A thesis submitted to the College of Dental Medicine of Nova Southeastern University of the degree of Master of Science in Dentistry. ABSTRACT The significance of this research was to identify the optimal techniques to remove ceramic orthodontic appliances in order to prevent tooth-enamel fracture, pain, and esthetic complications. Discomfort and pain are common occurrences during orthodontic appliance removal. In debonding (bracket removal) appointments, less force, measured as reduced shear bond strength (SBS) is preferable because greater force creates more discomfort and pain. In a previous study, 24.3% of patients reported pain when metallic brackets were removed using a ligature-cutting plier, compared to 12.8% of patients reporting pain when a lift-off instrument was employed. These previous findings demonstrate the need to investigate new debonding removal methods which have less SBS to help reduce the pain experienced by orthodontic patients. Some recent studies have reported that orthodontic bracket debonding causes inevitable damage to the enamel surface. The debonding of ceramic orthodontic brackets can increase the risk of enamel damage. The application of heat to help debond a bracket can increase the temperature of the pulp chamber; this could injure pulp cells and threaten the long term vitality of the affected tooth. The purpose of this in-vitro study was to evaluate the safety and effectiveness of using a diode laser for the debonding of ceramic brackets in relation to the amount of debonding force required, the risk of direct force impact on enamel, and the risk of causing an adverse temperature increase inside the pulp chamber. The central hypothesis I investigated was that using a diode laser would facilitate the debonding of ceramic brackets by decreasing the SBS, increase the adhesive remnant index (ARI), and avoid causing an adverse temperature increase in the pulp chamber. I investigated these parameters with the goal of establishing an effective and safe protocol for debonding ceramic brackets. At present no guidelines exist, I recognized that guidelines are needed for using a diode laser to debond brackets in relation to the power level and duration of lasing. This study tested two types of ceramic brackets; a monocrystalline bracket called Radiance and polycrystalline ceramic bracket called Clarity. These brackets were selected because they are widely available and in common use. The experimental brackets were monocrystalline and polycrystalline: the laser power settings and lasing times were; negative control (not lased), lased at 2.5 watts for 3 and 6 seconds, and lased at 5.0 watts for 3 and 6 seconds. The diode laser treatments had little effect on the debonding SBSs for the removal of the Radiance monocrystalline brackets. Alternatively, the debonding of the Clarity polycrystalline brackets with laser treatment using 2.5 watts for 6 seconds, 5.0 watts for either 3 seconds or 6 seconds reduced the SBS. The debonding of the Radiance monocrystalline brackets with laser treatment using 2.5 watts for 3 seconds, and 5.0 watts for 6 seconds increased the ARI. The debonding of the Clarity polycrystalline brackets with laser treatment using 2.5 watts for 6 seconds, 5.0 watts for 3 seconds and 6 seconds increased the ARI. The increase in pulp chamber temperature likely to cause thermal injury to the pulp cells was measured against Zack and Cohen¡¯s in vivo standards (2.2¢ªC and, 5.5¢ªC).30 When compared to the 2.2¢ªC standard; the debonding of Radiance monocrystalline brackets with laser treatment using 2.5 watts for 3 seconds were within the standard, and the debonding of Clarity polycrystalline brackets using 2.5 watts for 3 seconds was cooler. When compared to the 5.5¢ªC standard, the debonding of Clarity polycrystalline brackets using 2.5 watts for 6 seconds was cooler. The research results showed that using a diode laser for debonding at 2.5 watts for 6 seconds decreased the SBS for Clarity polycrystalline brackets (reduced the force needed for debonding), increased ARI for Clarity polycrystalline brackets (increased adhesive on enamel), and did not increase the pulp chamber temperature by an injurious amount. The difference in the debonding SBS, ARI and pulp chamber temperatures of the two bracket types probably arose because of the difference in the designs of the two bracket pads. My research results demonstrate the long-term need to design brackets with pads which can be removed easily with a diode laser, leave more adhesive on enamel, and that do not cause injurious temperature increases within the pulp chamber. My research results also demonstrate why guidelines for bracket debonding using diode lasers are needed, which limit the power setting and lasing times. The debonding of brackets using diode lasers could benefit orthodontic patients and become more common if it can reduce the risk of tooth fracture, lower the sensation of pain, reduce the amount of enamel damage, and maintain the vitality of teeth in future studies.

No description available.

No description available.

