Volume 51, Issue 4

Abstract: The paper presents a brief overview of the polymeric materials recycling problems and especially those connected with polypropylene reprocessing. It is pointed out the manner in which reprocessing of polymeric materials determines the change of the polymeric melts viscous-elastic properties and, as a consequence, the change of rheological behaviour during the recycling process. It was chosen to do the study of the extrusion reprocessing, so, it was determined, after a significantly number of recycling, the modifying of the process parameters needed in order to obtain the best performances and the highest quality of the product. There were compared the screw extruder performances in the case of the first processing and after ten times recycling of the PP. Keywords: recycling, rheological behavior, polymeric materials, polypropylene, screw extruder

Abstract: This paper presents the tribological behaviour of four polymeric materials, polybutylene terephthalate (PBT), PBT + 10% micro glass beads, PBT + 10% polytetrafluoroethylene (PTFE) and PBT + 10% aramid fibers, in order to rank them in dry sliding regime. Tests were done using a block-on-ring module. The test parameters were: the sliding speed was set for 0.25 m/s, 0.50 m/s and 0.75 m/s, respectively, the load and the sliding distance being kept constant (5 N and 5000 m, respectively). There were analyzed the dependence of friction coefficient and linear wear rate on the adding material. Particular wear mechanisms were identified with the help of SEM images. Keywords: PBT-based materials, PTFE, glass beads, aramid fibers, friction coefficient, linear wear rate

Abstract: In this paper we study the influences on mechanical behavior of nonuniformity that appear in bars reinforced with carbon fibers fabric, and respectively carbon-kevlar fibers fabric. We studied the manner in which nonuniformity produced by interruption of a layer or two layers of reinforcement affects the modulus of elasticity, tensile strength and elongation at rupture. In addition to these mechanical properties, we have experimentally determined the coefficient of uniformity for samples with matrix of epoxy resin, reinforced by carbon and carbon-kevlar fibers fabric and which having one and two layers with interruptions. By changing the dimensions of interruptions from layers we analyzed the effect of these nonuniformity on the mechanical properties studied. Keywords: composite materials, uniformity coefficient, elasticity modulus, tensile strength

Abstract: In this study the results of the dry wear tests of composite material used to repair brass made parts are presented. The material belongs to Multimetall Messing category. It has a polymer matrix reinforced with Cu, Zn, Sn particles, and various allotropic forms of silicon dioxide (SiO2). This composite material was tribologically tested in dry friction reciprocating conditions, in ball-on-flat configuration, using the tribometer CETR-UMT-2. The counterpiece was a steel ball. The tests were performed at normal loads of 20, 30, 40 and 50N, over a distance of 100 m, at an average sliding speed of 3.5 mm/s, at room temperature and relative humidity of 50-60% . The results of the analysis were compared with the similar ones obtained under the same conditions for brass. Keywords: composite material, brass, wear track, profilometer, tribometer, reciprocating, ball-on-flat

Abstract: Polymer-bonded explosives (PBXs) are widely used in various engineering applications. Thus, the safety of PBXs has received much attention. In this study, dynamic experiments on a typical PBX were conducted and the mechanical behaviour was studied. Based on the statistical crack mechanics (SCRAM) model, two constitutive models, the Visco-SCRAM model and the Elastic-Plastic-SCRAM model, were developed. Finite element simulations have also been carried out by applying the Visco-SCRAM model and the Elastic-Plastic-SCRAM model in the simulations and good agreement was found between the simulation results and the experimental results. It is suggested that the Elastic-Plastic-SCRAM model can be used for simulating the dynamic behaviour of PBXs under high strain rate conditions. Keywords: PBXs; Elastic-Plastic-SCRAM model; Visco-SCRAM model

Abstract: An experimental study was conducted to investigate the flexural behaviour of the pre-damaged reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP). 25 beams with the size of 2200mm×150mm×200mm (length, width and height) were tested to bending loads. The parameters of the investigation included two pre-damage levels of RC beam, four shear span-depth ratios and two CFRP thicknesses. The effects of these parameters were analyzed on the failure modes, load carrying capacity, flexural stiffness and midspan CFRP strain of the strengthened beams. The results show that CFRP can significantly improve the flexural load carrying capacity of load-damaged RC beams. The pre-damage level has no obvious effects on the flexural behaviour of the strengthened RC beams with CFRP. With the decrease of the shear span-depth ratio, the failure mode of the strengthened beams may transform from debonding induced by intermediate crack (IC) to cover separation near CFRP end. For the strengthened beams failed by IC debonding, more CFRP can provide the higher load carrying capacity and flexural stiffness, but it is not the case for the beams failed by cover separation near CFRP end. Keywords: Carbon Fiber reinforced polymer (CFRP), StrengtheningÿPre-damage, Reinforced Concrete (RC), Shear span-depth ratio, Debonding

