Improving the Fit of Implant-Supported Superstructures Using the Spark Erosion Technique

Purpose: The purpose of this study was to determine whether the passive fit of the implant-retained single-cast framework could be improved by spark erosion treatment. Materials and Methods: An initial cast was produced in a transparent resin material. Five Brånemark System implants were arranged in the interforaminal region, and abutments were placed on them with a torque of 20 Ncm. An impression was made using a standard impression technique described by Brånemark. A corresponding master cast suitable for the spark erosion post-framework fabrication was produced. From this master cast, 12 frameworks were produced in a conventional single-cast procedure. Six of these were made of a high-gold alloy (Stabilor G); the other 6 were made of pure titanium (Biotan). These frameworks were then refined using the SAE Secotec Spark Erosion System. To measure the accuracy of the framework fit, the frameworks were measured before and after the spark erosion treatment using 2 different measurement methods-scanning electron microscopy to measure the gap widths (Sheffield test) and photoelastic stress analysis. Results: The results of both measurement techniques correlated and demonstrated significant improvement in the accuracy of fit or in the passive fit for all 12 frameworks after spark erosion treatment. This improvement was statistically significant for the titanium frameworks. Discussion: Dental practitioners and technicians should strive to achieve a precise passive fit of frameworks and superstructures to minimize additional stress at the interfaces of the prosthesis, abutment, and implant. Conclusion: The clinical use of the spark erosion technique to refine framework fit is recommended. (More than 50 references.)