Objectives: The purpose of this in-vitro study was to evaluate the effects of three different surface preparation methods on the shear bond strength of orthodontic brackets bonded to zirconia and determine the most appropriate method. Methods: 45 zirconia and 30 leucite-reinforced porcelain mandibular premolar crowns were divided into 5 groups and received the following surface preparations: 37% phosphoric acid and non-hydrolyzed silane, 4% hydrofluoric acid and hydrolyzed silane, microetch with 50μ Al 2 O3 particles. A universal adhesive primer containing MDP was applied and the brackets were bonded with a bis-GMA composite resin. Shear bond strength (SBS) at bond failure and ARI score were recorded. Results: There was a statistically significant difference among the studied groups for the SBS. The highest mean SBS (11.03 MPA) was recorded for the zirconia/microetch group, and the lowest SBS (3.49 MPa) for the zirconia/phosphoric acid group. The leucite-reinforced porcelain/ hydrofluoric acid group had significantly more fractures than any other debond pattern. The zirconia/hydrofluoric acid group was the only one with a SBS (8.08 MPa) that fell within the recommended range of 6-8 MPa. This group also had a favorable debond pattern with most composite remaining on the bracket. Conclusions: Important consideration should be given to the surface preparation of porcelain and zirconia prior to bonding orthodontic attachments. Phosphoric acid etch is not an adequate surface preparation when bonding to zirconia. Hydrofluoric acid is not suitable when bonding to leucite-reinforced porcelain, as it is associated with a higher rate of surface fracture. Microetch with 50μ Al 2 O3 particles in combination with an MDP containing universal adhesive primer provided optimal mean shear bond strength, along with favorable debond patterns when bonding to zirconia. Hydrofluoric acid etch in combination with a silane and a universal primer containing MDP provided acceptable shear bond strength to zirconia. This protocol was not significantly different from zirconia prepared with microetch and either method can be successfully employed.

A thesis submitted to the College of Dental Medicine of Nova Southeastern University of the degree of Master of Science in Dentistry. Objective: The objectives of this study were 1) to evaluate the effect of enamel deproteinization on the shear bond strength(SBS) of orthodontic brackets bonded with a resin modified glass-ionomer (RMGI) adhesive and a composite resin, 2) to determine the mode of bond failure according to the adhesive remnant index (ARI) and 3) to evaluate the effect of these adhesives in the prevention of white spot lesions (WSLs). Background: WSLs are a concern for orthodontic patients. RMGI orthodontic adhesives are capable of absorbing fluoride from the oral environment and releasing it continuously over time, however, they are not frequently used as they exhibit low SBS. Techniques such as non-invasive enamel deproteinization with 5.25% sodium hypochlorite prior to acid etching rid the surface of organic components and have the potential to enhance the etching pattern. Methods: Eighty-eight extracted bovine incisors were randomly divided into two groups. 48 incisors in group (A) underwent SBS testing, through debonding of brackets with the Universal Testing Machine and subsequent measurement of the ARI. 40 incisors in group (B) underwent demineralization testing by measuring the depth of WSLs formed after exposure to an acidic challenge for 96 hours. In groups A and B, the teeth were divided to have brackets bonded with GC Fuji ORTHO™ LC adhesive or Transbond™ XT adhesive and a self-etching primer. Each adhesive group had an experimental group receiving the intervention of enamel deproteinization prior to etching and bonding and a control group. Results: The highest mean SBS was observed in the Transbond™ XT control group (12.48 ± 6.23 MPa) and the lowest mean SBS was observed in the Fuji ORTHO™ experimental group (5.49 ± 2.97 MPa). ANOVA and Post-Hoc Tukey tests revealed statistically significant differences (p<0.05) in the SBS of both Fuji ORTHO™ groups compared to the Transbond™ XT control group. A significantly greater percentage of Transbond™ XT control teeth had an ARI score of 0 and a greater percentage of Fuji ORTHO™ experimental teeth had an ARI score of 3. The Transbond™ XT experimental group had the largest average demineralization lesions (62.97 ± 10.95 micrometers). The smallest lesion depths were found in the Fuji ORTHO™ groups, with an average of 7.74 micrometers in the experimental group and 6.57 micrometers in the control group. ANOVA and Post-Hoc Tukey tests revealed significant differences (p<0.001) in the depth of white spot lesions when comparing both composite resin groups to each other, and when each glass ionomer group was compared to each composite resin group. Conclusions: Enamel deproteinization did not increase the SBS of orthodontic brackets bonded with either Fuji ORTHO™ adhesive or Transbond™ XT adhesive. However, according to the ARI, more bond failures occurred at the bracket-adhesive interface in the Fuji ORTHO™ experimental group. Also, both Fuji ORTHO™ adhesive groups showed greater protection against enamel demineralization, when compared to the Transbond™ XT adhesive groups.

