Effect of ethyl cellulose coating as an evaluation agent against contamination on the bond strength of zirconia restorations: An in vitro study.

STATEMENT OF PROBLEM: During the trial placement of zirconia restorations, contamination of the bonding surface is inevitable. Although cleaning methods for contaminated surfaces have been described, a method of preventing saliva contamination of the bonding surface of zirconia restorations is lacking. PURPOSE: The purpose of this in vitro study was to investigate an ethyl cellulose coating as an evaluation agent to mitigate the effects of saliva contamination on the bond strength of zirconia restorations. MATERIAL AND METHODS: Experimental groups representing different cleaning methods of tetragonal yttria-stabilized tetragonal zirconia polycrystal (4Y-TZP) surfaces were investigated for shear bond strength with a resin luting agent, and the failure mode was analyzed. The 9.0×7.0×5.0-mm zirconia blocks (n=72) were assigned as follows: Group N: uncontaminated control; Group CU: contaminated with saliva, followed by ultrasonic cleaning with ethanol; Group CI: contaminated with saliva, followed by application of a zirconia cleaner; Group PCW: preapplication of a zirconia primer, contaminated with saliva, followed by cleaning with water spray; Group ECU: precoating with the ethyl cellulose agent, contaminated with saliva, followed by removal of the agent in an ultrasonic bath with ethanol. Each group was divided into 3 subgroups (immediate, short-term aging, and long-term aging), and the shear bond strength was measured (n=24). To analyze the bonding surface characteristics, the contact angle was measured (n=5). The surfaces of the zirconia specimens in each experimental group were evaluated by using a field emission scanning electron microscope (n=5). Time-of-flight secondary ion mass spectroscopy was used for the chemical analysis of the conditioned surfaces (n=3). A 2-way analysis of variance (ANOVA) with main effect model for shear bond strength results and a 1-way ANOVA for contact angle data were performed as statistical analysis, followed by the Bonferroni post hoc test (α=.05). RESULTS: The shear bond strength was significantly higher in the ECU group than in the groups with the other cleaning methods (P<.05). After the removal of ethyl cellulose with ethanol, the contact angle and surface topography were found to be similar to those of the control group, and no saliva contaminants were identified in the spectroscopy analysis. CONCLUSIONS: Coating with ethyl cellulose may protect the bonding surface of zirconia restorations from salivary contamination better than cleaning a contaminated surface.

Effect of bioactive glass addition on the physical properties of mineral trioxide aggregate.

BACKGROUND: The addition of bioactive glass (BG), a highly bioactive material with remineralization potential, might improve the drawback of weakening property of mineral trioxide aggregates (MTA) when it encounters with body fluid. This study aims to evaluate the effect of BG addition on physical properties of MTA. METHODS: ProRoot (MTA), and MTA with various concentrations of BG (1, 2, 5 and 10% BG/MTA) were prepared. Simulated body fluid (SBF) was used to investigate the effect of the storage solution on dentin remineralization. Prepared specimens were examined as following; the push-out bond strength to dentin, compressive strength, setting time solubility and X-ray diffraction (XRD) analysis. RESULTS: The 2% BG/MTA showed higher push-out bond strengths than control group after 7 days of SBF storage. The 2% BG/MTA exhibited the highest compressive strength. Setting times were reduced in the 1 and 2% BG/MTA groups, and solubility of all experimental groups were clinically acceptable. In all groups, precipitates were observed in dentinal tubules via SEM. XRD showed the increased hydroxyapatite peaks in the 2, 5 and 10% BG/MTA groups. CONCLUSION: It was verified that the BG-added MTA increased dentin push-out bond strength and compressive strength under SBF storage. The addition of BG did not negatively affect the MTA maturation reaction; it increased the amount of hydroxyapatite during SBF maturation.

Effect of Novel Bioactive Glass-Containing Dentin Adhesive on the Permeability of Demineralized Dentin.

