Artificial sweetener doesn't strike me as solid enough for a control. How could you know the effect wasn't in fact the artificial sweetener negatively affecting the "control"? Or some combination of the two?
Your link doesn't actually mention what the placebo was, though.
A different study, but I think it's similar: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2683964/ "The placebo (PLA) mouth rinse solution was made from 150 ml of a commercially available non-caloric concentrate sweetened with aspartame and saccharin (Robinsons Soft Drinks Ltd, UK) diluted to 1000 ml with water. The GLU mouth rinse contained 64 g glucose (Roquette, France) per 1000 ml of the same solution. The MALT mouth rinse contained 64 g maltodextrin (Roquette, France) per 1000 ml of the same solution. The strong artificial sweetness reduced any sensory clues that subjects might use to consciously differentiate between the GLU, MALT and PLA mouth rinses."
Your link doesn't actually mention what the placebo was, though.