Accuracy and bias of high-frequency ultrasonography in measuring white spot lesion depth: an in-vitro comparison with micro-CT

Objectives: This in vitro study aimed to evaluate the accuracy and bias of Ultrasound (US) in measuring the depth of white spot lesions (WSLs), in comparison to micro-CT (µ-CT). Materials and methods: The study included 120 bovine maxillary incisors. Artificial WSLs were created on the facial surface of each incisor. Incisors were categorized into two groups, shallow WSLs and deep WSLs and subjected to 2-day and 4-day pH cycling protocols, respectively. All samples were imaged with both µ-CT and US using second harmonic imaging at 12/24 MHz. WSL depth was measured and the average calculated. Enamel thickness was assessed on the µ-CT images using the same methodology. Results: Mean lesion depths in the shallow WSLs group were 138.3±17.8 μm (µ-CT) and 169.2 ± 37.8 μm (US), while in the deep WSLs group, depths averaged 299.9 ± 47.7 μm (µ-CT) and 309.3 ± 75.7 μm (US). The absolute mean differences between µ-CT and US were significantly different from zero (p < 0.001). US consistently overestimated lesion depth compared to µ-CT in both groups, with a significant difference in the shallow WSLs group (p < 0.001). Conclusions: US demonstrates lower accuracy than µ-CT in measuring WSL depth, consistently overestimating lesion depths, particularly in the shallow WSLs group. Clinical relevance: The ability of a diagnostic method to measure WSLs of varying depths is clinically important, as treatment efficacy depends on lesion depth and the extent of enamel demineralization. US in non-invasive and demonstrates potential for clinical use; however, further validation is required before it can be reliably applied to the clinical assessment of WSL depth. Clinicians must also consider practical factors such as equipment cost and size, the need for coupling materials, and requirements for operator training and calibration.