Postdevelopmental Effects of Boron, Fluoride, and Their Combination on Dental Caries Activity in the Rat F. T. Y. LIU Department of Physiology, University of Missouri-Kansas City School of Dentistry, Kansas City, Missouri 64108 USA
Drinking water of rats aged 21 days was supplemented with 1, 10, 30, 50, 100, or 283 ppm of boron or 10 or 25 ppm of fluoride individually or in combination. All rats were fed a cariogenic diet. Boron did not reduce dental caries activity in erupted molars after eight weeks. When given in combination, it partially antagonized the cariostatic effect of fluoride. Epidemiological surveys and animal experihave suggested that a slightly higher content of boron (B) in drinking water, food, or soil exerts a cariostatic effect1-9 and that B may enhance the effect of fluoride (F) in reducing dental caries activity.2 However, conflicting results of B on caries activity of preeruptive molars also have been reported in animal experiments.10'11 The present studies determined the cariostatic effects of B at multidose levels supplemented in drinking water and the synergistic effects of B with F in reducing dental caries activity of postdevelopmental molars in the rat. ments
ments, groups of rats were supplied, ad libitum, drinking water or drinking water supplemented with 1, 10, 30, 50, 100, or 283 ppm of B (as Na2B407* 10 H20) or 10 or 25 ppm of F (as NaF) individually or in combination as shown in Table 1. With increase in concentration the pH values of sodium borate solutions increased proportionately above the neutral value. Therefore, the pH of all trace element-containing solutions and drinking water were adjusted to approximately pH 7 by adding dilute HCI. The B and F contents of the water and diet were analyzed and found to be 0.05 and 0.2 ppm TABLE 1 DOSE LEVELS OF FLUORIDE AND BORON SUPPLEMENTED IN DRINKING WATER IN THREE EXPERIMENTS Fluoride (ppm)
Boron (ppm)
EXPERIMENT 1
Group 1 Group 2 Group 3 Group 4
Materials and Methods Sprague-Dawley female ratsa aged 21 days were assigned randomly into desired groups. All rats were supplied a cariogenic diet,b ad libitum, for the entire experimental period of eight weeks. In three separate experi-
EXPERIMENT 2
Supported, in part, by the General Research SunnortUSPH-RR-05323-12 of the School of Dentistry and the Faculty Research Grant 2681-2100 of the University of Missouri-Kansas City. This paper was presented at the 52nd general session of the IADR in Atlanta, Ga, March 1974. Received for publication December 19, 1973. Accepted for publication June 18, 1974. a Holtzman Co., Madison, Wis. b Diet 2000, General Biochemical, Chagrin Falls, Ohio.
Group 1
.. 25 . 25
...
283 283
Group 1
..
Group 2 Group 3 Group 4
10
. . .
. . . . . 10
10 30 10 30
Group 5 Group 6 EXPERIMENT 3
Group Group Group Group Group Group Group
2 3 4 5 6
7 8
10
.. 10
. . .
. . . ..
1 50 100 1
.. 10 10 10
50 100 97
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98
J Dent Res January-February 1975
LIU
and 0.6 and 1.9 ppm,c respectively. During the first four days of the experiments all rats received a daily oral inoculation of 0.2 ml of a freshly prepared culture of cariesconducive Streptococcus mutans.d Colonization tests for oral S mutans were done three weeks after the last inoculations. A positive result was found in all rats, thus indicating that the oral inoculation of S mutans was successful and that their growth in the oral cavity was not influenced by B or F or by both. Daily water consumptions were measured by using specially designed, J-shaped, graduated glass drinking tubes.e Body weights were recorded weekly, food consumption was measured daily on the third, fifth, and seventh weeks of the experiment. To avoid contamination by other trace elements, porcelain food jars and stainless steel cages were used. The rats were kept at 72 ± 1 F and exposed to artifical light automatically from 7:00 AM to 7:00 PM. At autopsy, the salivary gland weights of some rats and the final body weights of all rats in each group were recorded. All molars were freed from soft tissues as described previously12 and dental caries was assessed by the method of Keyes.13 The dental caries activity was judged, on per-rat basis, by the mean areas of carious enamel lesions, the areas and depth of dentinal involvement of carious lesions, and the numbers (regardless of size) of carious enamel lesions on all molars as well as the percentages of molars affected with caries. These parameters and the body weight gain, major salivary gland weights, and daily water and food consumptions of treated groups of rats were compared with those of the appropriate controls by Student s t test at the 5% level of significance. Comparisons of some of these parameters were also made between the treated groups of rats. In addition, the relative salivary gland weights (gland weight in mg/ 100 gm body weight) were calculated and compared with those of the controls.
