Vitro Caries Studies

Carious-like lesions can be produced in extracted human teeth by exposure to a nutrient medium suitable for bacterial growth and by innocula-tion of the solution with oral microorganisms. Lesions were produced in the early work of E. Magitot (around 1870) and later by W. D. Miller and many subsequent research workers 110). In vitro studies of this type have been greatly improved by the introduction of the Artificial Mouth in which many of the important oral conditions are reproduced. Under appropriate conditions, the entire tooth structure will be destroyed. In order to produce localized lesions, regular cleansing of the exposed tooth surfaces is required (111). 

By the use of the Artificial Mouth, it has been demonstrated that two general types of attack on teeth can be distinguished. These, in turn, are dependent upon the amount of available carbohydrate in the nutrient medium. When glucose is present in the medium to an extent of about 100 mg. % or less, sound teeth are not attacked, but any previously decalcified matrix protein is rapidly destroyed. When glucose is present to an extent greater than about 300 mg. %, the inorganic portion of the tooth is rapidly removed, but the exposed matrix is attacked only slowly. At intermediate concentrations, probably 200 to 300%, both types of attack proceed simultaneously, and the entire tooth substance is destroyed 112). 

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Boonstra WD, De Vries J, Ten Bosch JJ, Ogaard B and Arends J (1993) Inhibition of bovine dentin demineralization by a glutardialdehyde pretreatment an in vitro caries study. Scand J Dent Res 101, 72-77. 

Katz S, Park KK and Palenik CJ (1987) In-vitro root surface caries studies. J Oral Med 42, 40-48. 

Grenby TH, Philips A, Mistry M. Studies on the dental properties of lactitol compared with five other bulk sweeteners in vitro. Caries Res 1989 23 315-319. 

Eisenburger M, Shellis RP, Addy M Comparative study of wear of enamel induced by alternating and simultaneous combinations of abrasion and erosion in vitro. Caries Res 2003 37 450 t55. Hannig M The protective nature of the salivary pellicle. Int Dent J 2002 52 417—423. 

In this study the mechanical properties, hardness and reduced elastic modulus, were determined using nanoindentation, as discussed in the previous section. Nanoindentation was used to plot the mechanical properties throughout the lesion in order to evaluate the changes in hardness and reduced elastic modulus in the various regions of the in vitro caries-like lesions. 

Chlorhexidine initially was used as a general disinfectant because of its broad antibacterial action (9). It was later shown to inhibit dental caries and reduce the formation of dental plaque (10). In vitro inhibition studies have shown chlorhexidine to be effective against species found in infected root canals such as Enterococcus faecalis (11) and Streptococcus mutans (12), and because of this, it was introduced as an endodontic irrigant in the early 1960 s (10). Chlorhexidine is increasingly being incorporated into endodontic materials due to its ability to increase antimicrobial properties and improve prognosis. 

Root caries can occur when tooth roots are exposed to the oral environment, for example after periodontal surgery or gingival recession. Two stages are distinguished microscopically. First, the dentin mineral is dissolved and bacteria penetrate the tubules. Second, the demineralized dentin matrix is degraded, and bacteria infiltrate the intertubular area (Frank et al., 1989 Frank, 1990 Schiipbach et al., 1989). This sequence of events may indicate that the degradation of the dentin matrix occurs after it has become accessible by the removal of mineral. In an in vitro study, Klont and Ten Cate (1991) confirmed that the dentin matrix cannot be degraded unless it is demineralized. 

Unfortunately, the in vitro studies mentioned-above sometimes employed rather unnatural reactant concentrations and reaction conditions for simulation of the Maillard reaction. Little attention was paid to the likeliness of the reaction under the circumstances prevailing in the caries lesion in vivo. To provide a better understanding of the different... 

Hurst V, Frisbie HE, Nuckolls J and Marshall MS (1948) In vitro studies of caries of the enamel in the Syrian hamster. Science 107, 42-44. 

In the course of dentin caries, both demineralization and reactions with the organic matrix take place. Matrix reactions include proteolysis and covalent modifications. From the introduction (Chapter 2) and the review on discoloration in caries (Chapter 3), it becomes clear that there are still few reports on the effect of matrix modifications on dentin caries. In Chapters 2, 4, and 5, the investigations were aimed at filling the information gap concerning the effect of reactions of dentin matrix on caries. To this end, degradation and modification of dentin were studied in demineralized specimens in vitro. In addition, specimens placed in dentures in situ and caries lesions in extracted teeth were analysed for modifications. 

J. Arends, J. Ruben, A.G. Dijkman, The effect of fluoride release from a fluoride-containing composite resin on secondary caries An in vitro study, Quintessence Int. 21 (1990) 671-674. 

The clinical evidence presented in section 1.2 unequivocally supports an inverse association between calculus and caries experience for subjects of similar age. There are many possible reasons for this finding. In section 1.4 a variety of saliva and plaque factors were discussed which have been shown to influence mineralisation processes in vitro or to have the potential to influence such processes. A number of studies have sought correlations between particular factors and either calculus or caries almost none involved both. 

