Bonding Endocrowns with Silane and Resin Cement

Etching with 5% hydrofluoric acid (IPS Ceramic Etching Gel, Ivoclar Vivadent, Schaan, Liechtenstein) for 20 seconds was done on the tissue surfaces of endocrowns in IPS e.max CAD and Vita Suprinity groups and 60 seconds for Vita Enamic. After etching, each restoration was cleaned in an ultrasonic apparatus for five minutes and then dried with oil-free air spray. A thin layer of silane coupling agent (Prosil; FGM) was applied to the internal walls of the endocrowns for 60 seconds and then air-dried.
Self-adhesive resin composite cement (RelyX Unic-em 2 Automix, 3 M ESPE, Seefeld, Germany) with a 1: 1 base-catalyst ratio was mixed to obtain a uniform consistency. The cement was used on the tissue surface of the endocrowns. The restoration was placed on the tooth with a 3 kg weight in a load applicator. The excess cement was removed after 2-3 minutes from the start of the mix. Then the cement was light-activated for 20 seconds. A light-emitting diode curing unit (Demetron A.1, Kerr/Sybron, Orange, CA, USA) with a 12-mm diameter curing light tip
and irradiance output of 1000±50mW/cm² was used. The surface-tip distance was 0.5mm (Figure 5).
After cementation, all samples were kept in an incubator (Model 2; Precision Scientific Co., Columbus, OH, USA) at 37°C for 24 hours.