Milk Matters? Comparing Dairy and Plant-Based Milks for Post-Erosive Enamel Mineral and Hardness Recovery: An In Vitro Study

Background/Objectives: The effects of commercial plant-based beverages on eroded enamel remain uncertain. This study compared post-erosive enamel elemental composition, SEM image-derived surface roughness, and microhardness after exposure to one bovine, one almond, and one coconut milk product. Methods: Fifty bovine incisors were randomly allocated to five groups (n = 10): a never-eroded water control; a cola-eroded water control; and three cola-eroded groups treated with the respective milk products. Each tooth was immersed individually in a separate container containing 250 mL of the assigned medium. Each daily cycle comprised 3 h of cola exposure followed by 3 h of milk or water exposure, repeated for four consecutive days, with interim storage at 37 °C. Endpoint calcium, phosphorus, and Ca/P ratio were assessed by energy-dispersive X-ray spectroscopy, microhardness by Vickers indentation, SEM image-derived Ra by standardized grayscale analysis, and morphology by scanning electron microscopy. Tooth-level outcomes were compared using one-way ANOVA followed by Tukey HSD tests (α = 0.05). Results: Significant group differences were identified for elemental composition, image-derived Ra, and microhardness (p < 0.001). All milk groups had higher calcium, phosphorus, and microhardness and lower image-derived Ra than the eroded water control. The bovine product had the highest treatment-group calcium and microhardness and the lowest image-derived Ra, followed by almond and coconut. Phosphorus did not differ significantly between the bovine and almond groups. The bovine-group Ca/P ratio did not differ significantly from the never-eroded control; this does not establish equivalence or mineral-phase restoration. Conclusions: The tested bovine product showed more favorable endpoint calcium, image-derived Ra, and microhardness than the tested plant-based products under this accelerated in vitro protocol. The findings support product-specific differences in mineral/property recovery, not demonstrated enamel regeneration or clinical efficacy.