Flávia Pires Rodrigues

Colour-stability and gloss-retention of silorane and dimethacrylate composites with accelerated aging

OBJECTIVES To evaluate the colour-stability and gloss-retention of silorane versus dimethacrylate composites exposed to accelerated aging from daylight radiation. METHODS Five disc-shaped specimens of photo-cured resin-composites were prepared and manually polished for each material (Filtek Silorane, Herculite XRV, Tetric Evoceram and QuiXfil). Colour and gloss were evaluated before and after periods (baseline, 24, 72, 120 and 192 h) of accelerated photo-aging in xenon light following ISO 7491:2000. Colour measurements were performed with a colourimeter according to the CIE-Lab colour-space. The colour change (DeltaE) for each time was calculated. The surface gloss was measured using a glossmeter. Results were evaluated using one-way ANOVA and Tukey tests (alpha=0.05). Correlations between logtime, DeltaE and gloss were evaluated using Pearsons correlation (alpha=0.05). RESULTS Materials generally decreased in L and a and increased in b. The strong exception was Filtek Silorane which maintained a and b. DeltaE was found to be a positive linear function of logtime for all materials. Materials varied in the magnitude and rate of increase of DeltaE with logtime: QuiXfil>Tetric EvoCeram>(Filtek Silorane>or=Herculite XRV). DeltaE remained<3.3 for Filtek Silorane and Herculite XRV. Gloss was found to be a negative linear function of logtime. Gloss was maximal in the sequence: Filtek Silorane approximately Tetric EvoCeram>Herculite XRV>QuiXfil. CONCLUSIONS Silorane gave the best overall performance in stability over time, compared to a set of representative dimethacrylate composites.

Effectiveness of self-adhesive luting cements in bonding to chlorhexidine-treated dentin

OBJECTIVES The aim was to investigate the microtensile bond strength (μ-TBS) and failure pattern of self-adhesive luting cements (SLC) to dentin pre-treated with different concentrations of chlorhexidine (CHX) solutions. METHODS The occlusal enamel was removed from 30 extracted sound human molars in order to expose a flat dentin. Resin-composite (Filtek Z250, 3M ESPE) discs (12 mm in diameter, 6.0mm thickness) were cemented to the smear layer-covered dentin using the SLC [RelyX U100, 3M ESPE (U100); Multilink Sprint, Ivoclar Vivadent (MS)] with 0.2% or 2.0% CHX solutions. Results were compared with the control, untreated dentin. Six groups were then created based on the SLC and dentin pre-treatment (n=5). After 24h of water storage, restored teeth were serially sectioned into beams with a cross-sectional area of 0.8mm(2) at the bonded interface. Subsequently, specimens were tested in tension with a crosshead speed of 0.5mm/min in a universal testing machine, and the failure patterns were classified. Two-way ANOVA and Tukeys tests were performed (α=0.05). Additionally, 18 teeth were subjected to energy-dispersive X-ray spectroscopy (EDS) analysis and micromorphology characterization of the smear layer-covered dentin and 0.2% or 2.0% CHX-treated dentin surfaces. RESULTS The μ-TBS obtained for both control groups were significantly higher, regardless of the CHX concentration and/or the cement used. Bond strengths were significantly higher for U100 than for MS, except when 2.0% CHX was applied. Fractographic analysis indicated that most failures in the control groups occurred cohesively in the SLC. Pre-treated dentin with 0.2% and 2.0% CHX solutions presented higher incidences of adhesive failures. EDS/SEM analysis exhibited varied concentrations of chlorine ions and crystal-shaped precipitates, depending upon the CHX concentration. SIGNIFICANCE Pre-treatment of dentin with 0.2% or 2.0% CHX adversely affects the bonding efficacy when associated with the SLCs tested.

