primarily salivary proteins and enzymes, lipids, or intended to promote periodontal health, antimicrobial capacity), not on only calcium polarized light microscopy and microradiog- and inorganic phosphates.30 Moreover, while raphy of transverse sections revealed the present study revealed significant differ- increased mineral gain and reduced lesion ences among the various types of fluorides, depths, as well as clearly accentuated sur- this result does not seem to be attributable to face layers. With group 3, deposition of stan- clinical benchmarks. When considering clini- nous ions into the lesion is conceivable,24 cal studies on tartar-control dentifrices, it and this could be due to the soaking and seems clear that mineralization inhibitors do brushing effects of the present study. not appear to clinically affect caries protection However, even if the apparent calcium phos- of dentifrices.31,32 phate redeposition in this group possibly In recent years, many dentifrices claiming interfered with stannous compounds, the whitening effects have become available. In clinical importance of this effect remains the European market, whitening effects of speculative. Because these compounds dentifrices usually are achieved by the incor- potentially were responsible for the observed poration of abrasives (not by active perox- changes of birefringence (as seen in Fig 1),25 ides), and this results in a pronounced clean- further studies are warranted to resolve the ing action. In contrast, small amounts of true corresponding issues. With the present bleaching compounds are added to some results, former studies indicating pro- degree outside Europe.12 Therefore, since nounced dentifrice effects in both the sur- most dentifrices comprise abrasives (eg, face layer2 and the lesion body3 could be bicarbonate, alumina, or polyphosphates), confirmed, and the first hypothesis was most regular dentifrices could claim stain rejected. Additionally, the present results removal and tooth brightening, at least to were according to previous studies demon- some extent; thus, there should be only strating the beneficial effects of frequent minor differences with regard to whitening applications of low concentrated fluorides on dentifrices, and this has been corroborated lesion recovery.23,26,27 in an in situ study revealing that a whitening Interestingly, remineralization effects dentifrice did not significantly increase the revealed with the sodium fluoride–containing wear of softened enamel compared with a dentifrices of group 2 were less pronounced regular dentifrice.33 Moreover, whitening den- when compared to groups 1 and 3. With pro- tifrices have been designed for regular (and longed experimental periods (remembering unsupervised) surrogate use, even if the that remineralization is a continuum process), whitening effect seems to be far less than it might be assumed that remineralization that obtained with the bleaching techniques enhanced by this dentifrice should also have conventionally used by the profession. differed significantly from baseline values.27,28 Therefore, any of the whitening dentifrices However, this anticaries dentifrice (represent- (including the recently marketed ones) ing a promising concept simultaneously sup- should contain fluorides. Hence, these prod-

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ucts should conjecturally be anticario- Similar effects are conceivable with the pres- genic8,9,13,14,22,34 (and antierosive35). With ent study; the final outcome observed with regard to the anticaries action of fluoridated group 4 was significantly different from the (whitening) dentifrices, the use of pyrophos- pyrophosphate-free experimental dentifrice phates has been controversial, and some with regard to lesion depth reduction (group uncertainty regarding the effects of pyro- 5, control). Importantly, this indicates a pro- phosphates on caries reversal has been doc- nounced remineralization with pyrophos- umented.30 However, neither fluoride uptake22 phates (and fluorides) and seems to obvert nor remineralization14 of enamel was hampered the restrainedly expressed assessments.12,30 by pyrophosphates. This was in accordance All in all, no clear effect on retarding reminer- with another study focusing on inhibition of alization was observed, and the second lesion progression and enhancement of rem- hypothesis could not be rejected. ineralization,13 revealing that even higher As expected, the whitening dentifrice con- amounts of soluble pyrophosphates did not taining polyphosphates (group 6; control) impair the efficacy of fluoride-containing den- and fluorides (and sodium monofluorophos- tifrices. With the present study, these effects phate as the anticaries agent) did not reveal could be reemphasized; the pyrophosphate- any considerable remineralization. This was containing dentifrice (group 4) induced in accordance with several in vitro studies remarkable mineral gain (+25%) and lesion that indicated that other fluorides are superi- depth (+18%) reductions, although not sig- or to monofluorophosphates.1,3,21,27,39 Again, nificantly differing from baseline values and these results are difficult to extrapolate to the performing worse than the products of in vivo situation, since, in particular, hydroly- groups 1 and 3 (see Figs 2 and 3). sis is an important factor for the anticaries To explain these observations, it seems activity of this decay-preventive molecule. worth mentioning that pyrophosphates Moreover, other aspects (eg, experimental (described as small, hydrolytically labile mol- techniques, morphology of the surface layer) ecules) are present in saliva.36 From a recent seem to be relevant,3 along with stability and article compiling several studies on calculus (bio-)availability of the fluorides.39 and caries, it became clear that caries preva- lence is significantly lower in calculus-prone patients than in calculus-free subjects, thus indicating that salivary calcium and phos- CONCLUSION phate concentrations appear to be important variables found to correlate with both condi- The results of the present study confirm that tions.30 It might be argued that pyrophos- ionic fluoride compounds may be effective in phates could influence these effects; however, enhancing remineralization, at least for shal- pyrophosphate-containing dentifrices have low subsurface enamel lesions. This could not revealed any effects on the state of calcium be revealed even for adequately formulated and phosphate in saliva.37 Instead, increased dentifrices primarily designed for periodontal pyrophosphate concentrations (as used in reasons. Within the limitations of the current dentifrices and mouthrinses10) are able to experimental conditions, compared to base- block the adsorption sites available for crys- line values, the used stannous and/or amine tal growth; thus, phosphate ions cannot absorb fluoride–containing dentifrices performed onto the apatite crystals, and crystal growth better than the tested whitening dentifrice. is inhibited. Below this level, the addition of Pyrophosphates obviously do not hamper sodium fluoride can induce a short period of remineralization; nevertheless, in particular, slow precipitation, which is followed by rapid caries-active patients should gain more ben- crystal growth gradually burying the inhibitors efits from well-formulated anticaries compo- and generating a new surface without sitions, at least with regard to the products inhibitors; now, crystal growth proceeds at studied here. Since there is only scanty infor- rates comparable with those of the control mation on the efficacy of whitening denti- systems in the absence of any inhibitors.38 frices, the present results clearly indicate the

