Contraction stress of low-shrinkage composite materials assessed with different testing systems

2010-10-01

Abstract: Objectives: The contraction stress of a silorane-based material and a new low-shrinkage nanohybrid composite were compared to three conventional dimethacrylate-based resin composites using two different measuring systems. It was hypothesized that the silorane-based material and the low-shrinkage nanohybrid composite would exhibit lower contraction stress than dimethacrylate-based composites irrespective of measuring system.Methods: The materials tested were Filtek Silorane LS (3M ESPE), Venus Diamond (Heraeus Kulzer), Tetric EvoCeram (Ivoclar Vivadent), Quixfil (Dentsply DeTrey), and Filtek Z250 (3M ESPE). Shrinkage stress was assessed using a stress–strain analyzer consisting of two opposing attachments, one connected to a load sensor and the other fixed to the device, or a system fixed to a universal testing machine with an extensometer as a feedback system. All specimens were light-cured with 20J/cm2; the contraction force (N) generated during polymerization was continuously recorded for 300s. Contraction stress (MPa) was calculated at both 40s and 300s. Data were statistically analyzed by three-way ANOVA and Tukey's post hoc test (α=0.05).Results: Venus Diamond exhibited the lowest stress under both experimental conditions. Stress values scored as follows: Venus Diamond

Five-year survival of 3-unit fiber-reinforced composite fixed partial dentures in the posterior area

2010-10-01

Abstract: Objectives: The purpose of this clinical study was to evaluate the long-term outcome of three-unit posterior fixed partial dentures (FPDs) made of fiber-reinforced resin composite (FRC), and to identify design factors influencing the survival rate.Methods: 77 patients (52 females, 25 males) received 96 indirectly made FRC FPDs, using pre-impregnated unidirectional glass-fibers, requiring manual wetting, as framework material. FPDs were surface (n=31) inlay (n=45) or hybrid (n=20) retained and mainly located in the upper jaw. Hybrid FPDs consisted of a wing retainer at canine and an inlay retainer at distal abutment tooth. Surface FPDs consisted of uplay and wing combinations. Follow-up period was at minimum 4.5 years, with checkups at every 1–2 years. The study was carried out by six operators in three centers in the Netherlands, Finland and Sweden. Survival rates, including reparable defects of FPDs, and success rates were determined.Results: Kaplan–Meier survival rate at 5 years was 71.2% (SE 4.8%) for success and 77.5% (SE 4.4%) for survival. Differences were not significantly different. Main failure modes were delamination and fracture of the FPD. Only FPDs with surface retainers showed debonding.Conclusions: A success rate of 71% and a survival rate of 78% after 5 years was found. Survival rates of inlay, hybrid and surface retained FPDs did not significantly differ.

Bilateral treatment: A strategy for enhancing the mechanical strength of machinable veneers

Su Chen, Yong-jie Wei, Ming-ming Chen, Zhen-ting Zhang — 2010-10-01

Abstract: Objective: To investigate the potential application of bilateral treatment of glazing plus staining in machinable veneer mechanical strength improvement.Methods: Standard laminate specimens (n=105) were sliced from machinable ceramic blocks and divided into seven batches for further treatments: (1) batch C, standard specimens; (2) batch P, one specimen surface polished; (3) batch F, fired in glaze-firing-program without glaze; (4) batch G, fired with glaze on one surface; (5) batch S, fired with stain on one surface; (6) batch GA, fired with glaze on one surface, then re-fired in stain-firing-program without stain, and (7) batch GS, fired with glaze on one surface then fired with stain on the other side. The flexural strength of all specimens was tested with a three-point-bending test and the results statistically evaluated. Scanning electron microscopy (SEM) was used to analyze fractographs of bilateral treatment specimens. X-ray diffraction (XRD) analysis was performed to evaluate the influence of thermal annealing effect on strength improvement in bilateral treatment.Results: The flexural strength of bilateral treated GS (143.23±14.02MPa) was significantly higher (P<0.05) than unilateral treated G (125.92±14.01MPa) and P (114.48±8.45MPa) and other batches, including C (100.11±6.65MPa), F (99.48±8.61MPa), S (119.28±19.34MPa) and AG (126.65±9.83MPa). SEM imaging showed that no underlying separation between the glaze–matrix or stain–matrix could be found in the fractured GS specimen. No evidence of Bragg diffraction peak broadening could be seen in XRD spectra compared with specimens from batches C and AG.Significance: To improve machinable laminate strength, a bilateral treatment comprising staining and glazing gave higher strength than unilateral glazing or polishing alone. It was the surface layer effect achieved by glazing and staining, not the thermal annealing effect achieved during glaze and stain sintering, which contributed to the laminate strength improvement.

