Leaching of monomers from bulk-fill composites: An in vitro study

The Dark Art of Light Curing in Dentistry

OBJECTIVE

This study was designed to show that the commonly reported irradiance values that are quoted in most publications are inadequate to describe the light output from light curing units (LCUs).

METHODS

The total spectral radiant power (mW) output from 12 contemporary LCUs was measured with a fiberoptic spectroradiometer and a calibrated integrating sphere. Five recordings were taken for each LCU and exposure mode. In addition, the irradiances (mW/cm²) delivered at 0-mm, 5-mm and 10-mm distances were recorded through a 6-mm diameter aperture and radiant exposures (J/cm²) from the LCUs were calculated. Light beam profiles from the LCUs were recorded using a beam profiler, and the images were overlaid on a molar tooth to simulate a clinical setting. Data were analyzed using ANOVA followed by Tukey post-hoc test (α=0.05).

RESULTS

The mean power outputs from the LCUs ranged from 380 to 2472 mW (p<0.0001). The highest irradiance was recorded from the Cicada CV 215-G7 (3091 mW/cm² in its highest mode) and the lowest from the Radii Cal CX (731 mW/cm²). The emission spectra differed, even among the multi-peak and single-peak LCUs. Radiant exposures from the entire light tip ranged from 18.3 J/cm², Radii Cal CX, in its standard 25 s exposure mode to 3.9 J/cm² from the Monet Laser in a 3 s exposure setting. Half (50%) of the measured irradiance values from the LCUs differed from the manufacturers' value by more than 10%. There were significant differences in the impact of distance from the tip. The beam profiles visually highlighted the varying effects of distance from the LCU tip among different units.

CONCLUSION

There were significant differences in the emission spectra, power outputs, tip diameters, irradiances, radiant exposures, and the effect distance from the light tips. These differences underline the importance of manufacturers and researchers correctly measuring and reporting the output from the LCU to ensure that research is reproducible and that patients receive acceptable dental restorations.

Evaluation of the Impact of Irradiance Lamps and Storage Media on Elution of TEGDMA from Dental Composites

OBJECTIVES

 The aim of this study was to evaluate and compare the effect of irradiance light and storage media on the elution of triethylene glycol dimethacrylate (TEGDMA) from conventional Filtek Z350XT 3M ESPE and two bulk-fill composites Shofu Beautifil-Bulk and Filtek Bulk fill flowable 3M ESPE using high-performance liquid chromatography (HPLC).

MATERIALS AND METHODS

 Shofu Beautifil-Bulk, Filtek Bulk fill flowable 3M ESPE, and Filtek Z350XT 3M ESPE were the three types of composites used in this study. Disk shaped samples of 4-mm thickness and 10-mm diameter were fabricated using a stainless steel mold and were polymerized using light emitting diode (LED) and quartz tungsten halogen (QTH) lamps. After polymerization, the samples were immersed in ethanol, artificial saliva with betel quid extract, and distilled water for 1, 7, and 30 days, respectively. The elution of monomer TEGDMA was evaluated using HPLC.

STATISTICAL ANALYSIS

 To evaluate the mean concentration difference, mixed way analysis of variance (ANOVA) was applied. Between different light, materials, and within the time duration, Tukey's post hoc test was used. A p value of 0.05 was considered significant.

RESULTS

 During the first day of storage, a significant amount of monomer TEGDMA elution was seen in all the materials. The highest values observed to be in the disks cured with QTH lamp. However, the highest elution was seen when the disks were immersed in ethanol/water solution. While the most stable medium was distilled water, artificial saliva with betel nut extract also had a significant effect on the elution of TEGDMA. The highest value obtained was of Filtek Bulk fill flowable 3M ESPE after 30 days of immersion in both LED and QTH cured disks.

