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Lithium disilicate glass-ceramic (LS2) can be biomimetically textured by crystal orientation, mimicking the microstructure of dental enamel and inducing anisotropic mechanical responses to crack growth. The deliberate texturization of LS2 plays to the clinical advantage of reinforcing weak sites of typical fracture initiation in dental prosthetic constructs. Similar to enamel, adhesion of biomimetically textured LS2 could also show anisotropic behavior. Therefore, tensile bond strength (TBS) before and after thermocycling (TC) and interfacial characterization of biomimetically textured LS2 (parallel (PAR) or perpendicular (PER) crystal orientation) after different pre-treatment modes (hydrofluoric acid etching (HFE), grit blasting (GBL) and self-etching glass-ceramic primer (SGP)) were investigated. TC reduced significantly TBS for all specimens except for GBL. Biomimetic textured LS2 after HFE showed anisotropic behavior regarding adhesion. Crystal orientation reduced TBS for the PER HFE specimens after TC significantly. In general, the TBS of HFE specimens was still higher or not significantly lower compared to other pre-treatment modes like GBL or SGP. For the GBL and SGP specimens, crystal orientation had no influence on TBS and interfacial characteristics. In contrast HFE specimens showed different interfacial characteristics depending if they were PAR or PER texturized. Based on these findings, HFE of biomimetic textured LS2 can be recommended. For bonding, the PAR orientation is recommended as its adhesion potential is less prone to degrade.

We intend by this short critical review to highlight important aspects regarding the mechanical testing of fracture toughness. The final aim is to increase the awareness to the test sensitivity, ultimately increasing the quality and reliability of reported testing results. In a well-intended attempt to facilitate testing procedures or provide alternatives for testing material interfaces, authors are resorting to adaptation of testing methodologies without proper theoretical and experimental validation. The assumption of validity in such cases endangers the perpetration of testing strategies that are not safeguarded by sound theoretical bases. The use of improper statistical treatments based on extreme-value distributions further aggravates this scenario. We supply here some directions for authors concerning method selection, interpretation of data scatter, statistical treatment, and possibilities for test validation.

We subjected a commercial dental composite formed by interconnecting polymer-ceramic scaffolds to extensive quasi-static, static and cyclic experiments under biaxial flexure. By this we meant to obtain static and cyclic subcritical crack growth exponents that, based on established relationships describing the degradation of frictional bridging mechanisms, challenging the notion of a suggested R-curve behavior. By exploring the fracture statistics of specimens with increasing effective volumes and effective areas, we demonstrated the presence of a bi-modal defect size distribution in disaccord with the Weibull behavior across length scales. Lifetime distributions seemed to follow the strength distributions, and were used to derive crack growth velocity diagrams for combined levels of applied stress. Ultimately, the claim of an R-curve behavior could not be supported based on the absence of any significant cyclic fatigue effect, i.e. bridging degradation.

To investigate the tensile bond strength of silane-containing universal adhesives and self-etch glass-ceramic primer to lithium disilicate glass ceramics (LS2).960 rectangular LS2 bars (7 mm x 3 mm x 9 mm, IPS e.max CAD, Ivoclar Vivadent) were manufactured and divided into 4 groups (n = 240). Group 1 was etched with ~5% hydrofluoric acid (HF) for 20 s (VITA Ceramics Etch, Vita Zahnfabrik), group 2 was etched with ~5% HF for 20 s and silanized (ESPE Sil, 3M Oral Care), group 3 was pre-treated with a self-etching glass-ceramic primer (Monobond EtchPrime, Ivoclar Vivadent, and group 4 received no pre-treatment. Three universal adhesives (iBOND Universal, Heraeus Kulzer; Scotchbond Universal Adhesive, 3M Oral Care; Futurabond U, Voco) were applied to the differently pre-treated surfaces, with Heliobond (Ivoclar Vivadent) serving as control. The bars from each group were paired and luted perpendicularly, forming a square bonded area of 9 mm2, using Variolink II (Ivoclar Vivadent) with a constant pressure of 10 N, followed by light curing (40 s at 800 mW/cm2, Elipar Trilight, 3M Oral Care). The resulting specimens were stored for 24 h at 37°C in distilled water. Half of the specimens of each group were submitted to tensile bond strength testing, the other half were thermocycled ([TC] 5000 cycles, 5°C/55°C, 30-s dwell time) before testing. Data were analyzed using three-way ANOVA (α = 0.05).Group 2 (HF etched and silanized) and group 3 (self-etching glass-ceramic primer) reached significantly higher mean bond strengths than did groups 1 (only HF etched) and 4 (no pre-treatment).Additional silanization of HF-etched LS2 statistically signficantly improved the tensile bond strength of the silane-containing universal adhesive (Scotchbond Universal). The self-etching glass-ceramic primer Monobond EtchPrime achieved mean bond strengths that did not differ significantly from HF-etched and silanized specimens.

