Vesna Miletic

Comparison of the hybrid layer formed by Silorane adhesive, one-step self-etch and etch and rinse systems using confocal micro-Raman spectroscopy and SEM.

OBJECTIVES To determine the extent of the hybrid layer (HL) of the novel adhesive system (Silorane, 3M ESPE) compared to one-step and etch and rinse adhesive systems, using 2D confocal micro-Raman spectroscopy and SEM. METHODS Silorane adhesive system was compared to two one-step self-etch (G Bond, GC; AdheSE One, Ivoclar Vivadent) and etch and rinse (Excite, Ivoclar Vivadent) as controls. Adhesives were applied to human dentine, cured and sections prepared perpendicular to the flat adhesive-dentine surface. Two-dimensional micro-Raman mapping was performed over 20mumx20mum areas across the adhesive-dentine interface. SEM micrographs of the same specimens were obtained. One-way ANOVA (Tukeys post-test) was used to analyse the differences in HL thickness among the four adhesive systems and the paired t-test to compare the results obtained by micro-Raman and SEM for each adhesive. RESULTS Silorane adhesive system formed a HL of comparable thickness to methacrylate-based but thicker than the acrylamide-based one-step self-etch adhesives from SEM analysis. A gradual decrease in adhesive penetration was observed in all systems. A 1-mum zone, between the cured primer and bond was identified by Raman but not visualised on SEM. Compared to SEM, HL calculated from Raman data were always greater. CONCLUSIONS Micro-Raman spectroscopy gives a more precise indication of dentine demineralisation and monomer infiltration and highlights the intermediate zone of approximately 1mum between Silorane primer and bond, not visible with SEM at x10,000 magnification. Giving as it does, a compilation of many linear scans it allows HL mean values to be calculated.

Degree of conversion and microhardness of TPO-containing resin-based composites cured by polywave and monowave LED units

OBJECTIVES To determine the degree of conversion (DC) and Knoop microhardness (KHN) of resin-based composites (RBCs) containing trimethylbenzoyl-diphenylphosphine oxide (TPO) cured by polywave or monowave LED light-curing units (LCUs). METHODS Three groups (each n = 5) of Tetric EvoCeram (Ivoclar Vivadent), Vit-l-escence (Ultradent) and Herculite XRV Ultra (Kerr) were prepared in Teflon moulds (5mm in diameter and 2mm thick) and cured with polywave Bluephase(®) G2 (Ivoclar Vivadent), polywave Valo (Ultradent) or monowave Bluephase(®) (Ivoclar Vivadent; control) resulting in 9 groups. DC and KHN were determined using micro-Raman spectroscopy and Knoop microhardness, respectively. High-performance liquid chromatography and nuclear magnetic resonance spectroscopy were used to confirm the presence or absence of TPO in the three uncured materials. Data were statistically analysed using two-way and one-way ANOVA and DC and KHN were correlated using Pearsons correlation (α = 0.05). RESULTS TPO was confirmed in Tetric EvoCeram and Vit-l-escence but not in Herculite XRV Ultra. All three LCUs produced comparable KHN for Tetric EvoCeram and Herculite XRV Ultra (p > 0.05). Both polywave LCUs resulted in significantly higher KHN for Vit-l-escence and higher DC in Tetric EvoCeram and Vit-l-escence than the monowave Bluephase(®) (p < 0.05). Conversely, Bluephase(®) showed higher DC than the two polywave LCUs in Herculite XRV Ultra (p < 0.05). Pearsons correlation coefficient was r = 0.818. CONCLUSIONS Polywave LED LCUs improved monomer to polymer conversion and KHN in the two TPO-containing RBCs, but not in Herculite XRV Ultra. DC and KHN were linearly correlated in all three RBCs. Vit-l-escence showed the highest DC and KHN of the three materials tested. CLINICAL SIGNIFICANCE The use of polywave LEDs significantly improves both the DC and KHN of materials which contain TPO. This should be taken into account when curing bleached shades of RBCs even if the manufacturers do not indicate the presence of TPO in their materials.

