Key Engineering Materials Vol. 638

Abstract: The literature reports that dental cavities are an international public health challenge and treatment of decays especially for young children is a medical problem of great importance. Early childhood caries progress rapidly and can cause functional, physical and dentofacial aesthetic impairment. Recent studies show that caries lesions can compromise children’s quality of life due to the pain and discomfort which could lead to disfigurement, acute and chronic infections and to alteration of meals and sleeping habits. Tooth decay occurs when acids in the mouth dissolve the outer layers of the tooth, stripping the tooth of important minerals. Because dental decay often goes untreated, the cavity grows and more tooth structure is lost. Restorative dentistry has the main purpose of rehabilitating the function and aesthetic of tooth. The structural integrity of the restored teeth depends on the state of stress in their different regions due to occlusal loads. The aim of this study performed with the finite element method is to evaluate the stress and strain distributions in bone structure-primary canine-restorative material assembly when a load of 120N is applied all over the upper surface of the model. Particular attention was given to an accurate computer reconstruction of the canine. Therefore with the aid of a CT scanner the tomography images obtained were processed with a special software (Mimics). Two dental restorative materials, commonly used in practice were chosen for the analysis and the results acquired are compared. Also the contact pressure at the interface bone-deciduous canine and deciduous canine-dental material is evaluated in both cases.

Abstract: Centromedullary nailing is the most preferred surgical technique for the treatment of lower limb fractures and sometimes also on the upper extremity. It is a minimal invasive surgical intervention used mainly for long bones fractures that permits treatment without opening the fracture site thus preserving the local vascularization. With the improved knowledge and understanding of the fracture pattern and of the implantation technique good stability and rapid bone healing is obtained.We present a study on 8 patients with long bones fractures (femur, tibia, humerus) that were surgically treated with intramedullary nailing which failed due to non-union. Implant failure usually occured at 6 to 10 months after surgery. In our group of patients the primary causes of non-union was improper fracture reduction, infection and faulty surgical technique. The implant usually failed several months after loading when the nail was not sharing but bearing all the weight. In this cases the metallic implant usually fails due to fatigue in its weakest point. Loss of reduction, inadequate fixation, a need to change implant and breakage of nails were considered as implant failure.Inappropriate usage of intramedullary nailing technique will lead to nonunion or delayed union and after loading the affected limb the metallic implant will bear all the mechanical forces. This will lead to implant failure and a new difficult surgery for the patients.Revision surgery should address both the biological part and the mechanical part of bone union .

Abstract: The aesthetic composite inlay or ceramic ones are useful for restoring posterior teeth affected by decay processes. The choice of the inlay type can sometimes be a challenge for the dentist. The aim of this study is to identify the optimal type of an inlay used for second-class cavities that can assure a good long-term prognosis of dental restoration. In order to achieve this study, it was performed an 3D analysis of stresses recorded in a premolar restored with a composite inlay and a ceramic inlay, the simulation being done by finite elements method (FEM) using Ansys program. The study results showed that stresses registered in the tooth restored through ceramic inlay are more favorable than those recorded in the case of the tooth restored with composite inlay. The aesthetic composite inlays are preferred instead ceramic ones by many practitioners because of the advantages it presents: requires minimal preparations, technique is easier thanks to the easier handling of composite material, allow future adjustment of the occlusal surface, being easily adjusted and repaired, are radiopaque and, last but not least, have a lower cost. The question that arises frequently in medical practice is related to inlays behavior in case of functional requirements, depending on the material from which they are made. Configuration of preparation, the technique and the materials used for cementing, and restorative materials can influence the type of resistance to fracture of these restorations. The ability of restorative materials to support the masticatory forces and distribution of stresses in the vicinity of the adhesive interface constitutes a decisive factor in acquiring a restoration with a high degree of resistance to fracture.

Abstract: The need for reliable data on thermophysical properties of materials has increased continuously in the last period. The existing data, except for some pure elements or alloys and compounds, often unreliable, and in many cases the need for accurate and acceptable data, can only be achieved by measuring a given property. This paper focuses on elements of the used test methods associated with the description of the newly introduced parameter (effectiveness of dental coating). The selected method was the “pulse method” for determining thermal diffusivity (the method allows simultaneous determination of thermal diffusivity, specific heat capacity and thermal conductivity) directly applicable in the study of the thermal compatibility of metal-ceramic systems in dental applications.

Abstract: In whole wide world, lots of individuals lose teeth from different causes. In these cases, in first phase, a dental implant is the best solution. In some cases, as the last solution, a dental prosthesis is needed. To correct these disorders, rehabilitation treatments with adequate dentures, either fixed or removable, are indicated. [6] The forces that appear during mastication are influenced by occlusion type and space distribution of teeth. In case of persons that have a dental prosthesis the forces that occurred during mastication can be reduced if the dental prosthesis is correctly generated. A mastication simulator is any device that reproduces the conditions present during the process of chewing in order to reconstruct the complicated process of mastication outside the body. [5] The aim of this paper is to produce a device that can simulate the mastication and use it to determinate the mastication forces that appears during the mastication of different foods types. On the device that was build can be placed different dental prosthesis. [2] Using the device adjustment facilities we are able to simulate any type of occlusion. Using this device, a mechanical testing equipment and different types of food we are able to determinate the vertical force that occur. Base on these results we will be able to determinate if the dental prosthesis was correctly produced.

