Composite Resin Systems Research Articles

Mucotoxicity of dental composite resins on a tissue-engineered human oral mucosal model

Objective Tissue-engineered human oral mucosal models have been developed for biocompatibility assessment of biomaterials. The aim of this study was to evaluate the biological effects of three different composite resin systems on a three-dimensional human oral mucosal model. Methods Full-thickness oral mucosal models were engineered by air/liquid interface culture of a human oral keratinocyte cell line on a lamina propria composed of oral fibroblasts seeded into a porous scaffold. The surface of the tissue models was exposed to three types of experimental composite resins: a TEGDMA-based, a UDMA-based, and a BisGMA/TEGDMA (80:20)-based composite resin for 24 h. The response of the engineered oral mucosa to the test materials was assessed using routine histology, the Alamar Blue tissue viability assay and IL-1β release measured by ELISA. Results Compared to the other materials tested, the TEGDMA-based composite resin caused significant damage to the oral mucosal model. Statistical analysis by one-way ANOVA followed by Tukey's analysis showed that there was a significant decrease in the viability of tissue models after 24 h exposure to TEGDMA-based composite resin. Also exposure to TEGDMA-based composite resin significantly increased the amount of IL-1β released from the oral mucosal model. Conclusion The 3D human oral mucosal model has the potential to be a more relevant and more informative model than monolayer cell culture systems for biocompatibility testing of dental materials. The results obtained from multiple-endpoint analysis of the oral mucosal model indicate significant mucotoxicity of high TEGDMA-containing composite resins.

Influence of irradiant energy on degree of conversion, polymerization rate and shrinkage stress in an experimental resin composite system

Objective This study evaluated the degree of conversion (DC), maximum rate of cure ( R p max ), and polymerization stress (PS) developed by an experimental dental composite subjected to different irradiant energies (3, 6, 12, 24, or 48 J/cm 2) under constant irradiance (500 mW/cm 2). Methods DC and R p max were monitored for 10 min on the bottom surface of 2-mm thick disks and on 150-μm thick films (representing the top of the specimen) using ATR-FTIR. PS was monitored for 10 min in 2-mm thick disks bonded to two glass rods (Ø = 5 mm) attached to a universal testing machine. One-way ANOVA/Tukey tests were used and differences in DC and R p max between top and bottom surfaces were examined using Student's t-test. Statistical testing was performed at a pre-set alpha of 0.05. Results For a given surface, DC showed differences among all groups, except at the top between 24 and 48 J/cm 2. R p max was similar among all groups at the same surface and statistically higher at the top surface. PS also showed significant differences among all groups. Data for 48 J/cm 2 were not obtained due to specimen failure at the glass/composite interface. Significance Increases in irradiant exposure led to significant increases in DC and PS, but had no effect on R p max .

A Review of Two Animal Studies Dealing with Biological Responses to Glass-Fibre-Reinforced Composite Implants in Critical Size Calvarial Bone Defects in Rabbits

