Plasma Arc Curing Research Articles

Color changes induced by different staining solutions and different light curing units in dental resin composites

PurposeTo evaluate color changes induced by three different staining solutions and three different light curing devices in two different resin composites.Materials and methodsTwo different resin composites (ESTELITE Σ QUICK and ESTHET.X HD) were tested in this study. Hundred discs (5 mm diameter × 2 mm thick) of each tested material were made. Ten specimens were used as control, while other 90 specimens subdivided into three subgroups (n = 30); (a) cured with halogen-light curing-unit, (b) cured with plasma-arc unit, and (c) cured with argon laser of 488 nm. Each subgroup was further subdivided into three classes (n = 10): (a) immersed in tea for 10 min three times daily for 3 months, (b) immersed in coffee for 10 min three times daily for 3 months, and (c) immersed in Arabic coffee for 10 min three times daily for 3 months. Between staining challenges, specimens were immersed in artificial saliva. Specimens were tested for quantitative color changes using Quanta Environmental Scanning Electron Microscope. Data was statistically analyzed using three-way analysis of variance and Tukey's post-hoc test (P ≤ 0.05).ResultsThe mean color change of coffee (126.53 pixel) showed the highest value. This was followed by tea (117.96 pixel) and Arabic coffee (113.5 pixel) with no statistically significant difference between the two solutions. Meanwhile, laser showed the highest mean value (122.55 pixel) whereas; there was no statistically significant difference between QHL (117.9 pixel) and plasma arc curing (117.54 pixel). No significant difference was found between the two tested materials ESTELITE Σ QUICK and ESTHET.X HD.ConclusionThe two tested composites performed similarly under the test conditions. Curing with argon laser along with the coffee as staining solution affected the color stability of the tested materials.

Visible Light Curing Devices - Irradiance and Use in 302 German Dental Offices.

To determine the irradiance delivered by visible-light curing (VLC) units and obtain information about the exposure times and the maintenance protocols used by dentists. The irradiance (mW/cm2) delivered by 526 VLCs from 302 dental offices from the Rhine-Main area, Germany, was measured using an integrating sphere (IS) and a MARC patient simulator (M-PS); additional information was gathered using a survey. Irradiance was measured from 117 standard quartz-tungsten-halogen (QTH), 5 high-power QTH, 2 LED 1st-generation, 333 LED 2nd-generation, 61 LED 3rd-generation, and 8 plasma-arc curing (PAC) units. Depending on the measurement method, 8% (IS) or 11% (M-PS) of the VLCs delivered < 400 mW/cm2. Depending on the VLC, the shortest exposure times required to deliver a radiant exposure of 16 J/cm2 ranged from 7 to 294 s. The number of exposure cycles used by dentists when light curing a restoration ranged from 1 to 14. The shortest total exposure time used by dentists on a restoration was 5 s, the maximum was 200 s, and the median was 20 s. Of the 526 VLCs, 41% had intact, undamaged light tips. Only half of the dental offices checked the irradiance from their VLCs regularly, 97% disinfected the VLC, and 86% used eye protection. Approximately 10% of the VLCs delivered < 400 mW/cm2 and 14% of the dental offices used no form of eye protection. To achieve sufficient light curing of RBC restorations, more awareness about the VLCs used in the dental office is required.

Effect of High Irradiance on Depth of Cure of a Conventional and a Bulk Fill Resin-based Composite.

