Scribal points to iamnot for identifying this fifteenth century tool as a set of dental pliers. The photo comes from the Institut für Realienkunde des Mittelalters und der frühen Neuzeit via the Medieval and Renaissance Material Culture website. (Although in a pinch, you could probably pinch witches with it . . .).
Here's an illustration of a medieval "dentist" (probably a barber) pulling a tooth with a set of dental pliers (looks like a different design from the featured item). My guess is that the rope with the teeth in it is attached to the pliers -- sort of like a pair of glasses on a necklace -- and went around the tooth-puller's neck to advertise his trade. The scene is set in the letter D for dentes (teeth) and comes from a fourteenth-century encyclopedia called Omne Bonum (all good things). According to Lucy Freeman Sandler, The Omne Bonum was "a unique illustrated encyclopedia composed in London between 1360 and 1375 by James le Palmer, Treasurer’s Scribe in the Exchequer."
In a review of Lucy Freeman Sandler's edition of Omne Bomun. A Fourteenth-century Encyclopedia of Universal Knowledge (Harvey Miller, London 1996), Michael Michael writes:
The compilation of encyclopaedias is one of the most important developments in European cultural history. The Omne Bonum of James le Palmer not only stands at a major turning point in the development of this phenomenon but is one of the great untapped resources for the study of the fourteenth century. No one had created an alphabetical list of subjects of this size before James compiled what he called his “Every good thing” . . .