Primary precutting versus conventional over-the-wire sphincterotomy for bile duct access: a prospective randomized study - de Weerth, A; Seitz, U; Zhong, Y; Groth, S; Omar, S; Papageorgiou, C; Bohnacker, S; Seewald, S; Seifert, H; Binmoeller, K F; Thonke, F; Soehendra, N (Endoscopy, 2006)