Abstract: Rapid Heat Cycle Molding is a new environmental-friendly technology to access high surface quality of plastic products. In this paper, the influence of processing parameters of this technology on weld line of High density polyethylene (HDPE) plastics has been investigated using the orthogonal experiment method. Weld line is evaluated by dE(Euclidean distance). All the parameters influencing weld line have been respectively discussed, while the result shows that heating temperature is the most important factor in the process of forming weld line. From this point of view, the influence of heating temperature on weld line is then further studied from a micro prospective. Keywords: weld line, Rapid Heat Cycle Molding, processing parameters, orthogonal experiment, heating temperature

Abstract: Consolidation of old frail wood by impregnation with polymers is a key step in wooden cultural heritage conservation. Paraloid B72 is an acrylic polymer widely used for this purpose. FTIR spectroscopy, though microdestructive, was found to be a versatile method able to reveal the presence / penetration of Paraloid B72 into the wood structure. A semiquantitative method of investigation was developed with the aim of correlating FTIR data with gravimetric analysis. Relative consolidant retention indexes were calculated based on the integrated areas of relevant absorption bands and compared with gravimetric data of consolidant retention, resulting a fairly good correlation. The method developed on laboratory treated samples made of new sound wood (poplar Populus tremula) was further applied on three case studies, representing heavily degraded wooden artefacts from cultural heritage. Keywords: Paraloid B72, wood consolidation, FTIR, cultural heritage

Abstract: Dental restorative materials due to their composition and structure relatively easily reacts in oral environment, subject to a chemical, electrochemical and biological degradation process. Effects vary from material discoloration and pigmentation, leading to cracks or fractures of fillings. Saliva as oral biotope is a continuous environment favouring these changes. In this saliva are dissolved chemicals coming from the external environment (food, beverages), which modifies the composition and the pH of the saliva, elements which are playing a main role inside the degradation processes, and in particular in electrochemical process. The intensity and its effects are heavily determined both by the composition, structure and quality of materials used and the composition and pH of saliva. Keywords: composite materials, restorative dentistry, artifcial saliva

Abstract: This is a study between ultra-high molecular weight polyethylene (UHMWPE) reinforced with zinc oxide (ZnO) under various filler loadings. These composites were then incorporated with chitosan for hybridization purposes. All composite specimens were prepared by using a hot compression mold through dry ball milling process. Wear and tensile tests were carried out using specific experimental techniques namely pin on disc method as well as universal testing machine, respectively. Results indicated that the addition of ZnO filler up to optimum percentage (12 wt%) has significantly increase the wear resistance of tested composites, in accordance with the minimal weight loss. Contrary, the incorporation of chitosan (1, 2, 3 wt%) in the optimum percentage (12 wt%) of UHMWPE/ZnO composites has slightly reduced the wear resistance of the hybrid composites. For the tensile properties point of view, the results indicated that the yield strength, tensile strength and Young modulus were perpendicularly increased with increasing of ZnO filler loading, up to 12 wt%. Meanwhile, the elongation at break show contradict trend where it was gradually decreased with an increasing ZnO particle loadings. Interestingly, the incorporation of 2 wt% of chitosan in the optimum percentage (12 wt%) of UHMWPE/ZnO composites has further increased the yield strength as well as the elongation at break values of tested hybrid composites. Ultimately, the morphology analysis was also carried out in order to visually justify the state of hybridization and dispersion of fillers within UHMWPE matrix. Keywords: ultra-high molecular weight polyethylene (UHMWPE), hybrid filler, wear resistance, tensile properties, morphology analysis

