Magister Scientiae - MSc / Amalgam bonding agents have been shown to enhance retention of amalgam restorations by mechanical means. However, recent studies showed that the use o glass ionomer cements and resin cements as lining and bonding materials to amalgam restorations will increase the retentive strength of the amalgam restorations, hence reducing the micro leakage and secondary caries. The purpose of this study was to compare the relative retentive strength of conventional amalgam restorations and bonded amalgam restorations using resin adhesive, glass ionomer cements and resin cements. / South Africa

Des matériaux sandwichs fabriqués sans colle époxy on été conçu pour réduire les contraintes mécaniques, ou “stress shielding”, entre l’os environnant et l’implant. Le titane (Ti) et le polyméthacrylate de méthyle (PMMA) sont les matériaux les plus utilisés dans les applications biomédicales, et on été choisi comme composants de base. Pour cela, on a élaboré des interfaces Ti/polymère dans lesquelles le métal et le polymère sont liés par une liaison covalente; cette couche de polymère permettra ultérieurement l’adhésion entre le métal et une feuille de polymère qui constituera le cœur du sandwich. Dans ce but, une stratégie en trois étapes permettant d’obtenir une fonctionnalisation de la surface du titane a été développé. Tout d’abord, la surface du Ti a été activée chimiquement; ensuite un initiateur de polymérisation y a été greffé de façon covalente. Enfin, la croissance des chaines polymères a été obtenue en utilisant une polymérisation par transfert d’atomes à partir de l’initiateur (SI-ATRP). Les sandwichs ont été préparés en insérant une feuille de polymère entre les deux feuilles de Ti recouvertes de polymère greffé et en pressant les trois composants à une température supérieure à celle de la transition vitreuse du polymère. / A procedure aimed at designing innovative epoxy resin-free sandwich materials (i.e., layered structure composed of two metal skin and a polymer core) able to reduce stress-shielding effect at the implant/bone interface was developed. For this purpose, titanium (Ti) and poly methymethacrilate (PMMA), the most extensively materials used for biomedical applications, were employed. In particular, surface-confined PMMA layers were proposed as adhesives to stick a PMMA foil (used as core of the structure) on the metallic Ti skin sheets exploiting the miscibility between the tethered polymer chains (previously grown on the Ti) and those of an adhering PMMA foil.To this purpose, a three steps strategy based on a suitable functionalization of Ti surface was developed. First of all, a chemical activation of Ti surface was performed. Then, a “grafting from” method was used to immobilize a polymerization initiator on the activated Ti surface. Finally, the polymer chains were grown from the initiator-modified surfaces using a surface initiation atom transfer radical polymerization (SI-ATRP). Biocompatible Ti/PMMA/Ti sandwiches were then prepared by hot-pressing, inserting between the two PMMA-coated Ti surfaces a thick PMMA foil.

The functionalization of renewable and abundant carbon dioxide as a building block for industrial polymer production leads to safer designs in manufacturing of materials, decreases the dependence of fossil fuel feedstocks, and diminishes plastic waste generation due to engineered biodegradability. Through judicious catalyst design, the copolymerization of carbon dioxide and oxiranyl small molecules has not only opened new synthetic routes towards the manufacturing of novel polycarbonate architectures, but in addition, allows for the mass production of commodity plastics via raw materials derived entirely from biomass. This environmentally friendly methodology pioneered by Shohei Inoue not only accommodates polymer product with an eco-design, but in tandem serves as a means of carbon capture, mitigating the effects of global climate change. With a global market value anticipated to reach 2 billion dollars by 2026, polyacrylate resins are ubiquitous in the paint, automotive, and adhesive industries. However, the production of these non-degradable polymers compounds the rising concern of plastic pollution in the environment. Herein, the design and synthesis of polyacrylate mimetics bearing a degradable carbonate moiety in the backbone is described. The synthetic methodology utilizes a green pathway through the use of carbon dioxide as the C1 source. The thermal, chemical, and rheological properties of the materials are evaluated and compared to commercial acrylates and adhesives. Additional modification of the materials through terpolyermization is conducted, and their ability to perform as smart adhesive surfaces as well as clinical use in lung resection surgery is covered. / 2020-11-12T00:00:00Z

