Post-polymerization of three-dimensional printing resin using a dental light curing unit.

Background/Purpose: In vat photopolymerization, post-polymerization of the three-dimensional (3D) printing resin is necessary to ensure the optimum physical properties of the printed objects. This study aimed to evaluate the potential use of a handheld polywave light-emitting diode (LED) dental light-curing unit (LCU) for post-polymerizing 3D printed resins by measuring the microhardness and biaxial flexural strength of the post-polymerized resin. Material and methods: 3D printed 1- and 2-mm-thick disks were irradiated with a dental LCU at 3200 mW/cm2. Post-polymerization was repeated either on one side from the top surface: two cycles (T2), four cycles (T4), and eight cycles (T8), or on both sides from the top and bottom surfaces: one cycle (T1B1), two cycles (T2B2), and four cycles (T4B4) for each side. The microhardness and biaxial strength of the disks were compared to those post-polymerized by a conventional desktop polymerizing unit (PC) and those without post-polymerization (NC). Results: Microhardness of the disks varied between the top and bottom surfaces of the 1-mm and 2-mm-thick disks, depending on the post-polymerization methods. T8 and T4B4 produced comparable microhardness on the top surface to PC for both thicknesses. In contrast, PC, T2B2, and T4B4 exhibited the highest microhardness on the bottom surface. Except for NC, the 1-mm-thick disks had a higher biaxial flexural strength than the 2-mm-thick disks. T4B4 resulted in the highest biaxial flexural strength for both thicknesses, which was comparable to that of the desktop polymerizing unit. Conclusion: The microhardness and biaxial flexural strengths of the post-polymerized 3D-printed disks increase with polymerization time. With sufficient polymerization from both sides, the polywave LCU has the potential to be a viable alternative to desktop polymerization units.

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.

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.

Real-time multispectral transmission of hard tooth tissues and dental composites with their heating.

The objective of the study was to investigate the real-time transmission of Violet, Blue, Red and Near Infra-Red (NIR) irradiation through 2 or 4 mm thick dental composites and tooth tissue samples at varying positions of Light Curing Unit (LCU) with polymerization temperature monitoring. METHODS: The composites tested were: Filtek Universal Restorative (FUR), Filtek One Bulk Fill (FBF), Tetric EvoCeram (TEC), Tetric Bulk Fill (TBF) and Tetric PowerFill (TPF). The new LCU Pinkwave (a four-wavelength source manufactured by Vista Apex, USA) was placed either centrally or eccentrically for 3 mm above the sample. A Fiber spectrometer detected irradiation and Infrared Thermal camera polymerization temperatures. RESULTS: All eccentric LCU positions significantly weaken transmitted spectra for all composites in both thickness, jeopardizing Blue light. The LCU position did not affect transmitted irradiation for tooth tissues. The reduction in wavelength intensity when penetrating through thicker compared to thinner composite samples was 62%, 50% and 31% for Blue, NIR and Red, respectively, and 90%, 50% and 35% for tooth tissue samples, respectively. The temperature of bulk fill composites with additional photoinitiators rises faster. Eccentric LCU positions cause a significant decrease in both speed and the maximal value of temperature rise. Red and NIR irradiations contribute to the polymerization temperature. SIGNIFICANCE: Tested LCU source cause considerable inhomogeneity in the emitted and transmitted spectra. Tooth tissues homogenize irradiation, but drastically attenuates it. Red light has better potential than Blue light concerning penetration and could be further investigated as the wavelength for activation of an adjusted photoinitiator.

Effects of nanohybrid flowable resin-based composites on fibroblast viability using different light-curing units.

PURPOSE: To investigate the in vitro cytotoxic effects of Bis-GMA-containing and Bis-GMA-free flowable resin-based composites (RBCs) on primary human gingival fibroblast cells (hGFc) using direct and indirect curing methods and three different light-curing units (LCUs). MATERIALS AND METHODS: Cells were isolated and cultured in vitro in 24-well plates. The plates were divided into treatment (cells with RBC), control (cells only), and blank (media only) groups. In the treatment groups, two types of nanohybrid flowable RBCs were used: Bis-GMA-free and Bis-GMA groups. Each treatment group was subdivided according to the curing method, i.e., direct curing (RBC was injected into the wells and cured directly on the attached cells) and indirect curing (the samples were pre-cured outside of the well plate and then added to the well plate with cells). To vary the LCU, the subgroups were further divided into three groups: multiple-emission peak light-emitting diode, single-emission peak light-emitting diode, and quartz-tungsten-halogen units. Curing was conducted for 20 seconds. The hGFc cytotoxicity was evaluated via 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay after 24, 48, and 72 hours of culturing. RESULTS: The MTT assay results showed that both RBCs were significantly cytotoxic toward hGFc compared to the control group (p < 0.0001). The Bis-GMA group was significantly more cytotoxic to the cells compared to the Bis-GMA-free group. In addition, the curing method and time interval affected cell viability regardless of the LCU used. CONCLUSION: The Bis-GMA flowable RBC and direct curing method had the highest cytotoxic effects on hGFc regardless of the LCU used. Careful selection of flowable RBCs and proper curing techniques are required to decrease the cytotoxic effects on hGFc and improve the clinical handling of oral tissues.

