Introduction

Dental caries is a bacterial disease caused by the dissolution of tooth mineral by acids from bacteria in dental plaque followed by the destruction of the organic matrix (1). It is a preventable disease that can be effectively controlled. Saliva is considered protective against dental caries; serving to flush away non-adherent bacteria and other debris while neutralizing damaging fluids and acids. Saliva is also a reservoir for ions (i.e., calcium, phosphorus), increasing the  ikelihood of remineralization, and containing antimicrobial and anti-plaque agents (2, 3).

The caries process begins with the fermentation of carbohydrates by bacteria, followed by the production of organic acids which in turn ends up with pH reduction. As the reduction in pH continues to the critical level, dental enamel starts to dissolve (4). Dental caries is a dynamic process and a continuum of many cycles of demineralization and remineralization. The occurrence of remineralization depends on two factors: dental plaque pH and saturation of mineral materials in plaque (5). As mentioned above, saliva stimulation can play a major role in both items and chewing gum is an efficient and pleasant way to increase saliva. Salivary flow increases as a result of both gustatory and mechanical (chewing) stimuli produced by chewing gum. At the same time, chewing gum increases salivary and plaque pH levels and promotes enamel remineralization (6) .

Nowadays, many different kinds of chewing gum in various forms and flavors and commercial packages are available. It has been reported that chewing any of the sugar-free gums after meals can decrease the acidogenicity of dental plaque, increase the flow of saliva, and the remineralization of the incipient caries
(7, 8). Studies indicate that the sugar-free gums can decrease dental caries by 40%(9). Sorbitol and xylitol are two kinds of non-cariogenic sugars; the anti-cariogenicity of the former is lower than the latter(10). The continuous consumption of xylitol gums reduces the streptococcus mutans of saliva (11, 12). In contrast, the use of sugar-containing chewing gum lowers plaque pH and increases the amount of plaque, and habitual use increases carie (13).

Van sugar-free gums, which are the product of the Van factory, contains xylitol and has the medical benefits of Baneh tree extract. This ingredient is used in the medical, chemical, and food industry (14). Gum produced from Baneh tree extract have numerous usages in medicine and has been consumed for over 2500 years for gastrointestinal problems, such as gastralgia, digestion disorders, and peptic ulcers (15). It has been shown that this gum has anti-bacterial, anti-inflammatory, anti-fungi, and anti-cancer features(16). Moreover, its anti-bacterial effects on the accumulation of streptococcus mutans of dental plaque has been proven (17).

Therefore, the objective of this study was to examine the effects of natural gum produced from Baneh tree extract and two artificial sugar-free gums on dental plaque acidity.

Material and Methods

This randomized, controlled, single-blind, crossover, clinical trial was approved by the research and ethics committee, of the School of Dentistry, of the Mashhad University of Medical Sciences, and experiments were performed at the pediatric department of the Mashhad Dental School (Mashhad, Khorasan Razavi Province, Iran). The study has been conducted according to the Declaration of Helsinki principles.

      Selection

The study was conducted on 15 subjects, consisting of healthy dental students (3 males, 12 females, age: 20 to 25 years), after signing an informed, written consent form. The average of the decay-missing-filled-teeth (DMFT) was 7.7. The criteria for inclusion were: being healthy with a normal unstimulated salivary flow rate, not taking any medication that may interfere with salivary flow rate, and not having cavitated lesions.

      Intervention

The present study was conducted during five
 48-hour periods (one control and four experimental) with a one-week washout interval between the sessions
 (Fig. 1). The subjects were trained to remove their dental plaque completely by tooth brushing and dental floss at the beginning of each 48-hour period. They were also asked to check if they removed plaque successfully using disclosing tablets. Subjects were instructed not to practice any kind of oral hygiene measures or chew gum for the next 48 hours and on day three, when they had not consumed anything except water for four hours, plaque sampling was done.

The subjects, according to chewing gums used, and the control group were randomized into five groups, through which they passed in a randomized sequence. The amount of gum used in all groups was equal to 1.3 g. The synthetic gums were banana-flavored gum (sugar-containing gum), Orbit and Orbit Complete (sugar-free gums), and Van (natural sugar-free gum). The components of each chewing gum are given in Table 1.

