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PubMed1994

The video camera compared with the densitometer as a scanning device for microradiography.

In the recent past image analysis systems, comprising a video (CCD) camera and dedicated software, have replaced densitometer-based systems to analyze mineral content profiles using transversal microradiography (TMR). The main reasons for the introduction of the CCD camera were the ease and speed at which it can be operated. The densitometer, as a scanning device for TMR, has in the recent years been validated and is in this study considered as 'gold standard'. Comparisons of the two scanning devices for measuring the optical density of microradiograms have never been reported in the literature. The focus of this study was on accuracy and reproducibility of the scanning devices with the emphasis put on possible limitations of the CCD camera relative to the densitometer. These include resolution, number of gray levels and homogeneity of illumination of the scan area. The microscope was arranged in such a way that the same area on the microradiogram could be assessed by both scanning devices. Three different types of lesions were analyzed: a subsurface lesion, a surface-softened lesion and a laminated lesion. Paired t tests showed no significant difference between the mineral content profiles produced by the two scanning devices. The integrated mineral loss values were calculated and compared with analysis of variance and showed no significant differences. It is therefore concluded that mineral content profiles and integrated mineral loss obtained by the CCD camera are as accurate and reproducible as those obtained by the densitometer.

Analysis of Variance↗

PubMed1994

Clinical diagnosis of occlusal dentin caries.

An occlusal restoration is usually considered necessary when a lesion extends into the dentin. This study aimed to assess the relationship between the clinical appearance of occlusal caries and the lesion depth. Special attention was paid to differentiate the inner, partly demineralitzed layer of carious dentin that should be preserved from the outer carious layer that should be removed before placing a restoration. Fissures in extracted premolars and molars were classified clinically by the authors. The mean pairwise interobserver agreement, weighted Cohen's kappa (kappa), was 0.73, which indicated 'substantial agreement'. The depth of zones revealing softness by probing and/or discoloration was assessed on ground surfaces. Of the carious fissures that were scored sound by clinical examination (n = 17), 76% revealed enamel lesions on the ground surfaces. Of those occlusal surfaces with a discoloration only but no cavitation (n = 57), 13 showed dentin lesions, but only 5 of these revealed softness by probing. Of those lesions with very small cavitations (n = 60), 19 were confined to enamel, 41 showed dentin lesions and of these 32 revealed softness by probing. All but 1 of the lesions with small cavitations (n = 28) showed dentin involvement and all but 2 of these revealed softness. If cavitation in the occlusal lesion was used as a criterion for identifying dentin lesions with softness, the sensitivity and specificity values were 0.92 and 0.69, which means a relatively high frequency of overregistration.

Bicuspid↗

PubMed1995

The effect of sucrose-containing chewing-gum use on in situ enamel lesion remineralization.

Two independent cross-over studies have now been carried out to evaluate the effect of a regime of chewing sucrose-containing gum on enamel lesion remineralization. The first study has been reported in detail elsewhere. This further study aimed to increase the data set with an additional 13 volunteers. Similar protocols were followed in both studies. Weighted averages from the two studies showed delta z values corresponding to 16.8% remineralization for the gum versus 11.6% remineralization for the control (p = 0.046, two-sided). A significant difference between test and control was evident for lesion body (p = 0.0004, two-sided) but not for surface zone (p = 0.32, two-sided).

Adult↗

PubMed1996

Monitoring de- and remineralisation of enamel in vitro using an infrared reflectance meter.

The aim of this study was to design and investigate the use of an inexpensive method of monitoring the progress of demineralisation and subsequent remineralisation in artificial carious lesions. A small infrared (IR) reflectance meter was built which illuminated a 4 mm x 4 mm area on the buccal surface of a tooth and measured the reflected IR intensity. Repeated measurements were taken over a period of 25 days, during which the enamel surface was exposed to demineralising and subsequently remineralising solutions. Thirty-six teeth were studied under a variety of de- and remineralising conditions. It was observed that the IR specular reflectance of the tooth surfaces decreased with time during lesion formation and increased with time during remineralisation. It is suggested that the decrease in IR specular reflectance during demineralisation and the increase during remineralisation are a result of continuous changes in the crystals at the enamel surface during these processes.

