A study of the relationship between trace elements in saliva and dental caries in children

Mass spectrometry-based proteomic approaches for salivary protein biomarkers discovery and dental caries diagnosis: A critical review

Dental caries is a multifactorial chronic disease resulting from the intricate interplay among acid-generating bacteria, fermentable carbohydrates, and several host factors such as saliva. Saliva comprises several proteins which could be utilized as biomarkers for caries prevention, diagnosis, and prognosis. Mass spectrometry-based salivary proteomics approaches, owing to their sensitivity, provide the opportunity to investigate and unveil crucial cariogenic pathogen activity and host indicators and may demonstrate clinically relevant biomarkers to improve caries diagnosis and management. The present review outlines the published literature of human clinical proteomics investigations on caries and extensively elucidates frequently reported salivary proteins as biomarkers. This review also discusses important aspects while designing an experimental proteomics workflow. The protein-protein interactions and the clinical relevance of salivary proteins as biomarkers for caries, together with uninvestigated domains of the discipline are also discussed critically.

Metal mixtures and oral health among children and adolescents in the National Health and Nutrition Examination Survey (NHANES), 2017-2020

INTRODUCTION

Dental caries is the most common non-communicable human disease, yet little is known about the role of environmental metals, despite teeth consisting of a hard matrix of trace elements. We conducted a cross-sectional study of associations between environmental metals and objective assessment of dental caries and subjective assessments of oral health among a representative sample of U.S. children and adolescents.

METHODS

Data were from the 2017-March 2020 pre-pandemic data file of the National Health and Nutrition Examination Survey (NHANES). To account for metal mixtures, we used weighted quantile sum (WQS) regression to estimate the joint impact of multiple trace elements assessed in blood and urine with oral disease outcomes.

RESULTS

The blood metal mixture index was associated with a 32% (95% CI: 1.11, 1.56) increased risk of decayed surfaces while the urine metal mixture index was associated with a 106%, RR (95% CI = 2.06 (1.58, 2.70) increased caries risk. For both blood and urine, Mercury (Hg) had the largest contribution to the mixture index followed by Lead (Pb). The WQS blood metal mixture index was also significantly associated with poorer self-rated oral health, although the magnitude of the association was not as strong as for the objective oral disease measures, RR (95% CI) = 1.04 (1.02, 1.07).

DISCUSSION

Increased exposure to a metal mixture was significantly related to poorer objective and subjective oral health outcomes among U.S. children and adolescents. These are among the first findings showing that metal mixtures are a significant contributor to poor oral health.

Human saliva modifies growth, biofilm architecture, and competitive behaviors of oral streptococci

The bacteria within supragingival biofilms participate in complex exchanges with other microbes inhabiting the same niche. One example is the mutans group streptococci (Streptococcus mutans), implicated in the development of tooth decay, and other health-associated commensal streptococci species. Previously, our group transcriptomically characterized intermicrobial interactions between S. mutans and several species of oral bacteria. However, these experiments were carried out in a medium without human saliva. To better mimic their natural environment, we first evaluated how inclusion of saliva affected growth and biofilm formation of eight Streptococcus species individually and found saliva to positively benefit growth rates while negatively influencing biofilm biomass accumulation and altering spatial arrangement. These results carried over during evaluation of 29 saliva-derived isolates of various species. Surprisingly, we also found that addition of saliva increased the competitive behaviors of S. mutans in coculture competitions against commensal streptococci that led to increases in biofilm microcolony volumes. Through transcriptomically characterizing mono- and cocultures of S. mutans and Streptococcus oralis with and without saliva, we determined that each species developed a nutritional niche under mixed-species growth, with S. mutans upregulating carbohydrate uptake and utilization pathways while S. oralis upregulated genome features related to peptide uptake and glycan foraging. S. mutans also upregulated genes involved in oxidative stress tolerance, particularly manganese uptake, which we could artificially manipulate by supplementing in manganese leading to an advantage over its opponent. Our report highlights observable changes in microbial behaviors through leveraging environmental- and host-supplied resources over their competitors.

IMPORTANCE

Dental caries (tooth decay) is the most prevalent disease for both children and adults nationwide. Caries are initiated from demineralization of the enamel due to organic acid production through the metabolic activity of oral bacteria growing in biofilm communities attached to the tooth's surface. Mutans group streptococci are closely associated with caries development and initiation of the cariogenic cycle, which decreases the amount of acid-sensitive, health-associated commensal bacteria while selecting for aciduric and acidogenic species that then further drives the disease process. Defining the exchanges that occur between mutans group streptococci and oral commensals in a condition that closely mimics their natural environment is of critical need toward identifying factors that can influence odontopathogen establishment, persistence, and outgrowth. The goal of our research is to develop strategies, potentially through manipulation of microbial interactions characterized here, that prevent the emergence of mutans group streptococci while keeping the protective flora intact.

Salivary elemental signature of dental caries: a systematic review and meta-analysis of ionomics studies

Trace- and macro-chemical elements are crucial for cellular physiological functioning, and their alterations in biological fluids might be associated with an underlying pathological state. Hence, this study aimed to examine and summarize the published literature concerning the application of salivary ionomics for caries diagnosis. An extensive search of studies was conducted using PubMed, EMBASE, Web of Science, and Scopus, without any language and year restriction for answering the following PECO question: "In subjects (i.e., children, adolescents, or adults) with good systematic health, are there any variations in the salivary concentrations of trace- or macro-elements between caries-free (CF) individuals and caries-active (CA) subjects?" A modified version of the QUADOMICS tool was used to assess the quality of the included studies. The Review Manager Version 5.4.1. was used for data analyses. The analysis of salivary chemical elements that significantly differed between CF and CA subjects was also performed. Thirty-four studies were included, involving 2299 CA and 1669 CF subjects, having an age range from 3 to 64 years in over 16 countries. The meta-analysis revealed a statistically significant difference (p < 0.05) in the salivary levels of calcium, phosphorus, chloride, magnesium, potassium, sodium, and zinc between CA and CF subjects, suggesting higher levels of calcium, phosphorus, potassium, and sodium in CF subjects while higher levels of chloride, magnesium, and zinc in CA patients. Half of the included studies (17/34) were considered high quality, while the remaining half were considered medium quality. Only zinc and chloride ions were found to be higher significantly and consistent in CF and CA subjects, respectively. Conflicting outcomes were observed for all other salivary chemical elements including aluminum, bromine, calcium, copper, fluoride, iron, potassium, magnesium, manganese, sodium, ammonia, nitrite, nitrate, phosphorus, lead, selenium, and sulfate ions.

Environmental tobacco smoke exposure is associated with increased levels of metals in children's saliva

BACKGROUND

Exposure to environmental tobacco smoke (ETS) has been associated with detectable levels of cotinine (a nicotine metabolite) in children's saliva. However, tobacco smoke also contains toxic and essential trace metals, including chromium (Cr), copper (Cu), lead (Pb), manganese (Mn), nickel (Ni) and zinc (Zn).

OBJECTIVE

The current study examines whether there is a relationship between ETS exposure, as gauged by salivary cotinine, and salivary levels of these metals in a subset (n = 238) of children from the Family Life Project.

METHODS

Using inductively-coupled-plasma optical emission spectrophotometry, we measured levels of metals in saliva from children at ~90 months of age. Salivary cotinine was measured using a commercial immunoassay.