Mechanical characterization of proanthocyanidin–dentin matrix interaction

2010-10-01

Abstract: Objectives: To characterize the properties of dentin matrix treated with two proanthocyanidin rich cross-linking agents and their effect on dentin bonded interfaces.Methods: Sound human molars were cut into 0.5mm thick dentin slabs, demineralized and either treated with one of two cross-linking agents (grape seed—GSE and cocoa seed—COE extracts) or left untreated. The modulus of elasticity of demineralized dentin was assessed after 10 or 60min and the swelling ratio after 60min treatment. Bacterial collagenase was also used to assess resistance to enzymatic degradation of samples subjected to ultimate tensile strength. The effect of GSE or COE on the resin–dentin bond strength was evaluated after 10 or 60min of exposure time. Data were statistically analyzed at a 95% confidence interval.Results: Both cross-linkers increased the elastic modulus of demineralized dentin as exposure time increased. Swelling ratio was lower for treated samples when compared to control groups. No statistically significant changes to the UTS indicate that collagenase had no effect on dentin matrix treated with either GSE or COE. Resin–dentin bonds significantly increased following treatment with GSE regardless of the application time or adhesive system used.Significance: Increased mechanical properties and stability of dentin matrix can be achieved by the use of PA-rich collagen cross-linkers most likely due to the formation of a PA–collagen complex. The short term resin–dentin bonds can be improved after 10min dentin treatment.

Apatite formation on bioactive calcium-silicate cements for dentistry affects surface topography and human marrow stromal cells proliferation

2010-10-01

Abstract: The effect of ageing in phosphate-containing solution of bioactive calcium-silicate cements on the chemistry, morphology and topography of the surface, as well as on in vitro human marrow stromal cells viability and proliferation was investigated. A calcium-silicate cement (wTC) mainly based on dicalcium-silicate and tricalcium-silicate was prepared. Alpha-TCP was added to wTC to obtain wTC-TCP. Bismuth oxide was inserted in wTC to prepare a radiopaque cement (wTC-Bi). A commercial calcium-silicate cement (ProRoot MTA) was tested as control. Cement disks were aged in DPBS for 5h (‘fresh samples’), 14 and 28 days, and analyzed by ESEM/EDX, SEM/EDX, ATR-FTIR, micro-Raman techniques and scanning white-light interferometry. Proliferation, LDH release, ALP activity and collagen production of human marrow stromal cells (MSC) seeded for 1–28 days on the cements were evaluated. Fresh samples exposed a surface mainly composed of calcium-silicate hydrates CSH (from the hydration of belite and alite), calcium hydroxide, calcium carbonate, and ettringite. Apatite nano-spherulites rapidly precipitated on cement surfaces within 5h. On wTC-TCP the Ca-P deposits appeared thicker than on the other cements. Aged cements showed an irregular porous calcium-phosphate (Ca-P) coating, formed by aggregated apatite spherulites with interspersed calcite crystals. All the experimental cements exerted no acute toxicity in the cell assay system and allowed cell growth. Using biochemical results, the scores were: fresh cements>aged cements for cell proliferation and ALP activity (except for wTC-Bi), whereas fresh cements

