CLI:NICAL AND MATERIALS SCIENCES Plaque Minerals and Caries Experience: Associations and Interrelationships R. G. SCHAMSCHULA,* M. BUNZEL,t HELEN M. AGUS,* B. L. ADKINS,+ D. E. BARMES,t and G. CIHARLTON§
*Institute of Dental Research, 2 Chalmers Street, Sydney, N.S.W. Australia 2010, tWorld Health Organization, Geneva, Switzerland, $University of Queensland, Brisbane, Australia, and §University of Sydney, Sydney, Australia Inverse associations were demonstrated between DMFT and total calcium, phosphorus, magnesium, strontium, potassium, and fluoride concentrations in individual plaques. Lithium, strontium, fluoride, and zinc contents were inversely related to plaque mass. Consistent interdependence patterns between elements indicate the operation of a mineral level regulating mechanism, effective under diverse environmental conditions.
Materials and Methods The sample consisted of 72 schoolchildren (42 males and 30 females, between 9.7 and 13.0 years of age; mean = 11.4, SD = 0.8 years), lifelong residents of one of three New South Wales towns: Katoomba (n = 26), Sydney (n= 21) and Yass (n= 25). The towns were selected according to the fluoride level in the public water supplies; Katoomba was deficient (< 0.1 ppm) while Sydney and Yass had been fluoridated at 1 ppm 4 and 16 years prior J Dent Res 57(3):427-432, March 1978. to sampling. The paucity of information concerning the poThe procedures employed for clinical extential influence of plaque minerals on caries amination,1 plaque collection,' and chemical experience led to a study of selected major analyses2'3 have been previously reported. and trace elements in plaque samples collected The linearity of the relationships studied from Australian children. has been examined in detail. Relationships beTwo previous reports dealt with specific came more nearly linear and the correlation aspects of the results. In one of the papers, in- coefficients increased in size when the variables verse associations were reported between the were transformed according to the normal probtotal fluoride content of plaque and individual ability integral; plaque quantity and mineral caries experience and inverse trends were shown values were submitted to statistical analysis in between the quantity of plaque and its fluoride this form. Associations between variables were concentration.' A subsequent publication de- examined using correlation matrices and bitailed the mean values and variation in the total variate and multiple linear stepwise regression content of another nine elements in plaque.2 analyses (MLSRA). Discriminant analyses This report deals with associations between (DA) were employed for classifying subjects caries experience and the total concentrations with contrasting levels of caries experience on of calcium, phosphorus, potassium, magnesium, the basis of the mineral content of plaques. Difstrontium, lithium, zinc, copper, and lead in ferences between mean values were examined individual plaque samples, the interrelation- using student t tests. Statistical analyses were ships between the concentrations of elements carried out separately for subjects in each town and with closely related parameters. Plaque flu- and for the whole sample, using standard biooride is included in the analyses where joint medical programs. effects or interactions of variables are examined. Results Received for publication April 5, 1977. Accepted for publication September 15, 1977. Individual caries prevalence ranged from 0 This study was supported by the World Health Orto 14 DMFT and was directly associated with ganization. Vol. 57 No. 3 427 Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
428
J Dent Res March 1978
SCHAMSCHULA ET AL TABLE 1
PRODUCT-MOMENT CORRELATION COEFFICIENTS BETWEEN PLAQUE QUANTITY (DRY WT) AND THE CONCENTRATIONS OF MINERALS IN PLAQUE
Li Sr F Zn
Overall n=72
Yass n=25
Katoomba n=26
Sydney n=21
-0.37t
-0.36* -0.14 -0.16 -0.36*
-0.19 -0.27 -0.17 -0.42*
-0.55t -0.28 -0.32 0.16
-0.20* -0.16 -0.15 * P < 0.05.
t P < 0.01.