RESULTS

We found that Cr, Cu, Mn, and Zn were detected in most samples (85-99%) with lower levels of detection for Pb and Ni (9.3% and 13.9% respectively). There were no significant differences in any of the metal concentrations between males and females, nor were levels associated with body mass index, although significant differences in salivary Cr and Mn by race, state and income-to-needs ratio were observed. Children with cotinine levels >1 ng/ml had higher levels of Zn (b = 0.401, 95% CI: 0.183 to 0.619; p = 0.0003) and Cu (b = 0.655, 95% CI: 0.206 to 1.104; p = 0.004) compared to children with levels <1 ng/ml, after controlling for multiple confounders, including sex, race, BMI and income-to-needs ratio. Further, we show that children whose cotinine levels were >1 μg/L were more likely to have detectable levels of Pb in their saliva (b = 1.40, 95% CI: 0.424 to 2.459; p = 0.006) compared to children with cotinine levels <1 ng/ml, also considering confounders.

IMPACT STATEMENT

This is the first study to demonstrate significant associations between salivary cotinine and salivary levels of Cu, Zn and Pb, suggesting that environmental tobacco smoke exposure my be one source of increased children's exposure to heavy metals. This study also demonstrates that saliva samples can be used to measure heavy metal exposure, and thus serve as a non-invasive tool for assessing a broader range of risk indicators.

Human Saliva Modifies Growth, Biofilm Architecture and Competitive Behaviors of Oral Streptococci

The bacteria within supragingival biofilms participate in complex exchanges with other microbes inhabiting the same niche. One example are the mutans group streptococci (Streptococcus mutans), implicated in the development of tooth decay, and other health-associated commensal streptococci species. Previously, our group transcriptomically characterized intermicrobial interactions between S. mutans and several species of oral bacteria. However, these experiments were carried out in a medium that was absent of human saliva. To better mimic their natural environment, we first evaluated how inclusion of saliva affected growth and biofilm formation of eight streptococci species individually, and found saliva to positively benefit growth rates while negatively influencing biomass accumulation and altering spatial arrangement. These results carried over during evaluation of 29 saliva-derived isolates of various species. Surprisingly, we also found that addition of saliva increased the competitive behaviors of S. mutans in coculture competitions against commensal streptococci that led to increases in biofilm microcolony volumes. Through transcriptomically characterizing mono- and cocultures of S. mutans and Streptococcus oralis with and without saliva, we determined that each species developed a nutritional niche under mixed-species growth, with S. mutans upregulating carbohydrate uptake and utilization pathways while S. oralis upregulated genome features related to peptide uptake and glycan foraging. S. mutans also upregulated genes involved in oxidative stress tolerance, particularly manganese uptake, which we could artificially manipulate by supplementing in manganese to give it an advantage over its opponent. Our report highlights observable changes in microbial behaviors via leveraging environmental- and host-supplied resources over their competitors.

Small regulatory RNAs are mediators of the Streptococcus mutans SloR regulon

Dental caries is among the most prevalent chronic infectious diseases worldwide. Streptococcus mutans , the chief causative agent of caries, uses a 25 kDa manganese dependent SloR protein to coordinate the uptake of essential manganese with the transcription of its virulence attributes. Small non-coding RNAs (sRNAs) can either enhance or repress gene expression and reports in the literature ascribe an emerging role for sRNAs in the environmental stress response. Herein, we identify 18-50 nt sRNAs as mediators of the S. mutans SloR and manganese regulons. Specifically, the results of sRNA-seq revealed 56 sRNAs in S. mutans that were differentially transcribed in the SloR-proficient UA159 and SloR-deficient GMS584 strains, and 109 sRNAs that were differentially expressed in UA159 cells grown in the presence of low versus high manganese. We describe SmsR1532 and SmsR1785 as SloR- and/or manganese-responsive sRNAs that are processed from large transcripts, and that bind SloR directly in their promoter regions. The predicted targets of these sRNAs include regulators of metal ion transport, growth management via a toxin-antitoxin operon, and oxidative stress tolerance. These findings support a role for sRNAs in coordinating intracellular metal ion homeostasis with virulence gene control in an important oral cariogen.

IMPORTANCE

Small regulatory RNAs (sRNAs) are critical mediators of environmental signaling, particularly in bacterial cells under stress, but their role in Streptococcus mutans is poorly understood. S. mutans, the principal causative agent of dental caries, uses a 25 kDa manganese-dependent protein, called SloR, to coordinate the regulated uptake of essential metal ions with the transcription of its virulence genes. In the present study, we identified and characterize sRNAs that are both SloR- and manganese-responsive. Taken together, this research can elucidate the details of regulatory networks that engage sRNAs in an important oral pathogen, and that can enable the development of an effective anti-caries therapeutic.

A modified TEGDMA-based resin infiltrant using polyurethane acrylate oligomer and remineralising nano-fillers with improved physical properties and remineralisation potential

OBJECTIVES

This study aimed to modify an experimental triethylene glycol dimethacrylate (TEGDMA) based resin infiltrant using PUA oligomer and two remineralising fillers, including fluorohydroxyapatite (FHA) and fluoride-doped bioactive glass (FD-BG), to improve the mechanical and physical properties and induce remineralising potential.

MATERIALS AND METHODS

The polyurethane acrylate oligomer (PUA) was synthesised and characterised. Experimental resin infiltrant was prepared by mixing 10% of synthesised PUA with 88% TEGDMA. Water contact angle, penetration coefficient, and penetration depth were then measured. The FHA and FD-BG fillers were synthesised and characterised. To prepare nano-filled resin infiltrant, 5% of each powder was mixed with the prepared resin infiltrant. The prepared resin infiltrants were characterised to evaluate their degree of conversion, mechanical properties, water sorption, and solubility. The ion release of filled resin was also assessed. The non-infiltrated and infiltrated enamel specimens underwent fourteen days of pH-cycling, and a surface microhardness was done to assess the resistance to demineralisation.

RESULTS

The results showed that the addition of PUA to TEGDMA increased the mechanical properties and decreased water sorption and solubility. The addition of synthesised FD-BG fillers to resin infiltrant significantly improved the resistance to demineralisation of enamel samples compared with other groups (p ≤ 0.001). The FHA fillers also improved the resistance to demineralisation; however, the produced changes were not statistically meaningful (p > 0.05).

CONCLUSIONS

Based on the results, the PUA+TEGDMA+ FD-BG/FHA composite can be used as an alternative material for pure TEGDMA in enamel infiltration approaches owing to its better mechanical properties, lower water sorption and solubility, and also remineralisation potential.

CLINICAL SIGNIFICANCE

A resin infiltrant with remineralisation potential, lower water sorption and solubility and higher mechanical properties may enhance the management of early caries lesions.

Estimation of Copper Levels in Saliva and Its Relation to Dental Caries and Hemoglobin Levels

Context

A very small quantity of trace elements will be present in saliva. Salivary composition influences caries inhibition and promotion based on the different organic, inorganic, and trace elements.

Aim and objective

To evaluate the levels of copper in saliva in children with caries-active and caries-free group and to associate copper levels of saliva with hemoglobin (Hb) levels of blood.

Materials and methods

Sixty subjects between the ages of 6 and 14 years were divided into group I—caries-free and group II—caries-active. The caries-active group was further subdivided into group IIa (deft/DMFT < 3) and group IIb (deft/DMFT > 3). To maintain the uniformity of salivary composition, unstimulated saliva (5 mL) was collected in noontime before food from all the participants. The copper levels were estimated by atomic absorption spectrophotometry. Hemoglobin levels in the blood and their relation with copper levels in saliva were estimated.

Statistical analysis

The results thus obtained were analyzed by t-test and Karl Pearson's correlation coefficient. It was considered significant if the “p” value is 0.05 or less.

Results

Copper levels were higher in group II showing statistically highly significant results compared with that of group I with p ≤ 0.00001. The results were no significant with respect to Hb scores among the groups.

Conclusion

A definite positive correlation is seen with dental caries and levels of copper in saliva. Hence, the amount of copper in saliva can be considered as a caries risk assessment tool.

