The Effect of Fluoride and Strontium Application on Dentin: i n V i v o and in V i t r o Studies*
and the response was evaluated by an arbitrary pain scoring system which is described later. Before the examination each sensitive tooth was isolated with a cotton wool roll and dried with an airstream. To assess the effect of thermal stimulation, water at a tempera ture of 7°C was dropped onto the examined area from a syringe. A cold temperature was chosen because teeth are generally more sensitive to low than to high temperatures. To assess the response to mechanical stimulation the cervical area was carefully scratched by a standard dental explorer (S. S. White No. 23). A piece of cotton wool soaked in 2% NaF solution was placed on the exposed cervical dentine of the teeth on either side of the dental arches for a period of 3 minutes. During this period, 2% NaF solution was dropped onto the cotton wool each minute. The sensi tive teeth of one of the jaws were pretreated with 10% SrCl solution in a similar manner and then after 10 minutes by NaF solution. The sequence of the com bined strontium and fluoride treatments was chosen, taking into consideration the greater permeability of strontium than calcium-apatite to fluoride ions. Eight treatments were carried out, twice weekly for 4 weeks. In order to avoid a decrease in sensitivity due to oral hygiene procedures, the patients were instructed not to change their usual habits of oral hygiene during the experimental period. The oral hygiene index was deter mined according to the method of Greene and Vermil lion; it was found to be almost identical before, during and at completion of the experiment. The range of severity of the pain response for individual teeth could be classified as none, slight, or moderate according to the patients reaction. Severe pain was accompanied by closing of the eyelids, facial expression, or head movement. The pain categories were given numerical values of 1 (no pain), 2 (discom fort only), 3 (pain), 4 (severe pain) and 5 (unbearable pain). Sensitivity measurements were carried out before the first application, and throughout the experiment after 1 week and after 1-, 2- and 3-months intervals. Although the number of patients was small the fact that the comparison of both treatments was carried out in the same person permitted a statistical evaluation. The Wilcoxon matched-pairs signed-ranks test was used for statistical examination. In Vitro Study. Twenty intact teeth were obtained from human subjects of different ages and stored in physiological saline solution. Two adjacent dentin sec tions of about 1 mm thickness were machine cut, under a water cooling spray, from each tooth at the same distance from the dentinoenamel junction. Enamel, cementum and pulp remnants were carefully removed with a diamond disc at high speed. Each pair of sections was cut into six specimens. To eliminate the variations in dentin composition and age of different parts of the same tooth and in similar areas of different teeth, optical density (OD) comparisons were carried out on
by I. GEDALIAf
L . BRAYER† N.
KALTERf
M.
RlCHTERt
A . STABHOLZ†
2
8
for reducing cervical and root hypersensitivity of a tooth have shown that treat ment with either fluoride or strontium is highly effec tive. The exact mechanism whereby fluoride or strontium treatment causes reduction in the sensitivity is unknown. Either fluoride incorporation accompa nied by an increased resistance of the dentin surface to acid decalcification or precipitation of the fluoride in the dentinal tubules, or both processes may relieve hypersensitivity. The desensitizing action of strontium may be the result of a biochemical blocking of the neural transmission of stimuli through the nerve fibers. The possibility of a remineralization process by both fluoride or strontium also should not be excluded. The present investigation was undertaken to compare in the same patient, the effectiveness of fluoride with and without strontium pretreatment on the reduction of hypersensitive dentin. In addition, the radiopacity of fluoride- or strontium-treated dentin was studied in CLINICAL
INVESTIGATIONS
9
1,2
10
3
4,5
6
7
vitro.
MATERIALS A N D METHODS
In Vivo Experiment. Eleven male and female pa tients, aged 19 to 51 years, who complained of dentinal hypersensitivity, were selected. Seventy-one pairs of homologous intact teeth, showing similar degrees of hypersensitivity to thermal and mechanical stimuli, were chosen from the left and right sides of the jaws. Each tooth was examined for dentin hypersensitivity * This paper is part of the theses submitted by N . Kalter and M . Richter in partial fulfillment of the requirements for the degree of D.M.D. †Department of Preventive Dentistry, ‡Department of Perio dontics and Endodontics, Faculty of Dentistry founded by the Alpha Omega Fraternity, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel.
