Reduction In Bond Strength Research Articles

Improving bonding strength by non-thermal atmospheric pressure plasma-assisted technology for A5052/PEEK direct joining

The direct bonding of A5052 aluminum (Al) alloy to the engineering polymer poly(ether ether ketone) (PEEK) using an atmospheric pressure plasma-assisted process was demonstrated. The effect of plasma irradiation on the bonding surface of metal resin on the bonding strength following thermal press fitting method was investigated. Specimens bonded by plasma irradiation on the PEEK surface only showed a high tensile shear stress of 15.5 MPa. With increasing plasma irradiation time, the bond strength of the samples bonded to the PEEK surface by plasma irradiation increased. The increase in the bond strength between metals and polymers following direct bonding is caused by the addition of oxygen functional groups on the polymer. In contrast, specimens in which only the Al was exposed to the plasma showed a decrease in bond strength compared with unirradiated samples. This reduction in bond strength is attributed to the forming magnesium oxide, which forms in the early stages of participation due to plasma irradiation.

The Effect of 10% Sodium Ascorbate and Er: YAG Laser on the Microtensile Bond Strength of Composite Resin to Bleached Enamel

Background: There are various methods proposed to prevent the reduction of substrate micro tensile bond strength to bleached enamel. Therefore, this study aims to evaluate and compare the effectiveness of two common methods, namely 10% sodium ascorbate and Er:YAG laser irradiation, in increasing the microtensile bond strength of composite resins to bleached enamel. Methods: In this in vitro study, 72 maxillary premolar teeth were divided into four equal groups: bleached control group, unbleached control group, treated with 10% sodium ascorbate, and Er:YAG laser-treated group (60 mJ, frequency = 10 Hz, and power of 0.6 W with a 400-µm diameter tip). The samples were cut by a CNC cutting machine for a microtensile bond strength test. Results: The Er:YAG laser group showed the highest mean bond strength (27.3 MPa), while the bleached control group had the lowest (15.06 Mpa). There was a significant difference between the bleached and unbleached control groups (P<0.001). Samples prepared with 10% sodium ascorbate and the Er:YAG group had higher tensile bond strength than the bleached control group (P<0.0001). Tensile bond strengths were not significantly different between the 10% sodium ascorbate and the Er:YAG laser preparation groups (P=0.361). Conclusion: The findings of this study indicate that the microtensile bond strength of composite resins to bleached enamel can be increased by 10% sodium ascorbate and Er:YAG laser irradiation.

Pull-out behaviour of steel fibres embedded in ultra-high-performance concrete after exposure to high temperatures

The paper examined the bond-slip behaviour of steel fibres embedded in ultra-high-performance concrete (UHPC) after exposure to elevated temperatures. Different types of steel fibres were cast into the halved UHPC dog-bone-shaped samples, including straight fibres, three types of hooked-end fibres and corrugated fibres. The bond response was investigated through single fibre pull-out tests on the samples unheated and heated to 200, 400 and 600 °C. In addition, the effects of polypropylene (PP) fibre addition and heating rate on steel fibre’s bond behaviour were also investigated. The results revealed an increase in bond strength when the straight and hooked-end fibre samples were heated to 200 °C, while the bond strength of the corrugated fibre decreased at the same temperature. Bond strength reductions were observed at higher temperatures. In addition, the straight fibres led to the lowest pull-out resistance as both the hooked-end and the corrugated fibres significantly enhanced the bond strength. With the hooked-end or corrugated fibres, the failure mode gradually shifted from pull-out failure to fibre rupture. Besides, adding PP fibres increased the bond strength of straight fibres at 400 °C but reduced the bond strengths of hooked-end fibres at ambient and high temperatures. High heating rate also led to a greater bond strength for the straight fibres at 200 °C and 400 °C.

