Salivary clearance of sugar before and after insertion of fixed orthodontic appliances Carl-Magnus Forsberg, DDS, PhD, ~ Anette Oliveby, DDS, PhD, b and Folke Lagerl6f, DDS, PhD b
Huddinge, Sweden This study was conducted for the purpose of establishing the possible influence of orthodontic therapy with fixed appliances on salivary clearance of sugar. Fifteen consecutive patients between the ages 12 and 17 years took part in the investigation. Unstimulated salivary flow rate, residual volume of saliva in the mouth after swallowing (RESID), and salivary clearance of sugar was determined on two occasions, before treatment commenced and after a minimum of 3 weeks of appliance wear. Analysis of the data showed that both RESID and salivary flow rate exhibited significantly increased levels during orthodontic therapy. The insertion of fixed appliances did not seem to have any effect on the rate of salivary clearance of sugar. It was assumed that this finding could be a consequence of the combined effects of the changes in salivary flow rate and RESID. (AMJ ORTHOO DENTOFACORTHOP 1992;102:527-30.)
For the development of dental carious lesions, an acid-producing oral microflora must be present in the mouth. In the orthodontic patient the numbers of acid-producing microorganisms in the saliva increase considerably after the insertion of a fixed appliance, t-6 Furthermore, the components of the appliance create new retention areas for microorganisms and impede proper access to the tooth surfaces for optimal cleaning. Plaque formation is therefore more extensive in orthodontic patients undergoing treatment than in subjects without appliances, and high numbers of bacteria in the plaque have been reportedJ '7'8 For their activity in the caries process, the bacteria in the plaque are dependent on sugar, which diffuses from the saliva after intake of carbohydrate products. The sugar serves as a substrate for fermentation by the plaque microflora, which forms organic acids and causes demineralization of tooth enamel. Sugar is eliminated from the mouth by dilution with newly secreted saliva, followed by swallowingma process generally referred to as sugar clearance. 9 The clearance rate is related to several factors such as the initial sugar concentration, the salivary flow rate, and the volumes of saliva in the oral cavity before and after swallowing. '~ Whether the insertion of a fixed orthodontic appliFrom the Departments of Orthodontics and Cariol~y, Karolinska Instituter, tluddinge, Sweden. This study ,,,,.as supported by the Swedish Medical Research Council (project no. 7203) and by a grant from the Swedish Dental Society. "Acting professor of Orthodontics. bAssociate professor of Cariology. 8 / 1132343
ance has any effect on the pattern of salivary clearance of sugar has not been previously established. A reasonable hypothesis, however, is that the rate of sugar clearance is indeed affected by arch wires, brackets, ligatures, and elastics that may impede the flow of saliva on tooth surfaces and increase the residual volume of saliva in the oral cavity after swallowing. Both these factors could prolong the salivary clearance of sugar after food intake. From a cariologic point of view, a delayed salivary clearance would be particularly disadvantageous during orthodontic treatment with fixed appliances, considering that these patients also exhibit high intraoral levels of acid-producing microorganisms. It was the aim of the present study to test the hypotheses that (1) fixed orthodontic appliances increase the residual volume of saliva in the mouth after swallowing (RESID), and that (2) the salivary clearance of sugar is delayed. SUBJECTS AND METHODS
Fifteen consecutive patients, 2 boys and 13 girls (Table I), scheduled for orthodontic treatment with fixed appliances took part in the investigation. Before the start of the investigation, the subjects and their parents had given their consent to participate after having received written information about the aim and design of the study. Unstimulated salivary flow rate, RESID, and salivary clearance of sugar was determined on two occasions, before the start of treatment and after between 21 and 105 days (mean value = 41 days) of fixed appliance wear in the upper or lower jaw, Table I. Both samples in each patient were collected at the same time of the day. There was no reason to believe that the effect of the appliance on the variables studied 527
528
Forsberg, Oliveby, and L a g e r l t f
Am. J. Orthod.
