A randomised, observer-blind, clinical study investigating the effect of fluoridated milk on artificially created early enamel caries using transverse microradiography.

Much of the research regarding the efficacy of fluoridated milk was obtained prior to the routine use of fluoridated dentifrices. The aim was to investigate, in situ, the effect of fluoridated and non-fluoridated milk on mineral change in artificial caries lesions, with the additional use of fluoridated dentifrice. The roles of different milk fluoride concentrations, volumes and frequencies in mineral change were studied. In total, 29 edentulous subjects were recruited and tooth blocks, containing artificial caries lesions, were inserted into their full dentures at 4 areas (sites). Each subject followed 5 randomly ordered, 6-week beverage experiments: 0.5 mg of F in 200 ml of milk, 3 times per day; 1.5 mg of F in 200 ml of milk, once per day; 200 ml of milk, once per day; 200 ml of milk, 3 times per day, and no beverage (negative control). In addition, the subjects were allocated to 1 of 2 groups; experimental treatment only or treatment and dentifrice. Mineral change was measured with transverse microradiography. Statistical analysis was performed using 2-sample t tests and a general linear modelling procedure. For integrated mineral loss there was a statistically significant effect of group (p = 0.001), indicating fluoridated toothpaste significantly increased remineralisation. For lesion depth there was a statistically significant combined effect of 'group and site'. 'Experiment' had no statistically significant influence on change in integrated mineral loss or lesion depth. The study demonstrated that the use of fluoridated dentifrice twice per day had a positive effect on the remineralisation of caries lesions. However, no additional significant effect of fluoridated milk was observed.

The permeability of artificial dentine carious lesions.

OBJECTIVE: This study aimed to verify whether two demineralisation solutions, with different fluoride concentrations, would produce subsurface lesions in dentine, as assessed by microradiography, with different mineral loss profiles and, subsequently, to determine the dentine permeability of the two altered tissues. METHODS: Forty-five human coronal portions were prepared and randomly divided into two test groups (20 specimens each) with the remaining five as a control group. Each test group was exposed to a demineralisation solution containing either 1 or 5 ppm fluoride for five days. RESULTS: There were highly significant differences between the two test groups for all microradiographic parameters, except for lesion depth. The increase in dentine permeability from baseline to day 5 was statistically significant within each of the two test groups, but not for the control group. CONCLUSION: The differences in the mineral content profile of the two lesions did not influence the magnitude of change in their permeability.

Development of fibre-optic confocal microscopy for detection and diagnosis of dental caries.

We report on the development of a fibre-optics-based confocal imaging system for the detection and potential diagnosis of early dental caries. A novel optical instrument, capable of recording axial profiles through caries lesions using single-mode optical fibres, has been developed. The practical study illustrates that miniature confocal devices based around single-mode optical fibres may provide additional diagnostic information for the general dental practitioner.

In vitro dentine permeability: the relative effect of a dentine bonding agent on crown preparations.

OBJECTIVE: The aim of this study was to determine whether a dentine bonding agent (DBA) had an effect in reducing fluid filtration under cemented provisional crowns. METHODS: Crown preparations on 34 premolars, randomly allocated to two equal-sized test and control groups, were assessed for dentine permeability by a fluid filtration technique. In the test group, prepared crowns were acid-etched and then treated with a DBA (Prime & Bond NT). In the control group, no such DBA was applied. Provisional crowns were cemented on both groups of teeth using non-eugenol zinc oxide cement. Fluid filtration rates were measured repeatedly after crown preparation, at cementation, 1 h, 1 day, 1 week and 3 weeks following crown cementation for both groups. Filtration rates were also measured after acid-etching and dentine bonding for the test group. RESULTS: There was insufficient evidence to suggest any statistically significant differences either between the two groups or, on average, across the five time points in each group in terms of the relative percentage of fluid filtration. CONCLUSION: The DBA used did not seal dentinal tubules any more than did the smear layer and provisional crowns luted with a non-eugenol ZnO cement.