Within the past few decades a new technology has emerged using Fiber Reinforced Polymers (FRP) to rehabilitate and retrofit reinforced concrete (RC) structures. In FRP shear strengthening applications it is largely recognized that debonding is the prevailing failure mode. FRP debonding typically occurs prematurely as a brittle failure mode that limits the efficiency of the strengthening technique. No systematic tests have been conducted to investigate the capacity gained by anchoring FRP laminates to RC elements in shear applications. The objective of this research program was to study the effects of anchoring FRP laminates to RC members with FRP anchors thereby delaying or potentially eliminating debonding of FRP sheets from the concrete surface. FRP anchors used in this research were made from fibers used as part of FRP sheets that get bundled into a roll with a fanned upper end of the anchor allowing the fibers to be splayed over the FRP sheet. A single shear pull test experiment was developed to study the effects of anchoring FRP laminates using FRP anchors with varying anchor diameters, lengths, and patterning. The results of the experimental portion of this research project were used in combination with finite element analyses to develop models for anchored FRP sheets that can be used in design of shear strengthening applications.

Over the past three decades the use of externally bonded fiber reinforced polymer (FRP) materials for structural strengthening applications has become an accepted and widely used method. A primary concern of FRP structural strengthening systems is that the FRP often debonds from the concrete well before the load capacity of the FRP material is reached. In addition, debonding failures are often brittle and occur with little warning. Past research concluded that fastening FRP sheets with FRP anchors is an effective method for delaying or preventing debonding failures. However, there is a clear lack of research pertaining to fastening FRP sheets with FRP anchors, and a corresponding lack of design guidance. The primary objective of this research program was to better understand the behavior of bonded FRP sheets that are secured with FRP anchors to aid in future development of design recommendations of this anchorage system. This thesis deals with carbon fiber unidirectional sheets applied using the wet layup system. Design parameters that were investigated include: manufacturer of the FRP materials, unanchored and anchored sheets, number of anchor rows and spacing between rows, number of sheet plies (single or double), and length of bonded sheet behind the anchors. A total of sixteen specimens were tested. Experimental results show that FRP anchorage systems are very effective in increasing load capacity by delaying debonding. Finite element models were also developed of anchored and unanchored bonded FRP sheets.

No description available.

No description available.

<p>Premature debonding of externally bonded FRP laminate from retrofitted reinforced concrete (RC) members can lead to inefficient use of FRP and can limit the level of strength increase that can be achieved. In this investigation, novel carbon FRP anchors were used in an attempt to delay the onset of premature debonding and to achieve superior strength. Nine double shear tests were performed on small scale concrete prisms to determine the most suitable epoxy for bonding the anchors to the laminate and the concrete. One type of epoxy increased the ultimate load of the prism retrofitted with two anchors at each end of the laminate 83.7% over the control specimens without anchors. The second phase of the investigation consisted of testing six large scale T-beams with a 4500 mm span, 400 mm height and 500 mm flange width under four point bending. Two beams were tested without FRP reinforcement as control beams, one beam was tested with FRP only epoxy bonded and the remaining three beams were tested with the FRP epoxy bonded and anchored. One of the beams with 30 anchors exhibited a 46% increase in the debonding load over the beam without anchors while the FRP laminate attained a maximum strain equal to 80% of its ultimate strain capacity, a 94% increase over the beam strengthened with only epoxy bonded FRP. The results demonstrate the anchoring system’s effectiveness and a feasible way to efficiently utilize the FRP laminate.</p>