Dentofac. Orthop. December 1992
Table I. A g e and sex distributions and o b s e r v a t i o n times Age ()'ears)
Boys Girls TOTAL
2 13 15
Observation time (days)
13.8 14.5 14.4
-1.6 1.5
60 38 41
-22 25
28-92 21-105 21-105
Table Ii. M e a n salivary flow rate (milliliter per minute), R E S I D (milliliters), and area under the salivary sucrose concentration c u r v e , ( A U C , minutes • with fixed orthodontic appliances (N = 15)
m i l l i g r a m s / m i l l i l i t e r s ) b e f o r e and during active treatment
Without appliance
Flow rate RESID AUC
With appliance
x
SO
x
SO
Mean difference
SD
t value
0.46 0.66 156.8
0.23 0.23 17.60
0.57 0.76 163.3
0.30 0.22 18.73
0.1 i 0.10 6.5
0.17 0.16 23.76
2.51" 2.42* 1.06
*p < 0.05.
Determination of salivary clearance of sugar would be different in boys and girls. Therefore the skewed sex distribution was not expected to adversely influence the results of the study.
Determination of flow rate The patient was asked to swallow. Unstimulated saliva was then collected in a weighed beaker for 5 minutes with the subject seated upright and with the head bent forward. This procedure was repeated five times. The volume of saliva in each beaker was measured, and the average flow rate (milliliters per minute) calculated.
Determination of RESID The volume of saliva in the mouth after swallowing was measured by a dilution method." Approximately 0.5 ml of unstimulated whole saliva was first collected in a test tube. The subject was then asked to swallow, and then immediately take about 5 ml of deionized water from a beaker into the mouth, rinse for 5 seconds, and finally expectorate into another container. The volume of water used was .determined by the difference in weight of the beaker before and after rinsing. Five such trials were performed on each subject. The whole saliva and the expectorate were analyzed for potassium by atomic absorptioa spectrophotometry" and for chloride by a coulometric technique, j2 If V is the volume of water introduced into the mouth after swallowing, and C, and C~are the concentrations of potassium or chloride in the saliva and expectoration, respectively, RESID may be calculated according to the formulag: RESID = V • Cf C i - Cf
The subject rinsed with 10 ml of a 10% sucrose solution for 30 seconds. At 0, 2, 5, 10, and 20 minutes after the start of the experiment, a small saliva sample (0.1 ml) was collected in a test tube that had been pretreated by 5 m m o l / L iodoacetic acid according to the method described by Swenander-Lanke." This substance has a strong antibacterial effect and inhibits the activity of the microorganisms that would otherwise reduce the sucrose content of the saliva sample. For determination of the sucrose concentration ~4 in each sample, 20 mm 3of saliva was transferred to a test tube. Protein was precipitated by adding 10 mm 3 of Carrez-I solution (3.60 gm potassium hexacyanoferrate-II to 100 ml water), 10 mm 3 of Carrez-II solution (7.20 gm zinc sulfate to 100 ml water), and 20 mm 3 0.1 m o l / L sodium hydroxide. The contents of the sealed test tube was then whirl mixed for 30 seconds and subsequently allowed to stand at room temperature for 60 minutes, after which it was centrifuged for 2 minutes. From the supematant, 40 mm 3 was used for determination of the sucrose concentration by an enzymatic method (sucrose/glucose UV method, Boehringer).
Statistical analyses Means and standard deviations were calculated for salivary flow rate and RESID before and after insertion of fixed orthodontic appliances. Differences between means were tested with the paired t test. The values of saliva sucrose concentration were plotted in graphs, and the points joined by straight lines, Fig. 1. The area under the curve (AUC) was computed. The mean difference between AUC values recorded before and after insertion of the orthodontic appliances was tested with the paired t test.
Salivary clearance and orthodontic therapy 529
Voh,me 102 Number 6
The null hypothesis was rejected at a probability less than 0.05.