269
270
G e d a l i a , Brayer,
Kalter,
Richter,
specimens of the same tooth. Half of the samples were demineralized for 20 minutes in acetate buffer at a pH of 5.8. Treatments were carried out by immersion for 24 hours in 2% NaF or 25% SrCl solutions or saline (control) respectively of each intact and demineralized specimen. The specimens were thoroughy rinsed afterwards with water and were air dried. The optical density measurements were carried out under standardized conditions, from radiographs taken before and after the treatments. The same automatic film developing machine was used for all films.* The densities were assessed quantitatively with a photometer attached to a Kompensographt which recorded the differences in light transmission following the experimental treat ments. For each radiograph the mean of 10 O D readings was taken. The Mann-Whitney test was used for estimating the significance of the differences (P < 0.05). 2
RESULTS
In
Vivo
(Tables
J. Periodontol. May, 1978
Stabholz
1 and l a ) . On the basis of all
examined teeth the sensitivity of the cervical dentin to mechanical or thermal stimuli was significantly reduced after the first NaF treatment (P < 0.01). The sensitivity decreased further during the experimental period (P < 0.001) whether or not a strontium pretreatment was carried out. The significance calculated on the basis of the subject number was lower: P < 0.05 and P < 0.01 for the fluoride treatment alone and P < 0.01 for the combined fluoride and strontium treatment. A t com pletion of the experiment (2 and 3 months post-treat ment) the combined treatment was significantly more effective than that of NaF alone in reducing sensitivity to cold (P < 0.02 andP < 0.05 respectively). In Vitro (Table 2 ) . The increase in radiodensity of the intact and demineralized dentin samples immersed in SrCl solution increased significantly (P < 0.05) whereas the radiodensity of the intact and demineral ized dentin samples immersed in NaF solution in creased, but not significantly. 2
DISCUSSION
Fluoride-treated dentin has a high ability to incor porate fluoride with a concomitant decrease in solubil ity. Although the fluoride content was not analyzed in the in v i v o and in v i t r o fluoride-treated dentin of the present study, it may be assumed that a fluoride uptake occurred. The evaluation on a standardized scoring of the reduction of the dentinal sensitivity in our subjects (Table 1) by topical application with concentrated fluoride solution confirms findings in the literature that 11
* Kodak periapical ultra speed DF-57, 10 mA and 55 kv during half a second exposure. †Siemens and Halske A G , Karlsruhe.
12,13
fluoride treatment is highly efficient. In v i v o up take following topical fluoride application to enamel and exposed dentin is presumably accompanied by an increase in the degree of mineralization due possibly to the precipitation of calcium salts of the oral fluid environment in the presence of fluoride . Weatherell, Robinson and Hallsworth found positive correla tions between the fluoride content and density of enamel. No appreciable changes in the density was observed in the in v i t r o fluoride immersed intact and demineralized dentin samples of our experiment (Table 2). This may be due to the fact that no calcium was present in the fluoride-immersion solution; the slight insignificant increase in density possibly may be ex plained by a reprecipitation of the released calcium of the dentinal