Les chaussées subissent des sollicitations liées au trafic et au climat conduisant à leur dégradation, par fissuration notamment. Il est nécessaire dans le contexte actuel de pouvoir modéliser le comportement de ces structures multicouches endommagées afin de prévoir leur durée de vie résiduelle ou dimensionner des solutions de renforcement. L’objectif de la thèse est ainsi de proposer un outil de calcul dédié à l'analyse 3D des chaussées fissurées ou comportant des discontinuités. L’approche retenue repose sur la modélisation simplifiée d’une chaussée par un empilement de plaques du Modèle Multi-particulaire des Matériaux Multicouches à 5n équations d’équilibre (M4-5n). Un outil de calcul rapide de référence de chaussées 2D fissurées et une méthode de résolution générale du M4-5n par Eléments Finis mixtes sont développés. Le point de départ de la méthode de résolution est l’écriture, pour le M4-5n, du principe variationnel basé sur le théorème de l'énergie complémentaire où la condition de contraintes statiquement admissibles est assurée à partir de multiplicateurs de Lagrange. La discrétisation des efforts généralisés utilise des espaces d’interpolation permettant le bon conditionnement du système d’équations algébriques à résoudre et garantissant la stabilité de la solution. La méthode est implémentée dans FreeFem++. Elle ramène le problème 3D initial à une modélisation EF 2D et conduit à des valeurs finies des efforts généralisés au niveau des fissures ou décollement d’interface. L’outil de calcul final ainsi développé est validé et appliqué à l’étude de la réponse d’une structure fissurée,représentative d’une chaussée testée en vraie grandeur sur le site de l’IFSTTAR. / Pavements are multilayer structures which undergo cracking distress due to traffic and climatic factors. It is important nowadays to be able to model the mechanical response of such damaged pavements in order to assess their residual lifetime or to design reinforcement solutions. In this context, the present thesis aims at developing a numerical tool dedicated to the analysis of pavements incorporating cracks or discontinuities. In the developed approach, the pavement structure is modeled as a stacking of “plate” elements of typeM4-5n (Multi-Particle Models of Multilayer Materials) which considers 5n equilibrium equations. A reference quick 2D calculation tool for cracked pavements and a general solving of M4-5n by the mixed Finite Element (FE) method was developed. The starting point for this method is the derivation for M4-5n of the variational principle based on the complementary energy theorem whose condition of statically admissible stress is taken into account using Lagrange multipliers. Discretization of the generalized stresses involves interpolation spaces, proposed to avoid ill-conditioned system of algebraic equations after discretization and to insure stability of the solution. The developed method is implemented in a FreeFem++ script. In this method, the initial 3D problem can be handled through FE simulations in 2D and finite values of the generalized stresses are obtained at crack and interlayer debonding locations. The developed numerical tool was validated and applied to the study of the mechanical response of a structure with cracks representative of a pavement tested underfull-scale conditions during an accelerated fatigue test performed at IFSTTAR.

Mitigation of the blast risk associated with terrorist attacks and accidental explosions threatening critical infrastructure has become a topic of great interest in the civil engineering community, both in Canada and abroad. One method of mitigating blast risk is to retrofit vulnerable structures to resist the impulsive effects of blast loading. A comprehensive re-search program has been undertaken to develop fibre reinforced polymer (FRP) retrofit methodologies for structural and non-structural elements, specifically reinforced concrete slabs and walls, subjected to blast loading. The results of this investigation are equally valid for flexure dominant reinforced concrete beams subject to blast effects. The objective of the research program was to generate a large volume of research data for the development of blast-resistant design guidelines for externally bonded FRP retrofit systems. A combined experimental and analytical investigation was performed to achieve the objectives of the program. The experimental program involved the construction and simulated blast testing of a total of thirteen reinforced concrete wall and slab specimens divided into five companion sets. These specimens were subjected to a total of sixty simulated explosions generated at the University of Ottawa Shock Tube Testing Facility. Companion sets were designed to study one- and two-way bending, as well as the performance of specimens with simply-supported and fully-fixed boundary conditions. The majority of the specimens were retrofitted with externally bonded carbon fibre reinforced polymer (CFRP) sheets to improve overall load-deformation characteristics. Specimens within each companion set were subjected to progressively increasing pressure-impulse combinations to study component behaviour from elastic response up to inelastic component failure. The blast performance of companion as-built and retrofitted specimens was quantified in terms of measured load-deformation characteristics, and observed member behaviour throughout all stages of response. The results show that externally bonded FRP retrofits are an effective retrofit technique to improve the blast resistance of reinforced concrete structures, provided that debonding of the composite from the concrete substrate is prevented. The test results also indicate that FRP retrofitted reinforced concrete structures may survive initial inbound displacements, only to failure by moment reversals during the negative displacement phase. The experimental test data was used to verify analytical techniques to model the behaviour of reinforced concrete walls and slabs subjected to blast loading. The force-deformation characteristics of one-way wall strips were established using inelastic sectional and member analyses. The force-deformation characteristics of two-way slab plates were established using commonly accepted design approximations. The response of all specimens was computed by explicit solution of the single degree of freedom dynamic equation of motion. An equivalent static force procedure was used to analyze the response of CFRP retrofitted specimens which remained elastic after testing. The predicted maximum displacements and time-to-maximum displacements were compared against experimental results. The analysis indicates that the modelling procedures accurately describe the response characteristics of both retrofitted and unretrofitted specimens observed during the experiment.