Micro-hardness evaluation of a micro-hybrid composite resin light cured with halogen light, light-emitting diode and argon ion laser

Effect of Radiant Exposure on the Physical and Mechanical Properties of 10 Flowable and High-viscosity Bulk-fill Resin Composites

OBJECTIVES

To evaluate the effect of the different radiant exposures from a multipeak light curing unit on the physical and mechanical properties of flowable and high-viscosity bulk-fill resin-based composites (RBC).

METHODS

Five flowable bulk-fill RBCs (Tetric N-Flow Bulk-fill, Ivoclar Vivadent; Filtek Bulk Fill Flow, 3M Oral Care; Opus Bulk Fill Flow APS, FGM; Admira Fusion x-base, Voco and; and SDR Plus Bulk Fill Flowable, Dentsply Sirona) and five high-viscosity bulk-fill RBCs (Tetric N-Ceram Bulk-fill, Ivoclar Vivadent; Filtek One Bulk Fill, 3M Oral Care; Opus Bulk Fill APS, FGM; Admira Fusion x-tra, Voco; and SonicFill 2, Kerr) were photo-cured using a VALO Cordless light (Ultradent) for 10, 20, and 40 seconds at an irradiance of 1200, 800, or 400 mW/cm2, resulting in the delivery of 4, 8, 12, 16, 24, 32, or 48 J/cm2. Post-gel shrinkage (Shr) was calculated using strain-gauge test. The degree of conversion (DC, %) was calculated using FTIR. Knoop hardness (KH, N/mm2) and elastic modulus (E, MPa) were measured at the top and bottom surfaces. Logarithmic regressions between the radiant exposures and mechanical properties were calculated. Radiodensity was calculated using digital radiographs. Data of Shr and radiodensity were analyzed using two-way analysis of variance (ANOVA), and the DC, KH, and E data were analyzed with two-way ANOVA using split-plot repeated measurement tests followed by the Tukey test (a = 0.05).

RESULTS

Delivering higher radiant exposures produced higher Shr values (p<0.001) and higher DC values (R2=0.808-0.922; R2=0.648-0.914, p<0.001), KH (R2=0.707-0.952; R2=0.738-0.919; p<0.001), and E (R2=0.501-0.925; R2=0.823-0.919; p<0.001) values for the flowable and high-viscosity RBCs respectively. Lower KH, E and Shr were observed for the flowable bulk-fill RBCs. All bulk-fill RBCs had a radiopacity level greater than the 4-mm thick aluminum step wedge. The radiant exposure did not affect the radiopacity.

CONCLUSION

The Shr, DC, KH, and E values were highly correlated to the radiant exposure delivered to the RBCs. The combination of the higher irradiance for longer exposure time that resulted in radiant exposure between 24 J/cm2 to 48 J/cm2 produced better results than delivering 400 mW/cm2 for 40 s (16 J/cm2), and 800 mW/cm2 for 20 seconds (16 J/cm2) or 1200 mW/cm2 for 10 seconds (12 J/cm2). All the bulk-fill RBCs were sufficiently radiopaque compared to 4 mm of aluminum.

Physicochemical and mechanical properties of preheated composite resins for luting ceramic laminates

This study analyzed and compared the physicochemical and mechanical properties of preheated resin composite with light-cured resin cement for luting indirect restorations. 210 specimens of resin cement/resin composite were prepared according to preheating treatment heated (Htd) or not (NHtd). Light-cured resin cement (Variolink Veneer, Ivoclar), and resin composite (Microhybrid-Z100, 3 M; Nanohybrid-Empress direct, Ivoclar; and Bulk fill-Filtek One, 3 M) were used (n = 10). Resin cement specimens were not preheated. The response variables were (n = 10): film thickness, microhardness, liquid sorption and solubility. Data were analyzed by 2-way ANOVA and Tukey HSD post-test (α = 0.05). Bulk fill NHtd resin had the highest film thickness values (p < 0.001). Microhybrid and nanohybrid Htd resins had the smallest thicknesses and did not differ from the cement (p > 0.05). The highest microhardness values were found for Bulk fill NHtd and Bulk fill Htd resins. The nanohybrid and microhybrid Htd resins showed the lowest microhardness values, with no difference in cement (p > 0.05). For liquid sorption, there was no significant difference between the groups (p = 0.1941). The microhybrid Htd resin showed higher solubility values than the other materials (p = 0.0023), but it did not differ statistically from resin cement (p > 0.05). Preheating composite resins reduced the film thickness. After heating, nanohybrid and Bulk fill resins retained stable microhardness, sorption, and solubility values.

