Microhardness of a Resin Cement Polymerized by Light-Emitting Diode and Halogen Lights through Ceramic

Purpose: This study evaluated the curing efficiency of light-emitting diode (LED) and halogen [quartz tungsten halogens (QTH)] lights through ceramic by determining the surface microhardness of a highly filled resin cement.
Materials and Methods: Resin cement specimens (Variolink Ultra; with and without catalyst) (5-mm diameter, 1-mm thick) were condensed in a Teflon mold. They were irradiated through a ceramic disc (IPS Empress 2, diameter 5 mm, thickness 2 mm) by high-power light-curing units as follows: (1) QTH for 40 seconds (continuous), (2) LED for 20 seconds, and (3) LED for 40 seconds (5-second ramp mode). The specimens in control groups were cured under a Mylar strip. Vickers microhardness was measured on the top and bottom surfaces by a microhardness tester. Data were analyzed using analysis of variance (ANOVA) and a post hoc Bonferroni test at a significance level of p < 0.05.
Results: The mean microhardness values of the top and bottom surfaces for the dual-cured cement polymerized beneath the ceramic by QTH or LED (40 seconds) were significantly higher than that of light-cured cement ( p < 0.05). The top and bottom surface microhardness of dual-cured cement polymerized beneath the ceramic did not show a statistically significant difference between the LED and QTH for 40 seconds ( p > 0.05).
Conclusions: The efficiency of high-power LED light in polymerization of the resin cement used in this study was comparable to the high-power QTH light only with a longer exposure time. A reduced curing time of 20 seconds with high-power LED light for photopolymerizing the dual-cured resin cement under ceramic restorations with a minimum 2-mm thickness is not recommended.     

Polymerization efficiency of different photocuring units through ceramic discs

This study compared the ability of a variety of light sources and exposure modes to polymerize a dual-cured resin composite through ceramic discs of different thicknesses by depth of cure and Vickers microhardness (VHN). Ceramic specimens (360) (Empress 2 [Ivoclar Vivadent], color 300, diameter 4 mm, height 1 or 2 mm) were prepared and inserted into steel molds according to ISO 4049, after which a dual-cured composite resin luting material (Variolink II [Ivoclar Vivadent]) with and without self-curing catalyst was placed. The light curing units used were either a conventional halogen curing unit (Elipar TriLight [3M/ESPE] for 40 seconds), a high-power halogen curing unit (Astralis 10 [Ivoclar Vivadent] for 20 seconds), a plasma arc curing unit (Aurys [Degré K] for 10 seconds or 20 seconds) or different light emitting diode (LED) curing units (Elipar FreeLight I [3M/ESPE] for 40 seconds, Elipar FreeLight II [3M/ESPE] for 20 seconds, LuxOmax [Akeda] for 40 seconds, e-Light [GC] for 12 seconds or 40 seconds). Depth of cure under the ceramic discs was assessed according to ISO 4049, and VHN at 0.5 and 1.0 mm distance from the ceramic disc bottom was determined (ISO 6507-1). Medians and the 25th and 75th percentiles were determined for each group (n=10), and statistical analysis was performed using the Mann-Whitney-U-test (p < or = 0.05). The results showed that increasing ceramic disc thickness had a negative effect on the curing depth and hardness of all light curing units, with hardness decreasing dramatically under the 2-mm thick discs using LuxOmax, e-Light (12 seconds) or Aurys (10 seconds or 20 seconds). The use of a self-curing catalyst is recommended over the light-curable portion only, because it produced an equivalent or greater hardness and depth of cure with all light polymerization modes.     

Cytotoxicity of composite materials polymerized with LED curing units

The proper intensity and illumination time of a curing light is of great importance for the complete polymerization of resin composites and long-lasting resin composite restorations. Inadequately cured resin composites can have a cytotoxic effect on pulp tissue by releasing unreacted monomers. This study determined whether there is any difference in cytotoxicity between composite materials illuminated with different curing modes of LED curing units. Thin layers of two composite materials were polymerized using three different modes of the Bluephase C8 LED curing unit: a high intensity mode (HIP-800 mW/cm2, 20 seconds), a soft-start mode (SOF-650 mW/cm2 first 5 seconds, 800 mW/cm2 next 25 seconds) and a low intensity mode (LOP-650 mW/cm2, 30 seconds). Lymphocyte cultures were treated with both polymerized and unpolymerized composites using one of the modes stated above. Cells were analyzed using the trypan blue exclusion test, the acridine orange/ethidium bromide dying technique and an alkaline comet assay. Significant cytotoxicity was observed for 120 mg of unpolymerized composites and those polymerized with the HIP polymerization mode. A significant level of DNA damage was detected for 120 mg of unpolymerized composites. However, curing via the LOP program exhibited the lowest genotoxicity. Longer curing time with lower intensity results in less cytotoxicity than shorter curing exposure using a higher intensity of light emitted from the curing light source.     