Dental Caries Activity Tests↗

PubMed1997

Laser fluorescence quantification of remineralisation in situ of incipient enamel lesions: influence of fluoride supplements.

The aims of this study were to test the laser fluorescence method for quantification of remineralisation in situ of enamel with incipient lesions and to evaluate the enhancement of remineralisation by fluoride (F) supplements when a F dentifrice was used on a regular basis by healthy young subjects. Enamel samples were cut from extracted premolar teeth with the natural surface kept intact, and subjected to a pH-cycling system to produce subsurface demineralisation in vitro. The enamel blocks were then inserted into composite holders bonded to the buccal surfaces of both upper first molars of 12 panelists. Each panelist participated in 3 separate experiments in a randomised order; each lasted for 5 weeks with washout intervals of 2 weeks between experiments; experiment 1: F dentifrice (0.145% F as NaF) only; experiment 2: F dentrifice + F lozenges (0.25 mg F x 6/day); experiment 3: F dentifrice + F chewing-gum (0.25 mg F x 6/day). Fluorescence radiance was measured before, during, and after in vitro demineralisation, and once a week during the in situ experimental periods. The enamel samples were then sectioned and analysed with transverse microradiography (TMR). Anova and Pearson correlation coefficient were used for the statistical analysis. At the end of the 5-week in situ periods, fluorescence radiance had been regained to a level of 80-100% of the value before in vitro demineralisation, indicating remineralisation of the enamel samples. There were no differences in the fluorescence radiance gain between the 3 different F exposures. However, there was a statistically significant time trend (p < 0.001), and a highly significant linear dependence (p < 0.001) between the final measurements obtained with the laser fluorescence method (LAF) and the data obtained from TMR, r = 0.76. It was concluded that: (1) with the sensitive LAF method it was possible to register the small changes in the enamel week by week during in situ remineralisation: (2) when F dentrifice was used regularly, F supplements such as F lozenges or F chewing-gum did not significantly enhance the in situ remineralisation of incipient enamel lesions in healthy, young adults with normal salivary flow.

Adult↗

PubMed1997

Effect of a two-solution fluoride mouth rinse on deposition of loosely bound fluoride on sound root tissue and remineralization of root lesions in vitro.

A constant-composition fluoride (F) titration method was used to measure the amount of leachable F deposited on root surfaces in vitro by a 1-min rinse with a 12 mmol/l sodium fluoride (228 micrograms/g F) solution or a two-solution rinse that contained 2 mmol/l sodium fluorosilicate (228 micrograms/g total F ) and 10 mmol/l calcium chloride. The mean +/- standard deviations (n = 3) F uptake from the two rinse treatments were 0.70 +/- 0.24 micrograms/cm2 and 3.25 +/- 0.74 micrograms/cm2, respectively. In a separate experiment, the effects of sodium fluoride and the two-solution rinses on remineralization of root lesions were evaluated in an in vitro pH cycling model. The results showed that the average decrease in mineral loss (delta Z) in the two-solution rinse group (60%) was significantly greater than that obtained in the NaF rinse (41%) or the control (9%) group.

Aluminum Compounds↗

PubMed1990

Facts and artefacts in research on human dental plaque fluid.

