Efficacy and Safety of Probiotics for Dental Caries in Preschool Children: A Systematic Review and Meta-analysis

Abstract

Background:

Early childhood caries is one of the most serious and high-priced oral health conditions among young children. With advancing dental sciences, the focus of dental caries treatment is shifted from restorative procedures to preventive measures, and a modality grabbing attention is probiotics. Probiotics exert their effects in many ways as chemical inhibition of pathogenic bacteria and stimulation of the immune response through the production of immunoglobulin A and many more.

Objective:

This systematic review aims to explore the efficacy and safety of probiotics in dental caries in preschool children.

Methodology:

The study was registered in the PROSPERO International Prospective Register of Systematic Reviews (registration number: CRD42020159058). The search was done for randomized control trials in electronic databases such as Cochrane, PubMed, ClinicalTrials.gov, Medline, and Embase. It has further included manual searches of journals, conference abstracts, and books. Three reviewers done the selection of the study as per the criteria and also did the risk of bias assessment independently and wherever required, a fourth reviewer resolved the discrepancy in case of disagreement.

Results:

The nine randomized control trials were included in the study, and the pooled analysis revealed probiotics as an effective intervention in preschool children with dental caries.

Conclusion:

The results about the efficacy of probiotics in the prevention of dental caries are very encouraging, though the level of evidence is still inadequate.

Introduction

Literature suggests that the people who maintain oral hygiene and have caries-free dentition live an average of 10 years longer than those who lose their teeth. It is important to maintain or preserve natural teeth. Dental caries is the most common oral disease in adults and children in developed countries. Dental caries, if remained untreated, would cause discomfort, pain, and inability to eat or can cause nonvitality of the tooth and more serious consequences such as cysts, osteomyelitis, and facial space infections adding physical or financial burden for its treatment.[1,2,3,4,5]

It is estimated that oral diseases affect nearly 3.5 billion people, among which tooth decay or dental caries is the most common health condition (Global Burden of Disease, 2017).[6,7,8] The microorganisms that are mainly identified from carious lesions are Streptococcus mutans, Lactobacillus acidophilus, and Actinomyces viscosus. S. mutans is one of the most significant bacterial species involved in the early colonization and demineralization of tooth enamel to initiate dental caries. Improper brushing or inadequate exposure to fluoride may aggravate dental decay in children.[3,5,6] Early childhood caries (ECC) is defined as the presence of one or more decayed (noncavitated or cavitated lesions), missing (due to caries), or filled tooth surfaces in any primary tooth in a preschool-age child between birth and 71 months of age. The term “Severe Early Childhood Caries” refers to “atypical” “progressive” “acute” or “rampant” patterns of dental caries.”[9] The reported prevalence rate of ECC is 1%–12% in developed countries and as high as 70% in developing countries making it a major health problem and economic burden, especially in the socially disadvantaged population.[1,10]

According to the WHO and FAO, probiotics are “live microorganisms which when administered in adequate amounts confer a health benefit on the host.” Probiotics are live microorganisms that are either the same or similar to microorganisms found naturally in the human body and beneficial to health.[6,11,12,13] Some examples of food products from which we can get probiotics are sourdough bread, yogurt, and pickles. Probiotics are also available in capsule, tablet, powder, and liquid form. The use of such advantageous bacteria has gained attention within dental research society with a focus on caries progression, periodontal disease, and oral malodor.[14] Many works of literature suggested uncertain results regarding the consumption of probiotics for dental caries in a pediatric population. A few studies found a reduction in S. mutans, while other studies reported no change; this could be due to dissimilarity in the methodology used in the studies, inadequate sample size, or duration of intervention.[15,16] Therefore, the aim of this systematic review was to investigate the effect of probiotic therapy in pediatric populations.