Sequential software processing of micro-XCT dental-images for 3D-FE analysis

OBJECTIVES The aim was to describe a sequential software processing of mu-XCT molar-images for 3D-FE tooth/restoration model geometries based on a representative molar tooth, giving attention on each step of data-processing. This paper first gives an overview of a sequential processing and then applies the resulting model to the particular case. METHODS An intact mandibular molar was scanned using a micro-XCT instrument (1072, SkyScan, Belgium) in which 960 slices were obtained. Sixty-three non-adjacent bitmap slices were then optimally selected for model-creation. Enamel/dentin boundaries were clarified, for each slice, using image control-system software (ScanIP, Simpleware), generated a file which was sequentially converted into a mesh in a reconstruction software (ScanFE, Simpleware) and posteriorly converted into a STL-file (triangulated-2D-stereolithography). This was imported into a FE-software package (Patran, MSC.Software, USA) and all elements were re-meshed. From these elements, surfaces were created and exported to another FE-software (Hypermesh, Altair Hyperworks) to build the dental-cavities. Finally, the volumetric-mesh was created and the model was imported back to FE-software to apply the boundary-conditions, material-properties and initiate post-processing (using Patran and Marc, MSC Software). To demonstrate the use of the resulting model, this was applied to the particular case of a Class I restoration subjected to distributed loading. The analysis was performed as linear and structural and outputs of maximum principal (MP) and maximum shear (MS) stresses were then evaluated. RESULTS A 3D-model of a mandibular molar was processed without generating errors in the FE-package used. The maximum deviation between the tooth and the model was less than 0.1%. Stress concentrations were found at the surface where the load was applied and in the vicinity of the tooth-composite interface. SIGNIFICANCE The described procedure is a successful method able to produce a highly detailed 3D finite element model of restored molar teeth with any cavity configuration and combination of restorative materials and this method can also be used for other biological or biomaterials applications.

Methacrylate- and silorane-based composite restorations: Hardness, depth of cure and interfacial gap formation as a function of the energy dose

OBJECTIVES To investigate the influence of the energy dose on the hardness, polymerization depth, and internal adaptation of silorane and methacrylate-based posterior composites in Class II restorations with different bonding approaches. MATERIALS AND METHODS Class II preparations were made on the mesial and distal surfaces of extracted third molars and randomly distributed into 6 groups (n=20), according to the restorative systems [methacrylate-based composite: Filtek P60+Adper Single Bond 2 (etch-and-rinse adhesive) - P60/SB; Filtek P60+Adper Easy One (self-etching adhesive) - P60/EO; silorane-based composite: Filtek P90+P90 System Adhesive - P90 (self-etching adhesive)] and the energy dose (20 and 40 J/cm(2)). Resin composites were applied in two increments, individually photoactivated using an LED light-curing unit. After 24 h, all restorations were mesio-distally sectioned. Hardness was evaluated along the transversal section of the fillings (1-4 mm below the restoration surface) using a load of 50 g for 5 s. In order to evaluate the internal gap formation, specimens were air dried and 1% acid red propylene glycol solution was applied to the internal margins for 20 s. Specimens were then water rinsed, air dried, and digitally image recorded. The internal gap (%) was calculated as the ratio between the stained margins and the total length of the internal margin. Kruskal-Wallis test was conducted to evaluate internal gap formation, and three-way ANOVA and Tukeys test were performed to evaluate hardness/polymerization depth (α=0.05). RESULTS Regarding the internal gap formation, a significant difference was observed among all groups (P60/EO<P90<P60/SB), regardless of the energy dose. For 40 J/cm(2), a significant increase in gap formation was seen for P60/EO and P90 when compared to 20 J/cm(2). The KHN of both resin composites was not affected by the depth of evaluation, but the influence of the material was significant (P60>P90; p<0.05). The highest energy dose (40 J/cm(2)) produced significant increase in the KHN only for Filtek P90 (p<0.05). SIGNIFICANCE Although a higher energy dose produces a slight increase in hardness for the silorane based composite, it also increases the internal gap formation. Dose of 20 J/cm(2) seems to be more suitable as it provides reduced internal gaps and satisfactory hardness. In addition, gap formation seems to be a consequence of an underperformed bonding approach rather than the differences in the resin-composite formulation.

