Mamoun John S
Dent Assist. 2011 Jan-Feb;80(1):8, 10, 12-4 passim.
XCP dental x-ray film positioning devices help to increase the dimensional accuracy of dental x-ray images. (XCP stands for "extension cone paralleling." Some dental assistants refer to them as "Rinn" devices, after a company that manufactures them.) The XCP device has a collimator ring that is parallel with the film-holding plane of the x-ray film holder. This positioning helps an assistant to align the plane of the unseen, intraorally located x-ray film parallel with the plane of the cross section of the x-ray beam. XCP devices also help to prevent dental x-ray film cone cuts, since the extraoral collimator ring helps to indicate the boundary of the unseen x-ray film. Unfortunately, the devices can be confusing to assemble because each device consists of three pieces that can be assembled in multiple ways, and there are three types of such devices for anterior, posterior and bitewing radiographs (in addition to a fourth accessory device for taking endodontic radiographs). It can be challenging to determine which piece goes with which type of XCP, and to choose the correct XCP assembly for taking a desired x-ray. This article describes some clinical techniques of assembling XCP radiographic film-holding devices, describes the clinical use of XCP devices, and ways of overcoming intraoral obstacles to device placement.
XCP牙科X线胶片定位装置有助于提高牙科X线影像的尺寸准确性。（XCP代表“延长锥平行技术”。一些牙科助理人员根据生产该装置的公司名称，将其称为“林恩”装置。）XCP装置有一个准直器环，它与X线胶片夹的胶片固定平面平行。这种定位有助于助手将位于口腔内、看不见的X线胶片平面与X线束横截面的平面平行对齐。XCP装置还有助于防止牙科X线胶片出现锥形切割，因为口外准直器环有助于指示看不见的X线胶片的边界。不幸的是，这些装置组装起来可能会让人困惑，因为每个装置由三个部件组成，这些部件可以以多种方式组装，而且有三种类型的此类装置用于拍摄前牙、后牙和咬合翼片X线片（此外还有用于拍摄牙髓X线片的第四种辅助装置）。确定哪个部件适用于哪种类型的XCP，以及选择正确的XCP组件来拍摄所需的X线片可能具有挑战性。本文介绍了一些组装XCP X线摄影胶片固定装置的临床技术，描述了XCP装置的临床应用，以及克服装置放置时口腔内障碍的方法。
