Effect of ethylene oxide sterilization on enamel and dentin demineralization in vitro

Assessing the antimicrobial properties of copper-iodide doped adhesives in an In vitro caries model: A pilot study

Context:

Recurrent caries are the leading cause of composite resin failure.

Aims:

The purpose of this pilot study was to test the efficacy of a novel copper iodide (CuI) containing dental adhesive in an in vitro caries model.

Subjects and Methods:

Streptococcus mutans and Lactobacillus acidophilus were grown individually on the complex medium for 48 h at 37°C. The pH of the mixed medium was 7.0 initially and tested every 24 h. 40 extracted teeth were prepared with standardized cavity preparations and coated with control or experimental CuI adhesives and imaged using a micro-computed tomography (microCT). Four study groups were evaluated: (1) control (2) 0.5 μg/ml CuI (3) 1.0 μg/ml CuI, 4) 5.0 μg/ml CuI. After incubation, the teeth were re-imaged using the microCT. Utilizing AnalyzePro software the three-dimensional data sets were overlaid and demineralization was measured and statistics were run.

Statistics:

Stratified ANOVA models were run to determine if there were differences between the control and experimental adhesive groups. Similarly, pH and bacterial concentrations were evaluated to ensure the viability of polymicrobial specimen.

Results and Conclusions:

Significant differences were found between the control group and the 1.0 and 5.0 CuI adhesive groups. No differences in pH were noted between the groups. Overlaid changes in demineralization were recorded as volume loss. CuI adhesives with 5 mg/ml or higher have the potential to limit tooth demineralization after bacterial penetration of a dental restoration in an in vitro caries model. Further testing is needed.

Protective effect of green tea catechins on eroded human dentin: an in vitro/in situ study

The present study sought to evaluate the protective effect of Epigallocatechin-3-gallate (EGCG) and commercial green tea (GT) on eroded dentin using in vitro and in situ experimental models. For the in vitro experiment, matrix metalloproteinases (MMPs) were extracted from demineralized human coronary dentin powder (citric acid, pH 2.3) and assessed via a colorimetric assay and electrophoresis in gelatin. The gels were exposed to buffers with: control (no treatment), 0.05% sodium fluoride (NaF), 0.12% chlorhexidine digluconate (CHX), GT infusion, and 0.1% EGCG, and their respective activity was analyzed by zymography. For the in situ experiment, 20 healthy volunteers (aged 20-32 years) participated in this single-center, blind, crossover study. The subjects wore upper removable devices containing four human dentin blocks. Erosive challenge (coke-1 min) was performed four times/day/5 days. Blocks were treated for 1 min with: control (No treatment), 0.05% NaF, 0.1% EGCG, and GT. Thereafter, the specimens were subjected to stylus profilometry and SEM. ANOVA was used to evaluate dentin roughness and wear, with a significance level of 5%. In the zymography analysis, 0.12% CHX, GT, and 0.1% EGCG were found to inhibit the action of MMPs; however, in the colorimetric assay, only green tea inhibited the activity of MMPs. There were no significant differences observed in dentin roughness or wear (p > 0.05). Herein, EGCG and GT inhibited the activity of endogenous proteases, resulting in protection against erosion-induced dentin damage; however, they could not prevent tooth tissue loss in situ.

Repurposing Napabucasin as an Antimicrobial Agent against Oral Streptococcal Biofilms

Objectives

Disruption of microbial biofilms is an effective way to control dental caries. Drug resistance and side effects of the existing antimicrobials necessitate the development of novel antibacterial agents. The current study was aimed at investigating the antibacterial activities of the repurposed natural compound napabucasin against oral streptococci.

Methods

The minimum inhibitory concentration, minimum bactericidal concentration, minimum biofilm inhibition concentration, and minimum biofilm reduction concentration of Streptococcus mutans, Streptococcus gordonii, and Streptococcus sanguinis were examined by a microdilution method. Cytotoxicity of napabucasin against human oral keratinocytes, human gingival epithelia, and macrophage RAW264.7 was evaluated by CCK8 assays. The dead/live bacterium and exopolysaccharide in the napabucasin-treated multispecies biofilms were evaluated by confocal laser scanning microscopy. Microbial composition within the napabucasin-treated biofilms was further visualized by fluorescent in situ hybridization and qPCR. And the cariogenicity of napabucasin-treated biofilms was evaluated by transverse microradiography.

