Hygroscopic dimensional changes of self-adhering and new resin-matrix composites during water sorption/desorption cycles

Objectives

To study hygroscopic dimensional changes in new resin-matrix composites during water sorption/desorption cycles.

Methods

Five materials were examined: a self-adhering flowable composite: Vertise^® Flow (VF), a universal composite: GC Kalore (GCK), two micro-fine hybrid composites: GC Gradia Direct Anterior (GDA) and GC Gradia Direct Posterior (GDP), and a posterior restorative composite: Filtek^® Silorane (FS). Five disk-shaped specimens of each material were prepared (15 mm diameter × 2 mm thickness) according to ISO 4049. The mean diameter of each specimen was measured by a custom-built laser micrometer (to a resolution of 200 nm) periodically over 150 d water immersion and 40 d recondition periods at (37 ± 1) °C. Perspex controls were used. Data analysis was performed by repeated measures ANOVA, one-way ANOVA and Tukey's post hoc test (p < 0.05).

Results

Differences in hygroscopic expansion were found for all test materials during sorption, ranging from 0.74% (±0.05) for FS to 4.82% (±0.13) for VF. The differences were significant for all materials (p < 0.001), except between GCK and GDA. The mathematical relationship between diametral expansion and square root of time was non-linear. VF exhibited significant dehydration shrinkage.

Significance

The silorane composite FS had the lowest hygroscopic expansion. The extent of compensation of polymerization shrinkage by hygroscopic expansion depends on materials, specimen dimensions and time-scale. So the clinical situation must be taken into consideration in the application of these findings.     

COMPARATIVE ANALYSIS OF THE SHRINKAGE STRESS OF COMPOSITE RESINS

The aim of this study was to compare the shrinkage stress of composite resins by three methods. In the first method, composites were inserted between two stainless steel plates. One of the plates was connected to a 20 kgf load cell of a universal testing machine (EMIC-DL-500). In the second method, disk-shaped cavities were prepared in 2-mm-thick Teflon molds and filled with the different composites. Gaps between the composites and molds formed after polymerization were evaluated microscopically. In the third method, the wall-to-wall shrinkage stress of the resins that were placed in bovine dentin cavities was evaluated. The gaps were measured microscopically. Data were analyzed by one-way ANOVA and Tukey''s test (α=0.05). The obtained contraction forces were: Grandio = 12.18 ± 0.428N; Filtek Z 250 = 11.80 ± 0.760N; Filtek Supreme = 11.80 ± 0.707 N; and Admira = 11.89 ± 0.647 N. The gaps obtained between composites and Teflon molds were: Filtek Z 250 = 0.51 ± 0.0357%; Filtek Supreme = 0.36 ± 0.0438%; Admira = 0.25 ± 0.0346% and Grandio = 0.16 ± 0.008%. The gaps obtained in wall-to-wall contraction were: Filtek Z 250 = 11.33 ± 2.160 μm; Filtek Supreme = 10.66 ± 1.211μm; Admira = 11.16 ± 2.041 μm and Grandio = 10.50 ± 1.224 μm. There were no significant differences among the composite resins obtained with the first (shrinkage stress generated during polymerization) and third method (wall-to-wall shrinkage). The composite resins obtained with the second method (Teflon method) differed significantly regarding gap formation.     

Incisional hernia: challenge of re-operations after mesh repair

Background and aims The widespread use of meshes for the repair of incisional hernia is currently followed by an increasing number of re-operations. The incidence of incisional hernia recurrence after mesh repair varies between 3 and 32%. The problem of mesh failure and options for another surgical intervention seem rather unattended. Methods We present our experience of 77 re-operations after previous mesh repair that were performed between 1995 and 2004 out of a total of 1,070 operations for incisional hernia. The retrospective analysis focused on recurrence in relation to location, material of the previous mesh repair and the surgical procedure to resolve the problem. Results The locations of the preceding meshes were epifascial as onlays (n=23), retromuscular as sublays (n=46), within the defect as inlays (n=6) or intraperitoneally (n=2). The direction of the incision was vertical medial (n=41) or horizontal crossing the linea semilunaris (n=36). Recurrences after median incisional hernia mesh repair mainly occurred at the cranial border of the mesh subxiphoidal. Except for two patients, all recurrences manifested at the margin of the enclosed mesh. Conclusions Re-operation after previous mesh repair is a surgical challenge. The type of revision procedure has to consider the position and material of the previous mesh. In our clinic recurrences, heavyweight polypropylene meshes were mostly treated with mesh exchange and lightweight polypropylene meshes could be treated by extension with a second mesh. In contrast to suture techniques, deficient mesh repairs are more evidently related to technical problems.     