Most dental ceramics are produced from partially crystallized glass. Even though these materials are hard, they are extremely susceptible to damage, especially due to the glass phase content. A strategy for strengthening these materials makes use of their microstructure to form reinforcing sites within the structural design. Such approach has potential for application with lithium disilicate (LS 2 ) glass–ceramics, which contain needle-form Li 2 Si 2 O 5 crystals that deflect oncoming cracks. By press injection of the glass melt through specifically oriented injection channels, crystals are aligned in patterns that lead to high mechanical anisotropy. Here we apply this approach in the context of monolithic dental bridges simulated by beams under 3-point bending. Notches at different distances from the midspan play the role of connectors, and the mixed-mode fracture toughness is measured at varying positions for a LS 2 and a 3Y-TZP material. A strong anisotropic fracture behavior is obtained with the LS 2 glass–ceramic through local crystal alignment, leading to fracture energies higher than for the isotropic 3Y-TZP ceramic. Further, the anisotropic nature of the LS 2 microstructure is successfully reproduced in dental bridge geometries, validating the use of bending beams for the study of the mechanical behavior of ceramic dental bridges.

Selbstadhasive Befestigungszemente sind in der Praxis beliebt, da sie keine zusatzliche Vorbehandlung der Zahnhartsubstanzen erfordern. Fur den Erfolg einer Zementierung spielt im Praxisalltag die Adhasion der Restauration eine entscheidende Rolle. Uber die Verbundfestigkeit dieser Zemente zu Dentin sind die Untersuchungsergebnisse hinlanglich bekannt, wie aber sieht diese bei den indirekten Restaurationsoberflachen Zirkonoxid und Lithiumdisilikat-Keramik aus? Die nachfolgend vorgestellte In-vitro-Studie untersuchte den Einfluss von Selbst- und Dualhartung auf die Haftung von unterschiedlichen, handelsublichen selbstadhasiven Befestigungszementen auf Zirkonoxid- und Lithiumdisilikat-Keramik vor und nach thermischer Belastung – und kommt zu interessanten Ergebnissen fur die Anwendung in der Praxis.

The objective of the study was to investigate the relationship between pH-neutralization, hydrophilicity, and free hygroscopic expansion stress of self-adhesive resin cements (SARCs) after storage in artificial saliva. The SARCs RelyX Unicem Automix 2 (RX2, 3 M ESPE), iCEM (iCEM, Heraeus) and Maxcem Elite (MCE, Kerr) were under investigation in this study. Cylinders (height × diameter, 6 × 4mm) were prepared from each material and stored in artificial saliva (7d at 37 °C). Cylinder height was measured at baseline and after 7 days. After storage, the compression modulus was measured to calculate the free hygroscopic expansion stress. For pH-neutralization and hydrophilicity assessment, disks (height × diameter, 1 × 1.5 mm) were prepared, covered with electrolyte, and monitored over 24 h at 37 °C. Hydrophilicity was assessed using the static sessile drop technique at baseline and at different time intervals up to 24 h. Data were analyzed using one-way ANOVA and post hoc Student-Newman-Keuls test (S-N-K, α = 0.05). After 24 h, RX2 (pH24h 4.68) had a significantly higher (p

Objectives This study was intended to separate residual stresses arising from the mismatch in coefficients of thermal expansion between glass and zirconia (ZrO2) from those stresses arising solely from the cooling process. Slow crack growth experimentes were undertaken to demonstrate how cracks grow in different residual stress fields. Methods Aluminosilicate glass discs were sintered onto ZrO2 to form glass–ZrO2 bilayers. Glass discs were allowed to bond to the ZrO2 substrate during sintering or prevented from bonding by means of coating the ZrO2 with a thin boron nitrade coating. Residual stress gradients on “bonded” and “unbonded” bilayers were assessed using birefringence measurements. Unbonded glass discs were further tested under biaxial flexure in dynamic fatigue conditions in order to evaluate the effect of residual stress on the slow crack growth behavior. Results When fast-ccoling was induced, residual tensile stresses on the glass increased significantly on the side toward the ZrO2 substrate. By allowing the bond between glass and ZrO2, those tensile stresses observed in unbonded specimens are overwhelmed by the contraction mismatch stresses between the ZrO2 substrate and the glassy overlayer. Specimens containing residual tensile stresses on the bending surface showed a time-dependent strength increase in relation to stress-free annealed samples in the dynamic biaxial bending test, with this effect being dependent on the magnitude of the residual tensile stress. The phenomenon observed is explained here on the basis of the water toughening effect, in which water diffuses into the glass promoting local swelling. An additional residual tensile stress at the crack tip adds an applied-stress-independent (Kres) term to the total tip stress intensity factor (Ktip), increasing the stress-enhanced diffusion and the shielding of the crack tip through swelling of the crack faces. Significance Residual stresses in the glass influence the crack growth behavior of veneered-ZrO2 bilayered dental prostheses. The role of water in crack growth might be of higher complexity when residual stresses are present in the glass layer.

