Oral tissues are exposed to biomaterials in combination with optical radiation during dental treatments. Therefore, it is of interest to investigate if tissue changes occur. Previously, we have reported data obtained from near-infrared reflection spectroscopy (NIRS) used to non-invasively monitor tissue changes after optical exposure. The results indicated that oral mucosa may be more sensitive than skin to blue light. In this pilot study, visible data from NIRS (VNIRS) was used to observe differences between exposure groups with respect to the following parameters:  pigmentation (melanin index; MI), blood oxygenation (OX) and erythema (erythema index; EI). The material chosen is a frequently applied methacrylate-based bonding material for dental restorations. Pigmented rats (Long-Evans) were exposed to bonding material/blue light, bonding only, blue light only, UV only or left unexposed on oral mucosal sites and abdominal skin sites for control. Blue light treatment was performed with a dental halogen polymerisation lamp (λpeak: 494 nm) with irradiance (E) = 566 mW/cm² and radiant exposure (H) = 23 J/cm². UV treatment was performed with a sunbed fluorescent tube with ECIE = 0.05 mW/cm² (E= 16 mW/cm²) and HCIE = 25 mJ/cm² (2.5 SED). Spectral reflectance was assessed by VNIRS, and MI and EI were calculated (Randeberg LL et al, Acta Pædiatrica 2005;94:65-71). OX was evaluated at 660/805 nm. The values obtained were used to evaluate differences in reflectance between exposure groups for each parameter at baseline (0 h), immediately after exposure (0.5 h) and 24 h later. Preliminary results showed that in skin the bonding/light group was different from control for all parameters at 0 h and 0.5 h , but the values returned to control level for the three parameters when assessed 24 h later. Contrary, in oral mucosa only few differences between groups were observed at 0 h and 0.5 h, but after 24 h OX values were significantly different between the bonding- and UV-exposed groups. The high OX value obtained for bonding may be due to increased blood flow typical of mucosal irritation. We speculate that the low OX value in the UV-exposed group may be related to the previously reported increased NIRS value possibly indicating oedema in this exposure group. VNIRS data indicated that oral mucosal tissue changes are delayed after exposure to bonding material or UV compared with skin.

Optical characterization of biomaterial/radiation-exposed oral mucosa by reflection spectroscopy
Randeberg LL, Dahl JE, Bruzell E.
14th Congress of the European Society for Photobiology, Geneva, Switzerland, September 1 – 6, 2011