In these studies, E-glass-fibre-reinforced composite (FRC) implants with photopolymerisable resin systems and bioactive glass granules (BAG) were evaluated as a reconstructive material in the critical size bone defects made to rabbits’ calvarial bones. In the first study, a new experimental resin system, DD1/MMA/BDDMA, was used to impregnate the doubleveil FRC-implants, while in the second study, a commercial resin system composed of BisGMA/MMA/PMMA was used in impregnation. These double-veil FRC-implants were coated with bioactive glass granules (BAG, 315-500 0m). In the second study, an experimental FRC consisting of two laminates of woven fibres, was also tested as an implant material. These implants were filled with BAG-granules and pure fused quartz fibers (Quartzel wool). In the first study, implantation time was 4 or 12 weeks, while in the second study, it was 12 weeks for both the implant types. Results: In the first study, the healing of the defects had started in the form of new bone growth from the defect margins, as well as small islands of woven bone in the middle of the defect, at 4 weeks postoperatively. Ingrowth of dense connective tissue into the pores of the implant was widely seen. At 12 weeks postoperatively, more bony islands were seen as compared to the animals studied at 4 weeks. Part of the newly formed bone had an appearance of lamellar structure. The porous structures of the implant were deeply filled with fibroconnective tissue. Ingrowth of maturing bone to the implant structures was occasionally seen. The inflammatory reaction was moderate, and was mostly found inside the upper part of the implant. In the second study, inflammatory reactions caused by both types of the FRC implants were very slight. Small amount of new bone had started to grow from the defect margins in doulble-veil implanted defects. No ingrowth of connective tissues or new bone formation was seen inside these implants. Instead, both the connective tissues and newly formed, mineralizing bone were seen inside the experimental double-laminate implants. SiO2-fibres seemed to cause moderate inflammatory reaction inside the implants, while BAG granules did not. In both the study groups, the brain tissue was oedemic, but no obvious serious damage was found. Conclusions: The structural properties of the FRC-implants had an influence on the healing process of the bone defect. BAG, as a constituent of the FRCimplants, enhanced the bone formation process. After some modifications to the properties of the FRC, this type of implant has possibilities to become one material alternative in clinical bone defect reconstruction at the craniofacial area in the future.

Flexure strength evaluation of a laboratory-processed fiber-reinforced composite resin

A fiber-reinforced composite resin system has been introduced for posterior restorations; however, little information is known regarding possible degradation of its flexure strength with respect to aging and cyclic loading. The aim of this in vitro study was to determine whether the fiber reinforcement improved the flexure strength of an indirect composite resin aged in air and water for 3 months and then subjected to static and cyclic loading. The materials tested in this study, non-fiber-reinforced composite resin (n=160) (Tescera Dentin) and fiber-reinforced composite resin (n=160) (Tescera U-beam and Rod), were fabricated as bars, 25.0 x 4.5 x 4.5 mm, and polished with 120- to 320-grit silicon carbide grinding paper. The static (n=15) and cyclical (n=25) flexure strengths (MPa) of specimens were tested initially and after 3 months' aging in air and water. The specimens were tested in 3-point loading in their respective aging media at a loading rate of 2 mm/min. Cyclic testing followed the staircase approach of either 1000 cycles or until specimen fracture. Statistical analysis for the static-loaded specimens consisted of a 3-way analysis of variance (media, aging, and fiber-reinforced versus unreinforced) (alpha=.05), whereas the cyclic-loaded specimens used confidence levels of .95 for the respective variables (media, aging, and fiber-reinforced versus unreinforced) and to compare static versus cyclic loading. The statistical analysis of the static specimens showed no significant difference between control (unaged) groups and aged groups and aging media, but a significant difference (P<.001) between reinforced versus unreinforced specimens. For the cyclic-loaded specimens, the confidence levels at .95 showed no difference between control (unaged) groups and aged groups and aging media (air or water), but a difference between reinforced versus unreinforced specimens, and static-loaded versus cyclic-loaded specimens. During testing, the specimens separated into several pieces when the fiber reinforcement was on the compressive side, whereas the specimen remained intact when the fiber reinforcement was on the tensile side. When compared to indirect composite resin without fiber reinforcement, the addition of fibers is an effective method to improve the flexure strength of indirect composite resin for the materials tested.

Enhanced thermal conductivity of carbon fiber/phenolic resin composites by the introduction of carbon nanotubes

The authors report a significant enhancement in the thermal conductivity of a conventional carbon fiber/phenolic resin composite system when adding highly crystalline multiwalled carbon nanotubes. They demonstrate that 7wt% of carbon nanotubes dispersed homogeneously in a phenolic resin acted as an effective thermal bridge between adjacent carbon fibers and resulted in an enhancement of the thermal conductivity (e.g., from 250to393W∕mK). These results indicate that highly crystalline carbon nanotubes can be used as a multifunctional filler to enhance simultaneously the mechanical and thermal properties of the carbon fiber/phenolic resin composites.

