Instruments And Materials For Operative Dentistry And Their Influence On Mr-Images M.A. Baumann*, P. Theissen (1) And M. Schmidt (Dental School and Department of Nuclear Medicine (1), University of Cologne, 50931 Köln - Germany) An increasing number of people undergo diagnosis with magnetic resonance tomo-graphy (MRT). Dental treatment involves materials which may interfere with images of the head-neck region. The purpose of our study was to examine the influence of various instruments and materials for operative dentistry on MRT images in differing sequences. A total of 30 samples (filling materials like amalgam, GIC, composites, ceramics, Au-alloys, endodontic tools and posts) was embedded in gelatine in a plastic box. Four standard sequences (SE, TSE, FFE and IR) were applied in a supraconducting 1 T whole body tomograph (Philips Gyroscan NT 10), two sequences (SE, TSE) in a tomograph of the same type but with 1.5 T (Philips Gyroscan ACS-NT). The original sizes of the samples were measured with a vernier gauge and the resulting image size after application of MR sequences with the computer software. The artifacts were characterized by quality and quantity (four categories: I: original size up to + 10%, II: +10-50%, III: +50-100%, IV: >+100%). The endodontic files slipped and had to be removed from the plastic box. In contrast to most filling materials belonging to category I the resins Tetric and Compoglass showed category II artifacts. The posts made of titan also appeared in category II.   The biggest artifacts were created with the FFE-sequence. Size and form of the artifacts varied depending on the morphology and suscep-tibility of the samples. Sharp tapers of devices caused an increased signal extin-guish perpendicular to the direction of preparation with caplike zones of signal enhancement. The stronger magnetic field amplified the appearance of artifacts. In contrast to former studies it could be shown that precious alloys and composites cause artifacts which should be recognized by physicians and dentists when using MRT.