CAD/CAM - international magazine of digital dentistry

ThechoiceofappropriatebasesforthePositioning TRIPOD is critical for its accuracy. Owing to its com- pressibility,softgingivaltissuehastobeavoided.Prob- lems with remaining teeth may arise owing to ad- vancedperiodontaldiseasecausingexcessivemobility. In some cases, temporary mini-implants are used, but often the amount of maxillary residual bone is so re- duced that these implants only interfere with defini- tiveimplantplacement.Nevertheless,theymaybeuse- ful when no other alternative is available. Anecdotal cases in which there is sufficient bone for temporary anddefinitiveimplantsatthesametimehavebeenre- ported, but are rare. The best choice is to use posteri- orly placed implants before inserting anterior im- plants.Inthiscase,anextremelyprecisepositioningis notrequired,sincethelargevolumeofthecorrespon- ding teeth provides some degree of freedom to the laboratory technician designing the prostheses. These posterior areas often require some bone reconstruc- tion (such as sinus lift or onlay bone grafts), thereby prolonging time to loading. The corresponding im- plants will then ensure the most precise positioning not only for radiographic templates and surgical guides, but also for the occlusal guide and impression tray, since all these parts will be screw-connected to thesepreviouslyplacedandosseointegratedimplants. In order to transfer the planned implant position from the planning software to the surgical guide, a Computing TRIPOD is necessary. This Computing TRIPOD is made with three SKYplanX reference pins (bredent)placedontheradiographictemplatewiththe reference plate (Fig. 3a). The patient is scanned with the radiographic template fixed on the Positioning TRIPOD.ThepositionofthestandardisedX-rayopaque referencepinsisdetectedbythesoftware,buildingthe Computing TRIPOD (Fig. 3b), and used to calculate the implant coordinates (Fig. 4). This data is then set in the transfer table (Fig. 5a) to place the drill sleeves accordinglyandtransfertheradiographictemplateto asurgicalguide(Fig.5b). Some days prior to the full-arch surgery, once an adequateTRIPODhasalreadybeenplannedandinitial implants placed, an initial impression (Fig. 6) will be taken for the model to prepare the impression tray, occlusal guide, surgical guide from the radiographic template, and the provisional prostheses. The surgi- cal guides are produced in sterilisable resin with ra- diopaquesleeves(DéPlaque).Specialattentionisgiven to the impression tray that will extend to all maxillary surfaces, but room for the impression material is ex- clusively limited to the planned implant sites. They mustbereadyatthetimeofsurgery. On the day of the surgery, the practitioner begins byreducingallremainingcrownsthatwouldinterfere with the surgical guide, which is then placed on teeth orpreferablyscrewedontopreviouslyplacedimplants, forming the Positioning TRIPOD (Fig. 7). A CT is per- formed to verify all drilling sites. If any modification has to be done, there is still time to adjust the drill sleeves to suitable positions and to re-sterilise the guide. Thenextstepisthetransferoftheocclusiontothe articulator. Usually an occlusion guide is engineered before surgery and screwed into a suitable position. It Fig. 5a_The implant coordinates for the transfer table. Fig. 5b_The drill sleeves being placed in the radiographic template with the transfer table. Fig. 6_Initial impression of two initially placed implants. Fig. 7_Surgical guide placed on teeth and screwed onto previously placed implants forming the Positioning TRIPOD. Fig. 5a Fig. 5b I clinical technique _ TRIPOD 18 I CAD/CAM 3_2011 Fig. 6 Fig. 7