Probiotics provide a health benefit when administrated in appropriate amounts. Exposure to probiotic bacteria from early in life may have a more positive impact on general and oral health than adults.[17,18] There are various mechanisms by which probiotics exert their effects on the host. Probiotics may act by chemical inhibition of pathogenic bacteria through decreasing luminal pH, production of certain inhibitory compounds, or reducing the availability of substrate to other bacterial populations. Moreover, it has been reported to stimulate nonspecific immune response leading to host resistance to microbial pathogens, immune elimination through the production of immunoglobulin A and cytokines, downregulation of hypersensitivity reactions, and decreased production of metalloproteinase.[19,20,21,22] Claudia et al., 2017, revealed that probiotics can produce antimicrobials, compete for cell adhesion sites, modulate the immune system, and degrade toxins.[19] The adhesion and colonization of the probiotics in the oral cavity is also of paramount importance since adhesion may increase the retention time of a probiotic on the host surfaces leading to prolonged action.[20,21,22]

Introducing a nonpathogenic microbial strain into the microflora of host not only aids in restoring oral health but also generates conditions that serve the dominance of nonpathogenic bacteria and inhibition of pathogenic microorganisms in the oral cavity. The probiotics will promote the diversity of health-associated microbes in the oral biofilm. Consequently, it seems rational to observe the effect of probiotics which have a positive influence on oral flora to help in the reduction of dental caries.[23]

Methodology

The protocol of the present systematic review was designed according to the PRISMA guidelines 2009 and was registered in the PROSPERO International Prospective Register of Systematic Reviews (registration number: CRD42020159058).[24]

Search methodology for inclusion of studies

This systematic review and meta-analysis included detailed search strategies for identification of the studies. Search terms included MeSH or equivalent terms and text words from databases such as PubMed, Scopus, Cochrane, Google Scholar, and ScienceDirect databases from inception till 2019, while Medline and CENTRAL from inception till date. The search also included additional resources such as www.ClinicalTrials.gov, conference proceedings, and abstracts. Additionally, reference lists of the selected studies and reviews were scanned manually to identify the articles missed by electronic search. The Google search engine was also used to do an all-inclusive search on the World Wide Web to ensure completeness. Besides, the manual library search and the communication with experts were done.

Criteria for considering studies for this review

This systematic review and meta-analysis have included the studies with randomized controlled trials having full journal publications; the in vivo studies in humans were selected.

Eligibility criteria

Eligibility criteria for inclusion of the studies according to PICO format (participant, intervention, comparator, and outcome), is as mentioned:

• Participants (P): Healthy children in the age group 1–6 years

• Intervention (I): Probiotic in any form

• Comparator (C): Placebo/alternative treatment/as an adjunct

• Outcomes (O): Main and additional outcomes.

Inclusion criteria

• Healthy children in age group 1–6 years with or without dental caries

• Exposure: Probiotics, in any form/preparation, frequency, or duration.

Ice creams or dairy foods such as cheese, yogurt and milk, lozenges, toothpaste, tablets, drinks, and syrups

• Randomized controlled trials (in vivo studies)

• Years of search: Inception to 2019.

Exclusion criteria

• Elderly children/children above 6 years of age

• The children with a history of dental treatment, systemic antibiotics 3 months before baseline, habitual use of dairy probiotics, xylitol chewing gums, severe medical conditions, and who are allergic to dairy products

• Use of agents other than probiotics or other therapeutic or preventive modalities

• Animal studies, in vitro studies, systematic reviews or meta-syntheses, and observational studies.

Outcomes to be measured

Outcomes are categorized under

• Main outcomes

  • Reduction of dental caries: Using visual and tactile detection of lesions of dental caries and its severity is depicted by various standard criteria such as ICDAS (International Caries Detection and Assessment System)/WHO Criteria (Decayed, Missing, and Filled Teeth and Decayed, Missing, and Filled surfaces, [DMFT]/dmfs/dmft)

  • Reduction in salivary S. mutans level/counts: The number of S. mutans levels in saliva was measured before and after the intervention

  • Observed/associated adverse effects/side effects/complications.

• Additional outcomes

  • Reduction in Biofilm formation: Measured as visible plaque index

  • Increase in pH.

Data collection and analysis

Selection of studies

The studies were selected as per the criteria. Firstly, titles and abstracts of the studies which were appropriate to the review were screened and a complete text of eligible studies was extracted. There was no language barrier in the selection process of studies. The PRISMA flow diagram illustrated the entire selection process as per recommended guidelines.

Data extraction and management

A complete text of the included studies was extracted and assessed. Any discrepancy or confusion therein was discussed among review authors for mutual settlement, and wherever required, a fourth review author was requested to resolve the inconsistency. The risk of bias (RoB) assessment was done to resolve any discrepancy. The selected randomized control trials were summed up into a “summary table.” [Tables 1-3].[25,26,27,28,29,30,31,32]

Table 1.

