before discussing the methodology , a detailed understanding of finite element method and its significance is essential . the basic idea in finite element method is to find the solution for a complicated problem by replacing it by a simpler one . in finite element method , the actual continuum or body of the matter these elements are considered to be interconnected at specified points , which are called nodes or nodal points . a variety of element types and shapes are available to provide users with the required flexibility to meet the compatibility and completeness requirements . it is useful in solving complex structural problems by dividing the complex structures into many simpler and smaller segments . the technical improvement in computers and finite element software , has improved accuracy and speed of this analysis . in the general field of medicine microsoft windows 98 se ( operating system)computer aided designing ( cad ) or modeling software  proe-2001msc microsoft windows 98 se ( operating system ) computer aided designing ( cad ) or modeling software  proe-2001 msc the creation of geometric model , mesh generation , and boundary conditions were applied . in the case of postprocessing simulating , creation of geometric model before developing a finite element model of any system , a geometric model should be generated using cad software . the three - dimensional model to create is a maxillary four incisors and its surrounding structures such as alveolar bone and its periodontal ligament . the morphological dimensions of the teeth used were as given by wheeler 's dental anatomy ( 6 edition ) . from the standard dimensions , the bounding points of the cross - section ( in space x , y , and z coordinates ) were determined and plotted in the cad graphics screen . with the bounding points called the key points , smooth lines were drawn connecting all the key points simulating the profile of the natural tooth . with the sketch model , volume for the section of the body is created ( solid modeling ) [ figures 1 and 2 ] . in a similar manner , the periodontal ligament surrounding the tooth and alveolar bone as it was difficult to obtain the hourglass shape of the periodontal ligament in our study , it was assumed to be 0.25 mm thickness around the radicular portion , although the thickness varies from the alveolar crest to the apex . the alveolar bone was modeled as a rectangular block of structure with labial thickness of 3 mm apically and 5 mm distally to the existing tooth [ figure 4 ] . sectioned natural tooth sectioned natural tooth periodontal ligament surrounding alveolar bone and tooth are modeled alveolar bone modeled in rectangular block finite element model generation ( mesh generation ) this forms the backbone of the finite element analysis . in this stage , the geometric model is converted into the finite element model . the cad model was meshed or divided into several three - dimensional tetrahedral shaped finite elements [ table 1 ] . tetrahedral elements are used in order to precisely mesh the curved and irregular regions present in the tooth [ figure 5 ] . the mechanical properties of each material such as bone , periodontal ligament and the tooth are taken from the previously published values [ table 2 ] . number of elements and nodes in the model mechanical properties for tooth , periodontal ligament and alveolar bone superior surface of bone model the boundary conditions with the areas where the model was restrained from any further movements were assigned as follows , at the superior surface of the bone model ( area representing the palatal surface ) , the area was constrained at their bases to avoid overall rigid body motion 3 [ figure 5 ] . the three - dimensional model was oriented in such a way that the mesiodistal plane was represented by x axis , the vertical plane by the y axis and the labiolingual plane by the z axis . to evaluate the center of resistance the force was applied at a distance of 5.2 mm from the incisal edge of the modeled tooth in the labiolingual direction ( along the z axis ) . the magnitude of force given was 15 g of intrusive force and 120 g of retractive force for each tooth . determination of center of resistance center of resistance of a tooth is a point through which a pure force if acts will produce linear movement without rotation . since , it is a geometric property the finite element analysis itself can easily locate it . microsoft windows 98 se ( operating system)computer aided designing ( cad ) or modeling software  proe-2001msc microsoft windows 98 se ( operating system ) computer aided designing ( cad ) or modeling software  proe-2001 msc the creation of geometric model , mesh generation , and boundary conditions were applied . in the case of postprocessing simulating , the tooth movement and determination of center of resistance were done . creation of geometric model before developing a finite element model of any system , a geometric model should be generated using cad software . the three - dimensional model to create is a maxillary four incisors and its surrounding structures such as alveolar bone and its periodontal ligament . the morphological dimensions of the teeth used were as given by wheeler 's dental anatomy ( 6 edition ) . from the standard dimensions , the bounding points of the cross - section ( in space x , y , and z coordinates ) were determined and plotted in the cad graphics screen . with the bounding points called the key points , smooth lines were drawn connecting all the key points simulating the profile of the natural tooth . with the sketch model , volume for the section of the body is created ( solid modeling ) [ figures 1 and 2 ] . in a similar manner , the periodontal ligament surrounding the tooth and alveolar bone as it was difficult to obtain the hourglass shape of the periodontal ligament in our study , it was assumed to be 0.25 mm thickness around the radicular portion , although the thickness varies from the alveolar crest to the apex . the alveolar bone was modeled as a rectangular block of structure with labial thickness of 3 mm apically and 5 mm distally to the existing tooth [ figure 4 ] . sectioned natural tooth sectioned natural tooth periodontal ligament surrounding alveolar bone and tooth are modeled alveolar bone modeled in rectangular block finite element model