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.

Resin Composites in Posterior Teeth: Clinical Performance and Direct Restorative Techniques

Resin composites are the most versatile restorative materials used in dentistry and the first choice for restoring posterior teeth. This article reviews aspects that influence the clinical performance of composite restorations and addresses clinically relevant issues regarding different direct techniques for restoring posterior teeth that could be performed in varied clinical situations. The article discusses the results of long-term clinical trials with resin composites and the materials available in the market for posterior restorations. The importance of photoactivation is presented, including aspects concerning the improvement of the efficiency of light-curing procedures. With regard to the restorative techniques, the article addresses key elements and occlusion levels for restoring Class I and Class II cavities, in addition to restorative strategies using different shades/opacities of resin composites in incremental techniques, restorations using bulk-fill composites, and shade-matching composites.

Longitudinal analyses of composite resin restoration on erosive lesions

Aim: To evaluate the influence of the biomodification of erosive lesions with a chitosan nanoformulation containing green tea (NanoCsQ) on the clinical performance of a composite resin. Methods: The study was performed in a split-mouth, randomized and double-blinded model with 20 patients with 40 erosive lesions. The patient’s teeth were randomized into two groups (n=20) according to the surface treatment: 1) Without biomodification (control), and 2) Biomodification with NanoCsQ solution (experimental). The lesions were restored with adhesive (Tetric N-bond, Ivoclar) and composite resin (IPS Empress Direct, Ivoclar). The restorations were polished and 7 days (baseline), 6 months, and 12 months later were evaluated according to the United States Public Health Service (USPHS) modified criteria, using clinical exam and photographics. Data were analyzed by Friedman’s and Wilcoxon signed-rank tests. Results: No significant differences were found between the control and experimental groups (p=0.423), and also among the follow-up periods (baseline, six months, and 12 months) (p=0.50). Regarding the retention criteria, 90% of the restoration had an alpha score in the control group. Only 10% of the restorations without biomodification (control) had a score charlie at the 12-month follow-up. None of the patients reported post-operatory sensitivity. Conclusion: The NanoCsQ solution did not negatively affect the performance of the composite resin restorations after 12 months.

Characterization and effectiveness of a violet LED light for in-office whitening

OBJECTIVES

This study characterized a violet LED light (V-LED; bright max whitening) tooth whitening device and evaluated its efficacy on stained enamel compared to hydrogen peroxide (HP).

MATERIALS AND METHODS

Characterization of the V-LED beam profile was performed using a laser beam-profiler. The irradiance was measured throughout an exposure cycle at 0- and 8-mm distances using an integrating sphere and a spectral radiometer. Bovine enamel/dentin blocks stained with black tea (BT), cigarette smoke (CS), or without staining (CONT) were subjected to V-LED or 40% HP (n = 10/group). Color parameters (ΔL, Δa, Δb, and ΔE₀₀) were measured using a digital spectrophotometer. Light transmission was estimated through 1-mm-thick bovine enamel slices (n = 5). ΔL, Δb, ΔE₀₀, and irradiance were analyzed by two-way ANOVAs and Tukey's tests, Δa by Kruskal-Wallis and Mann-Whitney tests, and light transmission by t-test (α = 5%).

RESULTS

Heterogeneous beam distribution was observed for the emitting V-LED chips. After 20 sequential exposures, irradiance levels were reduced 25-50%, regardless of the distance from V-LED. Localized irradiance values were statistically different between beam locations and different distances from the target. V-LED produced lower ΔE_00, ΔL, Δa, and Δb values than HP for CONT and BT, with no differences for CS. Light transmittance decreased approximately 98% through 1-mm thick enamel.

CONCLUSIONS

V-LED irradiance was heterogeneous and decreased throughout the exposure cycles and was also greatly reduced with increasing tip distance. V-LED produced a significantly lower whitening effect on BT and control teeth.

CLINICAL RELEVANCE

This study contributes to the knowledge of V-LED and its clinical use.