Clinical performance of cervical restorations—A meta-analysis

Siegward D. Heintze, Christiane Ruffieux, Valentin Rousson — 2010-10-01

Abstract: Objectives: To carry out a meta-analysis in order to assess the influencing factors on retention loss and marginal discoloration of cervical restorations made of composites and glass ionomer (derivates).Methods: The literature was searched for prospective clinical studies on cervical restorations with an observation period of at least 18 months.Results: Fifty clinical studies involving 40 adhesive systems matched the inclusion criteria. On average, 10% of the cervical fillings were lost and 24% exhibited marginal discoloration after 3 years. The variability ranged from 0% to 50% for retention loss and from 0% to 74% for marginal discoloration. Hardly any secondary caries was detected. When linear mixed models with a study and experiment effect were used, the analysis revealed that the adhesive/restorative class had the most significant influence, with 2-step self-etching adhesive systems performing best and 1-step self-etching adhesive systems performing worst; 3-step etch-and-rinse systems, glass ionomers/resin-modified glass ionomers, 2-step etch-and-rinse systems and polyacid-modified resin composites were ranked in between. Restorations placed in teeth whose dentin/enamel had been prepared/roughened showed a statistically significant higher retention rate than those placed in teeth with unprepared dentin (p<0.05). Beveling of the enamel and the type of isolation used (rubberdam/cotton rolls) had no significant influence.Significance: The clinical performance of cervical restorations is significantly influenced by the type of adhesive system used and/or the adhesive class to which the system belonged and whether the dentin/enamel is prepared or not. 2-Step self-etching- and 3-step etch&rinse systems shall be chosen over 1-step self-etching systems and glass ionomer derivates. The dentin (and enamel) surface shall be roughened before placement of the restoration.

Durability of four composite resin cements bonded to dentin under simulated pulpal pressure

Jun Lin, Christian Mehl, Bin Yang, Matthias Kern — 2010-10-01

Abstract: Objectives: This study aimed to investigate the durability of four adhesive luting systems bonded to dentin with and without simulated hydrostatic pulpal pressure (PP).Methods: Composite blocks were bonded to dentin with four adhesive systems: Multilink Automix (MA), Multilink Sprint (MS), Clearfil Esthetic cement (CE) and RelyX ARC (RAC) under either a PP of 0 or 15cm H2O. After 3d water storage at 37°C or thermal cycling (TC), of 30d with 5000 TC or 90d with 15,000 TC micro-tensile bond strength (μTBS) was tested. Failure analysis of the bonding interface was performed using a scanning electron microscope (SEM).Results: Independent of PP application groups MA and RAC showed significantly higher μTBS than CE and MS (P≤0.05). A significant decrease in μTBS was found for RAC and MS when subjected to PP (P≤0.05), whereas CE and MA showed no significant difference (P>0.05). TC had no significant influence on the μTBS in RAC, MA and CE without PP application (P>0.05), whereas CE with PP and MS showed a significant decrease in μTBS (P≤0.05) when subjected to TC.Significance: Based on these results, there were significant differences between materials. Pulpal pressure and artificial aging also seem to have an effect on in-vitro evaluation of bonding durability. If considered relevant to the materials’ service performance then these conditions should be applied in the materials’ testing.

Covalent adaptable networks as dental restorative resins: Stress relaxation by addition–fragmentation chain transfer in allyl sulfide-containing resins

Hee Young Park, Christopher J. Kloxin, Timothy F. Scott, Christopher N. Bowman — 2010-10-01

