Caries Res. 12: 52-59 (1978)
The Effect of Demineralization on SnF2-Treated White Spot Enamel Lesions D. J. Purdell-Lewis, A. Groeneveld and J. Arends Caries Research Unit, Organisation for Health Research TNO, Laboratory for Microbiology, University of Utrecht, Utrecht, and Laboratory for Materia Technica, University of Groningen, Groningen
Key Words. Demineralization • Enamel Fluoride, stannous • Remineralization White spot lesions
Current experimental results indicate that topical application of stannous fluoride (SnF2) solution on sound enamel increases the resistance of the enamel to deminerali zation. This was found when the effect was measured in terms of both hardness [Pigman and Newbrun, 1962; Takimoto et al., 1970] and dissolution kinetics [Feagin et al., 1972]. More recently, the effect of 8% SnF2 on
lightly demineralized surfaces has been studied in vivo [Keller et al., 1975]. These authors found, using microhardness and mi croradiographical techniques, that the pro tection given by SnF2 was enhanced if the surface had been subjected to carious attack prior to fluoride application. Mellberg and Loertscher [1972] demon strated that fluoride uptake is influenced not only by pH but also by temperature. They
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Abstract. It has been shown that the application of stannous fluoride (SnF2) solution increases the resistance of sound enamel to demineralization. The effect of SnF2 on de mineralized enamel was investigated in this study, as was the effect of an increased application temperature on the reaction products. Artificial white spot lesions were formed in intact human buccal enamel. They were then subjected to a second period of acid attack either with or without pretreatment with 10% SnF2 solution applied for 30 min at 37 or 50 °C. The results of this treatment were investigated on cross-sections using microhardness and microradiographical techniques. SnF2 applied at either treatment temperature, resulted in an increase in the linear absorption coefficient of the microradiograms. It also reduced the degree of demineralization of the second attack when this was measured both in terms of microhardness and of lesion depth. SnF., application at 50 °C gave significantly better results than those achieved at 37 °C. This could be due to the enhanced formation of Sn3F3P 0 4 and fluorapatite and indicates that more attention should be paid to the appli cation temperature.
53
Demineralized SnF2-Treated Lesions
suggested that clinical applications at tem peratures higher than 37 °C might give im proved results. In an earlier work [Purdell-Lewis et al., 1976] we have shown that a freshly made solution of 4% SnF., has a rehardening ef fect when applied to standardized artificial white spot lesions at a temperature of 50 °C. The purpose of this paper is to ex amine the effects of demineralization on ar tificial white spot enamel lesions treated with 10°/o SnF2 for 30 min at either 37 or 50 °C. In preliminary experiments it was found that almost all the stannous deposi tion occurred within this time limit, a result which is in agreement with the findings of Meckel ([1975]. We also found that al though SnF2 solutions are unstable no signi ficant changes occurred in these heated solu tions over the 30-min experimental period.
Experiment 3. E: 10% SnF2 for 30 min at 50 °C followed by a further l>/2 days deminerali zation at 20 °C; F: a further l>/2 days deminerali zation at 20 °C. The tooth segments were placed in 10 ml of the warmed, freshly prepared SnF2 solution which was held at the correct temperature in a thermo stat. The tooth segments were then sectioned, ground piano-parallel to a thickness of between 60 and 80 ,um and microradiographed. For further details of this method see Groeneveld and A rends [1975], The sections were embedded, polished and set up on a Leitz hardness tester (Leitz Durimet interference light hardness tester), fitted with a Knoop diamond and 15 g load, at the same time as the respective microradiogram was placed on a Leitz microdensitometer (Leitz microscope-pho tometer, type MPV). The section and its microra diogram were then aligned, as near as possible to the mid-point of the lesion, by using anatomical landmarks, so that the hardness and densitométrie measurements were made along approximately the same pathway [Purdell-Lewis et al., 1976].
Materials and Methods 30 extracted human premolars were used in this study. They were cleaned with pumice and covered with blue inlay wax with the exception of one central window on the buccal surface. Artifi cial white spot lesions were formed by demineral izing the exposed windows at pH 4.0 for 2‘/ 2 days in an 0.10 M lactic acid, 1.8°/o hydroxyethyl cellu lose solution at 20 °C. The teeth were then divid ed into 3 groups of 10 and sectioned longitudinal ly to provide a central control section. The enamel and dentine exposed by sectioning the teeth were coated with nail polish before the following treat ments were completed on the demineralized half windows. Experiment 1. A: 10°/o SnF2 for 30 min at 37 °C; B: 10°/o SnF2 for 30 min at 50 °C. Experiment 2. C: 10°/o SnF2 for 30 min at 37 °C followed by a further l '/ 2 days deminerali zation at 20 °C; D: 10% SnF2 for 30 min at 50 °C followed by a further l>/2 days demineralization at 20 °C.