age over the whole sample (r = 0.58, P < 0.001). The mean DMFT scores (SD) were: overall 4.4 (3.1); Sydney 6.6 (2.7); Katoomba 4.7 (2.9) and Yass 2.2 (2.0). Mean caries scores for males and females did not differ significantly (t- 0.91, df = 70). Examination of the data by sex showed that over the whole sample the mean zinc content of plaque was significantly higher for males than for females.2 Corresponding differences were not significant within towns and no differences were detected between sexes for the other elements. Therefore, the analyses were conducted with sexes combined. Plaque quantity (dry wt of plaque)1Ivas positively associated with individual caries experience (DMFT) in Sydney (r =0.58, P < 0.005). The plaque concentrations of four elements appear to be dependent upon plaque quantity (Table 1). Most correlation coefficients are low, but six reach statistical significance; with a single exception (zinc in Sydney, not significant) the associations are consistently inverse. Because of the apparent dependence of element concentrations on plaque quantity, the latter parameter was included in MLSRA-s and DA-s, to permit assessment of its contribution to the combined effect of the elements. Clusters of bivariate correlation coefficients for the concentrations of selected pairs of elements in plaque are given in Table 2, which shows interdependence between elements at various levels. Considering biological variation and sources of cumulative error, the strength of correlations between calcium and phosphorus and calcium and strontium indicates that the concentration ratios of these elements are nearly conistant. Other pairs, such as calcium and fluoride or phosphorus and magnesium are strongly interdependent. Potassium is firmly as-
sociated with magnesium and shows strong common ground with phosphorus, but practically no dependence on calcium. In contrast, lead is practically independent of both calcium and phosphorus (as are copper and zinc). However, with one exception the interrelationshops between zinc, copper and lead are significant. Variations in the calcium/phosphorus ratio are almost entirely dependent on calcium. Lithium (not in Table 2) is independent of all other elements. The consistency in the magnitude of the correlation coefficients between towns and over the whole sample is high. Values which tend to weaken the consistency occur invariably in Katoomba, the fluoride-deficient town; here the correlation coefficients for calcium versus phosphorus, strontium, and fluoride; for phosphorus versus potassium; for phosphorus versus calcium/phosphorus ratio; and for potassium versus magnesium are lower than in other towns or over the whole sample. All but four of the correlation coefficients are positive, indicating a common trend in concentration levels for interdependent elements. All four negative coefficients are associated with lead; they are trivial TABLE 2 PRODUCT-MOMENT CORRELATION COEFFICIENTS BETWEEN SELECTED MINERALS IN PLAQUE: CALCIUM, PHOSPHORUS, POTASSIUM, AND ZINC Overall n = 72
Yass 25
n =
.751t
.78:t
.811: .40$
.911: .39*
.511t K .16 Pb -.04 Ca/P .961
.13 .25 .96:
Ca versus P
Sr Mg F
.611t
Katoomba Sydney n=26 n=21
.61 t .641:
.871: .921: .39* .44* .661 .43* .19 .15 -.22 -.14 .981: .951:
P versus Mg Sr F K Pb Ca/P
.641: .711: .40: .51 .15 .60:
.751: .751: .45* .60: .26 .611:
.53t
.57t
Zn versus Cu Pb
.33t .441
.34* .35*
.44* .44*
.24 .39*
K versus Mg
.671
.791:
.39*
.701
.73: .671: .42* .62t .50* .32 .17 -.14 .771 .44*
* P < 0.05. t P < 0.01. t P < 0.001.
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
VZol. 57 No. 3
CARIES & PLAQUE MINERALS: INTERCOMPARISONS
TABLE 3 PRODUCT-MOMENT CORRELATION COEFFICIENTS BETWEEN TOTAL CONCENTRATIONS OF ELEMENTS IN PLAQUE (DRY WT) AND INDIVIDUAL CARIES EXPERIENCE (DMFT), OVERALL AND PER AREA Overall n =72
Yass =25
Katoomba
n
n=
-.46t
-.43* -.49t -.38*
.-.48*
-.02 -.15 -.14
-.45* .-.42* -.36
p
-.41::
Mg K F Ca Sr
-.39t
-.27
-.30t
-.09
*
-.28t
-.28
-.25* -.23*
-.41* -.32
26
Sydney n=
21
-.32 -.20
P < 0.05.
t P < 0.01. t P < 0.001.
compared to others in Table 2, and nonsignificant.
Table 3 shows the bivariate correlation coefficients between individual DMFT scores and the content of those elements in plaque for which significant associations or suggestive trends were found. The associations are inverse for every element in all areas and reach high levels of significance in numerous instances. Of the four elements not included in Table 3, a consistent inverse trend between DMFT and lithium failed to reach significance in all sample divisions. For the remaining elements associations were not consistent through sample divisions; however in Sydney copper (r = 0.18, NS), lead (r = 0.34, NS), and zinc (r = 0.50, P < 0.02) showed a common trend of positive association with caries.
