Translucent zirconia, manufactured by increasing the yttria content, offers improved translucency, but may have a negative effect on esthetic outcomes under clinical conditions such as discolored abutment because of the reflection of the underlying color. The purpose of this in vitro study was to compare the translucency parameter and masking ability of 3 mol % yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP (Katana HT)), 4Y-ZP (Katana STML), and 5Y-ZP (Katana UTML) with those of lithium disilicate (Rosetta SM). Zirconia and lithium disilicate specimens of 10 mm diameters and 0.8 and 1.5 mm thicknesses were fabricated. Their CIE L*a*b* values (L*, brightness; a*, red-green value; b*, yellow-blue value) were measured at the center of the specimens against black and white backgrounds using a spectrophotometer, and translucency parameter (TP) values were determined. The microstructure of the specimens was observed using scanning electron microscopy. Four cylindrical backgrounds of different shades were prepared. The zirconia and lithium disilicate specimens were placed on the backgrounds without any intervening medium. CIE L*a*b* values were obtained, and the color difference value (ΔE) was calculated. Thresholds for acceptability and perceptibility were assumed as ΔE = 5.5 and ΔE = 2.6, respectively, to evaluate masking ability. Data were compared using one-way analysis of variance and post-hoc was performed using Scheffe’s test (α = 0.05). In zirconia specimens, the TP value increased as the yttria content increased from 3 mol %, through 4 mol % to 5 mol %, and all zirconia specimens showed lower TP values than lithium disilicate specimens did. All zirconia specimens showed optimal masking ability against a normal dentin shade (ND3) and acceptable masking ability against titanium at a minimum thickness of 1.5 mm. However, no zirconia specimen could mask severely discolored dentin (ND9), regardless of thickness. The decrease in zirconia thickness from 1.5 to 0.8 mm significantly increased translucency. Monolithic Y-TZP ceramics could mask a normal dentin background but could not mask severely discolored dentin at either 0.8 or 1.5 mm thicknesses.

Kim SY, et al. J Adv Prosthodont. 2024 Aug;16(4):255-266. https://doi.org/10.4047/jap.2024.16.4.255

Eun-Bi Park, Young-Eun Cho. J Dent Rehabil Appl Sci 2024;40:169-78. https://doi.org/10.14368/jdras.2024.40.3.169

Purpose: The precision of implant prostheses, which requires accurate impression acquisition, can significantly impact a patient's treatment prognosis. This study therefore aimed to compare the accuracy of the scan data obtained using an encoded healing abutment with a scan body for digital implant impressions. Materials and Methods: A resin model was constructed using an implant analog (ISLA500, Neobiotech) at sites #15, #17, and #21. After the scan body was connected to on the model, it underwent scanning using a model scanner to produce reference data. The scan body (IS D5, Neobiotech) and encoded healing abutment (IS 4004S, Neobiotech) were connected to the model, and 20 scans per each group were performed using an intraoral scanner (Trios ® , 3Shape Dental Systems). The data obtained from these two groups were compared with the reference data using two-way analysis of variance and t-tests. Results: The mean distance from the reference point was 0.089 mm in the scan body group and 0.217 mm in the encoded healing abutment group, indicating that the scan body was closer to the reference value than the encoded healing abutment. Conclusion: Digital implant impressions obtained with the scan body were more accurate than those acquired with the encoded healing abutment when taking digital implant impressions.

윤석원, et al. J Korean Acad Prosthodont. 2024 Apr;62(2):95-103. https://doi.org/10.4047/jkap.2024.62.2.95

조영은, et al. J Korean Acad Prosthodont. 2020 Oct;58(4):349-355. https://doi.org/10.4047/jkap.2020.58.4.349