Lower Bond Strength Research Articles

Effect of different surface treatments on the bonding potential and physical and mechanical properties of ultratranslucent zirconia

Statement of problemStudies to determine a suitable surface treatment that improves bonding without compromising the strength or translucency of ultratranslucent zirconia are scarce. PurposeThe purpose of this in vitro study was to evaluate the effect of different surface treatments on translucency, surface topography, phase transformation, biaxial flexural strength, bond strength, and durability. Material and methodsA total of 169 ultratranslucent zirconia disks were randomly divided into 4 groups according to the surface treatment applied: airborne-particle abrasion (APA) (n=46), tribochemical silica airborne-particle abrasion (TS) (n=46), nonthermal oxygen plasma (NTP) (n=46), and no treatment, control (C) (n=31). The translucency parameter (ΔTP00) was evaluated with a spectrophotometer (n=15), phase transformation was assessed with an X-ray diffractometer (n=5), surface topography was evaluated with a scanning electron microscope (SEM) (n=3), and biaxial flexural strength (BFS) was tested with a universal testing machine (n=15). For the microshear bond strength (μSBS) test, 40 composite resin specimens were attached to 8 disks and tested with a universal testing machine; 20 specimens were tested after 24 hours, and 20 specimens after hydrothermal aging in a thermocycler (TC). The data were analyzed with ANOVA followed by the Tukey post hoc test (α=.05). Weibull analysis was performed for the flexural strength and μSBS results. ResultsSignificant ΔTP00 differences were found among all groups and were highest for the APA group (7.33) and lowest for the NTP group (4.79). The NTP group had a significantly higher monoclinic weight fraction value (4.54%) than other groups. The NTP group had significantly higher BFS (581.31) than other groups, while the APA group showed significantly lower values than other groups (340.43). The APA group had significantly higher μSBS values after 24 hours (13.51 MPa) and after TC (13.68 MPa) than the other groups (P<.05). ConclusionsAlthough APA and TS are effective techniques for improving resin-zirconia bonding, they result in significantly higher deterioration of translucency and strength. NTP significantly improved the BFS of zirconia; however, it showed lower bond strength values than other methods.

Performance evaluation of lightweight insulating plaster for enhancing the fire endurance of high strength structural concrete

Structural concrete is a widely used building material due to its versatile characteristics including higher compressive strength and longevity. However, when exposed to fire, concrete experiences faster degradation in its mechanical properties and is also susceptible to spalling. To overcome this problem, the possibility of lightweight plaster application on High Strength Concrete (HSC) is explored in the presented investigation. Insulation plasters, namely Sand Plaster (SP), Gypsum Perlite Plaster (GPP), and Gypsum Mineral Wool Plaster (GMP) were developed. This investigation evaluates the compressive strength, bond strength, and shear strength of concrete which is exposed to the standard fire temperature. Varying cooling conditions which involved air and water were adopted to cool the concrete specimens after the elevated temperature test. Further, the damaged concrete and the plaster were examined to analyse the physical changes. Analysis of the study reveals that more number of denser surface cracks and higher mass loss was observed for reference and SP specimens. Temperature penetration at the core of cube, bond, and shear specimens is less for the GPP and GMP specimens when compared with the SP specimens. At higher temperatures (986 °C), the reference and SP specimens show a lower bond and shear strength with higher slip values. Specimens insulated with GPP and GMP exhibited a low-temperature penetration at the core portion. Also, the results of the study reported the higher residual compressive, bond, and shear strength compared to other specimens.

