An attempt to develop an optical probe to assess dental pulp vitality led to the conclusion that it would be difficult to construct an effective optical probe for the middle-aged and older patient who is a common candidate for pulpal assessment. In such patients, vascularity of the gingiva is so much greater than that of the pulp that signals originating in the gingiva overwhelm pulpal effects. This conclusion applies to photoplethysmography,
pulse oximetry, and laser Doppler flowmetry, and probably to spectrophotometry as well. The effect of the gingiva was first demonstrated by placing opaque plastic film in the gingival sulcus, which caused attenuation of light passing through molar and bicuspid teeth. More dramatically, the remaining
pulsatile signal could be much further attenuated by vasoconstricting the gingiva. An unusually sensitive
photoplethysmograph was developed (noise floor, with signal averaging, was near 10 fA), as were a variety
of optical probes (including two that approached the tooth below the gingival margin). The tools, methods,
and conceptual models that were developed are intended also to be of use to investigators who are developing optical probes for use in younger subjects, in whom such probes appear to be useful.