Insights into the human oral microbiome

Commensal and Pathogenic Biofilms Alter Toll-Like Receptor Signaling in Reconstructed Human Gingiva

The balance between the host and microbe is pivotal for oral health. A dysbiotic oral microbiome and the subsequent host inflammatory response are causes for the most common dental problems, such as periodontitis and caries. Classically, toll-like receptors (TLRs) are known to play important roles in host-microbe interactions by recognizing pathogens and activating innate immunity. However, emerging evidence suggests that commensals may also exploit TLRs to induce tolerance to the benefit of the host, especially in oral mucosa which is heavily colonized by abundant microbes. How TLRs and downstream signaling events are affected by different oral microbial communities to regulate host responses is still unknown. To compare such human host-microbe interactions in vitro, we exposed a reconstructed human gingiva (RHG) to commensal or pathogenic (gingivitis, cariogenic) multi-species oral biofilms cultured from human saliva. These biofilms contain in vivo like phylogenic numbers and typical bacterial genera. After 24 h biofilm exposure, TLR protein and gene expression of 84 TLR pathway related genes were investigated. Commensal and pathogenic biofilms differentially regulated TLR protein expression. Commensal biofilm up-regulated the transcription of a large group of key genes, which are involved in TLR signaling, including TLR7, the MyD88-dependent pathway (CD14, MyD88, TIRAP, TRAF6, IRAKs), MyD88-independent pathway (TAB1, TBK1, IRF3), and their downstream signaling pathways (NF-κB and MAPK pathways). In comparison, gingivitis biofilm activated fewer genes (e.g., TLR4) and cariogenic biofilm suppressed CD14, IRAK4, and IRF3 transcription. Fluorescence in situ hybridization staining showed the rRNA of the topically applied and invaded bacteria, and histology showed that the biofilms had no obvious detrimental effect on RHG morphology. These results show an important role of TLR signaling pathways in regulating host-microbe interactions: when a sterile gingival tissue is exposed to commensals, a strong immune activation occurs which may prime the host against potential challenges in order to maintain oral host-microbe homeostasis. In contrast, pathogenic biofilms stimulate a weaker immune response which might facilitate immune evasion thus enabling pathogens to penetrate undetected into the tissues.

Intraoral appliances for in situ oral biofilm growth: a systematic review

Background: Oral biofilms are the root cause of major oral diseases. As in vitro biofilms are not representative of the intraoral milieu, various devices have been manufactured over the years to develop Appliance Grown Oral Biofilm (AGOB). Objective: To review various intraoral appliances used to develop AGOB for microbiological analysis, and to judge the optimal means for such analyses. Design: Four databases (PubMed, Science Direct, Scopus and Medline) were searched by two independent reviewers, and articles featuring the key words 'device' OR 'splint' OR 'appliance'; 'Oral biofilm' OR 'dental plaque'; 'in vivo' OR 'in situ'; 'Microbiology' OR 'Bacteria' OR 'microbiome'; were included. The standard Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) were adopted for data gathering. Results: Of the 517 articles which met the initial inclusion criteria, 24 were deemed eligible for review. The age of the AGOB, sampled at various intervals, ranged from 30 min to 28 days. The most commonly used microbiome analytical methods were fluorescence microscopy, total cell count using conventional, and molecular tools including Next Generation Sequencing (NGS) platforms. Conclusions: No uniformly superior method for collecting AGOB could be discerned. NGS platforms are preferable for AGOB analyses.

Fusobacterium nucleatum, the communication with colorectal cancer

Colorectal cancer (CRC) is the fourth most common cancer in 2018 with poor prognosis. Fusobacterium nucleatum (F.n), an anaerobe, is found to be enriched in both stools and tumor tissues of CRC patients. As surveys show, tumor initiates before the collection of F.n. In return, F.n helps cancer cells to build up tumor microenvironment and benefit for their chemo-resistant. The elements constituted the tumor environment, including neutrophils, macrophages and lymphocytes, contribute to the existing of tumor cells respectively. However, the integrated and interactive roles of those elements are poorly investigated. The intracellular molecular alteration MSI is a result of F.n infection and the microbiology-molecular pathological epidemiology (MPE) has become a new trend to analysis F.n and tumorigenesis. Chemoresistance of tumor cells is also affected by F.n induced microenvironment, or F.n achieves it directly. Finally, F.n could be a biomarker of CRC. All in all, our review will lay a foundation for the therapy of CRC through the interference of F.n and perspective to follow-up studies.