Results

Napabucasin exhibited good antimicrobial activity against oral streptococcal planktonic cultures and biofilms but with lessened cytotoxicity as compared to chlorhexidine. Napabucasin reduced the cariogenic S. mutans and increased the proportion of the commensal S. gordonii in the multispecies biofilms. More importantly, napabucasin significantly reduced the demineralization capability of biofilms on tooth enamels.

Conclusion

Napabucasin shows lessened cytotoxicity and comparable antimicrobial effects to chlorhexidine. Repurposing napabucasin may represent a promising adjuvant for the management of dental caries.

Evaluation of the effectiveness of nonthermal plasma disinfection

As concern has increased regarding the interaction between efficiency and safety of disinfection, plasma becomes a viable alternative for disinfection in comparison with traditional methods. Dielectric barrier discharge (DBD) is applied to deactivate Bacillus subtilis and Escherichia coli , respectively, and disinfection efficiency is experimentally evaluated in this study. Tests are conducted with different working gases to investigate their effects on disinfection. Results show that Ar plasma diluted with 25% O₂ enhances the germicidal effects to5.9 and 6.9 (log reduction) for B. subtilis and E. coli, respectively, and OES results show that active Ar and O species play important roles to weaken cell wall of microbes and further disinfect E. coli and B. subtilis. Analysis of protein and total sugar release indicates that active species such as ozone, NO and Ar* produced by plasma result in hydrolysis of the cell. In the meantime, charged particles produced by plasma would affect the amount of sugar released, resulting in different germicidal effects. Overall, plasma can disinfect microorganisms mainly via the generation of oxidising agents including ozone, NO and UV with a comparatively short treatment period, which is typically less than 5 min.

Cariogenicity induced by commercial carbonated beverages in an experimental biofilm-caries model

Objectives

Frequent consumption of sugars-containing carbonated beverages has been associated with caries, but the consequences on the dental biofilm remain unclear. The aim was to evaluate the effect of commercial carbonated beverages and their sugar-free version on enamel and dentine demineralization and on the cariogenic properties of Streptococcus mutans biofilms.

Materials and Methods

Biofilms of S. mutans UA159 were grown on enamel and dentin slabs and exposed 3 times/day for 5 min, to a commercial cola or orange-flavored carbonated beverage or to their sugar-free version. Biofilms/slabs were recovered to assess biomass, viable microorganisms, protein content and polysaccharides. Demineralization was estimated by the variation of Knoop surface microhardness.

Results

Exposures to the biofilm with sugars-containing carbonated beverages resulted in similar biomass, viable microorganisms, proteins, and polysaccharides than sucrose (P < 0.05). The sugar-free cola and orange-flavored drink showed lower effect on the biofilm, as compared with sucrose or their sugared version (P < 0.05). All of the products tested, included the sugar-free, showed higher demineralization than the negative control (P < 0.05).

Conclusions

Sugars-containing carbonated beverages enhance cariogenic activity of S. mutans biofilms, comparable with sucrose. Sugar-free carbonated beverages also have a high demineralizing potential, without affecting biofilm properties.

Anticaries activity of egg ovalbumin in an experimental caries biofilm model on enamel and dentin

OBJECTIVES

Limited evidence suggests a putative inhibitory effect of dietary proteins on demineralization during the carious process. The aim was to explore a potential anticaries activity of the egg protein ovalbumin on a relevant in vitro approach.

MATERIALS AND METHODS

Biofilms of Streptococcus mutans UA159 were formed on saliva-coated enamel and dentin bovine slabs. Biofilms were challenged with 10% sucrose followed by either a 200 μg/mL solution of ovalbumin or 1:10, 1:100, and 1:1000 (v/v) serial dilutions of that ovalbumin solution, for the entire length of the experiment. Biofilms exposed to 10% sucrose followed only by 0.9% NaCl served as caries-positive control. Once completed the experimental phase, biofilms were analyzed for biomass, viable bacteria, and polysaccharide formation. Final surface hardness (SH) was obtained to calculate %SH loss (demineralization). Two independent experiments were conducted, in triplicate. Data were analyzed by ANOVA and a post hoc test at the 95% confidence level.