MLSRA-s were conducted with DMFT as dependent variable and identical sets of independent variables comprising the elements determined in plaque, selected concentration ratios and plaque quantity. The analyses were allowed to proceed without restriction until the reduction in the error sum of squares ceased to be significant (Table 4). This point was reached after three to nine variables had entered the analyses. For practical purposes these results reflect the combined effect of the sets of independent variables, as subsequent entries to the end point have no material effect the outcome of the analyses. Elements entered MLSRA-s with the following frequencies: phosphorus entered in all four sample divisions; fluoride, magnesium, and copper in two divisions and calcium, strontium, lithium, potassium, and zinc in one division each. Stepwise DA-s (Table 5) determined the extent to which the information contained in individual plaque mineral values could separate subjects with different levels of caries experience (DMFT %). The limiting caries levels of the groups were defined to include the maximum number of subjects in the analyses and to represent the low and high caries groups by approximately equal numbers, without overlap in caries experience. As the scope of choosing contrasting groups from the whole sample was greater than in any one town, in the overall analysis discrimination was tested at two levels. In DA-s, the classification of subjects is based on a linear combination of the variables, the discriminant function (DF), which produces the maximum separation of groups. The on
BLE 4 MULTIPLE CORRELATION COEFFICIENTS (R) FROM MLSRA-s BETWEEN DMFT AND IDENTICAL SETS OF VARIABLES RELATED TO THE MINERAL CONTENT OF PLAQUE Overall n=72 R %
At "critical" F level
(step number) At end point+ (step number)
.50t 25 (4) .55* 30 (14)
429
Yass n=25 R %
.66
44 (6)
.82 67 (19)
Katoomba n=26 R % .76* 58 (9) .89 79 (19)
Sydney n=21 R % .77t 59 (3) .84 71 (19)
% = R2 X 100 = The proportion of variation in DMFT which can be explained in terms of the combined effect of independent variables. + = Where no further reduction in the error sum of squares was possible. * P < 0.05.
t P < 0.01. $ P < 0.001.
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
430
SCHAMSCHULA ET AL
J Dent Res March 1978
TABLE 5 SUMMARY OF DISCRIMINANT ANALYSES: CLASSIFICATION OF SUBJECTS INTO GROUPS (A AND B) ACCORDING TO CARIES EXPERIENCE (DMFT %) BASED ON THE MINERAL CONTENT OF PLAQUE DMFT % A B
Yass (P,CU,Pb,K,P/F)* Katoomba (Ca/Li, P, Sr, F, Li)* Sydney (F, Zn, Ca/Sr, plaquewt)* Overall
(P, Pb,F)*
Overall (P, Pb, F, Sr)*
A
B
Correctly Classified n %
10
8
17
n
Step
F
94.4
5
5.33
0.01
94.7
5
2.40
NS
4
13.15
0.001
P
9
< 18
> 23
9 10
18
< 23
> 29
9
8
17
0
> 35
9
10
17
89.5
3
4.16
0.025
8
> 25
14 20
27
79.4
4
5.27
0.001
100
* Variables included in discriminant function at step indicated in order of entry.
discriminatory power of plaque elements is substantial; the proportion of correctly classified subjects ranges from 79 to 100% with no more than five variables. The consistency of variables which make the most substantial contribution to the classification of subjects is strong; phosphorus appears in all five, fluoride in four, and lead and strontium in three analyses. The direction of the effect of an element can be determined by contrasting the mean concentration values associated with the low or high caries prevalence groups. With two exceptions, lead and zinc in Sydney, the higher mean concentrations of elements which were shown to be important in their own right or collectively were associated with the low caries group.
refined sucrose.6'7 It was shown67 that the pattern was the consequence of selective assimilation and concentration of some elements (fluoride, magnesium, zinc, lead, and lithium) from seemingly meager sources, and the rejection of massive excess of others (calcium and strontium) when offered in the form of lime used with betel chewing. The close similarity of the two sets of findings is a strong indication that the basic mechanism regulating mineral levels in plaque is very similar, or identical in Western and primitive communities with diverse social, geochemical and socio-economic backgrounds, consuming vastly different diets, exposed to high and low caries challenge rates, and receiving extensive and no dental care, no
respectively. Discussion The caries experience4 and level of dental care5 of the subjects were representative of corresponding Australian populations with similar exposure to water-borne fluoride. The concentration ratios of elements in plaque, reflected by the intercorrelations shown in Table 2, were not influenced appreciably by considerable individual variations in the concentration levels of specific elements.2 The strength, consistency and pattern of associations between elements (Table 2) is almost identical with those demonstrated for plaque minerals in a substantial sample drawn from a primitive population, exposed to differing levels of environmental fluoride, whose diet contained negligible amounts of mono- or disaccharides and
As the concentration ratios of elements are the consequences of the concentrations of the respective elements, the factors controlling concentration levels also control the ratios. It is assumed that the bacterial population plays a substantial role in the selective regulation (homeostasis) of the mineral levels in individual plaques. In addition, physico-chemical factors, such as concentration gradients and diffusion properties of a biomass and the chemical attributes of an element in the form offered are expected to play significant roles. Availability must be of decisive importance, but present knowledge is insufficient to determine the relative contribution of biological and physicochemical factors to the regulation of plaque mineral levels. However, the similarity of mineral ratios in populations representing extremes
