Misfit of suprastructures on implants processed by electrical discharge machining or the Cresco method

Objective: To assess the accuracy of fit of frameworks on implants processed with electrical discharge machining (EDM) or the Cresco technique (Astra Tech). Method and Materials: On 12 identical master casts with implants at positions 9(21), 11(23), and 13(25), high-gold alloy frameworks were produced by standard casting procedure. Six frameworks were used for the Cresco technique (group CRE) by employing specific fixed partial denture supports. The remaining 6 frameworks were cast with prefabricated gold copings and served as control. The finished frameworks were screwed onto implant 25 of the corresponding master cast. Dimensions of the marginal gaps were measured at 4 locations on each implant under the scanning electron microscope, applying the replica technique. Subsequently, the control group was processed by EDM (SAE EDM 2000) (group EDM) and analyzed alike. Statistical analysis of the results was performed with Kruskal-Wallis and Mann-Whitney U tests. Results: The mean marginal gaps were measured as follows (CRE / EDM / control): position 25: 0.0 µm / 1.0 ± 1.6 µm / 1.5 ± 2.1 µm; position 23: 5.2 ± 5.6 µm / 18.7 ± 29.3 µm / 23.6 ± 30.7 µm; and position 21: 36.0 ± 21.6 µm/ 40.7 ± 31.0 µm / 46.0 ± 41.1 µm. The only statistically significant difference was found at location 23 between group CRE on one side and both group EDM and control on the other side. The strong increase of misfit for group CRE from location 23 to location 21 indicates that laser welding is the crucial parameter in this technique. Conclusion: The Cresco technique has a potential to reduce the marginal gap between implants and suprastructures. Schlagwörter: Cresco, electrical discharge machining, fixed partial denture, implant, marginal fit, suprastructure