Plasma arc curing lights for orthodontic bonding

Xenon plasma arc lights were introduced recently for light-cured orthodontic bonding. Compared with a conventional tungsten-quartz-halogen light source, these high-intensity lights promise a dramatic reduction in curing time. The purpose of this in vitro investigation was to evaluate bond strength with 2 commercially available plasma arc lights and reduced curing intervals. Brackets were bonded to 150 extracted human teeth (75 premolars, 75 incisors) with a composite adhesive. Intervals of 2 and 6 seconds were used for curing with the plasma arc lights; a control group was bonded with a halogen light source and 20 seconds of light exposure per bracket. Bond strength testing was performed with a universal testing machine. A substantial reduction in curing time was possible with both plasma arc units. Significantly lower bond strength values were found for premolar brackets bonded with plasma arc curing lights and the shortest curing interval of 2 seconds compared with the longer curing time of 6 seconds or the standard curing time with the halogen light. Although 2 seconds of curing might be adequate to achieve acceptable bond strength values for the incisors, the Weibull analysis indicated a higher probability of bond failure for premolar brackets in particular. Six seconds of curing time is recommended for bonding stainless steel brackets with xenon plasma arc light sources.     

An in vivo study to compare a plasma arc light and a conventional quartz halogen curing light in orthodontic bonding

The purpose of this study was to compare the effectiveness of a plasma arc lamp with a conventional tungsten quartz halogen lamp in orthodontic bonding. Twenty consecutive patients had their brackets bonded either with Transbond XT (n = 10) or Fuji Ortho LC (n = 10). In total, 352 teeth were bonded, 176 in each group. Using a randomized cross-mouth control study design, where diagonally opposite quadrants were assigned a particular treatment, the bonds were then either cured with the control light, namely a halogen lamp, or a plasma arc lamp. The halogen light was used for 20 seconds per tooth and the plasma arc lamp for 3 seconds per tooth. The measurement parameter used was bond failure and the patients were monitored for a period of 6 months following initial bond placement.In the Transbond XT group, the proportion of bond failures was 3.41 per cent for both the halogen and the plasma arc lamp. For the Fuji Ortho LC group, the proportions were 11.4 and 10.2 per cent, respectively. No difference was observed with respect to in-service bond failure proportions between bonds cured with the plasma arc or the conventional halogen lamp, irrespective of the bonding agent. Use of the plasma arc lamp could therefore lead to considerable savings in clinical time. However, this must be weighed against the increased purchase price of the plasma arc lamp.     

Effects of fast halogen and plasma arc curing lights on the surface hardness of orthodontic adhesives for lingual retainers

The aims of this study were to (1) identify the optimum cure times of 2 different lingual retainer adhesives with a conventional halogen, a fast halogen, and a plasma arc light by measuring Vickers surface hardness, and (2) determine whether different lights produce similar surface hardness values for the same adhesive resin material. The investigated plasma arc curing unit was the PowerPac (American Dental Technologies, Corpus Christi, Tex), and the fast halogen unit was the Optilux 501 (Kerr, Orange, Calif). A conventional curing unit, the Ortholux XT (3M Dental Products, St. Paul, Minn) was used as the control. Two orthodontic lingual retainer adhesives were used: Transbond Lingual Retainer (3M Unitek, Monrovia, Calif) and Light Cure Retainer (Reliance Orthodontic Products, Itasca, Ill). Concise (3M Dental Products) and diluted Concise were used as controls. Transbond Lingual Retainer was polymerized by the PowerPac light in 6 seconds, by the Optilux in 10 seconds, and by the conventional halogen light in 20 seconds. The minimum curing times for Light Cure Retainer adhesive were 15 seconds for PowerPac, 10 seconds for Optilux, and 40 seconds for conventional halogen. Surface hardness values for each resin did not differ significantly with different curing units. However, different adhesives demonstrated significantly different surface hardness values. Final Vickers surface hardness values (averaged across curing units) of Transbond Lingual Retainer, Concise, diluted Concise, and Light Cure Retainer were 62.8, 52.4, 46.0, and 40.4, respectively. Plasma arc or fast halogen units polymerize resin composite adhesive in much shorter times than do conventional curing units, without a significant loss in surface hardness. Therefore, these units are suggested for clinical use to save chairside time.     

