Dynamic elastic modulus of 'packable' composites

Teeth Restored with Bulk–Fill Composites and Conventional Resin Composites; Investigation of Stress Distribution and Fracture Lifespan on Enamel, Dentin, and Restorative Materials via Three-Dimensional Finite Element Analysis

Objectives: the aim of this study was to examine the stress distribution of enamel, dentin, and restorative materials in sound first molar teeth with restored cavities with conventional resin composites and bulk–fill composites, as well as to determine their fracture lifetimes by using the three-dimensional finite element stress analysis method. Materials and Methods: an extracted sound number 26 tooth was scanned with a dental tomography device and recorded. Images were obtained as dicom files, and these files were transferred to the Mimics 12.00 program. In this program, different masks were created for each tooth tissue, and the density thresholds were adjusted manually to create a three-dimensional image of the tooth, and these were converted to a STL file. The obtained STL files were transferred to the Geomagic Design X program, and some necessary adjustments, such as smoothing, were made, and STP files were created. Cavity preparation and adhesive material layers were created by transferring STP files to the Solidworks program. Finally, a FE model was created in the ABAQUS program, and stress distributions were analyzed. Results: when the bulk–fill composite and conventional resin composite materials were used in the restoration of the cavity, the structures that were exposed to the most stress as a result of occlusal forces on the tooth were enamel, dentin, restorative material, and adhesive material. When the bulk–fill composite material was used in restoration, while the restorative material had the longest fracture life as a result of stresses, the enamel tissue had the shortest fracture life. When the conventional resin composite material was used as the restorative material, it had the longest fracture life, followed by dentin and enamel. Conclusion: when the bulk–fill composite material was used instead of the conventional resin composite material in the cavity, the stress values on enamel, dentin, and adhesive material increased as a result of occlusal forces, while the amount of stress on the restorative material decreased. In the fracture analysis, when the bulk–fill composite material was used instead of the conventional resin composite material, a decrease in the number of cycles required for the fracture of enamel, dentin, and restorative materials was observed as a result of the forces generated in the oral cavity.

Crack propensity of different direct restorative procedures in deep MOD cavities

OBJECTIVE

The purpose was to evaluate the crack formation associated with different direct restorative procedures of the utilized resin composites (RC) right after and 1 week later of the restoration.

MATERIALS AND METHODS

Eighty intact, crack-free third molars with standard MOD cavities were included in this in vitro study and randomly divided into four groups of 20 each. After adhesive treatment, the cavities were restored either with bulk (group 1) or layered (group 2) short-fiber-reinforced resin composites (SFRC); bulk-fill RC (group 3); and layered conventional RC (control). Right after the polymerization and a week later, crack evaluation on the outer surface of the remaining cavity walls was performed with a transillumination method utilizing the D-Light Pro (GC Europe) with the "detection mode." Between- and within-groups comparisons Kruskal-Wallis and Wilcoxon tests were used, respectively.

RESULTS

Post-polymerization crack evaluation showed significantly lower crack formation in SFRC groups compared to the control (p<0.001). There was no significant difference within SFRC groups and non-SFRC groups (p=1.00 and p=0.11, respectively). Within group comparison revealed significantly higher number of cracks in all groups after 1 week (p≤0.001), however, only the control group differed significantly from all the other groups (p≤0.003).

CONCLUSIONS

Post-polymerization shrinkage induced further crack formation in the tooth 1 week after the restoration. SFRC was less prone to shrinkage-related crack formation during the restorative procedure; however, after 1 week, besides SFRC, bulk-fill RC also showed less prone to polymerization shrinkage-related crack formation than layered composite fillings.

CLINICAL RELEVANCE

SRFC can decrease the shrinkage stress-induced crack formation in MOD cavities.

Young's modulus and Poisson ratio of composite materials: Influence of wet and dry storage

In the oral environment dental materials are subject to a wet condition what might in time change their elastic properties. In this article, we evaluated the influence of the storage condition (dry versus wet) on the Young's modulus and the Poisson ratio in compression of three composite materials. The data of the Young's modulus and Poisson ratio published of dental composite materials are not always comparable, due to different test methods and sample dimensions influencing the results. Therefore, we established the degree of exactness of the results out of the test set-up used. Since the present study depicted differences of the properties after dry and wet storage, the elastic properties should be measured after wet storage. The bonding between the matrix and the filler particles showed to have an influence on the elastic properties and on the influence of a wet environment.

Cuspal Deflection in Premolar Teeth Restored with Bulk-Fill Resin-Based Composite Materials

The present study investigated the effect of three high-viscosity bulk-fill resin-based composite materials on cuspal deflection in natural teeth. Thirty-two sound maxillary premolar teeth with large slot mesio-occlusal-distal cavities were distributed into four groups (n=8). Three groups were restored with bulk-fill resin composite materials (Tetric EvoCeram Bulk Fill, Ivoclar Vivadent, Schaan, Liechtenstein; x-tra fil, VOCO, Cuxhaven, Germany; and SonicFill, Kerr, Orange, CA, USA) in a single 4-mm increment. The conventional composite group, Filtek Z100 (3M ESPE, St Paul, MN, USA), was used to restore the cavities in 2-mm increments. Cusp deflection was recorded postirradiation using a Nikon measurescope UM-2 (Nikon, Tokyo, Japan) by measuring the changes in the bucco-palatal widths of the teeth at five minutes, 24 hours, and 48 hours after completion of the restorations. Cuspal deflection was significantly higher in the conventional composite than in the Tetric EvoCeram Bulk Fill (p=0.0031), x-tra fil (p=0.0029), and SonicFill Bulk (p=0.0002) groups. There were no significant differences in cuspal deflection among the three bulk-fill materials (all p&lt;0.05). In conclusion, all the investigated bulk-fill resin composites exhibited cuspal deflection values that were smaller than those associated with a conventional incrementally placed resin composite.

