literature classifies maintenance approaches to Preventive (PM), predictive (PDM), total productive (TPM), reliability-Centred (RCM), and others. however, careful reading leads to a conclusion that many of them are integrated. researchers say that PM is part of PDM. they also say that to have a good TPM you should be applying PM and PDM in the first place. this can sometimes create confusion for managers that are not interested in academic research.
my personal conclusion of this is that there is one maintenance approach which is the latest that approves success. other maintenance approaches should become practices that are included in the latest approach. what is the value of having all these classification if the aim is to practice? for example if I am fully applying PM, someone can just suggest that I am 50% applying TPM. and this can be true for other approaches too.
I think that the most important thing in maintenance is practice rather than having theories. one approach is enough if it is annually updated to include all the practices that prove beneficial.