Abstract: The aim of this study is to assess the histological efficiency of low level laser therapy (LLLT) with respect to the acceleration of bone regeneration after surgical treatment of intrabony defects. Twenty patients with intrabony defects, aged between 20-45, non-smokers, good health condition present at the time of the surgery, were randomly divided in two groups, control, ten parients, and test group, ten patients. Informed consent was obtained. Each patient presented at least one periodontal defect treated by bone allograft. The test group received postsurgical treatment with low lever laser therapy (LLLT). The equipment used was OsseoPulse AM300, at an intensity of 20mW/cm², for 20 minutes per day, for 21 consecutive days. The control group received no treatment with LLLT. The bone formation was evaluated in both groups at baseline and 6 months postoperative by the means of tissue biopsy followed by a histological analysis. The histological study of the test samples at 6 months after regeneration showed bone formation without inflammatory cells and occasional nonviable bone consistent with regenerating bone. No evidence of the grafted material was present. The histological study suggests that in 6 months there was new bone formation in the defects treated with LLLT. Clinical data indicate the possibility of more rapid wound closure and subsequent healing in zones treated with LLLT as compared with control.

Abstract: Dental medicine represents a very important part of our life. As our appearance or looks is a major concern for us, a beautiful smile can improve our life. Moreover, our teeth health reflects on our overall health. This paper presents a method for highlighting the differences between a natural tooth and a prosthetic one. In order to determine the stress distribution in teeth during the use of prosthetics pivots, several virtual geometric models of the teeth were created (canine, first premolar, first molar and second molar), both in their natural form and when using pivots. The results obtained from these analyses were compared in order to reveal the behavior of a prosthetic tooth during normal life loads. Such results of real life behavior can be used by dental medics in order to predict the life span of restored teeth.

Abstract: The elbow total implant is in appearance a simple orthopedic device, with few components and no complex mechanisms. In spite of the reported successful surgical interventions, there are still many medical reports which show that a certain percentage of the implants fails.In our work we conceptually approach a computer assisted design of a Coonrad-Morrey like total elbow implant and simulate the mechanical behavior by finite element analysis, for three different loads (10 N, 50 N, and 100 N). Materials used for simulation were Ti, TiNi and Ti6Al4V for the metallic components, and UHMWPE for bushing polymeric components. Through our results we confirmed the practical observations, namely that the hinge mechanism is an important region where the failures initiates from, as the highest stress is concentrated on the polymeric components.

Abstract: The purpose of this paper is to analyze the overdenture fixed on two mandibular implants anchored on staples, determining the behavior of the prosthesis. It‘s consider this ansamble must operate under of occlusal forces present during various functional activities such as mastication proccess. To analyze the stresses induced by masticatory forces on the anchoring system and mandibular overdenture retention using two implants by type staple system, and its displacement, was built, using the finite element method, a three-dimensional numerical model of a mandibular overdenture with mixed support: implant and mucosa. Geometrical model was developed having as reference a real mandibular complete denture that was 3D scanned previously. These images, which contains three-dimensional size of the prosthesis was imported into a CAD program (Computer Analysis Design) for obtaining geometrical model consisting of lines, surfaces and volumes. The numerical model designed examines various cases of arrangement of total prosthesis implant support in relation to the median axis of the mandible in order to determine the best case form for fixing the prosthesis. Numerical analyzes were performed using Ansys software, a program that uses the finite elements method.

Abstract: The mathematical theories of bone mechanical adaptation are based on a nonlinear ordinary differential equation which governs the evolution of bone density with respect to the applied loads. If the density distribution achieved within a certain bone model resembles the expected distribution observed in the real bone, then the mathematical theory is usually thought to be suited for such simulations. As test problem, it was extensively used the coronal section of the proximal femur. This section inspired the very creation of the mathematical models following Wolff’s observations regarding trabecular architecture. However, the lack of quantitative data when using the bi dimensional femur model prevents the quantitative validation of the adaptation mathematical models. Using computed tomography is now possible to reconstruct the three dimensional geometry of bones and also to estimate the apparent density based on correlations with the Hounsfield units. This method was already used to quantitatively validate the simulation of bone remodeling into different bones and proved to be efficient. The paper presents the apparent density distributions achieved into the 3D model of the proximal femur by coupling the finite element method with the Stanford bone adaptation equation. The densities obtained in this manner are compared by those determined from the tomographic data of the same bone. The purpose relies on establishing whether the three dimensional end proximity of the femur bone can be used for quantitative validation of remodeling simulations.