The two sides of the C-factor

Objective

The aim of this paper is to investigate the effects on shrinkage strain/stress development of the lateral constraints at the bonded surfaces of resin composite specimens used in laboratory measurement.

RAFT-mediated control of nanogel structure and reactivity: Chemical,physical and mechanical properties of monomer-dispersed nanogel compositions

Objective

This study examines how nanogel structure correlates with photopolymerization and key polymer properties upon addition of nanogels with latent reactivity into a monomer dispersant to produce polymer/polymer composites.

Methods

Two nanogels that retained RAFT functionality based on the synthetic approach were prepared to have different branching densities. These reactive nanogels were dispersed in triethylene glycol dimethacrylate at 0–40 wt%. Reaction kinetics, volumetric shrinkage and shrinkage stress associated with the photopolymerization of nanogel-modified formulations were measured in real time with mechanical properties of the polymers also evaluated. The basic structure of RAFT-derived nanogel particles was examined by the preparation of a separate nanogel constructed with degradable disulfide crosslinking groups. The model nanogel molecular weight and polydispersity were compared before and after degradation.

Results

Despite the controlled radical synthetic approach, the nanogels, which are composed of multiple interconnected, short primary chains, presented relatively high polydispersity. Through addition of the reactive nanogels to a monomer that both infiltrates and disperses the nanogels, the photopolymerization rate was moderately reduced with the increase of nanogel loading levels. Volumetric shrinkage decreased proportionally with nanogel concentration; however, a greater than proportional reduction of polymerization-induced stress was observed. Mechanical properties, such as flexural strength, storage modulus were maintained at the same levels as the control resin for nanogel systems up to 40 wt%.

Significance

This study demonstrated that beyond the use of RAFT functionality to produce discrete nano-polymeric structures, the residual chain end groups are important to maintain reactivity and mechanical properties of nanogel-modified resin materials.     

Temperature-dependent polymerization shrinkage stress kinetics of resin-composites

Objectives

To determine temperature dependence of shrinkage stress kinetics for a set of resin composites formulated with dimethacrylate monomer matrices.

Methods

Six representative resin composites with a range of resin matrices were selected. Two of them were considered as low shrinking resin composites: Kalore and Venus Diamond. The shrinkage stress kinetics at 23 °C and 37 °C were measured continuously using a Bioman instrument for 60 min. Stress levels between materials were compared at two intervals: 2 min and 60 min. Specimen temperatures were controlled by a newly designed heating device. Stress measurements were monitored for 1 h, after irradiation for 40 s at 550 mW/cm² (energy density = 22 J/cm²). Three specimens (n = 3) were used at each temperature per material.

Results

Shrinkage stress at 23 °C ranged from 2.93 MPa to 4.71 MPa and from 3.57 MPa to 5.42 MPa for 2 min and 60 min after photo-activation, respectively. The lowest stress-rates were recorded for Kalore and Venus Diamond (0.34 MPa s⁻¹), whereas the highest was recorded for Filtek Supreme XTE (0.63 MPa s⁻¹). At 37 °C, shrinkage stress ranged from 3.27 MPa to 5.35 MPa and from 3.36 MPa to 5.49 MPa for 2 min and 60 min after photo-activation, respectively. Kalore had the lowest stress-rate (0.44 MPa s⁻¹), whereas Filtek Supreme XTE had the highest (0.85 MPa s⁻¹). Materials exhibited a higher stress at 37 °C than 23 °C except for Kalore and Venus Diamond. Positive correlations were found between shrinkage stress and stress-rate at 23 °C and 37 °C (r = 0.70 and 0.92, respectively).

Significance

Resin-composites polymerized at elevated temperature (37 °C) completed stress build up more rapidly than specimens held at 23 °C. Two composites exhibited atypical reduced stress magnitudes at the higher temperature.     

