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In vitro evaluation of different remineralization periods in improving the resistance of previously eroded bovine dentine against tooth-brushing abrasion
Archives of Oral Biology 46 (2001) 871– 874 www.elsevier.com/locate/archoralbio
Short communication
In vitro evaluation of different remineralization periods in improving the resistance of previously eroded bovine dentine against tooth-brushing abrasion Thomas Attin a,*, Wolfgang Buchalla b, Barbara Putz a a
Department of Operati6e Dentistry and Pre6enti6e Dentistry, Uni6ersity of Go¨ttingen Georg-August-Uni6ersita¨t Go¨ttingen, Robert-Koch-Str. 42, D-37075 Gottingen, Germany b Indiana Uni6ersity School of Dentistry, Oral Health Research Institute, 415 North Lansing Street, Indianapolis, IN 46202, USA Accepted 13 March 2001
Abstract One dentine specimen was prepared from each of 90 bovine incisors. The samples were then evenly distributed among nine groups (A–I) and submitted to 10 alternating de- and re-mineralization cycles, including abrasion by tooth brushing. Each cycle started with a demineralization using the erosive soft drink Sprite Light® for 1 min, followed by storing the samples in pooled human saliva for a total of 240 min. The specimens were removed from the saliva at different intervals (group A, 0 min; B, 15 min; C, 30 min; D, 45 min; E, 60 min; F, 90 min; G, 120 min) and brushed in an automatic brushing machine. Groups H (erosion, but no brushing) and I (no erosion, but brushing), which were also stored in saliva for 240 min, served as controls. After these cycles, loss of dentine was determined by profilometry, producing the following values (mean 9S.D.), which were analysed statistically (P 0 0.05): group A (5.03 9 1.49 mm), B (4.4491.09 mm), C (4.91 90.95 mm), D (5.47 9 1.52 mm), E (5.29 9 1.45 mm), F (4.76 90.74 mm), G (5.16 9 0.71 mm), H (2.61 91.31), I (1.11 9 0.39). Groups A – G had no significant differences, but they showed a significantly greater loss of dentine than groups H and I. It is concluded that the abrasion resistance of eroded bovine dentine is still decreased after a remineralization period of 120 min. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Erosion; Remineralization; Brushing abrasion; Dentine
The erosion of teeth by, for example, acidic drinks or foodstuff, leads to demineralization and softening of the tooth surface (Lussi et al., 1995). Brushing the eroded softened enamel and dentine then increases tooth wear (Davis and Winter, 1980). In order to * Corresponding author. Tel.: + 49-551-392884; fax: +49551-392037. E-mail address: [email protected] (T. Attin).
minimize loss of tooth substance by toothbrush abrasion, the advice is to avoid brushing for at least an hour after the consumption of acidic soft drinks (Edwards et al., 1998). This delay should allow for rehardening of the softened eroded surface, supported by the action of saliva. Generally, human saliva is supersaturated with respect to apatite, which not only prevents the dental hard tissue from dissolving but also has the capacity to reharden demineralized tissue (Larsen, 1975; Featherstone, 1983). With respect to dental enamel, the recom-
0003-9969/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 3 - 9 9 6 9 ( 0 1 ) 0 0 0 3 9 - 5
T. Attin et al. / Archi6es of Oral Biology 46 (2001) 871–874
872
mendation to postpone brushing after the consumption of acidic drinks was recently confirmed by the results of in situ studies (Jaeggi and Lussi, 1999; Attin et al., 2001). With respect to dentine, there are as yet no scientific data on the appropriate length of time that should elapse before brushing can be performed without increasing tooth wear. Consequently, our aim now was to evaluate the period of remineralization needed to re-establish the resistance of dentine to brushing abrasion after demineralization with an acidic soft drink. The crowns of 90 bovine incisors were embedded in acrylic resin (Technovit 4071®; Kulzer, Wehrheim, Germany) and the enamel surface was ground until dentine was just visibly exposed. The specimens were then ground flat with water-cooled carborundum discs (500 – 4000 grit, waterproof silicon carbide paper; Struers, Erkrath, Germany) and polished with diamond spray (3 and 1 mm, DP-Spray P3; Struers). Grinding and polishing resulted in approx. 