Multimodal analysis of physicochemical changes in dental enamel under plaque and calculus coverage

This study aimed to compare changes in enamel morphology, mineral composition, crystal structure, and mechanical properties under naturally formed dental plaque at different maturation stages versus dental calculus, using an intraoral in situ device and multimodal characterization.

Six groups were analyzed (n = 5/group): a blank control group (fully bone-impacted mandibular third molars), a calculus group (extracted molars with naturally adherent dental calculus), and plaque groups formed in vivo for 1, 7, 14, and 28 days using an intraoral in situ device. Mirror-polished longitudinal sections were examined by EDS, Raman spectroscopy, and nanoindentation, followed by SEM for morphology.

With increasing plaque coverage time, enamel prisms became progressively disrupted, with widened interprismatic spaces and more microcracks. Mean Ca/P across 5-100 μm decreased from 2.09 ± 0.08 (blank control) to 1.73 ± 0.09 (28-day plaque; P < 0.05). The ν₁(PO₄³⁻) band downshifted and broadened (960.85 ± 0.42-957.19 ± 0.56 cm^-1; FWHM 16.03 ± 1.01-26.35 ± 1.06 cm^-1; P < 0.05) with increased I(1070)/I(960) and I(1450)/I(960). Hardness and elastic modulus declined from 4.44 ± 0.72 and 88.67 ± 12.94 GPa to 3.45 ± 0.55 and 71.77 ± 14.34 GPa in the 28-day plaque group (P < 0.05). The calculus group showed changes in the same direction, but with a smaller magnitude within the measured indicators and depth range.

Natural plaque and calculus coverage promoted dissolution of the enamel inorganic phase, increased lattice disorder, and deterioration of mechanical performance; however, mature plaque (e.g., the 28-day group) caused substantially greater damage than dental calculus. Early inhibition of plaque maturation may be more important for maintaining enamel structural stability than removal of dental calculus.