Influence of Fluorides on the Properties of Set Product of Silicate Cement

Transcription

1 Influence of Fluorides on the Properties of Set Product of Silicate Cement by Masahide NIHEI,* T.E. FISCHER, "Kunio ODA,* Kiyoshi USUI,* Tomikazu NISHIKAWA,* Hajime OGOSHI* and Masayoshi OHASHI* 1. Introduction The inhibition of the development of dental caries by fluoride has already been established by numerous reports[1-3] and the use of fluoride for the purpose of prevention of dental caries is constantly widening through the addition of fluoride to communal drinking water and filling with amalgam mixed with stannous fluoride. Silicate cement was reported to inhibit secondary carious change[4], since fluorides are mixed during the process of production as the flux, but controversies for this were also advanced[5]. Though the fluoride mixed into the silicate cement was not added for the purpose of prevention of carious changes, the mixed fluoride is probably present between the alveolar wall of the dentin and the silicate cement filling to seal the dentinal tubule and to inhibit secondary carious change according to a popular theory[6]. Attempts of applying especially large amount of fluoride to silicate cement were also reported[7] based on this assumption. The amount of fluoride in dissolved away from the filling material made of silicate cement was reported to be so small as to make it impossible to expect enzyme inhibition or antibacterial activity. The effect of fluoride in preventing carious change, is well known. Many people visit the dental clinic for periodically painting their teeth with fluoride and mass fluoride application is conducted in a company or school. The entrance of fluoride in daily life has thus become quite conspicuous. In recent years, dental paste and gurgle containing fluoride are widely available commercially, especially in the United States. Tooth pastes such as Colgate, Crest and Gleem II widely used in the United States emphasize their fluoride content. Zircate produced by Caulk containing as much as 10% fluoride is commercially available for dentists along with Nupro-paste and others. Fluorine, one of the halogen elements, has a high reactivity, reacting well with unhydrous silisic acid. Since fluorine is well known to react well with amorphous SiO2, a component of glass, fluorine may naturally be assumed to act on the filling material consisting of silicate cement, influencing its various properties. When fluoride is applied, consequently, care should probably be taken to prevent a direct contact between the tooth repaired with silicate cement and the painting material. In order to confirm this assumption, the author attempted to study the effect of University School of Dentistry, Tokyo (Director: Prof Setsuo Higashi) ** T.E. FISCHER: Department of Biomaterials, University of Alabama School of Dentistry, Alabama, U.S.A. (Director: Prof T.E. Fischer)

2 fluoride in dental use on the set product of silicate cement. Various fluoride compounds were applied on the test material consisting of silicate cement or the material was immersed in these solutions containing fluoride, to study the influence on the compressive strength and tensile strength, hardness of the surface and opacity. Extracted natural teeth and teeth of the patients were filled with silicate cement and made to react with fluoride compound daily to study the changes to compare the results of the technological experiments described above. 2. Materials and Methods 2.1. Experimental materials Fluoride compounds used in the experiment consisted of 2% NaF and 5% SnF2 shown in Fig. 1, Brudevold solution[8] shown in Table 1, Colgate, Crest and Gleem II containing fluoride commercially available and Zircate and Nupro for the use by dentists. The silicate cement consisted of Smith's Certified Enamel Improved [9] (Batch No C) (Fig. 2). This cement had satisfied the ADA specification, being widely used not only in the United States, but also in European Countries and Japan. Fig. 1. Fluoride compounds used in the experiments. On the left upper and lower side are 3% Nupro, on the right upper is fluoride reagent and on the right inferior, from the front, Gleem II, Crest, Colgate and Zircate. Table 1. Brudevold solution 2.2. Experimental methods (1) Tests for compressive strength and tensile strength The strength of silicate cement was tested according to the ADA Specification No. 9[10] on a cylindrical test material with the diameter of 6 mm and height of

3 Fig. 2. Silicate cement used in the experiment (Smith's certified enamel improved). Fig. 3. Test materials immersed in various solutions. Table 2. Greenwood's artificial saliva 12mm, using Instron at a load speed of 0.127cm/min. The tensile strength was tested by the method of Diametral Tensile Test. As shown in Fig. 3, the test materials were immersed in distilled water, Brudevold

