O objetivo do presente estudo foi avaliar o efeito da Terapia Fotodinâmica Antimicrobiana (aPDT) com a utilização de azul de metileno a 0,01%, combinado ao laser de diodo, na viabilidade e na produção de polissacarídeos, de biofilmes de S. mutans. Biofilmes de cepas de S. mutans UA159 foram cultivados em discos de resina acrílica e expostos oito vezes por dia, durante 1 min, à solução de sacarose a 10%. Após 48 horas da formação do biofilme, as amostras foram distribuídas aleatoriamente em relação aos tratamentos (n=4): aplicação de solução salina a 0,9% (controle negativo), aplicação de 0,12% de digluconato de clorexidina (controle positivo), ou aplicação da terapia fotodinâmica antimicrobiana. Para aplicação da terapia fotodinâmica antimicrobiana, foi utilizado azul de metileno a 0,01%, combinado ao laser de diodo com comprimento de onda de 660 nm. Foram usados os seguintes parâmetros: área da secção transversal do feixe de laser 0,028 cm&sup2;, potência de 100 mW, energia de 9J, densidade de energia de 320J/cm&sup2;, durante 90s. Os tratamentos foram realizados duas vezes ao dia. Após 120 h, os biofilmes de S. mutans formados sobre cada disco de resina acrílica foram coletados, de modo a determinar o número de bactérias viáveis e a concentração do polissacarídeo extracelular insolúvel (PECI) e do polissacarídeo intracelular (PIC). A análise variância um critério (ANOVA) e o teste de Tukey revelaram que as contagens das bactérias nos biofilmes formados foram significativamente diferentes entre os tratamentos. A aPDT mostrou inibição do crescimento do biofilme, quando comparado ao grupo do NaCl (p<0,05). A concentração de PECI e PIC foi maior no biofilme exposto ao NaCl do que a encontrada nos outros grupos (p<0,05) e não foi observada diferença significativa entre os grupos digluconato de clorexidina e aPDT (p>0,05). De acordo com as condições experimentais do presente estudo, sugere-se que o tratamento realizado duas vezes ao dia com aPDT utilizando-se azul de metileno a 0,01%, combinado ao laser de diodo (&lambda; = 660 nm; 320 J/cm&sup2;; 100 mW; 90s; 9J), diminui a viabilidade do biofilme e afeta sua organização estrutural. / The aim of this study was to evaluate the effect of Antimicrobial Photodynamic Therapy (aPDT) using methylene blue 0.01% combined with diode laser on biofilm viability and polysaccharides produced by Streptococcus mutans. S. mutans UA 159 biofilms were grown on acrylic resin discs and exposed eight times/day for 1 min in a 10% sucrose solution. After the biofilms were allowed to grow for 48 h, they were treated two times/day according to the treatments (n=4): 0.9% saline solution (negative control), 0.12% chlorhexidine digluconato (positive control) or Antimicrobial Photodynamic Therapy (aPDT). For the application of Antimicrobial Photodynamic Therapy has been used methylene blue 0.01% in combination with the diode laser with 660 nm wavelength. The parameters adopted were: spot size of 0.028 cm&sup2;, fixed output power of 100 mW, energy density of 320 J/cm&sup2;, time exposure of 90 s and energy of 9 J. Treatments were performed twice daily. After 120 h of growth, the biofilm formed on each disc was collected to determine the number of viable bacteria, and concentration of the insoluble exopolysaccharide (IEPS) and intracellular polysaccharide (IPS). The analysis of variance one-way (ANOVA) and Tukey test revealed that the counts of bacteria in the biofilms formed differ significantly among the treatments and aPDT showed biofilm inhibition when compared to NaCl group (p<0.05). The concentration of IEPS and IPS was higher in biofilm exposed to NaCl than that found in the other groups (p<0.05) and no significant difference was observed among CHX and aPDT groups (p>0.05). According to experimental conditions of the present work, the results suggest that a twice-daily treatment with aPDT using methylene blue 0.01% in combination with the diode laser (&lambda;=660 nm, 320 J/cm&sup2;, 100 mW, 90 s; 9J) decreases biofilm viability and affects its structural organization.