In 1966, Jenkins suggested that the plaque fluid environment was likely to have higher concentrations of extracellular solutes than was apparent from analyses of total plaque concentrations. Early work on plaque fluid confirmed this contention, but some artefact was also generated by the prolonged centrifugation used for separation. The solute concentrations in plaque fluid mostly exceed those in saliva or crevicular fluid. Thus, the environmental conditions are distinctly different from those based on the assumption that saliva readily permeates films of dental plaque. In contrast, the presence of serum proteins suggests a crevicular input to plaque fluid. These data suggest that exchange between dental plaque and its environment is apparently restricted. Diffusion rates measured in dental plaque by different methods do not agree on how restricted it is. However, measuring diffusion in plaque introduces artefacts in packing density, a major determinant of the diffusion rate. The conditions used for collection and analysis have been reported to produce artefactual changes in plaque fluid potassium, a predominantly intracellular ion. Measurements of predominantly extracellular ions, such as calcium, are no less prone to artefact, whether based on ion-selective electrodes or on total calcium. We have much to learn about the fluid environment of the teeth and about dynamic changes in plaque fluid composition and properties during perturbations. Such information can give insights into pathological processes such as tooth demineralization and dental caries, calculus formation, and gingival inflammation.

Buffers↗

PubMed1992

An in situ enamel section model for assessment of enamel re/demineralization potential.

An enamel-section-carrying intra-oral appliance to predict the results of double-blind anti-caries studies has been developed. Initial validation was against the F concentration effect attained in a clinical trial where three sodium monofluorophosphate (SMFP) dentifrices were used. Original appliance-based work showed significant differences in remineralization between non-F and F dentifrices, but not between different F dentifrices. However, it was shown later that acidified gel-prepared lesions were not as responsive as solution-prepared lesions to de- and remineralizing processes, and lesion remineralization rates were found to be dependent on initial lesion size. An in situ cross-over study was then repeated with use of acid-solution-created lesions, and seven volunteers completed the project. Each brushed twice daily x 2 min with either 0, 1000, or 2500 ppm F, as SMFP dentifrice. After a two-week wash-out, subjects wore the appliances for four weeks. Enamel mineral content was assessed at 0, two, and four weeks via microradiography/microdensitometry, and a statistically significant dose-response was obtained between non-F and F as well as between 1000 and 2500 ppm F pastes, i.e., as per the three-year clinical trial data. Hence, the model's suitability for pre-clinical screening was confirmed. It has also been used in caries microbiological studies, in root caries investigations, and currently in chewing gum cariogenicity experiments.

Dental Enamel↗

PubMed1992

Intra-oral models for studying de- and remineralization in man: methodology and measurement.

A wide range of different methodologies and measurement techniques has been employed in laboratories around the world for the study of de- and remineralization of enamel and dentin in intra-oral systems. These different approaches are summarized and discussed in relation to the nature of the different research questions to be studied by means of the intra-oral model.

Animals↗

PubMed1992

The effect of chewing gum use on in situ enamel lesion remineralization.

Two independent cross-over studies investigated the possibility of enhanced early enamel lesion remineralization with the use of chewing gum. The first study involved a sorbitol-containing chewing gum, and the second, which had an identical protocol, tested a sucrose-containing chewing gum. In each study, 12 volunteers wore in situ appliances on which were mounted enamel sections containing artificial caries lesions. Subjects brushed twice daily for two min with a 1100-ppm-F (NaF) dentifrice (control and test) and in the test phase chewed five sticks of gum per day for 20 min after meals and snacks. Microradiographs of the enamel lesions were made at baseline and at the end of the seven-week experimental period. In the sugar-free gum study, the weighted mean total mineral loss (delta z) difference [(wk7-wk0) x (-1)] was 788 vol.% min. x micron for the gum, corresponding to remineralization of 18.2%, vs. the control value of 526 vol.% min. x micron, 12.1% remineralization (p = 0.07). There were no significant differences for the surface-zone (p = 0.20) and lesion-body (p = 0.28) values. In the sucrose-containing gum study, the delta z difference was 743 vol.% min. x micron for the gum, corresponding to a remineralization of 18.3%, vs. the control value of 438 vol.% min. x micron, 10.8% remineralization (p = 0.08). The surface-zone values were not significantly different (p = 0.55). For the lesion body, however, the sucrose-containing gum value of 6.11 vol.% min. was significantly different (p = 0.01) from that of the control (2.81 vol.% min.).