This study evaluated the effect of using three commercial light curing units (LCUs) delivering a range of irradiance values, but delivering similar radiant exposures on the depth of cure of two different resin-based composites (RBCs). A conventional hybrid RBC (Z100 shade A2, 3M ESPE) or a bulk fill RBC (Tetric EvoCeram Bulk Fill shade IVA, Ivoclar Vivadent) was packed into a 10-mm deep semicircular metal mold with a 2-mm internal radius. The RBC was exposed to light from a plasma-arc-curing (PAC) light (Sapphire Plus, DenMat) for five seconds, a quartz-tungsten-halogen (QTH) light (Optilux 501, Kerr) for 40 seconds, or a light-emitting-diode (LED) light (S10, 3M ESPE) for 20 seconds and 40 seconds (control). The Knoop microhardness was then measured as soon as possible at the top surface and at three points every 0.5 mm down from the surface. For each RBC, a repeated measures analysis of variance (ANOVA) model was used to predict the Knoop hardness in a manner analogous to a standard regression model. This predicted value was used to determine at what depth the RBC reached 80% of the mean hardness achieved at the top surface with any light. The PAC light delivered an irradiance and radiant exposure of 7328 mW/cm(2) and 36.6 J/cm(2), respectively, to the RBCs; the QTH light delivered 936 mW/cm(2) and 37.4 J/cm(2) and in 20 seconds the LED light delivered 1825 mW/cm(2) and 36.5 J/cm(2). In 40 seconds, the control LED light delivered a radiant exposure of 73.0 J/cm(2). For Z100, using 80% of the maximum hardness at the top surface as the criteria for adequate curing, all light exposure conditions achieved the 2.0-mm depth of cure claimed by the manufacturer. The LED light used for 40 seconds achieved the greatest depth of cure (5.0 mm), and the PAC light used for five seconds, the least (2.5 mm). Tetric EvoCeram Bulk Fill achieved a 3.5-mm depth of cure when the broad-spectrum QTH light was used for 40 seconds delivering 37.4 J/cm(2). It required a 40-second exposure time with the narrow-spectrum LED, delivering approximately 73 J/cm(2) to reach a depth of cure of 4 mm. When delivering a similar radiant exposure of 37 J/cm(2), the QTH (40 seconds) and LED (20 seconds) units achieved a greater depth of cure than the PAC (five seconds) light. For both resins, the greatest depth of cure was achieved when the LED light was used for 40 seconds delivering 73 J/cm(2) (p<0.05).

EFFECT OF LIGHT CURING UNIT CHARACTERISTICS ON LIGHT INTENSITY OUTPUT, DEPTH OF CURE AND SURFACE MICRO-HARDNESS OF DENTAL RESIN COMPOSITE.

Modern dental composite restorations are wholly dependent on the use of Visible Light Curing devices. The characteristics of these devices may influence the quality of composite resin restorations. To determine the characteristics of light curing units (LCUs) in dental clinics in Nairobi and their effect on light intensity output, depth of cure (DOC) and surface micro-hardness (SMH) of dental resin composite. Laboratory based, cross-sectional analytical study. Public and private dental clinics in Nairobi, Kenya. Eighty three LCUs which were in use in private and public dental health facilities in Nairobi, Kenya and resin composite specimens. Of the 83 LCUs studied, 43 (51.8%) were Light Emitting Diodes (LEDs) and 39(47.0%) were Quartz-Tungsten-Halogen (QTH) and 1 (1.2%) was Plasma Arc Curing (PAC) light. Mean light intensity for QTH and LED lights was 526.59 mW/cm2 and 493.67 mW/cm2 respectively (p=0.574), while the mean DOC for QTH lights was 1.71 mm and LED was 1.67 mm (p=0.690). Mean Vickers Hardness Number (VHN) for LED was 57.44 and for QTH was 44.14 (p=0.713). Mean light intensity for LCUs < or = 5 years was 596.03 mW/cm2 and 363.17 mW/cm2 for units > 5 years old (p=0.024). The mean DOC for the two age groups was 1.74 mm and 1.57 mm respectively (p=0.073). For SMH, the < or = 5 years and >5 years age groups gave a mean VHN of 58.81 and 51.46 respectively (p=0.1). On maintenance history, the frequency of routine inspection, duration since the last repair/replacement of a part or other maintenance activity and the nature of the last maintenance activity were determined and were not found to have influenced the light intensity, DOC and SMH. The LCU age has a statistically significant influence on its light intensity (p=0.024) while the type and maintenance history have no significant influence on its light intensity and composite DOC and SMH (p=0.574, p=0.690, p=0.713 respectively).

