Dental Tribune Indian Edition

22 Dental Tribune Indian Edition - September 2013Implant Therapy _Dental technician’s perspective When the laboratory (Laboratoire Dentaire Crown Ceram) received this case, we were asked to create three customised anatomical abut- ments with a titanium interface for an individual and more precise fit, respecting the requirements of biocompatibility and biomechanics, and a coronary part in zirconia for a better aesthetic result. Once the moulds had been cast, we determined that the considerable angulation of the implants in regions 24 and 25 and their shallow position in the tissue posed difficulties regar- ding the design of titanium–zirconia abutments. However, Dr Lachkar explained to us that in this case (i.e. the patient’s reluctance to undergo pre- implant surgery) he was forced to place the implants in the bone available and not necessarily in the ideal situation according to a prosthetic plan. In this case, the titanium interface would have considerably exceeded the buccal surface and it would therefore have been necessary to reduce it. The bonding surface would therefore have been limited, which would have resulted in a great loss of mechanical resistance. We thus decided to use a titanium abutment manufactured from a single block and specially made to allow for such substantial angulations for teeth 24 and 25. For tooth 23, the implant angle allowed for a titanium–zirconia abutment, which was preferred to a titanium abutment for a better aesthetic result.DT Figure 9&10: Final result. Dr Thierry Lachkar is a dental surgeon (Paris Diderot University) and has been a practitioner for 15 years. He is a general practitioner and he works at a dental surgery in Paris. He has specialist post- graduate training in conservative dentistry and in endodontics. He can be contacted at drlachkar@ yahoo.fr. Contact Info was inserted into the replica and cut back by 3 mm from the occlusal table. This was then powdered and scanned using the CEREC Bluecam, and an IPS e.max CAD C 14 block was milled. The CEREC 4.2 software was instructed to mill a hole that cor- responded to the screw-insertion path on the abutment. This was finished using a high-speed diamond bur with copious irrigation. The crown was glazed and sintered, allowed to cool and bonded to the abutment using Variolink II (Ivoclar Vivadent). The final crown was screwed directly onto the implant and a final check for contacts and occlusion was done. This process shows just how far CAD/CAM technology has come. An implant can be planned, inserted and restored all in-house, using the current available technology. The final result is equal to any laboratory- based restoration, albeit for simple units. The process does have its limits in terms of multiple-span bridges and placement of multiple implants, especially in edentulous areas. As the technology develops, with further advances being made, the scope of what is possible for the implant dentist is always expanding.DT → DT page 20 → DT page 19 Figure 8A & B: Cortical bone deflection in vertical direction (A) wide implant; (B) two implants. Figure 9: Strain energy = area under stress strain curve. Figure 10: Equation 2 (stress energy). in cortical bone are less by 20% while the stresses are less by about 40%. The stresses and displacements 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. Although 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 energy** which led to reduction of stress concentration and rate of stress deterioration by moving away from implants. That is considered 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 increasing 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 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, the following conclusions can be pointed out; the total results favourise 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 the alveolar bone is classified to D1,2,3,4 23 in a descending order. So, provided that the edentulous space after the molar extraction permits, it’s recommended in the harder bone quality (D1,2 ) to use one wide diameter implant and in the softer bone (D3,4 ) quality two average sized implants. Therefore more detailed study to compromise between the two implants size/design and intermediate space can put this stress values in safe, acceptable, and controllable region under higher levels of loading. ** The area under the __-__ curve up to a given value of strain is the total mechanical energy per unit volume consumed by the material in straining it to that value (Fig. 9). This is easily shown as follows in equation 2: _Summary Restoration of single molar using implants encounters many problems; mesio-distal cantilever due to very wide occlusal table is the most prominent. An increased occlusal force posteriorly worsens the problem and increases failures. To overcome the overload, the use of wide diameter implants or two regular sized implants were suggested. The aim of this study was to verify the best solution that has the best effect on alveolar bone under distributed vertical loading. Therefore, a virtual experiment using Finite Element Analysis was done using ANSYS version 9. A simplified 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 wide implant and two regular implants under the same boundary conditions and load application. The three main stresses compressive, tensile, shear and the equivalent stresses in addition to the vertical deformity and the total deformities were considered in 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 relatively increase in maximum compressive stresses and deformations of order 12 % and 0.3 % respectively. The stresses and displacements on the cortical bone are higher in the two implant model due to having two close holes, which results in weak area in-between. The spongy bone response to the two implants was found to be better considering the stress distribution (energy absorbed by spongy bone**). Therefore, it was concluded that, using the wide diameter implant or two average ones as a solution depends on the case primarily. Provided that the available bone width is sufficient mesio-distally and bucco-lingualy, the choice will depend on the type of bone. The harder D1,2 types having 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, are more suitable to the two implant solution.DT Editorial note: A complete list of references is available from the author. 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. El­Anwar Researcher, Mechanical Engineering Department, National Research Center, Egypt anwar_eg@yahoo.com Contact Info Figure 7A & B: Spongy bone deflection in vertical direction (A) wide implant; (B) two implants. → DT page 15