Homogeneity of dental curing unit beam profile and its effect on microhardness of dental composites with varying thicknesses.

OBJECTIVES: The dental curing unit (DCU) has been reported to emit inhomogeneous light. However, there are no studies on which elements could affect the inhomogeneity of DCUs. This study aimed to analyze the effect of attenuating factors such as the aperture of the lens or neutral density (ND) filters on the DCU's beam profile and evaluate the effect of DCU's inhomogeneous beam profile on the microhardness distribution on composite resin specimens with different thicknesses. METHODS: Radiant emittance and spectrum of eight DCUs were investigated with and without ND filters using different optical density (OD) values. Beam profiles of eight DCUs were photographed while increasing the OD values of the ND filter. The change in the beam profile while changing the f-number of the aperture and the OD value of the ND filters were recorded. The Vickers microhardness of Filtek Z350XT and SDR cured by Bluephase Style 20i with 1, 2, 3, and 4 mm specimens of nine points on each surface was measured. RESULTS: Irradiance and spectrum of DCUs uniformly decreased after attenuation by the ND filters. The beam profile of the DCUs blurred when the f-number of the aperture was higher. The microhardness of Filtek Z350XT showed differences between the central and peripheral areas, and between the points under violet LED and the center on the bottom surface of the 4 mm specimen. The microhardness of the SDR did not show any differences. SIGNIFICANCE: The inhomogeneity of the beam profile can be affected by attenuation conditions. DCU's inhomogeneous beam profile may have different effects on the composites depending on the thicknesses and types of composite resin used.

Influence of irradiation distance on the mechanical performances of resin composites polymerized with high-irradiance light curing units.

BACKGROUND: The aim of this study was to evaluate the influence of increased irradiation distance on the flexural strength (FS), dentin micro-shear bond strength (µSBS), and the degree of conversion (DC) of bulk-fill flowable, conventional flowable, and packable resin composites. METHODS: The resin composites tested were Surefil® SDR™ (SDR), Filtek Z350 XT Flowable Restorative A2 shade (Z3F), and Filtek Z350 XT Universal Restorative A2 shade (Z3P). Specimens were cured at four irradiation distances (0, 2, 4, and 8 mm) with an Elipar DeepCure-S LED curing light for 20 s. FS tests were performed (n = 15) using bar-shaped specimens (8 mm × 2 mm × 2 mm) of the resin composites. µSBS tests were performed on the occlusal surfaces of extracted third molars from humans that were ground to expose dentin (n = 15). DC was measured by using Raman spectroscopy on the top and bottom surfaces of disk specimens (2-mm thick) (n = 3). To further investigate whether extended irradiation times could compensate for reduced irradiance, additional Z3P specimens were prepared, which were light-cured at 8-mm distances for 40 and 60 s and subjected to FS tests, µSBS tests, and Raman spectroscopy. Both two-way and one-way ANOVA were used for statistical analyses. RESULTS: Both FS and DC of Z3P specimens cured at an 8-mm distance were significantly lower than those cured at shorter distances (p < 0.05), whereas the FS and DC of the Z3F and SDR specimens were not significantly influenced by increasing distances. The µSBSs of the three types of resin composites reduced with increasing irradiation distances. The FS, µSBS, and DC of the Z3P specimen light-cured at 8 mm for 40 s were comparable to those of the Z3P specimen cured at 0 mm for 20 s. CONCLUSIONS: Increasing the irradiation distance to 8 mm can have a deleterious influence on mechanical performances, including the FS, DC, and dentin µSBS, of the resin composites polymerized with high-irradiance light curing units.

Effects of 3 different light-curing units on the physico-mechanical properties of bleach-shade resin composites.