2 ,L~ 10
Sucrose cone. (mg/ml)
RESULTS
The statistical data for the three variables studied are presented in Table II. The salivary flow rate before the start of orthodontic treatment was 0.46 ml/min on average. After a period (21 to 105 days) of fixed appliance wear, the mean value of 0.57 ml/min was recorded. This increase (0.11 ml/min) was statistically significant (p < 0.05). The orthodontic appliance had a similar effect on the residual volume of saliva in the mouth after swallowing. Before start of treatment, a mean value of 0.66 ml was recorded. Insertion of fixed appliances caused this volume to increase by 0.10 ml (p < 0.05), on average, to a mean value of 0.76 ml. The mean area under the salivary sucrose concentration curve (AUC) increased from 156.8 m i n x mg/ml before start of treatment to 163.3 min • mg/ml recorded during active treatment. The difference, 6.5 min • mg/ml, was not statistically significant. The mean sucrose clearance curves obtained with and without orthodontic appliances are illustrated in Fig. 1. DISCUSSION
Previous investigations have shown that the oral microflora in the orthodontic patient changes after insertion of a fixed appliance, and that the levels of both Streptococcus mutans and Lactobacilhts are considerably raised. 1-6 Of these two groups of bacteria, Streptococcus mutans is recognized as the most virulent organism. Two major characteristics contribute to the caries-induced properties of these bacteria: (1) the capability to form insoluble extracellular polysaccharides (dental plaque), and (2) the capability to produce organic acids through fermentation of carbohydrate products. For both these processes, the bacteria need to be supplied with a suitable substrate (such as sucrose) of a certain concentration. Consequently, variations in acid production ~5 and pH changes ~4 in the plaque are. closely related to the oral clearance of sucrose. It is obvious therefore that factors affecting the clearance rate are of considerable cariologic importance. The present investigation was undertaken to test the hypotheses that the salivary clearance of sugar is prolonged after the insertion of a fixed orthodontic appliance, and that the residual volume of saliva after swallowing increases. If the hypotheses were true, it would mean that the duration of both plaque formation and acid production by the plaque microftora after consumption of food containing sugar would be prolonged
--m- Without appliance ] 0.
~
,
i
~
1 .-~- Withappliance
J
-1
-2
t 2
i 5
i 10 Time (minutes)
i 20
Fig. 1. Graph illustrates mean sucrose concentration in saliva of 15 orthodontic patients at 0, 2, 5, 10, and 20 minutes after sucrose challenge. Determinations were made both with and without fixed orthodontic appliances.
during active orthodontic treatment. It was surprising to find, however, that the salivary clearance did not seem to be affected at all by the fixed appliance. From an orthodontic point of view this result is very satisfactory, as it shows that one of the most frequently used orthodontic appliances does not promote the caries process by increasing the access time of the oral microflora to a substrate for plaque formation and acid production. It seems logical that the residual volume of saliva after swallowing increased after insertion of a fixed orthodontic appliance. The appliance consists of many retentive components that provide numerous recesses and minor pits where fluid may be trapped. Theoretically, the recorded increase in RESID should result in delayed sugar clearance) ~ The fact that this was not the case in this study may be explained by the finding that the insertion of the orthodontic appliances also caused an average increase in salivary flow rate by 24%. It is a well-known fact that a foreign body put in the mouth will initially increase the flow of saliva, 17"~8and a temporary change of this kind might affect the result of a study such as the present one. During the planning of this investigation it was therefore decided that a minimum time of 3 weeks should elapse from the start of treatment until the second occasion when samples of saliva were collected. After such a comparatively long period, it was presumed that the patient should have adapted to the appliance and that the salivary flow had resumed a normal rate. The minimum observation time of 3 weeks applied in only three patients. In the
530
Forsberg, Oliveby, and Lagerliif
other subjects the observation times varied between 4 and 15 weeks. The result that the patients exhibited significantly higher values of flow rate at the second registration therefore was not expected. It cannot be ruled out that lower values of saliva flow rate would have been recorded during appliance wear, if an even longer period of adaptation had been allowed before the saliva samples were collected on the second occasion. The present data do not, however, support such a contention. If a simple association exists between the variables adaptation time and flow rate, patients with short adaptation times in this material should have exhibited higher flow rate than those with comparatively longer adaptation times. A statistical analysis indicated, however, that these variables were not linearly related
(r = 0.06). In addition to the effect on sugar clearance, the increased level of secretion may aIso favorably influence the capacity of the saliva to mechanically rinse away food debris, bacteria, and their soluble products. With greater volumes o f saliva in the mouth, the buffering action and the possible antibacterial activity of the saliva may also be of importance in reducing the risk for development of dental caries during orthodontic treatment. In conclusion, insertion of a fixed orthodontic appliance results in an average increase of both RESID and salivary flow rate by 15% and 24%, respectively. From a clinical and physiolog~ic point of view, both these changes may be considered great. Furthermore, the findings of this study clearly indicate that orthodontic therapy with fixed appliances does not prolong the salivary clearance of sugar during the first months of treatment. Further studies with longer intervals between the collections and analyses of saliva samples should be undertaken to clarify whether the present results are also of relevance to a whole treatment period. Although the present results indicate that the sugar clearance rate is comparable in persons with and without fixed appliances, the orthodontic patient still faces the problem of high intraoral levels of microorganisms and increased plaque accumulation on tooth surfaces. Because of these factors, caries and demineralization will continue to be matters of concern during orthodontic treatment. We gratefully acknowledge the technical and analytical assistance of Mrs. Agneta Guslafsson.