How to cite this article

Reddy VR, Devakar S, Chowdhary N, et al. Estimation of Copper Levels in Saliva and Its Relation to Dental Caries and Hemoglobin Levels. Int J Clin Pediatr Dent 2021;14(2):235–237.

Phosphorylation Impacts Cu(II) Binding by ATCUN Motifs

ATCUN (amino terminal Cu(II) and Ni(II) binding) motifs chelate Cu(II) ions strongly. However, the impact of the phosphorylation of neighboring residues on such complexation has not been elucidated. The copper(II) dissociation constants of original and phosphorylated peptides from human histatin-1 and human serum albumin were compared using spectroscopic methods. Phosphorylation markedly weakened Cu(II) binding. Thus, these results indicate that phosphorylation may be a vital mechanism governing metal ion binding.

The phosphorylation of serine residues within or nearby an ATCUN motif markedly weakens Cu(II) binding. It indicates that phosphorylation may be a vital mechanism of metal ion binding regulation.

The predictive power of saliva electrolytes exceeds that of saliva microbiomes in diagnosing early childhood caries

Early childhood caries (ECC) is one of the most prevalent chronic diseases affecting children worldwide, and thus its etiology, diagnosis, and prognosis are of particular clinical significance. This study aims to test the ability of salivary microbiome and electrolytes in diagnosing ECC, and their interplays within the same population. We here simultaneously profiled salivary microbiome and biochemical components of 331 children (166 caries-free (H group) and 165 caries-active children (C group)) aged 4-6 years. We identified both salivary microbial and biochemical dysbiosis associated with ECC. Remarkably, K⁺, Cl^-, NH₄⁺, Na⁺, SO₄^2-, Ca²⁺, Mg²⁺, and Br^- were enriched while pH and NO₃^- were depleted in ECC. Moreover, the dmft index (ECC severity) positively correlated with Cl^-, NH₄⁺, Ca²⁺, Mg²⁺, Br^-, while negatively with pH and NO₃^-. Furthermore, machine-learning classification models were constructed based on these biomarkers from saliva microbiota, or electrolytes (and pH). Unexpectedly, the electrolyte-based classifier (AUROC = 0.94) outperformed microbiome-based (AUROC = 0.70) one and the composite-based one (with both microbial and biochemical data; AUC = 0.89) in predicting ECC. Collectively, these findings indicate ECC-associated alterations and interplays in the oral microbiota, electrolytes and pH, underscoring the necessity of developing diagnostic models with predictors from salivary electrolytes.

Antimicrobial Peptides and Copper(II) Ions: Novel Therapeutic Opportunities

The emergence of new pathogens and multidrug resistant bacteria is an important public health issue that requires the development of novel classes of antibiotics. Antimicrobial peptides (AMPs) are a promising platform with great potential for the identification of new lead compounds that can combat the aforementioned pathogens due to their broad-spectrum antimicrobial activity and relatively low rate of resistance emergence. AMPs of multicellular organisms made their debut four decades ago thanks to ingenious researchers who asked simple questions about the resistance to bacterial infections of insects. Questions such as "Do fruit flies ever get sick?", combined with pioneering studies, have led to an understanding of AMPs as universal weapons of the immune system. This review focuses on a subclass of AMPs that feature a metal binding motif known as the amino terminal copper and nickel (ATCUN) motif. One of the metal-based strategies of hosts facing a pathogen, it includes wielding the inherent toxicity of copper and deliberately trafficking this metal ion into sites of infection. The sudden increase in the concentration of copper ions in the presence of ATCUN-containing AMPs (ATCUN-AMPs) likely results in a synergistic interaction. Herein, we examine common structural features in ATCUN-AMPs that exist across species, and we highlight unique features that deserve additional attention. We also present the current state of knowledge about the molecular mechanisms behind their antimicrobial activity and the methods available to study this promising class of AMPs.

Relationship of levels of trace elements in saliva and dental caries in preschool children using total reflection X-ray fluorescence technique (TXRF)⋆

BACKGROUND

Considering that studies on the relationship between dental caries and trace elements present contradictory and inconclusive results, the purpose of this study was to determine the levels of salivary trace elements in saliva samples of preschool children and investigate their relationship with dental caries.

METHODS

In total, 120 samples of unstimulated saliva were collected from children aged 36-72 months, of both sexes, who participate in the preventative educational program in oral health at the State University of Londrina, Brazil. The children were divided into two groups, caries (n = 60) and non-caries (n = 60). Levels of Al, Cu, Fe, Mn, and Zn were analyzed by total reflection X-ray fluorescence (TXRF). Descriptive statistics, the Student's t-test, Mann-Whitney U test, and Pearson's Chi-squared test were performed (P < 0.05).

RESULTS

The concentrations of Mn and Fe were significantly higher in the caries group (Mn =0.015 mg/L [0.007-0.020]; Fe =0.080 mg/L [0.031-0.239] than the non-caries group (Mn =0.010 mg/L [0.001 - 0.017]; Fe =0.044 mg/L [0.023 - 0.107]).

CONCLUSION

The results suggest a relationship between trace elements and dental caries, indicating possible involvement of these elements in the metabolism of microorganisms involved in the carious process. In addition, the use of TXRF presented satisfactory results, with a simple and fast methodology for the detection of the studied elements.

Changes in the salivary electrolytic dynamic after sucrose exposure in children with Early Childhood Caries

This study sought to explore if the effect of 20% sucrose rinse (SR) on the salivary electrolytic concentration of calcium (Ca2+), phosphate (Pi) and fluoride (F-) in children with Early Childhood Caries (ECC) is different from healthy children. Here, fifty-eight  preschoolers aged 3 to 5 years were divided into 2 groups: caries-free (CF) and with ECC. Changes in saliva flow rate, pH and buffering capacity (BC), as well as in concentrations of Ca2+, Pi, and F-, and the degree of saturation in relation to hydroxyapatite (DSS HAp) and fluorapatite (DSS FAp) were evaluated. The pre-rinse [Ca2+] was higher in the ECC group in the CF group. A significant increase in [Ca2+] was demonstrated after SR in the CF group (p = 0.05). The [Pi] was reduced by 18% after SR in the ECC group (p = 0.007). The [F-] reduced in both groups after SR (p < 0.000). There was a moderate positive correlation between [Ca2+] and the DSS HAp and DSS FAp. Multivariate analysis showed that children with a higher [Ca2+] in pre-rinse saliva are more likely to have ECC. In conclusion, the effect of a 20% sucrose rinse on the electrolytic concentration of Ca2+, Pi and F- was different when children with ECC were compared with CF children.