Indiana University-Purdue University Indianapolis (IUPUI) / MICROTENSILE BOND STRENGTH OF NEW PASTE/PASTE RESIN-MODIFIED GLASS IONOMER CEMENT SYSTEMS: THE EFFECT OF DENTIN PRETREATMENT by Yasser Fawaz Al-fawaz Indiana University School of Dentistry Indianapolis, Indiana Background: In order to improve the clinical performance of RMGIC 3M ESPE and GC America introduced paste/paste resin-modified glass ionomer cements, Ketac™ Nano and Fuji Filling™ LC, respectively. Both companies developed non-rinse substrate conditioners (i.e., Ketac Nano Primer-3M ESPE and GC Self-Conditioner-GC America) that should be used with these new materials instead of the conventional polyacrylic acid. It has been also advised by both manufacturer’s to use this novel substrate conditioner with the previously marketed RMGICs. Objective: to investigate whether the use of novel non-rinse conditioners (i.e., Ketac Nano Primer 3M ESPE and GC Self Conditioner GC America) as substrate pre-treatment and the new paste/paste resin-modified glass-ionomer cement, RMGIC (Ketac™ Nano 3M ESPE and Fuji Filling™ LC GC America) would affect the microtensile dentin bond strength (µTBS) of the material when compared to the traditional RMGIC with polyacrylic acid as a surface substrate pre-treatment. Materials and Methods: 96 extracted non-restored human molar were sectioned to expose occlusal dentin. Dentin surface was finished with SiC paper to standardize the smear layer. Bonding protocols of the different materials to dentin were performed following the use of two dentin conditioners. Eight groups (n=12) were tested: G1: Ketac Nano Primer + Ketac Nano, G2: Ketac Conditioner + Ketac Nano, G3: Ketac Nano Primer + Photac Fil, G4: Ketac Conditioner + Photac Fil, G5: GC Self Conditioner + Fuji Filling LC, G6: GC Cavity Conditioner + Fuji Filling LC, G7: GC Self Conditioner + Fuji II LC and G8: GC Cavity Conditioner + Fuji II LC. The specimens were stored in 37°C for 24h in 100% humidity before cutting non-trimmed beams for the µTBS with cross-sectional areas of approximately 0.8 × 0.8 mm2. Nine beams were used from each specimen. Test was done using universal testing machine at a cross-head speed of 1mm/min. Debonded specimens were examined under a stereomicroscope at 45× magnification to evaluate the failure mode. Eight randomly chosen representative debonded beams were imaged under a scanning electron microscope (SEM). Results: µTBS in MPa (mean ± SE) were: G1: 9.5±1.0, G2: 11.0±1.0, G3:20.0±1.0, G4:16.8±0.9, G5: 15.1±1.0, G6: pre-test failure, G7: 20.0±1.0, G8:14.1±0.9. Weibull-distribution survival analysis was used to compare the differences in microtensile peak stress among the groups. Group5 has cohesive predominant faultier mod while the other groups have adhesive predominant failure. Conclusion: Within the limitations of this study, the use of the novel non-rinse conditioners did not improve the microtensile bond strength of new paste/paste RMGIC to dentin. In fact, the use of the novel non-rinse conditioners enhanced the bond strength of the traditional RMGIC to dentin.

No description available.