Light-emitting diodes (LED) technology applied to the photopolymerization of resin composites

An adequate polymerization of resin composites can significantly contribute to increase the longevity of a restoration. In this field, the choice of the operative technique and the characteristics of the lamp are very important. The aim of this review was to evaluate the effectiveness of cure of the light-emitting diodes (LED) lamps comparing them to the others currently available for resin composites photopolymerization. At present, halogen lamps are the most commonly used light sources, but this technology does not allow further developments; even plasma arc and laser lamps have some drawbacks. The innovative LED technology, based on semiconductors, opened new and interesting views in the field of photopolymerization; to the advantages of a soft-start polymerization they add the safety, efficiency, economy and long lifetime of LED light. A careful review of the literature revealed that, although their lower emission of light, these lamps are capable of a polymerization qualitatively comparable to other light sources. Physical and mechanical properties, degree of conversion, depth of cure and final hardness of the composites cured with a LED light are similar to the values achieved with the halogen lamp, whereas the temperature increase is significantly lower and does not pose a threat to the pulp tissue. Undoubtedly, more tests of the mechanical properties of composites processed with LED units need to be carried out but, as the technology improves, LED curing will become an interesting alternative to existing curing methods.     

Curing units' ability to cure restorative composites and dual-cured composite cements under composite overlay

This study compared the efficacy of using conventional low-power density QTH (LQTH) units, high-power density QTH (HQTH) units, argon (Ar) laser and Plasma arc curing (PAC) units for curing dual-cured resin cements and restorative resin composites under a pre-cured resin composite overlay. The microhardness of the two types of restorative resins (Z100 and Tetric Ceram) and a dual-cured resin cement (Variolink II) were measured after they were light cured for 60 seconds in a 2 mm Teflon mold. The recorded microhardness was determined to be the optimum microhard-ness (OM). Either one of the two types of restorative resins (Z100, Tetric Ceram) or the dual cured resin cement (Variolink II) were placed under a 1.5-mm thick and 8 mm diameter pre-cured Targis (Vivadent/Ivoclar AG, Schaan, Liechtenstein) overlay. The specimens that were prepared for each material were divided into four groups depending upon the curing units used (HQTH, PAC, Laser or LQTH) and were further subdi-vided into subgroups according to light curing time. The curing times used were 30, 60, 90 and 120 seconds for HQTH; 12, 24, 36 and 48 seconds for the PAC unit; 15, 30, 45 and 60 for the Laser and 60, 120 or 180 seconds for the LQTH unit. Fifteen specimens were assigned to each sub- group. The microhardness of the upper and and lower composite surfaces under the Targis overlay were measured using an Optidur Vickers hardness-measuring instrument (G?ttfert Feinwerktechnik GmbH, Buchen, Germany). In each material, for each group, a three-way ANOVA with Tukey was used at the 0.05 level of significance to compare the microhardnesses of the upper and lower composite surfaces and the previously measured OM of the material. From the OM of each material, 80% OM was calculated and the time required for the microhardness of the upper and lower surface of the specimen to reach 100% and 80% of OM was determined. In Z100 and Tetric Ceram, when the composites were light cured for 120 seconds using the HQTH lamp, microhardnesses of the upper and lower surfaces reached OM. When they were cured with the PAC unit, only 48 seconds was needed for the upper and lower surfaces to reach OM. When they were cured using the laser, the lower surface did not reach OM in any of the groups. When the specimens were cured using the LQTH lamp, 180 seconds of curing was needed for Z100 to reach OM, whereas Tetric Ceram did not reach OM. In Z100, 60, 12, 30 and 60 seconds were needed in HQTH, PAC, Laser and LQTH, respectively, for the specimens to reach 80% OM. Tetric Ceram was needed 60,24,45 and 180 seconds to reach 80% OM. In the Variolink II specimen, microhardness of the upper and lower surfaces did not reach OM even though they were light cured with the HQTH lamp for 120 seconds. When they were cured with the PAC unit, 48 seconds was insufficient for them to reach OM. When they were cured with laser for 45 and 60 seconds, microhardness reached OM on the upper surface but not on the lower surface. However, when they were cured using the LQTH lamp, microhardness did not reach OM on the upper and lower surfaces even though the curing time was extended to three minutes. In Variolink II, 120, 36, 45 and >180 seconds were needed in HQTH, PAC, Laser and LQTH, respectively, for the specimens to reach 80% OM. In conclusion, the PAC system is the most effective curing system to cure the restorative composite and dual cured resin cement under the 1.5 mm Targis overlay, followed by the laser, HQTH and LQTH units. In addition, the restorative composites cured more efficiently than the dual-cured resin cements.     

