Impact of optical fiber-based photo-activation on dental composite polymerization.

OBJECTIVES: The study aimed to introduce a novel two-step optical fiber-based photo-activation of dental resin-based composites (RBCs) for reducing polymerization shrinkage stress (PSS). METHODS: Proposed protocol design - in the first step, two flexible plastic optical fibers connected to a dental light curing unit (LCU), were used as light guides inserted into the filling to initiate low-irradiance polymerization from within; in the second step, fibers were extracted and remaining voids were filled with RBC, followed by conventional high-irradiance curing to finalize polymerization. Three bulk-fill RBCs were tested (Beautifil-Bulk Restorative, Filtek Bulk-fill Posterior, Tetric PowerFill) using tooth cavity models. Three non-invasive examination techniques were employed: Digital Holographic Interferometry, Infrared Thermography, and Raman spectroscopy for monitoring model deformation, RBC temperature change, and degree of conversion (DC), respectively. A control group (for each examined RBC) underwent conventional photo-activation. RESULTS: The experimental protocol significantly reduced model deformation by 15 - 35 %, accompanied by an 18 - 54 % reduction in RBC temperature change, emphasizing the impact of thermal shrinkage on PSS. Real-time measurements of deformation and temperature provided indirect insights into reaction dynamics and illuminated potential mechanisms underlying PSS reduction. After a 24-hour dark-storage period, DC outcomes comparable to conventional curing were observed, affirming the clinical applicability of the method. CONCLUSIONS: Protocol involving the use of two 1.5 mm fibers in the first step (300 mW/cm2 x 10 s), followed by a second conventional curing step (1000 mW/cm2 x 10 s), is recommended to achieve the desired PSS reduction, while maintaining adequate DC and ensuring efficient clinical application. CLINICAL SIGNIFICANCE: Obtained PSS reduction offers promise in potentially improving the performance of composite restorations. Additionally, leveraging the flexibility of optical fibers improves light guide approach for restorations on posterior teeth. Meanwhile, implementation in clinical practice is easily achievable by coupling the fibers with commercial dental LCUs using the provided plastic adapter.

Toxicity and cytokine release from human dental pulp stem cells after exposure to universal dental adhesives cured by single peak and polywave LEDs.

OBJECTIVES: to assess the impact of universal adhesives, cured with single-peak and polywave LEDs, on the metabolic activity and cytokine release of human dental pulp stem cells (hDPSCs). In addition, analyze the degree of conversion (DC) of the adhesives cured with the different LEDs. METHODS: Discs (5 mm diameter, 1 mm thick) were prepared using three universal adhesives: Single Bond Universal (SBU, 3 M ESPE), Optibond Universal (OBU, Kerr), and Zipbond Universal (ZBU, SDI). These discs were cured for 40 s using a single-peak (DeepCure, 3 M ESPE) or a polywave light-emmiting diode (LED) curing unit (Valo Grand, Ultradent). After 24 h, the specimens were placed in 24-well culture plates, each containing 1 mL of culture medium for 24 h. hDPSCs (1.8 ×104) were seeded in 96-well plates and allowed to grow for 24 h. Subsequently, the cells were exposed to the extracts (culture medium containing eluates from the adhesive discs) for an additional 24 h. Cells not exposed to the extracts were used as a control group. The mitochondrial metabolism was assessed using the MTT assay and the cytokine release evaluated through MAGPIX. The degree of conversion of the adhesives was analyzed using FTIR (n = 5). The results were analyzed by ANOVA two-way and Tukey's test. RESULTS: OBU and ZBU eluates caused a statistically significant reduction in mitochondrial metabolism, regardless of the LED used, indicating their cytotoxicity. In contrast, SBU did not significantly affect the MTT results, resembling the control group. A higher release of cytokines IL-1, IL-6, IL-10, and TNF-α were found in association to ZBU. SBU, on the other hand, increased the release of IL-8. OBU did not influenced the cytokine release. SBU presented the higher DC, while OBU and ZBU had similar DC, lower than SBU. SIGNIFICANCE: In conclusion, universal adhesives exhibit toxicity towards hDPSCs, but the extent of toxicity varies depending on the adhesive material. ZBU was associated with increased cytokine release, particularly pro-inflammatory mediators, from hDPSCs. The different LEDs did not influenced the cytotoxicity of the evaluated adhesives.

Polymerization efficiency of different bulk-fill resin composites cured by monowave and polywave light-curing units: a comparative study.