Am. J.
Orthod. Oentofac. Orthop. December 1992
REFERENCES 1. Owen OW. A study of bacterial counts (lactobacilli) in saliva related to orthodontic appliances. A.',iJ Ot~'mOD1949;35:672-8. 2. DikemanTL. A studyofacidogenicandaciduricmicroorganisms in orthodontic and non-orthodonticpatients. (Abstract) A.'.I J ORYHOD1962;48:627-8. 3. Bloom RH, Brown LR. A study of the effects of orthodontic appliances on the oral microbialflora. Oral Surg Oral Med Oral Pathol 1964;17:658-67. 4. ScheieAA, Ameberg P, Krogstad O. Effect of orthodontictreatmenton prevalenceof Streptococcus mutans in plaqueand saliva. Scand J Dent Res 1984;92:211-7. 5. Lundstr6mF, Krasse B. Streptococcus mtttans and laetobacilli frequency in orthodonticpatients; the effect of chlorhexidine treatments. Eur J Orthod 1987;9:109-16. 6. ForsbergC-M, Brattstr6m V, Malmberg E, Nord CE. Ligature wires and elastomeric rings; two methods of ligation and their association with microbialcolonizationof streptococcus mutans and lactobacilli. Eur J Orthod 1991;13:416-20. 7. BalenseifenJW, MadoniaJV. Study of dental plaque in orthodontic patients. J Dent Res 1970;49:320-4. 8. Corbett JA, Brown LR, Keene HJ, Horton IM. Comparisonof Streptococcus nzttlans concentrationsin non-bandedand banded orthodontic patients. J Dent Res 1981;60:1936-.42. 9. Lagerl6fF, Dawes C. The volumeof saliva in the mouth before and after swallowing. J Dent Res 1984;63:618-21. 10. Dawes C. A mathematicalmodel of salivaryclearance of sugar from the oral cavity. Caries Res 1983;17:321-34. 11. Dawes C. The effects of flow rate and duration of stimulation on the concentrationsof protein and the main electrolytes in human parotid saliva. Archs Oral Biol 1969;14:277-94. 12. Cotlove E, Trantham HV, Bowman RL. An instrument and method for automatic, rapid, accurate, and sensitivetitration of chloride in biologicsamples. J Lab Clin Med 1958;51:461-8. 13. Swenander-LankeL. Influenceon salivarysugarof certainproperties of foodstuffs and individualoral conditions. Acta Odont Scand 1957;15:23(Suppl). 14. LindforsB, Lagerl6fF. Effect of sucrose concentrationin saliva after a sucrose rinseon the hydroniumion concentrationin dental plaque. Caries Res 1988;12:7-10. 15. OlivebyA, WeetmanDA, Geddes DAM, Lagerl6fF. The effect of salivaryclearanceof sucroseand fluorideon the humanplaque acidogenecity. Archs Oral Biol 1990;35:907-11. 16. Lagerlrf F, Oliveby A, Ekstrand J. Physiologicalfactors influencing salivary clearance of sugar and fluoride. J Dent Res 1987;66:430-5. 17. O'Rourke JT, Miner LMS. Oral physiology. St. Louis: CV Mosby, 1951:270-1. 18. Smyth DH. Secretion of digestion juices. In: Davson H, Eggleton MG, eds. Principles of human physiology. London: J & A Churchill Ltd., 1968:610-28. Reprblt requests to:
Professor Carl-MagnusForsberg Department of Orthodontics Karolinska Insitutet Box 4064 S-141 04 Huddinge, Sweden
Huddinge, Sweden This study was conducted for the purpose of establishing the possible influence of orthodontic therapy with fixed appliances on salivary clearance of sugar. Fifteen consecutive patients between the ages 12 and 17 years took part in the investigation. Unstimulated salivary flow rate, residual volume of saliva in the mouth after swallowing (RESID), and salivary clearance of sugar was determined on two occasions, before treatment commenced and after a minimum of 3 weeks of appliance wear. Analysis of the data showed that both RESID and salivary flow rate exhibited significantly increased levels during orthodontic therapy. The insertion of fixed appliances did not seem to have any effect on the rate of salivary clearance of sugar. It was assumed that this finding could be a consequence of the combined effects of the changes in salivary flow rate and RESID. (AMJ ORTHOO DENTOFACORTHOP 1992;102:527-30.)
