Eine effektive Reinigung und die Formung des Wurzelkanals sind wesentliche Faktoren der Wurzelkanalbehandlung. In den Jahren seit Entwicklung der maschinellen Präparation der Wurzelkanäle wurden viele verschiedene Techniken und Instrumente entwickelt. Die Techniken sollten die Handhabung erleichtern und die Instrumente - durch ihr Design und Material - eine sichere und effiziente Präparation ermöglichen. Die ständige Weiter- und Neuentwicklung machen standardisierte Untersuchungsmethoden zum Vergleich der Instrumente notwendig. In dieser Arbeit wurden folgende Parameter untersucht: Veränderungen des anatomischen Kanalverlaufs durch die Präparation, insbesondere Begradigung gekrümmter Wurzelkanäle, qualitative und quantitative Veränderung der Form des Wurzelquerschnittes im apikalen, medialen und koronalen Kanalanteil, Bewertung der Reinigungsqualität an der Wurzelkanalwand in Bezug auf Smear Layer und Debris, Arbeitssicherheit, bezogen auf Art und Häufigkeit von Zwischenfällen, wie z.B. Instrumentenfrakturen, apikale Blockaden, Perforationen und Arbeitslängenverlusten, Zeitaufwand der Arbeitsschritte Der standardisierte Versuchsaufbau gewährleistete die simultane Analyse dieser Präparations-parameter. An 45 Unterkiefermolaren mit einem Krümmungswinkel zwischen 20° und 40° wurden die mesialen Wurzelkanäle mit den Single-File-Systemen RECIPROC®, Wave One™ und One Shape® aufbereitet und untersucht. Auch eine Anwendung in stark gekrümmten Wurzelkanälen führt nur zu einer geringen Wurzelkanalbegradigung. Es konnten keine signifikanten Unterschiede zwischen den Sys-temen festgestellt werden. Die mittleren Werte der Begradigung sind bei allen Systemen als gering einzustufen. Sie lagen zwischen 1.20° und 1,28°. Die Systeme RECIPROC® und Wave One™ zeigen im Vergleich zu One Shape® kleinere Werte bei der Kanalbegradigung. Die drei Systeme respektieren den originalen Kanalverlauf sehr gut. Die Konizität des One Shape®-Systems scheint bei der qualitativen Präparationsform nach-teilig zu sein. Es lässt sich ein signifikanter Unterschied im medialen Kanalbereich feststellen. Die quantitative Querschnittsanalyse zeigt Mängel im apikalen Bereich. Es wurden vermehrt unbearbeitete Anteile der Kanalwand dokumentiert. Die Systeme unterscheiden sich jedoch nicht. Die Sauberkeit der Kanalwand nach der Präparation lässt bei allen Systemen ein Defizit im apikalen Bereich erkennen. Sowohl beim Debris und auch beim Smear Layer ist die Reinigung in ca. 50% der Wurzelkanäle nicht ausreichend. Der Zeitbedarf für die reine Präparation ist deutlich reduziert. Die reinen Instrumentierungs-zeiten lagen konzentriert bei weniger als 40 sec pro Kanal. Das System One Shape® unter-scheidet sich signifikant. Mit einer Präparationszeit von 36,3 sec ist es das schnellere der drei untersuchten Systeme. Alle Systeme sind als sicher einzustufen. Die Zwischenfälle waren gering und zum größten Teil der verwendeten Methode der Studie zuzuschreiben. Die Fraktur des RECIPROC®-In-struments wurde durch den Spalt zwischen den Sägefragmenten verursacht. Die Untersuchung der drei neuen Single-File-Systeme RECIPROC®, Wave One™ und One Shape® zeigt, dass eine adäquate Präparation des Wurzelkanals mit einer Feile möglich ist. Hinsichtlich der Verschleppung von Keimen in sterile Bereiche der Pulpa und der nicht vertretbaren Kreuzkontamination mit Prionen und anderen Erregern sind die Single-File-Systeme eine ernsthafte Alternative zu Multi-Use-Systemen.