Temperature rise and degree of photopolymerization conversion of nanocomposites and conventional dental composites

The aim of the study was to investigate the temperature rise of a nanocomposite and a conventional hybrid dental composite during photopolymerization when cured with halogen curing lamp (QHT) and light-emitting diode (LED). Temperature rise during photopolymerization of two commercially available composites (Filtek Supreme® and TetricCeram®) were measured using a K-type thermocouple and a digital thermometer. Different curing modes were utilized to cure the composites: a high-intensity QHT unit (Optilux 501) in two different modes (standard and ramp), a low-intensity QHT unit (Coltolux 50), and an LED unit (Ultralume-2). Total temperature rise, polymerization reaction exotherm, and irradiation-induced temperature rise of the composites were determined. Degree of conversion of the specimens was measured using FTIR spectroscopy. The results revealed that the Filtek Supreme® nanocomposite showed lower temperature rise and degree of conversion in comparison with the hybrid composite (p?相似文献   

Evaluation of curing performance of light-emitting polymerization units

The depth of cure of resin composites is affected by material physical qualities and polymerization source variables. This study evaluated the spectral distribution and intensity of light-emitting diode (LED) and conventional quartz-tungsten halogen curing units, with depth of cure as the testing parameter. The depth of cure was determined using a scraping test, modified from an International Organization for Standards protocol. The light energy spectral distribution (peak wavelength) from each curing unit was determined using a visible-ultraviolet light spectrophotometer. The intensity of each unit (LED and halogen) was measured using LED and conventional radiometers. Data analysis using ANOVA revealed significant differences between the curing units. Based upon depth of cure measurements, the LED units generally were more effective than the conventional halogen unit at polymerizing resin composite. Dentists should be aware that LED curing units offer portability, reduced heat production, and more consistent intensity output per life of the unit.     

Influence of light intensity from different curing units upon composite temperature rise

The unavoidable consequence of composite resin photopolymerization is temperature rise in tooth tissue. The temperature rise depends not only on the illumination time, but also on light intensity, distance of light guide tip from composite resin surface, composition and shade of composite resin and composite thickness. The most commonly used units for polymerization today are halogen curing units, which emit a large spectrum of wavelengths. A proportion of the spectrum has no influence on degree of conversion and therefore causes unnecessary temperature rise. Units based on light source - blue light emitting diodes (LED), as an alternative for halogen curing units, have been introduced in clinical practice. The aim of this study was to show the influence of the light intensity of curing units Elipar Trilight, Astralis 7 and Lux-o-Max unit on temperature rise in composite resin sample of Tetric Ceram. The temperature was measurement with Metex M-3850 D multimeter with the tip of temperature probe put into unpolymerized composite resin sample 1 mm depth. The highest temperature rise was recorded with standard curing mode for Elipar Trilight halogen curing unit (13.3 +/- 1.21 degrees C after 40 s illumination), while the lowest temperature rise was recorded for the Lux-o-Max unit based on LED technology (5.2 +/- 1.92 degrees C after 40 s illumination).     