Evaluation of the Interlayer Bond Strength of Micro-Surfacing Mixes

This paper presents the results of the first study to evaluate the effects of the tack coat and micro-surfacing mix properties on the interlayer bond strength between the micro-surfacing layer(s) and existing pavement surface. Several factors were investigated, which included the type of tack coat material, tack coat application rate, and the residual binder content of the micro-surfacing mix. To this end, a total of 14 field micro-surfacing test sections were installed on Ohio State Route 03 in Wayne County, Ohio. While the first seven sections were constructed with a single micro-surfacing layer, the other seven sections had double micro-surfacing layers. Five tack coat application rates and two residual binder contents were evaluated. The testing plan involved obtaining core samples from the constructed sections 1 week, 4 months, and 12 months after construction. The obtained field cores were tested in the laboratory using two types of pull-off tests and a torque bond strength test. The results of bond strength tests on obtained field cores and the statistical analysis performed on these results indicated that sections with no tack coat had significantly lower bond strength than those with tack coat with at least 0.05 gallons per square yard (gsy) total application (0.0083 gsy residual application rate). Furthermore, results indicated that the use of 0.75% lower residual asphalt binder content in micro-surfacing mixes resulted in significantly lower bond strength between the micro-surfacing and existing pavement. The tack coat material properties had some effect on the interlayer bond strength; however, this effect was statistically insignificant.

Effect of photosensitizers on modulating bond strength of different luting cements used for cementation of resin modified composite fiber posts.

The aim of the study was to evaluate the tensile BS of FPs luted with conventional and self-adhesive resin modified GIC cement on disinfection of post-space radicular dentin with various photo-activated photosensitizer (chitosan, TB and Clp6). Sixty-six orthodontically extracted mandibular pre-molars were selected on specific exclusion/inclusion criteria, trailed by thorough debridement of plaque/calculus and disinfected by immersion in Chloramine T trihydrate solution for 48 hrs. The selected teeth were sectioned from the cement-enamel junction removing the crown. The radicular region of the samples was entrenched perpendicularly in heat cure resin modified acrylic. The pulpal tissue was detached using K-files trailed by canal shaping with ProTaper Next rotary NiTi (Dentsply Sirona, Gloucestershire, UK) files under continuous irrigation with NaOCl. The canals were dried using paper points trailed by obturation by Pro Taper Next Obturators gutta-percha points (Dentsply, UK) coated with ADSEAL (Meta Biomed, Chungcheongbuk-do, South Korea). After incubation for seven days in an environment mimicking oral cavity, post space was created using peso reamers. The space was disinfected by G1: chitosan 3 mg/mL; G2: 13-15 mg/mL TB and G3: Clp6. After photo-irridation the FPs were luted with conventional (n=11) and resin modified self-adhesive cement (n=11) for each group respectively. The specimens were incubated for 48 hrs prior to tensile BS testing. The type of bond fracture/failure was evaluated under 30x magnification. The tensile BS was statistically analyzed using ANOVA trailed by Tukey's test to respective groups. FPs luted using self-adhesive resin modified cement with prior to disinfection by TBs displayed highest tensile BS 291.47 N ± 5.36. On the contrary, post-space disinfected by Clp6 displayed statistically significant (p ≤ 0.05) lowest bond strength (276.62 N ± 4.31). Intra-group analysis displayed statistically significant difference in bond strength of the luting dental materials (p ≤ 0.05). The self-adhesive resin modified cement revealed utmost bond strength on pre-treatment of post-space with respective photo-activated photosensitizer (chitosan, TB & Clp6) in contrast to conventional GIC.

Comparative Assessment of Qmix as Endodontic Irrigant on Reversal of Bond Strength in Teeth Subjected to Irradiation: An Scanning Electron Microscope Study