CONCLUSION

 Filtek Bulk fill flowable 3M ESPE shows better properties in relation to the release of monomer TEGDMA as it releases less amount of monomer in the storage media. The release of monomer was highest in ethanol as compared to artificial saliva and distilled water with the passage of time.

A Blinded Comparative Study of Four Commercially Available LEDs and a Laser Light Curing Device

OBJECTIVE

 This study determined the effectiveness of five light-curing units (LCUs; four light-emitting diode [LED] and one laser) used on different settings to photo-activate four conventional resin-based composites (RBCs).

MATERIALS AND METHODS

 A total of 108 RBC specimens were photo-activated in a white Delrin mold representing a mesial-occlusal-distal (MOD) class II restoration in a molar tooth. The proximal boxes were 5 mm deep, and the mesial-distal length was 12 mm. Immediately after photo-curing, the RBC specimens were immersed in a solvent to remove the uncured materials, after which they were photographed and deidentified. A Research Electronic Data Capture survey was created using these images and sent to respondents who blindly assessed the ability of the various LCUs to photo-cure the MOD restorations.

RESULTS

 There were significant differences in how the five curing lights had cured RBCs. One-way analysis of variance (ANOVA), pairwise t-test, Welch's one-way ANOVA, and Kruskal-Wallis rank test in the blinded survey data showed significant differences between the LED curing lights used for two 10-second cures and the laser curing light used for 1 second, and LED lights at lower settings.

CONCLUSION

 There was a significant difference in how the curing lights could photo-cure the RBCs used in this study. The laser curing light used for 1 second produced the worst results in all four RBCs.

The clinical performance of bulk-fill versus the incremental layered application of direct resin composite restorations: a systematic review

OBJECTIVES

To systematically review the scientific evidence comparing the clinical effectiveness of bulk-fill versus incrementally layered conventional resin composites and to evaluate if one method offers clear merits with specific clinical outcomes.

MATERIALS AND METHODS

Using relevant mesh terms and pre-established eligibility criteria in PubMed, Embase, Scopus and Web of Science, a thorough scientific search was conducted with an end-date of 30.04.2023. Randomized controlled clinical trials that involved the direct comparison of Class I and Class II resin composite restorations applied using incremental layering techniques versus bulk-filled in permanent teeth with an observation period of at least six months were considered. To evaluate the bias risk of the finalized records, a revised version of the Cochrane risk-of-bias tool for randomized trials was implemented.

RESULTS

Out of the 1445 records determined, 18 eligible reports were chosen for qualitative analysis. Data obtained was categorized as per, the cavity design, the intervention, the comparator(s), the methods of success/failure assessment, the outcomes, and follow-up. Two studies demonstrated an overall low-risk of bias, fourteen studies raised some concerns, and two studies exhibited high-risk.

CONCLUSION

Bulk filled resin composite restorations demonstrated clinical outcomes similar to those of incrementally layered resin composite restorations within a review interval of 6 months to 10 years.

Effect of topical fluoride applications on residual monomer release from resin-based restorative materials

BACKGROUND

The effects of topical fluoride applications on the release of monomer ingredients from resin-based dental materials by immersion in various extraction solutions are unclear. The aim of this study was to determine the effect of topical fluorides (APF and NaF) on the elution of residual monomers (Bis-GMA, TEGDMA, UDMA, and HEMA) from resin-based materials.

METHODS

Ninety specimens were prepared, 30 bulk-fill composite resin, 30 nanohybrid universal composite resin, and 30 polyacid-modified composite resin (compomer). These were randomly divided into three groups based on fluoride application procedures. Each specimen was kept in 75% ethanol solution, and residual monomers released from materials were analyzed using high-performance liquid chromatography (HPLC) after 10 min, 1 h, 24 h, and 30 days. The groups were compared using the Mann Whitney U and Kruskal Wallis tests. Measurements were analyzed using the Friedman and Wilcoxon signed-rank tests.

