Superfast Set, Strong and Less Degradable Mineral Trioxide Aggregate Cement.

PURPOSE: Despite the good sealing ability and biocompatibility of mineral trioxide aggregate (MTA), its slow setting, high degradation, and weakness limit its use in surgical endodontics and high stress-bearing areas. This study aimed to develop two new liquids to control these drawbacks. They were prepared from calcium chloride, fumed silica, and hydroxyapatite or calcium phosphate and coded "H" and "P," respectively. METHODS: Portland cement, Grey ProRoot® MTA, and white ProRoot MTA were mixed with distilled water (control) or liquid "H" or "P." The pH, setting time, degradation rate, leachant/precipitate' composition, compressive strength, and morphology were assessed. RESULTS: Both liquids maintained MTA's high alkalinity and reduced the setting time by 1-2 orders of magnitude. Both liquids, H in particular, significantly reduced the degradation rate of Grey ProRoot and White ProRoot MTA®. Calcite has been identified as the main phase of the leachant or precipitate formed during the cement's degradation. Calcium hydroxide or hydroxyapatite was also identified with Grey ProRoot MTA mixed with H liquid. These liquids also significantly increased the compressive strength with no statistical differences between them; this was associated with the production of dense, consolidated structures. CONCLUSIONS: The modified MTA could be used in surgical endodontics and high stress-bearing areas.

In vitro shear bond strength of two self-adhesive resin cements to zirconia.

STATEMENT OF PROBLEM: Although the use of anatomic-contour zirconia restorations has expanded in the recent past, disagreement still exists as to reliable cementation techniques and materials. PURPOSE: The purpose of this in vitro study was to compare the immediate and artificially aged shear bond strength of 2 commercially available self-adhesive resin cements to zirconia: one with silica coating and silanation as a zirconia surface treatment and the other contained a phosphate monomer, which eliminated the need for a separate primer. MATERIAL AND METHODS: Sixty composite resin rods (2.5 mm in diameter and 3 mm in length) were fabricated from a nano-optimized composite resin by using a polypropylene mold, then light polymerized with a light-emitting diode. zirconia plates (10×10×4mm) were sectioned from an yttrium-stabilized zirconia puck, sintered, and then mounted in autopolymerizing acrylic resin custom tray material. Composite resin rods were cemented to the zirconia plates with 2 different cements. The surface treatment of zirconia followed the manufacturers' instructions for each cement. The specimens were tested for shear bond strength at 3 aging conditions: immediate, after 24 hours of moist storage, and after 30 days of moist storage with 10000 thermocycles. Specimens were loaded to failure in a universal testing machine, and the data were analyzed with 2-way ANOVA (α=.05). Weibull parameters (modulus and characteristic strength) also were calculated for each group. RESULTS: Two-way ANOVA revealed that only the aging condition significantly affected the bond strength to zirconia. The cement and the interaction of the cement and aging did not significantly affect the shear bond strength to zirconia. The highest bond strength for both cements was achieved at 24 hours, whereas the lowest bond strength values were recorded in the immediate groups. CONCLUSIONS: No significant differences in bond strength to zirconia were observed between a cement with a silane priming step and an methacryloxydecyl dihydrogen phosphate-containing cement without a separate primer. Aging had a significant effect on the shear bond strength of the 2 self-adhesive resin cements to zirconia.

Size-dependent strength of dental adhesive systems.

OBJECTIVE: The aim of this study is to explain the influence of peripheral interface stress singularities on the testing of tensile bond strength. The relationships between these theoretically predicted singularities and the effect of specimen size on the measured bond strength are evaluated. METHODS: Finite element method (FEM) and boundary element method (BEM) analyses of microtensile bond strength test specimens were performed and the presence of localized high stress concentrations and singularities was analyzed. The specimen size effect predicted by the models was compared to previously published experimental data. RESULTS: FEM analysis of single-material trimmed hour-glass versus cast cylindrical specimens showed different theoretical stress distributions, with the dumbbell or cylindrical specimens showing a more homogeneous distribution of the stress on the critical symmetry plane. For multi-material specimens, mathematical singularities at the free edge of the bonded interface posed a computational challenge that resulted in mesh-dependence in the standard FEM analysis. A specialized weighted-traction BEM analysis, designed to eliminate mesh-dependence by capturing the effect of the singularity, predicted a specimen size effect that corresponds to that published previously in the literature. SIGNIFICANCE: The results presented here further support the attention to specimen dimensions that has already broadened the empirical use of the microtensile test methods. FEM and BEM analyses that identify stress concentrations and especially marginal stress singularities must be accounted for in reliable bonding strength assessments. Size-dependent strength variations generally attributed to the effects of flaw distributions throughout the interfacial region are not as relevant as the presence of singularities at bonded joint boundaries - as revealed by both FEM and BEM analyses, when interpreted from a generalized fracture mechanics perspective. Furthermore, this size-dependence must be considered when evaluating or designing dental adhesive systems.