200 mm of the dentine being removed, which was controlled with a micrometer (Digimatic; Mitutoyo-Meßgera¨ te, Leonberg, Germany). The exposed dentine surface was scrutinized under a light microscope (Zeiss, Oberkochen, Germany) at 40× magnification to make sure that no enamel islands were left. The dentine specimens were covered with tape (Tesa®; Beiersdorf, Hamburg, Germany), leaving a window of 1.2 ×10.0 mm2 in their centre. This procedure ensured the presence of reference surfaces when measuring the depth of the abrasion grooves (Attin et al., 1998). The tape was fixed so that the long axis of the exposed window was orientated in the mesiodistal direction of the crown. The specimens were assigned randomly to one of nine experimental groups (A–I; n=10 in each group). The samples in groups A –G were submitted to 10 alternating de- and remineralization episodes with tooth-brushing abrasion. The specimens in groups H and I, which served as controls, were subjected to the specific cycles described below. Before
the cycles all specimens were stored in human saliva for 12 h in order to create an acquired pellicle. The samples in groups A – G were submitted to 10 demineralization–remineralization regimens, including tooth-brushing abrasion, as follows: 1. demineralization in Sprite Light® (1 min), 2. first remineralization in human saliva, 3. brushing abrasion, 4. second remineralization in human saliva. The length of the remineralization periods was varied between the different groups, but the total time of remineralization (remineralization before and after brushing) amounted to 240 min in all groups (Table 1). After erosion and after brushing, the specimens were rinsed with distilled water for 20 s and blotted dry. Demineralization was accomplished by storing the specimens in a fresh lot of 50 ml of Sprite Light® (Nordwest Getra¨ nke, Osnabru¨ ck, Germany) under constant agitation on an orbital shaker. Sprite Light® (pH 2.84 with CO2; citric acid, 18.4 g/100 ml; fluoride, 0.3 parts/106) was chosen for the demineralization because of its proven erosive capacity (Attin et al., 1998). It was chosen instead of citric acid because we intended to use the solution intraorally in an in situ investigation in which we sought to mimic the demineralizing effects of sipping an acidic beverage. For remineralization the specimens were immersed in 30 ml unstimulated human saliva (37°C) collected from 10 volunteers aged between 20 and 60 years. For the experiments the saliva samples of all volunteers were pooled, mixed with 1 ml 0.2% sodium azide per 1000 ml saliva, and then centrifuged at 2000 rev/min for 1 min. The supernatant was stored at 4°C until needed for remineralization. The 30 ml of saliva used for each specimen in each cycle was renewed after the total period of 240 min. An automatic toothbrushing machine (VDD Elektronik, Freiburg) was used for the brushing abrasion (Attin et al., 2000). Toothbrushes with medium bristle stiffness were used (Medoral Clip™; Diedenhofen, St.
Table 1 Characterization of the nine experimental groups (A–I) with respect to differences in the duration of remineralization and the erosion and brushing procedures
A B C D E F G H I
Erosion
First remineralization (min)
Brushing
Second remineralization (min)
Yes Yes Yes Yes Yes Yes Yes Yes No
0 15 30 45 60 90 120 0 0
Yes Yes Yes Yes Yes Yes Yes No Yes
240 225 210 195 180 150 120 240 240
T. Attin et al. / Archi6es of Oral Biology 46 (2001) 871–874 Table 2 Mean loss (mm) of dentine (9 S.D.) in the nine experimental groups (A–I)a (0 min remineralization before brushing)A (15 min remineralization before brushing)A (30 min remineralization before brushing)A (45 min remineralization before brushing)A (60 min remineralization before brushing)A (90 min remineralization before brushing)A (120 min remineralization before brushing)A (erosion, no brushing)B (brushing, no erosion)C
A B C D E F G H I
5.09 1.5 4.49 1.1 4.99 0.9 5.59 1.5 5.39 1.4 4.89 0.7 5.29 0.7 2.69 1.3 1.19 0.4
a
Short descriptions of the groups are given in parentheses. Groups with the same superscript letter were not significantly different. A,B,C
Augustin, Germany) and renewed after brushing five specimens of the same experimental group. In each cycle the specimens were submitted to 100 brushing strokes (100 strokes/min) at a load of 4 N in 25 ml of an abrasive slurry consisting of 5 ml artificial saliva (Attin et al., 2000) mixed with 1 ml of the dentifrice Elmex® (Gaba, Therwil, Switzerland). Elmex® contains 0.125% fluoride as amine fluoride (Olaflur) and has a REA value of 4.2 90.3 and a RDA value of 77 92 (Barbakow et al., 1989). It is a water-based dentifrice (50%) with 30% hydrated silica particles with a mean size of 8.1 mm (90% B2 mm) and a maximum size of 30 mm serving as abrasives. After the 10 cycles, the tapes were removed and the loss of the dentine was determined quantitatively with a laser profilometer (UBM Meßtechnik, Ettlingen, Germany), as described in detail by Attin