O presente avalia a qualidade da remoção de tecido pulpar após o preparo químico-cirúrgico realizado com a técnica da lima única, descrita por Ghassan Yared. Ainda não há publicado pesquisa sobre os resultados desta técnica. Este estudo compara o percentual de tecido pulpar remanescente em canais radiculares ovais e circulares de incisivos inferiores recém-extraídos que possuíssem polpa viva e armazenados em formol a 10%. Foram comparadas duas técnicas: ProTaper Universal e a técnica da lima única F2. Após uma rigorosa seleção, quarenta e oito dentes com polpa viva que possuíam indicação de extração, foram preparados, classificados em canais ovais e circulares, separados aleatoriamente em 4 grupos e instrumentados com as duas técnicas. O grupo controle, com 12 espécimes, não recebeu nenhum tipo de intervenção. G1 (n=12), canais ovais, instrumentados com a técnica ProTaper Universal; G2 (n=12), canais ovais instrumentados com a técnica da lima única F2; G3 (n=12), canais circulares instrumentados com a técnica ProTaper Universal; G4 (n=12), canais circulares instrumentados com a técnica da lima única F2. Então, seções transversais foram preparadas para avaliação histológica. A análise da quantidade de tecido pulpar remanescente foi avaliada digitalmente. A análise preliminar dos dados brutos em conjunto de todos os grupos experimentais revelou um padrão de distribuição normal por meio do uso do teste Kolmogorov-Smirnov. A análise foi realizada, e os dados brutos foram avaliados através de métodos não-paramétricos: Teste H Kruskal-Wallis. O valor percentual mínimo de tecido remanescente foi de 0% e o máximo de 37,78% entre todos os grupos. Os valores relativos a quantidade de tecido pulpar remanescente variaram entre 0 a 43.47% m2. Os resultados do Teste H Kruskal-Wallis não revelaram diferenças entre as seções mais apicais (p > 0.05). Entretanto, foi encontrada diferença significante entre as seções mais apicais e a seção do terço médio (p < 0.05). Também foram encontradas diferenças significantes quando canais circulares foram comparados com canais ovais independente da técnica de instrumentação utilizada (p < 0.05). Porém, entre as duas técnicas de instrumentação estudadas, tanto nos canais ovais quanto para os os canais circulares, não houve diferença estatística significante (p > 0.05). A proposta deste estudo é a de fazer uma reflexão sobre a real necessidade de um grande número de instrumentos para o total preparo de canais radiculares, uma vez que nenhuma das técnicas foi capaz de debridar por completo o espaço do canal radicular. / The present study evaluates the quality of the pulp tissue removal after chemical and surgical preparation performed with the single file technique, described by Ghassan Yared. This study compares the percentage of remaining pulp tissue in root canals, oval and circular incisors freshly extracted possessing vital pulp and stored in formaldehyde 10%. Two techniques were compared: ProTaper Universal and the single file F2 technique. After careful selection, forty-eight teeth with vital pulp that were likely to extraction, were prepared and divided into oval and circular root canals, divided into 4 groups and instrumented with both techniques. The control group, with 12 specimens, received no intervention. G1 (n = 12), oval canals instrumented with the ProTaper Universal technique G2 (n = 12), oval canals instrumented using the single file F2 technique, G3 (n = 12), the circular canals instrumented with ProTaper Universal, G4 (n = 12), the circular canals instrumented with the single file F2 technique. After biomechanical preparation, cross sections were prepared for histological evaluation. The analysis of the amount of remaining pulp tissue was assessed digitally. Preliminary analysis of the raw data set of all experimental groups revealed a normal distribution pattern by using the Kolmogorov-Smirnov test. The statistical analysis was performed, and the raw data were evaluated by non-parametric methods: H Test Kruskal-Wallis. The minimum percentage was 0% and maximum of 37.78% among all groups. The images for the amount of remaining pulp tissue ranged from 0 to 43.47% m 2. H Test Kruskal-Wallis results revealed no differences among the most apical sections (p> 0.05). However, a significant difference was found at most apical section of the middle third (p <0.05). Significant differences were also found when the circular root canals were compared with oval canals, independent of instrumentation technique used (p <0.05). Neither these techniques studied, on oval or circular root canals had significant statistic difference (p> 0.05). The aim of this study is to reflect about the real need for a large number of files for the preparation of the total root area, since no technique was able to completely debride the root canal space.

