Evaluation of spatial accuracy in imaging using a Cone-beam CT

Objectives: A limited cone-beam CT has been used in treatment of dental implant. The research on patient dose using the CT was recently reported, however the accuracy of length measurement is unclear. The purpose of this study was to assess the accuracy of the measurement in the situation of the treatment of dental implant.

Material and Methods: An mandibular phantom and 6 implants (ReplaceŽ　Select Tapered, Nobel Biocare ) were used. The phantom surface was made of Teflon sheet simulating the cortical bone and the inside made of acrylic resin simulating the cancellous bone and vinyl chloride pipes simulating the mandibular nerve were placed. The implants were placed in 3 ways of the respective positions. This model was set into a cylinder-type tank water made of acrylic resin simulating the head. The tank included the model was scanned with 80kV,3mA and 1.0mm thickness using a limited cone-beam CT (3DX multi-image micro CT FPD, Morita).The following dimensions were measured on a monitor: the diameter and length of the implant, the buccolingual diameter of the cortical bone, the distance of the implant-bottom to alveolar nerve. Each measurement was compared with the actual length.

Results: The measured diameter was almost equal to the actual value and, the measured length was longer than the actual lengths. Conversely, the measured distance of the implant-bottom to alveolar nerve was 0.5 to 0.9mm shorter. The measured buccolingual distance of the cortical bone were different among each region. Furthermore, false images were found around implant on the image.

Conclusions: The accuracy of length measurement in a limited cone-beam CT was not so high as expected in case of the existence of metals. Positioning in imaging as well as metal artifact greatly influenced length measurement.