Hardness and surface roughness of differently processed denture base acrylic resins after immersion in simulated gastric acid

STATEMENT OF PROBLEM

The effect of gastric acid on the surface properties of denture base acrylic resin is unknown.

PURPOSE

The purpose of this in vitro study was to evaluate changes in the surface roughness and hardness of denture base acrylic resins after immersion in simulated gastric acid.

MATERIAL AND METHODS

Acrylic resin specimens (n=10) were prepared with 3 different processing techniques (compression-molded, injection-molded, and computer-aided design and computer-aided manufacturing [CAD-CAM] milled) and exposed to either gastric acid or artificial saliva (control). Surface roughness and hardness were measured at baseline (T0) and after 24-hour (T24) and 96-hour (T96) immersion in the solutions. The surface roughness and hardness data were analyzed by 3-way ANOVA and the Tukey HSD test (α=.05).

RESULTS

At T24, the greatest change in surface hardness was observed for compression-molded specimens in gastric acid (P<.05). At T96, changes in hardness values were higher in compression-molded specimens than those in milled specimens (P<.05). Regarding surface roughness, at T24, compression-molded and injection-molded specimens showed higher values than milled specimens in gastric acid (P<.05). Concerning specimens in artificial saliva, compression-molded specimens showed significantly higher changes in roughness than those of the others (P<.05). At T96, injection-molded specimens had the greatest roughness values (P<.05). Among specimens immersed in artificial saliva, milled specimens showed lower roughness values than the injection-molded or compression-molded specimens (P<.05).

CONCLUSIONS

Gastric acid exposure adversely affected the roughness and hardness of all the acrylic resins evaluated. CAD-CAM milled specimens showed better resistance to acid exposure after 24 and 96 hours in terms of roughness and hardness.

Influence of water aging on surface hardness of low-shrinkage light-cured composite resins

This study evaluated the microhardness of four types of low-shrinkage composite resins and two types of universal composite resins with either 12 or 16 J/cm² light power energy. Three disks were made for each group (n = 3) for a total of 36 specimens. The specimens were prepared by condensing the composite resin into a circular copper mold (diameter: 6 mm; height: 2 mm) and polymerizing with 700 mW/cm² light power density. The microhardness values of the resin specimens were measured using a Vickers hardness tester after different storage durations. Z250 and Clearfil Majesty Posterior composites showed softer subsurfaces when comparing the 24 h samples for all six types. Conversely, Kalore GC and Admira (AD) composites showed harder subsurfaces during the 24 h samples. All the composite resins showed significant differences (P < 0.05) in microhardness values at one of the aging times when they were polymerized with either 12 or 16 J/cm² light power energy. Composite resin AD had a higher microhardness value after polymerization with 12 J/cm² than with 16 J/cm². The results indicated that low-shrinkage composite resins have better subsurface characteristics, and the light power energy of 16 J/cm² is better for the polymerization of most composites.

