Caries lesions

The inactive, arrested caries lesion is black, remineralized, and hard on probing, whereas the active lesion is brownish and soft. Increased oral... 

Beighton D and Lynch E (1995) Comparison of selected microflora of plaque and underlying carious dentine associated with primary root caries lesions. Caries Res 29, 154-158. 

Bjorndal L and Thylstrup A (1995) A structural analysis of approximal enamel caries lesions and subjacent dentin reactions. Eur J Oral Sci 103, 25-31. 

Clarkson BH, Hall DL, Heilman JR and Wefel JS (1986) Effect of proteolytic enzymes on caries lesion formation in vitro. J Oral Pathol 15, 423-429. 

Schiipbach P, Osterwalder V and Guggenheim B (1996) Human root caries microbiota of a limited number of root caries lesions. Caries Res 30, 52-64. 

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... 

Peroxidases from saliva, crevicular fluid, bacteria, and fungi may contribute to this reaction in caries lesions. Although deeper layers of the carious microflora are assumed to be anaerobic, the oxygen required for the reaction may reach the deeper parts of the plaque via oxygen channels (Marquis, 1995). Lactobacilli, however, cause browning of dentin in the absence of tyrosinase (Dreizen et ah, 1957). 

Histochemical evidence for melanins in caries lesions has been presented, based on silver staining and bleaching by hydrogen peroxide. These reports, however, are contradictory as far as the pigment location is concerned circumventing the lesion (Opdyke, 1962), diffuse throughout the lesion (Ermin, 1968), and superficial (Meyer and Baume, 1966). 

Humic substances. Analogous to the reactions described above, humic substances (the polymeric pigments from soil (humus) and marine sediments) can be formed by both enzymatic and non-enzymatic browning. High concentrations of free calcium and phosphate ions and supersaturation with respect to hydroxyapatite can sustain in soil, because adsorption of humic acids to mineral surfaces inhibits crystal growth (Inskeep and Silvertooth, 1988). A similar adsorption to tooth mineral in a caries lesion can be anticipated for polycarboxylic polymers from either the Maillard reaction or enzymatic browning. 

Bacterial pigments. Some bacteria commonly found in caries lesions are known to produce pigments. For example, the black staining of plaque is related with Actinomyces (Slots, 1974), but its chemical nature remains unknown. Black pigmented Prevotella produces both iron sulphide and heme pigments (Shah et ah, 1979). In addition, Propionibacterium forms porphyrins (Lee et al., 1978). Bacterial iron-binding peptides, which can contribute to discoloration, increase in the saliva of subjects with a high caries frequency (Nordh, 1969). 

From carious enamel, a brown pigment-producing Actinomyces has been isolated (Hurst et al., 1948). Black caries lesions contained higher numbers of Actinomyces, Lactobacillus, and Veilonella (but not black pigmented Prevotella) than unstained lesions (Boue et al., 1987). 

Heme and iron. Aside from bacterial heme, the host him/herself may contribute to heme- and iron-derived pigmentations. Heme and iron compounds may originate from either the pulp or the oral cavity. Pulp-derived discolorations are known, for example, from traumatic teeth (Stanley et al., 1978). The pulp underlying caries lesions may become... 

Food pigments. Well-described are footh discolorations associated with the consumption of coffee, fea, wine, and betel nuts. This discoloration by food and beverages has been mimicked in vitro with caries lesions (Kidd et al., 1990) and sound teeth (Chan et al., 1981). 

So far, the most convincing evidence for fhe discoloration of caries lesions has been provided for fhe Maillard reaction. Since few investigations have attempted to identify Maillard producfs sfraighfforwardly in carious material, further research in this field should be underfaken. In addition, the influence of discolored demineralized matrix, resistant to degradation, on the accessibility of fhe underlying sound tissue for acids and infiltrating bacteria should be established. 

Lynch E and Beighton D (1994) A comparison of primary root caries lesions classified according to colour. Caries Res 28, 233-239. 

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. 

From the literature reviewed in Chapter 3, it can be concluded that the Maillard reaction between carbohydrates and proteins is the likely cause of the discoloration of caries lesions. Research in the following chapters focused on this reaction. 

Chapter 4 describes the in vitro reaction of glucose wifh demineralized dentin. Preliminary tests revealed that use of disfilled insfead of deionized water accelerated browning, consistent with the effect of frace metals on the Maillard reaction. The yellow discolored slices were more resistant than controls to pepsin-mediated breakdown, but not to trypsin-mediated breakdown. It would be worthwhile to investigate proteolysis of denfin collagen covalently bound by the Maillard reaction to proteins, which penetrate into a caries lesion. 

The general finding fhat the Maillard reaction occurs in caries lesions both raises new questions about and provides new insights into the treatment and arrestment of caries. 

Aside from the Maillard reaction, other covalent modifications of amino acids and proteins are possible within the caries lesion, which merit future investigation. For example, certain oral microorganisms excrete y-glutamyl transferases. These enzymes catalyse the formation of cross-links between glutamic acid and lysine residues of proteins. In addition, N-acyl amino acids are present in plaque, which adsorb to mineral surfaces. 

Pulpitis- If the caries lesion progresses, infection of the dental pulp may occur, causing acute pulpitis (Pulpal inflammation). The tooth become sensitive to hot or cold, and then severe continuous throbbing pain ensues. In reversible pulpitis, filling is an option but in case of... 

Fig. 9.10. Artificial caries lesion in human tooth enamel by the ten Cate method (a) z = 0 (b) z = —14 m 370MHz (Peck and Briggs 1986).

The variation of contrast with defocus can be illustrated by a series of snapshots from the examination of another caries lesion, this time one that had occurred naturally in a tooth (Peck and Briggs 1987). The sequence in Fig. 9.11 shows what would be seen over the shoulder of the microscopist as he... 

Peck, S. D. and Briggs, G. A. D. (1986). A scanning acoustic microscope study of the small caries lesion in human enamel. Caries Res. 20, 356-60. [182,184]... 

Early dental caries (incipient lesions) are non-cavitated and limited to the outer enamel surface. Clinically, these lesions are identified as visible white spots when the tooth is air-dried (Fig. 11.1). The incipient lesion is known as a subsurface lesion since the surface appears intact. However, histological investigations have shown that below the surface, there are zones that vary in porosity (voids from mineral loss) as well as biochemical composition (e.g. fluoride, water and carbonate content) [29]. The enamel caries can vary from a depth of 100-250 J.m (for incipient caries) to entirely through the enamel ( 1.5mm deep), at which point the cavitated lesion has extended into the underlying dentin [35]. The diagnostic challenge remains early caries detection and the focus has been on caries lesions that form on the tooth crown affecting the enamel. The remainder of the discussion will therefore concentrate on enamel caries. 

---