Adequate Bond Strength Research Articles

Antibacterial Effect and Tensile Bond Strength of Self-etching Adhesive Resins with and without Methacryloyloxydodecylpyridinium Bromide: Anin vitroStudy

Aim: The aim of the present study was to compare the antibacterial activity of a self-etching primer containing antibacterial monomer methacryloyloxydodecylpyridinium bromide (MDPB) (Clearfil protect bond) with a conventional self-etching primer without MDPB (Clearfil SE bond) against Streptococcus mutans and the effect of incorporation of MDPB on the tensile bond strength of the experimental self-etching primer (Clearfil protect bond). Materials and methods: The antibacterial activity of the self-etching primers was assessed using agar disk diffusion method and the diameters of the zones of inhibition were measured and ranked. For tensile bond strength testing, 20 noncarious human molars were selected and randomly divided into two groups comprising 10 teeth in each group. Group I specimens were treated with Clearfil SE bond (without MDPB). Group II specimens were treated with Clearfil protect bond (with MDPB). Composite material was placed incrementally and cured for 40 seconds in all the specimens. Tensile bond strength was estimated using the Instron Universal testing machine at a crosshead speed of 1 mm/min. Results: The addition of MDPB into a self-etching primer exerts potential antibacterial effect against S. mutans. The tensile bond strength of MDPB containing self-etching primer was slightly lower than that of the conventional self-etching Clearfil protect bond primer, but the difference was not statistically significant. Conclusion: Thus, a self-etching primer containing MDPB will be a boon to adhesive dentistry as it has bactericidal property with adequate tensile bond strength. Clinical significance: The concept of prevention of extension in adhesive dentistry would result in micro/nanoleakage due to the presence of residual bacteria in the cavity. Self-etching primers with MDPB would improve the longevity of such restorations by providing adequate antibacterial activity without compromising the bond strength. Keywords: Antibacterial property, Methacryloyloxydodecy-lpyridinium bromide, Self-etching primers, Tensile bond strength.

Evaluation of bond strength of orthodontic brackets after rebonding of different protocols removal of residual resin

Proper selection of instrumental is essential for efficient removal of residual resin enamel, which can positively influence the bond strength of orthodontic brackets after rebonding. To evaluate different protocols for removal of residual resin enamel in order to maintain an adequate bond strength of orthodontic brackets in rebonding. A total of 40 bovine incisors were divided into 4 groups (G1, G2, G3 and G4), with 10 teeth each. Was made a resin matrix after conditioning with phosphoric acid for each specimen to simulate the adhesive remaining on tooth enamel, then was made to remove this remaining as the proposed protocols. The teeth were worked with the G1 tip uniangulada CVD. The teeth of G2 were worked with carbide bur low speed. The teeth were worked with the G3 high speed carbide bur. The teeth of the G4 were worked with diamond drill. After these steps, the incisors were again subjected to acid etching, bonding orthodontic brackets and were taken to shear stress. Thus, one can evaluate the bond strength in the different groups, allowing visualization method that causes greater resistance to shear. Were subjected to statistical test of Kruskal-Wallis indicated that no statistical difference among the groups (p = 0.2383).

Slant shear strength of fibre reinforced polyvinyl acetate (PVA) modified mortar

Strengthening of reinforced concrete elements can be carried out using a variety of materials and techniques. One of such materials is textile reinforced concrete (TRC). This material consists of a matrix, usually made of mortar, and textile as reinforcement. This study aims to produce mortar that meets the characteristic of a TRC matrix with respect to an adequate bond strength. The type of mortar developed in this study was fibre reinforced polyvinyl acetate (PVA) modified mortar. The bond strength of this material to the parent concrete was tested by the slant shear method. The results indicate that the amount of PVA content affects the magnitude of the bond strength. The higher the PVA content, the higher the bond strength. The results also confirm that the relationship between the bond strengths and their corresponding compressive strengths tends to be linear.