An analysis on the potential of diode-pumped solid-state lasers for dental materials

Material structure-property relationship is strongly related to the employed process technology. Over the past years, laser processing of engineering materials has been proposed in many fields and different uses for diode lasers have been found in dentistry. In this contest, the potential of GaN- and InGaN-based laser diodes to cure dental materials was analysed. Two wavelengths of 405 nm and 445 nm were used as heat or light sources for warm condensation of gutta-percha, light transmission in dental posts and brackets or light curing of dental composites. Additive manufacturing approach was considered to fabricate 3D root analogues, suitable supports, positioning systems and moulds for optical measurements. A three-axis CAD/CAM system was implemented for positioning and aligning the laser beam. The ability of diode-pumped solid-state lasers to cure dental materials or to transmit light was compared to that of a traditional instrument. Temperature profile at the apex of an additive manufactured root canal sealed with gutta-percha, light transmission through translucent quartz fiber post or through aesthetic ceramic bracket, bending properties and morphological features of light cured dental composites (Gradia Direct - GC Corporation and Venus Diamond - Heraeus Kulzer) were measured. Results showed a very high potential of diode-pumped solid-state lasers to be used in endodontics, orthodontics and restorative dentistry.

Effectiveness of photopolymerization in composite resins using a novel 445-nm diode laser in comparison to LED and halogen bulb technology

Challenges especially in the minimal invasive restorative treatment of teeth require further developments of composite polymerization techniques. These include, among others, the securing of a complete polymerization with moderate thermal stress for the pulp. The aim of this study is to compare current light curing sources with a blue diode laser regarding curing depth and heat generation during the polymerization process. A diode laser (445 nm), a LED, and a halogen lamp were used for polymerizing composite resins. The curing depth was determined according to the norm ISO 4049. Laser output powers of 0.1, 0.5, 1, and 2 W were chosen. The laser beam diameter was adapted to the glass rod of the LED and the halogen lamp (8 mm). The irradiation time was fixed at 40 s. To ascertain ΔT values, the surface and ground area temperatures of the cavities were simultaneously determined during the curing via a thermography camera and a thermocouple. The curing depths for the LED (3.3 mm), halogen lamp (3.1 mm) and laser_{(0.5/1 W)} (3/3.3 mm) showed no significant differences (p < 0.05). The values of ΔT_surface as well as ΔT_ground also showed no significant differences among LED, halogen lamp, and laser_{(1 W)}. The ΔT_surface values were 4.1_LED, 4.3_{halogen lamp}, and 4.5 °C for the laser while the ΔT_ground values were 2.7_LED, 2.6_{halogen lamp}, and 2.9 °C for the laser. The results indicate that the blue diode laser (445 nm) is a feasible alternative for photopolymerization of complex composite resin restorations in dentistry by the use of selected laser parameters.

Mechanical and Thermal Properties of Dental Composites Cured with CAD/CAM Assisted Solid-State Laser

Over the last three decades, it has been frequently reported that the properties of dental restorative composites cured with argon laser are similar or superior to those achieved with conventional halogen and light emitting diode (LED) curing units. Whereas laser curing is not dependent on the distance between the curing unit and the material, such distance represents a drawback for conventional curing units. However, a widespread clinical application of this kind of laser remains difficult due to cost, heavy weight, and bulky size. Recently, with regard to the radiation in the blue region of the spectrum, powerful solid-state lasers have been commercialized. In the current research, CAD (computer-aided design)/CAM (computer-aided manufacturing) assisted solid-state lasers were employed for curing of different dental restorative composites consisting of micro- and nanoparticle-reinforced materials based on acrylic resins. Commercial LED curing units were used as a control. Temperature rise during the photopolymerisation process and bending properties were measured. By providing similar light energy dose, no significant difference in temperature rise was observed when the two light sources provided similar intensity. In addition, after 7 days since curing, bending properties of composites cured with laser and LED were similar. The results suggested that this kind of laser would be suitable for curing dental composites, and the curing process does not suffer from the tip-to-tooth distance.

Polymer-Based Direct Filling Materials

After a brief review of current restorative materials and classifications, this article discusses the latest developments in polymer-based direct filling materials, with emphasis on products and studies available in the last 10 years. This will include the more recent bulk fill composites and self-adhesive materials, for which clinical evidence of success, albeit somewhat limited, is already available. The article also introduces the latest cutting edge research topics on new materials for composite restorations, and an outlook for the future of how those may help to improve the service life of dental composite restorations.