et al. (1999, 2000). The sensitivity of the laser profilometer amounted to 0.1 mm and the laser recorded 200 points per mm. The profilometer software allowed for calculating the average depth of the abraded part of the specimens relative to the non-abraded surface areas. Five measurements were performed in the centre of each specimen at intervals of about 200 mm and averaged. The data were analysed with the program SAS (SAS Institute Inc., Cary). Analysis of variance and covariance with repeated measurements was applied to the data. Comparisons between experimental groups were made with Tukey’s standardized range test. The level of significance was set at PB 0.05. In the samples of group H, which were demineralized but not brushed, laser profilometry revealed an even loss of dentine in the exposed area. The contour of the brushed specimens was, however, coarser due to the impact of the toothbrush bristles. The distinctly lowest loss (Table 2) of dentine occurred in the specimens of group I, which had not been
873
demineralized before brushing. Erosion without brushing (group H) resulted in less loss of dentine than in all other specimens (groups A –G). However, no significant difference was observed between the experimental groups A –G, which were different with respect to the remineralization period before and after brushing. As a consequence, brushing the eroded dentine after as long as 120 min remineralization (group D) resulted in a statistically significantly greater loss of dentine than in the control group H. Demineralization of our dentine samples was accomplished by storing them in the acidic beverage Sprite Light® for 1 min in order to simulate conditions during sipping of a beverage. All specimens were stored in human saliva for a total of 240 min in each cycle. This period was chosen to simulate the interval between two meals. The specimens were brushed with 100 strokes in each cycle. Heath and Wilson (1974) have shown that individuals brush their teeth at a frequency of 4.5 strokes/s. Assuming that each sextant is brushed for 10–20 s approximately during meticulous oral hygiene, about 45–90 brushing strokes per tooth would be applied during a single brushing episode. Hence, the number of brushing strokes applied here may simulate the clinical conditions very well. The artificial saliva used for mixing the dentifrice slurry contained calcium and phosphate in concentrations similar to those found in human saliva (Diem and Lentner, 1975; Poff et al., 1997). A fluoridated dentifrice was chosen for the slurry in order to simulate the clinical condition, as it may be assumed that the majority of people use dentifrices containing fluoride (Bratthall et al., 1996). We used two control groups to obtain an impression of dentine loss due to brushing abrasion only (group I) and erosion only (group H). The small amount of dentine removed in group I showed that abrasion due to brushing only was negligible. Group H reflected the inevitable loss of dentine during demineralization with an erosive beverage. Therefore, the amount of dentine removed in this group acted as a target value that the other experimental groups (A – G) had to compete with. However, the outcome of the experiment revealed that even a remineralization period of 120 min before brushing was not able to attain this goal. Interestingly, there was no difference in dentine loss among the groups that were brushed at different intervals after the erosive attack. It is important that all these groups were different not only with respect to the length of the first period but also that of the second period of remineralization; the shorter the first period, the longer the second. The second period was followed by the erosive challenge of the next cycle. It should also be remembered that brushing was with a slurry of fluoridated dentifrice (0.125% fluoride) mixed with artificial saliva. It is well known that fluoride application
874
T. Attin et al. / Archi6es of Oral Biology 46 (2001) 871–874 Attin, T., Kno¨ fel, S., Buchalla, W., Tu¨ tu¨ ncu¨ , R., 2001. In situ evaluation of different remineralization periods to decrease brushing abrasion of demineralized enamel. Caries Res., in press. Attin, T., Deifuß, H., Hellwig, E., 1999. Influence of acidified fluoride gel on abrasion resistance of eroded enamel. Caries Res. 33, 135 – 139. Attin, T., Zirkel, C., Hellwig, E., 1998. Brushing abrasion of eroded dentin after application of sodium fluoride solutions. Caries Res. 32, 344 – 350. Attin, T., Buchalla, W., Gollner, M., Hellwig, E., 2000. Use of variable remineralization periods to improve the abrasion resistance of previously eroded