Effect of extended light activation and increment thickness on physical properties of conventional and bulk-filled resin-based composites

OBJECTIVES

To evaluate the biaxial flexural strength (BFS), flexural modulus (BFM), and Knoop microhardness (KHN) of incremental and bulk-filled resin-based composites (RBCs) using extended curing exposure times.

MATERIALS AND METHODS

Disc specimens (n = 8; 6-mm diameter) were fabricated using three stacked molds (0.5-mm thick for the top and bottom molds, and a 1-mm-thick center mold for the conventional and 3-mm thick for the bulk-fill RBCs). Conventional (Tetric EvoCeram/TCE and Filtek Z250/FIZ) and bulk-fill RBCs (Tetric EvoCeram Bulk Fill/TBF and Filtek One Bulk Fill Restorative/FOB) were evaluated. The stacked RBC-filled molds were light-cured for (1) the manufacturer-recommended exposure (MRE) duration; (2) 50%, and (3) 100% extension of the MRE. The BFS, BFM, and KHN of the top and bottom discs were measured. BFS and BFM were analyzed by three-way ANOVA (material*curing time*depth) and Tukey's post hoc (α = 0.05). KHN was analyzed by two-way ANOVA (curing time*depth) and Tukey's post hoc (α = 0.05).

RESULTS

Extending the exposure duration did not change the BFS and BFM on the top of the RBCs, but the BFS and KHN increased at the bottom of bulk-fill RBCs. For the conventional RBCs, TCE showed the highest increase on BFS at the bottom, going from 53.6 MPa at T1 to 69.9 at T3. Among the bulk-fill RBCs, FOB presented the highest increase on the bottom BFS (T1: 101.0 ± 19.9 MPa, T3: 147.6 ± 12.9 MPa). For all RBCs and exposure times, BFS and KHN were lower at the bottom. Only FIZ and FOB reached a bottom-to-top hardness ratio of 80%, at T3 and T2.

CONCLUSION

A significant increase on the BFS and KHN on the bottom of bulk-fill RBCs can be observed when the time of exposure to the curing light is double the MRE. However, extended exposure does not eliminate differences on the BFS and KHN between the shallow and deep regions of RBCs. TCE and TBF failed to reach an acceptable B/T hardness ratio at all evaluated exposure times.

CLINICAL RELEVANCE

Mechanical properties of RBCs can be affected by insufficient polymerization, specially at deeper regions of the increment. Therefore, clinicians should consider applying twice the MRE to curing-light to polymerize the maximal increment thickness of bulk-fill RBCs.

Improper Light Curing of Bulkfill Composite Drives Surface Changes and Increases S. mutans Biofilm Growth as a Pathway for Higher Risk of Recurrent Caries around Restorations

How dentists cure a resin-based material has deleterious effects on the material's properties and its interaction with surrounding dental tissues. Biofilm accumulation has been implicated in the pathogenesis of carious lesions around dental restorations, with its composition manifesting expressed dysbiosis in patients suffering from dental caries. To evaluate the influence of varying radiant exposure on the degree of conversion (DC%), Streptococcus mutans biofilm growth, and surface roughness of bulk-fill composites under different light-curing conditions. Two light-curing units (LCU) at 600 and 1000 mW/cm² were used to simulate curing conditions with different angulations (∢20° and ∢35°) or 2 mm-distance displacements of the LCU tip. The radiant exposure (RE) was assessed, and the composites were analyzed for DC%. Biofilm formation was induced over the bulk-fill composites and analyzed via colony-forming units counting and scanning electron microscopy (SEM). The surface roughness was analyzed via a profilometer and SEM after biofilm formation. Curing conditions with different angulation or displacement decreased RE compared to the "optimal condition". The moderately (∢35°) angulated LCU tip and low (600 mW/cm²) radiant emittance significantly reduced the DC% (p < 0.05). The difference in DC% between the top and bottom of the composites ranged from 8 to 11% for 600 mW/cm² and 10 to 20% for 1000 mW/cm². Greater S. mutans biofilm and surface changes were found in composites with non-optimal RE delivery (e.g., tip displacement and angulation) (p < 0.05). Inadequate polymerization of bulk-fill composites was associated with more biofilm accumulation and surface topography changes. Overall, non-optimally performed curing procedures reduced the amount of delivered RE, which led to low DC%, more biofilm formation, and higher surface roughness. The improper light-curing of bulk-fill composites compromises their physicochemical and biological properties, which could lead to inferior clinical performance and reduced restorative treatments' longevity.