Objectives: This study investigated the microhardness, flexural strength, and color stability of bleach-shade resin composites cured with 3 different light-curing units. Materials and Methods: In this in vitro experimental study, 270 samples were fabricated of bleach and A2 shades of 3 commercial resin composites (Point 4, G-aenial Anterior, and Estelite Sigma Quick). Samples (n = 5 for each trial) were cured with Bluephase N, Woodpecker LED.D, and Optilux 501 units and underwent Vickers microhardness and flexural strength tests. The samples were tested after 24 hours of storage in distilled water. Color was assessed using a spectrophotometer immediately after preparation and 24 hours after curing. Data were analyzed using 3-way analysis of variance and the Tukey test (p ≤ 0.001). Results: Samples cured with Optilux exhibited the highest and those cured with LED.D exhibited the lowest microhardness (p = 0.023). The bleach shade of Point 4 composite cured with Optilux displayed the highest flexural strength, while the same composite and shade cured with Sigma Quick exhibited the lowest (p ≤ 0.001). The color change after 24 hours was greatest for the bleach shade of G-aenial cured with Bluephase N and least for the A2 shade of Sigma Quick cured with Optilux (p ≤ 0.001). Conclusions: Light curing with polywave light-emitting diode (LED) yielded results between or statistically similar to those of quartz-tungsten-halogen and monowave LED in the microhardness and flexural strength of both A2 and bleach shades of resin composites. However, the brands of light-curing devices showed significant differences in color stability.

Thermal effect of light irradiation time on the setting time of mineral trioxide aggregate and calcium-enriched mixture cements.

This study aimed to assess the thermal effect of different light irradiation times on the setting time of mineral trioxide aggregate (MTA) and calcium-enriched mixture (CEM) cements. This in vitro experimental study evaluated 40 hydraulic cement specimens, including 20 MTA and 20 CEM specimens, according to the manufacturers'instructions. For each cement, the specimens were divided into 3 test groups light cured with a halogen light-curing unit (n = 5 per group) and 1 control group (n = 5) that was not exposed to irradiation. The specimens in the MTA test groups were light cured for 20, 40, or 60 seconds, and the specimens in the CEM test groups were light cured for 60, 90, or 120 seconds. All test and control groups had 60 seconds of rest time. Setting of the cements was assessed at different timepoints using a Gillmore needle weighing 113.4 g with a 12.2-mm diameter according to ASTM C266-03 standards. The data were analyzed with the Fisher exact test and the Mann-Whitney U test (α = 0.05). The setting of MTA specimens after different curing times was significantly different (P < 0.05). The setting time of MTA control specimens was significantly longer than that of test specimens (P = 0.008). The setting of CEM specimens after different curing times was not significantly different (P > 0.05). However, the setting time for CEM control specimens was significantly longer than that for test specimens (P = 0.008). Light curing with a halogen light-curing unit can significantly decrease the setting time for MTA and CEM cements.

Effectiveness of Using an Instructional Video in Teaching Light-Curing Technique.

PURPOSE: To investigate dental students' ability to deliver satisfactory amounts of irradiance and radiant exposure to simulated cavities by teaching the light-curing technique using instructional video compared to verbal instructions. METHODS: Students attended the didactic light-curing lecture explaining the light-curing technique. Participants were divided into two groups (n=60). Each participant light-cured a class III and a class I simulated cavities with sensors built-in a Managing Accurate Resin Curing-Patient Simulator (MARC-PS) system, using a multiple-emission-peak light-emitting-diode unit. Each student either 1) watched an instructional video (V) showing the light-curing technique, or 2) received individual verbal instruction (I). The light-curing performance, in terms of the mean irradiance and radiant exposure, was recorded. Each student performed light-curing again on the simulated cavities. Students' feedback for the corresponding teaching method was collected. Comparisons between before and after each instructional method were analyzed using the Wilcoxon signed-rank test. Comparisons between both instructional methods were analyzed using a Mann-Whitney U-test (α=0.05). RESULTS: The students' light-curing performance improved after both methods, as observed on the MARC-PS laptop monitor. The mean irradiance values were anterior-V=1280.6 (183.2), anterior-I=1318.0 (143.5), posterior-V=1337.5 (181.1), posterior-I=1317.6 (248.2) mW/cm2. The mean radiant exposure values were for anterior-V=13.5 (2.7), anterior-I=13.3 (1.6), posterior-V=13.7 (1.9), posterior-I=13.7 (2.5) J/cm2. No significant difference was found between both instruction methods. Students reported that each method was effective. CONCLUSION: Using V was comparable to I and an effective tool for teaching the light-curing technique per the students' ability to deliver sufficient amounts of irradiance and radiant exposure to simulated cavities.

