# Assessment of Negative Gingival Recession: A Critical Component of Periodontal Diagnosis
## 6 Clinical Assessment Approaches
### Imaging Technologies  
Radiographic techniques including intra-oral radiography and cone-beam computed tomography (CBCT) have been employed to assess the soft-tissue dimension in relation to the CEJ, but the scatter radiation and low-contrast resolution of soft tissue and CEJ outline limits their use in determining negative GR [92; 93]. Alternatively, dental ultrasonography, a noninvasive and nonionizing modality, has been proposed to image periodontal tissues [94]. Ultrasonography functions by transmitting sound waves from the ultrasound transducer (probe) though a medium and then recording time-dependent reflections from tissues to determine its dimensions. Efforts have been made to develop an ultrasonic device to measure periodontal pocket depths, but the approach has failed to demonstrate reproducibility [95]. The device consisted of a thin probe inserted into the sulcus that directs the sound wave into the pockets in the presence of water (for coupling), and a computer algorithm then identifies the junction between the junctional epithelium and the connective tissue via the impedance difference of returning echo signals which infers the depth of the periodontal pocket. More promising outcomes in mapping the periodontal tissue dimensions have come with the evolution of transducers with higher frequency (higher image resolution). These have included studies in porcine models [96; 97; 98; 99], human cadavers [100; 101], and live humans [102; 103; 104; 105]. Figure 2: Visualization of negative recession using an operating microscope with magnification (10\(\times\)) and co-axial illumination during ultrasonic scaling (Supplemental Video). In an early study, a dermatological ultrasonic transducer with a frequency of 20 MHz was shown to yield a better repeatability of linear measurements between an inscribed notch and the alveolar crest in pig jaws, when compared to the direct measurement and transgingival probing [96]. [PERSON] et al. also used a 20-MHz dermatological ultrasonic device to measure the periodontal ligament width, alveolar bone thickness, and gingiva thickness [99], and found significantly higher correlation among ultrasound, CBCT, and microscopy techniques [97]. [PERSON] et al. used a linear broadband 8-40 MHz transducer that was designed for musculoskeletal and peripheral vascular exams to identify the distance from the gingiva margin to CEJ and alveolar crest. They observed a high degree of accuracy with the use of ultrasound when compared to CBCT measurements with less than 10% difference [98]. The same research team used a 20 MHz transducer to image the CEJ and found a high agreement of up to 97% between ultrasound and micro-CT images [106]; high inter-examiner reliability (\(\geq\)0.98) in CEJ identification was also demonstrated [104]. Recently, dental ultrasonography has been modernized to a miniature-sized (comparable to a toothbrush) ultrasound transducer suitable for use in the oral cavity with higher-frequency (24 MHz) and high-resolution imaging (Figure 3). Its accuracy in the evaluation of periodontal and peri-implant tissue dimensions was validated by comparing these measures to direct bone sounding and CBCT [105; 107; 108]. Figure 4 provides an example of a cross-sectional scan at mid-facial and interproximal planes of a periodontal healthy maxillary central incisor using a modern commercially available ultrasound scanner (ZS3, Zonare, Mindray, Mahwah, NJ, USA) coupled with a 24 MHz miniature-sized imaging probe. In this example, the CEJ is clearly visualized and negative GR was measured to be 0.5 mm higher at distal papilla than at the mid-facial site. In contrast to probing, ultrasonography allows for noninvasive imaging of the CEJ and alveolar bone crest without the measurement variability caused by the inflamed gingiva tissues.