An In Vivo Comparison of the Effect of Sugar-Free Chewing Gum on Salivary Flow Rate and pH in Children at High Risk and Low Risk for Dental Caries

Introduction

Dental caries is a bacterial disease with a multifactorial etiology.¹ Dental caries form through a complex interaction over time between fermentable carbohydrates, oral microflora, and other host factors including teeth and saliva. The influence of salivary flow on the caries process is fundamental. Saliva is the principal defensive factor in the mouth and reduction in its flow rate affects our dental health. There is a clear correlation between low salivary flow and low salivary buffer capacity with an incidence of caries. According to WHO classification, the low caries risk group has a score of 1.2 to 2.6 DMF(t), and the high caries risk group has a score of 4.6 to 6.5 DMF(t).² Maintenance of an alkaline oral environment definitely results in lower caries incidence.

The low caries incidence can be achieved by effective application of suitable preventive measures.³ Chewing gum stimulates the salivary glands to increase salivary flow resulting in clearance of food debris and microorganisms from the oral cavity.⁴

The undeniable influence of sugar as the principal dietary substrate which increases the incidence of caries has led to a growing interest in sugar substitutes.⁵ The sugar substitutes used in chewing gum are polyols which are low caloric substances. Xylitol is a sugar substitute with sweetness equal to that of table sugar. Xylitol is a sugar alcohol of pentitol type, Penta hydroxy pentane which is a five-carbon polyol. Food and Drug Administration approved xylitol as a safe sugar substitute in chewing gums and safe for use in children.^6,7 Xylitol competes with sucrose for its cell-wall transporter and its intracellular metabolic processes.^8,9 Past reviews of the human clinical caries trials have demonstrated both the efficacy and safety of xylitol.¹⁰ Recently, controlled clinical research trials have been conducted to know the effects of sugar-free chewing gums on dental plaque pH and salivary pH in caries-free children. A few studies have been carried out to determine the effects of sugar-free chewing gums on salivary flow rate and salivary pH in children at high risk for dental caries and these claims need to be researched further. Therefore, the present study was conducted with an aim to compare the changes in salivary pH and flow rate after chewing xylitol-containing chewing gum in children at high risk and low risk for dental caries.

Materials

Diagnostic instruments and WHO forms (According to Academy of Pediatric Dentistry-AAPD revised version, 2014) were used for caries assessment. Sterile graduated Eppendorf tubes were used to collect saturated and unsaturated saliva samples [Figure 1]. Sugar-free chewing gum (Orbit for kids, Wrigley Jr Company, Chicago, with 15% xylitol) was used as the intervention [Figure 2]. HORIBHA LAQUA twin digital pH meter was used to assess salivary pH [Figure 3]. Distilled water was used for the standardization of the pH meter.

Inclusion criteria

Children at high risk for dental caries

(According to AAPD revised version, 2014)

1. Children with >1 interproximal caries

2. Children consuming >3 between meals sugar-containing snacks or beverages

3. Children from low socioeconomic status

4. Children with active white spot lesions

5. Children with low salivary flow

6. Cooperative children

Children at low risk for dental caries

1. Children with DMFT <0

2. Cooperative children

Exclusion criteria

Children at high risk for dental caries

1. Uncooperative children

2. Medically compromised children and children with special needs

3. Children wearing any intraoral appliance

4. Children on any systemic medication and treatment

Children at low risk for dental caries

1. Uncooperative children

2. Children on any systemic medications

Methodology

Sample size

Z α/2 =Type 1 error (5%) =1.96

Z β = Type1 error (10%) =1.28 (Power of the study 90%)

SD =Standard deviation =0.13 (From literature)

d =minimally detectable difference =0.15

samples (per group)

Hence the present study was designed with 20 samples in each group with 90% power to detect a difference of 0.15 between the study groups. Forty school children aged nine to twelve years were selected according to the inclusion and exclusion criteria and were divided into two different groups - Group A (20 children at high risk for dental caries) and Group B (20 children at low risk for dental caries). Ethical clearance was obtained prior to the study. Informed consent was obtained from the parents of children of both the groups. Children in Group A (five children per day) were first asked to report to the Department by 10.30 AM., after brushing and finishing their breakfast.

