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 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.     

Bond strength of Gradia veneering composite to fibre-reinforced composite

This study investigated the shear bond strength of light-curing veneering composite resin to glass fibre-reinforced composite (FRC). Polymer pre-impregnated FRC reinforcement was further impregnated with dimethacrylate monomer resin. The light polymerized FRC substrate was ground and dimethacrylate intermediate resin was applied on the surface before the light-curing veneering composite. Adhesional behaviour of veneering composite to the initially light polymerized FRC substrate was compared with well-polymerized FRC substrate. The treatment time of FRC substrate by the intermediate resin for 5 s and 5 min were also compared. Shear bond strength of veneering composite to FRC was determined for dry and thermocycled specimens (n = 6). The analysis of variance (anova) revealed significant differences (P = 0.042) between the shear bond strengths when 5 s and 5 min intermediate resin treatment times were compared. The highest shear bond strength (21.0 MPa) for FRC substrates was achieved when the well-polymerized FRC substrate was treated for 5 min with the intermediate resin and stored dry before tests. Thermocycling reduced the shear bond strengths. The results of this study suggest that applying the intermediate resin increased the shear bond strength values of veneering composite to FRC with multiphase polymer matrix. It was also concluded, that the use of multiphase polymer matrix FRC can be polymerized to high degree of conversion without deferiorating the shear bond strength of veneering composite to the FRC.     

The effect of fiber position and polymerization condition on the flexural properties of fiber-reinforced composite

The aim of this study was to investigate the influence of the position of the fiber rich layer on the flexural properties of fiber-reinforced composite (FRC) construction. In addition, the total residual monomer content of FRC was quantitatively determined to find out the difference of the effectiveness of two types of light-curing units using liquid chromatography (HPLC). Unidirectional continuous E-glass FRC and hybrid particulate filler composite resins were used in the fabrication of test specimens. Four different positions of the FRC layer were used: compression, neutral, tension, and vertical side position. A three-point bending test (ISO 10477) was performed to measure the flexural properties of the specimens. Position of the FRC layer had a significant effect on the flexural strength (p<0.001, ANOVA). Also, the type of light-curing device had an effect on flexural strength (p<0.001). Specimens with FRC positioned on the compression side showed flexural strength of approximately 250 MPa, whereas FRC positioned on the tension side showed strength ranging from 500 to 600 MPa. Mean flexural modulus with FRC placed horizontally ranged between 9-12 GPa; no significant difference was found between these groups. However when fiber reinforcement was positioned vertically, the flexural modulus raised up to 16 GPa. Specimens with 24 vol% glass fibers contained 52% less residual monomer than specimens without glass fibers. The monomer content was lower in specimens polymerized with the curing device with higher polymerization temperature. In order to optimize flexural strength of low fiber volume fraction, the fibers should be placed at the tension side of the specimen.     

In vitro mechanical testing of glass fiber-reinforced composite used as dental implants

AIM: The aim of this study was to evaluate the design of fiber-reinforced composite (FRC) on some mechanical properties of a dental implant. METHODS AND MATERIALS: FRC implants were fabricated using different polymerization conditions and designs of the glass-fiber structure. Specimens were tested with a cantilever bending test and a torsional test. The degree of monomer conversion (DC%) was measured using a Fourier transform infrared spectroscopy (FTIR). RESULTS: Statistical analysis showed significant differences between groups revealing mean fracture load values from 437 N to 1461 N. The mean torsional force in fracture varied from 0.01 to 1.66 Nm. The DC% varied from 50% to 90%. CONCLUSION: This study suggests by modifying the polymerization conditions and fiber orientation of FRC implants, the biomechanical properties of an FRC can be tailored to the needs of dental implants.     

The effect of glass fiber reinforcement on the residual monomer content of two denture base resins.