Introduction The purpose of this study was to evaluate the amount of calcium hydroxide (Ca[OH] 2 ) removed by irrigation with different volumes and activation methods. Methods One hundred thirty extracted straight, single-rooted human teeth were instrumented to size 45/.04. One hundred twenty teeth were filled with radioactively marked Ca(OH) 2 and a gutta-percha point; 10 teeth with only gutta-percha served as a negative control. All specimens were stored in saline solution (7 days at 35°C). After storage, teeth were randomly divided into 12 groups ( n = 10). The gutta-percha was taken out, and Ca(OH) 2 was removed either by irrigation with different volumes (0 mL, 0.5 mL, 1 mL, 2 mL, 4 mL, or 8 mL) or mechanical activation with a 2- or 4-mL volume using a file (Instr) (FlexMaster size 45/.04; VDW, Munich, Germany), a brush (CanalBrush [CB]; Coltene/Whaledent, Langenau, Germany), or passive ultrasonic irrigation (PUI, smooth wire). Irrigation was performed by alternating 40% citric acid and 3% sodium hypochlorite. Residual Ca(OH) 2 was measured by scintillation and expressed as a percentage of the original Ca(OH) 2 . Results Increasing the irrigation volume led to a significant decrease ( P 2 (0 mL [98.5%], 0.5 mL [21.7%], 1 mL [16.5%], 2 mL [12.9%], 4 mL [8.7%], 8 mL [5.0%], and negative control [0.0%]). Activation led to less residual Ca(OH) 2 (2 mL Instr [12.0%], 2 mL CB [11.7%], 2 mL PUI [9.1%], 4 mL Instr [8.5%], 4 mL CB [7.4%], and 4 mL PUI [6.2%]), with significant differences according to the PUI ( P Conclusions No irrigation procedure was able to remove Ca(OH) 2 completely. PUI was the most effective activation method. However, irrigation with an 8-mL volume was the most effective.

To evaluate the bonding performance of self-adhesive resin cements to zirconia and lithium disilicate in self- and dual-curing modes before and after thermocycling.Rectangular bars (3 mm high, 3 mm wide, 9 mm long) were manufactured from zirconia (Vita In-Ceram YZ for inLab, VITA) and lithium disilicate blocks (IPS e.max Press, Ivoclar Vivadent) (n=240 per material). Zirconia bars were sandblasted (35 μm Al2O3, 1.5 bar pressure). Lithium disilicate bars were HF etched (20 s, IPS Ceramic Etching Gel, Ivoclar Vivadent) and silanized with ESPE Sil (3M ESPE). Forty bars of zirconia were luted in twos perpendicular to each other as were 40 bars of lithium disilicate using RelyX Unicem Automix 2 (3M ESPE), G-Cem LinkAce (GC Europe) or Maxcem Elite (Kerr) in self- or dual-curing mode. Half of the specimens from each material were submitted to tensile bond strength (TBS) testing after 24-h storage in distilled water at 37°C, and half underwent TBS testing after thermocycling (5000 cycles, 5°C/55°C, 30-s dwell time). Bond strength values for each bonding substrate were analyzed using one-way ANOVA (Student-Newman- Keuls, α=0.05).On zirconia, dual-curing resulted in significantly (p0.05) higher tensile bond strengths compared to self-curing, with the exception of RelyX Unicem 2 after thermocycling. Thermocycling significantly (p0.05) reduced the tensile bond strength of Maxcem Elite to zirconia in both curing modes. The TBS of self-adhesive cements to lithium disilicate showed no significant (p0.05) difference between the different curing modes and after thermocycling.For most of the investigated self-adhesive cements, bond strengths to zirconia were increased by dual curing; this was not true for lithium disilicate. For luting on zirconia with self-adhesive cements, dual curing is strongly recommended in clinical situations.

