Subsurface Lesions Research Articles

Enamel remineralization as a factor in the pathogenesis of dental caries.

This paper described an investigation of local resistance acquired in response to cariogenic attacks and remineralization periods from environmental fluids. Surfaces from extracted human teeth with yellow and brown areas indicative of consolidated carious lesions were exposed to acid buffers. Subsurface lesions were developed on areas of sound enamel adjacent to, but not in areas of, consolidated lesions. The development of higher tooth resistance to acid through demineralization and remineralization was demonstrated experimentally on bovine enamel presoftened in acid, treated with fluoride, exposed to the oral environment, and finally exposed to acid buffers for development of subsurface lesions. These results are interpreted as an extension of theory of tissue adaptation to an injurious challenge, in that the tooth surface is primed by the challenge for possible remineralization and the development of higher resistance. This, cariogenic challenges can result in either local adaptation of the enamel to the challenge through lesion consolidation or to open cavitation. As in any biological adaptation, the determining factors for the final outcome are: (a) the frequency and duration of the challenge, (b) the frequency and duration of remineralizing conditions, and (c) the composition of the remineralizing fluid. The implications of the theory in the pathogenesis of caries are discussed in the light of clinical and laboratory investigations.

A scanning electron microscopic and microradiographic study of pits in fluorosed human enamel

The aim of the present study has been to correlate the surface appearance of pitted, fluorosed enamel in the scanning electron microscope (SEM) with the microradiographic features of the underlying tissue. Intact enamel surfaces of severely fluorosed teeth appeared similar to that of normal enamel. In the unabraded surfaces discrete pits were sharply demarcated from the surrounding intact enamel surface leaving steep walls of parallel running rods. The microradiographic appearance of sections made through pits indicated that focal loss of surface enamel occurred corresponding to the inner highly hypomineralized part of the fluorotic subsurface lesion. The abrupt wall formation and the finding that the striae of Retzius never changed direction along the margins of the lesions indicated that pits in fluorosed enamel may be secondarily produced defects rather than true hypoplasias. Further evidence of the posteruptive origin of the defects was derived from the observation that enamel lamellae occasionally formed part of the lateral border. The relatively higher degree of radiopacity observed in the tissue surrounding the pit indicates a posteruptively acquired deposition of minerals in the exposed porous enamel.

Microhardness indentations on artificial white spot lesions.

In this study, Knoop hardness experiments on artificial carious enamel (pH 5.0, 4.5 and 4.0) are presented with the load perpendicular to the subsurface lesion. The results show that for human and bovine enamel the indentation length is proportional to the square root of the load. The proportionality constant is numerically estimated for all pH values for human and bovine enamel. The indentation measurements reflect the decalcification despite the presence of surface layer covering the lesion.

The Effect of Differing Concentrations of SnF2on Demineralized Enamel

The effect of different concentrations of stannous fluoride (SnF₂) on demineralized enamel was studied, on cross-sections, using microhardness and densitometric measurements. SnF₂ solutions, ranging in concentration from 0.5 to 8%, were applied to artificially demineralized enamel surfaces. It was found that the hardness increase in the surface layer was similar in all groups but that the radiodensity increased significantly with increasing concentration. It is suggested that these results are due to the maximum formation of fluorapatite from the available brushite, thus improving the crystalline structure and giving equal hardness in all groups, whilst the increase in radiodensity demonstrates the incorporation of stannous ions resulting in an increase in mineralization. In the subsurface lesion there was an increase in hardness with increasing concentration. This trend was also seen in the microradiographic results but to a much greater degree. This more demineralized area requires a greater SnF₂ influx for the formation of stannous compounds which appear primarily to have a space-filling and mineralizing function. It can be concluded that: maximum surface rehardening occurred after the application of an 0.5% SnF₂ solution; maximum increase in hardness and radiodensity in both the surface layer and subsurface lesion occurred after the application of an 8% SnF₂ solution; (c) hardness increases are not directly correlated to the increase in radiodensity.

Microradiography of developing artificial dental caries-like lesions in man

Forty-eight human premolars were exposed to eight hydroxyethyl cellulose demineralizing solutions containing different lactic acid concentrations at pH 4.5 and pH 4.0 respectively and the consequent lesions examined by microradiography and quantitative densitometry. The maximum mineral content in the surface layer, the minimum mineral content in the subsurface lesion, the depth of the lesion and the thickness of the surface layer were investigated. A linear correlation was found between the mineral content of the subsurface lesion and its depth. The depth of the lesion increased with demineralization time, increasing molarity and decreasing pH. The surface layer became thicker after a longer period of demineralization in the 0.100 mol/l and pH 4 group. There was no significant difference between the mineral content of the surface layer of all the experimental groups.

Surface etching and subsurface demineralization of dental enamel induced by a strong acid

Intact enamel surfaces were exposed to 20 ml of 0.1% HCl for various periods. When the acid was unsaturated with respect to both hydroxyapatite and fluorapatite the surface enamel was etched away. With time the liquid close to the enamel became supersaturated with respect to fluorapatite but remained unsaturated with respect to hydroxyapatite. Under this condition subsurface lesions developed. These observations are discussed with reference to the use of diffusion-restricting agents in laboratory caries experiments.

Remineralization of artificial caries lesions by stannous fluoride.

