Sir, I read with interest the recent well-reported and discussed review paper by O'Connor and Gavriil that addressed factors that increase the success of bonding of adhesive indirect restorations.1

Diverse clinical restorative scenarios are solved with adhesive indirect restorations, a practice that is becoming more common. Thus, dental professionals are expected to understand their mechanism of action to maximise predictability and excellent clinical performance.

Nonetheless, I intend to draw attention to controversial points raised when bonding indirect restorations preclude solid clinical recommendations. For instance, to adhesively cement indirect composites, precious alloys, or polycrystalline ceramics, there is not a single established protocol considered superior. More specifically, indirect composites' bonding options range from air-particle abrasion alone; air-particle abrasion with silanisation; and tribochemical coating with silanisation.

In conclusion, there are controversies in adhesive cementation of different indirect restorations that I hope become less blurry soon as biomaterial science advances to deliver long-lasting, biocompatible restorative materials.