Effect of Light-Emitting Diode (LED) Curing Modes on Resin/Dentin Bond Strength

Effects of the conventional, soft start, and pulse delay modes produced by light-emitting diode device on microleakage beneath metal brackets: An in vitro comparative study

BACKGROUND

This study aimed to evaluate microleakage beneath metal brackets cured by different light curing modes.

MATERIALS AND METHODS

Sixty extracted human premolars were randomly divided into three groups according to the light curing mode. Metal brackets were bonded in all groups according to the manufacturer's recommendations with a light-emitting diode device. Light curing was applied as follows: group 1: conventional mode (10 s mesial+10 s distal); group 2: soft start mode (15 s mesial+15 s distal); group 3: pulse delay mode (3 s mesial+3 s distal, followed by 3min of no photoactivation, then 9 s mesial+9 s distal). Radiant exposure was the same in all study groups. After curing, the teeth were incubated at 37 degrees for 24hours, then thermocycled 500 times. Next, they were sealed with nail varnish, immersed in methylene blue 1% for 24hours, sectioned, and examined under a stereomicroscope. Microleakage was measured at both enamel-adhesive and bracket-adhesive interfaces, and the total microleakage for each tooth was computed. Statistical analyses were performed using Kruskal-Wallis and Welch test for comparing microleakage among groups. Wilcoxon signed ranks test was used for comparing microleakage between the bracket-adhesive and enamel-adhesive interfaces.

RESULTS

There was no significant difference in microleakage at the bracket-adhesive interface among study groups. At the enamel-adhesive interface and total microleakage, the pulse delay group exhibited significantly lower microleakage than the conventional group. Whereas there was no significant difference between the soft start group and other study groups. In all study groups, microleakage at the enamel-adhesive interface was greater than that at the bracket-adhesive interface.

CONCLUSION

The pulse delay mode caused lesser microleakage than the conventional mode. This supports the use of this mode in orthodontic bonding.

Evaluation of bond strength of molar orthodontic tubes subjected to reinforcement with flowable and bonding resins

OBJECTIVE

The goal was to evaluate the adhesive shear bond strength (SBS) of orthodontic tubes bonded to molar teeth and reinforced with Transbond XT (3M Science, St. Paul, MN, USA) and flowable resin.

MATERIALS AND METHODS

In all, 120 molar teeth, previously extracted from patients with a mean age of 30 were included. Orthodontic molar tubes were bonded on the vestibular surface of these teeth with one of two types of adhesive (Transbond XT [3M Science, St. Paul, MN, USA] or Orthobond [Morelli, Sorocaba, Brazil]). Each of these groups was subsequently divided into four further groups: control and those subjected to the use of resin reinforcement on the occlusal surface of the bonded tubes with one of three materials (Transbond XT, Tetric N Flow [Ivoclar Vivadent, Ellwangen, Germany], Z 350 Flow [3M Science, St. Paul, MN, USA]). SBS and adhesive remnant index tests were performed to evaluate bond strength and type of fracture of the tubes bonded with the different methods.

RESULTS

The use of resin reinforcement with Transbond XT significantly increased the SBS of tubes bonded with both materials. Flowable composites did not increase the SBS when used as a reinforcement. Less than 50% of the adhesive remained on the vestibular surface after the SBS test in most samples of all groups.

CONCLUSION

Transbond XT orthodontic adhesive and Orthobond adhesive had appropriate bonding strengths for clinical use. Furthermore, the use of a resinous reinforcement with Transbond XT significantly increased the SBS of tubes bonded. However this technique with flowable adhesives (Tetric N Flow and Z350 Flow) did not significantly increase SBS when orthodontic tubes were bonded with Transbond XT or Orthobond.

Effectiveness of high-power LEDs to polymerize resin cements through ceramics: An in vitro study

STATEMENT OF PROBLEM

The cementation of ceramic veneers using light-polymerized resin cement is largely dependent on the proper light activation of the cement. Light activation using high irradiance could shorten the time required to lute multiple restorations.

PURPOSE

The purpose of this in vitro study was to evaluate the light transmission of dental light-polymerizing units through ceramic cylinders and its effect on the polymerization kinetics of a resin cement.

MATERIAL AND METHODS

Ceramic ingots (IPS Empress Esthetic, shade ET1) were sectioned to produce cylinders 0.5, 1.0, and 2.0 mm thick. Two light-emitting diode units were evaluated: SmartLite Focus and Valo Cordless, the latter used in either Standard or Xtra Power (XP) modes. Light transmission (average of irradiance, total energy, and light-emission profile) through the cylinders was measured (n=3). The polymerization kinetics of a resin cement light polymerized through the ceramic was monitored for 5 minutes (n=3). The degree of conversion was measured again after 72 hours. Data were individually analyzed with 2-way ANOVA and the Tukey HSD test (α=.05).

RESULTS

Valo at XP presented the highest values of irradiance and SmartLite the lowest, irrespective of the ceramic thickness. Regarding the total energy, XP showed the lowest values. The total energy and irradiance lessened with the increase in ceramic thickness. In general, except for Valo at XP, the ceramic thickness did not affect the degree of conversion. Valo at XP and interposing 2.0 mm ceramic resulted in the lowest values of Rp_max.

CONCLUSIONS

The reduction of total energy and irradiance by ceramic interposition had only a slight effect on polymerization kinetics.

Effects of light curing modes and ethanol-wet bonding on dentin bonding properties

OBJECTIVE

This study explored the effects of different light curing modes and ethanol-wet bonding on dentin bonding strength and durability.

METHODS

A total of 54 molars were randomly divided into three groups: Single Bond 2, Gluma Comfort Bond, and N-Bond. Based on the three light-curing modes and presence or absence of ethanol pretreatment, the samples were assigned to six subgroups: high-light mode, ethanol pretreatment+high-light mode, soft-start mode, ethanol pretreatment+soft-start mode, standard mode, and ethanol pretreatment+standard mode. All samples were bonded with resin based on the experimental groups. After 24 h and 6 months of water storage, a universal testing machine was used to measure microtensile bond strength. Scanning electron microscopy (SEM) was applied to observe mixed layer morphology.

RESULTS

The 24-h and 6-month microtensile bond strengths of the ethanol pretreatment groups were significantly higher than those of the non-ethanol pretreatment groups at the same light modes (P<0.05). With or without ethanol pretreatment, the microtensile bond strengths of the high-light modes were significantly lower than those of the soft-start modes and standard modes (P<0.05). The microtensile bond strengths of samples from the 6-month water storage group significantly decreased compared with those of samples from the 24-h water storage group (P<0.05). The soft-start groups and standard groups formed better mixed layers than the high-light mode groups, whereas the ethanol pretreatment groups formed more uniform mixed layers than those without ethanol pretreatment.

CONCLUSIONS

Ethanol-wet bonding technique, soft-start, and standard modes could improve dentin bonding properties.