Manganese Uptake, Mediated by SloABC and MntH, Is Essential for the Fitness of Streptococcus mutans

Early epidemiological studies implicated manganese (Mn) as a possible caries-promoting agent, while laboratory studies have indicated that manganese stimulates the expression of virulence-related factors in the dental pathogen Streptococcus mutans To better understand the importance of manganese homeostasis to S. mutans pathophysiology, we first used RNA sequencing to obtain the global transcriptional profile of S. mutans UA159 grown under Mn-restricted conditions. Among the most highly expressed genes were those of the entire sloABC operon, encoding a dual iron/manganese transporter, and an uncharacterized gene, here mntH, that codes for a protein bearing strong similarity to Nramp-type transporters. While inactivation of sloC, which encodes the lipoprotein receptor of the SloABC system, or of mntH alone had no major consequence for the overall fitness of S. mutans, simultaneous inactivation of sloC and mntH (ΔsloC ΔmntH) impaired growth and survival under Mn-restricted conditions, including in human saliva or in the presence of calprotectin. Further, disruption of Mn transport resulted in diminished stress tolerance and reduced biofilm formation in the presence of sucrose. These phenotypes were markedly improved when cells were provided with excess Mn. Metal quantifications revealed that the single mutant strains contained intracellular levels of Mn similar to those seen with the parent strain, whereas Mn was nearly undetectable in the ΔsloC ΔmntH strain. Collectively, these results reveal that SloABC and MntH work independently and cooperatively to promote cell growth under Mn-restricted conditions and that maintenance of Mn homeostasis is essential for the expression of major virulence attributes in S. mutansIMPORTANCE As transition biometals such as manganese (Mn) are essential for all forms of life, the ability to scavenge biometals in the metal-restricted host environment is an important trait of successful cariogenic pathobionts. Here, we showed that the caries pathogen Streptococcus mutans utilizes two Mn transport systems, namely, SloABC and MntH, to acquire Mn from the environment and that the ability to maintain the cellular levels of Mn is important for the manifestation of characteristics that associate S. mutans with dental caries. Our results indicate that the development of strategies to deprive S. mutans of Mn hold promise in the combat against this important bacterial pathogen.

Investigations on the adhesion of new composites for restoring cervical lesions using energy dispersive X-ray analysis and scanning electron microscopy

Restoration of noncarious cervical lesions with resin composites is one of the treatment options, but the retention of the restorations located at the crown-root junction is still a cause of clinical concern. The aim of this study was to evaluate the adhesive properties of three experimental resin composites and two commercial materials used to restore cavities prepared on extracted teeth as well as to determine the relative elemental composition of these materials. We tested the null hypothesis, which considered that the adhesive behaviours of different resin composites did not differ. The microleakage test using tracers showed that all tested materials exhibited some degree of dentinal microleakage, although they all had good dentinal adhesion. The results failed to reject the null hypothesis. The scanning electron microscopy revealed completely adapted adhesive interfaces underneath the restorations along with well-developed hybrid layers depending on the adhesive system. Energy dispersive X-ray analysis analyses showed that the restorative materials have similar chemical compositions, with some differences between the samples from the same material. The results support the implementation of experimental resins in clinical settings.

The Role and Impact of Salivary Zn Levels on Dental Caries

Introduction

Minimal attention has been given to the role of salivary microelements, the importance they have in reducing the intensity of caries, and the effect of caries prophylaxes.

Aim

This research aimed to determine the concentration and quantity of Zn and its impact on the prevention and the reduction of the intensity of caries in schoolchildren aged 12-13 years with permanent dentition.

Methods

For this research, we analyzed the stimulated and nonstimulated full saliva of 106 schoolchildren divided into three groups by mean decayed, missing, and filled teeth (DMFT) index. The control group consisted of 25 caries-free children, the second group had 47 children with mean DMFT index of 1 to 6, and the third group had 34 children with DMFT index of ≥ 6. Complete saliva was collected from all children in a sterile test tube.

Results

The concentration of Zn in saliva before stimulation in caries-free children has variations of the order of 0.001+ to 0.01 mmol/l. The maximum concentration after stimulation is 6.72 mmol/l, while the maximum value is 64.38 mmol/l.

Conclusion

The Zn concentration in the stimulated saliva showed a significant increase in the group of caries-free children and could be described as a positive value for the reduction of caries.

The Effect of Copper on Demineralization of Dental Enamel

Previous studies have concluded that copper might inhibit enamel demineralization in vitro. Our aim was to assess the effect of copper (Cu2+), with and without amine fluoride, on human dental enamel under cariogenic challenge in situ. In a double-blind randomized four-leg crossover trial, 14 individuals wore a removable appliance containing 2 enamel slabs, 1 containing an artificial caries lesion. During each leg, the appliance was exposed twice daily to one of the test solutions: 1.25 mM CuSO4, amine fluoride (250 ppm F), copper and amine fluoride combined, or a placebo (water). A cariogenic challenge was provided in all cases by 5 daily exposures to 10% sucrose. Slabs were assessed before and after 21 days’ exposure by Knoop microhardness and transverse microradiography. Significantly less demineralization was observed with Cu2+ and fluoride in combination than with fluoride treatment alone (p < 0.05), whereas copper alone had no significant protective effect.

Cytotoxicity of Experimental Resin Composites on Mesenchymal Stem Cells Isolated from Two Oral Sources

Resin composite materials that are used to restore tooth cervical lesions associated with gingival recessions can hamper healing after root coverage surgeries. This study evaluates the in vitro cytotoxic effect of five resin composites (two commercial and three experimental) on oral mesenchymal stem cells (MSCs) and the persistence of stemness properties in high passage MSCs. Sorption and solubility tests were made for all materials. MSCs were isolated from re-entry palatal and periodontal granulation tissues and were characterized and cultured on composite discs. Cytotoxicity of the materials was evaluated by the Alamar Blue viability test, by Paul Karl Horan (PKH) labeling, and by immunocytochemical staining for actin. Water and saliva sorption and solubility data revealed that two of the experimental materials behaved comparable with the marketed resin composites. The Alamar Blue viability test shows that both cell lines grew well on composite discs that seemed to induce no apparent toxic effects. No signs of disruption of cytoskeleton organization was seen. Experimental resin composites can be recommended for further investigation for obtaining approval for use. The standard minimal criteria were fulfilled for high passage MSCs. Palatal tissue regains its regenerative properties in terms of MSC presence in the re-entry area after 6 months of healing.

Streptococcus mutans copper chaperone, CopZ, is critical for biofilm formation and competitiveness

The oral cavity is a dynamic environment characterized by hundreds of bacterial species, saliva, and an influx of nutrients and metal ions such as copper. Although there is a physiologic level of copper in the saliva, the oral cavity is often challenged with an influx of copper ions. At high concentrations copper is toxic and must therefore be strictly regulated by pathogens for them to persist and cause disease. The cariogenic pathogen Streptococcus mutans manages excess copper using the copYAZ operon that encodes a negative DNA-binding repressor (CopY), the P1-ATPase copper exporter (CopA), and the copper chaperone (CopZ). These hypothetical roles of the copYAZ operon in regulation and copper transport to receptors led us to investigate their contribution to S. mutans virulence. Mutants defective in the copper chaperone CopZ, but not CopY or CopA, were impaired in biofilm formation and competitiveness against commensal streptococci. Characterization of the CopZ mutant biofilm revealed a decreased secretion of glucosyltransferases and reduced expression of mutacin genes. These data suggest that the function of copZ on biofilm and competitiveness is independent of copper resistance and CopZ is a global regulator for biofilm and other virulence factors. Further characterization of CopZ may lead to the identification of new biofilm pathways.

Caries prevalence and manganese and iron levels of drinking water in school children living in a rural/semi-urban region of North-Eastern Greece

OBJECTIVE

The aim of this study was to correlate different combinations of manganese (Mn) and iron (Fe) concentration in drinking water with prevalence of dental caries in both primary and permanent dentition, among school children with similar socio-demographic characteristics.

METHODS

Evros region, in North-Eastern Greece, was divided into four areas, according to combinations of levels of Mn and Fe in drinking water (High Mn-high Fe; High Mn-low Fe; Low Mn-high Fe; Low Mn-low Fe). Children of similar socio-economic background, attending either first or sixth grade (primary or permanent dentition, respectively) of elementary schools, were clinically assessed for caries by three dentists. Caries was defined by the use of dmft/DMFT index. A questionnaire answered by the parents was also analysed.

