Effect of new light curing units on microleakage and microhardness of resin sealants

Assessment of influence of LED curing units used on microhardness of resin-modified glass ionomer sealants

Aim: Resin modified glass ionomer (RMGI) is class of material that can be used as sealant for preventing and arresting the progression of caries in pits and fissures. As these are hybrid materials, their properties can be affected by factors related to the polymerization process. Therefore, this study aimed to evaluate the influence of different generations of LED curing units (Elipar DeepCure-L and VALO Grand) on Knoop microhardness values (KHN) of RMGI sealants (Clinpro XT and Vitremer). Methods: Forty cylindrical specimens (6mm ø x 1 mm high) were prepared according to the manufacturer’s instructions and divided into four groups (n=10) according to the type of RMGI and LED used. The KHN of the top surface of each sample was calculated 7 days after light-curing. Data were submitted to two-way ANOVA (α = 0.05). Results: Vitremer had higher KHN values than Clinpro XT after using both LEDs (p<0.0001), but especially when light-cured with the use of VALO Grand (p<0.0001). Whereas the KHN value of Clinpro was not influenced by the LED device (p>0.05). Conclusions: Top surface microhardness values of RGMI sealants were affected by both material composition and generations of LED curing units used. Third generation LED curing units seemed to be more efficient for the polymerization of RMGI-based sealants.

Effect of Optical Properties of Lithium Disilicate Glass Ceramics and Light-Curing Protocols on the Curing Performance of Resin Cement

This study aimed to investigate the effects of optical properties of lithium disilicate glass ceramics and the light-curing protocols (LCP) on the curing performance of light-cured resin cement. Lithium disilicate glass-ceramics with different optical properties were sectioned to produce ceramic specimens of 0.8 mm thickness. Irradiance through the ceramic specimens was measured by a radiometer. Light transmittance of ceramics was assessed using a UV/Vis spectrophotometer. The light-cured resin cement was injected into a Teflon mold and ceramics with different optical properties were placed on it, cured under different LCPs, and the degree of conversion (DC) and Vickers microhardness of the resin cement were separately measured by Micro-ATR/FTIR spectrometry and the microhardness tester. The shade (p < 0.001) and transparency (p < 0.001) of ceramics affect the irradiance of the light-curing unit. The transparency (p < 0.001) of the ceramic and light-curing protocols (p < 0.001) affect the DC and microhardness of resin cements. When the thickness of the ceramic is 0.8 mm, the light transmittance of the ceramic and the curing performance of the resin cement increase with the increase of the transparency of the ceramic. An appropriate increase in irradiance and exposure time can optimize the curing performance of resin cement. These factors should be taken into account by the clinician when designing the bonding solution for porcelain veneers.

Effect of light irradiation condition on gap formation under polymeric dental restoration; OCT study

OBJECTIVE

To investigate the effect of two light-curing systems; quartz tungsten-halogen (QTH) and light-emitting diode (LED), and irradiation time on interfacial gap formation of dental composite resin restorations bonded with an adhesive resin using optical coherence tomography (OCT).

MATERIALS AND METHODS

Forty cavities were prepared in extracted human molar teeth and divided into four groups (n=10) based on the type of light curing system QTH (LITEX 680A) and LED (Demi Plus) and curing duration (10 s or 40 s). A single-step self-etching dental adhesive (Tetric® N-Bond; Ivoclar Vivadent AG, Schaan, FL, Liechtenstein) was applied and polymerized with QTH for 10 s (QTH-10), or for 40 s (QTH-40). Similarly, the adhesive in LED-10 and LED-40 groups was polymerized with an LED for 10 s or 40 s, respectively. Then, all specimens were restored with Filtek™ Z350 XT flowable composite (3M ESPE AG, St. Paul, MN, USA) and immersed in ammoniacal silver-nitrate contrasting solution. Cross-sectional images were recorded at every 250μm using cross-polarization OCT system (CP-OCT; IVS-300, Santec, Komaki, Aichi, Japan). Image analysis to quantify the percentage of gap at resin-dentin interface was performed using a custom plugin for ImageJ software.