Over 200 million dental restorations are performed each year in America. A dental restoration require a strong bonding of restoration to tooth structure and relies on the dental adhesive to create this mechanical and chemical bonding. Dental adhesion or bonding is the process of forming an adhesive joint between the composite and tooth substrate: dentin or enamel. Clinical problems such as microleakage at the restoration tooth interface, influx of fluids, or bacteria growth at the cavity wall can be prevented with adhesives that obtain a more intimate bonding. Longevity of the restoration can be enhanced by the adhesive that creates the tight bonding to reduce problems such as postoperative sensitivity, marginal staining, and recurrent caries. The goal of this research project is to investigate the influence of active scrubbing application as compared to passive non-scrubbing application of the etchant component in 4th generation etch-and-rinse adhesive systems. Shear bond stresses have been measured and compared between application techniques. Verification of resin infiltration depth with each etchant application has been examined with scanning electron microscopy by mounting the etched and bonded enamel surface of the tooth in epoxy and slicing the tooth longitudinally producing a transverse, depth-wise view. Results from this study have clarified the role of resin tag formation as well as tooth morphology during an active acid etchant application for dental restoration.

Indiana University-Purdue University Indianapolis (IUPUI) / Cementing of indirect restorations with resin cements generally requires the pre-treatment of dentin with an adhesive. When dual-cured or chemical-cured resin cements are used with these single-step adhesives, incompatibility issues exist. This has resulted in manufacturers making chemical changes in their products. Kerr Dental markets a new resin cement, Nexus Third generation (NX3), which utilizes a proprietary redox system different from the second generation of composite luting agent (NX2). The aim of this study was to evaluate microtensile bond strength and mode of failure of NX3 and NX2 with two different adhesive systems (total-etch and self-etch) after 1 week and after 3 months of storage. Methods: Sixty-four non-carious teeth were sectioned to expose the dentin using a low-speed saw. Dentin surfaces were ground with 320-grit SiC paper. The adhesives Optibond Solo Plus (SOL), and Optibond All In One (AIO) were applied, and resin cements (NX2, NX3) were used to lute 4-mm composite discs to the treated dentin surfaces. Microtensile bond strength was determined at 1 week (IM) and after 3 months (3MON) of storage using a universal testing machine (MTS). All specimens were examined under the stereomicroscope to determine the mode of failure. Random specimens from each failure group were examined using scanning electron microscopy. Statistical Analysis: Comparisons between the treatment combinations for differences in microtensile bond strength were performed using Weibull-distribution survival analysis. Comparisons between the treatment combinations for differences in the failure mode were performed using Fisher’s Exact tests. The group NX3 SOL IM (30.5 MPa) had significantly higher bond strength than NX3 SOL 3MON (13.4 MPa); NX3 AIO IM (11.3MPa); NX3 AIO 3MON (8.2 MPa; NX2 AIO 3MON (5.8 MPa); NX2 SOL IM (6.3 MPa), and NX2 SOL 3MON (3.2 MPa). The group NX2 AIO IM (19.3 MPa) was not significantly different from NX3 SOL IM. The group NX2 SOL 3MON and group NX2 SOL IM had a significantly higher percentage of teeth with mixed failure than all of the other groups. None of the other groups had significantly different failure mode. The group NX3 SOL IM had 90-percent beam survival beyond 17 MPa, and NX2 AIO IM had 50 percent of beams surviving beyond 17 MPa, a better performance. For all the other groups, more than 50 percent of beams failed below 17 MPa. Results show high evidence of degradation for all groups considered in this investigation. The use of these types of cement adhesive combinations in clinical situations should be used with this understanding.

No description available.