Abstract: Objectives: The aim is to demonstrate significant polymerization shrinkage stress reduction in model resins through incorporation of addition–fragmentation chain transfer moieties that promote network stress accommodation by molecular rearrangement. Monomers containing allyl sulfide linkages are incorporated to affect the shrinkage stress that arises during photopolymerization of model resins that contain an initiator and dimethacrylates. Radical-mediated allyl sulfide addition–fragmentation is enabled during polymerization. We hypothesize that allyl sulfide incorporation into methacrylate polymerizations promotes stress relaxation by enabling network adaptation.Methods: A 1:2 mixture of tetrathiol and allyl sulfide-containing divinyl ethers is formulated with glass-forming dimethacrylates and compared to controls where the allyl sulfide is replaced with a propyl sulfide that is incapable of undergoing addition–fragmentation. Simultaneous shrinkage stress and functional group conversion measurements are performed. The Tg is determined by DMA.Results: Increasing allyl sulfide concentration reduces the relative stress by up to 75% in the resins containing the maximum amount of allyl sulfide. In glassy systems, at much lower allyl sulfide concentrations, the stress is reduced by up to 20% as compared to propyl sulfide-containing systems incapable of undergoing addition–fragmentation chain transfer.Significance: Shrinkage stress reduction, typically accompanying free-radical polymerization, is a primary focus in dental materials research and new product development. Allyl sulfide addition–fragmentation chain transfer is utilized as a novel approach to reduce stress in ternary thiol-ene-methacrylate polymerizations. The stress reduction effect depends directly on the allyl sulfide concentration in the given ternary systems, with stress reduction observed even in systems possessing super-ambient Tgs and low allyl sulfide concentrations.

Cytotoxicity of monomers, plasticizer and degradation by-products released from dental hard chairside reline resins

2010-10-01

Abstract: Objectives: The aim of this study was to evaluate the cytotoxic effect of the monomers isobutyl methacrylate (IBMA) and 1,6-hexanediol dimethacrylate (1,6-HDMA), the plasticizer di-n-butyl phthalate (DBP), and the degradation by-products methacrylic acid (MA) and benzoic acid (BA) on L929 cells. Based on previous investigations on the release of these compounds from hard chairside reline resins, a range of concentrations (μmol/L) were selected for the cytotoxicity tests (IBMA, 5.49–1406.57; 1,6-HDMA, 1.22–39.32; DBP, 1.12–143.8; MA, 9.07–581; BA, 3.19–409).Methods: Cytotoxic effects were assessed using MTT and 3H-thymidine assays after the cells had been exposed to the test compounds at the given concentrations for 24h. Cytotoxicity was rated based on cell viability relative to controls (cells exposed to medium without test substances).Results: DNA synthesis activity was inhibited by all compounds. Mitochondrial dehydrogenase activity decreased in cells treated with monomers, plasticizer and MA by-product, whereas no cytotoxic effect was observed on contact with BA at the majority of concentrations tested. The ranges of suppression for 3H-thymidine assay were: IBMA, 25–95%; 1,6-HDMA, 95–98%; DBP, 40–98%; MA, 97–99%; BA, 54–71%. For MTT assay, the ranges of suppression were: IBMA, 0–96%; 1,6-HDMA, 26–89%; DBP, 17–80%; MA, 52–66%; BA, 0–27%. The 3H-thymidine assay was more sensitive than the MTT assay.Significance: This study evaluated the cytotoxicity of a wide range of concentrations of monomers (IBMA and 1,6-HDMA), plasticizer (DBP) and degradation by-products (MA and BA), including those expected to be released from hard chairside reline resins. The differences observed in the cytotoxicity of these compounds, along with other properties, may assist the dental practitioners in the selection of reline materials with improved service life performance and low risk of adverse reactions in patients who wear relined dentures.

Effect of shrinkage strain, modulus, and instrument compliance on polymerization shrinkage stress of light-cured composites during the initial curing stage