The demineralization of all 30 enamel windows was very even. There were no sig nificant differences between any of the mean control values of the 3 experimental groups. The mean maximum hardness of the surface layer of all groups is presented in figure 1, expressed in Knoop hardness num bers (KHN). The control columns, num bered to indicate the experiment, are shown in the middle of the figure. After the initial demineralization, surface layer hardness dropped from a sound enamel value of 341 KHN to approximately 122 KHN. This fig ure increased to 147 KHN after treatment with 10°/o SnF2 at 37 °C (column A) and to 192 KHN after treatment at 50 °C (column B). These increases were significant with re spect to the control (p < 0.01 and p < 0.005)
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Results
54
Purdell-Lewis/Groeneveld/Arends
and to each other (p < 0.005). Demineraliza tion without SnF2 treatment (column F) re sulted in a non-significant hardness drop, with respect to the control, of 10 KHN. Af ter SnF2 treatment and a second period of demineralization, there were similar non significant hardness drops in both the 37 °C (column C) and 50 °C (columns D, E) groups. These groups were still significantly harder than either their controls or the un treated group F. The 50 °C treated groups (columns D, E) were also significantly har der than the 37 °C treated group C (p < 0.005). The mean minimum hardness of the sub surface lesion of all the groups is presented in figure 2. As with the surface layer, treat ment with 10% SnF2 at 37 °C (column A) resulted in a significant increase with re spect to the control (p < 0.025). Application at 50 °C (column B) resulted in a larger in crease (p < 0.005). This result was also sig nificantly greater than that recorded at
37 °C (p < 0.025). Demineralization without SnF2 treatment (column F) resulted in a sig nificant hardness drop with respect to the control (p < 0.05), whilst both 37 °C (col umn C) and 50 °C (columns D, E) SnF2treated demineralized groups remained al most unchanged. The microradiographical results are giv en graphically in figures 3 and 4. They show both the extent and position of the stannous deposition. It should be noted that the linear absorption coefficients (LAC) have been given here since the formula of Angmar for the volume percentage mineral cannot be applied to demineralized SnF2-treated en amel. For simplification, only the group 3 control curve has been included. Results for groups 1 and 2 were as follows: LAC sur face layer 163 (SD 7.0) and 176 (SD 3.4); LAC subsurface lesion 72.1 (SD 8.2) and 72.1 (SD 8.3), respectively. It is notable that, in the control groups, the points with the maximum and minimum LAC values in
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Fig. 1. Mean surface layer hardness results expressed in Knoop hardness numbers. The vertical bars show the standard deviation of the mean.
Demineralized SnF2-Treated Lesions
55
Fig. 3. Graphs to show the mean linear absorp tion coefficients of the groups treated with SnF2 at 37 °C, drawn from the anatomical surface in wards. — = C ontrol;-------- = group A: SnF2; ----- = group C: SnF2 + demineralization; • • • = group F: demineralization.
the surface layer and the surface lesion very nearly coincided with the positions of maxi mum and minimum hardness. These posi tions were, measured from the surface, ap proximately 13 /tm (SD 1.5) for the surface
layer and 47 um (SD 2.5) for the subsurface lesion. In the 37 °C SnF2-treated group A (fig. 3), stannous ions appear to have been deposited in the inner part of the surface layer (peak 1) and to the full depth of the subsurface lesion (peak 2). After demineral ization (group C), the slope of the curve was similar to that of group A. There was, how ever, a significant drop in the LAC of peaks 1 and 2 and in the minimum value in the subsurface lesion (p < 0.005). There was also a notable loss of material in the surface layer and at the advancing front of the le sion. Despite this, the curve remains above that of the control section, particularly in the subsurface lesion (p < 0.005). The results of the untreated demineral ized group F have been included in this fig ure. It can be seen that there was a signifi cant drop in the surface layer LAC (p < 0.05) with respect to the control, and a large increase in lesion depth with the for mation of a new and clearly defined demin eralizing front. Comparison with the SnF2treated demineralized group C shows that all differences were highly significant (p < 0.005). The figures for the total lesion depth,
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Fig. 2. Mean subsurface le sion hardness results expressed in Knoop hardness numbers. The vertical bars show the standard deviation of the mean.