lesions (major and minor sulcal, buccolingual, and proximal) in rats treated with 25 ppm of F in drinking water decreased (P < 0.01), whereas, those of rats receiving B at 283 ppm were essentially the same as the controls. Furthermore, addition of 283 ppm of B to drinking water containing 25 ppm of F caused a borderline significant increase in the areas of carious enamel lesions compared with those of rats receiving 25 ppm of F alone, although the mean areas in treated rats were still slightly but not significantly less than the controls. When the mean areas of different types of carious enamel lesions of treated rats were compared with the appropriate controls or were compared between treated groups, similar results were obtained. No carious proximal enamel lesion was found in rats treated with F alone. As shown in Table 2, when the number, regardless of the size, of carious enamel lesions as well as the areas of carious lesions with slight dentinal involvement were compared, results were similar to those expressed by the areas of carious enamel lesions (Fig 1). Body weight and absolute and relative submandibular gland weights of rats treated with B and B in combination with F were significantly smaller than the controls (Table 2). However, the absolute and relative parotid gland weights of B- and B-F-treated rats were essentially the same as the controls. Fluoride alone did not affect these parameters significantly. The daily water and food consumptions of B- and B-F-treated rats were essentially the same as the controls. EXPERIMENT 2.-Figure 2 shows that the
*MAJOR SULCAL EMINOR SULCAL *IBUCCOLINGUAL OZPROXIMAL NC F
FB
Results
EXPERIMENT 1.-Figure 1 shows that the mean areas of all types of carious enamel The B and F concentrations in water and diet were analyzed by the Environmental Trace Substances Center of the University of Missouri, Columbia, Mo. d S mutans 6715 supplied by NIDR, Bethesda, Md. e Fisher Scientific Co., St. Louis, Mo. c
0I
10
CARIOUS ENAMEL AREAS
20
FIG 1.-Effects of higher dose level of boron, fluoride, or both in drinking water on mean
areas of carious enamel lesions per rat. NC, normal control; F, 25 ppm of F; B, 283 ppm of B; FB, 25 ppm of F plus 283 ppm of B.
Downloaded from jdr.sagepub.com at SIMON FRASER LIBRARY on June 1, 2015 For personal use only. No other uses without permission.
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Drinking water of rats aged 21 days was supplemented with 1, 10, 30, 50, 100, or 283 ppm of boron or 10 or 25 ppm of fluoride individually or in combination. All rats were fed a cariogenic diet. Boron did not reduce dental caries activity in erupted molars after eight weeks. When given in combination, it partially antagonized the cariostatic effect of fluoride. Epidemiological surveys and animal experihave suggested that a slightly higher content of boron (B) in drinking water, food, or soil exerts a cariostatic effect1-9 and that B may enhance the effect of fluoride (F) in reducing dental caries activity.2 However, conflicting results of B on caries activity of preeruptive molars also have been reported in animal experiments.10'11 The present studies determined the cariostatic effects of B at multidose levels supplemented in drinking water and the synergistic effects of B with F in reducing dental caries activity of postdevelopmental molars in the rat. ments
ments, groups of rats were supplied, ad libitum, drinking water or drinking water supplemented with 1, 10, 30, 50, 100, or 283 ppm of B (as Na2B407* 10 H20) or 10 or 25 ppm of F (as NaF) individually or in combination as shown in Table 1. With increase in concentration the pH values of sodium borate solutions increased proportionately above the neutral value. Therefore, the pH of all trace element-containing solutions and drinking water were adjusted to approximately pH 7 by adding dilute HCI. The B and F contents of the water and diet were analyzed and found to be 0.05 and 0.2 ppm TABLE 1 DOSE LEVELS OF FLUORIDE AND BORON SUPPLEMENTED IN DRINKING WATER IN THREE EXPERIMENTS Fluoride (ppm)
Boron (ppm)
EXPERIMENT 1
Group 1 Group 2 Group 3 Group 4
Materials and Methods Sprague-Dawley female ratsa aged 21 days were assigned randomly into desired groups. All rats were supplied a cariogenic diet,b ad libitum, for the entire experimental period of eight weeks. In three separate experi-
EXPERIMENT 2
Supported, in part, by the General Research SunnortUSPH-RR-05323-12 of the School of Dentistry and the Faculty Research Grant 2681-2100 of the University of Missouri-Kansas City. This paper was presented at the 52nd general session of the IADR in Atlanta, Ga, March 1974. Received for publication December 19, 1973. Accepted for publication June 18, 1974. a Holtzman Co., Madison, Wis. b Diet 2000, General Biochemical, Chagrin Falls, Ohio.
