Dental Tribune United Kingdom Edition

multaneously shows two parts: the first part corresponding to the initial impression and the other corresponding to the second im- pression (Fig 12). The provisional prostheses are fitted to the model and occlusion is validated. When this laboratory phase is over, the protective caps are removed, and the prostheses are screwed into position (Figs 13a & b). If well done, occlusal adjustments should be minimal, even perhaps none being required. Thommen SPI®VARIOmulti temporary caps on are filled with temporary light- cured material to close the screw channel and the patient is advised to treat the temporary bridge- works in a gentle manner. Sutures are removed after ten days. The aesthetics are re-evalu- ated three months after surgery, before initiating the final prosthe- ses, owing to subsequent loss of tissue volume. Additional tempo- rary bridgework is often required to test that the final aesthetic will be adequate before proceeding with the definitive prostheses. The final prostheses are either manufactured as a casted bridge using SPI®VARIOmulti caps or by CAD/CAM technology such as No- belProcera from Nobel Biocare. Discussion There are multiple technical ben- efits of the TRIPOD procedure. Precision implant placement is achieved by removing positional and mechanical artefacts, par- ticularly when the actual surgical guide is screwed onto stable im- plants. In other words, there is no movement evoked by a bite vari- ation or tissue differences, and if the patient moves during the CT scan, the guide moves with the anatomical structures. How- ever, there is no way to conquer geometric, hardening or digital artefacts. There is still room for a small degree (<1mm) of free- dom in implant placement and, if necessary, final correction can be done after the initial drilling with the 2.8mm drill. This results in a maximum freedom of approxi- mately 0.7 mm in diameter for a final implant site with a diameter of 3.5mm. However, considering that the last drill at the centre is just half of this value, this freedom corresponds radially to 0.35mm, providing an opportunity to adapt the implant site preparation to an- atomical conditions slightly. This distance of 0.35mm is sufficiently important to become particularly significant for leaving some buc- calbone,butitisstillsmallenough to be handled by the dental tech- nician for ideal prosthetic screw placement. Nevertheless, the ini- tial implant placement cannot ex- ceed this limit, which evokes the necessity of very precise initial drilling and, at the time, an addi- tional step to verify that the surgi- cal guide is actually suitable for use. Compared with flapless tech- niques, open flap surgery not only allows the visual opportunity for controlling bone site preparation, but also retains precious kerati- nised tissue that is important for both marginal tissue stability and volume. The patient’s reaction to this procedure, with its associated pain and discomfort, still has to be examined in future studies. Another benefit of this proce- dure is that sterility is maintained throughout the surgery, since all materials used can be sterilised, which is not the case with com- mon guides such as NobelGuide or the SAFE SurgiGuide®, which are both made of a stereolithic resin and are currently not capa- ble of undergoing sterilisation. In addition, the precision of the pro- cedure allows the impression tray to remain unmodified - and thus sterile - throughout the surgery. Yong and Moy8 state that im- plant loss was probably primarily related to the absence of proper cooling ability when using No- belGuide, since most of the late implant failures involved long implants in cases in which the guide was used directly at the gingival contact. Indeed, only the rear part of the drill (thus far from the tip) can be cooled efficiently, and thereby probably makes the cooling procedure ineffective. In contrast, during the described TRIPOD procedure, the guide is placed on the gingiva at the time of fabrication, leaving an open space for cooling at the time of the open flap surgery. In addition, the bone becomes visible, which allows the practitioner to visual- ise the depth marks of the drill right at the crestal ridge, making the instrumentation less expen- sive and easier, as no special drill with mechanical depth limitation is required. Site preparation may be modified by using piezoelectric bone surgery, since this device can grind bone on a particular wall from the previous drilling, in contrast to conventional drilling, which grinds all walls from the previous drilling, with a prefer- ence for softer tissue and result- ing in facial bone perforation. In some situations, one might also consider changing from drills to bone spreaders; this would com- pact the surrounding bone and provide additional stability to the corresponding implant. Finally, the