T. Koulourides

Cariogenicity of Nine Sugars Tested with an Intraoral Device in Man

Nine sugars and sugar alcohols were assessed for their effect on experimental caries with an Intraoral Cariogenicity Test (ICT). Sample bovine enamel surfaces were submitted to simulated cariogenic co

Enhancement of Fluoride Effectiveness by Experimental Cariogenic Priming of Human Enamel

An intraoral cariogenicity test (ICT) was used to study the enhancement of fluoride treatments (2% NaF or 8% SnF2) that resulted from prior cariogenic challenge to human enamel surfaces. Measurements of enamel microhardness and microradiography indicated higher resistance to the cariogenically primed than for the unprimed surfaces. These results are interpreted as an adaptation of enamel to a challenging local environment by the formation of highly caries resistant minerals in the microspaces created by the priming challenge. With this adaptive reaction, tooth surfaces at risk were converted to surfaces of higher resistance than nonprimed surfaces. It is suggested that the concept of enamel adaptation to the cariogenic challenge can be applied clinically to arrest incipient caries, especially in patients who respond well to preventive disciplines that include the use of fluoride treatments.

Fluoride Incorporation into and Retention in Remineralized Enamel

This study assessed the incorporation of fluoride into remineralized enamel and the stability of the incorporated fluoride under various test conditions. Lesions were produced on bovine enamel slabs by a two-day immersion in 0.01 mollL lactic acid buffer containing 3.0 mmol/L Ca, 1.8 mmol/L P, and 1% CMC adjusted to pH 4. 0 at 37°C. The remineralizing solution contained the same amount of Ca, P, and CMC, plus 150 mmol/L NaCl and 3 ppm F, and was adjusted to pH 7.0 at 37°C. All slabs were exposed to this unstirred solution, which was changed every two days during the ten-day remineralizing period. The remineralized slabs were divided into four groups. Group A (the control group) received no further treatment. The other three groups were exposed for 24 h to either the intra-oral environment (Group B), a 1. 0 mol/L KOH solution (Group C), or a 0.01 mol/L lactic acid buffer (Group D). Fluoride incorporation assessed by abrasion biopsy in 10-μm layers showed about 10,000 ppm F maximum in Group A. Similar levels of fluoride concentration from the surface to approximately 30μm thick were found in Groups A, B, and C. No appreciable fluoride was released from remineralized slabs from Groups B or C, and only a small fraction from Group D. Statistical analyses of the fluoride values showed no significant differences between the various test conditions in any of the layers sampled. No difference was evident in the CalP ratio between the ten-day remineralized enamel (Group A) and the treatment groups. The lack of appreciable fluoride loss from enamel with any of the above three conditions indicated a stable fixation of fluoride in the remineralized enamel lesions.

Mineral Density and Fluoride Content of in vitro Remineralized Lesions

This in vitro investigation studied the remineralization of experimental caries lesions in bovine enamel by use of three methods: (1) surface microhardness, (2) microradiography, and (3) abrasion biopsy for mineral density and fluoride content. The lesions were produced by a two-day exposure to 0.01 mol/L lactic acidlsodium hydroxide buffer partially saturated with 3.0 mmol/L Ca, 1.8 mmol/L P, in 1% CMC, at pH 4.0 and 37°C. The lesions were exposed to a remineralizing solution containing 3.0 mmol/L Ca, 1.8 mmol/L P, and 3 ppm F in 1% CMC at pH 7.0 and 37°C for two, six, and ten days, with solution changes every two days. The data derived from the three methods are presented in sequence from the baseline and at days two, six, and ten of the remineralizing treatment. Microhardness measurements showed hardness recoveries of 35.9, 78.9, and 87.5%, respectively. Microradiography suggested complete recovery with the ten-day remineralization. Abrasion biopsy of successive 10-μm layers to a depth of 100 μm indicated 15.2, 39.8, and 68.8% mineral density recoveries, with fluoride content of the surface layer increasing from a baseline of 300 ppm to 4600, 9000, and 9800 ppm F for the 2, 6, 10 days of remineralization, respectively. Subsequent acid-etching of thin sections from the ten-day-remineralized specimens showed that the fluoride-enriched remineralized area was more resistant to acid dissolution than was the underlying nonnal enamel.

Microbial Characterization of an Experimental Cariogenic Plaque in Man

Experimentally induced plaque seemed to originate by direct contact inoculation from the vestibular mucosa and saliva. During the next seven days, this plaque developed its own characteristics. Populations of Streptococcus mutans, usually less than 2% of total streptococci population in plaques that were less than three days old, increased between days 3 and 7. Proportions of S sanguis, high in early samples, decreased after day 3. Populations of S salivarius, which usually outnumbered other streptococci, fluctuated widely through day 3, and then increased in proportion in subjects who were more productive of experimental caries, but decreased in subjects who were less productive. Proportions of plaque flora comprising lactobacilli paralleled those of S salivarius.