specimens following their treatment with a high fluoride concentration solution. The converted hydroxyl groups of the hydroxyapatite, by exhange with fluoride to fluorapatite, due to greater crystal size, presents another possible explanation of the small increase in the radiopacity. Similarly strontium has a strong desensitization ef fect. It was therefore understandable that an addi tional desensitization effect was achieved with the combined treatment of the exposed dentin in our subjects (Table la). Dentin has a high strontium-uptake ability owing to the high permeability and adsorption on or in the organic connective tissue of dentin and the odontoblast process within the tubules. It is known that some strontium may exchange for calcium in the hydroxyapa tite crystals of dentin immersed in a SrCl solution. The first step in fixation is an ion exchange displacement of calcium ions from the surfaces of the small apatite crystals of dentin. Thereafter a slow isomorphous sub stitution of calcium for strontium takes place in the crystal interior. The extent of the exchange of hydroxyl by fluoride in the hydroxyapatite may be larger with the mixed strontium-calcium apatite. A n increased fluoride incorporation could have exerted an additional desensitization effect. It has to be pointed out, however, that an increased fluoride uptake was not observed in enamel samples treated with fluoride after pretreatment with strontium. In fact an increased solubility was observed in the enamel after the com bined strontium and fluoride treatment, possibly due to the formation of the more soluble SrCa hydroxyapa tite or SrF . The in v i t r o intact and demineralized dentin samples, after immersion into the SrCl solution, increased significantly in radiopacity (Table 2). Kun reported that topical application of concentrated SrCl solution on abraded dentinal surface causes the forma tion in the dentin of very compact superficial layers, composed of fine granules, with a high degree of radiodensity. The fundamental mechanism in the for mation of strontium deposits is an exchange with the calcium of the dentinal tissue and reprecipitation of the released calcium into the immersion solution with the 3 , 1 4
15
14
1,6
6,15
2
15-19
8
20
2
2
7
2
Volume 49 Number 5
F l u o r i d e and Strontium T A B L E 1. T h e Effect
o f T o p i c a l F l u o r i d e A p p l i c a t i o n i n Reducing Dentin
Hypersensitivity
o f Exposed
Application
271
Cervical
Pain scores Stimuli
Mechanical (46 teeth, 10 patients) Mean Range Cold (67 teeth, 11 patients) Mean Range
T A B L E la. T h e Effect
Initial exam ination
First appli cation
1 Week
2.9 2-5
2.7 1-5
1.9 1-5
1.7 1-4
1.7 1-4
1.6 1-4
3.4 2-5
2.9 1-5
2.3 1-5
2.3 1-4
2.1 1-4
2.0 1-4
o f T o p i c a l S t r o n t i u m a n d F l u o r i d e Applications Exposed Cervical Dentin
1 Month 2 Months 3 Months
i n Reducing
Hypersensitivity
of
Pain scores Stimuli
Mechanical (46 teeth, 10 patients) Mean Range Cold (67 teeth, 11 patients) Mean Range
Initial exam ination
First appli cation
1 Week
3.2 2-5
2.8 1-5
1.9 1-5
1.8 1-4
1.6 1-4
1.6 1-4
3.5 2-5
3.2 1-5
2.4 1-5
2.3 1-4
1.9 1-4
1.9 1-4
T A B L E 2. I n c r e a s e i n O p t i c a l Density of Fluoride- and StrontiumTreated, Intact and Demineralized Dentin
Dentin
Number of
Mean optical density increase with treatment
sUCCllllCIls
Intact Demineralized
20 18
Strontium*
Fluoridet
1.40 ± 1.19 1.20 ± 1.22
0.80 ± 0.82 0.61 ± 0.97
* ± S D ; P < 0.05. †± S D ; P > 0.05.
