Polymerization shrinkage,stress, and degree of conversion in silorane‐ and dimethacrylate‐based dental composites

To compare two kind of resin‐based dental composites, the polymerization shrinkage, contraction stress (CS), and degree of conversion (DC) of four dimethacrylate‐based and one silorane‐based composite were investigated. To determine shrinkage, the composites were packed, respectively, into a cylindrical cavity in human teeth and imaged using X‐ray microcomputed tomography to determine the precise volume before and 30 min after photopolymerization. To determine CS, the sample was applied in a similarly sized cylinder in a universal testing machine and monitored for 30 min. FTIR spectroscopy was used to determine DC. The volumetric shrinkage (range: 1.1–3.1%) and maximum CS (range: 1.2–3.5 MPa) differed significantly among the tested composites but not the final DC (range: 62.3–69.1%). The silorane‐based composite displayed the lowest volumetric shrinkage and CS of all composites. No correlation was observed between the stress and volumetric shrinkage values of the dimethacrylate‐based composites. A moderate correlation was found between stress and DC (r = 0.836), which was significant at 20 and 40 s. The silorane‐based composite exhibited superior shrinkage behavior compared with conventional dimethacrylate composites with comparable polymerization kinetics. The CS was dependent on multiple variables, including the volumetric shrinkage, DC, and curing rate. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Photopolymerization of a novel tetraoxaspiroundecane and silicon‐containing oxiranes

New multifunctional silorane‐based systems were investigated, with respect to their photoreactivity, as potential matrix resins for low‐shrinkage/stress dental composites. The objective of this investigation was to synthesize and evaluate the reactivity of a silicon‐analogue oxaspirocyclic monomer with silorane‐based matrix resin systems during visible‐light polymerization. The experimental formulations contained (1) a silicon‐containing 1,5,7,11‐tetraoxaspiro[5.5]undecane (TOSU– IV ), (2) a phenylmethylsilane containing two cyclohexyloxiranyl groups, (3) a cyclotetrasiloxane containing four cyclohexyloxiranyl groups, and (4) a photocationic initiator system. Three main aspects were studied: (1) the photoreactivity of the tetraoxaspiroundecane (TOSU)/silorane reactant mixtures with differential scanning photocalorimetry, (2) oxirane ring‐opening reactions of siloranes during binary photopolymerization with Fourier transform infrared (FTIR), and (3) oxaspirocyclic ring‐opening reactions of the TOSU reactant during homophotopolymerization and binary photopolymerization with FTIR and NMR. A diallyl ether precursor of TOSU– IV was also included in selected studies. The main findings were as follows: (1) a feasible route for the successful synthesis of a silicon analogue (TOSU– IV ) was developed; (2) TOSU– IV was compatible and photoreactive, making possible the reduction of polymerization stress in silorane‐based matrix resins; and (3) spectroscopic evidence for both oxirane and oxaspirocyclic ring opening during the visible‐light photopolymerization of the test formulations was found. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 336–344, 2007     

Compatibility of silorane composite repaired with methacrylate-based restorative systems

The aim of this study was to evaluate the repair bond strength of silorane composites using either the silorane or methacrylate-based restorative systems. Expired silorane composite was used as the substrate material in all experimental groups. Silorane blocks (5?×?5?×?4?mm) were fabricated and stored at 37?°C for 24?h. Six experimental groups were developed according to the repair: I-silorane composite (no intermediary); II-P90 Bond/Silorane; III-P90 Adhesive System (primer/bond)/silorane; IV-P90 bond/Scotchbond Universal/methacrylate composite (Filtek P60); V-Scotchbond Universal/methacrylate; and VI-silane/Adper Single Bond 2/methacrylate. The repaired blocks were stored for 24?h at 37?°C, and then sectioned, yielding stick-shaped specimens (0.5?mm²) that were tested in tensile (0.5?mm/min). The results were analyzed using ANOVA/Tukey test (α?=?0.05). The interfacial micromorphology and nanoleakage were also analyzed under SEM. Scotchbond Universal/methacrylate composite, either associated with the P90 bond or not, exhibited similar bond strength to that of P90 Adhesive System/silorane composite. Scotchbond Universal either associated with the P90 Bond or not to repair the silorane allowed no pre-testing failures. The worst scenarios were repairing the silorane with no intermediary (G-I) or combination silane/Adper Single Bond 2/methacrylate composite (G-VI) that presented significantly lower bond strengths and higher incidences of pre-failure testing. The importance of the silane was not confirmed. Characteristic micromorphology and no signs of nanoleakage were identified in all experimental groups. The silane-containing, phosphorylated methacrylate-based adhesive associated with a methacrylate composite was proven to reliably repair the expired composite in a similar way to that of the application of dedicated silorane adhesive.     

