**7. Concluding remarks**

Dental porcelains have been used for many decades because of their excellent aesthetic qualities, including the possibility to mimic natural teeth, besides other favorable character‐ istics. However, the low strength and fracture toughness, and high susceptibility to mechanical degradation by slow crack growth result in relatively low lifetimes in the oral environment. The introduction of a compressive surface layer by ion exchange is a promising process to enhance the mechanical behavior of dental porcelains. Exchanging small ions (e.g., Na+ ) by larger ones (e.g., K+ ) in the glassy matrix at temperatures lower than its glass transition temperature (Tg) can result in a steep gradient of residual compressive stress, which signifi‐ cantly increases the fracture toughness (*KIc*) in the porcelain surface. This increase leads to significant strengthening effects, even using the paste method, which is carried out in short times (less than 1 h). However, the strengthening is more pronounced for shallow surface flaws, because of the limited thickness of compressive layer and decreasing resistance curve (R-curve) behavior, which increases the variability of fracture stress and decreases the mechanical reliability (decreases the Weibull modulus, *m*). On the other hand, strengthening by ion exchange also significantly increases the resistance to slow crack growth phenomenon (stable crack propagation at low stresses intensified by water corrosion). This results in lower strength degradation over time and counterbalances the negative effect of decreasing reliabil‐ ity, leading to higher strength retention after long lifetimes (decades) even at a level of low fracture probability (e.g., 5%). The two-step ion exchange method has the advantage of increasing the material reliability, but at the expense of longer periods of treatment (above 10 h). In conclusion, it is expected that the application of chemical tempering (strengthening by ion exchange) can improve the lifetime of dental porcelain restorations.
