The reflectance probe was designed in Fusion 360 from Autodesk (San Francisco, CA) and 3D printed using a Form 3 printer from Formlabs (Boston, MA). The reflectance probe body was printed using biocompatible and autoclavable Formlabs Biomed black resin. The probe is approximately 8 cm long and 14 mm in diameter at the distal end. Attached to the probe is a right-angle aluminum mirror to collect light from the occlusal surface and an assembly for the attachment of the reflectance fiber. SWIR light is delivered through a 0.4-mm diameter low-OH optical fiber from a 1466 nm superluminescent laser diode (SLD), from EXALOS (Zurich, Switzerland) with an output of 14 mW and a bandwidth of 40 nm. The fiber is inserted into a cylindrical Teflon plug (3.2x40 mm). Light exiting the plug is directed toward the tooth occlusal surface by a 5 mm polarizing beamsplitter cube. The probe employs cross-polarization to reduce specular reflection. There is an 1/8 inch air nozzle attached to the reflectance body and air exits the air channel near the mirror to prevent the fogging of the mirror and dehydrate the lesion surface to assess lesion activity [8, 9, 17]. In existing probes, the air dehydration channels are directed parallel to the probe surface (Fig. 1B). This nozzle design has worked well on tooth root surfaces [21], however dehydration in the pits and fissures of tooth occlusal surfaces has been more difficult [26]. We experimented with new preliminary nozzle designs and found that the dehydration rate can be increased markedly for occlusal surfaces by narrowing the nozzle opening and angling the nozzle. The new design is shown in Fig. 1A next to the old design along with a dehydration curve acquired from a deep fissure with an active lesion using the new nozzle prototype. In the old design (Fig. 1B) the exit ports were each 8 x 0.7 mm and oriented parallel to the long axis of the probe. In the new design (Fig. 1A), the top slit is 2 x 1.4 mm and oriented parallel to the long axis of the probe while the lower exit port is 2 x 0.75 mm and angled by 38° to the long axis.