Preparation and characteristic of a sodium alginate/carboxymethylated bacterial cellulose composite with a crosslinking semi‐interpenetrating network

A novel ionic crosslinking sodium alginate (SA)/carboxymethylated bacterial cellulose (CM‐BC) composite with a semi‐interpenetrating polymer network (semi‐IPN) structure was developed in this study. The composite was prepared through the blending of an SA gel with CM‐BC then crosslinking by Ca²⁺ followed by a freeze‐drying process. Scanning electron microscopy showed the composite matrix organized in a three‐dimensional network of CM‐BC interpenetrated against SA molecular chains with a quantity of calcium alginate microspheres upon the surface. The swelling ratios of the composite were enhanced by 183, 198, and 212% with the supplementation of CM‐BC weight fractions of 25, 50, and 75%, respectively; the swelling ratios changed with changing pH. The tensile modulus, tensile strength, and elongation at break of SA were enhanced by 165, 152, and 188%, respectively, with the addition of 50 wt % CM‐BC. This study demonstrated that the semi‐IPN structure dramatically changed the swelling and mechanical properties of the composite, and the semi‐IPN will be a promising candidate for biomedical applications such as wound dressings and skin tissue engineering. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39848.     

Thin film composite sodium alginate membranes for dehydration of acetic acid and isobutanol

Dehydration of widely used organic solvents such as acetic acid (AA) and isobutanol (IB) is challenging tasks, which form close boiling mixtures with water. Sodium alginate (SA) thin film composite membranes were prepared and crosslinked with 2,4‐toluene diisocyanate (TDI) and glutaraldehyde for dehydration of IB and AA/water mixtures through pervaporation (PV). The crosslinked and uncrosslinked SA composite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and universal testing machine for intermolecular interactions, crystalline nature, thermal stability, surface morphology, and tensile strength, respectively. At a feed composition of 98 wt % IB and 95 wt % AA aqueous solutions, the TDI crosslinked SA composite membrane exhibited separation factors of 3229 and 708 with reasonable fluxes of 0.021 and 0.012 kg m^?2 h^?1, respectively. The results obtained in the study for IB and AA systems were compared with other SA membranes reported in the literature. The membranes appeared to have potential for commercial PV ability to dehydrate the solvents up to desirable purity levels (>99%) and feasibility of preparing them in a composite form which would enable scale‐up into modular configurations. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40018.     

Development of low‐shrinkage composites based on novel crosslinking vinylcyclopropanes

Polymerization shrinkage of methacrylate‐based dental composites remains a major concern in restorative dentistry. Cyclic monomers that undergo ring‐opening polymerization are known to exhibit reduced polymerization shrinkage compared to methacrylates. In this article, the synthesis of four crosslinking 1,1‐disubstituted 2‐vinylcyclopropanes bearing rigid spacers is described. These monomers were synthesized by esterification of 1‐ethoxycarbonyl‐2‐vinylcyclopropane‐1‐carboxylic acid with the corresponding diols. The photopolymerization kinetics of these monomers was investigated by photo‐differential scanning calorimeter using bis(4‐methoxybenzoyl)diethylgermane as the photoinitiator. The synthesized vinylcyclopropanes (VCPs) were shown to be more reactive than the frequently used reactive diluent triethylene glycol dimethacrylate. Composites based on these VCPs showed good mechanical properties and exhibited a significantly reduced volumetric shrinkage and shrinkage stress compared to a corresponding dimethacrylate‐based restorative material. This work highlights the excellent potential of VCPs as alternatives to methacrylates in the development of low‐shrinkage dental composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45577.     

