*3.3.2 Quantitative light-induced fluorescence*

Benedict was the first to state in his research that the organic components of human teeth show fluorescent properties. In addition, he also mentioned the difference between the fluorescent properties of healthy and carious enamel in his studies [23]. The purpose of the QLF device is to determine caries at an early stage. This device can also be used for imaging lesions in remineralization treatments. The resulting image can be saved by transferring it to the computer. On the other hand, it is insufficient in imaging lesions in the approximal area [24].

#### *3.3.3 Ultrasonografi*

The basic principle of ultrasound is the application of high-frequency waves (1–20 MHz) generated by the device to the biological tissue, the returning waves are absorbed and converted into electrical impulses and detected as echoes. Each tissue has a unique internal echo level. Changes recorded at the echo level of the tissue indicate that pathological changes have occurred in the tissue [25]. It has been shown by studies that ultrasonic methods give good results in the diagnosis of early caries [26].