OBJECTIVES: The objective was to evaluate the polymerization efficiency of different bulk-fill resin-based composites cured by monowave and polywave light-curing units, by assessment of the degree of conversion and Vickers microhardness at different depths. METHOD AND MATERIALS: Two commercially available bulk-fill resin-based composites were used: Filtek One Bulk Fill Restorative (3M ESPE) and Tetric N-Ceram Bulk Fill (Ivoclar Vivadent). The light-curing units utilized were two LED light-curing units: a monowave LED light-curing unit (BlueLEX LD-105, Monitex) and a polywave LED light-curing unit (Twin Wave GT-2000, Monitex). For each test, 20 cylindrical specimens (4 mm diameter, 4 mm thickness) were prepared from each bulk-fill resin-based composite using a split Teflon mold. Ten specimens were light-cured by the monowave light-curing unit and the other ten were light-cured by the polywave light-curing unit according to the manufacturer's recommendations. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used to assess the degree of conversion, and a Vickers microhardness tester was used to assess Vickers microhardness. Statistical analysis was performed using three-way ANOVA and Tukey post-hoc tests (P < .05). RESULTS: The degree of conversion and Vickers microhardness in bulk-fill resin-based composites containing only camphorquinone as photoinitiator were similar when cured with either monowave or polywave light-curing units. However, bulk-fill resin-based composites containing a combination of photoinitiators exhibited significantly higher degree of conversion and Vickers microhardness when cured with a polywave light-curing unit. Although all groups showed statistically significant differences between the top and bottom surfaces regarding degree of conversion and Vickers microhardness, all of them showed bottom/top ratios > 80% regarding degree of conversion and Vickers microhardness. CONCLUSION: The polywave light-curing unit enhanced the polymerization efficiency of bulk-fill resin-based composites especially when the latter contained a combination of photoinitiators, but does not prevent the use of a monowave light-curing unit.

Thermography and conversion of fast-cure composite photocured with quad-wave and laser curing lights compared to a conventional curing light.

OBJECTIVES: This study investigated effects of the different emittance-mode protocols from three light curing units (LCUs): (i) a Laser (Monet); (ii) a quad-wave (PinkWave); (iii) a conventional LED (Elipar S10) on the temperature rise (ΔT) and degree of conversion (DC) when photo-curing fast or conventional bulk-fill resin-based composites (RBC). The aim was to correlate ΔT and DC, and the radiant exposure delivered to RBC specimens. METHODS: A 3D-printed resin mold of 4 mm depth was filled with two bulk-fill RBCs: Tetric PowerFill® (fast photo-polymerised composite) (TPF) or Tetric EvoCeram® Bulk-Fill (EVO). Three LCUs were used: (i) Monet laser for 1 s and 3 s (MONET-1 s, MONET-3 s); (ii) PinkWave quad-wave used for 3 s in Boost mode (PW-3 s) and for 20 s in standard mode (PW-20 s); (iii) Elipar S10 for 5 s (S10-5 s) and for 20 s in standard mode (S10-20 s). 2-dimensional temperature maps were obtained before, during and for 60 s after the LCU had turned off using a thermal imaging camera. Thermal changes were analysed at five depths: (0, 1, 2, 3, and 4 mm from the top surface of the RBC). The maximum temperature rise (Tmax) and the mean temperature rise (ΔT) were determined. Cylindrical-shaped specimens were prepared from each material using a stainless-steel split mold (4 × 4 mm) and light-cured with the same protocols. The DC was measured for 120 s and at 1 h after LCU had turned off using Fourier Transform Infrared Spectroscopy (FTIR). Data were analysed using Three-way ANOVA, One-way ANOVA, independent t-tests, and Tukey post-hoc tests (p < 0.05). RESULTS: Radiant exposures delivered by the various irradiation protocols were between 4.5-30.3 J/cm2. Short exposure times from MONET-1 s and PW-3 s delivered the lowest radiant exposures (4.5 and 5.2 J/cm2, respectively) and produced the lowest ΔT and DC. The longer exposure times in the standard modes of PW-20 s, S10-20 s, and MONET-3 s produced the highest Tmax, ΔT, and DC for both composites. The ΔT range among composites at different depths varied significantly (31.7-49.9 °C). DC of TPF ranged between 30-65% and in EVO between 15.3-56%. TPF had higher Tmax, ΔT for all depths and DC compared to EVO, across the LCU protocols (p < 0.05), except for PW-20 s and MONET-3 s. The coronal part of the restorations (1-2 mm) had the highest ΔT. There was a positive correlation between ΔT and DC at 4-mm depth after 120 s SIGNIFICANCE: Longer, or standard, exposure times of the LCUs delivered greater radiant exposures and had higher DC and ΔT compared to shorter or high-irradiance protocols. The fast photo-polymerised RBC had comparatively superior thermal and conversion outcomes when it received a high irradiance for a short time (1-5 s) compared to the conventional Bulk-Fill RBC.