Gap Formation between Different Cavity Walls and Resin Composite Systems on Primary and Permanent Teeth

The aim of this study was to compare the effectiveness of five self-etching and etch-rinse dentin-bonding agents in achieving a gap-free adaptation between the restorative material and the dentin in primary and permanent teeth. Gaps located at the restoration dentin interface were evaluated using scanning electron microscopy (SEM). There were more gaps on the corner of the cavities, but no significant difference was detected between different cavity walls (p>0,05). Statistical results of the SEM analysis revealed fewer gaps in the restorations made with self-etching dentin bonding agents than etch-rinse agents at the restoration-dentin interface in both primary and permanent teeth. Self-etching bonding systems were preferable in primary and permanent teeth according to the results of this study. However, further studies should be conducted to determine a favorable strategy to eliminate the gaps on the corners of cavities and maintain a gap-free adaptation between resin composite and tooth structure.

Influence of silanated filler content on the biodegradation of bisGMA/TEGDMA dental composite resins

It has been shown that an increase in the content of nonsilanated submicron colloidal silica filler particles within dental composites resulted in the release of more bis-phenol-A diglycidyl dimethacrylate (bisGMA)-derived product, bis-hydroxy-propoxyphenyl propane, following incubation with cholesterol esterase (CE). This work further investigates the enzyme-catalyzed biodegradation of fine composite resin systems, containing silanated micron-size irregular glass fillers, commonly used in clinical restorations. Model composite resin samples (10 or 60% weight fraction silanated barium glass filler, 1 mum average particle size) based on bisGMA/triethylene glycol dimethacrylate (TEGDMA) were incubated in buffer or buffer with CE (pH = 7.0, 37 degrees C) solutions for 32 days. The incubation solutions were analyzed using high-performance liquid chromatography, UV spectroscopy, and mass spectrometry. Both groups were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. In contrast with previous findings for nonsilanated submicron filler systems, the higher filler containing composite showed an increase in its stability with time, following exposure to esterase and when compared to the lower filler content material. As well, the 60% filler composite leached less unreacted monomer TEGDMA. Since the model composite resins studied here were identical and only the filler content varied, the differences in biostability could be specifically associated with the relative amount of resin/filler distribution. The clinical use of different materials in varied dental applications (ranging from fissure sealant to tooth-colored highly filled materials) must consider the potential for different degradation profiles to occur as a function of filler content.

Reattachment of a fractured permanent molar cusp: a 12‐month follow‐up

A posterior crown fracture due to acute trauma is an uncommon type of dental injury. This case report presents combined endodontic-bioadhesive treatment of a complicated crown fracture of a permanent molar due to a horse riding accident. Endodontic therapy was initiated following surgical removal of the fractured mesiolingual cusp, which was stored frozen until bonding procedures could be carried out. Subgingival and proximal contours of the missing cusp were maintained by an interim glass-ionomer restoration during endodontic therapy. Following root-canal obturation, the fractured cusp was reattached using a total-etch adhesive and composite resin system. The patient was recalled at 1, 3, 6 and 12 months, demonstrating excellent clinical and radiographic findings.