Saliva collection

Children were made to sit in the chair in an upright position. Baseline saliva sample was collected in Eppendorf tube over a period of one minute by the spitting method. Before baseline saliva collection, mouth was emptied by an initial swallow. Since there is a circadian variation in the salivary flow rate and salivary ion concentration of saliva produced from all the salivary glands, baseline saliva was collected from all the subjects at a specified time in the morning (10.30 AM). The children were asked to spit the collected saliva into the Eppendorf tubes every 30 seconds with counting for 1 minute [Figure 1]. First, unstimulated saliva samples collected were subjected to the pH measurements [Figure 4]. The pH meter was standardized using buffer solution between 4 and 7 and it was standardized every day after multiple pH measurements. Once the froth disappeared in the Eppendorf tube, the salivary flow rate (in milliliters per minute) was calculated and these values were taken as control values.

Later the children were given one pellet each of xylitolcontaining sugar-free chewing gums to chew for 10 minutes. Immediately after the prescribed time, chewing gum was discarded and stimulated saliva was collected at intervals of 0, 15, 30, 45, and 60 minutes to evaluate the effects of sugar-free gum on salivary pH and salivary flow rate. Salivary pH was measured immediately. After the disappearance of froth, the salivary flow rate in milliliters per minute was calculated. These values were taken as experimental values.

The entire procedure mentioned above was also carried out in children with low risk for dental caries (Group B) (five children per day).

Results

The data obtained were analysed statistically using repeated measure ANOVA. On comparing the salivary flow rate before and after chewing sugar-free gum, the salivary flow rate did not show a statistically significant difference (p<0.05) between the two groups (Group A and Group B). However, salivary pH showed a statistically significant difference (p<0.001) between the two groups of children at different time intervals of 0,15, 30, 45 and 60 minutes.

Table 1 (Group A), Table 2 (Group B), and Graph 1 (Group A and Group B) show the average values and standard deviation of the salivary flow rates of both the groups. Table 3 (Group A), Table 4 (Group B), and Graph 2 (Group A and Group B) show average values and standard deviation of salivary pH of both the groups.

Salivary flow rate

The mean baseline salivary flow rate of the high-risk group was 0.855 mL/min, and after chewing xylitolcontaining sugar-free chewing gum, it increased up to 1.6050 mL/min immediately at 0 minutes. Salivary flow rate decreased to 1.3400 mL/min at fifteen minutes, 1.1150 mL/min at the thirtieth minute and it went below the baseline values of 0.8300 mL/min at forty-fifth minute and further decreased to 0.6950 mL/min at the sixtieth minute.

The mean baseline salivary flow rate of the low-risk group was 0.9050 mL/min, and after chewing xylitol-containing sugar-free chewing gum, it increased up to 1.5400 mL/min immediately at 0 minutes. Salivary flow rate decreased to 1.2500 mL/min at fifteen minutes, 1.1050 mL/min at the thirtieth minute and it went below the baseline value of 0.8850 mL/min at the forty-fifth minute. It further increased to 0.9200 mL/min at the sixtieth minute.

The salivary flow rate increased at 0, fifteen, and thirty minutes in both the groups (Group A and Group B). The pattern of salivary flow rate in the high-risk (Group A) group decreased at the forty-fifth minute and was below baseline by the sixtieth minute, while the salivary flow rate for the low-risk (Group B) group decreased at the forty-fifth and sixtieth minute to the baseline value (Table 1, 2).

Salivary pH

The mean salivary pH of the high-risk group was 6.900. After chewing xylitol-containing sugar-free chewing gum, it increased up to 7.2900 immediately at 0 minutes. Salivary pH decreased to 6.9850 at fifteen-minutes, 6.9700 at the thirtieth minute and again it increased up to 7.055 at forty-fifth minute and further increased to 7.100 at the sixtieth minute.

