If it was you who performed the interventions then it is an Intervention trial either randomized or non randomized depending on the method of patients allocation ,,,, if it was not you who performed the intervention then it is an observational study ,,, then you ask yourself did I already classify my patients in the past into exposed n non n i am now doing the ortho pantograph to detect the resorption ,, coz if this the case then the study design is retrospective cohort ,,, if you just crosssectionally identified both exposures n outcomes at the same time then this is cross sectional study l ,,, so it always depends on the way of data collection n if u have intervened or not :) 

If it was you who performed the interventions then it is an Intervention trial either randomized or non randomized depending on the method of patients allocation ,,,, if it was not you who performed the intervention then it is an observational study ,,, then you ask yourself did I already classify my patients in the past into exposed n non n i am now doing the ortho pantograph to detect the resorption ,, coz if this the case then the study design is retrospective cohort ,,, if you just crosssectionally identified both exposures n outcomes at the same time then this is cross sectional study l ,,, so it always depends on the way of data collection n if u have intervened or not :) 

If the study is prospective, then it will be a clinical trial (either randomised or not).

If the study is retrospective, then it will be a case-control one (observational)

Thanks for the reply. But let me take you Iman and Giuseppe to a deeper insight. First, let's agree that experimental studies are meant to detect "causality" between "intervention" and control, while observational ones are intended to detect "association" between "exposure" and control. Thus, it would be weird to the effectiveness of intervention "causality" using an observational design. 

I am aware of many examples of studies being published for interventions being assessed under cohort or even case-control studies. The question: Is this rationale?

A table attached to show differences between observational and experimental designs. Which of the following items you agree/disagree with?

Ahmed let me first rephrase what u just said observational studies can detect association between OUTCOME and exposure while intervention al studies can reveal causality between treatment and OUTCOME ,,,,, SO IF WE WOULD LIKE TO DETECT CAUSAL ASSOCIATION WE WILL DEFINITELY DO AN INTERVENTION AL TRIAL ,,,,,,, unless Bradford hill criteria can establish sufficient causality :) 

I strongly agree with the reply of Iman Radi