Dynamic thermo-mechanical properties of various flowable resin composites

Background

This study compared the storage modulus (E’), the loss modulus (E’’) and the loss tangent (tan δ) of various flowable resin composites.

Material and Methods

Grandio Flow (GRF), GrandioSo Heavy Flow (GHF), Filtek Supreme XTE (XTE) and Filtek Bulk Fill (BUL) flowable resins and Clinpro Sealant (CLI) ultra-flowable pit and fissure sealant resin were used. 25 samples were tested using a dynamical mechanical thermal analysis system in bending mode. Measurements were taken within a temperature range of 10 to 55°C. The results were statistically analyzed using mixed-effect and repeated-measure analysis of variance followed by paired multiple comparisons.

Results

For all the materials, the E’ values decrease with temperature, whereas the tan δ values increase. Irrespective of the temperature, GHF and GRF present E’ and E’’ values significantly higher than all the other materials and CLI presents values significantly lower than all the other materials. Observation of the values for all the materials reveals a linear progression of the tan δ values with temperature.

Conclusions

A variation in temperature within a physiological range generates modifications in mechanical properties without damaging the material, however. Filler content in volume terms appears to be the crucial parameter in the mechanical behavior of tested materials.

Key words:Dynamic mechanical thermal analysis, elastic modulus, filler content, flowable resin composites, loss modulus, loss tangent.

Filler Content, Surface Microhardness, and Rheological Properties of Various Flowable Resin Composites

Objectives:

The objectives of this study were to determine the filler content, the surface microhardness (at baseline and after immersion in water for 2 years), and the rheological properties of various flowable resin composites.

Methods:

Three flowable resin composites (Grandioso Heavy Flow [GHF], Grandio Flow [GRF], Filtek Supreme XTE Flow [XTE]), one pit and fissure sealant resin composite (ClinPro [CLI]), and three experimental flowable resin composites with the same matrix and a variable filler content (EXPA, EXPB, EXPC) were tested. The filler content was determined by calcination. The Vickers surface microhardness was determined after polymerization and then after immersion in distilled water at 37°C for 7, 60, 180, 360, and 720 days. The rheological measurements were performed using a dynamic shear rheometer.

Results:

The determined filler contents differed from the manufacturers' data for all the materials. The materials with the highest filler content presented the highest microhardness, but filler content did not appear to be the only influencing parameter. With respect to the values recorded after photopolymerization, the values were maintained or increased after 720 days compared with the initial microhardness values, except for GHF. For the values measured after immersion for 7 days, an increase in microhardness was observed for all the materials over time. All the materials were non-Newtonian, with shear-thinning behavior. At all the shear speeds, GRF presented a lower viscosity to GHF and XTE.

Conclusions:

GRF presented a low viscosity before photopolymerization, associated with high filler content, thereby providing a good compromise between spreadability and mechanical properties after photopolymerization.

Effect of short glass fiber/filler particle proportion on flexural and diametral tensile strength of a novel fiber-reinforced composite

PURPOSE

To evaluate the effect of glass fiber/filler particles proportion on flexural strength and diametral tensile strength of an experimental fiber-reinforced composite.

METHODS

Four experimental groups (N=10) were created using an experimental short fiber-reinforced composite, having as a factor under study the glass fiber (F) and filler particle (P) proportion: F22.5/P55 with 22.5 wt% of fiber and 55 wt% of filler particles; F25/P52.5 with 25 wt% of fiber and 52.5 wt% of filler particles; F27.5/P50 with 27.5 wt% of fiber and 50 wt% of filler particles; F30/P47.5 with 30 wt% of fiber and 47.5 wt% of filler particles. The experimental composite was made up by a methacrylate-based resin (50% Bis-GMA and 50% TEGDMA). Specimens were prepared for Flexural Strength (FS) (25 mm × 2 mm × 2 mm) and for Diametral Tensile Strength (DTS) (3×6 Ø mm) and tested at 0.5 mm/min in a universal testing machine.

RESULTS

The results (in MPa) showed significance (different superscript letters mean statistical significant difference) for FS (p<0.009) and DTS (p<0.001)--FS results: F22.5/P55: 217.24±20.64(B); F25/P52.5: 245.77±26.80(AB); F27.5/P50: 246.88±32.28(AB); F30/P47.5: 259.91±26.01(A). DTS results: F22.5/P55: 21.82±4.42(B); F25/P52.5: 22.00±7.40(B); F27.5/P50: 18.63±4.41(B); F30/P47.5: 31.05±2.97(A). In SEM analysis, areas without fiber reinforcement demonstrated to be more prone to the presence of bubbles and crack development. The group F30/P47.5 showed areas with a great quantity of fibers without empty spaces for crack propagation.

CONCLUSION

Increasing fiber content results in higher flexural and diametral tensile strength of an experimental composite reinforced with glass fibers.

Investigation of the correlation between the different mechanical properties of resin composites

The aim of this study was to investigate the relationship between the different mechanical properties with the filler fraction of various resin composites. Mechanical properties of eighteen different resin composites were investigated in this study; flexural strength (FS), flexural modulus (FM), fracture toughness (FT), compressive strength (CS), diametral tensile strength (DTS), Barcol hardness (BH), Vickers hardness (HV), and Knoop hardness (HK). The mean values of mechanical properties and the filler fractions (V(f )) obtained from the literature and the manufacturer were analyzed using Pearson's correlation test at p<0.01. The relationships were compared with the data retrieved from previous studies. Strong correlations between Vf and BH/HV/HK and V(f) and FM were evident in the results of the present study and these results were supported by the retrieved data from previous studies. The other relationships between mechanical properties, such as that between FS and FM and between CS and HV were not significant.