Characteristics of studies included in meta-analysis

Parameters Outcomes	Rodriguez 2016		Pahumunto 2018		Stecksen-Dlicks 2009		Villavicencio 2018		Hasslöf 2013
	Continuous data
	Mean of intervention±SD Probiotics +	Mean of control±SD Probiotics −	Mean of intervention±SD Probiotics +	Mean of control±SD Probiotics −	Mean of intervention±SD Probiotics +	Mean of control±SD Probiotics −	Mean of intervention±SE Probiotics +	Mean of control±SE Probiotics −	Mean of intervention±SD Probiotics +	Mean of control±SE Probiotics −
Caries increment measurement (cavitated)	BL (n=123): 1.62±2.51 12 months (n=123): 2.86±3.64	BL (n=82): 1.69±2.75 12 months (n=82): 3.58±3.66	BL (n=59): 10.61±5.81 6 months (n=51): 11.37±5.60	BL (n=52): 8.85±6.09 6 months (n=52): 10.10±5.55	BL (n=133): 0.5±1.7 21 months (n=110): 0.9±2.2	BL (n=115): 0.6±1.6 21 months (n=76): 2.2±3.7	BL (n=136): 2.23±3.57 9 months (n=119): 2.22±32.32	BL (n=227): 2.22±3.49 9 months (n=202): 1.88±30.57	BL (n=89): 0±0 6 years (n=84): 0.6±1.7	BL (n=90): 0.2±1.0 6 years (n=87): 0.7±2.4
Caries increment measurement (noncavitated)	BL (n=123): 0.67±1.71 12 months (n=123): 1.30±2.31	BL (n=82): 0.69±1.56 12 months (n=82): 1.68±2.69					BL (n=136): 0.71±1.64 9 months (n=119): 0.60±1.65	BL (n=227): 0.65±1.81 9 months (n=202): 0.70±1.80
SM counts					BL (n=133): 0.6±3.4 21 months (n=110): 0.2±1.7	BL (n=115): 0.6±2.4 21 months (n=76): 0.8±5.5	BL (n=136): 0.84×105±3.13×105 9 months (n=119): 0.16×105±0.80×105	BL (n=227): 1.02×105±3.89×105 9 months (n=202): 0.42×105±2.86×105

SD: Standard deviation; SE: Standard error; BL: Basal Level; SM: Streptococcus Mutans

Table 3.

Study-wise risk of bias

	Pahumunto 2018	Villavicencio 2018	Alamoudi 2018	Hasslo 2013	Hajikand 2012	Taipale 2012, 2013	Stecksen- Dlicks 2009
Random sequence generation (selection bias)	L	L	L	U	U	U	L
Allocation bias: Allocation concealment	L	L	U	U	U	U	L
Performance bias: Blinding of participants and personnel	L	L	L	L	L	L	L
Detection bias: Blinding of outcome assessment	L	L	L	L	L	L	L
Attrition bias: Incomplete outcome data addressed	L	L	L	H	L	L	H
Reporting bias: Selective reporting	H	L	H	U	L	L	U

Table 2.

Characteristics of studies included in meta-analysis

Parameters Outcomes	Hajikand 2012		Alamoudi 2018		Taipale 2012, 2013
	Continuous data
	Mean of intervention SD % Probiotics +	Mean of control SD % Probiotics −	Mean of intervention SD % Probiotics +	Mean of control SD % Probiotics −	Mean of intervention SD % Probiotics +	Mean of control SD% Probiotics −
						Xylitol	Sorbitol
	DMFT					BL (n=32): NA 2 years (n=32): 0% 4 years (n=32): 9%	BL (n=35): NA 2 years (n=35): 0% 4 years (n=33): 21%	BL (n=29): NA 2 years (n=29): 0% 4 years (n=28): 7%
SM counts			BL (n=90): 90 (100%) 28 days (n=90): 46 (51.1%)	BL (n=88): 88 (100%) 28 days (n=88): 79 (89.8%)	BL (n=32): NA 2 years (n=32): 6% 4 years (n=32): 56%	BL (n=35): NA 2 years (n=35): 31% 4 years (n=32): 70%	BL (n=29): NA 2 years (n=29): 10% 4 years (n=32): 46%
Caries prevalence	BL (n=54): 13 (24%) 12 months (n=54): 13 (24%)	BL (n=56): 15 (27%) 12 months (n=56): 26 (47%)
Visible plaque index	BL (n=54): 18 (34%) 12 months (n=54): 29%	BL (n=56): 22 (40%) 12 months (n=56): 25%