Quantitative micro-Raman assessment of dentine demineralization, adhesive penetration, and degree of conversion of three dentine bonding systems

Unreacted monomers in adhesive systems may cause a reduction in material properties, an increase in the long-term instability of the restoration, and pulpal irritation. The degree of dentine demineralization, adhesive penetration, and the degree of conversion (DC) across the dentine-adhesive interface of self-etch adhesives were measured using micro-Raman spectroscopy. Two-step, self-etch AdheSE, one-step self-etch AdheSE One, and etch-and-rinse Excite (control) (Ivoclar Vivadent AG, Schaan, Liechtenstein) were studied. Nine human molars were allocated to three groups and a flat dentine surface was prepared. A smear layer was produced by grinding dentine with 600-grit silicone-carbide discs under water. After application and polymerization of the adhesive, teeth were sectioned to produce four 1-mm-thick slices per tooth for micro-Raman spectroscopy. There were statistically significant differences in the depth of dentine demineralization between all adhesives. The depth and degree of demineralization decreased in the order: Excite>AdheSE>AdheSE One. The mean +/- standard deviation (SD) values for DC within the adhesive layer were 85.2 +/- 2.9% (Excite), 81.4 +/- 4.2% (AdheSE), and 54.3 +/- 10.1% (AdheSE One), and within the hybrid layer were 55.2 +/- 22.5% (Excite), 65.1 +/- 16.9% (AdheSE), and 42.0 +/- 16.2% (AdheSE One). All systems showed a discrepancy between dentine demineralization and adhesive penetration. A significant amount of unreacted monomers were associated with all systems but particularly with the etch-and-rinse system.

Monomer elution from nanohybrid and ormocer-based composites cured with different light sources

OBJECTIVES To study monomer elution from four resin-based composites (RBCs) cured with different light sources. METHODS Twenty-eight premolars were randomly allocated to four groups. Standardized cavities were prepared and restored with a nanohybrid (Filtek Supreme XT or Tetric EvoCeram), an ormocer (Admira) or a microhybrid RBC (Filtek Z250) which served as control. Buccal restorations were cured with a halogen and oral restorations with an LED light-curing unit. Elution of diurethane dimethacrylate (UDMA), Bisphenol A diglycidylether methacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) was analyzed using high-performance liquid chromatography (HPLC) 1h to 28 days post-immersion in 75% ethanol. Data were analyzed using multivariate and repeated measures analysis of variance (α = 0.05). RESULTS The greatest elution of UDMA and BisGMA occurred from Tetric EvoCeram and the least from Filtek Z250 (p < 0.05). LED and halogen light-curing units gave similar results for all RBCs (p > 0.05) except Tetric EvoCeram which showed greater elution for the LED unit (p < 0.05). TEGDMA was below the limit of quantification. HEMA eluted in similar concentrations from Filtek Supreme and Tetric EvoCeram (p > 0.05). SIGNIFICANCE The two nanohybrid RBCs eluted more cross-linking monomers than the ormocer and the control microhybrid RBC. Continuous elution over 28 days indicates that RBCs act as a chronic source of monomers in clinical conditions. Light source may affect monomer elution since differences were found for one out of four RBCs. Mathematical models for elution kinetics of UDMA and BisGMA indicated two elution mechanisms.

Quantification of monomer elution and carbon–carbon double bonds in dental adhesive systems using HPLC and micro-Raman spectroscopy

OBJECTIVES To quantify monomer elution from different adhesive systems using reverse-phase high-performance liquid chromatography (HPLC) and correlate this elution with the ratio of carbon-carbon double bonds from monomer to polymer (RDB) obtained using micro-Raman spectroscopy. METHODS Thirty dentine discs were cut from 30 human, intact, third molars and randomly allocated to five groups according to the adhesive applied: total-etch, Excite (Ivoclar Vivadent), two-bottle self-etch, Clearfil SE (Kuraray), one-bottle self-etch, Clearfil 3S (Kuraray), ormocer-based, Admira (Voco) and Filtek Silorane adhesive system (FS) (3M ESPE). Monomer elution was studied 1h, 6h, 24h, 96h and 7 days after immersion in 75% ethanol/water. The RDB was calculated immediately after light-curing and thereafter at 24h and 7 days. The data were statistically analysed using one-way ANOVA and Pearsons correlation coefficient (p<0.05). RESULTS More than 90% of the whole elution occurred during the first 1h, except for BisGMA in FS, with the highest absolute amount from Clearfil SE and the highest wt% from Admira. Initial RDB was in the ascending order FS<Admira<Excite<Clearfil SE<Clearfil 3S. In all groups, the RDB was significantly higher after 24h and 7 days than immediately after light-curing (p<0.05). Negative correlation was found only for the elution of HEMA and the RDB of Clearfil 3S. CONCLUSIONS Different adhesive systems showed different monomer elution kinetics. In all systems, the RDB increased after monomer elution. Overall, no direct correlation exists between the RDB of adhesives and the elution of unreacted monomers.