Contact fatigue response of porcelain-veneered alumina model systems

Fatigue damage modes and reliability of hand-veneered (HV) and over-pressed (OP) aluminum-oxide layer structures were compared. Influence of luting cement thickness on mechanical performance was investigated. Sixty-four aluminum-oxide plates (10 × 10 × 0.5 mm) were veneered with hand built-up or pressed porcelain (0.7 mm) and adhesively luted (50- or 150-μm cement thickness) to water-aged composite resin blocks (12 × 12 × 4 mm). Single-load-to-failure and fatigue tests were performed with a spherical tungsten carbide indenter (d = 6.25 mm) applied in the center of the veneer layer. Specimens were inspected with polarized-reflected-light and scanning electron microscopy. Use-level probability Weibull curves were plotted with two-sided 90% confidence bounds, and reliability at 75,000 cycles and 250 N load was calculated. For all specimens but two OP with 50-μm cement thickness, failure was characterized by flexural radial cracks initiating at the bottom surface of the alumina core and propagating into the veneering porcelain before cone cracks could extend to the porcelain/alumina interface. HV specimens showed higher reliability compared to OP. Those with 50-μm cement thickness were more reliable relative to their 150-μm counterparts (HV_50 μm: 95% (0.99/0.67); HV_150 μm: 55% (0.92/0.01); OP_50 μm: 69% (0.84/0.48); OP_150 μm: 15% (0.53/0.004)). Similar failure modes were observed in HV and OP specimens. Radial cracks developing in the core and spreading into the veneer are suggested to cause bulk fracture, which is the characteristic failure mode for alumina core crowns. However, the highest resistance to fatigue loading was found for the HV specimens with thin cement thickness, while the lowest occurred for the OP with thick cement layer.

Effects of different ceramic and composite materials on stress distribution in inlay and onlay cavities: 3-D finite element analysis

To reduce loss of tooth tissue and to improve esthetic results, inlay and onlay restorations are good treatment choices for extensive cavities in posterior teeth. The aim of this paper was to evaluate, by means of three-dimensional finite element analysis, the effects of restorative material and cavity design on stress distribution in the tooth structures and restorative materials. Two different nanofilled composites and two different all-ceramic materials were used in this study. A permanent molar tooth was modeled with enamel and dentin structures. 3-D inlay and onlay cavity designs were created. Von Mises, compressive, and tensile stresses on the restorative materials, core materials, enamel, and dentin were evaluated separately. On the effect of restorative material, results showed that in the case of materials with low elastic moduli, more stress was transferred to the tooth structures. Therefore, compared to the nanofilled composites, the all-ceramic inlay and onlay materials tested transferred less stress to the tooth structures. On the effect of cavity design, the onlay design was more efficacious in protecting the tooth structures than the inlay design.

Effect of light-curing units and activation mode on polymerization shrinkage and shrinkage stress of composite resins

The aim of this study was to evaluate the polymerization shrinkage and shrinkage stress of composites polymerized with a LED and a quartz tungsten halogen (QTH) light sources. The LED was used in a conventional mode (CM) and the QTH was used in both conventional and pulse-delay modes (PD). The composite resins used were Z100, A110, SureFil and Bisfil 2B (chemical-cured). Composite deformation upon polymerization was measured by the strain gauge method. The shrinkage stress was measured by photoelastic analysis. The polymerization shrinkage data were analyzed statistically using two-way ANOVA and Tukey test (p≤0.05), and the stress data were analyzed by one-way ANOVA and Tukey's test (p≤0.05). Shrinkage and stress means of Bisfil 2B were statistically significant lower than those of Z100, A110 and SureFil. In general, the PD mode reduced the contraction and the stress values when compared to CM. LED generated the same stress as QTH in conventional mode. Regardless of the activation mode, SureFil produced lower contraction and stress values than the other light-cured resins. Conversely, Z100 and A110 produced the greatest contraction and stress values. As expected, the chemically cured resin generated lower shrinkage and stress than the light-cured resins. In conclusion, The PD mode effectively decreased contraction stress for Z100 and A110. Development of stress in light-cured resins depended on the shrinkage value.

A two-stage shape optimization process for cavity preparation

OBJECTIVES

Clinical data indicate that previously restored teeth are more likely to fracture under occlusal loads. The reason for this is attributed to the high stresses at the tooth-restoration interface, especially following debonding of the restoration from the tooth. This work aims to minimise these interfacial stresses by optimizing the cavity shape using modern shape optimisation techniques.

METHODS

Shape optimisation methods based on the principle of biological adaptive growth were incorporated into a finite element program and used to optimize the design of cavity preparations as previous work had successfully used one such method to minimise stresses at the internal line angles of conventional restorations with defective bonds. The overall shapes of the cavity preparations were maintained while the profiles of the internal line angles were modified. In the present study, the overall shape of the cavity preparation was also subject to modification in the optimization process. A topological optimization method which placed the restorative material according to the stress distribution was first used to obtain a draft design for the cavity shape, assuming perfect bonding at the tooth-restoration interface. The draft shape was then refined using the method employed in the previous study, to allow for deterioration in the interfacial bond strength. These optimization methods were incorporated into the commercial finite element package ABAQUS as a User Material Subroutine (UMAT) to automate the optimization process.

RESULTS

Compared with the conventional design, the stress level at the tooth-restoration interface in the optimized design was reduced significantly, irrespective of the bonding condition.

CONCLUSIONS

Finite-element based shape optimization methods provide a useful tool for minimizing the interfacial stresses in dental restorations. The longevity of restored teeth using the optimized designs is therefore expected to be prolonged.

Dynamic thermomechanical properties and sorption characteristics of two commercial light cured dental resin composites

OBJECTIVES

The first objective of this work is the study by DMTA of viscoelastic properties (E', E'', tandelta, Tg) of two current dental resin composites Tetric EvoCeram (nanohybrid) and Heliomolar (microfilled) in dry condition and in water for up to 30 days. The second objective is to determine the sorption characteristics of these composites in water and ethanol/water solution 75vol.%.

