Characterization of Clinical Enamel Remineralization Using High-Resolution TOF-SIMS and HR-TEM

Objectives: The use of time-of-flight secondary-ion mass spectrometry (TOF-SIMS) and high-resolution transmission electron microscopy have rarely been applied to study enamel remineralization. In contrast, other, common, electron-based imaging techniques have some limitations that prevent clear identification and distribution of remineralized tissue within the original, native enamel structure. We have previously developed these techniques on laboratory derived samples. For the first time, they are applied here to study the remineralization of clinically derived samples.
Methods: A series of MFP dentifrices were prepared at 0, 250, 1100 and 2800 ppm F as MFP with soluble MFP confirmed analytically. These dentifrices were evaluated in an established, randomized, controlled crossover trial using an in situ denture chip method remineralizing model in 16 volunteers. Shallow artificial caries lesions were prepared in enamel discs and surface microhardness was measured. Enamel specimens were mounted in modified partial dentures with gauze coverings to encourage plaque formation. Volunteers brushed daily with MFP pastes and wore their dentures 24h/day throughout a 3-week test period. Specimens were removed at days 7, 14 and 21 and re-measured for surface microhardness and assayed for fluoride uptake using a microdrill biopsy method. Remineralization was calculated based on % surface microhardness recovery.
Results: TOF-SIMS images indicated that the distribution of F was more widespread throughout the remineralized lesion and increased in accordance with the dose of MFP in the treatment. Fluoride penetrated the inter-rod spaces at the interface of sound and demineralized enamel. HR-TEM images indicating a return to crystallinity with respect to the fluoride placebo treatment. In situ % Hardness Recovery (14 day e.g.) = 10.49, 24.76, 38.08 and in situ F Uptake (14 day e.g.) = 3.86, 11.53, 18.92. All results were significantly different, p<0.05, using analysis of (co)variance models (AN(C)OVA) as appropriate for a crossover study.
Conclusions: High-resolution techniques proven here highly useful for studying enamel remineralization in a clinical context illustrating widespread fluoride throughout the remineralized tissue and a return of crystallinity during the three-week treatment period with respect to a placebo control.