Shear bond strength of metal-ceramic repair systems

When clinical fractures of the ceramic veneer on metal-ceramic prostheses can be repaired, the need for remake may be eliminated or postponed. Many different ceramic repair materials are available, and bond strength data are necessary for predicting the success of a given repair system. This study evaluated the shear bond strength of different repair systems for metal-ceramic restorations applied on metal and porcelain. Fifty cylindrical specimens (9 x 3 mm) were fabricated in a nickel-chromium alloy (Vera Bond II) and 50 in feldspathic porcelain (Noritake). Metal (M) and porcelain (P) specimens were embedded in a polyvinyl chloride (PVC) ring and received 1 of the following bonding and resin composite repair systems (n=10): Clearfil SE Bond/Clearfil AP-X (CL), Bistite II DC/Palfique (BT), CoJet Sand/Z100 (CJ), Scotchbond Multipurpose Plus/Z100 (SB) (control group), or CoJet Sand plus Scotchbond Multipurpose Plus/Z100 (CJSB). The specimens were stored in distilled water for 24 hours at 37 degrees C, thermal cycled (1000 cycles at 5 degrees C to 55 degrees C), and stored at 37 degrees C for 8 days. Shear bond tests between the metal or ceramic specimens and repair systems were performed in a mechanical testing machine with a crosshead speed of 0.5 mm/min. Mean shear bond strength values (MPa) were submitted to 1-way ANOVA and Tukey honestly significant difference tests (alpha=.05). Each specimen was examined under a stereoscopic lens with x30 magnification, and mode of failure was classified as adhesive, cohesive, or a combination. On metal, the mean shear bond strength values for the groups were as follows: MCL, 18.40 +/- 2.88(b); MBT, 8.57 +/- 1.00(d); MCJ, 25.24 +/- 3.46(a); MSB, 16.26 +/- 3.09(bc); and MCJSB, 13.11 +/- 1.24(c). On porcelain, the mean shear bond strength values of each group were as follows: PCL, 16.91 +/- 2.22(b); PBT, 18.04 +/- 3.23(ab); PCJ, 19.54 +/- 3.77(ab); PSB, 21.05 +/- 3.22(a); and PCJSB, 16.18 +/- 1.71(b). Within each substrate, identical superscript letters denote no significant differences among groups. The bond strength for the metal substrate was significantly higher using the CJ system. For porcelain, SB, CJ, and BT systems showed the highest shear bond strength values, and only SB was significantly different compared to CL and CJSB (P<.05). This study suggests that when fracture involves only feldspathic porcelain, any of the evaluated systems may be used, since the fracture occurred on the porcelain substrate and not on the bond interface of porcelain-restorative material. However, for the nickel-chromium alloy tested, the CoJet Sand system showed the best results for repair.

Effect of cyclic loading on fracture strength of endodontically treated teeth restored with conventional and esthetic posts

Introduction:Esthetic post and core systems were recently introduced. There are few reports regarding their behavior under cyclic loading.Objectives:This study compared the effect of cyclic loading on survival rate, residual strength and mode of fracture of endodontically treated teeth restored with esthetic and direct metallic post systems subjected to mechanical cyclic loading.Materials and Methods:Thirty canines were endodontically treated, decoronated and prepared for metal free ceramic crowns, leaving 1.5 mm of dentin for ferrule effect. They were distributed in 3 groups and restored as follows: group 1 with zirconia posts (Cosmopost) and glass-ceramic cores (IPS Empress Cosmopost); group 2 with fiber reinforced composite posts (FibreKor) and group 3 with titanium posts (AZthec Anchor). Direct resin composite (Build It FR Resin Composite) was used as core in groups 2 and 3. All specimens were restored with all ceramic crowns (IPS Empress 2). A resin cement/adhesive system (Cement It/Bond It Primer A+B) was used to lute the posts to root canals and metal free porcelain crowns to the teeth preparation. Specimens were subjected to mechanical load of 250 N for 500,000x at a frequency of 1.7 Hz and then to static load until failure in a universal testing machine. Data were analyzed using One-way ANOVA and Fischer Exact tests α=0.05.Results:All groups had 100% survival rate after cyclic loading; fracture strength values (SD) in N were: group 1 = 886.5(170.6), group 2 = 762.2(113.6) and group 3 = 768.9(72.9); there was no difference among groups (p=0.08); the percentage of mode of favorable fracture found was: group 1 = 60%, group 2 = 90% and group 3 = 50%; there was no correlation between the mode of failure and post and core system used (P=0.142).Conclusions:Esthetic post and core systems showed statistically equivalent fracture strength values, mode of failure and survival rate compared to conventional direct metallic post and resin composite core system after cyclic loading.

