Detection threshold of non-contacting laser profilometry and influence of thermal variation on characterisation of early surface form and textural changes in natural human enamel.

Objectives: To determine the detection threshold of non-contacting laser profilometry (NCLP) measuring surface form and surface roughness change in natural human enamel in vitro, characterise how ambient scanning thermal variation affects NCLP measurement, and calculate bulk enamel loss in natural human enamel.

Methods: NCLP repeatability and reproducibility accuracy was determined by consecutively scanning natural human enamel samples with/without sample repositioning. Ambient thermal variation and NCLP sensor displacement over short (30 s), medium (20 min), and long (2 h) scanning periods were evaluated for their standard deviation. Natural human enamel specimens (n = 12) were eroded using citric acid (0.3% w/w pH3.2) for 5, 10, and 15 min and characterised using surface profilometry, tandem scanning confocal microscopy (TSM), and optical coherence tomography (OCT).

Results: Repeatability and reproducibility error of NCLP for surface form was 0.28 μm and 0.43 μm, and for surface roughness 0.07 μm and 0.08 μm. Ambient thermal variation resulted in NCLP sensor displacement of 0.56 μm and 1.05 μm over medium and long scanning periods. Wear scar depth (μm) was calculated between 0.72-1.61 at 5 min, 1.72-3.06 at 10 min, and 3.40-7.06 at 15 min. Mean (SD) surface roughness (μm) was 1.13 (0.13), 1.52 (0.23), 1.44 (0.19), and 1.43 (0.21) at baseline, 5, 10, and 15 min. Qualitative image analysis indicated erosive change at the surface level, progressing after increasing erosion time.

Significance: Minimum detectable limits for NCLP measuring surface form and surface roughness changes were characterised. Ambient thermal variation, subsequent sensor displacement, and its impact on NCLP performance were characterised. Dental erosion lesions in natural human enamel could be characterised using surface profilometry, surface roughness, OCT, and TSM. Step height formation could be calculated within NCLP and temperature operating limits using profile superimposition and profile subtraction techniques. Natural enamel samples can now be used in in-vitro studies to investigate the formation and development of early acid erosive tooth wear, as well as the assessment of methods for enamel lesion remineralisation and repair.