O presente avalia a qualidade da remoção de tecido pulpar após o preparo químico-cirúrgico realizado com a técnica da lima única, descrita por Ghassan Yared. Ainda não há publicado pesquisa sobre os resultados desta técnica. Este estudo compara o percentual de tecido pulpar remanescente em canais radiculares ovais e circulares de incisivos inferiores recém-extraídos que possuíssem polpa viva e armazenados em formol a 10%. Foram comparadas duas técnicas: ProTaper Universal e a técnica da lima única F2. Após uma rigorosa seleção, quarenta e oito dentes com polpa viva que possuíam indicação de extração, foram preparados, classificados em canais ovais e circulares, separados aleatoriamente em 4 grupos e instrumentados com as duas técnicas. O grupo controle, com 12 espécimes, não recebeu nenhum tipo de intervenção. G1 (n=12), canais ovais, instrumentados com a técnica ProTaper Universal; G2 (n=12), canais ovais instrumentados com a técnica da lima única F2; G3 (n=12), canais circulares instrumentados com a técnica ProTaper Universal; G4 (n=12), canais circulares instrumentados com a técnica da lima única F2. Então, seções transversais foram preparadas para avaliação histológica. A análise da quantidade de tecido pulpar remanescente foi avaliada digitalmente. A análise preliminar dos dados brutos em conjunto de todos os grupos experimentais revelou um padrão de distribuição normal por meio do uso do teste Kolmogorov-Smirnov. A análise foi realizada, e os dados brutos foram avaliados através de métodos não-paramétricos: Teste H Kruskal-Wallis. O valor percentual mínimo de tecido remanescente foi de 0% e o máximo de 37,78% entre todos os grupos. Os valores relativos a quantidade de tecido pulpar remanescente variaram entre 0 a 43.47% m2. Os resultados do Teste H Kruskal-Wallis não revelaram diferenças entre as seções mais apicais (p > 0.05). Entretanto, foi encontrada diferença significante entre as seções mais apicais e a seção do terço médio (p < 0.05). Também foram encontradas diferenças significantes quando canais circulares foram comparados com canais ovais independente da técnica de instrumentação utilizada (p < 0.05). Porém, entre as duas técnicas de instrumentação estudadas, tanto nos canais ovais quanto para os os canais circulares, não houve diferença estatística significante (p > 0.05). A proposta deste estudo é a de fazer uma reflexão sobre a real necessidade de um grande número de instrumentos para o total preparo de canais radiculares, uma vez que nenhuma das técnicas foi capaz de debridar por completo o espaço do canal radicular. / The present study evaluates the quality of the pulp tissue removal after chemical and surgical preparation performed with the single file technique, described by Ghassan Yared. This study compares the percentage of remaining pulp tissue in root canals, oval and circular incisors freshly extracted possessing vital pulp and stored in formaldehyde 10%. Two techniques were compared: ProTaper Universal and the single file F2 technique. After careful selection, forty-eight teeth with vital pulp that were likely to extraction, were prepared and divided into oval and circular root canals, divided into 4 groups and instrumented with both techniques. The control group, with 12 specimens, received no intervention. G1 (n = 12), oval canals instrumented with the ProTaper Universal technique G2 (n = 12), oval canals instrumented using the single file F2 technique, G3 (n = 12), the circular canals instrumented with ProTaper Universal, G4 (n = 12), the circular canals instrumented with the single file F2 technique. After biomechanical preparation, cross sections were prepared for histological evaluation. The analysis of the amount of remaining pulp tissue was assessed digitally. Preliminary analysis of the raw data set of all experimental groups revealed a normal distribution pattern by using the Kolmogorov-Smirnov test. The statistical analysis was performed, and the raw data were evaluated by non-parametric methods: H Test Kruskal-Wallis. The minimum percentage was 0% and maximum of 37.78% among all groups. The images for the amount of remaining pulp tissue ranged from 0 to 43.47% m 2. H Test Kruskal-Wallis results revealed no differences among the most apical sections (p> 0.05). However, a significant difference was found at most apical section of the middle third (p <0.05). Significant differences were also found when the circular root canals were compared with oval canals, independent of instrumentation technique used (p <0.05). Neither these techniques studied, on oval or circular root canals had significant statistic difference (p> 0.05). The aim of this study is to reflect about the real need for a large number of files for the preparation of the total root area, since no technique was able to completely debride the root canal space.