enamel. Caries Res. 34, 48– 52. Barbakow, F., Imfeld, T., Lutz, F., Stookey, G., Schemehorn, B., 1989. Dentin abrasion (RDA), enamel abrasion (REA) and polishing scores of dentifrices sold in Switzerland. Schweizer Monatsschrift fu¨ r Zahnmedizin 99, 408 – 413. Bratthall, D., Ha¨ nsel Petersson, G., Sundberg, H., 1996. Reasons for the caries decline: what do the experts believe? Eur. J. Oral Sci. 104, 416 – 422. Davis, W.B., Winter, P.J., 1980. The effect of abrasion on enamel and dentine after exposure to dietary acid. Br. Dent. J. 148, 253 – 256. Diem, K., Lentner, C., 1975. Documenta Geigy-Wissenschaftliche Tabellen. Thieme Verlag, Stuttgart. Edwards, M., Ashwood, R.A., Littlewood, S.J., Brocklebank, L.M., Fung, D.E., 1998. A videofluoroscopic comparison of straw and cup drinking: the potential influence on dental erosion. Br. Dent. J. 185, 244 – 249. Featherstone, J.D.B., 1983. Remineralization of artificial carious lesions in vivo and in vitro. In: Leach, S.A., Edgar, W.M. (Eds.), Demineralisation and remineralisation of the teeth. IRL Press, Oxford, pp. 89 – 110. Hannig, M., Balz, M., 1999. Influence of in vivo formed salivary pellicle on enamel erosion. Caries Res. 33, 372 – 379. Heath, J.R., Wilson, H.J., 1974. Forces and rates observed during in vivo toothbrushing. Biomed. Eng. 9, 61 – 64. Hellwig, E., 1992. Fluoride retention in dentin after topical application of aminefluoride. J. dent. Res. 71, 1558 – 1560. Jaeggi, T., Lussi, A., 1999. Toothbrush abrasion of erosively altered enamel after intraoral exposure to saliva: An in situ study. Caries Res. 33, 455 – 461. Larsen, M.J., 1975. Degrees of saturation with respect to apatites in parotid saliva at various pH values. Scand. J. dent. Res. 83, 7 – 12. Lussi, A., Jaeggi, T., Jaeggi-Scha¨ rer, S., 1995. Prediction of the erosive potential of some beverages. Caries Res. 29, 349 – 354. Poff, A.M., Pearce, E.I.F., Larsen, M.J., Cutress, T.W., 1997. Human supragingival in vivo calculus formation in relation to saturation of saliva with respect to calcium phosphates. Arch. Oral Biol. 42, 93 – 99. Teranaka, T., Koulourides, T., 1987. Effect of a 100-ppm fluoride mouthrinse on experimental root caries in humans. Caries Res. 21, 326 – 332. Zahradnik, R.T., Propas, D., Moreno, E.C., 1978. Effect of salivary pellicle formation time on in vitro attachment and demineralization by Streptococcus mutans. J. Dent. Res. 57, 1036 – 1042.
results in increased concentrations of both structurally and KOH-soluble fluoride in dentine (Hellwig, 1992), which supports remineralization of demineralized dentine (Arends et al., 1990). Furthermore, contact with saliva leads to the formation of an outer mineral-rich layer in dentine, which is more resistant to acid attacks (Teranaka and Koulourides, 1987). Contact between dental hard tissue and saliva also results in the time-dependent formation of acquired pellicle (Zahradnik et al., 1978), which is able to reduce the harmful effects of acids on the underlying tooth surface (Hannig and Balz, 1999). It is therefore conceivable that the longer the (second) period of remineralization after brushing, the greater the interaction between fluoride, saliva and dentine. This prolonged interaction would presumably result in better remineralization and an improvement in the acid resistance of dentine in those groups with a longer period of remineralization after brushing. We therefore speculate that, under the present conditions, shorter periods of remineralization before brushing may be outweighed by longer periods of remineralization after brushing. In contrast to previous findings for enamel (Jaeggi and Lussi, 1999; Attin et al., 2001), the remineralization of eroded dentine did not lead to an improvement in its susceptibility to abrasion . We speculate that, because of the tubular structure of dentine, surface softening is more pronounced than in enamel. It is therefore conceivable that a period long enough for the remineralization of eroded enamel is insufficient for rehardening the surface of previously softened dentine. Under the chosen in vitro conditions, we conclude that the abrasion resistance of dentine is drastically decreased after erosion. Even after 2 h of remineralization, the tooth-brushing abrasion of previously eroded dentine was still increased and was not different from the abrasion susceptibility of eroded dentine immediately after erosion.
Acknowledgements We thank Prof. Dr Ju¨ rgen Schulte-Mo¨ nting (University of Freiburg, Institute of Med. Biometry and Med. Informatics (IMBI)) for the statistical analysis of the data. The study was supported by grants (AT 26/1–2) from Deutsche Forschungsgemeinschaft (DFG).