Estimation of the tolerance threshold for the irradiance of modern LED curing units when simulating clinically relevant polymerization conditions.

The study aims to characterize various LED light curing units (LED-LCU) in order to determine the tolerance threshold for varying the polymerization conditions. Two violet-blue and two blue LED-LCUs were analyzed by using a laboratory-grade spectrophotometer system. Fifty-five curing conditions were simulated in each LED-LCU by varying the position (centered and with an offset of 3-mm to the left, right, lower and upper direction) and the exposure distance (0 mm to 10 mm in 1-mm steps). Irradiance decreased with increasing exposure distance, while the effect of the LCU position was significant and LCU-specific. Only one LED-LCU enables the irradiance threshold of 1,000 mW/cm2 to be achieved in all positions up to an exposure distance of 4 mm. LCUs with a more homogeneous light beam profile more easily tolerate deviations from the ideal curing conditions. The study enables dentists to identify the limits of modern LED-LCUs and to estimate potential deviations from ideal curing conditions for clinically relevant situations.

Initial curing characteristics of composite cements under ceramic restorations.

PURPOSE: To assess the degree of conversion (DC) of dual-curing composite cements when cured through ceramic-veneered zirconia disks. METHODS: Portions of mixed cement, either G-CEM LinkForce (GC), Panavia V5 (Kuraray Noritake) or ResiCEM (Shofu), were placed on the ATR crystal of a Fourier Transform Infrared Spectroscope (FTIR; iS50, Thermo Scientific) and squeezed to a 100-µm film thickness using a microscopy cover glass. DC (%) of the composite cements applied in self-curing mode was measured in the dark at 37°C. Following the dual-curing mode, the cements were light-cured directly (positive control) or through a ceramic-veneered zirconia disk (0.5-mm thick zirconia with a 1.0-mm thick veneering ceramic) for 40 sec using two light-curing units (G-Light Prima 2, GC; PenCure, Morita). Per experimental group, 5 tests were conducted to measure DC in self-cure and dual-cure mode (n=5). FTIR spectra of the composite cement films were acquired to determine DC every min up to 30 min. DC of the composite cements was statistically compared using two-way repeated-measures ANOVA (α=0.05). RESULTS: For all cements investigated, the self-curing mode resulted in significantly lower DC at 10, 20 and 30 min than the light-curing mode. When the composite cements were light-cured through the zirconia disk, DC at 30 min dropped significantly for ResiCem (Shofu), while not for Panavia V5 (Kuraray Noritake) and G-CEM LinkForce (GC). CONCLUSIONS: Self-curing slows down polymerization but does not reach for all composite cements the highest (light-cured) DC. Ceramic-veneered zirconia-based restorations may affect DC of some composite cements.

Effect of light-curing distance and curing time on composite microflexural strength.

This study investigated the influence of curing distance on µ-flexural strength (µ-FS) of a nano-hybrid composite, cured using the manufacturer-recommended curing time (MCT), compared to a consistent radiant exposure (CRE) using three different light-curing units (LCUs). Beams (6×2×1 mm) were cured using the MCT or CRE with a quartz-tungsten-halogen (QTH); a single-emission-peak light-emitting-diode (SLED), or a multiple-emission-peak light-emitting-diode (MLED) LCU. Specimens were cured at 0-, 2- or 8-mm distances (n=10) and the bottom irradiance and CRE were measured using a Managing Accurate Resin Curing-Resin Calibrator spectrometer. µ-FS testing was performed, and data analyzed using two-way ANOVA and Tukey multiple comparison tests (α=0.05). Mean bottom irradiance was (25.4-99.7 mW/cm2) and CRE (0.31-1.11 J/cm2). µ-FS was 422.1-516.6 MPa (MCT) and 440.4-490.4 MPa (CRE). Comparing CRE to MCT showed that µ-FS significantly decreased using the CRE at 2-mm (QTH) or the MCT at 2- and 8-mm (SLED). µ-FS may be significantly impacted by the curing protocol.

Effect of Different LED Light-curing Units on Degree of Conversion and Microhardness of Bulk-fill Composite Resin.