In vitro Evaluation of Microleakage under Ceramic and Metal Brackets Bonded with LED and Plasma Arc Curing

The aim of the present study was to evaluate these two high intensity light curing units regarding microleakage beneath metal and ceramic brackets. A total of 60 freshly extracted human premolar teeth were randomly divided into four groups of 15 samples; group I: Metal bracket + LED cured, group II: Ceramic bracket + LED cured, group III: Metal bracket + plasma arc cured, group IV: Ceramic bracket + plasma arc cured. After photopolymerization, the teeth were immersed in water and thermocycled (500 cycles between 5 and 55). Specimens were further sealed with nail varnish and stained with 5% basic fuchsin for 24 hours. All of the teeth were sectioned with two parallel longitudinal occlusogingival cuts and examined under a stereomicroscope. The microleakage was measured with a digital caliper and scored from 0 to 3 for marginal microleakage at the bracket-adhesive and adhesive-enamel interfaces from both the occlusal and gingival margins. Microleakage was detected in all groups. The plasma arc cured group showed less microleakage than light emitting diode (LED) cured in all samples at the enamel-adhesive interface at the gingival margin (ceramic brackets, p = 0.009 and metal brackets, p = 0.005). The plasma arc cured samples showed less microleakage than LED cured in metal brackets at the adhesive-brackets interface at the occlusal margin (p = 0.033). While curing with an LED unit, ceramic brackets displayed significantly less microleakage than metal ones at the gingival margin of adhesive-enamel interface (p = 0.013). The gingival margin in all groups exhibited higher microleakage compared with those observed in occlusal sides in all sample groups (p < 0.001). 1. LED units cause more microleakage than plasma arc units. 2. In all groups the microleakage at the gingival margin is greater than the occlusal margin. The microleakage formation permits the passage of bacteria and oral fluids initiating white spot lesions beneath the bracket base.

Evaluation of Microleakage in Class V Composite Restoration using Different Techniques of Polymerization

ABSTRACT Aims The purpose of this study was to evaluate the effect of light intensity and curing cycle of quartz tungsten halogen (QTH) and plasma arc curing (PAC) lights on the microleakage of class V composite restorations. Materials and methods A total of 60 freshly extracted human maxillary premolars were used for this study. Standardized class V cavities were prepared and restored with microhybrid resin composite. According to the curing protocol, the teeth were then divided into three groups (n = 20): QTH curing (standard and soft start mode) and PAC high intensity irradiation. The microleakage was evaluated by immersion of the samples in 50% silver nitrate solution. The samples were then sectioned, evaluated under a stereomicroscope and scored for microleakage. Statistical analysis used Dye leakage scores were obtained, and analysis was done using Student's t-test. Results Light curing with QTH light in the soft start mode, showed the least leakage in the composite restoration, which was highly significant when compared with the other groups (p &lt; 0.01). Light curing with QTH light in the standard mode, showed moderate microleakage, which was statistically significant (p &lt; 0.05), when compared with the PAC high intensity curing. Curing with PAC light in high intensity mode resulted in severe microleakage along the cavity margins. Conclusion Within the limitations of the study, it may be concluded that: 1. The high intensity PAC light resulted in maximum leakage, when compared to the other groups in the study. 2. The soft start polymerization mode offers a distinctive advantage over the standard curing protocol, in terms of microleakage, for the QTH curing lights. Clinical significance In the clinical scenario, soft start curing regimen offers a distinctive advantage over the conventional mode of the QTH curing and the high intensity rapid curing offered by the PAC light. How to cite this article Chandurkar AM, Metgud SS, Yakub SS, Kalburge VJ. Evaluation of Microleakage in Class V Composite Restoration using Different Techniques of Polymerization. Int J Prosthodont Restor Dent 2012;2(1): 10-15.