Effect of high light intensity on cavity wall adaptation of a resin composite with a self‐etching primer system

This study evaluated the effect of high light intensity using a plasma arc lamp on the cavity wall adaptation of photo-polymerized composite restorations. Bowl-shaped cavities were prepared on the labial surfaces of extracted bovine teeth. Each cavity was restored with a resin composite restorative system (SE Bond & Clearfil AP-X) and then polymerized using a plasma arc lamp (Arc Light II) with a series of light intensities, including 1100, 1200, 1300, 1400, 1500, and 1600 mW/cm(2), and a halogen lamp (Candilux) with 400 mW/cm(2) light intensity (n = 10). The photo-irradiation time was adjusted for each group to receive a total energy output of approximately 16,000 mJ/cm(2). The specimens were subjected to 2500 cycles of thermal fatigue and sectioned bucco-lingually through the center of the restoration. Contraction gaps on the sections were measured using a replica-SEM observation technique. The degree of gap formation was determined as the ratio of the total length of the contraction gaps to the total length of the cavity wall on each sectioned specimen. The value was converted to a percentage. The data were statistically analyzed with Kruskal-Wallis and Mann-Whitney U tests at a 0.05 level of significance. There were no significant differences (p > 0.05) in the cavity adaptation among the composites polymerized by the plasma arc lamp with high light intensities and the composite polymerized with the halogen lamp with 400 mW/cm(2) light intensity. There were no significant differences (p > 0.05) in the degree of cavity adaptation among the specimens polymerized with light intensities higher than 1100 mW/cm(2).

Clinical performance of bonded leucite-reinforced glass ceramic inlays and onlays after eight years

Objective: Ceramic inlays and onlays are a tooth colored alternative to metallic restorations. Clinical long-term data are scarce though, especially about inlays and onlays having proximal margins in dentin. The present prospective controlled clinical study evaluated the clinical performance of IPS Empress inlays and onlays with cuspal replacements and proximal margins below the cementoenamel junction over eight years. Methods: Ninety six ceramic restorations were placed in 34 patients by six dentists. The restorations were bonded with an enamel/dentin bonding system (Syntac Classic) and four different resin composite systems. The restorations were assessed after placement by two calibrated investigators using modified USPHS codes and criteria at the following time periods: baseline, 1,2,4,6 and 8 years. Results: Eight of the 96 restorations investigated had to be replaced (failure rate 8%; Kaplan–Meier): Six inlays suffered cohesive bulk fractures, two teeth required endodontic treatment. After eight years of clinical service, significant deterioration (Friedman 2-way ANOVA; P<0.05) was found for marginal adaptation of the remaining restorations. 98% of the surviving restorations exhibited marginal deficiencies, independent of the luting composite. Conclusions: IPS Empress inlays and onlays demonstrated to be successful even in large defects. Neither the absence of enamel margins, nor cuspal replacement significantly affected the quality of the restorations.

Mechanical stability of resin–dentin bond components

Objectives: To evaluate the effects of long-term storage on the mechanical properties of the components of resin–dentin bonds, that is, resin composite, adhesive system, demineralized and mineralized dentin. Methods: Specimens of resin composite (Z250) and adhesive systems (Single Bond-SB; One-Step-OS and Clearfil Liner Bond 2V-CL) were cast in molds. Dentin specimens were prepared from dentin discs obtained from the crowns of extracted human molars. Specimens of demineralized dentin were obtained by immersion of dentin discs for 6 days in 0.5 mol/l EDTA (pH 7.0). Both dentin and resin-based substrates were shaped to hourglass or I-beam specimens that were used to determine the true stress (TS) or apparent modulus of elasticity ( E), respectively. Control specimens were subjected to tensile testing at 0.6 mm/min after 24 h of immersion in distilled water. Experimental specimens were stored at 37 °C in either distilled water or mineral oil and tested after 12 months. The data of each group were individually analyzed by ANOVA and Tukey's test. Results: Both TS and E of the resin-based materials decreased significantly after 12 months of storage in water ( p<0.05), except the TS of SB ( p>0.05). No changes were observed for specimens of mineralized dentin, regardless of storage condition ( p>0.05). Storage of demineralized dentin in water did not cause any significant effect in either TS or E ( p>0.05), however, significant reductions of TS and E of demineralized dentin occurred after storage in oil for 1 year ( p<0.05). Significance: Storage time and medium may be deleterious to the mechanical properties of the resin–dentin bond components, which ultimately could compromise the durability of resin–dentin bonds.

