Dimensional Stability of Software Based Cone Beam CT Image Composition

Objectives: X-ray devices combining panoramic imaging and optional cephalometric modality with cone beam computed tomography (CBCT) widen the diagnostic tools in dental practice cost effectively. Resolution must face structures covered in dentistry (periodontal gap: 0.15-0.2mm; root channel >=0.06mm; non-dislocated teeth- and bone-fractures <=.2mm). A software solution increasing the field of view (FOV) by connecting small separate volumes was evaluated for dimensional stability, image discrepancies and the influence of movement artefacts between exposures. Methods: A Kodak 9000 3D extraoral imaging system (voxel-size: 0.076mm) with built-in stitching software was used for the evaluation of a human mandible with three endodontic instruments as markers. The distances between several reproducible points were measured directly and the results compared to the values measured on screen. Displacements of the mandible along all axes between exposures as well as angular displacements were conducted to test the capability of the system. Results: The standard deviations (SD) of the results for the vertical distances varied between 0.21mm and 0.41mm (approximately 1-2 voxels; range: 0.6-1.3mm) and may be considered the systematic error. The standard deviation of the results for the horizontal and diagonal distances varied between 0.20mm and 0.57mm (approximately 1-3 voxels; range: 0.6-1.7mm) if the group with overall horizontal angulations of 10° and a central rotation of 20° was omitted. Displacements exceeding determined limits lead to “software error”, source volumes are still available for diagnostics. Conclusion: The evaluated stitching software is a useful tool to expand the options of combined CBCT with an initial small high resolution FOV by allowing a merger of up to three component volumes to yield a larger FOV of about 90 × 75 × 37.5mm, corresponding to a complete jaw. The dimensional stability was acceptable when seen in relation to the induced displacement and may be useful for postproduction like implant drill templates.