4 32 solution, 2% NaF, 5% SnF2 and Greenwood's artificial saliva[11] (Table 2) to be changed with the new one every 24 hours) prior to the experiment. (2) Test for the surface hardness The surface hardness was tested on the cement material mixed according to the ADA Specification No. 9 filling a stainless ring with the internal diameter of 10mm and height of 5mm, compressed between 2 glass plates by the use of an upper and low clamps. At 3 minutes after the beginning of mixing, the set with the clamps was was taken out 1 hour later and the upper and lower surfaces were worked up with silicon carbide of 200 mesh and water to obtain the test material. This was preserved After immersing these materials in each solution described above for 15 ays, they were thoroughly washed with water and the surface water was wiped off. The measurement was carried out by the use of Wilson type Noop apparatus for the hardness measurement under a load of 500 grams. (3) Test for opacity The influence of fluoride on the opacity of silicate cement was tested according to the ADA Specification No. 9, the test for the opacity. In ADA Specification No. 9, the criteria for the measurement of opacity are defined for the measurement of the transparency of silicate cement. As shown in Fig. 4, the test material and milk-white glass with the Co. 70 value of the control ratio of 0.35 and 0.55 were placed before the background of white and black stripes, to evaluate the degree of opacity. The diameter of the test material was 30 mm, and the thickness 1mm. After 3 minutes of mixing, the material was placed in a thermostatic chamber of 23 hours. After the tests in the specification described above was conducted to confirm the Co. 70 value between 0.35 and 0.55, this was immersed in distilled water, 2% Fig. 4. Test for opacity.

5 NaF, 5% SnF2, Brudevold solution and artificial saliva (exchanged every 24 hours), to study the degree of opacity. In order to compare the difference in the degree of transparency between the portion immersed in various fluoride solution and the portion not immersed, 3/4 of the test material was immersed to compare macroscopically the mode of discoloration between this portion and the remaining 1/4 not immersed. (4) Clinical tests Following 3 kinds of experiments were conducted as the clinical test. 1) An extracted natural tooth was filled with silicate cement and the material was brought in contact with the fluoride along with the tooth. As shown in Figs. 6 and 7, it was fixed with the natural tooth in the self-curing resin, to form a cavity with the depth of 4mm. The occlusive surface was painted with cocoa butter and covered Fig. 5. Test method through half-immersing. Fig. 6. Cut surface of the natural tooth forming cavity.

6 Fig. 7. Test material filled with silicate cement. Fig. 8. Artificial tooth filled with silicate cement. taking the material out and washed in water, it was polished with silicon carbite powder (mesh 200) and water. Caulk's varnish was then painted on 1/2 of the surface of the filling material and the material was immersed in 2% NaF, 5% SnF2, Brudevold solution and distilled test material was taken out, washed with water and the degree of influence of fluoride was tested by staining with crystal violet. 2) In an artificial tooth (resin tooth) attached to the denture with floor, a fifth class cavity was formed as shown in Fig. 8 and this was filled with silicate cement and

7 Fig. 9. Application of fluoride. allowed to react with fluoride. As the fluoride, 2% NaF, 5% SnF2, Brudvold solution, Colgate, Crest, Nupro and Zircate were used. The application was performed 5 days a week continuously, twice a day in the morning and afternoon for 3 minutes each, for 90 days in 7 test subjects (Fig. 8). When silicate cement is used to fill the artificial tooth, an excessive amount of cement is mixed, to be used for filling a stainless ring with the internal diameter of 10mm and height of 5mm. This was immersed in artificial saliva and preserved in a fluoride was applied on the artificial tooth, it was also applied on the silicate cement within the ring, to compare the changes with staining. The fluoride-blocking effect of Caulk Varnish (produced by Caulk), Cocoat (produced by Creso) and Model Spray (produced by Jelenko) was also studied (Fig. 9). 3) The repairing material of the test subject already repaired with silicate cement was removed and the filling with silicate cement was carried out for this experiment by the ordinary method. Painting was carried out once daily for 3 minutes each over a period of 90 days. As the fluoride, 5% SnF2, Colgate, Nupro and Zircate were used. In this cases, as in the artificial tooth 2), the ring was filled and observed under the same condition. 3. Experimental Results 3.1. Tests for compressive strength and tensile strength Fig. 10 shows the result of test for the compressive strength. Each represents the results of immersing in various solutions for 15 days. Those immersed in distilled water and artificial saliva showed approximately similar compressive strength, 1,710 and 1,750 kg/cm2. Those immersed in 2% NaF, 5% SnF2 and Brudevold solution gave the value of 1,350, 1,280 and 780kg/cm2 respectively, corresponding to 79.0, 74.8 and 45.7% of the value obtained after immersing in distilled water respectively. Especially after immersion in Brudevold solution, the strength was markedly decreased being as low as 1/2 of the value obtained in distilled water.