Weakening of mechanical parameters of ion-absorbed rare-earth ores subjected to leaching

Ion-adsorbed rare-earth ores are mined using in-situ leaching, and their mechanical properties significantly affect the efficient and safe recovery of rare earth elements. However, the mechanism of the change in the mechanical properties of the ore body due to the physicochemical processes caused by leaching remains unclear. To explore the strength evolution characteristics of the ore body during the leaching process, unconsolidated undrained triaxial tests were conducted to confirm how the stress–strain curve and shear strength of rare-earth samples change during leaching. Magnetic resonance imaging and T2 spectral characterizations were obtained by using nuclear magnetic resonance technology to measure the interior pore structure of samples during leaching. A scanning electron microscope equipped with an energy dispersive spectrometer was used to investigate the morphology evolution and the composition changes of the internal micro-area of the samples, to demonstrate the correlation between the microstructural change and the macroscopic mechanical properties. The results show that when a 2% ammonium sulfate solution is employed for mineral leaching, the effective leaching duration is 0–3 h. During this time, ion exchange occurs along the direction of solution seepage, resulting in the dispersion and migration of fine particles from the top to the bottom of the sample, which further triggers a change in the sample's pore structure and pore size. In addition, the local loss of fine particles resulted in a reduced bond strength between minerals, forming an unstable soil structure with a loose upper part and a dense lower part, which is macroscopically expressed as a declining shear strength parameter of the rare-earth sample.Graphical abstract

Thermally reversible prototype adhesive via the furan–maleimide Diels–Alder reaction

The development of structural epoxy adhesives with the capacity to bond and de-bond on-demand would open many opportunities for the assembly, inspection, repair, and end of life disposal of structural bonded assemblies. Herein, a reversible cross-linking mechanism enabling bonding and debonding of an epoxy adhesive based on Diels–Alder (DA) chemistry is investigated and demonstrated. The Diels–Alder incorporated multifunctional diamine cross-linker was initially synthesised, followed by forming a covalently cross-linked network with DGEBA epoxy at low temperature (80 °C) that breaks via cleavage of DA adducts at elevated temperature (150 °C). Upon cooling the covalent cross-links reform enabling the epoxy to retain adhesive properties, and the bonding/de-bonding effect was performed over two complete cycles advancing a thermally reversible adhesive based on the retro-DA mechanism. The viscoelastic properties of the prototype adhesive including viscosity, storage and loss modulus were retained after bonding and de-bonding cycles, affirming retro-DA reaction occurs at about 150 °C upon heating cycle and DA reaction upon cooling cycle. Mechanical testing demonstrates maximum of 39.5% reduction in bond strength in debonding cycle, followed by maximum of 100% bond strength in re-bonding cycle with no additional application of the prototype adhesive, revealing excellent adhesive performance.

Early performance and bonding mechanism of metakaolin (MK)- ground granulated blast furnace slag (GGBS) based geopolymer road repair mortar

ABSTRACT Metakaolin (MK) and ground granulated blast furnace slag (GGBS) based geopolymers have been utilised as materials for concrete road repair. However, their early-stage performance and bonding mechanism as rapid repairs are not well understood. This research investigated the workability, early strength development and bonding mechanism of geopolymer repair mortars with different GGBS contents. The reaction kinetics and reaction products of the geopolymer repairs were analyzed through reaction heat evolution and FTIR, and the microstructure of the bonding interface was examined using BSE-EDS. Results showed that geopolymer repair mortars with higher GGBS content exhibited shorter setting times, higher flowability, and higher compressive strength. Geopolymers demonstrated a one-dimensional rod-shaped nucleation pattern during hardening, and the crystallization rate decreased with GGBS addition. GGBS increased the formation of C-A-S-H gels and accelerated the geopolymerization process. However, excessive GGBS reduced bond strength due to the introduction of microcracks. A GGBS content of 60 wt.% is recommended in this investigation. The study also revealed that the cement substrate could absorb alkali activator, leading to the formation of high-Ca gels and strengthening the interface.

