“…Two [ 26 , 27 ] included studies followed a cross-over trial design, while eighteen [ 10 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 ] had a split-mouth design. One study [ 45 ] followed a two parallel-arms trial, five studies [ 46 , 47 , 48 , 49 , 50 ] provided one treatment per patient while five studies [ 15 , 51 , 52 , 53 , 54 ] had one or more treatment per patient.…”