8 Fig. 10. Compressive strength after immersing in various solutions for 15 days. Fig. 11. Tensile strength after immersing in various solutions for 15 days. The tensile strength (Fig. 11) also showed a similar tendency, after immersing in distilled water for 15 days, it was 188 kg/cm2, 144 in 2% NaF, 114 in 5% SnF2 and 62 in Brudevold solution, corresponding to 76.6, 61.7 and 33.0% of the value obtained in distilled water respectively. The fall was especially pronounced in Brudevold solu-

9 tion. After immersion in artificial saliva, however, the strength was 206 kg/cm2, slightly higher than in distilled water. Fig. 12 shows the test material broken by Diametral method after immersing in distilled water for 15 days, indicating a distinct division into two. Fig. 13 shows the mode of breaking of each test material immersed in fluoride. The lower panel indicates the material immersed in 2% NaF for 15 days, the middle column that immersed in 5% SnF2 for 15 days and the upper column that immersed in Brudevold solution. These represent typical pictures obtained following immersion in various fluoride solutions. Fig. 12. Mode of disruption by diametral method (after immersing in distilled water for 15 days). Fig. 13. Mode of disruption by diametral method. Upper: after immersing in Brudevold solution for 15 days. Middle: after immersing in 5% SnF2 for 15 days. Lower: after immersing in 2% NaF for 15 days.

10 The test material for the compressive strength immersed in distilled water broke giving a high pitched noise, whereas those immersed in fluoride broke giving a low heavy noise. A difference was also felt from such sounds. The material immersed in artificial saliva was cleanly divided into two as in distilled water. Fig. 14. Knoop hardness after immersing in various solutions for 15 days. Fig. 15. Test material half-immersed in 2% NaF (The right side immersed).

11 Fig. 16. Test material half-immersed in 5% SnF2 (The right side was immersed) Test for surface hardness Fig. 14 shows the results of measurement of surface hardness. The Knoop hardness of the material immersed in distilled water for 15 days was 77, rather superior to the values in many reports[12] on the Knoop hardness of the silicate cement. The value for the material immersed in artificial saliva was 82, slightly higher than this. The hardness value was 60 after immersion in 2% NaF, 51 after immersion in SnF2 and 33 after immersion in Brudevold solution, corresponding to 78.0, 66.3 and 42.8% of the values obtained after immersion in distilled water. The decrease was especially pronounced after immersion in Brudevold solution Test for opacity As the result of the test for opacity according to ADA Specification No. 9, influence of various fluorides was so pronounced as to be macroscopically distinguished. Fig. 15 shows the material immersed in 2% NaF for 15 days, with the opacity of 100, indicating a complete loss of the transparency. The transparency of the silicate cement used in this experiment was not very good, approximately similar to that of the standard opal glass Co. 70 in the ADA specification test, The materials immersed in 5% SnF2 and Brudevold solution have completely lost their transparency. Those painted with Colgate, Crest and Gleem II showcd scarcely any changes. Those painted with Nupro and Zircate have slightly lost their transparencies, being less transparent than 0.55 of the standard opal glass Co. 70. Through immersing 3/4 of the disc-shaped test material in fluoride solution or painting it with fluoride solution, its influence was studied through comparing the relative change of the color of the same test material. Fig. 15 shows the example of immersing in 2% NaF and Fig. 16, that of immersing in 5% SnF2 for 15 days each. A

12 Fig. 17. State of the surface after staining and washing with water (after immersing in distilled water for 15 days). Fig. 18. State of the surface after staining and washing with water (after immersing in 2% NaF for 15 days). distinct borderline was noted from the part left in the air. Similar results were obtained with Nupro and Zircate. The same application with Colgate, Crest and Gleem II for 15 days also produced a farely recognizable border. Brudevold solution gave such a profound effect as destriction of the shape of the disc Clinical tests As the first experiment, the extracted tooth was filled with silicate cement and made to react with fluoride to study the influence on the border surface between the

