Balancing Demineralisation and Collagen Integrity: A Nanoscale Analysis of Etching Time in Human Dentin

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OBJECTIVES: To investigate the effect of varying phosphoric acid etching times on dentin demineralisation and collagen fibril morphology and to identify a time-dependent balance between sufficient mineral removal and preservation of collagen nanostructure. METHODS: Dentin specimens from human third molars were etched with 37% phosphoric acid for 6 different durations: 0, 5, 10, 15, 30, and 60 seconds. Demineralisation was assessed using attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy by calculating the phosphate-to-amide I absorbance ratio. Collagen integrity was evaluated using scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging, with the percentage of visible D-banding serving as a morphometric indicator. RESULTS: FTIR analysis revealed a progressive reduction in the phosphate signal with increasing etching time, following an exponential decay pattern and approaching a plateau at approximately 10 seconds. AFM imaging revealed that the D-banding periodicity reached its peak at 10 seconds (mean: 71.7%) and subsequently decreased, with notable degradation observed at 30 and 60 seconds. Statistical analysis indicated significant differences in D-banding between the 10-second group and longer etching durations (P < .05). CLINICAL SIGNIFICANCE: This study provides nanoscale evidence that phosphoric acid etching of dentin for approximately 10 seconds achieves effective demineralisation while preserving collagen integrity. Longer etching times compromise fibril structure, underscoring the need for precise, time-controlled protocols to optimise resin-dentin bonding performance.