OBJECTIVE: The amount of residual monomer is one of the principal factors affecting the properties of acrylic resin denture bases. In recent years, glass fibers have been used to strengthen denture base resins. The purpose of this study was to investigate the effect of glass fiber reinforcement on the amount of residual methyl methacrylate released from two different denture base resins (heat cured and autopolymerized). METHOD AND MATERIALS: Continuous unidirectional and woven preimpregnated glass fiber reinforcements (Stick and Stick Net) were used to reinforce heat-curing and autopolymerizing denture base resins. RESULTS: The release of residual methyl methacrylate from heat-cured and autopolymerized test specimens reinforced with glass fibers was significantly higher than that from unreinforced test specimens. Stick Net glass fiber reinforcement resulted in significantly higher residual monomer release than did Stick glass fiber reinforcement. Test specimens made from heat-cured denture polymethyl methacrylate released less residual methyl methacrylate than did specimens made from autopolymerized polymethyl methacrylate. CONCLUSION: Glass fiber reinforcement increases the residual monomer content of denture base resins. The level of residual monomer ranged from 0.11% to 0.37% in heat-cured resin and from 0.18% to 0.46% in autopolymerized denture base resin.     

Effect of nanofiller fractions and temperature on polymerization shrinkage on glass fiber reinforced filling material.

OBJECTIVES: The aim was to evaluate the effect of different nanofiller fractions and temperature on polymerization shrinkage strain and degree of monomer conversion of short glass fibers reinforced semi-interpenetrating polymer network (semi-IPN)-polymer matrix composite resin. METHODS: Experimental composite resin was prepared by mixing 22.5 wt% of short E-glass fibers (3 mm in length) to the 22.5 wt% of resin matrix with various weight fractions of nanofillers (0, 10, 20, 30, 40, 50 wt%) and then 55 wt% of silane treated silica filler were added gradually using high speed mixing machine. Another study group contained composite resin prepared by mixing 22.5 wt% of resin matrix (without nanofillers) to 77.5 wt% of filler particles (without fiber fillers). As control material, commercial particulate filler composite resin was used. The shrinkage strain of the specimens was measured using the bonded-disk technique at 26 and 37 degrees C with respect to time. Degree of conversion of the experimental composites containing different nanofiller fractions was measured using FTIR spectroscopy. RESULTS: ANOVA revealed that fraction of nanofillers and polymerization temperature had significant effect (p<0.05) on the shrinkage strain and degree of conversion of the composite resin. Shrinkage strain correlated with nanofiller fraction and polymerization temperature (r2=0.96 and 0.95). SIGNIFICANCE: The use of high nanofiller fraction with short fiber fillers and IPN-polymer matrix yielded improved rate of shrinkage strain.     

The effect of fiber orientation on the thermal expansion coefficients of fiber-reinforced composites.

OBJECTIVES: The aim of this study was to characterize the thermal expansion and dimensional changes of fiber-reinforced composite (FRC) according to the fiber orientation, brand of FRC product and polymerization conditions. METHODS: Cubic specimens (n=5) were prepared from different brands of FRC and particulate filler composites and dimethacrylate monomer resin. The specimens were polymerized with a light-curing device for 40 s or additionally with prolonged polymerization in the light-curing oven for 15 min. Linear coefficients of thermal expansion (LCTE) values for different materials and for FRC with different fiber orientations were determined using a thermomechanical analyzer. RESULTS: All specimens exhibited linear increase in the value of LCTE between 37 and 67 degrees C. The analysis of ANOVA revealed that orientation of fiber and brand of material had significant effect (P<0.001) on LCTE values for 37-67 degrees C interval. Some interaction between factors also existed. Also, temperature interval 110-150 degrees C had significant effect on the LCTE values according to the curing unit, brand and orientation of fibers. SIGNIFICANCE: The results of this study suggest that the anisotropic nature of FRC exists also with regard to thermal expansion. The variation of LCTE of FRC compared to that of particulate filler composites might influence the interfacial adhesion of FRC appliances.     

Modification of glass fibers to improve reinforcement: a plasma polymerization technique.

