Effect of Distance on Light Transmission Through Polymerized Resin Composite.

OBJECTIVE: Light transmittance of dental composites varies between products and shades, but also light curing units differ to each other in their irradiance and fiber optic structure of curing tip. The aim of this study was to investigate whether there is linear relationship between the distance of the curing tip to the resin composite and irradiance at lower surface of the resin composite. MATERIALS AND METHODS: Disks of 1 mm thickness (6mm diameter) were fabricated. Light transmittance (intensity) through the disk was measured at distance of 0, 2, 4, 6, 8, 10 mm from the light tip with two light curing units Elipar S10 (3M-ESPE) and Silverlight (GC). Irradiance ratio (irradiance on the sensor surface without the composite disk / with the composite disk) was calculated and plotted against the distance of the light curing tip. Statistical analysis was carried out using analysis of covariance (ANCOVA, Tukey's, α =0.05). RESULTS: Irradiance ratio varied between 18% to 24% with Silverlight and 21% to 26% with Elipar S10 light curing units. There were statistically significant differences between the ratios with different distances of the light curing tip (p⟨0.05). Interestingly, the highest irradiance ratio for Elipar S10 unit was found with 4 mm distance of the tip, whereas Silverlight unit had the highest ratio with 6 mm distance. Out of two tested resin composites, the flowable composite showed higher irradiance ratio than regular packable resin composite. CONCLUSIONS: Increase of distance of the light curing tip from the composite surface decreased the absolute irradiance underneath of composite, as expected. However, there seemed to be device dependent optimal distance of 4-6 mm to reach the most efficient irradiance ratio through the composite resin keeping in mind that most efficient transmission of light through the material is reached by having light curing tip in contact to the material.

Effect of several intracanal medicaments on the push-out bond strength of ProRoot MTA and Biodentine.

AIM: To evaluate the effect of prior application of several intracanal medicaments on the push-out bond strength of ProRoot MTA and Biodentine. METHODOLOGY: Sixty freshly extracted maxillary anterior teeth were sectioned below the cementoenamel junction, and the root canals instrumented using rotary files. Thereafter, a parallel post drill was used to obtain a standardized root canal dimension. The roots were randomly assigned into one of the following groups with respect to the intracanal medicament applied: group 1: calcium hydroxide (CH) powder (Merck, Darmstadt, Germany) mixed with distilled water; group 2: a mixture of metronidazole, ciprofloxacin and minocycline (triple antibiotic paste); group 3: a combination of amoxicillin and clavulanic acid (Augmentin; Champs Pharmacy, San Antonio, TX, USA); group 4: an antibiotic-corticoid compound paste (Ledermix; Riemser, Greifswald, Germany); and group 5: no medicament (control). Following removal of medicaments with instrumentation and irrigation, the roots were cut into 1-mm-thick parallel transverse sections in a coronal-to-apical direction (5 slices/tooth). Thereafter, the specimens were divided into two subgroups according to the calcium silicate cement applied (n = 30/group): (i) ProRoot MTA (Dentsply Tulsa Dental, Tulsa, OK, USA) and (ii) Biodentine (Septodont, Saint-Maur-des-Fosses, France). A push-out test was performed, and the data were analysed statistically using two-way anova and Tukey's post hoc test. RESULTS: Regardless of the type of intracanal medicament used, Biodentine had significantly higher bond strength than MTA (P < 0.05). The highest push-out bond strength results were obtained in CH-treated dentine. Compared with other medicaments, this value was only significantly higher than that of Ledermix (P < 0.05). In both the MTA and Biodentine groups, pairwise comparisons between other medicaments showed similar debonding values (P > 0.05). CONCLUSIONS: Biodentine had a higher bond strength to root canal dentine than ProRoot MTA. Prior CH in distilled water intracanal placement increased the dislodgment resistance of both calcium silicate cements.

Effect of monomer composition of polymer matrix on flexural properties of glass fibre-reinforced orthodontic archwire.

