This sort of uncertainty means that the reader has to decide what the author has in mind. If we turn to the standard dictionaries on epidemiology, we find they are not particularly helpful. That is a broad and rather loose definition that leaves unanswered questions about causal role, strength of association, and modifiability. An attribute or event that is associated with increased probability of disease, but is not necessarily a causal factor. A determinant that can be modified by intervention, thereby reducing the probability of disease.
Risk factors are part of the causal chain, or expose the host to the causal chain.
Once disease occurs, removal of a risk factor may not result in a cure. This definition is longer than the one offered by Last, but in my view it is much clearer. Beck argues convincingly that it must be clearly established that the action or event occurred before the outcome, or before conditions exist that make the outcome likely. This in turn means that longitudinal studies are necessary to demonstrate risk factors. However, there are many situations in biomedicine, and certainly in dentistry, where this has not been done, and indeed where it is unlikely that it will ever be done.