Multiscale assessment of performance of limestone calcined clay cement (LC3) reinforced with virgin and recycled carbon fibers

The carbon fibers (CFs) recovered from end-of-life CFRP scraps via pyrolysis have recently aroused ascending interest due to their highly retained fiber strength and lowered carbon footprint. However, the utilization of recycled CFs (rCFs) within cementitious matrices, as well as the exploration of their interfacial interactions, remains notably limited. In this study, we have first time incorporated rCFs into sustainable Limestone Calcined Clay Cement (LC3) composite and comprehensively investigated the microstructural changes and physical characteristics of LC3-blended mixtures. The incorporation of LC3 results in a reduction in setting times and the flowability of fresh mortar, accompanied by a decrease in cumulative heat release. Analytical analysis indicated the generation of a substantial quantity of ettringite crystallites and highly polymerized C-A-S-H gel in LC3 mixtures, which benefited the enhancement of flexural strengths but increased the micropores in the matrices. Compromised compressive strengths, with reductions ranging from 5% to 46%, were observed upon the incorporation of LC3, aligning closely with the porosity findings. Measurements of autogenous shrinkage revealed an expansion tendency as LC3 proportions increased, likely attributed to bleeding and ettringite formation. A thorough investigation into the properties of CFs after undergoing thermal recycling was undertaken. A quantitative assessment of the bonding at the fiber-cement interface revealed a progressive reduction in bond strength for both virgin and recycled CFs, diminishing from 5.1 MPa and 2.5 MPa to 0.4 MPa and 0.5 MPa, respectively, along with the addition of LC3 content. Our findings have provided a comprehensive understanding of the hydration and microstructure evolution within LC3 blends, as well as the influence of CF additions on the matrices’ properties.

Bond strength of corroded reinforced recycled aggregate concrete with treated wastewater and fly ash

This study investigates the bond strength of steel-to-concrete of 36 cubical pull-out specimens with a side length of 200 mm. The specimens were produced with treated wastewater (TWW), recycled concrete aggregates (RCA), and fly ash (FA) and subjected to corrosion. Potable water and natural coarse aggregates were entirely replaced by TWW and RCA, respectively, whereas FA partially replaced cement by 20%. Three target corrosion levels (CL) were evaluated (0%, 2%, and 10%). Experimental results revealed that TWW and RCA reduced the bond strength of concrete by 30% and 18%, respectively, whereas 20% FA enhanced the bond strength by 10%. In the view of corrosion effect, it was observed that a slight CL of 3.56% or less can improve the bond strength of concrete. In addition, TWW and RCA concrete specimens with a 10% target CL had a 36% and 46% reduction in bond strength compared to their respective non-corroded specimens, respectively. Nonetheless, corroded specimens with FA recorded a drop of only 3% in the bond strength. Furthermore, the specimens’ bond strength was analytically predicted using the available analytical formulations. The models of Seara-Paz et al., Chung et al., and Yalciner et al. provided the most accurate prediction for uncorroded, 2% CL, and 10% CL specimens, respectively.

Modelling of long-term performance of RC beams under coupling steel corrosion and bond deterioration

The steel-to-concrete bond deterioration due to corrosion in the reinforced concrete (RC) structures still needs more investigation because the existing models were established based on pull-out tests, which do not represent the real RC beams owing to the flexural cracks. This paper presents a new approach that discusses the bond deterioration of corroded steel bars embedded in RC beams. The study presents simulations for an experimental database of existing corroded RC beams from previous papers using a nonlinear finite element model. The simulated specimens were divided into two categories: accelerated and long-term (after 14,23, and 28 years) corroded beams to identify the key corrosion parameters in these two conditions. The results indicated that the behavior of the RC beams, which corroded via the accelerated method, failed by concrete crushing after steel yielding, and it could be simulated considering the reduction of both steel area and bond strength only. On the other hand, the spalling pressure is a key parameter to simulate the long-term corroded RC beams because it controls the ultimate deflection, and the failure is governed by concrete cover spalling due to concrete deterioration. As an innovative result, a novel bond-slip model was proposed to predict bond deterioration due to corrosion in the RC beams, and it showed excellent accuracy compared to the existing models.

