Orthodontic Bracket Induced Contrast Changes in NewTom and iCAT images

Objectives:

This study evaluated artifacts generated by stainless steel orthodontic brackets in images produced by the NewTom 3G and iCAT cone-beam CT machines.

Methods:

Three cadaver heads were prepared for NewTom 3G and iCAT scanning by extracting all teeth containing restorations and replacing them with unrestored teeth. Holes were drilled through the buccal (2 mm from bracket) and lingual (6 mm from bracket) cusp tips of the maxillary premolars. Thermoplastic trays were constructed to hold a set of ten stainless steel orthodontic brackets in ideal positions on each maxillary dental arch. Twenty 6” field of view scans were performed on each cadaver using both CBCT machines. Standardized 0.5 mm thick axial slices were analyzed with NIH ImageJ analysis software for grayscale contrast between the artificial dentin defects and adjacent dentin. A Mann-Whitney U-Test was performed at significance level of a= 0.05.

Results:

In NewTom images, at small distances (2 mm) between the stainless steel orthodontic brackets and artificial dentin defects, the brackets caused a statistically significant reduction in mean greyscale contrast values (gcv) when compared with the control (p=.034). In NewTom images at larger diatances (6 mm) there was no statistically significant difference in mean gcv (p=.227).

In iCAT images, at 2 mm and at 6 mm, there were no statistically significant differences in the dentin gcv between the bracket and the control groups (p=.109 and p=.060).

The iCAT control mean gcv (buccal and lingual) were lower than the NewTom control mean gcv (p=.001 and p<.0001).

Conclusions:

1) No bracket-induced artifacts were observed in iCAT images or in 6 mm NewTom images.

2) Bracket-induced artifacts were observed in 2 mm NewTom images.

3) When default settings are used in primary reconstruction, secondary reconstruction and DICOM image viewing software, NewTom images of artificial dentin defects have more contrast than iCAT images.