Pulpal Temperature Variances During Step-by-step Adhesive Restorative Procedure Using Three Different High-irradiance Light-curing Units.

The rise in temperature in pulp tissues is related not only to heat transfer by high-irradiance light-curing units (LCUs), but also to restorative procedures. This research aimed to compare the rise in pulp temperature (PT) induced by three LCUs at each restorative step while considering the influence of resin composite shade and thickness. To accomplish this, the investigators used a proposed experimental model replicating pulp fluid circulation with a controlled, simulated intraoral temperature in bovine incisors. The recorded external and internal PT ranged from 36.7°C to 37.1°C and 32.7°C to 33.0°C, respectively. A significant decrease of internal temperature was recorded during class V preparation, followed by a progressive and representative rise of temperature in the subsequent restorative steps. The temperature was significantly higher during light curing of the adhesive system using Valo compared to light curing using Elipar and Radii Cal. However, none of the analyzed devices produced a temperature that exceeded the pulp tolerance limit (a temperature increase over 5.5°C). The paired test showed no significant difference in pulp temperature associated with the thickness of the increment of resin composite. However, shade was found to have more influence on the amount of energy absorbed by pulp tissue-A1 samples showed significantly higher temperature variation compared to samples using the A4 shade of resin composite. To conclude, the microcirculation and the performance of procedures under constant air-water flux dissipate the heat absorbed by the pulp. Additionally, the data suggest that all three LCUs analyzed can be safely used in clinical procedures, and that the resin composite shade may influence the amount of irradiance delivered to the tooth surface and represents a significant factor in pulp temperature variance.

Comparison of Adhesion Performance of a Self-curing and a Light-curing Universal Adhesive to Various Dental Substrates and CAD/CAM Materials.

PURPOSE: To compare the adhesion of a self-curing (Tokuyama Universal Bond, TUB) and a light-curing (Scotchbond Universal, SBU) universal adhesive to CAD/CAM materials, enamel, and dentin. This study also assessed differences in enamel adhesion between self-etch vs selective etching modes, as well as immediate and long-term adhesion to dentin for both adhesives. MATERIALS AND METHODS: Shear bond strength (SBS) testing was used to assess adhesion to enamel, dentin, Lava Ultimate (LU), Vita Enamic (VE), IPS e.max CAD (LD), IPS e.max ZirCAD (3Y-Zir), and Lava Esthetic (5Y-Zir) (n = 10). Moreover, bonding to enamel in self-etch and selective etching modes (n = 10) as well as immediate and aged resin-dentin bond strength (24 h after bonding, after 100,000 thermal cycles [TC] and long-term storage) was evaluated using the microtensile bond-strength test (n = 30). Failure mode was also determined for the bonding to dentin. Statistical analyses consisted of one-way and two-way ANOVA with appropriate post-hoc Tukey-Kramer or two-sample t-tests, as well as the chi-squared or Fisher's exact test (α = 0.05). RESULTS: TUB and SBU universal adhesives presented similar bonding to LU, VE, 3Y-Zir, and 5Y-Zir. However, SBS for TUB was superior to SBU when bonding to lithium-disilicate glass-ceramic (IPS e.max CAD). SBU showed better adhesion to dentin and enamel when used in the self-etch mode, while TUB promoted strong bond strength to enamel in the selective etching mode. TUB after TC was the only aging condition that yielded a significant reduction in resin-dentin bond strength. CONCLUSION: In-vitro adhesion performance of the self-curing and light-curing universal adhesives varies depending on the dental substrate or CAD/CAM restorative material used for bonding.

Multi-peak Light-emitting Diode Curing Units and Polymerization of 3D-printed Crown and Bridge Resin.

PURPOSE: This study aimed to evaluate the substitutive and additive efficacy of multi-peak light-emitting diode (LED) curing units for post-curing of a three-dimensional- (3D-) printed crown and bridge resin. METHODS: A total of 792 disc- and 180 bar-shaped specimens were printed with a crown and bridge resin (NextDent C&B MFH) and post-cured using two LED curing units (VALO Cordless and Bluephase N G4) in fast and standard modes. Conventional post-curing (LC-3D Print Box, Group PC) was compared with LED-only curing (Groups V1, V2, B1, and B2) and LED-combined curing (Groups PV1, PV2, PB1, and PB2) in terms of microhardness, flexural strength, degree of conversion (DC), and CIE L*a*b* color and translucency parameters. Cytotoxicity of the resin eluates was evaluated using the WST-1 assay. Temperature increases on the resin surface were measured with infrared thermography. Data were statistically analyzed using ANOVA and Kruskal-Wallis tests (α=0.05). RESULTS: The microhardness and flexural strength in Groups V1, V2, B1, and DC in all LED-only groups were lower than in other groups (p<0.05). Larger color disparities existed between Group PC and all LED-only groups than between Group PC and the others (p<0.05). There was no significant difference in cytotoxicity among the groups. The temperature increase was lowest in Groups V1 and PV1 during light curing (p<0.05). CONCLUSIONS: Post-curing by multi-peak LED curing units was not as effective as the conventional post-curing device. Additional post-curing by LED curing units did not improve the material properties.