Bond conditions in wall-type steel-reinforced self-compacting concrete element

This work looks into the variations in the bond conditions between steel and self-compacting concrete (SCC). The bond conditions along the height and span of wall elements are compared with column and beam elements. The study involved pull-out bond tests and compressive strength tests on module samples derived from a wall element having 2240 × 160 × 1600 mm in length, width and height, respectively. SCC mixture casting was performed from a single point located at one of the short edges of the element. The pull-out tests were conducted on samples having deformed steel rebars with a diameter of 16 mm. We examined in detail the top-bar effect occurring across the entire wall element. The bond strengths at different heights within the element were compared to that at its bottom. On average, the reduction in the bond strength was 22%, and as much as 39% at the top of the wall. The bond strength increased by an average of 13% within the end part of the element as a result of the rebound effect. The phenomenon of bond strength reduction with an increasing depth of concrete under a reinforcing bar seems universal across different types and heights of elements.

Textile Reinforced Mortar/masonry joints under reverse cyclic in-plane shear

This study investigates for the first time the effect of reverse cyclic loading on the shear bond capacity of Textile Reinforced Mortar (TRM)/masonry joints. The single-lap/single-prism set-up was adopted for monotonic tests, whereas a modified version thereof was developed for reverse cyclic tests making use of a single piston. Specimens comprised wallettes reinforced with glass fiber TRM overlays of various bond lengths (BL = 250–50 mm, step = 50 mm). Reverse cyclic loading: (i) bore no effect on the joints’ failure modes; (ii) resulted in a reduction of the shear bond strength by <20%.

Comparative bond-slip response of ribbed CFRP bar to UHPC after exposure to high temperature

Ribbed carbon fiber reinforced polymer (CFRP) bar and ultra-high-performance concrete (UHPC) have high potential in terms of utilization of load-carrying capacity and maintenance of the concrete structure. Bonding behavior of ribbed CFRP bars to UHPC after exposure to elevated temperature is of importance due to its susceptibility of thermal effects. This study investigated the residual bond strength of the ribbed CFRP bar embedded in UHPC at ambient temperature and after exposure to elevated temperature. The bond strength of ribbed CFRP bars with different embedded length and cover thickness were also considered and the bond strength was compared with the sand coated CFRP bars. Both at ambient temperature and after exposure to elevated temperature, the bond strength of the ribbed CFRP bar increased with an increased embedment length and cover layer due to the mechanical resistance of the ribs. However, the difference reduced as the elevated temperature increased. Compared with the sand coated CFRP bars, the decreasing rate of bond strength is slightly lower in ribbed CFRP bars and the residual bond strength after exposure to elevated temperature at 400 ℃ was more than 10 MPa, which satisfies bond strength of FRP bar suggested by ACI 440.5 M. The critical temperature of the ribbed and sand coated CFRP bars was suggested as 300 ℃ with consideration of decreasing rate in this study. The modified bond equations were presented to reflect the reduction of bond strength due to the elevated temperature, and the bonding behavior of the ascending branch was compared using the modified BPE and CMR models and presented the coefficient of each parameter.

Evaluation of the push-out bond strength of an adjustable fiberglass post system to an endodontically treated oval root canal.

