The progress of artificial caries-like lesions created in human, bovine, equine, and ovine enamel has been studied. Lesions were produced by exposure to an acid gel system or by 5-day exposure to a sequential batch culture technique using Streptococcus mutans NCTC 10832. Longitudinal ground sections were prepared. The lesions were of similar appearance in all species when examined in polarized light. The depth in human enamel was approximately half that in the animal species. Microradiography confirmed subsurface demineralization in all four species. Similar depth ratios were seen in the scanning electron microscope, but there were structural differences between lesions in human and animal teeth. Lesions in bovine teeth were more like those in human, but lesions in equine and ovine teeth were markedly different. Substitution of these animal enamels for human enamel in caries experiments demands that these differences be taken into account. Scanning electron microscopy is capable of resolving features in artificial caries lesions which cannot be differentiated by polarized light techniques. The latter will demonstrate generalized mineral loss, but scanning electron microscopy is required to characterize the sites of mineral loss.

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One potential advantage of glass-ionomer materials for the treatment of root caries is their ability to release fluoride and so resist cariogenic attack. A commercially available composite material has also been reported to release fluoride which reduced caries lesions in the tooth tissue adjacent to it. The aim of this study was to assess the effectiveness of a conventional glass-ionomer restoration compared with a dentin-bonded, fluoride-releasing, composite restoration when exposed to a microbial artificial caries system. Artificial caries-like lesions produced in relation to the restorations were examined and classified either as outer (surface) lesions or as wall lesions. A split-unit experimental design allowed for within-tooth comparisons of the 2 experimental restorations at different sites on the root surface. These were either totally within the root surface or positioned at the amelo-cemental junction. Outer lesion depths were significantly (p < 0.001) shallower at all sites adjacent to the glass ionomer when compared with the composite restorations. Wall lesions were significantly (p < 0.01) more prevalent adjacent to the composite material. In addition, the cavity margin position significantly (p < 0.05) affected the incidence of wall lesions, particularly in the composite group. In conclusion, glass ionomer was successful in reducing the caries-like lesion production in the adjacent root surface. This resulted from improved marginal integrity and fluoride release from this material when compared with the composite bonding system used.

The aim of this study was to assess microleakage along restored cavity walls using a new in vitro microbial technique. Extracted human teeth containing cavities restored with a microfine posterior composite were incubated in broth inoculated with a single strain of Streptococcus mutans for 10 days, using a sequential batch culture technique. Each margin of the cavities was finished in one of three ways: butt joint and etching; butt joint and no etching, or; bevel joint and etching. The assessment of microleakage was achieved by examining sections of the teeth histologically using polarized light for the presence or absence of caries-like cavity wall lesions. Outer (surface) lesions were also examined and displayed the characteristic zones of early natural caries lesions. The cavity wall lesions were observed as a translucent zone in 31% of butt and unetched margins, 16% of butt and etched margins, and 5% of bevelled and etched margins.

A microbial artificial caries system was used to produce caries-like lesions adjacent to amalgam and composite restorations. Polarised microscopy allowed measurement of outer and wall lesions depths. Comparison was made of the depths found in relation to the restorative materials, margin finishing procedures (composite group) varnish application (amalgam group) and thermal stressing. It was found that differences were detectable between the different restorative materials and the type of margin finishing procedure used in the composite group. Varnish application and thermal stressing had little effect. Some comparison is made between this microbial technique, other artificial caries techniques, and other methods of assessing marginal leakage.

It has been recognised for some years that it is possible to produce caries-like areas of demineralisation in human enamel using relatively simple acidified-gel techniques [Silverstone, 1966]. Attempts to produce similar lesions by means of bacterial action have, in general, been thought to require complex apparatus in the form of ‘artificial mouths’ [Pigman et al., 1952; Sidaway et al., 1964; Levine and Coulter, 1976; Yaari and Bibbby, 1976]. Such apparatus is expensive as well as being difficult to sterilise and maintain sterile. In most instances only one specimen can be processed at a time. Artificial ‘white spot’ lesions have been produced using sequential batch culture techniques [Jordan and Keγes, 1966] but doubt has been cast on the comparability of these lesions to natural caries [Hardie et al., 1971]. The present technique uses simple inexpensive apparatus which is easily sterilised and which can be readily replicated.

Longitudinal clinical studies indicate consistently that secondary caries is the major cause of failure of restorations. Recently there has been an increase in the number of fluoride-containing materials coming to the market place and this has renewed the debate about the cariostatic effectiveness of such materials. The present study examined the histologic appearance of caries-like lesions adjacent to a non-fluoride-containing material (amalgam), a low fluoride-containing material (composite) and a moderate fluoride-containing material (glass-ionomer). The artificial caries system used to produce lesions has been previously reported and is a microbial system using Streptococcus mutans NCTC 10832. The lesions produced were similar to naturally occurring lesions in many respects, indicating the usefulness of this in vitro technique. Variations in the appearance of lesions were found adjacent to the different materials and the effect of the fluoride contained within two of the materials is discussed.

An in vitro investigation was performed to assess the extent of apical dye leakage in relation to root fillings made by Thermafil obturators and the lateral condensation of gutta-percha in extracted human teeth under conditions of passive dye penetration, centrifugation, a vacuum technique and an increased air pressure technique. One hundred and twenty-eight extracted teeth were selected and prepared. The specimens were allocated into eight closely matched experimental groups. Four groups were obturated with Thermafil obturators and four with the lateral condensation technique. Microleakage was assessed after exposing one group of specimens from each of the obturation techniques to each of the four dye penetration systems using India ink as the leakage detector. The teeth were demineralized and cleared prior to examination and the maximum dye penetration for each specimen was recorded. The statistical analysis on transformed data revealed no significant differences between the four microleakage techniques and no differences between the two obturation techniques.