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CAD/CAM - international magazine of digital dentistry

I research _ single molar restoration 26 I CAD/CAM 1_2013 werefoundonthegoldcrownplacedontwoimplants due to its volume reduction (less material under the same load). This is clearly seen in increasing stresses on the two implants, that more load effect was trans- ferred through the weak crown to the two implants. That showed maximum stresses in the area under the crown, while the wide implant showed maximum stresses at its tip. Looking to energy** absorption and stress concentration on whole system starting from coating to cortical and spongy bone, although the stress levels found was too low and far from cracking danger,thefollowingconclusionscanbepointedout; the total results favourise the two implants in spongy bone and the wide implant in the cortical layer, but thealveolarboneconsistsofspongybonesurrounded by a layer of cortical bone. It’s also well known that according to the degree of bone density the alveolar bone is classified to D1,2,3,4 23 in a descending order. So, providedthattheedentulousspaceafterthemolarex- tractionpermits,it’srecommendedintheharderbone quality (D1,2) to use one wide diameter implant and in the softer bone (D3,4) quality two average sized im- plants. Therefore more detailed study to compromise betweenthetwoimplantssize/designandintermedi- atespacecanputthisstressvaluesinsafe,acceptable, andcontrollableregionunderhigherlevelsofloading. **Theareaunderthe - curveuptoagivenvalueofstrainisthetotal mechanicalenergyperunitvolumeconsumedbythematerialinstrain- ingittothatvalue(Fig.9).Thisiseasilyshownasfollowsinequation2: _Summary Restoration of single molar using implants en- counters many problems; mesio-distal cantilever due to very wide occlusal table is the most prominent. An increased occlusal force posteriorly worsens the problemandincreasesfailures.Toovercometheover- load,theuseofwidediameterimplantsortworegular sized implants were suggested. The aim of this study wastoverifythebestsolutionthathasthebesteffect on alveolar bone under distributed vertical loading. Therefore, a virtual experiment using Finite Element AnalysiswasdoneusingANSYSversion9.Asimplified simulation of spongy and cortical bones of the jaw as two co-axial cylinders was utilized. Full detailed with high accuracy simulation for implant, crown, and coating was implemented. The comparison included different types of stresses and deformations of both wideimplantandtworegularimplantsunderthesame boundaryconditionsandloadapplication. Thethreemainstressescompressive,tensile,shear and the equivalent stresses in addition to the vertical deformityandthetotaldeformitieswereconsideredin the comparison between the two models. The results were obtained as percentages using the wide implant as a reference. The spongy bone showed about 5% less stresses in the two implants model than the one wide diameter implant. The exceptions are the rela- tively increase in maximum compressive stresses and deformationsoforder12%and0.3%respectively. Thestressesanddisplacementsonthecorticalbone arehigherinthetwoimplantmodelduetohavingtwo closeholes,whichresultsinweakareain-between.The spongyboneresponsetothetwoimplantswasfound tobebetterconsideringthestressdistribution(energy absorbed by spongy bone**). Therefore, it was con- cluded that, using the wide diameter implant or two averageonesasasolutiondependsonthecaseprima- rily.Providedthattheavailablebonewidthissufficient mesio-distally and bucco-lingualy, the choice will de- pendonthetypeofbone.TheharderD1,2 typeshaving harder bone quality and thicker cortical plates are more convenient to the wide implant choice. The D3,4 types consist of more spongy and less cortical bone, aremoresuitabletothetwoimplantsolution. Editorial note: A complete list of references is available fromtheauthor. Fig. 9_Strain energy = area under stress strain curve. Fig. 10_Equation 2 (stress energy). Fig. 8b Fig. 9 Fig. 10 Prof.Amr Abdel Azim Professor,Faculty of Dentistry,Cairo University drazim@link.net Dr Amani M.Zaki GBOI.2009,Egypt amani.m.zaki@gmail.com Dr Mohamed I.El-Anwar Researcher,Mechanical Engineering Department, National Research Center,Egypt anwar_eg@yahoo.com CAD/CAM_contact