To evaluate the push-out bond strength of the adjustable fiberglass post system to dentin. Twenty maxillary canine roots were endodontically treated and divided into two groups (n=10): conventional fiberglass posts (CFPs) and with single adjustable post (SAP) system. Two slices of each third were subjected to the push-out and failure pattern test and the most apical slice was subjected to analysis of the adhesive interface by scanning electron microscopy (SEM). Data were analyzed by the three-way analysis of variance, Tukey, and Friedman tests, and linear regression (α=0.05). The results showed higher push-out bond strength in the initial time interval for SAP (10.3±5.3, p<0.01). After 6 months, there was reduction in push-out bond strength for both (p<0.001). A higher percentage of adhesive and cohesive failures to dentin. After 6 months areas of maladaptation were noted (p=0.000). The SAP is completed to the promissory root canal in relation to alternative CFP.

Investigating the lap shear adhesion of coir and glass-fibre reinforced epoxy bonding to mild steel with varying volume fractions

Bonding synthetic fibres to metals to improve strength, durability, and corrosion resistance is a prevalent practise in the automotive, marine, and aerospace industries. Lap shear adhesion, a measurement of the bonding strength between composites and metallic substrates, is essential for structural integrity. The emergence of natural fibre composites as sustainable alternatives to synthetic composites makes it essential to investigate their lap shear behaviour and the effect of fibre volume fraction on composite properties. This research investigates the adhesion behaviour of coir and glass fibre epoxy composites to mild steel. Coir fibres, which are known for their resilience and tenacity, were treated with an alkaline solution to improve their adhesion to the resin. Samples of lap shear adhesion were prepared in accordance with ASTM specifications, and tests were conducted using a tensile machine. Increasing the volume fraction of coir or glass fibres decreased the bond strength, as demonstrated by the results. Due to the fibres’ greater tensile strength and rigidity, glass fibre composites exhibited superior strength. However, under tensile loading conditions, coir fibres exhibited superior adhesion to mild steel surfaces. SEM micrographs confirmed that coir composites exhibit shear failure while glass composites exhibit fibre pull-out behaviour. This study concludes by highlighting the engineering potential of coir fibres, considering their natural properties and cost-effectiveness. It is necessary to further optimise the fiber-matrix interface and comprehend the mechanical behaviour of coir composites in order to maximise their effectiveness. To assure the long-term durability of composite-metal joints, surface preparation, adhesive type, application procedure, and environmental conditions must also be considered. At a content percentage of 10%, glass fibres exhibited 100% higher shear strength compared to coir fibres in epoxy composites. Conversely, coir fibres at 10% content demonstrated approximately 75% greater shear strength than the values obtained with 40% glass fibres. The failure mechanisms observed are delamination or fibre fracture in the bonding area under tensile and shear loading. Increasing the fibre volume fraction reduces bond strength. Factors such as limited space for the matrix, tension concentrations, and the mechanical properties of the fibres contribute to weakened bonds. Glass fibres have better strength and rigidity than coir fibres, affecting load transfer and adhesion. Interfacial bonding is crucial, and maintaining it becomes more difficult with higher fibre volume fractions, resulting in weakened bonds.

Silver diamine fluoride and resin-dentin bonding: Optimization of application protocols

ObjectiveTo evaluate the effect of SDF-based treatments following delayed bonding and surface treatment approaches on resin-dentin bonding efficiency of a universal adhesive under different application modes. MethodsMid-coronal dentin surfaces from sound third molars were randomly treated with 38% silver diamine fluoride (SDF) and/or additionally with potassium iodide (SDF/KI). Untreated dentin served as control. SDF-treated teeth were assigned to groups according to surface treatment approaches (air-abrasion and water rinsing), the application mode of a mild universal adhesive (etch-and-rinse or self-etch) and delayed bonding (immediate, 7, 15 or 30 days). Microtensile bond strength (n = 5), SEM analyses of hybrid layer formation and dentin etching patterns and dentin permeability were evaluated. Data were analyzed with factorial ANOVA. ResultsSDF-based treatments affected dentin bonding depending on application mode and surface treatment approaches (p<0.001). Etch-and-rinse bonding was not affected by SDF-based treatments (p<0.05), producing more homogenous hybrid layers. While dentin etching patterns of etch-and-rinse application were not affected by SDF-based treatments, self-etching presented limitations. Bond strength reductions of self-etched dentin were restored by silver-removal strategies containing a water-rinsing step (p<0.05). Delayed bonding additionally reduced dentin permeability (p<0.05), further decreasing with longer periods (p<0.05). ConclusionAlthough the negative effect of SDF-based treatments on resin-dentin bonding can be avoided by strategies incorporating water-rinsing before hybridization, delayed bonding brings additional advantages due to higher mineral deposition. Clinical significanceWhile the etch-and-rinse technique avoids major bonding drawbacks to SDF-treated dentin, self-etch bonding requires removal of excess silver deposits before hybridization. Performing SDF-based treatments and dentin hybridization in separate sessions (>15 days apart) potentialize mineral deposition improving caries control and service life of composite restorations.

