## 2 Materials and Methods
The zirconia specimens were designed using the Exocad DentalCAD 3.0 Galway (Darmstadt, Germany) software and milled on a Yenadent D15 milling machine (Yena Makina, Istanbul, Turkey). After milling, the samples were sintered in a Protherm PLF 110/6 dental furnace (Protherm Furnaces, Ankara, Turkey) according to the manufacturer's sintering parameters. The thickness of all lithium disilicate and zirconia samples was checked with an electronic caliper (Absolute Digimatic Caliper, Mitutoyo, Kawasaki, Japan). To standardize the surface quality, the specimens were polished using 600-, 800-, 1000-, and 1200-grit silicon carbide papers (3M ESPE, St. Paul, MN, USA) under running water for 30 s. The samples were cleaned in 100% distilled water for 10 min in an ultrasonic cleaner (Ultrasonic Cleaner Cd 4820, Codyson, Shenzhen, China) before finishing. Mechanical polishing of the lithium disilicate samples was carried out with the G&Z Instrumente DPLT-14 RA (EVE Ernst Vetter GmbH, Keltern, Germany) set, specially produced for mechanical polishing of feldspathic ceramics and lithium disilicate ceramics; it was used in order according to the grain size and color code. Mechanical polishing of the monolithic zirconia specimens was performed with the G&Z Instrumente DCAT-14 RA set (EVE Ernst Vetter GmbH, Germany), which is specially designed for mechanical polishing of zirconia ceramics. The polishing process was applied with a contra-angle rotary instrument (Contra angle 500, Kavo, Germany) under water cooling at a speed of 12,000 rpm according to the manufacturer's recommendation, and carried out by a single investigator. The specimens were polished for 30 s in one direction and for another 30 s at 90 degrees to the first direction [33; 34; 35; 36]. Glazing applications were performed with the glazing pastes and liquids recommended by the manufacturer for each different ceramic group. All samples were fired in the glaze programs recommended by the manufacturers. The glazed specimens in each ceramic group were ground with a red-striped fine-grit (27-76 \(\upmu\)m) diamond bur (Meisinger 881Z3-017-FG, Hager & Meisinger GmbH, Neuss, Germany) especially recommended for grinding ceramic restorations [37; 38; 39]. Surface roughness measurements of the samples were made using a profilometer device (S)-210, Mitutoyo, Japan) before the surface finishing procedures (control) and after the mechanical polishing, glazing, and grinding processes were completed. Three parallel readings were performed per sample and the Ra parameter (\(\upmu\)m) was evaluated. The surface roughness was further observed by scanning electron microscope analysis (Zeiss, Evo LS10, Jena, Germany) at a \(\times\)1000 magnification to investigate the effects of the surface finishing procedures. A glossmeter (Novo Curve Benchtop Glossmeter 60\({}^{\circ}\), Rhopoint, UK) with a 60\({}^{\circ}\) angle was used for the gloss evaluation [40; 41; 42]. Gloss measurements were made of the samples before the surface finishing (control) and after the completion of mechanical polishing, glazing, and grinding. During the measurement, the samples were covered with a black film container to block the external light. Three gloss unit (GU) values were calculated from each specimen and the average value was calculated.