RESULTS

A reduction (p < 0.05) in biomass and extracellular polysaccharide formation, but not in the number of viable cells, was observed for both dental substrates. All ovalbumin concentrations tested showed lower demineralization than the positive control (p < 0.05), in a dose-dependent manner. The highest concentration showed a reduction in the %SH loss of about 30% for both enamel and dentin.

CONCLUSION

Egg ovalbumin presented to sucrose-challenged biofilms of Streptococcus mutans seems to reduce cariogenicity of a biofilm-caries model.

CLINICAL RELEVANCE

Ovalbumin may counteract the cariogenic effect of sugars. If these findings are clinically confirmed, novel preventive approaches for caries are warranted.

Evaluation of photosensitizer penetration into sound and decayed dentin: A photoacoustic spectroscopy study

BACKGROUND

Photodynamic therapy (PDT) may have topical indications. In those cases it is important for a topical photosensitizer to penetrate into the tissue to which it has been applied. This study aimed to compare the penetration of two different concentrations of erythrosine into intact and in vitro decayed dentin samples.

METHODS

This in vitro study evaluated erythrosine (0.3 and 5%) penetration into sound (intact) and decayed dentin. A total of 11 dentin discs were prepared and divided into two equal halves, in order to keep one half sound while the other half was submitted to sterilization and an in vitro demineralization model for 5 days. Before erythrosine application, the organic and inorganic composition of all samples was evaluated by Fourier Transform Raman spectroscopy, and after erythrosine application for 30 min, the penetration depth was determined by Photoacoustic spectroscopy technique.

RESULTS

The results indicated that 0.3% erythrosine showed a higher penetration depth into sound dentin (p = 0.002); and 5% erythrosine higher penetration into decayed dentin (p < 0.001). However considering clinical parameters, no statistically significant difference was found between any of the conditions tested.

CONCLUSIONS

Erythrosine demonstrated ability to penetrate into dentin, irrespective of sound or decayed condition. Photoacoustic spectroscopy can be considered a method for estimating the penetration into hard tissues, and in conjunction with Raman spectroscopy, these are effective methods for evaluating the spectral response of dentin. Considering that erythrosine is capable of penetrating into decayed dentin, clinical trials are needed to test the effectiveness of this photosensitizer in Photodynamic therapy and Antimicrobial Photodynamic therapy.

Validation of a Cariogenic Biofilm Model to Evaluate the Effect of Fluoride on Enamel and Root Dentine Demineralization

Due to gingival recession both enamel and root dentine are at risk of developing caries. Both tissues are exposed to a similar environment, however there is not a validated model to evaluate the effect of fluoride on these dental substrates simultaneously. Hence, this study aimed to validate a caries model to evaluate the effect of fluoride to prevent demineralization on enamel and root-dentine. Streptococcus mutans UA159 biofilms were formed on saliva-coated bovine enamel and root dentine slabs (n = 12 per group) mounted in the same well of culture plates. The biofilms were exposed 8×/day to 10% sucrose and treated 2×/day with fluoridated solutions containing 0, 150, 450, or 1,350 ppm F; thus, simulating the use of low to high fluoride concentration toothpastes. The pH values of the culture medium was monitored 2×/day as a biofilm acidogenicity indicator. After 96 h, biofilms were collected for fluoride concentration analysis. The percentage of surface hardness loss (%SHL) was calculated for slabs. The fluoride uptake by the enamel and dentine was also determined. The model showed a dose-response because the biofilm and fluoride uptake increased and %SHL decreased at increasing fluoride concentrations (p < 0.05). Fluoride in the biofilm formed on dentine and fluoride uptake by dentine were higher than those for enamel. With the same fluoride concentration treatment, the percentage of reduction of demineralization was lower for dentine than for enamel. In conclusion, the model was validated in terms of a dose-response effect of fluoride on enamel and root dentine. Furthermore, the findings support the clinical data, suggesting that higher fluoride concentrations are necessary to control caries of root dentine than of enamel.