The aim of this current study was to compare and evaluate the reversal efficacy of Qmix and chitosan-based irrigation materials quantitatively through the assessment of the push-out bond strength of bioceramic sealer employing universal testing machine and to qualitatively analyze the sealer/dentin interface by scanning electron microscope (SEM) in the teeth subjected to fractioned radiation. Ninety single-rooted straight human maxillary central incisors were randomly divided into six groups (n = 15) where in three groups comprise Chitosan, Qmix, and EDTA/sodium hypochlorite which were not exposed to irradiation while other three groups were challenged with irradiation protocols. Root canals were prepared with ProTaper universal system and all the samples were irrigated according to the final irrigation protocols and obturated with bioceramic sealers. Dentin slices were prepared with 1 mm thickness from each root third for the estimation of bond strength of sealers to dentin. Qualitative assessment of the sealer-dentin interface was done by scanning electron microscopy. Bond strength data were scrutinized by independent t-test and failure modes using the Chi-square test. Significantly lower bond strength (p <0.05) was recorded after irradiation compared with nonirradiated group. To quantify the results irrigation protocols, Qmix had highest bond strength followed by chitosan and EDTA/sodium hypochlorite group irrespective of irradiation status. Bond strength values reduced after irradiation in all root thirds irrespective of the irrigation materials. Scanning electron microscope images revealed traces of repair process for Qmix-based irrigation materials than the chitosan-based materials for both irradiated and nonirradiated specimens. All the irrigation materials employed in this study had good bond strength. The specimen irrigated with Qmix had comparatively higher bond strength than the chitosan-based materials. The teeth subjected to irradiation challenge were associated with a decrease in the push-out bond strength of sealers to intraradicular dentin with formation of more gaps and fewer tags at the sealer/dentin interface. Selection of ideal irrigation protocols still remains a challenge for the clinical practitioners, and this study explored the utilization of novel materials used for irrigation, especially in the teeth subjected to radiation.

Effect of Artificial Aging Test on PEEK CAD/CAM Fabricated Orthodontic Fixed Lingual Retainer

Background: The purpose of this study was to evaluate the effect of in vitro long-term simulation of oral conditions on the bond strength of PEEK CAD/CAM lingual retainers. Material and methods: The sample consisted of 12 PEEK CAD/CAM retainers each composed of 2 centrally perforated 3x4mm pads joined by a connector. They were treated by 98% sulfuric acid for 1 minute and then conditioned with Single Bond Universal and bonded to the lingual surface of premolar teeth by 3M Transbond TM System. Half of the retainers were artificially aged using a 30-day water storage and 5000 thermocycling protocol before bond strength testing to compare with the non-aged specimens. Results: The artificially aged retainers showed a marginally lower bond strength than the non-aged retainers. However, independent sample t-test indicated that this difference was statistically not significant. Conclusion: The durability of the PEEK lingual retainer adhesive system has been confirmed using the well-known oral simulating artificial aging protocol of water storage and thermocycling.

Evaluation of the Bond Strength of Self-Etching Adhesive Systems Containing HEMA and 10-MDP Monomers: Bond Strength of Adhesives Containing HEMA and 10-MDP.

The aim of this in vitro study was to assess the bond strength of self-etching adhesives containing HEMA and 10-MDP monomers. Twenty-four bovine teeth were divided into three groups. Two cylinders of composite resin were made in each tooth (n = 16): G1-Prime and Bond Universal (control); G2-OptiBond All-in-One (HEMA); and G3-Clearfil SE (10-MDP and HEMA). After 24-hour storage in distilled water, the specimens were fixed to a universal testing machine (Kratos Equipamentos Ltda.) for the microshear test at a speed of 0.5 mm/min. A qualitative analysis of the fracture pattern was also performed using scanning electron microscopy (500× magnification). The normality of sample data distribution was determined using the Shapiro–Wilk test. The results were assessed using the Kruskal–Wallis test, and α level of 5% was used for the analysis. The results indicated a statistical difference (p > 0.05) between G3 (15.6080 MPa) and G2 (11.2180 MPa). No statistical difference was observed when G1 (14,6325 MPa) was compared with the other two groups. It was also observed that a mixed fracture pattern was predominant in all groups. The self-etching adhesive containing HEMA and 10-MDP monomers showed to be promising in increasing the bond strength between the dental substrate and the composite resin, whereas the adhesive containing only HEMA exhibited lower bond strength to dentin.

Study on relative shrinkage of cement-based micro-concrete for durable concrete repair

This paper presents the investigation into the crack formation in micro-concrete due to their bond strength and drying shrinkage under normal and accelerated drying conditions at the interface between the substrate and micro concrete in a concrete repair. Investigated six different cement-based micro-concretes about their grain size, compressive strength, bond strength, and relative shrinkage values due to normal and raised drying temperature. Finite element analysis and microscopic study of crack development at the interface were investigated to strengthen the analysis of the crack developments. It was observed that the bond strength and drying shrinkage of the micro concretes influence the formation of cracks at the interface due to the relative shrinkage of the substrate and the micro concrete. The micro-concrete having high bond strength as compared to low bond strength micro-concrete, exhibits low crack width even though free drying shrinkage values are high in both case. Early detection of cracks at the interface in 3 days due to the combined effect of bond strength and drying shrinkage under accelerated drying conditions can be a helpful tool for selecting the micro concretes for concrete repair.