AIM: The aim of this study is to compare the effect of the use of second-generation and third-generation LED light-curing units (LCUs) on the degree of conversion (DC) and microhardness (VHN) of bulk-fill resin composites. MATERIALS AND METHODS: Thirty cylindrical specimens (each n = 5) of Tetric N-Ceram Bulk-Fill, Filtek™ Bulk-Fill Posterior Restorative, and SDR flow were prepared in metal molds (5 mm in diameter and 4 mm in thickness) and cured with second-generation LED (SmartLite® Focus®, Dentsply Sirona) and third-generation LED (Bluephase® style, Ivoclar Vivadent) resulting in six groups. Degree of conversion was determined using Fourier transform infrared spectroscopy (FTIR), and microhardness with Vickers microhardness tester. Data were statistically analyzed using one-way ANOVA and least significance difference (LSD) test, and DC and microhardness were correlated using Pearson's correlation (α = 0.05). RESULTS: There was a significant difference between DC and VHN between all groups of bulk-fill which were cured by second-generation LED curing light and third-generation LED curing light. Then there is no significant difference between DC of the three composite bulk-fill resins by (second-generation LED vs third-generation LED curing light). CONCLUSION: The second-generation LED curing light can still be used to cure bulk-fill resin composites by increasing the duration of irradiation. CLINICAL SIGNIFICANCE: In the microhardness test, there was a significant difference in the Filtek™ Bulk-Fill Posterior Restorative resin composites.

Effect of infection control barriers on the light output from a multi-peak light curing unit.

OBJECTIVES: Curing lights cannot be sterilized and should be covered with an infection control barrier. This study evaluated the effect of barriers when applied correctly and incorrectly on the radiant power (mW), irradiance (mW/cm2), emission spectrum (mW/nm), and beam profile from a multi-peak light-curing unit (LCU). METHODS: Five plastic barriers (VALO Grand, Ultradent; TIDIShield, TIDI Products; Disposa-Shield, Dentsply Sirona; Cure Sleeve, Kerr; Stretch and Seal, Betty Crocker) and one latex-based barrier (Curelastic, Steri-Shield) were tested. The radiant power (mW) and emission spectrum (mW/nm) from one multi-peak LCU (VALO Grand, Ultradent) was measured using an integrating sphere. LCU tip internal diameter (mm) was measured, then the tip area and irradiance (mW/cm2) were calculated. The beam profiles were measured using a laser beam profiler. RESULTS: When applied correctly, the plastic barriers reduced the radiant power output by 5-8%, and the latex-based barrier by 16%. When the plastic seam or barrier opaque face was positioned over the LCU tip, the power output was reduced by 8-11%. When the plastic barriers were wrinkled, the power output was significantly reduced by 14-26%. The wrinkled latex-based barrier reduced by 28%, and further reduced the violet light. The beam profiles illustrated the importance of correctly barrier use without wrinkles over the tip. CONCLUSIONS: Plastic barriers applied correctly reduced the light output (mW) by 5-8%. The barriers applied incorrectly significantly reduced the light output by 14-26%. The latex-based barrier wrinkled also reduced the amount of violet light. CLINICAL RELEVANCE: Infection control curing light barriers should be used to prevent cross-infection between patients. However, they must be applied correctly to reduce their negative effects on the light output.

Effect of exposure time and moving the curing light on the degree of conversion and Knoop microhardness of light-cured resin cements.

OBJECTIVE: To evaluate the effect of exposure time and moving the light-curing unit (LCU) on the degree of conversion (DC) and Knoop microhardness (KH) of two resin cements that were light-cured through ceramic. METHODS: Two resin cements: AllCem Veneer APS (FGM) and Variolink Esthetic LC (Ivoclar Vivadent) were placed into a 0.3 mm thick matrix in 6 locations representing the canine to canine. The resins were covered with 0.5 mm thick lithium disilicate glass-ceramic (IPS e.max CAD, Ivoclar Vivadent). A motorized device moved the LCUs over the ceramic when the LCU was on. Two single-peak LCUs: Elipar DeepCure-L (3M Oral Care) and Emitter C (Schuster), and one multi-peak: Bluephase G2 (Ivoclar Vivadent) were used with 3 different exposure protocols: a localized exposure centered over each tooth for 10 or 40 s; moving the tip across the 6 teeth for a total exposure time of 10 or 40 s; and moving the tip across the 6 teeth resins for a total exposure time of 60 or 240 s. After 24 h, the DC and KH were measured on the top surfaces and the data was analyzed using three-way ANOVA and Tukey's tests (α = 0.05). RESULTS: Interposition of 0.5 mm of ceramic reduced the irradiance received by the resin by approximately 50%. The 40 s localized exposure over each tooth always produced significantly higher DC and KH values. Moving the LCUs with a total exposure time of 10 s resulted in the lowest DC and KH. There was no beneficial effect on the DC or KH when the multi-peak (violet-blue) LCU (Elipar DeepCure-L or Bluephase G2), but the lower light output from a small tip LCU reduced the DC and KH values (Emitter C). SIGNIFICANCE: Moving the LCUs when photo-curing light-cured resin cements is not recommended. This study showed that a single-peak LCU could activate a resin cement that uses Ivocerin™ as well as the multi-peak LCU.