Figure1. Flowchart of the phases of study (sequences of the 5 phases was randomly determined for each volunteer)

Table 1. Chewing gums used in the study

Control group: At first, the baseline dental plaque pH was measured, and then the subjects were asked to keep 10 cc sucrose syrup (10%) in their mouth for 30 seconds and then spit out. The plaque pH values were then measured at 5, 10, 15, 20, and 30 minutes after rinsing with sucrose solution.

Experimental (chewing gum) groups: After measuring the baseline dental plaque pH and rinsing with sucrose 10% solution, each subject was asked to chew the assigned gum for 30 minutes. Afterward, the pH was recorded at the mentioned intervals. There were four chewing gum groups and four studied chewing gums.

      Determination of acidity of dental plaque

In each of the groups, dental plaque was measured by the “plaque sampling” method. To minimize the salivary contamination, the subjects were asked to swallow their saliva before sampling and a lip retractor was used. The plaque samples were collected from whole (mesial, middle, distal) buccal surfaces of all maxillary and mandibular teeth (up to the first molar) with the help of a sterile amalgam carver for 30 seconds. The plaque pH was then immediately measured by a pH meter Sentron (type Argus X, Sentron Inc.) in conjunction with a CupFET micto-combination electrode (ISFET, Sentron Inc, Gig Harbor, Wash., USA). The pH values were recorded after stirring the sample in distilled water in the electrode for 30 seconds and after the readings stabilized within four minutes. The pH meter was calibrated with standard buffers at pH 4, pH 7, and pH 9 before the beginning of each experimental day, and between each reading the electrode was cleaned with a stream of distilled water and placed in a standard solution of pH 7.0 to ensure that the calibration of the pH meter remained constant.

      Randomization and blinding

The patients were randomized into one of five treatment sequences. The randomization process was performed using the Research Randomizer Program, available at www.randomized.org (copyright©1997-2012 by Geoffrey C. Urbaniak and Scott Plous). The principal investigator did the randomization process before beginning the study. The principal operator and the patients could not be blinded, but the assessor who did the plaque sampling and determination of dental plaque pH was blinded.

Sample size

 Sample size calculation was based on a previous study.(18) With a confidence level of 95% and a power of the statistical test of 80%, 15 samples were calculated.

       Ethical approval

 All procedures performed in our study were in accordance with the research and ethics committee of the School of Dentistry, of the Mashhad University of Medical Sciences, Number: 89629 and with the 1964 Helsinki Declaration and its later amendments for comparable ethical standards.

Statistical analysis

The results were analyzed using ANOVA, LSD and repeated measure tests. P-value < 0.05 was considered significant.

Results

There was no significant interaction between the two variables “time” and “group” (p=0.21). The mean plaque pH of samples at different time intervals (before and after chewing gum) in the studied groups is shown in Table 2 and the changes of mean plaque pH compared to baseline pH at different time intervals after chewing gum are presented in Table 3.

 As shown in Table 2, the baseline pH values in the five groups were not significantly different (p=0.15). Table 3 shows that the least plaque pH decrease was seen in the Orbit Complete group and the most was in the banana-flavored group. The pH increased faster with the natural gum (Van) and Orbit Complete gum. After 5 and 10 minutes of sucrose challenge, it was observed that the pH changed with natural and synthetic sugar-free chewing gums, which were not statistically different. However, at 15 and 20 minutes, Van increased plaque pH statistically more than Orbit (p=0.04), while it was almost the same as Orbit Complete. The plaque pH was more than baseline pH after 20 minutes in the Van and Orbit Complete groups. At 30 minutes, the final plaque pH in the control group was not statistically different from its baseline pH, like the three sugar-free chewing gums, while plaque pH in the banana-flavored group was significantly less than its baseline pH (p=0.001) .

Table 2. Mean plaque pH of subjects (±SD) at different time intervals (before and after chewing gum)
in the studied groups

Within each column, means with the same superscript letters a,b,c,d,e or f are not statistically different from each other

Table 3. Mean plaque pH changes compared to baseline pH at different time intervals after chewing
gum in the studied groups

Within each column, means with the same superscript letters a,b or c are not statistically different from each other