To compare force levels obtained from glass fibre-reinforced composite (FRC) archwires. Specifically, FRC wires were compared with polymer matrices having different dimethacrylate monomer compositions. FRC material (E-glass provided by Stick Tech Ltd, Turku, Finland) with continuous unidirectional glass fibres and four different types of dimethacrylate monomer compositions for the resin matrix were tested. Cross-sectionally round FRC archwires fitting into the 0.3 mm slot of a bracket were divided into 16 groups with six specimens in each group. Glass fibres were impregnated by the manufacturer, and they were initially light-cured by hand light-curing unit or additionally post-cured in light-curing oven. The FRC archwire specimens were tested at 37°C according to a three-point bending test in dry and wet conditions using a span length of 10 mm and a crosshead speed of 1.0 mm/minute. The wires were loaded until final failure. The data were statistically analysed using analysis of variance (ANOVA). The dry FRC archwire specimens revealed higher load values than water stored ones, regardless of the polymer matrix. A majority of the FRC archwires showed higher load values after being post-cured. ANOVA revealed that the polymer matrix, curing method, and water storage had a significant effect (P < 0.05) on the flexural behaviour of the FRC archwire. Polymer matrix composition, curing method, and water storage affected the flexural properties and thus, force level and working range which could be obtained from the FRC archwire.

The effect of chlorhexidine and dimethyl sulfoxide on long-term sealing ability of two calcium silicate cements in root canal.

OBJECTIVES: To evaluate the long-term effect of chlorhexidine (CHX) and dimethyl sulfoxide (DMSO) on the sealing ability and biomineralization of two different calcium silicate cements (CSC) in root canal. METHODS: Sixty human third molar root canals were obturated with ProRoot MTA or Biodentine. Before obturation the canals were irrigated with saline (control), 2% CHX or 5% DMSO. Microleakage was tested after three days and after six months. After additional six months (12 months after root filling) the roots were cut into 2 mm thick dentine discs. The discs were stored in artificial saliva for one year. The bond strength was measured with the push-out method, and the failure mode was evaluated with a stereomicroscope. The most apical disc of each tooth was used for Vickers hardness test. RESULTS: No significant differences between the groups was found in initial microleakage. The leakage increased significantly during the 6-month storage in all groups except in Biodentine-CHX group and Biodentine-DMSO group. CHX and DMSO irrigation significantly increased the leakage with ProRoot MTA with time, but there was no statistically significant difference compared to the ProRoot MTA-control group at six months' time point. CHX significantly reduced the push-out bond strength of ProRoot MTA. With Biodentine irrigation with CHX or DMSO resulted with significantly higher push-out strength compared to the Biodentine control group. Fracture analysis showed statistically significant difference in the distribution of the fractures between the groups, but neither CHX nor DMSO change the fracture pattern statistically significantly. With Vickers hardness test ProRoot MTA with and without DMSO as the final irrigant showed significantly higher dentin hardness than any Biodentine-group. SIGNIFICANCE: Considering that aging increased the leakage in all groups except with Biodentine-DMSO and the differences in the push-out strength and surface microhardness data, it appears that the time-related biomineralizing effect of MTA and Biodentine does not improve sealing to dentin. CHX significantly reduced ProRoot MTA bond strength and increased pure adhesive failures with both cements.

Effects of heat treatment of wood on hydroxylapatite type mineral precipitation and biomechanical properties in vitro.

Wood is a natural fiber reinforced composite. It structurally resembles bone tissue to some extent. Specially heat-treated birch wood has been used as a model material for further development of synthetic fiber reinforced composites (FRC) for medical and dental use. In previous studies it has been shown, that heat treatment has a positive effect on the osteoconductivity of an implanted wood. In this study the effects of two different heat treatment temperatures (140 and 200 degrees C) on wood were studied in vitro. Untreated wood was used as a control material. Heat treatment induced biomechanical changes were studied with flexural and compressive tests on dry birch wood as well as on wood after 63 days of simulated body fluid (SBF) immersion. Dimensional changes, SBF sorption and hydroxylapatite type mineral formation were also assessed. The results showed that SBF immersion decreases the biomechanical performance of wood and that the heat treatment diminishes the effect of SBF immersion on biomechanical properties. With scanning electron microscopy and energy dispersive X-ray analysis it was shown that hydroxylapatite type mineral precipitation formed on the 200 degrees C heat-treated wood. An increased weight gain of the same material during SBF immersion supported this finding. The results of this study give more detailed insight of the biologically relevant changes that heat treatment induces in wood material. Furthermore the findings in this study are in line with previous in vivo studies.