Effect of airborne particle abrasion and primer application on the surface wettability and bond strength of resin cements to translucent zirconia

The purpose of this study was to evaluate the effect of sandblasting and primer application on the immediate and long-term shear bond strength of resin cements to translucent zirconia. Zirconia plates (Katana STML, Kuraray Noritake Dental) were divided into six groups (n = 10) for shear bond strength evaluation using three resin cements (Panavia V5, Kuraray Noritake Dental; Variolink Esthetic LC, Ivoclar-Vivadent; and Panavia SA Cement Universal, Kuraray Noritake Dental). The zirconia was sandblasted or left unabraded. Each cement was used with the indicated primer. Two cylinders of cement were placed on the zirconia, one for evaluation after 24 h and the other after 1 year of storage in water. The fracture pattern and the contact angle were observed on all groups. At 24 h, there were no differences in bond strength of the cements for equal sandblasting conditions. After 1-year, the bond strength of all groups decreased, except for Panavia V5 associated with sandblasting. For all the cements, the unabraded zirconia showed a lower bond strength and a higher rate of adhesive failures. The application of primers reduced the contact angle. Higher bond strength is obtained when primers are combined with sandblasting using aluminum oxide particles. Clinical significance: Translucent zirconia restorations should be treated by airborne particle abrasion and phosphate-based primers before bonding, to improve the wettability of the cements and obtain a more durable bonding between the cement and the zirconia.

Correlation between Interface Microstructure and Bond Strength of Al6061/Al6061 HIP-Bonded Plates for Fuel Cladding Application

The effects of hot isostatic pressing (HIP) processing parameters on microstructure and bond strength of Al6061/Al6061 plate interfaces were systemically investigated at the micro- and nanoscale. The HIP bonding of the two aluminum plates was performed at four temperatures: 350°C, 400°C, 450°C, and 560°C. The results reveal the formation of micron scaled Mg2Si precipitate and uniform nano scaled Mg2Al2O5 oxide at the interface. The formation of Mg2Al2O5 is closely associated with the fast bulk diffusion of Mg from the Al matrix to the amorphous Al2O3/Al interface and subsequent reaction between Mg and Al2O3. The highest and lowest bond strengths were observed in samples HIP bonded at 450°C and 350°C, respectively.

Bond Behavior of FRP Bars in Lightweight SCC under Direct Pull-Out Conditions: Experimental and Numerical Investigation.

In recent decades, lightweight aggregate concrete (LWC) became a popular building material due to its desired properties. However, various attributes of LWC, such as bond behavior of used reinforcing, have not been described thoroughly. In this regard, LWC produced with 0%, 50%, and 100% expanded clay aggregate was designed, and the physical–mechanical properties were assessed for material characterization. Subsequently, the bond behaviors of LWC reinforced with steel, glass fiber reinforced polymer (GFRP), and basalt fiber reinforced polymer (BFRP) bars were evaluated by pull-out tests. The results of the experimental program allowed the effects of expanded clay aggregate incorporation on LWC properties to be quantified. The bond strength of BFRP bars was not affected by the replacement of coarse aggregate by expanded clay aggregate, whilst the GFRP bars showed lower bond strength values of LWC specimens. Contrarily, in the case of steel bars, both the bond strength and bond stiffness were higher for LWC specimens than for those of normal concrete. Finite element software ATENA 3D was used for simulation of the bond behavior of LWC, and the model validated by the experimental results referred to reasonably corresponding outputs.

