The formation of cariogenic plaque to contemporary adhesive restorative materials: an in vitro study.

The research exploiting the ability of dental materials to induce or prevent secondary caries (SC) development still seems inconclusive. Controlling bacterial adhesion by releasing bacteriostatic ions and improving the surface structure has been suggested to reduce the occurrence of SC. This paper analyses the impact of five distinctively composed dental materials on cariogenic biofilm formation. Forty-five specimens of three composites (CeramX Spectra ST, Admira Fusion, Beautifil II) and two glass-ionomers (Fuji II LC, Caredyne Restore), respectively, were incubated in bacterial suspension composed of Streptococcus mutans, Lactobacillus acidophilus, Streptococcus mitis, Streptococcus sanguinis, and Streptococcus salivarius at pH 7.0 and 5.5. Coverslips were used as a control. Adhered bacteria were collected after 2, 4, 6, 12, 24, and 48 h and analyzed using quantitative polymerase chain reaction (qPCR). Fluoride leakage was measured at each collection. The specimens' surface topography was assessed using interferometry. In the present study, surface roughness seemed to have a partial role in bacterial adhesion and biofilm formation, together with chemical composition of the materials tested. Despite differences in fluoride leakage, biofilm accumulation was similar across materials, but the number of adhered bacteria differed significantly. A release of other ions may also affect adhesion. These variations suggest that certain materials may be more prone to initiating secondary caries.

Residual stress associated with crystalline phase transformation of 3-6 mol% yttria-stabilized zirconia ceramics induced by mechanical surface treatments.

Monolithic dental prostheses made of 3-6 mol% yttria-stabilized zirconia (3-6YSZ) have gained popularity owing to their improved material properties and semi-automated fabrication processes. In this study, we aimed to evaluate the influence of mechanical surface treatments, such as polishing, grinding, and sandblasting, on the residual stress of 3-6YSZ used for monolithic prostheses in association with crystalline phase transformation. Plate specimens were prepared from five dental zirconia blocks: Aadva Zirconia ST (3YSZ), Aadva Zirconia NT (6YSZ), Katana HT (4YSZ), Katana STML (5YSZ), and Katana UTML (6YSZ). The specimens were either polished using 1, 3, or 9 µm diamond suspensions, ground using 15, 35, or 55 µm diamond discs, or sandblasted at 0.2, 0.3, or 0.4 MPa. The residual stress, crystalline phase, and hardness were analyzed using the cosα method, X-ray diffraction (XRD), and Vickers hardness test, respectively. Additionally, we analyzed the residual stress on the surfaces of monolithic zirconia crowns (MZCs) made of 4YSZ, 5YSZ, and 6YSZ, which were processed using clinically relevant procedures, including manual grinding, followed by polishing using a dental electric motor on the external surface, and sandblasting on the internal surface. Residual stress analysis demonstrated that grinding and sandblasting, particularly the latter, resulted in the generation of compressive residual stress on the surfaces of the plate specimens. XRD revealed that the ground and sandblasted specimens contained a larger amount of the rhombohedral phase than that of the polished specimens, which may be a cause of the residual stress. Sandblasting significantly increased the Vickers hardness compared to polishing, which may possibly be due to the generation of compressive residual stress. In the case of MZCs, compressive residual stress was detected not only on the sandblasted surface, but also on the polished surface. The difference in the residual stress between the plate and crown specimens may be related to the force applied during the automated and manual grinding and polishing procedures. Further studies are required to elucidate the effects of the compressive residual stress on the clinical performance of MZCs.

Inhibition of tooth demineralization caused by Streptococcus mutans biofilm via antimicrobial treatment using hydrogen peroxide photolysis.

