The State of the Art in Endodontics

Nowadays, we use the term “modern endodontics” thanks to new technologies, novel materials, and revolutionary techniques. Various equipment is available to facilitate and improve our endodontic treatments, such as operating microscopes, ultrasounds, lasers, modern alloys for rotary files, powerful irrigation systems, new materials for filling root canals, 3D radiology, and several more. With the aid of the previously mentioned advances, complex endodontic treatments can be carried out safely, hence guaranteeing patients a high level of care and, above all, saving teeth that would otherwise be doomed for extraction. General practitioners and, even more importantly, specialists in endodontics should implement these modern technologies in their practice. This Special Issue will focus on modern endodontics regarding all the recent updates. Full papers of original articles, short communications, and review articles are all invited

Quantitative assessment of covariants of root canal treatment efficacy in human teeth

Clinically relevant cofactors that can demonstrate aspects of root canal treatment quality are of importance to clinicians, researchers and dental instrument manufacturers. Endodontics has been one of the most developing fields of dental science in recent years. There have been new instruments, materials, and methods introduced, which have been very rapidly adopted since most facilitate the root canal treatment process. Considering the current rate of technological developments and the long-term follow-ups required for clinical evaluation of root canal treatment success, clinical trials are not feasible for assessing every variable in treatment. In search of cofactors that could be used to demonstrate the efficacy and quality of a root canal treatment, the effect of surface roughness was investigated in the present thesis. Clinical relevance of surface roughness and its effect on endodontic treatments was assessed in the second chapter. This aim was achieved by comparing biofilm formation on rough and smooth dentine surfaces. Enterococcus faecalis was the microorganism tested to form biofilms on these surfaces because of its role as one of the most important endodontic pathogens in persistent endodontic infections. A novel methodology utilizing flow cytometry to quantify bacteria attached to the surfaces was designed for this experiment. The results showed that rough surfaces harboured a significantly higher number of bacteria compared to smooth surfaces. This indicated that achieving a final smooth surface in root canal treatment reduces the chance of bacterial biofilm formation. Considering the wide range of instrument designs and functions that are used in endodontic treatments, the results demonstrated the necessity for further investigations into their effect on a treated canal's final surface quality. Practical aspects of root canal treatment that may be effective on the canal surface roughness were the focus of the next experiments of this thesis. The third chapter compares the effect of two different filing motions, continuous rotary and adaptive reciprocation, on root canal surface roughness. Continuous rotation and reciprocation are the two most frequently used filing techniques in root canal instrumentation. In this experiment, a filing system that was compatible to work in both rotary and adaptive reciprocation modes was used to answer whether filing motion can affect surface roughness of a root canal. Experiments showed that surface roughness was significantly higher overall in the root canals of teeth prepared with adaptive reciprocation compared to continuous rotary. The results of this chapter showed that roughness of the root canal is a cofactor that can be modified by the clinician. Treatment strategies with different techniques can be implemented even while using identical instruments to achieve smoother treated surfaces. Based on the findings of this study, using a continuous rotary system to prepare canals or to finish the cleaning and shaping stage of a root canal treatment can be beneficial to reducing roughness of the canal surface. Differences between filing systems consists of differences in a mixture of variables including alloy, surface treatment, cross-section, taper, motion, design, etc. The fourth chapter in this series was aimed to evaluate the effect of three different filing systems with different concepts, on the final root canal surface quality. Cleaning and shaping was carried out on teeth with either a single-file reciprocating (Reciproc), continuous rotary (HyFlex EDM) or oscillating self-adjusting file (SAF) system. The results from this chapter showed that the three completely different filing systems resulted in similarly rough root canal surfaces. The high level of roughness in all groups suggested that the three filing systems tested in this experiment were relatively aggressive. File wear results in reduced cutting efficiency and aggressiveness. Since each file undergoes a life cycle and it is eventually worn out, the fifth chapter of this thesis was designed to assess how the effect of file wear translates into changes on the treated root canal surface roughness. In order to evaluate the impact of file wear effectively, Reciproc single-file reciprocating instruments were used for this study. Reciproc files endure the same stress that is usually distributed among a number of files in multi-file systems. This study showed that the amount of wear during three uses, which is within the range of use recommended by the manufacturer, does not affect the final root canal surface roughness. Without consideration of safety of these files in terms of file separation risk, these files can be used up to three times while expecting a similar treatment outcome. However, similar to the previous study, these files left a relatively rough surface in all cases. The key findings in the present thesis were that root canal surface roughness is an effective and modifiable cofactor that can be used to determine the quality of root canal instrumentation and the performance of the instruments used. The two new methodologies developed can be used to test other available endodontic instruments and techniques. These methods can provide a foundation for generating comparable and quantitative data regarding the roughness values and thresholds associated with biofilm formation and different endodontic instruments. Standard levels can be set for future instrument designs once enough research is available regarding the performance of the current instruments and the ideal levels of surface roughness