Evaluation of the effect of moisture and saliva on the shear bond strength of brackets bonded with conventional bonding system and moisture insensitive primer: An in vitro study

Introduction: Bonding of orthodontic attachments with acid etching is the most commonly used orthodontic procedure. However, there are certain limitations with acid etching procedure like/moisture contamination, etching time, the concentration of adhesive, etc., Moisture insensitive primers (MIPs) were introduced to overcome these limitations. Objectives: The aim of this study is to compare the shear bond strength of orthodontic brackets bonded with a MIP (Transbond MIP, 3M Unitek) against a conventional primer (Transbond XT, 3M Unitek) when contaminated with saliva – in vitro study. Methodology: Sixty maxillary premolars extracted for orthodontic purpose or due to periodontal involvement with sound buccal surfaces were collected, cleaned thoroughly, and stored in 0.1% (wt/vol) thymol at room temperature for 2 weeks. Following materials were used: Transbond XT Light cure adhesive (3M unitek), Transbond XT primer (3m unitek), Transbond MIP primer (3M unitek), and Metal brackets (3M unitek). A commercially available artificial saliva (AQWET, CIPLA) was used for contamination purpose. Ivoclarbluephase N LED light curing unit were used for curing purpose. Results: Mean bond strength was well above the clinically acceptable bond strength values indicating the use of these hydrophilic bonding materials in contaminated environments (8.5 Mpa for Transbond XT and 9.25 Mpa for Transbond MIP). On comparison of bond strengths of MIP and XT when contaminated with saliva, statistically significant values were obtained with contamination with saliva after primer application. There was a statistically significant increase in the bond strength after primer application (P = 0.233) and before and after primer application (P = 0.027*). Transbond MIP can be used to achieve adequate bond strength in saliva contaminated condition. Conclusion: Under dry condition, the shear bond strength of conventional primer (TRANSBOND XT) was significantly increased when compared to MIP. Under wet conditions MIP (TRANSBOND MIP) showed the highest shear bond strength and hence can be considered as a material of choice in wet conditions.

Formation Mechanisms of Needles in Porous Silicon Based Needle-like Surfaces

Formation mechanisms of needle-like surfaces generated by anodization of Si in the transition region (region between pore formation and electropolishing) is studied. Formation of needles is monitored via SEM surface images taken after different anodization times and their formation mechanisms is modeled based on current burst (CB) model and Lehmann macro-pore formation model. Anodization is a well-known technique for porous silicon (PS) formation or electropolishing of silicon wafer. Although the technique is known for several decades, it has attracted renewed interest since 1990 resulting from discovery of luminescence properties of PS. Anodization has emerged in micromachining applications because of its low cost, easy implementation, and compatibility with standard microelectronic processes [1]. Usage of anodization technique to create rebondable (needle-like) Si surfaces with adequate bond strength for low temperature chip/wafer bonding applications has currently attracted attentions [2]. Needle-like Si surfaces with different needle sizes and distributions are obtained by anodization of lowly doped p-type Si in aqueous HF solutions in the transition region. For 12-17 Ωcm p-type Si, anodized in a 7.2 wt.% aqueous HF solution, morphology of generated surfaces (Fig. 1) were clearly related to positions of current peaks (critical current density (J-PS) and electropolishing current density (J-El)) on the I-V curve (Fig. 2). Formation of needles was studied through SEM surface images taken after different anodization times (Fig. 3). Initiation of needles is started by inhomogeneous dissolution of Si, roughening and pitting of the surface (Fig. 3a), and is followed by nucleation of pores (Fig. 3b). As morphology of PS varies in depth from surface to bulk, it results in two-layers PS, a meso PS above a macro PS [3]. Ununiform dissolution of meso-pores results in formation of small irregular islets (remaining bulk Si) at certain times during the anodization (Fig. 3c). With increasing time, small islets are completely etched away and given access to overlapping and widening macro-pores underneath. Remaining bulk Si between widened and overlapped macro-pores results in large islets (Fig. 3d). Further etching of the surface reshapes islets to pyramid-like structures by slightly narrowing their side walls and increasing their heights (Figs. 3e and f). As the time, increased, side walls are narrowed more and their heights are increased further (Fig. 3g). Further etching of the side walls results in formation of semi-cylindrical needles in which their tips are attached together and made cluster of needles (Fig. 3.h). At this stage, with increasing time, only heights of needles are increased and no significant reduction in diameter of needles are occurred (Fig. 3i). Nucleation of pores and formation of islet can be explained through the CB model [4]. At current densities above J-PS, CBs begin to correlate in time and space. This results in assembling of CBs and formation of either a meso-pore or a macro-pore depending on density of CB events in a particular area (Fig. 4). In a condition where the oxidation reaction is low, CBs result in macro-pores covered with meso-porous (transition layer). However, for the condition where oxidation reaction is dominant (e.g., in aqueous electrolytes), oxidation takes over CBs and smoothes the area. This results in macro-pores with no meso-pores coverage (complete dissolution of the transition layer). In the transition region, Si surface is not completely covered by oxide; hence, both inhomogeneous and homogenous dissolutions may occur on different parts of the surface [3]. This may result in inhomogeneous dissolution of the transition layer and formation of small islets above macro-pores. With increasing time, the transition layer dissolve entirely and give accesses to underneath macro-pores which have already overlapped and widened (Fig. 5). The remaining bulk Si between overlapped macro-pores results in large islets. Assuming large islets with diameters of ~ 4.5 ± 1.4 µm (obtained from Fig. 3i) as remaining and surrounding walls of widened macro-pores in which their wall thickness is greater than the space charge region length (1 – 1.2 µm for 12-17 Ωcm p-type Si), the Lehmann model [5] can be simply used to describe growth and narrowing of side walls of islets and formation of needles.