OBJECTIVES: An antimicrobial technique utilizing hydroxyl radicals generated by the photolysis of 3% H2O2 has been developed recently. The present study aimed to evaluate the effect of H2O2 photolysis treatment on tooth demineralization caused by Streptococcus mutans biofilm. MATERIALS AND METHODS: To induce tooth demineralization, S. mutans biofilm was allowed to form on the maxillary first molars collected from Wistar rats via 24-h culturing. The samples were immersed in 3% H2O2 and irradiated with 365-nm LED (H2O2 photolysis treatment). Viable bacterial counts in the biofilm were evaluated immediately after treatment and after an additional 30-h culturing by colony counting. The acidogenicity of the biofilm, re-established 30 h after treatment, was assessed by measuring the pH. The effect of H2O2 photolysis treatment on tooth demineralization was assessed by measuring the depth of the radiolucent layer in micro-CT images. RESULTS: H2O2 photolysis significantly reduced viable bacterial counts in the biofilm to 3.7 log colony forming units (CFU)/sample, while the untreated group had 7.9 log CFU/sample. The pH of the biofilm re-established after treatment (6.6) was higher than that of the untreated group (5.3). In line with the pH measurement, the treatment group had a significantly lower depth of radiolucent layer in dentin than the untreated group. CONCLUSIONS: H2O2 photolysis treatment was effective not only in killing the biofilm-forming S. mutans but also in lowering the acidogenicity of the biofilm. Thus, this technique could inhibit tooth demineralization. CLINICAL RELEVANCE: H2O2 photolysis can be applicable as a new dental caries treatment.

Influence of crystalline phase transformation induced by airborne-particle abrasion and low-temperature degradation on mechanical properties of dental zirconia ceramics stabilized with over 5 mol% yttria.

Monolithic dental prostheses fabricated from 5 mol% yttria-stabilized zirconia (5YZ) have been developed to improve the translucency of conventional 3 mol% yttria-stabilized zirconia. In this study, we aimed to evaluate the influence of airborne-particle abrasion (APA) and low-temperature degradation (LTD) on the mechanical properties of 5YZ in association with the crystalline phase transformation. In total, 120 disc-shaped specimens of two brands of 5YZ (Lava Esthetic and Katana UTML) were prepared. The specimens were divided into four groups (n = 15 for each group): (i) control, (ii) APA, (iii) LTD, and (iv) APA + LTD groups. APA was performed with 50 µm alumina particles, and LTD was induced by autoclaving at 134 °C for 50 h. The biaxial flexural strength of the specimens was assessed using a piston-on-three-ball test according to ISO 6872:2015, and Vickers hardness was determined using a microhardness tester. The crystalline phase was analyzed by the Rietveld refinement of X-ray diffraction patterns. APA significantly increased the flexural strength of the Lava Esthetic specimens, whereas LTD hardly affected the strength of both materials. APA and APA + LTD significantly increased the Vickers hardness of both materials. According to Rietveld analysis, the pseudocubic phase was predominant in both materials, i.e., 66 mass% and 81 mass% in the Lava Esthetic and Katana UTML specimens, respectively. APA induced the rhombohedral phase at approximately 37 mass% in both materials, while LTD induced the monoclinic phase at 2.8 mass% in the Lava Esthetic specimens and 0.9 mass% in the Katana UTML specimens. APA + LTD weakly affected the amount of the rhombohedral phase but slightly increased the amount of the monoclinic phase. These findings suggest that APA may improve the mechanical properties of 5YZ, particularly hardness, via the generation of the rhombohedral phase. In contrast, the influence of LTD on the mechanical and microstructural properties of 5YZ was limited.

Light-curing units used in dentistry: Effect of their characteristics on temperature development in teeth.

This study aimed to investigate pulp chamber and surface temperature development using different LED light curing units (LCUs). Eight brands of LED-LCUs were tested in a laboratory bench model. The pulp chamber and surface temperature were recorded with a type T thermocouple and infrared cameras, respectively. The highest pulp chamber and surface temperature increase was 6.1±0.3°C and 20.1±1.7°C, respectively. Wide-spectrum LED-LCUs produced higher pulp chamber temperature increase at 0 mm and 2 mm but lower at 4 mm. Narrow-spectrum LED-LCUs produced higher surface temperature increase. LED-LCU featuring modulated output mode resulted in lower increase in pulp chamber temperature but higher on surface temperature. LED-LCU with light guide tip delivering an inhomogeneous beam caused higher increase in temperature on the surface and in the pulp chamber. LED-LCUs with different spectral emission, output mode and light guide tip design contributed to different temperature development in the pulp chamber and at the surface of teeth.

Opportunities for caries prevention using an ion-releasing coating material: a randomised clinical study.