For the development of dental carious lesions, an acid-producing oral microflora must be present in the mouth. In the orthodontic patient the numbers of acid-producing microorganisms in the saliva increase considerably after the insertion of a fixed appliance, t-6 Furthermore, the components of the appliance create new retention areas for microorganisms and impede proper access to the tooth surfaces for optimal cleaning. Plaque formation is therefore more extensive in orthodontic patients undergoing treatment than in subjects without appliances, and high numbers of bacteria in the plaque have been reportedJ '7'8 For their activity in the caries process, the bacteria in the plaque are dependent on sugar, which diffuses from the saliva after intake of carbohydrate products. The sugar serves as a substrate for fermentation by the plaque microflora, which forms organic acids and causes demineralization of tooth enamel. Sugar is eliminated from the mouth by dilution with newly secreted saliva, followed by swallowingma process generally referred to as sugar clearance. 9 The clearance rate is related to several factors such as the initial sugar concentration, the salivary flow rate, and the volumes of saliva in the oral cavity before and after swallowing. '~ Whether the insertion of a fixed orthodontic appliFrom the Departments of Orthodontics and Cariol~y, Karolinska Instituter, tluddinge, Sweden. This study ,,,,.as supported by the Swedish Medical Research Council (project no. 7203) and by a grant from the Swedish Dental Society. "Acting professor of Orthodontics. bAssociate professor of Cariology. 8 / 1132343
ance has any effect on the pattern of salivary clearance of sugar has not been previously established. A reasonable hypothesis, however, is that the rate of sugar clearance is indeed affected by arch wires, brackets, ligatures, and elastics that may impede the flow of saliva on tooth surfaces and increase the residual volume of saliva in the oral cavity after swallowing. Both these factors could prolong the salivary clearance of sugar after food intake. From a cariologic point of view, a delayed salivary clearance would be particularly disadvantageous during orthodontic treatment with fixed appliances, considering that these patients also exhibit high intraoral levels of acid-producing microorganisms. It was the aim of the present study to test the hypotheses that (1) fixed orthodontic appliances increase the residual volume of saliva in the mouth after swallowing (RESID), and that (2) the salivary clearance of sugar is delayed. SUBJECTS AND METHODS
Fifteen consecutive patients, 2 boys and 13 girls (Table I), scheduled for orthodontic treatment with fixed appliances took part in the investigation. Before the start of the investigation, the subjects and their parents had given their consent to participate after having received written information about the aim and design of the study. Unstimulated salivary flow rate, RESID, and salivary clearance of sugar was determined on two occasions, before the start of treatment and after between 21 and 105 days (mean value = 41 days) of fixed appliance wear in the upper or lower jaw, Table I. Both samples in each patient were collected at the same time of the day. There was no reason to believe that the effect of the appliance on the variables studied 527
528
Forsberg, Oliveby, and L a g e r l t f
Am. J. Orthod.
Dentofac. Orthop. December 1992
Table I. A g e and sex distributions and o b s e r v a t i o n times Age ()'ears)
Boys Girls TOTAL
2 13 15
Observation time (days)
13.8 14.5 14.4
-1.6 1.5
60 38 41
-22 25
28-92 21-105 21-105
Table Ii. M e a n salivary flow rate (milliliter per minute), R E S I D (milliliters), and area under the salivary sucrose concentration c u r v e , ( A U C , minutes • with fixed orthodontic appliances (N = 15)
m i l l i g r a m s / m i l l i l i t e r s ) b e f o r e and during active treatment
Without appliance
Flow rate RESID AUC
With appliance
x
SO
x
SO
Mean difference
SD
t value
0.46 0.66 156.8
0.23 0.23 17.60
0.57 0.76 163.3
0.30 0.22 18.73
0.1 i 0.10 6.5
0.17 0.16 23.76
2.51" 2.42* 1.06
*p < 0.05.
