Evaluation and comparison of contrast-to-noise ratio generated by lithium disilicate and zirconia: A phantom study

This study evaluated how restorative materials-specifically, lithium disilicate (LD) (IPS e.max; Ivoclar Vivadent, Liechtenstein, Switzerland) and zirconia-affect the contrast-to-noise ratio (CNR) in cone-beam computed tomography (CBCT) imaging.

CNR was compared between LD and zirconia (NexxZr T; Sagemax Bioceramics, Federal Way, USA; and Zirlux Transitions; Zahn Dental, New York, USA) using 2 CBCT machines-Planmeca ProMax 3D Mid 2015 (Planmeca, Helsinki, Finland) and PreXion 3D Excelsior (PreXion Inc., San Mateo, USA)-under multiple exposure settings, with and without metal artifact reduction (MAR). Four cylindrical ingots were scanned in a saline phantom under 10 conditions (Planmeca: Low, Normal, High, ±MAR; PreXion: Rapid, Standard, HD, UHD). CNR was calculated in ImageJ (National Institutes of Health, Bethesda, MD, USA) and analyzed with the paired t-test.

LD showed the highest CNR on Planmeca without MAR and across all PreXion settings. With MAR on Planmeca, zirconia outperformed LD. For zirconia, CNR improved with larger voxel sizes and MAR, whereas for LD it was optimal with smaller voxel sizes and MAR. Optimal Planmeca settings were Low (400 µm)+MAR for zirconia and High (150 µm)+MAR for LD. On PreXion, Rapid (200 µm) favored zirconia, while HD (100 µm) favored LD.

CBCT settings should be tailored to the restorative material, diagnostic need, and radiation dose. For zirconia, larger voxel sizes with MAR enhance CNR; for LD, smaller voxel sizes with MAR are optimal. These findings support imaging optimization for patients with dental restorations.