Ion-releasing materials (containing fluoride and boron, for example) have shown caries-preventive effects in vitro. The purpose of the present study was to investigate the impact of multi-ion-releasing coating material on pH stabilisation, plaque accumulation and the bacterial composition of dental plaque during a time period of 90 days. The null hypothesis tested here was that the evaluated material would not show any differences in pH stabilisation, plaque accumulation or bacterial composition compared with control material.The study was carried out as a double-blind, split-mouth, randomised, controlled clinical trial in 28 volunteers. Over the evaluation period (days 4, 30, 60 and 90), pH measurements, plaque index and plaque sampling for bacterial analyses were conducted in a calibrated, standardized manner. The study received ethical permission and was carried out in accordance with the Helsinki Declaration.A significant difference was observed, with less plaque accumulation over time in the subjects in whom the ion-releasing material was applied in comparison to the non-active group. No significant difference was evident in terms of either pH stabilisation or plaque levels of mutans streptococci.The null hypothesis relating to plaque accumulation was rejected, with a lower plaque index shown for the test group up to 60-90 days. No adverse effects during the observation period were observed. Since the studied cohort was healthy from a caries perspective, more clinical studies are needed to further evaluate the caries-prevention potential of the ion-releasing material in other patient groups.

Reactions of dental pulp to hydrogen peroxide photolysis-based antimicrobial chemotherapy under ultraviolet-A irradiation in rats.

Hydrogen peroxide photolysis-based antimicrobial chemotherapy that utilizes ultraviolet-A irradiation (UVA-H2O2 photolysis) has been previously proposed as a method of treatment of cariogenic biofilm. Therefore, in the present study, we aimed to assess time-dependent reactions in the dental pulp of rats after UVA-H2O2 photolysis. Maxillary first molars were treated. UVA irradiation (wavelength: 365 nm) with 3 wt% H2O2 was performed for 90 s at a radiant emittance of 500-2000 mW/cm2 on the rats for 3 consecutive days or only 1 day. The animals were sacrificed at Days 1, 3, 7, and 21 after the treatment for the histological evaluation of inflammatory cells and immunohistochemistry of heat shock protein (HSP)-25, a marker of odontoblasts. Tertiary dentin formation was evaluated at Day 21 by histomorphometry and micro-CT analysis. UVA-H2O2 photolysis elicited little infiltration of inflammatory cells, but disturbances in the odontoblast layer and/or presence of localized degenerative tissue were observed on Day 3. This condition was followed by a healing process that was characterized by the reappearance of HSP-25 positive odontoblast-like cells at Day 7 and tertiary dentin formation at Day 21. The amount of tertiary dentin formed was dependent on the intensity of treatment; repeated UVA irradiations of H2O2 at 2000 mW/cm2 resulted in the largest amount of tertiary dentin formation at the pulp horn regions. Our findings suggest that UVA-H2O2 photolysis treatment can be used to treat dental caries clinically because the post-treatment inflammatory reaction was minimal and tertiary dentin formation was substantial, which may prove effective in protecting dental pulp from external irritants. As a cautionary consideration, the radiant emittance of the UVA irradiation should be carefully optimized before clinical application.

Heat Development in the Pulp Chamber During Curing Process of Resin-Based Composite Using Multi-Wave LED Light Curing Unit.

OBJECTIVE: The study aimed to investigate factors contributing to heat development during light curing of a flowable bulk-fill resin-based composite (SDRTM, Lot # 602000876, Dentsply Sirona, Konstanz, Germany) (RBC). MATERIALS AND METHODS: Temperatures were measured with calibrated thermocouples. A multi-wave light-emitting diode (LED) light curing unit (LCU) was used (Ivoclar Vivadent, Schaan, Lichtenstein). In all experiments, the RBC was first cured (cured) for 30 s and, after 5 min of recovery time, received a second LCU irradiation (post-cured) for 30 s. The exothermic reaction was measured by calculating the Δ temperature between cured and post-cured RBC. In a cylinder-shaped polymer mold, temperature was recorded inside of RBC during curing (part 1) and light transmission through RBC during curing was investigated (part 2). Pulpal temperatures were assessed in an extracted third molar during light curing (part 3). Data were statistically analyzed using one-way ANOVA (α=0.05). RESULTS: Increased thickness of RBC led to decreased pulp chamber temperatures. Inside RBC, there was a large variation in heat development between the cured and post-cured groups (p<0.05). The cured group absorbed more LCU irradiation than the post-cured group. CONCLUSION: The irradiance of the LCU seemed to be a more important factor than exothermic reaction of RBCs for pulp chamber heat development. Flowable bulk-fill RBCs can act as a pulpal insulator against LCU irradiation, despite their exothermic curing reaction.

Mechanical and microstructural properties of ultra-translucent dental zirconia ceramic stabilized with 5 mol% yttria.

