Marginal Fit of Single-Crown and Three-Unit Fixed Dental Prostheses Fabricated From Digital and Conventional Impressions: An In Vitro Cross-Sectional Study.

INTRODUCTION

With the current surge into digital dentistry, several options are available for clinicians, for example, when providing indirect restorations. There is a need for evidence on the quality of fixed dental prostheses (FDPs) fabricated using either digital or conventional impressions. This study aimed to evaluate the marginal fit of single-crown and three-unit FDP frameworks fabricated from digital and conventional impressions.

MATERIALS AND METHODS

Crown preparations were made on a maxillary typodont model (KaVo Dental GmbH, Biberach, Germany) on the right central incisor for a single-crown framework and the right first premolar and first molar for a three-unit framework to replace the second premolar. Four scanners (Dental Wings (DW, Straumann Group, Montreal, Canada), Carestream 3600 (CS, Carestream Dental, Atlanta, GA, USA), Medit i700 (M700, MEDIT Corp., Seoul, Republic of Korea), and Medit i500 (M500, MEDIT Corp.)) were used to record digital impressions of the preparations. Conventional impressions using polyether monophase impression material were also made, and stone casts were fabricated using high-strength stone and scanned using a laboratory scanner (Dental Wings, Straumann Group). Stereolithography files and computer-aided design and computer-aided manufacturing (CAD-CAM) were used to produce 50 zirconia FDPs (25 each of single crowns and three-unit frameworks). The marginal fit of the prostheses was determined by marginal gap measurements while seated on the typodont, a gap of ≤150µm being deemed acceptable. Results were summarized as means, standard deviations, medians, and interquartile ranges (IQRs). The independent t-test and one-way ANOVA followed by Tukey's post hoc test for means and Kruskal-Wallis test followed by Dunn's post hoc test for medians were performed for hypothesis testing at α<0.05.

RESULTS

The respective marginal gap measurements for single-crown and three-unit FDPs were 151.3±60.1µm and 153.9±50.1µm (polyether), 185.0±63.7µm and 224.2±81.7µm (DW), 177.1±81.3µm and 146.4±44.9µm (CS), 158.0±48.7µm and 184.3±86.2µm (M700), and 195.9±61.7µm and 202.8±71.1µm (M500). The marginal gap measurements of single crowns were significantly different among the five impression methods (F = 2.54, p = 0.042; χ = 14.68, p = 0.005) but not among the four digital methods (F = 1.83, p = 0.146), with the specific differences being between polyether and DW (p<0.01) and between polyether and M500 (p<0.001). The marginal gap measurements of the three-unit prostheses were significantly different among all five impression methods (F = 13.52, χ = 46.64, p<0.001) and the four digital methods (F = 12.32, p<0.001). The specific differences were between polyether and DW (p<0.001), M700 (p=0.02), and M500 (p<0.001), respectively; between CS and the other three digital methods (DW, p<0.001; M700, p=0.024; M500, p<0.001); and between DW and M700 (p=0.016).

CONCLUSION

Considering the means and standard deviations, all five impression techniques produced FDPs with acceptable marginal gap measurements. Significant differences were observed between conventional and digital impression techniques, with polyether and CS producing single-crown and three-unit FDPs having the least marginal gaps, respectively.