O objetivo do presente estudo foi avaliar o efeito antibacteriano do laser diodo com diferentes comprimentos de onda em blocos de dentina infectados com Enterococcus faecalis, por meio de análise microbiológica com espectrofotometria e alterações ultraestruturais por meio de microscópio eletrônico de varredura. Treze dentes unirradiculares foram seccionados de forma a obter 100 blocos de dentina intrarradicular. Inicialmente, os blocos foram imersos por 5 minutos em EDTA 17% e em seguida lavados por 5 minutos com água destilada, e então autoclavados por 30 minutos a 120&deg;C. As amostras de dentina foram inoculadas com 1mL de suspensão de E. faecalis em 5mL de BHI (Brain Heart Infusion) e incubadas a 37&deg;C por cinco dias. Após a contaminação, os espécimes foram distribuídos em dez grupos (n=10) de acordo com tratamento de superfície: GI - 5 mL NaOCl 2,5%, GII - 5 mL NaOCl 2,5% + diodo 808nm, GIII - 5 mL NaOCl 2,5% + diodo 970nm, GIV - diodo 808nm, GV - diodo 970nm, GVI - CHX 2%, GVII - CHX 2% + diodo 808nm, GVIII - CHX 2% + diodo 970nm, GIX - controle positivo e GX controle negativo. O crescimento bacteriano foi analisado pela turbidez e densidade óptica do meio de cultura por espectrofotometria (nm). Em seguida, os espécimes foram preparados para análise das alterações ultraestruturais da superfície dentinária em MEV. Os dados foram submetidos ao teste ANOVA um fator e evidenciaram que o GI (77,5 ± 12,1), GII (72,5 ± 12,2), GIII (68,7 ± 8,7), GV (68,3 ± 8,7), GVI (62,0 ± 5,5) e GVII (67,5 ± 3,3) foram semelhantes entre si e diferente estatisticamente dos grupos GIV (58,8 ± 25,0), GVIII (59,2 ± 4,0) e grupos controles (p<0,05). A análise em MEV evidenciou uma matriz orgânica amorfa e derretimento da dentina intertubular quando submetidos à irradiação do laser diodo 970nm, e erosão da dentina intertubular quando irradiada com laser 808nm, sendo que ao associar NaOCl 2,5% ao laser com diferentes comprimentos de onda, observou-se maior erosão intertubular. Conclui-se que todos os protocolos terapêuticos foram capazes de reduzir o contingente bacteriano dos blocos de dentina e ao associar o laser diodo e soluções não houve melhora significativa na redução do contingente bacteriano. / The objective of this study was to evaluate the disinfection degree of dentin blocks contaminated by Enterococcus faecalis caused by different diode laser wavelengths through microbiological analysis with spectrophotometry and ultrastructural alterations by scanning electron microscope. Thirteen uniradicular teeth were sectioned into 100 dentin Intraradicular blocks. Initially, the blocks were immersed for 5 minutes in 17% EDTA and then washed for 5 minutes with distilled water, and then esterilized for 30 minutes at 120&deg;C. The dentin samples were inoculated with 1mL of E. faecalis suspension in 5mL BHI (Brain Heart Infusion) and incubated at 37&deg;C for five days. After contamination, the specimens were distributed into ten groups (n = 10) according to surface treatment: GI - 5 mL NaOCl 2.5%, GII - 5 mL NaOCl 2.5% + diode 808nm, GIII - 5 mL NaOCl 2.5% + diode 970nm, GIV - diode 808nm, GV - diode 970nm, GVI - CHX 2%, GVII - CHX 2% + diode 808nm, GVIII - CHX 2% + diode 970nm, GIX - positive control and GX - Negative control. Bacterial growth was analyzed by turbidity and optical density of the culture medium by spectrophotometry (nm). Afterwards, the specimens were processed for analysis of the ultrastructural changes of the dentin surface in SEM. The data was subject to the One-way ANOVA test and showed that GI (77,5 ± 12,1), GII (72,5 ± 12,2), GIII (68,7 ± 8,7), GV (68,3 ± 8,7) and GVII (67,5 ± 3,3) were statistically similar and statistically different from GIV (58,8 ± 25,0), GVIII (59,2 ± 4,0) and control groups (p <0.05). SEM analysis showed a modified organic matrix layer with an amorphous, intertubular dentin melting when dentin samples were irradiated with 970nm diode laser, erosion of the intertubular dentin in blocks submitted to 808nm diode laser, and a increased erosion of the intertubular dentin when associating NaOCl 2,5% to the laser with different wavelengths. All the therapeutic protocols were able to reduce the bacterial contingent in dentin blocks with the association of laser diode and solutions did not significantly improve the reduction of the bacterial contingent.

