## 2 Materials and Methods  
### Fabrication of Test Samples  
Two standardized all-ceramic tooth preparations were achieved on maxillary right central incisor typodont teeth (Practicon, Greenville, NC, USA) according to the following guidelines: an incisal reduction of 2 mm, an axial reduction of 1.2-1.4 mm, a shoulder width of 1 mm, and 2 plane reductions of the labial surface. The first model was prepared with a 10\({}^{\circ}\) taper, whereas the second model was prepared with a 20\({}^{\circ}\) taper. The preparation was smoothened and prepared free of any sharp points or line angles (Figure 1).  
These models were scanned using a Bench Top Scanner (3 Shape, Copenhagen, Denmark, Model No. 4). After scanning the models, the scan data were retrieved using the design software, and the working model from each group was 3D-printed using the corresponding resin material (DentaModel, Asiga, Alexandria, Australia, Lot: MO/16020), and a 3D printing machine (Asiga 3D printer, Alexandria, Australia, Serial Number 70B3D5362C6A, Model Number PN01233) with a layer thickness of 50 micrometer, exposure time of 2.975 s, and an orientation of printing of \(-\)0 degrees. The design of the base was made compatible to the size and configuration of the universal testing machine holding clamp.  
Many previous studies using standardized metal dies similar to the 3D-printed models in the current study have evaluated the retentive strength of crowns based on different parameters [19; 20].  
Figure 1: Two standardized all-ceramic tooth preparations with 10-degree and 20-degree total occlusal convergence angles prepared on typhodont teeth.  
A computer system consisting of a stereomicroscope with a connected USB CCD camera (Amscope, Irvine, CA, USA), a personal computer, and compatible measurement software (Version No. 3.7.12924) was used to measure and verify the taper before printing the working models (Figure 2B).  
G* Power version 3.1.9.7 (2020) software (Heinrich Heine University Dusseldorf, Dusseldorf, Germany) was used to estimate the sample size. The effect size was computed as 1.23, alpha was set at 5%, and a power of 80% was used to calculate the sample size group. A total of 80 specimens were used in the study, with 10 samples in each group.  
Forty working models were 3D printed with the 10-degree taper and forty models were printed with the 20-degree taper. All of the samples were evaluated for integrity and suitability before being included in the study. The models were scanned individually to develop separate STL files, in which each file was processed individually. After setting the margin with a cement space of 50 \(\upmu\)m, as well as designing an incisal ring with a 4 mm external diameter and a 2 mm internal diameter, each STL file was saved and used to produce 40 samples of CAD/CAM-milled temporary crowns (twenty from each taper group) using a five-axis milling machine (DG SHAPE, Roland DGA, Irvine, CA, USA, Model DWX-52D) and PMMA temporary crowns blocks (CopraTemp Shade A1, WhitePeaks Dental Solutions GmbH, Wesel, Germany). Similarly, 40 samples of 3D-printed temporary crowns (twenty from each taper group) were produced using the same printing system on the working models with the corresponding resin material (DentaTooth Shade A1, Asiga, Alexandria, Australia, Lot MO/08782) (Figure 3A,B). All of the temporary crowns were checked for fit on the corresponding working models.  
Figure 3: (**A**) STL file saved with the margin set-up and the cement space set-up. (**B**) CAD/CAM-milled temporary crowns and 3D-printed crowns on working models.  
Figure 2: (**A**) Working models made with 3D-printed resin dies and 10\({}^{\circ}\) and 20\({}^{\circ}\) tapers. (**B**) Tapers measured using a computer system consisting of a stereomicroscope with a connected USB CCD camera, a personal computer, and compatible measurement software.