CAD/CAM - international magazine of digital dentistry

special _ guided implantology I Fig. 2_Surgery planning for the STL case. Figs. 3a & b_Surgery planning for the stone case. I 07CAD/CAM 1_2012 approach, however. A guard-rail-like guide is cer- tainly better than nothing. Many systems are available today, and from a theoretical perspective they have been categorised into semi-active and passive systems. The systems in the first category, whatever the technique used to make the surgical guide (STL or stone surgery), have metal smooth guiding sleeves, which the im- plant and the implant-driver must pass through, andthesecondsystems,alsocallednavigationsys- tems,donothaveanymetalsleevesandthesurgeon is guided by the monitor. In this category, the sur- gical handpiece is indexed to spatial markers inside a surgical guide that is inserted into the patient’s mouth,butnotinthesurgicalarea.Thesespatialco- ordinates are viewed by an infra-red system, which transfers data to the computer, allowing the clini- cian to follow the surgical steps on the monitor. Alarm lights and sounds will warn the clinician of deviations from the desired position. I propose a new definition of a passive system: a passive system must allow any operators (i.e. it must be operator independent) to achieve the same, repeatable results at an acceptable inac- curacy threshold.4 The accepted inaccuracy must allow clinicians to obtain a good metal-to-metal fit without placing tension on the implants. This “to what extent” predictability can determine the reliability of treatment. In fact, in fixed prostheses on natural teeth, passivity (at an acceptable gap) is about 40 to 50µ in the arch; the same values could be considered acceptable for prostheses on im- plants. According to this definition, none of the systems on the market has replicable results, and have metal or virtual smooth sleeves. They must thus be considered metal or virtual smooth semi- active systems. I have developed a new device according to the mathematical concepts of thread timing and im- plant phase, which can be applied to the implant movement while being screwed, thus allowing cli- nicians passivity during implant placement. In the future,owingtothepredictabilityofimplantplace- ment,theproposeddevicecouldbefundamentalto achieving the desired goals in computer-guided implantology. _Materials and methods The implants were placed using the bottle-neck- like device, which begins implant rotation before it cantouchthebone,therebyavoidingboneinterfer- encewithimplantmovementowingtobonedensity gradients (“bone guidance”). The prototype of the device (Fig. 1a) consists of: _an internally threaded sleeve (“embedded sleeve”, witha“helicalgear”featureatitstopthatisuseful during implant placement; Fig. 1b); _anexternallythreadedsleeve(“osteotomysleeve”), whichhastobeinsertedintotheembeddedsleeve and serves as a regular sleeve for the osteotomy drills (because it is internally smooth; Fig. 1c); _a modified extender for drills (Fig. 1d); _an externally threaded sleeve, longer than the osteotomy sleeve, that acts as a “bottle-neck” and Fig. 2 Fig. 3a Fig. 3b