Effect of universal adhesive pretreatments on the bond strength durability of conventional and adhesive resin cements to zirconia ceramic.

PURPOSE: This study aimed to evaluate the effect of pretreatment of three different universal adhesives (Single Bond Universal [SBU], All-Bond Universal [ABU], and Prime&Bond universal [PBU]) on the bonding durability of an adhesive (Panavia F 2.0, PF) and a conventional (Duo-Link, DL) resin cements to air-abraded zirconia. MATERIALS AND METHODS: Rectangular-shaped zirconia specimens were prepared. The chemical composition and surface energy parameters of the materials were studied by Fourier transform infrared spectroscopy and contact angle measurement, respectively. To evaluate resin bonding to the zirconia, all the bonding specimens were immersed in water for 24 h and the specimens to be aged were additionally thermocycled 10000 times before the shear bond strength (SBS) test. RESULTS: The materials showed different surface energy parameters, including the degree of hydrophilicity/hydrophobicity. While the DL/CON (no pretreatment) showed the lowest SBS and a significant decrease in the value after thermocycling (P < .001), the PF/CON obtained a higher SBS value than the DL/CON (P < .001) and no decrease even after thermocycling (P = .839). When the universal adhesives were used with DL, their SBS values were higher than the CON (P < .05), but the trend was adhesive-specific. In conjunction with PF, the PF/SBU produced the highest SBS followed by the PF/ABU (P = .002), showing no significant decrease after thermocycling (P > .05). The initial SBS of the PF/PBU was similar to the PF/CON (P = .999), but the value decreased after thermocycling (P < .001). CONCLUSION: The universal adhesive pretreatment did not necessarily show a synergistic effect on the bonding performance of an adhesive resin cement, whereas the pretreatment was beneficial to bond strength and durability of a conventional resin cement.

Flexible Pyroresistive Graphene Composites for Artificial Thermosensation Differentiating Materials and Solvent Types.

When we touch an object, thermosensation allows us to perceive not only the temperature but also wetness and types of materials with different thermophysical properties (i.e., thermal conductivity and heat capacity) of objects. Emulation of such sensory abilities is important in robots, wearables, and haptic interfaces, but it is challenging because they are not directly perceptible sensations but rather learned abilities via sensory experiences. Emulating the thermosensation of human skin, we introduce an artificial thermosensation based on an intelligent thermo-/calorimeter (TCM) that can objectively differentiate types of contact materials and solvents with different thermophysical properties. We demonstrate a TCM based on pyroresistive composites with ultrahigh sensitivity (11.2% °C-1) and high accuracy (<0.1 °C) by precisely controlling the melt-induced volume expansion of a semicrystalline polymer, as well as the negative temperature coefficient of reduced graphene oxide. In addition, the ultrathin TCM with coplanar electrode design shows deformation-insensitive temperature sensing, facilitating wearable skin temperature monitoring with accuracy higher than a commercial thermometer. Moreover, the TCM with a high pyroresistivity can objectively differentiate types of contact materials and solvents with different thermophysical properties. In a proof-of-principle application, our intelligent TCM, coupled with a machine-learning algorithm, enables objective evaluation of the thermal attributes (coolness and wetness) of skincare products.

Parent strategies for expanding food variety: Reflections of 19,239 adults with symptoms of Avoidant/Restrictive Food Intake Disorder.

