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special _ guided implantology I However, we cannot rely on the planning, since it cannot discriminate errors. As two superimposed low-resolution 3-D images cannot result in a high qualityimageoftheimplant,relyingontheplanning would increase imprecision in accuracy measure- ments. I therefore recommend platform position- ing according to mathematical criteria in order to achieve a correct, prosthetically driven position. When sleeve placement is considered, jig corre- spondence between the abutments on the master cast analogues and the same abutments’ clinical positionontheimplantscanhelpavoidinaccuracies in terms of either the sleeve position or the axes of thesurgicalguide.Furthermore,itcanhelpevaluate inaccuracies resulting from using a smooth sleeve. To date, no publications have reported on such a technique, presumably because this kind of veri- ficationcanimposetoomuchstressonanymethod owing to the time required to ensure precision this way. Indeed, repeatability seems incidental to the thread-timed sleeve. Thread timing can be an impasse on the way towards a precisely placed implant, since analogues and implants cannot be forced into the same positions both repeatedly and operatorindependently.Inotherwords,itisunlikely that all relevant parameters, such as the position in the ridge and the axis, the depth and the rotational feature orientation, can be taken into account. No publications have reported on such a tech- nique, either, simply because no method has been concerned with verifying accuracy so precisely. Repeatability is incidental to a thread-timed sleeve (that is, something able to force both analogues and implants into place in the same repeatable and operator-independent positions). Thread timing is essential. If we do not accept this, we must accept imprecision. The parameters that define the plat- form—position in the ridge and axis, depth and rotational feature orientation—should all be re- spected. If we miss one parameter with a smooth sleeve we miss them all. In the case reports cited, superimposition of the planning was done after the pts.hadbeenscannedagainpost-operatively.There was complete accuracy between the master model and the clinical results. In order to furthermore demonstratehowthisdevicecouldworkindepend- ently of the way the surgical guide is produced, no industrially manufactured surgical guides were used. Instead, a digital cast and a stone cast were used with an approximate protocol for transferring data from the software and the stone model, and plain resin was chosen as the provisional material. Moreover, it seemed important to understand that comparing post-operative clinical CT results to the planning through superimposition can be misleadinginmeasuringtheaccuracyofanimplant. Contrarily,acomparisonbetweentheclinicalresults with either an STL or stone model on which ana- logues were placed by using the same threaded guidingdeviceoffersbetteraccuracymeasurement. Although software is essential to planning and cre- atingasurgicalguidewithanaccuratelyembedded sleeve, accuracy relates to the concepts of thread timingandimplantphaseandnottosoftware.Inthe case reports cited, software was therefore used to provide qualitative data exclusively. In general, aggressive marketing tactics are an important ethical factor when computer-guided implant placement is considered. The Millennium Research Group has estimated a 20% growth in the number of guided implant placements by 2013. Similarly, dentists are likely to increasingly perceive the need for planning software and drilling tem- plates.Inthefuture,however,CAD/CAMtechniques will not only be applied in planning, but also be used for surgery in order to enhance prosthesis and tissue stability. A passive device that is easy to han- dle and based on thread timing can pave the way to computer-guided progress._ Editorial note: A list of references is available from the publisher. Part I of this series—New concepts in computer-guided implantologywaspublishedinCAD/CAMVol.3,Issue1/12. APDFisavailablefromthepublisher. Fig. 20d_Cone-beam effect interpolation. I 11CAD/CAM 2_2012 Fig. 20c Dr Gian Luigi Telara Studio Odontoiatrico LippiTelara ViaVorno,9/4 55060 Guamo Lucca Italy Tel.:+39 05 8394 7568 lippitelara@gmail.com CAD/CAM_contact Fig. 20d