RESULTS

573 children were included. Caries prevalence was high in both age groups (64.2 % with mean dmft 3.3 ± 3.6 in primary and 60.7 % with mean DMFT 2.3 ± 2.5 in permanent dentition, respectively). Residence in a high Mn-low Fe area was associated with a significant OR for caries in both age groups [OR (95 % CIs) for primary and permanent dentition was, respectively, 3.75 (1.68-8.37), p = 0.001 and 3.09 (1.48-6.44), p = 0.003], independently of factors like sugar consumption or brushing frequency.

CONCLUSION

Prevalence of caries was high in general, and was associated with the combination of high Mn/low Fe levels in drinking water, independently of various socio-demographic factors.

Toxicological importance of human biomonitoring of metallic and metalloid elements in different biological samples

Human biomonitoring has become an important tool for the assessment of internal doses of metallic and metalloid elements. These elements are of great significance because of their toxic properties and wide distribution in environmental compartments. Although blood and urine are the most used and accepted matrices for human biomonitoring, other non-conventional samples (saliva, placenta, meconium, hair, nails, teeth, breast milk) may have practical advantages and would provide additional information on health risk. Nevertheless, the analysis of these compounds in biological matrices other than blood and urine has not yet been accepted as a useful tool for biomonitoring. The validation of analytical procedures is absolutely necessary for a proper implementation of non-conventional samples in biomonitoring programs. However, the lack of reliable and useful analytical methodologies to assess exposure to metallic elements, and the potential interference of external contamination and variation in biological features of non-conventional samples are important limitations for setting health-based reference values. The influence of potential confounding factors on metallic concentration should always be considered. More research is needed to ascertain whether or not non-conventional matrices offer definitive advantages over the traditional samples and to broaden the available database for establishing worldwide accepted reference values in non-exposed populations.

Avaliação da microdureza do esmalte de dentes decíduos de crianças com paralisia cerebral

INTRODUÇÃO: Em indivíduos com paralisia cerebral, ocorre redução do fluxo salivar, o que pode predispor à hipomineralização do esmalte e à cárie dentária. OBJETIVO: Comparar a microdureza do esmalte de dentes decíduos anteriores e posteriores de crianças com paralisia cerebral (PC) e crianças normorreativas (NR). MATERIAL E MÉTODO: Foram utilizados 58 dentes decíduos esfoliados/extraídos, que foram distribuídos em quatro grupos: (A) anteriores de PC (n=14); (B) anteriores de NR (n=16); (C) posteriores de PC (n=14), e (D) posteriores de NR (n=14). Os dentes foram seccionados, incluídos em resina acrílica, lixados e polidos. A análise da microdureza longitudinal foi realizada em microdurômetro com endentador do tipo Knoop, com carga estática de 25 g/f e tempo de 5 segundos. Foram realizadas três fileiras de 12 endentações, distanciadas entre si em 100 mm, com profundidade entre 10 e 180 mm. Foram obtidas as médias de cada profundidade para cada dente e, posteriormente, as médias de cada profundidade para cada grupo avaliado. O teste estatístico empregado foi o de Mann-Whitney (α=5%). RESULTADO: As médias de microdureza foram 253,5 ± 55,3 (A), 247,6 ± 45,7 (B), 284,4 ± 68,7 (C) e 252,2 ± 53,8 (D). Não houve diferença estatisticamente significante entre os grupos A e B e os grupos C e D, para cada profundidade e para a média global (p>0,05). CONCLUSÃO: Pôde-se concluir que a microdureza de esmalte de dentes decíduos anteriores e posteriores de crianças com PC foi semelhante à microdureza de esmalte de dentes decíduos de crianças normorreativas.

The effect of social stress on salivary trace elements

Social stress can alter the saliva in favor of metabolism of trace elements. This study aimed to assess the effect of social stress on salivary copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) contents in dental students before and after a comprehensive English test. Twelve students with an average age of 27 years were selected from three dental schools. The students were carries-free, and salivary samples were collected 1 week before the test day and right before the comprehensive English test. Unstimulated saliva was collected from the participants. The pH of the saliva samples was measured using a portable pH meter, and the salivary trace element contents were determined using an atomic absorption spectrophotometer. After checking data to be normally distributed, Student's paired t test was used for statistical analysis. Salivary pH significantly increased right before the English test. Salivary Cu concentration decreased in students after the test (P > 0.05). The level of Zn, Mn, and Fe increased, while only Mn change was statistically significant (P < 0.001). Under the limitations of this study, induction of social stress led to a significant increase in Mn concentration in the saliva. The salivary Cu, Zn, and Fe contents, however, did not exhibit significant changes. Changes in salivary inorganic trace element content, as a result of physiological stress, might influence health of teeth, enamel, and oral mucosal tissues.

Iron binding modulates candidacidal properties of salivary histatin 5

Salivary protein histatin 5 (Hst 5) is fungicidal toward Candida albicans, the causative agent of oropharyngeal candidiasis. However, its activity in saliva is compromised by salivary protease-mediated degradation and interaction with salivary salts. Hst 5 has also been shown to bind various metals in saliva-namely, Zn, Cu, and Ni. Surprisingly, interactions of Hst 5 with Fe have not been studied, although iron is one of the most abundant metals present in saliva. Using circular dichroism, we show that Hst 5 can bind up to 10 equivalents of iron as measured by loss of its alpha-helical secondary structure that is normally observed for it in trifluoroethylene. A significant decrease in the candidacidal ability of Hst 5 was observed upon iron binding, with increasing iron concentrations being inversely proportional to Hst 5 killing activity. Binding assays showed that the decrease in killing was likely a result of reduced binding (10-fold reduction) of Fe-Hst 5 to C. albicans cells. Protease stability analysis showed that Fe-Hst 5 was completely resistant to trypsin digestion. In contrast, zinc binding had limited effects on Hst 5 fungicidal activity or protease susceptibility. RNA sequencing results identified changes in iron uptake genes in Hst 5-treated C. albicans cells. Our findings thus suggest that consequences of Hst 5 binding iron not only affect candidacidal ability and proteolyic stability of Hst 5, but may also contribute to a novel killing mechanism involving interference with cellular iron metabolism.

Ion release from, and fluoride recharge of a composite with a fluoride-containing bioactive glass

OBJECTIVES

Materials that are capable of releasing ions such as calcium and fluoride, that are necessary for remineralization of dentin and enamel, have been the topic of intensive research for many years. The source of calcium has most often been some form of calcium phosphate, and that for fluoride has been one of several metal fluoride or hexafluorophosphate salts. Fluoride-containing bioactive glass (BAG) prepared by the sol-gel method acts as a single source of both calcium and fluoride ions in aqueous solutions. The objective of this investigation was to determine if BAG, when added to a composite formulation, can be used as a single source for calcium and fluoride ion release over an extended time period, and to determine if the BAG-containing composite can be recharged upon exposure to a solution of 5000ppm fluoride.

METHODS

BAG 61 (61% Si; 31% Ca; 4% P; 3% F; 1% B) and BAG 81 (81% Si; 11% Ca; 4% P; 3% F; 1% B) were synthesized by the sol-gel method. The composite used was composed of 50/50 Bis-GMA/TEGDMA, 0.8% EDMAB, 0.4% CQ, and 0.05% BHT, combined with a mixture of BAG (15%) and strontium glass (85%) to a total filler load of 72% by weight. Disks were prepared, allowed to age for 24h, abraded, then placed into DI water. Calcium and fluoride release was measured by atomic absorption spectroscopy and fluoride ion selective electrode methods, respectively, after 2, 22, and 222h. The composite samples were then soaked for 5min in an aqueous 5000ppm fluoride solution, after which calcium and fluoride release was again measured at 2, 22, and 222h time points.