This study aimed to evaluate the effect of a novel bioactive glass (BAG)-containing dentin adhesive on the permeability of demineralized dentin. Bioactive glass (85% SiO2, 15% CaO) was fabricated using the sol-gel process, and two experimental dentin adhesives were prepared with 3 wt% silica (silica-containing dentin adhesive; SCA) or BAG (BAG-containing dentin adhesive; BCA). Micro-tensile bond strength (µTBS) test, fracture mode analysis, field-emission scanning electron microscopy (FE-SEM) analysis of adhesive and demineralized dentin, real-time dentinal fluid flow (DFF) rate measurement, and Raman confocal microscopy were performed to compare SCA and BCA. There was no difference in µTBS between the SCA and BCA (p > 0.05). Multiple precipitates were evident on the surface of the BCA, and partial occlusion of dentinal tubules was observed in FE-SEM of BCA-approximated dentin. The DFF rate was reduced by 50.10% after BCA approximation and increased by 6.54% after SCA approximation. Raman confocal spectroscopy revealed an increased intensity of the hydroxyapatite (HA) peak on the dentin surface after BCA application. The novel BAG-containing dentin adhesive showed the potential of both reducing dentin permeability and dentin remineralization.

Investigation on Mode I Fracture Toughness of Woven Carbon Fiber-Reinforced Polymer Composites Incorporating Nanomaterials.

This study experimentally investigated the effects of nanomaterials and interface fiber angle on the mode I fracture toughness of woven carbon fiber-reinforced polymer (CFRP) composites. Three different types of nanomaterials were used: COOH-functionalized short multi-walled carbon nanotubes (S-MWCNT-COOH), multi-walled carbon nanotubes (MWCNTs), and graphene nanoplatelets (GnPs). Double cantilever beam specimens were composed of 12 woven carbon fiber fabrics with/without 1 wt% nanomaterials, and were manufactured using the hand lay-up method. Furthermore, two different stacking sequence series were used; the first series comprised only on-axis carbon-fiber fabrics (0° or 90°), and the second series comprised both on- and off-axis carbon-fiber fabrics (0° or 90° and ±45°). The test results showed that adding S-MWCNT-COOH, MWCNTs, and GnPs significantly increased the mode I fracture toughness of the CFRP composites for both the stacking sequence series. Moreover, the specimens that used only on-axis carbon fiber fabrics exhibited higher fracture toughness values than those of the specimens that used on- and off-axis carbon fiber fabrics together. In addition, an empirical model was established to predict the fracture toughness of the CFRP composites with nanomaterials by using on- and off-axis carbon fiber fabrics together, and the prediction results showed a good agreement with the experimental results.

In Vitro Characterization of Dental Pulp Stem Cells Cultured in Two Microsphere-Forming Culture Plates.

Various three-dimensional (3D) culture methods have been introduced to overcome the limitations of in vitro culture and mimic in vivo conditions. This study aimed to evaluate two microsphere-forming culture methods and a monolayer culture method. We evaluated cell morphology, viability, osteo-, adipo-, and chondrogenic differentiation potential of dental pulp stem cells (DPSCs) cultured in 3D culture plates: ultra-low attachment (ULA) and U-bottomed StemFit 3D (SF) plates, and a two-dimensional (2D) monolayer plate. RNA sequencing (RNA-seq) revealed differentially expressed gene (DEG) profiles of the DPSCs. In contrast to an increasing pattern in the 2D group, cell viability in 3D groups (ULA and SF) showed a decreasing pattern; however, high multilineage differentiation was observed in both the 3D groups. RNA-seq showed significantly overexpressed gene ontology categories including angiogenesis, cell migration, differentiation, and proliferation in the 3D groups. Hierarchical clustering analysis revealed a similar DEG regulation pattern between the 3D groups; however, a comparatively different DEG was observed between the 2D and 3D groups. Taken together, this study shows that DPSCs cultured in microsphere-forming plates present superior multilineage differentiation capacities and demonstrate higher DEG expression in regeneration-related gene categories compared to that in DPSCs cultured in a conventional monolayer plate.

Tensile Behaviors of Lap-Spliced Carbon Fiber-Textile Reinforced Mortar Composites Exposed to High Temperature.

