implants - internationalmagazine of oral implantology

case study _ computer-guided implantology I Fig. 12c_Missed implant position parameters in the depth-control systems owing to congruent triangle considerations (implant axis deviation and endo-stop angle). Fig. 12d_Missed implant position parameters in the depth-control systems owing to congruent triangle considerations (implant axis deviation and endo-stop angle). Fig. 13a_Coca-cola screw plug analogy. Fig. 13b_Coca-cola screw plug analogy. Fig. 14a_Euler’s formula. Fig. 14b_Euler’s formula in applied mathematics. Fig. 14c_Euler’s formula in applied mathematics. Fig. 15_Vertical clearance paragon. I 33implants4_2011 Componentsandundercuts In the prototype device, a driver for a ratchet was used.Itwascompletelyredundantbecausetheratchet can cooperate directly with a plug-top feature for a ratchetatitstop;thus,thedriverissomethingthatcan beeliminated.Oncetheassemblyhasbeenfixedtothe embeddedsleeve,theplugcanbescrewedwiththefin- gers, at least until sufficient torque is found, when a ratchetcanbeused. Whenmultipleimplantshavebeenplanned,incase ofdivergentimplants,hexundercutscouldpreventthe surgicalguidefromreleasingitselffromthebone,once the implants have been placed. In order to resolve this, thedevice,atleastthemountingpart,mustberemoved fromthesurgicalguide.Thedeviceisthusdividedintwo componentsandthelid,whichisintegraltothedriver, canbeunscrewed,leavingthesurgicalguidealongwith alltheothercomponentsstillfastenedtoit,butdisen- gaged from the implants, freely and easily removable. For single implant placement, the lid is not necessary, becausetherearenohexundercuts.Inthiscase,abot- tle-plugwithonecomponentwillbesufficient. Crestmodule Theimplantcrestmodulemorphologydoesnotaf- fectthisguidingdevicebecausethebottle-neck’sinter- nal diameter is just a little wider than the implant di- ameter at any point (platform or below the platform). By the way, additional threads in the crest module are not important either because, mathematically speak- ing, they are harmonic waves of the implant period (threadpitch). Mastercast Thehelicalgearcaneasilybeorientedvestibularlyin thethreadedguidingdevicebeforepouringthemaster model. Verticalclearance To make the correct surgical guide, the helical gear must be engineered in the planning at a multiple pitch distance from the bone, just equalling the implant length(theimplantmuststartrotatingbeforeittouches thebonetoavoidboneguidance).Forinstance,thedis- tance will be 9 or 10 mm for 9 or 10 mm long implants witha1mmpitch,andthedistancewillbeamultipleof 0.75fora0.75mmpitch(9mmwillcorrespondto12im- plant 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 consideredbecausetheimplantapexcanentertheos- teotomyholewithoutbeingengaged.Toreduceverti- cal clearance, the device can be pre-assembled, thus obtaining a working length even shorter than that of the present systems (Fig. 15). A shorter vertical clear- anceispossiblealsowithtrans-mucosalimplantsbe- cause the platform results are more superficial._ Editorial note: A list of references is available from the publisher. Fig. 15 Fig. 14c Fig. 14b Dr Gian Luigi Telara Studio Odontoiatrico LippiTelara ViaVorno,9/4 55060 Guamo Lucca (Italy) Tel.:+39 0583 947568 lippitelara@gmail.com _contact implants Firstpublished:Dent.Implantol.8,p.374-382 (2004),SpittaVerlag