OBJECTIVES: This study evaluates the effect of plasma treated E-glass fiber to improve the mechanical properties of acrylic resin denture base material, polymethylmethacrlyate (PMMA). Plasma surface treatment of fibers is used as reinforcement in composite materials to modify the chemical and physical properties of their surfaces with tailored fiber-matrix bonding strength. METHODS: Three different types of monomer 2-hydroxyethyl methacrylate (HEMA), triethyleneglycoldimethylether (TEGDME) and ethylenediamine (EDA) were used in the plasma polymerization modification of glass fibers. A radiofrequency generator was used to sustain plasma in a glass vacuum chamber. Glass fibers were modified at the same glow-discharge power of 25 W and exposure time of 30 min for each monomer. Fibers were incorporated into the acrylic with 1% (w/w) loading except control group. Specimens were prepared using a standard mold of 3 cmx0.5 cmx0.8 cm in dimension with eight specimens in each group. Samples were subjected to a flexural strength test set up at a crosshead speed of 5mm/min. Scanning electron microscopy (SEM) was used to examine the microstructure and X-ray photoelectron spectroscopy (XPS) was used for chemical analysis of the surface. RESULTS: Data were analyzed by means of ANOVA and Duncan's tests. Test results revealed that fiber reinforcement had a significant effect on the flexural strength of the specimens (p<0.05). Among the fiber reinforced groups, plasma treatment with EDA monomer resulted in the most significant increase in flexural strength values (p<0.05). XPS results have shown an increasing number of nitrogenous compounds in EDA treated fibers. The chemical structure of the surface, especially with the increase in nitrogenous compounds could give an idea for the amine film deposition and SEM figures showed an increase in surface roughness. SIGNIFICANCE: The results showed that plasma treatment with EDA monomer was an effective alternative method of increasing the flexural strength of PMMA based denture base polymers through fiber reinforcement.     

Degree of conversion of dual-cure luting resins light-polymerized through various materials

OBJECTIVE: The aim of this study was to investigate the degree of monomer conversion of four dual-cure luting resins irradiated through various restorative materials or dentin. MATERIAL AND METHODS: RelyX ARC (3M-ESPE), RelyX Unicem (3M-ESPE), Variolink 2 (Ivoclar,Vivadent), and Panavia F 2.0 (Kuraray) were mixed in accordance with the manufacturer's instructions. They were placed under the disks (thickness 1.5 mm) representing a metal restoration, a composite restoration (Sinfony D A3), a fiber-reinforced composite (EverStick 0.5 mm + 1.0 mm Sinfony D A3) restoration, and dentin. Five specimens (thickness 0.6 mm) in each group were irradiated through the disks for 40 s (Optilux-501, 800 mW/cm(2)). Light polymerization of the dual-cure luting resin without the covering disk was used as control. The degree of monomer conversion (DC%) was determined by Fourier transform infrared spectroscopy (FT-IR)/ATR spectrometry from the bottom of the resin. The infrared spectra were recorded at every 5.2 s for 15 min beginning from the mixing of the resin. RESULTS: ANOVA revealed significant differences in DC% between the luting resins tested (p<0.001) and the different restorations (p<0.001). RelyX ARC showed the highest degree of conversion 15 min after the start of polymerization, whereas Panavia F 2.0 and RelyX Unicem showed the lowest. CONCLUSIONS: The degree of conversion of dual-cured luting resins differed significantly. Furthermore, the restorative material significantly influenced the DC% of the dual-cure luting resin underneath.     

高强玻璃纤维／树脂复合材料的力学性能研究

目的研究高强玻璃纤维增强丙烯酸类树脂的力学性能。方法按要求制作丙烯酸树脂浇铸体,测试其强度;将高强玻璃纤维按39.5%、48.7%、56.8%、72.4%质量分数,与丙烯酸树脂制成单向纤维/树脂复合材料,并测试其弯曲强度、弯曲模量和层间剪切强度。结果随着纤维含量增加,复合材料的弯曲强度和弯曲模量呈显著性增加(P<0.05),可达弯曲强度(1414.7±64.5)MPa,弯曲模量(39.6±1.6)Gpa;层间剪切强度呈先升后降趋势(P<0.01),最低为(58.7±4.4)MPa。结论高强玻璃纤维对丙烯酸树脂的弯曲性能具有增强作用。复合材料的纤维含量不应过高。     

