A LABORATORY MODEL FOR DENTAL RADIOGRAPHIC STUDIES

Though a number of laboratory models have been developed to study the effects of X-ray geometry on the appearance and relative positions of anatomical landmarks, such as the amelocemental junction and alveolar crest, many have failed to take into account the three-dimensional nat ure of the alveolus and its spatial relationships with the teeth. As a result, the findings of many ex vivo investigations must be questione d. The aim of this investigation was to develop and refine a new labor atory method for experimental dental radiography utilizing a series of anatomical radio-opaque acrylic models containing extracted teeth. Th e method allows adjustment of the beam-object relationship through the use of precision-made wedges, which are able to tilt the models throu gh a series of angles thus simulating in vivo changes in both vertical and horizontal X-ray beam angulation. The technique is capable of bei ng used in studies involving assessment of alveolar bone height or the depth of carious lesions. The precision of the method was tested by r adiographing in nine different positions a test device consisting of f our small cylindrical amalgam fillings embedded in a perspex sheet. Fo llowing removal and replacement, exposures of the test device were rep eated for each position. Five linear distances between pairs of fillin gs were selected and measured on each radiograph to give a total of 45 measurements per set of films. There was exact agreement in 39 of the measurements recorded and a discrepancy of +/-0.1 mm in the remaining six. The estimated standard deviation for variation on repeat radiogr aphy was 0.258 and the 95% confidence interval 0.214 to 0.325. The pre cision of the apparatus was thus found to be adequate for the measurem ent of differences in small distances.