A. Groeneveld

Experimental Evidence for a Gradient in the Solubility and in the Rate of Dissolution of Human Enamel

In this study evidence is provided for the existence of a gradient in solubility and rate of dissolution of human tooth enamel. These gradients were obtained quantitatively by applying calcium and pho

Effect of Time and Degree of Saturation of Buffer Solutions on Artificial Carious Lesion Formation in Human Tooth Enamel

The chemical systems to produce carious lesions described in the literature can be divided into three types: (a) gel systems, (b) systems containing a substance which decreases the dissolution rate of

Effect of the pH of buffer solutions on artificial carious lesion formation in human tooth enamel.

In this study a buffer system containing calcium and phosphate was used to produce caries-like lesions. The influence of the pH on the lesion characteristics was investigated. The degree of saturation

The mineral content of human enamel studied by polarizing microscopy, microradiography and scanning electron microscopy

The total observed birefringence and mineral content of the outer 300 micron of longitudinal sections of sound buccal premolar enamel were measured and three-dimensional contour maps were made. Using similar contour maps of calcium, carbonate and magnesium content from the literature, it seemed possible to explain the differences between the contour maps of total observed birefringence and mineral content. Scanning electron micrographs provided information about the orientation of the prisms. The cervical part of the enamel had a high intrinsic birefringence which may explain the difference between mineral content and total observed birefringence. This high intrinsic birefringence may be caused by a high carbonate content in cervical enamel.

Effect of time, degree of saturation, pH and acid concentration of buffer solutions on the rate of in-vitro demineralization of human enamel

The rate of demineralization of the artificial caries-like process was measured using two methods. The rate calculated from microradiography of the demineralized enamel appeared to be equal to the one calculated from calcium and phosphate analysis of the demineralizing buffer. In small volumes of demineralizing solution, the rate of demineralization decreased with time, due to the increase in saturation of the solution during the demineralization of the enamel. With increasing saturation, with respect to hydroxyapatite, and with increasing pH the rate of demineralization decreased. Increasing acid concentration had a marked influence only at the lower concentrations; a further increase had no effect on the rate of demineralization.

Relationships between Birefringence and Mineral Content in Artificial Caries Lesions of Enamel

The microradiographic mineral content and birefringence in water and Thoulets solution were measured at selected points in sections of caries-like lesions. Birefringence was not related to mineral content in sound superficial enamel immersed in Thoulets solution or in the lesion body immersed in water. For the surface layer of the lesion, birefringence in water could be used to obtain qualitative information about mineral content. For the lesion body, birefringence in Thoulets solution was linearly related to mineral content and can be used to estimate the latter with a standard error of about 7 vol%. The intrinsic birefringence for the lesion body was estimated as -34.5 (+/- 2.3) x 10(-4); This value may also be valid for other parts of the lesion. From consideration of ionic sizes, it is argued that Thoulets solution cannot necessarily penetrate all enamel pores accessible to water. It appeared that there is a progressive fall in the content of pores inaccessible to Thoulets solution in the surface layer of the lesion as demineralisation increases.

The Surface Layer during Artificial Carious Lesion Formation

This paper gives a detailed description of the development of the surface layer during demineralization of human enamel. Optical inspection of microradiograms of lesions in different stages of development can give the impression that the surface layer increases in thickness with time. Using a more objective method of inspection together with an explicit description, the development of the surface layer was followed with time more quantitatively. This method was based on the changes occurring at the inside of the surface layer. It appeared that the surface layer thickness was constant with time in all lesions investigated. These observations indicate that at constant composition of the buffer solutions, no dissolved material from the body of the lesion is deposited at the inside of the surface layer.

The effect of undissociated acetic-acid concentration of buffer solutions on artificial caries-like lesion formation in human tooth enamel

A chemical system for lesion production was used. The influence on lesion characteristics of the concentration of undissociated acetic acid in a calcium and phosphate-containing buffer solution was investigated. Artificial lesions obtained after demineralization in buffers with a pH of 4.0, 4.5, 5.0 or 6.0 at 5 or 6 different acid concentrations for different demineralization times were investigated micro-radiographically. The lesion characteristics studied were: the mineral content of the surface layer; the mineral content of the body of the lesion; and the depth at which these mineral levels were reached; the depth of the lesion. The concentration of undissociated acetic acid had little effect on the lesion characteristics at low pH. When lower concentration buffers at pH 6.0 were used, the effect was more pronounced. At this level, the buffer capacity of the acetic acid/acetate buffer is small.

The Influence of the Composition of Demineralizing Buffers on the Surface Layers of Artificial Carious Lesions

This paper deals with the influence of (1) the pH, (2) the degree of saturation with respect to hydroxylapatite (OHA) and (3) the fluoride concentration of demineralizing buffer solutions on the development of surface layers of artificial carious lesions. The pH did not affect the surface layer during demineralization. With increasing saturation with respect to OHA, the mineral content of the surface layer increased and the gradient of mineral content at the inside of the surface layer became less negative. The effect of the fluoride concentration depended on the degree of saturation of the solution with respect to OHA. At the highest undersaturation used in this study (pIoha126) an increase of the fluoride concentration caused an increase of the mineral content of the surface layer, an unchanged gradient in mineral content at the inside of the surface layer, and an increased intercept of this gradient. At low undersaturation with respect to OHA (pIoha122) an increasing fluoride concentration caused a less negative gradient. An explanation for the results is given on the basis of the driving forces for dissolution of enamel mineral and reprecipitation of less soluble mineral. It is concluded that the degree of saturation with respect to fluorapatite and the fluoride concentration are factors determining the development of the surface layer.