The preventive/therapeutic effect of CO2 laser and MI Paste Plus® on intact and demineralized enamel against Streptococcus mutans (In Vitro Study)

Background

To evaluate the preventive and therapeutic effects of CO2 laser and MI paste plus on intact and demineralized enamel surfaces and their impact on bacterial adhesion. Methods: 160 enamel slabs were prepared and randomly allocated into two main groups; sound and demineralized enamel (n = 80 per group), in which specimens were immersed in a demineralizing solution (50 mM acetic acid, pH 4.5) for 72 h at 37 °C. Each group was further divided into four subgroups (n = 20); the control (un treated surfaces), surfaces treated by CO2 laser, MI paste plus (Recaldent™, GC corporation/Germany), and those received a combination of CO2 and MI paste plus. Streptococcus Mutans biofilm was isolated, quantified, and then applied on treated enamel surfaces and incubated anaerobically for 24 h and then quantified by colony-forming unit (CFU). Meanwhile, surface changes were assessed by Vickers microhardness and Scanning Electron Microscope combined with Energy-Dispersive X-Ray Spectroscopy (SEM-EDX). Results: The combined use of CO2 laser followed by MI paste plus significantly (p < 0.000) enhanced surface microhardness of sound and demineralized enamel with a significant reduction in bacterial counts. However, each technique alone was beneficial as they exhibited higher microhardness with lower bacterial viability in comparison to the control. The treatment of demineralized enamel surfaces with MI paste significantly reduced the number of bacterial colonies with the presence of dispersed mineral deposits over the surface.

Conclusions

The combined use of CO2 laser and MI paste plus was effective as a preventive and/or therapeutic measures in enhancing surface properties of enamel and reducing the bacterial viability.

Effects of a 445 nm diode laser and silver diamine fluoride in preventing enamel demineralisation and inhibiting cariogenic bacteria

OBJECTIVE

To study the effects of a 445 nm diode laser (L) and silver diamine fluoride (F) on preventing enamel demineralisation and inhibiting cariogenic bacteria.

METHODS

Thirty-three enamel slices were sectioned each into four blocks for four groups to receive L with F (LF), F, L and Water (W, control). Ten blocks from each group were used to evaluate demineralization. Surface morphology, lesion depth and nanohardness of the blocks after pH-cycling were studied by scanning electron microscopy (SEM), nanohardness test, and micro-computed tomography, respectively. Twenty-three blocks per group were used for biofilm assessment. Morphology, viability, and growth kinetics of the Streptococcus mutans biofilm were assessed by SEM, confocal laser scanning microscopy, and the counting of colony-forming units (CFUs), respectively.

RESULTS

SEM images of LF-treated enamel showed an intact surface compared with other groups. Nanohardness (GPa) for LF, F, L and W were 1.43±0.17, 1.01±0.11, 1.04±0.13 and 0.73±0.14, respectively (p<0.001; LF>F, L>W). Their lesion depths (µm) were 46±8, 52±6, 88±13 and 111±9, respectively (p<0.001; LF, F<L<W). SEM showed few bacteria for LF and F compared with other groups. Their dead-live ratio were 1.67±0.13, 1.60±0.15, 0.39±0.05 and 0.32±0.05, respectively (p<0.001; LF, F>L>W). Log CFUs for LF, F, L and W were 4.2±0.3, 4.5±0.2, 7.9±0.3 and 9.4±0.2, respectively (p<0.05; LF<F<L<W). Two-way ANOVA analysis revealed an interaction effect on nanohardness and Log CFUs between the laser irradiation and SDF treatment (p<0.001).

CONCLUSION

This study showed a superior caries preventive effect of a combined treatment of the diode laser and SDF. Because diode laser and SDF are affordable and readily available, clinicians can provide this treatment to their patients for caries prevention.

CLINICAL SIGNIFICANCE STATEMENT

Diode lasers are handy, afforable and readily avaliable to clinicians. This study provides information of use of 445 nm diode laser for caries prevetion. The laser irradiation hopefully can be added before conventional topical SDF application.

