The literature search was conducted in three databases, including PubMed/Medline, Web of Science, and Scopus to identify the available studies evaluating the prevention of caries lesions with chewing gum.

The search strategy was developed as follows:

1.

“demineralization” OR “tooth demineralization” OR “teeth demineralization” OR “caries” OR “carious” OR “tooth decay” OR “teeth decay” OR “dental caries” OR “caries susceptibility”

English articles on the caries preventive effect of chewing gum in children or adults published from 2012 to 2022 were included. Randomized controlled trials, cross-sectional studies, pre-post trials, and any clinical studies designed with a comparative arm were identified and analysed for eligibility of further quantitative analysis (Figure 1).

The data on the clinical performance of chewing gum in caries prevention were extracted and analysed.

Based on the sugar content, chewing gum can be classified as sugar-containing chewing gum or sugar-free chewing gum. Sugar-containing chewing gum is chewing gum that contains simple carbohydrates, such as monosaccharides and disaccharides, in which monosaccharides include glucose, fructose, and galactose, and disaccharides include maltose, sucrose, and lactose. Chewing gum containing any of these are considered sugar-containing chewing gum (9, 10, 12, 20). Sugar-free chewing gum does not contain simple carbohydrates. It can be further classified into chewing gum containing sugar alcohol and chewing gum containing other sweeteners. Sugar alcohol includes polyols, such as xylitol, sorbitol, etc. Non sugar alcohol-containing gum is sugar-free chewing gum. They might contain other sweeteners, such as artificial sweeteners like aspartame and saccharin. Non sugar alcohol-containing gum can also be sweetener-free, which is plain chewing gum (9, 10, 12, 20).

Chewing gum can be classified by its active ingredients. Based on whether the chewing gum contains bioactive drug content or not, chewing gum can be classified as medicated chewing or nonmedicated chewing gum. Medicated chewing gum contains active ingredients. Examples include CPP-ACP-containing chewing gum, carbamide-containing chewing gum, fluoride-containing chewing gum, and chlorhexidine-containing gum (9, 10, 12, 20).

Four studies investigated the caries preventive effect of chewing gum compared to no gum (23, 26, 27, 29). Three out of four studies showed that chewing gum lowered caries increments in comparison to no gum use, with prevention ranging from 6.95% to 85.2% (26, 27, 29). One study did not find a caries preventive effect of chewing gum (23).

One study investigated the use of chewing gum compared to fluoride varnish (24). It showed chewing gum reduced more caries formation in comparison to fluoride varnish.

Three studies investigated the caries preventive effect of xylitol-containing chewing gum compared to polyol-containing chewing gum (25, 28, 30). One study showed that xylitol-containing chewing gum had a better caries preventive effect than other polyol-containing chewing gum in both initial enamel caries and dentine caries (25). Another two studies were conducted with the same clinical trial (28, 30). They showed xylitol-containing chewing gum had a better caries preventive effect for initial and extensive lesions as defined in the ICDAS than other polyol-containing chewing gum. However, such an effect was insignificant in moderated lesions. One study investigated the caries preventive effect of tea polyphenol-containing chewing gum compared to xylitol-containing chewing gum (26). The study showed that tea polyphenol-containing chewing gum had a superior caries preventive effect in comparison to xylitol-containing chewing gum. Another study investigated the caries preventive effect of magnolia-containing chewing gum compared to xylitol-containing chewing gum (30). The results indicated that magnolia-containing chewing gum had a superior caries preventive effect in comparison to xylitol-containing chewing gum for initial and extensive lesions but not moderate (30).

The caries preventive effect of chewing gum compared to no gum was found in a varied intervention period of daily chewing gum use, ranging from 12 weeks to two years (24, 26, 27, 29). With as short as a 12-week daily use of chewing gum, a reduced caries experience was observed (27).

One study compared the caries preventive effects of chewing gum to no gum with two different frequencies and durations (5 times a day and 12 min each time vs. 3 times a day and 20 min each time) yet the same daily total duration of 60 min (27). The group with higher frequency and lower duration of chewing gum daily presented a superior remineralization effect. However, it should also be noted that the total daily intake of xylitol is higher in the former group (5 g) than the latter (3 g).

Three studies investigated the caries preventive effect of chewing gum compared to no gum on children and adolescents (26, 27, 29). All studies showed that chewing gum lowered caries increments in comparison to no gum use, with prevention ranging from 6.95% to 85.2% (26, 27, 29). One study investigated the use of chewing gum on participants above 60 years old and compared to no gum (23). The results did not show chewing gum reduce caries experience on elderly. No included studies investigated the use of chewing gum compared to no gum on adults.

