Dentine root caries is a process of demineralization and degradation of the organic matrix by proteinases. In this in situ study, the presence and activity of the matrix metalloproteinases 1, 2 and 9 (MMP-1, MMP-2, MMP-9) in saliva and in completely demineralized dentine specimens were investigated. Furthermore, the activity of cathepsin B was determined in saliva. A correlation between these enzymes and the level of degraded collagen was investigated. Demineralized dentine specimens were mounted in the partial prosthesis of 17 volunteers. Saliva samples were taken at 0, 2 and 4 weeks. After 4 weeks, the enzymes were extracted from the dentine specimens and the collagen loss was assessed. The collagen loss varied between 0 and 40.3%. Zymography of the saliva and the dentine extract samples showed that (pro-)MMP-2 and (pro-)MMP-9 were present. The levels of active MMPs were assessed, using fluorogenic MMP-specific substrates. All but 3 of the 51 saliva samples showed MMP-1 activity ranging from 1.5 to 101.1 relative fluorescence units (RFU)/s. Forty-eight saliva samples showed gelatinolytic MMP-2/MMP-9 activity (1.7–141.1 RFU/s). MMP-1 activity was shown in all dentine extracts varying between 3.5 and 295.0 RFU/s. From the dentine extracts, 15 showed MMP-2/MMP-9 activity (0.2–13.7 RFU/s). The MMP activity from both saliva and dentine extracts did not correlate with the collagen loss. The activity of salivary cathepsin B varied from 4.8 to 42.2 arbitrary units/min. A positive correlation was found between salivary MMP activity and cathepsin B activity. This study revealed that gelatinolytic enzyme activity was present both in saliva and dentine collagen. No correlation could be observed, however, between the level of enzyme activity and the collagen loss of the dentine specimens.

A considerable shrinkage of dentinal lesions is the result of desiccation of dentine sections during contact microradiography. We introduce a simple modification which allows the dentine to be wet during the microradiographic procedure. The volume stability of both sound and demineralized dentine sections microradiographed under wet conditions is compared to sections microradiographed while being exposed to the air. Under wet conditions no shrinkage could be detected of both sound and demineralized sections. Within 15 min exposure to the air, demineralized sections showed their lesion depth to be significantly reduced by 21%, resulting in an underestimation of the mineral loss of 44%. No shrinkage was observed in the air-dried sound dentine. Especially when high-resolution plates are used, which require an extended exposure time, microradiography of dentine sections under wet conditions is recommended. In longitudinal de- and remineralization studies, the use of water instead of impregnation with low-volatility liquids is to be preferred because of the possible effects of these liquids on the mineralization processes.

The changing environment in a developing root lesion may result in a succession of the microbial flora in the dentine. As demineralization proceeds, the collagenous matrix is exposed, which could be conducive to the growth of specific microorganisms. In this study both sound and completely demineralized dentine were placed together in the partial prothesis of 8 individuals to test whether the type of substrate influenced the composition of the bacterial flora. After 6 weeks the degradation of the collagenous matrix, the demineralization of the dentine and the microbial composition were assessed. The collagen loss varied between 0 and 69 wt%. Mineral loss from the originally sound dentine specimens ranged from virtually none to complete demineralization. Percentages of total streptococci, mutans streptococci, Actinomyces and lactobacilli isolated from both dentinal substrates did not differ significantly. The percentage of lactobacilli in the dentine specimens was positively correlated to the lesion depth. The percentage of Actinomyces species was significantly higher in both the dentine specimens that had been demineralized in vitro and those that were found to be completely demineralized in situ compared to the partially demineralized dentine specimens. In vitro, no collagenolytic activity of the predominant flora isolated from both dentinal substrates could be shown.

Lesion formation in dentin involves demineralization followed by degradation of the exposed organic matrix. Proteinases from microorganisms present in the dentin are believed to play an important role in the breakdown of the dentinal collagen. In this study, the microflora colonizing decalcified dentin matrix, placed in situ, was identified. The gelatinolytic activity of the isolated strains was assessed and related to the degradation of the dentin matrix. The predominant species found were Streptococcus mitis, Peptostreptococcus productus, Lactobacillus casei, Propionibacterium species and Veillonella parvula. Marked interindividual variation in the composition of the microflora was observed. The microflora possessed gelatinolytic activity, although no correlation was found with the severity of dentin matrix degradation. The chemically determined loss of collagen varied between 0 and 67 wt% per participant and corresponded with the extent of collagen degradation observed by transmission electron microscopy.

The aim of this in situ investigation was to study the effect of an amine fluoride/sodium fluoride mouthrinse (total F = 250 ppm) in addition to an amine fluoride dentifrice (F = 1,250 ppm) on the amount of acquired fluoride in enamel and dentine. In the partial prosthesis of 12 participants a combined specimen of slightly demineralized enamel and dentine was placed. During two consecutive experiments, each lasting 3 weeks, the participants used an amine fluoride dentifrice alone or in combination with a fluoride mouthrinse. After the in situ period the specimens were retrieved and both the enamel and the dentine specimens were analysed for the amount of KOH–soluble fluoride and structurally bound fluoride. The results showed a significant increase in both KOH–soluble and structurally bound fluoride in enamel and dentine when a fluoride mouthrinse was used. Whether the rinsing procedure was performed immediately after toothbrushing or with a delay of 2 h did not influence the results. Furthermore it was shown that dentine acquired substantially more fluoride than enamel during the experimental period. The results indicate that a fluoride mouthrinse used in addition to a fluoride dentifrice may have a beneficial effect on the protection of enamel and dentine against caries.