The effect of dentine on fluorescence measurements of enamel lesions in vitro.

This study aimed to determine the contribution of the underlying dentine and the enamel-dentine junction to measurements of mineral loss from enamel recorded using quantitative light fluorescence (QLF). Sixteen square blocks (5 x 5 mm) were cut from the labial surfaces of extracted bovine incisor teeth. A dental drill was used to remove dentine and the enamel-dentine junction from half of each specimen. All specimens were embedded in epoxy resin and ground to produce a smooth, flat enamel surface. Half of the enamel surface of the block, perpendicular to where the dentine had been removed, was demineralised for 72 h prior to undertaking QLF measurements from the enamel surface to compare fluorescence loss from different areas of the block. QLF readings taken from lesions with no underlying dentine or enamel-dentine junction were very similar to readings from lesions with underlying dentine. A comparison of the two data sets demonstrated a linear relationship with a gradient of 0.95 and a y intercept of -1.24 (r(2) = 0.936). From these data, the underlying dentine and enamel-dentine junction did not influence mineral loss in enamel measured using QLF.

The intra- and inter-examiner reliability of quantitative light-induced fluorescence (QLF) analyses.

OBJECTIVE: To assess the reliability of the analysis stage of quantitative light-induced fluorescence (QLF). The QLF analysis involves subjective input from the user and this study examines the influence of this on the reproducibility of the QLF data. METHOD: QLF images were taken of 20 human molar teeth that had been previously subjected to a demineralizing solution (phosphoric acid 37%) to create artificial white spot lesions on their buccal surfaces. Following examination of the images, 16 were chosen to represent a range of lesion size and severity. Three copies were made of the images and each was allocated a different filename. 10 examiners in three centres were asked to analyse each of the 16 images on three occasions, with at least seven days between each attempt. Simple instructions describing the analysis procedure were supplied and examiners were asked to adhere to these directions. Examiners were asked to rate each of the 16 teeth on their first attempt both quantitatively (5 point scale) and qualitatively in terms of difficulty of analysis. Data reported were the delta Q at 5% threshold for each tooth on each of three attempts. RESULTS: Using ANOVA and paired t-tests to detect statistical differences, the three attempts of each examiner were used to determine intra-examiner reliability. Only one examiner (a novice at the technique) demonstrated differences between all three attempts and two demonstrated difference between one attempt. When the mean scores were compared to determine the inter-examiner reliability, only one examiner's results were statistically different when compared with two others. CONCLUSION: This study has demonstrated that the analysis stage of QLF is reliable between examiners and within multiple attempts by the same examiner, when analysing in vitro lesions. Novices at the technique should be trained before analysing experimental data.

An alternative hypothesis from veterinary science for the pathogenesis of noncarious cervical lesions.

An alternative hypothesis to abrasion and erosion for the pathogenesis of noncarious cervical lesions was put forward in 1984; the so-called occlusal theory suggested that tensile stresses from occlusal overload could be involved in the pathogenesis of noncarious cervical lesions and that bending stresses applied to teeth could cause disruption of the surface enamel, resulting in increased susceptibility to dissolution and abrasion at the affected sites and in the development of wedge-shaped lesions. This theory has gained increased acceptance in recent years, although absolute scientific evidence has been scant. These lesions also occur in animals, in particular, the domestic cat, in which they are called feline odontoclastic resorptive lesions. A variety of theories about pathogenesis of these lesions have been put forward, but there is some evidence that occlusal overload may be a contributory factor in the development of an inflammatory response in the periodontal membrane and the presence of enzymes associated with resorption in the gingival crevice. Further investigation may help define a common etiology between the pathogenesis of feline odontoclastic resorptive lesions and noncarious cervical lesions.

The effect of saliva on enamel and dentine erosion.