METHODS

For DMTA the bar-shaped specimens divided into five groups of three samples each. The first group consisted of dry samples measured 1h after curing. The second and third group consisted of samples, which had been heated in air at 80+/-1 degrees C for 1 day or had been stored in distilled water at 80+/-1 degrees C for 1 day. The fourth and fifth group consisted of samples, which had been stored in distilled water at 37+/-1 degrees C for periods 1 and 7 days correspondingly. Also specimen discs (15mm in diameter and 1mm in thickness) were immersed in water or a 75vol.% ethanol/water solution at 37+/-1 degrees C. At fixed time intervals they were removed, blotted dry to remove excess liquid, weighted and returned to the liquid. This process continued for 30 days.

RESULTS

The viscoelastic properties (E', E'', tandelta, Tg) of the two composites treated under different conditions were recorded and compared. Also the mass uptake, diffusion coefficient, solubility and volumetric changes for immersion of composites in water and ethanol/water solution 75vol.% at 37+/-1 degrees C were determined.

SIGNIFICANCE

Tetric EvoCeram a nanohybrid composite with similar about resin matrix with Heliomolar which is a microfilled showed better dynamic thermomechanical properties and sorption characteristics than Heliomolar.

Influence of restorative technique on the biomechanical behavior of endodontically treated maxillary premolars. Part II: strain measurement and stress distribution

STATEMENT OF PROBLEM

Unresolved controversy exists concerning the preferred cavity design and restorative technique used to restore endodontically treated maxillary premolars to minimize strain and improve stress distribution under occlusal load.

PURPOSE

The purpose of this study was to analyze the influence of cavity design and restorative material on strain measurement and stress distribution in maxillary premolars under occlusal loading conditions, and correlate these influences with the failure modes analyzed in Part I.

MATERIAL AND METHODS

For the strain gauge test, 21 additional specimens were prepared as described in Part 1 of this study (n=3). Two strain gauges were fixed on the buccal (B) and palatal (P) cusps of each specimen with cyanoacrylate adhesive. The specimens were submitted to continuous axial compression loading at a speed of 0.5 mm/min, using a 6-mm sphere, to a maximum limit of 150 N in a universal testing machine. Total strain values were obtained by combining the B and P cusp strain values. These values were submitted to 2-way ANOVA and the Dunnet test (alpha=.05). For finite element analyses, 7 numerical 2-D models were generated: MODd, direct mesio-occlusal-distal preparation; MODi, indirect mesio-occlusal-distal preparation; AM, MODd restored with amalgam; CR, MODd restored with composite resin; LPR, MODi restored with laboratory-processed composite resin; and LGC, MODi restored with leucite-reinforced glass ceramic; each corresponding to 1 of the experimental groups tested in Part I of this study. The models were analyzed with finite element software, using the von Mises criteria for stress distribution analysis.

RESULTS

With the strain gauge test, MODd, MODi, and AM groups showed significantly higher strain values than the CR, LPR, and LGC. Finite element analyses revealed that tooth structure removal and the type of restorative material altered the stress distribution pattern. The MODd, MODi, AM, and LPR models showed higher stress concentration within the tooth structure.

CONCLUSIONS

The specimens with adhesive restorations were shown to behave in a manner similar to the biomechanical behavior of healthy teeth, while the behavior of those restored with amalgam restorations was more like that observed for teeth with nonrestored cavity preparations. These results directly correlate with the fracture mode results obtained in Part I of this study.

Class I and Class II restorations of resin composite: An FE analysis of the influence of modulus of elasticity on stresses generated by occlusal loading

OBJECTIVES

It was the aim of the study to analyze by the FE method stresses generated in tooth and restoration by occlusal loading of Class I and Class II restorations of resin composite. On the basis of available information on the influence of the modulus of elasticity, the research hypothesis was that the marginal stresses would decrease with increasing modulus of elasticity of the restoration.

METHODS

A cylindrical tooth was modelled in enamel and dentin and fitted with a Class I or a Class II restoration of resin composite. In one scenario the restoration was bonded to the tooth, in another the restoration was left nonbonded. The resin composite was modelled with a modulus of elasticity of 5, 10, 15 or 20 GPa and loaded occlusally with 100 N. By means of the soft-ware program ABAQUS the von Mises stresses in enamel and dentin were calculated.

RESULTS

In the bonded scenario, the maximum stresses in the enamel were located at the occlusal margins (range 7-11 MPa), and in the dentin centrally at the pulpal floor (range 3.4-5.5MPa). The stresses decreased with increasing modulus of elasticity of the resin composite. In the nonbonded scenario, the stresses were higher in the dentin and lower in the enamel than in the bonded cases, and the influence of the modulus of elasticity was less pronounced. The marginal stresses in the restoration were below 6 MPa in the bonded scenario and below 3 MPa in the nonbonded scenario.

SIGNIFICANCE

Occlusal restorations of resin composite should have a high modulus of elasticity in order to reduce the risk of marginal deterioration.

Effect of restoration size on the clinical performance of posterior "packable" resin composites over 18 months

Fifty predominantly moderate or large Class II or multiple-surface Class I resin composite restorations were placed in molars under rubber dam isolation. The restorative systems used were: Alert Condensable (Jeneric/Pentron) and SureFil (Dentsply/Caulk). The restorations were classified according to size, with 7 small, 25 moderate and 18 large, of which 8 were cusp replacement restorations. Baseline, 6, 12 and 18-month double-blinded clinical evaluations were carried out using modified USPHS criteria. The independent variables: restorative material, restoration size and three other clinical factors, were tested using a Multiple Logistic Regression procedure to determine if any were predictive of failure. Of the 50 restorations, four failed by the 18-month recall, three failed due to fracture of the restoration and one due to secondary caries. Both restorative systems demonstrated a 92% success rate. No association between restoration size (p = 0.99) or restorative material (p = 0.65) and failure was found. Similarly, the additional variables, occlusal contact type, presence of occlusal wear facets and first or second molar, were not predictive of failure.

