What accounts for the longeivity of amalgam even though it does not bond chemically with dentin?

Amalgam attach to the tooth mechanically ..so the good preparation of cavity with depth in dentin not less than2mm and axiopulpal angle90 and no undermind enamel, will give longevity to the tooth and restoration at least5years

amalgam is brittle material so when we prepara a cavity an axiopulpal angle must be90 and depth a cavity2mm.then we have a retention forn. we need to cap acavity whih calcium hedroxida .an erosion in amalgam will preave an marginal leakage .we can cap an cavity with bond