Microtensile bond strength of composite-to-composite repair with different surface treatments and adhesive systems

Objectives: The purpose was to investigate the effect of different surface treatments and bonding agents on the repair bond strength of different resin-based restorative materials by microtensile bond strength (μTBS) testing protocol. Materials and Methods: 24 Grandio SO(VOCO) and 24 Filtek Z250(3?M) resin composite blocks were prepared. Half of the samples (N?=?12) were diamond bur-roughened and the other half (N?=?12) were sandblasted by 50?μm aluminum oxide particles. They were further divided into four sub-groups (n?=?3) and received the following: Sub-Group1: Adper Single Bond2 (Etch&Rinse) (3?M); Sub-Group2: Clearfil SE (Self-etch) (Kuraray); Sub-Group3: Beauty Bond (HEMA-free all-in-one) (Shofu); Sub-Group4: All Bond3 (HEMA-free, hydrophobic, etch&rinse) (Bisco). The samples were repaired by Filtek Z250 to form a block. All of the resultant sub-groups combinations consisted of one of the composite type, surface treatment type, and adhesive systems. A total of 18 groups were prepared including 2 homogeneous blocks. They were thermocycled and μTBS measurements were performed. Data were statistically analyzed with Kruskall–Wallis and Mann–Whitney U tests. Results: The experimental regroups’ μTBS reached to 34.67–66.36% and 43.44–95.52% of the cohesive bond strength for Grandio SO and Z250, respectively. The pre-existing composite type is found to be statistically important. When the surface is bur-finished Grandio performed better; when air-abrasion is considered Z250 showed higher bond strength. All-in-one adhesive system produced the weakest bond strength at all parameters. Conclusion: It may be suggested that when the pre-existing composite is unknown, air-abrasion may be performed with etch&rinse or two-step self-etch adhesives.     

Effect of ceramic surface treatments on the bond strength of different composite resins

This study was aimed to observe the relationship between the different surface treatments and the bond strength of both composite based adhesive cement and zirconia ceramic. Thirty-two zirconia ceramic discs were fabricated by following the instructions of manufacturer (5 × 5 × 1.5 mm). Four subgroups were obtained from the specimens according to the specified surface treatments respectively: (a) C: control groups: no treatment; (b) SB: sandblasting with 125 μm aluminum oxide particles for 10 s; (c) SC: silica coating for 10 s; (d) Nd :YAG laser . The composite resin specimens Panavia F and Clearfil SA were introduced and polymerized to the treated bonding areas. Afterwards the specimens were stored in distilled water at 37 °C during 24 h, and the shear test was applied. The data were statistically analyzed by ANOVA and Duncan tests. The bond strength was stated significantly higher in silica coating/Panavia F group (23.35 MPa). The lowest bond strength was stated in control groups cemented with Clearfil SA (12.25 MPa). As a result it was determined that the bond strength has affected the both surface treatments and cement types (p < 0.001). The silica coating –treated zirconia ceramic recorded a significant increase in mean bond strength values.     

Incorporation of EGCG into an etch-and-rinse adhesive system: mechanical properties and bond strength to caries affected dentin

This study evaluated how a matrix metalloproteinase (MMP) inhibitor (EGCG) incorporated into an etch-and-rinse adhesive system (AS) affects the long-term microtensile bond strength (MTBS) to caries affected dentin (CAD) and flexural strength (FS) of AS. Forty CAD surfaces received acid conditioning and were randomly divided into four groups (n?=?10): EGCG-PRE – dentin treatment with 200?μg/mL EGCG solution; EGCG-INC – 200?μg/mL EGCG solution incorporated into SA; CHX-PRE – dentin treatment with 2% digluconate solution; NT – no treatment. The AS (Adper Single Bond 2, 3M ESPE) was applied and resin composite blocks were built on the dentin. Beam-shaped specimens (0.8?mm²) were obtained submitted to MTBS testing following 24?h, 6 months or 1 year of water storage (WS). Adhesive interface was analyzed by SEM. FS testing was performed by preparing specimens with the adhesive system, with or without the EGCG solution (200?μg/mL) (n?=?10). Tests were carried out in a universal machine (0.5?mm/min). MTBS data were submitted to two-way ANOVA and Tukey’s test, whereas FS data, to the Student’s t-test (α?=?0.05). MTBS values were not affected by EGCG application, either incorporated or used as a dentin treatment agent, regardless of the WS period; however, CHX negatively affected MTBS to CAD (p?<?0.001). WS significantly reduced MTBS values (p?<?0.001) from the 6-months time point. FS was not affected by EGCG incorporation into the SA (p?=?0.2527). EGCG incorporation into AS was unable to maintain bond stability to CAD over time, whereas it did not compromise adhesive’s property.     