final formation of a mixed CaSr hydroxyapatite of an increased opacity. The fact that the strontium ion has a bigger radius than the calcium ion may also have contributed to the density increase. Both factors may explain the higher efficiency of the combined treatment in reducing exposed dentin sensitivity to cold which was observed in the patients on completion of the experiment (Table la). Strontium does not seem to be permanently taken up by dentin as there is a significant release of strontium after washing. The dentin sam ples in our in v i t r o experiment were thoroughly rinsed with water after immersion into the strontium solution pointing up the fact that the increased density cannot be attributed to a surface action. A double blind, supervised, clinical study was con ducted by Hernandez et al. to compare the desensitization effect of fluoride and strontium dentifrices. It was found that the fluoride dentifrice resulted in a statistically significant higher efficacy in sensitivity re duction (almost double the effect). In our in v i v o experiment, the synergistic fluoride and strontium ef 7
15
1
1 Month 2 Months 3 Months
fect was examined on dentin sensitivity. It was found to be somewhat more effective than that of fluoride alone (Table la). In the in v i t r o experiment radiopacity was significantly increased in the strontium, but not in the fluoride immersed dentin, probably primarily due to a reprecipitation of the exchanged calcium. The presumably increased opacity of the strontium and fluoride treated exposed dentin surfaces in v i v o should not be considered as the principal factor in reducing sensitivity since it may be assumed that due to the presence of salivary calcium the fluoride-treated only root surfaces will also undergo a mineralization effect. Penney and Karlsson stated that both fluoride and strontium interfere with internal components of the dentin but neither agent is likely to interfere with the sensitivity mechanisms at or proximal to the level of the odontoblast layer. Probably a mineralization and or remineralization process presents the effective mechanism for both fluoride and strontium in diminish ing the permeability of dentin followed by a decrease in sensitivity. This could explain the lack of a synergis tic strontium and fluoride treatment effect in further decreasing dentinal sensitivity in the present study. On this basis we believe that the mechanism of action of fluoride and strontium are similar. We recognize that more clinical experiments in humans are necessary in order to confirm or refute our conclusions. 7
3,14
2
SUMMARY
The effectiveness of topical 2 % sodium fluoride applied with and without 10% strontium chloride pre-
272
G e d a l i a , Brayer,
Kalter,
Richter,
J. Periodontol. May, 1978
Stabholz
treatment was compared in patients complaining of tooth hypersensitivity. In addition the radiopacity of 2% sodium fluoride and 25% strontium chloride treated dentin was studied in vitro. Reduction of sensi tivity to cold and mechanical stimuli was evaluated during a period of 3 months by pain scoring in the exposed cervical dentin of homologous teeth on the two sides of the jaws. There was a significant decrease in the sensitivity of the exposed cervical dentin after treatment with sodium fluoride solution with or without pretreatment with strontium chloride solution. A t the end of the experimental period the combined strontium and fluoride treatment was found to be more effective than that of fluoride alone in reducing sensitivity to cold. The increase in radiodensity of dentin samples im mersed in strontium chloride was statistically signifi cant, while there was no significant increase in density for the samples immersed in sodium fluoride solutions. A mineralization process is possibly the effective means by which fluoride or strontium diminishes sen sitivity of dentin. REFERENCES
1. Hernandez, F . , Mohammed, C , Shannon, I., V o l p e , A . , and K i n g , W . : Clinical study evaluating the desensitizing effect and duration of two commercially available dentifrices. J Periodontol
43: 367, 1972.
5. T a l , M . , O r o n , M . , Gedalia, I., and Ehrlich, J . : X-ray diffraction and scanning electron microscope investigations of fluoride-treated dentine in man. A r c h O r a l B i o l 21: 285,
1976. 6. Ross, M . R . : Hypersensitive teeth: Effect of strontium chloride in a compatible dentifrice. J P e r i o d o n t o l 32: 4 9 , 1961. 7. K u n , L . : Étude biophysique des modifications des tissus dentaires p r e v e q u é e s par Implication locale de stron tium. Schweiz
Monatsschr
Z a h n h e i l k d 86: 6 6 1 , 1976.
8. Saleeb, F . Z . , and D e B r u y n , P . L . : Surface properties of alkaline earth apatites.J E l e c t r o a n a l C h e m 37: 99, 1972. 9. Glickman, I.: C l i n i c a l P e r i o d o n t o l o g y , pp 119-122. Philadelphia, W . B . Saunders Company, 1972. 10. Greene, J . C , and Vermillion, J . R . : The simplified oral hygiene index.
J A m D e n t Assoc
68: 7, 1964.
11. Sandoval, F . , and Shanon, I. L . : Stannous fluoride and dentin solubility. T e x a s R e p B i o l M e d 27: 111, 1969. 12. Everett, F . C : Desensitization of hypersensitive ex posed root surfaces. D e n t C l i n N o r t h A m 3: 321, 1964. 13. M i n k o v , B . , M a r m a r i , I., Gedalia, I., and Garfunkel, A . : The effectiveness of sodium fluoride treatment with and without iontophoresis on the reduction of hypersensitive dentin. J P e r i o d o n t o l 46: 246, 1975. 14. Cariostatic Mechanisms of Fluorides (suppl.), Brown W . E . and Koenig K . G . (eds). C a r i e s R e s 1 1 , 1 , 1977. 15 Gedalia, I., Y a r i v , S., Brayer, L . , and Greenbaum, M . : Strontium uptake by powdered and intact human root dentine. A r c h O r a l B i o l 21: 4 1 3 , 1976.