OBJECTIVE: To characterize helpful parent feeding strategies using reflections on childhood eating experiences of adults with symptoms of Avoidant/Restrictive Food Intake Disorder (ARFID). METHOD: We explored a unique text-based dataset gathered from a population of N = 19,239 self-identified adult "picky eaters." The sample included adults with symptoms of ARFID as evidenced by marked interference in psychosocial functioning, weight loss/sustained low weight, and/or nutritional deficiency (likely ARFID), and non-ARFID participants. We leveraged state-of-the-art natural language processing (NLP) methods to classify feeding strategies that were perceived as helpful or not helpful. The best classifiers that distinguished helpful approaches were further analyzed using qualitative coding according to a grounded theory approach. RESULTS: NLP reliably and accurately classified the perceived helpfulness of caregivers' feeding strategies (82%) and provided information about features of helpful parent strategies using recollections of adults with varying degrees of food avoidance. Strategies perceived as forceful were regarded as not helpful. Positive and encouraging strategies were perceived as helpful in improving attitudes toward food and minimizing social discomfort around eating. Although food variety improved, adults still struggled with a degree of avoidance/restriction. DISCUSSION: Adults perceived that positive parent feeding strategies were helpful even though they continued to experience some degree of food avoidance. Creating a positive emotional context surrounding food and eating with others may help to eliminate psychosocial impairment and increase food approach in those with severe food avoidance. Nevertheless, additional tools to optimize parent strategies and improve individuals' capacity to incorporate avoided foods and cope with challenging eating situations are needed.

Effect of Incorporating a Dimethacrylate Monomer on the Shear Bond Strength of Two Adhesive Resin Cements to Zirconia Ceramic.

Self-assembled nano-layering resulting from interaction of the phosphate functional group of adhesive monomers with zirconia ceramic surface has been proposed. The purpose of this study was to investigate the bond strengths of two adhesive resin cements (Panavia F 2.0 and BisCem) containing phosphate monomers added with various concentrations (0.0, 1.0, 3.0, and 5.0 wt%) of triethylene glycol dimethacrylate (TEGDMA) to air-abraded zirconia ceramic. The polished/air-abraded zirconia plates (KaVo Everest® ZS-Ronde) were imaged using atomic force microscopy and the average surface roughness (Ra) values were calculated (n = 5). The surface energy parameters of the zirconia plates and the resin cements were calculated based on the extended Fowkes theory. All resin-bonded (diameter: 2.38 mm) zirconia specimens were stored in water at 37 °C for 24 h and then half of them additionally thermocycled 10,000 times before the shear bond strength (SBS) test (n = 10). Air-abrasion of zirconia surface significantly increased the γhS (hydrogen bonding component) value (p < 0.001), as well as greatly increasing the surface area (p < 0.001). For both resin cements, the γhS (dipole-dipole component) gradually increased with increasing incorporated TEGDMA concentrations, whereas the γhS gradually decreased. Overall, the addition of 3.0 wt% of TEGDMA consistently resulted in higher SBS values even after thermocycling. Under the tested condition, reducing the concentration of the adhesive monomers with phosphate functional group by adding the dimethacrylate monomer (up to 3.0 wt%) increased the bond strength between the resin cements and zirconia ceramic.

Evaluation of Resin Bonding to Tetragonal and Gradient-Shaded Cubic Zirconia Ceramics After Air-Abrasion.

Self-assembled nano-layering resulting from combined ionic and hydrogen-bonding interactions of phosphate functional monomers with zirconia have been proposed. The purpose of this study was to investigate the bond strengths of two phosphate monomer-containing adhesive resin cements (Panavia F 2.0 and RelyX U200) to a conventional tetragonal zirconia (Lava Plus, LP) and a new cubic zirconia (Lava Esthetic, LE), with three different shade zones, after air-abrasion. The structures of the zirconia surfaces were examined with scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Vickers hardness and fracture toughness of the surfaces were also evaluated using a hardness tester. After air-abrasion (with 50 µm Al2O3 at a pressure of 0.25 MPa), the surface roughness was measured using confocal laser scanning microscopy (CLSM) and the resin cements were bonded (diameter: 2.38 mm) to the surfaces. All bonded specimens were stored in water at 37 °C for 24 h before performing the shear bond strength (SBS) test (n = 15). In the SEM images, the LP group showed a finer grain size than the LE groups. The XRD patterns confirmed that LP and LE had tetragonal and cubic phases, respectively. Although there were no significant differences in Vickers hardness among the four groups (p = 0.117), the three LE groups revealed inferior fracture toughness to the LP group (p < 0.001). However, neither the surface roughness of the air-abraded zirconia surfaces nor SBS values of each resin cement bonded to them were significantly different (p > 0.05). In conclusion, no significant difference in SBS value was detected between the tetragonal and cubic zirconia within each resin cement used, probably due to the similar surface roughness of the air-abraded zirconia ceramics.