The mean salivary pH of the low-risk group was 7.1850 and after chewing xylitol-containing sugar-free chewing gum, it increased up to 7.4150 immediately at 0 minutes. Salivary pH decreased to 7.1400 at fifteen-minutes, it increased to 7.1600 at the thirtieth minute and again increased to 7.2350 at the forty-fifth minute. Later, it decreased to 7.2200 at the sixtieth minute.  

In the present in vivo study, both the study groups (Group A and Group B) showed the highest salivary pH at 0-minutes, i.e., immediately after disposing of the sugar-free gum, and a slight increase was noted at the forty-fifth minute. Children at low risk (Group B) for dental caries showed the lowest salivary pH at the interval of fifteen and thirtieth minutes. A significant higher salivary pH was recorded at 0-minutes, fortyfifth minute, and sixtieth minute in children at high-risk (Group A) for dental caries (Table 3, 4).

Discussion

Habitual consumption of xylitol-containing chewing gum improves oral health and reduces dental caries by reducing the number of Streptococcus mutans in dental plaque and saliva by breaking their energy-production cycle, causing cell death. It reduces the acid production potential of bacteria and the adhesion of bacteria on tooth surface.^11,12

A study done by Fraga CT et al., reported a reduction in salivary levels of mutans streptococci with short-term usage of xylitol chewing gum, beyond its interruption.¹³ Chewing xylitol-containing sugar-free gum is beneficial for a few reasons. Long-term use of xylitol increases the mineralization of teeth by increasing the salivary flow, when used in the form of chewing gum.

A study done by Miake Y et al., showed the possibility of inducing remineralization in the deep layer of artificial demineralized enamel by using a remineralizing solution containing xylitol.¹⁴ When children chew sugar-free gum, salivary production is stimulated and an additional volume of saliva is produced.^15,16 The salivary flow rate peaks during the first minute, followed by maintenance of high flow rates by continuous chewing. Salivary secretion increases reflexively with the taste of different flavoured sugar-free gums leading to an increase in salivary pH and buffering capacity.¹⁷

As the salivary flow rate increases, the salivary pH and concentrations of sodium, chloride, and bicarbonate ions increase, while fall in phosphate ion concentration occurs. The variations in amount of salivary flow may reflect the individual and procedural variations.¹⁸ A study done by Machiulskiene V et al., showed a direct relationship between the hardness of the chewing gum and salivary flow rate. They also stated that the act of chewing is essential to increase salivary flow rate, which leads to the prevention of dental caries, irrespective of the sweetener in chewing gum.¹⁹ Kandelman D et al., showed no statistical difference in the incidence and progression of dental caries with different concentrations of xylitol in chewing gum.²⁰ Another study done by Topitsoglou V et al., stated that chewing gum containing xylitol alone is more effective in reducing plaque formation than the mixture of sorbitol and xylitol combination when chewed for one minute.²¹

The pH of human saliva is considered normal when the value is between 6.0 and 7.5. In our study, baseline mean values of salivary flow rates (0.8550 -0.9050 mL/min) and salivary pH (6.94 - 7.18) of both the groups confirm findings previously reported.²

In this study, the mean values of salivary flow rates for both the groups were greater than the baseline values for up to thirty minutes. The increase in flow rate may be because of an increase in stimulation, organoleptic property of xylitol, and sweetener in sugar-free gum.^20,22,23 Upon analysing, salivary flow rate values in the highrisk group were below the baseline value, whereas those in the low-risk group were closer to the baseline values. A decrease in flow rate by forty-five and sixty minutes may be due to low gustatory stimulation, mechanical stimulation, or adaptation of tastants.¹⁷

