Purpose: To determine if the typical mechanical resistance of one-piece castings can be maintained with an elevated level of marginal precision, the authors evaluated 10 consecutive castings obtained using their normal laboratory techniques for one-piece castings. Materials and Methods: For the evaluation of the marginal precision of the castings, a new method that uses a scanning electronic microscope (SEM) integrated with a computerized measuring system was developed. This method proved to be precise and reliable. A total of 3,564 measurements at 3003 was made of the vertical marginal openings of 10 castings structured with 3 abutments and 2 pontics (casting length 43 mm, mean weight 10.4 g). Results: The mean of such measurements of the marginal openings was 22 µm, although if 2 castings that were judged to be clinically unsuitable when produced are excluded, the abovementioned average is 16 µm. Conclusion: The proposed casting technique can offer one-piece castings of higher quality, with a level of precision that introduces a new reference standard in the marginal accuracy of these castings in fixed prostheses.