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
VOl. 57- NO. 3
CARIES & PLAQUE MINERALS: INTERCOMPARISONS
in the oral environment of man suggests the operation of a fundamental mechanism effective under the diverse conditions tested. The fact that the first few variables entering the MLSRA-s reflect almost the total effect of all elements on DMFT (Table 4), is consistent with the close correlations found between the concentration levels of a large number of elements (Table 2). The actual proportion of variation in DMFT which can be explained in terms of the joint effect of plaque minerals (Table 4) is considerable when it is taken into account that the results are based on values obtained at one time point. Total mineral concentrations can not fully reflect the activity of biologically important ionized or ionizable components and that only a few of a very large number of factors which influence caries experience are being considered. Under these circumstances it may be assumed that, to some extent, plaque minerals reflect the effect of other etiologically related or even unrelated variables which influence caries experience. The higher R value within towns than over the whole sample (Table 4) is thought to be the consequence of relatively greater homogeneity within groups of subjects resident in any one town than across the sample. The high success rate of classification of subjects with different levels of caries experience, on the basis of the information contained in the mineral content of their plaques, supports the potential etiological significance of the major and trace element content of plaque. In accordance with the MLSRA results, the best separation of subjects was achieved within towns. With respect to potential effects on caries experience, the findings were inconclusive for two elements: the positive association between DMFT and potassium demonstrated in New Guinea6 was not confirmed, while a corresponding association for lead appeared only in Sydney. The prominence of specific elements in their inverse associations with caries experience differed only slightly, rather in extent than in kind, in Australia and New Guinea.6 Phosphorus and magnesium, prominent in Australia (Table 3), played lesser roles in New Guinea, but calcium, strontium, and fluoride were important in both populations. However, the overall conclusion that high concentrations of these elements in plaque, with the possible addition of lithium, are associated with low caries ex-
431
perience, appears to be beyond doubt. These findings corroborate those of Ashley8 with respect to calcium and phosphorus, emphasize the importance of plaque fluoride9 and form a firm basis for exploring in detail the roles of the other elements implicated. Conclusions The results show that the total concentrations of calcium, phosphorus, magnesium, strontium, fluoride, and lithium in plaque are inversely associated with cumulative individual caries experience (DMFT) in the sample examined. Recently developed analytical capabilities and increasing understanding of the use of statistical tools to assist with interpretation of results make in-depth studies of plaque minerals in human populations feasible. It is suggested that the ground has been prepared for: (a) Examination in detail of the individual and combined roles of plaque minerals in their biologically active ionized or ionizable form, in relation to variations in pH levels in human dental plaque. (b) Utilizing the information obtained for devising means of increasing the concentrations of potentially protective elements in plaque. (c) Testing the value of the findings for caries prevention in man.
The authors thank Associate Professor P. D. Barnard, Dr. R. Woods, and the Director and Staff of the Division of Dental Services, N.S.W. Department of Public Health, for their cooperation.
References 1. AGUS, H.M.; SCHAMSCHULA, R.G.; BARMES, D.E.; and BUNZEL, M.: Associations Between the Total Fluoride Content of Dental Plaque and Individual Caries Experience in Australian Children, Community Dent Oral Epidemiol 4:210-214, 1976. 2. SCHAMSCHULA, R.G.; AGUS, H.; BUNZEL, M.; ADKINs, B.L.; and BARMES, D.E.: The Concentrations of Selected Major and Trace Minerals in Human Dental Plaque, Arch Oral Biol 22: 321-325, 1977. 3. SCHAMSCHULA, R.G.; AGUS, H.; BLAINEY, B.; CHARLTON, G.; and DAVEY, B.: Laboratory Methods, Document 7, W.H.O. Study of Dental Caries Etiology, Papua New Guinea, World Health Organization, DNH/ ETIOL/75.7, Geneva, 1975. 4. BARNARD, P.D.: Dental Conditions in High School Students. Sydney, 1972, Aust Dent J 21:513-516, 1976. 5. BARNARD, P.D., and CLEMENTS, F.W.: Oral Health Care in Australia, Int Dent J 26:
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
432
SCHAMSCHULA ET AL 320-326, 1976.
6. SCHAMSCHULA, R. G.; ADKINS, B. L.; BARMES, D.E.; CHARLTON, G.; and DAVEY, B.G.: Caries Experience and the Mineral Content of Plaque in a Primitive Population in New Guinea, J Dent Res 56: C62-C70 (Special Issue C), 1977. 7. SCHAMSCHULA, R. G.; ADKINS, B. L.; BARMES, D.E.; CHARLTON, G.; and DAVEY, B.: WHO Study of Caries Etiology in Papua
J Dent Res March 1978 New Guinea, WHO Offset Publication No. 40, Geneva: The World Health Organization Monograph, Geneva, 1978. 8. ASHLEY, F.P.: Calcium and Phosphorus Concentrations of Dental Plaque Related to Dental Caries in 11- to 14-Year-Old Male Subjects, Caries Res 9:351-362, 1975. 9. JENKINs, G.N.: Recent Advances in Work on Fluorides and the Teeth, Brit Med Bull 31:142-145, 1975.