Influence of Emission Spectrum and Irradiance on Light Curing of Resin-Based Composites

PURPOSE

This study examined the influence of different emission spectra (single-peak and broad-spectrum) light-curing units (LCUs) delivering the same radiant exposures at irradiance values of 1200 or 3600 mW/cm² on the polymerization and light transmission of four resin-based composites (RBCs).

METHODS AND MATERIALS

Two prototype LCUs that used the same light tip, but were either a single-peak blue or a broad-spectrum LED, were used to deliver the same radiant exposures to the top surfaces of the RBCs using either standard (1200 mW/cm²) or high irradiance (3600 mW/cm²) settings. The emission spectrum and radiant power from the LCUs were measured with a laboratory-grade integrating sphere coupled to a spectrometer, and the light beam was assessed with a beam profiler camera. Four RBCs (Filtek Supreme Ultra A2, Tetric EvoCeram A2, Tetric EvoCeram T, and TPH Spectra High Viscosity A2) were photoactivated using four different light conditions: single-peak blue/standard irradiance, single-peak blue/high irradiance, broad-spectrum/standard irradiance, and broad-spectrum/high irradiance. The degree of conversion (N=5) and microhardness at the top and bottom of 2.3-mm-diameter by 2.5-mm-thick specimens (N=5) were analyzed with analysis of variance and Tukey tests. The real-time light transmission through the RBCs was also measured.

RESULTS

For all light conditions, the 2.3-mm-diameter specimens received a homogeneous irradiance and spectral distribution. Although similar radiant exposures were delivered to the top surfaces of the RBCs, the amount of light energy emitted from the bottom surfaces was different among the four RBCs, and was also greater for the single-peak lights. Very little violet light (wavelengths below 420 nm) reached the bottom of the 2.5-mm-thick specimens. The degree of conversion and microhardness results varied according to the RBC (p<0.05). The RBCs that included alternative photoinitiators had greater microhardness values at the top when cured with broad-spectrum lights, while at the bottom, where little violet light was observed, the results were equal or higher when they were photoactivated with single-peak blue lights. With the exception of the microhardness at the top of TPH, equivalent or higher microhardness and degree-of-conversion values were achieved at the bottom surface when the standard (1200 mW/cm²) irradiance levels were used compared to when high irradiance levels were used.

CONCLUSIONS

Considering the different behaviors of the tested RBCs, the emission spectrum and irradiance level influenced the polymerization of some RBCs. The RBCs that included alternative photoinitiators produced greater values at the top when cured with broad-spectrum lights, while at the bottom, results were equal or higher for the RBCs photoactivated with single-peak blue lights.

Ability of four dental radiometers to measure the light output from nine curing lights

OBJECTIVES

To evaluate the accuracy of four dental radiometers when measuring the output from nine light curing units (LCUs).

METHODS

The light output from nine light-emitting diode LCUs was measured with a laboratory-grade power meter (PowerMax-Pro 150 HD) and four dental radiometers (Bluephase Meter II, SDI LED Radiometer, Kerr LED Radiometer, and LEDEX CM4000). Ten measurements were made of each LCU with each radiometer. Analysis of variance (ANOVA) followed by Tukey tests (α=0.05) were used to determine if there was a difference between the calculated irradiance values from the power meter and those from the radiometers. Where applicable, the LCUs were ranked according to their power and irradiance values. The emission spectra from the LCUs was measured using an integrating sphere attached to a fiber-optic spectrometer (N=10). The beam profile of the LCUs was measured with a beam profiler camera.

RESULTS

Of the dental radiometers, only the Bluephase Meter II could measure power. ANOVA showed no significant difference between power values measured with the laboratory-grade meter and the Bluephase Meter II (p=0.527). The difference between the mean irradiance reported by the various radiometers for the same LCU was up to 479mW/cm². The ranking of the power values obtained using the laboratory-grade meter was the same for the Bluephase Meter II.

