Dental Tribune Pakistan Edition

CLINICAL PRACTICE 2014 Pakistan Edition DENTAL TRIBUNE 5 advantages: platform switching and indexing trilobe morse taper connection. The latter greatly facilitates abutment placement. A tight stable connection guarantees integrity of the soft tissue (Fig. 8). In the laboratory, the master model with the embedded analogue was used to fabricate a master plaster cast. A high-rigidity cobalt-chromium and resin temporary bridge was fabricated, tried in, and transferred to the patient’s mouth 48 hours after the implants had been placed. This provisional device would serve as an external fixator during osseo- integration of the implants. A control radiograph was taken to confirm the passive fit of the framework. The temporary bridge was hand tightened to a torque of 10 Ncm. The occlusion was accurately adjusted (Figs. 7a-b). The patient wore the temporary bridge for six months. During that period, a number of parameters were evaluated, including occlusion, osseointegration status, oral hygiene, mastication, phonetics, aesthetics and lip support. The temporary bridge should be rigid (framework) and easily removable (screw fixation). Site #27 healed uneventfully, protected as it was from mechanical stress. Final bridge At the end of the six-month healing period, preparation for the final restoration began. Wearing the temporary bridge had allowed adjustment of the abovementioned parameters (e.g. aesthetics, phonetics and lip support) and validation of the vertical dimension and intermaxillary relationship. The temporary bridge was removed, an implant stability percussion test was performed, and control radiographs were taken. The straight conical abutments that had been placed concomitant with the implants were tightened to 25 Ncm (as recommended by the manufacturer), except abutment #23, which was angled (Fig. 8). An impression of the final bridge was taken with the same impression tray used for the temporary bridge. Pick-up transfer copings were interconnected using LuxaBite resin (DMG), and the impression was made using Impregum (3M ESPE). The master model, including the conical abutment analogues and silicone soft tissue (representing the patient’s gingiva), was fabricated and then validated in the dentist’s office via a wax bite block (into which extra-hard plaster material was poured). The wax bite block was then tried in (Figs. 9a–d). Using silicone indices (vestibular, occlusal and palatal) from the temporary bridge, a wax-up was fabricated in the laboratory (Fig. 10). The wax-up had to meet the aesthetic demands of the patient and be an exact replica of the temporary bridge (both anatomically and aesthetically). The validated master modeland wax-up were sent to the SIMEDA machining centre, where the master model was scanned and a CAD model was designed (Figs. 11a–d). A PDF 3-D file is used to validate the design, after which the manufacturing process can be initiated. All pieces are machined from titanium blocks using high-precision five-axis milling machines (Figs. 12a–c). Titanium is a lightweight material and, more importantly, it is highly biocompatible and has superior mechanical properties. It is four times lighter than commonly used semiprecious alloys. Actually, it is the lightest metal used in dentistry. Furthermore, titanium is a self-passivating metal: it readily reacts with oxygen in air to form a tough layer of oxide, which protects against corrosion. Titanium is known to resist corrosion and chemical attacks extremely well. Furthermore, it is bactericidal, a key advantage for dental implants. Material density is a crucial factor in implantology. We believe that the weight of a maxillary implantsupported prosthesis is the most important factor for the outcome of the restoration. A few days later, we received the framework for try-in. It had a perfect passive fit and was returned to the laboratory for veneering. The metal preparation in the laboratory entailed sandblasting, titanium etching and the application of opaque porcelain to conceal the metal core. The bisque- baked restoration was then tried in to allow the patient to validate the aesthetics of the restoration. This step is necessary to assess static and dynamic occlusion and perform minor adjustments (Figs. 13a–g). The bisque-baked restoration was then returned to the laboratory for fine tuning and glazing. CAD/CAM benefits Although conventional casting techniques have evolved, they are still fraught with inaccuracies owing to the nature of the materials and to their handling. This includes the risk of errors during investment processing, risk of metal deformation and poor metal homogeneity. The CAD/CAM technologies used for producing metal frameworks are essential to the quality of the final restoration. The CT scan data is converted into a format that allows the 3-D images to be utilised by the selected treatment planning software. The case is then planned in the software. The CAD software has databases that allow the creation of virtual models for the desired restoration using different materials, including zirconia, titanium, cobalt–chromium, IPS e-max and PMMA. If the dental laboratory has its own scanner, an STL file is sent directly to the production centre by e-mail. Otherwise, both the model and the wax- up are forwarded to the production centre by courier. If the computer settings are correct, one is ensured of perfect reproducibility in the manufacturing process and consistency in the result (i.e. a truly passive framework fit). Optimal setting of the coping thickness parameter or the pontic connection parameter may prevent torsion or deformation of the framework during firing of the ceramic. Subtractive manufacturing, combined with digital modelling, eliminates the risk of alteration of the material structure. The resulting metal framework will have optimal homogeneity and density. As regards fabrication of implant superstructures, machining is the technique of choice for achieving high precision and near passive fit. Practitioners can expect consistent and reproducible results, excellent framework fit, and regular, accurate prosthetic seals. Conclusion Today, dental laboratories are using high-tech scanning equipment, which allows digitisation of the master model (to determine the implant index) and the wax-up. CAD/CAM offers a level of quality and accuracy unsurpassed by any of the traditional techniques. Passive fit, which is critical to the outcome of an implant-supported prosthesis, is a determinant of the long-term success of a restoration. Passive fit of the framework for a long- span restoration is much easier to achieve and reproduce with CAD/CAM than with the traditional pouring techniques. The use of CAD/CAM machining for implantsupported restorations guarantees a highly accurate and predictable framework fit (< 10 m). In addition, machining centres can produce restorations using fully biocompatible materials, such as titanium and zirconia. In order to take advantage of the accuracy of CAD/CAM, using safe and reliable implant systems with superior biological and biomechanical characteristics is required. CAD/CAM will soon be essential. Current CAD/CAM solutions are easily accessible to any dentist and do not require fundamental changes to his or her work habits. Acknowledgement: Special thanks to G. Nauzes and J. Bellany, laboratory technicians at Socalab. Fig. 13f Fig. 10 A wax-up of the framework. Figs. 11a–d CAD of the model. Figs. 12a–c Machining from a titanium block. Figs. 13a & b The machined titanium framework. Figs. 13c–f The final bridge. Fig. 13g The patient’s new smile. Fig. 13h A post-op panoramic radiograph with the bridge in place. Fig. 10 Fig. 11bFig. 11b Fig. 11dFig. 11c Fig. 12a Fig. 12b Fig. 12c Fig. 13bFig. 13a Fig. 13dFig. 13c Fig. 13fFig. 13e Fig. 13g Fig. 13h November

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