Forty-five square specimens were produced using cast, milling, and laser-sintering techniques. The production techniques and materials of the titanium specimens used in the study are shown in Table 1.
Table 1
Production techniques of titanium frameworks and materials
Production Technique | Product name | Manufacturer | Composition |
Milling | DC Titan | DCS Dental AG, Allschwil, Switzerland | Titanium, Grade 2 |
Casting | Tritan | Dentaurum, Ispringen, Germany | Titanium, Grade 1 |
Laser-sintering | EOS-Titanium | EOS GmbH, Munich, Germany | Ti64, Grade 5 |
Fifteen square titanium specimens (10x10x1mm) were cast with titanium grade 1 (Tritan, Dentaurum, Ispringen, Germany) by using the lost-wax method. For the casting of the specimens were used a special investment material (Rematitan Plus, Dentaurum, Ispringen, Germany). The invested rings were heated in the furnace at the temperature recommended by the manufacturer. Then, they were allowed to cool at room temperature. Casting surpluses were trimmed with a carbide cutter (Changzhou Lihao Tools Co., Ltd., Jiangsu, China).
Fifteen square titanium specimens (10x10x1mm) were produced from a block of pure titanium by using CAD/CAM method. (DC-Titan, DCS Dental AG, Allschwil, Switzerland). Square specimen geometry was defined by using a CAD software and the data of the specimens were sent to the CAM unit.
Fifteen laser-sintered titanium specimens (10x10x1mm) were fabricated in pieces formed by layer-by-layer adding with the EOSINT M 290 system (EOS GmbH, Munich, Germany). The EOSINT M 290 is a machine that has advanced hardware and software control, using a focused laser beam. EOS Titanium Ti64 powder was melted by EOSINT M 290 machine and fused into a solid piece. Thus, specimens were automatically fabricated from 3D CAD data without requiring manual manipulation.
600-grit silicon carbide papers were used for polishing of the bonding surfaces of the specimens (Sankyo Rikagaku Co., Ltd., Saitama, Japan). This process was performed under water cooling by a polisher machine (Ecomet 30, Buehler, Germany) to ensure standard surface roughness. Then, the sizes of all specimens were checked from six different points using a digital caliper (Digital Caliper, World Precision Instruments, Sarasota, FL, USA). Inappropriate samples were excluded from the study and reproduced.
The veneering porcelain Super Porcelain Ti 22 (Kuraray Noritake Dental Inc., Japan) was used for all specimens (A1, body shade). Specimens were abraded 15 seconds at 3.5 bar pressure with 50-µm aluminum oxide (Al2O3) particles by airborne particle abrasion. They were ultrasonically cleaned in acetone solution for 10 minutes. After the cleaning process, the specimens were fired at 500°C to 800°C with a heat rate of 50°C/min., a holding time of 3 minutes under a vacuum of 99kPa for oxidation treatment of titanium. (Sintra Shenpaz Industries Ltd., Tel Aviv Israel). Bonding porcelain was applied on the surface of titanium framework and baked at 800°C under a vacuum of 99kPa. After baking, it was sandblasted lightly with alumina sand to 3MPa and cleaned ultrasonically in acetone solution for 5 min. Opaque porcelain and opaque liquid were mixed and applied on the porcelain bonding surface of the specimens as 0,1mm thickness (A1, opaque shade). All specimens were fired at 780°C under a vacuum of 96kPa. After firing, the thicknesses of the opaque layers were gauged by the coating thickness tester device (Würth, Würth GmbH & Co., Künzelsau, Germany). The device was calibrated by a calibration foil with 120µm thickness. For each specimen was carried out three measurements and the results were registered. The layer thickness of the specimens with an opaque porcelain layer larger than 0,1mm in the thickness measurement was grinded by sandpaper. Porcelain was mixed with the forming liquid and applied. All specimens were fired at 760°C under vacuum. In the thickness measurement, the layer thickness of the specimens with a porcelain layer larger than 1 mm were grinded by sandpaper and which were glazed in the porcelain furnace. Color measurements of all specimens were performed under illumination, xenon filtered with approximate D65 on a spectrophotometer. (Datacolor spectrophotometer, Spectra Flash SF600 Plus, Datacolor AG, Lawrenceville, NJ, USA). The devices used in the research are shown in Table 2.
Table 2
The devices used in the research
Device | Model/Brand | Manufacturer |
Coating Thickness Tester Device | Würth | Würth GmbH & Co., Künzelsau, Germany |
Spectrophotometer | Datacolor, Spectra Flash SF600 Plus | Datacolor AG, Lawrenceville, NJ, USA |
Digital Caliper | Digital Caliper | World Precision Instruments, Sarasota, FL, USA |
The measurement geometry was diffuse illumination and 8-degree viewing. Color measurements were recorded as CIE L*, a*, b* values. A spectrophotometer that automatically makes 3 measurements for each sample was used to determine the mean L*, a*, b* values and the results were recorded. Measurements were performed in three stages as before opaque application, after opaque application, and after porcelain + glaze application. ΔE00 values between different laboratory steps of different production techniques and the same steps of binary groups were calculated using the CIEDE2000 formula. The calculation of color difference (ΔE00) was performed as follows CIEDE2000 formula [24, 25, 31].
ΔE00 = [(ΔL'/KLSL)2 + (ΔC'/KCSC)2 + (ΔH'/KHSH)2 + RT(ΔC'/KCSC) (ΔH'/KHSH)]1/2
In this formula, ΔL’, ΔC’ and ΔH’ express differences in lightness, chroma, and hue. KL, KC, and KH are the parametric factors. These parametric factors were used to correct the illuminating and viewing conditions and were set as 1.0 under the reference conditions defined by CIE. The weighting functions for the lightness, hue, and chroma components are shown as SL, SC, and SH symbols, respectively. RT (rotation term) is used for improving the performance of hue and chroma in the blue zone [32].
PSPP statistical software (GNU Software, General Public License) and Microsoft Excel computer programs were used. The outcomes of this study were evaluated at the 95% confidence interval, at the p < 0.05 statistical significance level. As a statistical method in the analysis of data in the research; descriptive analyzes (mean, standard deviation, 95% CI) were used. Shapiro Wilks (Normality) and ANOVA (Post Hoc:Bonferroni) tests were applied.