Fig. 4. Graphs to show the mean linear absorp tion coefficients of the groups treated with SnF2 at 50 °C, drawn from the anatomical surface in wards. ---- = C ontrol;-------- = group B: SnF2; ----- = group D: SnF2 + demineralization; • ■• = group F: demineralization.
Purdell-Lewis/Groeneveld/Arends
measured from the microradiographical tracings, are given in the left-hand side of figure 5. The difference between the control and the demineralized group F was signifi cant (p < 0.005), as was the difference be tween the control and the 37 °C SnF2treated demineralized group C (p < 0.005). The 10-/«m increase in lesion depth after SnF2 treatment and a second demineraliza tion was, however, significantly less than the 40 pm recorded without SnF2 treatment (p < 0.005). The microradiographical results of the 50 °C SnF2-treated groups are presented in figure 4. After SnF2 treatment (group B), LAC values for the surface layer and peaks 1 and 2 were significantly higher than those found at 37 °C (p < 0.005). Demineraliza tion after SnF2 treatment, group D [group E omitted for clarity, results: peak 1, 323 (SD 18.2), peak 2, 332 (SD 15.8)] resulted in a non-significant drop in the minimum LAC of the subsurface lesion. In both group D, presented here, and group E it was no
Fig. 5. Total lesion depths (,«m) of all the experimental groups.
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56
longer possible to distinguish between the surface layer and the deposition which had occurred at the inner front of the surface layer (peak 1). The loss of the surface layer peak and the slightly deeper position of the maximum hardness values (174 KHN at a depth of 15 ,«m) indicate that there was a loss of material in the outer part of the sur face layer. The values for peaks 1 and 2 were, however, significantly greater than those found at 37 °C (p < 0.005). The un treated demineralized group F results are included for comparison with the SnF2-treated demineralized group D. The lesion depths are presented on the right-hand side of figure 5. It was found that in both the 50 °C SnF2-treated demineral ized groups (D and E) the increase in le sion depth was a non-significant 2 /
The Effect of Demineralization on SnF2-Treated White Spot Enamel Lesions D. J. Purdell-Lewis, A. Groeneveld and J. Arends Caries Research Unit, Organisation for Health Research TNO, Laboratory for Microbiology, University of Utrecht, Utrecht, and Laboratory for Materia Technica, University of Groningen, Groningen
Key Words. Demineralization • Enamel Fluoride, stannous • Remineralization White spot lesions
Current experimental results indicate that topical application of stannous fluoride (SnF2) solution on sound enamel increases the resistance of the enamel to deminerali zation. This was found when the effect was measured in terms of both hardness [Pigman and Newbrun, 1962; Takimoto et al., 1970] and dissolution kinetics [Feagin et al., 1972]. More recently, the effect of 8% SnF2 on
lightly demineralized surfaces has been studied in vivo [Keller et al., 1975]. These authors found, using microhardness and mi croradiographical techniques, that the pro tection given by SnF2 was enhanced if the surface had been subjected to carious attack prior to fluoride application. Mellberg and Loertscher [1972] demon strated that fluoride uptake is influenced not only by pH but also by temperature. They
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 6:12:50 AM
Abstract. It has been shown that the application of stannous fluoride (SnF2) solution increases the resistance of sound enamel to demineralization. The effect of SnF2 on de mineralized enamel was investigated in this study, as was the effect of an increased application temperature on the reaction products. Artificial white spot lesions were formed in intact human buccal enamel. They were then subjected to a second period of acid attack either with or without pretreatment with 10% SnF2 solution applied for 30 min at 37 or 50 °C. The results of this treatment were investigated on cross-sections using microhardness and microradiographical techniques. SnF2 applied at either treatment temperature, resulted in an increase in the linear absorption coefficient of the microradiograms. It also reduced the degree of demineralization of the second attack when this was measured both in terms of microhardness and of lesion depth. SnF., application at 50 °C gave significantly better results than those achieved at 37 °C. This could be due to the enhanced formation of Sn3F3P 0 4 and fluorapatite and indicates that more attention should be paid to the appli cation temperature.
