Objective       To determine the effect of optical imaging powder on the accuracy of digital model of full crowns in Cerec inlab MC XL system.       Methods       A upper first right molar in the standard model were prepared

and 8 scanned models made of esthetic-base gypsum were duplicated

of which each model including digital models were digitally imaged by scanning in inEos unit before and after powder spraying. The changing paradigm of each digital model at its marginal area

shoulder area

axial area and pit and fissure of occlusal areas were measured by inlab 3D software (version 3.65). Finally

the results were analyzed statistically by SAS programs.       Results        No statistical difference was observed between the two reports of the digital model before and after a week (P0.05) in terms of measured values. The resolution of digital model after powder spraying was better than before

and optical imaging powder had certain effect on the model’s marginal area

shoulder area

axial area

and pit and fissure of occlusal areas. The floor impact counter of them were 0.073±0.042

0.106±0.077

0.044±0.025

0.128±0.060 and 0.102±0.056 mm respectively. Such differences were considered with statistical significance (P0.01).       Conclusion       Optical imaging powder has different effect on the accuracy of digital model in different area

which shows stronger on shoulder and occlusal area than on marginal and axial area. It is suggested that different regional spray powder should be treated differently.