Thermal emission and curing efficiency of LED and halogen curing lights

The purpose of this study was to compare the thermal emission and curing efficiency of LED (LEDemetron 1, SDS/Kerr) and QTH (VIP, BISCO) curing lights at maximum output and similar power, power density and energy density using the same light guide. Also, another LED curing light (Allegro, Den-Mat) and the QTH light at reduced power density were tested for comparison. Increase in temperature from the tips of the light guides was measured at 0 and 5 mm in air (23 degrees C) using a temperature probe (Fluke Corp). Pulpal temperature increase was measured using a digital thermometer (Omega Co) and a K-type thermocouple placed on the central pulpal roof of human molars with a Class I occlusal preparation. Measurements were made over 90 seconds with an initial light activation of 40 seconds. To test curing efficiency, resin composites (Z100, A110, 3M/ESPE) were placed in a 2-mm deep and 8-mm wide plastic mold and cured with the LED and QTH curing lights at 1- and 5-mm curing distances. Knoop Hardness Numbers (KHN) were determiped on the top and bottom surfaces (Leco). Bottom hardness values were expressed as a percentage of maximum top hardness. No significant differences were found in maximum thermal emission or KHN ratios between the LED (LEDemetron 1) and the QTH (VIP) at maximum output and similar energy densities (ANOVA/Tukey's; alpha=0.05).     

A randomized clinical trial comparing 'one-step' and 'two-step' orthodontic bonding systems

OBJECTIVE: The primary objective of this prospective clinical trial was to assess the clinical bond failure rates of orthodontic brackets bonded using a self-etching primer (SEP), compared with brackets bonded using a conventional acid-etched technique with control adhesive (Transbond). A secondary aim was to investigate whether characteristics of the operator, patient or tooth bonded had any influence on bracket failure. DESIGN: Single-centre randomized controlled clinical trial. Thirty-four patients were bonded, each being randomly assigned to either the test or control adhesive. SETTING: NHS Hospital Orthodontic Department, Chester, UK. SUBJECTS: Orthodontic patients requiring fixed appliance treatment. MAIN OUTCOME MEASURES: Bond failure. MAIN OUTCOME RESULTS: Failure rates over the initial 6-month period were 2.0% (Transbond) and 1.7% (SEP) with no statistically significant difference between the two groups. Over the duration of the fixed appliance treatment, bond failure rates increased, but remained acceptable at 7.4 % (TB) and 7.0% (SEP), respectively. When operator, patient and tooth characteristics were analysed, only the bracket location was found to be significant. Maxillary brackets were more likely to fail than mandibular brackets (RR 0.47%; 95% CI 0.22, 1.03). The failure rate for brackets in our study was low when compared with previous studies. CONCLUSIONS: Both the acid-etched control and self-etching primer in combination with adhesive pre-coated brackets were successful for clinical bonding. Their combined failure rate was lower than that reported in similar trials.     

The efficacy of a plasma arc light in orthodontic bonding: a randomized controlled clinical trial

Abstract

Objective: To evaluate the clinical performance of a plasma arc light (Ortho LITE, 3M Unitek, Monrovia, CA, USA) against a conventional tungsten–quartz halogen curing light (Visilux 2, 3M Unitek, Monrovia, CA, USA) for direct orthodontic bonding.

Design: A single centre prospective randomized controlled clinical trial.

Setting: The Orthodontic Department at St Luke’s Hospital, Bradford, UK.

Subjects and methods: Forty-three consecutive patients requiring fixed appliances from the orthodontic waiting list. A split mouth technique was adopted; with quadrants randomly assigned to either the plasma arc light or the conventional halogen curing light and bonded directly with APC pre-adjusted edgewise brackets (3M Unitek, Monrovia, CA, USA).

Main outcome measure: Bracket failures.

Secondary outcome measures: Time taken to bond-up the appliances, patient sensitivity or discomfort during curing and time to replace failed brackets were investigated.

