IM0410

research _ restoration I I 09implants4_2010 Fig. 7a & b_Spongy bone deflection in vertical direction (a. wide implant; b. two implants). Figs. 8a & b_Cortical bone deflection in vertical direction (a. wide implant; b. two implants). Tab. 2_Results. _Results and Discussion Results of FEA showed a lot of details about stressesanddeformationsinallpartsofthetwomod- els under the scope of this study. Figures 6a & b showed a graphical comparison between the crowns of the two models which are safe under this range of stresses(porcelaincoating,goldcrown,andimplants showed the same ranges of safety). No critical differ- ence can be noticed on these parts of the system. All differences might be found are due to differences in supporting points and each part volume to absorb load energy (equation 2).** Generally a crown placed on two implants is weaker than the same crown placedononeimplant.Thisfactisdirectlyreflectedon porcelain coating and the two implants that have more deflections. Comparing wide implant model with the two implants from the geometrical point of view it is simply noted that cross sectional area was reduced by 43.3% while the side area increased by 6.5%.Usingoneimplantresultsasareferenceinade- tailed comparison between the two models by using equation (1) resulted in Table 2 for porcelain coating, goldcrown,implant(s),spongyandcorticalbonesre- spectively. Difference%={OneimplantResult—Twoimplants Result}*100/OneimplantResult…(1) Spongy bone deformation and stresses (Table 2) seems to be the same in the two cases. Simple and fast conclusioncanbetakenthatusingonewideimplantis equivalent to using two conventional implants. On the otherhandaveryimportantconclusioncanbeexerted that,underaxialloading,about10%increaseinimplant sideareacanovercomereductionofimplantcrosssec- tion area by 50 %. In other words, effectiveness of in- creasing implant side area might be five times higher than the increasing of implant cross section area on spongy bone stress level under axial loading. Starting fromFigure7a&b,slightdifferencescanbenoticedon spongy bone between the two models results. The stressesonthespongybonearelessbyabout5%inthe two implants model than the one wide diameter im- plant.Theexceptionsaretherelativelyincreaseinmax- imum compressive stresses and deformations of order 12 % and 0.3 % respectively. The bone is known to re- spond the best to compressive and the least to shear stresses22 ,soconsideringthedifferenceincompressive stresseslesssignificant,thetwoimplantswerefoundto haveabettereffectonspongybone. Contrarily, Figures 8a&b,showedbetterperformancewithcorticalbonein caseofusingonewideimplantoverusingtwoimplants, that, deformations in cortical bone are less by 20% while the stresses are less by about 40 %. The stresses anddisplacementsweresignificantlyhigherinthetwo implantmodelduetohavingtwocloseholes,whichre- sultsinweakareain-between. _Conclusions This study showed various results between cortical and spongy bone. It was expected that the maximum stressesinthecorticalbonewasplacedintheweakarea betweenthetwoimplants.Inadditiontobehigherthan the case of using one wide implant. Although the mid- dle part of spongy bone was stressed to the same level in the two cases, using two implants resulted in more volumeofthespongybone absorbed the load energy** whichledtoreductionofstressconcentrationandrate of stress deterioration by moving away from implants. That is considered better distribution of stresses from themechanicspointofview,whichmayresultinlonger lifetime.Porcelaincoatingshowedlessstressincaseof twoimplants,longerlifeforthebrittlecoatingmaterial Fig. 7b Fig. 8aFig. 7a Differences % Porcelain coating (1mm) Gold crown Implants Spongy bone Cortical bone Usum -17.86 -16.70 -8.18 -0.28 -19.57 Uz -11.10 -11.10 -2.72 -0.03 -19.62 S1 31.59 -179.99 -6.72 5.96 -37.17 S3 0.71 -33.44 -310.74 -11.24 -70.43 Sint -1.26 -18.08 -166.39 4.75 -31.82 Seqv 0.25 -10.22 -196.86 4.00 -39.17