Experimental study on seismic performance of resilient recycled aggregate concrete shear walls

A type of recycled aggregate concrete shear wall was proposed in this work, which used the painted ultra-high-strength steel (UHSS) reinforcements with low bond strength and high yield strength in the boundary elements. For investigating the seismic resistance and resilient performance of this shear wall, six shear walls with the shear-to-span ratio of 1.5 were fabricated and tested under the cyclic loads. The variables studied in this paper were the types of the longitudinal reinforcement in the boundary elements, the existence of steel fibers, the presence of the concealed bracings (X-shaped) and the different axial compression ratios. The test results indicated that specimens with the UHSS reinforcement in the boundary elements decreased the residual deformation substantially and improved the resilient properties. The higher axial compression ratio enhanced lateral force resistance of shear wall but aggravated concrete damage which was adverse to the resilience. In addition, the utilization of steel fibers in concrete significantly reduced the crack width. The shear wall including concealed bracing not only showed much higher lateral force resistance, but also had desirable resilient performance under the large deformation. Finally, a simplified calculation model for such shear walls was proposed on the basis of experiment. And the good accuracy of the calculation model was verified by comparing the calculation results and the measured results.

Repairability of aged dimethacrylate-free ORMOCER-based dental composite resins with different surface roughening methods and intermediate materials

Statement of problemThe repair of damaged composite resin restorations has been recommended as a conservative treatment option. However, a reliable protocol for repairing ORMOCER-based restorations is lacking. PurposeThe purpose of this in vitro study was to investigate the effect of different surface roughening methods, repair composite resins, and intermediate materials on the repair bond strength of a dimethacrylate-free ORMOCER-based composite resin. Material and methodsCylindrical composite resin specimens (Admira Fusion) were roughened by using hydrofluoric acid (HF) or a diamond rotary instrument. In both groups, 4 types of intermediate materials were used (Monobond-S, Clearfil SE bond [second bottle], Clearfil Universal bond, GC Composite Primer), and then half of the specimens were repaired with a similar composite resin, and the other half with dimethacrylate composite resin (Clearfil-APX). The specimens (n=20) were then subjected to repair bond strength and failure mode evaluation. The data were analyzed by using the Weibull test, 3-way and 1-way ANOVA, and the Tukey honestly significant difference (HSD) test (α=.05). ResultsAll variables, including the surface roughening method, intermediate material, and repair composite resin, had a significant effect on repair bond strength (P<.001). The lowest repair bond strength values were obtained in the group roughened with HF, prepared with Monobond-S, and repaired with Admira Fusion, and the highest values were obtained in the group roughened with a rotary instrument, prepared with GC Composite Primer, and repaired with Clearfil APX (P<.05). All experimental groups had a lower bond strength than the cohesive and control groups (P<.05). In all experimental groups, the predominant failure modes were adhesive and mixed. ConclusionsThe use of a diamond rotary instrument was a more reliable method of creating roughness, and different intermediate materials based on the clinical situation can be used to repair dimethacrylate-free ORMOCER-based composite resin with similar or different composite resins. However, in general, the highest repair bond strengths were achieved with Clearfil APX-repaired specimens.

The Effectiveness of Various Functional Monomers in Self-adhesive Resin Cements on Prosthetic Materials.

ABSTRACTAim:This study examined the influence of various functional monomers in two self-adhesive resin cements (SACs) on prosthetic materials.Materials and Methods:Base metal alloy, lithium disilicate glass-ceramic, and zirconia were used as bonding materials. Silicon carbide paper was used to polish the specimens. Two self-adhesive resin cements (Panavia SA luting multi, PAM, and Maxcem elite chroma, MAC) were used. Ten specimens for each material were produced and resin cements were bonded to each material. The specimens were stored in 37°C distilled water in an incubator for 24 hours. A universal testing machine was used to measure the shear bond strength. The data were statistically examined using one-way ANOVA and Tukey’s test.Results:In all prosthetic materials, PAM had the highest bond strength. In lithium disilicate glass-ceramic, the lowest bond strength was found with MAC.Conclusion:The self-adhesive resin cement (PAM) containing 10-MDP monomer and long carbon-chain silane was performed the greatest outcome in the shear bond strength on the prosthetic materials and self-adhesive resin cement interface.