[Therapeutic Relevance of Human Microbiota and Lung Cancer]

人体菌群与人类健康状态密切相关，如人体菌群的失调可能导致糖尿病、胃肠道疾病、肥胖等疾病的发生。人体内微生物与约20%的恶性肿瘤有关，肺癌（lung cancer, LC）是目前最为常见的恶性肿瘤之一，我国男性LC发病率及死亡率高居所有恶性肿瘤之首。近来研究表明，人体菌群可能通过代谢、炎症或免疫等途径影响着LC的发生，同时影响LC对放化疗、基因治疗、免疫治疗等治疗方法的疗效，如免疫治疗，是用于治疗LC的一种极有前景的手段，但不同患者从中获益不一，包含以肺癌细胞株的实验表明肠道微生物群可通过与宿主免疫系统的相互作用调节对免疫治疗的反应。但针对肺癌患者，肠道菌群是否仍能对免疫治疗进行调节仍存在争议。本文就人体菌群与LC的治疗相关性的近来研究进展进行综述。

Smoking and microbiome in oral, airway, gut and some systemic diseases

The human microbiome harbors a diverse array of microbes which establishes a mutually beneficial relation with the host in healthy conditions, however, the dynamic homeostasis is influenced by both host and environmental factors. Smoking contributes to modifications of the oral, lung and gut microbiome, leading to various diseases, such as periodontitis, asthma, chronic obstructive pulmonary disease, Crohn’s disease, ulcerative colitis and cancers. However, the exact causal relationship between smoking and microbiome alteration remains to be further explored.

Beyond Head and Neck Cancer: The Relationship Between Oral Microbiota and Tumour Development in Distant Organs

An altered oral microbiota has been linked with the development of several oral diseases, such as dental caries, periodontal disease, and oral stomatitis. Moreover, poor oral health has been linked to head and neck cancer, particularly oral cancer. In recent years a growing number of studies indicate that oral microbiota could be involved in the development of primary tumours outside of head and neck region. The aim of this article is to review the recent studies based on high-throughput technology to present evidences of a relationship between oral microbiota and "non-head and neck tumours." Oral dysbiosis seem to be more pronounced in patients with tumours of gastrointestinal tract, in particular oesophageal, gastric, pancreatic, and colorectal cancers, paving the way for developing specific oral microbiota test to allow early cancer detection. Regarding other tumour types, the results are promising but highly preliminary and still debated. Currently, there are several factors that limit the generalization of the results, such as the small sample size, the lack of adequate clinical information about patients, the different sequencing techniques used, and biological sample heterogeneity. Although only at the beginning, the analysis of oral microbiota could be the next step in the evolution of cancer therapy and will help clinicians to develop individualised approaches to cancer prevention and treatment.

Dysbiotic salivary microbiota in dry mouth and primary Sjögren's syndrome patients

Objectives

Primary Sjögren’s syndrome (pSS) is an autoimmune disease characterized by reduced lacrimal and salivary secretion. Sicca symptoms together with fatigue and musculoskeletal pain can significantly reduce the patients’ quality of life. Furthermore, low salivary secretion may disrupt the oral microbial homeostasis. The aim of this study was to compare the salivary microbiota from pSS patients with patients with sicca symptoms not fulfilling the classification criteria for pSS (non-SS), and with healthy controls without sicca complaints.

Methods

Pellets from centrifuged chewing-stimulated whole saliva from pSS patients (n = 15), non-SS sicca patients (n = 15) and healthy controls (n = 15) were prepared. DNA was extracted and analyzed by 16S rRNA gene sequencing. The acquired sequencing data were performed using the human oral microbiome database (HOMD).

Results

We detected 42, 45, and 34 bacterial genera in saliva samples from pSS patients, non-SS sicca patients, and healthy controls, respectively. The most abundant genera in all samples were Prevotella, Veillonella, Streptococcus, and Haemophilus. At species level Streptococcus intermedius, Prevotella intermedia, Fusobacterium nucleatum subsp. vincentii, Porphyromonas endodontalis, Prevotella nancensis, Tannerella spp., and Treponema spp. were detected in the samples from pSS and non-SS only, while Porphyromonas pasteri was mostly found among the healthy controls.