Gap size and wall lesion development next to composite

This in situ study investigated whether there is a relationship between gap size and wall lesion development in dentin next to 2 composite materials, and whether a clinically relevant threshold for the gap size could be established. For 21 days, 14 volunteers wore a modified occlusal splint containing human dentin samples with 5 different interfaces: 4 gaps of 50 µm, 100 µm, 200 µm, or 400 µm and 1 non-bonded interface without a gap. Eight times a day, the splint with samples was dipped in a 20% sucrose solution for 10 minutes. Before and after caries development, specimens were imaged with transversal wavelength-independent microradiography (T-WIM), and lesion depth (LD) and mineral loss (ML) were calculated at the 5 different interfaces. After correction for the confounder location (more mesial or distal), a paired t test clustered within volunteers was performed for comparison of gap widths. Results showed no trend for a relationship between the corrected lesion depth and the gap size. None of the differences in lesion depth for the different gap sizes was statistically significant. Also, the composite material (AP-X or Filtek Supreme) gave no statistically significant differences in lesion depth and mineral loss. A minimum gap size could not be established, although, in a non-bonded interface without a measurable gap, wall lesion development was never observed.

Caries arresting effect of silver diamine fluoride on dentine carious lesion with S. mutans and L. acidophilus dual-species cariogenic biofilm

OBJECTIVES

This in vitro study investigated the effects of silver diamine fluoride (SDF) on dentine carious lesion with cariogenic biofilm.

STUDY DESIGN

Thirty human dentine blocks were inoculated with Streptococcus mutans and Lactobacillus acidophilus dual-species biofilm to create carious lesion. They were equally divided into test and control group to receive topical application of SDF and water. After incubation anaerobically using micro-well plate at 37oC for 7 days, the biofilms were evaluated for kinetics, morphology and viability by colony forming units (CFU), scanning electron microscopy (SEM), and confocal microscopy (CLSM), respectively. The carious lesion underwent crystal characteristics analysis, evaluation of the changes in chemical structure and density of collagen fibrils using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and immune-labeling.

RESULTS

The log CFU of S. mutans and L. acidophilus in the test group was significantly lower than control group. SEM and CLSM showed confluent biofilm in control group, but not in test group. XRD showed the loss of crystallinity of dentine due to the dissolution of hydroxyapatite crystal structure in test group was less than control group. FTIR showed that log [Amide I: HPO42-] for test vs. control group was 0.31±0.10 vs. 0.57±0.13 (p<0.05). The gold-labeling density in test vs. control group was 8.54±2.44/µm2 vs. 12.91±4.24/µm2 (p=0.04).

CONCLUSIONS

SDF had antimicrobial activity against the cariogenic biofilms and reduced demineralization of dentine.

Preventing root caries development under oral biofilm challenge in an artificial mouth

Objectives: To study the preventive effects of chlorhexidine against root caries under oral biofilm in an artificial mouth. Study Design: Sixteen human tooth-root disks were inoculated with a salivary sample that was produced by mixing the unstimulated saliva of three adults who had no untreated caries. The disks were incubated in an artificial mouth fed with a 5% sucrose solution three times daily for one week. Eight disks received a twice daily rinse of 0.12% chlorhexidine (test group). The other eight disks were rinsed in distilled water (control). The biofilm was then studied with three techniques: colony forming unit (CFU) counting, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The changes in the chemical structure of the root surface were studied using Fourier transform infra-Red spectroscopy. Type-I collagen and proteoglycans on the root surface were quantified using immunocytochemical staining. Results: The log CFU for the test and control groups were 4.21 and 8.27, respectively (p<0.001). The CFU count of Streptococci and Lactobacilli were negligible. Both the SEM and the CLSM showed suppressed bacteria growth in the test group. The log [amide-I: HPO42-] of the test and control groups were 1.11 and 1.93, respectively (p=0.02). The mean counts of sound type-I collagen in the test and control groups were 16.8/?m2 and 13.0/?m2, respectively (p<0.001), whereas the mean counts of intact proteoglycans were 5.6/?m2 and 3.5/?m2, respectively (P<0.001). Conclusions: Chlorhexidine suppressed the growth of selected cariogenic bacteria in oral biofilm on the root surface and thus protected tooth-root from cariogenic challenge.