The Antibacterial and Remineralization Effect of Silver-Containing Mesoporous Bioactive Glass Sealing and Er-YAG Laser on Dentinal Tubules Treated in a Streptococcus mutans Cultivated Environment

The aim of this study was to evaluate the remineralization and antibacterial effect of silver-containing mesoporous bioactive glass (MBG-Ag) sealing combined with Er:YAG laser irradiation on human demineralized dentin specimens in a Streptococcus mutans cultivated environment. A total of 48 human dentin specimens were randomly divided into four groups. The characteristics of MBG-Ag and the occlusion efficiency of the dentinal tubules were analyzed using X-ray diffraction patterns, Fourier-transform infrared spectroscopy, scanning electron microscope images and energy dispersive X-ray spectroscopy. Moreover, the antibacterial activity against Streptococcus mutans was evaluated by colony formation assay. The results showed that the dentin specimens with Er:YAG laser irradiation can form a melted occlusion with a size of 3–4 µm. MBG-Ag promoted the deposition of numerous crystal particles on the dentinal surface, reaching the deepest penetration depth of 70 μm. The results suggested that both MBG-Ag and laser have the ability to enhance the remineralization and precipitation of hydroxyapatite crystals. While the results showed that MBG-Ag sealing combined with the thermomechanical subablation mode of Er:YAG laser irradiation-induced dense crystalline deposition, reaching a penetration depth of more than 300 µm, silver nanoparticles without good absorption of the Er:YAG laser resulted in a heterogeneous radiated surface. Er:YAG laser irradiation with a low energy and pulse rate cannot completely inhibit the growth of S. mutans, but MBG-Ag sealing reached the bactericidal concentration. It was concluded that the simultaneous application of MBG-Ag sealing and Er:YAG laser treatment can prevent the drawbacks of their independent uses, resulting in a superior form of treatment for dentin hypersensitivity.

Tuning Microbial Activity via Programmatic Alteration of Cell/Substrate Interfaces

A wide portfolio of advanced programmable materials and structures has been developed for biological applications in the last two decades. Particularly, due to their unique properties, semiconducting materials have been utilized in areas of biocomputing, implantable electronics, and healthcare. As a new concept of such programmable material design, biointerfaces based on inorganic semiconducting materials as substrates introduce unconventional paths for bioinformatics and biosensing. In particular, understanding how the properties of a substrate can alter microbial biofilm behavior enables researchers to better characterize and thus create programmable biointerfaces with necessary characteristics on demand. Herein, the current status of advanced microorganism-inorganic biointerfaces is summarized along with types of responses that can be observed in such hybrid systems. This work identifies promising inorganic material types along with target microorganisms that will be critical for future research on programmable biointerfacial structures.

Characterization and effect of nanocomplexed fluoride solutions on the inhibition of enamel demineralization created by a multispecies cariogenic biofilm model

OBJECTIVES

The aim of this study was to assess the in vitro caries preventive effect of nanocomplexed solutions of hydroxypropyl-β-cyclodextrin and γ-cyclodextrin associated with titanium tetrafluoride (TiF₄) after different complexation times (12 or 72 h).

MATERIALS AND METHODS

Enamel blocks were randomly distributed in 9 groups (n = 11): negative control, hydroxypropyl-β-cyclodextrin, γ-cyclodextrin, TiF₄, hydroxypropyl-β-cyclodextrin:TiF₄ 12 h, hydroxypropyl-β-cyclodextrin:TiF₄ 72 h, γ-cyclodextrin:TiF₄ 12 h, γ-cyclodextrin:TiF₄ 72 h, and NaF (positive control). The solutions were applied for 1 min and the blocks were exposed to a biofilm model. Nanocompounds were characterized by differential scanning calorimetry and X-ray powder diffraction. The percentage of surface microhardness loss (%SML), mineral density changes (ΔZ), lesion depth, surface morphology (scanning electron microscopy-SEM), and chemical characterization (energy-dispersive spectroscopy-EDS) were assessed.

RESULTS

No oxidation was observed, and the formation of the nanocomplexes was evidenced by changes in the melting point compared to pure cyclodextrins and the loss of crystallinity of the materials. Hydroxypropyl-β-cyclodextrin:TiF₄ 72 h resulted in lower %SML than negative control, hydroxypropyl-β-cyclodextrin, γ-cyclodextrin, and TiF₄ (p < 0.05). NaF differed from all groups (p < 0.05), except for hydroxypropyl-β-cyclodextrin:TiF₄ 72 h (p = 0.83). ΔZ of hydroxypropyl-β-cyclodextrin:TiF₄ 72 h was higher than negative control, hydroxypropyl-β-cyclodextrin, γ-cyclodextrin, γ-cyclodextrin:TiF₄ 1 2 h, γ-cyclodextrin:TiF₄ 72 h, and NaF (p < 0.05) and similar to TiF₄ and hydroxypropyl-β-cyclodextrin:TiF₄ 12 h (p > 0.05). SEM/EDS detected Ti in the blocks subjected to TiF₄-products.