Evaluation of the Effect of Different Antioxidants on Resin Bond Strength to Enamel after Bleaching: An In Vitro Study.

To compare and evaluate the efficacy of 10% sodium ascorbate (SA) solution, 10% alpha-lipoic acid (ALA) solution, 10% propolis solutions (PLS), and 10% pomegranate peel extract (PPE) solution on the shear bond strength (SBS) between composite resin and bleached enamel after 60 minutes. Ninety extracted teeth were divided into 6 subgroups (n = 15) based on the antioxidant applied: Group I: Bleaching + application of 10% SA solution for 60 minutes. Group II: Bleaching + application of 10% ALA solution for 60 minutes. Group II: Bleaching + application of 10% PLS for 60 minutes. Group IV: Bleaching + application of 10% PPE solution for 60 min. Group V: Positive control (PC) bleaching without antioxidant application. Group VI: Negative control (NC) specimen neither subjected to bleaching nor application of an antioxidant solution. About 35% hydrogen peroxide (HP) was used for bleaching the labial surfaces in the groups considered. Labial surfaces were then bonded with composite using a customized cylindrical mold followed by storage in distilled water for 24 hours and shear bond strength was tested using universal testing machine. The mean shear bond strength values for groups I, II, III, IV, V, and VI are 5.04, 2.29, 5.02, 4.07, 1.42, and 9.08 respectively. The peak shear bond strength value is obtained for the negative control group; whereas the lowest mean SBS value is obtained for the positive control group. All herbal extracts used in the present study have demonstrated a reversal of reduced SBS between resin composite and bleached enamel surface. The reduction in bond strength of adhesive restorations was conventionally overcome by delaying the bonding procedure for a specified period resulting in prolonged treatment duration and multiple appointments. Sodium ascorbate is most commonly used but it is postulated to form a porous scaffold capable of harboring bacteria. Herbal antioxidants are gaining popularity in this regard as they are naturally derived, effective and affordable phytochemicals in addition to being viable alternatives against drug-resistant strains of microorganisms.

Bond durability of a silane-containing self-adhesive and conventional resin cements to CAD/CAM glass and hybrid ceramics

To evaluate the effect of CAD/CAM materials surface treatments for bonding of different cementing systems on shear bond strength, including conventional and silane-containing resin cements, after 24 h and one year of water storage. Samples (12 mm × 6 mm × 1 mm) of each CAD/CAM material (IPS E.Max; Suprinity; Enamic; Cerec Bloc; IPS Empress) were divided into 4 groups: G1) 4.5% hydrofluoric acid (HFA) + silane + adhesive + RelyX Veneer (conventional); G2) HFA + Clearfil Ceramic Primer + Tooth Primer + Panavia V5 (conventional); G3) HFA + Panavia SA Cement Universal; G4) blasting with Al2O3 + Panavia SA Cement Universal. After the bonding procedures, two resin cement cylinders (1.5 mm × 1.5 mm) were constructed on each sample and tested after 24 h or one year of water-storage, using shear bond strength testing (n = 10). Data were submitted to generalized linear models’ analysis (p < .05). The conventional treatment for glass ceramics with HFA and silanization or priming (G1 and G2) did not necessarily yielded higher bond strength than the simplified technique (G3 and G4). For IPS E.Max and Suprinity, all protocols had bond strength reduction after one year. For Enamic, Cerec Bloc and IPS Empress, G3 did not reduced statistically at one year. Panavia SA Cement Universal seemed not appropriate when IPS E.Max and Suprinity were blasted with Al2O3. On the other hand, the bond strength to etched or blasted with Al2O3 Enamic, Cerec Bloc and IPS Empress showed no difference or was higher than conventional luting protocols.