Key words:Chlorhexidine, biofilm, caries risk, root, caries, artificial mouth, demineralization, streptococci, lactobacilli, proteoglycans, collagen I.

Cariogenic potential of commercial sweeteners in an experimental biofilm caries model on enamel

OBJECTIVE

Scarce evidence is available on the cariogenic potential of the widely used commercial sweeteners. The aim of this study was to evaluate the effect of several sweeteners on enamel demineralisation and on the cariogenic properties of Streptococcus mutans biofilms in an artificial caries model.

METHODS

S. mutans-UA159 biofilms were cultured on bovine enamel slabs and exposed to one of the following commercial sweeteners in tablet or powder form: stevia, sucralose, saccharin, aspartame or fructose. Ten percent sucrose and 0.9% NaCl were used as caries-positive and caries-negative controls, respectively. Slabs/biofilms were exposed to the sweeteners three times per day for 5min each time. After 5 days, biofilms were recovered to determine: biomass, bacterial counts and intra- and extracellular polysaccharides. Surface microhardness was measured before and after the experiment to assess enamel demineralisation, expressed as percentage of surface hardness loss (%SHL). Data were analysed using analysis of variance (ANOVA) and Bonferroni (p<0.05).

RESULTS

All tested commercial sweeteners, except fructose, showed less enamel demineralisation than sucrose (p<0.05). Only saccharine showed less biomass and intracellular polysaccharides than the rest of the groups (p<0.05). Stevia, sucralose and saccharine reduced the number of viable cells when compared with sucrose (p<0.05). All sugar alternatives reduced extracellular polysaccharide formation when compared with sucrose (p<0.05).

CONCLUSIONS

Most commercial sweeteners appear to be less cariogenic than sucrose, but still retaining some enamel demineralisation potential. Products containing stevia, sucralose and saccharine showed antibacterial properties and seem to interfere with bacterial metabolism. Further studies are necessary to deepen these findings.

Antibacterial effects of silver diamine fluoride on multi-species cariogenic biofilm on caries

Backgrounds

Silver diamine fluoride (SDF) has clinical success in arresting dentin caries, this study aimed to investigate its mechanism of action.

Methods

Using a computer-controlled artificial mouth, we studied the effect of 38% SDF on cariogenic biofilms and dentin carious lesions. We used five common cariogenic bacteria (Streptococcus mutans, Streptococcus sobrinus, Lactobacillus acidophilus, Lactobacillus rhamnosus and Actinomyces naeslundii) to form a cariogenic biofilm that generated carious lesions with a depth of approximately 70 um on human dentin blocks. We applied 38% SDF to the lesions in the test group and water to those in the control group. The blocks were incubated in the artificial mouth for 21 days before evaluation. Microbial kinetics, architecture, viability and distribution were evaluated every 7 days using colony forming unit (CFU), scanning electron microscopy and confocal laser scanning microscopy. The physical properties of the carious lesions were evaluated with microhardness testing, energy dispersive spectroscopy (EDS) and Fourier transform infra-red spectroscopy (FTIR).

Results

The CFU results revealed fewer colony forming units in the test group compared with the control group (p < 0.01). Scanning electron microscopy and confocal microscopy showed less bacterial growth in the test group, and confluent cariogenic biofilm in the control group (p < 0.01). The microhardness and weight percentages of calcium and phosphorus in the test group from the outermost 50mum were higher than in the control group (p < 0.05). EDS showed that calcium and phosphous were higher in outer 50 mum in test groups than in the control FTIR revealed less exposed collagen I in the test lesions compared with the control group (p < 0.01).

Conclusions

38% SDF inhibits multi-species cariogenic biofilm formation on dentin carious lesions and reduces the demineralization process.