Microtensile bond strength of bulk-fill restorative composites to dentin.

BackgroundTo facilitate the easier placement of direct resin composite in deeper cavities, bulk fill composites have been introduced. The Mechanical stability of fillings in stress bearing areas restored with bulk-fill resin composites is still open to question, since long term clinical studies are not available so far. Thus, the objective of the study was to evaluate and compare the microtensile bond strength of three bulk-fill restorative composites with a nanohybrid composite.Material and MethodsClass I cavities were prepared on sixty extracted mandibular molars. Teeth were divided into 4 groups (n= 15 each) and in group I, the prepared cavities were restored with nanohybrid (Filtek Z250 XT) restorative composite in an incremental manner. In group II, III and IV, the bulk-fill composites (Filtek, Tetric EvoCeram, X-tra fil bulk-fill restoratives) were placed as a 4 mm single increment and light cured. The restored teeth were subjected to thermocycling and bond strength testing was done using instron testing machine. The mode of failure was assessed by scanning electron microscope (SEM). The bond strength values obtained in megapascals (MPa) were subjected to statistical analysis, using SPSS/PC version 20 software.One-way ANOVA was used for groupwise comparison of the bond strength. Tukey’s Post Hoc test was used for pairwise comparisons among the groups.ResultsThe highest mean bond strength was achieved with Filtek bulk-fill restorative showing statistically significant difference with Tetric EvoCeram bulk-fill (p< 0.003) and X-tra fil bulk-fill (p<0.001) composites. Adhesive failures are mostly observed with X-tra fil bulk fill composites, whereas mixed failures are more common with other bulk fill composites.ConclusionsBulk-fill composites exhibited adequate bond strength to dentin and can be considered as restorative material of choice in posterior stress bearing areas. Key words:Bond strength, Bulk-fill restoratives, Configuration factor, Polymerization shrinkage.

Resistance to Dislodgement of REBILDA® Post System to Intraradicular Dentin

Currently there is controversy in the literature about clinical and adhesive effectiveness with respect to adhesive systems aimed to root reinforcement. Thus, the objective of this study was to evaluate the Push-Out bond strength between the Rebilda® post system and the intraradicular dentine. Thus, 28 unirradicular teeth were used, cut and standardized in 16 mm. The root segments were submitted to endodontic treatment; and then randomly divided into two groups, Group 1 (n = 14): Rebilda® DC + Futurabond DC; Group 2 (n = 14): RelyX ARC + Adper Scothbond Multipurpose Plus. Ten specimens from each group were submitted to the Push-Out Test. The remaining 4 specimens from each group were prepared for Scanning Electron Microscopy (SEM) in order to evaluate the formation of resinous extensions at the post-cement-dentin interface. Group 2 showed better results when compared to Group 1 regarding bond strength and in formation of resinous extensions or tags, but there was no statistically significant difference (p&gt;0.05). It was concluded that the REBILDA® Post System promotes adequate bond strength to intraradicular dentin.

Six-month bracket failure rate with a flowable composite: A split-mouth randomized controlled trial.

