Scripties UMCG - Rijksuniversiteit Groningen
 
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De nauwkeurigheid van volumebepalingen van kaakbot bij het gebruik van Cone Beam Computed Tomography

(2016) Blomsma, I. (Ivar)

Aim The aim of this research was to investigate the validity and reliability of volume measurements of bone with aid of the cone beam CT scanner. The influence of applied materials, like osteosynthesis screws and sutures, on the measurements was also investigated.
Methods A comparison is made between volume measurements on bone derived from a pig’s jaw created by the cone beam CT scanner and the golden standard. The golden standard consists of applying dental wax on the bone to avoid influx of water. The volume of the bone has been measured according to the water displacement method. A volume of water inside a beaker is compared to the watervolume after adding the bone and filling the beaker to the same level. With these measurements the bone volume can be calculated. 24 pieces of bone were used. On each piece 3 measurements were done, resulting in 72 measurements. To investigate the influence of applied materials, six bone augmentations were simulated. A CBCT scan was made after augmentation, a second CBCT scan was made after detaching the bone block from the augmentation site. The retreived volumes were compared.
Results Most of the volumes retrieved with aid of the CBCT differed significantly (α=0.05) from the measurements according to the golden standard. The measurements turn out the be very reliable. (Pearson correlatie test, r = .991, p = .000.) The influence of applied materials has not been verified in this investigation. (Wilcoxon-Signed Rank Test, z = -1.153, p = .249.)
Discussion The differences between volume measurements are mostly due to the ‘partial-volume’ effect, where voxels wich contain a little bit of bone will account for a completely filled voxel. Any trapped air bubbles during appliance of dental wax will result in a greater deviation of the retreived volumes. An analysis of grey values retreived from a CBCT scan is manually done, so the volume is also influenced by the analist. Conclusion It turns out that a volume measurement determined by the CBCT scanner is very reliable but not valid. The CBCT scanner with the used ‘threshold’ is not useful for determining exact bone volumes. Relative differences before and after bone augmentation can be measured with great reliability. The influence of applied materials like osteosynthesis-screws has not been verified.






 
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