We read with interest the article on 3-dimensional (3D) imaging for indirect-direct bonding in the June issue (El-Timamy AM, El-Sharaby FA, Eid FH, Mostafa YA. Three-dimensional imaging for indirect-direct bonding. Am J Orthod Dentofacial Orthop 2016;49:928-31). It stated that clinicians could be influenced by many factors during bracket placement, and the authors suggested using 3D imaging and printers to avoid problems. However, the ethical limitations in taking CBCT records are obstacles for using the method in routine clinical practice (there are exceptions such as impacted teeth, and severe skeletal anomalies). Furthermore, we would like to know your opinions concerning undermentioned issues about the method you use.
The authors stated that the 3D images of brackets were acquired by CBCT scanning. How reliable and accurate are CBCT images for bracket modeling? The brackets need to be built in a highly detailed manner for adaptation of brackets to the tray or tooth surfaces precisely. If we consider the slice thickness of CBCT images, it seems possible that building them with CBCT images may affect the precision of the method. Using 3D CAD models of the brackets may increase the usability of the method as stated in the conclusions of the study. In addition, the thresholds determined for segmentation of teeth are quite important. The contours and the volume of the tooth could change due to setting low or high segmentation thresholds. Also, different segmentation threshold values need to be set for each tooth and even for different parts of a single tooth to get the most detailed and accurate tooth models. What precautions did you take in your study during tooth segmentation? The other point that may affect the method is the slice thickness of CBCT images. Ye et al concluded that with increases in voxel size, the volume measurements of the teeth tend to be larger because of the surface surrounding artifacts. Maret et al stated that the sharpness of images decreases at a voxel size of 300 μm. and the underestimation of the measurements becomes statistically significant at 300 μm and higher voxel sizes. If we consider the voxel size of the image used in this study, what is the possibility that the tooth and the tray fit perfectly? Vestibular surfaces of teeth can be obtained with much more detail by superimposing plaster cast scanning images onto CBCT images. When considering the above-mentioned issues, it seems that some difficulties may be dealt with during the process of fitting brackets and implementing the rigid bonding tray to the patient.