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need for further evaluation of the recently 8. Pfarrer AM, White DJ, Featherstone JD. Anticaries introduced whitening dentifrices with regard profile qualification of an improved whitening dentifrice. J Clin Dent 2001;12:30–33. to possible anticaries effects. 9. Watanabe MM, Rodrigues JA, Marchi GM, Finally, the results of the present study are Ambrosano GM.In vitro cariostatic effect of whiten- not representative of other types of whitening ing toothpastes in human dental enamel— dentifrices, and, therefore, whitening denti- Microhardness evaluation. Quintessence Int 2005; frices should be recommended to caries- 36:467–473. prone patients only after deliberate consider- 10. White DJ, Bowman WD, Nancollas GH. Physical- ation (unless anticaries activity is proven). chemical aspects of dental calculus formation and inhibition: In vitro and in vivo studies. In: ten Cate Future investigations should focus on the JM (ed). Recent Advances in the Study of Dental influence of further compounds usually Calculus. Oxford: IRL Press at Oxford University added to whitening dentifrices and should Press, 1989:175–188. include other lesion types and study protocols. 11. Rølla G, Saxegaard E. Critical evaluation of the composition and use of topical fluorides, with emphasis on the role of calcium fluoride in caries inhibition. J Dent Res 1990;69(spec no):780–785. ACKNOWLEDGMENTS 12. Fischman SL, Yankell SL. Dentifrices, mouth rinses, and tooth whiteners. In: Harris NO, Garc¸ía-Godoy F (eds). Primary Preventive Dentistry, ed 5. Stamford, The authors are indebted to Dr D. Steiner (Albert- CT: Appleton & Lange, 1999:103–124. Ludwigs-Universität Freiburg) for his most valuable 13. Featherstone JD,Shariati M,Brugler S,Fu J,White DJ. contribution to this work and to Mr M. Quast Effect of an anticalculus dentifrice on lesion pro- (GlaxoSmithKline) for the preparation of the experi- gression under pH cycling conditions in vitro.Caries mental dentifrice (group 6). Prof Dr J. Schulte-Mönting’s Res 1988;22:337–341. (Albert-Ludwigs-Universität Freiburg) assistance with the statistical analysis is greatly appreciated. 14. Mellberg JR, Petrou ID, Fletcher R, Grote N. Evaluation of the effects of a pyrophosphate-fluoride anticalculus dentifrice on remineralization and fluoride uptake in situ. Caries Res 1991;25:65–69. 15. Kielbassa AM, Shohadai SP, Schulte-Monting J. REFERENCES Effect of saliva substitutes on mineral content of demineralized and sound dental enamel. Support 1. Arnold WH, Dorow A, Langenhorst S, Gintner Z, Care Cancer 2001;9:40–47. Banoczy J, Gaengler P.Effect of fluoride toothpastes 16. Klimek J, Hellwig E, Ahrens G. Fluoride taken up by on enamel demineralization.BMC Oral Health 2006; plaque, by the underlying enamel and by clean 6:8. enamel from three fluoride compounds in vitro. 2. Joyston-Bechal S, Kidd EA. Remineralisation of cari- Caries Res 1982;16:156–161. ous lesions in enamel by exposure to a fluoride- 17. Lynch RJ. Model parameters and their influence on containing toothpaste in vitro. Br Dent J 1986;161: the outcome of in vitro demineralisation and rem- 133–136. ineralisation studies. Monogr Oral Sci 2006; 3. White DJ. Reactivity of fluoride dentifrices with arti- 19:65–85. ficial caries. II. Effects on subsurface lesions: F 18. Kielbassa AM, Hellwig E, Meyer-Lueckel H. Effects of uptake, F distribution, surface hardening and rem- irradiation on in situ remineralization of human and ineralization. Caries Res 1988;22:27–36. bovine enamel demineralized in vitro. Caries Res 4. Marinho VC, Higgins JP, Sheiham A, Logan S. One 2006;40:130–135. topical fluoride (toothpastes, or mouthrinses, or 19. Kielbassa AM, Gillmann L, Zantner C, Meyer-Lueckel gels, or varnishes) versus another for preventing H, Hellwig E, Schulte-Monting J. Profilometric and dental caries in children and adolescents. Cochrane microradiographic studies on the effects of tooth- Database Syst Rev 2004:CD002780. paste and acidic gel abrasivity on sound and dem- 5. ten Cate JM, Exterkate RA, Buijs MJ.The relative effi- ineralized bovine dental enamel. Caries Res 2005; cacy of fluoride toothpastes assessed with pH 39:380–386. cycling. Caries Res 2006;40:136–141. 20. Meyer-Lueckel H, Chatzidakis AJ, Kielbassa AM. 6. Twetman S,Axelsson S,Dahlgren H,et al.Caries-pre- Effect of various calcium/phosphates ratios of car- ventive effect of fluoride toothpaste: A systematic boxymethylcellulose-based saliva substitutes on review. Acta Odontol Scand 2003;61:347–355. mineral loss of bovine enamel in vitro. J Dent 2007; 35:851–857. 7. Seymour KG. Whitening toothpastes: Meeting needs or satisfying demands? Br Dent J 1996;180: 278.

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