Laser Doppler Flowmetry

Laser Doppler Flowmetry 

This is a non invasive, objective, painless, semi-quantitative method, which is more reliable in measuring the blood flow to the pulp. As it doesn’t cause any noxious stimuli, apprehensive or distressed, patients accept it more readily than the current methods to assess the pulp vitality. Laser light is transmitted to the pulp by means of a fiber optic probe. Laser Doppler flowmetry uses Helium Neon (HeNe) and Gallium Aluminum ( Ga AlAs) as semiconductor diode lasers at a power of 1 to 2 mW. The wave length of the HeNe laser is 632.8nm and that of the semiconductor diode laser is 780 to 820nm

The scattered light from the moving red blood cells in the circulation will be frequency-shifted, while those from the static tissues remain unshifted. The reflected light composed of Doppler shifted and unshifted light is returned by the afferent fibers and a signal is produced. This technique can be successfully employed for estimating the vitality of the pulp in both adults and children. The tooth to be checked should be isolated. The closer the probe is positioned to the gingival margins, the higher the signal output because of the greater volume of the pulp tissue .At the same time, the potential gingival contamination is also higher. The ideal position to place the probe is 2 to 3 mm from the gingival margin

Different ranges of band width can be set to filter the reflected signal, with a wider frequency being more sensitive to the moving red blood cells with a wider range of velocity .Theoretically, a wider bandwidth such as 15kHz is preferred, but in case of pulp vitality testing, a much narrower 3 kHz bandwidth may be ideal The end of the LDF which contacts the tooth contains both sending and receiving optic fibers, with one of the configuration being one source and two detectors in a triangular arrangement at the probe end Calibration of the probes is important to ensure accurate readings .

The larger the optical fiber separation distance on the probe, the higher the signal output as a larger surface area is covered, and also there is potentially a higher chance of blood flow signal contamination of the non pulp sources. To date, the 0.5mm or 0.25mm separation distances seem to be preferred in experiments. Due to the pulsatile nature of the blood flow, many studies.... have observed that the LDF recordings in the teeth with an intact pulp blood flow have rhythmic fluctuations or oscillations. In teeth without pulp blood flow, however, usually only irregular fluctuations can be observed in contrast to the concurrent ECG readings.