ABSTRACTINTRODUCTION: The use of flowable composites as an orthodontic bonding adhesive merits great attention because of their adequate bond strength, ease of clinical handling and reduced number of steps in bonding. OBJECTIVE: The aim of this Randomized Controlled Trial was to comparatively evaluate over a 6-month period the bond failure rate of a flowable composite (Heliosit Orthodontic, Ivoclar Vivadent AG, Schaan) and a conventional orthodontic bonding adhesive (Transbond XT, 3M Unitek).METHODS: 53 consecutive patients (23 males and 30 females) who fulfilled the inclusion and exclusion criteria were included in the study. A total of 891 brackets were analyzed, where 444 brackets were bonded using Heliosit Orthodontic and 447 brackets were bonded using Transbond XT. The survival rates of brackets were estimated with the Kaplan-Meier analysis. Bracket survival distributions for bonding adhesives, tooth location and dental arch were compared with the log-rank test.RESULTS: The failure rates of the Transbond XT and the Heliosit Orthodontic groups were 8.1% and 6% respectively. No significant differences in the survival rates were observed between them (p= 0.242). There was no statistically significant difference in the bond failure rates when the clinical performance of the maxillary versus the mandibular arches and the anterior versus the posterior segments were compared.CONCLUSIONS: Both systems had clinically acceptable bond failure rates and are adequate for orthodontic bonding needs.

Effect of Capillary Forces in Room Temperature Si-Si Direct Bonding Technique Using Velcrolike Surfaces

Silicon surfaces were functionalized using the anodization technique to create needle-like surfaces. Such needle-like surfaces allows a Velcro-like bonding, repeated bonding and debonding of the same surfaces with an adequate bond strength at room temperature. A simple porous silicon-based technology to generate such rebondable surfaces is described. The adhesion between such needle-like surfaces is expressed by capillary forces. The proposed adhesion model is a further development of the previously presented van der Waals forces model. The model considers the existence of condensed vapor and capillary bridges resulting from humidity, which can make capillary forces dominant over van der Waals forces at any separation distance between needles above the interatomic spacing (0.3 nm) in the bonding mechanism. The capability of the technique and the validity of the model are demonstrated by comparison with experimental results and simulation results based on the van der Waals forces model. [2016-0245]

Interfacial Property of Dental Cobalt–Chromium Alloys and Their Bonding Strength with Porcelains.

Porcelain-fused-to-metal crown is one of the widely-used prostheses among the dental porcelain restorations. Nonprecious metals like Ni–Cr and Co–Cr have extensively been used for metal-ceramic restorations due to advantages such as inexpensive price, hardness, durability, resistance to deformation, thin thickness of metal of porcelain area, and other mechanical and physical properties. However, the immediate advantage of the Co–Cr alloy is comparable performance to other base metal alloys, but without an allergenic nickel component. To achieve clinical longevity of porcelain-fused-to-metal (PFM) crowns, it is essential to have adequate bond strength between the metal substrate and porcelain. Any type of metal-ceramic fracture failure can become a costly and timeconsuming problem, both in the clinic and laboratory. Therefore, the suitability of the Co–Cr alloy for dental applications is critically associated with its ceramic bonding capacity. In this study, Co–Cr metal alloys modified by acid-etching and sandblasting, oxide layer was formed for subsequent bonding to porcelain ceramics. By both acid-etching and sandblasting oxide layer was formed and showed higher bonding strength at a proper condition, but debonding was occurred at porcelain layer so that they showed highest bonding strength by combined these two kind of surface treatment. Because the oxide film was formed more densely in a vacuum at the portions where more sophisticated concavo-convex were formed on the surface of a metal.

Tratamento de superfície para a cimentação adesiva de cerâmicas à base de zircônia: revisão de literatura

Objetivo: analisar, por meio de uma revisão da literatura, os diferentes métodos de tratamento de superfície de peças protéticas à base de zircônia e os seus efeitos sobre a cimentação adesiva. Material e Métodos: a seleção dos artigos foi realizada por meio de uma busca na base de dados PubMed/MEDLINE. A amostra final foi composta por 31 estudos publicados entre 2011-2016. Resultados: as cerâmicas à base de zircônia (ZrO2) têm propriedades importantes, como durabilidade química, alta tenacidade à fratura, módulo de elasticidade e dureza. Apesar da dificuldade de ligação da superfície da ZrO2 aos cimentos resinosos, estes são uma boa opção para unir as restaurações indiretas aos tecidos dentários. Entretanto, o condicionamento com ácido hidrofluorídrico e a silanização não melhoram a força de união entre o cimento resinoso convencional e cerâmica de alto conteúdo cristalino. Por esta razão, é necessário um modo de tratamento de superfície diferente para proporcionar uma força de ligação adequada. Conclusão: os estudos disponíveis sugerem que o jateamento com partículas de óxido de alumínio e a silicatização proporcionam rugosidade superficial e uma adequada resistência adesiva, no entanto, induzem à transformação de fase tetragonal em monoclínica. Por outro lado, a infiltração seletiva por vidro demonstra não gerar danos à superfície da ZrO2, porém, há a necessidade de mais pesquisas sobre esse recente método.