Shedding light on the problem: Proficiency and maintenance practices of light-curing units among dental assistants.

BACKGROUND: Proper light curing is crucial for the success of restorative dentistry and to bond brackets to teeth, yet the responsibility is often delegated to dental assistants (DAs). This study assessed the proficiency and maintenance protocols of DAs when using light-curing units (LCUs) in Saudi Arabia. METHODS: Self-administered questionnaires were distributed to practicing DAs. The questionnaire contained sections on knowledge, adherence to best practices, and how to maintain the LCU. Demographic data were collected as well. Descriptive statistics and linear regressions at a significance level of (p = 0.05) were conducted to identify any relationships that influenced the DAs' LCU knowledge, practice, and maintenance protocols. RESULTS: Among the surveyed DAs, 66% were responsible for using the LCU during treatment, 16% used their fingers for support when light curing, 50% held the LCU tip 1-2 mm from the restoration during curing, and 51% did not have a specific maintenance protocol at their workplace. 70% did not know the output from the LCU, and their educational background correlated with knowledge (b = -14.42, p < 0.001). The type of institution type correlated with adherence to best practices (b = -13.65, p = 0.011), and level of knowledge and adherence to maintenance protocols showed a direct correlation (b = 0.002, p = 0.041). CONCLUSIONS: The findings revealed that a significant percentage of the DAs who replied had insufficient knowledge and did not follow the best practices and maintenance protocols for the LCUs they were using. Their educational background and workplace factors influenced this knowledge gap, while the absence of a maintenance protocol and suboptimal practices were associated with the type of institution. CLINICAL SIGNIFICANCE: To maintain the best practice, clinicians and institutions should improve the education and training of DAs. Otherwise, inadequate light curing by the DAs may jeopardize the long-term success of many dental procedures.

Influence of light exposure techniques on in vitro pulp temperature rise during bulk fill composite Class I restorations.

This in vitro study assessed peak temperature and temperature increase (ΔT) within the pulp chamber during different extended photoactivation techniques (EPT-applying similar radiant exposure values) to resin-based composites (RBCs) placed in a Class I cavity preparation in an extracted human lower third molar. A T-type thermocouple was placed in the pulp chamber and connected to a temperature analysis device (Thermes, Physitemp). The tooth was attached to an assembly simulating the in vivo environment (controlled baseline pulp chamber temperature and fluid flow). The real-time pulp chamber temperature was evaluated throughout the photoactivation (Bluephase N, Ivoclar Vivadent) of two bulk-fill RBCs: Tetric N Ceram Bulk Fill (TBF; shade: IVA; Ivoclar Vivadent); Surefill SDR flow + (SDR, shade: Universal; Dentsply Sirona), which were exposed to different curing techniques: 40 s-occlusal surface; 20 s-occlusal + 10 s-buccal + 10 s-lingual surfaces; 10 s-buccal + 10 s + lingual + 20 s-occlusal surfaces. Each EPT delivered 42.4 J/cm2. Vickers hardness (VHN) was measured on the removed, sectioned RBC restorations at the top and bottom middle areas after curing. ΔT and VHN data were analyzed using 2-way ANOVA followed by Bonferroni post-hoc test (α = 0.05). Peak temperature data were analyzed using one-way ANOVA and Dunnett's post-hoc test (α = 0.05). SDR showed higher ΔT values than TBF (p = 0.008) in some EPTs. Neither technique resulted in ΔT values greater than 5.5 °C. Both composites had acceptable bottom/top hardness ratios (greater than 80%), regardless of the photoactivation technique. The evaluated EPTs may be considered safe as a low-temperature increase was noticed within the pulp chamber.

Effect of four different mono and multi-wave light-curing units on the Knoop hardness of veneer resin composites.