Comparison of bond strength by plasma-xenon arc curing system in relation to L.E.D and conventional light curing system for orthodontic attachments: An in-vitro study

Aim : The study was aimed to evaluate efficacy of plasma arc curing light in reducing curing time as claimed by manufacturer, without compromising bond strength and compare it with LED and Tungsten Halogen Light (conventional light cure) at different curing times. Methods : One hundred and twenty human premolars extracted for orthodontic treatment purpose were taken and divided into three groups: group 1(conventional cure, 45 teeth), group 2(LED, 30 teeth) and group 3(plasma arc, 45 teeth). The groups were further subdivided into subgroups of 15 samples each for different curing periods.The shear bond strength was tested on a universal testing machine. Results : Shear bond strength for the three groups were; Group 1A(conventional cure 20sec):7.71MPa, Group 1B (conventional cure 40sec):12.56MPa,Group 1C(conventional cure 60sec):13.20MPa ,Group 2A(LED 20sec):12.27MPa ,Group 2B(LED 30 sec):14.90MPa ,Group 3A(plasma arc 4sec):9.39MPa, Group 3B(plasma arc 6 sec): 13.11 MPa, Group 3C(plasma arc 10sec):16.7 MPa. The total exposure time required by different curing systems was evaluated. Analyses of variance indicated no significant difference in intra group or inter group values. Student ttest were performed to evaluate the difference in the means of different subgroup.Z test was done to check the difference in the total exposure times of different light curing units. The mean shear bond strengths of different subgroups were more than the minimal required bond strength. Conclusion : plasma arc curing system saved a significant amount of time without compromising on bond strength.

Effect of light curing sources on microhardness of different composite resins

This study evaluated the influence of light-curing units (LCUs) on Knoop microhardness (KHN) of different composite resins formulations. Four LCUs, one Quartz-Tungsten-Halogen (QTH) for 20 s, one Argon-Ion-Laser (AL) for 10 s, one Plasma-Arc-Curing (PAC) for 9 s, and one Light-Emitting-Diode (LED) for 20 s, and three composite resins, nanofill and easy cure (Filtek™ Supreme), microhybrid and medium cure (Herculite XRV), and microfill and difficult cure (Heliomolar) were used. Discs (4 × 2 mm2) of each composite resin were divided in 12 Groups and KHN was measured at the top (T) and bottom (B) surfaces. Data were analyzed using two-way ANOVA and Tukey’s test (p < 0.05). Top presented significantly higher KHN than bottom surface for all composite resins and LCUs tested. Statistical significant differences were observed among the LCUs. At the bottom surface QTH and LED presented higher KHN than PAC and LA. However, at the top surface PAC and LA presented similar results than QTH for nanofill and microhybrid composite resins. Different LCUs play an important effect on Knoop microhardness and the composite resin formulations were significant factor on the photosensitivity.

Effect of resin luting cement polymerisation mode and high powered polymerisation unit type on shear bond strength of leucite reinforced full ceramic system to dentine

This in vitro study evaluated the effects of light polymerised (LP) and dual polymerised (DP) modes of a resin luting cement polymerised with different high powered polymerisation units on the shear bond strength of a leucite reinforced full ceramic system to dentine. Ceramic specimens (n = 15) were bonded to dentine surfaces with a resin luting cement (Variolink II) in either LP or DP mode and polymerised according to one of four polymerisation profiles as follows: control group: 600 mW cm−2 conventional halogen light, 40 s; light emitting diode polymerisation unit group: 1500 mW cm−2 light emitting diode, 10 s; plasma arc curing (PAC) polymerisation unit 10 s group: 1370 mW cm−2 PAC, 10 s; and PAC 3 s group: 1370 mW cm−2 PAC, 3 s. Bond strength (MPa) data were analysed using two-way analysis of variance and Duncan’s test (α = 0·05). Polymerisation mode (p<0·01), type of light unit (p<0·01) and the interactions between the two were statistically significant (p<0·05). No significant differences were found between LP and DP modes except for the PAC 3 s group, in which the LP mode resulted in significantly lower shear bond strength values (10·43±1·02 MPa) compared with the DP mode (12·88±1·73 MPa).