Fracture resistance of teeth restored with different resin-based restorative systems

The aim of the present study was to evaluate the fracture resistance of teeth restored with resin composite. Forty-eight maxillary premolar teeth were chosen and randomly divided to six groups: G1 (control): sound teeth; G2: MOD preparation, unrestored; G3: MOD + Adper Single Bond 2/P60; G4: MOD + Adper Easy One/P60; G5: MOD + P90 restorative system; G6: MOD + Adper Easy One/P90 Bond/P90. Specimens were subjected to compressive axial loading (0.5 mm/min). Flexural strength and the modulus of elasticity were also tested (n = 7). The only statistical equivalence with sound teeth was noted for G3 (p < 0.05). Flexural strength and the modulus of elasticity varied among the composites tested (n = 10). The reestablishment of the resistance to fracture in premolars subjected to Class II MOD preparations is restorative-system-dependent. The silorane restorative system is not able to recover the resistance to fracture.

Experimental and FE displacement and polymerization stress of bonded restorations as a function of the C-Factor, volume and substrate stiffness

OBJECTIVES To determine the free surface displacement of resin-composite restorations as a function of the C-Factor, volume and substrate stiffness, and to compare the results with interfacial stress values evaluated by finite element analysis (FEA). METHODS Surface displacement was determined by an extensometer using restorations with 4 or 6mm diameter and 1 or 2mm depth, prepared in either bovine teeth or glass. The maximum displacement of the free surface was monitored for 5 min from the start of photoactivation, at an acquisition rate of 1s(-1). Axisymmetric cavity models were performed by FEA. Structural stiffness and maximum stresses were investigated. RESULTS For glass, displacement showed a stronger correlation with volume (r=0.771) than with C-Factor (r=0.395, p<0.001 for both). For teeth, a stronger correlation was found with C-Factor (r=0.709; p<0.001) than with volume (r=0.546, p<0.001). For similar dimensions, stress and displacement were defined by stiffness. Simultaneous increases in volume and C-Factor led to increases in stress and surface displacement. Maximum stresses were located at the cavosurface angle, internal angle (glass) and at the dentine-enamel junction (teeth). The displacement of the restorations free surface was related to interfacial stress development. CONCLUSIONS Structural stiffness seems to affect the shrinkage stress at the tooth/resin-composite interface in bonded restorations. Deep restorations are always problematic because they showed high shear stress, regardless of their width. FEA is the only tool capable of detecting shear stress due to polymerization as there is still no reliable experimental alternative.

3D-FE analysis of soft liner-acrylic interfaces under shear loading.

AIM To analyze the distribution of stresses at the bond interface of Molloplast-B soft-liner attached to PMMA acrylic surface of different geometries (smooth and rough) and at different load-application distances by 3D-FEA modeling of typical shear-bond test. Methodology Three-dimensional finite element analysis (3D-FE) was performed utilizing Patran and Marc softwares (MSC.Software, USA). Models of Molloplast-B disk liner (diameter: 8mm, thickness: 3mm) bonded to smooth and rough acrylic geometries were designed. A total of 8 models (4 models for each surface geometry) were used to analyze Von Mises, maximum principal and shear stresses for the nodes corresponding to the vertical diameter of the acrylic-liner interface when applying a uniform shear-loading at different distances from the interface; 0.25, 0.5, 1, and 2mm. Materials properties were assumed to be isotropic, homogeneous, linear and elastic. RESULTS Shear loadings, at various distances from the bond-interfaces, produced different magnitudes of shear and tensile stresses. They were more uniform for both smooth and rough geometries when loading was applied at smaller distances from the interface (0.25 and 0.50). The maximum shear stress did not surpass maximum tensile stress in the areas subjected to the highest stress. These values were higher for the models with increased distances and bending moment associated with rough surfaces. CONCLUSIONS It can be concluded that in conducting shear bond tests, shear and tensile stresses are present regardless of the distance from the bond interface at which the shearing stress is applied. However, at increased distances from the bond interface, tensile stresses are greater than shear stresses. When shear stress is applied at shorter distances from the bond interface (0.25 or 0.50mm), and regardless of bond-interface geometry; there is more uniform stress distribution and lower effect of bending moment. However, in vitro studies of bond strengths between soft liners and acrylic substrates obtained by shear test should be approached with caution, considering the distance of load application and the surface treatment of the substrate as the most important factors that could interfere with the shear test values.