Bobby sox homolog regulates tooth root formation through modulation of dentin sialophosphoprotein.

Tooth root development occurs through the interaction of multiple growth factors and transcription factors expressed in Hertwig's epithelial root sheath (HERS) and dental mesenchyme. Previously, we demonstrated that bobby sox homolog (Bbx) regulates odontoblast differentiation of human dental pulp stem cells. Here, we generated Bbx knockout (Bbx-/- ) mice to address the functional role of Bbx in tooth formation. During tooth development, Bbx was expressed in both dental epithelium and mesenchyme. However, molar and incisor morphology in Bbx-/- mice at postnatal Day 0 (P0) exhibited no prominent abnormalities compared with their wild-type (Bbx+/+ ) littermates. Until P28, the crown morphology in Bbx-/- mice was not distinctively different from Bbx+/+ littermates. Meanwhile, the length of the mandibular base in Bbx-/- mice was notably less at P28. Compared with Bbx+/+ mice, the mesial and distal root lengths of the first molar were reduced by 21.33% and 16.28% at P14 and 16.28% and 16.24% at P28, respectively, in Bbx-/- mice. The second molar of Bbx-/- mice also showed 10.16% and 6.4% reductions at P28 in the mesial and distal lengths, compared with Bbx+/+ mice, respectively. The gene expression analysis during early tooth root formation (P13) showed that the expression of dentin sialophosphoprotein (Dspp) was significantly decreased in Bbx-/- mice. Collectively, our data suggest that Bbx participates in tooth root formation and might be associated with the regulation of Dspp expression.

Influence of Sandblasting Particle Size and Pressure on Resin Bonding Durability to Zirconia: A Residual Stress Study.

The influence of residual stress induced by sandblasting the zirconia ceramic surface on the resin bonding to the ceramic is still unclear. The effect of four different sandblasting conditions (with 50 and 110 µm alumina at pressures of 0.2 and 0.4 MPa) on the bonding of adhesive resin cement (Panavia F 2.0) to zirconia (Cercon® ht) was investigated in terms of residual stress. The surface roughness and water contact angle of the zirconia surfaces were measured. The tetragonal-to-monoclinic (t-m) phase transformation and residual stresses (sin2ψ method) were studied by X-ray diffraction. The resin-bonded zirconia specimens were subjected to shear bond strength (SBS) tests before and after thermocycling (10,000 and 30,000 cycles) (n = 10). As the particle size and pressure increased, the roughness gradually and significantly increased (p = 0.023). However, there were no significant differences in roughness-corrected contact angle among all the sandblasted groups (p > 0.05). As the particle size and pressure increased, the m-phase/(t-phase + m-phase) ratios and compressive residual stresses gradually increased. After thermocycling, there were no significant differences in SBS among the sandblasted zirconia groups (p > 0.05). In conclusion, increased surface roughness and residual stress do not directly affect the resin bonding durability.

Effect of Incorporating Zirconia Powder into a Primer on the Resin Bond Strength to Zirconia Ceramic.

The adhesion property of zirconia powder-incorporated primers was investigated in vitro with the aim of enhancing the resin bond strength to zirconia ceramic. A commercial zirconia primer was modified through the addition of 0 (control), 5, 10, 25, and 50 wt% of a zirconia powder (codes: ZP0, ZP5, ZP10, ZP25, and ZP50, respectively). Prior to primer modification, the powder was characterized via differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectrophotometry. The surfaces of dental zirconia ceramic discs were air-abraded and treated with one of the five primers. One resin composite cylinder (diameter: 2.38 mm) was bonded on one specimen surface (n = 12/group). The bonded specimens were all stored for 24 h in distilled water at 37 °C and subjected to 5000 thermal cycles prior to shear bond strength (SBS) testing. The DSC and FTIR analyses confirmed that the zirconia powder contained an organic binder. The SBS test results showed that the groups could be arranged as follows, ZP25 > ZP10 > ZP5 > ZP0, i.e., in descending order of the mean value. The lowest SBS value was obtained for the ZP50 group. The results suggest that the incorporation of a zirconia powder into a primer represents a promising modification method for improving the resin bond strength to zirconia ceramic.