The Effect of Chlorhexidine and Dimethyl Sulfoxide on Long-Term Microleakage of Two Different Sealers in Root Canals.

OBJECTIVE: The aim of root canal obturation is to prevent leakage and inhibit microbial invasion. This study aimed to determine the effect of chlorhexidine (CHX) and dimethyl sulfoxide (DMSO) as final irrigants on microleakage of root filling immediately and after 18 months. The hypothesis was that either CHX or DMSO would not affect the immediate or long-term microleakage. METHODS: A total of 120 human third molar root canals were obturated with RealSeal SE or Topseal and gutta percha. Before obturation, the canals were irrigated with saline (control), 2% CHX or 5% DMSO. Microleakage of half of each groups (n=10) was measured after 3 days, and of the other half was measured after 18 months with fluid filtration method. RESULTS: In immediate measurements, RealSeal SE performed significantly better in CHX-irrigated group (p=0.035; Mann-Whitney test). For both sealers, DMSO had the lowest mean microleakage values, which were also statistically significantly lower than with CHX irrigation within sealers (p<0.009 for Topseal and p=0.04 for RealSeal SE; Mann-Whitney test). With RealSeal SE, the microleakage with CHX was significantly higher than that in controls (p=0.022; Mann-Whitney test). CONCLUSION: Neither final irrigant showed statistically significant differences in the immediate microleakage within the two sealers. Irrigation with DMSO caused significantly less microleakage than CHX for both sealers after 18 months.

Incremental layers bonding of silorane composite: the initial bonding properties.

OBJECTIVES: Lack of oxygen inhibition layer of silorane composite with cationic polymerization raises the question of the bonding of incremental layers of the composite. This study aimed to evaluate the bond strength of the silorane composite layers. METHODS: Fresh, 20 s, 5 min aged silorane composite (Silorane, 3M-ESPE) was used as substrate to adhere new silorane composite. For a comparison, dimethacrylate-based composite resin (Z250, 3M-ESPE) was adhered to the silorane composite with or without intermediate adhesive resin. As a control, dimethacrylate composite with oxygen inhibition layer was attached to fresh dimethacrylate composite. The bonded specimens (n=12/group) were water stored for 24 h. The shear bond strengths (SBS) were measured with a crosshead speed of 1.0 mm/min. Failure modes were assessed. Data were analysed by ANOVA, Tukey's post hoc tests and Chi-square tests (p=0.05). RESULTS: Dimethacrylate-dimethacrylate composite resin combination showed the highest mean SBS (33.0 MPa) values with no adhesive failures. Fresh silorane-silorane SBS was slightly lower (26.7 MPa) and was further decreased by aging the substrate for 20s (25.4 MPa) and 5 min (22.4 MPa). The percent of adhesive failures increased from 25% to 75%, respectively. The failure modes were significantly different (Chi-square, p<0.001). Silorane-dimethacrylate composite showed the lowest (4.0 MPa) SBS among the groups, which was increased significantly by use of phosphate-methacrylate-based intermediate resin (p<0.05). CONCLUSION: In order to bond dimethacrylate composite to silorane composite, a phosphate-methacrylate-based intermediate resin is required. The silorane composite showed slightly lower incremental bonding properties than conventional dimethacrylate composites.

Frontal bone defect repair with experimental glass-fiber-reinforced composite with bioactive glass granule coating.

