Detection of pulsed blood flow through a molar pulp chamber and surrounding tissue in vitro

Due to severe limitations of dental pulp sensitivity tests, the direct recording of pulsed blood flow, using photoplethysmography (PPG), has been proposed. In vivo evaluation is methodologically difficult and in vitro models have hitherto been adversely influenced by shortcomings in emulating the in vivo situation. Consequently, the aim of this study was to test an improved data acquisition system and to use this configuration for recording pulsed blood in a new model.

We introduced a PPG signal detection system by recording signals under different blood flow conditions at two wavelengths (625 and 940 nm). Pulsed blood flow signals were measured using an in vitro model, containing a molar with a glass pulp and a resin socket, which closely resembled in vivo conditions with regard to volumetric blood flow, pulp anatomy, and surrounding tissue.

The detection system showed improved signal strength without stronger blanketing of noise. On the tooth surface, it was possible to detect signals emanating from pulsed blood flow from the glass pulp and from surrounding tissue at 625 nm. At 940 nm, pulp derived signals were recorded, without interference signals from surrounding tissue.

The PPG-based method has the potential to detect pulsed blood flow in small volumes in the pulp and (at 625 nm) also in adjacent tissues.

The results show the need for clear differentiation of the spatial origins of blood flow signals of any vitality test method to be applied to teeth.