Dentin Bonding of TheraCal LC Calcium Silicate Containing an Acidic Monomer: An In Vitro Study.

The purpose of this study was to evaluate whether the incorporation of an acidic monomer into the pulp-capping material TheraCal LC, which has a weak dentin bonding, increases the shear bond strength (SBS) to dentin. Di-2-hydroxyethyl methacryl hydrogenphosphate was incorporated into the material at 0.0 (TL0, control), 5.0 (TL5), and 10.0 (TL10) wt%. The water contact angle (CA) and mechanical properties for each material were also studied (n = 6). Debonding was performed at two different times (immediate and after 24 h) (n = 12). Hydroxyl and calcium ion releases in water at 37 °C were monitored up to 28 days (n = 6). The addition of the acidic monomer decreased the CAs (p < 0.001) and increased the flexural moduli (p < 0.001). The debonding time did not significantly affect the SBS values (p = 0.600). The TL10 group exhibited the highest SBS values, followed by the TL5 group. The TL10 group released significantly more calcium ions than the other two groups from 3 days (p < 0.05). The incorporation of the acidic monomer at 10.0 wt% into TheraCal LC enhanced bonding to dentin, while not negatively affecting the mechanical properties and ion-leaching capacity of the material.

The capacity of wastewater treatment plants drives bacterial community structure and its assembly.

Bacterial communities in wastewater treatment plants (WWTPs) affect plant functionality through their role in the removal of pollutants from wastewater. Bacterial communities vary extensively based on plant operating conditions and influent characteristics. The capacity of WWTPs can also affect the bacterial community via variations in the organic or nutrient composition of the influent. Despite the importance considering capacity, the characteristics that control bacterial community assembly are largely unknown. In this study, we discovered that bacterial communities in WWTPs in Korea and Vietnam, which differ remarkably in capacity, exhibit unique structures and interactions that are governed mainly by the capacity of WWTPs. Bacterial communities were analysed using 16S rRNA gene sequencing and exhibited clear differences between the two regions, with these differences being most pronounced in activated sludge. We found that capacity contributed the most to bacterial interactions and community structure, whereas other factors had less impact. Co-occurrence network analysis showed that microorganisms from high-capacity WWTPs are more interrelated than those from low-capacity WWTPs, which corresponds to the tighter clustering of bacterial communities in Korea. These results will contribute to the understanding of bacterial community assembly in activated sludge processing.

Risk factors for linezolid-induced thrombocytopenia in patients without haemato-oncologic diseases.

This study aimed to describe the occurrence and to evaluate the predictive factors of thrombocytopenia caused by parenteral linezolid in hospitalised patients without haemato-oncologic diseases. Using electronic medical records, a retrospective safety evaluation was performed among all hospitalised adult patients who received parenteral linezolid therapy between January 2005 and June 2016. Of all identified 264 patients with an average age of 63.4 (SD 15.8) years, thrombocytopenia occurred at a rate of 29.2% after an average of 11.2 (SD 7.4) days of the initiation of linezolid therapy. Significant predictive factors for thrombocytopenia included the duration of linezolid therapy longer than or equal to 7 days (adjusted odds ratios [ORs] 7.25, 19.51 and 28.80; 95% confidence intervals [CIs] 1.92-27.38, 4.76-79.95 and 6.48-127.92 for 7-13 days, 14-20 days and ≥21 days, respectively; P < 0.01 for all values), baseline platelet count <150 × 103 /mm3 (adjusted OR, 5.08; 95% CI, 2.06-12.55; P < 0.001), creatinine clearance <30 mL/min (adjusted OR, 4.19; 95% CI, 1.59-11.06; P = 0.004) and concurrent low-dose aspirin therapy (adjusted OR, 2.99; 95% CI, 1.26-7.08; P = 0.013). Baseline platelet count less than 150 × 103 /mm3 was an independent predictor of early-onset (≤6 days) thrombocytopenia (adjusted OR, 5.07; 95% CI, 1.46-17.58; P = 0.011). Closer monitoring of platelet count is required in patients who receive parenteral linezolid therapy for 7 days or more, and have low baseline platelet counts or impaired renal function.