Adult↗

PubMed1993

Effect of intermittent delivery of fluoride to solution on root hard-tissue de- and remineralization measured by 125I absorptiometry.

The effect of intermittent fluoride levels on root hard-tissue de- and remineralization was studied once daily for 21 days in a pH-cycling caries model with simulated fluoride clearance curves. Four root hard-tissue blocks, from each of 12 human teeth, were cut out parallel to the cementum surface. During a daily 15-hour period, the blocks were subjected 12 times to pH changes similar to those which occur in plaque after a carbohydrate intake. The fluoride was delivered immediately before a daily nine-hour remineralization period. Four experiments were independently carried out: One block from each tooth was subjected to pH-cycling without and with fluoride delivery, simulating a rinse with 0.025, 0.2, and 1.0% sodium fluoride (NaF), respectively. The mineral change in the blocks was monitored by 125I absorptiometry and expressed as the change in transmission (delta T). The surface between the data points (delta T values) and the x axis (time points) was used as a summary measure, i.e., the area under the curve (AUC). When no fluoride was delivered, the delta T increased over 21 days, indicating loss of mineral. The AUC was, on average, 5.85 +/- 0.68 (mean +/- S.E.) %.day. In the 0.025% NaF-rinse experiment, there was a marked reduction in mineral loss, indicated by an average AUC of 1.66 +/- 0.59%.day. In both the 0.2 and 1.0% NaF-rinse experiments, a decrease in delta T, indicating gain of mineral, was observed from day 2. Negative delta T values occurred after 7 and 3 days, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1993

A single-section model for enamel de- and remineralization studies. 1. The effects of different Ca/P ratios in remineralization solutions.

A prerequisite for the accurate measurement of differences between pre- and post-experimental mineral profiles in single sections by quantitative microradiography is a high degree of reproducibility of the analytical procedures. We have determined the reproducibility of both the production and analyses of microradiographs. Lesions were made in seven single bovine enamel sections and radiographed three times. Each microradiograph was then analyzed on three different occasions by use of an image analysis system. This resulted in only small standard deviations in the lesion parameters. The method was used to determine the sites of mineral deposition in lesions in single sections during remineralization in three different solutions, one of which contained 1.5 mmol/L Ca and 0.9 mmol/L PO4 (standard solution); the other two solutions were low in either Ca or PO4, but all three had the same degree of supersaturation. The mineral profiles and lesion parameters were determined after lesion formation and after remineralization for 4 days, 1, 2, and 3 weeks. The decrease in IML (integrated mineral loss) in the lesions remineralized in the standard solution was greatest during the first week. Lesion profiles revealed that, under non-standard conditions, mineral deposition was retarded in the deeper part of the lesion, in contrast to the even distribution of mineral deposition from the standard solution. Differences in IML changes and lesion profiles between these bovine enamel experimental groups diminished when remineralization continued for 2 and 3 weeks. Possibly, the reactivity of mineral surfaces in newly made lesions affected the diffusion of remineralizing ions from low concentration solutions to the lesion front.

Animals↗

PubMed1997

Remineralization of enamel subsurface lesions by casein phosphopeptide-stabilized calcium phosphate solutions.

