ABSTRACT
OBJECTIVES: To evaluate the microtensile bond strengths of different resin composites used as core materials around fiber posts. METHODS: Forty DT Light-Posts (RTD) were randomly divided into eight groups, according to the resin composite used. They included two core materials specifically developed for core build-up--Group 1: Core-Flo (Bisco Inc.) and Group 2: UniFil Core (GC Corp.); three hybrid composites--Group 3: Tetric Ceram (Ivoclar-Vivadent), Group 4: Gradia Direct (GC Corp.), Group 5: Bisfil 2B (Bisco, Inc.); and three flowable composites--Group 6: AEliteflo (Bisco, Inc.), Group 7: Filtek Flow (3M ESPE) and Group 8: UniFil Flow (GC Corp). A cylindrical plastic matrix was placed around the silanized post and filled with the respective resin composite. Each bonded post provided five to eight sticks for microtensile testing. Each stick was loaded to failure under tension at a cross-head speed of 0.5mm/min. One-way ANOVA and Tukey's test were used for statistical analysis. Scanning electron microscopy (SEM) was used to evaluate the interface of the fractured sticks. RESULTS: Resin composites exhibited a significant influence on microtensile bond strength (p<0.05). Core-Flo showed the highest bond strength (11.00+/-0.69 MPa) although it was not statistically significantly different from all groups, except from the flowable composites. Under SEM, all the composites adapted well to the fiber post, with a variable extent of voids observed along the fractured composite interfaces. SIGNIFICANCE: Although good adaptation to the post surface was achieved, bond strength to fiber post remains relatively weak. Core build-up and hybrid composites are better alternatives to flowable composites as core build-up materials.
Subject(s)
Composite Resins/chemistry , Dental Bonding , Dental Materials/chemistry , Post and Core Technique , Barium Compounds/chemistry , Bisphenol A-Glycidyl Methacrylate/chemistry , Dental Prosthesis Design , Dental Stress Analysis/instrumentation , Humans , Materials Testing , Microscopy, Electron, Scanning , Post and Core Technique/instrumentation , Silanes/chemistry , Silicon Dioxide/chemistry , Stress, Mechanical , Surface Properties , Tensile StrengthABSTRACT
OBJECTIVES: To verify whether substrate, shape, or thickness of microtensile specimens have a significant influence on their measured bond strength. METHODS: Sixty-four extracted molars provided microtensile specimens, which were prepared on enamel and dentin, in different shapes and thicknesses. The teeth were randomly divided into 16 groups (n = 4). Groups 1-8 included hourglass-shaped specimens. In Groups 1-4 specimens were prepared from enamel and in a thickness at the bonding interface of 0.5 mm x 0.5 mm, 1 mm x 1 mm, 1.5 mm x 1.5 mm, and 2 mm x 2 mm, respectively. In these same thicknesses, hourglasses were trimmed in Groups 5-8, but the specimens were prepared from dentin. Groups 9-16 included specimens obtained following the non-trimming technique. Groups 9-12 provided enamel sticks in the four evaluated thicknesses. In these same thicknesses and shape but from dentin were cut the specimens of Groups 13-16. Two specimens from each group were viewed using a scanning electron microscope. On the other ones, microtensile bond strength was measured and the values were statistically analyzed. RESULTS: Substrate, shape, and thickness of the specimens had a significant effect on their recorded bond strength (p < 0.05). Higher bond strength values were recorded by dentin versus enamel specimens and by sticks versus hourglasses. Also, bond strength decreased as specimen thickness increased. SEM analysis revealed that the trimmed specimens, especially if from enamel, often exhibited lines of fracture in the area of action of the bur. SIGNIFICANCE: It seems advisable to avoid the trimming action particularly on enamel specimens. If the hourglass shape is preferred, the cross-sectional area should not exceed 1 mm x 1 mm.
