## 2 Materials and Methods  
### Specim Preparation  
Specimen preparation process is shown in Figure 1. Twenty-six recently extracted human molars were used. Teeth were kept in distilled water during the waiting period for specimen preparation. Each tooth specimen was prepared past dentino-enamel junction into dentin to accommodate a lithium disilicate or zirconia crown with material thickness of approximately 1 mm (mm) axially and 1.5 mm occlusally using a dental rotary handpiece and diamond burs with generous air and water coolant. A 0.5 mm deep chamfer finishing line was used. After the tooth preparation, the specimen was scanned using an intraoral scanner (Emerald, Planmeca, Helsinki, Finland). The crown was virtually designed using CAD software (Romexis version 5.1, Planmeca, Helsinki, Finland). The material thickness of -0.5 mm at the crown margin and \(\sim\)1-1.5 mm axially and occlusally was used. The cement gap was designed as 100 \(\upmu\)m.  
For the lithium disilicate crown, the crown design was exported into a standard tessellation language (STL) format to be milled. A pre-sintered monolithic lithium disilicate block (IPS e.max CAD C14 LT A2, Ivoclar Vivadent, Schaan, Liechtenstein) was milled using a single spindle desktop milling machine (PlanMill 30S, Planmeca, Helsinki, Finland). The pre-sintered milled crown was then stained, characterized with feldspathic porcelain, and sintered using the manufacturer's recommended combined staining, glazing, and crystallization protocol in a ceramic furnace (Programat CS3, Ivoclar Vivadent, Schaan, Liechtenstein) for \(\sim\)15 min in the furnace or \(\sim\)45 min total time including the preheating and subsequent cooling of the furnace. The excess glaze around the margin was removed and the crown was polished. The luting protocol was based on the manufacturer's recommendation. The crown was tried to determine appropriate fitting and then luted with composite resin cement (Multilink Automix, Ivoclar Vivadent, Schaan, Liechtenstein). Briefly, the crown was steam-cleaned, etched with 5% hydrofluoric acid (IPS Ceramic Etching Gel, Ivoclar Vivadent, Schaan, Liechtenstein) for 20 s (sec), rinsed with water and air dried, conditioned with silane for 60 s (Monoband Plus, Ivoclar Vivadent, Schaan, Liechtenstein) and then air dried. The abutmen was primed for 30 s with a  
Figure 1: **Specimen preparation. ** (**A**) Recently discarded extracted natural teeth were selected and cleaned, (**B**) the tooth was prepared for the crown, (**C**) the tooth was scanned using an intraoral scanner and the digital design was done, (**D**) the crown was milled, (**E**) the crown was cemented and the temperature probe was inserted. mixture of two primers per the manufacturer's recommendation (Primer A and B, Multilink, Ivoclar Vivadent, Schaan, Liechtenstein). The crown was pressed with finger-pressure for about 5 min. Light polymerization for 20 s for each axial and occlusal surface was performed. The cemented specimen was kept in a 100% humidity chamber using distilled water for at least 48 h before crown retrieval. For the zirconia crown, the crown design was exported and milled using a single spindle desktop milling machine (PlanMill 30S, Planmeca, Helsinki, Finland) out of a monolithic 3 mol% yttria stabilized tetragonal zirconia polycrystal (3Y-TZP) block (IPS e.max ZirCAD LT C17 A2, Ivoclar Vivadent, Schaan, Liechtenstein). The milled crown was sintered for 45 min per the manufacturer's recommendation using a sintering furnace (Programat CS4, Ivoclar Vivadent, Schaan, Liechtenstein). After sintering, the crown was characterized and stained using the same furnace (Programat CS4, Ivoclar Vivadent, Schaan, Liechtenstein). The intaglio surface of the glazed crowns was then again air-abraded with 50 um aluminum oxide particles. Excess glaze around the margin was removed. The crown was polished and tried on the abutment to determine the fitting. The crown was conditioned with silane containing primer for 60 s (Monobond Plus, Ivoclar Vivadent, Schaan, Liechtenstein) and then air dried.