Effectiveness of an infiltrant on sealing of composite restoration margins with/without artificial caries.

AIM: The aim of this in vitro study was to evaluate the effectiveness of a resin infiltrant (ICON) on marginal sealing ability of class II resin restorations with/without-caries. MATERIALS AND METHODS: Forty-eight noncarious human pre-molar teeth were embedded and MO and DO preparations of standard dimensions were prepared. The left side of dentin margins of the cavities were left nonbonded (UB) while the right side were bonded using total etch-bonding agent and all restored with a Nanohybrid composite. The teeth were thermocycled and half of the specimens in the UB and B groups were subjected to an artificial caries process. ICON was applied to caries and noncaries subgroups following the manufacturer's directions. Impressions were made at each step: after the restorations were completed, thermocycling, artificial caries procedures, and infiltrant application and the silicone tag lengths were measured with a stereomicroscope. The specimens were immersed in 0.5% basic fuchsine at 37° C for 24 hours, sectioned and microleakage was evaluated with a stereomicroscope. Selected samples and their replicas were assessed for marginal quality under a stereomicroscope and SEM. Statistical evaluation of the data were made using Kruskal-Wallis, Mann-Whitney U and Wilcoxon Sign Rank tests. RESULTS: While bonding application did not create a meaningful difference, the thermocycling and artificial caries significantly increased the gap length and microleakage (p < 0.05). ICON application was decreased the microleakage, created gap-free margins and closed the gaps which were previously occurred at the same cavities (p < 0.05). CONCLUSION: A resin infiltrant (ICON) application decreased the microleakage, created gap-free margins and closed the gaps, which previously occurred at the same cavities. CLINICAL SIGNIFICANCE: Approximal application of resin infiltrant may increase the success of the class II composite restorations also reduced the risk of needing more complex restoration therapy.

Effect of hydration on assessment of early enamel lesion using swept-source optical coherence tomography.

Establishing reproducible methodologies for assessment of early enamel lesions using optical coherence tomography (OCT) appears to be challenging. This in vitro study longitudinally evaluated the subsurface enamel lesion progression after 3, 9 and 15 days by cross-sectional scanning using 1310 nm centered swept-source OCT (SS-OCT) under hydrated and dry conditions. The positive difference between the depth-integrated OCT signals at dry and hydrated conditions were calculated and adopted as dehydration parameter (DH). A linear regression was found between DH and the square root of demineralization time (R(2) = 0.99). Significant differences were found in DH between sound and demineralized enamel, and between different periods of demineralization (p < 0.001). Hydration state affects the reflectivity of demineralized porous enamel, and the effect can be potentially used for assessment of early enamel lesion using OCT.

Effect of laser preparation on bond strength of a self-adhesive flowable resin.

The aim of this in vitro study was to evaluate the effect of laser treatment on shear bond strength of a self-adhesive flowable resin composite to human dentin. Eighty extracted sound human molar teeth were used for the study. The teeth were sectioned mesiodistally and embedded in acrylic blocks. The dentin surfaces were ground wet with 600-grit silicon carbide (SiC) paper. They were randomly divided into two preparation groups: laser (Er:YAG laser, with 12 Hz, 350 mJ energy) and control (SiC). Each group was then divided into two subgroups according to the flowable resin composite type (n = 20). A self-adhesive flowable (Vertise Flow) and a conventional flowable resin (Premise Flow) were used. Flowable resin composites were applied according to the manufacturer's recommendations using the Ultradent shear bond Teflon mold system. The bonded specimens were stored in water at 37 °C for 24 h. Shear bond strength was tested at 1 mm/min. The data were logarithmically transformed and analyzed using two-way analysis of variance and Student-Newman-Keul's test at a significance level of 0.05. The self-adhesive flowable resin showed significantly higher bond strength values to laser-prepared surfaces than to SiC-prepared surfaces (p < 0.001). The conventional flowable resin did not show such differences (p = 0.224). While there was a significant difference between the two flowable resin composites in SiC-prepared surfaces (p < 0.001), no significant difference was detected in laser-prepared surfaces (p = 0.053). The bond strength of a self-adhesive flowable resin composite differs according to the type of dentin surface preparation. Laser treatment increased the dentin bonding values of the self-adhesive flowable resin.