The effect of bulk-fill flowable composites on the fracture resistance and cuspal deflection of endodontically treated premolars

The aim of this study was to evaluate the effect of bulk-fill flowable composites on cuspal deflection and fracture resistance of endodontically treated teeth. Forty-two maxillary premolars were subjected to endodontic treatment followed by the preparation of mesioocclusodistal cavities. Teeth were divided into six groups according to restorative materials as follows: Group 1: Clearfil Majesty Flow and Clearfil Majesty Posterior; Group 2: Venus Bulk Fill and Clearfil Majesty Posterior; Group 3: Clearfil Majesty Posterior; Group 4: Vertise Flow and Clearfil Majesty Posterior; Group 5: SDR and Clearfil Majesty Posterior; and Group 6: x-tra base and Clearfil Majesty Posterior. A single-step self-etch adhesive (OptiBond All-in-One) was applied to all groups, except Group 4. The cavities were restored with a centripetal incremental insertion technique and flowable composites using a 2-mm-thick base material, except for Group 3. The distance between cusp tips was measured before and after the cavity preparations, after the restorations, and after thermal cyclus with a digital micrometer. After measuring, each tooth was subjected to compressive loading with a stainless steel ball (4 mm diameter) perpendicular to the occlusal surface with a crosshead speed of 1 mm/min, and mean loads necessary to fracture were recorded in Newtons. The data were statistically analyzed by Kruskal–Wallis test. No statistically significant differences were found between groups in fracture strength or cuspal deflections (p > 0.05). Bulk-fill flowable composite bases did not change the cuspal deflection or fracture resistance of endodontically treated teeth, compared with that of a conventional flowable base and conventional resin composite.     

NaOCl degradation of one-step one-bottle self-etch adhesives bonded to bovine dentine

Objective: The aim of the present study was to assess the influence of an in vitro aging regime (NaOCl storage) on dentine microtensile bond strength (μTBS) of five one-step one-bottle self-etch adhesives in comparison with bond strength of two-step self-etch adhesive.

Material and methods: Flattened dentine surfaces from 30 bovine incisors were bonded with five one-step one-bottle self-etch adhesives (iBond, Clearfil S3 Bond, AdheSE One F, G-Bond, Optibond all-in-one) and one two-step self-etching adhesive (Clearfil SE Bond). Composite buildups were done with microhybrid resin composite. Bonded samples were sectioned into resin–dentine sticks of 0.8 mm² cross section. Randomly selected 20 sticks were tested directly by microtensile bond strength testing machine, whereas another randomly selected 20 sticks were tested after being stored in solution of 10% NaOCl for 5 h. Data were analyzed by two-way analysis of variance (ANOVA) and Tukey’s honest significant difference (HSD) tests (p < 0.05).

Results: All adhesives exhibited similar dentine bond strength with exception of G-Bond. After NaOCl storage, μTBS reduced in all groups significantly. The lowest μTBS were found for G-Bond. Rest of one-step self-etch adhesives presented similar μTBS with two-step self-etch adhesive.

Conclusion: Interfaces of resin–dentine bonding are susceptible to NaOCl degradation. The amount of the destruction depends on adhesive system. NaOCl degradation of the nonresin encapsulated collagen fibers might decrease long-term stability of resin bonding with dentine.     

