The change of the configuration of hydroxyapatite crystals in enamel by changes of pH and degree of saturation of lactic acid buffer solution

Article information

Restor Dent Endod. 2007;32(6):498-513

Publication date (electronic) : 2007 November 30

doi : https://doi.org/10.5395/JKACD.2007.32.6.498

Young-Eui Chon , Il-Young Jung , Bung-Duk Roh , Chan-Young Lee

Department of Conservative Dentistry, College of Dentistry, Yonsei University, Korea.

Corresponding Author: Chan-Young Lee. Department of Conservative Dentistry, College of Dentistry, Yonsei University, 134 Shinchon-Dong, Seodaemun-Ku, Seoul, 120-752, Korea. Tel: 82-2-2228-8700, Fax: 82-2-313-7575, chanyoungl@yumc.yonsei.ac.kr

Received 2007 September 18; Revised 2007 October 03; Accepted 2007 October 10.

Abstract

Since it was reported that incipient enamel caries can be recovered, previous studies have quantitatively evaluated that enamel artificial caries have been remineralized with fluoride, showing simultaneously the increase of width of surface layer and the decrease of width of the body of legion. There is, however, little report which showed that remineralization could occur without fluoride. In addition, the observations on the change of hydroxyapatite crystals also have been scarcely seen.

In this study, enamel caries in intact premolars or molars was induced by using lactic acidulated buffering solutions over 2 days. Then decalcified specimens were remineralized by seven groups of solutions using different degree of saturation (0.212, 0.239, 0.301, 0.355) and different pH (5.0, 5.5, 6.0) over 10 days. A qualitative comparison to changes of hydroxyapatite crystals after fracturing teeth was made under SEM (scanning electron microscopy) and AFM (atomic force microscopy).

The results were as follows:

1. The size of hydroxyapatite crystals in demineralized area was smaller than the normal ones. While the space among crystals was expanded, it was observed that crystals are arranged irregularly.

2. In remineralized enamel area, the enlarged crystals with various shape were observed when the crystals were fused and new small crystals in intercrystalline spaces were deposited.

3. Group 3 and 4 with higher degree of saturation at same pH showed the formation of large clusters by aggregation of small crystals from the surface layer to the lesion body than group 1 and 2 with relatively low degree of saturation at same pH did. Especially group 4 showed complete remineralization to the body of lesions. Group 5 and 6 with lower pH at similar degree of saturation showed remineralization to the body of lesions while group 7 didn't show it. Unlike in Group 3 and 4, Group 5 and 6 showed that each particle was densely distributed with clear appearance rather than crystals form clusters together.

Keywords: Enamel; Remineralization; pH; Degree of saturation; Atomic force microscopy; Scanning electron microscopy

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Figure 1

SEM micrograph of normal enamel.

A and B are shown at 10 µm and 30 µm area from the surface layer, respectively (× 100,000).

Figure 2

SEM micrograph of demineralized enamel.

A and B are shown at 10 µm and 30 µm area from the surface layer, respectively (× 100,000).

The white arrow indicates intercrystalline spaces dissolved by demineralization process.

Figure 3

SEM micrograph of remineralized enamel of group 1.

A and B are shown at 10 µm and 30 µm area from the surface layer, respectively (× 100,000).

The white arrow indicates the combined crystals.

Figure 4

SEM micrograph of remineralized enamel of group 2.

A and B are shown at 10 µm and 30 µm area from the surface layer, respectively (× 100,000).

The white arrow indicates crystals with central defects.

Figure 5

SEM micrograph of remineralized enamel of group 3.

A and B are shown at 10 µm and 30 µm area from the surface layer, respectively (× 100,000).

The white arrow indicates a large cluster built as a result of the growth of newly formed crystals.

Figure 6

SEM micrograph of remineralized enamel of group 4.

A and B are shown 10 µm and 30 µm area from the surface layer respectively (× 100,000).

Figure 7

SEM micrograph of remineralized enamel of group 5.

A and B are shown at 10 µm and 30 µm area from the surface layer, respectively (× 100,000).

Figure 8

SEM micrograph of remineralized enamel of group 6.

A and B are shown 10 µm and 30 µm area from the surface layer, respectively (× 100,000).

Figure 9

SEM micrograph of remineralized enamel of group 7.

A and B are shown 10 µm and 30 µm area from the surface layer, respectively (× 100,000).

Figure 10

AFM image of hydroxyapatite crystals of normal enamel (1.0 µm × 1.0 µm).

Figure 11

AFM image of hydroxyapatite crystals of demineralized enamel (1.0 µm × 1.0 µm).

Figure 12

AFM image of hydroxyapatite crystals of the remineralized enamel of group 1 at 30 µm area from the surface layer (1.0 µm × 1.0 µm). The black arrow indicates a large crystal formed as a result of the growth of pre-existing or newly formed crystals. The white arrow indicates newly formed small crystals.

Figure 13

AFM image of hydroxyapatite crystals of remineralized enamel of group 2 at 30 µm area from the surface layer (0.5µm × 0.5 µm).

Figure 14

AFM image of hydroxyapatite crystals of remineralized enamel of group 4 at 30 µm area from the surface layer (1.0 µm × 1.0 µm).

Figure 15

AFM image of hydroxyapatite crystals of remineralized enamel of group 6. A and B are 30 µm and 40 µm area from the surface layer, respectively (1.0 µm × 1.0 µm).

Table 1

Initial composition of the demineralization solution

Table 2

Initial composition of the remineralization solution

^*: Degree of saturation