Fracture Strength of an Endodontically Treated Teeth with Different Access Cavity Designs

AIM AND OBJECTIVES: The aim of this study was to compare the fracture resistance of endodontically treated teeth with different access cavity designs in premolars and molars. OBJECTIVES: 1. This study was designed to compare the fracture resistance in extracted endodontically treated upper and lower first molars and premolars with intact normal teeth . 2. The study was designed to compare the fracture resistance following preparing the root canal access using traditional endodontic cavities, conservative endodontic cavities and ultra conservative endodontic access cavities (Ninja technique) in upper and lower first molars and premolars. 3. The fracture resistance was compared after 24 hours, following restoration of the access cavity with visible light cure composite resin 3M ESPE, after acid etching with 37% phosphoric acid (Actinogel) and using a single coating of two step 7th generation bonding agent (tetric N bond). 4. The resistance to fracture for each specimen was evaluated using universal testing machine (Instron) with a sharp pointer having a ball ended tip with a diameter of 6mm. The ball end was directed towards the central fossa of each specimen irrespective of type of the teeth.The force at which the fracture occurred was noted in Newtons . 5. The resistance to fracture (in newtons) for each type of tooth and each technique of access cavity preparation was recorded and the results were analysed and compared using SPSS software. 6. From the results conclusions were elucidated for the maximum resistance to fracture for upper and lower first premolars and molars following different access cavity preparations and restoring them with visible light cure composite resin. METHODOLOGY: Sixty four maxillary and mandibular premolars and molars were selected for experimental procedure and debris, calculus were removed using ultrasonic scaler and polishing was done using pumice powder and rubber cup. A total of sixty extracted teeth(15 in each group)- upper premolars, and molars and lower premolars and molars were mounted on wax mould. Specimens were assigned into 4 groups TYPE NEC - Traditional access cavity preparation, TYPE CEC - Conservative access cavity preparation, TYPE NEC- Ultra conservative access cavity preparation, GROUP D-Control group(4 teeth). Each group consisted of 15 upper first molars and premolars and 15 lower first molars and premolars. The groups were allocated based on the type of access cavity preparation design that would later be performed.The samples were initially scanned using a 3-D sirona (Sirona Dental Systems, Charlotte, NC, USA) CBCT scanner with spatial resolution of 200μm. The specimens were mounted in custom jigs and scanned in groups of four samples per scan. Then, teeth were endodontically treated and restored with composite resin .Sixty four samples were then loaded to fracture in a mechanical material testing machine (LR30 K; Lloyd Instruments Ltd, Fareham, UK). The maximum load at which fracture occurred were recorded in Newtons. Fractureloads were compared statistically, and the data were analysed using SPSS V20. Significance was set at p ≤ .05. Normality was checked using Shapiro Wilks test and data was found to follow non normal distribution. Kruskal Wallis test .ANOVA was used to compare between the three groups and was followed by Mann Whitney U test for comparison between 2 groups. RESULTS: The resistance to fracture was the least when using the traditional technique (TEC) irrespective of the type of tooth (640-1292 N). Maximum force needed to fracture the specimens was seen in the ultraconservative technique group (NEC) [1600-2900 N]. In GROUP A, mandibular molars while using the traditional technique type (TEC) values ranged between 930-961 N; with conservative technique type(CEC) values ranged between 1859-2100 N; with ultraconservative technique type (NEC) the values ranged between 2320-2450 N; In the maxillary molar Group (B), the values for the traditional technique were between 1000-1292 N; the values for the conservative technique were between 1800-1814 N; and the values for the NEC technique were between 2068-2900 N. In the case of maxillary premolars (Group C), the traditional technique preparation (TEC) resisted the force between 750-1089 N; the conservative preparation (CEC) resisted from 1011-1047 N; and the ultraconservative (NEC) showed resistance values of 1908-2019 N. In the case of mandibular premolars(group D), when using the traditional technique(TEC), the resistance to fracture varies between 640-742 N; whilst using the conservative technique(CEC), the values are between 1600-1842 N. TEC showed significantly lower values than the CEC,NEC(Ninja), and control groups for all types of teeth (P < .05). CONCLUSION: Among the three techniques of access cavity preparation the least resistance value was seen in the traditional technique (TEC) in mandibular first premolar and the maximum resistance value was seen in the ultraconservative access cavity design (NEC) group in maxillary first molar. Overall when comparing the techniques alone the ultraconservative access cavity preparation (NEC) showed the maximum resistance to fracture in comparison with the other two techniques irrespective of type of the tooth

