Hi. Amalgam replacement is not a painful procedure. But if the cavity is very deep.. You might experience a bit of sensitivity during the procedure.u can always ask for local anaesthesia if needed. There are also chances.. Less likely though.. If the cavity is very deep and close to the pulp... After the excavation of old restoration.. There might be a need to consider a root canal treatment if the cavity is very deep or pulp for some reason gets exposed

Hello First an x ray will be taken and if the filling is not very deep a mercury free filling called as composite will be done which is tooth coloured and appears exactly as your tooth shade If it's very deep then the procedure will be different but even that won't be painful so don't be scared Get this done asap