CONCLUSION

When compared to the calculated irradiance values from the laboratory-grade power meter, the Bluephase Meter II provided the most accurate data.

CLINICAL SIGNIFICANCE

Considering the great variation between the irradiance values provided by radiometers and their overall inaccuracy when compared to a laboratory-grade meter, dentists should not place too much faith in the absolute irradiance value. However, hand-held radiometers can be used to monitor changes in the light output of LCUs over time.

Comparison of Surface Hardness of Various Shades of Twinky Star Colored Compomer Light-cured with QTH and LED Units

Introduction

Colored compomers are a group of restorative materials that were introduced in 2002 to repair primary teeth, and they provide attractive color and ease of use in pediatric dentistry. The aim of this study was to evaluate the effect of QTH and LED light-curing units on the surface hardness of different colors of Twinky Star compomers.

Methods

In this experimental study, a composite resin (Z250, 3M, and USA), an ionosit compomer (DMG, Germany) with A3 shade and 8 different Twinky Star colored compomer (Voco, Germany) samples were used. In all, 100 samples were prepared with 10 samples in each group, i.e., 10 Z250 composite resin, 10 ionosit compomers, and 10 Twinky Star compomer samples of each color. The samples were prepared in a 4×4-mm Teflon mold. Half of the samples were light-cured with QTH and the other half with LED units. Then, the surface microhardness was measured by Vickers hardness test. The data were analyzed with IBM-SPSS version 22, using the t-test and ANOVA.

Results

Two-way ANOVA showed that the mean surface hardness of the compomer samples cured with the QTH unit was significantly higher than that cured with the LED unit (p < 0.001). In each curing unit, surface hardness of some materials exhibited significant differences with the highest hardness being observed in the Z250 composite resin (650.35 ± 56.320) and the lowest hardness being detected in the ionosit compomers (461.10 ± 96.170). One-way ANOVA also showed that, among the different colors of the Twinky Star compomer, the lowest hardness with both units (QTH and LED) was observed in the gold color (214.32 ± 22.026 and 175.116 ± 15.918, respectively).

Conclusion

The colored compomer and the type of light-curing unit affected the microhardnesses of the surfaces. Different colors of Twinky Star compomers exhibited different surface microhardnesses.

Microhardness of composite resin cured through different primary tooth thicknesses with different light intensities and curing times: In vitro study

Objective:

The aim of this study was to evaluate the effect of increased exposure time and light intensity on microhardness of cured composite through different thicknesses of tooth structure in primary teeth.

Materials and Methods:

One hundred and seventy cylindrical resin composite specimens were prepared. All specimens were divided into 17 experimental and control groups. “Light-emitting diode” light curing unit (LCU) applied directly or through 1, 2, and 3 mm thicknesses tooth slices for experimental groups. The irradiation protocols were 25 and 50 s at 650 mW/cm² and 15 and 30 s at 1100 mW/cm². The “quartz-tungsten-halogen” LCU (400 mW/cm²) for 40 s was used in control group. Microhardness was measured by the Vickers hardness test.

Results:

Indirectly cured specimens and those cured through a 1 mm thick tooth structure, an increase in intensity caused hardness drop. In the specimens cured through 2 and 3 mm thick tooth structures, increased intensity and/or exposure time did not show any appropriate changes on microhardness.

Conclusion:

Irradiation through a 1.0 mm thick tooth slice resulted in reduced microhardness although it was still within the clinically acceptable level. The hardness values of the specimens cured through 2 or 3 mm thick tooth slices fell below the clinically acceptable level even after doubling the exposure time and/or light intensity.

Five second photoactivation? A microhardness and marginal adaptation in vitro study in composite resin restorations

INTRODUCTION

Studies defining the characteristics of light curing units and photoactivation methods are necessary to allow the correct choices to be made in daily practice. This study aimed to determine whether different photoactivation protocols for composite resins [periodic level shifting (PLS) - 5 second and soft-start] are able to maintain or enhance the mechanical properties and marginal adaptation of restorations.