The present study aims to assess the ability of saliva, both in vitro and in situ, to prevent surface mineral loss from enamel and dentine when exposed to an erosive challenge. Fifteen groups of four varnished thin tooth sections were stored in saliva collected from individuals taking part in the in situ study and a further eight groups, each containing four sections, were stored in deionised water. In vitro, sections were stored in saliva or water for 14 days. In addition, fifteen subjects each wore an appliance with four varnished sections. Appliances with sections were worn for 14 days. All sections were exposed to 25 ml of erosion solution for 5 min twice daily. Microradiography and image analysis of the recovered sections demonstrated significant protection of surface mineral loss from enamel and dentine by saliva in vitro and in situ compared with deionised water (p < 0.05). Significantly less mineral loss (p < 0.05) was observed for enamel and dentine stored in situ compared with storage in saliva in vitro. Generalised linear modelling demonstrated both the subject and protocol had significant effect on mineral loss. A weak positive correlation (r = 0.64) was noted when in situ and in vitro mineral loss from enamel were compared, demonstrating greater reactivity of the in vitro enamel specimens to the erosion challenge. The dentine data did not show any linear correlation. Saliva protected against mineral loss by erosion and, for enamel, in vitro results demonstrated a weak positive correlation with in situ results.

Beat averaging alternatives for transmitral Doppler flow velocity images.

To characterize diastolic function from transmitral Doppler data, the image's maximum velocity envelope (MVE) is fit by a model for flow velocity. To reduce the physiologic beat-to-beat variability of best-fit determined model parameters, averaging of multiple cardiac cycles is indicated. To assess variability mathematically, we modeled physiologic noise as a random (normally-distributed) process and evaluated three methods of averaging (1, averaging model parameters from single images; 2, averaging images; and 3, averaging MVEs) using clinical datasets (50 continuous beats from 5 subjects). Method 2 generates a positive bias because low-velocity beats will not contribute to the composite MVE. The difference between Methods 3 and 1 is less than 2.0 E-5 (m/s)2 for uncorrelated model parameters. Input having 10% beat-to-beat variation yields a bias of <4% for model parameter mean. Hence, Method 1 was, in general, more robust than Method 3.

Evaluation of model-based processing algorithms for averaged transmitral spectral Doppler images.

In an effort to characterize more fully diastolic function using Doppler echocardiography, we have previously developed an automated method of model-based image processing for spectral Doppler images of transmitral blood flow. In this method, maximum velocity envelopes (MVEs) extracted from individual Doppler images are aligned and averaged over several cardiac cycles. The averaged waveform is fit by the solution of a kinematic model of diastolic filling. The results are estimates of the model parameters. As expected, the mean and standard deviation of the model parameter estimates depend on many factors such as noise, the number of cardiac cycles averaged, beat-to-beat variation, waveform shape, observation time and the processing methods used, among others. A comprehensive evaluation of these effects has not been performed to date. A simulation was developed to evaluate the performance of three automated processing methods and to measure the influence of noise, beat-to-beat variation and observation time on the model parameter estimates. The simulation's design and a description and analysis of the three automated processing methods are presented. Of the three methods evaluated, using the inflection point in the acceleration portion of the velocity contour as the first data point to be fit was found to be the most robust method for processing averaged E-wave MVE waveforms. Using this method under nominal conditions, the average bias was measured to be < 3% for each of the model parameters. As expected, the biases and standard deviations of the estimates increased as a result of increased noise levels, increased beat-to-beat variation and decreased observation time. Another important finding was that the effects of noise, beat-to-beat variation and waveform observation time on the parameter estimates are dependent on the location in model parameter space.

Can trasmitral Doppler E-waves differentiate hypertensive hearts from normal?

