Evaluate and Compare the Effect of Different Marginal Cement Space Parameter Setting in the CAD Software on the Marginal and Internal Fitness of Monolithic Zirconia Crowns with Different Types of Luting Agents (A comparative in vitro study)

Objectives: The purpose of this in vitro study was to evaluate and compare the effect of different marginal cement space parameter setting in the CAD software on the marginal and internal fitness of monolithic zirconia crowns with different luting agent. Materials and method: 48 sound human maxillary first permanent premolar teeth of comparable size and shape extracted for orthodontic purposes were collected and selected to be used in this in vitro study. All the dimensions of each crown were tested with using one way ANOVA in order to reduce the confounding variables. The teeth samples were divided into two main groups according to the different marginal cement space parameter setting (n=24) as following: Group I: 0 cement space around the margin and additional cement space of 80 Mm starting 1mm above the finish lines of the teeth. Group II: 25 Mm cement space around the margin and additional cement space of 80 Mm starting 1mm above the finish lines of the teeth. Each group was subdivided into three subgroups according to the type of luting material (n=8) :(IA, IIA) cemented with Rely X (TM) Ultimate adhesive,(IB, IIB) cemented with Rely X (TM) Unicem 200 self-adhesive and (IC, IIC) cemented with conventional Riva luting plus glass ionomer. The standard preparation for full counter monolithic zirconia crown restorations was done with light chamfer finishing line 0.8mm, axial reduction 1-1.5mm,occlso-axial height 4mm (palataly and buccally),anatomical occlusal reduction and total convergence angle 6 degree. The teeth were scanned with inEos X5 extra-oral digital scanner (Sirona, Germany), then fabricated with Sirona In-Lab MC X5 milling device. The internal and marginal fitness of crown was evaluated by direct measurement of cement film thickness through sectioning procedure using a digital microscope at a magnification of 60 X at eleven different measuring points for each specimen, which represented four different areas of measurement (margin, chamfer, axial and occlusal). Results: The results of this study showed that the different marginal cement space parameter setting used was significantly improve the marginal and internal adaptation of monolithic zirconia crown restoration. The Rely X (TM) Ultimate adhesive luting agent had a lowest mean value of marginal discrepancy as compared with the other types of luting agent that was used in this study. Conclusions: using of 25 mu m cement space at the marginal area resulted in reducing the marginal and internal gaps. The Rely X (TM) Ultimate adhesive luting agent provided the lowest marginal and internal gaps as compared with other types of luting used in this study.