This thesis reports on the research outcome of corrosion mechanism and corrosion rate of mild steel in different environments (saline, alkaline solutions and concrete media) using potentiodynamic polarization technique. The study also included the effect of corrosion on bond strength between reinforcing steel and concrete using pull-out test. Corrosion of mild steel and 316L stainless steel with different surface conditions in 1, 3 and 5% saline (NaCl + Distilled water) was investigated. Specimens ground with 200 and 600 grit silicon carbide grinding paper as well as 1¿m surface finish (polished with 1¿m diamond paste) were tested. In case of mild steel specimens, reduction in surface roughness caused increase in corrosion rate, while in 316L stainless steel corrosion rate decreased as the surface roughness improved. Metallographic examination of corroded specimens confirmed breakdown of passive region due to pitting corrosion. Corrosion of mild steel was also investigated in alkaline solution (saturated calcium hydroxide, pH =12.5) contaminated with 1, 3 and 5% saline. A series of corrosion experiments were also conducted to examine the efficiency of various concentrations of calcium nitrite (CN) on corrosion behaviour of both as-received and polished mild steel in alkaline solution containing 3% saline after 1 hour and 28 days of exposure. Corrosion rate was higher for the as-received than polished mild steel surface under the same testing conditions in NaCl alkaline solution with and without nitrites due to the effect of surface roughness. Morphology investigation of mild steel specimens in alkaline solution ii containing chlorides and nitrites showed localized pits even at nitrite concentration equal to chloride concentration. Corrosion of steel bars embedded in concrete having compressive strengths of 20, 30 and 46MPa was also investigated. The effect of 2 and 4% CN by weight of cement on corrosion behaviour of steel bar in low and high concrete strengths specimens were also studied. All reinforced concrete specimens were immersed in 3% saline solution for three different periods of 1, 7 and 15 days. In order to accelerate the chemical reactions, an external current of 0.4A was applied. Corrosion rate was measured by retrieving electrochemical information from polarization tests. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel/concrete bond characteristics. Experimental results showed that corrosion rate of steel bars and bond strength were dependent on concrete strength, amount of CN and acceleration corrosion period. As concrete strength increased from 20 to 46MPa, corrosion rate of embedded steel decreased. First day of corrosion acceleration showed a slight increase in steel/concrete bond strength, whereas severe corrosion due to 7 and 15 days corrosion acceleration significantly reduced steel/concrete bond strength. Addition of only 2% CN did not give corrosion protection for steel reinforcement in concrete with 20MPa strength at long time of exposure. However, the combination of good quality concrete and addition of CN appear to be a desirable approach to reduce the effect of chloride induced corrosion of steel reinforcement. At less time of exposure, specimens without CN showed higher bond strength in both concrete mixes than those with CN. After 7 days of corrosion acceleration, the higher concentration of CN gave higher bond strength in both concrete mixes. The same trend was observed at 15 days of corrosion acceleration except for the specimen with 20MPa compressive strength and 2% CN which recorded the highest deterioration in bond strength.

No description available.

No description available.

No description available.

Yes / This paper investigates the bond performance of recycled coarse aggregate (RCA) concrete with un-corroded/corroded reinforcing steel bars, with the main parameters being RCA content, corrosion level, bar diameter and embedment length. For this purpose, 60 pull-out specimens containing different percentages of RCA (i.e. 0%, 25%, 50% and 100%) and steel bars of two diameters (12 and 20 mm) and different embedment lengths were tested. In order to establish various levels of corrosion, specimens were exposed to an electrochemical corrosion for 2, 5, 10 and 15 days. The bond strength between RAC concrete and un-corroded/corroded steel are compared to current codes and equations proposed by other researchers. Experimental results showed that larger corrosion rate of steel bars was observed with the increase of the replacement level of RCA due to its high porosity and water absorption. The use of RCA had a slight influence on bond strength for un-corroded specimens compared to that obtained from conventional concrete. Furthermore, the bond strength of RCA concrete was strongly affected by corrosion products; bond strength slightly enhanced for up to about 2% corrosion rate, and then significantly decreased as the corrosion time further increased, similar to that of conventional concrete. However, the rate of bond degradation between RCA concrete and corroded steel bars was much faster than that observed in corroded conventional concrete.

Yes / Limited information related to the application of nano silica in recycled aggregate concretes has been available in the literature. However, investigations on the effect of nano silica on the bond performance of reinforcement embedment length in recycled aggregate concrete have not been conducted yet. Therefore, the present study aimed at investigating the bond strength for recycled aggregate concretes incorporating nano silica under different levels of corrosive environments. The experimental work consisted of testing 180 pull-out specimens prepared from different mixtures. The main parameters studied were the amount of recycled aggregate (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), embedment length (5 and 13Ø) as well as reinforcement diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. Finally, the experimental results were compared with the existing models. Experimental results showed that the bond performance between un-corroded steel and RCA concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of a small quantity of NS (1.5%) showed between 8 and 21% bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence was observed with the increase of corrosion periods, reflecting the improvement in corrosion resistance. NS particles showed a more effective role with RCA concretes rather than conventional concretes in terms of enhancing bond and corrosion resistance. Therefore, it was superbly effective in recovering the poor performance in bond for RCA concretes. By doubling the content of NS (3%), the bond resistance slightly enhanced for non-corroded samples, while its influence becomes more pronounced with increasing RCA content as well as exposure time to corrosion.