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CAD/CAM - international magazine of digital dentistry

16 I I clinical technique _ TRIPOD _Immediate loading of complete maxillary im- plant-supportedbridgeworkisanincreasingrequest by patients who have high aesthetic and functional demands and attach great importance to a neat ap- pearance and their self-image. Since 1977, positive results have been obtained in immediate loading,1,2 but these were limited to mandibular, bar-retained removabledentures.In1997,Tarnowetal.3 published a study showing similar results for maxillary and mandibularfull-arch,implant-supportedbridgework, and, more recently, the focus has turned to the de- velopment of computer-based techniques for im- proved results. Highly sophisticated technical tools such as NobelGuide(NobelBiocare)andtheSAFESurgiGuide (MaterialiseDental)haveenteredthemarketandre- latedtechniquessuchasAll-on-4(NobelBiocare)are being promoted4,5 to help meet patients’ demands. Alltechniquesarebasedonfullmaxillarybridgework with a screw-based retention. The screw-retained bridgework allows all procedures to be performed during the treatment, i.e. impression taking, bridge modification and repair for aesthetic or functional purposes. Amongstthemorechallengingdifficultiesincar- ryingoutsuchatherapyisimplantpositioning,espe- ciallyforasinglecrownintheanteriorregion.Precise placement is essential in achieving good aesthetics, phonetics, function and cleanability. Most of the time, implant placement has to be within the limits of 0.5 mm (Fig. 1). Another factor to consider is the possible loss of alveolar bone after tooth extraction, leaving a minimal residual volume, and thereby in- creasing the difficulty of the procedure. The positioning of implants depends on the guide’spositionalaccuracyinadefinitiveplaceatthe time of the surgery and on the accuracy of the guide itself.InthecaseofNobelGuide,accuratepositioning depends on the patient’s ability to bite reproducibly and precisely, with even gingival thickness and con- sistency, and assumes that bone shows a similar de- gree of hardness at different screw-retention sites. Unfortunately, as recently reviewed by Schneider et al.6 and de-tailed by Valente et al.,7 the deviation between entry point and orientation consistently differs between the planned and actual position of the implants. This generally accounts for the results obtained by guides used in flapless surgery. Other failure factors may be related to poor cooling ability during the drilling procedure.8 As cited above, inaccuracies may arise from the positioningoftheguideorofthepatient,orberelated totheradiologicaltechniqueitself.Inthecaseofflap- CAD/CAM 3_2011 Figs. 1a–c_Precision positioning of dental implants is mandatory for adequate abutment and screw placement. TRIPOD—Anew protocol for immediate loading of complete implant-supported prostheses Authors_ Dr Jean-Nicolas Hasson, Dr Jacques Hassid & Dominique Fricker, France Fig. 1a Fig. 1b Fig. 1c