References Arends, J., Ruben, J.L., Christoffersen, J., Jongebloed, W.L., Zuidgeest, T.G.M., 1990. Remineralization of human dentin in vitro. Caries Res. 24, 432 –435. .
Short communication
In vitro evaluation of different remineralization periods in improving the resistance of previously eroded bovine dentine against tooth-brushing abrasion Thomas Attin a,*, Wolfgang Buchalla b, Barbara Putz a a
Department of Operati6e Dentistry and Pre6enti6e Dentistry, Uni6ersity of Go¨ttingen Georg-August-Uni6ersita¨t Go¨ttingen, Robert-Koch-Str. 42, D-37075 Gottingen, Germany b Indiana Uni6ersity School of Dentistry, Oral Health Research Institute, 415 North Lansing Street, Indianapolis, IN 46202, USA Accepted 13 March 2001
Abstract One dentine specimen was prepared from each of 90 bovine incisors. The samples were then evenly distributed among nine groups (A–I) and submitted to 10 alternating de- and re-mineralization cycles, including abrasion by tooth brushing. Each cycle started with a demineralization using the erosive soft drink Sprite Light® for 1 min, followed by storing the samples in pooled human saliva for a total of 240 min. The specimens were removed from the saliva at different intervals (group A, 0 min; B, 15 min; C, 30 min; D, 45 min; E, 60 min; F, 90 min; G, 120 min) and brushed in an automatic brushing machine. Groups H (erosion, but no brushing) and I (no erosion, but brushing), which were also stored in saliva for 240 min, served as controls. After these cycles, loss of dentine was determined by profilometry, producing the following values (mean 9S.D.), which were analysed statistically (P 0 0.05): group A (5.03 9 1.49 mm), B (4.4491.09 mm), C (4.91 90.95 mm), D (5.47 9 1.52 mm), E (5.29 9 1.45 mm), F (4.76 90.74 mm), G (5.16 9 0.71 mm), H (2.61 91.31), I (1.11 9 0.39). Groups A – G had no significant differences, but they showed a significantly greater loss of dentine than groups H and I. It is concluded that the abrasion resistance of eroded bovine dentine is still decreased after a remineralization period of 120 min. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Erosion; Remineralization; Brushing abrasion; Dentine
The erosion of teeth by, for example, acidic drinks or foodstuff, leads to demineralization and softening of the tooth surface (Lussi et al., 1995). Brushing the eroded softened enamel and dentine then increases tooth wear (Davis and Winter, 1980). In order to * Corresponding author. Tel.: + 49-551-392884; fax: +49551-392037. E-mail address: [email protected] (T. Attin).
minimize loss of tooth substance by toothbrush abrasion, the advice is to avoid brushing for at least an hour after the consumption of acidic soft drinks (Edwards et al., 1998). This delay should allow for rehardening of the softened eroded surface, supported by the action of saliva. Generally, human saliva is supersaturated with respect to apatite, which not only prevents the dental hard tissue from dissolving but also has the capacity to reharden demineralized tissue (Larsen, 1975; Featherstone, 1983). With respect to dental enamel, the recom-
0003-9969/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 3 - 9 9 6 9 ( 0 1 ) 0 0 0 3 9 - 5
T. Attin et al. / Archi6es of Oral Biology 46 (2001) 871–874
872
mendation to postpone brushing after the consumption of acidic drinks was recently confirmed by the results of in situ studies (Jaeggi and Lussi, 1999; Attin et al., 2001). With respect to dentine, there are as yet no scientific data on the appropriate length of time that should elapse before brushing can be performed without increasing tooth wear. Consequently, our aim now was to evaluate the period of remineralization needed to re-establish the resistance of dentine to brushing abrasion after demineralization with an acidic soft drink. The crowns of 90 bovine incisors were embedded in acrylic resin (Technovit 4071®; Kulzer, Wehrheim, Germany) and the enamel surface was ground until dentine was just visibly exposed. The specimens were then ground flat with water-cooled carborundum discs (500 – 4000 grit, waterproof silicon carbide paper; Struers, Erkrath, Germany) and polished with diamond spray (3 and 1 mm, DP-Spray P3; Struers). Grinding and polishing resulted in approx. 200 mm of the dentine being removed, which was controlled with a micrometer (Digimatic; Mitutoyo-Meßgera¨ te, Leonberg, Germany). The exposed dentine surface was scrutinized under a light microscope (Zeiss, Oberkochen, Germany) at 40× magnification to make sure that no enamel islands were left. The dentine specimens were covered with tape (Tesa®; Beiersdorf, Hamburg, Germany), leaving a window of 1.2 ×10.0 mm2 in their centre. This procedure ensured the presence of reference surfaces when measuring the depth of the abrasion grooves (Attin et al., 1998). The tape was fixed so that the long axis of the exposed window was orientated in the mesiodistal direction of the crown. The specimens were assigned randomly to one of nine experimental groups (A–I; n=10 in each group). The samples in groups A –G were submitted to 10 alternating de- and remineralization episodes with tooth-brushing abrasion. The specimens in groups H and I, which served as controls, were subjected to the specific cycles described below. Before