Sun-Hong Min, Jack Ferracane, In-Bog Lee — 2010-10-01

Abstract: Objectives: The aim of this study was to investigate the influence of shrinkage strain, modulus, and instrument compliance on the polymerization shrinkage stress measurement of light-cured composites, and to determine whether the silorane-based low-shrinkage composite shows a low-polymerization shrinkage stress.Methods: A universal hybrid; Z250 (Z2), a flowable; Z350 (Z3), and a silorane-based; P90 (P9) composite was examined. A modified “bonded disc method” was used to measure the axial shrinkage strain of the composite. For the measurement of the initial modulus development of composites during light curing, a dynamic oscillatory shear test was undertaken using a custom-made oscillation rheometer. A frequency of 6Hz and strain amplitude of 0.0091rad for 20s was employed and the complex shear modulus (G*) was determined. A newly designed stress–strain analyzer was made to measure the shrinkage stress of the composites with two modes: (1) high compliance, or (2) low compliance. The shift between the two modes was controlled by an On–Off switch of a negative feedback circuit. Theoretical shrinkage stress was calculated from the shrinkage strain and modulus measured above, and compared with experimentally measured stress. Data were analyzed with one-way ANOVA and Tukey's post hoc test (α=0.05), and correlation analysis was done to investigate the relationship between measured stress and shrinkage strain, modulus, and theoretical stress.Results: The shrinkage strain of Z3 (4.12%) at 10min was the highest, followed by Z2 (2.31%) and P9 (0.77%). At 10s after light curing, Z2 showed the highest modulus (466.2MPa), Z3 (154.1MPa), and P9 the lowest (130.7MPa). The measured stresses with low compliance were much higher than those with high compliance. With high compliance, the contraction stress of Z3 was the highest (2.75MPa), followed by Z2 (1.54MPa) and P9 (0.48MPa). In low-compliance mode, the stresses of Z3 (7.93MPa) and Z2 (7.48MPa) were similar (p=0.323) while the stress of P9 (3.23MPa) was much lower. A strong correlation was observed between the theoretical stress and the measured stress with low compliance (R=0.996). In high-compliance mode, the shrinkage strain also showed a near-linear relationship with the stress measured (R=0.937), but the modulus showed a low correlation with the measured stress (R=0.398).Significance: Depending on the instrument compliance, polymerization shrinkage stress showed significant differences for each material. In high-compliance shrinkage strain played a greater role, while in low-compliance shrinkage strain and elastic modulus contributed comparably in determining the shrinkage stress. The low-shrinkage silorane-based composite demonstrated considerable reduction in shrinkage strain and stress.

A comparison of two-dimensional and three-dimensional measurements of wear in a laboratory investigation

Jose M. Rodriguez, David W. Bartlett — 2010-10-01

Abstract: Objectives: The aim of this research was to compare two-dimensional (2D) and three-dimensional (3D) tooth measuring techniques after subjecting enamel samples to tooth wear in vitro on an erosion–abrasion model.Method: 80 polished mid-coronal enamel sections were subjected to 10 wear cycles. Each cycle consisted of remineralization for 2h in artificial saliva, followed by 10min immersion in one of four acidic fruit drinks or distilled water and finally toothbrush abrasion with a non-fluoridated tooth paste. The resulting wear scars were measured using 2D and 3D techniques using surface matching software.Results: The 2D step heights measurements from the exposure to the four acidic drinks showed no statistically significant differences (median wear range=22.4–32.5μm) between them (p=0.99) but there were differences with distilled water (median wear=10.0μm) (p=0.01). The 3D measurements showed that two drinks produced more wear compared to the others and water when the whole surface and volume exposed to wear was accounted for (p=0.01).Significance: The difference in data from the two techniques showed that 3D measurements gave a more accurate assessment of the impact of the wear regime.

Dental Materials

Editorial Board

Contraction stress of low-shrinkage composite materials assessed with different testing systems

Five-year survival of 3-unit fiber-reinforced composite fixed partial dentures in the posterior area

Bilateral treatment: A strategy for enhancing the mechanical strength of machinable veneers

Mechanical characterization of proanthocyanidin–dentin matrix interaction

Apatite formation on bioactive calcium-silicate cements for dentistry affects surface topography and human marrow stromal cells proliferation

Clinical performance of cervical restorations—A meta-analysis

Durability of four composite resin cements bonded to dentin under simulated pulpal pressure

Covalent adaptable networks as dental restorative resins: Stress relaxation by addition–fragmentation chain transfer in allyl sulfide-containing resins

Cytotoxicity of monomers, plasticizer and degradation by-products released from dental hard chairside reline resins

Effect of shrinkage strain, modulus, and instrument compliance on polymerization shrinkage stress of light-cured composites during the initial curing stage

A comparison of two-dimensional and three-dimensional measurements of wear in a laboratory investigation