The role of the ionomer glass component in polyacid-modified composite resin dental restorative materials.

In order to model the processes that occur within polyacid-modified composite resin ("compomer") dental restoratives, a series of experiments has been carried out with silanated and silane-free ionomer glass G338, and silanated and silane-free unreactive glass (Raysorb T-4000). In an acid-base reaction with dental grade aqueous maleic acid-acrylic acid copolymer solution, the setting time of the silanted G338 was found to be 9 min, compared with 5 min for the silane-free glass. Inclusion of each glass in an experimental composite resin system showed that the formulations which contained G338 absorbed more water than the formulations which contained Raysorb T-4000, regardless of whether or not the glass was silanted. Biaxial flexure strength was superior for experimental composites containing Raysorb T-4000, with highest results being obtained with the silanated glass. Overall these results demonstrate that silanation of the filler is essential for optimal physical properties but that, for the ionomer glass, it inhibits the acid-base reaction. The presence of ionomer glass led to an increase in water uptake compared with the unreactive glass, regardless of the presence of silane.

Resin composite monomers alter MTT and LDH activity of human gingival fibroblasts in vitro

Objectives. Substances such as monomers may be released from composite resin systems and may induce adverse effects in biological tissues. The aim of this study is to investigate the cytotoxic concentrations of resin composite monomers on cultures of human gingival fibroblasts. Methods. A range of dilutions of five resin composite monomers (HEMA, HPMA, DMAEMA, TEGDMA, and Bis–GMA) were added to the culture medium of human gingival fibroblasts for 24 h. Their cytotoxic effects were measured by using two colorimetric functional assays, mitochondrial dehydrogenase activity (MTT) and lactate dehydrogenase activity (LDH) assay. The log P values (water/octanol partition) of test monomers were also calculated computationally. Results. Mitochondrial reducing activity assessed with the MTT test was inhibited by all monomers and all the monomers increased the LDH release in a reproducible dose dependent manner. A wide range of TC 50 values (concentrations altering MTT and LDH activity by 50%) (0.32–5.8 mM by MTT assay and 0.36–6.7 mM by LDH assay) was observed. Ranking of composite resin monomer cytotoxicities (TC 50) were similar for both the MTT and LDH assays, (Bis–GMA>TEGDMA>DMAEMA>HPMA >HEMA). However, the MTT assay was found to be more sensitive than the LDH assay, particularly when lower doses of the tested monomers were determined. The ranking of TC 50 concentrations correlated with the calculated log P values. Significance. Monomers used in dental restorative materials show a variety of toxic effects on gingival fibroblasts. A combination approach using MTT and LDH assays provides valuable information about their toxic effects.

Microleakage of various composite resin systems

The object of this study was to compare the microleakage between various composite resin systems of multistep, one-bottle, and self-etching systems using electrical conductivity. After making class V cavities ( around CEJ), they were bulk filled with three kinds of resins of A3. Teeth were storaged in a saline solution for one day, after then, they were finished and polished using Sof-Lex system. Another stress of thermocycling was made for 500 times from with each dwelling time of 10 seconds. Electrical conductivity (microamphere, ) was checked four times: before and after cavity preparation, after filing, after thermocycling. One-way ANOVA and 95% Scheffe Post Hoc test was used for checking any statistical difference among groups. Another 95% Paired Samples T-test was also used for estimating any significant difference within group after cavity filling or thermocycling. The results were as follows: 1 Every specimen showed various range of microleakage after filing. There was, however, no difference between composite resin systems. 2. All composite resin systems showed marked increase in microleakage with a thermocycling (p

