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13Implant TribuneJanuary 2014United Kingdom EditionUnited Kingdom Edition UK’s No.1 Producer of * With Our Cash Back Stickers Only £55.00 Per UnitE l i t e The Complete Service Dental Laboratory RevolutionaryRestoration * Based on research of other UK based BruxZir registered laboratories. ** Results are based on research carried out by Glidewell Laboratories in the USA. E&OE. Photos courtesy of Glidewell Laboratories Copyright ©2012. Subject to availability andT&C. More than 2.8 million BruxZir solid zirconia restorations have been placed, making it one of the most prescribed solid zirconia restorations worldwide** .Visit www.bruxzir.com for further information. Simply peel of and stick one sticker to every docket to get cash back! Ofer valid until 31st January 2014. One sticker per docket only. FurtherT&C May Apply. £720 SAVEON YOUR LAB BILL ProfessorP. 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Moreaestheticthanmetalandfull-castgoldcrowns. Zirconiahasprovenbiocompatibility,havingbeenusedin medicalimplants. Compatiblewithanypreparation. “Get my cash back stickers by calling CosTech”Call CosTechToday 01474 320076 @CosTechEliteFollow us onTwitter for the latest oferswww.costech.co.uk were subjected to 120 N vertical load equally distributed (20 N on six points simulate the occlusion; one on each cusp and one in the central fossa). On the other hand, the base of the cortical bone cyl- inder was fixed in all directions as a boundary condition.17-21 Results and Discussion Results of FEA showed a lot of de- tails about stresses and deforma- tions in all parts of the two models under the scope of this study. Fig- ures 6a & b showed a graphical comparison between the crowns of the two models which are safe under this range of stresses (porcelain coating, gold crown, and implants showed the same ranges of safety). No critical dif- ference can be noticed on these parts of the system. All differenc- es might be found are due to dif- ferences 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 placed on one implant. This fact is directly re- flected on porcelain coating and the two implants that have more deflections. Comparing wide implant model with the two im- plants from the geometrical point of view it is simply noted that cross sectional area was reduced by 43.3 per cent while the side area increased by 6.5 per cent. Using one implant results as a reference in a detailed compari- son between the two models by using equation (1) resulted in Ta- ble 2 for porcelain coating, gold crown, implant(s), spongy and cortical bones respectively. 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 taken that using one wide implant is equiv- alent to using two conventional implants. On the other hand a very important conclusion can be exerted that, under axial load- ing, about 10 per cent increase in implant side area can overcome reduction of implant cross sec- tion area by 50 per cent. In other words, effectiveness 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 Fig- ures 7 a & b, slight differences can be noticed on spongy bone between the two models 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 rela- tively increase in maximum com- pressive stresses and deforma- tions of order 12 per cent and 0.3 per cent respectively. The bone is known to respond the best to compressive and the least to shear stresses22 , so con- sidering the difference in com- pressive stresses less significant, the two implants were found to have a better effect on spongy bone. Contrarily, Figures 8a & b, showed better performance with cortical bone in case of us- ing one wide implant over using two implants, that, deformations in cortical bone are less by 20 per cent while the stresses are less by about 40 per cent. The stresses and displacements were signifi- cantly higher in the two implant model due to having two close holes, which results in weak area in-between. Conclusions This study showed various re- sults 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 ad- dition 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 vol- ume of the spongy bone absorbed page 14DTà Table 1 01474320076 01474320076