53
Demineralized SnF2-Treated Lesions
suggested that clinical applications at tem peratures higher than 37 °C might give im proved results. In an earlier work [Purdell-Lewis et al., 1976] we have shown that a freshly made solution of 4% SnF., has a rehardening ef fect when applied to standardized artificial white spot lesions at a temperature of 50 °C. The purpose of this paper is to ex amine the effects of demineralization on ar tificial white spot enamel lesions treated with 10°/o SnF2 for 30 min at either 37 or 50 °C. In preliminary experiments it was found that almost all the stannous deposi tion occurred within this time limit, a result which is in agreement with the findings of Meckel ([1975]. We also found that al though SnF2 solutions are unstable no signi ficant changes occurred in these heated solu tions over the 30-min experimental period.
Experiment 3. E: 10% SnF2 for 30 min at 50 °C followed by a further l>/2 days deminerali zation at 20 °C; F: a further l>/2 days deminerali zation at 20 °C. The tooth segments were placed in 10 ml of the warmed, freshly prepared SnF2 solution which was held at the correct temperature in a thermo stat. The tooth segments were then sectioned, ground piano-parallel to a thickness of between 60 and 80 ,um and microradiographed. For further details of this method see Groeneveld and A rends [1975], The sections were embedded, polished and set up on a Leitz hardness tester (Leitz Durimet interference light hardness tester), fitted with a Knoop diamond and 15 g load, at the same time as the respective microradiogram was placed on a Leitz microdensitometer (Leitz microscope-pho tometer, type MPV). The section and its microra diogram were then aligned, as near as possible to the mid-point of the lesion, by using anatomical landmarks, so that the hardness and densitométrie measurements were made along approximately the same pathway [Purdell-Lewis et al., 1976].
Materials and Methods 30 extracted human premolars were used in this study. They were cleaned with pumice and covered with blue inlay wax with the exception of one central window on the buccal surface. Artifi cial white spot lesions were formed by demineral izing the exposed windows at pH 4.0 for 2‘/ 2 days in an 0.10 M lactic acid, 1.8°/o hydroxyethyl cellu lose solution at 20 °C. The teeth were then divid ed into 3 groups of 10 and sectioned longitudinal ly to provide a central control section. The enamel and dentine exposed by sectioning the teeth were coated with nail polish before the following treat ments were completed on the demineralized half windows. Experiment 1. A: 10°/o SnF2 for 30 min at 37 °C; B: 10°/o SnF2 for 30 min at 50 °C. Experiment 2. C: 10°/o SnF2 for 30 min at 37 °C followed by a further l '/ 2 days deminerali zation at 20 °C; D: 10% SnF2 for 30 min at 50 °C followed by a further l>/2 days demineralization at 20 °C.
The demineralization of all 30 enamel windows was very even. There were no sig nificant differences between any of the mean control values of the 3 experimental groups. The mean maximum hardness of the surface layer of all groups is presented in figure 1, expressed in Knoop hardness num bers (KHN). The control columns, num bered to indicate the experiment, are shown in the middle of the figure. After the initial demineralization, surface layer hardness dropped from a sound enamel value of 341 KHN to approximately 122 KHN. This fig ure increased to 147 KHN after treatment with 10°/o SnF2 at 37 °C (column A) and to 192 KHN after treatment at 50 °C (column B). These increases were significant with re spect to the control (p < 0.01 and p < 0.005)
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 6:12:50 AM
Results
54
Purdell-Lewis/Groeneveld/Arends
and to each other (p < 0.005). Demineraliza tion without SnF2 treatment (column F) re sulted in a non-significant hardness drop, with respect to the control, of 10 KHN. Af ter SnF2 treatment and a second period of demineralization, there were similar non significant hardness drops in both the 37 °C (column C) and 50 °C (columns D, E) groups. These groups were still significantly harder than either their controls or the un treated group F. The 50 °C treated groups (columns D, E) were also significantly har der than the 37 °C treated group C (p < 0.005). The mean minimum hardness of the sub surface lesion of all the groups is presented in figure 2. As with the surface layer, treat ment with 10% SnF2 at 37 °C (column A) resulted in a significant increase with re spect to the control (p < 0.025). Application at 50 °C (column B) resulted in a larger in crease (p < 0.005). This result was also sig nificantly greater than that recorded at
37 °C (p < 0.025). Demineralization without SnF2 treatment (column F) resulted in a sig nificant hardness drop with respect to the control (p < 0.05), whilst both 37 °C (col umn C) and 50 °C (columns D, E) SnF2treated demineralized groups remained al most unchanged. The microradiographical results are giv en graphically in figures 3 and 4. They show both the extent and position of the stannous deposition. It should be noted that the linear absorption coefficients (LAC) have been given here since the formula of Angmar for the volume percentage mineral cannot be applied to demineralized SnF2-treated en amel. For simplification, only the group 3 control curve has been included. Results for groups 1 and 2 were as follows: LAC sur face layer 163 (SD 7.0) and 176 (SD 3.4); LAC subsurface lesion 72.1 (SD 8.2) and 72.1 (SD 8.3), respectively. It is notable that, in the control groups, the points with the maximum and minimum LAC values in
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 6:12:50 AM
Fig. 1. Mean surface layer hardness results expressed in Knoop hardness numbers. The vertical bars show the standard deviation of the mean.