Effects of silver diamine fluoride on dentine carious lesions induced by Streptococcus mutans and Actinomyces naeslundii biofilms

BACKGROUND. Silver diamine fluoride (SDF) has been shown to be a successful treatment for arresting caries. However, the mechanism of SDF is to be elucidated. AIM. To characterize the effects of SDF on dentine carious induced by Streptococcus mutans and Actinomyces naeslundii. DESIGN.  Thirty-two artificially demineralized human dentine blocks were inoculated: 16 with S. mutans and 16 with A. naeslundii. Either SDF or water was applied to eight blocks in each group. Biofilm morphology, microbial kinetics and viability were evaluated by scanning electron microscopy, colony forming units, and confocal microscopy. The crosssection of the dentine carious lesions were assessed by microhardness testing, scanning electron microscopy with energy-dispersive x-ray spectroscopy and Fourier transform infrared spectroscopy. RESULTS. Biofilm counts were reduced in SDF group than control (P < 0.01). Surfaces of carious lesions were harder after SDF application than after water application (P < 0.05), in S. mutans group, Ca and P weight percentage after SDF application than after water application (P < 0.05). Lesions showed a significantly reduced level of matrix to phosphate after SDF treatment (P < 0.05). CONCLUSION. Present study showed that SDF posses an anti-microbial activity against cariogenic biofilm of S. mutans or A. naeslundii formed on dentine surfaces. SDF slowed down demineralization of dentine. This dual activity could be the reason behind clinical success of SDF.

Gamma Irradiation Studies I. Dental Grafts

The development of nanoceramics-polymer composites and bioactive materials such as calcium phosphates and bioglasses and ceramics especially hydroxyapatite (HAp) and β-tricalcium phosphate (TCP) for bone regeneration has been carried out for bone regeneration. Due to their resorption in the body and direct contact with tissues, it is necessary to sterilize the dental graft before administration to the patient. Three different dental graft materials including TCP, bioglass, and equine bone tissue (G1, G2, and G3, respectively) were studied in this study. The effects of γ irradiation were evaluated with different analytical methods (organoleptic analysis, FTIR, DSC, TGA, and SEM) and microbiological analysis (sterility, pyrogenity, and sterility assurance level (SAL) determination). The physicochemical results indicated that G1 is the most γ stable (optimum) dental graft material for γ radiation sterilization with minimum changes in chemical and physical properties in comparison with other two dental graft materials. G3, was the most sensitive dental graft material according to organoleptic investigations, TGA and SEM analysis. Another aspect of this study was, to investigate the effect of ethylene oxide (EtO) sterilization on optimum dental graft material, G1 and the comparison of two sterilization methods with analytical and microbiological examinations. The resorption times and resorption characteristics of γ sterilized dental graft material (G1G) and EtO sterilized one (G1E) were evaluated on New Zealand rabbits for 12 weeks. Histological studies showed that TCP containing dental graft material, G1, did not induce inflammation in bone and soft tissue. Resorption and bone formation of G1G was faster than G1E. Total resorption time of G1 was 12 weeks for both sterilization groups. The analytical, microbiological and in vivo results suggest that the dental graft G1 can be sterilized with γ radiation safely with validated doses lower than medical γ sterilization dose, 25 kGy.

Capillary-tube-based oxygen/argon micro-plasma system for the inactivation of bacteria suspended in aqueous solution

PURPOSE

An aqueous solution containing Escherichia coli can be completely inactivated within a short treatment time using a capillary-tube-based oxygen/argon micro-plasma source.

MATERIALS AND METHODS

A capillary-tube-based oxygen/argon micro-plasma system with a hollow inner electrode was ignited by a 13.56 MHz radio frequency power supply with a matching network and characterised by optical emission spectroscopy. An aqueous solution containing E. coli was then treated at various the working distances, plasma exposure durations, and oxygen ratios in argon micro-plasma. The treated bacteria were then assessed and qualitatively investigated. The morphologies of treated bacteria were examined using a scanning electron microscope (SEM).

RESULTS

In the proposed oxygen/argon micro-plasma system, the intensities of the main emission lines of the excited species, nitric oxide (NO), hydrated oxide (OH), argon (Ar), and atomic oxygen (O), fluctuated with the addition of oxygen to argon micro-plasma. Under a steady state of micro-plasma generation, the complete inactivation of E. coli in aqueous solution was achieved within 90 s of argon micro-plasma exposure time with a working distance of 3 mm. SEM micrographs reveal obvious morphological damage to the treated E. coli. The addition of oxygen to argon micro-plasma increased the variety of O-containing excited species. At a given supply power, the relative intensities of the excited species, NO and OH, correlated with the ultraviolet (UV) intensity, decreased.