METHODS

Restorations were placed in bovine teeth using the following photoactivation methods: continuous light for 20 seconds (control group); PLS technology (PLS - 5 second group); and continuous light and a light guide tip distance of 6 mm after which the tip was placed at the surface of the restoration (soft-start group). The teeth were transversely sectioned in the incisal-cervical direction. Thirty halves were randomly selected for Knoop microhardness testing (n = 10). The other 30 halves were subjected to scanning electron microscopy analysis. The images obtained were measured to identify the highest marginal gap, and statistical tests for variance analysis were conducted.

RESULTS

Microhardness tests showed no statistically significant difference between the photoactivation methods analysed (P ≥ 0.01). The tests showed a difference among depths (P < 0.01), with the deeper layers being the hardest. In analysing marginal adaptation, no significant difference was identified between the higher marginal gap values in the continuous (mean = 10.36) and PLS - 5 second (mean = 10.62) groups, and the soft-start group (mean = 5.83) presented the lowest values (P < 0.01).

CONCLUSIONS

The PLS - 5 second and soft-start protocols did not alter the hardness of the restorations. Moreover, the PLS - 5 second protocol did not alter the marginal adaptation, whereas the soft-start protocol improved marginal adaptation.

Influence of extended light exposure curing times on the degree of conversion of resin-based pit and fissure sealant materials

PURPOSE

The aim of present study was to evaluate extended curing times on the degree of conversion (DC) of filled and unfilled resin-based materials used as pit and fissure sealants.

MATERIALS AND METHODS

The materials examined were a flowable composite (Filtek™ Z350 XT Flowable) and a pit and fissure sealant (Clinpro™ Sealant). Thirty disks of each material were prepared. The 30 made of the flowable composite were divided into three groups (n = 10 each) according to the three different curing times studied: 20 s (group 1), 40 s (group 2), and 60 s (group 3). Similarly, the 30 disks made of the pit and fissure sealant were divided into three groups (n = 10 each) according to the three different curing times: 20 s (group 4), 40 s (group 5), and 60 s (group 6). After polymerization, the disks were removed from the mold and stored in dry, lightproof containers in an incubator at 37 °C for 24 h. The DC was obtained using an Avatar 320 FTIR spectrometer. Then the data were analyzed using the Kruskal-Wallis test and the Fisher's least significant difference post hoc test for multiple comparisons (alpha = 0.05).

RESULTS

DC values for the flowable composite (Filtek™ Z350 XT) were higher (p = 0.002) than those for the pit and fissure sealant (Clinpro™ Sealant). Group 2 and group 5 showed significantly higher DC values than group 1 and group 4, respectively. There was no difference between groups 2 and 3 or between groups 5 and 6 (p = 2.93).

CONCLUSION

An extended curing time improves the DC to some extent for both materials.

Hardness Evaluation of Composite Resins Cured with QTH and LED

Background and aims. Today light cured composites are widely used. Physical and mechanical properties of composites are related to the degree of conversion. Light curing unit (LCU) is an important factor for composite polymerization. Aim of this study is evaluation of composite resins hardness using halogen and LED light curing units.

Materials and methods. In this study, 30 samples of Filtek Z250 and C-Fill composite resins were provided. Samples were light cured with Ultralume2, Valo and Astralis7. Vickers hardness number (VHN) was measured in 0, 1, 2 mm depth. Statistical analysis used: Data were analysed by SPSS software and compared with each other by T-test, one-way and two-way ANOVA and Post-hoc Tukey test.

Results. In Filtek Z250, at top surface, VHN of Ultralume2 was higher than VHN of Valo (P = 0.02) and Astralis7 (P =0.04), but in depth of 1, 2 mm, VHN of Ultralume2 and Astralis7 were almost the same and both LCUs were more than Valo which the difference between Ultralume2 and Valo was significant in depth of 1mm (0.05) and 2mm (0.02). In C-Fill composite, at top surface, Astralis7 showed higher VHN, but in depth of 2 mm, performance of all devices were rather simi-lar.

