A study on a noninvasive pulp diagnostic method using transmitted light photoplethysmography

为了构建一种最佳的透射光检测系统，用分光光度计研究了人拔牙和外周血在400~800 nm范围内的光透过率特性。光源为钨白炽灯，光电导池为CdS-CdSe光电导池。光谱分析表明，波长小于600 nm的光比波长较长的光更容易被血液吸收。透射式光体积图(TLP)应用于健康志愿者的上颌中切牙。用三种不同的光源(钨灯、峰值波长为565 nm的LED(LED565)和峰值波长为695 nm的LED(LED695))作为光源。光照射牙冠的腭面，透射光从唇侧收集。光电导池采用CdS-CdSe作为光电探测器。LED565在大多数被检查的牙齿上都能观察到脉搏波，但用钨光和LED695很难识别脉搏波。结果表明，LED565适合于牙髓TLP。取人上中切牙，确定光的透射区。一个LED(强度峰值565 nm)和一根光纤(直径2.2 mm)分别与牙釉质-水泥结合部约2 mm处的腭面和唇面接触。穿过牙齿的透射光通过光纤被引导到CDS-CdSe光电导单元(峰值灵敏度560 nm)。结果表明，我们的方法可以检测到牙釉质-水泥结合部附近约2 mm的牙髓血流。

In order to construct an optimal detection system for the transmitted light, light transmittance characteristics of the human extracted teeth and the human peripheral blood were investigated between 400 and 800 nm using a spectrophotometer. A tungsten incandescent light and a CdS-CdSe photoconductive cell were used as the light source and the photodetector, respectively. The spectrum analysis showed that the light of its wavelength shorter than 600 nm was more absorbable by the blood than the longer wavelength.Transmitted light photoplethsmography (TLP) was applied to vital human upper central incisors of healthy volunteers. Three different light sources (the tungsten light, a LED with its peak at 565 nm (LED565) and a LED with its peak at 695 nm (LED695)) were used as the light source. The light illuminated the palatal surface of the tooth crown and the transmitted light was collected form the labial side. The Cds-CdSe photoconductive cell was used as the photodetector. Pulse waves were observed on most of the examined teeth with the LED565, however, it was difficult to recognise the pulse wave with the tungsten light and the LED695 The results indicated the LED565 was suitable for the pulpal TLP.Then, the detectable area of the root pulp blood flow by our method was assessed. Human extracted upper central incisors were used to determine the transmitted area of the light. An LED (intensity peak 565 nm) and an optical fiber (o.d.2.2 mm) were placed in contact with the palatal and the labial surface of the teeth approximately 2 mm from the enamel-cement junction, respectively. The transmitted light throught the teeth was guided to the CdS-CdSe photoconductive cell (peak sensitivity 560nm) via the optical fiber. The results indicated that our method can detect the root pulp blood flow as far as app.2 mm from the enamel-cement junction.