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ePaper created 2016-03-24, 17:16:09 | version 1.38.0
| research 26 implants 1 2016 prosthetic planning should start prior to any scan being taken. A scanning appliance can be fabri- cated from a duplicate of a patient’s existing well-fitting denture, or a new diagnostic set-up which positions the teeth at the ideal vertical di- mension of occlusion, centric relation, and func- tional/aesthetic components (Fig. 3a). The patient wears the scannographic appliance during the scan, ideally held in place with a pre-determined bite registration to minimize movement. The scan reconstruction will then contain both the tooth position and the underlying bone (Fig. 3b). The combination of the anatomical scan data with the radiopaque template allows unprece- dented diagnostic potential. The template reveals the tooth position (red arrows) in relationship to the underlying bone in the cross-sectional slice (Fig. 4a). The thin cortical plates can be clearly vi- sualized, along with the extension of the labial ves- tibule (red arrow, Fig. 4b). The relationship to the maxillary sinus is important when deciding if im- plants might be an option in the posterior region (Fig. 4c). In this example the pneumatisation of the sinus has resulted in extremely thin lateral cortical plate (see red arrows). 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 im- plants need to fall within the envelope of the teeth, and it is even more practical to visualize the abut- ments that might be utilized (Fig. 5b). For this ex- ample a realistic stock “ball type” abutment was utilized on the virtual realistic implant. In order to provide some guidance, it is the author’s preference to place the implant within a defined zone of avail- able bone (Figs. 6a & b). This zone has been previ- ously 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). Po- sitioning the implant within the zone of the TOB, or actually bisecting the triangle, allows for the most bone volume to surround the implant. Following this formula, the implant and abutment will be po- sitioned in a favourable restorative position. Further inspection through the utilization of additional views can be extremely enlightening with regard to the final positioning of the implants. 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. Figs. 7a & b: The occlusal view of the volumetric rendering aids in the implant-to-implant positioning within the bone (a). Superimposing a translucent scannographic template over the maxilla provides the information to position implants within the restorative envelope (b). Figs. 8a & b: Use of “selective transparency” with abutment 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. Fig. 7a Fig. 8b Fig. 10a Fig. 7b Fig. 9a Fig. 10b Fig. 8a Fig. 9b Fig. 11 12016