CONCLUSION

For the proposed capillary-tube-based micro-plasma system with a hollow inner electrode, the oxygen/argon micro-plasma source is efficient in inactivating E. coli in aqueous solution. The treatment time required for the inactivation process decreases with decreasing working distance or the increasing synthesised effect of reactive species and UV intensity.

Design of a randomized controlled double-blind crossover clinical trial to assess the effects of saliva substitutes on bovine enamel and dentin in situ

Background

Hyposalivation is caused by various syndromes, diabetes, drugs, inflammation, infection, or radiotherapy of the salivary glands. Patients with hyposalivation often show an increased caries incidence. Moreover, hyposalivation is frequently accompanied by oral discomfort and impaired oral functions, and saliva substitutes are widely used to alleviate oral symptoms. However, preference of saliva substitutes due to taste, handling, and relief of oral symptoms has been discussed controversially. Some of the marketed products have shown demineralizing effects on dental hard tissues in vitro. This demineralizing potential is attributed to the undersaturation with respect to calcium phosphates. Therefore, it is important to modify the mineralizing potential of saliva substitutes to prevent carious lesions. Thus, the aim of the present study was to evaluate the effects of a possible remineralizing saliva substitute (SN; modified Saliva natura) compared to a demineralizing one (G; Glandosane) on mineral parameters of sound bovine dentin and enamel as well as on artificially demineralized enamel specimens in situ. Moreover, oral well-being after use of each saliva substitute was recorded.

Methods/Design

Using a randomized, double-blind, crossover, phase II/III in situ trial, volunteers with hyposalivation utilize removable dentures containing bovine specimens during the experimental period. The volunteers are divided into two groups, and are required to apply both saliva substitutes for seven weeks each. After both test periods, differences in mineral loss and lesion depth between values before and after exposure are evaluated based on microradiographs. The oral well-being of the volunteers before and after therapy is determined using questionnaires. With respect to the microradiographic analysis, equal mineral losses and lesion depths of enamel and dentin specimens during treatment with SN and G, and no differences in patients' experienced oral comfort after SN compared to G usage are expected (H₀).

Discussion

Up to now, 14 patients have been included in the study, and no reasons for early termination of the trial have been identified. The design seems suitable for determining the effects of saliva substitutes on dental hard tissues in situ, and should provide detailed information on the oral well-being after use of different saliva substitutes in patients with hyposalivation.

Trial registration

ClinicalTrials.gov ID. NCT01165970

Effect of gamma irradiation on fluoride release and antibacterial activity of resin dental materials

This study evaluated the effect of gamma irradiation on fluoride release and antibacterial activity of FluroShield (FS) and Clearfil Protect Bond (CPB). Four groups were formed: G1-FS + gamma; G2-FS without gamma; G3-CPB + gamma; G4-CPB without gamma. For fluoride release analysis, 12 disks of each material were prepared and covered with nail polish, except for one side (50.4 mm(2) area). G1 and G3 were sterilized with a 14.5 KGy dose at 27 degrees C for 24 h, while G2 and G4 (controls) were not sterilized and were maintained under the same time and temperature conditions. Fluoride release measurements were made in duplicate (n=6) by an ion specific electrode. The antibacterial activity of the CPB and FS against Streptococcus mutans after gamma sterilization was evaluated by the agar-disc diffusion method. The diameter of the zones of microbial growth inhibition was recorded after 48 h. Data were analyzed statistically by ANOVA and Tukey's test (alpha=5%). Gamma sterilization decreased the fluoride release of FS by approximately 50%, while CPB was not affected. There was no statistically significant difference (p>0.05) in the antibacterial effect of CPB between gamma and non-gamma sterilization groups. FS presented no antibacterial activity. Gamma irradiation decreased the fluoride release of FS, but did not affect the antibacterial activity of the studied materials.