The latter authors believed that their well-controlled study, where test solutions were applied to plaque samples in vitro, reflected the true difference between high and low caries groups better than the earlier in vivo studies. An alternative, and mechanistically more attractive, explanation for the greater discrimination achieved in vivo is that, in the mouth plaque acid is continuously subjected to the buffering, dilution and clearance effects of saliva. Saliva may be... 

Of interest, lipid-containing pellicle was less permeable to lactic acid diffusion in vitro than lipid-depleted pellicle and pellicles from caries-resistant subjects were less permeable than pellicles from caries-susceptible subjects [102], These observations suggest a possible protection mechanism against caries without highlighting the particular lipids responsible. Other studies have indicated that lipids adversely affect the association of calcium with salivary glycoprotein [105]. It has also been speculated that because lipids modify the hydrophobic nature of the pellicle, they may facilitate bacterial adhesion [102,105],... 

We have discussed some of the many factors which should be considered when designing in vitro experiments to study enamel de- and remineralisation processes. Relatively minor modifications to the treatment regime and the substrate environment, and intrinsic differences in the substrate composition, can all have a profound effect on the outcome of such studies. However, these modifications and differences can be (a) used to increase the relevance of the studies to the corresponding in vivo situation or (b) deliberately exaggerated to gain useful information on, for example, the effect of enamel structure on caries. 

Damato FA, Strang R, Stephen KW Effect of fluoride concentration on remineralization of carious enamel an in vitro pH-cycling study. Caries Res 1990 24 174-180. 

Lynch RJM, Mony U, ten Cate JM The effect of lesion parameters at baseline on subsequent de-and remineralisation during in vitro and in situ studies. Caries Res 2003 37 310. 

White spot lesions vary from person to person, from tooth to tooth and from surface to surface, as well as with age of the lesion. Their nonstandard nature makes analysis of the lesion incredibly difficult. In order to increase the level of control over experiments with lesions, a standard method of producing in vitro lesions has been used in this study. Many of the features of white spot lesions can be mimicked by in vitro lesions, though no method completely replicates the development of the natural lesion. The lesions produced are usually referred to as caries-like lesions indicating that they are not a natural white spot lesion, but an artificially produced lesion for experimental analysis. These artificial lesions provide invaluable information about the formation, the processes of demineralization and remineralization, and the composition of the lesion at different stages, in addition to being the basis for the understanding of possible treatments of the lesion. 

The ability of tooth mineral itself to buffer pH, and hence restrict the cari-ogenic challenge from plaque acids, has been demonstrated in recent laboratory studies. Zaura et al. [60] showed that the pH at the bottom of in situ plaque, in grooves cut into different materials to simulate tooth fissures, decreased in the order polyacrylate > enamel > dentine after an in vitro glucose treatment, i.e. the inverse of the solubility. In chapter 3, Lynch describes his own in vitro work in which the presence of dentine adjacent to a block of enamel could act as a sacrificial source of Ca and Pi and inhibit enamel dissolution in solutions initially undersaturated with respect to both materials. 

There is debate about whether the relatively low level of fluoride is effective in preventing caries. It has been shown to be effective in vitro [41], but in the most detailed study, the conclusion was that it was not, and that there was no advantage in using polyacid-modified composite resins over amalgam in terms of any observable anti-caries effect of the fluoride release [42],... 

The fluoride electrode has dramatically extended in vivo and in vitro studies on the relation between fluoride in tooth enamel and the incidence of dental caries and the incorporation of fluoride from ingested and topical fluorides. 

Several important experimental procedures have been devised to study the factors influencing the development of caries during the post-eruptive period. Three general procedures are of special importance. These are the controlled studies of human nutrition, the use of experimental animals, and the in vitro studies of caries development in extracted teeth. Because of the difficulty of the direct control of human groups, studies on human beings are difficult to carry out and interpret. On the other hand, much information has been obtained by the use of experimental animals and by the in vitro studies. 

Namba T, Hattori M, Tsunezuka M, Yamagishi T et al. 1982 Studies on dental caries prevention by traditional Chinese medicines. 3. In vitro susceptibility of a variety of bacteria to magnolol and honokiol. Shoyakugaku Zasshi 36 222-227... 

Robinson, C., Brookes, S.J., Kirkham, J., Wood, S.R., Shore, R.C. In vitro studies of the penetration of adhesive resins into artificial caries-tike lesions. Caries Res. 35, 136-141 (2001)... 

Gray, G.B., SheUis, P. Infiltration of resin into white spot caries-tike lesions of enamel an in vitro study. Eur. J. Prosthodontics. Restorative. Dentistry. 10, 27-32 (2002)... 

Huang, S. et al (2011) Remineralization potential of nano-hydroxyapatite on initial enamel lesions an in vitro study. Caries Res., 45 (5), 460-468. 

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