Monolithic dental prostheses fabricated from 3 mol.% yttria-stabilized zirconia (3YZ) are becoming increasingly popular. Recently, 5 mol.% yttria-stabilized zirconia (5YZ) which significantly improves the translucency of 3YZ has been prepared. However, its mechanical and microstructural properties, especially those affected by low-temperature degradation (LTD), have not been fully elucidated yet. The objective of the present study was to establish the relationship between the flexural strength of 5YZ with or without autoclave-induced LTD and its microstructural properties. For this purpose, a total of 320 bar-shaped specimens were cut from 5YZ and 3YZ blocks, and half of the specimens in each group were autoclaved at 134 °C for 50 h. Their flexural strengths were determined by conducting three-point bending tests, and the obtained results were analyzed by the Weibull statistical method. Grain sizes and crystalline structures of the specimens were analyzed by scanning electron microscopy (SEM) and X-ray diffraction, respectively. Additionally, the LTD-induced phase transformation was examined by Raman microscopy and cross-sectional surface analysis. The characteristic strengths of 5YZ and 3YZ were approximately 620 and 950 MPa, respectively, and 5YZ was found to be more resistant to LTD in terms of phase transformation than 3YZ. However, a low amount of the monoclinic phase was detected even in 5YZ after 50 h of autoclaving, which significantly decreased its flexural strength and reliability. The results of SEM analysis revealed that 5YZ was composed of two distinct regions: a dominant matrix with large grains (median size: 0.8 µm) and scattered areas with small grains (median size: 0.4 µm). Phase transformation analysis and fractography data indicated that the small-grain region was strongly affected by LTD and likely represented a fracture origin. The described properties should be considered during the clinical application of monolithic 5YZ dental prostheses.

Suboptimal light curing and direct exposure to water of two contemporary composites: degree of conversion, sorption, solubility, and Knoop hardness.

The water sorption and solubility of two polymer resin-based dental composite materials were assessed in order to evaluate the effects of immediate post-cure water exposure on the water sensitivity of the composites. Each material was tested with two different light curing setups. The radiant exposure of the two curing setups differed by a factor of 5. After exposure to water and subsequent drying, the Knoop surface hardness was measured. The change in the degree of conversion in both water and air storage medium within the first 24 h after curing was monitored by Raman spectroscopy. No significant differences in the degree of conversion were detected 24 h after curing. Samples exposed to the lower irradiation dose showed higher solubility and a lower surface hardness than the samples exposed to the higher irradiation dose. Early exposure to water did not cause detectable differences in the ongoing polymerization process. Increase in radiant exposure reduced the fraction of unbound constituents and increased the crosslink density, thereby reducing the plasticity of the material.

Airborne exposure to gaseous and particle-associated organic substances in resin-based dental materials during restorative procedures.

Dental composite dust has been shown to act as a vehicle for methacrylates in vivo/in vitro. The objective of this study was to assess airborne exposure of dental personnel to gaseous and particle-associated organic constituents from resin-based dental materials in a simulated clinic. Sampling of total aerosol fractions and gaseous substances was performed by dental students carrying particle filters and gas sorbents attached to a personal pump during preclinical restorative procedures in phantom models (n = 13). Water from the phantoms was sampled. Organic substances were extracted from the sampled water, particle filters, and gas sorbents. Qualitative and quantitative analyses were performed by gas chromatography-mass spectrometry (GC-MS) and ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS). The methacrylates 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) and the additives camphorquinone (CQ), butylated hydroxytoluene (BHT), and ethyl 4-(dimethylamino)benzoate (DMABEE), were quantified in the gas and particle fractions sampled. A positive-control experiment was conducted. No methacrylates were detected in the gas or particle fractions sampled, whereas strong signals for methacrylates were detected in the positive controls, matching the analysis of the uncured material. In addition, TEGDMA and DMABEE were quantified in the sampled water. Airborne exposure to constituents in resin-based dental materials was below the detection limit. However, the extent of exposure is probably dependent on the procedure, preventive measures, and type of materials used.

Hydroxyl radicals generated by hydrogen peroxide photolysis recondition biofilm-contaminated titanium surfaces for subsequent osteoblastic cell proliferation.