Abstract: The emergence of self reinforced polymers relaunched the osteosynthesis with resorbable materials, especially in the case of the long bone ends fractures. The improved mechanical resistance and the slow resorbtion are the main advantages compared with previous generations of bioresorbable materials. These qualities prompted us to conduct this study, which focuses on assessing the strength of new implants made of self reinforced polylactic acid (SR-PLA). The implants are designed for osteosynthesis of transcondylar fractures, one of the most common types of distal humerus fractures. Our innovation in terms of implants is to amend a malleolar bone screw so that it can be locked with a Kirschner wire or a thin screw. Thus, an assembly consisting of two screws of this type and a locking wire significantly increases the contact surface between the fragile epiphyseal bone and the implant. The study uses the finite element method and simulates the postoperative loading conditions of the bone-implant assembly. Two CAD models were created representing a stable and an unstable fracture fixed with these implants having the properties of SR-PLA. The models were imported, edited and analyzed in a state of the art finite element program. The evaluation of the interfragmentary displacements, normal stresses in bone and equivalent stresses in implants shows that the osteosynthesis of the stable fracture successfully bears the loads imposed on the entire arc of flexion-extension, while the unstable fracture fixation is fragile at the extremes of the range of motion. The weak point of both assemblies is the metaphyseal cancellous bone. For both models the screws made of SR-PLA held up very well in the given circumstances: the equivalent stresses were low relative to material mechanical resistance. SR-PLA appears as a suitable material for this type of osteosynthesis, but additional biomechanical studies are needed to confirm these results. Keywords: self-reinforced polylactic acid, transcondylar fracture, finite element analysis

Abstract: The paper present the experimental results of a comparative research study between classical and ultrasonically processing by extrusion of the HDPE-220J (High Density Polyethylene) polymeric material. For this material, often used in engineering, have been obtained, in flow activated using ultrasonic waves, relatives increases of the flow rate up to 77% of polymer flowing through extrusion compared with the processing without ultrasounds. These results have been obtained in laminar flowing and no imperfections have been presented due to the extrusion process. The experimental results of the state transition using the differential scanning calorimetry analysis DSC (Differential Scanning Calorimeter), realized for classical and ultrasonically flow activation, confirms that ultrasonic microvibrations produced no changes in the internal structure of the polymer. The ultrasonic device used in this research is subject to a patent application registered at OSIM with number A/00979/2013. Keywords: polymeric materials, extrusion, ultrasounds, flow rate

Abstract: The work is dedicated to the study of the tensile properties of the seven layers of materials which compose the firemen protective clothing. Protective clothing is used to improve the working place safety, diminishing the action of risk factors, which can be of thermal, chemical, biological, mechanical, physical or electric nature and have direct influence on the life and health of the person who carries out a certain activity. The basic material used in manufacturing these products must possess special characteristics, thus ensuring the accomplishment of certain activities which imply the existence of risk factors. The studied firemen equipment has in its composition NOMEX and KEVLAR technical yarns. The analysis of textile material behaviour in the wearing process shows that these are subject to simple or repeated uniaxial or biaxial tensile stresses. The level of these stresses can be close to breaking strength or it can have small, insignificant values; therefore the designer must anticipate the behaviour to such stresses, and this can be done by determining the indices inferred from the stress - strain diagram. Keywords: protection equipment, stress-strain curve, risk factors, Kevlar, Nomex

Abstract: This paper analyses the influence of the grind percentage on some mechanical properties, obtained by the injection of different technical items, which are made of polyamide 6.6 Grivory HTV-3H1 noir 9205, polyamide 6.6 Grivory HTV-45H1 noir 9205 and polyamide 6.6 Grivory HTV-6H1 noir 9205. The specimens are made of the following compositions: new material 100%, new material 80% + grind 20%, new material 60% + grind 40%, new material 40% + grind 60%, new material 20% + grind 80% and grind 100%. The mechanical properties were measured using tensile tests, the Izod impact test and the Shore Durometer hardness test. It has been observed that the hardness of the three tested polymers is hardly influenced by the increase in grind percentage. The shock resistance decreases along with the increase in the grind percentage, and the tensile strength at break increases along with the increase in the grind percentage. Keywords: polyamide 6.6 (PA 6.6), tensile tests, the Izod impact test, the Shore Durometer hardness test