Relationship Between the Cost of 12 Light-curing Units and Their Radiant Power, Emission Spectrum, Radiant Exitance, and Beam Profile

OBJECTIVES

To correlate the radiant power (mW), radiant exitance (or tip irradiance in mW/cm2), emission spectrum (mW/cm2/nm), and beam irradiance profile of 12 light-curing units (LCUs) available in the Brazilian market with their market cost.

METHODS AND MATERIALS

Six LCUs that cost more than US$900 (Bluephase G4,VALO Grand, VALO Cordless, Radii Xpert, Elipar DeepCure-S, and Radii plus) and six low-cost LCUs costing less than US$500 (Radii Cal, Optilight Max, High Power LED 3M, Emitter D, Emitter C, and LED B) were examined. Radiant power (mW) and emission spectrum (mW/nm) were measured using an integrating sphere connected to a fiber-optic spectroradiometer. The internal tip diameter (mm) of each LCU was measured using a digital caliper and was used to calculate the average radiant exitance (mW/cm2). Irradiance profiles at the light tip were measured using a commercial laser beam profiler. The cost of each LCU in Brazil was correlated with internal tip diameter, radiant power, and tip irradiance.

RESULTS

None of the low-cost LCUs were broad spectrum multiple peak LCUs. There was no correlation between the cost of the LCUs and their averaged tip irradiance; however, there was a high positive correlation between the cost of the LCUs and the radiant power and tip diameter. The VALO Grand, Elipar DeepCure-S, VALO Cordless, and Bluephase G4 all emitted a higher radiant power. They also had a significantly greater tip diameter than other LCUs. For the LCUs with a nonuniform output, some areas of the light tip delivered less than 400 mW/cm2, while other areas delivered more than 2500 mW/cm2.

CONCLUSIONS

In general, LCUs that had a higher cost (US$971-US$1800) delivered more power (mW) and had a greater tip diameter (mm), which covered more of a tooth. In general, the low-cost LCUs (US$224-US$470) emitted a lower radiant power and had a smaller tip diameter.

Resin composite adhesion to dentin using different curing lights and adhesive systems applied under electric current

OBJECTIVES

To evaluate the effect of electric current application on the resin composite-tooth bond strength and hybrid layer of three adhesive systems light-cured by two light-curing units (LCUs).

MATERIALS AND METHODS

Human molar teeth were distributed into 12 groups (n=6). Three adhesive systems were used: two-step etch-and-rinse (SB2; Adper Single Bond 2, 3M ESPE); two-step self-etch (CSE; Clearfil SE Bond, Kuraray); and one-step self-etch (SBU; Single Bond Universal, 3M ESPE) applied with (50μA) and without (control; conventional application) electric current, and light-cured with different LCUs. Resin composite blocks (Filtek Z350XT, 3M ESPE) were produced and cut into sticks (~1mm²) for microtensile bond strength (μTBS). Fracture patterns were analyzed on stereomicroscope and classified as cohesive-dentin, cohesive-resin, adhesive, or mixed. Specimens were prepared for scanning electron microscope observation. The hybrid layer analysis was carried out using a confocal laser scanning microscopy (n=2). Data were submitted to three-way ANOVA followed by Tukey's post hoc test (α=0.05).

RESULTS

The electric current increased the μTBS for all adhesive systems light-cured with single-emission peak and multiple-emission peak LCUs. Both LCUs presented similar μTBS values. CSE applied under electric current showed the highest μTBS mean values. The adhesive failure pattern was more frequently observed in all groups. The electric current formed long resin tags for all adhesive systems.

CONCLUSIONS

The adhesive systems applied under electric current increased the bond strength using single-emission peak and multiple-emission peak LCUs.

CLINICAL RELEVANCE

Electric current at 50μA applied throughout the dentin is a safe mode and results in better impregnation of the adhesive systems.