Micromechanics for Fiber Volume Percent With a Photocure Vinyl Ester Composite

Micromechanics for fiber volume percent (Vf) from 0.0Vf to 54.0 Vf were conducted using (3 mm long × 9 µm diameter) high-purity quartz fibers in a visible-light vinyl ester particulate-filled photocure resin. MTS fully articulated four-point bend fixtures were used with a 40 mm test span and 50 × 2 × 2 mm3 sample dimensions. Specimens were tested following the combined modified ASTM standards for advanced ceramics ASTM-C-1161-94 and polymers ASTM-D-6272-00 for modulus, flexural strength, and yield strength. Experimental data provided reliable statistical support for the dominant fiber contribution expressed through the rule-of-mixtures theory as a valid representation of micromechanical physics. The rule-of-mixtures micromechanics described by Vf could explain 92, 85, and 78% of the variability related to modulus, flexural strength, and yield strength respectively. Statistically significant improvements with fiber addition began at 10.3Vf for modulus, 5.4Vf for flexural strength, and 10.3Vf for yield strength, p < 0.05. In addition, correlation matrix analysis was performed for all mechanical test data. An increase in Vf correlated significantly with increases in modulus, flexural strength, and yield strength as measured by the four-point bending test, p < 10-10. All mechanical properties in turn correlated highly significantly with one another, p < 10-9.

Comparative study of the wear behavior of composites for posterior restorations

This investigation sought to compare the abrasive wear rates of resin composites designed for posterior applications. Seventy-five specimens were fabricated with conventional hybrid (Charisma and Filtek Z250) or packable composites (Filtek P60, Solitaire II and Tetric Ceram HB), according to a randomized complete block design (n = 15). Specimens were finished and polished metallographically and subjected to abrasive wear which was performed under a normal load of 13N at a frequency of 2 Hz using a pneumatic device (MSM/Elquip) in the presence of a mucin-containing artificial saliva. Wear was quantified profilometrically in five different locations of each specimen after 1,000, 5,000, 10,000, 50,000 and after every each 50,000 through 250,000 cycles. A split-plot ANOVA showed a significant difference between the wear resistance of composites (alpha = 0.05). Tukey's test ascertained that while the composites Filtek Z250 and Charisma wore significantly less than any other of the materials tested, Tetric Ceram HB experienced the greatest wear rates. Filtek P60 and Solitaire II showed intermediate rates of material removal. The wear pattern of composites proved to be biphasic with the primary phase having the faster wear rate. In conclusion, packable resin composites may not have superior wear compared to conventional hybrid composites.

Shrinkage stress in light-cured composite resins: influence of material and photoactivation mode

OBJECTIVES

The aim of this study was to record the effect of composite type and photoactivation mode on the stresses resulting from polymerization of five established composite resins: packable (Solitaire, Solitaire 2), micro-hybrid (Aelitefil, Z100) and hybrid (Clearfil AP-X).

METHODS

A mechanical testing machine was used to record the polymerization contraction stress (MPa) of cylindrical composite specimens (d=5mm; h=2mm; C-factor=1.25) at 0.1s intervals over a period of 400s. The samples were photopolymerized using a halogen light curing device under two types of light exposure: group 1, Standard (800mW.cm(-2)x60s); group 2, Exponential (logarithmic increase from 150 to 800mW.cm(-2) over 15s+800mW.cm(-2)x45s). The stress rate (SR: slope(MPa>0-60s)) and the maximum shrinkage stress (MSS: MPa(400s)) of each material (five replications) were statistically analysed by one-way ANOVA/Scheffe's test and Pearson's correlation procedure (alpha=0.05). Finally, Student's t-test (two matched series) enabled the assessment of the effect of the irradiation method on the results.

RESULTS

For group 1, in decreasing order, the MSS was 1.51+/-0.07MPa (Solitaire) statistically equivalent to 1.45+/-0.06MPa (Aelitefil), 1.29+/-0.08MPa (Solitaire 2), and 1.04+/-0.03MPa (Z100) statistically equivalent to 0.92+/-0.05MPa (Clearfil AP-X). Z100 showed the highest SR (0.045+/-6x10(-3)) and Solitaire, the lowest (0.017+/-2x10(-3)). There was no correlation between SR and MSS (r<-0.33, p<0.05). For group 2, the MSS and SR values were distributed in a similar way to those from group 1. There was a negative correlation between SR and MSS (r<-0.43 and p<0.01). The exponential ramp successfully reduced the MSS (-3.9%) and SR (-11%) values.

SIGNIFICANCE

There is no relationship between composite resin type, stress rate and shrinkage stress levels. The slower stress rate development, resulting from ramped light intensity, helped slightly to reduce the maximum polymerization stress.

Clinical Evaluation of a Nanofilled Composite in Posterior Teeth: 12-month Results

Nanofilled resin composite showed excellent clinical performance, similar to microhybrid and packable composites after 12-months.

Fatigue of packable dental composites

OBJECTIVE

The purpose of the study was to measure the fatigue properties of four dental resin composites using a dynamic mechanical analysis and to relate the results with viscoelastic properties.

METHODS

Dynamic torsional loading was conducted at resonance at 30-50Hz. Specimens were thoroughly cured and tested dry at 21 degrees C.

RESULTS

All of the specimens showed a loss of strength following repeated stress, due to material fatigue. The material with the highest shear modulus had the lowest damping and the highest fatigue strength.

SIGNIFICANCE

Dental composites exhibit a modest loss of strength due to fatigue. Since mastication involves many cycles of stress during the life of a restoration, fatigue properties should be taken into account in restoration design.