Effect of the degree of conversion of resin-based composites on cytotoxicity, cell attachment, and gene expression.

OBJECTIVE: This study investigated the influence of the degree of conversion (DC), resin-based composites (RBC) composition, and the effect of additional violet light from one light curing unit (LCU) on cell attachment/growth, eluate cytotoxicity, and gene expression. METHODS: The effect of different DC of RBCs on human gingival fibroblasts (HGFs) when cultured directly onto cured RBCs, and when exposed afterwards to eluates in cell culture medium was examined. Venus® (RBC-V; Bis-GMA-based) and Venus Pearl® (RBC-P; TCD-DI-HEA and UDMA-based) were cured using a single emission peak (blue) light, Translux Wave®; TW and a dual emission peak (blue-violet) light, Translux 2 Wave®; T2W. To determine the value of the additional violet light from the T2W, exposure times and distances were adjusted to deliver similar radiant exposures (RE) from the blue region of both lights at five different RE levels from 1.5 J/cm² to 28.9 J/cm². RESULTS: Both RBCs light-cured with the T2W at higher REs resulted in higher DC, increased cell adhesion and decreased eluate cytotoxicity. RBC-V induced greater cell adhesion, lower mRNA levels of pro-inflammatory markers, and higher mRNA levels of a proliferation marker than RBC-P. Wettability was the same for both RBCs. Toxicity decreased with increasing number of elution cycles. The initial eluates from RBC-P had a lower toxicity than from RBC-V. SIGNIFICANCE: RBCs cured with T2W (delivering both blue and violet light) at higher RE had greater DCs. The greatest DC and the least cell reactions were observed when the RE was >25 J/cm².

The effect of curing time by conventional quartz tungsten halogens and new light-emitting diodes light curing units on degree of conversion and microhardness of a nanohybrid resin composite.

BACKGROUND: Little is known about the relationship between the minimal light-curing time required for proper polymerization on various quartz-tungsten-halogen (QTH) and light-emitting diode (LED) light-curing units that have different light intensities. AIM: To evaluate the effects of curing time by QTH and LED light-curing units on the degree of conversion (DoC) and surface microhardness of a nanohybrid resin composite. SETTING AND DESIGN: Experimental design. MATERIALS AND METHODS: One hundred and twenty cylindrical specimens (4.0 mm in diameter, 2.0 mm thick) of shade A2 resin composite were prepared and polymerized with either QTHs or LEDs for 20 and 40 s. The DoC and the top and bottom surface microhardness were recorded. STATISTICAL ANALYSIS USED: Two-way analysis of variance, Tukey's test, and the t-test (α = 0.05) were used. RESULTS: Surface microhardness and DoC values were affected by light intensity and curing time (P < 0.05). In terms of microhardness and DoC, LED groups gave significantly more values than QTH groups (P < 0.05). CONCLUSION: Curing time affected surface microhardness and DoC values of a nanohybrid resin composite in both conventional QTH and new LED light-curing units.

Investigation of the reliability of light-curing units in Sivas City, Turkey.

BACKGROUND: The number of studies investigating the physical properties of light-curing units used in city centers in terms of the light intensity, presence of residues fractures at the tips, how long they have been used, and hardness measurements of the composite resins polymerized by these is limited. There is no such study in Turkey and Sivas province. The objective of this study is to examine the light-curing units used in Sivas city center and determine the reliability of light-curing units by measuring the surface hardness of composite samples polymerized with these devices. MATERIALS AND METHODS: The power of the light-curing units that used in all private clinics in Sivas city center was measured. Then, the Vickers surface hardness measurements of the composite resin samples polymerized with these devices were made, and they were statistically evaluated. RESULTS: The light intensity was found to be below from the acceptable value of 400 mW/cm2 in 10.7% of the devices. It was observed that with increasing years of usage, the light intensity of light-curing units decreased (P < 0.05). CONCLUSION: It was observed that as the power of light-curing units increased, the hardness values of the bottom and top surfaces increased significantly.