An Evaluation of Wetting and Adhesion of Three Bioceramic Root Canal Sealers to Intraradicular Human Dentin.

Root canal sealers should have good wetting and adhesion with intraradicular dentin. This study evaluated the wetting and adhesion properties of three bioceramic root canal sealers on dentin using contact angle (CA) measurements and calculations based on the Owens⁻Wendt⁻Rabel⁻Kälble (OWRK) model and compared the properties with those of a resin sealer. Three bioceramic sealers (EndoSequence BC Sealer (BC); Endoseal MTA (EM); and MTA Fillapex (MF)) were tested, together with one epoxy resin-based sealer (AH Plus (AP)). Disc-shaped sealer specimens and human premolar teeth with flat and polished intraradicular dentin surfaces were prepared (n = 12). The CAs of two liquids (water and methylene iodide) were measured on the surfaces using the sessile drop method. The wetting and adhesion properties of the four sealers were calculated using the wetting envelope and isogram diagram, respectively. Group BC showed the best wettability among the four sealer groups. The best adhesion was achieved for group EM, followed by group BC, with a significant difference being present between the two groups (p < 0.05). The OWRK-based calculation indicated that the bioceramic BC and EM sealers showed superior wetting and adhesion properties to the AP sealers.

MPC1 is essential for PGC-1α-induced mitochondrial respiration and biogenesis.

Mitochondrial pyruvate carrier (MPC), which is essential for mitochondrial pyruvate usage, mediates the transport of cytosolic pyruvate into mitochondria. Low MPC expression is associated with various cancers, and functionally associated with glycolytic metabolism and stemness. However, the mechanism by which MPC expression is regulated is largely unknown. In this study, we showed that MPC1 is down-regulated in human renal cell carcinoma (RCC) due to strong suppression of peroxisome proliferator-activated receptor-gamma co-activator (PGC)-1 alpha (PGC-1α). We also demonstrated that overexpression of PGC-1α stimulates MPC1 transcription, while depletion of PGC-1α by siRNA suppresses MPC expression. We found that PGC-1α interacts with estrogen-related receptor-alpha (ERR-α) and recruits it to the ERR-α response element motif located in the proximal MPC1 promoter, resulting in efficient activation of MPC1 expression. Furthermore, the MPC inhibitor, UK5099, blocked PGC-1α-induced pyruvate-dependent mitochondrial oxygen consumption. Taken together, our results suggest that MPC1 is a novel target gene of PGC-1α. In addition, low expression of PGC-1α in human RCC might contribute to the reduced expression of MPC, resulting in impaired mitochondrial respiratory capacity in RCC by limiting the transport of pyruvate into the mitochondrial matrix.

Root Canal Shaping Effect of Instruments with Offset Mass of Rotation in the Mandibular First Molar: A Micro-computed Tomographic Study.