Enamel Fluoride Uptake and Acid Resistance in Subjects with High and Low Experimental Cariogenicity

The response of bovine enamel to intra-oral cariogenic environments was studied in human volunteers. Enamel slabs were mounted in dentures and treated with either 10% sucrose or 10% sucrose plus 20 ppm fluoride mouthrinses for one minute five times daily. After one week, these enamel slabs were studied for change in surface hardness and for the degree of fluoride incorporation, or for their resistance to acid acquired by the intra-oral exposure. Among the eight subjects, those with the highest experimental cariogenicity exhibited the highest benefit of enamel from the fluoride in terms of fluoride incorporation and in their resistance to the subsequent acid test. The results suggest that cariogenic activity and fluoride will synergistically improve the tooth resistance to subsequent attack, apparently through mineral exchange that favors the formation of acid-resistant minerals with high fluoride content within enamel lesions.

Effect of a 100-ppm fluoride mouthrinse on experimental root caries in humans.

The cariostasis of a mouthrinse containing 100-ppm fluoride versus a vehicle control was evaluated against experimental root caries on human and bovine cementum mounted on prosthetic devices. Subjects

Effect of fluoride on in vitro root surface lesions.

Root surfaces of teeth extracted because of periodontal disease were evaluated with microradiography for their resistance to acid in vitro. The roots were compared in two categories: (1) surfaces exposed to the oral environment in periodontal pockets versus those unexposed, (2) surfaces exposed in periodontal pockets and scaled versus surfaces exposed in periodontal pockets and root-planed. In addition, three commonly used fluoride topical treatments were evaluated for their effectiveness in increasing the resistance of root surfaces to acid demineralization. The acid challenge was 0.01 M lactic acid buffer, pH 4.0, in 1% carboxymethylcellulose, containing 3.0 mM calcium and 1.8 mM inorganic phosphate, at 37 °C. Root surfaces exposed to the oral environment were more resistant than unexposed surfaces. Scaled roots were more resistant than those which were root-planed. All fluoride treatments increased the resistance of root surfaces to acid in vitro, and contributed to the formation of a thick layer of high mineral density over the body of the lesion.

Combined Effects of Sucrose and Fluoride on Experimental Caries and on the Associated Microbial Plaque

In an experimental model, slabs of sound and presoftened bovine enamel were worn in the human mouth for seven days except for periodic removal for in vitro exposure to experimental variables. Supplementation with 3% sucrose for 10 minutes, four times daily for seven days yielded predicted levels of experimental caries. Parallel exposure to 3% sucrose containing 100 ppm fluoride sharply reduced or negated the resultant caries in originally sound enamel, and reversed the simulated pre-experimental caries in most samples of presoftened enamel. Serial layers of test enamel surfaces showed high levels of fluoride accumulated in the originally sound enamel, and even higher levels in the presoftened enamel that had been supplemented with sucrose-fluoride solution. Quantitation of the plaque microbial flora showed that the fluoride ion exerted no detectable influence. Consistent with the findings in previous studies, some correlation appeared to exist between the degree of experimental caries and that proportion of total plaque that was comprised of S salivarius, S mutans, or lactobacilli.

Abrasion Biopsy in Studies of Mineral Density of Experimental Enamel Lesions

The profile of mineral density of experimental enamel lesions was determined by means of sampling with a new abrasion biopsy technique. Three types of lesions were produced on bovine enamel slabs: (1) pre-softened in lactic acid buffer for 16 hr; (2) pre-softened and exposed to a test for acid resistance for seven days; and (3) pre-softened, exposed to the seven-day Intra-oral Cariogenicity Test with extra-oral immersions in 1000 ppm F solutions for one min twice daily (ICT/F), plus the seven-day test for acid resistance. Lesions were assessed with measurements of surface microhardness, microradiography of thin sections, and abrasion biopsy. For abrasion biopsy of the experzmental lesions, 15 parallel layers of approximately 10 μm each were abraded simultaneously with reference slabs of sound enamel on strips of lapping film. The depth of abrasion for each sample was calculated from the phosphorus content of the reference sample. Exposure to the ICT/F formed an acid-resistant zone within the lesion which diminished the microhardness change, although it did not have an appreciable effect on the total lesion depth as assessed with microradiography; abrasion biopsy indicated the formation of a mineral-dense zone within the lesion. This recently-developed technique of abrasion biopsy of experimental lesions offers the opportunity to link the composition of the lesion to controlled experimental conditions which will improve our understanding of demineralizing and remineralizing reactions on a standard tooth substrate.