2006 Volume 49 Issue 3 Pages 468-480
Many types of light-curing units have been marketed in recent years. Light sources for use instead of the halogen lamp (HL) have been developed and used in the dental field, such as the xenon lamp (XL) and the blue Light Emitting Diode (LED). However, little is known about the influence of the polymerization and the adhesion of the newly developed fluoride-releasing one-step bonding systems to teeth by using different types of curing units. The purpose of this study was to investigate the tensile bond strength and nanohardness of a fluoride-releasing one-step resin bonding system cured by three types of light curing units. An LED curing unit (DC®] BlueLex, Yoshida), a conventional HL curing unit (Coltlux4, Coltene), and an XL curing unit (Apollo™ 95E, DMD) were tested. The light intensities of the light-curing units were measured. Two resin restorative systems: One-Up Bond F Plus/Palfique Estelite Σ(shade A3, Tokuyama Dental) and Fluoro Bond Shake One/Beautifil (shade A3, Shofu), were used. Bovine freshly extracted incisors were mounted in self-curing resin facial surfaces and were ground with 800 grit SiC paper. The enamel and dentin surfaces were tested according to each manufacturer's instructions, and the composite resins were condensed into a Teflon mold (1 mm height, 3 mm internal diameter). The adhesives were cured with the HL for 10 seconds, the XL for 6 seconds, and the LED for 10 seconds, respectively. The composite resins were cured with the HL for 40 seconds, the XL for 6 seconds, and the LED for 20 seconds. The specimens were stored in distilled water at 37℃ for 24 hours, and then the enamel and the dentin bond strength were tested in a tensile mode using universal testing machine at a cross-head speed of 1.0 mm/min (n=10). Selective SEM examinations were made on the interfaces of debonded specimens. Nano hardness of the resin adhesives was also measured using a nano-indentation tester (MZT-522) with 20 mN load. Means and standard deviation were calculated for all tests. One-way Anova and Scheffe's test (post-hoc test) were performed to compare the results of each material (p<0.05). As results, the tensile bond strength of Fluoro Bond Shake One/Beautifil was about 8.5-14.9 MPa to the enamel, and about 8.7-12.8 MPa to the dentin, which was not significantly different from One-Up Bond F Plus/Palfique Estelite Σ (enamel:8.3-20.6 MPa, dentin: 9.4-14.6 MPa). The tensile bond strength of Fluoro Bond Shake One/Beautifil with the XL curing was higher than the strengths obtained with the HL and the LED curing. The tensile bond strength of One-Up Bond F Plus/Palfique Estelite Σ with the XL curing was lower than the strengths obtained with the HL and the LED curing. However, there was no statistically significan difference in average tensile bond strength among the three light-curing units. The SEM images of debonded surfaces showed a higher number of cohesive failures in enamel and dentin for specimens. The most common failure pattern was mixed type (cohesive and adhesive failure). Nano-hardness in One-Up Bond F Plus cured with the XL was significantly lower than the hardness cured with the HL and the LED, however; the hardness in Fluoro Bond Shake One cured with the XL was significantly higher than that cured with the HL and the LED. The light intensity for the HL, the XL, and the LED was regulated in the range from 150-300 mW/cm^2, 1,200-1,350 mW/cm2 and 900-1,050 mW/cm2 by measuring the Light Checker (3M), respectively. These results suggested that compatibility between catalytic system and light sources was to be considered as well as energy of light-curing units in resin adhesives.