Diffusion is defined as the movement of a substance down a concentration gradient. The physics of diffusion is well described by Fick’s law. A density-dependent diffusion process is a one in which the diffusion coefficient is a function of the localized density of the diffusing substance. In my thesis I analyze the density-dependent diffusion behavior of two independent processes of biological interest. The first is tumor growth and invasion. The second is single-file diffusion, which in turn has a considerable biological significance, since it has been recently used to model transitions of proteins through DNA molecules. Tumor invasion of normal tissue is a complex process, involving cell migration and proliferation. It is useful to mathematically model tumor invasion in an attempt to find a common, underlying mechanism by which primary and metastatic cancers invade and destroy normal tissue. In our approach we make no assumptions about the process of carcinogenesis, that is, we are not modeling the genetic changes which result in transformation, nor do we seek to understand the causes of these changes. Similarly, we do not attempt to model the large-scale morphological features of tumors such as central necrosis. Rather, we concentrate on the microscopic-scale population interactions occurring at the tumor-host interface, reasoning that these processes strongly influence the clinically-significant manifestations of invasive cancer. We analyze a reaction-diffusion model due to Gawlinski, Gatenby, and others of the acid-mediated tumor invasion mechanism that incorporates the ion concentration as a reaction factor affecting the tumor growth and invasion process. It also adds density-dependent diffusion parameters to the reaction terms yielding independent reaction-diffusion equations for the normal, tumor, and acid populations. For reasonable biological parameters we study the fixed-points of the partial differential equations central of the model and their stability. The fixed-points determine the balance reached by the normal, tumor, and acid populations. As for the second application we present on density-dependent diffusion processes, we consider a model for single-file diffusion that is relevant in a variety of biological processes, for example ion transport in channels. The model is of mathematical and physical as well as biological interest because it exhibits an anomalously-slow tracer diffusion fundamentally different from diffusion without the single-file restriction. We carry out extensive computer simulations to study the role of particle adhesion and space availability (hard-core exclusion) in the model. Both tracer (tagged-particle) and bulk or collective diffusion are considered. Tracer diffusion focuses on the diffusion of the individual particles relative to their starting points, whereas bulk diffusion focuses on the diffusion of the particle distribution as a whole. The nature of the diffusion depends strongly on the initial particle distribution, and both homogeneous and inhomogeneous (for example Gaussian) distributions are considered. For all these models a density-dependent diffusion behavior is confirmed by studying the time evolutions of the moments and widths of these distributions. / Physics

No description available.

This thesis deals with several aspects of translational and reorientational dynamics of water molecules confined inside narrow carbon nanotubes. Water molecules confined in a non-polar, nanoscopic pore exhibit extremely unusual structural and dynamical properties. Adding to the list of anomalies which are already present in bulk liquid water, the confined water “chains” and “shells” springs many more surprises. The relatively weak interaction with the surrounding walls in conjuction with the strong inter-water hydrogen bonds lead o several novel structural and dynamical features, very special to this “strange” phase of water. In this thesis, we present our findings on the detailed molecular level description of translational and reorientational dynamics of this novel phase of anomalously “soft” water. Chapter 1 introduces the varied theoretical, numerical and experimental attempts to demystify the properties of bulk, interfacial and confined water. It also motivates the aspects of diffusion in low dimensional systems, which are often termed “anomalous”. In Chapter 2, we study the structure and dynamics of water molecules inside an open ended carbon nanotube placed in a bath of water molecules. The size of the nanotube allows only a single file of water molecules inside the nanotube. The water molecules inside the nanotube show solid-like ordering at room temperature, which we quantify by calculating the pair correlation function. It is shown that even for the longest observation times, the mode of diffusion of the water molecules inside the nanotube is Fickian and not sub-diffusive. We also propose a one-dimensional random walk model for the diffusion of the water molecules inside the nanotube. We find good agreement between the mean-square displacements calculated from the random walk model and from MD simulations, thereby confirming that the water molecules undergo normal-mode diffusion inside the nanotube. We attribute this behavior to strong positional correlations that cause all the water molecules inside the nanotube to move collectively as a single object. The average residence time of the water molecules inside the nanotube is shown to scale quadratically with the nanotube length. In Chapter 3, we study the diffusion of water molecules confined inside narrow (6,6) carbon nanorings. The water molecules form two oppositely polarised clusters. It is shown that the effective interaction between these two clusters is repulsive in nature. The computed mean-squared displacement (MSD) clearly shows a scaling