NA: Not available; SD: Standard deviation; DMFT: Decayed, Missing, and Filled Teeth; BL: Basal Level; SM: Streptococcus Mutans

Assessment of risk of bias in included studies

The RoB assessment was done for included studies; any ambiguity or differences were discussed to reach a common conclusion. Whenever needed, a third review author brought the terms to a mutual decision.

A domain-based evaluation for RoB was done for each study; accordingly, studies were judged for seven domains and assigned either “low risk,” “high risk,” or “unclear risk” of bias [Figures 1-3].

Figure 1.

Risk of bias summary

Figure 3.

Forest plot for cavitated lesions

Figure 2.

Risk of bias graph

Data synthesis

This systematic review has provided the narrative synthesis of the findings from the included studies, structured around the target population characteristics, type of intervention, type of outcomes, and intervention content. It has provided summaries of intervention effects for each study by calculating the risk ratios (for dichotomous outcomes) or standardized mean differences (for continuous outcomes). However, where studies have used the same type of intervention and comparator with the same outcome measure, we have pooled the results using a random-effect meta-analysis and calculated 95% confidence intervals and two-sided P values for each outcome.

In this study, the subgroup analysis according to the type of probiotic strain was not done. The studies rather focused on the effect of probiotics on the reduction in dental caries and associated adverse effects if any. Heterogeneity in the studies was assessed by using the Chi-square test and I² statistics.

Observations

Cavitated lesions [Figure 3]

For cavitated lesions, the study showed that the intervention was effective with a reduction in cavitated lesions. All the studies favored the outcome except for Pahumunto et al.’s study which showed the intervention was ineffective.[26]

The mean difference was found to be −0.44 (−0.89, 0.01), with significant overall effect. The heterogeneity test suggests that there were insignificant differences in the studies. All the studies favored the outcome except for Pahumunto et al. which showed that the intervention was ineffective and was given only for 6 months.[26] While, for studies by Rodríguez et al. and Stecksén-Blicks et al., the findings were significant with 12 months and 21 months of intervention, respectively.[25,32]

Caries prevalence

Hedayati-Hajikand et al., 2012, studied and compared the caries prevalence in participants taking probiotics and not on probiotics.[29] It was demonstrated that the intervention was effective and there was a reduction in the prevalence of carious lesions in participants on probiotics. The mean difference was found to be 0.52 (0.30 0.90), and the overall effect was found to be significant (0.02). Being a single study that mentioned caries prevalence, the heterogeneity test was not applicable.

Streptococcus mutans count

Stecksén-Blicks et al. studied and compared the S. mutans count in participants taking probiotics and not on probiotics.[32] For S. mutans count, the study showed that the intervention was effective with the reduction in S. mutans count.

The mean difference was found to be −0.60 (−1.88, 0.680), and the overall effect was found to be nonsignificant. Being a single study that mentioned S. mutans count, the heterogeneity test was not applicable.[32]

Discussion

The present systematic review and meta-analysis were carried out to evaluate the effect of probiotics on dental caries anticipating outcomes such as a reduction in dental caries, salivary S. mutans count and biofilm formation, and an increase in pH. Additionally, the present work has also assessed adverse/side effects or complications of probiotic use.

The articles included in the present review work were subjected to the RoB assessment; overall, the risk was found to be low for selection bias, allocation, and blinding. The results about the efficacy of probiotics in the prevention of dental caries as an intervention were very encouraging, although the level of evidence is still inadequate.