Ce mémoire présente les résultats de travaux portant sur l’analyse de la fiabilité de diodes laser de pompe émettant à 980 nm et de photodiodes InGaAs pour des applications spatiales. La sévérité de l’environnement spatial (vide, radiations, contraintes thermomécaniques) impose d’évaluer la robustesse de ces deux technologies qui ont été spécialement conçues pour des applications de télécommunications sous-marines. L’objectif de ce mémoire est donc de proposer une méthodologie d’évaluation de la fiabilité en s’appuyant la caractérisation électro-optique, l’analyse physico-chimique et la modélisation. Les diodes laser ont été vieillies sous ultravide (pression de 10-7 mbar) pendant 5000h sous 800 mA et 60°C. Certains composants, dont l’herméticité du boîtier a été volontairement rompue, ont présenté des défaillances de type COD (Catastrophic Optical Damage). Les caractéristiques des composants, dont le boîtier est resté hermétique, n’ont cependant pas dérivé. Après avoir modélisé les caractéristiques électriques du composant, mené des analyses physiques (AFM, MEB, MET, cathodoluminescence et ToF-SIMS) et calculé la variation de la pression à l’intérieur du boîtier, nous avons estimé la durée de vie du composant fonctionnant sous ultravide à 26 ans.Les photodiodes ont été irradiées par des protons d’énergie comprise entre 30 et 190 MeV sous une fluence comprise entre 5.1010 et 1012 p/cm², entrainant une augmentation du courant d’obscurité de trois décades. La modélisation du courant d’obscurité a permis d’estimer la durée de vie du composant en environnement spatial à 15 ans.Ces travaux ont également contribué à mettre en évidence des mécanismes de dégradation peu documentés (COD sous vide, difficulté d’ajustement avec le NIEL, dégradation du réseau de Bragg exposé aux rayonnements ionisants), ce qui permet de mieux appréhender le comportement des diodes laser et des photodiodes exposées à l’environnement spatial. / In this work, the reliability of 980 nm pump laser diode and InGaAs photodiode modules has been estimated for space applications. The space environment is particularly harsh (vacuum, radiation, thermal and mechanical stresses) for these electro-optical devices, which were designed for long-haul submerged telecommunication applications. The main objective of this thesis is to provide a guideline for the space evaluation of optoelectronic devices, using characterization, physical analysis and modeling.Eight laser diodes were aged in vacuum (10-7 mbar) during 5000h, at 60°C and 800 mA bias current. The hermeticity of four of them was voluntarily broken to simulate a long term vacuum exposition. Three of four non-hermetic devices failed during the ageing, because of COD (Catastrophic Optical Damage) whereas the electro-optical characteristics of hermetic devices remained unchanged. The MTBF of laser diodes operating in vacuum was estimated to 26 years, by means of modeling (electro-optics and pressure) and physical analyses (AFM, SEM, TEM, cathodoluminescence, ToF-SIMS).InGaAs photodiodes were irradiated by protons, with energies ranging from 30 to 190 MeV and fluences ranging from 5.1010 to 1012 p/cm². The dark current increased by three decades after irradiation. The photodiode MTBF was then estimating to 15 years using dark current modeling.This study also permitted to show up almost new failure mechanisms (COD under vacuum, NIEL scaling errors in InGaAs, Bragg grating degradation under ionizing radiation and its effects on laser diode stabilization), which could contribute to the space evaluation of laser diodes and photodiodes for future missions.

