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ePaper created 2016-03-24, 17:16:09 | version 1.38.0
research | 271 2016 implants Superimposing a translucent scannographic template over the maxilla provides the important information to position the implants within the restorative envelope (Fig. 7b). The prosthesis de- sign can be evaluated to determine whether to fabricate a complete denture that would extend to incorporate 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 con- cept of “selective transparency”, and extend the abutments above the occlusal plane (Fig. 8a). “Se- lective transparency” is a software tool which can help separate one anatomical structure from an- other by adjusting the opacity of the various ob- jects. Once the implants are placed, the ball abut- ments can then be positioned at the proper tissue cuff height (Fig. 8b). Rotating the views can sub- stantiate 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. Using the power of digital technology and selective transparency, the realistic im- plant and ball abutment can be seen through the prosthesis and the underlying bone (Figs. 10a & b). These illustrations reveal that the two right implants are par- allel, while the left implants are seen to follow the natural trajectory of the max- illary alveolus (a), and the reverse is true after rotating the maxillary volumetric re- construction to view the left side (b). Fi- nally, when considering the mechanical forces of mastication and movement of the prosthesis, a line can be drawn be- tween the two most anterior implants that establishes the potential for rotation in the occlusal plane (Fig. 11). A second line can be drawn at the most anterior as- pect of the maxillary teeth. The distance between the two anterior implants and the max- illary incisor teeth (red arrows) represents a can- tilever that could result in tipping of the denture when the patient bites into an apple. The ball-abutment is only one potential stock abutment choice for an over-denture application. Another widely used abutment is the Locator attachment (Zest Anchors). The use of realistic Locator attachments allows for a precise under- standing of the implant-to-implant relationship, and spacing around the arch which is necessary to gain maximum retention of the prosthesis to resist dislodgement during mastication (Figs. 12a & b). In addition, the utilization of virtual abutments aids in determining the correct tissue cuff heights of the abutments above the bone, and through the soft tissue (Fig. 13). The vertical distance can be evaluated within the framework of the prosthetic design (Fig. 14a). The new digital tools allow for new paradigms to be established assessing the relationship of the implant position, abutment position, and prosthesis prior to the scalpel ever touching the patient. Crown-to-root ratios and the trajectory of the implant-abutment complex can be visualized within the virtual plan, providing valuable surgical and restorative information during the planning phase (Fig. 14b). 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. Figs. 15a & b: The top of the implant (red line) serves as the foundation for the abutment at a specific tissue cuff height (green line) (a); the metal housing represented in gold also has a vertical component (yellow line) (b). Fig. 16: Once the implant position has been confirmed, the software will generate the virtual design of the template. Fig. 14a Fig. 15a Fig. 15b Fig. 16 Fig. 14b Fig. 12a Fig. 12b Fig. 13 2712016