Influence of abrasive particle size on surface properties of flowable composites.

The purpose of this investigation was to measure and compare both the surface roughness and gloss of flowable composites polished with standardized silicone carbide (SiC) papers. Four flowable and two conventional composites were used in this study. Polymerized specimens were subjected to a polishing procedure comprising 12 sequential steps from coarser to finer grits of SiC paper. At the initial polishing stage, flowable composites were more sensitive to the size of the polishing particles and thus yielded surfaces rougher than the conventional composites. Surface roughness became stable when polishing particles less than 13 microm size were used. However, although surface roughness was reduced, an esthetic gloss quality was not achieved on the resultant polished surface. On the influence of filler shape, composites with spherical fillers seemed to have the upper-hand advantage of attaining a high gloss by polishing. On the influence of polishing particle size, it was suggested that polishing should be completed with polishing particles less than 12 microm size so as to achieve clinically satisfactory surface roughness and gloss.

Effect of incremental filling technique on adhesion of light-cured resin composite to cavity floor.

The purpose of this study was to evaluate the effect of various incremental filling techniques on adhesion between composite and cavity floor using light-cured resin composite. Black ABS resin and hybrid resin composite were used as mold materials--instead of dentin--for the preparation of cavities, and standardized to 5x5x5 mm. Each cavity was then treated with a bonding system (Clearfil SE bond). Resin composite (Clearfil Photo Core) was placed on the bonding resin using different incremental filling techniques or in bulk and irradiated for a total of 80 seconds using a halogen light unit. Specimens were subjected to the micro-tensile bond test at a crosshead speed of 1 mm/min. Data were analyzed by two-way ANOVA. The results indicated that an incremental filling technique was more effective in improving adhesion to the cavity floor than a bulk filling technique.

Influence of elasticity on gap formation in a lining technique with flowable composite.

The purpose of this study was to investigate the effect of flowable composites as liners for direct composite restorations, with key focus on the elastic moduli of flowable and condensable composites. After treating the composite mold cavity surface with an adhesive system, one of the flowable composites was placed as a 1 mm-thick layer on the cavity floor and irradiated for 20 seconds. The rest of cavity was subsequently filled with a condensable composite and irradiated for 40 seconds. Gap formation at both interfaces--between the cavity floor and flowable composite, and between the flowable and condensable composites--was examined. No gaps were detected at the interface between the cavity floor and flowable composite. Gap percentage at the interface between the flowable and condensable composites was dependent on the difference in elastic modulus. It was concluded that flowable composite with high elastic modulus could inhibit gap formation between flowable and condensable composites.

Evaluation of the light intensity of high intensity light units.

PURPOSE: To determine the intensity of PAC (plasma arc curing) light compared with conventional QTH (Quartz tungsten halogen) light using a hardness test. METHODS: The spectral distribution of two light sources was analyzed with a spectroradiometer, after the light intensity was determined. AP-X composite was packed into a black mold (4 mm in diameter and 4 mm in depth) to prepare a cylindrical specimen. The irradiating conditions for the PAC unit in the current study were fixed at 6-second irradiation with 600 mW/cm2 (P600-6), 900 mW/cm2 (P900-6), 1200 mW/cm2 (P1200-6), 1500 mW/cm2 (P1500-6), 1800 mW/cm2 (P1800-6) and 40-second irradiation with 600 mW/cm2 (P600-40). The conventional irradiating condition for QTH was 600 mW/cm2 for 40 seconds (Q600-40). After storage in 37 degrees C water for 24 hours, the hardness of the resin composite was measured with a nanoindentation testing machine. Triplicate readings were made at a distance of every 0.5 mm down to 3.0 mm from the top irradiated surface. The comparison of means was statistically analyzed applying one-way ANOVA and Fisher's PLSD test at a significant level of P< 0.05. RESULTS: Although the peak height of the PAC lamp was different due to the light intensity, the waveforms were parallel with one another and the wavelength of peaks was located at the same number. The hardness value at a depth of 2.0 mm and at values of P1800-6 was not significantly different from the control.

Effect of cavity form on adhesion to cavity floor.

PURPOSE: To investigate the influence of cavity form, namely the C-factor, on adhesion at the interface on the cavity floor using light-cured resin-based composite. METHODS: Black ABS resin molds were used and were formed into five types of cavities having configuration factors that ranged from 0.5 to 5.0. The cavity size was standardized to cubes of 5 x 5 x 5 mm. Each cavity was treated using a bonding system (Clearfil SE Bond) and was filled with resin-based composite (Clearfil Photo Core). The composite was irradiated in the cavity and then cured for 40 seconds using a halogen light unit. Specimens were subjected to the microtensile test at a cross-head speed of 1 mm/minute. RESULTS: There was no significant difference in bond strength among the five different cavity forms. It was concluded that the difference of cavity forms had little effect on the adhesion to the cavity floor when using light-cured composites.

Effects of light intensity through resin inlays on the bond strength of dual-cured resin cement.