Evaluation of physico-mechanical properties and filler particles characterization of conventional, bulk-fill, and bioactive resin-based composites

OBJECTIVE

This study evaluated physical and mechanical properties and characterized the filler particles of seven composites.

MATERIALS AND METHODS

Filtek Supreme (FS, 3M Oral Care), Forma (FO, Ultradent), Charisma Diamond (CD, Kulzer), Spectra Smart (SS, Dentsply), Filtek Bulk Fill (FB, 3M Oral Care), Tetric N-Ceram Bulk Fill (TB, Ivoclar), and Cention N (Ivoclar) in self- (CNSC) or dual-curing (CNDC) were evaluated. Fillers size, shape, and content were analyzed by scanning electron microscopy (SEM) and X-ray dispersive energy spectroscopy (EDX). Disk-shaped specimens (n = 5) were prepared for sorption (SP) and solubility (SL). Flexural strength and elastic modulus were tested at 24 h and 12 months (n = 10). Degree of conversion (DC%) and maximum rate of polymerization (Rp^max) were evaluated using micro-Raman spectroscopy. SP and SL results were submitted to Kruskal-Wallis one-way ANOVA and Dunn's pairwise test (α = 0.05). Mechanical properties were analyzed by 2-way ANOVA and Tukey's test (α = 0.05). DC% of CNSC and CNDC was compared by independent t-test (α = 0.05). Rp^max results were analyzed by 1-way ANOVA and Tukey's test (α = 0.05).

RESULTS

The composites differed regarding filler size, shape, and content. CD and CNSC showed lower SP than FS. SS had lower SL than CNSC and CNDC. CNDC presented higher DC% than CNSC. CD, TB, and CNDC showed the highest Rp^max. TB, CNSC, and CNDC showed the lowest 24-h flexural strengths. Mechanical properties of CD did not decrease, while FO, TB, and CNSC showed a significant reduction after storage.

CONCLUSIONS

Monomer composition and fillers characteristics greatly influenced the physico-mechanical properties of the tested composites.

Influence of beam homogenization on bond strength of adhesives to dentin

OBJECTIVE

This study evaluated the effect of beam homogeneity on the microtensile bond strength (μTBS) of two adhesive resins to dentin.

METHODS

One polywave light-emitting-diode (LED) LCU (Bluephase Style, Ivoclar Vivadent AG) was used with two different light guides: a regular tip (RT, 1010 mW/cm² emittance) and a homogenizer tip (HT, 946 mW/cm² emittance). The emission spectra and beam profiles were measured from both light guides. Extracted third molars were prepared for μTBS evaluation using two adhesive systems: Excite F (EXF) and Adhese Universal (ADU). Bond strength was calculated for each specimen (n = 10) at locations that correlated with the output of the two LED chips emitting blue (455 nm) and the one chip that emitted violet light (409 nm) after 24-hs and after one-year water-storage. The μTBS was analyzed using a four-way analysis of variance (factors: adhesive system, light guide, LED wavelength, and storage time) and post-hoc Tukey test (α = 0.05).

RESULTS

EXF always delivered a higher μTBS than ADU (p < 0.0001), with the μTBS of ADU being about 20% lower than EXF. The light guide (p = 0.0259) and storage time (p = 0.0009) significantly influenced the μTBS. The LED wavelengths had no influence on the μTBS (p > 0.05).

SIGNIFICANCE

Homogeneity of the emitted light beam was associated with higher 24-h μTBS to dentin, regardless of the adhesive tested. Also, differences in the composition of adhesives can affect their compatibility with restorative composites and their ability to maintain bonding over one year.

The light-curing unit: An essential piece of dental equipment

INTRODUCTION

This article describes the features that should be considered when describing, purchasing and using a light-curing unit (LCU).

METHODS

The International System of Units (S.I.) terms of radiant power or radiant flux (mW), spectral radiant power (mW/nm), radiant exitance or tip irradiance (mW/cm² ), and the irradiance received at the surface (also in mW/cm² ) are used to describe the output from LCU. The concept of using an irradiance beam profile to map the radiant exposure (J/cm² ) from the LCU is introduced.