Chewing gum prevents caries by clearing the oral cavity. Two systemic reviews concluded the anti-plaque effect of sugar free chewing gum (31, 32). When debris of food containing fermentable carbohydrates is retained in the oral cavity, it can be fermented by cariogenic bacteria to produce acid (33). Chewing gum can facilitate the mechanical removal of food debris, which contains dietary sugars (34). In addition, chewing gum increases salivary flow rates, which creates an increased flushing effect against food debris. Through stimulating saliva and reducing plaque mechanically, chewing gum can improve oral hygiene (35).

The acidity of oral cavity will reduce after the oral cavity being exposure to fermentable carbohydrates. When the pH level is below 5.5, the critical pH of enamel, demineralization of the underlying enamel occurs (36). Chewing gum can increase the secretion of saliva. The increased salivary stimulation can last for 9 min with a 187% increase of saliva in the first minute, and a 86% increase in the subsequent minute in comparison to unstimulated status (37). Besides, the buffering capacity of stimulated saliva is higher compared to unstimulated saliva (38, 39). Furthermore, some studies suggested that there will be a slight increase of the unstimulated salivary pH (40). All these facilitate the neutralization of acidity in the oral cavity and reduced enamel demineralization.

Chewing gum can stimulate the production of saliva, which is supersaturated with calcium and phosphate ions. These ions can precipitate to the demineralized enamel surface and promote remineralization (34, 41).

Previous studies show that xylitol-containing chewing gum can reduce the level of Streptococcus mutans in the oral cavity by inhibiting the attachment of S. mutans to the tooth surface (42, 43). In addition, xylitol cannot be metabolized by S. mutans, but it can compete with mono- and polysaccharides in the metabolic pathways of S. mutans and inhibit the production of lactic acid by the bacteria (44).

Consuming chewing gum after a meal might lower the appetite of the consumer and subsequent snack intake (33). A clinical trial reported that the group chewing gum after lunch experienced a lower level of snack intake, desire for sweet food, and subjective feeling of hunger in comparison to the no-gum group (45). In another trial, the group chewing gum after lunch also experienced a lower level of snack intake, especially carbohydrate-containing food in comparison to the no-gum group (46).

In order to achieve the caries preventive effects of chewing gum, the amount, duration, and time of intake is important. According to the included clinical studies, a positive caries preventive effect was found with participants chewing gum after a meal at least 3 times per day. Therefore, the best time to chew gum is after a snack or meal at least 3 times per day. The European Food Safety Authority suggests chewing gum for 20 min each time (48). However, the anti-caries effect of chewing gum can be achieved after 5 min of chewing per use according to the included studies (47).

Sugar-free gum is suggested for caries prevention. Despite multiple clinical studies (49) favouring xylitol-containing gum over sorbitol-containing gum, a systemic review in 2012 (49) suggested that the current evidence supporting xylitol over sorbitol is contradictory. More research is needed on the topic. Although studies showed a superior caries preventive effect of magnolia bark extract-containing gum and tea polyphenol-containing gum in comparison to xylitol-containing gum (20, 25, 30), they are not available commercially. Research on the caries preventive effect of chewing gum containing other active ingredients, such as CPP-ACP, fluoride, and urease, is lacking.

There have been incidents of choking on chewing gum, especially in young children (50, 51). According to the U.S. Department of Agriculture, children under the age of 4 should not chew gum. As for children above that age, the risk of chewing during eating is smaller. Good eating habits are believed to prevent choking (52).

There are studies reporting arthralgia and myofascial pain after the excessive chewing of gum for over three hours per day (53, 54). The prolonged exercise of the jaw muscle which exceeds its capacity may lead to temporo-mandibular joint disorder (TMD) and a pain in the jaw muscles (55). It is, therefore, important to avoid prolonged gum chewing.

Some studies suggested excessive chewing gum use is related to chronic headaches among adolescents (56). The mechanism behind this is still unclear. The chronic headache is hypothesized to be related to the temporo-mandibular joint dysfunction provoked by excessive gum chewing or the consumption of aspartame that chewing gum contains (56, 57).

Chewing gum can accelerate the release of mercury for individuals with dental amalgam fillings. The amount of mercury in plasma and urine for individuals with regular gum chewing habits are significantly higher than those without such habits (58).

There are cases reporting diarrhoea and abdominal discomfort after chewing gum consumption (59). This can be related to the over consumption of polyols in gum, which can cause gastrointestinal disturbances and lead to irritable bowel syndrome. This negative effect is dose-dependent (60). The amount of polyol in chewing gum is low and would not cause any gastrointestinal effects in most individuals (60, 61).