Curing efficiency of a photo- and dual-cured resin cement polymerized through 2 ceramics and a resin composite

PURPOSE: The influence of the curing mode (dual vs light) and of the photopolymerization through ceramic or resin composite on the degree of remaining carbon bonds was investigated via infrared spectroscopic analysis for 1 resin cement (Calibra, Caulk/Dentsply). MATERIALS AND METHODS: The 0.5-mm cement layer was photopolymerized for 40 s through the 2-mm-thick ceramic Empress 2 (Ivoclar) and Vitadur Alpha (Vident) and the laboratory-processed resin composite Sinfony (3M/ESPE). RESULTS: The dual-cured system polymerized better than the light mode. Photopolymerization of the resin cement through the translucent materials reduced its curing efficiency in both curing modes. The resin composite induced a more negative effect than the 2 ceramics tested. CONCLUSION: The curing mode and photopolymerization of dual-cured resin cements through esthetic restorative materials affects the degree of remaining double carbon bonds.     

Effect of interfacial bond quality on the direction of polymerization shrinkage flow in resin composite restorations

Shrinkage in light curing resin composites is assumed to be directed toward the light source. However, the strong bond at the dentin-resin interface achieved by newer generation dentin bonding systems may affect the direction of polymerization shrinkage. In this study, various curing modes of adhesive resin simulating different bond qualities were applied to determine the extent of interfacial gap formation with a scanning electron microscope. We also measured the free surface depression with a profilometer. The direction of polymerization shrinkage was inferred from the ratio of the interfacial gap measurement at the floor to the free surface depression. Various curing modes used in this study include Group 1: light curing of resin composite without the bonding agent as the negative control; Group 2: simultaneous light curing of the bonding agent and resin composite; Group 3: start of the chemical cure of the dual-cured bonding agent before light curing the resin composite; Group 4: curing the light-initiated bonding agent before insertion and light curing of the resin composite. When the bonding agent was light cured prior to inserting the resin composite (Group 4), the free surface depression was the greatest and the interfacial gap smallest among those in all groups. Therefore, if a good bond between dentin and resin composite can be established, the shrinkage flow will be directed toward a center located near the bonded interface rather than toward the incident light, thus reducing detrimental shrinkage stress.     

Microhardness of resin composites polymerized by plasma arc or conventional visible light curing

This study evaluated the effectiveness of the plasma arc curing (PAC) unit for composite curing. To compare its effectiveness with conventional quartz tungsten halogen (QTH) light curing units, the microhardness of two composites (Z100 and Tetric Ceram) that had been light cured by the PAC or QTH units, were compared according to the depth from the composite surface. In addition, linear polymerization shrinkage was compared using a custom-made linometer between composites which were light cured by PAC or QTH units. Measuring polymerization shrinkage for two resin composites (Z100 and Tetric Ceram) was performed after polymerization with either QTH or PAC units. In the case of curing with the PAC unit, the composite was light cured with Apollo 95E for two (Group 1), three (Group 2), six (Group 3) or 2 x 6 (Group 4) seconds. For light curing with the QTH unit, the composite was light cured for 60 seconds with Optilux 500 (Group 5). The linear polymerization shrinkage of composites was determined in the linometer. Two resin composites were used to measure microhardness. Two-mm thick samples were light cured for three seconds (Group 1), six seconds (Group 2) or 12 (2 x 6) seconds (Group 3) with Apollo 95E or they were conventionally light cured with Optilux 500 for 30 seconds (Group 4) or 60 seconds (Group 5). For 3 mm thick samples, the composites were light cured for six seconds (Group 1), 12 (2 x 6) seconds (Group 2) or 18 (3 x 6) seconds (Group 3) with Apollo 95E or they were conventionally light cured with Optilux 500 for 30 seconds (Group 4) or 60 seconds (Group 5). Twenty samples were assigned to each group. The microhardness of the upper and lower surfaces was measured with a Vickers hardness-measuring instrument under load. The difference in microhardness between the upper and lower surfaces in each group was analyzed by paired t-test. For the upper or lower surfaces, one-way ANOVA with Tukey was used. For Tetric Ceram, the amount of polymerization shrinkage was lower when cured with the Apollo 95E for two or three seconds than when cured for six and 12 (2 x 6) seconds, or for 60 seconds with Optilux 500 (p<0.05). For Z100, the amount of linear polymerization shrinkage was lower when cured with the Apollo 95E for two, three and six seconds than for 12 (2 x 6) seconds with Apollo 95E or for 60 seconds with the Optilux 500 (p<0.05). The results of the microhardness test indicated that there was no statistically significant difference in microhardness between groups for the upper surface. However, for the lower surface, when the composites were light cured with Apollo 95E for three seconds as recommended by the manufacturer, microhardness of the lower surface was usually lower than that of the upper surface and did not cure sufficiently. Conclusively, when compared with conventional QTH unit, the PAC unit, Apollo 95E did not properly cure the lower composite surface when the layer thickness exceeded 2 mm. In addition, three seconds of curing time, which the manufacturer recommended, was insufficient for optimal curing of composites.     