RESULTS

Even small changes in the active tip diameter of the LCU will have a large effect on the radiant exitance. The emission spectra and the effects of distance on the irradiance delivered are not the same from all LCUs. The beam profile images show that using a single averaged irradiance value to describe the LCU can be very misleading. Some LCUs have 'hot spots' of high radiant exitance that far exceed the current ISO 10650 standard. Such inhomogeneity may cure the resin unevenly and may also be dangerous to soft tissues. Recommendations are made that will help the dentist when purchasing and then safely using the LCU.

CONCLUSIONS

Dental manufacturers should report the radiant power from their LCU, the spectral radiant power, information about the compatibility of the emission spectrum from the LCU with the photoinitiators used, the active optical tip diameter, the radiant exitance, the effect of distance from the tip on the irradiance delivered, and the irradiance beam profile from the LCU.

Effects of extending duration of exposure to curing light and different measurement methods on depth-of-cure analyses of conventional and bulk-fill composites

This study evaluated the effect of extending the duration of exposure to curing light on the depth of cure of two conventional (RBC1-conventional and RBC2-conventional) and two bulk-fill (RBC1-bulk and RBC2-bulk) resin composites. Polywave and single-peak photocuring units were used. Cylinder-shaped specimens were exposed to curing light either for the time period recommended by the manufacturer or twice the length of that time, and depth of cure was estimated using manual scraping (similar to the ISO-4049 standard) and solvent immersion techniques. Depth of cure was analyzed, using two-way ANOVA, for the factors measurement method and exposure time. For RBC1-conventional and RBC1-bulk, the solvent immersion technique estimated a greater depth of cure than did manual scraping; for RBC1-conventional, both techniques and both light-exposure time periods resulted in a depth of cure of >2 mm; and for RBC1-bulk, only the solvent method after photocuring for twice the manufacturer's recommended time resulted in a depth of cure of 5 mm. For RBC2-conventional and RBC2-bulk, neither technique nor exposure time resulted in estimated depths of cure that matched those indicated by the manufacturer. The results suggest that extending the duration of photopolymerization increases depth of cure. Also, calculation of depth of cure can vary according to the measurement technique used.

Influence of Multiple Peak Light-emitting-diode Curing Unit Beam Homogenization Tips on Microhardness of Resin Composites

This study evaluated the effect of light curing unit (LCU) guide type (regular or homogenizing) on top and bottom microhardness of conventional and bulk-fill resin-based composites (RBCs). A polywave light-emitting-diode (LED) LCU (Bluephase Style, Ivoclar Vivadent AG) was used with two different light guides: a regular tip (RT, 935 mW/cm2 emittance) and a homogenizer tip (HT, 851 mW/cm2 emittance). Two conventional RBCs (Herculite Ultra [HER], Kerr Corp; Tetric EvoCeram [TEC], Ivoclar Vivadent AG) and two bulk-fill RBCs (SonicFill [SOF], Kerr Corp; Tetric EvoCeram Bulk Fill [TBF], Ivoclar Vivadent AG) were tested. Disc-shaped samples (10 mm Ø), 2-mm thick for conventional composites and 4-mm thick for bulk-fill composites were prepared. Samples were light cured according to manufacturer-recommended times. Knoop microhardness values (KHN) were obtained on the top and bottom surfaces of each specimen at locations correlated with the output of the three LED chips emitting blue (456 nm) or violet light (409 nm). Beam profile analysis using both light guides was also performed. Microhardness of each composite was analyzed using three-way analysis of variance and Tukey honestly significant difference post hoc test (α=0.05). Beam profile images showed better light distribution across the surface of the HT light guide. Use of the HT decreased KHN of HER at the locations of the blue LED chips at bottom of the sample but had no effect on the top surface. For TEC, use of HT increased KHN of all three LED locations at the top surface. Use of the HT increased KHN of SOF at locations corresponding to one of the blue and the violet LED chips at the bottom surface. For TBF, HT increased KHN at all top surface locations. All RBCs showed higher mean KHN at the top compared with the bottom surfaces. In general, all composites presented a higher KHN at the blue LED areas regardless of the surface or the tip used. Results suggest that the homogenizer light guide resulted in significantly increased microhardness at the top, in composite resins containing alternative photoinitiators; however, that effect was not observed at the bottom surfaces.

