Cerec primescan

Before cavity preparation, all teeth were scanned with an intraoral scanner in the Biogeneric Copy mode (CEREC Primescan, Dentsply Sirona, Bensheim, Germany). After cavity preparation, the samples were scanned again, and then restorations were designed with Computer-Aided Design (CAD) software (CEREC SW 5.2, Dentsply Sirona, Bensheim, Germany), using the biogeneric copy from the initial scan to recreate the natural features of the original, unprepared tooth in the restorations. All overlay restorations were created from zirconia-reinforced lithium disilicate ceramic shade A2 (Celtra Duo^®, Dentsply Sirona, Bensheim, Germany) in a milling unit (Primemill, Dentsply Sirona, Bensheim, Germany). After the milling process, heat treatment was performed using a sintering furnace (CEREC SpeedFire, Dentsply Sirona, Bensheim, Germany) at a temperature of 820 °C for 10 min and 45 s. The tooth preparation and the overlay restoration design for each experiment group are shown in Fig. 2.Figure 2

The tooth preparation and the overlay restoration design for each experiment group.

A prepared maxillary dentiform (CEREC AC Model, Dentsply Sirona, Charlotte, NC, USA) was used for die fabrication. A maxillary left first molar (#26) prepared with a chamfer margin with a width of 1 mm was scanned with an intra-oral scanner (CEREC Primescan, Dentsply Sirona, Charlotte, NC, USA). After obtaining a marginal thickness of 1.0 mm as a control group, experimental groups with margins of 0.8 mm (group A), 0.6 mm (group B) and 0.4 mm (group C) were obtained by using the CEREC design software (Inlab, Dentsply Sirona, Charlotte, NC, USA). The abutment die models were printed with a resin-based printing material (Structomer DentaPro, Structo 3D, MacPherson Rd, Singapore) using a 3D printer (Dentaform, Structo 3D, MacPherson Rd, Singapore). A total of 40 abutment dies (10 for each group) were fabricated in the form of maxillary first molars; the bottoms of the dies were of the same size, measuring 9 mm in height, 12 mm in width, and 18 mm in length, in accordance with the size of the jig being used in the fracture load test. The design of the abutment die and crown is shown in Figure 1, and the mechanical properties of the materials used to fabricate the abutment die are shown in Table 1.

The volumetric wear of the materials was measured by superimposing pre- and post-brushing test scans obtained with an intraoral optical scanner (CEREC Primescan; Dentsply Sirona, Bensheim, Germany). The data acquired from the digitization of each sample were imported in STL format into the OraCheck software 5.0 (Dentsply Sirona, Germany), which allows for a 3D comparison between two or more digital scans using the best-fit algorithm.