A comparison between in vitro and randomized in situ models for remineralization of artificial enamel lesions

Abstract

The randomized study aimed to evaluate the comparability of in situ (iS) and in vitro (iV) study protocols regarding remineralization of artificial enamel lesions. Two toothpastes (group A: 1450 ppm sodium fluoride, group B: placebo 0 ppm F-), were investigated. IV, a pH-cycling model with toothpaste slurry treatment was applied for 10d. IS, remineralization was performed in 9 participants wearing splints with embedded enamel samples for 10 and 21d, randomly allocated to groups A and B. Samples were scanned by X-ray micro-computed tomography (μCT) and grayscale value line profiles corresponding to mineral density (rel.ΔZ) were analyzed. Statistical analyses were performed using MedCalc Statistical Software, v22.021. T-Test for dependent and independent data and analysis of variance (ANOVA) were used for further analyses (α = 0.05). Rel.ΔZ of fluoride treated samples (A) were iV = 40.2%, iS 10d = 11.5% and iS 21d = 46.1% (p > 0.05). Rel.ΔZ of placebo treated samples (B) were: iV = - 6.2%, iS 10d = 25.2% and iS 21d = 11.0% (p > 0.05). Remineralization potential of both toothpastes was significantly different regarding iV (p < 0.001) and iS after 21d (p = 0.034), while in case of iS 10d no significant difference was detected (p = 0.4). Despite different study protocols the μCT results after remineralization were comparable between iV and iS. The results suggest that selected studies can be carried out in faster, simplified iV studies using pH-cycling instead of iS studies.

Keywords: Demineralization; Dentifrice; Enamel; Fluoride; In-situ; In-vitro; Micro-ct; Remineralization.

Fig. 1

Flow diagram of the study design.

Fig. 2

Enamel sample (whitish slab) embedded in clear epoxy resin.

Fig. 3

Consort diagram.

Fig. 4

Splint with the attached specimen. The blue marks are the labels on the back of the sample for exact allocation.

Fig. 5

Generation of a digital cross section from µCT 3D data set. A sample range of interest (250 µm) was chosen from the surface view (a). Cross section image (b) depicts mean gray values of each voxel within the defined range of 250 µm width. Three line profiles each for demineralized (red) and remineralized (black) region were generated.

Fig. 6

Raw profiles (a), normalized and averaged profiles (b) and the mean gray value profiles for demineralized (c, red) and remineralized (d, black) region. Area A (ΔZ) is calculated from sound to demin (light red) and remin (gray) mean line, respectively.