The tensile behaviors of textile-reinforced mortar (TRM) composites made with carbon fiber textile and alumina cement-based mortar were investigated through direct tensile tests. Three different surface treatment details in the lap splice area were used to improve the tensile behaviors of the TRM composites: carbon fiber textile impregnated by epoxy, carbon fiber textile coated with aluminum oxide powder following epoxy impregnation, and carbon fiber textile coated with aluminum oxide powder following both carbon fiber fabric attachment and epoxy impregnation. Three different lap splice lengths were used 180, 200, and 220 mm. In addition, the tensile properties of TRM composites following exposure to high temperature were investigated as well. In this test, TRM test specimens were exposed to two different temperature histories with maximum values of 250 and 350 °C. The results of the test specimens according to the test parameters were analyzed in terms of initial stiffness, cracking strength, corresponding strain at cracking, modulus of elasticity in the cracked stage, peak strength, and ultimate strain. The influence of lap splice length on the tensile behaviors of the TRM composites was analyzed and discussed. The surface treatment in the overlapping region showed ductile behavior and resulted in a significant improvement of the peak strength and ultimate strain over the untreated lap splice textile. Following exposure to high temperature, the TRM composites showed a reduction of tensile responses compared to those cured at room temperature. In addition, a prediction model developed in the previous study was used to predict the tensile behaviors of the lap-spliced carbon fiber-textile reinforced mortar composites exposed to high temperature, and the prediction by the model showed a good agreement with the experimental results.

Effect of various agitation methods on adhesive layer formation of HEMA-free universal dentin adhesive.

This study evaluates the effects of various agitation methods on the adhesive layer formation of a new HEMA-free universal dentin adhesive. The µTBS of the universal adhesive, G-Premio BOND in the self-etch mode was evaluated using three agitation methods [passive agitation (PA), active agitation (AA), ultrasonic agitation (UA)], with and without aging treatment. Two-way analysis of variance revealed that aging treatment was not a statistically significant factor. Tukey's HSD test showed significant differences based on the application method, UA>AA>PA. TEM images of the PA group revealed multiple water blisters in the adhesive layers; AA and UA groups presented significantly less or no blisters within the adhesive layers; thus, AA and UA groups exhibited better bonding performance for the HEMA-free universal adhesive. It is assumed that the entrap ped blisters can be reduced with the active application of dentin adhesive, and thus improving the bonding performance.

Virtual Simulation of Autotransplantation Using 3-dimensional Printing Prototyping Model and Computer-assisted Design Program.

This case report describes an innovative virtual simulation method using a computer-aided rapid prototyping (CARP) model and a computer-aided design (CAD) program for autotransplantation of an immature third molar.A compromised left mandibular second molar (#18) was extracted and replaced by autotransplantation using an immature left mandibular third molar (#17). In order to minimize the surgical time and injury to the donor tooth, a virtual 3-dimensional (3D) rehearsal surgery was planned. Cone-beam computed tomographic images were taken to fabricate the 3D printing CARP model of the donor tooth and tentative extraction socket. Subsequently, both CARP models were scanned with an intraoral scanner (CEREC Omnicam; Dentsply Sirona, Bensheim, Germany) followed by superimposition and virtual simulation of osteotomy preparation of the recipient alveolus using the CAD analysis program. During the surgery, the extraction socket was precisely prepared according to the predetermined location and dimensions via virtual simulation rehearsal surgery using CAD analysis. The donor tooth was atraumatically transplanted into the prepared socket. The follow-up examination revealed that the root developed with a normal periodontal ligament and lamina dura.Virtual simulation using a 3D printing CARP model and a CAD program could be clinically useful in autotransplantation of an immature third molar by ensuring an atraumatic and predictable surgery.

Effect of zinc on the collagen degradation in acid-etched dentin.