Results: No statistically significant difference in bracket failure rates over the full course of treatment was found between the plasma arc light (6.7%; 95% CI 4.5–10.0) and the halogen curing light (9.5%; 95% CI 6.8–13.1). There was no statistically significant difference in bracket survival times. The bond-up times were typically reduced by 204 seconds per patient with the plasma arc light. There were no differences in patient reported sensitivity or discomfort or rebond times.

Conclusion: The plasma arc light is a viable clinical alternative to the conventional halogen curing light with benefits for both the clinician and patient due to reduced bonding times.     

The efficacy of a plasma arc light in orthodontic bonding: a randomized controlled clinical trial

Objective: To evaluate the clinical performance of a plasma arc light (Ortho LITE, 3M Unitek, Monrovia, CA, USA) against a conventional tungsten-quartz halogen curing light (Visilux 2, 3M Unitek, Monrovia, CA, USA) for direct orthodontic bonding. Design: A single centre prospective randomized controlled clinical trial. Setting: The Orthodontic Department at St Luke's Hospital, Bradford, UK. Subjects and methods: Forty-three consecutive patients requiring fixed appliances from the orthodontic waiting list. A split mouth technique was adopted; with quadrants randomly assigned to either the plasma arc light or the conventional halogen curing light and bonded directly with APC pre-adjusted edgewise brackets (3M Unitek, Monrovia, CA, USA). Main outcome measure: Bracket failures. Secondary outcome measures: Time taken to bond-up the appliances, patient sensitivity or discomfort during curing and time to replace failed brackets were investigated. Results: No statistically significant difference in bracket failure rates over the full course of treatment was found between the plasma arc light (6.7%; 95% CI 4.5-10.0) and the halogen curing light (9.5%; 95% CI 6.8-13.1). There was no statistically significant difference in bracket survival times. The bond-up times were typically reduced by 204 seconds per patient with the plasma arc light. There were no differences in patient reported sensitivity or discomfort or rebond times. Conclusion: The plasma arc light is a viable clinical alternative to the conventional halogen curing light with benefits for both the clinician and patient due to reduced bonding times.     

Polymerization of orthodontic adhesives using modern high-intensity visible curing lights.

This study was undertaken to assess the efficacy of 3 visible curing lights: a conventional halogen light and 2 high-intensity halogen lights in the polymerization of a polymer-based and resin-modified glass ionomer orthodontic cement. Degree of polymerization was measured by Fourier transform infrared spectroscopy and the development of mechanical properties by Barcol hardness. The results were analyzed with either 2- or 3-way analysis of variance. It was shown that, for the polymer-based material, there was a significant increase in degree of cure and hardness with time of application of the light for each light source. For chemical conversion, there was no significant difference between the lights. However, there was a difference in hardness: the higher intensity lights produced greater hardness in shorter time. Thus, there was poor correlation between degree of polymerization and hardness. For the resin-modified glass ionomer, similar trends were found, but there was a difference in hardness between the top and the bottom of the specimens. It was concluded that the higher intensity lights could aid in the more rapid development of mechanical properties of the tested adhesives.     

Rapid curing of bonding composite with a xenon plasma arc light

The use of light-cured orthodontic adhesives is an increasingly popular method for the bonding of orthodontic brackets. However, one of the disadvantages of light-cured adhesives is their long curing times. The xenon plasma arc curing light is purported to dramatically reduce the required curing time. The purpose of this study was to test the efficiency of a xenon plasma arc light versus a conventional tungsten-quartz halogen light in producing effective bond strengths for orthodontic brackets. Standardized brackets were bonded to bovine enamel with 3 different orthodontic bonding materials. The bonding materials were exposed to the tungsten-quartz halogen light for 40 seconds and to the xenon light for 3, 6, and 9 seconds. Bond strength was tested 30 minutes and 24 hours after light-curing. The results showed that bond strength with the application of the xenon light was greater with longer exposures. There were no statistically significant differences between the bond strengths of the brackets exposed to the tungsten-quartz halogen light for 40 seconds and those exposed to the xenon light for 3, 6, or 9 seconds. However, xenon light exposures of 6 or 9 seconds were required to create bond strengths equal to those produced by the tungsten-quartz halogen light. The xenon light produced equivalent bond strengths at very short light exposures.     

