Accuracy of tooth color determination by dental students using daylight-calibrated dental operatory lighting sources.

STATEMENT OF PROBLEM: Lighting conditions are an essential factor for accurately determining tooth color. However, the ideal lighting conditions for determining tooth shade are rarely met and are difficult to quantify. While the use of a standardized daylight lamp D55 can improve accuracy, its high cost limits its use in dental offices. The use of modern operatory treatment units for tooth color determination is promising, as they now allow for the adjustment of light source settings such as color temperature and intensity. However, studies are needed to determine whether they provide accurate color determination. PURPOSE: The purpose of this study was to assess the accuracy of visual tooth shade determinations under the adjusted light sources of 2 different dental treatment units in comparison with a standardized daylight lamp D55. MATERIAL AND METHODS: Dental treatment units from 2 manufacturers KaVoLUX 540 LED (LK) and LEDview Plus (LDS) were tested. The light sources of these units were adjusted to match daylight conditions. A daylight lamp (Dialite Color 7; Eickhorst & Co. KG) was used as a control (D55). A total of 49 participants (median age of 25 years, 30 women) underwent the Ishihara screening and received standardized training calibration. A total of 2205 clinical visual tooth shade determinations were performed with the Toothguide Training Box using the Vita 3D-Master shade guide under the 3 different lighting types. Each participant had 15 color determinations made under each of the 3 light settings. Color differences were analyzed by using the Kruskal-Wallis, Wilcoxon rank-sum, and chi-squared tests (α=.05). RESULTS: The type of lighting used for tooth shade determination had no significant effect on the accuracy of selected shade based on the ΔE00 metric (P=.133). Perfect matches were achieved in 50.8% of the cases under LK, 49.8% under LDS, and 53.6% under D55 light, with no significant difference among percentages (P=.315). Although there was a significant difference in time elapsed for shade determination by light type (P=.004), this difference was not clinically relevant (20.8 seconds for LK, 23.9 seconds for LDS, 21.9 seconds for D55). CONCLUSIONS: The accuracy of color determination for both examined dental operatory lamps was found to be comparable with that of the standard D55 daylight lamp when adjusted to specific settings.

Effect of grinding on the optical properties of monolithic zirconia.

OBJECTIVES: The purpose of this study was to analyze the color infiltration in monolithic zirconia after grinding, which plays an essential role in the color stability of restorations after occlusal adjustment. METHODS: One hundred and eight white zirconia plates (36 Dentsply Sirona-Cercon high translucency [C], 36 Zirkonzahn-Prettau [P], 36 Zirkonzahn-Prettau anterior [Pa]) were stained by infiltration with target colors Vita A2, A3.5, and A4. In a standardized experimental setup, all plates were grinded in nine successive steps (from baseline to 500 µm), and color was measured with a spectroradiometer at each grinding step. Color differences ΔE00 between initial color and after each grinding step were calculated. The data was analyzed using regression, Kruskal-Wallis test, inverse prediction, and simultaneous 95%-confidence intervals. RESULTS: Grinding had a significant effect on color stability across all zirconia types and target colors (p < 0.001). At each cut level and target color, ΔE00 means for groups C, P, and Pa were statistically different (p < 0.05). Among the three zirconia types, Pa had the lowest ΔE00 mean score for cut levels 20-100 µm for A2 and between 50 and 300 µm for A3.5 and A4. For all other cut levels, differences between Pa and P were not significant (α = 0.05). C had the largest mean ΔE00 except for A4 until 100 µm, where it was second best. CONCLUSION: Zirconia type had a significant effect on the color infiltration depth across all target colors. Pa showed the best color stability until 150 µm material reduction, whereas C presented significantly less color stability than the other two zirconia materials. CLINICAL SIGNIFICANCE: Color stability is important for minimizing the risk of restoration failure due to unacceptable color changes after grinding. Pa is less susceptible to color change and has an additional buffer of 60 µm until exceeding the color acceptability threshold. When higher flexural strength is needed, P is to be preferred.

Effect of grinding adjustments on the color of monolithic zirconia.

STATEMENT OF PROBLEM: Monolithic zirconia restorations have become popular because of their excellent mechanical properties and acceptable esthetics. While the biomechanical properties of zirconia have been investigated, research into their esthetic properties is sparse. Zirconia can be colored by infiltration before sintering, although how occlusal adjustment can affect restoration color is unclear. PURPOSE: The purpose of this in vitro study was to analyze the color of differently characterized monolithic white and precolored zirconia specimens after standardized grinding. MATERIAL AND METHODS: White and precolored monolithic zirconia plates (Cercon ht) (n=36) were stained by infiltration with target colors Vita A2, A3.5, and A4. In a standardized experimental arrangement, all plates were ground in 9 steps, and the color was measured with a spectroradiometer at each step. Color differences (ΔE00) were analyzed by using regression analysis, the Kruskal-Wallis test, and the inverse prediction with confidence intervals (α=.05). RESULTS: Mechanical material removal had a significant effect on the color stability (P<.05) of both white and precolored monolithic zirconia. For each grinding step and each target color, the precolored groups had a significantly lower ΔE00 mean than the white groups (P<.05), except at the 20-µm step for groups W-A4 and P-A4 (P>.05). For target color A2, the difference was significant with P<.001 at all 9 grinding steps. For target color A3.5, the difference was significant with P=.003 at grinding level 20 µm, and P<.001 for all other grinding steps. For target color A4, the difference was not significant with P=.603 at grinding level 20 µm, whereas the difference was significant with P=.007 at grinding level 50 µm, and with P<.001 for all other grinding steps. CONCLUSIONS: Precolored zirconia had less color change after grinding than white zirconia. This study established grinding depths for white and precolored zirconia corresponding to color perceptibility and acceptability thresholds.