The oldest device used for detecting carious lesions, apart from the probe, is the X-ray machine. Radiography is reliable for detecting carious lesions in approximal tooth surfaces but considered unreliable in occlusal surfaces, particularly for diagnosing carious lesions in enamel and in the outer one third to one half of the dentine.
Fibre-Optic Trans-Illumination (FOTI) appears to be a very reliable device for detecting carious lesions in approximal surfaces, particularly in anterior teeth. In contrast, an infrared laser fluorescence device (e.g. DIAGNOdent; Kavo GmbH, Bibberach, Germany) has been reported to be invalid in detecting carious lesions in occlusal surfaces because it not only detects organic carious tissues, and putatively, the porphyrins from bacterial metabolism, but also other organic material such as plaque, calculus, stain and food remnants.
Its validity is further compromised by the presence of enamel hypomineralisation of origin other than that of dental caries. Similar disadvantages apply to quantitative light-induced fluorescence (QLF, Inspektor, Amsterdam, The Netherlands), which uses the fluorescence differences between sound and demineralised enamel to detect and quantify enamel carious lesions, although its reliability appears to be higher than that of the infrared laser fluorescence-based devices. A new system using light fluorescence technology (Sopralife, Acteon, Bordeaux, France) utilizes a different wavelength than QLF to detect carious lesions, in conjunction with a camera.
Currently, the value of QLF systems for carious lesion detection in clinical practice seems to be limited. Other methods, such as electrical impedance (CarieScan PRO™, CarieScan Ltd, Dundee, Scotland) and photothermal radiometry (Canary System™, Quantum Dental Technologies, Toronto, Canada) have recently been developed. However more research is required before they can be advised.
It appears that both X-ray and FOTI devices are suitable for use for carious lesion detection on approximal surfaces and that infrared laser fluorescence and light-induced fluorescence devices are not sufficiently reliable for assessing carious lesions in pits and fissures of occlusal surfaces. This also applies to the deciduous dentition, in which newer technology-based systems have not been found to be reliable for the accurate detection of carious lesions on approximal surfaces. Therefore, different techniques should be used for assessing carious lesions on occlusal and smooth tooth surfaces. One such technique employs visible-tactile methods.
Want To read in detail Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3490231/