CONCLUSION

The hydroxypropyl-β-cyclodextrin:TiF₄ 72 h solution showed caries preventive effect on the surface and subsurface of the enamel.

CLINICAL RELEVANCE

A hydroxypropyl-β-cyclodextrin nanosystem, in association with TiF₄ after 72 h of complexation, may be a promising agent for the prevention of enamel demineralization.

Proteomic profile of the saliva and plasma protein layer adsorbed on Ti-Zr alloy: the effect of sandblasted and acid-etched surface treatment

Titanium-zirconium (Ti-Zr) alloy has been widely used as a biomaterial for implant devices, and it is commonly treated by sandblasting followed by acid etching (SLA) to improve biological responses. Although protein adsorption is the first biological response, the effect of this SLA treatment on the proteomic profile of proteins adsorbed from saliva and blood plasma has not been tested. In this study, the proteomic profile was evaluated by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Streptococcus sanguinis was used to test whether the protein layer affects bacterial adhesion. SLA treatment affected the proteomic profile, showing exclusive proteins adsorbed from saliva (14) and plasma (3). However, both groups exhibited close patterns of intensity for common proteins, molecular functions and biological processes mediated by proteins. Interestingly, Ti-Zr_SLA showed higher bacterial adhesion (∼1.9 fold over) for the surface coated with plasma proteins. Therefore, SLA treatment of Ti-Zr alloy changed the proteomic profile, which may affect bacterial adhesion.

Effect of Er:YAG laser irradiation on deciduous enamel roughness and bacterial adhesion: An in vitro study

Laser irradiation has been proposed as a preventive method against dental caries since it is capable to inhibit enamel demineralization by reducing carbonate and modifying organic matter, yet it can produce significant morphological changes. The purpose of this study was to evaluate the influence of Er:YAG laser irradiation on superficial roughness of deciduous dental enamel and bacterial adhesion. Fifty-four samples of deciduous enamel were divided into three groups (n = 18 each). G1_control (nonirradiated); G2_100 (7.5 J/cm² ) and G3_100 (12.7 J/cm² ) were irradiated with Er:YAG laser at 7.5 and 12.7 J/cm² , respectively, under water irrigation. Surface roughness was measured before and after irradiation using a profilometer. Afterwards, six samples per group were used to measure bacterial growth by XTT cell viability assay. Adhered bacteria were observed using confocal laser scanning microscopy (CLSM) and a scanning electron microscopy (SEM). Paired t-, one-way analysis of variance (ANOVA), Kruskal-Wallis and pairwise Mann-Whitney U tests were performed to analyze statistical differences (p < .05). Before treatment, samples showed homogenous surface roughness, and after Er:YAG laser irradiation, the surfaces showed a significant increase in roughness values (p < .05). G3_100 (12.7 J/cm² ) showed the highest amount of Streptococcus mutans adhered (p < .05). The increase in the roughness of the tooth enamel surfaces was proportional to the energy density used; the increase in surface roughness caused by laser irradiation did not augment the adhesion of Streptococcus sanguinis; only the use of the energy density of 12.7 J/cm² favored significantly the adhesion of S. mutans.

Adhesion of Streptococcus mutans and Streptococcus sanguinis on Er:YAG Laser-Irradiated Dental Enamel: Effect of Surface Roughness