INTRODUCTION: The aim of this study was to evaluate the root canal shaping effect of 2 nickel-titanium rotary instruments with offset mass of rotation compared with an instrument with a conventional centered mass of rotation. METHODS: Thirty-six extracted human mandibular first molars with 2 independent mesial canals and 1 oval distal canal were selected and divided equally into 3 groups for instrumentation with ProTaper Next (PTN; Dentsply Maillefer, Ballaigues, Switzerland), Revo-S (RS; Micro-Mega, Besançon, France), and ProTaper Universal (PTU, Dentsply Maillefer) systems (n = 12). For apical preparation, PTN X2 (#25/0.06), RS SU (#25/0.06), and PTU F2 (#25/0.08) were used in the mesial canals and PTN X3 (#30/0.07), RS AS30 (#30/0.06), and PTU F3 (#30/0.09) were used in the distal canals. Specimens were scanned before and after instrumentation using a SkyScan 1272 scanner (Bruker micro-CT, Kontich, Belgium) at 10-µm isotropic resolution. Changes in the canal area, volume, structure model index (SMI), and untouched canal area were evaluated. Canal transportation and centering ratio were measured at 1, 3, 5, and 7 mm from the apical foramen. Data were statistically analyzed using 1-way analysis of variance with the Tukey post hoc test. RESULTS: The PTN and RS systems showed significantly less transportation and better centering ability compared with the PTU system at 1 mm from the apical foramen (P < .05). All instrumentation increased the canal area, volume, and SMI values without significant differences among the 3 groups (P > .05). CONCLUSIONS: Regardless of the differences in the cross-sectional design, alloy type, and taper variation, instruments with offset mass of rotation showed better root canal shaping ability compared with an instrument with a centered mass of rotation.

Green tea extracts for the prevention of metachronous colorectal polyps among patients who underwent endoscopic removal of colorectal adenomas: A randomized clinical trial.

OBJECTIVES: To determine the preventive effect of green tea extract (GTE) supplements on metachronous colorectal adenoma and cancer in the Korean population. MATERIALS AND METHODS: One hundred seventy-six subjects (88 per each group) who had undergone complete removal of colorectal adenomas by endoscopic polypectomy were enrolled. They were randomized into 2 groups: supplementation group (0.9 g GTE per day for 12 months) or control group without GTE supplementation. The 72-h recall method was used to collect data on food items consumed by participants at baseline and the 1-year follow-up during the past 48 h. Follow-up colonoscopy was conducted 12 months later in 143 patients (71 in control group and 72 in the GTE group). RESULTS: Of the 143 patients completed in the study, the incidences of metachronous adenomas at the end-point colonoscopy were 42.3% (30 of 71) in control group and 23.6% (17 of 72) in GTE group (relative risk [RR], 0.56; 95% confidence interval [CI], 0.34-0.92). The number of relapsed adenoma was also decreased in the GTE group than in the control group (0.7 ± 1.1 vs. 0.3 ± 0.6, p = 0.010). However, there were no significant differences between the 2 groups in terms of body mass index, dietary intakes, serum lipid profiles, fasting serum glucose, and serum C-reactive protein levels (all p > 0.05). CONCLUSION: This study of GTE supplement suggests a favorable outcome for the chemoprevention of metachronous colorectal adenomas in Korean patients (ClinicalTrials.gov number, NCT02321969).

Magnesium phosphate ceramics incorporating a novel indene compound promote osteoblast differentiation in vitro and bone regeneration in vivo.

Incorporating bioactive molecules into synthetic ceramic scaffolds is challenging. In this study, to enhance bone regeneration, a magnesium phosphate (MgP) ceramic scaffold was incorporated with a novel indene compound, KR-34893. KR-34893 induced the deposition of minerals and expression of osteoblast marker genes in primary human bone marrow mesenchymal stem cells (BMSCs) and a mouse osteoblastic MC3T3-E1 cell line. Analysis of the mode of action showed that KR-34893 induced the phosphorylation of MAPK/extracellular signal-regulated kinase and extracellular signal-regulated kinase, and subsequently the expression of bone morphogenetic protein 7, accompanied by SMAD1/5/8 phosphorylation. Accordingly, KR-34893 was incorporated into an MgP scaffold prepared by 3D printing at room temperature, followed by cement reaction. KR-34893-incorporated MgP (KR-MgP) induced the expression of osteoblast differentiation marker genes in vitro. In a rat calvaria defect model, KR-MgP scaffolds enhanced bone regeneration and increased bone volume compared with MgP scaffolds, as assessed by micro-computed tomography and histological analyses. In conclusion, we developed a method for producing osteoinductive MgP scaffolds incorporating a bioactive organic compound, without high temperature sintering. The KR-MgP scaffolds enhanced osteoblast activation in vitro and bone regeneration in vivo.