Temperature changes in silorane-, ormocer-, and dimethacrylate-based composites and pulp chamber roof during light-curing.

STATEMENT OF THE PROBLEM Light-curing of resin-based composites (RBCs) is associated with temperature increase in the pulp chamber, which may have a detrimental effect on the vital pulp. PURPOSE The purpose of the study was to evaluate temperature changes of silorane-, ormocer-, and dimethacrylate-based RBCs at the bottom surface of the RBC and in the pulp chamber roof dentin (PCRD) during curing. MATERIALS AND METHODS In part A, temperatures were measured for Filtek LS (3M ESPE, St. Paul, MN, USA), Admira (Voco GmbH, Cuxhaven, Germany), and Herculite XRV (Kerr Corp., Orange, CA, USA) with a high-power light-emitting diode (LED) unit by placing thermocouples in contact with the bottom surface of the material in standardized acrylic molds. In part B, temperature changes in PCRD were measured in extracted molars during light-curing of adhesives and RBCs in 2-mm-deep cavities with a remaining dentin thickness (RDT) of 1 mm. RESULTS Filtek LS showed a different temperature curve compared with Admira and Herculite XRV. Significantly higher temperatures were recorded for Filtek LS (p < 0.001) than for Admira and Herculite XRV in acrylic molds. Temperature rises recorded in PCRD for adhesives and RBCs were between 4.1 and 6.4 degrees C. No significant differences in PCRD temperatures were found between the three groups during adhesive curing and RBC curing (p > 0.05). CONCLUSIONS Filtek LS showed a different heat-generation pattern from and significantly higher temperatures than Admira and Herculite XRV when the materials were tested in acrylic molds. Similar temperatures were recorded in the PCRD during curing of adhesives and RBCs. CLINICAL SIGNIFICANCE Although a substantial temperature rise in the bulk material occurred during light-curing of the three resin-based composites, a remaining dentin thickness of 1 mm caused a significant reduction in pulp chamber roof dentin temperatures. Temperatures measured in the pulp chamber roof dentin corresponding to the zone occupied by the postmitotic odontoblast layer were not statistically different for the three types of resin-based composites.

Effects of a low-shrinkage methacrylate monomer and monoacylphosphine oxide photoinitiator on curing efficiency and mechanical properties of experimental resin-based composites.

This study investigated the degree of conversion, depth of cure, Vickers hardness, flexural strength, flexural modulus and volumetric shrinkage of experimental composite containing a low shrinkage monomer FIT-852 (FIT; Esstech Inc.) and photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO; Sigma Aldrich) compared to conventional composite containing Bisphenol A-glycidyl methacrylate (BisGMA) and camphorquinone-amine photoinitiator system. The degree of conversion was generally higher in FIT-based composites (45-64% range) than in BisGMA-based composites (34-58% range). Vickers hardness, flexural strength and modulus were higher in BisGMA-based composites. A polywave light-curing unit was generally more efficient in terms of conversion and hardness of experimental composites than a monowave unit. FIT-based composite containing TPO showed the depth of cure below 2mm irrespective of the curing light. The depth of cure of FIT-based composite containing CQ and BisGMA-based composites with either photoinitiator was in the range of 2.8-3.0mm. Volumetric shrinkage of FIT-based composite (0.9-5.7% range) was lower than that of BisGMA-based composite (2.2-12% range). FIT may be used as a shrinkage reducing monomer compatible with the conventional CQ-amine system as well as the alternative TPO photoinitiator. However, the depth of cure of FIT_TPO composite requires boosting to achieve clinically recommended thickness of 2mm.