Effects of curing units and staining solutions on the color susceptibility of a microhybrid composite resin

Background/purpose To examine the effect of different light-curing units and staining solutions on a microhybrid composite resin. Materials and methods Two shades (A3 and B3) of a light-activated composite (Ecusit resin) were cured in polytetrafluoroethylene disk rings (45 each) using 3 different light-curing units: 1) a quartz–tungsten–halogen (QTH) unit, 2) a light-emitting diode (LED) unit, and 3) a plasma-arc curing (PAC) unit. Two beverages (coffee and tea) were used as staining solutions, and distilled water was used as a control. Evaluations were made after 1, 7, 15, and 30 days by means of reflectance spectrophotometry. Results Data were statistically analyzed using one-way analysis of variance, and post-hoc comparisons were made using Tukey’s test with a significance level of 5%. A Kruskal–Wallis multiple-comparison test was performed to evaluate ΔE ∗ values among water, tea, and coffee immersion with 2 shades of the composite. Statistically significant color changes were observed between water and coffee, and tea and coffee for different time periods; whereas no difference was seen between water and tea in LED-cured A3 Ecusit resin specimens after either 1 or 15 days of immersion, those cured by PAC after 15 days of immersion, or in LED-cured B3 Ecusit resin specimens after 7 days. Conclusions PAC-cured Ecusit resin specimens showed significantly higher discoloration than the other specimens. The staining solutions produced discoloration, while water caused the least changes.

Effects of high-intensity curing lights on microleakage under orthodontic bands

Our objective was to compare the effects of 3 light-curing units (LCUs) (quartz-tungsten-halogen [QTH], light-emitting diode [LED], and plasma-arc curing [PAC]) on the microleakage patterns of a polyacid-modified composite (PAMC) for band cementation between the cement-enamel and the cement-band interfaces from the buccal, lingual, occlusal, and gingival margins. Sixty freshly extracted third molars were randomly divided into 3 groups of 20 teeth each. Microetched molar bands were cemented in all groups with the PAMC (Ultra Band-Lok, Reliance Orthodontic Products, Itasca, Ill) and cured for 30 seconds with the QTH (Hilux 350, Express Dental Products, Toronto, Ontario, Canada), for 20 seconds with the LED (Elipar Freelight 2, 3M Espe, Seefeld, Germany), or for 6 seconds with the PAC (Power-Pac, American Medical Technologies, Hannover, Germany). A dye penetration method was used for microleakage evaluation. Microleakage was determined with a stereomicroscope for the cement-band and cement-enamel interfaces from the buccal and lingual sides at the occlusal and gingival margins. Statistical analyses were performed with the Kruskal-Wallis and Mann-Whitney U tests. The level of significance was set at P <0.05. The gingival sides in the LED and PAC groups had higher microleakage scores compared with those observed on the occlusal sides at both the cement-band and cement-enamel interfaces. The buccal sides had similar microleakage values compared with those on the lingual sides for the cement-enamel and cement-band interfaces in all LCU types. Statistical comparisons showed that there were statistically significant differences among the investigated LCUs at the cement-enamel interface (P <0.05). Post hoc comparisons showed statistically significant microleakage differences between the PAC (median, 0.950 mm), the QTH (median, 0.383 mm) (P <0.01), and the PAC and the LED (median, 0.558 mm) (P <0.05) LCUs at the cement-enamel interfaces. The high-intensity curing device PAC is associated with more microleakage than the LED and QTH at the cement-enamel interface.