In vitro pulp chamber temperature rise from irradiation and exotherm of flowable composites

Objective.  The aim of this study was to investigate the pulpal temperature rise induced during the polymerization of flowable and non-flowable composites using light-emitting diode (LED) and halogen (quartz–tungsten–halogen) light-curing units (LCUs).
Methods.  Five flowable and three non-flowable composites were examined. Pulpal temperature changes were recorded over 10 min in a sample primary tooth by a thermocouple. A conventional quartz–tungsten–halogen source and two LEDs, one of which was programmable, were used for light curing the resin composites. Three repetitions per material were made for each LCU.
Results.  There was a wide range of temperature rises among the materials ( P  < 0.05). Temperature rises ranged between 1.3 °C for Filtek Supreme irradiated by low-power LED and 4.5 °C for Grandio Flow irradiated by high-power LED. The highest temperature rises were observed with both the LED high-power and soft-start LCUs. The time to reach the exothermic peak varied significantly between the materials ( P  < 0.05).
Conclusions.  Pulpal temperature rise is related to both the radiant energy output from LCUs and the polymerization exotherm of resin composites. A greater potential risk for heat-induced pulp damage might be associated with high-power LED sources. Flowable composites exhibited higher temperature rises than non-flowable materials, because of higher resin contents.     

Comparison of composite curing parameters: effects of light source and curing mode on conversion, temperature rise and polymerization shrinkage

This study analyzed the degree of conversion, temperature increase and polymerization shrinkage of two hybrid composite materials polymerized with a halogen lamp using three illumination modes and a photopolymerization device based on blue light emitting diodes. The degree of conversion of Tetric Ceram (TC) (Ivoclar Vivadent) and Filtek Z 250 (F) (3M/ESPE) was measured by Fourier transformation infrared spectroscopy at the surface and 2-mm depth; temperature rise was measured by digital multimeter, and linear polymerization shrinkage was measured during cure by digital laser interferometry. Composite samples were illuminated by quartz-tungsten-halogen curing unit (QTH) (Astralis 7, Ivoclar Vivadent) under the following modes: "high power" (HH) 40 seconds at 750 mW/cm2, "low power" (HL) 40 seconds at 400 mW/cm2 and "pulse/soft-start" (HP) increasing from 150 to 400 mW/cm2 during 15 seconds followed by 25 seconds pulsating between 400 and 750 mW/cm2 in 2-second intervals and by light emitting diodes (LED) (Lux-o-Max, Akeda Dental) with emitted intensity 10 seconds at 50 mW/cm2 and 30 seconds at 150 mW/cm2. A significantly higher temperature increase was obtained for both materials using the HH curing mode of halogen light compared to the HP and HL modes and the LED curing unit after 40 seconds. Significantly lower temperature values after 10-second illumination were obtained when LED was used compared to all halogen modes. For all curing modes, there was no significant difference in temperature rise between 20 and 40 seconds of illumination. Results for the degree of conversion measurements show that there is a significant difference in the case of illumination of resin composite samples with LED at the surface and 2 mm depth. For polymerization shrinkage, lower values after 40 seconds were obtained using LED compared to QTH.     

Should my new curing light be an LED?

The new generation LED curing light units have significantly improved curing performance compared to first generation lights, and even some second generation LED curing light units. This study compared the curing performance of 10 new generation LED light curing units (FLASH-lite 1401, LE Demetron 1, Coltolux, Ultra-Lume 5, Mini LED, bluephase, Elipar FreeLight 2, Radii, Smartlite IQ and Allegro) for depth of cure against a high-powered halogen curing light unit (Optilux 501). Depth of cure measurements were utilized per the ANSI/ADA No 27 standard to detect differences between the lights at three time intervals (10, 20 and 40 seconds). A total of 660 samples were prepared (n=10/group). A full factorial ANOVA and Tukey's HSD test showed FLASH-lite 1401 performed significantly better than the other lights at 10- and 20-second time intervals (p<0.01). This study also demonstrated that an exposure time of 20 seconds or longer assures a better depth of cure, 40 seconds being the optimal polymerization time for all of the curing light units.     

