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ePaper created 2015-05-29, 13:18:43 | version 1.38.0
technique _ virtual planning I bone in the cross-sectional slice (Fig. 4a). The thin cortical plates can be clearly visualized, along with the extension of the labial vestibule (red arrow, Fig. 4b). The relationship to the maxillary sinus is important when deciding if implants might be an option in the posterior region (Fig. 4c). In this ex- amplethepneumatisationofthesinushasresulted in extremely thin lateral cortical plate (see red ar- rows). The radiopaque template is helpful when evaluating other receptor sites, and positioning a simulated implant within the cross-sectional view (Slice 63, Fig. 5a). For an over-denture application the positioning of implants need to fall within the envelope of the teeth, and it is even more practical to visualize the abutments that might be utilized (Fig.5b).Forthisexamplearealisticstock“balltype” abutment was utilized on the virtual realistic im- plant. In order to provide some guidance, it is the author’s preference to place the implant within a defined zone of available bone (Figs. 6a & b). This zone has been previously defined as the “Triangle of Bone” (TOB) that also acts as a decision tree to connect the implant placement to the restorative outcome (Fig. 6c). Positioning the im- plantwithinthezoneoftheTOB,oractuallybisect- ing the triangle, allows for the most bone volume to surround the implant. Following this formula, the implant and abutment will be positioned in a favourable restorative position. Further inspection through the utilization of additional views can be extremely enlightening withregardtothefinalpositioningoftheimplants. The occlusal view of the volumetric reconstruction aids in the implant-to-implant positioning within the bone (Fig 7a). However, without a complete understanding of the tooth position, the implants may not be ideally located based upon the pros- thetic plan. Superimposing a translucent scannographic template over the maxilla provides the important information to position the implants within the restorativeenvelope(Fig.7b).Theprosthesisdesign canbeevaluatedtodeterminewhethertofabricate a complete denture that would extend to incorpo- rate a conventional post-palatal seal, or an open- palate horseshoe type prosthesis. To aid in the final positioning, it is helpful to visualize the outline of the occlusion using the author’s concept of “selec- tive transparency”, and extend the abutments above the occlusal plane (Fig. 8a). “Selective trans- parency”isasoftwaretoolwhichcanhelpseparate one anatomical structure from another by adjust- ing the opacity of the various objects. Once the im- plants are placed, the ball abutments can then be positioned at the proper tissue cuff height (Fig. 8b). Rotating the views can substantiate the plan to place the implants where they will be support the removable prosthesis (Figs. 9a & b). It is important to assess the clearance within the denture to allow for sufficient thickness of acrylic within the over-denture abutment housing avoiding potential fracture of the prosthesis. This “prosthetic space” requirement may be different depending upon the type of attachment used. Usingthepowerofdigitaltechnologyandselective transparency, the realistic implant and ball abut- ment can be seen through the prosthesis and the underling bone (Figs. 10a & b). These illustrations revealthatthetworightimplantsareparallel,while the left implants are seen to follow the natural extensions above the occlusal plane (a). Ball abutments positioned at the proper tissue cuff height (b). Figs. 9a & b_Rotating the views help position implants where they will best support the removable prosthesis. Figs. 10a & b_Selective transparency allows the realistic implants and ball abutments to be seen through the prosthesis and the maxillary bone. Fig. 11_The distance between the two anterior implants and the maxillary incisor teeth (red arrows) represents a cantilever that could result in tipping of the denture. Figs. 12a & b_The use of realistic attachments allows for implant- to-implant positioning around the arch necessary to gain maximum retention and resistance of the prosthesis to dislodgement during mastication. Fig. 13_Utilization of virtual abutments aids in determining the correct tissue cuff heights of the abutments above the bone, and through the soft tissue. Figs. 14a & b_The vertical distance can be evaluated within the prosthetic design (a), crown- to-root ratios, and the trajectory of the implant-abutment complex can be visualized within the virtual plan. I 09cone beam2_2015 Fig. 17a Fig. 17b Fig. 17c Fig. 18a Fig. 18b Fig. 18c