Functionalization of a Ti-based alloy with synthesized recombinant fibronectin fragments to improve cellular response

According to a study of the European Commission, approximately one million hips are replaced by prostheses worldwide every year. The interaction of the human body with foreign materials that are subjected to alternating mechanical load in a highly corrosive environment still provides challenges. The main factors affecting prosthesis failure are stress shielding effect and poor osseointegration. In this thesis the problem of prosthesis failure has been approached from the material and from the osseointegration point of view trying to give a global solution to the problem. Niobium and hafnium, which are demonstrated to be totally biocompatible, were used to design a Ti-based alloy. The effect of the alloying elements regarding microstructure and elastic modulus was studied and the best composition was deeply characterized in terms of microstructure, elastic modulus, corrosion resistance and superficial energy. Recombinant fragments of fibronectin were synthesised spanning the cell attachment site and the heparin binding domain which are important for cell viability. These motifs were used to functionalise the surface of the TiNbHf alloy. Two tethering methods were studied: physisorption and silanisation. Silanisation was not used before to immobilise fibronectin recombinant fragments onto metallic substrates and in this thesis, its good performance was demonstrated. In vitro studies were made with each fragment and with different combinations of the fragments, which showed the importance of the heparin binding domain to obtain a cell response equivalent to that of fibronectin in terms of cell adhesion, proliferation and differentiation.De acuerdo con un estudio de la Comisión Europea, aproximadamente un millón de caderas son remplazadas por prótesis en el mundo anualmente. La interacción del cuerpo humano con materiales externos sujetos a una carga mecánica alternante en un medio altamente corrosivo todavía presenta ciertos desafíos. Los factores que contribuyen principalmente al fallo de una prótesis son el apantallamiento de cargas y la pobre osteointegracion. En la presente tesis el problema de la fallida de prótesis ha sido abordado desde el punto de vista del material y de la osteointegracion en un intento de dar una solución global al problema. El niobio y el hafnio, cuya total biocompatibilidad ha sido demostrada, se han utilizado para diseñar una aleación de titanio. El efecto de dichos aleantes respecto a la microestructura y el módulo elástico ha sido estudiado y la mejor composición ha sido profundamente caracterizada en términos de microestructura, módulo elástico, resistencia a la corrosión y energía superficial. Fragmentos recombinados de fibronectina han sido sintetizados abarcando la zona de adhesión celular y la unión de heparina, las cuales son esenciales para la viabilidad celular. Dichos motivos han sido utilizados para funcionalizar la superficie de la aleación TiNbHf. Dos métodos de unión diferentes han sido estudiados: fisisorción y silanización. La silanización es un método que no se ha utilizado hasta el momento para inmovilizar fragmentos de fibronectina sobre superficies metálicas y en la presente tesis su idoneidad ha sido demostrada. Finalmente, estudios celulares in vitro se han llevado a cabo con cada fragmento y con diferentes combinaciones de ambos, lo cual ha mostrado la importancia de la zona de unión de heparina para obtener una respuesta celular equivalente a la obtenida con la molécula de fibronectina en cuanto a adhesión celular, proliferación y diferenciación