OBJECTIVE: The aim of this preliminary study was to test the bioactive glass-coated fiber-reinforced composite (FRC) as a reconstruction material in the treatment of experimental defects in the frontal bone of rabbits. METHODS: FRC made of E-glass fiber and BisGMA-PMMA resin matrix system was used in the study. Pieces of nonpolymerized FRC were coated with particulate bioactive glass granules S53P4 (BAG), and then the FRC was polymerized and post-cured by heat in air to reduce the quantity of residual monomers, and to sterilize the material for the animal study. Two round defects (5 mm in diameter) were drilled in the upper bony walls of 12 NZW rabbits' frontal sinuses, and rectangular FRC plates were applied over the defects. In the control group, no FRC plates were used. The bone defect healing process was evaluated on histological sections at 3, 6, and 8 weeks, postoperatively. SEM-EDX analysis was used to determine reactive layers of bioactive glass granules. RESULTS: The healing progressed from the fibroconnective tissue phase at 3 weeks to lamellar bone formation at 6 and 8 weeks. The difference in new bone formation between the implantation groups and control groups was not statistically significant, although in some animals the effect of the implant on bone healing was clearly positive. A moderate foreign body reaction was seen on the implant surface where BAG granules did not uniformly cover the implant's polymer matrix. CONCLUSIONS: This study suggests that the tested FRC implant with bioactive glass coating provides an alternative for bone defect reconstruction. However, more research on this composite material and its biocompatibility is needed.

The effect of fiber orientation on the polymerization shrinkage strain of fiber-reinforced composites.

OBJECTIVE: The aim of this study was to characterize the linear polymerization shrinkage strain of glass fiber-reinforced composite (FRC) according to the fiber orientation. METHODS: Test specimens (n=5) (10.0 x 10.0 x 1.5mm) were prepared from different brands of photopolymerizable resin-preimpregnated FRC; unidirectional continuous FRC, experimental random-oriented FRC, and bidirectional continuous FRC. As control materials, particulate filler composite resin and unfilled dimethacrylate monomer resin were used. Two uniaxial strain gages (gage length 2mm) were used to measure shrinkage strains in two directions: longitudinally and transversally to the fiber direction. The uncured composite or resin was placed on top of the strain gages, covered with a separating sheet and a glass plate, and irradiated for 40s with a light-curing unit. The shrinkage strain was monitored for 300 s. ANOVA and Tukey's posthoc test were used at a significance level of 0.05. RESULTS: ANOVA revealed that orientation of fiber and brand of material had a significant effect (P<0.05) on shrinkage strain. The unidirectional FRC revealed no shrinkage longitudinally to the fiber direction, whereas the shrinkage occurred transversally to the fiber direction. Particulate filler composite resin and unfilled resin revealed equal shrinkage strain in both of the measured directions. SIGNIFICANCE: Anisotropic nature of FRC exists with regard to polymerization shrinkage strain. The variation of polymerization shrinkage strains of FRC compared to those of particulate filler composites and unfilled resin might be important for future clinical applications.

The effect of a novel silane blend system on resin bond strength to silica-coated Ti substrate.

OBJECTIVES: The adhesive performance of 3-acryloyloxypropyltrimethoxysilane and a silane blend consisting of 3-acryloyloxypropyltrimethoxysilane and 1,2-bis(triethoxysilyl)ethane, adhering an experimental dendrimer-based resin to a silica-coated titanium surface, conditioned by CoJet method, was evaluated in vitro. METHODS: 3-Acryloyloxypropyltrimethoxysilane (1.0 vol%) and a blend of 3-acryloyloxy-propyltrimethoxysilane and 1,2-bis(triethoxysilyl)ethane (both 1.0 vol%) were prepared in acidified 95 vol% ethanol. A commercial 3-methcryloyloxypropyltrimethoxysilane (ESPE Si) was used as control. The silanes were applied onto tribochemically silica-coated titanium surfaces. Fresh silane solution hydrolysis (activation) was monitored by Fourier transform infrared (FTIR) spectrometry. Experimental dendrimer resin stubs were applied and photo-polymerized on titanium. The specimens were thermocycled (6000 cycles, 5-55 degrees C). Before measuring shear bond strength of the resin to titanium, surface imaging was carried out with a scanning electron microscope (SEM) with elemental analysis applying energy dispersive X-ray analysis (EDXA). RESULTS: Statistical analysis (ANOVA) showed that the highest shear bond was obtained with 1.0 vol% 3-acryloyloxypropyltrimethoxysilane+1.0 vol% 1,2-bis(triethoxysilyl)ethane blend (5.2+/-1.3 MPa), and the lowest result with fresh commercial 3-methacryloyloxypropyltrimethoxysilane, ESPE Sil (2.1+/-0.8 MPa). 3-Acryloyloxypropyltrimethoxysilane yielded 4.1+/-1.0 MPa. The type of silane affected significantly the shear bond strength (ANOVA, p<0.001). All silanes were activated according to the infrared spectra. The SEM/EDXA analysis revealed an uneven distribution of titanium, silicon, and aluminum on silica-coated Ti surfaces. CONCLUSION: Silanization with 3-acryloyloxypropyltrimethoxysilane might offer better bonding of a novel dendrimer resin to silica-coated titanium than using a pre-hydrolyzed 3-methacryloyloxypropyltrimethoxysilane.

