Impact of Experimental Protocols on the Flexural Strength Testing of Lithium Disilicate-Based Dental Glass-Ceramics

The transition of dental ceramics and glass-ceramics (for fixed all-ceramics and metal-ceramics restorations and prostheses) from laboratory to clinic requires the materials to pass through a series of tests following the protocols and requirements discussed in the standard ISO 6872:2015. However, the literature reveals that the researchers in the dental ceramics community usually do not adhere to the ISO standard’s specifications when measuring their materials’ flexural strength, assuming that these deviations from the protocols exhibit minimal or no impact on the materials’ strength. Therefore, the present study aims to fill that gap by elucidating the impact of the following experimental protocols – (i) polishing, (ii) edge chamfering and (iii) adhesive tape on the non-tensile side – on three-point flexural strength of lithium disilicate based glass-ceramics. The result reveals that polishing increases flexural strength and tends to introduce edge or corner flaws in the specimen. Though edge chamfering of specimens did not help remove the edge defects in our study, it leads to a tighter flaw distribution, increasing the reliability of the flexural strength results. The application of adhesive tape (on the compressive side) exhibits an insignificant impact on the glass-ceramic specimens’ flexural strength. Accordingly, revisions have been suggested in the ISO 6872 standard. GRAPHICAL ABSTRACT