Purpose:This study evaluated the marginal fit of experimental and custom-made fixed prosthetic restorations through a new 360-degree external examination. The minimum number of gap measurements required to produce relevant results for gap analysis was also investigated. Materials and Methods:The marginal fit of six experimental and eight custom-made crowns was observed microscopically by means of a mechanical device, and software was employed to measure the gap. Two crowns, chosen from among the 14 previously evaluated, were reanalyzed to determine the minimum number of gap measurements required to produce significant results for gap analysis. Results:The precision obtained with the custom-made crowns differed from that of the experimental specimens. The minimum number of measurements required to produce a sample mean value within ± 5 µm of the mean, calculated over 360 measurements, taking standard error of the means
4 µm, was 18 for experimental and 90 for custom-made crowns, for both equidistant measurement spacing and randomly selected points. Conclusion:Differences in fit between experimental specimens and custom-made ones showed that experimental results might not always be obtained in clinical practice. Within the limitations of the protocol of this study, the minimum number of measurements required to ensure relevant results for gap analysis was 18 for experimental and 90 for custom-made crowns. Int J Prosthodont 2004;17:218–223.