The effect of three silane coupling agents and their blends with a cross-linker silane on bonding a bis-GMA resin to silicatized titanium (a novel silane system).

OBJECTIVES: Three activated organofunctional silane coupling agents alone and blended with a non-functional cross-linker silane were evaluated as adhesion promoters in an experiment where a bis-GMA (bis-phenol-A-diglycidyldimethacrylate) resin was bonded to silicatized titanium. The adhesive performances of the silanes were assessed as shear bond strength values. MATERIALS AND METHODS: 3-Methacryloyloxypropyltrimethoxysilane, N-[3-(trimethoxysilyl)propyl]ethylenediamine and [3-(triethoxysilyl)propyl]urea were prepared as 1.0vol.% solutions in 95 vol.% ethanol. They were each also blended with 1.0 vol.% 1,2-bis-(triethoxysilyl)ethane solutions that were activated for 1 or 24 h. Titanium slides were cleaned, silicatized, distributed randomly to study groups and silanized with nine silane solutions. After silanization experimental bis-GMA resin stubs were photo-polymerized and post-polymerized in a light-curing unit. The shear bond strength was measured as 'dry samples' and after thermo-cycling (6000 cycles at 5-55 degrees C). RESULTS: The type of silane affected significantly the shear bond strength (p<0.001) and the use of cross-linker silane (p<0.005) according to the statistical analysis (ANOVA). It showed that the highest shear bond strength for thermo-cycled resin stub samples (n=8/group) was obtained with a blend of 1.0vol.% 3-methacryloyloxypropyltrimethoxysilane+1.0 vol.% 1,2-bis-(triethoxysilyl)ethane blend (10.4+/-3.5 MPa). The lowest results were obtained with 1.0 vol.% [3-(triethoxysilyl)propyl]urea (4.5+/-1.0 MPa), and with 1.0 vol.% N-[3-(trimethoxysilyl)propyl]ethylenediamine (4.5+/-1.4 MPa). CONCLUSIONS: Silanization with a blend of a functional silane and a cross-linker silane (a novel silane system) might improve the hydrolytic stability of a siloxane film between silicatized titanium and a bis-GMA resin.

Evaluation of five dental silanes on bonding a luting cement onto silica-coated titanium.

OBJECTIVES: Five commercial dental silanes were evaluated in vitro as adhesion promoters bonding a luting cement to silica-coated titanium surfaces. METHODS: Titanium slides (n=20) were cleaned with alumina sand and then silica-coated with a special sand consisting of alumina particles coated with silica. The bonding of a resin composite cement (3M ESPE, Seefeld, Germany) to silica-coated and silanized titanium was evaluated by using the dental silane (RelyX Ceramic Primer) that belongs to the RelyX ARC cementing kit, and comparing it to four other dental silanes (Bisco Porcelain Primer, Cimara, ESPE Sil, and Pulpdent Silane Bond Enhancer). The resin composite cement stubs (n=8) were light-polymerized onto a silanized silica-coated titanium surface. The shear bond strength of the cement stubs was measured after dry storage and thermo-cycling 6000 times between 5 and 55 degrees C. The silanes and their reactions were chemically monitored by using Fourier transform infrared analysis. RESULTS: Statistical analysis using ANOVA revealed that the brand of silanes and the types of storage condition differ significantly (p<0.005). The highest shear bond strength was obtained with RelyX ceramic silane in dry conditions (19.5+/-4.3 MPa), and after thermo-cycling (16.6+/-3.5 MPa). The lowest results were obtained using Pulpdent Silane Bond Enhancer, in dry conditions (7.8+/-2.2 MPa), and after thermocycling (5.3+/-2.4 MPa). The analysis showed that silanes had different pH values. Some differences were detected between the silanes and their reactions. CONCLUSIONS: Dental silanes provide different bonding strengths and have differences in their pH, solvent system and silane concentration.

