The search was performed on March 18, 2024, on the Web of Science Core Collections (WoSCC) database. When performing a bibliometric analysis, WoSCC is one of the most popular scientific source databases for the superiority of supplying data for reference analysis. The retrieval was Topic = (dental caries) AND Title = (Lactobacilli OR Lactobacillus). The inclusion criteria for this analysis were original research articles that explored the role of Lactobacillus in dental caries, either in terms of prevention or progression. Exclusion criteria included studies that did not involve Lactobacillus or dental caries, those that did not report caries-related outcomes, and studies that were non-peer-reviewed or just abstracts or reviews. The full record and cited references of the retrieved articles were exported in plain text format for subsequent analyses.

The article selection process followed a previously reported methodology (18). In brief, two independent reviewers (D.F and L.Y) conducted an autonomous screening of titles and abstracts, and when required, evaluated full texts to identify pertinent studies. Disagreements between the two reviewers were resolved through discussions facilitated by a third reviewer with substantial experience (L.Z).

The final included literature was exported and analyzed using the professional bibliometric analysis software VOSviewer, owing to its capability to generate clear and easily interpretable visualizations (19).

A total of 274 articles related to Lactobacillus and dental caries were retrieved. After screening, 21 articles were excluded (unrelated to dental caries = 16, non-article = 5). A total of 253 articles on Lactobacillus and dental caries were published and indexed in WoSCC, and the number of publications was generally on the increase (Figure 1).

Table 1 shows the top 10 most productive countries in the Lactobacillus and dental caries research area. Sweden emerged as the country with the highest publications (n = 34), followed by China (24) and the USA (22). Figure 2 illustrates the collaboration among 17 countries with more than 4 publications. Each node in the graph represents a country. Nodes of the same color indicate countries belonging to the same cluster. The lines between nodes represent collaborative relationships between the corresponding countries.

Sweden, as the leading contributor in terms of publications, focuses its research primarily on two key areas: (1) the potential anti-caries properties of Lactobacillus as probiotics, including their effects on cariogenic pathogens such as S. mutans (20, 21) and their preventive efficacy in various populations, such as orthodontic patients, children with early caries lesions, high-caries-risk schoolchildren, and elderly individuals with root caries (22–25); (2) the load, and genotypes of Lactobacillus species in the oral environment or carious sites (26–29). The United States, the second-largest contributor to the publications, has placed particular emphasis on the interactions between various Lactobacillus species and other oral microorganisms, such as S. mutans, Candida albicans biofilms, and even multispecies biofilms (30–35).

Table 1 includes the top 10 institutions with the largest number of publications, with the University of Gothenburg being the only institution having more than 15 publications followed by Prince of Songkla University (15) and University of Turku (11).

The top 10 most productive authors are shown in Table 2. Teanpaisan R (15) emerge as the author with the highest publications, followed by Piwat S (11) and Twetman S (10). Besides, Twetman S acquires the highest 51 h-index. Teanpaisan R and Piwat S are affiliated with the same research institution, Prince Songkla University. Their research primarily focuses on the probiotic potential of Lactobacillus, particularly strains like L. rhamnosus SD11 and L. paracasei SD1 (36–41). Twetman's work has involved the use of L. reuteri and L. rhamnosus in the prevention of caries (23, 42, 43). In addition, his research has explored the potential of probiotics to bind fluoride (25, 44).

A total of 133 journals in the WoSCC database published studies relevant to Lactobacillus and dental caries. Table 3 shows the top 10 journals by the number of publications. Caries Research is the number one source with 24 articles, followed by Archives of Oral Biology with 20 articles and Journal of Dental Research with 10 articles.

The top 20 occurrent keywords are listed in Table 4. The “dental caries”, “Streptococcus mutans”, “lactobacilli”, “probiotics”, and “children” are the most used keywords. In VOSviewer, setting the minimum of occurrences of a keyword as 8, 45 keywords that met the requirement were used to depict the co-occurrence map (Figure 3). Nodes of the color correspond to the average time of the keywords appear. The lines between nodes represent the occurrence relationship. Table 4; Figure 3 shows the hot topics in the field of Lactobacillus and dental caries. The keywords “colonization,” “adherence,” “virulence,” and “pH” highlight a significant research focus on the pathogenic mechanisms of Lactobacillus in dental caries, while terms like “prevalence,” “strains,” and “risk” underscore efforts to elucidate the relationship between the abundance and distribution of Lactobacillus and the epidemiological characteristics of dental caries; (2) The frequent mention of the keyword “probiotics”, “prevention” and “milk” suggests a growing interest in exploring the potential probiotic effects of Lactobacillus in caries prevention and management; (3) early childhood caries (ECC).

Information on the top ten highly cited articles is presented in Table 5. The most frequently cited article, with 376 citations, was a long-term clinical follow-up study of L. rhamnoses used in children with caries or high caries risk (45). The second most cited article, with 269 citations, was a study published in 2004 by Byun et al., which explored the genetic diversity of lactobacilli at advanced dental caries based on 16S ribosomal DNA technology (8).