Flexural creep deformation and recovery in dental composites

Objectives: Three different popular composite resin systems for dental restorative applications are microfilled, minifilled and midifilled types in which deformation under stress and recovery after stress removal may be strongly influenced by filler parameters and resin formulation. The purpose of this in vitro study was to evaluate these differences in selected composite resins. Materials: Three composites, Clearfil (midifill), Charisma (minifill) and Durafill (microfill), were evaluated. Elastic, viscoelastic and viscous deformation of the composites under a constant stress and the subsequent recovery on removal of stress were measured. Dynamical mechanical properties of these materials were also characterized. Results: The mean values (and SD) of elastic, viscoelastic and viscous components of overall deformation (mm), respectively, under a constant stress of 45(5) KPa were as follows: Clearfil, 0.17(0.03), 0.06(0.02), 0.03(0.05); Charisma, 0.34(0.1), 0.09(0.04), 0.14(0.03); Durafill, 0.68(0.06), 0.14(0.03), 0.23(0.03) The results show that there are significant differences ( P<0.0001) between the different composite resins in the elastic, viscoelastic and viscous segments of deformation. The microfilled system deformed significantly more than the minifilled, and the minifilled system more than the midifilled. Storage modulus values evaluated by dynamic mechanical analysis were also significantly different ( P<0.0001). The observed differences were readily explained by the differences in the type and volume fraction of the filler content in the composites. Conclusions: Differences in time dependent deformation and recovery as well as dynamic mechanical properties of dental composites were strongly influenced by filler parameter differences. The clinical performance of restorations may be strongly influenced by the observed differences.

Effect of primers containing N-methylolacrylamide or N-methylolmethacrylamide on dentin bond durability of a resin composite after 5 years

Objectives: The effect of experimental dentin primers containing N-methylolacrylamide (MEAA) or N-methylolmethacrylamide (MEMA) on bond durability of a resin composite (Photo Clearfil A) with a bonding agent (Clearfil Photo Bond) to bovine dentin was investigated. Methods: The etching agents were 10% maleic acid (10% MA), 10% phosphoric acid (10% PA) and 10% citric acid–3% ferric chloride (10–3 solution). Water solutions of 35% hydroxyethyl methacrylate (HEMA), 50% MEAA or 30% MEMA were used as dentin primers. The etched dentin was pre-treated with the dentin primers for 30 s. The resin composite systems were applied in a Teflon tube positioned onto pre-treated dentin surfaces. After water immersion for 1 day and 5 years, the shear bond strengths were measured. The amounts of calcium dissolved with etching agents were measured using atomic absorption spectrometry. The thicknesses of hybrid layers at the dentin–resin interfaces treated with 6 mol/l HCl and 1% NaOCl were measured using scanning electron microscopy. Results: The bond strengths of the specimens (Controls) without primers to dentin etched with 10% MA and 10–3 solution significantly decreased after immersion in water for 5 years ( p<0.05) while other bond strengths did not decrease. The bond strengths of the composites to MEMA- and MEAA-primed dentin were significantly higher than that of the control after 1 day, regardless of the types of etching agents ( p<0.05). The 5 year bond strengths of the composites to HEMA-, MEMA- and MEAA-primed dentin were significantly higher than that of the control, regardless of the types of etching agents ( p<0.05). The 1 day and 5 year bond strengths of the composite to MEAA-primed dentin were significantly higher than those of the composites to HEMA-primed dentin, regardless of the types of etching agents ( p<0.05). The highest amount (182.3±8.0 μg/cm 2) of dissolved calcium was determined for the pre-treatment with 10% PA, followed by that (152.0±6.9 μg/cm 2) with 10% MA and that (140.1±2.8 μg/cm 2) with 10–3 solution ( p<0.05). The hybrid layer thicknesses (approximately 1 μm) for 10–3 solution were thinner than those (approximately 2 μm) for others after HCl immersion. For the controls, the hybrid layers after NaOCl immersion become narrower or disappeared. The main fracture pattern of specimens was a mixture of resin–dentin interface failure and dentin cohesive fracture after the bond test. Conclusions: MEAA solution was more effective in improving the bond strength of the controls to etched dentin than was HEMA after 1 day and 5 years. Clearfil Photo Bond created good hybrid dentin layers which could resist NaOCl-attack and showed good dentin bond durability when dentin primers were used, regardless of the type of etching agent.