with time, which is consistent with single file diffusion (SFD). The time up to which the water molecules undergo SFD is shown to be the lifetime of the water molecules inside these clusters. The inter-cluster repulsive interactions are electrostatic and hence long-ranged, which is in complete contrast with shorter ranged steric repulsion in other systems which exhibit SFD. In Chapter 4, we study the anisotropic orientational dynamics of water molecules confined in narrow carbon nanotubes and nanorings. We find that confinement leads to strong anisotropy in the orientational relaxation. The relaxation of the aligned dipole moments, occurring on a timescale of nanoseconds, is three order of magnitude slower than that of bulk water. In contrast, the relaxation of the vector joining the two hydrogens is ten times faster compared to bulk, with a timescale of about 150 femtoseconds. The slow dipolar relaxation is mediated by the hopping of orientational defects, which are nucleated by the water molecules outside the tube, across the linear water chain. In Chapter 5, we study the reorientational dynamics of water molecules confined inside narrow carbon nanotubes immersed in a bath of water. Our simulations show that the confined water molecules exhibit bistability in their reorientational relaxation, which proceeds by angular jumps between the two stable states. The energy barrier between these two states is about 2kBT. The effect of non-Markovian jumps shows up in the ratio of the timescales o the first and second order reorientational correlation functions, which exceeds the value of the ratio in the diffusive limit. The analytical solution of a proposed model is also presented, which qualitatively explains this “unusual” relaxation. These results will have important implications in understanding proton conduction in water-filled ion channels. In Chapter 6, we report the thermodynamic aspects of the translational and re-orientational dynamics of the strongly confined water molecules. Considering the energetics it is surprising that the water molecules spontaneously fill up the nanotube. Thus the thermodynamics of entry of water molecules in the hydrophobic cavity of nanotube. This is generally attributed to the rotational entropy gain by the water molecules on entering the tube, a fact which has not been demonstrated quantitatively so far. We show that the gain in rotational component of the entropy compensates the loss of energy of the water molecules upon entering the nanotube. In Chapter 7, we conclude by summarising the work done in the previous chapters and discuss the future course of actions. We would like to extend the studies on the diffusion of water inside finite nanotubes in the presence of bathwater outside, to nanotube lengths, where it is possible to observe the cross-over from an initial “single file” to and eventual, centre of mass dominated, “normal” diffusion. The mean field estimate of the length of the nanotube required so that one observes a crossover from the initial “single file” to “normal” diffusion at 100 ps is about 700 ˚A. Simulation of such a system would possibly provide an unambiguous answer to the question, whether it is possible to observe SFD in finite carbon nanotubes, filled with water. Regarding the reorientational dynamics, we would like to extend our understanding of the reorientational relaxation of water chains to more more complicated structures. Depending on the diameter of the confining nanotube water molecules form polygons of ice. In the present situation each water molecule can be in only two possible states of orientation. Hence, it would be interesting to predict the reorientational dynamics for other ice structures, where each water molecule can be more “orientational states”. In Chapter 8, we report a work which is unrelated to the rest of this thesis. The work has been done in collaboration with Prof. T. V. Ramakrishnan and Prof. Vijay B. Shenoy. We report a novel method for the calculation of elastic constants of a solid in the frame work of Ramakrishnan-Youssouf density functional theory. The structural aspect of the liquid to solid transition and how it affects the elastic constants of the solids is brought out very clearly. The calculation is analytical and we obtain explicit expressions for the elastic constants. The description of the solid is in terms of the structure factor, S(G), of the coexisting liquid. The elastic constants are expressed as a function of equilibrium parameters, such as c(0), relatedto the compressibility of the liquid. Another important quantity on which the elastic constants depend is the curvature, c"(|G|), of c(|q|)curve at its peak (q= G). These quantities are known experimentally for many systems, and can also be calculated accurately. The shear modulus depends only on c"(|G|), while the bulk modulus has contributions from both c"(|G|) and c(0). The obtained elastic constants do not satisfy the Cauchy relations, in that C12 is not equal to C44. Calculations have been performed for two-dimensional square and triangular lattices as well as bcc and fcc lattices in three dimensions. It is seen that in order to get good agreement between the theoretical and the experimental results of the elastic constants, three body correlations have to be introduced in the calculations for the bcc and the fcc lattices. For the last, in which two shells of reciprocal lattice vectors are appropriate, we point out the modifications needed for choosing the lattice parameter in the unstrained freezing problem. We obtain a new, first principles, quasiuniversal relation for elastic constants, scaled by the melting temperature, that is experimentally satisfied. It is similar to the famous Verlet criterion that S(|G|) = 2.9 at freezing and is free of some of the unphysical aspects of previous work.

