CHAPTER 18 THE USE OF COMPUTERIZED TREATMENT PLANNING AND A CUSTOMIZED SURGICAL TEMPLATE TO ACHIEVE OPTIMAL IMPLANT PLACEMENT
AN INTRODUCTION TO GUIDED IMPLANT SURGERY
Successful prosthetic dental rehabilitation depends on detailed planning that takes into account both anatomical limitations and restorative goals. That planning must be accurately transferred to the surgical field. To facilitate that task, the use of surgical guides has become well established in implant dentistry.1–7
Over the years, a variety of approaches to implant surgical-guide fabrication have developed. Attention has focused on the results that can be achieved by combining computed tomography (CT) diagnostic scanning with computer-aided design and manufacturing (CAD/CAM) and rapid prototyping. Studies by Ganz8–12 have suggested that the use of such technology can improve the outcome of implant placement by helping to ensure that the implant is placed in the best bone volume. The accuracy of these techniques has been confirmed by other research.13,14
Sophisticated three-dimensional (3-D) computer models of patients’ oral structures can be generated from CT scan data. Implants can be virtually placed in those computer models (planning images), and the prosthetic result can be instantly assessed, with refinements in positioning made until the placement has been optimized. A surgical guide that allows for precise reproduction of that positioning can then be generated. The guided implant surgery concept takes this approach further by combining presurgical planning and computerized surgical-guide fabrication with presurgical fabrication of a provisional or final prosthesis that can be delivered at the time of surgery. This chapter introduces this approach and presents a case in which it was utilized.
The concept of guided implant surgery enables the surgeon, restorative dentist, and laboratory to share in the diagnosis and treatment planning of each patient receiving implants. All members of the team can assess the three-dimensional computer model of the patient’s oral structures, in which the bone available for implant placement and the proximity of the placement site(s) to adjacent dentition, existing implants, the maxillary sinus, and inferior alveolar nerve can be evaluated easily. Using the 3-D computer model enables the implants to be placed within the greatest available volume of bone, improving stability. The emergence profile and aesthetics can be optimized, with adequate lip support and tongue space ensured.
The guided surgery approach begins with an evaluation of the patient’s dental aesthetics by both the restorative doctor and the surgeon. The length and shape of the prosthetic teeth, tooth exposure when smiling and talking, the relationship of the teeth to the gingival contours, the occlusion, and the phonetics are among the factors deserving attention.
Once an ideal restorative outcome has been agreed upon, an ideal prototype of the final restoration is fabricated. For fully edentulous cases, it may be possible to revise the patient’s existing prosthesis rather than creating a new one. A bite registration is then made and a #8 round bur is used to drill at least 10 to 12 points on the prototype prosthesis. The holes are prepared to a depth of 1 mm and placed at different levels in relation to the occlusal plane. Gutta percha is flowed into the holes, transforming the prosthesis into a radiographic guide. The planning software will later utilize the radiopacity of these markers to ensure that the prosthesis is properly aligned with the patient’s bone in the computer model.
In preparation for the CT scan, the patient, wearing the prototype prosthesis, is asked to bite evenly and firmly on the bite registration. Either a multislice or cone beam scanner may be used to take the scan. A second CT scan of the prototype prosthesis alone is then taken to compensate for the fact that the acrylic of the prototype in the first scan will become invisible after the planning software has adjusted the first scan’s density to reveal the presence of the bone. However, the gutta percha markers will remain visible. When both scans are imported into the NobelGuide software (Nobel Biocare, Yorba Linda, CA) the shape of the prosthesis, captured in the second scan, will be precisely aligned with the image of the surgical site, using the gutta percha markers as reference points.
Having a 3-D computer model of the bone in relation to the ideal prosthesis gives the surgeon an invaluable tool for deciding where the implant(s) should be placed for optimal anchorage, provision of support for the prosthesis, and a superior restorative outcome. Alternatively, the computer model may reveal that grafting is necessary. Either the surgical or the restorative doctor may do the initial planning, and then the computer model can be shared with the other team member(s).
After a final decision has been made about the implant(s) positioning, the planning software creates a rendition of a surgical guide that will enable precise placement of the actual implants in the predetermined positions and orientations. A computer file containing the 3D model of this surgical guide is then transmitted electronically for rapid prototyping by a suitable facility. Once fabricated, the surgical guide is sent to a dental laboratory trained in working with the guided surgery concept, to be used in making the surgical index (a special bite registration created on the articulator) and the master cast from which the restoration will be created.
After the master cast has been made, the surgical guide is returned to the surgeon. During implant placement surgery, the surgical guide is positioned using a surgical index and secured with guided anchor pins. The minimally invasive guided surgery is accomplished by using appropriate instrumentation and drilling sequentially with increasing diameters. The implants are then inserted, and the temporary or final premade restoration is delivered.
Guided surgery is not currently suitable for all cases of implant placement immediately following extraction. It can be used routinely when treating partially and fully edentulous ridges, as well as single-implant placement sites anywhere in the mouth.
A 56-year-old female patient presented who had been fully edentulous for a number of years. Her mandible had been restored with four implants and a bar-supported over-denture. Tired of the instability of her removable maxillary denture (Figure 18-1, A), she sought an implant-supported solution.
Figure 18-1. A, Preoperative clinical photo. The patient was seeking a more stable replacement for her removable maxillary denture. B, A thick edentulous ridge with healthy tissue and ideal tone. C, The clear acrylic radiographic guide. Some of the gutta percha markers can be seen.
Clinical examination of the edentulous arch (Figure 18-1, B) revealed a thick, healthy ridge. The tissue firmness and tone were ideal, with no preprosthetic surgery indicated. The patient was advised that she appeared to be an ideal candidate for Teeth In An Hour (Nobel Biocare). This is the treatment option the patient chose.
The patient’s dental aesthetics were evaluated, and it was decided to modify her existing denture, adjusting the contours and relining the intaglio surface with a soft-line material to achieve an intimate fit with her soft tissue. Because of the soft lining, it was necessary to duplicate the optimized denture in hard clear acrylic. (The exact thickness of the gingival and palatal tissue cannot be identified precisely with a soft-lined prosthesis.) Ten gutta percha radiographic markers were added to the clear acrylic denture (see Figure 18-1, C).
In the offices of the surgeon, an i-CAT CT scan (Imaging Sciences International, Inc., Hatfield, PA) was taken of the patient wearing the radiographic guide with the bite registration. The radiographic guide alone was then scanned. The data from the scans were loaded into the planning software. Three-dimensional/>