Anodized Ti-6Al-HV/adhesive bonds exhibit improved corrosion resistance and a higher strength-to-weight ratio compared to conventional metal bonding techniques for primary and/or secondary structural applications. This work was conducted to identify chromic acid (CA) anodization and bond process conditions which produced durable, structural anodized Ti-6Al-4V/heat resistant single lap bonds and to understand why these conditions were necessary. A structural single lap bond was defined as a bond tested at 298K ≤ 0.5 month after bonding and with a strength ≥ 6.9 MPa, based upon values reported in structural adhesive manufacturers' product literature. A durable, structural single lap bond was defined as a bond with a strength ≥ 6.9 MPa strength at 298K after 9 months aging at 433K. Heat resistant adhesives tested had reported service temperatures ≥ 423K, and were: polysulfone; eolyethersulfone; polyphenylquinoxaline; polyetherimide, both unfilled and 20% glass filled; and 50% calcium carbonate filled polyimide. Hydrofluoric acid (HF) added to the CA anodization solution was necessary to produce structural bonds. CA/HF oxide was more porous, and thicker than the CA anodic oxide (140 nm vs. 20 nm), perhaps promoting physical and oxide/adhesive interphase mechanical interlock. Structural, durable CA/HF anodized Ti-6Al-4V-adhesive bonds were produced for all adhesives tested except for the filled polyimide (5.5 MPa). The filler may have occluded oxide pores and prevented optimal adhesive/oxide interphase interlock, and there may have been competition of polyimide for calcium carbonate filler and for oxide. Average oxide thickness values of 65 to 410 nm did not affect bond strength; structural bonds were produced in all cases. CA/HF initial current density of 20 Amperes per square meter produced 33% stronger polysulfone bonds than 30 Amperes per square meter. Polysulfone microstructure may have been chemically degraded by the unnecessarily high fluoride concentration in the oxide from the higher current density. Lica® 44 titanate primer did not significantly influence bond strength or durability, except when unfilled polyetherimide was the adhesive. Polyphenylquinoxaline bond processing influenced bond strength. Structural bonds resulted for all the CA/HF anodization and process conditions described above. Single Iap bond fracture initiated in the adhesive (polymer) fillet. Fracture propagation in the bond overlap was through the polymer/anodic oxide interphase and/or cohesively in the polymer. / Ph. D.

Coumarin and cinnamate derivatives were positioned as either polymer chain ends or side groups to synthesize photoactive macromolecules and gain the ability to reversibly control molecular weight and crosslink density using UV light. The cinnamates and coumarins were reacted onto the polymers via multiple reaction pathways. Polymers were functionalized with coumarin or cinnamate groups via an esterification reaction between hydroxyl functionalities and an acid chloride derivatized coumarin group. In addition to the esterification reaction, cinnamates were also coupled to polymers via a ring opening reaction between a hydroxyl functionalized cinnamate derivative and a maleic anhydride repeat unit copolymerized into the polymer. Both functional groups undergo a [2π + 2π] photodimerization reaction (coumarin groups in the UVA and cinnamate groups in the UVB), which was utilized to crosslink and chain-extend macromolecules. Coumarin dimers possess the additional ability to photocleave and thus reverse when irradiated at 254 nm. The coumarin reversible photodimerization reaction was utilized to reversibly increase the molecular weight and molecular weight distribution of coumarin-functionalized PEG monols and diols. For example, the number average molecular weight of the coumarin-functionalized PEG diol doubled and the molecular weight distribution increased from 1.08 to 2.75 when exposed to 110 J cm⁻² of UVA irradiation. Subsequent photocleavage (UVC irradiation, 2 J cm⁻²) of the chain-extended PEGs, cleaved coumarin dimers decreasing the molecular weight and molecular weight distribution to their original values. A number of poly(alkyl acrylate) and poly(methyl acrylate) systems were functionalized with coumarin groups to study the effect of the glass transition temperature and alkyl ester side group composition on the photodimerization reaction and subsequent crosslinking. The glass transition temperature (T_g) acted as an on/off switch for the photodimerization reaction. While the absolute difference between T_g and irradiance temperature did not affect the rate or extent of photodimerization reaction, polymers with a T_g greater than the irradiance temperature displayed less reaction than those with a T_g lower than the irradiance temperature. The final extent of conversion was controlled by a complex combination of factors including alkyl ester side chain steric bulkiness. Coumarin-functionalized alkyl acrylates based on ethylhexyl acrylate were tested as detachable PSAs. A 98% decrease in the adhesive peel strength was observed after exposure to UVA irradiation. Cinnamate groups were utilized in the design and synthesis of UV-curable hot melt pressure sensitive adhesives (PSAs). The cinnamate groups were attached to the PSAs to provide a method to increase molecular weight and add a small amount of crosslinking leading to an increase the adhesive strength of the PSAs. Broadband UV irradiation from a laboratory scale industrial lamp increased the peel strength of the adhesives. Postcure of the irradiated cinnamate-functionalized UV-curable hot melt PSAs was reduced compared to photoinitiated free-radical photocurable UV-curable hot melt PSAs. / Ph. D.

