The effect of conventional, half-digital, and full-digital fabrication techniques on the retention and apical gap of post and core restorations

Statement of problem. Conventional cast metal posts and cores are fabricated using direct and indirect techniques, both of which need impression materials and considerable laboratory work. Digital techniques have the capacity to substitute for conventional methods in fabricating the posts and cores. However, the accuracy of restorations resulting from a digital workflow is unknown. Purpose. The purpose of this in vitro study was to compare the retention of posts and cores fabricated using full-digital, half-digital, and conventional techniques and to define the accuracy of each technique in terms of the apical gap. Method and materials. Thirty newly extracted mandibular first and second premolar teeth were selected for this in vitro study. Impressions were made using direct acrylic resin patterns (conventional), indirect silicone impressions of the intracanal which scanned with a 3Shape laboratory scanner (half digital), and intracanal scan posts captured with an intraoral 3Shape scanner (full digital). Casting and milling were conducted for the conventional impression and digital scans. The obtained posts were cemented using zinc phosphate cement. A universal pullout test was used to measure retention at a crosshead speed of 0.5 mm/min. The apical gap of each post in the canals was defined with parallel digital radiography. The data were analyzed using the Kruskal-Wallis test (alpha=.05) and Mann-Whitney test at the adjusted alpha=.016. Results. Significant differences were found among the conventional, full-digital, and half-digital techniques in terms of the apical gap (0.11, 0.29, and 0.66 mm; P<.001) and retention (171.6 +/- 1.9, 107.1 +/- 5.6 and 91.8 +/- 6.6 N; P<.001). The correlation between gap and retention in conventional (P=.43), full-digital (P=.09), and half-digital techniques (P=.06) was not statistically significantly different. Conclusions. The conventional technique was more accurate and resulted in higher retention than both the full- and half-digital techniques. However, the retention and gap of all the posts fell within clinical guidelines.