An Exploratory Investigation of the Mechanical Properties of the Nanostructured Porous Materials Deposited by Laser-Induced Chemical Solution Synthesis

Laser-induced chemical solution synthesis has been recently developed as a new generic method to create porous nanostructured materials for complex and miniaturized devices. The material made by this approach is successfully demonstrated for electrochemical catalytic, nanoscale powders, protective coatings, and other applications. One question has therefore been raised: What are the mechanical properties of the porous materials deposited by the laser-induced chemical solution synthesis? This paper has attempted to explore the mechanical properties of such porous nanostructured materials deposited by this new nanomanufacturing method. This process also offers an innovative opportunity to study the strength of a very simple bonding in additive manufacturing. A thin-film of copper nanoparticles is deposited on copper substrates; then, the microstructure of the deposited film is characterized by scanning electron microscope (SEM), and mechanical properties are investigated by a variety of experiments, such as microhardness test, nano-indentation test, bending test, and adhesion test. The mechanical properties of substrates with surface deposition have been shown to have adequate bond strength (&gt;60 g/mm) to allow effective usage in intended applications. Based on the test results, statistical regression and significant tests have also been carried out. A new model for the nano-indentation of the porous coating (film) is proposed. The empirical results have shown that the effect of coating thickness is more prominent on mechanical properties in the case of thick coating deposition.

Comparative evaluation of shear bond strength of metallic brackets bonded with two different bonding agents under dry conditions and with saliva contamination

BackgroundThis study compared the shear bond strength of metallic brackets bonded with Single Bond and Assure bonding agents under dry and saliva-contamination conditions. MethodsSixty sound premolar teeth were selected, and stainless-steel brackets were bonded on enamel surfaces with Single Bond and Assure bonding agents under dry condition or with saliva contamination. Shear bond strength values of brackets were measured in a universal testing machine. The adhesive remnant index scores were determined after debonding of the brackets under a stereomicroscope. One-way analysis of variance (ANOVA) was used to analyze bond strength. Two-by-two comparisons were made with post hoc Tukey tests (p<0.001). Frequencies of adhesive remnant index scores were analyzed by Kruskal–Wallis test. ResultsBond strength values of brackets to tooth structure were 9.29±8.56 MPa and 21.25±8.93 MPa with the use of Assure resin bonding agent under saliva-contamination and dry conditions, respectively. These values were 10.13±6.69 MPa and 14.09±6.6 MPa, respectively, under the same conditions with the use of Single Bond adhesive. Contamination with saliva resulted in a significant decrease in the bond strength of brackets to tooth structure with the application of Assure adhesive resin (p<0.001). There were no significant differences in the adhesive remnant index scores between the study groups. ConclusionApplication of Single Bond and Assure bonding agents resulted in adequate bond strength of brackets to tooth structures. Contamination with saliva significantly decreased the bond strength of Assure bonding agent compared with dry conditions.

Comparison of bracket bond strength to etched and unetched enamel under dry and wet conditions using Fuji Ortho LC glass-ionomer.

