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ePaper created 2015-03-07, 18:13:20 | version 1.33.01
case report _ use of CBCT I To ensure accurate restoratively driven planning, thelaboratoryfabricateddenturewax-upwasscanned with a desktop optical scanner and then, using ad- vancedsoftwaretools,theresultingSTLfile(standard triangulation language) was subsequently super- imposed on the 3-D volumetric reconstruction, and validated in all views using the radiopaque teeth and existinglocatorabutmentsasfiducialmarkers(Fig.5). In this way, the trajectories of the virtually planned implants could be sighted through the envelope of the denture teeth (the restorative space). Using the information from the 3-D planning, the holes to re- ceive the temporary abutments could be predrilled in the interim fixed prosthesis. Oncetheimplantpositioningwasconfirmedinthe 3-D plan, a CBCT-derived surgical guide was printed in resin by the rapid prototyping process (stereolith- ograpy) from an STL file (Fig. 6). This guide essentially carriesthe3-Dplantothemouthbyvirtueoftubesin the guide that will guide the drills to the same trajec- tory as the planned implant. Additionally, a biomed- icalmodelofthemandiblewasprintedtofurtheren- hance the pre-surgical planning process (Figs. 7 & 8). The virtually planned posterior implants were in closer proximity to the mandibular nerve than the ideal safety zone of 2mm; therefore, it was decided that enhanced stabilityof thesurgical guidecould be achieved by connecting the stereolithographic guide to the middle locator abutment with a locator hous- ing embedded in the resin. The increased stability of the guide would thereby improve drilling accuracy. Priortosurgicalintervention,apieceofrubberdam material was sized to the printed biomedical model of the mandible to fit around the Locator abutments to be used during the surgical intervention (Fig. 9). The rubber dam serves to help protect the bone from the potential cytotoxic effects of the methacrylate monomer8 used to capture the locator housing. _Surgical intervention At the time of surgery, the patient was anes- thetised and IV sedation was administered. A slightly lingual crestal incision was made starting just ante- riortotheretromolarpadtothesamelocationonthe contralateral side. A full thickness flap was then elevated to expose the underlying bone and the three pre-existing im- plants (Fig. 10). The fit of the bone-borne guide was first verified, ensuring that the flaps did not interfere withcompleteseatingoftheguideandthattheguide was stable on the bone. Once this was achieved, the area corresponding to the Locator abutments on the surgical guide was reamed out to facilitate proper seating of the guide. A Locator (female) housing with the black nylon processing male insert was seated on the Locator abutment intraorally. The guide was rechecked for proper circumferential clearance and subsequently picked up with a dual-cure acrylic (Chairside,ZestAnchors)andtherubberdammate- rial was subsequently removed (Fig. 11). Fig. 6_The 3-D printed stereolithographic template, without metal guide tubes. Fig. 7_The complete 3-D printed mandible. Fig. 8_Close-up view of the anterior mandible of the printed model used tosizeandfittherubberdammaterial. I 13cone beam1_2015 Fig. 6 Fig. 7 Fig. 8