Anatomical profile of the mesial root of the Burmese mandibular first molar with Vertucci's type IV canal configuration.

This study evaluated the anatomical profile of the mesial root canals of the Burmese mandibular first molar with Vertucci's type IV canal configuration (VT4) using microcomputed tomography analysis. Seventy-five mesial roots of extracted mandibular first molars were scanned and evaluated. Fourteen middle mesial canals (MMCs) were observed in the specimens; each specimen had an average of 1.63 lateral canals and 3.77 apical foramina. The lateral canals arising from the mesiobuccal canal, mesiolingual canal, MMC, and isthmus terminated at an average distance of 0.92, 0.73, 2.11, and 1.89 mm, respectively, from the apex. The mean distance between the centers of the mesiobuccal and mesiolingual canals at 1.5 mm coronal to the furcation was 2.60 mm. A higher incidence of isthmus was observed in the apical 2-6-mm region compared with the apical 0-2-mm region (P < 0.05). The incidence of lateral canals in the isthmus was similar to that of the mesiobuccal and mesiolingual canals (P > 0.05). This study shows that the mesial root of the Burmese mandibular first molar with VT4 has complex anatomical profiles comprising MMCs and isthmus and their lateral canals.

Influence of Curing Mode on the Surface Energy and Sorption/Solubility of Dental Self-Adhesive Resin Cements.

This study investigated the influence of curing mode (dual- or self-cure) on the surface energy and sorption/solubility of four self-adhesive resin cements (SARCs) and one conventional resin cement. The degree of conversion (DC) and surface energy parameters including degree of hydrophilicity (DH) were determined using Fourier transform infrared spectroscopy and contact angle measurements, respectively (n = 5). Sorption and solubility were assessed by mass gain or loss after storage in distilled water or lactic acid for 60 days (n = 5). A linear regression model was used to correlate between the results (%DC vs. DH and %DC/DH vs. sorption/solubility). For all materials, the dual-curing consistently produced significantly higher %DC values than the self-curing (p < 0.05). Significant negative linear regressions were established between the %DC and DH in both curing modes (p < 0.05). Overall, the SARCs showed higher sorption/solubility values, in particular when immersed in lactic acid, than the conventional resin cement. Linear regression revealed that %DC and DH were negatively and positively correlated with the sorption/solubility values, respectively. Dual-curing of SARCs seems to lower the sorption and/or solubility in comparison with self-curing by increased %DC and occasionally decreased hydrophilicity.

Post space preparation timing of root canals sealed with AH Plus sealer.

OBJECTIVES: To determine the optimal timing for post space preparation of root canals sealed with epoxy resin-based AH Plus sealer in terms of its polymerization and influence on apical leakage. MATERIALS AND METHODS: The epoxy polymerization of AH Plus (Dentsply DeTrey) as a function of time after mixing (8, 24, and 72 hours, and 1 week) was evaluated using Fourier transform infrared (FTIR) spectroscopy and microhardness measurements. The change in the glass transition temperature (Tg ) of the material with time was also investigated using differential scanning calorimetry (DSC). Fifty extracted human single-rooted premolars were filled with gutta-percha and AH Plus, and randomly separated into five groups (n = 10) based on post space preparation timing (immediately after root canal obturation and 8, 24, and 72 hours, and 1 week after root canal obturation). The extent of apical leakage (mm) of the five groups was compared using a dye leakage test. Each dataset was statistically analyzed by one-way analysis of variance and Tukey's post hoc test (α = 0.05). RESULTS: Continuous epoxy polymerization of the material with time was observed. Although the Tg values of the material gradually increased with time, the specimens presented no clear Tg value at 1 week after mixing. When the post space was prepared 1 week after root canal obturation, the leakage was significantly higher than in the other groups (p < 0.05), among which there was no significant difference in leakage. CONCLUSIONS: Poor apical seal was detected when post space preparation was delayed until 1 week after root canal obturation.