Background. Acid etching prior to orthodontic bracket bonding may result in enamel wear or cracks following bracket removal. The manufacturer of Fuji Ortho LC glass-ionomer (GI) claims that it can bond brackets to wet unetched enamel. This study aimed to compare the bracket bond strength to etched and unetched enamel under dry and wet conditions.Methods. In this in vitro study, 60 intact premolar teeth were randomly assigned to 6 groups (etched and dried, etched and moistened with distilled water, etched and moistened with saliva, unetched and dried, unetched and moistened with water, unetched and moistened with saliva). In all the groups, Leon 4 brackets were bonded to the enamel using Fuji Ortho LC GI. The teeth were immersed in distilled water at 37°C for 24 hours and subjected to shear loads at a crosshead speed of 5 mm/min in a Zwick machine for bond strength testing. Data were analyzed with ANOVA, Tukey test and independent t-test.Results. The mean bond strength values in groups 1 (etched, dry), 2 (etched, moistened with water), 3 (etched, moistened with saliva), 4 (unetched, dry), 5 (unetched, moistened with water) and 6 (unetched, moistened with saliva) were 21.86, 16.46, 10.49, 8.12, 9.15 and 9.52 MPa, respectively. Significant differences in bond strength were detected between groups 1 and 2 and all the other groups (P < 0.05), with no significant difference between groups 1 and 2 (P > 0.05).Conclusion. Fuji Ortho LC GI provided adequate bond strength between brackets and enamel. To acquire higher bond strength, brackets must be bonded to etched and dried enamel.

Effect of saliva decontamination procedures on shear bond strength of a one-step adhesive system.

To evaluate the effect of different saliva decontamination procedures on the shear bond strength of a one-step universal adhesive system (Single Bond™ Universal Adhesive, 3M ESPE, St. Paul, MN, USA). The occlusal surfaces of 75 human third molars were ground to expose dentin. The teeth were divided into the following groups: Group 1 (control group): Single Bond™ Universal Adhesive was applied to the prepared tooth according to the manufacturer's recommendations and light cured; no contamination procedure was performed. Group 2: Bonding, light curing, saliva contamination, and dry. Group 3: Bonding, light curing, saliva contamination, rinse, and dry. Group 4: After the procedure performed in Group 2, reapplication of bonding. Group 5: After the procedure performed in Group 3, reapplication of bonding. Then, composite resins were applied with cylindrical-shaped plastic matrixes and light cured. For shear bond testing, a notch-shaped force transducer apparatus was applied to each specimen at the interface between the tooth and composite until failure occurred. The data were statistically analyzed using one-way ANOVA. One-way ANOVA revealed significant differences in shear bond strength between the control group and experimental Groups 2 and 4 (P < 0.05). No significant difference was found for experimental Groups 3 and 5 when compared to the control group (P > 0.05). The present in vitro study showed that water rinsing is necessary if cured adhesive resin is contaminated with saliva to ensure adequate bond strength.

Orthodontic shear bond strength to porcelain surface in wet conditions

Objective: To evaluate the shear bond strength of orthodontic accessories bonded to a porcelain surface after storage in water.Methods: One-hundredand-twenty feldspathic porcelain discs were divided into 4 groups, according to the surface treatment: Group 1 – 37% phosphoric acid etching; Group 2 – 10% fluorhydric acid; Group 3 – 37% phosphoric acid and silane application; Group 4 – 10% fluorhydric acid and silane application. After the accessories were bonded, the sample was divided into two subgroups, according to the time interval of storage in distilled water: Control – 24 hours; and Test – 150 days. Shear bond strength was determined using a universal test machine, and failure type was verified by scanning electron microscopy.Results: In the test groups there was reduction in shear bond strength, particularly when silane was used. Test Groups 2 and 4 presented shear bond strength values within those proposed as adequate for orthodontic bonding. Groups 1 and 3 presented adhesive failures between porcelain and resin, whereas in Groups 2 and 4 cohesive failures in porcelain were recorded.Conclusion: Storage in water for 150 days decreased the bond strength at silanized interfaces. Fluorhydric acid etching generates adequate bond strength in wet conditions, however, increases the fracture rate in porcelain.

Determining the temporal development of dentin-composite bond strength during curing

ObjectivesAs composite restorations cure a competition develops between bond formation and shrinkage stress at the composite-dentin interface. Thus, understanding the temporal development of tooth-composite bond strength should enable better assessment of tooth-composite debonding. MethodsIn this study, bond strengths of composite-dentin specimens obtained from tensile test at different curing times were used to determine the bond formation rate. By varying the composite thickness and output from the curing light, their effects on the rate of bond formation for two different materials (a conventional and a bulk-fill composite) were also investigated. The proportions of cohesive and adhesive failure were determined by analysis of electron micrographs of the fractured surfaces. ResultsThe development of dentin-composite bond strength (S) with time (t) can be described by the equation: S=Smax(1−exp(−αt)), where Smax is the final bond strength (∼12MPa for both composites) and α the rate of bond formation. Using bulk-fill and thinner specimens gave faster bond formation. In fact, the higher the irradiance at the interface, the higher the rate of bond formation. However, α had a maximum value of ∼0.6s−1 and the rule of reciprocity did not hold. A minimum dose of ∼2J/cm2 was required to achieve adequate bond strength. The predominant failure mode changed from cohesive in the composite and adhesive to interfacial at the adhesive-dentin interface, indicating the latter to be the weakest link in the cured dentin-composite assemblies considered. SignificanceWhen combined with the temporal development of shrinkage stress, the current results will help determine the likelihood of tooth-composite debonding.