Influence of Light-curing Distances on Microflexural Strength of Two Resin-based Composites

Objective:

Our objective was to investigate the influence of different curing distances on microflexural strength and the microflexural modulus of two resin-based composites.

Methods:

Two nanohybrid composites were used; Filtek Z250 (Z250) and Tetric EvoCeram (TEC). Rectangular specimens were prepared (2-mm wide × 1-mm deep × 6-mm long) light cured according to the manufacturer's instructions at 0-mm, 2-mm, and 8-mm distances (n=10) and were stored wet at 37°C for 24 hours. A microflexural strength test was performed using a universal testing machine at a crosshead speed of 1 mm/min. The microflexural strength and microflexural modulus data were analyzed using a two-way analysis of variance followed by a Tukey multiple comparison post hoc test (α=0.05).

Results:

The TEC composite had a significantly higher microflexural strength at an 8-mm distance compared with the 0-mm distance. The Z250 composite expressed significantly higher microflexural strength, at 2-mm and 8-mm compared with the 0-mm distance. TEC showed a significantly higher microflexural modulus at an 8-mm distance compared with the 0-mm and 2-mm distances. Z250 also exhibited a significantly higher microflexural modulus at the 2-mm distance, compared with the 8-mm distance. In total, Z250 presented a significantly higher microflexural strength and modulus compared with TEC.

Conclusion:

Curing the explored composites at 2-mm or 8-mm distances from the specimen surface did not have a significant influence on microflexural strength but did significantly affect the microflexural modulus.

Accuracy of Irradiance and Power of Light-Curing Units Measured With Handheld or Laboratory Grade Radiometers

Abstract This study measured and compared exitance irradiance and power of 4 commercial dental light-curing units (LCU) (Elipar S10, Elipar DeepCure-S, Corded VALO and Bluephase Style) using different types of radiometers. The devices used to analyze the LCU were classified as either handheld analog (Henry Schein, Spring, Demetron 100A, Demetron 100B and Demetron 200), handheld digital (Bluephase 1, Bluephase II, Coltolux, CureRite and Hilux), or laboratory instruments (Thermopile and Integrating Sphere). The laboratory instruments and the Bluephase II radiometer were also used to measure the LCU’s power (mW). The LCU’s were activated for 20 s (n=5). Data were analyzed using Kruskal-Wallis and Student-Newman-Keuls multiple comparison test (a=0.05). Among the LCU, the laboratory instruments presented different irradiance values, except for Corded VALO. The Coltolux and Hilux radiometers measured greater irradiance values compared to the laboratory instruments for the four LCUs tested. Within a given LCU, handheld analog units measured lower irradiance values, compared to handheld digital and laboratory instruments, except using the Spring radiometer for the Elipar S10 LCU. None of the handheld radiometers were able to measure similar irradiance values compared to laboratory instruments, except for Elipar S10 when comparing Bluephase 1 and Thermopile. Regarding power measurement, Bluephase II always presented the lowest values compared to the laboratory instruments. These findings suggest that the handheld radiometers utilized by practitioners (analog or digital) exhibit a wide range of irradiance values and may show lower outcomes compared to laboratory based instruments.

Effect of Beam Profiles From Different Light Emission Tip Types of Multiwave Light-emitting Diodes on the Curing Profile of Resin-based Composites