Adhesion to a Zirconia-reinforced Lithium Silicate Ceramic: Effects of Ceramic Surface Treatments and Resin Cements

This study had the objective to test the effect of ceramic surface treatments on the microshear bond strength (μSBS) of different resin cements to a zirconia-reinforced lithium silicate (ZLS). ZLS blocks were sectioned, embedded in acrylic resin, and then allocated into nine groups considering two study factors: "ceramic surface treatment" (HF - hydrofluoric acid; EP - self-etching primer; TBS - tribochemical silica coating) and "resin cements" (nMDP - without MDP monomer; MDP - with MDP monomer; SA - self-adhesive). Starch tubes (n=36) were placed on the treated ceramic surface and the cement was applied. Starch tubes were removed after 24 hours of storage, and the specimens were thermocycled (5,000×; 5°C-55°C). Next, the μSBS test was performed using the wire-loop technique, and topographic and failure analyses were performed. The factors "ceramic surface treatment" and "resin cement" statistically influenced the μSBS results. Considering the surface treatment factor, the TBS produced statistically lower values when the MDP resin cement was applied, being only similar to the MDP plus EP group. For the resin cement factor, no difference was found for nMDP and SA groups, apart from the surface treatments. Failure analysis showed that the groups treated with EP had a greater number of pre-test failures. The surface treatments induced noteworthy topographic alterations when compared to control (no treatment). The ZLS ceramic surface treatment with tribochemical silica coating associated with the MDP-containing resin cement resulted in lower bond strength values.

Seismic performance of semi-precast high-strength recycled concrete columns with ultra-high-strength steel bar

The purpose of this study is to promote the application of high-strength reinforcement and recycled aggregate concrete in post-earthquake repairable precast structures. Three large-scale recycled concrete columns with ultra-high-strength steel bar were designed and tested under quasi-static cyclic loads. The feasibility of semi-precast columns is verified, i.e., the concrete shell of the outer tube is precast first, and then the precast external shell is used as a formwork to cast concrete into the tube. The design parameters include axial load and the addition of steel fibers. The results indicate that all specimens exhibited a good deformation capacity with an ultimate drift ratio greater than 4%. Increasing axial load will increase the lateral load capacity of the specimen by 21%, while the deformability and repairability decrease. Adding steel fibers to the precast external shell can increase the lateral load capacity by 10%, as well as the deformability and repairability of the specimen. Due to the low bond strength of ultra-high-strength steel bar, it slips at the column footing in the tensile side. Eventually, the fiber-based model simplified flexural capacity calculation model considering the ultra-high-strength steel bar slippage in the tensile zone are established.

Effect of PbO on the elastic and radiation shielding properties of B2O3–Bi2O3–Al2O3–CuO glasses

Investigations of quinary B2O3–Bi2O3–Al2O3–CuO–PbO glasses have been accomplished. The density and the ultrasonic velocities variations were exploited to establish the elastic parameters of the glasses. In addition, a correlation between the ultrasonic parameters and the structural modifications characterized by the FTIR spectra to clarify the function of PbO was achieved. The FTIR spectra suggest that PbO is possibly implanted into the aluminum-borobismuthate network forming [PbO6] units, while Bi2O3 and Al2O3 affect the network with [BiO6] and [AlO6] structural units. Furthermore, the changes of the structure and the elastic moduli were understood based on the vibrations of lead, aluminates, bismuthate, and borate structural units on one side and the substitution of high-bond strength B2O3 via low-bond strength PbO. The results of γ-ray attenuation-coefficients indicate that the values of the mass attenuation coefficient (μm), effective atomic number (Zeff), and electron density (Ne) of the prepared samples increase as a function of PbO content. Additionally, the half-value layer (HVL) and the mean free path (MFP) decrease with increasing PbO content. The glass sample 60.5B2O3–20Bi2O3–7Al2O3–0.5CuO–12PbO (mol%) exhibits the highest values of μm (0.15521 at 356 keV), Zeff (26.67 at 356 keV), and Nel (3.24 at 356 keV) and the lowest elastic moduli (Young’s modulus 80.7 GPa and bulk modulus 48.6 GPa).