PURPOSE: To evaluate the influence of the light intensity, irradiation time, and thickness of the indirect restoration composite on the bond strength of dual-cured resin cement immediately after cementation, applying the resin coating technique. MATERIALS AND METHODS: Three hundred forty composite blocks as an adhesive surface and four thicknesses of indirect restoration composite disks were prepared. The surface of the composite blocks was coated with low-viscosity resin composite and immersed in water for 24 h. After immersion, dual-cured resin cement was applied to the resin-coated surface and the indirect restoration composite disks were placed on it. Light irradiation was performed through four thicknesses of indirect restoration composite disks with conventional halogen (40 s) and high intensity (10, 20, 40 s) light units. The specimens were stored in water at 37 degrees C for 10 min or 24 h, and the tensile bond test was performed. RESULTS: For the 1-mm composite thickness, there were no significant differences in the bond strengths between 10 min and 24 h after cementation with the four light curing methods. For the composite thicknesses of 3 or 4 mm, the bond strength 24 h after cementation was significantly higher than that at 10 min after cementation with conventional halogen (40 s) and high-intensity light units at 10 s and 20 s, but there was no significant difference with the high-intensity light unit applied for 40 s. CONCLUSION: The bond strength of dual-cured resin cement immediately after cementation could be greatly influenced by the irradiation time and the light intensity penetrating the indirect restoration composite.

Comparison of PAC and QTH light sources on polymerization of resin composites.

PURPOSE: To evaluate the polymerization shrinkage, Knoop hardness number (KHN) and compressive strength and to suggest a suitable time for irradiating resin composite restorations, when using a high-intensity light source. METHODS: Two restorative resin composites, UniFil F, and Clearfil AP-X were employed. A high-intensity light unit (more than 1000mW/cm2) with a xenon discharge lamp (Apollo 95E), which is generally called a plasma arc light-curing unit (PAC), was compared with a conventional light-curing unit fitted with a quartz-tungsten-halogen lamp (QTH) (GC Newlight VL2). The resin composites were exposed to the light in four ways. For QTH, the irradiation time was for 40 seconds (QTH 40 seconds). For PAC, 3 seconds (PAC 3 seconds), 3+3 seconds (PAC 3+3 seconds) and 3+3+3 seconds (PAC 3+3+3 seconds) was used. Polymerization shrinkage using the bonded disk technique developed by Watts, Knoop hardness number (KHN), and compressive strength were then determined. RESULTS: Two-way ANOVA revealed that the two materials for PAC 3+3 seconds and PAC 3+3+3 seconds made no difference in polymerization shrinkage compared to QTH 40 seconds (P < 0.001). The polymerization shrinkage of the materials cured by PAC for 3 seconds was significantly lower than those cured by QTH for 40 seconds in a range from 61% to 72%, by the PAC for 3 + 3 seconds in a range from 65% to 88%, and those by PAC 3+3+3 seconds in a range of 61% to 72% (P < 0.001). With regard to microhardness, the composites in PAC 3+3+3 seconds exposure made no difference in hardness compared with QTH 40 seconds (P < 0.001). PAC 3+3 seconds exposure gave hardness at less than 3.0 mm depth equivalent to that of the QTH 40 seconds. PAC 3 seconds at 2.0 mm depth produced inferior hardness compared with the QTH 40 seconds. The compressive strength for the PAC 3 seconds exposure was significantly lower than that of PAC 3+3 seconds, PAC 3+3+3 seconds and QTH 40 seconds for each material. CLINICAL SIGNIFICANCE: Irradiation by the high-intensity light source for 3 seconds provided significantly lower microhardness and compressive strength for light-cured resin composites. The 3+3+3 seconds repeated irradiation with the PAC unit and QTH 40 second values were not significantly different.

The effects of luting resin bond to dentin on the strength of dentin supported by indirect resin composite.

OBJECTIVES: The purpose of this study was to evaluate the effects of thickness and adhesion of three resin cements on the fracture resistance of indirect resin composite bonded to dentin. METHODS: A disk of resin composite used for indirect restorations was bonded to a disk of bovine dentin using three kinds of resin cements with various bonding procedures. The bonding procedures were planned into five groups according to the materials and methods, and subsequently subdivided into three groups according to the cement thickness (50, 150 and 500 microm) in each bonding procedure. The thickness of the resin cement and that of the resin composite disk was changed simultaneously while maintaining a total specimen thickness of 2 mm. The prepared specimens were then stored in water at 37 degrees C for 24h at which time they were trimmed to a size of 2 x 2 x 8 mm. The trimmed specimens were subjected to a three point bending test and the fracture load determined. The tensile bond strength of each bonding procedure was measured and the correlation to the fracture load evaluated. RESULTS: The fracture load was affected by the dentin bond strength. The effect of cement film thickness on the fracture load was negligible. SIGNIFICANCE: When an indirect restoration is adhered to the tooth substrate, the adhesion of the luting cement to the tooth substrate is very important for the fracture resistance of indirect resin composite.