INFLUENCE OF LIGHT INTENSITY ON TWO RESTORATIVE SYSTEMS

ABSTRACT Objective: This in vitro study examined the effect of light intensity variations on several properties of two restorative systems. Materials and Methods: Two resin composite systems (Tetric, Ivoclar Vivadent, Schaan, Liechtenstein; 2100, 3M Dental Products Division, St. Paul, Minnesota) and two dentin bonding agents (Syntac, Ivoclar Vivadent; Scotchbond Multi‐Purpose, 3M Dental) were used. To evaluate marginal gap formation in dentin cavities (with a C factor of 2.5), 48 bovine incisors were embedded in epoxy resin. The labial enamel was removed, and the dentin surface was polished to 600‐grit. Preparations were made in dentin and restored using one of four combinations of bonding system and composite. The composite was polymerized with either a high‐intensity lamp (450 mW/cm2) or a low‐intensity lamp (250 mW/cm2). After storage in water for approximately 60 minutes, the surfaces of the samples were prepared for electron microscopy analysis. Also, the flexural strength and modulus of each composite were determined at 30 minutes and 24 hours after polymerization with either the high‐ or low‐intensity light. Volumetric shrinkage was measured using the density method at four time periods for both light intensities and for wet versus dry storage. Finally, Vickers hardness profiles were evaluated to determine depth of cure. Results: Marginal analysis showed that 2100, when used with either Scotch‐bond Multi‐Purpose or Syntac, had an increased incidence of gap formation when polymerized with the high‐intensity light. Tetric had better marginal adaptation than 2100, when used with either dentin bonding agent, and with both light intensities. The flexural strength and modulus of both composites were lower with low‐intensity light‐curing. There were no differences in volumetric shrinkage or depth of cure related to curing method for either composite. Conclusions: The results of this study suggest that marginal quality may be reduced when a high‐intensity light is used to cure composite. Also, the light intensity influences development of the elastic modulus and, therefore, affects shrinkage stress in the composite. The two composites tested in this study responded differently to the different methods of light‐curing. In general, Z100 showed inferior properties than Tetric when cured with either high‐ or low‐intensity light, for both marginal integrity and the flexural modulus and strength. Finally, with a polymerization time of 40 seconds, the composites were equally well cured to a depth of 4.5 mm, regardless of the light intensity used.

Contribution of particle structure to the viscosity of SiO 2 particle-filled epoxy resin composite systems

Abstract The contribution of particle structure to the viscosity of a SiO 2-filled epoxy resin system could be revealed as one of the intrinsic properties of SiO 2 by using transparent optical microscopy with normal/cross-polarized lights. This was found to be a reliable tool for identifying particle-aggregated structures and their peculiar viscosity characteristics. The SiO 2-filled epoxy resin system contained elliptical-shaped features under transparent microscopy in normal light, which were observed as brightened domains under cross-polarization. The elliptical features exhibited repeated bright and dark changes for rotating specimens at every 45° increment. The origin of the elliptical brightness was induced from the particle-aggregated structures. The elliptical brightness, i.e. optical anisotropic property, was often observed in SiO 2 particle systems with smaller amounts of fine particles on the surface of the SiO 2 filler core particles. The optical anisotropy explained the deconstruction/reconstruction process of particle agglomeration and viscosity in changing the particulate composite structures. However, their rheological properties remained unclear solely from the well-mentioned filler primary properties based on the characterization of the SiO 2-filled epoxy resin system: median diameters, size distributions, specific surface areas and surface hydroxyl group structures.