Rashmi V. Uddanwadiker

Optimum force system for intrusion and extrusion of maxillary central incisor in labial and lingual orthodontics

BACKGROUND The objective of the present study was to specify an optimum force system for intrusion and extrusion of maxillary central incisor and to compare the effects of bracket positioning at different heights from the incisal edge in Labial Orthodontics (LaO) and Lingual Orthodontics (LiO). METHODS A mathematical model of maxillary central incisor with normal inclination was developed. Four cases of heights of bracket slot from incisal edge were considered both in LaO and LiO viz. 3mm, 4mm, 5mm and 6mm. Based on a mathematical model, an optimum force system consisting of an intrusive or extrusive force (F) and a moment (M) was devised and moment (M) to force (F) ratio (M:F ratio) was estimated in each case. Then, three-dimensional Computer Aided Design (CAD) models of incisor and surrounding structures were prepared. To validate an optimum force system, finite element analysis was carried out and force system with derived M:F ratio was applied in each case. RESULTS In finite element analysis, results were shown in the form of vector graph of nodal displacements along with undeformed and deformed models. The desired intrusion or extrusion of incisor was observed. Thus, force system devised from a mathematical model was validated with finite element analysis in each case. CONCLUSION To achieve intrusion or extrusion, M:F ratios required in LaO were same i.e. 8:1 for aforementioned heights of bracket slot from incisal edge but different in LiO i.e. 0:1, 1:1, 2:1 and 3:1 for the heights of 3mm, 4mm, 5mm and 6mm respectively.

Investigation of effect of fiber orientation on mechanical behavior of skeletal muscle

Background Existing studies have included little discussion of anisotropic and material non linearity of muscle tissue, and fiber orientation–based material properties of skeletal muscle tissue are not reported well in literature. There has been some dispute about material response of muscle in different fiber directions. It is necessary to have a better understanding of fiber orientation based material properties of skeletal muscle, to ensure the accuracy of computational models of muscle. To this end, the aim of this study was to investigate fiber orientation–based material properties in vitro and simulate them with finite element analysis (FEA). Methods Tensile testing was performed on 5 samples of skeletal muscle from a goat at a strain rate of 0.15 s−1 with fiber orientation along the length (P) and 45° incline to the fiber direction (I). FEA was completed using the experimental condition to validate the results of the in vitro test. The cross-fiber direction was simulated using FEA. Results The stresses for all fiber directions at maximum stretch were 1,973.2 kPa for fiber direction P, 1,172 kPa for direction I and 430 kPa for the cross-fiber direction. The tensile strengths of the skeletal muscle were 0.44 MPa for P and 0.234 MPa for I. The elastic modulus of muscle tissue in all fiber directions was 1.59 MPa for fiber direction P (Ep), 0.621 MPa for 45° direction I (EI) and 0.43 MPa for the cross-fiber direction (Ec). The displacement of the muscle sample against the maximum load was small along the fiber direction. The results of the present study showed that muscle tissue was stiffer in the fiber direction than in the cross-fiber direction. Conclusions The stiffness of skeletal muscle is changed as the fiber orientation of skeletal muscle tissue changed.

Non Linear Finite Element Stress Analysis of a Restored Tooth in the Oral Cavity

The aim of the present study is to obtain the stress distribution pattern on the different domains of the tooth in the oral cavity, taking into account non linear properties of the periodontal ligaments (PDL)surrounding the tooth. The stresses and deformation under the action of chewing forces are studied to estimate the risk of tooth fractures. Initially, linear stress and deformation analysis is carried out with three posts different in constitution. However, considering the role of periodontal ligaments, which ensures uniform stress distribution in tooth structure, due to its elastic and non-linear properties, it is felt necessary to simulate the model for non linear analysis. The study reveals that non-linear analysis gives more realistic results as compared to linear analysis. It is observed that under similar loading conditions, the stresses are approximately 25% less in case of non linear analysis and the deformation is 50% more as compared to linear static analysis for an endodontically treated maxillary central incisor. The Dentist can do selection of optimum post core system with better accuracy.Copyright

Linear Finite Element Analysis of a 3-Dimensional Tooth and Its Prototype Model

Dentist, follow root canal therapy to treat teeth with pulpal involvement due to dental caries or as a result of trauma. In order to restore fractured and broken down teeth internal reinforcement is required in the form of a post-core restoration. The post extends into the root canal space and provides retention for the core, which subsequently helps to provide a foundation for the crown restoration. For the treatment procedure, post, core and crown are casted by an indirect procedure by taking the measurements from patient’s tooth in the form of impressions. These impressions are then converted into solid gypsum casts and then wax patterns are developed in order to facilitate casting by the lost wax technique. The final shape of the core and crown and success of the treatment entirely depends upon the skill of the dental technician and involves a number of variables in impressioning, cast poring and wax pattern fabrication. The treatment can be further simplified by making a prototype model of the post, core and the crown by taking the dimensions from the patient’s tooth. This paper presents four prototype models prepared from the solid model of the original tooth and three restored tooth.Copyright