Light-emitting Diode Curing Units Research Articles

Effect of power density of curing unit, exposure duration, and light guide distance on composite depth of cure

This in vitro study compared the depth of cure obtained with six quartz tungsten halogen and light-emitting diode curing units at different exposure times and light tip-resin composite distances. Resin composite specimens (Tetric Ceram, A3; diameter 4 mm, height 6 mm) were exposed from 0-, 3-, and 6-mm distance. The curing units (200-700 mW/cm2) were used for standard (20 and 40 s), pulse-delay mode (initial exposure of 3 s at 200 mW/cm2, followed by a resting period of 3 min and a final exposure of 10 or 30 s at 600 mW/cm2), or soft-start curing (40 s; exponential ramping). Curing depth was determined by measurement of Wallace hardness for each half millimeter starting at 0.5 mm from the top surface. For each specimen, a mean H(W) value was calculated from the H(W) values determined at the depths of 2.0 mm and less (0.5, 1.0, 1.5, and 2.0 mm, respectively). The depth of cure for each specimen was found by determining the greatest depth before an H(W) value exceeding the minimal H(W) value by 25% occurred. For all curing units, an increase in exposure time led to significantly higher depth of cure. Increasing the light tip-resin composite distance significantly reduced the depth of cure. With a light tip-resin composite distance of 6 mm, median values of depth of cure varied between 2.0 and 3.5 mm following a 20-s (or 3+10 s) exposure and between 3.0 and 4.5 mm following a 40-s (or 3+30 s) exposure. The composite situated above the depth of cure value cured equally well with all curing units. At both exposure times, Luxomax resulted in the significantly lowest depth of cure, and Astralis 7 yielded significantly higher depth. At both exposure times, a significant linear correlation was found between the determined power densities of the curing units and the pooled depth of cure values obtained. It seems that for the resin composite tested, the recommended exposure time of 40 s per 2-mm increment may be reduced to 20 s, or that increments may be increased from 2 to 3.5 mm. It may be that the absolute values of depth of cure found are material specific, but we believe that the relationships found between curing units, between exposure times, and between light guide distances are universal.

Evaluation of light curing units used for polymerization of orthodontic bonding agents.

This study evaluated the light intensity of various light curing units, the effect of distance of the light guide, and the validity of a tapered light guide. Light curing units tested included (1) four blue light-emitting diode curing units, Lux-O-Max, LEDemetronl, Ortholux LED, and The Cure; (2) two tungsten-quartz halogen curing units, Optilux 501 and Co-bee; and (3) one plasma arc curing unit, Apollo95E. The Optilux 501 was also evaluated for combinations of normal mode and boost mode and Standard tip and Turbo tip light guide. The spectral output of each unit was measured from 300 to 600 nm with a spectroradiometer. The light intensities at distances of zero, five, 10, 15, and 20 mm were determined with the radiometer. The peak value of Ortholux LED and The Cure surpassed that of Apollo95E. The light intensity significantly decreased with distance. Although The Cure showed a higher light intensity than the LEDemetron1 at zero-mm distance, the light intensity of the LEDemetron1 was higher than that of The Cure at five to 20 mm, resulting in no significant difference. The boost mode increased light intensity at any distance. Although the Turbo tip enhanced light intensity at zero-mm distance, reduction of light intensity by Turbo tip was demonstrated at five- to 20-mm distance.

Shear bond strength of orthodontic brackets bonded with light-emitting diode curing units at various polymerization times

Light emitting diode (LED) light-curing units have recently been used to polymerize resin-based orthodontic adhesives, and preliminary studies indicate their use has been successful. The purpose of this study was to evaluate the relationship between the shear bond strength of orthodontic brackets bonded to enamel and the duration of photopolymerization with LEDs and conventional quartz-tungsten-halogen light-curing units. Three LED light-curing units (GC e-light, GC America, Alsip, Ill; Elipar FreeLight, 3M ESPE Dental Products, St Paul, Minn; and UltraLume LED 2, Ultradent Products, South Jordan, Utah) and 1 halogen-based light-curing unit (Ortholux XT, 3M Unitek, Monrovia, Calif) were evaluated. Two hundred forty metal orthodontic brackets were bonded to extracted molars. Specimens were divided into 12 groups of 20 teeth each. Each group was cured with a different light-curing unit for 40, 20, or 10 seconds. The specimens were stored in water at 37° C for 24 hours and then subjected to a shear force with a universal testing machine until bracket failure. Two-way ANOVA detected significantly weaker mean shear bond strength with the GC e-light at 10 and 40 seconds ( P< .001) and higher mean shear bond strength for the UltraLume LED 2 at 40 seconds ( P< .001). All experimental groups had laboratory mean shear bond strengths greater than 8 MPa, even with a 10-second cure.

Polymerization of orthodontic resin cement with light-emitting diode curing units

Commercially available light-emitting diode (LED) light-curing units recently have been introduced to the dental products market. No published studies have evaluated the adequacy of cure of commercially available LEDs. The purpose of this study was to compare the shear bond strength of orthodontic brackets bonded to teeth with conventional halogen-based light-curing units and commercially available LED curing units. Two LED light-curing units (LumaCure and VersaLux) and 2 halogen-based light-curing units (Optilux 501 and ProLite) were tested. One hundred standard metal orthodontic brackets were bonded to extracted human third molars with a light-cured adhesive system. The specimens were divided into 4 groups of 25 teeth each. In each group, the brackets were cured for 40 seconds with a different light-curing unit. The specimens were stored in water at 37°C for 24 hours and then tested in shear with an Instron universal testing machine at a crosshead speed of 1 mm/min until the brackets debonded. One-way analysis of variance detected no differences in bond strength between the 4 groups (P =.78). Chi-square analysis detected no difference in the adhesive remnant index scores of the 4 groups (P =.89). Under the conditions of this study, the LED light-curing units bonded brackets to etched tooth enamel as well as the halogen-based light-curing units. Additional clinical studies are necessary before routine use of commercial LED light-curing units can be recommended. (Am J Orthod Dentofacial Orthop 2002;122:236-41)