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
*Institute of Dental Research, 2 Chalmers Street, Sydney, N.S.W. Australia 2010, tWorld Health Organization, Geneva, Switzerland, $University of Queensland, Brisbane, Australia, and §University of Sydney, Sydney, Australia Inverse associations were demonstrated between DMFT and total calcium, phosphorus, magnesium, strontium, potassium, and fluoride concentrations in individual plaques. Lithium, strontium, fluoride, and zinc contents were inversely related to plaque mass. Consistent interdependence patterns between elements indicate the operation of a mineral level regulating mechanism, effective under diverse environmental conditions.
Materials and Methods The sample consisted of 72 schoolchildren (42 males and 30 females, between 9.7 and 13.0 years of age; mean = 11.4, SD = 0.8 years), lifelong residents of one of three New South Wales towns: Katoomba (n = 26), Sydney (n= 21) and Yass (n= 25). The towns were selected according to the fluoride level in the public water supplies; Katoomba was deficient (< 0.1 ppm) while Sydney and Yass had been fluoridated at 1 ppm 4 and 16 years prior J Dent Res 57(3):427-432, March 1978. to sampling. The paucity of information concerning the poThe procedures employed for clinical extential influence of plaque minerals on caries amination,1 plaque collection,' and chemical experience led to a study of selected major analyses2'3 have been previously reported. and trace elements in plaque samples collected The linearity of the relationships studied from Australian children. has been examined in detail. Relationships beTwo previous reports dealt with specific came more nearly linear and the correlation aspects of the results. In one of the papers, in- coefficients increased in size when the variables verse associations were reported between the were transformed according to the normal probtotal fluoride content of plaque and individual ability integral; plaque quantity and mineral caries experience and inverse trends were shown values were submitted to statistical analysis in between the quantity of plaque and its fluoride this form. Associations between variables were concentration.' A subsequent publication de- examined using correlation matrices and bitailed the mean values and variation in the total variate and multiple linear stepwise regression content of another nine elements in plaque.2 analyses (MLSRA). Discriminant analyses This report deals with associations between (DA) were employed for classifying subjects caries experience and the total concentrations with contrasting levels of caries experience on of calcium, phosphorus, potassium, magnesium, the basis of the mineral content of plaques. Difstrontium, lithium, zinc, copper, and lead in ferences between mean values were examined individual plaque samples, the interrelation- using student t tests. Statistical analyses were ships between the concentrations of elements carried out separately for subjects in each town and with closely related parameters. Plaque flu- and for the whole sample, using standard biooride is included in the analyses where joint medical programs. effects or interactions of variables are examined. Results Received for publication April 5, 1977. Accepted for publication September 15, 1977. Individual caries prevalence ranged from 0 This study was supported by the World Health Orto 14 DMFT and was directly associated with ganization. Vol. 57 No. 3 427 Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
428
J Dent Res March 1978
SCHAMSCHULA ET AL TABLE 1
PRODUCT-MOMENT CORRELATION COEFFICIENTS BETWEEN PLAQUE QUANTITY (DRY WT) AND THE CONCENTRATIONS OF MINERALS IN PLAQUE
Li Sr F Zn
Overall n=72
Yass n=25
Katoomba n=26
Sydney n=21
-0.37t
-0.36* -0.14 -0.16 -0.36*
-0.19 -0.27 -0.17 -0.42*
-0.55t -0.28 -0.32 0.16
-0.20* -0.16 -0.15 * P < 0.05.
t P < 0.01.