Conclusion

Our study indicated dysbiosis in the salivary microbiota from pSS and non-SS patients compared to healthy controls. Additionally, the results showed that the salivary microbiome in the pSS group differed significantly from the non-SS group.

A Multispecies Biofilm In Vitro Screening Model of Dental Caries for High-Throughput Susceptibility Testing

There is a current need to develop and optimize new therapeutics for the treatment of dental caries, but these efforts are limited by the relatively low throughput of relevant in vitro models. The aim of this work was to bridge the 96-well microtiter plate system with a relevant multispecies dental caries model that could be reproducibly grown to allow for the high-throughput screening of anti-biofilm therapies. Various media and inoculum concentrations were assessed using metabolic activity, biomass, viability, and acidity assays to determine the optimal laboratory-controlled conditions for a multispecies biofilm composed of Streptococcus gordonii, Streptococcus mutans, and Candida albicans. The selected model encompasses several of the known fundamental characteristics of dental caries-associated biofilms. The 1:1 RPMI:TSBYE 0.6% media supported the viability and biomass production of mono- and multispecies biofilms best. Kinetic studies over 48 h in 1:1 RPMI:TSBYE 0.6% demonstrated a stable biofilm phase between 10 and 48 h for all mono- and multispecies biofilms. The 1:1:0.1 S. gordonii: S. mutans: C. albicans multispecies biofilm in 1:1 RPMI:TSBYE 0.6% is an excellent choice for a high-throughput multispecies model of dental caries. This high-throughput multispecies model can be used for screening novel therapies and for better understanding the treatment effects on biofilm interactions and stability.

Inspection of the Microbiota in Endodontic Lesions

The primary objective of endodontic therapy is to create a biologically acceptable environment within the root canal system that allows for the healing and maintenance of the health of the peri-radicular tissue. Bacteria are one of the main causes of pulp problems, and they have different methods of penetrating and invading the endodontic space such as through carious lesions, traumatic pulp exposures, and fractures. The types of bacteria found range from facultative anaerobes to aerobes, up to the most resistant species able to survive in nutrient-free environments; the bacterial species Enterococcus faecalis belongs to this last group. Enterococcus faecalis is considered one of the main causes of recurring apical periodontal lesions following endodontic treatment, with persistent lesions occurring even after re-treatment. The review presented in this paper was performed in accordance with the PRISMA protocol and covers articles from the related scientific literature that were sourced from PubMed, Scopus, and Google Scholar using the following terms as keywords: “endodontic treatment”, “endodontic bacteria”, “microbial endodontic”, and “endodontic failure”. Only the articles considered most relevant for the purposes of this paper were read in full and taken into consideration for the following review. The results show that Enterococcus faecalis, Actinomycetes, and Propionibacterium propionicum are the species most frequently involved in persistent radicular and extra-radicular infections.

Commensal and Pathogenic Members of the Dental Calculus Microbiome of Badia Pozzeveri Individuals from the 11th to 19th Centuries

The concept of the human oral microbiome was applied to understand health and disease, lifestyles, and dietary habits throughout part of human history. In the present study, we augment the understanding of ancient oral microbiomes by characterizing human dental calculus samples recovered from the ancient Abbey of Badia Pozzeveri (central Italy), with differences in socioeconomic status, time period, burial type, and sex. Samples dating from the Middle Ages (11th century) to the Industrial Revolution era (19th century) were characterized using high-throughput sequencing of the 16S ribosomal RNA (rRNA) gene V4 region. Consistent with previous studies, individuals from Badia Pozzeveri possessed commensal oral bacteria that resembled modern oral microbiomes. These results suggest that members of the oral microbiome are ubiquitous despite differences in geographical regions, time period, sex, and socioeconomic status. The presence of fecal bacteria could be in agreement with poor hygiene practices, consistent with the time period. Respiratory tract, nosocomial, and other rare pathogens detected in the dental calculus samples are intriguing and could suggest subject-specific comorbidities that could be reflected in the oral microbiome.