Compressive strength and compressive fatigue limit of conventional and high viscosity posterior resin composites

The purpose of this study was to compare the compressive strengths and compressive fatigue limits of three posterior composite resins (Filtek P-60, Surefil and Prodigy Condensable) and a universal restorative composite (Z-100). Cylindrical specimens (8 mm in length x 4 mm in diameter) were used. The dynamic test was performed using the staircase method, and the ratio between compressive fatigue limit and compressive resistance was also calculated (n = 15). The compressive strength and compressive fatigue limit data were analyzed by Anova and Tukeys test. The Z-100 composite demonstrated higher compression strength (307.20 MPa) than Surefil (266.93 MPa) and Prodigy Condensable (222.08 MPa). The resistance of Filtek P-60 (270.44 MPa) was similar to the resistances of Z-100 and Surefil, while Prodigy Condensable presented the lowest compressive strength. In the compressive fatigue limit tests, Filtek P-60 demonstrated a higher value (184.20 MPa) than Prodigy Condensable (155.50 MPa). Surefil (165.74 MPa) and Z-100 (161.22 MPa) presented limits similar to those of Filtek P-60 and Prodigy Condensable. The compressive fatigue limit/compressive strength ratio was 70.01% for Prodigy Condensable, 68.11% for Filtek P-60, 62.09% for Surefil and 52.48% for Z-100. It was concluded that the Z-100 universal composite was more sensitive to the dynamic test than the high viscosity materials.

3-Year clinical evaluation of posterior packable composite resin restorations

This study evaluated the clinical performance of four packable resin composite restorative materials in posterior teeth (Class I and II) compared with one hybrid composite after 3 years. Eighty-four restorations were placed in 16 patients. The tested materials were: (i) Solitaire + Solid Bond; (ii) ALERT + Bond-1; (iii) Surefil + Prime & Bond NT; (iv) Filtek P60 + Single Bond and (v) TPH Spectrum + Prime & Bond 2.1. All restorations were made using rubber dam isolation, and the cavity design was restricted to the elimination of carious tissue. Deeper cavities were covered with calcium hydroxide and/or glass-ionomer cement. Each adhesive system and composite resin was placed according to the manufacturer's instructions. One week later, the restorations were finished/polished and evaluated according USPHS modified criteria. Fourteen patients attended the 3-year recall and 75 restorations were evaluated at that time based on the same evaluation criteria. Friedman repeated measures analysis of variance by rank and Wilcoxon sign-ranked test for pair-wise comparison was used for data analysis (alpha = 0.05). The analysis was performed only for the baseline and for the 3-year period. Solitaire showed some fractures at marginal ridges in 25% of the cases. Solitaire and ALERT showed some concerns related to colour match (43 and 77%, respectively) and surface texture (86 and 77%, respectively). TPH Spectrum showed a great percentage of colour mismatch after 3 years, around 50%. Surefil and Filtek P60 showed an excellent clinical performance after 3 years, similar to the hybrid resin tested, TPH Spectrum. Solitaire did not fulfil the ADA acceptance criteria for restorative materials and, therefore, is not recommended for use in posterior restorations.

Micro-tensile bond strength of adhesives bonded to class-I cavity-bottom dentin after thermo-cycling

A widely used artificial aging methodology is thermo-cycling. The ISO TR 11450 standard (1994) recommends 500 cycles in water between 5 and 55 degrees C. Recent literature revealed that more cycles are needed to mimic long-term bonding effectiveness. Furthermore, the artificial aging effect induced by thermo-cycling is not clearly established. Two underlying mechanisms can be advanced: (1) hot water may accelerate hydrolysis and elution of interface components and (2) repetitive contraction/expansion stress can be generated.

OBJECTIVES

The purpose of this study was to evaluate the relative contribution of both chemical (hydrolysis and elution of interface components) and mechanical (repetitive contraction/expansion stress) degradation pathways on the thermo-cycling-induced artificial aging of dentin-adhesive interfaces at the bottom of class-I cavities.

METHODS

The micro-tensile bond strength (muTBS) of contemporary adhesives (a three-step etch and rinse, a two-step and a one-step self-etch adhesive) bonded to class-I cavity-bottom dentin was determined after 20,000 cycles as well as after 20 days of water storage (control). Restored class-I cavities (repetitive contraction/expansion stress) as well as prepared micro-specimens (diffusion-dependent hydrolysis and elution) were subjected to the thermo-cycling regimen.

RESULTS

Thermo-cycling did not enhance chemical or mechanical degradation of the bonds produced by a two-step self-etch and a three-step etch and rinse adhesive to dentin. The one-step self-etch adhesive tested was, however, not able to withstand polymerization shrinkage stress, nor thermo-cycling, when applied in class-I cavities.

SIGNIFICANCE

Thermo-cycling results in combined contraction/expansion stress and accelerated chemical degradation. However, the relative contribution of each is strongly dependent on the specific test set-up and the adhesive used.

Comparison of two video-imaging instruments for measuring volumetric shrinkage of dental resin composites

OBJECTIVES

The purpose of this study was to measure the polymerization shrinkage of three dental resin composites using two commercially available video-imaging devices to determine if the devices produced equivalent results.

METHODS

Small, semi-spherical specimens of a microhybrid (Venus), microfill (Filtek A110), and flowable (Esthet*X Flow) resin composite were manually formed and light activated for 40s using a light-curing unit. The volumetric polymerization shrinkage of fifteen specimens of each brand of resin composite was measured using the AcuVol and the Drop Shape Analysis System model DSA10 Mk2 (DSAS) video-imaging devices. Mean volumetric shrinkage values were calculated for each resin composite and equivalence was evaluated using the two one-sided tests approach. Differences between the means that were less than approximately 5% of the observed shrinkage were considered indicative of clinical equivalence.

RESULTS

Mean volumetric shrinkage values measured for the resin composites were: Venus (AcuVol, 3.07+/-0.07%; DSAS, 2.90+/-0.07%); Filtek A110 (AcuVol, 2.26+/-0.10%; DSAS, 2.25+/-0.09%); and Esthet*X Flow (AcuVol, 5.01+/-0.17%; DSAS, 5.14+/-0.11%). Statistical analysis revealed that the two imaging devices produced equivalent results for Filtek A110 and Esthet*X Flow but not for Venus.

CONCLUSIONS

Video-imaging systems provide an easy method for measuring volumetric shrinkage of resin composites. As with other methods for measuring volumetric shrinkage, however, they are best used to comparatively measure different materials within the same laboratory.