13 filling material and dentin, difference in the effect of application of fluoride between dentin and silicate cement and fluoride blocking effect of various varnish preparation's. While silicate cement tends to be readily stained by various pigments, the test material painted with crystal violet followed by washing with water after being immersed in distilled water for 15 days and polishing was found to be scarcely stained in the present experiment. Fig. 17 shows the state of the surface on staining after being immersed in distilled water for 15 days. Fig. 18 shows an example of the state of the surface on staining after being immersed in 2% NaF solution for 15 days following Fig. 19. State of the surface after staining and washing with water (after immersing in 5% NaF for 15 days). Fig. 20. State of the surface after staining and washing with water (after immersing in Brudevold solution for 15 days).

14 painting with Caulk Varnish on 1/2 of the test material. Fig. 19 shows the results obtained by the use of 5% SnF2 solution and Fig. 20 the result of immersion in Brudevold solution. In Fig. 18, pigment deposition or invasion by fluoride was found on the borderline between the filling material and dentin and the filling material without being covered by the varnish. The dentin was not stained except for the portion of fissure. Fig. 19 shows an approximately same result as in Fig. 18. Pigment deposition was more pronounced and the filling material was further invaded. In Fig. 20, the filling material was stained up to the varnished portion, indicating the infiltration of the silicate cement by Brudevold Solution, decreasing the blocking effect of the varnish. In this figure, the dentin in the non-varnished portion is stained, and the varnished portion is not stained, indicating the effect of varnish on the dentin portion. In this Figure, enamel also showed pigment deposition. Results of application of Colgate, Crest and Gleem II for 15 days were approximately similar to those in Fig. 18. When Nupro and Zircate are applide, results about the same as those in Fig. 19 were obtained. As the second experiment, Table 3 shows the results of the action of fluoride on silicate cement filling an artificial tooth. While filling of an artificial tooth with silicate cement is not practiced clinically, this experiment was conducted in order to study the effect of fluoride under the environment of the oral cavity to minimize the physical and psychological load to the test subject. According to this Table, despite the complete absence of changes in the artificial tooth made to react with 2% NaF solution, the test material within the ring tested in a parallel experiment showed positive effects. Such phenomenon is seen also as to the effect of other fluorides. Among the criteria of evaluation A-E, result always one grade higher was obtained in the material filling the ring. Table 3. Effect of application of various fluoride compounds for 90 days on silicate cement filling the artificial tooth Criteria of evaluation A: No change was seen at all. B: Margin was slightly stained. C: Margin and surface were stained. D: Margin was broken. E: Margin and surface were broken. Note: The sign in the parenthesis shows the result of filling within the ring, and the line indicates absence of application.

15 Table 4. Effect of application with various fluoride compounds for 90 days on silicate cement filling the natural tooth Criteria of evaluation A: No change was seen at all. B: Margin was slightly stained. C: Margin and surface were stained. Note: The sign in the parentheses shows the result of filling within the ring, and the line indicates absence of painting. In 5% SnF2, only the margin was slightly stained, and Fig. 8 shows such an example. Application of Brudevold solution only resulted in staining of the margin and surface in the oral cavity. The influence of application of Colgate, Crest, Nupro and Zircate was more pronounced than 2% NaF. In this experiment, Nupro and Zircate were applied with the use of a brush on the contraangle under 1500 revolutions according to the instructions for the use of these materials, and scarcely any blocking effect of the varnish was noted. Varnish was painted on the lower half of the filling of the artificial tooth, and 1/2 of the filling of the ring to study the effect. As the result, sufficient effects were noted except for the Nupro, Zircate and Brudevold solution described above but the order among the 3 could not be established. As the third experiment, fluoride was made to react with the silicate cement filling the live tooth, as shown in Table 4. In this experiment, 5% SnF2, Colgate, Nupro and Zircate alone were applied since the material was a live tooth of a test subject.a s the result, no changes were seen at all when Colgate was made to act for 3 minutes once daily. Application of 5% SnF2, Nupro and Zircate resulted in the staining of the margin. Materials filling the ring showed responses 1 or 2 grade higher. 4. Discussion 4.1. Technological test Various fluoride compounds used in the present study, 2% NaF, 5% SnF2 and Brudevold solution are used by many clinicians for the prevention of carious te eth. Nupro and Zircate are commercially available in a paste form for clinicians. Colgate, Crest and Gleem II are commercially available for general population in tubes with clear description of "fluoride content", finding a widespread use. Technological tests conducted with the material treated with 2% NaF, 5% SnF2 and Brudevold solution revealed a fall of the mechanical properties of silicate cement by the action of these fluoride compounds, and the degree of such fall varies greatly