BACKGROUND/PURPOSE: Matrix metalloproteinases (MMPs) play a crucial role in the pathogenesis of dental caries, collapse of adhesive interface, and chemical erosion of teeth. The objective of this study was to investigate the inhibitory effect of zinc on collagen degradation. MATERIALS AND METHODS: Human dentin was ground and demineralized by citric acid (pH 2.0). The demineralized ground dentin was incubated in six different media: artificial saliva (AS); 5 mg/ml doxycycline in AS; 3.33, 6.82, 13.63, and 27.26 mg/ml of zinc chloride (Zn) in AS. Each group was divided into two subgroups, and active MMP-2 was incorporated into one subgroup. Specimens were incubated for 24 h, 1 week, and 2 weeks. Collagen degradation product was assessed using ELISA. The results were analyzed using repeated measured ANOVA and Duncan's post hoc analysis (α = 0.05). RESULTS: The amount of collagen degradation was the lowest in Doxy group. Zn groups showed a significant inhibitory effect in collagen degradation for all concentrations (P < 0.05). In subgroups without exogenous MMP-2, zinc-mediated inhibition increased in a concentration-dependent manner with increasing zinc concentration. The amount of collagen degradation product slightly increased with increased incubation time from 24 h to 2 weeks. However, in subgroups with exogenous MMP, the inhibitory effect of zinc on collagen degradation did not depend on zinc concentration. CONCLUSION: All Zn groups for the four concentrations tested exhibited statistically significant inhibitory effect on collagen degradation.

Use of temporary filling material for index fabrication in Class IV resin composite restoration.

When a patient with a fractured anterior tooth visits the clinic, clinician has to restore the tooth esthetically and quickly. For esthetic resin restoration, clinician can use 'Natural Layering technique' and an index for palatal wall may be needed. In this case report, we introduce pre-restoration index technique on a Class IV defect, in which a temporary filling material is used for easy restoration. Chair-side index fabrication for Class IV restoration is convenient and makes a single-visit treatment possible.

Correlation between clinical clerkship achievement and objective structured clinical examination (OSCE) scores of graduating dental students on conservative dentistry.

OBJECTIVES: This study aimed to investigate the effect of clinical clerkship-associated achievements, such as performance of procedures at the student clinic, observation, and attitude towards a clerkship, on the objective structured clinical examination (OSCE) scores of dental students graduating in restorative dentistry. MATERIALS AND METHODS: The OSCEs consisted of two stations designed to assess students' clinical skills regarding cavity preparation for a class II gold inlay and a class IV composite restoration. The clerkship achievements, consisting of the number of student clinical procedures performed, observation-related OSCE, and scores of their attitudes towards a conservative dentistry clerkship, were assessed. Correlation and multiple regression analyses were conducted. RESULTS: The correlation coefficient between the OSCE scores for cavity preparation for a class II gold restoration and clerkship attitude scores was 0.241 (p < 0.05). Regarding a class IV composite restoration, OSCE scores showed statistically significant correlations with the observation (r = 0.344, p < 0.01) and attitude (r = 0.303, p < 0.01) scores. In a multiple regression analysis, attitudes towards a clerkship (p = 0.033) was associated with the cavity preparation for a class II gold inlay OSCE scores, while the number of procedure observations (p = 0.002) was associated with the class IV composite restoration OSCE scores. CONCLUSIONS: The number of clinical procedures performed by students, which is an important requirement for graduation, showed no correlation with either of the OSCEs scores.

The influence of chlorhexidine on the remineralization of demineralized dentine.

OBJECTIVES: To examine the differences in the amounts of bound chlorhexidine (CHX) on demineralized dentine blocks and to investigate the different aspects of remineralization of demineralized dentine according to different concentrations of CHX. METHODS: Dentine blocks (2 mm × 7 mm × 0.9 m) were demineralized in 0.2 M formic acid solution. Amount of bound CHX on the dentine blocks was measured on a spectrophotometer after the dentine block was soaked in 0.02%, 0.2%, or 2% CHX solutions for 1 min. The change in elastic modulus of dentine block stored in simulated body fluids was measured at 0 (baseline), 2, 4, and 6 weeks after storage. The micromorphological aspects of the samples were observed using a field emission scanning electron microscope after 6 weeks of storage. RESULTS: Higher concentrations of CHX caused a greater amount of CHX to bind to the dentine blocks (p<0.05). The group treated with the higher concentration of CHX had a smaller decrease in the elastic modulus at 2 weeks and a greater increase at 4 and 6 weeks. Dentine specimens with the 0.2% and 2% CHX had a greater deposition of granular minerals along the collagen fibrils compared to the 0.02% CHX-treated group. CONCLUSION: The application of the 0.2% and 2% CHX seemed to be effective in promoting the remineralization of demineralized dentine. CLINICAL SIGNIFICANCE: The application of the 0.2% and 2% CHX positively influences on the dentine remineralization.