Dynamic and static elastic moduli of packable and flowable composite resins and their development after initial photo curing

OBJECTIVE

The purpose of this study was to evaluate the dynamic (storage) shear modulus and the static shear modulus of elasticity of packable and flowable composite resins and to investigate their development after initial photo-curing.

METHODS

Three pairs of a packable versus a flowable composite and a microfill composite resin were tested (Alert/Flow It, Filtek P60/Filtek Flow, Admira/Admira Flow, A 110). Cylindrical specimens (0.85 mm x 18 mm) were made for each material. All specimens were conditioned and tested dry at 21 degrees C. The specimens were tested at 30 min, 24h and 1 week after the end of photo curing. Storage shear modulus and loss tangent were determined by conducting dynamic torsional loading in the frequency range from 1 to 150 Hz. Static shear modulus measurements were made by applying a constant load (below the proportional limit of the materials) for 10s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncan's Post hoc test (alpha=0.05).

RESULTS

Storage shear moduli (at 1 week measurement) ranged from 3.39 to 9.67 GPa, and loss tangents from 0.0735 to 0.0235; static shear moduli ranged between 2.66 and 9.80 GPa. High values of elastic moduli and low tandelta values were obtained with packable composites, while low moduli values were obtained with flowable composites. Statistically significant (alpha=0.05) differences were recorded between materials of the same category. Storage time, 24h and 1 week after initial polymerization, resulted in significant increases in both moduli of elasticity. Dynamic shear storage moduli were highly correlated to the static ones (r(2)=0.92; P<0.05).

SIGNIFICANCE

The results of the aging studies showed that the rigidity of these materials increases significantly even 1 week after the clinician turns off the curing unit.

Fatigue behavior of packable composites

The aim of this study was to investigate the flexural fatigue behavior of 11 packable composites. Of each material 30 rectangular samples (1.2 x 5 x 35 mm) for flexural fatigue test were prepared. The clamped fracture strength and flexural fatigue limit (FFL) of each material were determined using a custom-made fatigue machine, after storage of the samples for one month in water at 37 degrees C. All data were analyzed using one-way ANOVA and Bonferroni/Dunn's test for multiple comparisons (p<0.05). Regression analysis was used to evaluate the relationship between elastic modulus (Abe et al., 2001), clamped fracture strength or FFL and inorganic filler fraction (vol%). The fracture strengths of all but two materials were in between those of the compact-filled densified composites and the microfine ones. The FFL of the packable composites tested were significantly lower than those of the compact-filled densified composites. Three of the tested materials showed even significantly lower FFL than did the microfine composites. There were statistically significant relationships between both the elastic modulus and the volumetric filler fraction (R(2)=0.974, p=1.990 x 10(-7)). The great diversity in packable composites makes clinical assessment necessary with regard to a justified use in posterior teeth.

Effect of self-etching primer and adhesive formulations on the shear bond strength of orthodontic brackets

PURPOSE

Despite many published articles on the bond strength of self-etching primers and adhesives in the restorative dentistry literature, there have been relatively few laboratory studies of the bond strength of new orthodontic materials, and, in most of these published studies, investigators used various methodologic approaches during different stages of the in vitro testing procedures. The aim of this study was to compare the shear bond strength of 4 self-etching primer and adhesive formulations, a nonrinse conditioner and acetone adhesive system, and a conventional system.

MATERIAL

The self-etching products tested were Prompt L-Pop (3M ESPE, Seefeld, Germany), Clearfil SE Bond (Kuraray Dental, Osaka, Japan), FL Bond (Shofu Dental, Kyoto, Japan), and One-Up Bond F (Tokuyama, Tokyo, Japan); the nonrinse conditioner and acetone-based adhesive system was NRC and Prime&Bond NT (Dentsply International, Konstanz, Germany); the conventional acid-etch and bond system was Transbond XT (3M Unitek, Monrovia, Calif). Brackets were bonded to intact bovine mandibular incisors (n = 7 per group) according to each manufacturer's recommendations. The specimens were first stored in deionized water at 37 degrees C for 24 hours and then subjected to thermal cycling in deionized water at 5 degrees C +/- 2 degrees C to 55 degrees C +/- 2 degrees C for 1000 cycles. To facilitate degradation of bonds, the specimens were further stored in distilled water for 6 weeks before debonding procedures.

RESULTS

The shear bond strengths of the 5 experimental groups were all significantly lower (P < .05) than that of the control group (Prompt L-Pop, 1.72 +/- 0.13 MPa; Clearfil SE Bond, 1.75 +/- 0.19 MPa; FL Bond, 1.71 +/- 0.22 MPa; One-Up Bond F, 1.77 +/- 0.14 MPa; control, 10.5 +/- 0.86 MPa) but not different from one another (P > .05).

CONCLUSIONS

The tested self-etching primer and adhesive systems produced bond strength values much lower than that of the control product. Clinically, these products might not be suitable for orthodontic bracket bonding in terms of the shear bond strength achieved after thermal cycling and water storage.

Effect of cavity configuration and aging on the bonding effectiveness of six adhesives to dentin

OBJECTIVES

The purpose of this study was to determine the effect polymerization contraction stress may have on bond durability.

METHODS

Bonding effectiveness was assessed by micro-tensile bond strength testing (muTBS) and electron microscopy. The muTBS to flat dentin surfaces and in standardized cavities was determined (this after 1 day as well as 1 year water storage). Six adhesives representing all current classes were applied: two etch-and-rinse (OptiBond FL, Kerr; Scotchbond 1, 3M ESPE), two self-etch (Clearfil SE Bond, Kuraray; Adper Prompt, 3M ESPE) and two glass-ionomer (Fuji Bond LC, GC; Reactmer, Shofu) adhesives.

