ABSTRACT
Statement of the Problem: The adhesion of resin-modified glass-ionomer [RMGI] to composite resin has a very important role in the durability of sandwich restorations. Hydroxyapatite is an excellent candidate as a filler material for improving the mechanical properties of glass ionomer cement
Purpose: The aim of this study was to assess the effect of adding micro- and nano-hydroxyapatite [HA] powder to RMGI on the shear bond strength [SBS] of nanofilled and silorane-based composite resins bonded to RMGI containing micro- and nano-HA
Materials and Method: Sixty cylindrical acrylic blocks containing a hole of 5.5×2.5 mm [diameter × height] were prepared and randomly divided into 6 groups as Group 1 with RMGI [Fuji II LC] plus Adper Single Bond/Z350 composite resin [5.5×3.5 mm diameter × height]; Group 2 with RMGI containing 25 wt% of micro-HA plus Adper Single Bond/Z350 composite resin; Group3 with RMGI containing 25 wt% of nano-HA plus Adper Single Bond/Z350 composite resin; Group 4 with RMGI plus P90 System Adhesive/P90 Filtek composite resin [5.5×3.5 mm diameter × height]; Group 5 with RMGI containing 25 wt% of micro-HA plus P90 System Adhesive/P90Filtek composite resin; and Group 6 with RMGI containing 25 wt% of nano-HA plus P90 System Adhesive/P90 Filtek composite resin. The specimens were stored in water [37 degree C, 1 week] and subjected to 1000 thermal cycles [5 degree C/55 degree C]. SBS test was performed by using a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed by two-way ANOVA and Tukey test [p< 0.05]
Results: There were significant differences between groups 1 and 4 [RMGI groups, p= 0.025], and groups 3 and 6 [RMGI+ nano-HA groups, p= 0.012]. However, among Z350 and P90 specimens, no statistically significant difference was detected in the SBS values [p= 0.19, p= 0.083, respectively]
Conclusion: RMGI containing HA can improve the bond strength to methacrylate-based in comparison to silorane-based composite resins. Meanwhile, RMGI without HA has the best bond strength to silorane-based composite resins
ABSTRACT
Statement of the Problem: Composite resin may be used in different temperatures; it is crucial to determine the effect of temperature on mechanical properties of nanohybrid and silorane-based composite
Purpose: This in vitro study compared the flexural strength and modulus of elasticity of nanohybrid and silorane-based resin composite, at 4[degree]C, room temperature [25[degree]C], and 45[degree]C
Materials and Method: In this experimental study, 60 specimens were prepared in a metal split mold [2×2×25mm]. Two different resin composites, Filtek Z250 XT [3M/ ESPE] and Filtek P90 [3M/ESPE], were evaluated. The material were inserted into split molds at room temperature, 4[degree]C or 45[degree]C and cured with LED [1200 mW/cm2] for 20 seconds in four points [n=10]. Then, a three-point bending test was performed using a universal testing machine at a crosshead speed of 0.5 mm/min for measuring the flexural strength and flexural modulus of samples. The data were analyzed by the two-way ANOVA and Tukey test [p< 0.05]
Results: The mean highest flexural strength was observed at 45[degree]C, showing statistically significant difference with flexural strength at 4[degree]C [p= 0.0001] and 25[degree]C [p= 0.003] regardless of the type of resin composite. The flexural modulus at 45[degree]C was highest, showing the statistically significant difference with flexural modulus at 4[degree]C [p= 0.0001] and 25[degree]C [p= 0.002]. The flexural modulus was statistically different between nanohybrid and silorane-based resin composite [p= 0.01] in 25[degree]C and 45[degree]C, but there were no statistically significant differences between flexural strength of Filtek Z250 XT and Filtek P90 regardless of the temperatures [p= 0.062]. Conclusion: Preheating the resin composite at 45[degree]C improves flexural strength and modulus of nanohybrid and silorane-based resin composite. However, flexural strength and modulus of the tested materials were not affected by precooling. The flexural modulus of nanohybrid resin composite was significantly higher than siloranebased resin composite in 25[degree]C and 45[degree]C temperatures
ABSTRACT
Since bleaching causes changes on dental tissue and affects adhesive bond strengths, it is useful to recognize bonding systems which provide higher bond strengths on the dentin after bleaching. Forty eight human sound premolars were selected and sectioned 5mm below the CEJ. In order to do the bleaching process, the access cavity preparation was done and after the excavation of pulp tissue, and placement of the hybrid glass ionomer base at the apex, the teeth were bleached using the 35% hydrogen peroxide for 4 times. The teeth were then embedded in a self-cured acrylic resin and polished to obtain a flat dentin surface. The teeth were assigned into 4 groups according to the adhesive system used [n=12]: group 1: Single Bond [SB], group 2: Prime and Bond NT [P and B], group 3: Clearfil SE Bond [CSE] and group 4: Opti Bond [All in one] [OB]. The adhesive systems were used according to the manufacturer's instructions and a cylinder of composite resin Z100 was overlied. The teeth were thermocycled and the shear bond strength tests were performed in a universal testing machine with cross head speed of 1mm/min. CSE had the highest bond strength [15.18 MPa] and SB had the lowest one [8.10 MPa]. One Way ANOVA and independent sample t-test showed that the difference in bond strength values among the different types or generations of bondings was statistically significant except for the SB and P and B systems [P<0.05]. Within the limitations of this study, it is concluded that two step "self-etch" adhesives [CSE] are preferred to use for the teeth undergoing "Non vital tooth bleaching" with 35% hydrogen peroxide than the one step "self-etch" adhesives [OB] or two step "etch and rinse" adhesives [SB, P and B]