implant could be adapted to a recipient site by choosing an ap- propriate diameter, length and even the profile (eg from coni- cal to conical-cylindrical) once site preparation has almost been completed. The previously placed im- plants not only add useful preci- sion to implant site preparation with the guide, but also provide essential stability to immediately loaded bridgework in an area where stability in the initial heal- ing phase is probably vital to suc- cess. Most patients are already older, with a history of periodon- titis, tooth loss and associated impaired medical conditions, and possibly reduced healing capacity. Therefore, it is of major interest to be able to assess the healing ca- pacity by the stability of previously placed implants, before undergo- ing and performing a full-arch maxillary bridge immediately loaded on implants, preferably with advanced surface technol- ogy. Most of the cases require some sort of bone grafting in the posterior areas and this technique leaves time for initial healing before occlusal loading. In fact, some of the implants would be subjected to immediate loading, while others - the most critical in terms of bone volume availability and location - could be loaded ac- cording to a classical schedule. This should be considered when making a comparison with other procedures with surgical guides. The INICELL® surface found on Thommen Medical implants showed more bone-to-implant contact and a higher removal torque at two weeks than un- conditioned implants did.15 This aspect should be particularly use- ful in the early stages of healing and providing additional security in this crucial phase. In addition, this company provides implants of various diameters, length and profiles to satisfy various implant site requirements and which pro- vide the best possible stability. Conclusion The TRIPOD protocol is based on our latest clinical experiethe vast developments of implant place- ment planning software and com- puter-guided implant dentistry. The efficiency of the technique must still be validated by analy- sis of implant survival in different clinical environments, specifically investigating adequate position- ing between planned and final implant position, and the need to verify the surgical guide after the learning process has been com- pleted. Finally, a study on patients’ satisfaction with the procedure in terms of pain and aesthetic out- come needs to be performed. We must still determine whether the benefits of open flap surgery in combination with surgical guides outweigh the related discomfort and pain for the patient: does this pose a major problem for patients, are the final aesthetics improved by preserving keratinised tissue, and does such a technique fulfil expectations, considering that bone volume loss is often difficult to limit in these areas? The proposed TRIPOD proce- dure is certainly more labour-in- tensivethancurrentflaplessguide systems, since a flap has to be raised and no definitive prosthesis is placed right after surgery. Nev- ertheless, it is also more versatile because maintaining or increas- ing bone volume is considered in the treatment plan and is adapted to the individual situations. The risk of failure is considerably re- duced by connecting immediately placed implants to osseointegrat- ed implants. Furthermore, this procedure allows using the last millimetre, as typical cases show reduced bone volume and require the widest and longest implants within anatomical restrictions. Although knowledge and close collaboration with the laboratory technician are required, this pro- cedure adds fundamental security and predictability for success, and will certainly be adapted to differ- ent practice situations and one- day procedures. DT Editorial note: A list of references is avail- able from the publisher. page 21DTß Fig. 7 Surgical guide placed on teeth and screwed onto previously placed implants forming the Positioning TRIPOD Fig. 8 Occlusal guide screwed onto poste- rior implants Fig. 9 Adequate cooling and visualisation during drilling Fig. 10a Second impression taking at time of surgery with Thommen impres- sion copings on SPI®ELEMENT implants Figs. 10c & d Injection of silicone material and final second impression Fig. 10b Placing of the individualised open tray Fig. 11 Second impression secured to reduced initial model mounted in the articulator Fig. 12 Modified model: the yellow part corresponds to the initial impression; the pink part was poured at the time of surgery. Figs. 13a & b Initial provisional bridgework on Thommen SPI®VARIOmulti temporary caps in place Fig 7 Fig 8 Fig 9 Fig 10a Fig 10b Fig 10c Fig 10d Fig 11 Fig 12 Fig 13a Fig 13a November 19-25, 201222 Implant Tribune United Kingdom Edition About the author Dr Jean-Nicolas Hasson 5 Rue du Werkhof 68100 MULHOUSE France Tel.: +33 389 458984 Fax: +33 389 563112 E-mail: hasson@hrnet.fr