Plasma arc versus halogen light curing of orthodontic brackets: a 12-month clinical study of bond failures.

The purpose of this randomized clinical trial was to evaluate the clinical performance of brackets cured with 2 different light-curing units (conventional halogen light and plasma arc light); 83 patients treated with fixed appliances were included in the study. With the "split-mouth" design, each patient's mouth was divided into 4 quadrants. In 42 randomly selected patients, the maxillary left and mandibular right quadrants were cured with the halogen light, and the remaining quadrants were cured with the plasma arc light. In the other 41 patients, the quadrants were inverted. A total of 1434 stainless steel brackets were examined: 717 were cured with a conventional halogen light for 20 seconds; the remaining 717 were cured with the plasma arc light for 5 seconds. The number, cause, and date of bracket failures were recorded for each light-curing unit over 12 months. Statistical analysis was performed with the Fisher exact test, the Kaplan-Meier survival estimates, and the log-rank test. No statistically significant differences were found between the total bond failure rates of the brackets cured with the halogen light and those cured with the plasma arc light. Neither were significant differences found when the clinical performances of the maxillary versus mandibular arches or the anterior versus posterior segments were compared. These findings demonstrate that plasma arc lights are an advantageous alternative to conventional light curing, because they significantly reduce the curing time of orthodontic brackets without affecting the bond failure rate.     

Effect of plasma arc curing on polymerization shrinkage of orthodontic adhesive resins

The purpose of this study was to evaluate the polymerization shrinkage of three orthodontic adhesive resins when polymerized with a high-energy plasma arc light (1340 mW cm(-2)) and a conventional halogen light (500 mW cm(-2)), and to correlate the polymerization shrinkage with the degree of conversion. To equalize the total light energy delivered to the adhesive resin, irradiation time was varied between 3 or 6 s for a plasma arc-curing unit, and 8 or 16 s for a halogen light-curing unit. The polymerization shrinkage of adhesive resins during the light-curing process was measured using a computer-controlled mercury dilatometer and the degree of conversion was measured using Fourier transform infrared spectroscopy. A plasma arccuring unit produced significantly lower polymerization shrinkage than a halogen light-curing unit when the equivalent total light energy was irradiated to the orthodontic adhesive resins (P < 0.05). The magnitude of polymerization shrinkage was significantly different depending on the kind of adhesive resins (P < 0.05), but there was no significant correlation between the filler fraction and the polymerization shrinkage (r2 = 0.039). There was strong correlation (r2 = 0.787) between the polymerization shrinkage and the degree of conversion with a halogen light-curing unit, but poor correlation (r2 = 0.377) was observed with a plasma arc-curing unit.     

Comparison between a plasma arc light source and conventional halogen curing units regarding flexural strength, modulus, and hardness of photoactivated resin composites

The plasma arc curing light Apollo 95 E (DMDS) is compared to conventional curing lights of different radiation intensities (Vivalux, Vivadent, 250 mW/cm²; Spectrum, DeTrey, 550 mW/cm²; Translux CL, Kulzer, 950 mW/cm²). For this purpose, photoactivated resin composites were irradiated using the respective curing lights and tested for flexural strength, modulus of elasticity (ISO 4049), and hardness (Vickers, Knoop) 24 h after curing. For the hybrid composites containing only camphoroquinone (CQ) as a photoinitiator (Herculite XRV, Kerr; Z100, 3 M), flexural strength, modulus of elasticity, and surface hardness after plasma curing with two cycles of 3 s or with the step-curing mode were not significantly lower than after 40 s of irradiation using the high energy (Translux CL) or medium energy conventional light (Spectrum). However, irradiation by only one cycle of 3 s failed to produce adequate mechanical properties. Similar results were observed for the surface hardness of the CQ containing microfilled composite (Silux Plus, 3 M), whereas flexural strength and modulus of elasticity after plasma curing only reached the level of the weak conventional light (Vivalux). For the hybrid composites containing both CQ and photoinitiators absorbing at shorter wavelengths (370–450 nm) (Solitaire, Kulzer; Definite, Degussa), plasma curing produced inferior properties mechanical than conventional curing; only the flexural strength of Solitaire and the Vickers hardness of Definite reached levels not significantly lower than those observed for the weak conventional light (Vivalux). The suitability of plasma arc curing for different resin composites depends on which photoinitiators they contain. Received: 5 July 1999 / Accepted: 16 March 2000     

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.     