RESULTS

Prior to fluoride recharge, release of fluoride ions was similar for the BAG 61 and BAG 81 composites after 2h, and also similar after 22h. At the four subsequent time points, one prior to, and three following fluoride recharge, the BAG 81 composite released significantly more fluoride ions (p<0.05). Both composites were recharged by exposure to 5000ppm fluoride, although the BAG 81 composite was recharged more than the BAG 61 composite. The BAG 61 composite released substantially more calcium ions prior to fluoride recharge during each of the 2 and 22h time periods. Thereafter, the release of calcium at the four subsequent time points was not significantly different (p>0.05) for the two composites.

SIGNIFICANCE

These results show that, when added to a composite formulation, fluoride-containing bioactive glass made by the sol-gel route can function as a single source for both calcium and fluoride ions, and that the composite can be readily recharged with fluoride.

Impact of an anticaries mouthrinse on in vitro remineralization and microbial control

Objective. The objective of this research was to evaluate the caries control potential of a new fluoride mouthrinse that also contained antimicrobial agents and a biofilm disrupting agent using different in vitro models. Methods. Four in vitro studies were conducted to assess the performance of this three pronged approach to caries control: (1) traditional enamel fluoride uptake, (2) surface microhardness study using pH cycling model and subsequent fluoride uptake, (3) a salivary biofilm flow-through study to determine the anti-microbial activity, and (4) a single species biofilm model measuring effect on biofilm matrix disruption. Results. The data showed that a LISTERINE rinse with fluoride, essential oils and xylitol was superior in promoting enamel fluoride uptake and in enhancing antimicrobial activity over traditional commercially available fluoridated products. An increase of the surface microhardness was observed when the LISTERINE rinse was used in combination with fluoridated toothpaste versus the fluoridated toothpaste alone. Finally, it was demonstrated that xylitol solutions disrupted and reduced the biovolume of biofilm matrix of mature Streptococcus mutans. Conclusion. These in vitro studies demonstrated that a fluoride mouthrinse with antimicrobial agent and biofilm matrix disrupting agent provided multifaceted and enhanced anti-caries efficacy by promoting remineralization, reducing acidogenic bacteria and disrupting biofilm matrix.

Trace elements can influence the physical properties of tooth enamel

In previous studies, we showed that the size of apatite nanocrystals in tooth enamel can influence its physical properties. This important discovery raised a new question; which factors are regulating the size of these nanocrystals? Trace elements can affect crystallographic properties of synthetic apatite, therefore this study was designed to investigate how trace elements influence enamel's crystallographic properties and ultimately its physical properties. The concentration of trace elements in tooth enamel was determined for 38 extracted human teeth using inductively coupled plasma-optical emission spectroscopy (ICP-OES). The following trace elements were detected: Al, K, Mg, S, Na, Zn, Si, B, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se and Ti. Simple and stepwise multiple regression was used to identify the correlations between trace elements concentration in enamel and its crystallographic structure, hardness, resistance to crack propagation, shade lightness and carbonate content. The presence of some trace elements in enamel was correlated with the size (Pb, Ti, Mn) and lattice parameters (Se, Cr, Ni) of apatite nanocrystals. Some trace elements such as Ti was significantly correlated with tooth crystallographic structure and consequently with hardness and shade lightness. We conclude that the presence of trace elements in enamel could influence its physical properties.

Saliva fluoride before and during 3 years of supervised use of fluoride toothpaste

OBJECTIVES

The purpose of the study was to examine pre-brushing saliva fluoride concentrations before and during a large, 3-year, prospective toothpaste study on the effect of post-brushing rinsing on dental caries. The aims were to study saliva fluoride over time and the effect of rinsing on saliva fluoride and to relate saliva fluoride to caries increments and accumulation of plaque.

MATERIALS AND METHODS

Saliva samples (baseline and 1, 2, and 3 years) were collected from 11-year-old children attending two schools (A and B) in Kaunas, Lithuania, who refrained from brushing the evening and morning before saliva collection. Numbers of saliva samples collected varied from 264 at baseline to 188 at the 3-year follow-up. Children in school A rinsed with water after daily brushing, while children in school B did not rinse. Total caries and visible plaque were registered at baseline and after 3 years.

RESULTS

Mean saliva fluoride concentrations at baseline and after 1, 2, and 3 years from school A (rinsing) were 0.014, 0.026, 0.029, and 0.034 ppm and from school B (no rinsing) were 0.013, 0.028, 0.031, and 0.031 ppm, respectively. Increases in saliva fluoride from baseline were significant (Wilcoxon's test, p < 0.001), but the increase from baseline to year 1 was not statistically significantly different between schools. Saliva fluoride did not increase beyond year 1 and did at no time point differ between schools. Reductions in numbers of tooth surfaces with dental plaque were significantly positively related to the number of caries reversals over the 3 years.

CONCLUSIONS

Background saliva fluoride concentration is increased by brushing at least once daily on schooldays, does not increase further over 3 years, and is not affected by rinsing after brushing.

CLINICAL RELEVANCE

Continuous use of fluoride toothpaste produces ambient saliva fluoride levels similar to saliva fluoride in areas with fluoridated water.

Al and Fe levels in mixed saliva of children related to elution behavior from teeth and restorations

OBJECTIVES

The levels of trace elements in mixed saliva were not well-defined. This study was performed to determine Al and Fe concentrations in mixed saliva of children and to investigate the relationship between these levels and dental caries.

METHODS

Among 562 collected mixed saliva specimens, 514 and 548 samples for analyses of Al and Fe levels were obtained, respectively. The Al and Fe concentrations were determined using flameless atomic absorption spectrometry.

RESULTS

The Al and Fe concentrations in children without a history of caries were 0.093±0.136 and 0.121±0.128 μg/mL, respectively. The Fe level depended on sex. The Fe level in girls who experienced caries was significantly higher than that without caries history. The Al and Fe levels were significantly higher in children with treated caries than children without caries history. The Fe concentrations were affected by restoration type. Composite resin increased the Fe level significantly especially in girls, and the Fe level was also higher in boys treated with both composite resin and metal restorations. In children without caries history, the Al level was inversely proportional to the number of deciduous teeth and increased with the number of permanent teeth. In contrast, the Fe level showed the reverse tendency.

CONCLUSIONS

The Fe level in mixed saliva of children was influenced by the restoration type. It was suggested that Al was eluted more from sound permanent teeth than sound deciduous teeth, while Fe was eluted in the opposite manner.

Biomonitorization of cadmium, chromium, manganese, nickel and lead in whole blood, urine, axillary hair and saliva in an occupationally exposed population

Heavy metal contamination from occupational origin is a cause for concern because of its potential accumulation in the environment and in living organisms leading to long term toxic effects. This study was aimed to assess Cd, Cr, Mn, Ni and Pb levels in whole blood, urine, axillary hair and saliva from 178 individuals with occupational exposure to heavy metals. Levels of metal compounds were determined by atomic absorption spectrometry. We collected information on occupation, lifestyle habits and food intake by questionnaire. Multiple linear regression analyses for metal ion concentration in whole blood, urine, axillary hair and saliva were adjusted for age, gender, smoking and alcohol consumption, lifetime workplace exposure, residence area and food habits. Overall, blood and urine median concentrations found for the five metals analyzed do not exceed biological exposure indexes, so that they are very similar to a non-occupationally exposed population. Toxicokinetic differences may account for the lack of correlations found for metal levels in hair and saliva with those in blood or urine. For those heavy metals showing higher median levels in blood with respect to hair (Cd, Mn and Pb) indicating lesser hair incorporation from blood, the lifetime working experience was inversely correlated with their hair levels. The longer the lifetime working experience in industrial environments, the higher the Mn and Ni concentration in saliva. Axillary hair and saliva may be used as additional and/or alternative samples to blood or urine for biomonitoring hair Mn, and saliva Ni in subjects with occupational exposure.