The analysis of variance showed the highest salivary pH at 0-minutes, immediately after disposal of sugar-free gum in both the groups. The rise in salivary pH immediately at 0-minutes in both the groups could be because of salivary stimulation elicited by the reflection of taste and mastication leading to elevation of certain electrolyte concentrations of oral fluid and an increase in the buffering action of saliva.^15,16,20,23

The salivary pH in children in the low-risk group (Group B) was below the baseline value at the time intervals of fifteen and thirty minutes. Later at forty-five minutes, the salivary pH was above the baseline and reduced slightly nearing baseline by the sixtieth minute. Our results recorded in the low-risk group are similar to another study done by Widowaki et al on high risk and low risk for dental caries using sugar and maltitol snacks. ²

A study done by Scheie et al stated that in young adults with low caries experience, the use of xylitol and sorbitol combination of chewing gum showed no effect on microbial deposits on the surfaces of the teeth.

This could be the reason for the drop in salivary pH at fifteen and thirtieth minutes. The rise of salivary pH at the forty-fifth minute could be because of the sustained release of xylitol into saliva. At the sixtieth minute, a slight decrease in salivary pH may be due to different actions of xylitol in the low-risk group.²⁴

The pattern analysis of salivary pH in children at high risk for dental caries showed highest pH at 0-minutes, coming close to baseline values at the time interval of fifteen, thirty minutes, then increasing again at forty-fifth and sixtieth minutes. It has not gone below the baseline values. Our study results are in contrast with the study conducted by Widowaki et al., on salivary pH changes in adults with high and low caries risk for dental caries after consuming sucrose and maltitol snacks, where the salivary pH did not increase above the baseline value in the high-risk group.²

The salivary pH remained elevated and did not dip below baseline at fifteen minutes. This could be due to the highest concentration of xylitol.^25,26 The increase in salivary pH in children in the high-risk group (Group A) at the thirtieth minute, and further increase at forty-five and sixty minutes may be due to the increase in electrolyte concentrations by sustained release of xylitol into the saliva. Holgerson et al., observed an elevated concentration of xylitol in the whole saliva and dental plaque up to 8 to 16 minutes with xylitol-containing products and also observed the chemical composition of dental plaque depending on the type of polyol used.²⁶ Tapiainen et al., stated that active chewing completely releases xylitol from the gum within a few minutes. 100% xylitol-containing chewable tablets maintained an effective xylitol concentration in the whole saliva, compared with the chewing gums with only 50% xylitol. A slower elimination of xylitol in plaque samples compared to saliva was also observed.²⁷

Another study done by Pollland et al., stated that chewing gum for a longer period of time, up to 90 minutes, showed an increase in salivary flow rate up to 50 minutes and salivary pH remained high up to 90 minutes.²⁸

Another study done by Macpherson et al., stated that the decline in bicarbonate concentration is very minimal with time despite a drop in salivary flow rate and the plaque pH remained elevated even after the cessation of chewing the gum.^29,30 This could be the reason for the rise of salivary pH in the high-risk groups at the thirtieth, forty-fifth, and the sixtieth minutes, despite the reduction in flow rate.

The pattern of variation in the results may be due to different study designs. Our data indicates that very complex environmental conditions prevailing in the oral cavity may limit the values from simple experiments. Further studies are needed to be conducted in children to compare the high risk and low dental caries risk for a longer duration.

The limitations of our study are the smaller sample size and short duration of intervals in assessing the salivary flow rate and salivary pH.

Conclusion

The effects of xylitol-containing sugar-free chewing gum showed a significant increase in salivary pH in children at high risk for dental caries than the low-risk group, while it showed an equal effect on salivary flow rate in both the groups. In this study, we noticed a clear difference in the action of xylitol in children at high risk for dental caries. The results of our study conclude that since the salivary pH does not dip below the baseline values till the sixtieth minute despite reduced salivary flow rate in children at high risk for dental caries, it can be suggested that the use of xylitol-containing sugar-free gum is an effective method in reducing caries incidence in children at high risk of dental caries.

Conflict of interest

None