Dimensional accuracy of castings fabricated with ringless and metal ring investment systems for implant supported fixed dental prosthesis : An in-vitro comparative study

Abstract

Background: 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. Methods: An in-vitro study was undertaken to compare the vertical marginal accuracy of single full coverage metal restorations, between ring-less and metal ring investment techniques, using two different investment materials, for implant supported fixed dental prosthesis. Three groups were made of ten samples each. Group I consisted of metal ring with PCT® FlexVest (phosphate bonded investment material). Group II consisted of metal ring with Bellasun® investment material. Group III and the final group consisted of ring-less investment system and Bellasun® investment material. The wax patterns were prepared on a metal die, cast and finished. The cast restorations (samples) were again seated on the metal die and the accuracy of fit was evaluated by measuring the gap between the finish line on the die and the margins of the sample at four specific sites using a profile projector (Helios-350H, Microtecnica, LTF, Italy) having accuracy of 1µm. Result: Mean marginal accuracy for Group-III was found to be the least (58.87 + 17.87µm) followed by Group-II (97.23 + 16.37[m), and Group-I (109 + 7.55 µm). However, Group I showed the least variability among the readings (SD=7.55). Conclusion: Ring-less system of casting can be recommended for use in fabricating implant supported fixed dental restorations.