Precision of fit to implants : a comparison of Cresco™ and Procera® implant bridge frameworks

Background: The Cresco™ (Astra Tech AB, Molndal, Sweden) method aims to reduce the inevitable distortions when cast metal frameworks for implant-supported prostheses are fabricated. However, limited data are available for the precision of fit for this method. Purpose: To measure and compare the precision of fit of Cresco- and computer numeric controlled (CNC)-milled metal frameworks for implant-supported fixed complete prostheses. Materials and Methods: Two groups of frameworks were fabricated according to the Cresco method, either in titanium (Cresco-Ti, n = 10) or in a cobalt-chrome alloy (Cresco-CoCr, n = 10). A third group comprised CNC-milled titanium frameworks (Procera® Implant Bridge [PIB], Nobel Biocare AB, Goteborg, Sweden), made from individual model/pattern measurements (PIB, n = 5). Measurements of fit were performed by means of a coordinate measuring machine linked to a computer. The collected data on distortions were analyzed. Results: Overall, a maximal three-dimensional range of center point distortion of 279 µm was observed for measured frameworks. The framework width (x-axis) decreased for Cresco-CoCr, but increased in Cresco-Ti and PIB; Cresco-CoCr compared to Cresco-Ti (p = .0002) and Cresco-CoCr compared to PIB (p < .0001). In vertical dimension (z-axis), less distortions were present in PIB compared to Cresco-CoCr (p = .0007) and in PIB compared to Cresco-Ti (p < .0001). Conclusions: None of the frameworks presented a perfect, completely “passive fit” to the master. Although the direction of distortions varied, the horizontal distortions were of similar magnitudes. However, the PIB frameworks had statistical significant less vertical distortions as compared to the Cresco groups.