Casein phosphopeptides (CPP) stabilize amorphous calcium phosphate (ACP), localize ACP in dental plaque, and are anticariogenic in animal and in situ human caries model. In this vitro study, CPP-stabilized calcium phosphate solutions were shown to remineralize subsurface lesions in human third-molar enamel. Solutions were used to examine the effect of CPP-calcium phosphate concentration on remineralization. Other solutions were used to examine the effect of increasing pH, which decreased the concentrations of free calcium and phosphate ions and increased the level of CPP-bound ACP. Although most of the remineralizing solutions were supersaturated with respect to the amorphous and crystalline calcium phosphate phases, the solutions were stabilized by the CPP such that spontaneous precipitation of calcium phosphate did not occur. After a ten-day remineralization period, enamel lesions were sectioned, subjected to microradiography, and the mineral content determined by microdensitometry. All solutions deposited mineral into the bodies of the lesions, with the 1.0% CPP-calcium phosphate (pH 7.0) solution replacing 63.9 +/- 20.1% of mineral lost at an averaged rate of 3.9 +/- 0.8 x 10(-8) mol hydroxyapatite/m2/s. The remineralizing capacity was greater for the solutions with the higher levels of CPP-stabilized free calcium and phosphate ions. Remineralization was not significantly correlated with either the CPP-bound ACP of the degrees of saturation for hydroxyapatite, octacalcium phosphate, or ACP. However, remineralization was significantly correlated with the degree of saturation for dicalcium phosphate dihydrate (CaHPO4.2H2O), but his was attributed to the significant correlation of remineralization with the activity gradients from the solution into the lesion of some calcium phosphate ions and ion pairs, in particular the neutral ion pair CaHPO4(0). The CPP, by stabilizing calcium phosphate in solution, maintain high-concentration gradients of calcium and phosphate ions and ion pairs into the subsurface lesion and thus effect high rates of enamel remineralization.

Calcium↗

PubMed1998

CO2 laser inhibitor of artificial caries-like lesion progression in dental enamel.

Several studies during the last 30 years have demonstrated the potential of laser pre-treatment of enamel or tooth roots to inhibit subsequent acid-induced dissolution or artificial caries-like challenge in the laboratory. The overall objective of ongoing studies in our laboratories is to determine, systematically, the optimum sets of parameters for carbon dioxide laser irradiation that will potentially effectively inhibit dental caries in enamel and tooth roots. The aim of the present study was to examine the roles of wavelength and fluence in the prevention of caries progression in vitro in enamel by means of a pH-cycling model. The hypothesis to be tested was that the highly absorbed 9.3- and 9.6-microm wavelengths would be efficiently converted to heat, creating a temperature sufficiently high to reduce the acid-reactivity of the mineral and inhibit caries-like lesion progression in dental enamel. One hundred and sixty caries-free tooth crowns were cleaned and varnished with acid-resistant varnish, leaving one exposed window of enamel. Twelve groups of 10 enamel samples were irradiated in their individual windows by one of the four wavelengths (9.3, 9.6, 10.3, or 10.6 microm) of a tunable CO2 laser. Energy per pulse was 25, 50, 100, 200, or 250 mJ (25 pulses). Repetition rate was 10 Hz, and beam diameter was 1.6 mm. Fluence conditions of 1 to 12.5 J/cm2 per pulse were produced. All teeth, including 40 non-irradiated controls, were subjected to pH-cycling to produce artificial caries-like lesions. Results were assessed by cross-sectional microhardness testing. Inhibition of caries progression of from 40% to 85% was achieved over the range of laser conditions tested. At 9.3 and 9.6 microm, 25 pulses at absorbed fluences of 1 to 3 J/cm2 produced inhibition on the order of 70% with minimal subsurface temperature elevation (< 1 degree C at 2 mm depth), comparable with inhibition produced in this model with daily fluoride dentifrice treatments. Safety and efficacy studies will be required in animals and humans before these promising laboratory results can be applied in clinical practice.

Absorption↗

PubMed1992

Degradability of dental ceramics.