Contraction stress and bond strength to dentinfor compatible and incompatible combinations of bonding systems and chemical and light-cured core build-up resin composites.

OBJECTIVE: Recent studies have shown that adhesives containing acidic monomers combined with composites can adversely effect the polymerization reaction producing low bond strengths. This phenomenon may also occur in making composite build-ups, jeopardizing one of the key factors for a successful core build-up restoration. The aim of this study was to investigate the contraction stress development and bond strength to dentin of core build-up resin composites combined with adhesives of various acidities. In addition the hypothesis tested was that light irradiation through chemical-cured composites during curing does not influence contraction stress or bond strength to dentin. METHODS: The chemical-cured (Clearfil Core) and light-cured (Clearfil Photo Core) core build-up resin composites were combined with two light-cured adhesives, Clearfil SE Bond (pH=1.8) and One-Step Bond (pH=4.3) and two dual-cured adhesives, Clearfil Photo Bond (pH=2.5) and All-Bond 2 (pH=6.1). Contraction stress development (at C=3) was determined for a period of 30 min in a universal testing machine where the opposing bonding surfaces were glass and dentin. After the 30 min period, the specimens were loaded in tension to determine the bond strength to dentin. To test the hypothesis, the combinations of the chemical-cured composites with the four bonding systems were also light irradiated for 40s right at the start of curing. RESULTS: For all composite-adhesive combinations tested, the adhesion to dentin resisted the developing polymerization contraction stresses. Both, dentin as a substrate to bond at and the use of adhesives, were showed to play an important role in keeping the contraction stresses low. The chemical-cured composite (Clearfil Core) combined with the light-cured adhesive SE Bond (pH=1.8) showed for both contraction stress and bond strength significant lower values than the other combinations. The hypothesis was accepted for combinations of the chemical-cured composite with All-Bond 2 and One-Step Bond, but was not supported by combinations with Clearfil SE Bond or Clearfil Photo Bond, as a significant increase in contraction stress was found. The higher values found for bond strength were not significant. SIGNIFICANCE: Besides combinations of chemical-cured core build-up composites with light or dual-cured adhesives as recommended by the manufacturer, also combinations with adhesives of other manufacturers are compatible, provided that the pH is higher than approximately 4.3. Chemical-cured core build-up composites combined with light-cured adhesives with a pH as low as 1.8 lead to a significantly lower stress and bond strength compared to other combinations. Light irradiation during curing through a combination of a chemical-cured composite and a low pH adhesive reactivates polymerization.     

Polymerization efficiency of glass-ionomer and resin adhesives under molar bands

OBJECTIVE: To determine the degree of cure of a light-cured resin-modified glass ionomer (RMGI) under molar bands compared with a light-cured resin and a dual-cured resin. MATERIALS AND METHODS: The 3 cements used were Fuji Ortho LC, Eagle Spectrum resin, and Variolink II dual-cure. Each sample was indirectly light cured for 20 seconds (10 seconds occlusally, 10 seconds cervically) under sections of molar bands, and the degree of cure was evaluated with micro-MIR FTIR spectroscopy. RESULTS: The RMGI exhibited a significantly higher mean degree of cure (55.31%) than both of the resins (Eagle 19.23%; Variolink II, 25.42%), which did not differ significantly at alpha = .05 level of significance. CONCLUSION: Higher degree of conversion can be obtained from RMGIs under molar bands compared with composite resin adhesives provided the proper curing technique is used.     

Effect of light source and time on the polymerization of resin cement through ceramic veneers

