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CAD/CAM - international magazine of digital dentistry

research _ single molar restoration I I 25CAD/CAM 1_2013 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. underthescopeofthisstudy.Figures6a&bshoweda graphicalcomparisonbetweenthecrownsofthetwo models which are safe under this range of stresses (porcelain coating, gold crown, and implants showed the same ranges of safety). No critical difference can benoticedonthesepartsofthesystem.Alldifferences might be found are due to differences in supporting points and each part volume to absorb load energy (equation2).** Generallyacrownplacedontwoimplantsisweaker than the same crown placed on one implant. This fact is directly reflected on porcelain coating and the two implantsthathavemoredeflections.Comparingwide implant model with the two implants from the geo- metrical point of view it is simply noted that cross sectional area was reduced by 43.3% while the side area increased by 6.5%. Using one implant results as areferenceinadetailedcomparisonbetweenthetwo models by using equation (1) resulted in Table 2 for porcelaincoating,goldcrown,implant(s),spongyand corticalbonesrespectively. Difference%={OneimplantResult—Twoimplants Result}*100/OneimplantResult…(1) Spongy bone deformation and stresses (Table 2) seemstobethesameinthetwocases.Simpleandfast conclusion can be taken that using one wide implant is equivalent to using two conventional implants. Ontheotherhandaveryimportantconclusioncanbe exertedthat,underaxialloading,about10%increase in implant side area can overcome reduction of im- plantcrosssectionareaby50%.Inotherwords,effec- tiveness of increasing implant side area might be fivetimeshigherthantheincreasingofimplantcross section area on spongy bone stress level under axial loading.StartingfromFigure7a&b,slightdifferences can be noticed on spongy bone between the two models results. The stresses on the spongy bone are less by about 5 % in the two implants model than the one wide diameter implant. The exceptions are the relatively increase in maximum compressive stresses anddeformationsoforder12%and0.3%respectively. Theboneisknowntorespondthebesttocompressive and the least to shear stresses22 , so considering the differenceincompressivestresseslesssignificant,the two implants were found to have a better effect on spongybone.Contrarily,Figures8a&b,showedbetter performance with cortical bone in case of using one wideimplantoverusingtwoimplants,that,deforma- tionsincorticalbonearelessby20%whilethestresses arelessbyabout40%.Thestressesanddisplacements were significantly higher in the two implant model due to having two close holes, which results in weak areain-between. _Conclusions Thisstudyshowedvariousresultsbetweencortical and spongy bone. It was expected that the maximum stresses in the cortical bone was placed in the weak areabetweenthetwoimplants.Inadditiontobehigher thanthecaseofusingonewideimplant.Althoughthe middle part of spongy bone was stressed to the same level in the two cases, using two implants resulted in morevolumeofthespongybone absorbed the load energy** which led to reduction of stress concentra- tion and rate of stress deterioration by moving away fromimplants.Thatisconsideredbetterdistributionof stressesfromthemechanicspointofview,whichmay resultinlongerlifetime.Porcelaincoatingshowedless stressincaseoftwoimplants,longerlifeforthebrittle coating material is expected. Contrarily more stresses 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