Titanium dental implants have been successfully used for decades; however, some implants are affected by peri-implantitis due to bacterial infection, resulting in loss of supporting bone. This study aimed to evaluate the effect of an antimicrobial chemotherapy employing H2O2 photolysis-developed to treat peri-implantitis-on biofilm-contaminated titanium surfaces in association with osteoblastic cell proliferation on the treated surface. Titanium discs were sandblasted and acid-etched, followed by contamination with a three-species biofilm composed of Porphyromonas gingivalis, Fusobacterium nucleatum, and Streptococcus mitis. This biofilm model was used as a simplified model of clinical peri-implantitis biofilm. The discs were subjected to ultrasound scaling, followed by H2O2 photolysis, wherein 365-nm LED irradiation of the disc immersed in 3% H2O2 was performed for 5 min. We analysed proliferation of mouse osteoblastic cells (MC3T3-E1) cultured on the treated discs. Compared with intact discs, biofilm contamination lowered cell proliferation on the specimen surface, whereas H2O2 photolysis recovered cell proliferation. Thus, H2O2 photolysis can recover the degraded biocompatibility of biofilm-contaminated titanium surfaces and can potentially be utilised for peri-implantitis treatment. However, to verify the findings of this study in relation to clinical settings, assessment using a more clinically relevant multi-species biofilm model is necessary.

The dental monomer HEMA causes proteome changes in human THP-1 monocytes.

Resin-based biomaterials are widely used in medical and dental treatment, and both clinicians and patients are exposed to the materials. The knowledge of toxicity is mainly based on in vitro studies at exposure concentrations that induce cell death. However, severe cell damage and cell death signaling may overshadow essential cellular events caused by a possible toxicant. For dental resins, the knowledge of interaction with living cells at more clinical relevant exposure doses is sparse. 2-Hydroxyethylmethacrylate (HEMA) is a commonly used monomer in dental resins. Measuring cellular adaptation to HEMA at concentrations that did not reduce cell viability was the main focus of this study. Stable isotope labeling with amino acids in cell culture was used to measure proteome changes in cultured THP-1 cells exposed to HEMA. Western blotting verified the results. Cells exposed to HEMA increased their level of several cytoprotective proteins. The observed adaptation is compatible with increased oxidative burden caused by GSH depletion and the electrophilic characteristic of HEMA. The present approach to analyzing the toxic potential of HEMA yielded information on interactions with living cells is not previously reported. This detailed information is of great value to make better predictions of possible side effects in the clinic. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 851-859, 2019.

Surface properties of dental zirconia ceramics affected by ultrasonic scaling and low-temperature degradation.

Zirconia (3Y-TZP) dental prostheses are widely used in clinical dentistry. However, the effect of ultrasonic scaling performed as a part of professional tooth cleaning on 3Y-TZP dental prostheses, especially in conjunction with low-temperature degradation (LTD), has not been fully investigated. The present study aimed to evaluate the influence of ultrasonic scaling and LTD on the surface properties of 3Y-TZP in relation to bacterial adhesion on the treated surface. 3Y-TZP specimens (4 × 4 × 2 mm) were polished and then subjected to autoclaving at 134°C for 100 h to induce LTD, followed by 10 rounds of ultrasonic scaling using a steel scaler tip for 1 min each. Surface roughness, crystalline structure, wettability, and hardness were analyzed by optical interferometry, X-ray diffraction analysis, contact angle measurement, and nano-indentation technique, respectively. Subsequently, bacterial adhesion onto the treated 3Y-TZP surface was evaluated using Streptococcus mitis and S. oralis. The results demonstrated that the combination of ultrasonic scaling and LTD significantly increased the Sa value (surface roughness parameter) of the polished 3Y-TZP surface from 1.6 nm to 117 nm. LTD affected the crystalline structure, causing phase transformation from the tetragonal to the monoclinic phase, and decreased both the contact angle and surface hardness. However, bacterial adhesion was not influenced by these changes in surface properties. The present study suggests that ultrasonic scaling may be acceptable for debridement of 3Y-TZP dental prostheses because it did not facilitate bacterial adhesion even in the combination with LTD, although it did cause slight roughening of the surface.

Critical considerations on load-to-failure test for monolithic zirconia molar crowns.