A review of slow-release fluoride devices

BACKGROUND

Fluoride has been used to combat dental caries using a number of different clinical approaches. An exciting relatively new development is fluoride slow-releasing devices that consistently elevate intra-oral fluoride levels of plaque and saliva for prolonged periods of up to two years.

METHODS

The literature on the use of slow-releasing fluoride devices in dentistry were reviewed. A Medline search on key words was carried out. All papers in English were individually reviewed.

RESULTS

Slow-releasing fluoride devices have been shown to be effective in elevating salivary fluoride levels in both animals and human studies and to enhance the remineralisation of dental enamel. They have been demonstrated to be safe to use and without the risk of fluoride toxicity. A double blind randomised clinical trial demonstrated 76% fewer new carious surface increment in high caries-risk children after two years.

CONCLUSIONS

These devices have a number of potential uses in dentistry and in particular have great potential for caries prevention of non-compliant high caries-risk groups.

Mn and Cu concentrations in mixed saliva of elementary school children in relation to sex, age, and dental caries

To examine the standard Mn and Cu concentrations in mixed saliva from children and the relationship between these levels and dental caries, resting mixed saliva samples obtained from 527 children of an elementary school in Kitakyushu City were collected at 10:00-11:30 a.m. during December 2004. The Mn and Cu concentrations were determined using simultaneous multi-element atomic absorption spectrometry. The standard Mn and Cu levels were 22.0+/-15.2 and 3.8+/-4.1ng/mL, respectively, in the sound teeth group. Mn levels were significantly higher in boys (25.4+/-17.4ng/mL) than girls (19.1+/-12.3ng/mL) and also higher in upper (25.5+/-16.4ng/mL) than lower (19.0+/-13.5ng/mL) grades. The Cu level was unaffected by sex and age in the sound teeth group. The Cu level in children with caries experience (5.7+/-5.3ng/mL) was significantly higher than that of the sound teeth group. Moreover, the Cu levels in children with untreated caries were significantly higher than that of the sound teeth group, and increased with the number of untreated teeth. No significant difference was found in the Cu concentrations between the group in which all decayed teeth were treated and the sound teeth group. The Mn levels were similar with or without caries and treatment. These findings indicate that the Mn level in mixed saliva depended on sex and age, and suggest the possibility of Cu dissolving into mixed saliva by demineralization due to dental caries.

Study of salivary strontium and silver concentrations in primary school children related to dental caries

To investigate the relationship between the salivary Sr and Ag concentrations and tooth conditions, saliva was collected from 521 primary school children in Kitakyushu. The salivary Sr and Ag levels were determined using an atomic absorption spectrophotometry. The salivary Sr and Ag levels were 7.73 +/- 3.62 and 0.03 +/- 0.15 ng/ml, respectively, in the sound teeth group. No sex differences were noted in either element level, nor were there differences between the lower and upper grade groups. In the caries teeth group, the Sr and Ag levels were significantly higher than those in the sound teeth group. The Sr level was significantly increased by caries experience regardless caries being treated or untreated. In second to third grade children, in whom the fluoride experience rate was high, the Sr level tended to be lower than that in the other grades. The salivary Ag level increased as the number of teeth treated with silver alloy rose. These findings suggested that the salivary Sr level increases because of caries susceptibility, and F inhibits Sr dissolution from the teeth. The salivary Ag level varied depending on the type of dental filling and was dependent on the amount of silver alloy in children treated with low-fusing silver alloy.

Effects of manganese on Streptococcus mutans planktonic and biofilm growth

Streptococcus mutans, an agent of dental caries, was tested for growth in the presence or absence of manganese (Mn), since studies have linked Mn levels with cariogenic potential. Seven S. mutans serotype c strains were grown in chemically defined medium under different atmospheric conditions: 5% CO2, O2-enriched 5% CO2 (shaking) and anaerobic. There was significant strain variability with respect to Mn requirements under the various conditions tested. Both sucrose-dependent and sucrose-independent biofilm growth by strain UA159 were affected by the absence of Mn. S. mutans strains show highly variable responses to both high and low Mn concentrations.

Review on fluoride-releasing restorative materials--fluoride release and uptake characteristics, antibacterial activity and influence on caries formation

OBJECTIVES

The purpose of this article was to review the fluoride release and recharge capabilities, and antibacterial properties, of fluoride-releasing dental restoratives, and discuss the current status concerning the prevention or inhibition of caries development and progression.

METHODS

Information from original scientific full papers or reviews listed in PubMed (search term: fluoride release AND (restorative OR glass-ionomer OR compomer OR polyacid-modified composite resin OR composite OR amalgam)), published from 1980 to 2004, was included in the review. Papers dealing with endodontic or orthodontic topics were not taken into consideration. Clinical studies concerning secondary caries development were only included when performed in split-mouth design with an observation period of at least three years.

RESULTS

Fluoride-containing dental materials show clear differences in the fluoride release and uptake characteristics. Short- and long-term fluoride releases from restoratives are related to their matrices, setting mechanisms and fluoride content and depend on several environmental conditions. Fluoride-releasing materials may act as a fluoride reservoir and may increase the fluoride level in saliva, plaque and dental hard tissues. However, clinical studies exhibited conflicting data as to whether or not these materials significantly prevent or inhibit secondary caries and affect the growth of caries-associated bacteria compared to non-fluoridated restoratives.

SIGNIFICANCE

Fluoride release and uptake characteristics depend on the matrices, fillers and fluoride content as well as on the setting mechanisms and environmental conditions of the restoratives. Fluoride-releasing materials, predominantly glass-ionomers and compomers, did show cariostatic properties and may affect bacterial metabolism under simulated cariogenic conditions in vitro. However, it is not proven by prospective clinical studies whether the incidence of secondary caries can be significantly reduced by the fluoride release of restorative materials.

Differential regulation of Streptococcus mutans gtfBCD genes in response to copper ions

To persist in the oral cavity, bacteria must be able to tolerate environmental fluctuation, particularly in pH, nutrients, and essential elements. Glucosyltransferases B, C, and D of Streptococcus mutans synthesize glucans, and play essential roles in the sucrose-dependent adhesion of the organism to tooth surfaces. Transcriptions of gtfB, gtfC, and gtfD could be differentially regulated through independent promoters. To test the hypothesis that environmental factors frequently encountered in the dental plaque might serve as effector molecules involved in regulation, transcripts of individual gtfs were identified by reverse transcriptase-polymerase chain reaction assay and confirmed by Northern blot analysis using anti-sense RNA probes. When S. mutans was grown in different medium at low pH, differential regulation of the gtfs was observed. More specifically, the transcription and translational expression of gtfD but not gtfB and gtfC was specifically induced by copper ion (Cu(2+)). The up-regulation was independent of the Cu(2+)-transport operon copYAZ. These findings support the involvement of Cu(2+) as an effector molecule in the regulation of S. mutans gtfD. Nutrient change dominates influence of pH but not the effect of Cu(2+).

Role of a Streptococcus gordonii copper-transport operon, copYAZ, in biofilm detachment

Streptococcus gordonii is a pioneer oral bacterium that is associated with the initiation of dental plaque development. Located downstream of the S. gordonii adc operon, which is involved in competence and biofilm formation, were three open reading frames, designated copY, copA and copZ. These open reading frames were homologous to the copYAZ genes in Streptococcus mutans that are involved in copper homeostasis and biofilm detachment. This study examined whether copYAZ genes play any role in the biofilm formation and detachment of S. gordonii. The copY gene encodes a 143-amino acid protein homologous to the negative transcriptional regulator of a copper-transport operon, copA encodes a 748-amino acid copper-transporting P-type ATPase, and copZ encodes a 69-amino acid putative metallochaperone protein in S. mutans. Each open reading frame in the copYAZ operon in S. gordonii was inactivated by insertional mutation and the growth, biofilm formation and detachment of each mutant were examined. S. gordonii copY::specR, copA::specR, and copZ::specR mutants were able to form biofilms on both polystyrene and glass surfaces. However, inactivation of copZ and to a lesser extent copY resulted in phenotypes that were defective in biofilm detachment, which is consistent with previous observations in S. mutans and suggests that the trace element copper might influence biofilm detachment of bacterial biofilms.

