What the adhesive does
It bonds ceramic or composite to enamel and dentine, seals the margin and shares biting forces with the tooth. A good bond is what lets a thin veneer survive.
How it ages
Water, temperature cycling and chewing slowly degrade the bond line, particularly at margins on dentine. Well-bonded restorations on enamel last many years; those on dentine or with contaminated bonding fail sooner.
What it means for you
Restorations should be checked at hygiene visits for marginal staining or gaps. Renewal after many years is normal, not failure, and is easier when the tooth beneath was preserved at the first treatment.