RESULTS

Fluoride applications generally had no considerable effect on the amount of residual monomer released from resin-based restorative materials. The amount of monomer release after topical APF application was similar to the release in the control group and was lower than the release in the NaF group. The release of monomers from the resin-based material used in the study did not approach toxic levels at the applied time intervals. The compomer released lower amounts of monomer than other resin-based materials.

CONCLUSIONS

Fluoride applications do not increase monomer release from resin-based restorative materials. However, compomers should be employed by clinicians due to their lower monomer release compared to other resin restorative materials. The release of monomers from all the resin-based materials did not approach toxic levels at the applied time intervals.

Antibacterial and Cytotoxicity of Root Canal Sealer with the Addition of Chitosan Nanoparticle at Various Concentrations

OBJECTIVES

 The aim of this study was to evaluate the addition of chitosan nanoparticle with concentrations of 0, 10, 20, and 30% to the epoxy resin-based (ERB) sealer on its antibacterial and cytotoxicity effect.

METHODS AND MATERIALS

 This research was divided into two studies, the first study was the addition of chitosan with a concentration of 0% (as control), 10, 20, and 30% to an ERB sealer on its antibacterial effect, and the second study was on its cytotoxicity. An agar diffusion test was employed to determine the antibacterial effect on Enterococcus faecalis. An MTT (3-{4,5-dimethylthiazol-2-yl}-2,5-diphenyl tetrazolium bromide) assay was utilized to test the cytotoxicity by evaluating cell viability.

STATISTICAL ANALYSIS

 One-way analysis of variance and Tukey's test (α = 0.05) were used to analyze data obtained from each evaluation with a significance level of 95%.

RESULTS

 The addition of chitosan nanoparticles at concentrations 10, 20, and 30% produced a greater inhibition zone of E. faecalis (p < 0.05), however, had less cytotoxicity compared with no addition of chitosan (0%) (p < 0.05).

CONCLUSION

 The addition of chitosan nanoparticles at concentrations 10, 20, and 30% to the ERB sealer produced greater antibacterial and less cytotoxicity compared with no addition of chitosan (0%).

The effects of polymerization mode and layer thickness on monomer released from bulk fill composite resins

Background

Residual monomers released from composite resins have cytotoxic, mutagenic, and estrogenic effects. Mode of polymerization and application thickness are important for monomer release.

Aims

The aim of this study was to investigate the effects of different modes of a third-generation light-curing unit (LCU) and layer thickness on residual monomer released from two different bulk-fill composite resins. A total of 80 samples were prepared for each bulk-fill composite using a mold. Each bulk-fill composite was divided into four groups according to polymerization mode (standard and extra power) and layer thickness (2 and 4 mm). In addition, four groups were divided into four subgroups according to time periods (1 h, 24 h, 3 days, and 7 days).

Methods and Material

The samples were polymerized with VALO LED device. The amount of residual monomer was measured with High-Performance Liquid Chromatography (HPLC). All statistical analyses were processed using SPSS Version 23.0. The normal distribution of data was confirmed using Kolmogorov-Smirnov Normal Distribution Test and Shapiro-Wilk Normal Distribution Test. When the distribution was normal, parametric tests, Student's t test and one-way ANOVA, were used. When the distribution was not normal, non-parametric tests, Mann-Whitney U test, and Kruskal-Wallis testwere used.

Results

It was found that the standard mode of LCU produced lower amounts of TEGDMA, Bis-GMA, and UDMA in both composite materials. In addition, when the layer thickness increased, TEGDMA, Bis-GMA, and UDMA releases increased, too.

Conclusions

This study revealed that the amount of residual monomers released from bulk-fill composites was affected by layer thickness and polymerization time.