The effectiveness of cure of LED and halogen curing lights at varying cavity depths

This study compared the effectiveness of cure of two LED (light-emitting diodes) lights (Elipar FreeLight [FL], 3M-ESPE and GC e-Light [EL], GC) to conventional (Max [MX] (control), Dentsply-Caulk), high intensity (Elipar TriLight [TL], 3M-ESPE) and very high intensity (Astralis 10 [AS], Ivoclar Vivadent) halogen lights at varying cavity depths. Ten light curing regimens were investigated. They include: FL1-400 mW/cm2 [40 seconds], FL2-0-400 mW/cm2 [12 seconds] --> 400 mW/cm2 [28 seconds], EL1-750 mW/cm2 [10 pulses x 2 seconds], EL2-350 mW/cm2 [40 seconds], EL3-600 mW/cm2 [20 seconds], EL4-0-600 mW/cm2 [20 seconds] --> 600 mW/cm2 [20 seconds], TL1-800 mW/cm2 [40 seconds], TL2-100-800 mW/cm2 [15 seconds] --> 800 mW/cm2 [25 seconds], AS1-1200 mW/cm2 [10 seconds], MX-400 mW/cm2 [40 seconds]. The effectiveness of cure of the different modes was determined by measuring the top and bottom surface hardness (KHN) of 2-mm, 3-mm and 4-mm thick composite (Z100, [3M-ESPE]) specimens using a digital microhardness tester (n = 5, load = 500 g; dwell time = 15 seconds). Results were analyzed using ANOVA/Scheffe's post-hoc test and Independent Samples t-Test (p < 0.05). For all lights, effectiveness of cure was found to decrease with increased cavity depths. The mean hardness ratio for all curing lights at a depth of 2 mm was found to be greater than 0.80 (the accepted minimum standard). At 3 mm, all halogen lights produced a hardness ratio greater than 0.80 but some LED light regimens did not; and at a depth of 4 mm, the mean hardness ratio observed with all curing lights was less than 0.80. Significant differences in top and bottom KHN values were observed among different curing regimens for the same light and between LED and halogen lights. While curing with most modes of EL resulted in significantly lower top and bottom KHN values than the control (MX) at all depths, the standard mode of FL resulted in significantly higher top and bottom KHN at a depth of 3 mm and 4 mm. The depth of composite cure with LED LCUs was, therefore, product and mode dependent.     

Comparison of halogen, plasma and LED curing units

This study evaluated the characteristics of two kinds of recently developed light-curing unit; plasma arc and blue light emitting diodes (LED), in comparison with a conventional tungsten-halogen light-curing unit. The light intensity and spectral distribution of light from these light-curing units, the temperature rise of the bovine enamel surface and the depth of cure of composites exposed to each unit were investigated. The light intensity and depth of cure were determined according to ISO standards. The spectral distributions of emitted light were measured using a spectro-radiometer. The temperature increase induced by irradiation was measured by using a thermocouple. Generally, light intensities in the range 400-515 nm emitted from the plasma arc were greater than those from other types. Light in the UV-A region was emitted from some plasma arc units. The required irradiation times were six to nine seconds for the plasma arc units and 40 to 60 seconds for the LED units to create a depth of cure equal to that produced by the tungsten-halogen light with 20 seconds of irradiation. The temperature increased by increasing the irradiation time for every light-curing unit. The temperature increases were 15 degrees C to 60 degrees C for plasma arc units, around 15 degrees C for a conventional halogen unit and under 10 degrees C for LED units. Both the plasma arc and LED units required longer irradiation times than those recommended by their respective manufacturers. Clinicians should be aware of potential thermal rise and UV-A hazard when using plasma arc units.