Fixed full arch dental implants and retrofitted dentures what is the difference and how long do they last?

Hello. What is the difference between fixed full arch dental implants and retrofitting dentures so that they are implant supported and non removable? Do the "teeth" of fixed full arch dental implant teeth ever need to be replaced like retrofitted implant supported dentures do or do they last a lifetime? If so, why do they last a lifetime and implant supported fixed dentures do not? What is the difference between the two? Thank you.