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Implants

I 29 research_ Single molar restoration I implants1_2013 tively. Difference % = {One implant Result—Two implants Result}*100 / One implant Result… (1) Spongy bone deformation and stresses (Table 2) seems to be the same in the two cases. Simple and fast conclusion can be tak- en that using one wide implant is equivalent to using two conventional implants. On the other hand a very important conclusion can be exerted that, under axial loading, about 10 per cent increase in implant side area can overcome reduction of implant cross section area by 50 per cent. In other words, effective- ness of increasing 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 from Figure 7 a & b, slight differences can be no- ticed on spongy bone between the two mod- els results. The stresses on the spongy bone are less by about five per cent in the two implants model than the one wide diameter implant. The exceptions are the relatively in- crease in maximum compressive stresses and deformationsoforder12percentand0.3per cent respectively. The bone is known to respond the best to compressive and the least to shear stresses22 , so considering the difference in compressive stresses less significant, the two implants were found to have a better effect on spongy bone. Contrarily, Figures 8a & b, showed bet- ter performance with cortical bone in case of using one wide implant over using two im- plants, that, deformations in cortical bone are less by 20 per cent while the stresses are less by about 40 per cent. The stresses and dis- placements were significantly higher in the two implant model due to having two close holes, which results in weak area in-between. _Conclusions This study showed various results between cortical and spongy bone. It was expected that the maximum stresses in the cortical bone was placed in the weak area between the two implants. In addition to be higher than the case of using one wide implant. Al- though the middle part of spongy bone was stressed to the same level in the two cases, using two implants resulted in more volume of the spongy bone absorbed the load en- ergy** which led to reduction of stress con- centration and rate of stress deterioration by moving away from implants. That is consid- ered better distribution of stresses from the mechanics point of view, which may result in longer lifetime. Porcelain coating showed less stress in case of two implants, longer life for the brittle coating material is expected. Contrarily more stresses were found on the gold crown placed on two implants due to its volume reduction (less material under the same load). This is clearly seen in in- creasing stresses on the two implants, that more load effect was transferred 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 en- ergy** 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 crack- ing danger, the following conclusions can be pointed out; the total results favour the two implants in spongy bone and the wide implant in the cortical layer, but the alveolar bone consists of spongy bone surrounded by a layer of cortical bone. It’s also well known that according to the degree of bone density Fig. 9_Strain energy = area under stress strain curve. Fig. 8b Fig. 9