Early nanoscale erosive effects of dietary acids on dentine structure and mechanical properties

OBJECTIVES: To characterise early time-resolved demineralisation and associated mechanical degradation of peritubular (PTD) and intertubular dentine (ITD), and to determine whether citric acid (CA) pH or concentration is the dominant factor governing early dentine erosion. METHODS: Fifty human dentine specimens were assigned to five groups (n = 10/group): a PBS control and four CA conditions (1% buffered CA, pH 3.8; 1% unbuffered CA, pH 2.55; 6% buffered CA, pH 3.8; 6% unbuffered CA, pH 2.06). Each specimen was exposed only to its assigned solution and underwent six consecutive 20 s erosive challenges (0s-2 min). Nanoscale structural changes and modulus of elasticity (MoE) reductions were quantified using atomic force microscopy (AFM), supported by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Data were analysed using repeated-measures ANOVA with Bonferroni adjustment. RESULTS: PTD mineral was extensively lost after repeated acid exposures, while ITD changes plateaued beyond 60 s (p > 0.05). After 2 min, ITD extrafibrillar mineral was absent, while intrafibrillar mineral remained. The lowest pH solution (6% unbuffered) produced the greatest MoE reduction and the fastest PTD/ITD erosion rates (p < 0.001). At all timepoints, 1% unbuffered CA produced greater demineralisation than 6% buffered CA (p < 0.001). SIGNIFICANCE: Early dentine erosion is strongly time dependent. During the initial phase of acid exposure (first ∼60 s), demineralisation is governed predominantly by hydrogen-ion activity, rather than tissue-specific structure. Thereafter, the collagen matrix exerts a diffusion-limiting effect that preserves intrafibrillar mineral. Low pH dietary acids therefore present the greatest immediate risk, underscoring the critical role of early acid-dentine contact time in governing initial demineralisation.