A method to investigate the shrinkage stress developed by resin-composites bonded to a single flat surface.

OBJECTIVES To purpose a method for predicting the shrinkage stress development in the adhesive layer of resin-composite cylinders that shrink bonded to a single flat surface, by measuring the deflection of a glass coverslip caused by the shrinkage of the bonded cylinders. The correlation between the volume of the bonded resin-composite and the stress-peak was also investigated. METHODS A glass coverslip deflection caused by the shrinkage of a bonded resin-composite cylinder (diameter: d=8 mm, 4 mm, or 2 mm, height: h=4 mm, 2 mm, 1 mm, or 0.5 mm) was measured, and the same set-up was simulated by finite element analysis (3D-FEA). Stresses generated in the adhesive layer were plotted versus two geometric variables of the resin-composite cylinder (C-Factor and volume) to verify the existence of correlations between them and stresses. RESULTS The FEA models were validated. A significant correlation (p<0.01, Pearsons test) between the stress-peak and the coverslip deflection when the resin-composites were grouped by diameter was found for diameters of 2 and 4 mm. The stress-peak of the whole set of data showed a logarithmic correlation with the bonded resin-composite volume (p<0.001, Pearsons test), but did not correlate with the C-Factor. SIGNIFICANCE The described method should be considered for standardizing the stress generated by the shrinkage of resin-composite blocks bonded to a single flat surface.

Interfacial integrity of low-shrinkage composite restorations related to the filling technique and consistency

Purpose: To evaluate the influence of filling techniques and consistency of low-shrinkage composites on the bond strength and internal gap formation in Class I bonded restorations. Two low-shrinkage restorative systems (N’Durance/Septodont and Filtek Silorane/3M ESPE) were used to restore Class I preparations. Bulk increment, two oblique increments or two horizontal increments were performed and Filtek Z350XT was used as a control. Each increment was photoactivated for 40 s and the restored teeth were then stored for 24 h at 37 °C before being longitudinally sectioned and the internal margins of the restorations dyed with 1% acid-red propylene glycol solution for 20 s. The specimens were water rinsed and digital images were recorded for the internal gap formation (%) analysis. Stick-shaped specimens were also tested in tension to evaluate the bond strength. Comparative consistency of unset composites was also performed. N’Durance exhibited the highest incidence of internal gaps amongst all the filling techniques. Filtek Silorane showed no significant difference of internal gap formation in comparison with Filtek Z350XT, regardless of the filling technique. Filtek Z350XT exhibited the highest bond strength and N’Durance the lowest when horizontally applied; bond strength of Filtek Silorane was not influenced by the filling technique. Both Filtek Z350XT and N’Durance presented lower consistency. Low-shrinkage composites seem to present equivalent or inferior bond strength and internal gap formation when compared to the methacrylate composite. The quality of the Class I preparation is dependent on the material and filling techniques.

Finite Element Analysis of Shear Versus Torsion Adhesive Strength Tests for Dental Resin Composites

Stress distributions in torsion and wire-loop shear tests were compared using three-dimensional (3-D) linear-elastic finite element method, in an attempt to predict the ideal conditions for testing adhesive strength of dental resin composites to dentin. The torsion test presented lower variability in stress concentration at the adhesive interface with changes in the proportion adhesive thickness/resin composite diameter, as well as lower variability with changes in the resin composite elastic modulus. Moreover, the torsion test eliminated variability from changes in loading distance, and reduced the cohesive fracture tendency in the dentin. The torsion test seems to be more appropriate than wire-loop shear test for testing the resin composite–tooth interface strength.