The Effect of Microstructural Defects and Geometrical Features on Fatigue Behavior of Superelastic Nitinol Wires

Nitinol is an alloy of nickel and titanium, which exhibits outstanding functional properties, such as shape memory and superelastic behavior. Superelastic nitinol wires exhibit recoverable strains that are significantly greater than traditional alloys. In most of its applications, nitinol is exposed to cyclic loads, which results in functional and/or structural fatigue that ultimately leads to failure. The classical fatigue theories do not appropriately address the fatigue performance of superelastic nitinol due to the complex nature of the martensitic transformation. It has been shown that the main fatigue crack initiation sites, other than surfaces, are microstructural inhomogeneities such as voids and non-metallic inclusions. The effect of wire size on fatigue performance of superelastic nitinol is not clearly understood. In this research, nitinol wires with three different sizes are subjected to microstructural analysis and low-cycle fatigue tests to understand the effect of wire size on their phase transformations and fatigue life. For this purpose, advanced non-destructive characterization techniques such as X-ray microtomography (μCT) and far-field High Energy Diffraction Microscopy (ff-HEDM) were utilized. This allows for the acquisition of a comprehensive 3-D map of the distribution of microstructural defects within a material, determination of the crystallographic orientation of the material surrounding these defects, as well as the lattice strain of the grains before and during fatigue testing.This study indicated that the superelastic properties and fatigue response of the nitinol wires is strongly influenced by their size and microstructure. Comparing the fatigue data of the wires and analyzing the macroscopic scale results of the 3-D Digital Image Correlation (DIC) technique revealed that the smaller wires exhibited a better functional performance, although they were more vulnerable to surface defects. Conversely, larger wires experienced a more significant microstructural damage during cycling, which was linked to their cooling rate effects. Overall, the results of this research suggest that wire size and microstructure are crucial factors that must be carefully controlled in the design and development of nitinol-based devices

Tensile strength of pine and ash woods – experimental and numerical study

The mechanical properties define the behaviour of the timber under external loads, resulting directly from the timber anisotropic and heterogeneity characteristics. Depending upon the type of applied load the failure can be tensile, shear or torsion. When load enter the plastic regime, the stress-strain relationship passes through a maximum called the tensile strength. The tensile strength of wood being constant above the fibre saturation point, it increases with decreasing moisture content below the fibre saturation. This can be related to where the water is absorbed in the microstructure. Their study is of great interest allowing the rational use of different wood species for structural and building purposes

Aeronautical Engineering: A special bibliography, supplement 60

This bibliography lists 284 reports, articles, and other documents introduced into the NASA scientific and technical information system in July 1975

Physical and mechanical properties of various ceramic brackets, the effect of polishing, cyclic loading, and thermocycling on their properties, and the introduction of resin interpenetrated phase ceramic brackets

Thesis (D.Sc.)--Boston University, Henry M. Goldman School of Dental Medicine, 2002 (Orthodontics).Includes bibliographical references (leaves 136-141)

Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences