Dental students' ability for three-dimensional perception of two-dimensional images using natural stereopsis: its impact on radiographic localization.

OBJECTIVES: To investigate the ability of dental students to perceive 2D images in 3D using natural stereopsis and to evaluate whether the use of stereovision influences their interpretation of radiographic depth, with particular reference to intra-oral radiographs of third molars compared with scanograms.
METHODS: Seventy-two dental students (37 from sixth semester and 35 from fourth semester) who had all completed a course in the use of the buccal-object rule participated in the study. Lectures in 3D perception were given to the sixth semester students. They were trained in 3D perception using a 'single image colour field' stereogram and classical stereograms of circles. Both semester students diagnosed nine scanograms and nine intra-oral radiographs for: (1) the position of the crown of an impacted third molar in relation to the second molar and (2) root deviations in the bucco-lingual plane. The sixth semester students recorded whether they were able to achieve a 3D image in these cases.
RESULTS: Five students could not achieve a depth image from the training stereograms. Fifty-six per cent agreed on which two objects in the circles were nearest to the viewer and which were most distant, whereas 38% agreed on the opposite. Root deviation was a more difficult diagnostic task than crown position, and the sixth semester students made significantly more correct diagnoses than the fourth semester students (P < 0.001). Irrespective of semester, there was no significant difference between number of correct diagnoses of crown alignment in intra-oral radiographs and scanograms (P = 0.57), whereas root deviations were diagnosed significantly more accurately from the intra-oral radiographs (P < 0.001).
CONCLUSIONS: Most dental students can be taught to use natural stereovision to achieve a 3D image from two radiographs at different angles. 3D image is achieved equally well from intra-oral radiographs with a free-hand tube shift and scanograms. Those students who achieved a 3D image in a particular case, made more correct diagnoses than those who could not.