Diversity-disease relationships and shared species analyses for human microbiome-associated diseases

Diversity indices have been routinely computed in the study of human microbiome-associated diseases (MADs). However, it is still unclear whether there is a consistent diversity-disease relationship (DDR) for the human MADs, and whether there are consistent differences in the taxonomic composition of microbiomes sampled from healthy versus diseased individuals. Here we reanalyzed raw data and used a meta-analysis to compare the microbiome diversity and composition of healthy versus diseased individuals in 41 comparisons extracted from 27 previously published studies of human MADs. In the DDR analysis, the average effect size across studies did not differ from zero for a comparison of healthy versus diseased individuals. In 30 of 41 comparisons (73%) there was no significant difference in microbiome diversity of healthy versus diseased individuals, or of different disease classes. For the species composition analysis (shared species analysis), the effect sizes were significantly different from zero. In 33 of 41 comparisons (80%), there were fewer OTUs (operational taxonomic units) shared between healthy and diseased individuals than expected by chance, but with 49% (20 of 41 comparisons) statistically significant. These results imply that the taxonomic composition of disease-associated microbiomes is often distinct from that of healthy individuals. Because species composition changes with disease state, some microbiome OTUs may serve as potential diagnostic indicators of disease. However, the overall species diversity of human microbiomes is not a reliable indicator of disease.

Spatial and Temporal Analysis of the Stomach and Small-Intestinal Microbiota in Fasted Healthy Humans

Although the microbiota in the proximal gastrointestinal (GI) tract have been implicated in health and disease, much about these microbes remains understudied compared to those in the distal GI tract. This study characterized the microbiota across multiple proximal GI sites over time in healthy individuals. As part of a study of the pharmacokinetics of oral mesalamine administration, healthy, fasted volunteers (n = 8; 10 observation periods total) were orally intubated with a four-lumen catheter with multiple aspiration ports. Samples were taken from stomach, duodenal, and multiple jejunal sites, sampling hourly (≤7 h) to measure mesalamine (administered at t = 0), pH, and 16S rRNA gene-based composition. We observed a predominance of Firmicutes across proximal GI sites, with significant variation compared to stool. The microbiota was more similar within individuals over time than between subjects, with the fecal microbiota being unique from that of the small intestine. The stomach and duodenal microbiota displayed highest intraindividual variability compared to jejunal sites, which were more stable across time. We observed significant correlations in the duodenal microbial composition with changes in pH; linear mixed models identified positive correlations with multiple Streptococcus operational taxonomic units (OTUs) and negative correlations with multiple Prevotella and Pasteurellaceae OTUs. Few OTUs correlated with mesalamine concentration. The stomach and duodenal microbiota exhibited greater compositional dynamics than the jejunum. Short-term fluctuations in the duodenal microbiota were correlated with pH. Given the unique characteristics and dynamics of the proximal GI tract microbiota, it is important to consider these local environments in health and disease states.IMPORTANCE The gut microbiota are linked to a variety of gastrointestinal diseases, including inflammatory bowel disease. Despite this importance, microbiota dynamics in the upper gastrointestinal tract are understudied. Our article seeks to understand what factors impact microbiota dynamics in the healthy human upper gut. We found that the upper gastrointestinal tract contains consistently prevalent bacterial OTUs that dominate the overall community. Microbiota variability is highest in the stomach and duodenum and correlates with pH.

The bare necessities: Uncovering essential and condition-critical genes with transposon sequencing

Querying gene function in bacteria has been greatly accelerated by the advent of transposon sequencing (Tn-seq) technologies (related Tn-seq strategies are known as TraDIS, INSeq, RB-TnSeq, and HITS). Pooled populations of transposon mutants are cultured in an environment and next-generation sequencing tools are used to determine areas of the genome that are important for bacterial fitness. In this review we provide an overview of Tn-seq methodologies and discuss how Tn-seq has been applied, or could be applied, to the study of oral microbiology. These applications include studying the essential genome as a means to rationally design therapeutic agents. Tn-seq has also contributed to our understanding of well-studied biological processes in oral bacteria. Other important applications include in vivo pathogenesis studies and use of Tn-seq to probe the molecular basis of microbial interactions. We also highlight recent advancements in techniques that act in synergy with Tn-seq such as clustered regularly interspaced short palindromic repeats (CRISPR) interference and microfluidic chip platforms.

