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implants the journal of oral implantology United Kingdom Edition

30 I I clinical _ guided implantology implants2_2012 gone 360° all round) both in the bottle-neck plug and in the embedded sleeve (the coor- dinating feature inside the surgical guide), so that a vertical stop is realised in the de- vice. When the two vertical parts match up, we can be certain that the hex is just where we have engineered it to be. The device pitch must have the same implant pitch because differences will lead to bone stripping. In fact, a difference in implant and mount insertion speed (ie the distance covered in depth every 360°) and a different wave period (ie thread pitch), will lead to something different from an out of phase working device; it will lead to bone stripping. In particular, a longer mount- ing period will force the implant downwards into the bone, with consequent vertical bone stripping, whereas a shorter mounting period will force the implant to rotate horizontally, with consequent horizontal bone stripping. Self-tapping implants should show better torque control. _Components and undercuts In the prototype device, a driver for a ratchet was used. It was completely redun- dant because the ratchet can cooperate di- rectly with a plug-top feature for a ratchet at its top; thus, the driver is something that can be eliminated. Once the assembly has been fixedtotheembeddedsleeve,theplugcanbe screwed with the fingers, at least until suf- ficient torque is found, when a ratchet can be used. When multiple implants have been planned, in case of divergent implants, hex undercuts could prevent the surgical guide from releasing itself from the bone, once the implantshavebeenplaced.Inordertoresolve this, the device, at least the mounting part, must be removed from the surgical guide. The device is thus divided in two components and the lid, which is integral to the driver, can be unscrewed, leaving the surgical guide along with all the other components still fastened to it, but disengaged from the im- plants, freely and easily removable. For single implant placement, the lid is not necessary, because there are no hex undercuts. In this case, a bottle-plug with one component will be sufficient. _Crest module The implant crest module morphology does not affect this guiding device because the bottle-neck’s internal diameter is just a little wider than the implant diameter at any point (platform or below the platform). By the way, additional threads in the crest mod- ule are not important either because, mathe- matically speaking, they are harmonic waves of the implant period (thread pitch). _Vertical clearance To make the correct surgical guide, the he- lical gear must be engineered in the planning at a multiple pitch distance from the bone, justequallingtheimplantlength(theimplant muststartrotatingbeforeittouchesthebone to avoid bone guidance). For instance, the distance will be 9 or 10 mm for 9 or 10 mm longimplantswitha1mmpitch,andthedis- tance will be a multiple of 0.75 for a 0.75 mm pitch (9 mm will correspond to 12 implant revolutions and 10.5 mm to 14 revolutions). The average mouth opening values should be considered. In case of tapered implants, a short distance can be considered because the implant apex can enter the osteotomy hole without being engaged. To reduce vertical clearance, the device can be pre-assembled, thus obtaining a working length even shorter than that of the present systems. A shorter vertical clearance is possible also with trans- mucosal implants because the platform re- sults are more superficial._ implants Dr Gian Luigi Telara Tel.: +39 0583 947568 lippitelara@gmail.com contact CAD/CAM _contact