Application of monolithic zirconia crowns (MZCs) with reduced thickness to the molar region has been proposed, but potential complications have yet to be fully evaluated in laboratory tests. The present study aimed to develop a clinically relevant load-to-failure test in combination with fatigue treatments involving thermal and mechanical cycling (TC and MC) to evaluate the fracture resistance of molar MZCs. MZCs with a minimal thickness of 0.5 mm were bonded to dies made of resin-based composite (RBC), epoxy resin (EP), or polyoxymethylene-copolymer (POM-C). The samples were either untreated (UT) or subjected to TC (5-55 °C for 1â€¯× 105 cycles) and MC (300 N for 2.4â€¯× 106 cycles). The stress generated by TC and MC was simulated by finite element modeling. The load-to-failure test was performed using an inverse V-shaped two-plane indenter and was followed by fractographic analysis. The median values of fracture load for MZC/RBC and MZC/EP in the TC group were significantly lower than those in the UT group. MC also decreased the median value of fracture load for MZC/RBC significantly, but not that for MZC/EP and MZC/POM-C. Fractography revealed that the fracture started in the cervical area in all groups, which is similar to clinically failed crowns. The simulation confirmed stress concentration at the cervical area in both TC and MC groups. The present study suggests that the load-to-failure test using a two-plane indenter could induce clinically relevant fracture of MZCs, the vulnerability of the MZCs depends largely on the die material employed, and MZCs are more likely to be damaged by thermal fatigue than mechanical fatigue.

Dose- and time-dependent effects of triethylene glycol dimethacrylate on the proteome of human THP-1 monocytes.

Triethylene glycol dimethacrylate (TEGDMA) is commonly used in polymer resin-based dental materials. This study investigated the molecular mechanisms of TEGDMA toxicity by identifying its time- and dose-dependent effects on the proteome of human THP-1 monocytes. The effects of different concentrations (0.07-5 mM) and exposure times (0-72 h) of TEGDMA on cell viability, proliferation, and morphology were determined using a real-time viability assay, automated cell counting, and electron microscopy, and laid the fundament for choice of exposure scenarios in the proteomic experiments. Solvents were not used, as TEGDMA is soluble in cell culture medium (determined by photon correlation spectroscopy). Cells were metabolically labeled [using the stable isotope labeled amino acids in cell culture (SILAC) strategy], and exposed to 0, 0.3 or 2.5 mM TEGDMA for 6 or 16 h before liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. Regulated proteins were analyzed in the STRING database. Cells exposed to 0.3 mM TEGDMA showed increased viability and time-dependent upregulation of proteins associated with stress/oxidative stress, autophagy, and cytoprotective functions. Cells exposed to 2.5 mM TEGDMA showed diminished viability and a protein expression profile associated with oxidative stress, DNA damage, mitochondrial dysfunction, and cell cycle inhibition. Altered expression of immune genes was observed in both groups. The study provides novel knowledge about TEGDMA toxicity at the proteomic level. Of note, even low doses of TEGDMA induced a substantial cellular response.

Influence of microscale expansion and contraction caused by thermal and mechanical fatigue on retentive strength of CAD/CAM-generated resin-based composite crowns.

CAD/CAM-generated resin-based composite crowns have been proposed as an inexpensive alternative to conventional crowns. However, concerns have been raised about crown loosening in clinical use. Therefore, the present in vitro study aimed to evaluate the influence of thermal and mechanical cycling (TC and MC) on retentive strength of CAD/CAM resin-based crowns in relation to microscale expansion and contraction caused by fatigue. Eighty standardized dies were produced using a resin-based composite material. Crowns were milled from resin-based composite (n = 40) and glass-ceramic blocks (n = 40; control) using a dental CAD/CAM system. The crowns bonded to the dies were subjected to TC (temperature: 5 and 55 °C, cycles: 50,000) and MC (load: 200 N, cycles: 1.2 million). After fatigue treatment, retentive strength of the crowns was evaluated by a crown pull-off test at a crosshead speed of 1 mm/min. Coefficient of thermal expansion (CTE) and modulus of elasticity (E-modulus) of each material were also analyzed to estimate the microscale expansion and contraction during TC and MC. TC and MC significantly reduced the retentive strength of the CAD/CAM resin-based crowns whereas that of the CAD/CAM ceramic crowns was only affected by TC. In addition, the resin-based crowns showed a higher number of crown loosening during TC than the ceramic crowns. Analyses of CTE and E-modulus indicated that the resin-based crowns would be more deformed during TC and MC than the ceramic crowns. The present study demonstrated that the resistance of crowns to microscale expansion and contraction caused by thermal and mechanical fatigue would play an important role in maintaining retentive strength.