Durability of a variety of sheet molding compounds (SMC)/ adhesive /metal systems involving steel, aluminum, phase α-SMC, Budd SMC, and polyurea adherends and polyurethane and epoxy adhesives has been investigated. Three specimen geometries with different modes of stress were employed: lap shear, wedge, and butt torsion. Specimens were exposed to an environmental cycle or to fixed conditions of temperature and humidity with or without load. For phase α-SMC/urethane/ELPO steel adhesive bonds, all visually determined adhesive failure occurs at the SMC/adhesive interface, and it is in reality a mixture of interfacial failure and near surface SMC debonding. The near surface SMC material and the thin layer of primer on the SMC surface are the weak links in the bond. An improvement in durability of phase α-SMC/urethane/ELPO steel adhesive bonds requires an increase in the strength of the outer layer of the SMC material. The metal surface pretreatment proved to be very important for the durability of phase α-SMC /urethane/aluminum adhesive bonds. The adhesive bonds prepared with solvent cleaned aluminum primed with epoxy or phenolic primer displayed poor durability. This is attributed to the contaminants on the aluminum surface after solvent cleaning which hinder the interactions of aluminum surface species with primers. The use of alkaline cleaned aluminum primed with diisocyanate primer improved durability only in dry air conditions. This can be explained by the high susceptibility of the NCO functionality to water, which can rapidly weaken the primer/aluminum bonds. Priming alkaline cleaned aluminum adherends with phenolic or epoxy primers improved dramatically the adhesive bond durability under all testing conditions. Enhanced durability is attributed to chemical and hydrogen bonds established between components of phenolic and epoxy primers and aluminum surface species. Reflection absorption FTIR studies of the interactions between identical or similar compounds that exist in the primers, e.g. diglycidyl ether of bisphenol A, phenol, and methylene diphenyl diisocyanate, and alkaline cleaned aluminum surface species indicated chemical processes. Exposure of bonded samples at 60°C for up to seven days did not reduce the residual strength. Some loaded samples failed during durability tests, indicating that loading is a significant factor in durability. Butt torsion samples proved to be much more sensitive to stress and temperature than the lap shear and wedge samples, showing the important role of the mode of stress in durability. Humidity had a detrimental effect on durability for all systems investigated. For the system Budd SMC/adhesive/ELPO steel an epoxy adhesive exhibited better durability than a polyurethane adhesive. Enhanced durability is explained by higher cohesive strength, a lower moisture absorption rate and higher resistance to hydrolysis of the epoxy adhesive. An increase in bondline thickness proved to be beneficial for adhesive durability, a fact attributed to a more uniform stress distribution in thicker bonds. / Ph. D.

The goal of this project was improve the fundamental understanding of the wood-resin interaction, by looking at the relationship between the resin wetting onto wood and the resulting penetration into wood lumens. Wetting was analyzed with the sessile drop method, which observed the initial contact angle and change in contact angle over 35s. Penetration was measured within each individual tracheid. The Lucas-Washburn equation analyzed the wetting and penetration by calculating the penetration and comparing it to the measured penetration. Wetting of four resins was compared on 3 species, to improve the understanding of adhesive wetting behavior. This study agreed with previous research, that the non-aqueous resin exhibited favorable wetting and presumably better penetration than aqueous resins, with exception of urea-formaldehyde. Wetting and penetration of pMDI was studied on 5 wood species using the Lucas-Washburn equation. The wetting behaviors exhibited grain and species effects, which had implications on the resin availability for flake/strand-based composite products. The greater surface energy of loblolly pine most likely accounted for the significantly greater penetration of loblolly pine compared to Douglas-fir. The calculated penetration, via the Lucas-Washburn equation, exceeded the measured penetration, but it was concluded that the Lucas-Washburn equation predicted penetration reasonably well. Wetting and penetration of phenol-formaldehyde and subsequent adhesives was compared on 3 wood species using the Lucas-Washburn equation. All contact angles were unfavorable due to a skin formation. The Lucas-Washburn equation did not predict any penetration; however, penetration was observed with all systems. The findings suggest that the system was too complex for the Lucas-Washburn equation to be able to predict accurately. / Master of Science