Visualisation of dental anatomy in CBCT scans: Part 1.

To the trained eye, every tooth is different. An in-depth understanding of dental anatomy in cross-sectional images is a fundamental basic skill required when interpreting cone beam computed tomography (CBCT) scans. The conventional orthogonal planes of axial, coronal, and sagittal are not always the best planes in which to assess teeth because every tooth is at a slightly different angle to all these planes. In this chapter, the author demonstrates the characteristic anatomy of upper and lower incisors, canines, premolars, and molars in longitudinal and transverse sections, using carefully uprighted images. Some of these teeth are also shown in transverse section at various levels in the crown and root. The chronology of permanent teeth is shown. Developing teeth are discussed and incremental growth lines are mentioned.The author describes three well-known dental notation systems (Palmer, FDI, hybrid).There are four videos accompanying this chapter, including one fascinating video showing a scroll-through of all the cross-arch sections of a synthetic panoramic (curved multiplanar reconstruction) image that includes all the upper and lower teeth in a 16-year-old.

Novel use of ultrasound-guided surface marking of head and neck tumors invading facial skin.

Malignant tumors of deep head and neck structures can invade skin, but the tumor periphery is difficult to assess clinically. The surgeon's dilemma is achieving tumor clearance with safe margins while at the same time minimizing skin loss on the face. We show, in 2 cases involving the face, that high-resolution diagnostic ultrasound was superior to CT scan in demonstrating the periphery of the tumor. The tumor was distinguished from surrounding edema by its lower echogenicity and homogeneous echotexture. The maximum contour of the tumor was marked on the skin surface with ink under ultrasound guidance. The ink marking aided excision and reconstruction planning. Subsequent histology showed the surgical margins were clear of tumor. The patients remained tumor-free for more than 3 years. Ultrasound imaging therefore shows good potential for planning surgical resection with a safe margin and for aiding decisions on donor site and type of flap for reconstruction.