Determination of salivary clearance of sugar would be different in boys and girls. Therefore the skewed sex distribution was not expected to adversely influence the results of the study.
Determination of flow rate The patient was asked to swallow. Unstimulated saliva was then collected in a weighed beaker for 5 minutes with the subject seated upright and with the head bent forward. This procedure was repeated five times. The volume of saliva in each beaker was measured, and the average flow rate (milliliters per minute) calculated.
Determination of RESID The volume of saliva in the mouth after swallowing was measured by a dilution method." Approximately 0.5 ml of unstimulated whole saliva was first collected in a test tube. The subject was then asked to swallow, and then immediately take about 5 ml of deionized water from a beaker into the mouth, rinse for 5 seconds, and finally expectorate into another container. The volume of water used was .determined by the difference in weight of the beaker before and after rinsing. Five such trials were performed on each subject. The whole saliva and the expectorate were analyzed for potassium by atomic absorptioa spectrophotometry" and for chloride by a coulometric technique, j2 If V is the volume of water introduced into the mouth after swallowing, and C, and C~are the concentrations of potassium or chloride in the saliva and expectoration, respectively, RESID may be calculated according to the formulag: RESID = V • Cf C i - Cf
The subject rinsed with 10 ml of a 10% sucrose solution for 30 seconds. At 0, 2, 5, 10, and 20 minutes after the start of the experiment, a small saliva sample (0.1 ml) was collected in a test tube that had been pretreated by 5 m m o l / L iodoacetic acid according to the method described by Swenander-Lanke." This substance has a strong antibacterial effect and inhibits the activity of the microorganisms that would otherwise reduce the sucrose content of the saliva sample. For determination of the sucrose concentration ~4 in each sample, 20 mm 3of saliva was transferred to a test tube. Protein was precipitated by adding 10 mm 3 of Carrez-I solution (3.60 gm potassium hexacyanoferrate-II to 100 ml water), 10 mm 3 of Carrez-II solution (7.20 gm zinc sulfate to 100 ml water), and 20 mm 3 0.1 m o l / L sodium hydroxide. The contents of the sealed test tube was then whirl mixed for 30 seconds and subsequently allowed to stand at room temperature for 60 minutes, after which it was centrifuged for 2 minutes. From the supematant, 40 mm 3 was used for determination of the sucrose concentration by an enzymatic method (sucrose/glucose UV method, Boehringer).
Statistical analyses Means and standard deviations were calculated for salivary flow rate and RESID before and after insertion of fixed orthodontic appliances. Differences between means were tested with the paired t test. The values of saliva sucrose concentration were plotted in graphs, and the points joined by straight lines, Fig. 1. The area under the curve (AUC) was computed. The mean difference between AUC values recorded before and after insertion of the orthodontic appliances was tested with the paired t test.
Salivary clearance and orthodontic therapy 529
Voh,me 102 Number 6
The null hypothesis was rejected at a probability less than 0.05.
2 ,L~ 10
Sucrose cone. (mg/ml)
RESULTS
The statistical data for the three variables studied are presented in Table II. The salivary flow rate before the start of orthodontic treatment was 0.46 ml/min on average. After a period (21 to 105 days) of fixed appliance wear, the mean value of 0.57 ml/min was recorded. This increase (0.11 ml/min) was statistically significant (p < 0.05). The orthodontic appliance had a similar effect on the residual volume of saliva in the mouth after swallowing. Before start of treatment, a mean value of 0.66 ml was recorded. Insertion of fixed appliances caused this volume to increase by 0.10 ml (p < 0.05), on average, to a mean value of 0.76 ml. The mean area under the salivary sucrose concentration curve (AUC) increased from 156.8 m i n x mg/ml before start of treatment to 163.3 min • mg/ml recorded during active treatment. The difference, 6.5 min • mg/ml, was not statistically significant. The mean sucrose clearance curves obtained with and without orthodontic appliances are illustrated in Fig. 1. DISCUSSION
Previous investigations have shown that the oral microflora in the orthodontic patient changes after insertion of a fixed appliance, and that the levels of both Streptococcus mutans and Lactobacilhts are considerably raised. 1-6 Of these two groups of bacteria, Streptococcus mutans is recognized as the most virulent organism. Two major characteristics contribute to the caries-induced properties of these bacteria: (1) the capability to form insoluble extracellular polysaccharides (dental plaque), and (2) the capability to produce organic acids through fermentation of carbohydrate products. For both these processes, the bacteria need to be supplied with a suitable substrate (such as sucrose) of a certain concentration. Consequently, variations in acid production ~5 and pH changes ~4 in the plaque are. closely related to the oral clearance of sucrose. It is obvious therefore that factors affecting the clearance rate are of considerable cariologic importance. The present investigation was undertaken to test the hypotheses that the salivary clearance of sugar is prolonged after the insertion of a fixed orthodontic appliance, and that the residual volume of saliva after swallowing increases. If the hypotheses were true, it would mean that the duration of both plaque formation and acid production by the plaque microftora after consumption of food containing sugar would be prolonged
--m- Without appliance ] 0.