Physiological models of transmitral flow predict E-wave contour alteration in response to variation of model parameters (stiffness, relaxation, mass) reflecting the physiology of hypertension. Accordingly, analysis of only the E-wave (rather than the E-to-A ratio) should be able to differentiate between hypertensive subjects and control subjects. Conventional versus model-based image processing methods have never been compared in their ability to differentiate E-waves of hypertensive subjects with respect to age-matched control subjects. Digitally acquired transmitral Doppler flow images were analyzed by an automated model-based image processing method. Model-derived indexes were compared with conventional E-wave indexes in 22 subjects: 11 with hypertension and echocardiographically verified ventricular hypertrophy and 11 age-matched nonhypertensive control subjects. Conventional E-wave indexes included peak E, E, and acceleration and deceleration times. Model-based image processing-derived indexes included acceleration and deceleration times, potential energy index, and damping and kinematic constants. Intergroup comparison yielded lower probability values for model-based compared with conventional indexes. In the subjects studied, Doppler E-wave images analyzed by this automated method (which eliminates the need for hand-digitizing contours or the manual placement of cursors) demonstrate diastolic function alteration secondary to hypertension made discernible by model-based indexes. The method uses the entire E-wave contour, quantitatively differentiates between hypertensive subjects and control subjects, and has potential for automated noninvasive diastolic function evaluation in large patient populations, such as hypertension and other transmitral flow velocity-altering pathophysiological states.

Postextrasystolic left ventricular isovolumic pressure decay is not monoexponential.

OBJECTIVE: The relationship between the left ventricular (LV) relaxation time constant and early diastolic filling is not fully defined. This study provides additional evidence that LV isovolumic pressure fall in the normal intact heart in response to certain interventions is not adequately described by a model of monoexponential decay and that its relationship to filling is complex. METHODS AND RESULTS: To gain further insight into the relationship between LV relaxation and early rapid filling we measured LV isovolumic relaxation rate, peak early filling velocity (E), LV volumes, and transmitral pressures at baseline and in the first postextrasystolic beat after a short-coupled extrasystole in 9 anesthetized dogs. Postextrasystolic isovolumic relaxation rate was slowed as measured by 3 commonly used time constants, while E was increased 32%. LV contractility and peak pressure were also increased, while LV end-systolic volume was decreased. LV minimum pressure was deceased, while the early diastolic transmitral pressure gradient was increased. Although all relaxation time constants measured over the entire isovolumic relaxation phase indicated slowed relaxation, direct measurement of isovolumic relaxation time indicated no change in relaxation rate. Calculation of the time constants and direct measurement of isovolumic relaxation time during early isovolumic pressure decay indicated slowed postextrasystolic pressure decay rate compared with baseline, while calculation of time constants and direct measurement of isovolumic relaxation time during late isovolumic relaxation indicated augmented postextrasystolic pressure decay rate versus baseline. CONCLUSIONS: This non-exponential behavior of LV isovolumic pressure decay in postextrasystolic beats after short-coupled extrasystoles provides further evidence that the relationship that exists between ventricular relaxation and early filling is not simple. The results are interpreted in terms of current theoretical formulations that attribute control of myocardial relaxation to the interaction between inactivation-dependent and load-dependent mechanisms.

Left ventricular chamber stiffness from model-based image processing of transmitral Doppler E-waves.

BACKGROUND: Model-based image processing (MBIP) of Doppler E-waves eliminates the need for digitizing waveforms by hand or determining the contour 'by eye'. Little et al. (Circulation 1995, 92:1933-1939) used pressure-volume measurements for dogs to verify the physiologic-model-derived prediction that the left ventricular chamber stiffness, KLV1 can be determined from the deceleration time tdec, when that portion of the E-wave contour is fit by a cosine function. MBIP of clinical Doppler E-wave images to determine chamber stiffness KLV has not been performed. OBJECTIVE: We sought to determine KLV by MBIP of clinical Doppler E-wave images and elucidate the physiologic meaning of the harmonic oscillator filling model's parameter k. METHODS AND RESULTS: The unique mathematical relationship between the kinematic, harmonic oscillator model of filling and KLV predicts that the oscillator's spring constant k be linearly proportional to the chamber stiffness KLV. To verify this, digitally acquired, clinical Doppler transmitral flow velocity images from 21 subjects were analyzed. The parameter k and the stiffness KLV were computed independently for each subject and compared. In accordance with prediction, a linear relationship between k and the stiffness KLV, namely k = 1.16 [A/(rho L)]KLV+41, r = 0.96, was observed. CONCLUSIONS: The oscillator parameter k is linearly proportional to the left ventricular chamber stiffness KLV. The MBIP approach allows automated computation of k and KLV, provides a robust, automated, observer independent method of Doppler transmitral flow velocity analysis, and eliminates the need for visual determination of the contour or measurement of its attributes by eye. It provides a stimulus for further validation of the relationships among K, KLV, and catheterization-based diastolic chamber properties in humans and their correlations with selected diastolic function-altering syndromes.