OBJECTIVES: To evaluate the effect of mono and multi-wave light-curing units (LCUs) on the Knoop hardness of resin-based composites (RBC) that use different photoinitiators. METHODS: Central incisor-shaped specimens 12 mm long, 9 mm wide, and 1.5 mm thick were made from 2 RBCs that use different photoinitiators: Tetric N-Ceram (Ivoclar Vivadent) - and Vittra APS (FGM), both A2E shade. They were light-cured with 4 different LCUs: two claimed to be multi-wave - VALO Grand (Ultradent) and Emitter Now Duo (Schuster); and two were monowave - Radii Xpert (SDI) and Elipar DeepCure-L (3 M Oral Care) using 2 different light exposure protocols: one 40 s exposure centered over the specimen; and two 20 s light exposures that delivered light from two positions to better cover the entire tooth. 16 groups with 10 specimens in each group were made. The Knoop hardness (KH, kg/mm2) was measured at the top and bottom of the specimen in the center and at the cervical, incisal, mesial, and distal peripheral regions. The active tip diameters (mm) and spectral radiant powers (mW/nm) of the LCUs were measured with and without the interposition of the RBC, as well as the radiant exposure beam profiles (J/cm²) delivered to the top of the RBCs. The data was analyzed using Three-way ANOVA and Tukey's tests (α = 0.05). RESULTS: The VALO Grand (1029 mW) emitted twice the power of the Radii Xpert (500 mW). The KH values of VI and TN resin composite specimens were significantly affected by the LCU used (p < .001), the measurement location (p < .001), and the surface of the specimen (p < .001). LCUs with wider tip diameters produced greater Knoop hardness values at the peripheries of the 12 mm of long, 9 mm wide specimens. In general, the VALO Grand produced the highest KH values, followed by Elipar DeepCure-L, then by Radii Xpert. The Emitter Now Duo LCU produced the lowest values. Exposing the veneers from two locations reduced the differences between the LCUs and the effect of the measurement location. Only the VALO Grand could fully cover the composite veneer with light when the two locations were used. SIGNIFICANCE: The light tip must cover the entire restoration to photocure the RBC beneath the light tip.

Evaluation of microhardness of short fiber-reinforced composites inside the root canal after different light curing methods - An in vitro study.

OBJECTIVES: Short fiber-reinforced composite (SFRC) materials make it possible to reinforce root canal treated teeth with individualized, directly layered intraradicular posts (the Bioblock technique). The question arises, however, as to whether the photopolymerization of the material is sufficient deep within the root canal space and if it can be improved through different light-conducting options. Our study aimed to investigate the hardness of intraradicular SFRC material applied using the Bioblock technique and cured with various illumination methods, as measured through nanoindentation. MATERIALS AND METHODS: For this investigation, thirty plastic artificial teeth that had undergone root canal treatment were selected. These teeth were randomly divided into six study groups (Group 1-6; each group consisting of 5 teeth). The restoration procedures involved the use of SFRC or conventional composite materials, placed 6 mm apically from the root canal orifice. In Group 1 and 2, a conventional composite was used, whereas in Group 3-6, SFRC was employed for interradicular reinforcement (with a layered technique in Group 3 and 4 and a bulk-fill technique in Group 5 and 6). A modified light source was utilized for photopolymerization in Group 2, 4, and 6, whereas in Group 3 and 5, the polymerization light was directed through a prefabricated glass fiber posts. The control group (Group 1) utilized conventional composite material with a standard light-curing method. Following embedding and sectioning, the hardness of the composite materials was measured at 2 mm intervals within the root canal (1st, 2nd, 3rd measurements, in the coronal to apical direction). RESULTS: During the 1st measurement, light curing conducted through the glass fiber posts (Group 3 and 5) led to markedly higher hardness levels compared to the groups restored with conventional composite (control group with p = 0.002, p = 0.001, and Group 2 with p = 0.043, p = 0.034, respectively). In the 2nd measurement, only Group 5 demonstrated significantly greater hardness in comparison to the control group (p = 0.003) and Group 2 (p = 0.015). However, in the 3rd measurement, no statistically significant differences were observed among the groups. CONCLUSION: light curing through the glass fiber post provides outstanding hardness for the SFRC material in the apical layer in the root canal.

Evaluation of the effect of high-intensity light-curing device on micro-leakage of pits and fissure sealants.

Reducing treatment time is one of the most important trends in modern dentistry. This study aimed to compare the micro-leakage around the resin sealants when using both high and conventional intensity light-curing systems. The study sample consisted of 30 extracted human maxillary premolar teeth that were divided into two equal groups according to the light-curing system used: Group 1, High-Intensity Light-Curing System and Group 2, Conventional Light-Curing System. Light-curing by Woodpecker I-LED device with two intensities (high and conventional) has been used. All teeth were subjected to 500 cycles of thermocycling. Then, a methylene blue dye microleakage test was performed, and the teeth were sectioned longitudinally and studied under a stereo microscope. The mean of micro-leakage in the high-intensity group (1.33 ± 1.29) was less than in the conventional intensity group (1.63 ± 1.29) without any statistically significant differences (p = 0.320). The high-intensity light-curing system mode may be a good and acceptable alternative to conventional intensity light-curing system mode in polymerization of pits and fissure sealants.