Bond strength of luting cement to casting and soldering alloy.

Adjustment of metal alloy framework of the porcelain-fused-to-metal crown by soldering minor marginal deficiences prior insertion may sometimes be needed. The aim of this study was to compare shear bond strengths of four luting cements to casting metal alloy and soldering metal alloy. A total of 64 flame cast non-precious metal alloy and flame soldered metal alloy samples were used. Durelon, Panavia F, RelyX Unicem Applicap and RelyX ARC stubs were bonded to the alloy substrate surface. After stored in water at 37 degrees C for 1 week, shear bond strength of the cement to the alloy was measured. Differences were analyzed using one way ANOVA (p<0.05). There were no difference between the cast metal alloy and soldering metal alloy substrate.

Isocyanato- and methacryloxysilanes promote Bis-GMA adhesion to titanium.

In dentistry, adhesion promotion with 3-methacryloyloxypropyltrimethoxysilane is usually sufficient, but its hydrolytic stability is a continuous concern. The hydrolytic stability of an alternative, 3-isocyanatopropyltriethoxysilane, was compared with that of conventional 3-methacryloyloxypropyltrimethoxysilane. Two silanes, both in 0.1 and 1.0 vol-% in ethanol-water, were evaluated in the attachment of an experimental bis-phenol-A-diglycidyldimethacrylate (Bis-GMA) resin to grit-blasted (with two different systems) titanium. Silane hydrolysis was monitored by FTIR spectrometry. Bis-GMA resin was applied and photo-polymerized on titanium. The specimens were thermocycled (6000 cycles, 5-55 degrees C). Surface analysis was carried out with scanning electron microscopy. Statistical analysis (ANOVA) showed that the highest shear bond was achieved with 0.1% 3-isocyanatopropyltriethoxysilane (12.5 MPa) with silica-coating, and the lowest with 1.0% 3-methacryloyloxypropyltrimethoxysilane (3.4 MPa) with alumina-coating. The silane, its concentration, and the grit-blasting method significantly affected the shear bond strength (p < 0.05). SEM images indicated cohesive failure of bonding, and, in conclusion, 3-isocyanatopropyltriethoxysilane is a potential coupling agent.

Initial adhesion of glass-fiber-reinforced composite to the surface of porcine calvarial bone.

The aim of this preliminary study was to compare the initial bond strength of the glass-fiber-reinforced composite veil to the surface of the porcine calvarial compact bone using different adhesives. Fiber-reinforced composite (FRC) made of E-glass fiber veil with the BisGMA-PMMA resin system was used in the study. For the shear bond strength test, porcine calvarial bone cubes were mounted into resin matrix. FRC-veil discs were bonded to compact bone with different types of adhesives: (A) BisGMA-HEMA based (3M-ESPE Scotchbond Multi-Purpose Adhesive), (B) 4-META/UDMA/BisGMA based (Unifil Bond Bonding Agent) and MDP based (Clearfil Se Bond adhesive), (C) UDMA/BisGMA/PMMA-based experimental adhesive, and (D) silane-based (APS, ICS, MPS) experimental adhesives. The surface of the bone was mechanically roughened and was either used as such, treated with dental primers (Unifil Bond Self-etching Primer, Clearfil Se Bond Primer), or treated with an experimental silane mixture (APS, ICS, MPS), or with a mixture of the experimental silane liquid and Clearfil Se Bond Primer. The 3M-ESPE Scotchbond Multi-Purpose Adhesive and UDMA/BisGMA/PMMA experimental adhesive gave poor results in the shear bond test (0.58 and 0.40 MPa, respectively). Unifil Bond Bonding Agent and Clearfil Se Bond adhesive with respective primers markedly improved the shear bond strength; with Unifil the result was 3.40 MPa, and with Clearfil it was 6.19 MPa. When the bone surface was primed with a mixture of Clearfil Se Bond Primer and Clearfil Porcelain Bond Activator, the Clearfil Se Bond adhesive-impregnated FRC veil gave the best adhesion to the bone surface in this test: 9.50 MPa. The addition of bioactive glass granules between the veil and the bone lowered the shear bond strength in the test system described above to 6.72 MPa. The test systems with the silane mixture were also promising. In the SEM study, it was found that the mechanical treatment reveals the pores of the bone surface. Chemical treatments of the bone surface improved the adhesion of the FRC veil to the bone. The results showed that the adhesion of the FRC to the surface of the bone can be significantly improved with mechanical roughening and with special chemical treatments of the bone surface.