The relationship between compressive strength and sonic velocity depending on moisture content in case of historical masonry

Historical masonry structures made from locally available materials such as stone, brick, and mud are an integral part of our cultural identity. Moisture content is a critical environmental factor that can significantly impact the durability and strength of these structures. Moisture ingress in masonry can cause detrimental effects such as decreased strength, increased porosity, and reduced bond strength between the mortar and masonry units. Understanding this relationship is crucial for developing effective conservation strategies and maintenance decisions that can help protect these structures from moisture-related damage. This paper explores the impact of moisture content on the compressive strength of historical masonry structures and highlights the factors that can affect this relationship.

Effect of chloride-induced corrosion on bond performance of various steel fibers in cracked SFRC

This study investigates the chloride-induced corrosion behavior of various steel fibers and associated effects on their interfacial bond performance in cracked steel fiber reinforced concrete (SFRC). Three types of deformed fibers, including hooked-end (H), crimped (C), and milled-cut (M) fibers, were embedded in high strength matrix and then exposed to wet-dry cycles of chlorides under cracking conditions. The scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) technique were employed to gain insights into the surface morphologies and corrosion products at the micro-scale. The bond behaviors of corroded fibers were further evaluated through pull-out tests, where the influences of fiber type, corrosion duration, crack width, and embedded length were discussed. Three distinct corrosion morphologies were identified on the surfaces of three types of fibers owing to the difference in corrosion products. After 40 days of corrosion, the average bond strength of H fibers increased by 37.9% because of dense and rough rust layer, while those of C and M fibers deteriorated by 30.5% and 18.8% due to surficial groove loss and loose rust layer. The average bond strength of H, C, and M fibers improved by 12.4%, 11.7%, and 58.0% as the crack width increased from 0.1 to 0.3 mm, whereas significant reductions in pull-out energy and equivalent bond strength were obtained once the crack width exceeded 0.2 mm owing to fiber fracture. The corrosion-induced bond deterioration of M fibers became less severe as the embedded length increased up to 12 mm and remained unaffected thereafter.

Structural and Mechanical Investigation of Class I Biomimetic Composite Dental Filling by X-ray Computed Tomography, Scanning Electron Microscopy, and Microtensile Bond Strength Testing

Nowadays, short fiber-reinforced composites are broadly used in modern restorative dentistry. The tensile strength, Young's modulus, density, and polymerization shrinkage of these materials are developed to mimic the original teeth tissue best. The shrinkage, however, will occur during any polymerization process, which can cause residual stress and gap formation between the tooth and the filling. These can lead to the propagation of cracks, reduction in the adhesive bond strength, or even cause separation in the restoration. During this research, a biomimetic dental restoration was created on a surgically removed third molar with EverX short-fiber reinforced dental composite by bulk-filling technique. The restored tooth sample was examined by X-ray computed tomography to obtain a 3D image of the whole restoration. The volume of the used adhesive, the material discontinuities, and internal cavities were determined. A cut-out slice was further investigated by scanning electron microscopy to examine the adhesive layer thickness, the gap formation, and the quality of the filling. Finally, microtensile specimens were machined to evaluate the bond strength between the tooth dentin and the filling material.