Demineralized SnF2-Treated Lesions
55
Fig. 3. Graphs to show the mean linear absorp tion coefficients of the groups treated with SnF2 at 37 °C, drawn from the anatomical surface in wards. — = C ontrol;-------- = group A: SnF2; ----- = group C: SnF2 + demineralization; • • • = group F: demineralization.
the surface layer and the surface lesion very nearly coincided with the positions of maxi mum and minimum hardness. These posi tions were, measured from the surface, ap proximately 13 /tm (SD 1.5) for the surface
layer and 47 um (SD 2.5) for the subsurface lesion. In the 37 °C SnF2-treated group A (fig. 3), stannous ions appear to have been deposited in the inner part of the surface layer (peak 1) and to the full depth of the subsurface lesion (peak 2). After demineral ization (group C), the slope of the curve was similar to that of group A. There was, how ever, a significant drop in the LAC of peaks 1 and 2 and in the minimum value in the subsurface lesion (p < 0.005). There was also a notable loss of material in the surface layer and at the advancing front of the le sion. Despite this, the curve remains above that of the control section, particularly in the subsurface lesion (p < 0.005). The results of the untreated demineral ized group F have been included in this fig ure. It can be seen that there was a signifi cant drop in the surface layer LAC (p < 0.05) with respect to the control, and a large increase in lesion depth with the for mation of a new and clearly defined demin eralizing front. Comparison with the SnF2treated demineralized group C shows that all differences were highly significant (p < 0.005). The figures for the total lesion depth,
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 6:12:50 AM
Fig. 2. Mean subsurface le sion hardness results expressed in Knoop hardness numbers. The vertical bars show the standard deviation of the mean.
Fig. 4. Graphs to show the mean linear absorp tion coefficients of the groups treated with SnF2 at 50 °C, drawn from the anatomical surface in wards. ---- = C ontrol;-------- = group B: SnF2; ----- = group D: SnF2 + demineralization; • ■• = group F: demineralization.
Purdell-Lewis/Groeneveld/Arends
measured from the microradiographical tracings, are given in the left-hand side of figure 5. The difference between the control and the demineralized group F was signifi cant (p < 0.005), as was the difference be tween the control and the 37 °C SnF2treated demineralized group C (p < 0.005). The 10-/«m increase in lesion depth after SnF2 treatment and a second demineraliza tion was, however, significantly less than the 40 pm recorded without SnF2 treatment (p < 0.005). The microradiographical results of the 50 °C SnF2-treated groups are presented in figure 4. After SnF2 treatment (group B), LAC values for the surface layer and peaks 1 and 2 were significantly higher than those found at 37 °C (p < 0.005). Demineraliza tion after SnF2 treatment, group D [group E omitted for clarity, results: peak 1, 323 (SD 18.2), peak 2, 332 (SD 15.8)] resulted in a non-significant drop in the minimum LAC of the subsurface lesion. In both group D, presented here, and group E it was no
Fig. 5. Total lesion depths (,«m) of all the experimental groups.
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 6:12:50 AM
56
longer possible to distinguish between the surface layer and the deposition which had occurred at the inner front of the surface layer (peak 1). The loss of the surface layer peak and the slightly deeper position of the maximum hardness values (174 KHN at a depth of 15 ,«m) indicate that there was a loss of material in the outer part of the sur face layer. The values for peaks 1 and 2 were, however, significantly greater than those found at 37 °C (p < 0.005). The un treated demineralized group F results are included for comparison with the SnF2-treated demineralized group D. The lesion depths are presented on the right-hand side of figure 5. It was found that in both the 50 °C SnF2-treated demineral ized groups (D and E) the increase in le sion depth was a non-significant 2 /
