to support complete arched fixed implant supported restorations for completely edentulous patients , threaded root form osseointegrated implants were designed . in partially edentulous areas , to support single implant supported crowns and fixed partial dentures , this type of implant is used . many in vitro and animal studies attempted to predict the biomechanical and clinical behavior of dental material and the technique associated with implant - supported prosthesis . in vitro methods include conventional in vitro model analyses , photoelastic analyses , and finite element analyses . in vitro studies are less complicated and less expensive than clinical trials and produce results relatively quickly compared to randomized controlled trials . finite element method fem analysis has been used to provide analytical solutions to problems involving complex geometric forms . posterior teeth have two or three roots , having 450 - 533 mm total anchorage area in good - quality bone , whereas the surface area of a 3.75-mm implant varies from 72 to 256 mm , depending on its length . the molar has a crown surface area of approximately 100 mm , whereas a 3.75-mm implant has cross - sectional area of 10.9 mm the masticatory forces are exerted at an angle mesiodistally and buccolingually , creating bending and torquing vectors on the implant , whereas the tooth can dissipate the occlusal forces efficiently . the cross - sectional area of two 3.75 mm implants is 21.9 mm and of two 4-mm implants is 19.6 mm , whereas for a single 5-mm implant , it is 19.6 mm . for the placement of implant with a wide diameter the wide implant is primarily a means of salvaging a procedure when the previous implant failed , a site had been overenlarged , or the operator desired to place an implant in a recent extraction socket . hence , high abutment fracture and loosening of screws are seen in implants used as single molar replacements . although placing of double implant is technically more demanding than using wide implants , double implants more closely mimic the anatomy of roots being replaced , and double the anchorage surface area and also reduce the rotational forces . usage of double implants instead of single wide - diameter implant might help us to reduce the risk of implant failure and increase the ability of posterior implant to tolerate occlusal forces . immediate functional loading of dental implants has been advocated by several authors in order to minimize the delay between surgical and prosthetic phases . immediate loading is the placement of the prosthetic restoration in functional or nonfunctional loading immediately or within 48 h of surgical procedures . short - term prospective studies on immediate loading of wide - body implants supporting single mandibular molars have reported a cumulative survival rate of 96% . to our knowledge , there are no studies till date that compared single wide - diameter implant with double implant under immediate loading conditions . the purpose of this finite element study was to compare the stresses , strains , and displacements of double versus single implant in immediate loading for replacing mandibular molar . two 3d fem models were made to simulate implant designs . the first model used 5-mm - wide diameter implant to support a single molar crown and incorporated 44,026 nodes and 23,569 elements . the second model used 3.75 - 3.75 double implant design consisting of 71,577 nodes and 37,360 elements . 3d models were meshed using tetrahedral and octahedral elements and modeled by identifying the exact location of nodes after mathematical calculation by considering the inclination of threads . each implant design consisted of fixture of 10-mm length , incorporating v threads with a thickness of 0.2 mm , and having a constant pitch length and height of 0.8 mm and 0.3 mm , respectively , as shown in figure 1a . abutment of height was 5.5 mm with a metal ceramic crown of dimensions 13.5 mm mesiodistally and 10.5 mm buccolingually [ figure 1b ] , metal of thickness 0.4 mm , and layer of cement between abutment and crown of thickness 0.3 mm . a smooth surface collar height of 1.8 mm was incorporated . the implant with the crown was placed in a bone block of height 18.5 mm and width 17.4 mm . the bone consisted of 2 mm of cortical bone and the rest cancellous bone [ figure 1c ] . each model was analyzed with 100 n force applied 45 oblique to the vertical axes directed at central fossa of the crown [ figure 1d ] . the boundary conditions were defined by restraining all nodes at the base of 3d models . ( a - d ) implant dimensions , crown dimensions , bone block , and loading condition , respectively material properties assigned to the implant models the two designs experienced significantly different von mises stresses , von mises elastic strain , and micromotion or total deformation . the total deformation for double implants was 1.3 mm compared to 3.8 mm for 5-mm - wide implant [ figures 2 and 3 ] . the sliding distance of double implants was found out to be 3.6 mm compared to 7.4 mm for 5-mm implant [ figures 4 and 5 ] . the maximum and minimum principal stresses for double implant were 2.676 mpa and 21.58 mpa , respectively , compared to 11.76 mpa and 31.47 mpa , respectively , for 5-mm implant [ figures 6a & b and 7a & b ] . the von mises elastic strain was 1.6 mm for double ( 3.75 - 3.75 ) implant compared to 5 mm for 5-mm implant [ figures 8 and 9 ] . the von mises stress was 47.58 mpa for double implant compared to 186.2 mpa with 5-mm implant [ figures 10 and 11 ] . results obtained for wide and double implants total deformation of double implants total deformation of 5-mm implant sliding distance of double implants sliding distance of 5-mm implant figures 6 : ( a and b ) minimum principal stress of 5-mm and double implants ( a and b ) maximum principal stress of 5-mm and double implants von mises strains of double implants von mises strains of 5-mm implant von mises stresses of double implants von mises stresses of 5-mm implant the present study compared the stresses , strains , and