Title: Stochastic dynamics and energetics of biomolecular systems Author: Artem Ryabov Department: Department of Macromolecular Physics Supervisor: prof. RNDr. Petr Chvosta, CSc., Department of Macromolecular Physics Abstract: The thesis comprises exactly solvable models from non-equilibrium statistical physics. First, we focus on a single-file diffusion, the diffusion of particles in narrow channel where particles cannot pass each other. After a brief review, we discuss open single-file systems with absorbing boundaries. Emphasis is put on an interplay of absorption process at the boundaries and inter-particle entropic repulsion and how these two aspects affect the dynam- ics of a given tagged particle. A starting point of the discussions is the exact distribution for the particle displacement derived by order-statistics argu- ments. The second part of the thesis is devoted to stochastic thermodynam- ics. In particular, we present an exactly solvable model, which describes a Brownian particle diffusing in a time-dependent anharmonic potential. The potential has a harmonic component with a time-dependent force constant and a time-independent repulsive logarithmic barrier at the origin. For a particular choice of the driving protocol, the exact work characteristic func- tion is obtained. An asymptotic analysis of...

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo deste estudo foi avaliar a espessura mínima radicular remanescente e o desgaste porcentual do terço cervical em raízes mesiais de molares inferiores, após a instrumentação com as técnicas ProTaper Universal e Lima única F2. Foram obtidos 100 primeiros molares inferiores com raízes completamente separadas. Desse total, foram selecionados e incluídos no estudo somente 22 que possuíam dois canais distintos na raiz mesial, comprimento entre 20 e 22 mm e grau de curvatura da raiz mesial com angulação variando entre 10 e 20. Destes, 8 foram eliminados por possuírem uma anatomia muito discrepante, o que limitava o processamento e análise digital das imagens (PADI). Os dentes foram acessados e a patência apical foi realizada em todos os canais determinando o comprimento de trabalho. Em cada dente, cada canal mesial foi instrumentado por uma técnica diferente. As amostras foram posicionadas em um dispositivo de montagem e digitalizadas através de microtomografia computadorizada antes e depois de serem completamente instrumentadas. O volume de interesse, correspondente à região de zona de risco, com uma grande margem de tolerância, tanto em direção apical quanto em direção cervical, foi determinado por 234 fatias, totalizando um comprimento vertical de 3,5 mm, para avaliação quantitativa comparativa. Através de PADI mediu-se, de forma automática, a espessura mínima radicular nos dois canais mesiais, antes e após a instrumentação, para todas as fatias de todos os dentes. A partir destes dados foi calculado o desgaste porcentual. Após o tratamento estatístico das mais de 6500 medidas obtidas, pôde-se concluir que não existiu diferença no desgaste da zona de risco produzido pelas duas técnicas de instrumentação testadas. Em todos os casos a espessura radicular remanescente permaneceu dentro de uma margem de segurança, não havendo, portanto, nenhum caso de rasgo ou perfuração. Dessa forma, ambas as técnicas estudadas foram consideradas seguras quanto ao desgaste da zona de risco da raiz mesial dos molares inferiores. / The aim of the present study was to evaluate the minimal remaining root canal thickness and percentage of dentin removed of the cervical third of the mesial roots mandibular molars after instrumentation with the ProTaper Universal and Single File F2 Techniques. From a total of 100 teeth, only 22 were selected and included in the study by having two distinct canals in the mesial root with length between 20 and 22 mm and degree of curvature presenting angle between 10 and 20. Eight specimens were eliminated because they have a very disparate anatomy that limited the digital processing and analysis of the images (PADI). The teeth were accessed and patency was performed in all canals determining the working length. In each tooth, each mesial canal was instrumented by a different technique. The samples were placed in a mounting device and scanned by microcomputed tomography before and after instrumentation. The corresponding volume of interest to the region of the risk zone was determined by 234 slices, with a total vertical length of 3.5 mm, for quantitative comparative evaluation with a high degree of tolerance. The PADI performed the measures automatically of the minimal thickness of root in both mesial canals, before and after instrumentation for all slices of each tooth. From these data, the percentage of dentin removed was calculated. After statistical analysis of more than 6500 measurements, it was concluded that there was no difference in the wear of the risk zone produced by the two instrumentation techniques tested. In all instrumented specimens, the root thickness remained within a security margin, thus, no case of strip perforation was observed. Therefore, both techniques were considered safe to be used in mesial root of mandibular molars.