Effect of thickness and shade of CAD/CAM composite on the light transmission from different light-curing units.

The thickness and shade of a restoration will affect the transmission of light from the light-curing unit (LCU). This study determined the power (mW), spectral radiant power (mW/nm), and beam profile of different LCUs through various thicknesses and shades of a CAD-CAM resin composite (BRAVA Block, FGM). Five thicknesses: 0.5; 0.75; 1.0; 1.5, and 2.0 mm, in three shades: Bleach; A2 and A3.5 of a CAD-CAM resin (n = 5). Two single-peak LCUs: EL, Elipar DeepCure-S (3M Oral Care); and OP, Optilight Max (Gnatus), and one multiple-peak LCU: VL, VALO Grand (Ultradent), were used. The LCUs were positioned touching the surface of the BRAVA Block. The power and emission spectrum were measured using a fiberoptic spectrometer attached to an integrating sphere, and the beam profiles using a laser beam profiler. The effect of the material thickness on the light attenuation coefficients was determined. VL and EL delivered more homogeneous beam profiles than OP. The type of the BRAVA Block had a significant effect on the transmitted power, and wavelengths of transmitted light (p < 0.001). There was an exponential reduction in the power and emission spectrum as the thickness of the BRAVA Block increased (p < 0.001). The light transmission through the A2 shade was least affected by the thickness (p < 0.001). The attenuation coefficient was higher for the violet light and higher for A3.5 than the A2 or Bleach shades. No violet light from the VL could be detected at the bottom of 2.0 mm of the BRAVA Block.

Influence of high-irradiance light curing on the marginal integrity of composite restorations in primary teeth.

BACKGROUND: Reducing the necessary time to restore primary teeth improves the cooperation of paediatric patients. This study aimed to investigate the marginal integrity of restorations prepared with a bulk-fill resin-based composite (RBC) containing additional fragmentation chain transfer (AFCT) compared to a conventional RBC when light cured with a rapid high-irradiance (3 s) and a regular (10 s) curing mode. METHODS: Forty class-II cavities were prepared in 40 primary molars. The molars were randomly divided into four groups based on the applied light-curing modes (regular: 10 s @ 1200 mW/cm2 or high-irradiance: 3 s @ 3000 mW/cm2) and the used restorative material (AFCT-containing bulk-fill RBC "Power Fill" or AFCT-free conventional RBC "Prime"). After thermo-mechanical loading, the marginal integrity was analysed using scanning electron microscopy. A beta regression model and pairwise comparisons were used to statistically analyse the data. RESULTS: The mean marginal integrity (% ± SD) of the restorations for each group was as follows: Power Fill (10 s: 79.7 ± 15.6) (3 s: 77.6 ± 11.3), Prime (10 s: 69.7 ± 11.1) (3 s: 75.0 ± 9.7). The difference between the RBCs for the same light-curing mode was statistically significant (p ≤ 0.05). The difference between the light-curing modes for the same RBC was not statistically significant (p ˃ 0.5). CONCLUSIONS: AFCT-containing bulk-fill RBC "Power Fill" achieves similar marginal integrity when light-cured with either high-irradiance or regular light-curing modes. "Power Fill" achieves better marginal integrity than the conventional RBC "Prime" regardless of the applied light-curing mode.

Irradiance from 12 LED light curing units measured using 5 brands of dental radiometers.

OBJECTIVE: To evaluate the accuracy of five brands of radiometers in reporting the irradiance (mW/cm2 ) from twelve brands of LCUs compared to a 'Gold Standard' (GS) reference obtained from a hand-held laboratory-grade radiometer. MATERIALS AND METHODS: The irradiance was measured from two examples of twelve brands of previously used LCUs on two examples of five brands of dental radiometers. The emission spectrum was also obtained. Irradiance data from each brand of LCU against each meter was analyzed using the Shapiro-Wilk test for normality. The irradiance values were subjected to a two-way ANOVA followed by Bonferroni tests for each LCU brand. Finally, a descriptive analysis was made using a 95% confidence interval around the mean irradiance. RESULTS: The power output from the LCUs ranged from 271 mW to 1005 mW. Among the tested radiometers, only the Bluephase Meter II could accurately report the irradiance from 11 out of the 12 brands of LCU evaluated in this study. When measured using the "GS" system, the mean irradiance values from the two examples of nine brands of previously used LCU were not always within ±10% of the irradiance values stated by the manufacturer. CONCLUSIONS: The mean irradiance values from 9 of the 12 brands of used LCUs were beyond ±10% of the irradiance values stated by the manufacturer. Only the Bluephase Meter II could accurately report the irradiance from 11 out of the 12 brands of LCU evaluated in this study. CLINICAL SIGNIFICANCE: There was a wide range in the power output from the LCUs tested. It was impossible to accurately measure the irradiance from all the LCUs using the dental radiometers examined. However, dental radiometers should still be used in dental offices to monitor the light output from LCUs and verify that they are working correctly before they are used on patients.