Relationship of the fourth heart sound to atrial systolic transmitral flow deceleration.

The fourth heart sound (S4) is thought to be due to cardiohemic vibrations, powered by deceleration of transmitral blood flow, that occur when atrial systole leads to a disproportionately high rise in ventricular end-diastolic pressure (relative to diastasis), associated with an enhanced atrial systolic blood filling volume or a stiff ventricular wall. To characterize S4 production, we modeled the cardiohemic system as a forced, damped nonlinear harmonic oscillator. The forcing term used a closed-form expression for the Doppler A-wave contour. We simultaneously recorded transthoracic phonocardiograms and Doppler A waves in subjects with and without audible S4 and compared model predictions for S4 amplitude, frequency, and power spectrum with those of the recorded S4. Excellent agreement was observed between the model-predicted amplitude, duration, timing, and power spectrum and those of the phonocardiographic S4. We conclude that, with a normal mitral valve, there should always be an oscillation of the cardiohemic system during A-wave deceleration. However, oscillations may not have high enough amplitude, frequency, or coupling to the chest wall to be clinically audible as an S4.

Relative ability of laser fluorescence techniques to quantitate early mineral loss in vitro.

This in vitro investigation was undertaken to explore two different nondestructive methods to detect very early demineralization. These methods were based on the premise that the clinical detection of caries at a very early stage of formation might permit more efficient reversal of the caries process than may occur when lesions are detected at a more advanced stage, such as a so-called 'white spot'. The methods evaluated in this study were quantitative laser fluorescence (QLF) and an experimental dye-enhanced laser fluorescence (DELF) technique. Prepared and polished bovine enamel specimens were demineralized in a conventional lactic acid-Carbopol solution for varying periods of time between 0 and 24 h with an area of sound enamel retained on each specimen. The coded and randomized specimens were then analyzed for the presence and severity of enamel demineralization using QLF after which they were exposed to a selected dye (Pyrromethene 556) and similarly examined using DELF. The specimens were then sectioned and examined by conventional transverse microradiography and by confocal laser-scanning microscopy. Results were analyzed statistically with sensitivity and specificity determined using sound enamel as the reference. The results indicated that QLF could detect demineralization which occurred as a result of 8 h exposure to the decalcification solution and was able to quantify changes in lesion severity associated with longer demineralization. While DELF was capable of detecting enamel demineralization after only 2 h exposure to the decalcification solution, it was unable to quantify increasing amounts of demineralization associated with longer periods of exposure to the decalcification solution. In summary, while DELF was able to detect very early demineralization, only QLF was capable of detecting and quantifying changes in the extent of the decalcification occurring with demineralization periods up to 24 h.

Determination of plaque pH changes within the trough of an in situ appliance used to study mineral changes in early carious lesions.

Plaque pH was measured using a glass combination pH microelectrode of plaque deposits lining the trough of an intra-oral appliance which contained single sections of human teeth with artificial enamel lesions. Plaque exposure to a 10% sucrose solution produced significantly lower plaque pH levels than a solution of sorbitol gum extract. The subsequent flow of saliva over the plaque/pH electrode interface resulted in a significant and rapid increase in pH. Repeat experiments, using deionised water instead of saliva, demonstrated no increase in pH at the plaque/electrode interface. This system may provide a convenient method of producing plaque suitable for repeated pH analysis in intimate association with artificial enamel lesions. This may permit further study of the relationship between plaque acidogenicity, salivary buffering capacity and mineral change within the incipient enamel lesion.