One-Year Clinical Performance of the Fast-Modelling Bulk Technique and Composite-Up Layering Technique in Class I Cavities

The aim of this study was to assess the one year clinical performance of a new application method, the Fast-Modelling Bulk Technique (FMBT), in comparison to the Composite-Up Layering Technique (CULT) in posterior cavities. Thirty patients with two class I cavities on permanent human molars were enrolled in the present study. A total of sixty class I cavities were prepared and randomly divided according to the restoration technique used: 30 cavities restored by incremental layering technique and modelling of the last layer with Composite-Up Technique (CUT) using the composite Filtek Z250XT (3M ESPE; St. Paul, MN, USA) and the other 30 restored by Bulk Filling technique and modelling of the last layer by Fast-Modelling Technique (FMT) using the composite Filtek Bulk Fill Posterior Restorative (3M ESPE; St. Paul, MN, USA). Restorations were evaluated for up to one year by two observers according to Federation Dentaire Internationale (FDI) criteria, through clinical and radiological exams. Exact Fisher tests were used for statistical analysis. (p ≤ 0.05). From a biological perspective, at baseline, teeth restored with both techniques did not reveal any postoperative sensitivity. However, with time, FMBT showed less postoperative sensitivity and therefore more desirable results than CULT with a nonsignificant difference after one year (p > 0.05). Concerning secondary caries, fracture of the material, and marginal adaptation, no significant difference was noted between both techniques (p > 0.05). Regarding marginal staining, CULT resulted in more staining with a significant difference, as compared to FMBT (p < 0.05). Upon radiological examination, FMBT showed a good marginal fit during the first year, whereas CULT showed small empty voids from baseline with a nonsignificant difference (p = 1.00). After one year of clinical function, both techniques showed promising results. The present study indicates that the new FMBT could have a positive effect on the marginal staining of resin composite.

Effect of layer thickness on the elution of monomers from two high viscosity bulk-fill composites: A high-performance liquid chromatography analysis

Aim:

The aim is to evaluate the effect of different layer thickness on the amount of elution of monomers from two high viscosity bulk-fill composites after 24 h and 1 month storage in ethanol using high-performance liquid chromatography (HPLC) analysis.

Materials and Methods:

Forty-eight samples prepared from two high viscosity bulk-fill composite resins; Tetric EvoCeram Bulk Fill and x-tra fil were divided into three groups (n = 8) based on their layer thickness, i.e., Group 1 (2 mm), Group 2 (4 mm), and Group 3 (6 mm) and were then subdivided based on their storage period. The analysis of the eluates was performed using HPLC unit. Statistical analysis was performed using One-way ANOVA, independent sample t-test, and paired “t” test at a significance level of 0.05 (P < 0.05).

Results:

Increase in layer thickness resulted in increased amount of bisphenol A-glycidyl methacrylate (Bis-GMA) and urethane dimethacrylate (UDMA) elution for both composites, i.e., Group 3 > Group 2 > Group 1 and there was statistically significant difference among all the groups. Tetric EvoCeram Bulk Fill showed a statistically significant increase in amount of Bis-GMA and UDMA elution for all groups compared to x-tra fil. Furthermore, increase in storage period resulted in statistically significant increase in amount of Bis-GMA and UDMA elution for both composites, i.e., Group 1B > Group 1A, Group 2B > Group 2A, and Group 3B > Group 3A. The mean value of UDMA elution was higher when compared to that of Bis-GMA elution for both composites and there was statistically significant difference for all groups.

Conclusion:

Within the limitations of this in vitro study, it was concluded that increase in layer thickness resulted in increased amount of Bis-GMA and UDMA elution for both Tetric EvoCeram Bulk Fill and x-tra fil.

Influence of commercial adhesive with/without silane on the bond strength of resin-based composite repaired within twenty-four hours

Background/purpose

It is not clear whether the ground surface of resin-based composite (RBC) polymerized requires the application of an adhesive with/without a silane to improve bond strength. This study investigated the bond strength of RBC repaired within 24 h via the application of adhesive with/without a silane.

