Abstract: Objective To observe the influence of different space settings on the marginal adaptation of chair-side CAD/CAM IPS e.max all ceramic crowns to provide experimental evidence for clinical application. Methods A right maxillary first molar in the ivoclar vivadent standard model was used and subsequently replicated into silicone rubber negative mold. Respectively, twenty-five preparations of die stone were irrigated. Twenty-five digital images were obtained by using optical impression of Sirona Cerec AC system. Twenty-five of them were randomly divided into 5 groups，and luting spaces were set to 30 μm(A group)，60 μm(B group)，90 μm(C group)，120 μm(D group)and 50 μm(E group) by CEREC version 4.4.4 computer software. Twenty-five all-ceramic crowns with five ones in each group were obtained according to space settings by Digital Control Cutting equipment．The Variolink N system was used for bonding. The vertical marginal gaps of four datum points, buccal, lingual, mesio and distal points were measured by Leica microscope. The mans and standard deviations were calculated. And the data were analyzed by LSD -test using SPSS 20.0, and the inter-group and intra-group comparison was examined by LSD．Results The marginal adaptations of bucco-lingual and mesio-distal sides were higher than 120 μm in A group，and the marginal adaptations of bucco-lingual and mesio-distal sides were lower than 30 μm in E group. The marginal adaptations of bucco-lingual and mesio-distal sides in B, C and D groups were between 30 μm ~120 μm. There were statistically significant differences(P<0.05) comparing A group with B, C or D groups in the marginal adaptation of bucco-lingual and mesio-distal sides. There were statistically significant differences(P<0.05) comparing E group with B, C or D groups in the marginal adaptation of bucco-lingual and mesio-distal sides. There were no statistically significant differences(P>0.05) among B, C and D groups in the marginal adaptation of bucco-lingual and mesio-distal sides. There were no statistically significant differences(P>0.05) in the marginal adaptation of bucco-lingual and mesio-distal sides in each group. Conclusion The chair-side CAD/CAM IPS e.max all-ceramic crowns can obtain the clinical acceptable marginal adaptation when the space settings are set at 60,90,120 μm while using CEREC version 4.4.4.

Key words: CAD/CAM , all-ceramic crown, marginal adaptation, space setting