The cariogenic virulence of Lactobacillus has been summarized in the literature (46–48). The cariogenic potential of Lactobacillus is primarily attributed to its acidogenicity, aciduricity, adhesion collagen properties, and biofilm-forming capacity (Figure 4). Lactobacilli possess a diverse array of enzymes, including glycoside hydrolases, glycosyltransferases, and isomerases, which enable them to metabolize a wide range of carbohydrates, particularly the oligosaccharides and starches abundant in the oral cavity, resulting in acid production (46, 49). Various Lactobacillus species, including L. plantarum, L.salivarius, L. rhamnosus, and L. casei/paracasei, have demonstrated the ability to reduce the pH to the critical threshold for enamel demineralization (pH 5.5) within 2.5–3 h (50). Lactobacillus species have evolved complex physiological and molecular mechanisms to survive and adapt to acid stress. These mechanisms include modifications to the cell membrane, activation of ATPase proton pumps, metabolic regulation, and the production of macromolecular protective and repair proteins (51). Lactobacillus species exhibit relatively limited biofilm formation capabilities and weak adhesion to healthy tooth surfaces (31, 52, 53). However, it is noteworthy that when S. mutans and/or other early colonizers establish retention sites, the biofilm formation of Lactobacillus significantly increases (31, 54).

From an epidemiological point of view, the abundance and diversity of Lactobacillus are closely related to caries risk. Based on previous literature (46, 54, 55), we further summarized the species of Lactobacillus detected at caries sites (Table 6). It can be seen that the types of Lactobacillus detected in different populations/individuals are different.

Although Lactobacillus is frequently detected in the mouths of children with dental caries, it has not yet been definitively proven that the high detection rate of Lactobacillus directly leads to the development of caries. Some views suggest that Lactobacillus does not possess the conditions necessary to cause caries. On the contrary, the high detection rate may be more of a passive result of Lactobacillus being retained at the site of the lesion after caries develops (53, 54, 56). Future research should further explore the causal relationship between Lactobacillus and caries, considering its potential multiple mechanisms of action.

In recent years, probiotics have gained increasing attention in the prevention and treatment of dental caries biofilms. Numerous in vitro, animal, and clinical studies have demonstrated the significant potential of Lactobacillus in anti-caries activity. We have summarized these studies in Table 7 for the reader's reference. Certain Lactobacillus strains might demonstrate protective effects against caries through the production of bacteriocin (21, 32, 70), hydrogen peroxide (H₂O₂) and organic acid (71), competitive adhesion and colonization (72), inhibition of cariogenic biofilms (32, 73), and regulation of the host immune system (32, 41, 74) (Figure 4).

It is important to note that while lactobacilli have been extensively studied and applied in the prevention of dental caries, the individual variability in its probiotic efficacy remains incompletely understood. Individual differences in oral microbiota, dietary habits, and genetic factors significantly influence the efficacy of lactobacilli (75), with notable variability observed across different age groups, regions, and health conditions, posing challenges for its clinical application. Moreover, the long-term safety of lactobacilli remains an unresolved concern. The acidogenic properties of Lactobacillus may exacerbate the acidic environment in the oral cavity under certain conditions, thereby promoting the occurrence and progression of dental caries (76). Additionally, the adhesive properties and biofilm-forming ability of Lactobacillus may, in some cases, synergize with other cariogenic bacteria, increasing the risk of oral microbial dysbiosis (31, 77). Therefore, although Lactobacillus exhibits probiotic effects in promoting oral health, its safety in clinical applications requires further evaluation, particularly in high-risk populations such as individuals with a history of dental caries or those with compromised immune function (78).

It is notable that a particular type of caries emerged in the keyword analysis: early childhood caries (ECC). ECC, defined as the existence of one or more decayed teeth that have been extracted or filled in children under the age of 6, is one of the most prevalent diseases worldwide among children of this age group (79). Research on the relationship between ECC and Lactobacillus can be divided into two main categories: one group explores the anti-caries effects of Lactobacillus on children with ECC, while the other investigates the load of Lactobacillus in the oral environment of children with ECC, such as in saliva and dental plaque (Table 8). ECC progresses rapidly and, similar to rampant caries, can progress rapidly to dentin (90). Lactobacillus has a high affinity for dentin collagen (91–93). We speculate that this may be the reason why more lactobacilli tend to be detected at ECC lesion sites.

This study is founded on a bibliometric analysis of the included studies, which inherently possesses several limitations. Firstly, there exists the potential for publication bias. Although the utilization of the WoSCC database contributes to ensuring the credibility and authority of the included data, it might also constrain the comprehensiveness of the information. Additionally, the publications selected for the bibliometric analysis were initially identified through pre-searching with a predefined search formula and then manually filtered. However, the process of data exportation and filtering might result in data loss, misidentification of articles, or other problems. Moreover, analysis software VOSviewer still has scope for improvement. For instance, synonymous entities, such as authors, institutions, and keywords, might fail to be precisely identified or discriminated, giving rise to circumstances where the same institution, author, or synonym is not accurately merged. Furthermore, only English-language studies were encompassed within this analysis, which could have resulted in an underrepresentation of research capabilities from non-English-speaking countries.