Effects of Different Curing Units and Luting Agents on Push-out Bond Strength of Translucent Posts

Introduction The aim of this study was to evaluate the effects of different curing units and 2 luting cements on the push-out bond strength of a translucent fiber post. Methods Thirty maxillary incisor roots were endodontically treated. Post spaces were prepared, and the smear layers were removed. Posts (FRC Postec Plus) were luted with either a self-etch cement (Panavia F 2.0) or a self-adhesive cement (Maxcem). Luting agents were then light-activated with a quartz-tungsten-halogen, a blue light–emitting diode, or a plasma-arc curing unit. Roots/cemented posts were transversally sectioned from coronal to apical. Push-out tests were performed, and data were analyzed by using three-way analysis of variance and Tukey tests. Results Push-out bond strengths were significantly affected by the type of luting agent ( P < .05) and root region ( P < .05). The type of light source used in curing did not affect push-out bond strengths ( P > .05). Conclusions Self-adhesive resin cement provided higher bond strength than the self-etch cement when smear layer was removed before the post cementation. The push-out bond strength in the apical portion of the root was significantly lower than in the coronal region. The use of different curing units in the photoirradiation of dual-cured resin cement did not affect the retention of the fiber post as a result of the limited light transmission capability of this post.

Heat generation with the use of LED curing device

Objective: The purpose of this in vitro study was to evaluate heat generation with the use of LED curing device externally (on the outer surface of the tooth)&amp; internally (inside the pulp chamber), in compares with plasma arc &amp; conventional curing device Materials &amp; Methods: On the buccal and palatal surface of fifteen upper extracted premolar teeth a standardized class V cavity was prepared, the teeth were randomly divided into three groups according to the cure mode, group I cured with DentSuply (Conventional cure unit QTH), group II cured with Radii (LED cure unit) and group III cured with Flipe .( Plasma arc cure unit) .&#x0D; Each group consist of 5teeth (10 cavities), and filled with (micro-hybrid resin composite), before light curing of the composite resin a thermocouple was inserted into the pulp chamber .A second thermocouple was attached on the surface of the tooth; the other end of the thermocouple was connected with anelectrical thermometer. Two reading of temperature increasing were measured. Then the difference between the initial and final temperature was recordedexternally and internally.Results: Statistical analysis of the results revealed that the LED light curing unit had the least increase in the temperature with a significant difference (P&lt;0.001)when it was compared with plasma arc curing device externally &amp; internally. In spite of statistically a significant difference between LED &amp; conventional curingdevice externally (P&lt;0.001) and the lower temperature mean was found with LED internally, no significant difference between LED &amp; conventional curingdevice internally.Conclusion :LED light curing unit had the least increase in the temperature at the outer surface of the tooth and inside the pulp chamber.

Effect of simulated pulpal microcirculation on intrachamber temperature changes following application of various curing units on tooth surface

Objective The purpose of this study was to evaluate ex vivo the rise in intrachamber temperature induced by the application of various curing units on tooth surface, under conditions of continuous water flow inside the pulp chamber simulating pulp microcirculation. Methods Fifteen extracted intact human teeth were selected. Intrachamber temperature increases were induced by applying the following curing units to the buccal aspect of the tested teeth: a conventional halogen lamp, two high-intensity halogen lamps, a plasma arc curing light, a mercury/metal-halide lamp, and a diode laser. Temperature changes on the tooth surfaces were recorded using thermocouples connected to a data logger. The Greenhouse–Geisser and Bonferroni tests in the SPSS software package were used for analysis of the data. The level of significance was set at 0.05. Results Under conditions of water flow the average intrachamber temperature rise was less than 6 °C, for all curing units. Without water flow, the increase in pulp temperature exceeded 6 °C for all units except the conventional halogen lamp. The diode laser produced a significantly greater temperature increase than any other curing unit. Application of the diode laser and the two high-intensity halogen lamps to lateral incisor specimens produced significantly greater temperature increases than other teeth. Conclusions When the simulated pulp microcirculation was absent, the temperature increases produced by all curing units except the conventional halogen lamp were large enough to be potentially harmful to the pulp. On the contrary, with the cooling effect of water flow inside the pulp chamber, all units proved to be safe for use.

