the superior edge 330 of the retractor 100 or the trough 110 and away from the inferior edge 340 put another way the ridge is closer to the superior edge 330 than the inferior edge 340 this offset allows the ridge 140 to cover stenson 39 s duct reducing the amount of saliva actually introduced into the oral cavity or at least redirecting the saliva along the inner surface of the cheek the distance between the ridge 140 and the superior edge 330 can be considered the superior height 335 and the distance between the ridge 140 and the inferior edge 330 can be considered the inferior height 345 the superior height 335 can be about 0 3 inches the inferior height 345 can be about 0 7 inches in other embodiments the ratio of the superior height 335 to the inferior height 345 is from about 0 2 to about 0 8 including about 0 4 it should be noted that both retractors 20 30 have this offset of the ridge towards the upper lip thus the two retractors 20 30 can be considered mirror images of each other but they are not interchangeable with each other put another way one retractor 20 is considered a left retractor while the other retractor 30 is considered a right.