generation ( mesh generation ) this forms the backbone of the finite element analysis . in this stage , the geometric model is converted into the finite element model . the cad model was meshed or divided into several three - dimensional tetrahedral shaped finite elements [ table 1 ] . tetrahedral elements are used in order to precisely mesh the curved and irregular regions present in the tooth [ figure 5 ] . the mechanical properties of each material such as bone , periodontal ligament and the tooth are taken from the previously published values [ table 2 ] . number of elements and nodes in the model mechanical properties for tooth , periodontal ligament and alveolar bone superior surface of bone model the boundary conditions with the areas where the model was restrained from any further movements were assigned as follows , at the superior surface of the bone model ( area representing the palatal surface ) , the area was constrained at their bases to avoid overall rigid body motion 3 [ figure 5 ] . the three - dimensional model was oriented in such a way that the mesiodistal plane was represented by x axis , the vertical plane by the y axis and the labiolingual plane by the z axis . to evaluate the center of resistance the force was applied at a distance of 5.2 mm from the incisal edge of the modeled tooth in the labiolingual direction ( along the z axis ) . the magnitude of force given was 15 g of intrusive force and 120 g of retractive force for each tooth . determination of center of resistance center of resistance of a tooth is a point through which a pure force if acts will produce linear movement without rotation . since , it is a geometric property the finite element analysis itself can easily locate it . creation of geometric model before developing a finite element model of any system , a geometric model should be generated using cad software . the three - dimensional model to create is a maxillary four incisors and its surrounding structures such as alveolar bone and its periodontal ligament . the morphological dimensions of the teeth used were as given by wheeler 's dental anatomy ( 6 edition ) . from the standard dimensions , the bounding points of the cross - section ( in space x , y , and z coordinates ) were determined and plotted in the cad graphics screen . with the bounding points called the key points , smooth lines were drawn connecting all the key points simulating the profile of the natural tooth . with the sketch model , volume for the section of the body is created ( solid modeling ) [ figures 1 and 2 ] . in a similar manner , the periodontal ligament surrounding the tooth and alveolar bone were also modeled [ figure 3 ] . as it was difficult to obtain the hourglass shape of the periodontal ligament in our study , it was assumed to be 0.25 mm thickness around the radicular portion , although the thickness varies from the alveolar crest to the apex . the alveolar bone was modeled as a rectangular block of structure with labial thickness of 3 mm apically and 5 mm distally to the existing tooth [ figure 4 ] . sectioned natural tooth sectioned natural tooth periodontal ligament surrounding alveolar bone and tooth are modeled alveolar bone modeled in rectangular block finite element model generation ( mesh generation ) this forms the backbone of the finite element analysis . in this stage , the geometric model is converted into the finite element model . the cad model was meshed or divided into several three - dimensional tetrahedral shaped finite elements [ table 1 ] . tetrahedral elements are used in order to precisely mesh the curved and irregular regions present in the tooth [ figure 5 ] . the mechanical properties of each material such as bone , periodontal ligament and the tooth are taken from the previously published values [ table 2 ] . number of elements and nodes in the model mechanical properties for tooth , periodontal ligament and alveolar bone superior surface of bone model the boundary conditions with the areas where the model was restrained from any further movements were assigned as follows , at the superior surface of the bone model ( area representing the palatal surface ) , the area was constrained at their bases to avoid overall rigid body motion 3 [ figure 5 ] . the three - dimensional model was oriented in such a way that the mesiodistal plane was represented by x axis , the vertical plane by the y axis and the labiolingual plane by the z axis . to evaluate the center of resistance the force was applied at a distance of 5.2 mm from the incisal edge of the modeled tooth in the labiolingual direction ( along the z axis ) . the magnitude of force given was 15 g of intrusive force and 120 g of retractive force for each tooth . determination of center of resistance center of resistance of a tooth is a point through which a pure force if acts will produce linear movement without rotation . since , it is a geometric property the finite element analysis itself can easily locate it . the location of center of resistance has been studied over the years with numerous model systems , these studies include , analytical models , direct measurement in vivo , photo elastic technique , strain gauge technique , laser reflection technique , and holographic method , etc . although these model systems have provided some insight into the displacement characteristics of the tooth to the applied forces , these studies have obvious limitations such as direct measurement in vivo have a distinct disadvantage of being invasive . furthermore , it is difficult to apply controlled force variables on human subjects because of anatomic constraints . the major limitation in studies that used physical models was that synthetic substances were used to simulate the periodontal ligament . many of those materials did not have physical properties exactly duplicating that of the periodontal ligament . in the analytical techniques , the root morphology has been approximated to parabolid , conical or wedge shape leading to different results . to overcome the essence of this method is that a predetermined force is idealized into an assemblage of separated finite regions or elements . these are then considered to be interconnected at specific points called nodes on their common boundaries.[5 . the results obtained in this study is in accordance with the study of matsui et al .