الفهرس 
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Abstract
Background: Fixed restorations success requires perfect adaptation and marginal sealing.
Upon seating cement accumulates on the occlusal surface in case of excessive occlusal spacer.
By controlling the amount of space for cement on the occlusal surface, the fit of the fixed
restorations may be altered.
Aim of the study: This study is aimed to determine the effect of three different digital
occlusal spacers on the marginal fit of full contour zirconia crowns
Materials and Methods: A maxillary first molar acrylic tooth will be prepared to receive
zirconia crowns. The prepared abutment will be scanned, and the virtual dies will be used to
fabricate thirty-six 3D printed master dies. master dies will be scanned with Medit i700
intraoral scanner and full contour zirconia crowns will be designed and milled with
standardized axial spacer 80 μm, and 3 different occlusal spacers: group I (n=12) with
occlusal die spacer 80 μm, group II (n=12) with occlusal die spacer 40 μm and group III
(n=12) with occlusal die spacer zero μm. Zirconia crowns will be milled, and marginal and
internal fit will be assessed with replica technique.
Results: The modification of occlusal cement spacer significantly affected the marginal and
internal fit of digitally manufactured crowns (P<.05). group 0-80 and group 40-80 had similar
marginal gap values, which were significantly lower than those of group 80-80 (P<.017). For
internal fit accuracy, group 0-80 displayed significantly lower gap values than group 40-80
and group 80-80 for all measured areas. group 40-80 had significantly lower gap values than
group 80-80 at the mid-occlusal and axio-occlusal areas (P<.017).
Conclusions: Modifying occlusal cement spacer significantly affected the fit of digitally
fabricated zirconia crowns. Reducing or eliminating occlusal spacer resulted in significantly
improved fit accuracy.