Oral microbiome: Unveiling the fundamentals

The oral cavity has the second largest and diverse microbiota after the gut harboring over 700 species of bacteria. It nurtures numerous microorganisms which include bacteria, fungi, viruses and protozoa. The mouth with its various niches is an exceptionally complex habitat where microbes colonize the hard surfaces of the teeth and the soft tissues of the oral mucosa. In addition to being the initiation point of digestion, the oral microbiome is crucial in maintaining oral as well as systemic health. Because of the ease of sample collection, it has become the most well-studied microbiome till date. Previously, studying the microbiome was limited to the conventional culture-dependent techniques, but the abundant microflora present in the oral cavity could not be cultured. Hence, studying the microbiome was difficult. The emergence of new genomic technologies including next-generation sequencing and bioinformatics has revealed the complexities of the oral microbiome. It has provided a powerful means of studying the microbiome. Understanding the oral microbiome in health and disease will give further directions to explore the functional and metabolic alterations associated with the diseased states and to identify molecular signatures for drug development and targeted therapies which will ultimately help in rendering personalized and precision medicine. This review article is an attempt to explain the different aspects of the oral microbiome in health.

Keystone Species in Pregnancy Gingivitis: A Snapshot of Oral Microbiome During Pregnancy and Postpartum Period

It is well known that pregnancy is under the constant influence of hormonal, metabolic and immunological factors and this may impact the oral microbiota toward pregnancy gingivitis. However, it is still not clear how the oral microbial dysbiosis can modulate oral diseases as oral microbiome during pregnancy is very poorly characterized. In addition, the recent revelation that placental microbiome is akin to oral microbiome further potentiates the importance of oral dysbiosis in adverse pregnancy outcomes. Hence, leveraging on the 16S rRNA gene sequencing technology, we present a snapshot of the variations in the oral microbial composition with the progression of pregnancy and in the postpartum period and its association with pregnancy gingivitis. Despite the stability of oral microbial diversity during pregnancy and postpartum period, we observed that the microbiome makes a pathogenic shift during pregnancy and reverts back to a healthy microbiome during the postpartum period. Co-occurrence network analysis provided a mechanistic explanation of the pathogenicity of the microbiome during pregnancy and predicted taxa at hubs of interaction. Targeting the taxa which form the ecological guilds in the underlying microbiome would help to modulate the microbial pathogenicity during pregnancy, thereby alleviating risk for oral diseases and adverse pregnancy outcomes. Our study has also uncovered the possibility of novel species in subgingival plaque and saliva as the key players in the causation of pregnancy gingivitis. The keystone species hold the potential to open up avenues for designing microbiome modulation strategies to improve host health during pregnancy.

Mucins and Their Role in Shaping the Functions of Mucus Barriers

We review what is currently understood about how the structure of the primary solid component of mucus, the glycoprotein mucin, gives rise to the mechanical and biochemical properties of mucus that are required for it to perform its diverse physiological roles. Macroscale processes such as lubrication require mucus of a certain stiffness and spinnability, which are set by structural features of the mucin network, including the identity and density of cross-links and the degree of glycosylation. At the microscale, these same features affect the mechanical environment experienced by small particles and play a crucial role in establishing an interaction-based filter. Finally, mucin glycans are critical for regulating microbial interactions, serving as receptor binding sites for adhesion, as nutrient sources, and as environmental signals. We conclude by discussing how these structural principles can be used in the design of synthetic mucin-mimetic materials and provide suggestions for directions of future work in this field.

Comparison of initial oral microbiomes of young adults with and without cavitated dentin caries lesions using an in situ biofilm model

Dental caries is caused by acids released from bacterial biofilms. However, the in vivo formation of initial biofilms in relation to caries remains largely unexplored. The aim of this study was to compare the oral microbiome during the initial phase of bacterial colonization for individuals with (CC) and without (NC) cavitated dentin caries lesions. Bovine enamel slabs on acrylic splints were worn by the volunteers (CC: 14, NC: 13) for in situ biofilm formation (2 h, 4 h, 8 h, 1 ml saliva as reference). Sequencing of the V1/V2 regions of the 16S rRNA gene was performed (MiSeq). The relative abundances of individual operational taxonomic units (OTUs) were compared between samples from the CC group and the NC group. Random forests models were furthermore trained to separate the groups. While the overall heterogeneity did not differ substantially between CC and NC individuals, several individual OTUs were found to have significantly different relative abundances. For the 8 h samples, most of the significant OTUs showed higher relative abundances in the CC group, while the majority of significant OTUs in the saliva samples were more abundant in the NC group. Furthermore, using OTU signatures enabled a separation between both groups, with area-under-the-curve (AUC) values of ~0.8. In summary, the results suggest that initial oral biofilms provide the potential to differentiate between CC and NC individuals.