Conclusion. In Z250, which contains camphorquinone initiator, light cure LED Ultra-lume2 with narrow wavelength showed higher hardness number than Valo. In C-fill, in top surface, Astralis7 with more exposure time, resulted higher VHN. But In depth of 2 mm, various light curing devices had rather similar hardness number.

The effect of interincisal opening, cavity location and operator experience on the energy delivered by a light-curing unit to a simulated dental restoration

BACKGROUND

Curing of resin-based composites depends on the delivery of adequate total energy, which may be operator dependent. Aim To determine the effect of interincisal opening, cavity location and operator experience on the total energy delivered to simulated cavity preparation sites.

DESIGN

Three cohorts were included: junior dental nurses, senior dental nurses and qualified dentists (N=5, each cohort). Each operator (participant) followed the same procedure and light-cured two simulated restorations in a MARC patient simulator using a Demi light-curing unit for 20 seconds in each of the following situations: left upper second molar (UL7), interincisal opening at both 25 mm and 45 mm; upper central incisor (UR1), interincisal opening at 45mm. The light energy delivered by each operator in each situation was recorded. Five readings for each operator were taken at each interincisal distance. Statistical comparisons of delivered energy (J/cm2) between interincisal openings, location and groups in the total energy delivered were performed using the Kruskal-Wallis nonparametric test: alpha = 0.05.

RESULTS

Less total energy was delivered to the posterior cavity at 25mm (12.0 +/- 5.3 J/cm2) than at 45mm (16.9 +/- 5.6 J/cm2) by all operators (P < 0.05). At 45 mm, less total energy was delivered to the posterior cavity compared to the anterior cavity (25.1 +/- 7.4 J/cm2; P < 0.05). There was no statistically significant difference between junior nurses and qualified dentists (P > 0.05) but there was a significant difference in the total energy delivered between senior nurses (20.1 +/- 7.8 J/cm2) and junior nurses (17.5 +/- 7.6 J/cm2) and between senior nurses and qualified dentists (16.6 +/- 8.7 J/cm2) (P < 0.05).

CONCLUSIONS

Interincisal mouth opening, location of the cavity and operator experience affected the total energy delivered to cavities in a simulated clinical environment.

Effect of light polymerization time, mode, and thermal and mechanical load cycling on microleakage in resin composite restorations

This study evaluated the effect of polymerization mode and time and thermal and mechanical loading cycling (TMC) on microleakage in composite resin restorations. One hundred and eighty cavities were prepared and randomly divided according to the light curing time (20, 40, or 60 s), modes (quartz-tungsten-halogen (QTH)-420 mW/cm(2), LED 2 (2nd degree generation)-1,100 mW/cm(2), or LED 3 (3rd degree generation)-700 mW/cm(2)), and TMC. Following standard restorative procedures, the samples were prepared for analysis in an absorbance spectrophotometer. All results were statistically analyzed using the three-way ANOVA and Tukey test (p ≤ 0.05). The results revealed that the groups QTH and LED 3 submitted to TMC showed higher microleakage than those that were not submitted to TMC. Only for LED 3, 60 s showed higher microleakage than 20 s. For LED 2 and QTH, there were no differences between the times. QTH showed lower microleakage means than LED 2, when photoactivated for 20 s, without TMC. When photoactivated for 60 s, QTH showed lower microleakage means than LED 3, for the groups with or without TMC. It was concluded that TMC, the increase in polymerization time, and the irradiance were factors that may increase the marginal microleakage of class II cavities.