16. Hodge, H . C , Gavett, E . , and Thomas, E . : The adsorption of strontium at forty degrees by enamel, dentin, bone, and hydroxyapatite as shown by the radioactive iso
2. Penney, D . A . , and Karlsson, U . L . : Fast desensitiza tion of tooth roots by topically applied S n F and S r C l in
tope . J B i o l Chem 163: 1, 1946. 17. Neuman, W . F . : T h e C h e m i c a l Dynamics
dogs. A r c h O r a l B i o l 21: 339, 1976.
M i n e r a l . Chicago, Chicago University Press, 1958. 18. Likins, R . C , M c C a n n , H . G . , Posner, A . S., and Scott, D . E . : Comparative fixation of calcium and strontium by synthetic hydroxyapatite. J B i o l C h e m 253: 2152, 1960. 19. Glas J . E . , and Lagergren, C : Strontium fixation in the mineral phase of bone. B i o c h e m B i o l S p e r 1: 2 5 , 1961. 20. Gedalia, I., A l m o g , D . , and Y a r i v , S.: The effects of strontium and fluoride uptakes on the solubility of powdered enamel. C a r i e s R e s 11: 287, 1977.
2
2
3. Furseth, R . : A study of experimentally exposed and fluoride treated dental cementum in pigs. A c t a O d o n t o l Scand
28: 833, 1970.
4. Ehrlich, J . , Hochman, N . , Gedalia, I., and T a l , M . : Residual fluoride concentrations and scanning electron m i croscopic examination of root surfaces of human teeth after topical application of fluoride in vivo. J D e n t R e s 54: 897, 1975.
o f
Bone
and the response was evaluated by an arbitrary pain scoring system which is described later. Before the examination each sensitive tooth was isolated with a cotton wool roll and dried with an airstream. To assess the effect of thermal stimulation, water at a tempera ture of 7°C was dropped onto the examined area from a syringe. A cold temperature was chosen because teeth are generally more sensitive to low than to high temperatures. To assess the response to mechanical stimulation the cervical area was carefully scratched by a standard dental explorer (S. S. White No. 23). A piece of cotton wool soaked in 2% NaF solution was placed on the exposed cervical dentine of the teeth on either side of the dental arches for a period of 3 minutes. During this period, 2% NaF solution was dropped onto the cotton wool each minute. The sensi tive teeth of one of the jaws were pretreated with 10% SrCl solution in a similar manner and then after 10 minutes by NaF solution. The sequence of the com bined strontium and fluoride treatments was chosen, taking into consideration the greater permeability of strontium than calcium-apatite to fluoride ions. Eight treatments were carried out, twice weekly for 4 weeks. In order to avoid a decrease in sensitivity due to oral hygiene procedures, the patients were instructed not to change their usual habits of oral hygiene during the experimental period. The oral hygiene index was deter mined according to the method of Greene and Vermil lion; it was found to be almost identical before, during and at completion of the experiment. The range of severity of the pain response for individual teeth could be classified as none, slight, or moderate according to the patients reaction. Severe pain was accompanied by closing of the eyelids, facial expression, or head movement. The pain categories were given numerical values of 1 (no pain), 2 (discom fort only), 3 (pain), 4 (severe pain) and 5 (unbearable pain). Sensitivity measurements were carried out before the first application, and throughout the experiment after 1 week and after 1-, 2- and 3-months intervals. Although the number of patients was small the fact that the comparison of both treatments was carried out in the same person permitted a statistical evaluation. The Wilcoxon matched-pairs signed-ranks test was used for statistical examination. In Vitro Study. Twenty intact teeth were obtained from human subjects of different ages and stored in physiological saline solution. Two adjacent dentin sec tions of about 1 mm thickness were machine cut, under a water cooling spray, from each tooth at the same distance from the dentinoenamel junction. Enamel, cementum and pulp remnants were carefully removed with a diamond disc at high speed. Each pair of sections was cut into six specimens. To eliminate the variations in dentin composition and age of different parts of the same tooth and in similar areas of different teeth, optical density (OD) comparisons were carried out on
by I. GEDALIAf
L . BRAYER† N.