the cycles all specimens were stored in human saliva for 12 h in order to create an acquired pellicle. The samples in groups A – G were submitted to 10 demineralization–remineralization regimens, including tooth-brushing abrasion, as follows: 1. demineralization in Sprite Light® (1 min), 2. first remineralization in human saliva, 3. brushing abrasion, 4. second remineralization in human saliva. The length of the remineralization periods was varied between the different groups, but the total time of remineralization (remineralization before and after brushing) amounted to 240 min in all groups (Table 1). After erosion and after brushing, the specimens were rinsed with distilled water for 20 s and blotted dry. Demineralization was accomplished by storing the specimens in a fresh lot of 50 ml of Sprite Light® (Nordwest Getra¨ nke, Osnabru¨ ck, Germany) under constant agitation on an orbital shaker. Sprite Light® (pH 2.84 with CO2; citric acid, 18.4 g/100 ml; fluoride, 0.3 parts/106) was chosen for the demineralization because of its proven erosive capacity (Attin et al., 1998). It was chosen instead of citric acid because we intended to use the solution intraorally in an in situ investigation in which we sought to mimic the demineralizing effects of sipping an acidic beverage. For remineralization the specimens were immersed in 30 ml unstimulated human saliva (37°C) collected from 10 volunteers aged between 20 and 60 years. For the experiments the saliva samples of all volunteers were pooled, mixed with 1 ml 0.2% sodium azide per 1000 ml saliva, and then centrifuged at 2000 rev/min for 1 min. The supernatant was stored at 4°C until needed for remineralization. The 30 ml of saliva used for each specimen in each cycle was renewed after the total period of 240 min. An automatic toothbrushing machine (VDD Elektronik, Freiburg) was used for the brushing abrasion (Attin et al., 2000). Toothbrushes with medium bristle stiffness were used (Medoral Clip™; Diedenhofen, St.
Table 1 Characterization of the nine experimental groups (A–I) with respect to differences in the duration of remineralization and the erosion and brushing procedures
A B C D E F G H I
Erosion
First remineralization (min)
Brushing
Second remineralization (min)
Yes Yes Yes Yes Yes Yes Yes Yes No
0 15 30 45 60 90 120 0 0
Yes Yes Yes Yes Yes Yes Yes No Yes
240 225 210 195 180 150 120 240 240
T. Attin et al. / Archi6es of Oral Biology 46 (2001) 871–874 Table 2 Mean loss (mm) of dentine (9 S.D.) in the nine experimental groups (A–I)a (0 min remineralization before brushing)A (15 min remineralization before brushing)A (30 min remineralization before brushing)A (45 min remineralization before brushing)A (60 min remineralization before brushing)A (90 min remineralization before brushing)A (120 min remineralization before brushing)A (erosion, no brushing)B (brushing, no erosion)C
A B C D E F G H I
5.09 1.5 4.49 1.1 4.99 0.9 5.59 1.5 5.39 1.4 4.89 0.7 5.29 0.7 2.69 1.3 1.19 0.4
a
Short descriptions of the groups are given in parentheses. Groups with the same superscript letter were not significantly different. A,B,C
Augustin, Germany) and renewed after brushing five specimens of the same experimental group. In each cycle the specimens were submitted to 100 brushing strokes (100 strokes/min) at a load of 4 N in 25 ml of an abrasive slurry consisting of 5 ml artificial saliva (Attin et al., 2000) mixed with 1 ml of the dentifrice Elmex® (Gaba, Therwil, Switzerland). Elmex® contains 0.125% fluoride as amine fluoride (Olaflur) and has a REA value of 4.2 90.3 and a RDA value of 77 92 (Barbakow et al., 1989). It is a water-based dentifrice (50%) with 30% hydrated silica particles with a mean size of 8.1 mm (90% B2 mm) and a maximum size of 30 mm serving as abrasives. After the 10 cycles, the tapes were removed and the loss of the dentine was determined quantitatively with a laser profilometer (UBM Meßtechnik, Ettlingen, Germany), as described in detail by Attin et al. (1999, 2000). The sensitivity of the laser profilometer amounted to 0.1 mm and the laser recorded 200 points per mm. The profilometer