16 depending on the kind of fluoride. The fall was the least with the use of 2% NaF and the greatest with the use of Brudevold solution. Compared to the immersion in distilled water, 2% NaF caused a decrease of the compressive strength to 79.0%, tensile strength to 76.6% and surface hardness to 78.0%, each to a similar degree, while 5% SnF, caused a decrease to 74.8% of the compressive strength, to 61.7% of tensile strength, and to 66.3% of surface hardness, each more pronounced than in the use of 2% NaF. The decrease of tensile strength was especially pronounced. Brudevold solution caused a decrease of the compressive strength to 45.7%, tensile strength 33%, and surface hardness to 42.8%, all to less than 1/2 of the values obtained after immersion in distilled water. The tensile strength showed the most pronounced fall, to 1/3 of the control value. Silicate cement, an originally frail material, has become more fragile by the action of fluoride, to develop such a mechanical property. While artificial saliva was used in this experiment, the resistance against compression was similar to that after contact with distilled water. The tensile and surface hardness gave slightly higher values, without causing a decrease like fluoride compounds. Consequently, artificial saliva did not appear to cause an impediment of mechanical property of silicate cement. The surface hardness of the silicate cement is of extreme clinical importance. When the hardness is low, wearing becomes excessive and the repairing material is subject to a danger of falling off. In comparison with the hardness of dentin of 58 and that of enamel of 276, the hardness of this material was not as high as that of the enamel but slightly higher than that of dentin. In the set product of silicate cement, the surface of about 10% of the particle was invaded, and 20-30% of the gel is said to connect the surroundings of the unreacted particles[13]. Since giant particles remain on the surface, the measured value of the hardness considerably varies depending on the site of measurement. In the present experiment, 10 measurements were carried out on random sites on 1 test material, and the average of 10 test materials were obtained. The problems on measurement thus appear to be rather minor. The set product of silicate cement appears beautiful as a greatclinical advantage, but this characteristic is influenced by the degree of transparency. Even with a favorable degree of transparency in the beginning, a material with a change of the color in the course of years[14] would never be satisfactory. In the test for transparency, application of Colgate, Crest and Gleem II caused no change on the transparency of the silicate cement, but half-immersing test caused slight erosion and change of the color. Such difference was probably due to the difference in the method of test, since the latter method is convenient to detect even minor changes. Fluoride compounds other than the 3 kinds of pastes described above gave definite influence detected by the test of transparency and half-immersion test Clinical test Through the technological tests described above, fluorides were found to decrease the properties of silicate cement markedly. In order to clarify the actual clinical significance of such influence, these experiments were carried out. Though silicate cement is never used to fill the artificial teeth clinically, a cavity