The aim of the present study was evaluate the effect of microparticulate silver additions in adhesives on secondary caries formation using an artificial mouth model. One hundred eight intact human third molars received standardized Class-V resin composite restorations (Filtek Supreme XTE bonded with Syntac, Scotchbond 1 XT, Futurabond M). Adhesives were charged with different amounts of microparticulate silver (0 %/0.1 %/0.5 %). After storage for 4 weeks at 37 °C, teeth were subjected to 10,000 thermocycles (+5 °C and +55 °C), and impressions were taken. Streptococcus mutans 10449 was used in a nutrition medium for secondary caries simulation in a fully automated artificial mouth. After completion of thermocycling and biological load cycling, impressions were taken and replicas were investigated under a light microscope for gap widths at enamel and dentin margins. Evaluation of fluorescence was carried out using a special FITC filter. The demineralization depths at the cavity margin were evaluated using Xpert for Windows working at a pixel distance of 5 μm. After thermocycling, no difference in gap widths and demineralization depths was found (p > 0.05). After incubation, gap widths and demineralization depths were significantly reduced with higher amounts of silver loading in most of the adhesives (p

Objectives The aim was to evaluate the polymerization properties of bulk-fill resin composites using two different light-curing protocols, in terms of degree of conversion (%DC), Vickers hardness (HV), polymerization volume shrinkage (PVS) and polymerization shrinkage stress (PSS) and compare them to conventional condensable and flowable resin composites. Materials and methods Filtek BulkFill (FBF, 3MESPE, Germany), SDR (Dentsply, Germany), TetricEvoCeram BulkFill (TBF, Ivoclar-Vivadent, Liechtenstein), Venus BulkFill (VBF, Heraeus, Germany), X-traBase (XTB, Voco, Germany), FiltekZ250 (3MESPE) and Filtek Supreme XTE Flowable (FSF, 3MESPE) were investigated. Light-curing was performed for 30 s or according to manufacturers’ instructions (1200 mW/cm2, Bluephase20i, Ivoclar-Vivadent). For %DC and HV, discs (n = 5) of 2 or 4 mm in thickness were prepared and stored for 24 h in distilled water at 37 °C. %DC was determined by FTIR-ATR-spectroscopy. %DC and HV were measured at the top and bottom of the specimens. PVS was measured using Archimedes method (n = 6). PSS measurements (n = 10) were carried out using 5 mm diameter PMMA rods as bonding substrates with a specimen height of 1 mm in a universal testing machine. Data were analyzed using one- and two-way ANOVA (α = 0.05). Results Except Z250 in the manufacturers’ light-curing mode, all materials showed no significant inferior %DC at 4 mm thickness. When light cured for 30 s Z250 had no significant differences in %DC at 2 or 4 mm when compared to top. FBF, TBF, FSF and Z250 displayed significant reduced HV at 4 mm in both curing modes. Z250 and TBF showed the lowest PVS and FSF the highest PSS in both curing modes. Significance All investigated bulk-fill composites obtained sufficient polymerization properties at 4 mm depth. Enhanced curing time improved the investigated polymerization properties of bulk-fills and Z250.

Objective The aim of this study was to evaluate if pH-neutralization behavior of self-adhesive resin cements has an influence on their mechanical properties. Methods pH-neutralization, water sorption, solubility and flexural strength of G-Cem Automix (GCA), G CEM Capsules (GCC), Maxcem Elite (MCE), RelyX Unicem Clicker (RXC), RelyX Unicem Maxicap (RXM), RelyX Unicem 2 (RX2), and Speed-Cem (SPC) were tested in self-curing mode. Specimen's pH-values were recorded up to 24 h with a pH-electrode. Water sorption (WS) and solubility (SO) were measured. Flexural strength (FS) was evaluated before and after thermocycling (TC) and fracture surfaces analyzed under SEM. Results RX2 (pH 24 5.89), RXC (pH 24 5.49) and SPC (pH 24 5.42) showed highest 24 h pH-values, followed by GCA (pH 24 5.34). Capsulated products and MCE (pH 24 3.90) reached lower pH-values. GCC (75.78 μg/mm 3 ) showed the highest WS followed by MX (69.64 μg/mm 3 ), RXM (64.76 μg/mm 3 ), GCA (25.86 μg/mm 3 ) and SPC (30.42 μg/mm 3 ). Capsulated products RXM (56.58 μg/mm 3 ) and GCC (30.94 μg/mm 3 ) presented the highest SO, GCA (4.06 μg/mm 3 ) and SPC (4.26 μg/mm 3 ) revealed the lowest. GCA (114.03 MPa) had the highest initial FS followed by SPC (79.81 MPa), RXM (41.61 MPa) the lowest. FS of all materials decreased significantly after TC except for RXC (44.65 MPa) and RX2 (65.92 MPa). FS of GCC (16.47 MPa) and MCE (28.21 MPa) decayed the most. A highly linear correlation was observed between percentage decrease of FS after TC and 24 h pH-values ( R 2 = 0.861). Significance Within the limits of this study pH-neutralization behavior has an influence on mechanical stability. When using self-adhesive resin luting agents, automix-syringe products with improved pH-neutralization behavior should be favored.