Insights into the Human Virome Using CRISPR Spacers from Microbiomes

Due to recent advances in next-generation sequencing over the past decade, our understanding of the human microbiome and its relationship to health and disease has increased dramatically. Yet, our insights into the human virome, and its interplay with important microbes that impact human health, is relatively limited. Prokaryotic and eukaryotic viruses are present throughout the human body, comprising a large and diverse population which influences several niches and impacts our health at various body sites. The presence of prokaryotic viruses like phages, has been documented at many different body sites, with the human gut being the richest ecological niche. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and associated proteins constitute the adaptive immune system of bacteria, which prevents attack by invasive nucleic acid. CRISPR-Cas systems function by uptake and integration of foreign genetic element sequences into the CRISPR array, which constitutes a genomic archive of iterative vaccination events. Consequently, CRISPR spacers can be investigated to reconstruct interplay between viruses and bacteria, and metagenomic sequencing data can be exploited to provide insights into host-phage interactions within a niche. Here, we show how the CRISPR spacer content of commensal and pathogenic bacteria can be used to determine the evidence of their phage exposure. This framework opens new opportunities for investigating host-virus dynamics in metagenomic data, and highlights the need to dedicate more efforts for virome sampling and sequencing.

Recurrent bacterial translocation from gut and sepsis in Head and neck cancer patients and its prevention by probiotics

Head and neck cancers are the 6th most common cancer type in human malignant tumors and treated with chemoradiotherapy and surgery. Chemotherapy during these treatment modalities leads to damage of intestinal epithelial barriers and results in translocation of intestinal bacteria in bloodstream through invasion in these damaged regions. In this report, we report two cases of hypopharyngeal cancer patients, both of whom received chemotherapy before surgery. The patients demonstrated repeated sepsis before and after surgery, supporting translocation of intestinal bacteria. Proper continuous probiotic use prevented proliferation and intestinal bacterial translocation. Hypothesis of bacterial translocation and prevention by probiotics are discussed.

Inhibitory activity of a green and black tea blend on Streptococcus mutans

Through the years, tea consumption has been associated with good health, and some publications are related to oral health. The bioactive components of green tea are thought to be able to influence the process of caries formation through inhibition of proliferation of the streptococcal agent, interference with the process of bacterial adhesion to tooth enamel, and inhibition of glucosyl transferase and amylase; however, little is known about black tea and oral health. The aim of the present in-vitro study was to determine the inhibitory activity of a novel, patent-pending and proprietary blend of green and black tea aqueous extracts on Streptococcus mutans, a bacterium widely associated with plaque development and tooth decay. A minimum inhibitory concentration (MIC) of 12.5 mg/mL and a minimum bactericidal concentration (MBC) of 12.5 mg/mL was established against S. mutans, meaning that at concentrations of 12.5 mg/mL and higher, the proprietary tea blend is effective against the growth of S. mutans. This MIC concentration is lower than the ones reported in the literature for alcoholic black tea and green tea extracts tested separately. As a promising natural ingredient for oral health, this finding is a good indicator for the use of this proprietary blend of black and green tea water extracts.

Early Childhood Caries: Epidemiology, Aetiology, and Prevention

Early childhood caries (ECC) is one of the most prevalent diseases in children worldwide. ECC is driven by a dysbiotic state of oral microorganisms mainly caused by a sugar-rich diet. Additionally, poor oral hygiene or insufficient dental plaque removal leads to the rapid progression of ECC. ECC leads not only to dental destruction and pain with children, but also affects the quality of life of the caregivers. Children with extensive ECC are at high risk to develop caries with the permanent dentition or will have other problems with speaking and/or eating. To prevent ECC, several strategies should be taken into account. Children should brush their teeth with toothpastes containing gentle ingredients, such as mild surfactants and agents showing antiadherent properties regarding oral microorganisms. Parents/caregivers have to help their children with brushing the teeth. Furthermore, remineralizing and nontoxic agents should be included into the toothpaste formulation. Two promising biomimetic agents for children's oral care are amorphous calcium phosphate [Ca_x(PO₄)_yn H₂O] and hydroxyapatite [Ca₅(PO₄)₃(OH)].