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo deste estudo foi avaliar a espessura mínima radicular remanescente e o desgaste porcentual do terço cervical em raízes mesiais de molares inferiores, após a instrumentação com as técnicas ProTaper Universal e Lima única F2. Foram obtidos 100 primeiros molares inferiores com raízes completamente separadas. Desse total, foram selecionados e incluídos no estudo somente 22 que possuíam dois canais distintos na raiz mesial, comprimento entre 20 e 22 mm e grau de curvatura da raiz mesial com angulação variando entre 10 e 20. Destes, 8 foram eliminados por possuírem uma anatomia muito discrepante, o que limitava o processamento e análise digital das imagens (PADI). Os dentes foram acessados e a patência apical foi realizada em todos os canais determinando o comprimento de trabalho. Em cada dente, cada canal mesial foi instrumentado por uma técnica diferente. As amostras foram posicionadas em um dispositivo de montagem e digitalizadas através de microtomografia computadorizada antes e depois de serem completamente instrumentadas. O volume de interesse, correspondente à região de zona de risco, com uma grande margem de tolerância, tanto em direção apical quanto em direção cervical, foi determinado por 234 fatias, totalizando um comprimento vertical de 3,5 mm, para avaliação quantitativa comparativa. Através de PADI mediu-se, de forma automática, a espessura mínima radicular nos dois canais mesiais, antes e após a instrumentação, para todas as fatias de todos os dentes. A partir destes dados foi calculado o desgaste porcentual. Após o tratamento estatístico das mais de 6500 medidas obtidas, pôde-se concluir que não existiu diferença no desgaste da zona de risco produzido pelas duas técnicas de instrumentação testadas. Em todos os casos a espessura radicular remanescente permaneceu dentro de uma margem de segurança, não havendo, portanto, nenhum caso de rasgo ou perfuração. Dessa forma, ambas as técnicas estudadas foram consideradas seguras quanto ao desgaste da zona de risco da raiz mesial dos molares inferiores. / The aim of the present study was to evaluate the minimal remaining root canal thickness and percentage of dentin removed of the cervical third of the mesial roots mandibular molars after instrumentation with the ProTaper Universal and Single File F2 Techniques. From a total of 100 teeth, only 22 were selected and included in the study by having two distinct canals in the mesial root with length between 20 and 22 mm and degree of curvature presenting angle between 10 and 20. Eight specimens were eliminated because they have a very disparate anatomy that limited the digital processing and analysis of the images (PADI). The teeth were accessed and patency was performed in all canals determining the working length. In each tooth, each mesial canal was instrumented by a different technique. The samples were placed in a mounting device and scanned by microcomputed tomography before and after instrumentation. The corresponding volume of interest to the region of the risk zone was determined by 234 slices, with a total vertical length of 3.5 mm, for quantitative comparative evaluation with a high degree of tolerance. The PADI performed the measures automatically of the minimal thickness of root in both mesial canals, before and after instrumentation for all slices of each tooth. From these data, the percentage of dentin removed was calculated. After statistical analysis of more than 6500 measurements, it was concluded that there was no difference in the wear of the risk zone produced by the two instrumentation techniques tested. In all instrumented specimens, the root thickness remained within a security margin, thus, no case of strip perforation was observed. Therefore, both techniques were considered safe to be used in mesial root of mandibular molars.