Abstract: Acrylic resin materials are used for making dentures, artificial teeth, veneers, crowns, and temporary crowns, etc. The surface structure of acrylic resins as well as composite resin and ceramic are a favourable environment to the bacterial plaque development. Researches from domain lead to more qualitative acrylic resin and polymers: diacrylic composite resins, epoxide resins, etc. Diacrylic composite resins have superior mechanical and aesthetic properties but are inferior to ceramics. The prosthetic restorations and the presence of different materials in the oral cavity represent a proper environment for the development of microbial flora. The oral cavity health depends on correct prosthetic treatments and a balanced microbial flora that can be controlled with bacteriostatic substances, oral hygiene and correct prosthetic restorations. Bacteriostatic effect of silver nano-particles over plastic dental materials may influence and contribute to the activity of bacterial micro-flora and may influence the evolution of periodontal disease and gingivitis by destroying the dental plaque. Key words: acrylic resin, diacrylic composite resins, crowns, silver nano-particles

Abstract: During endodontic therapy, an important effect of the reparative materials used is to induce periapical recovery and stimulation of osteogenesis. The study aimed to assess the dynamics of alkaline phosphatase levels measured at different time intervals and was conducted by implanting three biomaterials in the rabbit subcutaneous connective tissue, next to the bone. The biomaterials used were: MTA (Mineral Trioxide Aggregate, Dentsply, Tulsa Dental, U.S.A.), Sealapex (Kerr, Switzerland), and DiaRoot Bioaggregate (Inovatore BioCaramixInc, Vancouver, BC, Canada). This study was focused on a quantitative analysis, based on biochemical examination. Keywords: alkaline phosphatase, osteogenesis, biomaterials, endodontic treatment, stomatognathic system homeostatis

Abstract: The purpose of this study was to analyze the interfacial morphology between dentin and a single-component dental adhesive system (Single Bond Universal, 3M ESPE), applied with or without preliminary phosphoric acid etching. In this study, 20 cavities were prepared in extracted teeth and restored with composite resin, using the tested adhesive. The axial sections were observed by scanning electron microscopy. When the adhesive was applied without etching, the hybrid layer was thin and not uniform. The resin tags could rarely be observed within the tubules. Preliminary acid etching of dentin resulted in thicker hybrid layers and augmented resin tags. However, for the tested adhesive, preliminary etching with phosphoric acid did not seem to significantly improve the quality of the dentin sealing. The EDX determination using the Line mode of the elements variation indicated a more severe drop of calcium in dentin when preliminary etching with phosphoric acid was applied comparing to the situations when the adhesive was applied in self-etching procedures. Keywords: bonding system, phosphoric acid, hybrid layer, dentin, self-etch, total-etch

Abstract: Acrylic resins are widely used today both in pediatric dentistry and orthodontics for the manufacturing of space maintainers, interceptive devices or removable orthodontic appliances. All removable orthodontic appliances are composed of porous materials in which microorganisms (fungi, bacteria and viruses) infiltrate, attach and can form biofilms. For this study, two types of materials were chosen in order to test their influence on biofilm formation. For biofilm quantification a strain of Candida spp. was selected among 12 strains isolated from 23 pediatric patients, 7 to 12 years of age, wearing space maintainers or removable orthodontic appliances for at least 4 months at the time of harvest. The materials used in this experiment were the cold-cure acrylic Palapress®vario (Heraeus-Kulzer GmbH, Hanau, Germany) and the visible light acrylic polymerizable system Eclipse (Dentsply DeTrey, Konstanz, Germany). Images of the biofilm formed were obtained using a confocal laser scanning microscope. The images were analyzed using Comstat 2 software. The results showed that in both materials used, the average maximum thickness of the biofilm was above 10 µm. No significant differences were observed in biomass development of the biofilm between the two types of materials tested. Differences were observed in average thickness and maximum thickness of the biofilm. The thickest biofilm was formed on Palapress material. The biofilm formed on Eclipse material surfaces covers 66% of the total aria, while on Palapress material the biofilm covers only 40% of the total aria. These results explain why there are no differences in biomass between the biofilms formed on both materials despite the thickness and average colony size. Keywords: acrylic resins, biofilms, space maintainers, removable orthodontic appliances