~
,
i
~
1 .-~- Withappliance
J
-1
-2
t 2
i 5
i 10 Time (minutes)
i 20
Fig. 1. Graph illustrates mean sucrose concentration in saliva of 15 orthodontic patients at 0, 2, 5, 10, and 20 minutes after sucrose challenge. Determinations were made both with and without fixed orthodontic appliances.
during active orthodontic treatment. It was surprising to find, however, that the salivary clearance did not seem to be affected at all by the fixed appliance. From an orthodontic point of view this result is very satisfactory, as it shows that one of the most frequently used orthodontic appliances does not promote the caries process by increasing the access time of the oral microflora to a substrate for plaque formation and acid production. It seems logical that the residual volume of saliva after swallowing increased after insertion of a fixed orthodontic appliance. The appliance consists of many retentive components that provide numerous recesses and minor pits where fluid may be trapped. Theoretically, the recorded increase in RESID should result in delayed sugar clearance) ~ The fact that this was not the case in this study may be explained by the finding that the insertion of the orthodontic appliances also caused an average increase in salivary flow rate by 24%. It is a well-known fact that a foreign body put in the mouth will initially increase the flow of saliva, 17"~8and a temporary change of this kind might affect the result of a study such as the present one. During the planning of this investigation it was therefore decided that a minimum time of 3 weeks should elapse from the start of treatment until the second occasion when samples of saliva were collected. After such a comparatively long period, it was presumed that the patient should have adapted to the appliance and that the salivary flow had resumed a normal rate. The minimum observation time of 3 weeks applied in only three patients. In the
530
Forsberg, Oliveby, and Lagerliif
other subjects the observation times varied between 4 and 15 weeks. The result that the patients exhibited significantly higher values of flow rate at the second registration therefore was not expected. It cannot be ruled out that lower values of saliva flow rate would have been recorded during appliance wear, if an even longer period of adaptation had been allowed before the saliva samples were collected on the second occasion. The present data do not, however, support such a contention. If a simple association exists between the variables adaptation time and flow rate, patients with short adaptation times in this material should have exhibited higher flow rate than those with comparatively longer adaptation times. A statistical analysis indicated, however, that these variables were not linearly related
(r = 0.06). In addition to the effect on sugar clearance, the increased level of secretion may aIso favorably influence the capacity of the saliva to mechanically rinse away food debris, bacteria, and their soluble products. With greater volumes o f saliva in the mouth, the buffering action and the possible antibacterial activity of the saliva may also be of importance in reducing the risk for development of dental caries during orthodontic treatment. In conclusion, insertion of a fixed orthodontic appliance results in an average increase of both RESID and salivary flow rate by 15% and 24%, respectively. From a clinical and physiolog~ic point of view, both these changes may be considered great. Furthermore, the findings of this study clearly indicate that orthodontic therapy with fixed appliances does not prolong the salivary clearance of sugar during the first months of treatment. Further studies with longer intervals between the collections and analyses of saliva samples should be undertaken to clarify whether the present results are also of relevance to a whole treatment period. Although the present results indicate that the sugar clearance rate is comparable in persons with and without fixed appliances, the orthodontic patient still faces the problem of high intraoral levels of microorganisms and increased plaque accumulation on tooth surfaces. Because of these factors, caries and demineralization will continue to be matters of concern during orthodontic treatment. We gratefully acknowledge the technical and analytical assistance of Mrs. Agneta Guslafsson.
Am. J.
Orthod. Oentofac. Orthop. December 1992
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Professor Carl-MagnusForsberg Department of Orthodontics Karolinska Insitutet Box 4064 S-141 04 Huddinge, Sweden