An in situ interproximal model for studying the effect of fluoride on enamel.

This crossover study determined the ability of an interproximal, intra-oral model to demonstrate a fluoride dose response to 0-, 250- and 1,100-ppm fluoride (sodium fluoride) dentifrices with respect to fluoride uptake into, and remineralization of, incipient subsurface enamel lesions. Following a 1 week 'lead in' period during which 30 panelists were randomly assigned to use one of the products, two enamel specimens with artificial carious lesions were mounted into a specially designed functional partial denture worn by each panelist. Panelists continued to brush three times daily with their test dentifrice for 4 weeks, after which the specimens were removed and analyzed for fluoride uptake and remineralization. The procedure was repeated until each panelist had followed all three treatment regimens. Fluoride analyses were performed using a microdrill biopsy technique, and mineral content changes were determined by transverse microradiography. Fluoride uptake data were significantly different (p < 0.01) for all three products with the effect of 1,100 ppm F > 250 ppm F > placebo. The 1,100 ppm F dentifrice also effected significantly greater remineralization (p < 0.01) than did the 250-ppm-F or placebo dentifrices. Relative efficacy of the three fluoride dentifrices tested in this study was similar to that established in a clinical trial, and, therefore, supports the use of this model for in situ studies of the effects of fluoride-containing products on enamel lesions.

Echo machine-imposed limit on transmitral spectral Doppler velocity-profile analysis.

We have previously developed a kinematic model of ventricular filling. Its application to in vivo transmitral Doppler velocity profiles provides a quantitative characterization of filling. However, the model parameters computed by solving the "inverse problem" may depend on ultrasound machine type and setting (e.g., gain, baseline filter, dynamic range). To determine machine-based effects on the computed model parameters, we performed a flow phantom study using Acuson and HP echocardiography machines at various settings. We compared maximum velocity envelopes (MVEs), as well as the model fit to these MVEs, for 3 simulated waveforms imaged by both machines. For all 3 waveforms, the machines generated comparable MVEs, fit by the model within a mean-square difference of 5E-5 (m/s)2. The associated variations in model parameters for the 3 waveforms were not uniform. Two waveforms showed slight variation between machines, with model parameters varying by less than 6%. The shortest duration waveform showed model parameter variations of 10-15%. Analysis of the parameter space for this waveform showed a constant mean-square error contour that was larger than that for the other two, causing similar small variations in measured MVEs to result in larger differences in the parameter estimates for this waveform. Because this method completely eliminates inter- and intraobserver variability, we conclude that, within the limits established, the slight contour variations due to machine type and setting should not affect this method's applicability in clinical Doppler-flow analysis.

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.

In vitro studies of laser fluorescence for detection and quantification of mineral loss from dental caries.

Laser fluorescence (LF) is thought to be a quantitative technique for the measurement of mineral loss from dental caries. These studies aimed to demonstrate the quantitative nature of LF, by means of transverse microradiography (TMR), in addition to the possible use of LF on small specimens suitable for in situ studies. Studies also aimed to determine the ability of LF to detect caries adjacent to amalgam restorations. The results demonstrated reasonable correlation between both the histological depth and mineral loss measured by TMR compared with the % change in mean fluorescence radiance measured by LF (r = 0.70 and 0.83, respectively). Studies with small specimens demonstrated that in vitro remineralization could be observed with LF for comparison of the demineralized specimen with an undemineralized reference. ANOVA showed significant mineral gain (p < 0.0001). The detection and quantification of mineral loss adjacent to amalgam restorations may have potential for the management of recurrent caries. Studies have demonstrated that LF can detect such mineral loss, and, with refinement of the image analysis system, LF was capable of detecting remineralization. Remineralization of such lesions is controversial, but it is suggested that LF may have a role in secondary caries management.