Effect of irradiation source on the dentin bond strength of a one-bottle universal adhesive containing an amide monomer

One-bottle universal adhesives have been widely used because of their simplicity of bonding procedures for various dental materials. The present study evaluated the effect of the polymerization light source on the micro-tensile bond strengths of a universal adhesive (Clearfil Universal Bond Quick) to dentin in comparison with a one-bottle self-etch adhesive (Clearfil S³ Bond Plus) and two 2-step self-etch adhesives (Clearfil SE Bond and Clearfil SE Bond 2). The adhesives were applied to extracted human dentin according to the manufacturer’s instructions and irradiated using either a quartz-tungsten-halogen (QTH) or blue light-emitting diode (LED). Subsequently, a resin composite was incrementally built on each adhesive and light-cured using the QTH. The bonded specimens were sectioned and subjected to micro-tensile bond strength tests. Both the type of adhesive and the light source were found to statistically affect the bond strength, with no interactions. The LED gave greater bond strength than the QTH. The bond strengths of the two-step adhesives were significantly higher than those of the one-bottle products, irrespective of the light source. The Clearfil Universal Bond Quick exhibited significantly higher bond strength than the Clearfil S³ Bond Plus. LED curing improved the performance of Clearfil Universal Bond Quick, and this product generated bond strength superior to that of the existing one-bottle adhesive Clearfil S³ Bond Plus.     

Synthesis of acidic vinylcyclopropanes for dental applications

The multistep synthesis of four new acidic vinylcyclopropanes is described. These monomers were fully characterized using ¹H NMR, ¹³C NMR and ³¹P NMR spectroscopy and high‐resolution mass spectrometry. The homopolymerization of the corresponding polymerizable di‐tert‐butyl phosphates as well as the copolymerization of each acidic monomer with 1,1‐diethoxycarbonyl‐2‐vinylcyclopropane were investigated using photo‐differential scanning calorimetry with bis(4‐methoxybenzoyl)diethylgermane as photoinitiator. Self‐etch adhesives based on the synthesized acidic vinylcyclopropanes are able to achieve a strong bond between a dental composite and both dentin and enamel. Flowable composites containing these acidic vinylcyclopropanes exhibit good mechanical properties. The replacement of methacrylates by vinylcyclopropanes leads to a significant reduction of the shrinkage stress of flowable composites. © 2017 Society of Chemical Industry     

Influence of Dynamic Loading and Different Adhesive Systems on the Microleakage in Root Canals

Abstract

The objective of this study was to evaluate the influence of dynamic loading and different adhesive systems on the microleakage in root canals.

80 human premolars were used in this study. The crowns of the teeth were sectioned at the cemento-enamel junction using a low speed diamond saw. After post space preparation, the roots were randomly assigned to 4 groups (n = 20) and restored with different adhesive systems. Group 1: Rely X ARC (RA) + Single Bond (SA), Group 2: Clearfil SA Cement (CL), Group 3: Panavia F 2.0 (PAN), Group 4: Rely X Unicem (RU). All the teeth were restored with the same type of glass fiber post and coronal cores built up with light-polymerizing hybrid composite resin. Half of the specimens of each group (n = 10) were subjected to additional dynamic loading in a universal testing machine. Apical parts of the roots were attached to computerized fluid filtration device for leakage measurement.

The two-way ANOVA test was used first to detect overall significance, followed by two-sample t-test to identify which pairs of groups had significant differences. For each outcome statistical significance was set at p < 0.05. Dynamic loading significantly increased the microleakage values for Rely X ARC (p = 0.005), Clearfil SA Cement (p = 0.002) and Rely X Unicem groups (p = 0.001) but Panavia F 2.0 group was not affected by the dynamic loading (p = 0.111). One-way ANOVA test was applied to detect any significant differences in microleakage values for the adhesive systems. In the unloaded groups, there is no difference between the adhesive systems (p = 0.13). For the dynamically loaded groups, there is only significant difference between PAN and RA groups (p = 0.010). Post-hoc pairwise comparisons were done using Tukey’s multiple comparisons. Differences between Rely X ARC-Clearfil SA Cement and Rely X ARC-Panavia F 2.0 are statistically significant (p = 0.009, 0.013).     

