Effect of Angulation on Quantification of Caries Lesions by Photothermal-Radiometry/Modulated-Luminescence

Objectives: The study aimed to investigate the effect of angulation on Photothermal-Radiometry and Modulated-Luminescence (PRT/LUM) technique.
Methods: Extracted human-premolars (N=86) with occlusal surfaces varying from International Caries Detection & Assessment System (ICDAS) scores 0 to 4 without sealants or restorations were selected (score 0: N=26; scores 1-4: N=15 each). Teeth were mounted on custom-made typodonts. A series of PTR/LUM-values was acquired perpendicular to the pit and fissure (90°) and at 10° intervals up to 20° below and above the perpendicular with the Canary system (Quantum Dental Technologies, Toronto, Canada). PRT/LUM-values were acquired by rotating the line of sight (LOS) about the bucco-lingual axis of the tooth, defining the roll angle. Next, LOS was acquired along the mesio-distal axis of the tooth, defining the pitch angle. The effects of the roll and pitch angles on values were examined using ANOVA, including fixed effects for motion-type (roll vs. pitch angles), angle, motion type-by-angle interaction, and a random effect to correlate the multiple observations from each tooth.
Results: For roll angle (mesio-distal direction), mean (standard error) PTR/LUM-values were 31.6 (1.8), 31.9 (2.1), 30.9 (2.1), 30.8 (2.0), and 28.3 (1.7) from 70° to 110°. For pitch angle (bucco-lingual direction), mean (standard error) values were 29.1 (1.7), 29.4 (1.8), 30.3 (1.9), 32.6 (2.2), and 29.3 (1.9) from 70° to 110°. No significant angulation effects were found for ICDAS-1, ICDAS-2, or ICDAS-3 (p>0.05). For ICDAS-0, PTR/LUM-values were higher for bucco-lingual 70° than for bucco-lingual 90° (p=0.0014), bucco-lingual 100° (p=0.0014) and bucco-lingual 110° (p=0.0018). For ICDAS-4, PTR/LUM-values were higher for 100° than for 70° (p=0.0420) and 110° (p=0.0140) regardless of motion-type. At 90°, the correlation between ICDAS-scores and PTR/LUM-values was 0.75-0.76.
Conclusions: Within the limitations of this study, it can be concluded that angulation may have an effect on PRT/LUM-values for ICDAS-4.