玻璃纤维预拉伸对增韧光固化树脂基桩力学性能的影响

目的 研究玻璃纤维预拉伸对自行研制的高强玻璃纤维增韧光固化树脂复合材料（FRC）桩力学性能的影响。方法 利用加载装置将高强玻璃纤维分别拉伸0%、0.5%、1.0%后,按60%体积比浸入自行配置的光固化树脂基质,采用压膜法制成玻璃纤维增韧树脂基齿科桩,三点弯曲测试各试样的弯曲模量、弯曲强度和弯曲载荷,测试结果进行统计学分析。使用扫描电子显微镜观察FRC桩横截面和断裂面的形态。结果 玻璃纤维拉伸率对FRC桩的力学性能影响有显著差异,其中拉伸率为1.0%的玻璃纤维制成的FRC桩综合性能最佳,弯曲模量(20.40±1.40) GPa,弯曲强度(573.38±29.45) MPa,弯曲载荷(180.42±5.88) N,与未预拉伸的玻璃纤维增韧的FRC桩有显著差异(P<0.05)。结论 玻璃纤维预拉伸对FRC桩有增韧效果。     

Fracture force, deflection at fracture, and toughness of repaired denture resin subjected to microwave polymerization or reinforced with wire or glass fiber

STATEMENT OF PROBLEM: The ultimate goal of denture repair is to restore the denture's original strength and avoid further fracture. The best materials and methods for repair have not been conclusively determined. PURPOSE: This study investigated the fracture force, deflection at fracture, and toughness of a heat-polymerized denture base material repaired with heat-polymerized resin, autopolymerized resin alone, or autopolymerized resin with glass fiber or wire reinforcement. MATERIAL AND METHODS: Eight groups were evaluated: 6 with autopolymerized resin repairs, 1 with heat-polymerized resin repairs, and a control group of intact specimens. The 6 autopolymerized resin groups included 1 group with no reinforcement, 1 treated with microwave irradiation after polymerization, 2 with monolayer or multilayer glass fiber reinforcement, and 2 with round or braided wire reinforcement. Each group consisted of 12 specimens. The experimental specimens were cut, and a 3-mm butt joint gap was repaired as indicated by the group assignment. A 3-point bending test was used to determine the fracture force, deflection at fracture, and toughness of the specimens. The data were analyzed with 1-way analysis of variance and the Tukey post-hoc test (alpha=.05). RESULTS: The fracture force (28.4 to 73.4 N), deflection (1.6 to 3.8 mm), and toughness (0.02 to 0.13 J) values for all repaired groups were significantly lower than those for the control group (82.79 N, 4.4 mm, and 0.16 J, respectively), with one exception: the mean fracture force of specimens reinforced with round wire (102.9 N). Failure mode was always adhesive, meaning that fracture occurred between the denture base and repair resin. CONCLUSION: Among the repair treatments tested, the most effective was microwave-irradiated, autopolymerized resin reinforced with round wire or monolayer glass fiber ribbon.     

Effects of barriers on chemical and biological properties of two dual resin cements

The aim of this study was to investigate the degree of conversion, monomer release, and cytotoxicity of two dual‐cure resin cements (Cement‐One and SmartCem2), light‐cured across two indirect restorative materials in an attempt to simulate in vitro the clinical conditions. The results obtained show that the degree of conversion was influenced by both barriers, but the effect of the composite material was greater than that of the ceramic one. The amount of monomers released from the polymerized materials in the absence of barriers was significantly lower than that released in the presence of either the ceramic or the composite barrier. However, a higher amount of monomers was released in the presence of the ceramic barrier. All materials, in all the experimental conditions employed, induced slight cytotoxicity (5–10%) on human pulp cells. Our examinations showed that the two resin cements had similar chemical and biological properties. The decreased degree of conversion of the dual‐curing self‐adhesive composite showed that the light‐curing component of these materials has an important role in the polymerization process. In clinical practice, it is therefore important to pay attention to the thickness of the material used for the reconstruction.     