Effect of hydroxyapatite spheres, whiskers, and nanoparticles on mechanical properties of a model BisGMA/TEGDMA composite initially and after storage

This study investigated the effect of shape, size, and surface modification of hydroxyapatite (HAP) fillers on the degree of conversion (DC) and mechanical properties of a model BisGMA/TEGDMA composite initially and after 4 weeks of storage. Ten percent of conventional glass fillers were replaced by HAP spheres (Sph), silicon-doped spheres (SphSi), whiskers (Wh), silicon-doped whiskers (WhSi), and nanosized HAP particles (Nano). Spheres were specifically structured agglomerates consisting of a central void and radially orientated primary particles, whereas whiskers were compact monocrystals. DC, Vickers hardness (HV), flexural strength (Fs), flexural modulus (Ef), compressive strength (Cs), and compressive modulus (Ec) were tested. There were no significant differences in the DC between all tested groups. HV decreased by 5.4-17% with the addition of HAP, while Fs increased by 13.9-29% except in Nano group (decrease by 13%). After storage, Sph and SphSi groups showed similar HV, Ef, Cs and Ec and higher Fs than the control. The fracture mode of HAP spheres was through the central void whereas whiskers showed longitudinal delamination, transverse, and mixed fractures. HAP spheres with or without silicon- doping have a potential to be part of the filler content of dental composites.

Mathematical modeling of cross-linking monomer elution from resin-based dental composites †

Elution of potentially toxic substances, including monomers, from resin-based dental composites may affect the biocompatibility of these materials in clinical conditions. In addition to the amounts of eluted monomers, mathematical modeling of elution kinetics reveals composite restorations as potential chronic sources of leachable monomers. The aim of this work was to experimentally quantify elution of main cross-linking monomers from four commercial composites and offer a mathematical model of elution kinetics. Composite samples (n = 7 per group) of Filtek Supreme XT (3M ESPE), Tetric EvoCeram (Ivoclar Vivadent), Admira (Voco), and Filtek Z250 (3M ESPE) were prepared in 2-mm thick Teflon moulds and cured with halogen or light-emitting diode light. Monomer elution in ethanol and water was analyzed using high-performance liquid chromatography up to 28 days postimmersion. The mathematical model was expressed as a sum of two exponential regression functions representing the first-order kinetics law. Elution kinetics in all cases followed the same mathematical model though differences in rate constants as well as the extent of monomer elution were material-, LCU-, medium-dependent. The proposed mechanisms of elution indicate fast elution from surface and subsurface layers and up to 100 times slower monomer extraction from the bulk polymer.

Local deformation fields and marginal integrity of sculptable bulk-fill, low-shrinkage and conventional composites.

OBJECTIVE To compare strain and displacement of sculptable bulk-fill, low-shrinkage and conventional composites as well as dye penetration along the dentin-restoration interface. METHODS Modified Class II cavities (N=5/group) were filled with sculptable bulk-fill (Filtek Bulk Fill Posterior, 3M ESPE; Tetric EvoCeram Bulk Fill, Ivoclar Vivadent; fiber-reinforced EverX Posterior, GC; giomer Beautifil Bulk, Schofu), low-shrinkage (Kalore, GC), nanohybrid (Tetric EvoCeram, Ivoclar Vivadent) or microhybrid (Filtek Z250, 3M ESPE) composites. Strain and displacement were determined using the 3D digital image correlation method based on two cameras with 1μm displacement sensitivity and 1600×1200 pixel resolution (Aramis, GOM). Microleakage along dentin axial and gingival cavity walls was measured under a stereomicroscope using a different set of teeth (N=8/group). Data were analyzed using analyses of variance with Tukeys post-test, Pearson correlation and paired t-test (α=0.05). RESULTS Strain of TEC Bulk, Filtek Bulk, Beautifil Bulk and Kalore was in the range of 1-1.5%. EverX and control composites showed 1.5-2% strain. Axial displacements were between 5μm and 30μm. The least strain was identified at 2mm below the occlusal surface in 4-mm but not in 2-mm layered composites. Greater microleakage occurred along the gingival than axial wall (p<0.05). No correlation was found between strain/displacements and microleakage axially (r2=0.082, p=0.821; r2=-0.2, p=0.605, respectively) or gingivally (r2=-0.126, p=0.729, r2=-0.278, p=0.469, respectively). SIGNIFICANCE Strain i.e. volumetric shrinkage of sculptable bulk-fill and low-shrinkage composites was comparable to control composites but strain distribution across restoration depth differed. Marginal integrity was more compromised along the gingival than axial dentin wall.