Are polywave light-emitting diodes more effective than monowave ones in the photoactivation of resin-based materials containing alternative photoinitiators? A systematic review.

OBJECTIVE: This systematic review aimed to analyze if using polywave light-emitting diodes (LED) to photoactivate resin-based materials (resin composites, adhesive systems, and resin cements) containing alternative photoinitiators provide better physicochemical properties than monowave ones. MATERIAL AND METHODS: Inclusion criteria were in vitro studies that evaluated the degree of conversion, microhardness and flexural strength in resin-based materials containing alternative photoinitiators and light-activated with mono and polywave LEDs. Exclusion criteria were studies that evaluated the physicochemical properties of composites through any material interposed between the LED and the resin composite and studies that exclusively compared different modes and/or light activation times. Selection of studies, data extraction, and risk-of-bias analysis was performed. Data from selected studies were qualitatively analyzed. A systematic search was performed in June 2021 using PubMed/Medline, Embase, Scopus, and ISI Web of Science databases and grey literature without language restriction. RESULTS: A total of 18 studies were included in the qualitative analysis. Nine studies used diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) as an alternative photoinitiator for resin composite. Polywave LED improved the degree of conversion of resin composite compared to monowave in 9 of the included studies. Polywave LED improved the microhardness of resin composite compared to monowave in 7 of the included studies. Polywave LED improved the degree of conversion for 11 studies and microhardness of resin composite compared to monowave for 7 included studies. No differences in the flexural strength medium between poly and monowave LEDs were observed. The evidence was graded as low quality due to the high risk of bias for 11 studies. CONCLUSION: The existing studies, with their limitations, revealed that the polywave light-emitting diode maximizes activation, resulting in a higher degree of double-bond conversion and microhardness of resin composites containing alternative photoinitiators. However, the flexural strength of these materials is not influenced by the type of light activation device.

3D light-curing printing to construct versatile octopus-bionic patches.

Reliable, fast and switchable gluing modes are critically important in medical adhesives and intelligent climbing robot applications. The octopus-bionic patch has attracted the attention of many scholars. The suction cup structure of the octopus achieves adhesion through differential pressure, showing strong adhesion in both dry and wet environments. However, the construction of the octopus-bionic patch remains limited in terms of adaptability, personalization and mass production. Herein, a composite hydrogel consisting of gelatin methacryloyl (GelMA), polyethylene glycol diacrylate (PEGDA) and acrylamide (AAM) was developed, and a structure mimicking the octopus sucker was constructed by digital light processing (DLP). The obtained octopus-bionic patch has strong adhesion, good biocompatibility and multi-functionality. Compared with the template method in most studies, the octopus-bionic patch constructed by the DLP printing method has the advantages of customizability and low cost. In addition, the DLP printing method endows the patch surface with an octopus-like groove structure for a better bionic effect.

Effect of Using Manufacturer-recommended Exposure Times to Photo-activate Bulk-fill and Conventional Resin-based Composites.