The degree of conversion of fiber-reinforced composites polymerized using different light-curing sources.

OBJECTIVES: Fiber-reinforced composites (FRC) with different polymer matrix compositions are available on the market. The aim of this study was to compare the degree of monomer conversion of FRC that contained either dimethacrylate resin matrix or semi-IPN resin matrix. In addition, the effect of different types of light-curing units and durations of light irradiation on the degree of conversion was evaluated. MATERIALS AND METHODS: Continuous unidirectional fibers impregnated with dimethacrylate or semi-IPN resin were compared. As control materials, a particulate filler composite resin and an unfilled resin were used. The materials were photopolymerized using various irradiation times and different types of light-curing units (quartz-tungsten-halogen with standard or turbo tip, light-emitting diode and plasma-arc). Degree of monomer conversion (DC%) was determined by FT-IR spectrometry. The infrared spectra were recorded at seven different time points after polymerization. RESULTS: ANOVA showed significant differences between the materials tested, and the curing units (P<0.05). The DC% of semi-IPN and dimethacrylate matrix FRC was not statistically different (P>0.05) compared to that of unfilled resin. Conventional quartz-tungsten halogen with turbo tip showed the highest DC% (69-72.3%), whereas the plasma-arc curing unit showed the lowest degree of conversion (47-62%). SIGNIFICANCE: Within the limitations of this study, it can be concluded that semi-IPN matrix of FRC did not show a difference in the degree of conversion compared to dimethacrylate resin FRC when quartz-tungsten or a light-emitting diode polymerization unit was used. The plasma-arc light-curing unit showed a lower degree of conversion with all materials compared to the light-emitting diode and quartz-tungsten-halogen lamps.

The shear bond strength of bidirectional and random-oriented fibre-reinforced composite to tooth structure.

OBJECTIVES: The objective of this study was to evaluate the bond strength and fracture pattern of fibre-reinforced composite (FRC) with two different fibre orientations and matrix compositions to dentine and enamel. MATERIALS AND METHODS: Extracted human molars were used as substrates (enamel and dentine) with a standard acid-etch technique. Light-polymerizable FRC with two different interpenetrating polymer network matrices and random or bidirectional fibre orientations was applied to the substrate, together with the adhesive resin. As a control, particulate filler composite resin was bonded to the substrates. The substrate-composite specimens (n=10) were either stored in water for 24h or additionally thermocycled for 6000 cycles. The shear bond strength of composite to substrate was measured and the fracture surfaces were evaluated visually and with SEM. RESULTS: Three-way factorial analysis of variance highlighted significant differences according to the substrate type, storage condition and composite material (p<0.05). Dentine specimens showed a significantly lower range of bond strength values (8.8-15.0 MPa), compared with enamel specimens (14.0-23.0 MPa). The highest mean bond strength in dentine was 15.0 MPa obtained with bidirectional FRC, whereas the highest bond strength in enamel was 23.0 MPa obtained with random-oriented FRC. Thermocycling did not identify a significant effect on the dentine bond strength, but did identify a significant decrease in enamel bond strength values (p<0.05). Several cohesive failures were observed in the tooth structure with the control material, whereas no cohesive bulk fracture of the tooth was observed when a thin layer of FRC was placed at the interface. CONCLUSIONS: The addition of bidirectional or random continuous fibres did not show any significant improvement in bond strength values compared to control of particulate filler. However, the difference in the fracture patterns observed may have implications for clinical applications.

Evaluation of intensity of artefacts in CBCT by radio-opacity of composite simulation models of implants in vitro.