This study aimed to evaluate, in vitro, the influence of Diode Laser on the evaporation of adhesive systems solvent applied on the dentin. The groups were distributed in relation to the adhesive systems (Adper Single Bond 2, Adper Scotchbond Multi Purpose, Single Bond Universal, Clearfil SE Bond e Optibond All-in-one) and also to the technique for the evaporation of the solvent (air dry stream or Diode Laser). The degree of evaporation (GE) was determined through the measuring of mass loss through the gravimetric method in an analytical digital balance. To do so, a hundred human third molars had cavities class I made of following a pattern with the diamond burs # 4054 (KG Soresen, Barueri, SP, Brasil), under refrigeration, on which 10 μL were dispensed of each adhesive system, then one of the both techniques of solvent evaporation was applied: air dry stream, from a distance of 10 cm for each 5 seconds (control technique) or Diode Laser irradiated in a continuous mode perpendicularly and from a distance of 1 cm, in the power of 3 W in the interval of 30 seconds (experimental technique). To each one of the adhesive systems and to each one of the evaporation techniques ten monitoring repetitions were realized (n=10). Regarding the experimental technique, the measurements were realized from 5 to 5 seconds, up to 30 seconds. The variation between the initial mass (mi) and the final mass (mf) of the samples, respectively, before and after the application methods of evaporation proposed were turned into GE, by using the following equation: (mi-mf/mi)x100. In this way, to each time interval (5, 10, 15, 20, 25 and 30 seconds) it happened a calculated GE outcome. Those values were submitted to variance analysis (ANOVA) of two factors and Tukey s test as well. To the comparison between both of the evaporation techniques in each adhesive system a t-student test (α=5%) was realized. Basing on the obtained values of the GE, verified on the current study, it is possible to conclude that the irradiation with Diode Laser was capable of inducing the solvent evaporation of the tested adhesive systems, being superior to the control technique when used in the time of 30 seconds, excepted to the Optibond-all-in-one adhesive system. / Este estudo objetivou avaliar, in vitro, a influência do Laser de Diodo sobre a evaporação do solvente de sistemas adesivos aplicados sobre dentina. Os grupos foram distribuídos em função dos sistemas adesivos (Adper Single Bond 2, Adper Scotchbond Multi Purpose, Single Bond Universal, Clearfil SE Bond e Optibond All-in-one) e da técnica para a evaporação do solvente (jato de ar ou Laser de Diodo). O grau de evaporação (GE) foi determinado através da mensuração da perda de massa pelo método gravimétrico. Para tal, 100 terceiros molares humanos tiveram cavidades classe I confeccionadas de forma padronizada com ponta diamantada em alta rotação (# 4054, KG Soresen, Barueri, SP, Brasil), sob refrigeração, nas quais foi dispensado 10 μL de cada sistema adesivo, seguido da aplicação de uma das técnicas de evaporação do solvente: jato de ar a uma distância de 10 cm por 5 segundos (técnica controle) ou Laser de Diodo irradiado em modo contínuo, perpendicularmente e a uma distância de 1 cm, na potência de 3W no tempo de 30 segundos (técnica experimental). Para cada um dos sistemas adesivos e para cada uma das técnicas de evaporação foram realizadas dez repetições de monitoramento (n=10). Para a técnica experimental as mensurações foram realizadas de 5 em 5 segundos, até 30 segundos. A variação entre massa inicial (mi) e final (mf) das amostras, respectivamente, antes e após a aplicação dos protocolos de evaporação propostos, foram transformadas em GE aplicando-se a seguinte equação: (mi-mf/mi)x100. Portanto, para cada intervalo de tempo, 5, 10, 15, 20, 25 e 30 segundos, houve um desfecho GE calculado. Os resultados foram submetidos à análise de variância (ANOVA) de dois fatores e teste de Tukey. Para comparação entre as técnicas de evaporação em cada sistema adesivo foi utilizado teste t-student (α = 5%).Com base nos valores obtidos do GE verificados no presente estudo, o laser provocou maior evaporação do solvente quando comparado ao Jato de ar, no tempo de 30 segundos, exceto para o sistema adesivo acetonado. Desta forma, a irradiação com Laser de Diodo foi capaz de provocar a evaporação do solvente dos sistemas adesivos testados, sendo superior à técnica controle quando utilizada no tempo de 30 segundos, exceto para o sistema adesivo Optibond-all-in-one.