OBJECTIVES: To analyze the effect of using the resin-based composite manufacturer's recommended exposure time on the degree of conversion (DC), Knoop hardness (KH), and elastic modulus (E) of conventional and bulk-fill resin-based composites (RBCs). METHODS: Three resin-based composites (RBCs) were tested: Tetric EvoCeram Bulk Fill (TET), Opus Bulk Fill APS (OPU), and RBC Vittra APS (VIT). They were photo-activated in 2 mm deep, 6 mm diameter molds for their recommended exposure times of 10 seconds, 20 seconds, or 40 seconds from four light-curing units (LCUs). Two delivered a single emission peak in the blue light region (Optilight Max and Radii-Cal) and two delivered multiple emission peaks in the violet and blue region (VALO Cordless and Bluephase G2). After 24 hours of dry storage at 37°C in the dark, the KH (Kgf/mm2), E (MPa) and DC (%) at the top and bottom surfaces of specimens (n=5) were measured and the results analyzed by 2-way analysis of variance (ANOVA) followed by a Tukey test (α=0.05). RESULTS: The irradiance (mW/cm2) and spectral irradiance (mW/cm2/nm) from the LCUs were reduced significantly (8-35%) after passing through 2.0 mm of RBC (p<0.001). The DC at the bottom of VIT and TET was less than at the top surface (p<0.001). OPU had the same DC at the top and bottom surface (p=0.341). The KH and E values at the top surface of VIT and TET were substantially higher than at the bottom (p<0.001). OPU exposed for 40 seconds achieved higher mechanical properties than TET that was photo-activated for 10 seconds (p<0.001). The opacity of different bulk-fill RBCs changed differently during the polymerization; OPU became more opaque, whereas TET became more transparent. When exposed for their recommended times, the 2 mm thick RBCs that used Ivocerin or the APS photoinitiator system were adequately photo-activated using either the single or multiple emission peak LCUs (p=0.341). CONCLUSION: After 24 hours' storage, all the 2 mm thick RBCs photo-cured in 6 mm diameter molds achieved a bottom-to-top hardness ratio of at least 80% when their recommended exposure times were used. TET, when photo-activated for 10 seconds, achieved lower mechanical properties than OPU that had been photo-activated for 40 seconds. The change in opacity of the RBCs was different during photo-activation.

Novel chairside spectrometer-trained system for measuring the irradiance of light-curing units.

The purpose of this study was to compare the performances of 5 different instruments in measuring the irradiance of light-curing units (LCUs). A novel spectrometer-trained radiometer (CheckUp), 2 conventional chairside radiometers (Bluephase Meter I and Bluephase Meter II), and 2 devices considered to be gold standards for measuring irradiance (an integrating sphere spectrometer and a thermopile sensor) were used to evaluate 7 LCUs. The irradiance of each LCU was measured 10 times with each meter. Data were analyzed using linear regression analysis and a 1-way analysis of variance with Tukey post hoc test (α = 0.05). The mean irradiance values of the LCUs differed significantly depending on which meter was used for measurement (P < 0.05). Bivariate regression analysis demonstrated that the highest correlations in the irradiance values were found between the CheckUp meter and both the integrating sphere (r2 = 0.980) and the thermopile (r2 = 0.933). The absolute mean (SD) percentage deviation between irradiance measured by the CheckUp instrument and irradiance measured by the other meters was 7.2% (2.0%) for the integrating sphere, 7.0% (3.6%) for the thermopile, 21.5% (16.1%) for Bluephase Meter I, and 13.1% (7.1%) for Bluephase Meter II. Compared with the 2 conventional chairside radiometers, the CheckUp meter provided the highest correlation with and lowest absolute percentage deviation from the irradiance measured by the gold standard spectrometers.

In-vitro pulpal temperature increases when photo-curing bulk-fill resin-based composites using laser or light-emitting diode light curing units.

OBJECTIVE: To evaluate the in vitro pulpal temperature rise (ΔT) within the pulp chamber when low- and high-viscosity bulk-fill resin composites are photo-cured using laser or contemporary light curing units (LCUs). MATERIALS AND METHODS: The light output from five LCUs was measured. Non-retentive Class I and V cavities were prepared in one upper molar. Two T-type thermocouples were inserted into the pulp chamber. After the PT values reached 32°C under simulated pulp flow (0.026 mL/min), both cavities were restored with: Filtek One Bulk Fill (3 M), Filtek Bulk Fill Flow (3 M), Tetric PowerFill (Ivoclar Vivadent), or Tetric PowerFlow (Ivoclar Vivadent). The tooth was exposed as follows: Monet Laser (1 and 3 s), PowerCure (3 and 20 s), PinkWave (3 and 20 s), Valo X (5 and 20 s) and SmartLite Pro (20 s). The ΔT data were subjected to one-way ANOVA followed by Scheffe's post hoc test. RESULTS: Monet 1 s (1.9 J) and PinkWave 20 s (30.1 J) delivered the least and the highest amount of energy, respectively. Valo X and PinkWave used for 20 s produced the highest ΔT values (3.4-4.1°C). Monet 1 s, PinkWave 3 s, PowerCure 3 s (except FB-Flow) and Monet 3 s for FB-One and TP-Fill produced the lowest ΔT values (0.9-1.7°C). No significant differences were found among composites. CONCLUSIONS: Short 1- to 3-s exposures produced acceptable temperature rises, regardless of the composite. CLINICAL SIGNIFICANCE: The energy delivered to the tooth by the LCUs affects the temperature rise inside the pulp. The short 1-3 s exposure times used in this study delivered the least amount of energy and produced a lower temperature rise. However, the RBC may not have received sufficient energy to be adequately photo-cured.