Programat p300

In this study, human enamel and three types of CAD/CAM restorative materials were tested (Table 1). For each type of CAD-CAM block, disk-shaped specimens (4 mm diameter and 2 mm thickness) were fabricated using CAD/CAM (Zenotec, Wieland, Germany). The IPS e.max CAD specimens were crystallized (Programat P300, Ivoclar Vivadent) according to the instructions from the manufacturer. Buccal enamel blocks (4 mm diameter and 1 mm thickness) were cut from extracted human molars and embedded into acrylic resin (dentin shade, New Century, Shanghai Kangqiao Dental Product, China) to achieve the same dimensions of the restorative material specimens. The specimens were polished with a three-step silicone polishing system (Ceramister, Shofu Inc, Kyoto, Japan) using a slow-speed handpiece by a single blinded operator. The operator was calibrated by a wireless dynamometer (T-measurement, Dalian Taijia Technology Co., Ltd, Dalian, China) and a press-on force of 2 N pressure was applied during polishing.
For each polisher, all specimens were polished for 30 s in the same direction (left to right) (Vrochari et al., 2017) . The polisher was discarded after being used once (Chavali et al., 2017) . The specimens were then ultrasonically cleaned in distilled water for 10 min.

Forty specimens including four different thickness (1, 2, 3, and 4 mm) were prepared for each of five glassceramic blocks (CD, CDc, EMHT, EMLT, and RL) and a resin nano ceramic block (LU), for a total of 240 specimens (6 materials×10 specimens×4 thicknesses). CDc, EMHT, EMLT, and RL were fired according to the manufacturer's instruction (Programat ® p300, Ivoclar Vivadent, Schaan, Liechtenstein). The glass-ceramic and resin nano ceramic blocks were cut with a low-speed water-cooled saw (DAIMO-100S, MTDI, Daejeon, South Korea) to obtain specimens with four different thickness (1, 2, 3, and 4 mm). After cutting the glass-ceramic and nano ceramic blocks, the specimens were polished with 600, 1000, 2000, and 4000 grit SiC papers, and they were measured with a caliper (500-181, Mitutoyo) with a precision of 0.05 mm. The specimens were prepared without glazing. Specimens with any defects on the surface were removed.

The materials and instructions used in this study are listed in Table 1. LDS (IPS e.max CAD, Ivoclar Vivadent) blocks were used in this study. A total of sixty-one LDS specimens (2 mm thickness×15 mm width×15 mm length) were obtained from the original LDS blocks using a lowspeed diamond saw (Isomet 1000, Buehler, Lake Bluff, IL, USA). The LDS specimens were submitted to the crystallization-firing process in a furnace (Programat P300, Ivoclar Vivadent) at 840-850°C for 30 min according to the manufacturer's recommendation.

A total of 16 CAD/CAM blocks (12 x 12 x 6 mm) of LD (IPS e.max CAD; Ivoclar Vivadent, Schaan, Liechnstein) were used in the study. Each block was cut into four square sections (6 x 6 x 6 mm; n=64) using a diamond disk cutter attached to a low-speed saw (Isomet, Buehler; Lake Bluff, IL, USA) using water as a coolant. After ultrasonic cleaning in distilled water for 15 min, the ceramic specimens were calcined following heating ramp from 25 o C to 850 o C for 20-31 min using a furnace (Programat P300, Ivoclar Vivadent) (10, 14) .
The 64 specimens were randomly divided for evaluation using three different methodologies. Forty were used for microshear bond strength (μSBS) testing, 12 specimens were used for evaluation of chemical interaction of MEP with the ceramic surface by Raman spectroscopy and 12 specimens were used for etching pattern.
Sample size calculation for bond strength to lithium disilicate was performed. The bond strength values of standard procedure were considered for sample size calculation. According to the literature (12, 14) , mean and standard deviation of HF + SI was 30.6±2.0. Using an α of 0.05, a power of 90% for equivalent test and a two-sided test, the minimal sample size was 10 specimens in each group in order will excluded a difference in means of more than 3 MPa among the tested groups.