KALTERf
M.
RlCHTERt
A . STABHOLZ†
2
8
for reducing cervical and root hypersensitivity of a tooth have shown that treat ment with either fluoride or strontium is highly effec tive. The exact mechanism whereby fluoride or strontium treatment causes reduction in the sensitivity is unknown. Either fluoride incorporation accompa nied by an increased resistance of the dentin surface to acid decalcification or precipitation of the fluoride in the dentinal tubules, or both processes may relieve hypersensitivity. The desensitizing action of strontium may be the result of a biochemical blocking of the neural transmission of stimuli through the nerve fibers. The possibility of a remineralization process by both fluoride or strontium also should not be excluded. The present investigation was undertaken to compare in the same patient, the effectiveness of fluoride with and without strontium pretreatment on the reduction of hypersensitive dentin. In addition, the radiopacity of fluoride- or strontium-treated dentin was studied in CLINICAL
INVESTIGATIONS
9
1,2
10
3
4,5
6
7
vitro.
MATERIALS A N D METHODS
In Vivo Experiment. Eleven male and female pa tients, aged 19 to 51 years, who complained of dentinal hypersensitivity, were selected. Seventy-one pairs of homologous intact teeth, showing similar degrees of hypersensitivity to thermal and mechanical stimuli, were chosen from the left and right sides of the jaws. Each tooth was examined for dentin hypersensitivity * This paper is part of the theses submitted by N . Kalter and M . Richter in partial fulfillment of the requirements for the degree of D.M.D. †Department of Preventive Dentistry, ‡Department of Perio dontics and Endodontics, Faculty of Dentistry founded by the Alpha Omega Fraternity, The Hebrew University-Hadassah School of Medicine, Jerusalem, Israel.
269
270
G e d a l i a , Brayer,
Kalter,
Richter,
specimens of the same tooth. Half of the samples were demineralized for 20 minutes in acetate buffer at a pH of 5.8. Treatments were carried out by immersion for 24 hours in 2% NaF or 25% SrCl solutions or saline (control) respectively of each intact and demineralized specimen. The specimens were thoroughy rinsed afterwards with water and were air dried. The optical density measurements were carried out under standardized conditions, from radiographs taken before and after the treatments. The same automatic film developing machine was used for all films.* The densities were assessed quantitatively with a photometer attached to a Kompensographt which recorded the differences in light transmission following the experimental treat ments. For each radiograph the mean of 10 O D readings was taken. The Mann-Whitney test was used for estimating the significance of the differences (P < 0.05). 2
RESULTS
In
Vivo
(Tables
J. Periodontol. May, 1978
Stabholz
1 and l a ) . On the basis of all
examined teeth the sensitivity of the cervical dentin to mechanical or thermal stimuli was significantly reduced after the first NaF treatment (P < 0.01). The sensitivity decreased further during the experimental period (P < 0.001) whether or not a strontium pretreatment was carried out. The significance calculated on the basis of the subject number was lower: P < 0.05 and P < 0.01 for the fluoride treatment alone and P < 0.01 for the combined fluoride and strontium treatment. A t com pletion of the experiment (2 and 3 months post-treat ment) the combined treatment was significantly more effective than that of NaF alone in reducing sensitivity to cold (P < 0.02 andP < 0.05 respectively). In Vitro (Table 2 ) . The increase in radiodensity of the intact and demineralized dentin samples immersed in SrCl solution increased significantly (P < 0.05) whereas the radiodensity of the intact and demineral ized dentin samples immersed in NaF solution in creased, but not significantly. 2
DISCUSSION
Fluoride-treated dentin has a high ability to incor porate fluoride with a concomitant decrease in solubil ity. Although the fluoride content was not analyzed in the in v i v o and in v i t r o fluoride-treated dentin of the present study, it may be assumed that a fluoride uptake occurred. The evaluation on a standardized scoring of the reduction of the dentinal sensitivity in our subjects (Table 1) by topical application with concentrated fluoride solution confirms findings in the literature that 11
* Kodak periapical ultra speed DF-57, 10 mA and 55 kv during half a second exposure. †Siemens and Halske A G , Karlsruhe.