Objective: To determine surface roughness caused by Er:YAG laser irradiation and its effect on the increase in bacterial adhesion. Background: Er:YAG laser was proposed as a strategic device to reduce caries by its ability to generate chemical and structural changes in tooth enamel; in turn, it produces undesirable effects on the tooth surface that could increase its roughness and allow a greater accumulation of microorganisms. Methods: Eighty-four samples of human enamel were divided into seven groups (n = 12): G1_control (no laser irradiation); G2_100/H₂O, G3_200/H₂O, and G4_300/H₂O were irradiated with Er:YAG laser (12.7, 25.5, and 38.2 J/cm², respectively) under water irrigation. In addition, G5_100, G6_200, and G7_300 were irradiated with the energy densities described above and no water irrigation. Surface roughness measurements were recorded before and after treatment using a profilometer. Afterward, three samples per group were incubated in a microorganism suspension for the tetrazolium salt (XTT) assay. Biofilm morphology was observed using scanning electron microscopy and confocal laser scanning microscope. One-way analysis of variance and t-tests were performed for statistical analysis (p < 0.05). Results: There were no statistically significant differences in roughness values in the G5_100 group before and after treatment, but there were statistically significant differences observed in the other groups evaluated (p < 0.05). No significant differences in adhesion of both strains were detected in irradiated groups compared with G1_control. Conclusions: The increase in roughness on dental enamel surfaces was proportional to the irradiation conditions. However, the increase in surface roughness caused by Er:YAG laser irradiation did not affect Streptococcus mutans and S. sanguinis adhesion.

In vitro evaluation of barrier function against oral bacteria of dense and expanded polytetrafluoroethylene (PTFE) membranes for guided bone regeneration

AIM

This study evaluates biofilm formation and barrier function against Streptococcus oralis of nonresorbable polytetrafluoroethylene (PTFE) guided bone regeneration membranes having expanded (e-PTFE) and dense (d-PTFE) microstructure.

MATERIALS AND METHODS

Three e-PTFE membranes of varying openness, one d-PTFE membrane, and commercially pure titanium discs were evaluated. All e-PTFE membranes consisted of PTFE nodes interconnected by fibrils. The d-PTFE membrane was fibril-free, with large evenly spaced indentations. The surfaces were challenged with S. oralis and incubated statically for 2-48h. Bacterial colonization, viability, and penetration were evaluated.

RESULTS

S. oralis numbers increased over time on all surfaces, as observed using scanning electron microscopy, while cell viability decreased, as measured by colony forming unit (CFU) counting. At 24h and 48h, biofilms on d-PTFE were more mature and thicker (tower formations) than on e-PTFE, where fewer layers of cells were distributed mainly horizontally. Biofilms accumulated preferentially within d-PTFE membrane indentations. At 48h, greater biofilm biomass and number of viable S. oralis were found on d-PTFE compared to e-PTFE membranes. All membranes were impermeable to S. oralis cells.

CONCLUSIONS

All PTFE membranes were effective barriers against bacterial passage in vitro. However, d-PTFE favored S. oralis biofilm formation.

Effect of water containing organic acids on aspiration pneumonia-causative bacteria in the biofilm on the tooth surface

Background/purpose

The tooth surface is a source of oral microbes in dentulous individuals, it is difficult for elderly people requiring nursing care to perform mechanical tooth cleaning by themselves. The objective of this study was to investigate the antimicrobial effect of water containing organic acids (WOA) made by some organic acids as food additives on chemical cleaning for elderly people on aspiration pneumonia-causative bacteria in the biofilm on the tooth surface.

Materials and methods

Ninety-six specimens made from bovine incisors were divided into four groups and incubated with one of four aspiration pneumonia-causative bacteria. Each group was further divided into six subgroups according to treatment as follows: control group (DW), chlorhexidine gluconate solution group (CHX), WOA group (WOA), ultrasonic treatment in distilled water group (DW-U), ultrasonic treatment in chlorhexidine gluconate solution group (CHX-U) or ultrasonic treatment in WOA group (WOA-U). After treatment, the levels of viable microbes in the biofilm were evaluated by quantitative adenosine triphosphate analysis and compared among the six groups.

Results

For every evaluated microbe, there were significant differences between DW and WOA, and DW and WOA-U. However, there was no significant difference among the WOA, DW-U, CHX-U and WOA-U groups. These results suggested that the antimicrobial effect of WOA on microbes attached to the tooth surface was similar to that of ultrasonic cleaning.

Conclusion

WOA has an antimicrobial effect on microbes in the biofilm on the tooth surface.