Effect of different light curing units on Knoop hardness and temperature of resin composite

To evaluate the influence of quartz tungsten halogen and plasma arc curing (PAC) lights on Knoop hardness and change in polymerization temperature of resin composite. Filtek Z250 and Esthet X composites were used in the shade A3. The temperature increase was registered with Type-k thermocouple connected to a digital thermometer (Iopetherm 46). A self-cured polymerized acrylic resin base was built in order to guide the thermocouple and to support the dentin disk of 1.0 mm thickness obtained from bovine tooth. On the acrylic resin base, elastomer mold of 2.0 mm was adapted. The temperature increase was measured after composite light curing. After 24 h, the specimens were submitted to Knoop hardness test (HMV-2000, Shimadzu, Tokyo, Japan). Data were submitted to ANOVA and Tukey's test (alpha = 0.05). For both composites, there were no significant differences (P > 0.05) in the top surface hardness; however, PAC promoted statistically lower (P < 0.05) Knoop hardness number values in the bottom. The mean temperature increase showed no significant statistical differences (P > 0.05). The standardized radiant exposure showed no influence on the temperature increase of the composite, however, showed significant effect on hardness values.

Effects of High-Intensity Curing Lights on Microleakage under Bonded Lingual Retainers

To evaluate the effects of high-intensity light curing units (light-emitting diode [LED] and plasma arc curing [PAC]) on the microleakage of flexible spiral wire retainers (FSWRs) at the composite/enamel and composite/wire interfaces. Forty-five human mandibular incisor teeth were separated into three groups of 15 teeth. Multistranded PentaOne wire of .0215 inch diameter was bonded to enamel and was cured with three different light curing units: a quartz-tungsten-halogen (QTH) unit and two high-intensity units (ie, LED and PAC). A conventional halogen light served as the control. Samples were sealed with nail varnish, stained with 0.5% basic fuchsine, and sectioned. Transverse sections were evaluated under a stereomicroscope and were scored for microleakage for the composite/enamel and composite/wire interfaces. Statistical analysis was performed by Kruskal-Wallis and Mann-Whitney U-tests with Bonferroni correction. Little or no microleakage was detected at the composite/enamel interface of the FSWR cured with three different light sources. However, at the composite/wire interface, statistically significant differences were found between the QTH (mean, 1.10 +/- 1.05 mm) and high-intensity curing units. The PAC resulted in the greatest amount of microleakage (mean, 2.63 +/- 1.49 mm), whereas no statistically significant difference was noted between the PAC and the LED (mean, 2.35 +/- 1.28 mm). High-intensity light curing units show statistically significant microleakage at the composite/wire interface and therefore may not be safe for use in bonding FSWRs.

Effect of Distance from Curing Light Tip to Restoration Surface on Depth of Cure of Composite Resin

While light-activating composite resins, the light tip may not always be close to the surface of the restoration. This may be intentional in an attempt to create a ramp cure. The aim of this study was to determine the effect of a range of separation distances between the light tip and the restoration surface on the depth of composite cure for different types of light-curing units with a broad range of outputs. Three halogen light units, one plasma arc-curing (PAC) light unit and two light-emitting diode (LED) curing lights in clinical use were tested, and a total of 570 restorations cured in a two-part human tooth model at separations ranging from 0 to 15 mm. The tooth was disassembled and depth of cure determined using the scrape test ISO 4049. Light intensity was also measured at each separation distance for each light. The depth of cure was generally found to decrease as the separation distance increased for all lights at the various cure times. However, the effect of increasing the separation distance was less than anticipated. The depth of cure was also related to the light output. Depth of composite cure was directly related to intensity and duration of light exposure and inversely related to distance of the light source from the surface for halogen and plasma lights. However, the effect of increasing the separation distance up to 15 mm was less than expected. Altering the separation distance in order to modify the polymerisation characteristics is unlikely to be effective.

