Marginal accuracy on titanium implant abutments with ring and ringless casting technique- An in vitro study

Purpose: The ring-less investment system is in use for dental casting, although there was no adequate scientific data to support its use either for conventional fixed dental prosthesis or implant retained fixed dental prosthesis. The purpose of this study was to determine whether the ringless casting and accelerated wax-elimination techniques can be combined to offer a cost-effective, clinically acceptable, and time-saving alternative for fabricating single unit castings in fixed prosthodontics. Materials and Method: An in-vitro study was undertaken to compare the vertical marginal accuracy of single full coverage metal copings, between ring-less and metal ring investment techniques, using two different investment materials and two different types of casting techniques, conventional and accelerated for implant supported dental prosthesis. Four groups were made of forty samples each. All copings were identical, Microscopic measurements were recorded at 80X magnification on the perpendicular to the axial wall at four predetermined sites. The measurements thus obtained were tabulated and statistically analyzed. Result and Conclusion:Within the limitation of the study the following conclusions were drawn from the data obtained in this study, Mean Vertical gap was the maximum for Group IV (53.58), followed by Group II (44.27), Group I (44.27) and Group III (36.11), which was statistically significant. Conventional casting using ringless (Group III) coping had shown least vertical marginal discrepancy and statistically significantly better marginal fit than that fabricated by conventional and accelerated casting with metal ring investments. Accelerated casting using ringless (Group IV) coping had shown statistically maximum vertical marginal discrepancy among the four methods. The methods used for accelerated casting technique with using ringless process are technique sensitive. Minor variations in the procedures shown defects such as nodules, fins and porosity. Ring-less system of casting can be recommended for use in fabricating implant supported fixed dental restorations.