Light activation is an important clinical step for achieving success in restorative procedures. This study evaluated the influence of beam profile from different light emission tip types of multiwave light-emitting diodes (LEDs) on the curing profile of resin-based composites. Experimental composites were produced containing either camphorquinone (CQ) or diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) as a photoinitiator. Multiwave LEDs with either a bundle light guide tip (Bluephase G2, Ivoclar Vivadent) or a microlens tip (VALO Cordless, Ultradent) were characterized using a beam profiler. Block-shaped samples (5×5×3 mm depth) of the two composites were cured in a custom-designed mold with the multiwave LEDs positioned to compare the regions exposed to the 420-495 nm (blue) and 380-420 nm (violet) emittances. To map the curing profile, the degree of conversion (DC) of longitudinal thin cross sections from each block was evaluated using transmission FT-NIR. Radiant exposure transmitted through the composites during curing was evaluated at different thicknesses. Data were analyzed using analysis of variance and Tukey test (α=0.05; β=0.2). The results indicated that there were differences in the beam profile and the overall radiant exposures transmitted through the composites using each multiwave LED (p&lt;0.01, df=1 F=73.18). However, there were no differences in the curing profiles provided by the two multiwave LEDs (p=0.89, df=12 F=0.52), and similar effects were found according to the different LED emittance regions (p=0.09, df=5, F=2.11). When considering up to 1 mm in depth, no differences in the DC were found between the composites containing either photoinitiators. Starting at 2 mm in depth, the composite containing TPO showed a decrease in DC in the 420-495 nm emittance region, while the composite containing CQ showed a similar decrease in cure efficiency only at 3-mm depth under both 380-420 nm and 420-495 nm emittance regions. Thus, despite the fact that the nonuniform light beam emitted from the two multiwave LEDs was visually distinctly different when delivering 24 J/cm2, this difference did not seem to affect the curing profile of the composites. However, light transmission within 380-420 nm seems to be reduced with depth, directly affecting the curing profile of composites containing a photoinitiator with absorbance falling within this emission range.

The Influence of Distance on Radiant Exposure and Degree of Conversion Using Different Light-Emitting-Diode Curing Units

Objectives:

To investigate the influence of curing distance on the degree of conversion (DC) of a resin-based composite (RBC) when similar radiant exposure was achieved using six different light-curing units (LCUs) and to explore the correlation among irradiance, radiant exposure, and DC.

Methods and Materials:

A managing accurate resin curing-resin calibrator system was used to collect irradiance data for both top and bottom specimen surfaces with a curing distance of 2 mm and 8 mm while targeting a consistent top surface radiant exposure. Square nanohybrid-dual-photoinitiator RBC specimens (5 × 5 × 2 mm) were cured at each distance (n=6/LCU/distance). Irradiance and DC (micro-Raman spectroscopy) were determined for the top and bottom surfaces. The effect of distance and LCU on irradiance, radiant exposure, and DC as well as their linear associations were analyzed using analysis of variance and Pearson correlation coefficients, respectively (α=0.05).

Results:

While maintaining a similar radiant exposure, each LCU exhibited distinctive patterns in decreased irradiance and increased curing time. No significant differences in DC values (63.21%-70.28%) were observed between the 2- and 8-mm distances, except for a multiple-emission peak LCU. Significant differences in DC were detected among the LCUs. As expected, irradiance and radiant exposure were significantly lower on the bottom surfaces. However, a strong correlation between irradiance and radiant exposure did not necessarily result in a strong correlation with DC.

Conclusions:

The RBC exhibited DC values &gt;63% when the top surface radiant exposure was maintained, although the same values were not reached for all lights. A moderate-strong correlation existed among irradiance, radiant exposure, and DC.

Polymerisation Shrinkage Profiling of Dental Composites using Optical Fibre Sensing and their Correlation with Degree of Conversion and Curing Rate

Traditional polymerisation shrinkage (PS) measurement systems measure average PS of dental composites, but the true local PS varies along the length and breadth of the composite. The PS depends on the curing light intensity distribution, resultant degree of conversion (DOC) and the curing rate. In this paper, optical fibre Bragg grating (FBG) sensing based technology is used to measure the linear post-gel PS at multiple locations within dental composite specimens, and is correlated with DOC and curing rate. A commercial dental composite is used, and its post-gel PS and DOC are mapped using embedded fibre Bragg grating sensors at different curing conditions. The distance between the curing lamp and the composite specimen is varied which resulted in different intensity distribution across the specimen. The effect of curing light intensity distribution on PS, curing rate and DOC are investigated for demonstrating a relationship among them. It is demonstrated that FBG sensing method is an effective method to accurately profiling post-gel PS across the specimen.