Effect of different luting agents on vertical marginal fit of full contour CAD/CAM zirconia crown restorations: a comparative in vitro study

Introduction
Marginal fit is crucial for the long-term success of zirconia restorations, because it directly impacts the restoration’s durability, function, and biological compatibility.

Objective
To evaluate and compare the vertical marginal fit of full contour CAD/CAM (computer-aided design and computer-aided manufacturing) zirconia crown restorations luted with different cement types.

Material and methods
Twenty-four upper first premolars were prepared to receive zirconia crown restorations under preparation guidelines as follow: Chamfer finish line of 1.5 mm above CEJ, 0.8 mm circumferential axial reduction, total convergence angle of 6°, and 4 mm bucco-gingival height. Prepared teeth were randomly divided into three groups (n = 8 per group) in accordance with the type of luting cement used. Each group was then subdivided into two subgroups, representing pre- and post-cementation conditions: Group A (A1, A2): Cementation with RelyX™ Ultimate adhesive resin cement; Group B (B1, B2): Cementation with RelyX™ U200 self-adhesive resin cement; Group C (C1, C2): Cementation with RIVA Luting Plus resin modified glass ionomer cement. The prepared teeth samples were digitally scanned, and zirconia crowns were fabricated by Sirona InLab MC X5 milling device. Zirconia crowns were then cemented relative to luting cement group. Pre- and post- cementation vertical marginal gaps (VMGs) were measured using a digital microscope at 280× magnification. Data were statistically analyzed with paired t-test and ANOVA, at 0.05 significance level.

Results
There was a significant difference (p ≤ 0.05) between pre- and post-cementation VMG values for each cement type. The highest VMG reading was observed in C2 subgroup (51.3238 µm), while the lowest was in B1 subgroup (22.1050 µm). ANOVA analysis confirmed a significant difference among the post-cementation subgroups. Duncan’s test revealed that C2 subgroup (51.3238 µm) differed significantly from both A2 and B2 subgroups, with values of 41.0163 µm and 41.9775 µm, respectively.

Conclusions
RelyX™ Ultimate adhesive luting agent demonstrated less marginal discrepancy as compared with the other luting agents investigated.