Time-kill kinetic analysis of antimicrobial chemotherapy based on hydrogen peroxide photolysis against Streptococcus mutans biofilm.

A recently developed antimicrobial technique utilizing hydroxyl radicals generated by hydrogen peroxide (H2O2) photolysis represents a promising new therapy for preventing and treating dental caries. The present study compared the antimicrobial time-kill kinetics of H2O2 photolysis, conventional antiseptics, and antimicrobial photodynamic therapy (aPDT) against biofilm-forming Streptococcus mutans (cariogenic bacteria) grown on hydroxyapatite disks. H2O2 photolysis was performed by irradiating the biofilm immersed in 3% H2O2 with 365-nm light-emitting diode (LED) light at an irradiance of 1000mW/cm2 for up to 1.5min. Antiseptic treatments consisted of 0.2% chlorhexidine gluconate, 0.5% povidone-iodine, and 3% H2O2. The biofilm was immersed in each antiseptic for up to 4min. aPDT was performed by irradiating the biofilm immersed in 100µM methylene blue or toluidine blue O with 655-nm laser light at 1000mW/cm2 for up to 4min. Based on the time-kill assay, the decimal reduction value (D-value) of each treatment was determined. With a D-value of 0.06min, H2O2 photolysis exhibited the highest bactericidal effect against biofilm-forming S. mutans. In contrast, antiseptics and aPDT exerted a slower bactericidal effect, with D-values of 0.9-2.7min. In conclusion, the antimicrobial technique based on H2O2 photolysis using 365-nm LED represents a strong adjunctive chemotherapy for dental caries treatment.

Photo-irradiated caffeic acid exhibits antimicrobial activity against Streptococcus mutans biofilms via hydroxyl radical formation.

An antimicrobial technique based on photo-oxidation of caffeic acid (CA) has recently been developed, but its effect on biofilm-forming bacteria is unknown. The present study aimed to evaluate the effect of photo-irradiated CA against Streptococcus mutans (cariogenic bacteria) biofilm as it relates to hydroxyl radical formation. S. mutans biofilms grown on hydroxyapatite disks were immersed in CA solution (0-2 mg/mL) and irradiated with LED light at wavelengths of 365, 385, and 400 nm and at irradiances of 500, 1000, and 2000 mW/cm2 for 4 min. Biofilm viable bacterial counts were determined by colony counting. The yield of hydroxyl radicals generated by the LED irradiation of CA solution was quantified by electron spin resonance analysis. Of the conditions tested, the highest bactericidal effect, with a > 5-log reduction in viable bacterial counts, was obtained by irradiation of a 1 mg/mL CA solution with 385 nm LED and at an irradiance of 2000 mW/cm2. Hydroxyl radical formation was related to this bactericidal effect. The present study suggests that the antimicrobial technique based on the 385 nm LED irradiation of CA is effective against cariogenic biofilms and can be applied as an adjunctive chemotherapy for dental caries.

Analysis of organic components in resin-modified pulp capping materials: critical considerations.

The purpose of this study was to elucidate the organic composition and eluates of three resin-based pulp-capping materials in relation to their indications and safety data sheets. Uncured samples of Theracal LC, Ultra-Blend Plus, and Calcimol LC were investigated using gas chromatography-mass spectrometry (GC-MS) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Identification/quantification of 7-d leachables of cured samples was performed using GC-MS for 2-hydroxyethyl methacrylate (HEMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), camphorquinone (CQ), ethylene glycol dimethacrylate (EGDMA), ethyl-4-(dimethylamino)benzoate (DMABEE), and triethylene glycol dimethacrylate (TEGDMA). A similar organic composition was found for Ultra-Blend and Calcimol; however, only Ultra-Blend is indicated for direct pulp-capping. In contrast to the other materials analysed, Theracal contained substances of high molecular weight. The safety data sheets of all materials were incomplete. We detected HEMA, CQ, and TEGDMA in eluates from Ultra-Blend and Calcimol, and it was considered that HEMA might have originated from decomposition of diurethane dimethacrylate (UDMA) in the GC-injector. For Theracal, additives associated with light curing (DMABEE and CQ) were detected in higher amounts (4.11 and 19.95 µg mm-2 ) than in the other materials. Pores were quantified in all samples by micro-computed tomography (micro-CT) analysis, which could influence leaching. The organic substances in the investigated materials might affect their clinical suitability as capping agents, especially for direct capping procedures.