紫外光(UV)固化胶黏剂收缩率与强度的研究

UV胶黏剂的固化收缩率与固化后的残留应力乃至粘接强度有着密切关系。对比UV胶黏剂中不同丙烯酸单体、几种低聚物和阳离子单体的收缩率和相应的粘接强度。讨论了单体和树脂类型对收缩率和粘接强度的影响。介绍了以低收缩丙烯酸酯树脂和阳离子树脂为主体树脂,以低收缩单体为稀释剂、配合填料和适当增强剂制备出混合型UV胶黏剂。该胶黏剂粘接强度和耐久性好,其固化收缩率为3．5％,远低于普通自由基型UV胶黏剂。经湿热老化试验后,粘接强度保持率仍保持在80％。     

Adhesion of substrate–adherent combinations for early composite repairs: Effect of intermediate adhesive resin application

This study evaluated the effect of intermediate adhesive resin application (IAR) on tensile bond strength (TBS) for early composite repairs in situations where substrate and repair composite bonded together were once of the same kind with the substrate (similar) and once other than the substrate material (dissimilar). Specimens from three types of composites (TPH Spectrum (TPH), Charisma (CHA) and Filtek Z250 (Z250)) were fabricated. The specimens in each composite group (n=72) were randomly divided into six subgroups (n=12). In each composite group, the similar and two dissimilar composites were bonded onto the substrates once using an IAR (Adper Single Bond Plus) and once without. After water storage for 1 week at 37 °C, substrate–adherent combinations were submitted to tensile test. Data were analyzed with three-way ANOVA and Tukey's tests (α=0.05). The substrate–adherent combination (p=0.0001), adherent (repair) composite (p=0.0001), and application of IAR (p=0.0001) significantly affected the results. Utilization of IAR improved the repair bond strength for all composite combinations.     

Effect of surface conditioning methods,adhesive systems and resin composite on repair strength of dimethacrylate and silorane resin composites

This study evaluated the effect of surface conditioning methods and adhesive systems on the repair bond strength of resin composites. Specimens (FLS: Filtek LS) (N = 144) were prepared using a silicone matrix. The specimens were stored in distilled water and then were randomly divided into the twelve groups (n = 12) according to the surface conditioning method (unground or diamond bur) and adhesive system (no adhesive, LS: Filtek LS, AS: Adper Scotchbond SE Plus) and resin composite (FLS: Filtek LS; FS: Filtek Supreme). The specimens were fixed in an hourglass-shaped silicone matrix and the other half of the specimen was restored. Hourglass-shaped specimens (n = 12) were used as positive control to measure the cohesive strength of the resin composite (Filtek LS). Microtensile bond test was performed (0.5 mm/min) and failure types were analyzed. Data were analyzed using two-way analysis of variance, Tukey’s and Dunnett’s tests (α = 0.05). Adhesive protocol and resin composite significantly affected the results (p < 0.05). For the FS composite, the highest results were obtained using LS adhesive with (18.4 ± 7.7) and without (18.8 ± 4.8) bur roughening. For FLS composite, the highest results were obtained using AS adhesive with (33.2 ± 7.1) and without (25.7 ± 3.6) bur roughening. Without the use of adhesive resin, significantly lower bond strength results were observed with both LS (5 ± 2.1, 4.5 ± 1.5) and FLS (2.2 ± 1.2, 4.4 ± 1.1) for unground and diamond bur roughened groups, respectively (p < 0.0001). Cohesive strength of the FLS (52.3 ± 7.6) was significantly higher than any of the repaired groups (p < 0.0001). FS–LS combination and the groups repaired without adhesive presented more adhesive (Type I) failures.     