displacements of double versus single implant in immediate loading for replacing mandibular molar . the present study design specifically addressed the problem of long - span edentulous space of more than 12.5 mm . the finite element method is a computer - based technique in which a structure is broken down into many small simple blocks or elements . hence , the stress and deflection of all parts of the structure can be calculated . immediate functional loading has gained importance , and comparable results were found in single - stage surgical procedure as compared to the usual two - stage protocol for implant placement . osseoconductive implant surface , good primary stability , and controlled loading conditions are the expected advantageous results for immediate function . the most commonly lost teeth leading to psychological discomfort to the patient are the mandibular first molars , and thus , they were selected for implant placement . promising results with immediate function for single mandibular molar replacement are available . in vitro and animal studies provide evidence that immediate loading may enhance bone healing and mineralization . the wide - diameter implants were introduced due to their high mechanical stability as compared to that of the standard - diameter ( 3.75 ) implants . this has led to better success with excellent osseointegration due to increased surface area at the bone  implant interface . despite encouraging data obtained from finite element analysis and animal studies , the initial experience with machined - surface wide - body implants showed lower success rates than those reported for standard - sized implants . a failure rate ranging from 10 to 19% in the mandible and from 9 to 29% in the maxilla was presented by earlier clinical studies . furthermore , an augmented marginal bone resorption was observed around the wide - body implants placed in the posterior mandible , as compared to the standard - sized implants . clinical reports have stated wide implants tend to fail more frequently when the posterior edentulous ridges are narrow . with respect to the implants length and width , the crown size restored to one implant has certain discrepancies . when the size of the crown exceeds the implant 's long axis , cantilevers are generated . the ideal replacement is with two implants for a single molar . according to saaduon et al . , a minimum of 12.5 - 14.0 mm of interdental space is needed to successfully replace double standard implants for a missing molar . for immediate loading situations , tensional forces are not transferred by contact zones , but they transfer only pressure and tangential frictional forces . under delayed loading , the fea models bonded the implants perfectly to cortical and cancellous bones . frictional contact is incorporated in this study to simulate the immediate load and to stabilize the implant . this study focused on the values of von mises stress and von mises strain on the surrounding bone . the property of transverse isotropy was given to the cortical and cancellous bone and modeled as homogenous materials . the elements were 10-node tetrahedral structural solid p - elements ( ansys solid 148 ) with three translational degrees of freedom at each node . boundary conditions included constraining all three degrees of freedom at each of the nodes located at the most external mesial or distal aspect of the model . loading was simulated by applying a vertical load of 100 n to the most coronal part of the crown through the long axis of the restoration and implant . it should be noted that great spectra of vertical loads / forces have been reported for patients with endosseous implants ( mean range : 91 - 284 n ) , and the loads appear to be related to the location of the implant , as well as to food consistency . in finite element analysis , a combined load ( oblique occlusal force ) along with the usual axial loads and horizontal forces ( moment causing loads ) is used , as oblique force gives local stresses in the cortical bone , which is more realistic in directing occlusal forces than the others . in this study , 45 oblique loads were considered and the location for force applications was on central fossa . measured bond strengths of many base metal cr alloys have high tensile strength ( 552 - 1034 mpa ) and high elastic modulus ( 200.000 mpa ) . the co  cr alloy used in the present study was also used by williams et al . cr alloy allowed more uniform distribution of stress within the framework , providing more efficient and durable load transfer . cibirka et al . , in an in vitro simulated study , compared the force transmitted to human bone by gold , porcelain , and resin occlusal surfaces and found no significant differences in the force absorption quotient of the occlusal surfaces among these three materials . the process of loosening failure in implants is one of the important determinants for the lack of primary stability . these relative micromovements in the bone  implant interface need accurate evaluation , as they are of more concern in preclinical and clinical contexts . micromotion of dental implant under immediate loading is reflected by evaluation of the gap distance and sliding distance . the gap distance and sliding distance for double implant were significantly less compared to those for single wide implant , with 12% and 51% reduction , respectively . the micromotion of double implant compared to that recorded for single wide implant was decreased by 65.78% . this fem study suggested that micromotion can be controlled better for double implants compared to single wide - diameter implants . when the mesiodistal space for artificial tooth is more than 12.5 mm , the double implant support should be considered . when the load was applied directing the ultimate stress of the cortical bone has been reported to be higher in compression ( 170 mpa ) than in tension ( 100 mpa ) . the maximum principal ( tensile ) and minimum principal stresses ( compressive ) for double implants and 5-mm implant were within the limits of ultimate stress . seong et al . reported least mesiodistal ( md ) strain with 5-mm implant design compared to double implants . authors stated that deeper analyses of experimental results , specifically related to md strains were required . the results of the present study implied the opposite . better mesiodistal support for double implant compared to artificial crown arrangement rangert and sullivan recently suggested that as a result of bending moments , molars replaced by one implant may fracture . they suggested that compared to single - standard 3.75-mm implant , wide implants or multiple implants may withstand the occlusal forces on molars better . in engineering terms , if the applied load is better distributed across the implant and the host bone , the better will be the bony support of the implant . but this only applies if all of the host bone is tightly bound to the implant . compressive and tensile strains are more evenly distributed under delayed loading protocol , which results in a bonded bone implant interface bii because of osseointegration . concentration of stresses at the areas where the implant surface contacts the bone during lateral loading is seen under immediate loading conditions . consequently , in immediate loading protocol , von mises stresses and strains were found , especially from middle to apical third of the implant . the von mises stress for double implant showed 74.44% stress reduction compared to that of 5-mm implant . the biologic response resulting in resorption and remodeling of the bone tissue is stimulated by strains at bone the physiologic loading zone has been reported to be in the 1000 - 3000 microstrain range . the von mises elastic strain was reduced by 67.96% for double implant compared to 5-mm implant . the reduction in von mises strain in double implant compared to single wide - diameter implant is roughly comparable to the experimental results of the study by seong et al . the application of force is directed to the central fossa , which extends along the junctions of slopes of all cusps except mesial and distal cusps . in fem analysis , the force can not be directed at a point ; so , there was dissipation of force along the central fossa as well as to the distal triangular minor fossa , which can be well appreciated from double - implant models , with the distal implant showing the maximum stress and strain compared to the mesial implant , but within limits . minimum of 7-mm ridge width throughout its length is required by wide - diameter 5-mm implant . screw loosening occurred primarily in the single - implant situation and may also be an indicator of overload . strengthening therefore , the use of two implants for the reduction of implant  bone stress is a biomechanically more advantageous solution . it not only minimizes the mechanical problems such as screw loosening but also lowers the stress on implant and bone . the dynamic loads of chewing movements of the mandible were not applied and would cause changes in stress patterns . flexure of posterior mandible during the opening and closing of mandible , along with loads applied were not considered . finally , biologic factors , such as potential difficulty in maintaining proper oral hygiene with the double - implant design , which resembles a molar with an advanced furcation invasion , were not considered , and oral hygiene problems may outweigh any mechanical advantages to this approach . because every molar is not equally wide and long , it is impossible to provide optimal support using only one implant ; however , two implants replace the missing tooth roots more naturally in position and direction . within the limitations of this fem analysis , the following conclusions were drawn for immediate loading of mandibular molar , replacing edentulous space of more than 12.5 mm . double ( 3.75 - 3.75 ) implants were better in eliminating stresses and strains than 5-mm - diameter implantthe micromotion was reduced , enhancing primary stability for double implants , and was lower than 100 m , reducing crestal bone loss and leading to better osseointegrationthe double implants give wider support to a molar restoration in both the mesiodistal and the buccolingual dimensions . this should help to preserve and maintain crestal bone and should also provide better support against buccolingual and mesiodistal bending by eliminating the mesiodistal cantilever . double ( 3.75 - 3.75 ) implants were better in eliminating stresses and strains than 5-mm - diameter implant the micromotion was reduced , enhancing primary stability for double implants , and was lower than 100 m , reducing crestal bone loss and leading to better osseointegration the double implants give wider support to a molar restoration in both the mesiodistal and the buccolingual dimensions . this should help to preserve and maintain crestal bone and should also provide better support against buccolingual and mesiodistal bending by eliminating the mesiodistal cantilever .
purpose : the purpose of this finite element study was to compare the stresses , strains , and displacements of double versus single implant in immediate loading for replacing mandibular molar.materials and methods : two 3d fem ( finite element method ) models were made to simulate implant designs . 
 the first model used 5-mm - wide diameter implant to support a single molar crown . 
 the second model used 3.75 - 3.75 double implant design . 
 anisotropic properties were assigned to bone model . 
 each model was analyzed with single force magnitude ( 100 n ) in vertical axis.results:this fem study suggested that micromotion can be controlled better for double implants compared to single wide - diameter implants . 
 the von mises stress for double implant showed 74.44% stress reduction compared to that of 5-mm implant . 
 the von mises elastic strain was reduced by 61% for double implant compared to 5-mm implant.conclusion:within the limitations of the study , when the mesiodistal space for artificial tooth is more than 12.5 mm , under immediate loading , the double implant support should be considered .