In the manufacturing process of float glass often atmospheric pressure chemical vapour deposition (APCVD) reactors are integrated on-line for the deposition of functional thin solid films. Such functional films have applications in architectural glass, flat panel displays and solar cells. As glass moves downstream in the process, the thin film is deposited at temperatures between 500 to 700°C. The high temperatures make it difficult to monitor the deposition process and thin film quality control is commonly done at the end of the line or at lower temperatures. A time delay therefore exists between the point of thin film deposition and subsequent quality control, which can lead to large quantities of defective product being produced before faults are detected. It is therefore desirable to monitor in the APCVD reactor for rapid feedback of unexpected deviations from desired process conditions, reaction progress and fault detection. High uniformity of film properties across the substrate are important, but APCVD reactors are often empirically designed and the detailed chemical reaction mechanism is unknown. This leads to inefficient gas flow patterns and precursor utilization as well as difficulties in the design of new reactors. The APCVD deposition of tin oxide from the mono-butyl-tin tri-chloride (MBTC) is an example of such a process. Optical monitoring instruments in-situ and in-line on the APCVD reactor provided rapid feedback about process stability and progress non-invasively. Near infrared diode laser absorption spectroscopy (NIR-LAS) monitored the concentration of the reaction species hydrogen chloride (HCl) in-situ and spatially in the coating zone. A mid-infrared grating absorption spectrometer (IR-GAS) with novel pyro-electric array detector monitored the concentration of precursor entering the coating system simultaneously. In combination these instruments provide the means for rapid process feedback. Fourier transform infrared absorption spectroscopy (FTIR) was used to investigate the unknown decomposition pathway of the precursor to find the yet unknown key tin radical that initiates film growth. Stable species forming during MBTC decomposition over a temperature range of 170 to 760°C were investigated but the tin intermediate remains unknown. Computational fluid dynamics (CFD) is routinely employed in research and industry for the numerical simulation of CVD processes in order to predict reactor flow patterns, deposition rates, chemical species distribution or temperature profiles. Two and three dimensional models with complex geometries and detailed reaction models exist. A three dimensional computational fluid dynamics (CFD) model of the used APCVD reactor was built using the Fluent CFD software. The numerical simulation included a chemical model that predicted qualitatively the chemical species distribution of hydrogen chloride in the gas phase. This was confirmed through comparison with NIR-LAS results. Design shortcomings due to inefficient flow patterns were also identified. In combination the optical tools developed provide the means for safe and efficient manufacturing of thin films in APCVD reactors. CFD simulations can be used to increase precursor utilization and film uniformity in the development of new reactor designs.

The Master’s thesis deals with the technology of surface hardening by laser. High power diode laser is used for this purpose. Surface hardening is performed on cast iron BS 1452-77, at different speeds laser head and laser power. In introduction, the theoretical part deals with possible ways of hardening focusing on the benefits of laser hardening. There are mentioned basic parts of laser, type industrial lasers and their application in industry. The final part is mentions the using of material and methods used to evaluate samples. The practical part describes the using devices and carries out evaluation macrostructure and microstructure and evaluation of hardness depending on the distance from the surface.

