Fracture strength testing of crowns made of CAD/CAM composite resins Ryota Okada, Masaki Asakura, Akihiro Ando, Hirokazu Kumano, Seiji Ban, Tatsushi Kawai, Jun Takebe  Journal of Prosthodontic Research  Volume 62, Issue 3, Pages 287-292 (July 2018) DOI: 10.1016/j.jpor.2017.10.003 Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 1 Photographs and an illustration of fracture strength test of CAD/CAM crowns. (A) Abutment made of stainless steel. (B) CAD design for a crown specimen with a thickness of 1.5–2.0mm at the occlusal surface and 1.0mm at the margin. (C) CAD/CAM composite resin crown bonded to the abutment. (D) Loading points on the occlusal surface for testing. (E) Universal testing machine (model 4481; INSTRON) used in testing. Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 2 Schematic diagram for biaxial flexural strength testing. P is the total load at fracture (N). r1 is the radius of support circle (5mm), r2 is the radius of the loaded area (1.2mm), r3 is the radius of the specimen (6mm), and b is the specimen thickness at the fracture origin (1.0±0.2mm). Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 3 Fracture strength of CAD/CAM crowns before degradation testing. Each bar represents the mean and standard deviation (SD) values of five measurements. Different letters above the bars indicate statistical significance (p<0.05). Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 4 Fracture strength of CAD/CAM crowns before and after degradation testing. Each bar represents the mean and standard deviation (SD) values of five measurements. Horizontal lines above bars denote groups of means that are statistical significance (p<0.05). Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 5 Biaxial flexural strength of CAD/CAM materials before degradation testing. Each bar represents the mean and SD of five measurements. Different letters above the bars indicate statistical significance (p<0.05). Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 6 Biaxial flexural strength of CAD/CAM materials before and after degradation testing. Each bar represents the mean and SD of five measurements. Horizontal lines above bars denote groups of means that are statistical significance (p<0.05). Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 7 SEM images of surface in CAD/CAM materials before degradation testing. Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 8 SEM images of surface in CAD/CAM materials after degradation testing. HC had cracks (yellow arrows) in the surrounding area of the spherical fillers, whereas KZR2 had void spaces (yellow arrows) due to the dissolution or desorption of the fillers. Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 9 SEM images of fracture surface in different CAD/CAM composite resin crowns and lithium disilicate glass-ceramic crown after fracture strength testing. HC and KZR had a depression at the compression site (yellow arrow). Radial cracks were observed in KZR, KZR 2 and AVE (blue arrow). Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions

Fig. 10 Photographic images of different CAD/CAM composite resin crowns and lithium disilicate glass-ceramic crown after fracture strength testing. While the CAD/CAM composite resin crowns were broken consistently at the lingual cusp, the lithium disilicate glass-ceramic crown only had cracks, but not major fractures. Journal of Prosthodontic Research 2018 62, 287-292DOI: (10.1016/j.jpor.2017.10.003) Copyright © 2017 Japan Prosthodontic Society Terms and Conditions