Insufficient cure under the condition of high irradiance and short irradiation time

Objectives To investigate if and why a plasma arc curing (PAC) light tends to undercure methacrylate-based resins or resin composites. Methods Model dimethacrylate resins, commercial dental adhesives, and commercial resin composites were cured using a PAC light and a halogen light with the similar radiant exposures but different combinations of irradiance and irradiation time. The degree of double bond conversion (DC) was measured with FTIR spectroscopy and analyzed as a function of radiant exposure. Results The PAC light produced a lower DC than the halogen light for the model resin with the lowest viscosity and for three of the four adhesives. With a high irradiance, the PAC light could cure three of the four composites as thoroughly as its halogen counterpart. When the irradiance was reduced, however, three composites yielded a lower DC. Conclusions Insufficient cure by PAC lights or any curing lights with very high irradiance is likely to happen when too short an irradiation time is used. It is because under higher irradiance, the lifetime of free radicals is shorter.

Effects of Different Light-curing Units and Obturation Techniques on the Seal of the Resilon/Epiphany System

The purpose of this study was to compare the sealing ability of a resin- and polymer-based root canal obturation system (Resilon; Resilon Research LLC, Madison, CT/Epiphany; Clinical Technologies, Wallingford, CT) used in conjunction with different light-curing units and obturation techniques. A total of 120 decrowned single-rooted human teeth were used. After preparation of the root canals with 0.06 taper nickel-titanium rotary files to size 30, the roots were randomly assigned into three experimental groups according to the obturation technique used: (1) single cone, (2) cold lateral compaction, and (3) System B + Obtura. In all groups, the specimens were randomly assigned into four subgroups according to the polymerization method that was used to cure Epiphany sealer from the coronal aspect: (1) quartz-tungsten-halogen (QTH), (2) light-emitting diode (LED), (3) plasma-arc curing (PAC), and (4) chemical cure (uncured). Leakage was measured by the fluid-filtration method at 1 day and 1 week. Statistical analysis was performed by using Kruskal-Wallis and Wilcoxon signed-rank tests at p < 0.001. Fluid conductance of all groups increased significantly within time (p < 0.001). The tested obturation techniques had no significant effect on the leakage values (p = 0.433). The following statistical ranking was obtained for fluid-filtration values: uncured > PAC > LED > QTH (p < 0.001).

Influence of Light Curing Unit and Ceramic Thickness on Temperature Rise during Resin Cement Photo-activation

The aim of this study was to determine the effect of different ceramic thickness on heat generation during resin cement photo-activation by QTH (quartz-tungsten-halogen), LED (light emitting diode), and PAC (plasma arc-curing) LCUs (light curing units). The resin cement used was Rely X ARC (3M-ESPE), and the ceramic was IPS Empress Esthetic (Ivoclar-Vivadent), of which 0.7-, 1.4- and 2.0-mm thick disks, 0.8 mm in diameter were made. Temperature increase was recorded with a type-K thermocouple connected to a digital thermometer (Iopetherm 46). An acrylic resin base was built to guide the thermocouple and support the 1.0-mm thick dentin disk. A 0.1-mm thick black adhesive paper matrix with a perforation 6 mm in diameter was placed on the dentin to contain the resin cement and support the ceramic disks of different thicknesses. Three LCUs were used: QTH, LED and PAC. Nine groups were formed (n=10) according to the interaction: 3 ceramic thicknesses, 1 resin cement and 3 photo-activation methods. Temperature increase data were submitted to Tukey's test (5%). For all ceramic thicknesses, a statistically significant difference in temperature increase was observed among the LCUs, with the highest mean value for the QTH LCU (p<0.05). For all the LCUs, a thickness of 0.7 mm produced the highest temperatures (1.4 and 2.0mm, p<0.05). There was no difference in temperature values between the latter two thicknesses (p>0.05). The interaction of higher energy density with smaller ceramic thickness showed higher temperature increase values.