The degradation of dental ceramics generally occurs because of mechanical forces or chemical attack. The possible physiological side-effects of ceramics are their tendency to abrade opposing dental structures, the emission of radiation from radioactive components, the roughening of their surfaces by chemical attack with a corresponding increase in plaque retention, and the release of potentially unsafe concentrations of elements as a result of abrasion and dissolution. The chemical durability of dental ceramics is excellent. With the exception of the excessive exposure to acidulated fluoride, ammonium bifluoride, or hydrofluoric acid, there is little risk of surface degradation of virtually all current dental ceramics. Extensive exposure to acidulated fluoride is a possible problem for individuals with head and/or neck cancer who have received large doses of radiation. Such fluoride treatment is necessary to minimize tooth demineralization when saliva flow rates have been reduced because of radiation exposure to salivary glands. Porcelain surface stains are also lost occasionally when abraded by prophylaxis pastes and/or acidulated fluoride. In each case, the solutes are usually not ingested. Further research that uses standardized testing procedures is needed on the chemical durability of dental ceramics. Accelerated durability tests are desirable to minimize the time required for such measurements. The influence of chemical durability on surface roughness and the subsequent effect of roughness on wear of the ceramic restorations as well as of opposing structures should also be explored on a standardized basis.

Biodegradation, Environmental↗

PubMed1995

In situ caries models.

By using in situ models, we have the potential to study both fundamental aspects of the caries process as well as more applied research problems such as the effect of food on dental caries and the role of fluoride in caries prevention in human subjects without actually causing caries in the natural dentition. The key experimental parameters that need to be considered in the development of an in situ model are the characteristics of the subject panel, the physical design of the model, the type of hard tissue substrate and the method of assessing mineral status, and the study design and clinical protocol. Each parameter must be carefully considered in relation to the objectives of the research, study design requirements, ethical considerations, impact on clinical relevance, and impact on the control of variation. The major source of variation associated with in situ models should be of biological and not experimental origin. The design and conduct of proper in situ model studies require a clear understanding of the caries process, sound analytical support, and a knowledge of how to work with research subjects to achieve a high level of compliance. Given the complex nature of caries, a combination of hard tissue substrates--including sound, surface-softened lesions and subsurface lesions--may be necessary to model all aspects of caries progression and prevention successfully. Internal validation of in situ models using fluoride dose-response controls is considered to be necessary for studies evaluating the efficacy of new fluoride dentifrice formulations.

Animals↗

PubMed1997

Reproducibility of TMR for the determination of longitudinal mineral changes in dental hard tissues.

Transverse microradiography (TMR) of thin sections is the principal method for determining mineral changes in experimental lesions. Because it has become also the standard by which newly-developed methods are validated, demands on all steps of the procedure are high. Thin sections of enamel and dentin require high-precision cutting or lapping to preserve surface structures, but their different brittleness and elasticity preclude a uniform procedure. Image analysis permits the measurement of fine details at a micron scale, but because most studies are aimed at overall mineral changes, they are usually lost on broadening of the scan areas and averaging of experimental groups. Small errors in repositioning of the scan areas for repetitive measurements may yield distorted lesion profiles, while quantitative data such as the integrated mineral loss are hardly influenced. A major reason for "irreproducibility" of TMR are the different definitions of the lesion parameters as used by various research groups. We recommend that these definitions be agreed on if the full potential of TMR as an international standard is to be utilized.

Absorptiometry, Photon↗

PubMed1997

Application of transverse microradiography for measurement of mineral loss by acid erosion.

This paper describes a novel application of transverse microradiography for the detection and quantification of mineral loss due to acid erosion in thin tooth sections. Sixty-four specimens were randomly divided into eight equal-sized groups and exposed to an orthophosphoric-acid-based erosive fluid (pH = 3) for 0, 0.25, 0.5, 1, 2, 5, 12, or 24 hrs. We made microdensitometric scans separately across both enamel and dentin to derive data for the total mineral loss and the minimum mineral content within the eroded area. We then analyzed specimens using a profilometer to determine (1) the area above a plot of penetration depth against distance and (2) the maximum depth of penetration. Correlation coefficients for comparisons between microradiographic and profilometric data for both enamel and dentin specimens varied between 0.87 and 0.96. Two-sample t tests demonstrated that the microradiographic technique could detect early erosion, i.e., discriminate between erosion times of less than 1 hr. It was concluded that this application of transverse microradiography was a useful and acceptable method for the measurement of early mineral loss in vitro, occurring as a result of acid erosion.

Absorptiometry, Photon↗