12,13
fluoride treatment is highly efficient. In v i v o up take following topical fluoride application to enamel and exposed dentin is presumably accompanied by an increase in the degree of mineralization due possibly to the precipitation of calcium salts of the oral fluid environment in the presence of fluoride . Weatherell, Robinson and Hallsworth found positive correla tions between the fluoride content and density of enamel. No appreciable changes in the density was observed in the in v i t r o fluoride immersed intact and demineralized dentin samples of our experiment (Table 2). This may be due to the fact that no calcium was present in the fluoride-immersion solution; the slight insignificant increase in density possibly may be ex plained by a reprecipitation of the released calcium of the dentinal specimens following their treatment with a high fluoride concentration solution. The converted hydroxyl groups of the hydroxyapatite, by exhange with fluoride to fluorapatite, due to greater crystal size, presents another possible explanation of the small increase in the radiopacity. Similarly strontium has a strong desensitization ef fect. It was therefore understandable that an addi tional desensitization effect was achieved with the combined treatment of the exposed dentin in our subjects (Table la). Dentin has a high strontium-uptake ability owing to the high permeability and adsorption on or in the organic connective tissue of dentin and the odontoblast process within the tubules. It is known that some strontium may exchange for calcium in the hydroxyapa tite crystals of dentin immersed in a SrCl solution. The first step in fixation is an ion exchange displacement of calcium ions from the surfaces of the small apatite crystals of dentin. Thereafter a slow isomorphous sub stitution of calcium for strontium takes place in the crystal interior. The extent of the exchange of hydroxyl by fluoride in the hydroxyapatite may be larger with the mixed strontium-calcium apatite. A n increased fluoride incorporation could have exerted an additional desensitization effect. It has to be pointed out, however, that an increased fluoride uptake was not observed in enamel samples treated with fluoride after pretreatment with strontium. In fact an increased solubility was observed in the enamel after the com bined strontium and fluoride treatment, possibly due to the formation of the more soluble SrCa hydroxyapa tite or SrF . The in v i t r o intact and demineralized dentin samples, after immersion into the SrCl solution, increased significantly in radiopacity (Table 2). Kun reported that topical application of concentrated SrCl solution on abraded dentinal surface causes the forma tion in the dentin of very compact superficial layers, composed of fine granules, with a high degree of radiodensity. The fundamental mechanism in the for mation of strontium deposits is an exchange with the calcium of the dentinal tissue and reprecipitation of the released calcium into the immersion solution with the 3 , 1 4
15
14
1,6
6,15
2
15-19
8
20
2
2
7
2
Volume 49 Number 5
F l u o r i d e and Strontium T A B L E 1. T h e Effect
o f T o p i c a l F l u o r i d e A p p l i c a t i o n i n Reducing Dentin
Hypersensitivity
o f Exposed
Application
271
Cervical
Pain scores Stimuli
Mechanical (46 teeth, 10 patients) Mean Range Cold (67 teeth, 11 patients) Mean Range
T A B L E la. T h e Effect
Initial exam ination
First appli cation
1 Week
2.9 2-5
2.7 1-5
1.9 1-5
1.7 1-4
1.7 1-4
1.6 1-4
3.4 2-5
2.9 1-5
2.3 1-5
2.3 1-4
2.1 1-4
2.0 1-4
o f T o p i c a l S t r o n t i u m a n d F l u o r i d e Applications Exposed Cervical Dentin
1 Month 2 Months 3 Months
i n Reducing
Hypersensitivity
of
Pain scores Stimuli
Mechanical (46 teeth, 10 patients) Mean Range Cold (67 teeth, 11 patients) Mean Range
Initial exam ination
First appli cation
1 Week
3.2 2-5
2.8 1-5
1.9 1-5
1.8 1-4
1.6 1-4
1.6 1-4
3.5 2-5
3.2 1-5
2.4 1-5
2.3 1-4
1.9 1-4
1.9 1-4
T A B L E 2. I n c r e a s e i n O p t i c a l Density of Fluoride- and StrontiumTreated, Intact and Demineralized Dentin
Dentin
Number of
Mean optical density increase with treatment
sUCCllllCIls
Intact Demineralized
20 18
Strontium*
Fluoridet
1.40 ± 1.19 1.20 ± 1.22
0.80 ± 0.82 0.61 ± 0.97
* ± S D ; P < 0.05. †± S D ; P > 0.05.