PURPOSE: The purpose of this study was to evaluate the efficiency of 3 different light sources to polymerize a light curing resin cement beneath 3 types of porcelain veneer materials. MATERIALS AND METHODS: A conventional halogen light, a plasma arc light, and a high intensity halogen light were used to polymerize resin cement (Variolink II; Ivoclar North America Inc, Amherst, NY) through disks of veneer materials. Equal diameter and thickness disks of feldspathic porcelain (Ceramco II; Ceramco Inc, Burlington, NJ), pressable ceramic (IPS Empress; Ivoclar North America Inc), and aluminous porcelain (Vitadur Alpha; Vident Inc, Brea, CA) were used as an interface between the curing light tips and the light polymerized resin cement. The resin cement/veneer combinations were exposed to 4 different photopolymerization time protocols of 5 seconds, 10 seconds, 15 seconds, and 20 seconds for high intensity light units (Apollo 95E [Dental Medical Diagnostic Systems Inc, Westlake Village, CA] and Kreativ 2000 [Kreativ Inc, San Diego, CA]), and 20 seconds, 40 seconds, 60 seconds, and 80 seconds for conventional halogen light (Optilux; Demetron Research Inc, Danbury, CT). A surface hardness test (Knoop indenter) was used to determine the level of photopolymerization of the resin through the ceramic materials with each of the light sources. The data were analyzed by one-way analysis of variance and a post-hoc Scheffe test (p < .05). RESULTS: The data indicates that the Variolink II Knoop Hardness Number values vary with the light source, the veneer material, and the polymerization time. For a given light and veneer material, Knoop Hardness Number increases with longer polymerization times. The Kreativ light showed statistically significant differences (p < .05) between all test polymerization times. Use of this light required a polymerization time of greater than 20 seconds to reach maximum resin cement hardness. For samples polymerized with the Apollo light, there were statistically significant (p < .05) differences in surface hardness between samples polymerized at all times, except for the 15-second and 20-second times. Samples polymerized with the halogen light showed no statistically significant (p < .05) differences in hardness between polymerization times of 60 seconds and 80 seconds. CONCLUSIONS: High intensity curing lights achieve adequate polymerization of resin cements through veneers in a markedly shorter time period than the conventional halogen light. However, the data in this report indicate that a minimum exposure time of 15 seconds with the Kreativ light and 10 seconds with the Apollo 95E light should be used to polymerize the Variolink II resin, regardless of the composition of the veneer. Conventional halogen lights required a correspondingly greater polymerization time of 60 seconds.     

Use of near-IR to monitor the influence of external heating on dental composite photopolymerization.

OBJECTIVES: This study was conducted to determine the effect of modest external heating on the photopolymerization kinetics and conversion of commercial dental composite restorative materials. METHODS: A transmission-mode, real-time near-infrared spectroscopic technique was used to monitor the photopolymerization process in the composite materials at various temperatures between 23 and 70 degrees C. Several light curing units, differing in spectral output and power densities were compared at the different cure temperatures. Several significantly different commercial composites were compared for their response. RESULTS: Regardless of the curing light or composite material used, photopolymerization at a moderate curing temperature of 54.5 degrees C resulted in significantly higher immediate and final conversion values compared with room temperature photocuring. Contrary to the room temperature cured materials, at the elevated cure temperature the extent of post-cure was minor and different curing lights produced very uniform conversion values within a given material. The time required to reach a given level of conversion, established as full conversion with the room temperature cure, was reduced typically by 80-90% using the elevated curing conditions. Complementary kinetic studies confirmed the effect of cure temperature on increasing the polymerization rate in dental composites as significant. SIGNIFICANCE: Increasing the temperature of composite resin within potentially biologically compatible limits can significantly influences resin polymerization. These increased rates and conversion could lead to improved properties of composite restorative materials.     

Degree of conversion and microhardness of bulk-fill dental composites polymerized by LED and QTH light curing units

ObjectivesThe degree of monomer conversion is crucial in determining the mechanical and clinical performance of dental resin composites. This study investigated the polymerization adequacy of two bulk-fill resin composites polymerized by Quartz-Tungsten-Halogen (QTH) and Light Emitting Diode (LED) light curing units at different depths.MethodsTwo bulk-fill resin composites (X-tra Fil; Voco and Tetric N-Ceram Bulk-fill; Ivoclar-Vivadent) with diameters of 7 mm and thicknesses of 1–4 mm were prepared and light-cured by LED or QTH. Then, the degree of conversion (DC) and microhardness of the two bulk-fill composites were evaluated.ResultsThe microhardness of X-tra fill was significantly higher than that of Tetric N-Ceram polymerized by LED or QTH. The microhardness and DC of X-tra fil exhibited no significant difference among the increments regardless of type of light source. The DC, however, significantly decreased in deep increments for Tetric N-Ceram polymerized by QTH.ConclusionsThe polymerization efficacies of the two bulk-fill composites were different in terms of the depth of cure and type of light source. The DC and microhardness of the X-tra fill bulk-fill composite polymerized by either QTH or LED did not decrease up to a thickness of 4 mm. Thus, new generations of LED light sources are better options for polymerizing the bulk-fill resin composites than QTH.