Gingival and pulpal bloodflow measurements in vitro using photoplethysmography

Photophlethysmography (ppg) is a noninvasive optical method to detect blood pulse in organs. This technique has been proposed for vitality testing of human tooth pulp tissue. However the influence of gingival bloodflow on photoplethysmographic signals derived from the tooth and the use of shielding materials for signal artefact reduction purposes has not been investigated yet.

Therefore the aim of the present study was to investigate the influence of gingival bloodflow on ppg pulpal bloodflow signals in vitro using different shielding materials.

Methods:

High power LEDs (625 nm (red), 940 nm (IR), Golden Dragon, Osram, Germany) were attached to the coronal part of a tooth gingiva model. Air, milipore water, and human erythrocyte-concentrate (HEC) were pulsed through the tooth and the gingiva model by two separate flexible tube pumps in three different ways (tooth alone, gingiva alone, and alternately tooth and gingiva). Signal-Intensity [ΔU, Volt] was detected by an individually designed photopletysmograph (J Dent Res 87[Spec Iss C],82.2008). Measurements were taken by shielding the gingiva with rubber dam (blue, purple, pink (Coltene Whaledent, Germany), black (Glyde Health, Australia)), aluminium foil and black antistatic plastic foil. Non-parametric statistical analysis was applied (n=5; a=0.05).

Results:

No signals were obtained using air and milipore water, HEC results were as follows.

Significantly higher signals for IR compared to red light corresponded with the literature. ΔU from gingiva compared to tooth was significantly lower for red and higher for IR.

Conclusions: Shielding the gingiva was effective for 940nm light and negligible for 625nm light.