Detection ability and direction effect of photothermal-radiometry and modulated-luminescence for non-cavitated approximal caries.

Objective: The objective was to evaluate the ability of photothermal-radiometry and modulated-luminescence (PTR/LUM) to detect non-cavitated approximal caries lesions, including the effect of scanning direction.

Methods: Thirty human extracted premolars were selected based on micro-computed tomography [μ-CT: μ-CT = 0: sound (n = 12), μ-CT = 1: lesions into outer-half of enamel (n = 6), μ-CT = 2: lesions into inner-half of enamel (n = 6), and μ-CT = 3: lesions into outer one-third of dentine (n = 6)]. Teeth were mounted in a custom-made device to simulate approximal contact. Each tooth was scanned from three directions: buccal, lingual, and occlusal, then repeated 48 h later. Statistical analyses were performed by bootstrap analyses using average and maximum values across all directions. Sensitivity, specificity, area under ROC-curve (AUC), intraclass correlation coefficient (ICC) and correlation with μ-CT were calculated. Sensitivity was further evaluated based on lesion extension.

Results: Using the manufacturer-suggested lesion cut-off, overall sensitivity ranged from 3%-61%, where the maximum value of all measurements (All-max) showed higher sensitivity (61 %) than other measurements except the buccal direction, which was also higher than the lingual and occlusal directions. As μ-CT score increased from μ-CT = 1-3, the sensitivity of All-max also increased from 50 % to 74 %. Specificity was 100 % regardless of direction, and AUC ranged from 0.65 to 0.88. All-max had the highest ICC (0.74). PTR/LUM values showed weak to moderate correlations with μ-CT.

Conclusion: Within the limitations of this in vitro study, PTR/LUM non-cavitated approximal caries lesion detection achieved best individual results from the buccal direction, while using the maximum value from all directions might improve performance.

Clinical Significance: Non-cavitated approximal caries detection is a challenging procedure. PTR/LUM is a nondestructive, no ionized-radiation caries detection method that can scan from buccal, lingual, and occlusal directions of an approximal surface. PTR/LUM seems suitable to detect deeper non-cavitated approximal caries. The maximum PTR/LUM value from three directions may be optimal.