Decreased interposition after closed reduction in the hip joint: a case of developmental dislocation of the hip observed by MRI

 A 4-month-old Japanese girl with a developmental dislocation of the right hip was treated with manual reduction under general anesthesia followed by cast immobilization. Serial magnetic resonance imaging (MRI) revealed that a large interposition of fat tissue in the acetabulum, observed immediately after cast immobilization, became remarkably small in size as the congruity improved after 3 weeks. These MRI findings demonstrate the mechanism of a “squeezing phenomenon” after reduction of the hip. Received: June 6, 2001 / Accepted: December 5, 2001     

New bulk-fill composite system with high irradiance light polymerization: Integrity and degree of conversion

ObjectiveThe study used optical coherence tomography (OCT) and micro Raman microscopy (mRM) to investigate internal defect (ID) and degree of conversion (DC) of two bulk-fill composite systems with high-irradiance or conventional light polymerization settings.MethodsThe ID and DC of the new bulk-fill composites; Tetric PowerFill (PwrPst) and Tetric PowerFlow (PwrFlw) were compared with the predecessor bulk-fill composites; Tetric EvoCeram Bulkfill (EvoPst) and Tetric EvoFlow Bulkfill (EvoFlw), using LED light curing unit in two settings; normal (LED-Nrm: 1000 mW/cm², 10-s) or PowerCure (LED-Pwr: 3000 mW/cm², 3-s). ID formation was observed in bonded cylindrical composite cavities (4-mm depth, 3-mm diameter) using Yoshida Dental OCT. From the vertically projected 2D image, ID area percentage (ID-A%) was calculated. DC at the top and bottom and bottom/top DC ratio (DC-R%) of 4-mm thick discs was calculated using mRM. All data were statistically analyzed at significance level of α = 0.05.ResultsFlowable composites in LED-Pwr showed smaller ID frequencies than other groups (PwrFlw: 0/8, EvoFlw: 2/8) (p < 0.05). Composite type significantly affected ID-A%, DC and DC-R% (p < 0.001), while light settings significantly affected ID-A% but not DC and DC-R% (p > 0.05). In both light settings, EvoPst showed the lowest DC-R% (<80%).SignificanceInternal defect and degree of conversion of bulk-fill composites were affected by their composition and light settings. There was a tendency for less defects and better polymerization for the flowable bulk-fills. The new flowable bulk-fill composite with 3-seconds high irradiance light curing showed no defect formation.     

A novel artificial neural network method for biomedical prediction based on matrix pseudo-inversion

Biomedical prediction based on clinical and genome-wide data has become increasingly important in disease diagnosis and classification. To solve the prediction problem in an effective manner for the improvement of clinical care, we develop a novel Artificial Neural Network (ANN) method based on Matrix Pseudo-Inversion (MPI) for use in biomedical applications. The MPI-ANN is constructed as a three-layer (i.e., input, hidden, and output layers) feed-forward neural network, and the weights connecting the hidden and output layers are directly determined based on MPI without a lengthy learning iteration. The LASSO (Least Absolute Shrinkage and Selection Operator) method is also presented for comparative purposes. Single Nucleotide Polymorphism (SNP) simulated data and real breast cancer data are employed to validate the performance of the MPI-ANN method via 5-fold cross validation. Experimental results demonstrate the efficacy of the developed MPI-ANN for disease classification and prediction, in view of the significantly superior accuracy (i.e., the rate of correct predictions), as compared with LASSO. The results based on the real breast cancer data also show that the MPI-ANN has better performance than other machine learning methods (including support vector machine (SVM), logistic regression (LR), and an iterative ANN). In addition, experiments demonstrate that our MPI-ANN could be used for bio-marker selection as well.     

Effect of resin-composite filler particle size and shape on shrinkage–strain

ObjectivesThe aim of this study was to investigate the effect of variations in filler particle size and shape on the polymerization shrinkage–strain kinetics of resin-composites.MethodsA model series of 12 VLC resin-composites were studied. The particulate dispersed phase volume fraction was 56.7%: these filler particles were systematically graded in size, and further were either spherical or irregular. The bonded disk method was used to determine shrinkage–strain kinetics. Displacement was recorded following 40 s irradiation (600 mW/cm²) at 23 °C (n = 3). All data were captured for 60 min and the final shrinkage–strain calculated.ResultsFor materials with spherical filler, shrinkage–strain was 2.66% (SD 0.18) for those with irregular filler it was 2.89% (SD 0.11). These differences were statistically significant (p < 0.001): the Scheffé test identified two subsets, those with irregular filler (including materials with a multimodal mix) and those with spherical filler (including materials with a multimodal mix). Additionally, there was a trend for higher shrinkage–strain values with decreasing filler particle size which was apparent for both those composites with spherical filler particles and those with irregular filler particles. For irregular filler particles, linear regression gave a high correlation (r² = 0.99).SignificanceStatistically significant differences were identified in the shrinkage behavior of resin-composites with differing filler size and shape.