Abstract: The aim of this study was to assess the effect of some foods consumed previous to an erosive beverage on dental enamel and cement. The study was performed on 40 human teeth unaffected, extracted for orthodontic braces. The teeth were cut to obtain 80 cervical slices including enamel and dentine/cement areas. The slices were randomly divided in four groups. The 20 samples of control group (group 1) were submitted in 72 hours to nine demineralisation cycles (3 cycles/24 hours) by immersion in Pepsi-Cola ® for 5 min (32 mL/sample). The samples from other three groups were immersed in cheese extract (group 2), broccoli extract (group 3) and undilluted cow milk (group 4) for 5 min (32 mL/sample) previous to Pepsi-Cola ® immersion. For each group, microhardness was measured using digital device CV 400 DAT on 10 samples and surface roughness was determined on another 10 samples by profilometric method using profilometer Taylor Hobson-Surtronic 25. For each sample mean value of Vicker hardness (VH) and mean value of roughness (Ra) were calculated as a result of 5 determinations. In enamel/cement areas the mean value Ra recorded for group 1 was 3,83/3,5 times higher than mean value Ra in study group 4, 2,99/2,95 times higher than mean value Ra in study group 3 and 2,81/3,04 times higher than mean value Ra in study group 2. The mean values of VH of enamel/cement before and after immersion in the tested food varied from 389/68 VH to 235/34 VH in group 4, from 367/64 VH to 354/58 VH in group1, from 382/69 VH to 371/61 VH in group 2 and from 393/63 VH to 381/57 VH for group 3. The consumption of foods like milk, cheese and broccoli before the ingestion of erosive beverages can significantly reduce the erosion of dental enamel and cement. Keywords: erosive potential, milk, broccoli, cheese, enamel, cement

Abstract: One of composite materials used in plumbing is the resin reinforced fiberglass or carbon. The most common applications in the field, refers to fluid storage tanks, piping, tubing, and given that storage tanks used in water supply systems are used to the action of the natural environment, the work deals with issues related to the influence of the external environment on behaviour in time of the composite material of a water storage tank. There are comparatively analyzed two sets of samples with 25-30% of reinforcement, made of 601 general used polyester resin reinforced with fiberglass, CSM 225, CSM 450 and Tesutino 300. The first set of samples was taken from a tank made in 2002 and exposed to the action of the external environment for 10 years. The second sets of samples was taken from a manufactured material in 2014. The research consists in determination of tensile strength after exposure period. By evaluating the tensile strength of the two sets of samples, there is comparatively analyzed the influence of the external environment on the material resistance degradation to the cumulative action of the following factors: UV, snow, rain, dust, wind. The study provides data on setting life of use of the stationary storage tanks, in safe conditions. Keywords: composite materials, tensile strength, stress, strain, storage tank

Abstract: In our study we aimed to identify the individual influence of the main components of wine on the studied composites. The samples were immersed in water, wine, alcohol, tartaric acid solution, at 370C. We measured the reflectance of the surfaces of the composite materials with UNICAM 4 UV-VIS spectrophotometer after 24 h, 7 days and 28 days. The t test results for delta %(xnm)ts of the dental composite material at the same moment in time and different solutions (within the group test) identified a single group which revealed no statistical significant difference. The studied materials at the same moment in time (between group tests) will respond statistically different to the immersing solution. We expect that the changes in the composition of composite materials, including activation systems, inorganic fillers, resin matrix, silane will change the response of the composite materials to the immersion solutions. Keywords: dental composite materials, wine components, reflectance changes

Abstract: The objective of the study was to evaluate the FGP friction fit system as alternative to other procedures for double-crown systems. FGP is a resin material that has a coefficient of friction more favourable than the metal, so it provides minimal wear and long lifetime, high patient comfort, eliminates complicated adjustments tensions arising due to metal to metal framework friction at multiple items. Keywords: FGP, resin, coefficient of friction

Abstract: The tracheal bronchus (TB) in man is described only as a rare anatomical variation, known as the “pig bronchus” or “bronchus suis”. The right-sited TB is normally present in swine. One of the employed method for the training of students and medical residents is the study of corrosion casts. A TB study was conducted on a total of 20 pig tracheobronchial corrosion casts. On the studied corrosion casts the distance between the origin of the TB to carina had an average of 45.1 ± 7.81 mm. The origin range of TB at the level of the right lateral trachea was between 37 and 61 mm above the carina. The mean angle that makes TB with the right lateral trachea ws of 40.29 ± 3.90 degrees with a variation of 15 degrees, ranging between 30-45 degrees. The increasing of the distance between the origin of TB and carina is associated with the decrease of the angle that makes TB with the right lateral trachea. Use of swine tracheobronchial corrosion casts with constant presence of TB, can compensate for lack of clinical material in training of medical students and residents. Keywords: corrosion casts, tracheobronchial system; trachel bronchus, training