The remineralizing property of SnF₂ was studied by treating artificial white spot enamel lesions for 0.5, 6 and 24 h and 1 week in a 4% SnF₂ solution at 50 °C. Remineralization as opposed to recalcification was observed in all treated samples and was studied using microradiography and microprobe analysis. It appeared that remineralization started in the outer part of the intact surface layer covering the sub-surface lesion. With increasing time, the centre of the sub-surface lesion became remineralized. In a fully remineralized lesion it was no longer possible to distinguish between the surface layer and the sub-surface lesion. Some sections appeared to be fully remineralized after only 6 h treatment with SnF₂. Microprobe analysis showed that the variation in density was highly correlated with the Sn concentration. Some possible mechanisms and reactions that may be involved in this remineralization are discussed.

Hardness tests on sound enamel and artificially demineralized white spot lesions.

The accuracy and reproducability of hardness measurements have been investigated in this study. Sound and demineralized enamel were used as the main test materials. The reproducability of hardness measurements on artificial white spot lesions produced by a hydroxyethyl cellulose/lactic acid demineralizing solution was also investigated on embedded cross-sections. The operator error was found to be less than 5% when reading both steel and enamel indentations. The maximum hardness of the surface layer and the minimum hardness of the subsurface lesion were measured in three positions in each of 10 artificial white spot lesions. An analysis of the results showed that: (a) the hardness values at the same distance from the surface but in different areas of the same lesion were very similar; (b) hardness values between lesions were also very even; (c) the drop in hardness after demineralization was related to the initial hardness of the enamel.

Variation in caries prevalence related to combinations of dietary and oral hygiene habits in 6-year-old children.

The original sample consisted of 179 randomly chosen children aged 6 years and 1 month at the time of examination. Of these children, those 88 were selected who had been exposed, since the age of 4, to consistent oral hygiene measures and dietary habits. The investigation involved clinical registration of caries, including subsurface lesions, and restorations in buccal and lingual surfaces in primary molars and cuspids. The mesial surface of second molars, distal and mesial surfaces of first molars, and the distal surface of cuspids were recorded from X-ray pictures. 85 children were classified as follows, beletary habits: (1) > 6 or (2) 5–6 meals and snacks a day including at least one ‘unsuitable’ Dack with a high-sucrose component, or (3)

Histologic studies of human coronal dentine following cavity preparations and exposure of ground facets in vivo

Decalcified, stained sections and microradiographs of undecalcified and decalcified sections of young premolars were studied after the dentine had been exposed to the oral environment for varying periods of time. Some cavity preparations were also performed after the fixation of the teeth. The absence of zone 3 ( Mjör, 1966b) was a striking feature as an immediate response to the denudation of dentine both in vivo and in vitro, and the observations suggested that flow or movement of the contents within the tubules occurred. Exposure of ground facets to the oral environment led to the re-establishment of zone 3. No marked changes were observed in the microradiographs, but in the undecalcified sections the surfaces of the exposed facets were often more radiopaque than the adjacent dentine, and lesions occasionally developed that resembled subsurface lesions in early enamel caries.

Betatron cancer therapy.

In the last few years we have all witnessed with varying degrees of interest a tremendous increase in the upper limits of supravoltage energies for possible therapeutic application. A variety of radiations have become available, some in adequate quantity for the first time. We have been using a 24,000,000-volt betatron which yields a very powerful beam of x-rays and a less well developed external beam of electrons (3, 6). Most of our work in the last year and a half has been with the x-ray beam, although at present we are diverting some of our attention to engineering problems and animal tissue effects of the electron beam. The betatron x-ray beam offers some very appealing distribution advantages in tissue (4). In Figure 1 is shown the distribution of density in a film phantom with a 200-kv. beam path and with the 24,000,000-volt betatron x-ray beam path. In the latter the sparing effect on the superficial tissues at the site of entrance of the beam (on the left in the illustration), the concentration of density deeper along the path, the extreme degree of useful penetration, and the lack of significant scatter along the edges of the path are important. In contrast, the 200-kv. beam path shows no sparing effect at the site of entrance of the beam but rather a concentration of density at the surface and for a few centimeters forward, limited penetration, and considerable side scatter. This distribution of density should clearly indicate separate zones of usefulness for the different types of equipment, although the decreased skin reactions with the betatron may eventually increase its applicability even for subsurface lesions. With conventional x-ray therapy equipment, dosage is conveniently measured and understood in terms of the roentgen. We have also been using the roentgen unit for dosage measurement with the betatron but are fully aware of the need for a method of measuring dissipated energy in terms of ergs per gram of tissue. For this purpose, we are investigating sensitive calorimetric methods of making a fundamental measurement of the actual energy dissipated by the x-ray beam. We use a 25-r Victoreen thimble chamber inserted in an 8-cm. cube of lucite. In the middle of this cube, the chamber is at the maximum or peak of the depth dose intensity. Our dose rate under these conditions, and with complete collimation and filtration of the beam, is usually around 100 r per minute at 84 em. from the target of the tube. The dose rate is about doubled without filtration. Biological investigations on relative effectiveness of the betatron roentgen by Quastler (5) and more recently by us (1, 2, 4) have shown that greater quantities of measured roentgens are required from the betatron than from machines of lower voltage to produce equal tissue effects. Unfortunately this of therapy, or have widespread terminal cancer.