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
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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
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
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
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
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
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
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
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
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