Influence of polymerization initiator for base monomer on microwave curing of composite resin inlays

Microwave polymerization was used to make composite resin inlays and the effect examined of the concentration of polymerization initiator for the base monomer. The monomers used were 2,2-bis [4-(3-methacriloxy-2-hydroxypropoxy) phenyl] propane (Bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA). Bis-GMA and TEGDMA were mixed in a ratio of 6:4 by weight and were separated into five groups. To each group was added benzoyl peroxide (BPO) in the ratios of 0.1, 0.3, 0.5, 0.7 and 0.9 wt% as the polymerization initiator. These were used as the base monomers. The results showed that the degree of conversion of the cured sample increased with increasing concentration of BPO from 0.1 to 0.5 wt%, however there was no significant difference at 0.5, 0.7 and 0.9 wt% (P> 0.01). Compression strength, diametral tensile strength and the Knoop hardness showed a similar tendency as the degree of conversion. No significant difference was recorded in the Knoop hardness between the top and the bottom surfaces (P> 0.01), which suggested a uniform polymerization in the cured sample. Thus, microwave polymerization would be an efficacious method for making resin inlays with the addition of BPO to the base monomer (Bis-GMA:TEGDMA, 6:4). The maximum conversion was found at a concentration of 0.5 wt%.     

The effect of the photopolymerization method on the quality of composite resin samples

An optimal degree of conversion and minimal polymerization shrinkage are generally antagonistic goals, as increased monomer conversion invariably leads to elevated polymerization shrinkage values. However, both parameters are indispensable for an optimal resin composite restoration. A number of approaches have been used to reduce the stress on the restoration cavity wall interface, such as dentine bonding agents to counteract polymerization shrinkage, stress‐absorbing lining materials and low‐intensity curing lights to control the flow capacity of the material during polymerization. However, the configuration of the cavity and cohesive fractures of the material and surrounding tooth tissues are still a problem in day‐to‐day clinical practice. A new photopolymerization light source, pulsed laser, ensures a higher degree of conversion and lower polymerization shrinkage, and differentiates this technique from standard polymerization methods and continuous‐wave argon laser polymerization. The coherence and monochromacity of pulsed laser light set at 468 nm and the far greater intensity of laser nanopulses produce a saturation effect in the depths of the composite, thus resulting in higher monomer conversion. The total amount of energy illuminating the sample surface, which is only one‐fifth of that of conventional methods, and the cooling and relaxation of the material between nanopulses may be responsible for the reduced net polymerization shrinkage.     

The influence of fiber reinforcement of composites on shear bond strengths to enamel

STATEMENT OF PROBLEM: Fiber-reinforced composites (FRC) are used in direct intra-oral applications as periodontal splints and chairside tooth replacement by bonding them to etched enamel with resin adhesives and composites. There is little information regarding the effect of FRC on the shear bond strength of composite to etched enamel. PURPOSE: The purpose of this study was to examine the effect of resin preimpregnated and non-preimpregnated fiber-reinforced composites on enamel to composite shear bond strength (SBS). MATERIAL AND METHODS: Specimen groups (n = 12) consisted of a control (composite with no fiber reinforcement), Ribbond, Splint-It Unidirectional, Splint-It Woven, and Connect, which were bonded to 37% phosphoric acid etched Prime and Bond NT adhesive-treated bovine enamel surfaces on a bed of Tetric Flow composite. Specimens were thermocycled 1000 times between 5 degrees and 55 degrees C and loaded on a universal testing machine in shear at a linear increasing load until fracture (MPa). The fractured surfaces of the debonded specimens were evaluated to determine the nature of the fracture with a light binocular microscope (x10). Shear bond strength data were subjected to analysis of variance (ANOVA) and Student-Newman-Kuels tests (P <.05). RESULTS: Mean MPa +/- SD for the test groups were as follows: Control, 15.6 +/- 2.4; Splint-It Unidirectional, 15.3 +/- 2.4; Splint-It Woven, 16.5 +/- 1.8; Connect, 18.8 +/- 1.5; and Ribbond, 15.8 +/- 2.2. The Connect FRC group had significantly higher (P <0.05) enamel SBS than all other groups. Fracture analysis showed varying types of failures among the groups, with cohesive fractures within the fiber reinforcement of Splint-It Unidirectional and Connect, cohesive fractures within the bonding resin/flowable composite for Ribbond and the control, and adhesive fracture at the fiber reinforcement interface with Splint-It Woven. CONCLUSION: Within the limitations of this study, no differences in SBS were observed with the addition of 3 of the 4 FRCs compared to composite without FRC, with the exception of the Connect product which provided significantly higher SBS values.     