age over the whole sample (r = 0.58, P < 0.001). The mean DMFT scores (SD) were: overall 4.4 (3.1); Sydney 6.6 (2.7); Katoomba 4.7 (2.9) and Yass 2.2 (2.0). Mean caries scores for males and females did not differ significantly (t- 0.91, df = 70). Examination of the data by sex showed that over the whole sample the mean zinc content of plaque was significantly higher for males than for females.2 Corresponding differences were not significant within towns and no differences were detected between sexes for the other elements. Therefore, the analyses were conducted with sexes combined. Plaque quantity (dry wt of plaque)1Ivas positively associated with individual caries experience (DMFT) in Sydney (r =0.58, P < 0.005). The plaque concentrations of four elements appear to be dependent upon plaque quantity (Table 1). Most correlation coefficients are low, but six reach statistical significance; with a single exception (zinc in Sydney, not significant) the associations are consistently inverse. Because of the apparent dependence of element concentrations on plaque quantity, the latter parameter was included in MLSRA-s and DA-s, to permit assessment of its contribution to the combined effect of the elements. Clusters of bivariate correlation coefficients for the concentrations of selected pairs of elements in plaque are given in Table 2, which shows interdependence between elements at various levels. Considering biological variation and sources of cumulative error, the strength of correlations between calcium and phosphorus and calcium and strontium indicates that the concentration ratios of these elements are nearly conistant. Other pairs, such as calcium and fluoride or phosphorus and magnesium are strongly interdependent. Potassium is firmly as-
sociated with magnesium and shows strong common ground with phosphorus, but practically no dependence on calcium. In contrast, lead is practically independent of both calcium and phosphorus (as are copper and zinc). However, with one exception the interrelationshops between zinc, copper and lead are significant. Variations in the calcium/phosphorus ratio are almost entirely dependent on calcium. Lithium (not in Table 2) is independent of all other elements. The consistency in the magnitude of the correlation coefficients between towns and over the whole sample is high. Values which tend to weaken the consistency occur invariably in Katoomba, the fluoride-deficient town; here the correlation coefficients for calcium versus phosphorus, strontium, and fluoride; for phosphorus versus potassium; for phosphorus versus calcium/phosphorus ratio; and for potassium versus magnesium are lower than in other towns or over the whole sample. All but four of the correlation coefficients are positive, indicating a common trend in concentration levels for interdependent elements. All four negative coefficients are associated with lead; they are trivial TABLE 2 PRODUCT-MOMENT CORRELATION COEFFICIENTS BETWEEN SELECTED MINERALS IN PLAQUE: CALCIUM, PHOSPHORUS, POTASSIUM, AND ZINC Overall n = 72
Yass 25
n =
.751t
.78:t
.811: .40$
.911: .39*
.511t K .16 Pb -.04 Ca/P .961
.13 .25 .96:
Ca versus P
Sr Mg F
.611t
Katoomba Sydney n=26 n=21
.61 t .641:
.871: .921: .39* .44* .661 .43* .19 .15 -.22 -.14 .981: .951:
P versus Mg Sr F K Pb Ca/P
.641: .711: .40: .51 .15 .60:
.751: .751: .45* .60: .26 .611:
.53t
.57t
Zn versus Cu Pb
.33t .441
.34* .35*
.44* .44*
.24 .39*
K versus Mg
.671
.791:
.39*
.701
.73: .671: .42* .62t .50* .32 .17 -.14 .771 .44*
* P < 0.05. t P < 0.01. t P < 0.001.
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
VZol. 57 No. 3
CARIES & PLAQUE MINERALS: INTERCOMPARISONS
TABLE 3 PRODUCT-MOMENT CORRELATION COEFFICIENTS BETWEEN TOTAL CONCENTRATIONS OF ELEMENTS IN PLAQUE (DRY WT) AND INDIVIDUAL CARIES EXPERIENCE (DMFT), OVERALL AND PER AREA Overall n =72
Yass =25
Katoomba
n
n=
-.46t
-.43* -.49t -.38*
.-.48*
-.02 -.15 -.14
-.45* .-.42* -.36
p
-.41::
Mg K F Ca Sr
-.39t
-.27
-.30t
-.09
*
-.28t
-.28
-.25* -.23*
-.41* -.32
26
Sydney n=
21
-.32 -.20
P < 0.05.
t P < 0.01. t P < 0.001.
compared to others in Table 2, and nonsignificant.
Table 3 shows the bivariate correlation coefficients between individual DMFT scores and the content of those elements in plaque for which significant associations or suggestive trends were found. The associations are inverse for every element in all areas and reach high levels of significance in numerous instances. Of the four elements not included in Table 3, a consistent inverse trend between DMFT and lithium failed to reach significance in all sample divisions. For the remaining elements associations were not consistent through sample divisions; however in Sydney copper (r = 0.18, NS), lead (r = 0.34, NS), and zinc (r = 0.50, P < 0.02) showed a common trend of positive association with caries.
MLSRA-s were conducted with DMFT as dependent variable and identical sets of independent variables comprising the elements determined in plaque, selected concentration ratios and plaque quantity. The analyses were allowed to proceed without restriction until the reduction in the error sum of squares ceased to be significant (Table 4). This point was reached after three to nine variables had entered the analyses. For practical purposes these results reflect the combined effect of the sets of independent variables, as subsequent entries to the end point have no material effect the outcome of the analyses. Elements entered MLSRA-s with the following frequencies: phosphorus entered in all four sample divisions; fluoride, magnesium, and copper in two divisions and calcium, strontium, lithium, potassium, and zinc in one division each. Stepwise DA-s (Table 5) determined the extent to which the information contained in individual plaque mineral values could separate subjects with different levels of caries experience (DMFT %). The limiting caries levels of the groups were defined to include the maximum number of subjects in the analyses and to represent the low and high caries groups by approximately equal numbers, without overlap in caries experience. As the scope of choosing contrasting groups from the whole sample was greater than in any one town, in the overall analysis discrimination was tested at two levels. In DA-s, the classification of subjects is based on a linear combination of the variables, the discriminant function (DF), which produces the maximum separation of groups. The on
BLE 4 MULTIPLE CORRELATION COEFFICIENTS (R) FROM MLSRA-s BETWEEN DMFT AND IDENTICAL SETS OF VARIABLES RELATED TO THE MINERAL CONTENT OF PLAQUE Overall n=72 R %
At "critical" F level
(step number) At end point+ (step number)
.50t 25 (4) .55* 30 (14)
429
Yass n=25 R %
.66
44 (6)
.82 67 (19)
Katoomba n=26 R % .76* 58 (9) .89 79 (19)
Sydney n=21 R % .77t 59 (3) .84 71 (19)
% = R2 X 100 = The proportion of variation in DMFT which can be explained in terms of the combined effect of independent variables. + = Where no further reduction in the error sum of squares was possible. * P < 0.05.
