In Vitro Assessment of Enamel Permeability in Primary Teeth with and without Early Childhood Caries Using Laser Scanning Confocal Microscope.

OBJECTIVE: To compare the permeability of the enamel of primary teeth from individuals free of Early Childhood Caries (ECC) with that from individuals affected with ECC by assessment of dye penetration using Laser Scanning Confocal Microscope (LSCM). STUDY DESIGN: Experimental in vitro study. Exfoliated primary maxillary anterior teeth (n = 44) were collected and divided into two groups (n=22 per group): samples with ECC (Group 1) and without ECC (Group 2). The samples were immersed in Rhodamine B dye solution for 1 day, cut longitudinally into 3 sections, observed using LSCM. Dye penetration depths in the incisal, middle, cervical thirds and on labial, lingual surfaces were recorded. Data were analyzed by the Mann-Whitney test (α = 5%, p < .005). RESULTS: The overall mean penetration depth for group 1 (100.6 µm ± 58.48 µm) was significantly higher than that of group 2 (31.55 µm ± 23.40 µm, p < .000). Mean penetration depth in the incisal, middle, and cervical thirds and on the labial and lingual surfaces of group 1 also presented significantly higher scores than in group 2 (p < .005). CONCLUSION: There was significantly more dye penetration in the ECC group than in the non-ECC group. This could be related to a higher level of enamel permeability in teeth affected with ECC.

In vivo scanning electron microscope assessment of enamel permeability in primary teeth with and without early childhood caries.

BACKGROUND: Over the years, certain primary teeth have been shown to be highly sensitive to dental caries, while others have remained caries-free. It has been hypothesized that this may be attributed to differences in the permeability of the enamel surface. AIM: The aim of the study was to evaluate the hypothesized differences in the permeability of primary tooth enamel in children with and those without Severe Early Childhood Caries (S-ECC) using scanning electron microscopy. MATERIALS AND METHODS: Sixteen children between 3 and 6 years of age were randomly selected and divided into two groups: Group 1, children without S-ECC (n = 8), and Group 2, children with S-ECC (n = 8). In each child, 4 teeth (the maxillary right and left central and lateral incisors) were subjected to evaluation. An impression was made with polyvinylsiloxane impression material, and scanning electron microscopy was used to inspect the negative replicas for droplets. RESULTS: The results indicated higher significance when individual regions (cervical, middle, and incisal thirds) in the two groups were evaluated and compared. Similarly, the overall results showed high statistical significance between S-ECC and non-S-ECC teeth. CONCLUSION: There could be a positive relationship between the permeability of tooth enamel and the development of caries, which needs further research.

Replacing Amalgam Restorations: A Standardized Protocol Based on Analyzing Tissue Physicochemical Modifications.

Almost 60% of operative dentistry is devoted to replacing restorations. When practitioners have to replace an amalgam restoration, they tend to opt for an adhesive restoration, as it is conservative of tooth tissues and mimics the natural appearance of teeth. Based on a literature review, the aim of this article is to determine the best tissue approach when replacing an old amalgam by a new adhesive restoration. After analyzing and understanding tissue alterations due to the amalgam corrosion process, the authors propose an analytical approach to managing the situation. Both tissue orientated and specific mechanical approaches are developed and should be implemented to carry out the optimal clinical procedure and achieve the most conservative and durable treatment.

[Dental caries resistance under conditions of a space flight]. / Ustoichivost' zubov k kariesu v usloviiakh kosmicheskogo poleta.

The maxillodental status of aeronauts attracts special interest of scientists and causes apprehensions of physicians and scientists of countries with aeronautic industry because of long duration of space missions. Some scientists consider that the realization of mission to Mars can lead to development of multiple dental caries in aeronauts. The aim of this study was to study the effects of space mission factors on the resistance of hard dental tissues and remineralizing activity of the saliva in a simulation experiment. The results demonstrated dynamic changes in the studied parameters under the effect of space mission factors; based on these results, we determined the criteria for selection of candidates for prolonged experiments and space missions.

Time-dependent decrease and seasonal variation of the porosity of recently erupted sound dental enamel in vivo.

Recently erupted teeth are more sensitive to dental caries than teeth that have remained free from caries lesions for a few years after eruption. It has been hypothesized that this may be ascribed to differences in enamel porosity. The objective of the present work was to assess the time-dependence of electrical conductance, as an indication of porosity, of occlusal enamel in recently erupted permanent molar teeth. Fifty children aged 5-15 years of age, receiving regular dental care at six-month intervals, participated in the study when their first molar teeth (in 5- to 6-year-olds) or their second molar teeth (in 11- to 15-year-olds) had not been exposed to the oral environment for more than six months. On the first semi-annual check-up after eruption of a first or second molar, baseline diagnostic measurements, i.e., visual inspection and electrical conductance measurements (ECMs), were made at three or four pre-defined sites in the fissures. Subsequently, data collection was repeated every six months for three years. Sites were excluded from ECMs when a caries lesion was observed at a site by visual inspection. After 36 months, there were 257 sites in teeth considered sound upon visual examination. The ECM values of these sound sites showed a clear decrease with time after the first examination. The conductance decreased on average from 0.13 (Momega)(-1) to 0.059 (Momega)(-1). Since the conductance is assumed to be proportional to the porosity of the enamel, the latter decreased by a factor of 2.2 over the 36-month period. The results furthermore indicated a higher conductance for maxillary than for mandibular enamel. Almost all sites in that sample appeared to be in teeth that were observed for the first time during the months September to December. Electrical conductance, and therefore enamel porosity, of the sites showed a periodic variation with season of observation: In the fall, the conductance was higher than in the spring. This implies that a dentist should be more prudent in the fall than in the spring when indicating restorative treatment of an incipient caries lesion.