Efficacy of a self-curing adhesive-resin cement system on luting glass-fiber posts into root canals: an SEM investigation

PURPOSE: The aim of this study was to evaluate the efficacy of a new bonding-luting system in resin tag, adhesive lateral branch, and hybrid layer formation when used in combination with an experimental fiber post. MATERIALS AND METHODS: Thirty anterior teeth extracted for periodontal reasons were selected for this study. They were endodontically treated and randomly divided into three groups of 10 samples each: group 1 = Excite light-cured bonding agent in combination with Variolink II resin cement; group 2 = Excite dual-cured bonding agent self-activated by an experimental microbrush in combination with MultiLink resin cement; and group 3 = one-step bonding system in combination with Dual Link resin cement. In groups 1 and 3, the primer-adhesive solution was light cured before placing the resin cement and the post, whereas in group 2 the adhesive/luting materials were not light cured. Twenty FRC Postec translucent posts (groups 1 and 2) and 10 EndoAesthetic translucent fiber posts (group 3) were used. One week later, the root samples were processed for scanning electron microscopic (SEM) observations. RESULTS: Microscopic examinations of restored interfaces from group 2 revealed a resin-dentin interdiffusion zone higher than that seen in samples from groups 1 and 3 (P < .05). At the apical and middle thirds, the samples from group 2 showed significantly more resin tags than the other two groups. CONCLUSION: The dual-cure self-activating system showed a more uniform resin tag and resin-dentin interdiffusion zone formation along root canal walls than light-curing systems.     

Effect of location of glass fiber-reinforced composite reinforcement on the flexural properties of a maxillary complete denture in vitro

Objective. To evaluate the effect of the location of glass fiber-reinforced composite (FRC) reinforcement on the flexural load at the proportional limit (FL-PL) and the flexural deflection of a maxillary acrylic resin complete denture. Material and methods. Maxillary acrylic resin complete dentures strengthened with and without FRC reinforcement were tested. The polymerized FRC was embedded in the denture base resin in the doughy state and placed (1) under the ridge lap region, (2) in the anterior region, (3) in the middle region or (4) in the anterior and posterior regions. The FL-PL and flexural deflection value at the 100-N loading point of the reinforced maxillary denture specimens were tested. Results. All of the reinforced dentures had a higher FL-PL than the denture without reinforcement but the FL-PL values of all the dentures were not significantly different from each other. The efficiency of the FRC reinforcement compared to the unreinforced denture was 1.54-1.75 times greater. All of the reinforced dentures showed significantly lower deflection compared to the unreinforced denture, but the flexural deflections of all the dentures were not significantly different from each other. Conclusions. The location of the FRC reinforcement did not affect the fracture resistance of the maxillary acrylic resin complete denture. All of the reinforced dentures had higher FL-PL and lower flexural deflection than the denture without reinforcement.     

Bonding of fibre-reinforced composite post to root canal dentin

OBJECTIVE: The aim of this study was to determine bonding properties of two types of fibre-reinforced composite (FRC) posts cemented into root canals of molars. Serrated titanium posts served as reference. METHODS: Prefabricated carbon/graphite FRC posts with cross-linked polymer matrix and individually formed glass FRC posts with interpenetrating polymer network (IPN) polymer matrix were compared. The crowns of extracted third molars were removed and post space (diameter: 1.5mm) was drilled, etched and bonded. The posts were treated with dimethacrylate adhesive resin, light-polymerized and cemented with a dual-polymerizing composite resin luting cement. After thermocycling (6000x) the samples were cut into discs of thicknesses: 1, 2 and 4mm (n=12/group). Push-out force was measured by pushing the post from one end. Assessment of failure mode was made under a stereomicroscope (1, adhesive failure between post and cement; 2, cohesive failure of post-system; 3, adhesive failure between cement and dentin). RESULTS: The push-out force increased with increased height of dentin disc in all groups (ANOVA, p<0.001). In the 4mm thick dentin discs the individually formed glass FRC posts showed highest push-out force and the difference to that of the titanium posts was significant (ANOVA, p<0.001). The other differences were not statistically significant. None of the individually formed glass FRC posts showed adhesive failures between the post and the cement. CONCLUSIONS: Contrary to the other posts, there were no adhesive (post-cement) failures with the individually formed glass FRC posts, suggesting better interfacial adhesion of cement to these posts.