Group 1
.. 25 . 25
...
283 283
Group 1
..
Group 2 Group 3 Group 4
10
. . .
. . . . . 10
10 30 10 30
Group 5 Group 6 EXPERIMENT 3
Group Group Group Group Group Group Group
2 3 4 5 6
7 8
10
.. 10
. . .
. . . ..
1 50 100 1
.. 10 10 10
50 100 97
Downloaded from jdr.sagepub.com at SIMON FRASER LIBRARY on June 1, 2015 For personal use only. No other uses without permission.
98
J Dent Res January-February 1975
LIU
and 0.6 and 1.9 ppm,c respectively. During the first four days of the experiments all rats received a daily oral inoculation of 0.2 ml of a freshly prepared culture of cariesconducive Streptococcus mutans.d Colonization tests for oral S mutans were done three weeks after the last inoculations. A positive result was found in all rats, thus indicating that the oral inoculation of S mutans was successful and that their growth in the oral cavity was not influenced by B or F or by both. Daily water consumptions were measured by using specially designed, J-shaped, graduated glass drinking tubes.e Body weights were recorded weekly, food consumption was measured daily on the third, fifth, and seventh weeks of the experiment. To avoid contamination by other trace elements, porcelain food jars and stainless steel cages were used. The rats were kept at 72 ± 1 F and exposed to artifical light automatically from 7:00 AM to 7:00 PM. At autopsy, the salivary gland weights of some rats and the final body weights of all rats in each group were recorded. All molars were freed from soft tissues as described previously12 and dental caries was assessed by the method of Keyes.13 The dental caries activity was judged, on per-rat basis, by the mean areas of carious enamel lesions, the areas and depth of dentinal involvement of carious lesions, and the numbers (regardless of size) of carious enamel lesions on all molars as well as the percentages of molars affected with caries. These parameters and the body weight gain, major salivary gland weights, and daily water and food consumptions of treated groups of rats were compared with those of the appropriate controls by Student s t test at the 5% level of significance. Comparisons of some of these parameters were also made between the treated groups of rats. In addition, the relative salivary gland weights (gland weight in mg/ 100 gm body weight) were calculated and compared with those of the controls.
lesions (major and minor sulcal, buccolingual, and proximal) in rats treated with 25 ppm of F in drinking water decreased (P < 0.01), whereas, those of rats receiving B at 283 ppm were essentially the same as the controls. Furthermore, addition of 283 ppm of B to drinking water containing 25 ppm of F caused a borderline significant increase in the areas of carious enamel lesions compared with those of rats receiving 25 ppm of F alone, although the mean areas in treated rats were still slightly but not significantly less than the controls. When the mean areas of different types of carious enamel lesions of treated rats were compared with the appropriate controls or were compared between treated groups, similar results were obtained. No carious proximal enamel lesion was found in rats treated with F alone. As shown in Table 2, when the number, regardless of the size, of carious enamel lesions as well as the areas of carious lesions with slight dentinal involvement were compared, results were similar to those expressed by the areas of carious enamel lesions (Fig 1). Body weight and absolute and relative submandibular gland weights of rats treated with B and B in combination with F were significantly smaller than the controls (Table 2). However, the absolute and relative parotid gland weights of B- and B-F-treated rats were essentially the same as the controls. Fluoride alone did not affect these parameters significantly. The daily water and food consumptions of B- and B-F-treated rats were essentially the same as the controls. EXPERIMENT 2.-Figure 2 shows that the
*MAJOR SULCAL EMINOR SULCAL *IBUCCOLINGUAL OZPROXIMAL NC F
FB
Results
EXPERIMENT 1.-Figure 1 shows that the mean areas of all types of carious enamel The B and F concentrations in water and diet were analyzed by the Environmental Trace Substances Center of the University of Missouri, Columbia, Mo. d S mutans 6715 supplied by NIDR, Bethesda, Md. e Fisher Scientific Co., St. Louis, Mo. c
0I
10
CARIOUS ENAMEL AREAS
20
FIG 1.-Effects of higher dose level of boron, fluoride, or both in drinking water on mean
areas of carious enamel lesions per rat. NC, normal control; F, 25 ppm of F; B, 283 ppm of B; FB, 25 ppm of F plus 283 ppm of B.
Downloaded from jdr.sagepub.com at SIMON FRASER LIBRARY on June 1, 2015 For personal use only. No other uses without permission.
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