Comparative Evaluation of Shear Bond Strength of Metallic Brackets With Two Bonding Agents With and Without Saliva Contamination

Objectives: The present study was carried out to compare the shear bond strength of metallic brackets bonded with single Bond and Assure bonding agents under dry and saliva contamination conditions. Materials and Methods: A total 60 sound premolar teeth were selected for the purpose of this in vitro study and stainless steel brackets were bonded on enamel surfaces with single bond and assure bonding agents under a dry condition or with salivary contamination. The shear bond strength values of the brackets were measured in a universal testing machine. The adhesive remnant index (ARI) scores were determined after debonding of the brackets under a stereomicroscope. One-way ANOVA was used to analyze bond strength. Two-by-two comparisons were made with post hoc Tukey tests (P < 0.001). The frequencies of ARI scores were analyzed with Kruskal-Wallis test. Results: The bond strength values of brackets to tooth structure were 9.29 ± 8.56 and 21.25 ± 8.93 MPa with the use of Assure resin bonding agent under saliva contamination and dry conditions, respectively. These values were 10.13 ± 6.69 and 14.09 ± 6.6 MPa, respectively, under the same conditions with the use of single bond adhesive. Contamination with saliva resulted in a significant decrease in the bond strength of brackets to tooth structure with the application of Assure adhesive resin (P < 0.001). There were no significant differences in the ARI scores between the different study groups. Conclusions: Application of single bond and assure bonding agents resulted in adequate bond strength of brackets to tooth structures. Contamination with saliva significantly decreased the bond strength of Assure bonding agent compared to dry conditions.

Bond strengths of brackets bonded to enamel surfaces conditioned with femtosecond and Er:YAG laser systems.

The aim of this study was to compare femtosecond and Er:YAG laser systems with regard to enamel demineralization and bracket bond strength. Human-extracted premolars were randomized to three groups (n = 17) depending on the conditioning treatment used for the buccal surfaces: 37% orthophosphoric acid, Er:YAG laser etching (MSP mode 120mJ, 10Hz, 1.2W), and femtosecond laser etching (0.4W, 800nm, 90fs/pulse, 1kHz). Metal brackets were bonded with Transbond XT to the conditioned surfaces and light cured for 20s. The samples were thermocycled (5000cycles, 5-55°C) and subjected to shear bond strength (SBS) testing using a universal testing machine. Failure types were analyzed under an optical stereomicroscope and SEM. The adhesive remnant index (ARI) was evaluated to assess residual adhesive on the enamel surface. The results revealed no significant differences in SBS between the Er:YAG laser (7.2 ± 3.3MPa) and acid etching groups (7.3 ± 2.7MPa; p < 0.05), whereas a significant difference was observed between the femtosecond laser etching group (3.3 ± 1.2MPa) and the other two groups (p < 0.01). ARI scores were significantly different among the three groups. The results of our study suggest that laser conditioning with an Er:YAG system results in successful etching, similar to that obtained with acid. The sole use of a femtosecond laser system may not provide an adequate bond strength at the bracket-enamel interface.

Laboratory and field evaluation of several types of soil nails for different geological conditions

For steep slopes with difficult access or slopes in a corrosive environment, there are various problems associated with the use of conventional steel reinforcement bars as soil nails. For loose-fill slopes or clay slopes, the development of adequate nail bond strength is another practical issue that should be considered. Carbon fiber–reinforced polymer (CFRP) and glass fiber–reinforced polymer (GFRP) in several forms and installation methods have been studied as the alternatives to the classical steel bar. Extensive laboratory tests on the materials and field tests on different types of soil nails with various methods of installation have been carried out in Hong Kong, Korea, and Australia. Test results support the use of these materials with an innovative installation method as soil nails under different geological conditions, and the suitability and performance of these materials under different conditions are assessed in the present study.