OBJECTIVES: The aim was to compare the intensity of artefacts in CBCT images caused by different percentages of radio-opacifying material in composite simulation models of implants. Titanium and zirconia models of implants were used as a reference for the evaluation of the intensity of artefacts. METHODS: Seven different percentages of radio-opacifying BaAlSiO2 fillers were added to composite resin to fabricate seven step wedges and simulation models of implants. Titanium and zirconia simulation models of implants were also fabricated. Aluminium step wedge was used as a reference for the measurement of grey values in intraoral radiographs. Step wedges were exposed with a Planmeca Intra X-ray machine (Planmeca Oy, Helsinki, Finland). All composite, titanium and zirconia simulation models of implants were exposed with a SCANORA(®) 3D dental X-ray machine (Soredex, Tuusula, Finland). Images and grey values were analysed with ImageJ software (National Institutes of Health, Bethesda, MD). To demonstrate possible artefacts between all the simulation models of implants, the images were also visually compared with each other using ImageJ software. RESULTS: Artefacts were clearly present in CBCT images caused by titanium and zirconia and when the composite material consisted at least 20% BaAlSiO2. The intensity of artefacts increased when the radio-opacity of the composite material increased. CONCLUSIONS: Materials containing less radio-opacity produce less pronounced artefacts. The cut-off point for artefacts is at 20% radio-opaque filling material in composite material.

The influence of short-term water storage on the flexural properties of unidirectional glass fiber-reinforced composites.

OBJECTIVE: The aim of this study was to determine flexural properties of unidirectional E-glass fiber-reinforced composite (FRC) with polymer matrices of different water sorption properties. METHODS: Rhombic polymer and FRC test specimens made of three commercially available diacrylate resin (Sinfony Activator, Triad Gel, 3M Scotchbond Adhesive) and different volume fractions of fibers were tested with three-point bending test according to ISO 10477 after storing in water for 30 days. Water sorption of specimens was also measured. RESULTS: Flexural strength of specimens with 45 vol% fraction E-glass fibers varied from 759 to 916 MPa in dry conditions. Water-stored specimens showed flexural strengths of 420-607 MPa. ANOVA analysis revealed that the fiber-volume fraction and the water sorption of the polymer matrix had a significant effect (p < 0.001) on the flexural properties. Dehydration of specimens recovered the mechanical properties. Decrease of flexural properties after water immersion was considered to be mainly caused by the plasticizing effect of water and the decrease depended on water sorption. SIGNIFICANCE: Use of polymers with low-water sorption seems to be beneficial in order to optimize the flexural properties of FRC.

Composite-composite repair bond strength: effect of different adhesion primers.

OBJECTIVES: Recently, new products have been introduced to repair composite restorations that may be used as 'one-step' primers or monomers and silane compounds which are used separately as 'multi-step' primers. The aim of this study was to compare the shear bond strength of the new composite resin to aged composite, by using different adhesion primers. METHODS: The substrates were particulate filler composite (Z250, 3M-ESPE), which was aged by boiling for 8 h and storing at 37 degrees C in water for 3 weeks. The aged substrate surfaces were wet-ground flat with 320-grit silicon carbide paper and subjected randomly (n=8) to either one-step adhesion primer: Compoconnect (CC) (Heraus Kulzer), or multi-step: Clearfil Repair (CF) (Kuraray) or an intermediate resin: Scothchbond Multi-purpose adhesive resin (3M-ESPE) according to the manufacturers' recommendations. Specimens with no surface treatment were used as control (C). New composite resin (Z250) was added to the substrate using 2 mm layer increments and light cured. The specimens were either water stored for 48 h or water stored for 24 h and then thermocycled for 6000 cycles. The shear bond strengths were measured with a crosshead speed of 1.0 mm/min using a universal testing machine. Data were analysed by two-way ANOVA and Tukey's post-hoc tests (p=0.05). RESULTS: All surface treatment methods showed significant difference compared to control (p<0.05). CF showed higher bond strength than CC and MP (p<0.05). Storage condition did not show a significant difference (p>0.05) in bond strength values. CONCLUSION: It was concluded that multi-step adhesion primer yielded higher bond strength compared to one-step primer or intermediate resin.