Thresholds of Non-contacting Laser Profilometry in Detecting Enamel Erosive Wear

Objectives: To determine the detection threshold of non-contacting laser profilometry (NCLP) in measuring surface form and surface roughness in natural human enamel in-vitro, and to characterise changes occurring after acid erosion challenges on natural enamel.

Methods: Natural human enamel (n=1) was scanned by NCLP with and without replacement ten times. Consecutive scans were subtracted from each other. Repeatability and reproducibility accuracy, and thus the detection threshold of NCLP, was determined by the standard deviation of absolute height difference between the residual data. Natural human enamel slabs (n=12) were produced (5mm x 5mm x 3mm) and fixed to glass microscope slides using epoxy resin. After taping, they underwent citric acid erosion (0.3% pH3.2) for 5, 10, and 15min. Resulting lesions were characterised quantitatively using changes in surface form (mean 3D step height change) and surface roughness (mean Sa), and qualitatively using tandem scanning confocal microscopy (TSM), and optical coherence tomography (OCT).

Results: Repeatability and reproducibility accuracy of the NCLP for surface form detection was 0.279µm and 0.431µm respectively; for Sa this was 0.072µm and 0.084µm respectively. For eroded samples, mean(SD) step height change (µm) was detected at all timepoints and were statistically significant versus baseline (p<0.05, one-way ANOVA): 1.490(0.260) (5min), 2.470(0.850) (10min), and 3.710(1.580) (15min). Mean (SD) surface roughness (μm) at baseline was 1.132(0.126) and after 5, 10, 15min erosion was 1.516(0.233), 1.435(0.191), and 1.432(0.207) respectively; this was statistically significant compared to baseline (p<0.0001, one-way ANOVA). Qualitative image analysis indicated reduction in surface reflectivity and enamel surface destruction with increased erosion time
Conclusions: This study demonstrated the minimum detectable limits for NCLP in measuring surface form and surface roughness of natural enamel was 0.279µm and 0.072µm respectively. Additionally, the study demonstrated the significant increase of bulk enamel loss (step height) and surface roughness in natural human enamel after citric acid erosion.