t P < 0.01. $ P < 0.001.
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
430
SCHAMSCHULA ET AL
J Dent Res March 1978
TABLE 5 SUMMARY OF DISCRIMINANT ANALYSES: CLASSIFICATION OF SUBJECTS INTO GROUPS (A AND B) ACCORDING TO CARIES EXPERIENCE (DMFT %) BASED ON THE MINERAL CONTENT OF PLAQUE DMFT % A B
Yass (P,CU,Pb,K,P/F)* Katoomba (Ca/Li, P, Sr, F, Li)* Sydney (F, Zn, Ca/Sr, plaquewt)* Overall
(P, Pb,F)*
Overall (P, Pb, F, Sr)*
A
B
Correctly Classified n %
10
8
17
n
Step
F
94.4
5
5.33
0.01
94.7
5
2.40
NS
4
13.15
0.001
P
9
< 18
> 23
9 10
18
< 23
> 29
9
8
17
0
> 35
9
10
17
89.5
3
4.16
0.025
8
> 25
14 20
27
79.4
4
5.27
0.001
100
* Variables included in discriminant function at step indicated in order of entry.
discriminatory power of plaque elements is substantial; the proportion of correctly classified subjects ranges from 79 to 100% with no more than five variables. The consistency of variables which make the most substantial contribution to the classification of subjects is strong; phosphorus appears in all five, fluoride in four, and lead and strontium in three analyses. The direction of the effect of an element can be determined by contrasting the mean concentration values associated with the low or high caries prevalence groups. With two exceptions, lead and zinc in Sydney, the higher mean concentrations of elements which were shown to be important in their own right or collectively were associated with the low caries group.
refined sucrose.6'7 It was shown67 that the pattern was the consequence of selective assimilation and concentration of some elements (fluoride, magnesium, zinc, lead, and lithium) from seemingly meager sources, and the rejection of massive excess of others (calcium and strontium) when offered in the form of lime used with betel chewing. The close similarity of the two sets of findings is a strong indication that the basic mechanism regulating mineral levels in plaque is very similar, or identical in Western and primitive communities with diverse social, geochemical and socio-economic backgrounds, consuming vastly different diets, exposed to high and low caries challenge rates, and receiving extensive and no dental care, no
respectively. Discussion The caries experience4 and level of dental care5 of the subjects were representative of corresponding Australian populations with similar exposure to water-borne fluoride. The concentration ratios of elements in plaque, reflected by the intercorrelations shown in Table 2, were not influenced appreciably by considerable individual variations in the concentration levels of specific elements.2 The strength, consistency and pattern of associations between elements (Table 2) is almost identical with those demonstrated for plaque minerals in a substantial sample drawn from a primitive population, exposed to differing levels of environmental fluoride, whose diet contained negligible amounts of mono- or disaccharides and
As the concentration ratios of elements are the consequences of the concentrations of the respective elements, the factors controlling concentration levels also control the ratios. It is assumed that the bacterial population plays a substantial role in the selective regulation (homeostasis) of the mineral levels in individual plaques. In addition, physico-chemical factors, such as concentration gradients and diffusion properties of a biomass and the chemical attributes of an element in the form offered are expected to play significant roles. Availability must be of decisive importance, but present knowledge is insufficient to determine the relative contribution of biological and physicochemical factors to the regulation of plaque mineral levels. However, the similarity of mineral ratios in populations representing extremes
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
VOl. 57- NO. 3
CARIES & PLAQUE MINERALS: INTERCOMPARISONS
in the oral environment of man suggests the operation of a fundamental mechanism effective under the diverse conditions tested. The fact that the first few variables entering the MLSRA-s reflect almost the total effect of all elements on DMFT (Table 4), is consistent with the close correlations found between the concentration levels of a large number of elements (Table 2). The actual proportion of variation in DMFT which can be explained in terms of the joint effect of plaque minerals (Table 4) is considerable when it is taken into account that the results are based on values obtained at one time point. Total mineral concentrations can not fully reflect the activity of biologically important ionized or ionizable components and that only a few of a very large number of factors which influence caries experience are being considered. Under these