Does luminosity and smear layer influence 810 nm laser energy transmission through human dentine?

The aim of this study was to evaluate the influence of luminosity values and smear layer on transmission characteristics of 810 nm near infrared laser energy through dentine, using extracted human teeth.

A total of 200 teeth treated with endodontic medicaments to cause discolouration (Ledermix, Doxypaste or Odontopaste) were selected, to give a range of values for tooth shade (luminosity values). Sectioned teeth had smear layer created or removed. Near-infrared laser energy transmission was assessed using an 810 nm diode laser (90 mW, CW mode) with the tip placed at 2 mm and 4 mm from the external root surface, and a laser power metre.

Both tooth shade and smear layer had independent attenuating effects. Transmission of laser energy was significantly lower in teeth with darker shades. There was a strong positive correlation between relative luminosity (lighter tooth colour) and transmitted laser power (r = 0.9271 for the Spearman rank correlation, P = 0.0022). When a smear layer was present, this significantly reduced the transmission of laser energy through the sample, compared to when no smear layer was present.

The results of this laboratory study highlight the attenuating influence of a darker tooth shade and the presence of smear layer on the transmission of 810 nm light when directed onto the surface of human dentine. Such effects may be relevant to photo biomodulation, Photodynamic Therapy and other dental laser treatments.