RESULTS

Data analysis using one-way ANOVA showed a significant difference in mean gap percentage between the four test groups (p<0.0001). Mean gap percentage values were 75.8%, 53.2%, 9.9% and 5.6%. The highest for LED-10 followed by LED-40 (p <0.05). QTH-40 revealed a slightly better adaptation compared with QTH-10, but the difference between them was not significant (p <0.05).

CONCLUSION

CP-OCT with a contrast agent is a useful non-invasive imaging tool for dental composite resin materials. QTH showed better results than LED under the experimental conditions. When using an LED light-curing unit, prolonged irradiation improved interfacial adaptation of dental composite bonded with a self-etching adhesive.

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.

Comparison of Light-Emitting Diode-Curing Unit and Halogen-Based Light-Curing Unit for the Polymerization of Orthodontic Resins: An In vitro Study

Aims and Objectives

Conventionally, composites are cured using halogen-based light-curing units (LCUs). However, recently, light-emitting diode (LED) LCUs have been introduced commercially, claiming many advantages, yet producing comparable bond strength even when cured with single LED LCUs. This present study was undertaken to compare the shear bond strength of orthodontic brackets bonded to teeth with conventional halogen LCU (3M ESPE Elipar 2500) and LED LCU (3M ESPE Elipar FreeLight 2) and to determine the site of bond failure.

Materials and Methods

Fifty extracted human bicuspid teeth were randomly divided into two groups of 25 each. All the teeth were etched and primed. Then, orthodontic brackets were bonded onto the teeth with the light-cured adhesive (Transbond XT, 3M Unitek), and the adhesive was cured with halogen LCU and LED LCU for Group I and Group II, respectively. The brackets were then subjected to shear stress using a Hounsfield universal testing machine at a crosshead speed of 1 mm/min. The force was recorded in Kgf and converted to MPa. The residual adhesive was scored based on the modified adhesive remnant index (ARI) using an optical stereomicroscope. The data were analyzed using the Student's t-test and the Mann-Whitney test at a significance level of 0.05.

Results

The results have shown that there is no significant difference between the shear bond strengths and the ARI scores of both the groups.

Conclusion

From this study, it can be concluded that (1) LED LCUs containing even only a single LED can cure the composite as well as a halogen-based LCU; (2) there is no statistically significant difference in the shear bond strengths of the two groups; and (3) the ARI scores show no significant difference.

Effects of delivering the same radiant exposures at 730, 1450, and 2920 mW/cm2 to two resin-based composites

Objective:

To evaluate the effects of curing two resin-based composites (RBC) with the same radiant exposures at 730, 1450, and 2920 mW/cm².

Materials and Methods:

Two types of RBC, Filtek Supreme Ultra and Tetric-EvoCeram-Bulk Fill, were light-cured to deliver the same radiant exposures for 5, 10, or 20 s by means of a modified Valo light emitted diode light-curing unit with the light tip placed directly over each specimen. The RBC was expressed into metal rings that were 2.0 and 4.0 mm in thickness, directly on an attenuated total reflectance Fourier transform infrared plate heated to 33°C, and the degree of conversion (DC) of the RBC was recorded. The specimens were then removed and the Knoop microhardness (KHN) was tested at both the bottom and the top of each specimen. The KHN was tested again after 24 h and 7 days of storage in the dark at 37°C and 100% humidity. The DC and KHN results were analyzed with Fisher's protected least significant difference at α = 0.05.

Results:

The DC values for the specimens cured at the three different irradiance levels were similar. However, at different depths, there were differences in the DC values. In general, there were no clear differences among the samples cured in the three different groups, and the KHN was always greater 24 h and 7 days later (P < 0.05).

Conclusions:

Despite the curing time, and as long as the samples were cured with the same radiant exposures, there were no significant effects on the DC and KHN of both RBCs.