circumstances it may be assumed that, to some extent, plaque minerals reflect the effect of other etiologically related or even unrelated variables which influence caries experience. The higher R value within towns than over the whole sample (Table 4) is thought to be the consequence of relatively greater homogeneity within groups of subjects resident in any one town than across the sample. The high success rate of classification of subjects with different levels of caries experience, on the basis of the information contained in the mineral content of their plaques, supports the potential etiological significance of the major and trace element content of plaque. In accordance with the MLSRA results, the best separation of subjects was achieved within towns. With respect to potential effects on caries experience, the findings were inconclusive for two elements: the positive association between DMFT and potassium demonstrated in New Guinea6 was not confirmed, while a corresponding association for lead appeared only in Sydney. The prominence of specific elements in their inverse associations with caries experience differed only slightly, rather in extent than in kind, in Australia and New Guinea.6 Phosphorus and magnesium, prominent in Australia (Table 3), played lesser roles in New Guinea, but calcium, strontium, and fluoride were important in both populations. However, the overall conclusion that high concentrations of these elements in plaque, with the possible addition of lithium, are associated with low caries ex-
431
perience, appears to be beyond doubt. These findings corroborate those of Ashley8 with respect to calcium and phosphorus, emphasize the importance of plaque fluoride9 and form a firm basis for exploring in detail the roles of the other elements implicated. Conclusions The results show that the total concentrations of calcium, phosphorus, magnesium, strontium, fluoride, and lithium in plaque are inversely associated with cumulative individual caries experience (DMFT) in the sample examined. Recently developed analytical capabilities and increasing understanding of the use of statistical tools to assist with interpretation of results make in-depth studies of plaque minerals in human populations feasible. It is suggested that the ground has been prepared for: (a) Examination in detail of the individual and combined roles of plaque minerals in their biologically active ionized or ionizable form, in relation to variations in pH levels in human dental plaque. (b) Utilizing the information obtained for devising means of increasing the concentrations of potentially protective elements in plaque. (c) Testing the value of the findings for caries prevention in man.
The authors thank Associate Professor P. D. Barnard, Dr. R. Woods, and the Director and Staff of the Division of Dental Services, N.S.W. Department of Public Health, for their cooperation.
References 1. AGUS, H.M.; SCHAMSCHULA, R.G.; BARMES, D.E.; and BUNZEL, M.: Associations Between the Total Fluoride Content of Dental Plaque and Individual Caries Experience in Australian Children, Community Dent Oral Epidemiol 4:210-214, 1976. 2. SCHAMSCHULA, R.G.; AGUS, H.; BUNZEL, M.; ADKINs, B.L.; and BARMES, D.E.: The Concentrations of Selected Major and Trace Minerals in Human Dental Plaque, Arch Oral Biol 22: 321-325, 1977. 3. SCHAMSCHULA, R.G.; AGUS, H.; BLAINEY, B.; CHARLTON, G.; and DAVEY, B.: Laboratory Methods, Document 7, W.H.O. Study of Dental Caries Etiology, Papua New Guinea, World Health Organization, DNH/ ETIOL/75.7, Geneva, 1975. 4. BARNARD, P.D.: Dental Conditions in High School Students. Sydney, 1972, Aust Dent J 21:513-516, 1976. 5. BARNARD, P.D., and CLEMENTS, F.W.: Oral Health Care in Australia, Int Dent J 26:
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
432
SCHAMSCHULA ET AL 320-326, 1976.
6. SCHAMSCHULA, R. G.; ADKINS, B. L.; BARMES, D.E.; CHARLTON, G.; and DAVEY, B.G.: Caries Experience and the Mineral Content of Plaque in a Primitive Population in New Guinea, J Dent Res 56: C62-C70 (Special Issue C), 1977. 7. SCHAMSCHULA, R. G.; ADKINS, B. L.; BARMES, D.E.; CHARLTON, G.; and DAVEY, B.: WHO Study of Caries Etiology in Papua
J Dent Res March 1978 New Guinea, WHO Offset Publication No. 40, Geneva: The World Health Organization Monograph, Geneva, 1978. 8. ASHLEY, F.P.: Calcium and Phosphorus Concentrations of Dental Plaque Related to Dental Caries in 11- to 14-Year-Old Male Subjects, Caries Res 9:351-362, 1975. 9. JENKINs, G.N.: Recent Advances in Work on Fluorides and the Teeth, Brit Med Bull 31:142-145, 1975.
Downloaded from jdr.sagepub.com at Univ of Connecticut / Health Center / Library on May 24, 2015 For personal use only. No other uses without permission.
