Measurement of Bone Volume Changes Using Cone-Beam Computed Tomography

Objective: Changes following bone augmentation procedures are primarily measured using two-dimensional images. These images do not always provide an accurate assessment of bone volume changes. We hypothesized that three-dimensional models created from cone-beam computed tomography (CBCT) scans could be used to calculate bone volume changes following maxillary sinus lift procedures.

Method: CBCT-generated DICOM files of ten patients taken before and after maxillary sinus lift procedures were used to create aligned and cropped 3D models in Avizo software. Cumulus software was used to crop non-essential tissue, align the before and after models, and calculate bone volume changes. The CBCT scans before and after sinus lift procedures were compared using four novel volume calculation methods: 1) slice; 2) triangle; 3) voxel and 4) subtraction.  Standardization of our volume calculation methods was performed by scanning two different spherical plastic shells of known volume and determining the difference between the two known volumes using the four calculation methods.

Result: The four methods calculated the mean volume change of the two plastic shells to be 1727 mm³ (SD±1000) compared to the known volume change of 2500mm³.  The narrowest variation in measuring the maxillary sinus lift procedure was obtained with the voxel method.

Conclusion: The results of the plastic shell trial indicate that the bone volume changes calculated by the voxel method are closest to the true value.  Extensive variability of the four methods of calculating bone volume changes after sinus lift procedure poses a problem of reliability.  Continued refinement of the voxel measuring method using Cumulus software should allow for more accurate volume calculation capabilities. Potential applications include comparing the effectiveness of novel bone grafting materials and evaluating the success of grafting procedures. 

Supported by the UMSOD Summer Fellowship Program