final formation of a mixed CaSr hydroxyapatite of an increased opacity. The fact that the strontium ion has a bigger radius than the calcium ion may also have contributed to the density increase. Both factors may explain the higher efficiency of the combined treatment in reducing exposed dentin sensitivity to cold which was observed in the patients on completion of the experiment (Table la). Strontium does not seem to be permanently taken up by dentin as there is a significant release of strontium after washing. The dentin sam ples in our in v i t r o experiment were thoroughly rinsed with water after immersion into the strontium solution pointing up the fact that the increased density cannot be attributed to a surface action. A double blind, supervised, clinical study was con ducted by Hernandez et al. to compare the desensitization effect of fluoride and strontium dentifrices. It was found that the fluoride dentifrice resulted in a statistically significant higher efficacy in sensitivity re duction (almost double the effect). In our in v i v o experiment, the synergistic fluoride and strontium ef 7
15
1
1 Month 2 Months 3 Months
fect was examined on dentin sensitivity. It was found to be somewhat more effective than that of fluoride alone (Table la). In the in v i t r o experiment radiopacity was significantly increased in the strontium, but not in the fluoride immersed dentin, probably primarily due to a reprecipitation of the exchanged calcium. The presumably increased opacity of the strontium and fluoride treated exposed dentin surfaces in v i v o should not be considered as the principal factor in reducing sensitivity since it may be assumed that due to the presence of salivary calcium the fluoride-treated only root surfaces will also undergo a mineralization effect. Penney and Karlsson stated that both fluoride and strontium interfere with internal components of the dentin but neither agent is likely to interfere with the sensitivity mechanisms at or proximal to the level of the odontoblast layer. Probably a mineralization and or remineralization process presents the effective mechanism for both fluoride and strontium in diminish ing the permeability of dentin followed by a decrease in sensitivity. This could explain the lack of a synergis tic strontium and fluoride treatment effect in further decreasing dentinal sensitivity in the present study. On this basis we believe that the mechanism of action of fluoride and strontium are similar. We recognize that more clinical experiments in humans are necessary in order to confirm or refute our conclusions. 7
3,14
2
SUMMARY
The effectiveness of topical 2 % sodium fluoride applied with and without 10% strontium chloride pre-
272
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Kalter,
Richter,
J. Periodontol. May, 1978
Stabholz
treatment was compared in patients complaining of tooth hypersensitivity. In addition the radiopacity of 2% sodium fluoride and 25% strontium chloride treated dentin was studied in vitro. Reduction of sensi tivity to cold and mechanical stimuli was evaluated during a period of 3 months by pain scoring in the exposed cervical dentin of homologous teeth on the two sides of the jaws. There was a significant decrease in the sensitivity of the exposed cervical dentin after treatment with sodium fluoride solution with or without pretreatment with strontium chloride solution. A t the end of the experimental period the combined strontium and fluoride treatment was found to be more effective than that of fluoride alone in reducing sensitivity to cold. The increase in radiodensity of dentin samples im mersed in strontium chloride was statistically signifi cant, while there was no significant increase in density for the samples immersed in sodium fluoride solutions. A mineralization process is possibly the effective means by which fluoride or strontium diminishes sen sitivity of dentin. REFERENCES
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o f
Bone