RESULTS

The conventional 3-step etch-and-rinse adhesive OptiBond FL bonded most effectively to dentin, and appeared insensitive to polymerization shrinkage stress and water degradation. The 2-step self-etch adhesive Clearfil SE Bond most closely approached this superior bonding effectiveness and only slightly lost bond strength after 1-year water exposure. The 2-step etch-and-rinse adhesive Scotchbond 1 and the 'strong' 1-step self-etch adhesive Adper Prompt appeared very sensitive to cavity configuration and water-aging effects. The 2-step resin-modified glass-ionomer adhesive Fuji Bond LC only suffered from shrinkage stress, but not from 1-year water-exposure. Remarkable also is the apparent repairability of the 'mild' 1-step glass-ionomer adhesive Reactmer when stored for 1 year in water, in spite of the very low 1-day muTBS.

SIGNIFICANCE

Simplified bonding procedures do not necessarily imply improved bonding performance, especially in the long term.

Dynamic mechanical analysis of viscoelastic functions in packable composite resins measured by torsional resonance

The objective of this study was to evaluate the viscoelastic functions of packable composite resins with the use of a resonant dynamic mechanical analysis technique in torsion. The materials tested were: Alert (Jeneric Pentron), Prodigy Condensable (Kerr Corporation), Surefil (Dentsply DeTrey), and Filtek P60 (3M Dental Products). Dynamic torsional loading was conducted in the frequency range from 1 to 150 Hz. Composite specimens were tested after storage in water at 37 degrees C for 24 h. One group was thermal cycled for 3000 cycles with temperatures of 5-37-50 degrees C. Measurements were taken at 21 degrees C dry, and at 37 and 50 degrees C wet. Storage modulus, loss tangent, and other viscoelastic parameters were determined from the amplitude/frequency curves. Data for storage modulus and loss tangent of the materials were analyzed by means of ANOVA and Student-Newman-Keuls test (alpha = 0.05). It was found that there were significant differences (P < 0.001) in storage modulus and loss tangent among the packable composites tested. The highest value of storage modulus, in measurements at 21 degrees C, was for Alert (10.3 GPa), followed by Filtek P60 (9.31 GPa), Surefil (7.29 GPa), and Prodigy Condensable (6.74 GPa). There were significant differences (P < 0.001) in storage modulus and loss tangent among the four different conditions tested. Storage modulus decreased at higher temperatures, whereas the loss tangent increased. Thermal cycling increased storage modulus and decreased loss tangent. The results showed that both monomer and filler composition and filler loading of the materials significantly affect their viscoelastic functions, and the mechanical properties of the products cannot be characterized from the packability alone.

Four-year water degradation of a resin-modified glass-ionomer adhesive bonded to dentin

Glass-ionomers are auto-adhesive to tooth tissue through combined micro-mechanical and chemical bonding. How much each of the two bonding components contributes to the actual bonding effectiveness is, however, not known and there is not much information available on long-term stability. The objective of this study was to assess the bonding effectiveness of a resin-modified glass-ionomer adhesive to dentin after 4 yr of water storage. Fuji Bond LC (GC) was applied without (i) and with pretreatment using (ii) a polyalkenoic acid conditioner and (iii) a 37.5% phosphoric acid etchant. The etchant was used to exclude any chemical interaction with hydroxyapatite. The micro-tensile bond strength ( microTBS) to dentin decreased significantly over the 4 yr period in all three experimental groups. After 24 h and 4 yr, the lowest micro TBS was recorded when dentin was not pretreated. The highest micro TBS was obtained following polyalkenoic acid pretreatment, although this was not significantly different from specimens that were pretreated using phosphoric acid. Pretreating dentin with phosphoric acid intensified micromechanical interlocking at the expense of chemical bonding potential to hydroxyapatite. Nevertheless, correlating the micro TBS data with failure analysis through scanning electron microscopy and transmission electron microscopy indicated that combined micro-mechanical and chemical bonding involving pretreatment with the polyalkenoic acid conditioner yielded the most durable bond.

Do condensable composites help to achieve better proximal contacts?

OBJECTIVES

Obtaining acceptable contact areas with adjacent teeth is a significant challenge when placing direct resin composite in Class II preparations. It was the purpose of this laboratory study to evaluate the influence of the type of resin composite ('packable' vs conventional) and of the matrix system on the quality of the proximal contact area in Class II composite restorations.

METHODS

A standardized DO cavity was prepared in 170 frasaco teeth. Two operators each filled 85 teeth in the same frasaco model using four resin composites [Solitaire (S), Surefil (Su), P60, Z100], three matrix systems [Automatrix (A), Palodent (P), Lucifix matrix (L)] and one hand instrument specially designed to achieve better proximal contacts [Belvedere Composite Contact Former (B)]. The teeth were subdivided into 17 groups (Z100/1-A, Z100/1-P, Z100/1-L, S-A, S-P, S-L, Z100/1-A-B, Z100/1-L-B, Su-A, Su-P, Su-L, P60-A, P60-P, P60-L, Z100/2-A, Z100/2-P, Z100/2-L). Each operator made five fillings of each group. The quality of the proximal contacts was assessed by measuring the maximum mesio-distal (M-D) diameter of the restored teeth using a digital micrometer and the tightness of the proximal contact area using standardized metal blades. All data were analyzed using two-way ANOVA and Bonferroni/Dunn's test for multiple comparisons with a significance level of P<0.05.

RESULTS

Regarding the matrix system, a significant larger M-D diameter and a stronger proximal contact area was achieved with the Palodent matrix system. The use of the Belvedere Composite Contact Former together with Lucifix matrix and Automatrix contributed to significantly stronger proximal contact areas. Concerning the type of resin composite, no significant differences were noted for both evaluation criteria when Palodent was used. Using Automatrix or Lucifix matrix, the more condensable resin composite P60 scored slightly better than Surefil and Z100. There was no operator effect. Both operators underwent a learning process. The longer they worked with a specific material/technique, the better proximal contacts they achieved.

SIGNIFICANCE

The best proximal contact areas in Class II composite restorations were obtained using a sectional matrix system. The 'packability' of the resin composite did not help to achieve better proximal contacts.