17 was formed in an artificial tooth used as a prosthesis, and filled with silicate cement for use in an experiment to see the effect of fluoride in the environment of oral cavity. Along with this experiment, the material filling a ring under the same condition was applied with fluorides as in the filling of the artificial tooth, to preserve it under approximately the same circumstance as the oral cavity (preserved in artificial saliva changed of the ring was found to be more profoundly influenced by fluorides than the filling of the artificial tooth. This is probably because of the action of constantly flowing saliva and food washing away the applied fluoride, which resulted in the decrease of its action in the oral cavity. When Colgate, Crest, Nupro and Zircate are applied, more profound influence than 2% NaF was noted. While NaF is under the form of solution, other compounds are in the paste form, with high adhesibility even if it is wiped after application, without disappearance of the material after washing with water, providing an explanation for this. The blocking effect of varnish, on the other hand, was found to be favorable in outline, but it is hardly conceivable that general public other than the clinician uses it during tooth brushing and mouth washing. According to the instruction for the use of Nupro and Zircate, these should be applied under a low speed of about 1,500 r.p.m. In the present experiment, no varnish effect was found probably because the varnish was removed by brushing. When Nupro and Zircate are applied, consequently, care should be taken to apply varnish on the portion modified by silicate cement, and measures should be applied to prevent the removal of this material. When silicate cement is applied to the live tooth, painting with Nupro and Zircate appears to have an unfavorable influence and such paste should be used with caution. When fluoride is applied on the tooth, filling material consisting of silicate material should either be blocked with varnish, or the painting on the tooth should be avoided. 5. Conclusions Application of fluoride compounds has been regarded highly as a method of prevention of carious teeth, and various devices were advanced to make it act on the tooth. In the present study, the influence of these fluoride compounds on the repairing material consisting of silicate cement was studied and the following conclusions were drawn. 1) Solutions for the prevention of carious teeth under clinical use, 2% NaF, 5% SnF2, and Brudevold solution markedly impeded the mechanical properties of hardened silicate cement, but the degree of the fall varies depending on the kind of fluorides, in the order of 2% NaF < 5 < SnF2 <Brudevold solution. 2) The solution for the prevention of carious tooth, pastes containing fluoride for use by the clinicians and several kinds of fluoride containing tooth paste commercially available all decreased the transparency of the set product of silicate cement. 3) When the fluorides used in the present experiment is made to act outside of the oral cavity, compounds other than 2% NaF corroded the filling material consisting of silicate cement.

18 4) The blocking effect of varnish used in the experiment was found to be effective when used correctly, but scarcely any effect was noted on Brudevold solution. 5) The application of fluoride to the tooth filled with silicate cement markedly impeded its mechanical property, so that a sufficient care should be taken. References [1] MUHLER, J.C. & DAY, H.G.: Effects of stannous fluoride, stannous chloride and sodium fluoride on the incidence of dental lesions in rats fed a caries producing diet; J. Amer. dent. Ass., Vol. 41, , (1950). [2] PHILLIPS, R.W. & SWARTZ, M.L.: Effects of certain restorative materials on solubility of enamel; J. Amer, dent. Ass., Vol. 54, , (1957). [3] GURSIN, A.V.: A study of the effect of stannous fluoride incorporated in dental cement; Northwestern Univ. Bulletin, Vol. 64, 8-18, (1964). [4] HENSCHERL, C.J.: Observations concerning in vivo disintegration of silicate cement restoration (Abstract); J. dent. Res., Vol. 28, 528, (1944). [5] LILIENTHAL, B.: The effects of fluoride on acid formation by salivary sediment; J. dent. Res., Vol. 35, , (1956). [6] SOUDER, W. & SCHOONOVER, I.C.: Experimental remineralization of dentin; J. Amer. dent. Ass., Vol. 31, , (1944). [7] VOLKER, J.F.: Effect of fluorine on solubility of enamel and dentin; Proc. Soc. Exp. Biol. Med., Vol. 42, (1939). [8] BRUDEVOLD, F., SAVORY, A., GARDNER, D.F., et al.: A study of acidulated fluoride solution; Arch oral Biol., Vol. 8, , (1963). [9] AMERICAN DENTAL ASSOCIATION: Guide to Dental Materials; 3rd Ed., American Dental Association, Chicago, p. 171, (1966). [10] AMERICAN DENTAL ASSOCIATION: Guide to Dental Materials. 3rd Ed., American. Dental Association, Chicago, pp , (1966). [11] GREENWOOD, J.N., DOWN, C.H. & WONER, H.K.: An investgation of failure of stainless inlay restoration posts; Austral. J. Dent., Vol. 41, 73, (1937). [12] PEYTON, F.A.: Restorative Dental Materials, 3rd Ed., The C.V. Mosby Co., Saint Louis, p. 438, (1968). [13] PHILLIPS, R.W.: Skinner's Science of Dental Materials, 7th Ed., W.B. Saunders Co., Philadelphia, pp , (1973). [14] PHILLIPS, R.W.: Skinner's Science of Dental Materials, 7th Ed., W.B. Saunders Co., Philadelphia, pp , (1973).