Materials and methods

Seventy RBC blocks were prepared and assigned to either 0 or 24 h repair stage. Each stage was divided into seven groups: a control group with no surface roughening or applied adhesive, a surface-roughened group with no applied adhesive, two surface-roughened groups treated with a G-aenial Bond adhesive and a BeautiBond Multi adhesive, two surface-roughened groups treated with the previously-mentioned adhesives as well as silane coupling agents, and one group treated with a Single Bond Universal silane-containing adhesive. Microtensile bond strength (μTBS) measurements were performed after the repaired RBC blocks of each group (n = 5) had been immersed in a 37 °C water bath for 24 h. The failure mode of each sample was determined, and the data were analyzed via one-way analysis of variance and Dunnett's test (p = 0.05).

Results

Regardless of the repair stage, the μTBS values of the adhesive-only and silane-adhesive groups did not differ significantly from those of the control group (p > 0.05). Only the no-adhesive groups exhibited a significantly time-dependent increase in adhesive failure rate.

Conclusion

Our results suggest that the application of adhesives either with or without silane can significantly increase the bond strength of repairs to RBCs polymerized within 24 h.

Ageing of Dental Composites Based on Methacrylate Resins-A Critical Review of the Causes and Method of Assessment

The paper reviews the environmental factors affecting ageing processes, and the degradation of resins, filler, and the filler-matrix interface. It discusses the current methods of testing materials in vitro. A review of literature was conducted with the main sources being PubMed. ScienceDirect, Mendeley, and Google Scholar were used as other resources. Studies were selected based on relevance, with a preference given to recent research. The ageing process is an inherent element of the use of resin composites in the oral environment, which is very complex and changes dynamically. The hydrolysis of dental resins is accelerated by some substances (enzymes, acids). Bonds formed between coupling agent and inorganic filler are prone to hydrolysis. Methods for prediction of long-term behaviour are not included in composite standards. Given the very complex chemical composition of the oral environment, ageing tests based on water can only provide a limited view of the clinical performance of biomaterial. Systems that can reproduce dynamic changes in stress (thermal cycling, fatigue tests) are better able to mimic clinical conditions and could be extremely valuable in predicting dental composite clinical performance. It is essential to identify procedure to determine the ageing process of dental materials.

Clinical performance of bulk-fill and conventional resin composite restorations in posterior teeth: a systematic review and meta-analysis

OBJECTIVES

The purpose of this systematic review was to compare the clinical performance of bulk-fill resin composites with conventional resin composites used for direct restorations of posterior teeth.

METHODS

This review followed the PRISMA statement. This review was registered at PROSPERO (registration number CRD42016053436). A search of the scientific literature was performed by two independent reviewers using the PubMed/MEDLINE, Embase, The Cochrane Library, and Web of Science databases from commencement until January 2018. The research question was "Do bulk-fill resin composites have a clinical performance comparable to conventional resin composites in posterior restorations?" Only studies evaluating class I and II direct restorations in permanent teeth with a follow-up period of at least 1 year were included. The RevMan 5 program was used for meta-analysis, calculating the relative risk (RR) and 95% confidence interval (CI) of the dichotomous outcome (restoration failure or success).

RESULTS

Ten articles were selected, comprising 941 analyzed restorations. The mean follow-up period was 33.6 months (12-72 months). No statistically significant differences in the failure rate were observed between conventional and base/flowable bulk-fill resin composites (p = 0.31; RR 1.49; 95% CI 0.69-3.25) or full-body/sculptable bulk-fill resin composites (p = 0.12; RR 1.89; 95% CI 0.84-4.24).

CONCLUSIONS

The present systematic review and meta-analysis indicate similar clinical performances of bulk-fill and conventional resin composites over a follow-up period of 12 to 72 months.

CLINICAL SIGNIFICANCE

Based on the results of this study, the bulk-fill resin composites could be an alternative for direct restorations in posterior teeth. However, clinical trials of longer duration are required.