Effect of bioceramic root canal sealers on the bond strength of fiber posts cemented with resin cements.

This study aimed to evaluate the influence of calcium silicate-based sealers on the bond strength of fiber posts using conventional and self-adhesive resin cement. Sixty single-rooted teeth were selected. The canals were prepared with a reciprocating instrument 40.06. The roots were randomly distributed in six groups (n = 10) according to the strategies for root canal filling and fiber posts cementation: AH Plus/RelyX ARC; AH Plus/RelyX U200; Bio C Sealer/RelyX ARC; Bio C Sealer/RealyX U200; Sealer Plus BC/RelyX ARC; and Sealer Plus BC/RelyX U200. The roots were transversally sectioned, and one slice per post-third was obtained. The push-out test was performed at a crosshead speed of 1mm/min. The failure patterns were described after assessment with a stereomicroscope with a 10× magnification. Bond strength was calculated and analyzed using the ANOVA and Tukey test. AH Plus did not influence the bond strength of fiber posts cemented with conventional (RelyX ARC) or with self-adhesive resin cement (RelyX U200). The lowest bond strength values were obtained when calcium silicate-based sealers were associated with conventional resin cement (Bio C Sealer/RelyX ARC and Sealer Plus BC/RelyX ARC). Except for Sealer Plus BC/RelyX ARC, all groups presented lower bond strength at the apical portion compared to the cervical portion of the post. Adhesive failures between cement and post and cement and dentin were predominant (55.3%). Calcium silicate-based sealers decreased the bond strength of fiber posts cemented with conventional resin cement.

Study on the strengthening and toughening design of the interlayer interface of GO-based bionic nacre composites and its optimization mechanisms

Inspired by the mineral bridge between hard phase layers of natural nacre, this paper investigates the mechanical properties and optimization strategies of GO-based bionic “brick-mortar” structural composites with interface modification by CNTs. After selectively combining CNTs with GO sheets of different sizes, four biomimetic composites with the same structure but different distributions of strong, medium and weak interfaces were obtained. A comparative study on the mechanical property tests and the finite element simulation results of the samples revealed that the difference in the distributions of different strength interfaces within the material/structure have a significant impact on their localized interfacial failures and subsequent crack extensions, making the deflection of cracks more inclined along the weak interface. Further analysis showed that the targeted and focused optimization of dangerous interfaces with low interfacial bond strength and high stress levels within the material is an effective way to improve the mechanical properties of bionic “brick-mortar” structural composites. The results of the above study will provide useful guidance for the interface optimization and lightweight strengthening and toughness design of composites.

Assessment of chemical, ultrasonic, diode laser,\xa0and Er:YAG laser application on debonding of ceramic brackets

BackgroundRisk of enamel damage that often accompanies ceramic brackets debonding raises the demand of finding an optimal method for debonding of them without adverse effects. Different techniques were proposed in an attempt to facilitate their debonding. Comparison of these techniques is crucial. The aim of this study was to evaluate and compare different techniques for debonding of ceramic brackets in terms of shear bond strength and adhesive remnant index.Materials and methodsA total of 100 extracted premolars were randomly allocated into 5 groups. Ceramic brackets were then bonded to teeth using light cure composite resin. Among test groups; group I: served as control, group II: chemical aided debonding via peppermint oil, group III: ultrasonic aided debonding, group IV: diode laser aided debonding, and group V: Er:YAG laser aided debonding. Brackets were shear tested using universal testing machine followed by ARI assessment and evaluation of enamel microstructure was performed using scanning electron microscopy.ResultsA significantly lower shear bond strength was found in ultrasonic, diode, and Er:YAG laser groups. However, no significant difference was found in the chemical group. A significantly higher adhesive remnant index was found solely in Er:YAG laser group with minimal enamel microstructure alterations.ConclusionsEr:YAG laser is a promising tool in debonding ceramic brackets. Ultrasonic and diode laser significantly reduced shear bond strength. Yet, adhesive remnant index in both groups revealed no difference. Chemical aided debonding had little effect and hence, it cannot be recommended without further development.