Non-destructive characterization of voids in six flowable composites using swept-source optical coherence tomography.

OBJECTIVE: The aim of this study was to evaluate the void frequency (V(F)) and void volume (V(V)) in different flowable composites using swept-source optical coherence tomography (SS-OCT). METHODS: Standard class I cavities were prepared and filled with six different flowable composites: Clearfil Majesty LV (MJ; Kuraray), MI Flow (MW; GC), MI Fil (ML; GC), Beautifil flow plus (BF; Shofu), Palfique Estelite low flow (EL; Tokuyama) and Surefil SDR flow (SF; Dentsply). The restorations were scanned under OCT. The OCT tomograms were analyzed and average V(F) and V(V) per restoration for each composite were calculated. Scanning electron microscope (SEM) was used to observe the structure of each composite. In addition, the flowability of the materials was evaluated measuring the displacement of each material placed up-right on a glass slide. V(F) and V(V) obtained by OCT were also compared to those calculated using micro-computed tomography (micro-CT). RESULTS: Kruskal-Wallis ANOVA and Mann-Whitney U tests revealed significantly different V(F) and V(V) values (p<0.05) among the composites. Voids ranging from 35 to 785 µm in diameter were detected in OCT tomograms. MJ showed highest V(F) and V(V) values followed by MW, but ML, BF, EL and SF showed no significant difference. Filler volume in composites showed a positive correlation with void formation, but flowability did not show a specific trend. Micro-CT evaluation validated the V(F) and V(V) calculation by OCT, with a significant correlation in void size (p<0.001, r=0.94). CONCLUSION: The results of this study indicate the reliability of SS-OCT for real-time void characterization of composite materials and restorations. Void formation in flowable composites is material dependent.

Influence of abutment height and surface roughness on in vitro retention of three luting agents.

PURPOSE: This study evaluated the effects of abutment height, airborne-particle abrasion, and type of cement on the tensile resistance to dislodgement of cement-retained implant restorations. MATERIALS AND METHODS: Three groups of 12 standardized abutments each were prepared with different heights (4 mm, 5 mm, and 6 mm) using a milling machine. Crowns were cast in cobalt-chrome using the lost-wax technique, airborne particle-abraded using 50-Μm aluminum oxide, and cleaned with acetone. Restorations were cemented using a noneugenol acrylic urethane cement, a resin-modified glass ionomer, or a zinc oxide-noneugenol cement. A 5-kg load was applied for 10 minutes. Samples were kept at 37°C and 100% humidity overnight. A tensile force was applied to the crown using a testing machine at a crosshead speed of 5 mm/minute until failure occurred. Next, the abutments were airborne particle-abraded with 50-Μm aluminum oxide, and the cementation and testing procedures were repeated. The effects of cement, abutment height, and surface treatment were evaluated statistically. RESULTS: There were significant differences among the cements. The resin-modified glass ionomer provided the greatest retention in all the tested conditions, while the zinc oxide-noneugenol cement produced the lowest retention values. Significant differences were also detected between 4-mm and 6-mm abutments, with the 6-mm abutments being more retentive. No differences were found between 4-mm and 5-mm abutments or between 5-mm and 6-mm abutments. The effect of airborne-particle abrasion was also found to be significant. A maximum increase of 90 N in retention force was observed after airborne-particle abrasion for the 5-mm abutments cemented with the acrylic urethane cement. CONCLUSIONS: Cement, airborne-particle abrasion, and abutment height can significantly influence retention of implant-supported crowns. Different parameters, including those specific to the patient, should be considered in the selection of a luting agent.