La capacité des sources laser à concentrer une quantité d’énergie énorme intéresse beaucoup le secteur industriel pour l’usinage et la structuration de la matière. Il faut pour cela rassembler une forte puissance optique sur une surface infime: on parle alors de luminance. La combinaison cohérente permet de répondre à la problématique de l’augmentation de la luminance d’un système laser. Dans le cadre du projet européen BRIDLE, ces travaux sont focalisés sur la combinaison cohérente de lasers à semi-conducteur. Ce type de combinaison nécessite un accord de phase stable entre les différents émetteurs. Plusieurs techniques permettent cette mise en phase; nous étudions en particulier les techniques d’amplification en parallèle ainsi que l’utilisation d’une cavité externe commune. L’originalité se situe dans le développement d’une architecture nouvelle, pensée pour optimiser l’extraction de puissance. La technique consiste à utiliser une cavité étendue commune aux émetteurs à combiner pour leur mise en phase, placée sur leur face arrière. Tout en fournissant un fort retour optique arrière nécessaire à la mise en phase, l’extraction de puissance est maximisée sur la face avant où les faisceaux sont par la suite combinés extracavité. Ce document démontre la bonne adéquation de cette architecture avec les meilleures diodes laser en termes de luminance : les émetteurs à section évasée. L’étude est étendue à une barrette de diodes par l’utilisation d’éléments diffractifs optique permettant la séparation et la combinaison des faisceaux. / Scaling up the brightness of laser diodes is a major research objective in the laser community. The coherent beam of several emitters is the most efficient technique to increase the brightness by constructive interference. An efficient combination can only be achieved in an arrangement that forces the required phase relation between the emitters. Different approaches are investigated: either active phase-locking of amplifiers seeded by a single-frequency laser split into N beams and amplified in parallel, or passive selforganization of emitters in a common laser cavity. We investigate a new coherent combining architecture using a common extended cavity on the back side of diode lasers for phase locking. As a result, the efficiency of the phase-locked laser cavity is increased as compared to standard front-side configurations. Moreover, such an extended cavity placed on the rear-side provides the strong optical feedback required for phase-locked operation. This configuration is demonstrated with high-brightness tapered devices, highlighting the capability of such setup for high power operation. This architecture is then extended to diode laser arrays by the use of diffractive optical elements.

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.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第19029号 / 農博第2107号 / 新制||農||1030(附属図書館) / 学位論文||H27||N4911(農学部図書室) / 31980 / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 谷 誠, 教授 北山 兼弘, 教授 川島 茂人 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

<p> Flexible manufacturing systems and lean production philosophies are in increasing industrial demand. Multiple manufacturing processes integrated into stand alone automated equipment can be utilized to greatly reduce operation costs. New technologies are continually being developed that can be easily combined with related manufacturing processes. Flexible machining and surface hardening operations can be realized in a single set-up by integrating a high-power diode laser (HPDL) within a machine tool structure.</p> <p> The following research presents the concept of integrated laser surface hardening within a machine tool environment. Experimental work was performed using a HPDL for transformation hardening of AISI 4140 steel.</p> <p> Both quasi-steady analytical and transient finite element heat transfer models have been developed. Solutions of the models are compared, which show that the more sophisticated finite element modeling is necessary only if accuracy of peak surface temperature is important. Otherwise, the simpler but faster analytical model can be used to describe the temperature profiles during laser heating.</p> <p> A novel approach using temperature indicating lacquers was shown to be a simple and reliable tool for temperature measurement. The analytical model was further used to find a best fit with the experimental measurements to estimate the fraction of laser power absorbed by the workpiece surface. With the aid of the model, it was shown that the austenite transformation temperature is highly dependent on the scanning speed. For slower speeds, the transform temperature was closer to the A3 temperature given by the iron-iron carbide phase diagram. Tests performed at faster scanning speeds indicated transformation temperatures as high as 1230 °C.</p> <p> Experiments were divided into three series. The first series was performed at slow scanning speeds (200-1000 mm/min) and low laser powers (200-500 W). Hardening was executed on flat workpieces with the laser scanning along a linear path. The second and third test series were performed at fast scanning speeds (2000-8000 mm/min) and higher laser powers (1000-2000 W) with hardening done on rotating cylindrical workpieces. The third tests series consisted of two laser passes in an attempt to increase the penetration depth of the hardened layer. These tests resulted in severe distortion due to melting that would require nearly the entire hardened layer to be machined away post heat treatment. However, if the melting temperature is not significantly exceeded multiple laser passes could be used to increase the thickness of the hardened layer.</p> <p> Higher case depths were realized for the slow tests since these tests have a greater laser-work interaction time. During laser treatment, the uncoated workpieces were left exposed to allow for oxidation and melting in order to increase the fraction of absorbed laser power. The absorptivity is shown to be as high as 85% for these tests.</p> <p> Results are presented in a form useful in selection of laser power and scanning speed to obtain the desired level of hardening, without having to resort to complex analytical or numerical models. Investigations into in-process monitoring show that measurement of surface temperature using an infrared thermometer could be used to control the generated hardened layer reducing process scrap.</p> / Thesis / Master of Applied Science (MASc)