Mechanical properties of composite resins light-cured using a blue DPSS laser

Lasers have many favorable features as a light source owing to their monochromaticity and coherence. This study examined the mechanical properties of composite resins that were light-cured using a diode-pumped solid state (DPSS) laser. Eight composite resins were light-cured using four different light sources (one quartz-tungsten-halogen (QTH), two light-emitting diodes (LEDs), and one DPSS laser with a wavelength of 473 nm). The light intensity of the DPSS laser and remaining light-curing units were approximately 500 and 900 mW/cm(2), respectively. The microhardness, flexural properties, and compressive properties were evaluated using the Vickers hardness test, three-point bending test, and compression test, respectively. In most cases, the microhardness, flexural properties, and compressive properties of the specimens light-cured using the DPSS laser were similar to those obtained using the other light-curing units. Within the limits of the study, the microhardness, flexural modulus, and compressive strength were linearly correlated with the filler content (in weight percent). The flexural modulus and compressive modulus were also linearly correlated with the microhardness. Even with a much lower light intensity, the DPSS laser with a wavelength of 473 nm can polymerize composite resins and give comparable mechanical properties to those obtained using the other light-curing units.

Influence of DPSS laser on polymerization shrinkage and mass change of resin composites

OBJECTIVES

This study evaluated the effectiveness of the diode-pumped solid state (DPSS) laser as a light source for light-curing dental resin composites.

BACKGROUND DATA

A DPSS laser of 473  nm may be useful because of its match with the absorption peak of camphorquinone (CQ), the photoinitiator.

MATERIALS AND METHODS

A DPSS laser (LAS) of 473  nm and a quartz-tungsten-halogen (QTH) light-curing unit (OP) were used as the light sources for light curing six different resin composites (four nanocomposites and two hybrid composites). Polymerization shrinkage and mass change (water sorption and solubility) were measured during and after light curing to determine the degree of polymerization. Mass change was evaluated by following the ISO 4049 standard.

RESULTS

According to the evaluation, the specimens light cured using LAS showed similar maximum polymerization shrinkage (12.3∼18.1  μm for LAS; 13.2∼16.2  μm for OP) and water sorption (11.4∼24.1  μg/mm(3) for LAS; 11.3∼22.8  μg/ mm(3) for OP) to the cases light cured using OP. The specimens light cured using LAS showed a significantly higher solubility than the cases light cured using OP (2.4∼6.6  μg/ mm(3) for LAS; 0.8∼1.6  μg/ mm(3) for OP). However, the maximum water sorption and solubility obtained from the specimens were lower than the values permitted by the ISO 4049 standard.

CONCLUSIONS

The results may suggest that the DPSS laser with an emission wavelength of 473  nm can be used as a light source for light-curing dental resin composites.

The effect of curing light and chemical catalyst on the degree of conversion of two dual cured resin luting cements

The aim of this study was to evaluate the influence of different curing lights and chemical catalysts on the degree of conversion of resin luting cements. A total of 60 disk-shaped specimens of RelyX ARC or Panavia F of diameter 5 mm and thickness 0.5 mm were prepared and the respective chemical catalyst (Scotchbond Multi-Purpose Plus or ED Primer) was added. The specimens were light-cured using different curing units (an argon ion laser, an LED or a quartz-tungsten-halogen light) through shade A2 composite disks of diameter 10 mm and thickness 2 mm. After 24 h of dry storage at 37°C, the degree of conversion of the resin luting cements was measured by Fourier-transformed infrared spectroscopy. For statistical analysis, ANOVA and the Tukey test were used, with p ≤ 0.05. Panavia F when used without catalyst and cured using the LED or the argon ion laser showed degree of conversion values significantly lower than RelyX ARC, with and without catalyst, and cured with any of the light sources. Therefore, the degree of conversion of Panavia F with ED Primer cured with the quartz-tungsten-halogen light was significantly different from that of RelyX ARC regardless of the use of the chemical catalyst and light curing source. In conclusion, RelyX ARC can be cured satisfactorily with the argon ion laser, LED or quartz-tungsten-halogen light with or without a chemical catalyst. To obtain a satisfactory degree of conversion, Panavia F luting cement should be used with ED Primer and cured with halogen light.