software allowed for calculating the average depth of the abraded part of the specimens relative to the non-abraded surface areas. Five measurements were performed in the centre of each specimen at intervals of about 200 mm and averaged. The data were analysed with the program SAS (SAS Institute Inc., Cary). Analysis of variance and covariance with repeated measurements was applied to the data. Comparisons between experimental groups were made with Tukey’s standardized range test. The level of significance was set at PB 0.05. In the samples of group H, which were demineralized but not brushed, laser profilometry revealed an even loss of dentine in the exposed area. The contour of the brushed specimens was, however, coarser due to the impact of the toothbrush bristles. The distinctly lowest loss (Table 2) of dentine occurred in the specimens of group I, which had not been
873
demineralized before brushing. Erosion without brushing (group H) resulted in less loss of dentine than in all other specimens (groups A –G). However, no significant difference was observed between the experimental groups A –G, which were different with respect to the remineralization period before and after brushing. As a consequence, brushing the eroded dentine after as long as 120 min remineralization (group D) resulted in a statistically significantly greater loss of dentine than in the control group H. Demineralization of our dentine samples was accomplished by storing them in the acidic beverage Sprite Light® for 1 min in order to simulate conditions during sipping of a beverage. All specimens were stored in human saliva for a total of 240 min in each cycle. This period was chosen to simulate the interval between two meals. The specimens were brushed with 100 strokes in each cycle. Heath and Wilson (1974) have shown that individuals brush their teeth at a frequency of 4.5 strokes/s. Assuming that each sextant is brushed for 10–20 s approximately during meticulous oral hygiene, about 45–90 brushing strokes per tooth would be applied during a single brushing episode. Hence, the number of brushing strokes applied here may simulate the clinical conditions very well. The artificial saliva used for mixing the dentifrice slurry contained calcium and phosphate in concentrations similar to those found in human saliva (Diem and Lentner, 1975; Poff et al., 1997). A fluoridated dentifrice was chosen for the slurry in order to simulate the clinical condition, as it may be assumed that the majority of people use dentifrices containing fluoride (Bratthall et al., 1996). We used two control groups to obtain an impression of dentine loss due to brushing abrasion only (group I) and erosion only (group H). The small amount of dentine removed in group I showed that abrasion due to brushing only was negligible. Group H reflected the inevitable loss of dentine during demineralization with an erosive beverage. Therefore, the amount of dentine removed in this group acted as a target value that the other experimental groups (A – G) had to compete with. However, the outcome of the experiment revealed that even a remineralization period of 120 min before brushing was not able to attain this goal. Interestingly, there was no difference in dentine loss among the groups that were brushed at different intervals after the erosive attack. It is important that all these groups were different not only with respect to the length of the first period but also that of the second period of remineralization; the shorter the first period, the longer the second. The second period was followed by the erosive challenge of the next cycle. It should also be remembered that brushing was with a slurry of fluoridated dentifrice (0.125% fluoride) mixed with artificial saliva. It is well known that fluoride application
874
T. Attin et al. / Archi6es of Oral Biology 46 (2001) 871–874 Attin, T., Kno¨ fel, S., Buchalla, W., Tu¨ tu¨ ncu¨ , R., 2001. In situ evaluation of different remineralization periods to decrease brushing abrasion of demineralized enamel. Caries Res., in press. Attin, T., Deifuß, H., Hellwig, E., 1999. Influence of acidified fluoride gel on abrasion resistance of eroded enamel. Caries Res. 33, 135 – 139. Attin, T., Zirkel, C., Hellwig, E., 1998. Brushing abrasion of eroded dentin after application of sodium fluoride solutions. Caries Res. 32, 344 – 350. Attin, T., Buchalla, W., Gollner, M., Hellwig, E., 2000. Use of variable remineralization periods to improve the abrasion resistance of previously eroded enamel. Caries Res. 34, 48– 52. Barbakow, F., Imfeld, T., Lutz, F., Stookey, G., Schemehorn, B., 1989. Dentin abrasion (RDA), enamel abrasion (REA) and polishing