Vitablocs mark 2

Square/rectangular ceramic slabs (5 mm long, height 1 mm) were cut from feldspathic ceramic blocks (VITABLOCS Mark II from VITA Zahnfabrik, Germany). These slabs were polished with sandpapers (240–4000 grit). For cleaning and disinfection purpose, the samples were placed in the ultrasonicator and immersed in isopropanol (70%) for 15 min, followed by ultrasonication with distilled water and finally dried before use.

Table 1 lists the product name, composition, lot number, and manufacturer for each material used in this study. An all-in-one adhesive system (Clearfil Universal Bond Quick; Kuraray Noritake Dental, Tokyo, Japan) was used alone or in combination with a flowable resin composite (Clearfil Majesty ES Flow; Kuraray Noritake Dental) for IDS treatment. An adhesive resin cement (PANAVIA SA Cement Universal; Kuraray Noritake Dental) that demonstrated self-adhesive ability not only to dentin but also to various restorative materials (e.g., ceramics, resin composite, metal alloy) was used for the luting of CAD/CAM ceramic restorations. The pretreatment of the inner surface of the restorative prior to luting was performed using 9.5% hydrofluoric acid (Porcelain Etchant; BISCO, Schaumburg, IL, USA). A typical chair-side CAD/CAM system (CEREC AC Omnicam SW v4.5 and CEREC MC XL; Dentsply Sirona, York, PA, USA) was used for the scanning, designing, and fabrication of the ceramic crown. A feldspathic ceramic block (VITABLOCS Mark II; VITA Zahnfabrik, Bad Säckingen, Germany) was selected as the material for the CAD/CAM crown. All light irradiation procedures were performed with a light-emitting diode (LED) curing source (G-Light Prima II, GC, Tokyo, Japan) in the normal mode (870 mW/cm²) after the confirmation of the light intensity prior to each irradiation.

The model of the upper arch was made of resin extending from half of the first molar to half of the first molar. The 18% gray color of resin was selected to reduce the scattering light around the samples. The space of the right central incisor (tooth number 11) was prepared to replace by milled restorations fabricated by CAD/CAM. To fabricate the central incisor, first, the model was scanned by an intraoral scanner (Trios 3 Basic, 3Shape^®, Copenhagen, Denmark). Second, the STL files were used to fabricate 30 milled restorations. Vitablocs^® mark II (VITA Zahnfabrik^®, Bad Sackingen, Germany) which is a monochromic feldspar ceramic was utilized because of the various shade providence in the market. Nine possible VITA 3D-Master shades including 1M1, 1M2, 2M1, 2M2, 2M3, 3M1, 3M2, 3M3, and 4M2 were used to fabricate 30 teeth. The identical size and shape of those milled restorations were double-checked by the measurement from the vernier caliper. The tooth was retained in the model by friction to minimize the adjustment of the restoration and the referent points were marked. The cross-section of the imaginary lines, at the middle third of the tooth, was indicated as a shade measuring point (Figure 3).