The truth is that existing dental work actually increases the chances of future decay and breakdown, so prevention of problems is key. The edges of your fillings and crowns are still subject to bacteria accumulation. Brushing after eating and daily flossing are the best ways to protect the work in your mouth.
Additionally, visiting your dentist for regular cleanings and check-ups can help since small issues that can arise, if caught early, are much easier to treat. Fillings and crowns can often be maintained for longer if the problems are caught early and addressed rather than waiting until the only option, at best, is full replacement. Also, if you are a clencher/grinder the lifespan of any dental work in your mouth is greatly decreased so wearing a night-guard, or otherwise addressing your grinding, will increase the lifespan of dental work.