TABLE 2.
Non-invasive OPMDs screening technique.
| Techniques | Procedures |
|---|---|
| Vital staining with toluidine blue (TB) and Lugol’s iodine (LI) | TB selectively stains neoplastic/dysplastic lesions rich in nucleic acids (high DNA and RNA content) and appears royal blue (TB positive) while normal tissue does not take up dye (TB negative) |
| LI stains healthy buccal mucosa tissue. Where iodine reacts with glycogen (iodine–starch reaction) and normal mucosa, the locations appear to be brown or orange in color. Enhanced glycolysis in cancer cells does not promote the reaction | |
| Devices based on autofluorescence | Oral tissue irradiated with any blue light at the wavelength of 400–460 nm excites endogenous fluorophores such as keratin, collagen, elastin, and NADH to emit green light (500–520 nm). The degree of emission of green light decrease and appears as a black spot as dysplasia progression to cancer due to an increase in hemoglobin, porphyrins, and melanin, which tends to absorb the blue incident light, reducing the emission of green light |
| Devices based on chemiluminescence | This consists of a disposable capsule with two compartments containing acetylsalicylic acid and an inner glass vial containing hydrogen peroxide. Breaking of the vial triggers the reaction of the chemicals contained in the two compartments. Consequently, a bluish-white light (430–580 nm) is produced; it lasts for 10 min and facilitates the identification of hyperkeratotic areas |
| Another chemiluminescence device contains the combination of chemiluminescence and toluidine blue (TB). Before taking the image, 1% acetic acid solution is used to rinse the mouth for 1 minute, to desiccate oral tissues, followed by an oral examination with 430–580 nm wavelength light. The altered epithelial cells appear as “aceto-white” lesions, whereas normal cells appear blue | |
| Narrow-Band Imaging (NBI)/virtual chromoendoscopy with magnification (VCM) | This is a novel endoscopic technique where optical filters are used to narrow the light bandwidth to enhance the visualization of the mucosal surface and microvasculature. Generally, blue (415 nm) and green lights (540 nm) are used as they are strongly absorbed by hemoglobin |
| Optical coherence tomography (OCT) | High-resolution cross-sectional imaging is done by OCT. It is based on low-coherence interferometry, when a ray of light (an electromagnetic wave) reflects and diffuses on the tissues in different ways, resulting in the echo time delay and intensity of backscattered or back-reflected light from internal tissues |
| High-Frequency Ultrasound (US) | Piezoelectric crystals are used to emit sound waves, and their echoes are capable of producing images of anatomical structures |
| In Vivo Confocal Microscopy | Perform virtual biopsy of the tissues in their living context, offering real-time cytological and histological details. Laser light at specific wavelengths is used to stimulate endogenous fluorophores resulting in the emission of fluorescent or refracted light from the living tissue |