In vitro remineralization of enamel by polymeric amorphous calcium phosphate composite: quantitative microradiographic study

Abstract

Objective: This study explores the efficacy of an experimental orthodontic amorphous calcium phosphate (ACP) composite to remineralize in vitro subsurface enamel lesions microradiographically similar to those seen in early caries.

Methods: Lesions were artificially created in extracted human molars. Single tooth sections a minimum of 120microm thick were cut and individually placed in holders exposing only the carious enamel surface. The exposed surfaces were either left untreated (control) or coated with a 1mm thick layer of the experimental ACP composite (mass fraction 40% zirconia-hybridized ACP and 60% photo-activated resin), or a commercial fluoride-releasing orthodontic cement. The composite-coated sections were then photo-cured and microradiographic images were taken of all three groups of specimens before the treatment. Specimens were then cyclically immersed in demineralizing and remineralizing solutions for 1 month at 37 degrees C to simulate the pH changes occurring in the oral environment. Microradiographs of all specimens were taken before and after treatment.

Results: Quantitative digital image analysis of matched areas from the contact microradiographs taken before and after treatment indicated higher mineral recovery with ACP composites compared to the commercial orthodontic F-releasing cement (14.4% vs. 4.3%, respectively), while the control specimens showed an average of 55.4% further demineralization.

Significance: Experimental ACP composite efficiently established mineral ion transfer throughout the body of the lesions and restored the mineral lost due to acid attack. It can be considered a useful adjuvant for the control of caries in orthodontic applications.

Fig. 1

Chemical structure of the monomers and photo-initiator system employed in formulation of ETHM resin.

Fig. 2

Schematic diagram containing both the assembly which isolates the tooth slice (left) and the glass slide mount which holds the assembly and composite during cycling (right).

Fig. 3

Digital photomicrograph showing a typically prepared tooth slice (a) and a corresponding plot profile determined from the grayscale intensities of the image (b).

Fig. 3

Digital photomicrograph showing a typically prepared tooth slice (a) and a corresponding plot profile determined from the grayscale intensities of the image (b).

Fig. 4

X-ray diffraction pattern (a), FTIR spectrum (b), volume particle size distribution (c) and the typical SEM image (d) and of Zr-ACP utilized in the experimental composite.

Fig. 4

X-ray diffraction pattern (a), FTIR spectrum (b), volume particle size distribution (c) and the typical SEM image (d) and of Zr-ACP utilized in the experimental composite.

Fig. 4

X-ray diffraction pattern (a), FTIR spectrum (b), volume particle size distribution (c) and the typical SEM image (d) and of Zr-ACP utilized in the experimental composite.

Fig. 4

X-ray diffraction pattern (a), FTIR spectrum (b), volume particle size distribution (c) and the typical SEM image (d) and of Zr-ACP utilized in the experimental composite.

Fig. 5

Mineral profiles (mean values ± standard deviation (indicated by vertical lines) of the uncoated control specimens (a), ACP composite-coated specimens (b), and Fluoride cement-coated specimens (c), before (blue) and after (pink) pH-cycling treatment. Number of specimens per group: 4 ≤ n ≤ 15; number of analyzed areas per group: 8 ≤ n ≤ 30.

Fig. 5

Mineral profiles (mean values ± standard deviation (indicated by vertical lines) of the uncoated control specimens (a), ACP composite-coated specimens (b), and Fluoride cement-coated specimens (c), before (blue) and after (pink) pH-cycling treatment. Number of specimens per group: 4 ≤ n ≤ 15; number of analyzed areas per group: 8 ≤ n ≤ 30.

Fig. 5

Mineral profiles (mean values ± standard deviation (indicated by vertical lines) of the uncoated control specimens (a), ACP composite-coated specimens (b), and Fluoride cement-coated specimens (c), before (blue) and after (pink) pH-cycling treatment. Number of specimens per group: 4 ≤ n ≤ 15; number of analyzed areas per group: 8 ≤ n ≤ 30.

Fig. 6

Change in the relative mineral content (mean value + SD (indicated by bars)) as a function of the lesion depth for ACP composite and F-cement specimens. Data derived from the mean mineral profile values presented in Fig. 5.

Fig. 7

Overall change in mineral content for each treatment (mean value + SD (indicated by bars)).

Fig. 8

Calcium and phosphate ion release from the experimental ACP composite and fluoride release from the commercial orthodontic cement. Indicated are mean values ± SD obtained from three repetitive measurements in each group.