scores of dentifrices sold in Switzerland. Schweizer Monatsschrift fu¨ r Zahnmedizin 99, 408 – 413. Bratthall, D., Ha¨ nsel Petersson, G., Sundberg, H., 1996. Reasons for the caries decline: what do the experts believe? Eur. J. Oral Sci. 104, 416 – 422. Davis, W.B., Winter, P.J., 1980. The effect of abrasion on enamel and dentine after exposure to dietary acid. Br. Dent. J. 148, 253 – 256. Diem, K., Lentner, C., 1975. Documenta Geigy-Wissenschaftliche Tabellen. Thieme Verlag, Stuttgart. Edwards, M., Ashwood, R.A., Littlewood, S.J., Brocklebank, L.M., Fung, D.E., 1998. A videofluoroscopic comparison of straw and cup drinking: the potential influence on dental erosion. Br. Dent. J. 185, 244 – 249. Featherstone, J.D.B., 1983. Remineralization of artificial carious lesions in vivo and in vitro. In: Leach, S.A., Edgar, W.M. (Eds.), Demineralisation and remineralisation of the teeth. IRL Press, Oxford, pp. 89 – 110. Hannig, M., Balz, M., 1999. Influence of in vivo formed salivary pellicle on enamel erosion. Caries Res. 33, 372 – 379. Heath, J.R., Wilson, H.J., 1974. Forces and rates observed during in vivo toothbrushing. Biomed. Eng. 9, 61 – 64. Hellwig, E., 1992. Fluoride retention in dentin after topical application of aminefluoride. J. dent. Res. 71, 1558 – 1560. Jaeggi, T., Lussi, A., 1999. Toothbrush abrasion of erosively altered enamel after intraoral exposure to saliva: An in situ study. Caries Res. 33, 455 – 461. Larsen, M.J., 1975. Degrees of saturation with respect to apatites in parotid saliva at various pH values. Scand. J. dent. Res. 83, 7 – 12. Lussi, A., Jaeggi, T., Jaeggi-Scha¨ rer, S., 1995. Prediction of the erosive potential of some beverages. Caries Res. 29, 349 – 354. Poff, A.M., Pearce, E.I.F., Larsen, M.J., Cutress, T.W., 1997. Human supragingival in vivo calculus formation in relation to saturation of saliva with respect to calcium phosphates. Arch. Oral Biol. 42, 93 – 99. Teranaka, T., Koulourides, T., 1987. Effect of a 100-ppm fluoride mouthrinse on experimental root caries in humans. Caries Res. 21, 326 – 332. Zahradnik, R.T., Propas, D., Moreno, E.C., 1978. Effect of salivary pellicle formation time on in vitro attachment and demineralization by Streptococcus mutans. J. Dent. Res. 57, 1036 – 1042.
results in increased concentrations of both structurally and KOH-soluble fluoride in dentine (Hellwig, 1992), which supports remineralization of demineralized dentine (Arends et al., 1990). Furthermore, contact with saliva leads to the formation of an outer mineral-rich layer in dentine, which is more resistant to acid attacks (Teranaka and Koulourides, 1987). Contact between dental hard tissue and saliva also results in the time-dependent formation of acquired pellicle (Zahradnik et al., 1978), which is able to reduce the harmful effects of acids on the underlying tooth surface (Hannig and Balz, 1999). It is therefore conceivable that the longer the (second) period of remineralization after brushing, the greater the interaction between fluoride, saliva and dentine. This prolonged interaction would presumably result in better remineralization and an improvement in the acid resistance of dentine in those groups with a longer period of remineralization after brushing. We therefore speculate that, under the present conditions, shorter periods of remineralization before brushing may be outweighed by longer periods of remineralization after brushing. In contrast to previous findings for enamel (Jaeggi and Lussi, 1999; Attin et al., 2001), the remineralization of eroded dentine did not lead to an improvement in its susceptibility to abrasion . We speculate that, because of the tubular structure of dentine, surface softening is more pronounced than in enamel. It is therefore conceivable that a period long enough for the remineralization of eroded enamel is insufficient for rehardening the surface of previously softened dentine. Under the chosen in vitro conditions, we conclude that the abrasion resistance of dentine is drastically decreased after erosion. Even after 2 h of remineralization, the tooth-brushing abrasion of previously eroded dentine was still increased and was not different from the abrasion susceptibility of eroded dentine immediately after erosion.
Acknowledgements We thank Prof. Dr Ju¨ rgen Schulte-Mo¨ nting (University of Freiburg, Institute of Med. Biometry and Med. Informatics (IMBI)) for the statistical analysis of the data. The study was supported by grants (AT 26/1–2) from Deutsche Forschungsgemeinschaft (DFG).
References Arends, J., Ruben, J.L., Christoffersen, J., Jongebloed, W.L., Zuidgeest, T.G.M., 1990. Remineralization of human dentin in vitro. Caries Res. 24, 432 –435. .