Abstract: This paper concerns with a method for automatic detection of voids as a result of epoxy die-attach process of a semiconductor chip to the package. A radiographic image is acquired from the inspected semiconductor chip and package and image processing techniques are employed in order to automatically compute the amount of epoxy die-attach voids. Keywords: image processing, X-ray imaging, image segmentation, artificial intelligence

Abstract: The aim of this study was to evaluate the topography of the main neurovascular bundle located in the posterior aspect of the shoulder and to establish a relatively safe area for a low-risk arthroscopic approach through a posterior portal. A slice anatomy study, using plastinated transparent shoulder joint sections, was performed on ten non-degenerative right shoulder body specimens. Measurements were performed at the level of the suprascapular notch, the coracoid process, and the acromion. The suprascapular nerve was 38.2 ± 0.1 mm, the suprascapular artery 39.4 ± 0.2 mm, and the circumflex scapular artery was 24.8 ± 0.5 mm away from the posterior rim of the acromion at the level of the suprascapular notch. At the level of the coracoid process the suprascapular artery was 34.2 ± 0.5 mm, and the circumflex scapular artery was 50.9 ± 0.3 mm away from the posterior rim of the acromion. Combined measurements of both arteries offered an average distance of 19.8 ± 0.3 mm. The mean distance to the posterior circumflex humeral artery and the axillary nerve was 47.7 ± 1.5 mm and 50.9 ± 0.9 mm, respectively. The present study suggests that, a posterior arthroscopic approach at a level of 4.5 to 5 cm below the posterior rim of the acromion and above the midline of the glenoid joint space poses a low risk for injuries to the neurovascular structures. Keywords: Plastinated cross-sections, arthroscopy, shoulder, axillar nerve

Abstract: For the optimization of the screw and extrusion process design one need to address issues such the interdependence between the geometrical, hydrodynamic, thermal parameters and material behaviour in each screw zone along with the correlations between successive screw zones. For that purpose, the process parameters (material temperature, barrel temperature, screw speed, pressure development in the screw channel), the screw geometry (flat and compression zones) and the matter behaviour (tribological, thermal and rheological) as a function of temperature and pressure were analyzed. The interdependence between the screw design and the extrusion process parameters from a practical point of view, with the aim of designing the most suitable screw with optimal process parameters for a given processed material, was established. Keywords: extrusion; screw design; optimization; process parameters

Abstract: The best tibial fixation technique in anterior cruciate ligament reconstruction remains a challenge to be solved. Due to the increased tension on the graft and the poor bone quality, the slippage of the graft is a determining factor of failure. We propose an alternative supplementary, cost-effective and reliable solution to improve the outcome of the grafts fixation. The results obtained on 10 freshly frozen porcine tibiae were significantly improved (p=0.012) compared to the standard method of fixation. The maximal and mean pull-out force was in conformity with the literature. The bones and tendons used simulates the real human ones, thus the results encourage us to extend the application of the method in clinical cases. Keywords: anterior cruciate ligament, tibial fixation reinforcement, graft slippage

Abstract: This workpaper presents the assessment of the interaction between the dimension of glycol-modified polyethylene terephthalate (PETG) and the attrition of occlusal appliances by determining the degree and area of attrition of dental mouth guards made of PETG plates of different sizes: 0.8mm, 1mm, 1.2mm, 1.5mm, 2mm, 2.2 mm thick. The samples were made by thermoformed using the Erkoform device and inserted into the oral cavity subjects. The evaluation was made 2 weeks, 4 weeks and 6 weeks later. For evaluation it was used coloured occlusal spray. The best results were obtained with the 2 mm thick, but in our study the occlusal appliances with 1,2 mm had good results too. Keywords: occlusal appliances, glycol-modified polyethylene terephthalate (PETG), thermoformed

Abstract: In order to obtain an ideal smile design for our today subjects, more often the dental treatment requires interdiciplinarity. Recent advances in dental materials and techniques promote the opportunity of bonding orthodontic attachments to surfaces other than enamel, like porcelain crowns, veneers, or bridges. This study aims to compare tensile bond strengths of metal brackets bonding to porcelain fused-to-metal crowns, using two different luting cements (RelyX™ Unicem U200 by 3M ESPE, respectively Blugloo by Ormco) and the same surface conditioning system, as well as to determine the findings’ statistical value. The results evaluated by ANOVA, Tukey and Kruskal-Wallis tests indicated no statistically significant differences among the two cements in terms of tensile bond strength. Keywords: metal brackets, ceramic crowns, tensile bond strength, luting cements