The effect of different restoration techniques on fracture strength of teeth with flared roots

The aim of this study was to investigate the effect of different restoration techniques on the fracture strength of roots with flared canals. The crowns of 50 extracted single-rooted human teeth were removed and the canals were flared. Five groups were created (n = 10): Group 1: ReforPost (Angelus) was luted using Clearfil SA Cement (Kuraray); Group 2: ReforPost and two accessory posts (Reforpin, Angelus) were luted with Clearfil SA Cement; Group 3: Restored with i-TFC post-core system (Sun Medical); Group 4: The thickness of the root-dentine was increased using composite resin (Clearfil AP-X, Kuraray) and cured with the help of Luminex. ReforPost was then luted; Group 5: Anatomic posts were created by relining ReforPost with Clearfil AP-X and then luted using Clearfil SA Cement. The cores were created with composite resin in all the samples. The crowns of sound teeth were prepared similar to a core (control, n = 10). The specimens were vertically loaded (1 mm/min), the force that was required to fracture each sample was recorded (N) and analyzed (One Way Anova, Tukey tests). No significant difference was found among the groups (p > 0.05). The roots restored by using accessory post and i-TFC post-core (Groups 2 and 3) indicated a 100% favorable fracture pattern. Ten percent of the root fractures were observed in other groups. All techniques saved the root structure and showed 80–100% favorable failure pattern. The use of i-TFC system in flared roots could be an alternative to anatomic, accessory, and prefabricated fiber posts.     

Influence of the base and diluent methacrylate monomers on the polymerization stress and its determinants

The aim of this study was to evaluate the effect of the association between bisphenol‐A diglycidyl dimethacrylate (BisGMA) or its ethoxylated version (BisEMA) with diluents derived from the ethylene glycol dimethacrylate (EGDMA), with increasing number of ethylene glycol units (1: EGDMA, 2: DEGDMA, 3: TEGDMA, or 4: TETGDMA), or trimethylol propane trimethacrylate (TMPTMA) or 1,10‐decanediol dimethacrylate (D₃MA) on polymerization stress, volumetric shrinkage, degree of conversion, maximum rate of polymerization (Rp_max), and elastic modulus of experimental composites. BisGMA containing formulations presented lower shrinkage and stress but higher modulus and Rp_max than those containing BisEMA. TMPTMA presented the lowest stress among all diluents, as a result of lower conversion. EGDMA, DEGDMA, TEGDMA, and TETGDMA presented similar polymerization stress which was higher than the stress presented by D₃MA and TMPTMA. D₃MA presented similar conversion when copolymerized with both base monomers. The other diluents presented higher conversion when associated with BisEMA. EGDMA showed similar shrinkage compared with DEGDMA and higher than the other diluents. The lower conversion achieved by TMPTMA did not jeopardize its elastic modulus, similar to the other diluents. Despite the similar conversion presented by D₃MA in comparison with EGDMA and DEGDMA, its lower elastic modulus may limit its use. Rather than proposing new materials, this study provides a systematic evaluation of off the shelf monomers and their effects on stress development, as highlighted by the analysis of conversion, shrinkage and modulus, to aid the optimization of commercially available materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Cationic copolymerization behavior of a bicyclic orthoester having hydroxy group with glycidyl phenyl ether and volume change on their copolymerization

This article describes cationic ring‐opening copolymerization of a bicyclic orthoester having hydroxy group (BOE‐OH) and glycidyl phenyl ether (GPE), and the volume shrinkage behavior during the copolymerization. THF soluble polyethers [poly(BOE‐OH‐co‐GPE)] were obtained by the copolymerizations at 80–180°C, while crosslinked poly(BOE‐OH‐co‐GPE) was obtained by the copolymerizations at 220–250°C. This crosslinking reaction may originate from the dehydration of methylol groups in the side chain of poly(BOE‐OH‐co‐GPE). The volume shrinkage during the cationic copolymerization reduced as the increase of the BOE‐OH feed ratio. By contrast, the volume shrinkage on the crosslinking polymerization was almost independent on the BOE‐OH feed ratio. Poly(BOE‐OH‐co‐GPE)s with higher BOE‐OH composition showed lower thermal weight loss temperature owing to the release of H₂O by dehydration of methylol groups. The BOE‐OH component in the THF soluble poly(BOE‐OH‐co‐GPE)s lowered the glass transition temperature (T_g), while that in the crosslinked poly(BOE‐OH‐co‐GPE) increased the T_g probably because of the higher crosslinking density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1356–1361, 2006