Cavitated lesions

For cavitated lesions, the study showed that the intervention was effective with a reduction in cavitated lesions. All studies favored the outcome except for Pahumunto et al. which showed the intervention of 6 months as ineffective.[26] While, for studies by Rodríguez et al. and Stecksén-Blicks et al., the findings were significant with the intervention of 12 months and 21 months, respectively.[25,32] Cagetti et al., 2013, mentioned the therapeutic effect of probiotics in the prevention of dental caries. Additionally, they studied the risk factors associated with caries for instance acid production by cariogenic microbials concerning probiotic administration. The probiotics were effective against S. mutans reducing their counts; however, the randomized controlled trials need to be conducted in humans to generate enough scientific evidence.[10]

Caries prevalence

The study by Hedayati-Hajikand et al., 2012, compared the caries prevalence in participants taking probiotics and not on probiotics where the intervention was effective with a reduction in the prevalence of carious lesions. The overall effect was found to be significant (0.02).[29] Poorni et al., 2019, evaluated the role of probiotics and streptococcus strains on the incidence of carious lesions doing systematicreview, the included clinical studies showed a high RoB. Although in vitro studies showed promising results, clinical studies have not demonstrated clear clinical outcomes. Thus, there is a vast scope for future research in this field.[4]

Streptococcus mutans count

The study by Stecksén-Blicks et al. compared the S. mutans count in participants taking and not taking probiotics. For S. mutans count, the study showed that the intervention was effective with the reduction in S. mutans count. The overall effect was found to be nonsignificant.[32] Dhawan R et al., 2013, examined the effect of probiotics on plaque, salivary S. mutans levels, and gingival index in cases of gingivitis.[33] The baseline evaluations were made followed by two posttreatment evaluations for 2 weeks, and there was a significant reduction in plaque index, S. mutans level, and gingival index.[33] Chuang et al., 2011, could not observe any difference between S. mutans levels in placebo and probiotic groups using Lactobacillus paracasei containing probiotics. However, the in vitro studies mentioned that Lactobacillus paracasei could restrain the growth of S. mutans.[21] Coqueiro et al., 2018, reviewed the therapeutic effects of probiotics containing Bifidobacterium and Streptococcus on levels of salivary S. mutans and found reduced incidence of dental caries and S. mutans levels. It was concluded that the effects of combined therapy using fluoride and probiotics would be more effective.[34]

Ahola et al., 2002, and Taipale et al., 2012, have demonstrated that specific probiotic strains can affect oral pathogens by reducing the counts of S. mutans and lactobacilli in the saliva and biofilm.[5,35] The scientific origin of oral probiotics makes use of genetically altered competitive microbes or a mixture of probiotics containing inhibitory oral microbes.[36,37,38] Streptococcal salivaris and thermophilus have been widely studied in vitro.[36,37,38] Schwendicke et al. revealed streptococcal thermophilus be capable to compete against cariogenic bacterial species in oral flora owing to its aciduric nature, although with limited efficiency as compared to Lactobacilli.[39,40] At similar, Lee and Kim showed that Lactobacillus strains formed wider bacteria-free zones than streptococcal thermophilus.[40] The strains K12 and M18 streptococcal salivaris are mostly researched compared to other strains. The streptococcal salivarius M18 was more effective in the reduction of biofilm and caries risk in vitro with an inhibitory effect on S. mutans and Streptococcus sobrinus.[41,42,43,44,45] However, there are still doubts about which is the best bacterial strains, its dose and period of administration, Consequently, prospective extended research work is desired.[11]

Soldering mentioned commonly researched probiotics such as Bifidobacterium lactis BB-12 (BB-12), Lactobacillus rhamnosus GG, and Lactobacillus reuteri.[46] The coronal and root caries occurrence was reduced with the use of Lactobacillus rhamnosus with or without fluoride.[46,47] The Bifidobacterium lactis BB-12 when administered in infants reduced the occurrence of caries. However, longitudinal studies are required to ascertain the adverse effects of probiotics on oral health.[30]

Conclusion

Overall, the meta-analysis has proved that probiotic as an intervention is effective in the reduction of carious lesions in preschool children. No adverse effects were noted in the studies for the period of probiotics use. Although probiotic intervention in dental caries was found to be effective, the demonstrated level of evidence is inadequate. Considering that common oral diseases arise out of deranged microbial equilibrium, the recent research on probiotic focus on reducing virulent strain and restoring healthy microbiota. The prospective extended research with broader representation would be desired to identify the specific probiotic strains with anticariogenic activity. Probiotics may be a promising aid for the prevention of dental caries; however, the ideal dose forms and duration of probiotic intervention need to be determined through supplementary high-quality research.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.