Oral fluoride retention in saliva following toothbrushing with child and adult dentifrices with and without water rinsing

Ten healthy adult volunteers were recruited to participate in this double-blind randomised 18-leg crossover designed study. The subjects either rinsed their mouth with 10 ml de-ionised distilled water for 10 s or just spat out once after 1-min brushing with one of nine different toothpastes: NaF (500, 1,000 and 1,450 ppm F), SMFP (525, 1,000, 1,450 ppm F), AmF (250, 1,400 ppm F) or fluoride-free dentifrice. Samples of whole mixed unstimulated saliva were collected at different time intervals. The results showed that the use of the AmF toothpaste (1,400 ppm F) resulted in the highest fluoride content of saliva without water rinsing after 120 min (0.52 ppm F, CI 0.23, 0.81). Two hours after brushing with fluoride toothpaste containing AmF and NaF, the salivary fluoride levels were still higher than baseline levels.

Involvement of the adc operon and manganese homeostasis in Streptococcus gordonii biofilm formation

Pioneer oral bacteria, including Streptococcus gordonii, initiate the formation of oral biofilms on tooth surfaces, which requires differential expression of genes that recognize unique environmental cues. An S. gordonii::Tn917-lac biofilm-defective mutant was isolated by using an in vitro biofilm formation assay. Subsequent inverse PCR and sequence analyses identified the transposon insertion to be near the 3' end of an open reading frame (ORF) encoding a protein homologous to a Streptococcus pneumoniae repressor, AdcR. The S. gordonii adc operon, consisting of the four ORFs adcR, adcC, adcB, and adcA, is homologous to the adc operon of S. pneumoniae, which plays a role in zinc and/or manganese transport and genetic competence in S. pneumoniae. AdcR is a metal-dependent repressor protein containing a putative metal-binding site, AdcC contains a consensus-binding site for ATP, AdcB is a hydrophobic protein with seven hydrophobic membrane-spanning regions, and AdcA is a lipoprotein permease with a putative metal-binding site. The three proteins (AdcC through -A) are similar to those of the binding-lipoprotein-dependent transport system of gram-positive bacteria. Reverse transcriptase PCR confirmed that adcRCBA are cotranscribed as an operon in S. gordonii and that the transposon insertion in S. gordonii adcR::Tn917-lac had resulted in a polar mutation. Expression of adcR, measured by the beta-galactosidase activity of the adcR::Tn917-lac mutant, was growth phase dependent and increased when the mutant was grown in media with high levels of manganese (>1 mM) and to a lesser extent in media with zinc, indicating that AdcR may be a regulator at high levels of extracellular manganese. A nonpolar inactivation of adcR generated by allelic replacement resulted in a biofilm- and competence-defective phenotype. The biofilm-defective phenotype observed suggests that AdcR is an active repressor when synthesized and acts at a distant site(s) on the chromosome. Thus, the adc operon is involved in manganese acquisition in S. gordonii and manganese homeostasis and appears to modulate sessile growth in this bacterium.

Slow-Release Devices for Fluoride Delivery to High-Risk Individuals

The latest fluoride research is investigating the use of slow-release devices for the long-term intra-oral provision of fluoride. 174 children aged 8 years with fluoride slow-releasing glass devices were shown to develop 67% fewer new carious teeth and 76% fewer new carious surfaces in a 2-year double-blind caries study. There were 55% fewer new occlusal fissure carious cavities showing that occlusal surfaces were also protected by the fluoride released from the devices. The fluoride devices release low levels of fluoride for at least 2 years and have great potential for use in preventing dental caries in high-caries-risk groups and irregular dental attenders in addition to a number of other applications.

Is salivary histatin 5 a metallopeptide?

Histatins are small histidine-rich salivary polypeptides which exhibit antimicrobial activity against Candida albicans. This antimicrobial activity has been ascribed in part to a high content of basic amino acids. However, unlike most other antimicrobial proteins histatins have a high content of histidine, tyrosine and acidic amino acids known to participate in metal ion coordination. This study was conducted to test whether histatin 5 could bind zinc and copper which are metals present in salivary secretions and whole saliva. Physical binding parameters and spectral properties of zinc- and copper-histatin complexes were investigated in order to obtain direct evidence of these interactions. A spectrophotometric competition assay using the metallochromic indicator murexide showed that histatin 5 dissociates metal indicator complexes containing zinc or copper ions. Absorption spectra of histatin 5 at increasing copper chloride concentrations resulted in higher absorbance in the 230-280 nm wavelength range and this spectral change was saturated at a peptide:metal molar ratio of approx. 1:1. A corresponding band was observed in the visible range of the spectrum with a maximum and molar extinction coefficient corresponding to that of copper binding to an ATCUN motif. Quantitative assessment of zinc and copper binding to histatin 5 using isothermal titration calorimetry revealed at least one high affinity site for each metal, with binding constants of 1.2x10(5) and 2.6x10(7) M(-1), respectively. These results indicate that histatin 5 exhibits metallopeptide-like properties. The precise biological significance of this has not yet been established but histatins may contribute significantly to salivary metal binding capacity.

Trace elements and electrolytes in human resting mixed saliva after exercise

OBJECTIVES

Exercise is known to cause changes in the concentration of salivary components such as amylase, Na, and Cl. The aim of this investigation was to evaluate the effect of physical exercise on the levels of trace elements and electrolytes in whole (mixed) saliva.

METHODS

Forty subjects performed a maximal exercise test on a cycle ergometer. Samples of saliva were obtained before and immediately after the exercise test. Sample concentrations of Fe, Mg, Sc, Cr, Mn, Co, Cu, Zn, Se, Sr, Ag, Sb, Cs, and Hg were determined by inductively coupled plasma mass spectrometry and concentrations of Ca and Na by atomic absorption spectrometry.

RESULTS

After exercise, Mg and Na levels showed a significant increase (p < 0.05) while Mn levels fell (p < 0.05). Zn/Cu molar ratios were unaffected by exercise.

CONCLUSIONS

Intense physical exercise induced changes in the concentrations of only three (Na, Mg, and Mn) of the 16 elements analysed in the saliva samples. Further research is needed to assess the clinical implications of these findings.

Trace elements in saliva and dental caries in young adults

The results of a study on Zn, Cu, Ca and Mg content in whole saliva and supernatant of young adults in relation to caries prevalence are reported. A total of 225 university students were selected for the study on the basis of voluntary participation. The salivary electrolytes showed a high intersubjective variability and females had significantly lower levels than males. In whole saliva, the trace elements were highly correlated, whereas the correlations were weaker in the supernatant. The ratio supernatant/whole saliva varied between subjects and according to the examined electrolytes. No association could be found between the measured trace elements and DMFT. When we analysed the relation with recent caries experience in the subgroup of subjects undergoing oral examinations for at least 1 year, we found evidence that the Zn/Cu molar ratios in whole saliva were significantly decreased in subjects with more than three decayed teeth compared with those with no caries (1.54 vs. 1.11, P < 0.05). No significant association was found when supernatant was analysed. We conclude that the electrolytes' levels in whole saliva might be more adequate than the levels in supernatant to evaluate the relationship with caries.