Changes in the permselectivity of human teeth during caries attack.

Previous studies have shown that enamel permselectivity can influence fluid composition within caries lesions during de- and remineralization. The permselectivity of human enamel, cementum, and dentin sections was examined, in a microwell model, by measurement of the membrane potential developed by KCl diffusion while the sections were immersed in solutions simulating resting (pH = 5.6) and cariogenic plaque fluid (pH = 4.8). In a second experiment, the effects of charged compounds (phytate and Zonyl-FSC) on the tooth permselectivity were examined. The average membrane potentials (+/- SD) in "resting plaque" solution were: sound enamel, 18.9 +/- 3.2 mV, n = 66; dentin, 0.9 +/- 9.2 mV, n = 59; and cementum, -0.8 +/- 8.2 mV, n = 42, with a positive sing indicating cation selectivity. The average membrane potentials became more negative in "cariogenic plaque" solution for all types of sections: sound enamel, 5.2 +/- 2.1 mV, n = 46; dentin, -8.1 +/- 7.4 mV, n = 45; and cementum, -14.3 +/- 8.0 mV, n = 34. In lesion enamel sections, the membrane potential was reduced from the non-lesion wells in both types of test solutions, while phytate treatment caused an increase of approximately 10 mV in potential (increased cation selectivity) in every enamel well in either "resting" or "cariogenic" solution. Treatment of enamel sections with Zonyl-FSC caused the membrane potential to become more negative in both test solutions, with many of the wells showing anion selectivity in the cariogenic "plaque-like" solution. However, the changes in enamel membrane potentials induced by Zonyl-FSC slowly increased toward the initial values after treatment, while the effects of the phytate pre-treatment persisted. Most dentin sections treated with phytate also showed an increase in potential after phytate treatment; however, Zonyl-FSC seemed to have little effect on the membrane potential of dentin. The results of this study suggest that modification of tooth permselectivity by surface-active agents may be a viable method of decreasing the rate of caries progression.

Limitations in the intraoral demineralization of bovine enamel.

A model system was used to examine the relation between the duration of plaque pH fall and enamel demineralization following the intake of dietary carbohydrate in humans. Subjects wore palatal appliances containing blocks of bovine enamel covered with Streptococcus mutans IB 1600, and rinsed with 5 or 10% sucrose. Changes in iodide penetrability (delta Ip) of the enamel, and the pH and extracellular calcium and inorganic phosphate (Pi) concentrations of the streptococcal plaque were determined. Following rinses with 5% sucrose, delta Ip increased with time and reached a maximum (11.2 +/- 2.2 units) at 45-60 min although the S. mutans plaque remained acidic (pH = 4.8 +/- 0.6). After 10% sucrose, the maximum (14.7 +/- 3.1 units) was reached while the plaque pH was 4.0 +/- 0.3. Second rinses with sucrose increased delta Ip at most by 30%. Thus, demineralization did not persist throughout the period of low plaque pH, but occurred primarily during the early phase of plaque acidogenesis. Enamel demineralization appeared to be limited by factors other than the pH of the streptococcal plaque. Calcium concentrations in the S. mutans plaque rose to a maximum of 10.9 +/- 2.8 mEq/l at 30 min after the 5% sucrose rinses, then fell; Pi reached a stable level of 12.2 +/- 2.3 mEq/l by 60 min. Calculations showed that conditions approached saturation with respect to enamel and dicalcium phosphate dihydrate as demineralization reached a maximum. Demineralization appeared to be limited at low plaque pH, therefore, by the accumulation of high levels of mineral ions in the streptococcal plaque.(ABSTRACT TRUNCATED AT 250 WORDS)

Permselectivity of sound and carious human dental enamel as measured by membrane potential.

A microwell technique was used for determination of the permselectivities of sound and carious enamel in the same slice of tooth. The permselectivity determination was accomplished by drilling microwells in the enamel and filling them with a simulated plaque fluid containing lactate, carbonate, and inorganic ions at concentrations similar to those in resting plaque fluid, but with different concentrations of KCl. The electrical potentials developed across the enamel membrane were measured with microreference electrodes placed in the wells or in the solution outside the tooth. The results showed that the membrane potential was a function of the composition of the solutions separated by the enamel membrane and was independent of the composition of the solutions in the adjacent wells. The enamel was found to be cation-permselective, and sound enamel was more permselective than carious enamel. The flux rate of K+ was estimated from the change in the K+ concentration of the well solution as a function of time. The flux rate and the membrane potential data were used in the Nernst-Planck Flux Equation for calculation of the diffusion coefficient of K+ through enamel. The results indicate that the permselectivity of enamel can greatly influence the diffusion of ions through enamel membranes.