Effect of EDTA treatment on the hybrid layer durability in total-etch dentin adhesives.

The effect of the ethylenediaminetetraacetic acid (EDTA) treatment on the hybrid layer durability of total-etch dentin adhesives was investigated. A flat dentin surface was exposed and treated with 37% phosphoric acid or 0.1 M EDTA. Dentin adhesive was applied and a 4 mm thick composite resin was built-up. Twenty 0.9×0.9 mm(2) resin-dentin beams were fabricated in each experimental group. Artificial aging with 10% NaClO was performed in half of the experimental groups for 1 hour. A micro-tensile bond strength (µTBS) test was performed and the bonded interface was analyzed with transmission electron microscopy (TEM). The 37% phosphoric acid-treated group showed a lower µTBS after artificial aging, whereas the 0.1 M EDTA-treated group did not. TEM analysis revealed collagen fibrils dissolved in the 37% phosphoric acid-treated group but not in the 0.1M EDTA-treated group. Undissolved minerals were observed in the 0.1 M EDTA-treated group. In conclusion, a dentin treatment with 0.1M EDTA is effective in improving the hybrid layer durability.

Imperfect hybrid layers created by an aggressive one-step self-etch adhesive in primary dentin are amendable to biomimetic remineralization in vitro.

Degradation of hybrid layers created in primary dentin occurs as early as 6 months in vivo. Biomimetic remineralization utilizes "bottom-up" nanotechnology principles for interfibrillar and intrafibrillar remineralization of collagen matrices. This study examined whether imperfect hybrid layers created in primary dentin can be remineralized. Coronal dentin surfaces were prepared from extracted primary molars and bonded using Adper Prompt L-Pop and a composite. One-millimeter-thick specimen slabs of the resin-dentin interface were immersed in a Portland cement-based remineralization medium that contained two biomimetic analogs to mimic the sequestration and templating functions of dentin noncollagenous proteins. Specimens were retrieved after 1-6 months. Confocal laser scanning microscopy was used for evaluating the permeability of hybrid layers to Rhodamine B. Transmission electron microscopy was used to examine the status of remineralization within hybrid layers. Remineralization at different locations of the hybrid layers corresponded with quenching of fluorescence within similar locations of those hybrid layers. Remineralization was predominantly intrafibrillar in nature as interfibrillar spaces were filled with adhesive resin. Biomimetic remineralization of imperfect hybrid layers in primary human dentin is a potential means for preserving bond integrity. The success of the current proof-of-concept, laterally diffusing remineralization protocol warrants development of a clinically applicable biomimetic remineralization delivery system.

Effects of cavity configuration on composite restoration.

This study evaluated the effects of various cavity configurations on the bond strength, microleakage, flexural strength and elastic modulus of a hybrid (Clearfil AP-X) and a microhybrid (Esthet-X) composite restorative. After the specimens were made with C-factors of less than 1, 2.4 and 3.4, flexural strength and elastic modulus were evaluated in three-point bending using a mechanical testing machine. Fragments of the fractured specimens were selected randomly and the fracture surfaces were examined in SEM. To evaluate the microtensile bond strength and microleakage of composite restorations in bovine cavities, C-factors (ratio of bonded to non-bonded cavity surface) were controlled as 1.0, 2.3, 3.0 and 3.7. All specimens were stored in distilled water at 37 degrees C for 24 hours and tested in a universal testing machine (EZ Test, Shimadzu, Japan). For the microleakage test, teeth with restorations were stained with silver nitrate and examined by two examiners under a stereomicroscope at 40x magnification. The hybrid composite showed higher mechanical properties than the microhybrid composite. The flexural strength and elastic modulus of both composites decreased when polymerized under greater constraint, that is, with increasing C-factor. Mean microtensile bond strength to dentin was also decreased with increasing C-factor for both types of composites. Microleakage scores for the hybrid composite restorations were generally higher than the microhybrid composite.