A New Laser-Processing Strategy for Improving Enamel Erosion Resistance

In the present study, a new automatic laser-processing strategy allowing standardized irradiation of natural tooth areas was investigated. The objective was to find a combination of laser parameters that could cause over a 600°C temperature increase at the enamel surface while not damaging enamel, avoiding temperature change above 5.5°C in the pulp and increasing enamel erosion resistance. Seventy-seven bovine enamel samples were randomly divided into 6 laser groups and 1 negative control (C/no treatment/ n = 11). A scanning strategy (7 × 3 mm) was used for the CO₂ laser treatment (λ = 10.6 µm, 0.1-18 J/cm²) with different pulse durations-namely, 20 µs (G20), 30 µs (G30), 55 µs (G55), and 490 µs (G490), as well as 2 modified pulse distances (G33d, G40d). Measurements of temperature change were performed at the surface (thermal camera/50 Hz), at the underside (thermocouples), and at the pulp chamber using a thermobath and human molars ( n = 10). In addition, histology and X-ray diffraction (XRD/ n = 10) were performed. Erosion was tested using an erosive cycling over 6 d, including immersion in citric acid (2 min/0.05 M/pH = 2.3) 6 times daily. Surface loss was measured using a profilometer and statistical analysis with a 2-way repeated-measures analysis of variance (α = 0.05). Only G20 fulfilled the temperature requirements at the surface (619 ± 21.8°C), at the underside (5.3 ± 1.4°C), and at the pulp (2.0 ± 1.0°C), and it caused no mineral phase change and significant reduction of enamel surface loss (-13.2 ± 4.0 µm) compared to C (-37.0 ± 10.1 µm, P < 0.05). A laser-scanning strategy (20 µs/2 kHz/1.25 J/cm², 3.4 mm/s) has been established that fulfilled the criteria for biological safety and significantly increased enamel erosion resistance (64%) in vitro.

Effects of Material Properties on Bacterial Adhesion and Biofilm Formation

Adhesion of microbes, such as bacteria and fungi, to surfaces and the subsequent formation of biofilms cause multidrug-tolerant infections in humans and fouling of medical devices. To address these challenges, it is important to understand how material properties affect microbe-surface interactions and engineer better nonfouling materials. Here we review the recent progresses in this field and discuss the main challenges and opportunities. In particular, we focus on bacterial biofilms and review the effects of surface energy, charge, topography, and stiffness of substratum material on bacterial adhesion. We summarize how these surface properties influence oral biofilm formation, and we discuss the important findings from nondental systems that have potential applications in dental medicine.

Evaluation of application possibility of water containing organic acids for chemical denture cleaning for older adults

AIM

The purpose of the present study was to evaluate the application possibility of water containing organic acids (WOA), made by some organic acids used as food additives, for chemical denture cleaning for older adults by microbial investigation.

METHODS

Using an in vitro biofilm study, we determined the effects of WOA on Streptococcus sanguinis, S. pneumoniae and Candida albicans attached to heat-cured acrylic resins. Specimens were divided into three groups as follows: control group (TW), commercial denture cleaner group (DC) and WOA group (WOA). Specimens were treated with each for 5 min, 30 min or 8 h, and the numbers of attached microbes were determined by counting colony-forming units or adenosine triphosphate analysis. Using an in vivo biofilm study, we studied the effects of these same solutions on 60 complete dentures. The dentures were divided randomly and blindness into three groups as described above, and treated for 10 min. The numbers of microbes attached to dentures before and after treatment were determined by counting colony-forming units.

RESULTS

For the in vitro biofilm study, there were significant differences in the numbers of microbes between WOA and TW, although there were no significant differences between WOA and DC except for C. albicans. For the in vivo biofilm study, there were significant differences between WOA, DC and TW, although there was no significant difference between WOA and DC.

CONCLUSION

We conclude that water containing organic acids exerts antimicrobial effects as strong as commercial denture cleaner, and it has an application possibility of use for safe chemical denture cleaning for older adults.

Anti-adhesion methods as novel therapeutics for bacterial infections

Anti-adhesion therapies for bacterial infections offer an alternative to antibiotics, with those therapies bacteria are not killed but are prevented from causing harm to a host by inhibiting adherence to host cells and tissues, a prerequisite for the majority of infectious diseases. The mechanisms of these potential therapeutic agents include inhibition of adhesins and their host receptors, vaccination with adhesins or analogs, use of probiotics and dietary supplements that interfere with receptor-adhesin interactions, subminimal inhibitory concentrations of antibiotics and manipulation of hydrophobic interactions. Once developed, these drugs will contribute to the arsenal for fighting infectious disease in the future, potentially subverting antibiotic resistance.