[A mathematical model of the development of dental caries]. / Matematicheskaia model' razvitiia kariesa zubov.

A mathematical model is suggested, simulating the development of carious process in a tooth, based on an analytical approach. The process of hydrogen ions diffusion into enamel microspaces is described via transport equation. A simplified model explaining the formation of the involvement of the body of the tooth under the enamel surface at the initial stages of caries development is described in detail. Analysis has shown that the theoretical model is in good correlation with experimental data on the rate of chemical reaction of Ca radionuclide accumulation in the enamel surface and deeper layers.

[The effect of calcium glycerophosphate and Remodent on the dental enamel permeability in dogs with fluorosis]. / Vliianie glitserofosfata kal'tsiia i remodenta na pronitsaemost' émali zubov sobak pri fliuoroze.

In 14 dogs aged 6 months with severe fluorosis, the authors studied the effects of intake of calcium glycerophosphate and local remodent application on 45Ca enamel incorporation and the depth of its penetration into the dental hard tissues. The treatment led to a substantial decrease in both enamel 45Ca accumulation and the depth of its penetration under severe fluorosis. Combined use of the drugs was more beneficial in terms of enamel 45Ca permeability.

[The effect of various concentrations of hydrochloric acid solutions on the enamel permeability for 45Ca in experimental fluorosis]. / Vliianie razlichnykh kontsentratsii rastvotov solianoi kisloty na pronitsaemost' émali dlia 45Ca pri éksperimental'nom fliuoroze.

In 96 months-old dogs with light fluorosis the effect of 10% HCl solution and the mixture of 36% HCl solution with concentrated HCl (1:2) on 45Ca incorporation into the superficial and deep enamel layers, and its penetration into the dental hard tissues. The increase in HCl concentration was directly related to enamel 45Ca incorporation and the depth of its penetration in fluorosis-afflicted teeth. Under effect of 12% HCl solution 45Ca penetrated across the whole enamel reaching the dentin. Further increases in HCl concentration is nonexpedient in bleaching the fluorosis-afflicted enamel.

Albumin interaction with caries-like lesions in bovine enamel.

The exposure of bovine enamel to an albumin-containing demineralizing solution results in penetration of protein into the porous enamel. Washing of this albumin-containing enamel results in a complete (low pretreatment albumin concentrations) or partial removal of the albumin (pretreatment concentrations greater than or equal to 200 micrograms/ml-1). Subsequent exposure to increasing salt concentrations of fluoride, phosphate, calcium or chloride shows a partial removal of albumin at fluoride or phosphate concentrations of 75 mM while complete removal occurred at 150-200 mM fluoride or phosphate. Exposure to either calcium or chloride, even at 3 M concentrations, showed a negligible albumin release. It is proposed that protein removed at high fluoride or phosphate concentrations is bound by a strong interaction between protein-carboxyl groups and calcium on the surface of the enamel mineral. The partial removal of albumin released at low fluoride or phosphate concentrations indicates an enamel-albumin interaction by means of Ca-bridging between protein-carboxyl groups and mineral phosphates. Finally, it is suggested that salt-free washing removes albumin that has lost its native form upon binding to the partially dissolved crystallites of the enamel. It is concluded that enamel is mainly protected from demineralization by the inhibitory effects of protein penetrated into the pores, in addition to possible protection by the pellicle on the surface.

Kinetics of acquisition and loss of calcium fluoride by enamel in vivo.

Two in vivo experiments were performed, concerning (1) the kinetics of the acquisition of calcium fluoride on enamel during daily rinses with a solution of 0.023% F as sodium fluoride, and (2) the loss of calcium fluoride from enamel slabs which had been topically treated with a neutral solution containing 0.9% F as sodium fluoride. Enamel slabs were carried in the mouth by 6 volunteers for 8 days in both experiments. Sound and etched enamel were included. (1) During mouthrinses moderate amounts of fluoride were acquired by sound enamel, and more as calcium fluoride than as fluoridated apatite, whereas on etched enamel, more fluoride was deposited as fluoridated apatite. On etched enamel there was also a tendency that the deposition of calcium fluoride levelled out whereas the incorporation of firmly bound fluoride continued. This may indicate that calcium fluoride was transformed into fluoridated apatite, probably through remineralization during pH cycling in plaque covering the etched enamel. (2) After single topical application, it was found that etched enamel initially took up more calcium fluoride than sound enamel, but also lost more during the 1st day of in vivo exposure. The loss of calcium fluoride was arrested after 1-2 days, on sound enamel at 70% and on etched enamel at 40% of the original level. It is suggested that the increased amounts of firmly incorporated fluoride in enamel originated from calcium fluoride on enamel, and that calcium fluoride is an important and clinically significant source of fluoride ions on enamel.