Using an operating microscope, this study assessed the effect of 16x magnification on the restorative treatment of posterior teeth and compared the results against an unaided visual examination in vitro. Three dentists examined 300 premolars and molars at different times using an unaided visual examination and an operating microscope at 16x magnification.. The observers examined the occlusal surfaces of teeth according to a patient model and selected a treatment protocol based on the following scale: 0: No Active Care (NC); 1: Preventive Care (PC) and 2: Operative Care and Preventive Care (OC+PC) advised. According to the results, there was good intra-observer agreement and moderate inter-observer agreement with both techniques. No significant difference was found between the treatment using an unaided visual examination and that using an operating microscope. The use of a microscope at 16x magnification did not aid in the restorative treatment decision-making on occlusal surfaces.