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Biomedical subjects

D M Parker

Publications and source records attributed to D M Parker.

At least 19 recordsLinked to original sources
PubMed2006

Erosion of enamel by non-carbonated soft drinks with and without toothbrushing abrasion.

OBJECTIVE: To investigate how enamel loss due to erosion, and due to cycling of erosion and abrasion, depends on compositional parameters of soft drinks, and particularly whether the thickness of the erosive softened layer is a function of drink composition. SETTING: University dental hospital research laboratory in the UK, 2004. MATERIALS AND METHODS: Six drinks were chosen based on their popularity and composition: apple juice, orange juice, apple drink, orange drink, cranberry drink and 'ToothKind' blackcurrant drink. Group A samples (n = 36) were exposed to soft drinks at 36 degrees C for six consecutive 10 minute periods. Group B samples (n = 36) were subjected to alternating erosion and toothbrushing, repeated six times. Enamel loss was measured using optical profilometry. RESULTS: Group A: significant enamel loss was seen for all drinks (p < 0.001). Erosion was correlated with pH and calcium concentration but not phosphate concentration or titratable acidity. Group B: significant additional material loss due to toothbrush abrasion occurred with all drinks. Abrasive enamel loss differed between the drinks and was positively correlated with drink erosive potential. CONCLUSION: Enamel loss by erosion is exacerbated by subsequent abrasion. The amount of softened enamel removed by toothbrushing is a function of the chemical composition of the erosive medium.

Analysis of Variance↗
PubMed2005

The relationship between enamel softening and erosion caused by soft drinks at a range of temperatures.

OBJECTIVES: Investigations of the erosive potential of soft drinks are usually performed at room or body temperature, but drinks are more frequently served chilled, with ice, or hot. Since the rate of chemical reactions usually increases with temperature, it is predicted that erosion is more severe at high temperatures and reduced at low temperatures. The aim of this study was to investigate the correlation between enamel softening, enamel erosion, and temperature. METHODS: Atomic force microscopy nanoindentation and non-contact optical profilometry were used to assess changes in enamel nanomechanical properties after 5 min and erosive material loss after 30 min exposure to two different non-carbonated soft drinks at 4, 25, 50 and 75 degrees C. RESULTS: For one drink (Robinson's Original Juice Drink), there was a statistically significant difference between nanomechanical properties and erosion depth at all temperatures, with softening and erosion increasing with temperature. For another drink (Ribena ToothKind Juice Drink), there was a slight softening and virtually no material loss, and temperature had no statistically significant impact on erosion. There was a good linear correlation (R2 = 0.94) between nanomechanical properties and material loss. CONCLUSIONS: The difference between the drinks can be explained by their composition. For the erosive drink, material loss increased, and nanohardness decreased, approximately linearly with temperature. The correlation between softening and erosion demonstrated that nanomechanical properties after very short erosion times can be considered a good predictor of bulk material loss after considerably longer erosion times.

Beverages↗
PubMed2005

Human enamel erosion in constant composition citric acid solutions as a function of degree of saturation with respect to hydroxyapatite.

The objective of this study was to investigate human enamel erosion under constant composition conditions, as a function of solution degree of saturation (DS) with respect to hydroxyapatite. The experimental conditions were relevant to the initial stages of enamel erosion by soft drinks. Nanoindentation was used to compare enamel surface softening caused by a control mineral water and two citric acid solutions with DS = 0.000 and DS = 0.032, both having pH 3.30. Enamel hardness and reduced elastic modulus were measured after 0, 30, 60, 120, 300 and 600 s exposure. A statistically significant change in enamel hardness was detected after 30 s exposure to both citric acid solutions, indicating that nanoindentation is extremely sensitive to the initial stages of erosion. There was a statistically significant difference between the mechanical properties of enamel exposed to the two citric acid solutions after 30, 60 and 120 s. At these times, the solution with DS = 0.000 caused twice as much enamel softening as that with DS = 0.032. This demonstrates that it may be possible to design a soft drink with a low erosive potential and a good taste by a small change in DS, at a typical drink pH.

Beverages↗
PubMed2005

Relationship between enamel erosion and liquid flow rate.

The association of severe erosion with certain habits of consuming soft drinks prompted a study of erosion in relation to fluid flow. In the main experiments, citric acid solution (pH 3.2) was directed at polished enamel surfaces at flow rates of 26, 67 or 126 ml min(-1) through outlets of diameters 1.0, 2.6 or 5.0 mm for up to 20 min. Erosion depth increased with time of exposure and total volume of solution, with increasing flow rate and with decreasing outlet diameter. Scanning electron microscopy of acid-treated surfaces and of the subsurface enamel indicated that the clearance of dissolution products, rather than the mechanical dislodgement of partly dissolved crystal bundles, was the main process involved. For an exposure time of 20 min, erosion increased with (liquid velocity)(1/4). In a secondary experiment, it was found that the erosive potential of a low-erosive drink did not increase with increasing liquid velocity. The rapid increase in the rate of erosion caused by citric acid at low liquid velocities shows that reproducible stirring is essential for precision and intercomparison of in vitro studies. It also accounts for the rapid erosion seen when erosive drinks are consumed from a straw placed labial to the anterior teeth, or are "swished" between the teeth.

Carbonated Beverages↗
PubMed2004

A comparison of enamel erosion by a new sports drink compared to two proprietary products: a controlled, crossover study in situ.

OBJECTIVE: The aim of the study was to measure the erosive potential of a prototype sports drink on enamel in a model in situ. METHODS: The study was a single centre, single blind, randomised crossover design balanced for residual effects involving 18 subjects. The drinks were the prototype formulation containing calcium and maltodextrin (test), two sports drink products containing sugars (drink with calcium and positive control) and water (negative control). During each 15-day study period, subjects wore a palatal removable appliance carrying two flat human enamel specimens. Drinks were imbibed as 250 ml volumes over 10 min 4 times per day. Loss of enamel was measured on days 5, 10 and 15 using a contacting profilometer. RESULTS: Very little erosion occurred with the test, drink with calcium and negative control drinks and differences between the test and negative control only reached significance at day 15. The positive control produced progressive erosion over time and significantly more than the test or negative control at all time points. CONCLUSION: The technology of adding calcium with appropriate pH adjustment, which has been applied previously to soft and carbonated drinks to markedly reduce erosive potential, can be applied to sports drinks to the same end. Significant variation in the carbohydrate composition does not influence this outcome.

Adult↗
PubMed2003

Development of low erosive carbonated fruit drinks. 1. Evaluation of two experimental orange drinks in vitro and in situ.

OBJECTIVES: To determine the in vitro erosive potential and in situ erosive effect of two new formulation low calorie carbonated orange drinks with that of two conventional diet products and water. METHODS: In the in vitro study, six specimens of deciduous and permanent enamel were randomly allocated to each of the five products and a '4h' protocol employed. In the in situ study, 15 healthy volunteers participated in a single centre, single blind, 5-phase crossover study, conducted according to Good Clinical Practice, and employing a validated model. RESULTS: The in vitro erosive potential of the experimental formulations was less than that of the comparators at all time points. Conversely, the observed erosive potential of both experimental formulations was greater than that of the control. Consistent statistically significant differences were found in relation to permanent enamel only. Unfortunately, the in situ study did not produce results entirely consistent with those of the in vitro study. Notably, a generally progressive loss of enamel was observed in specimens exposed to the control. CONCLUSIONS: The data from the in vitro study show the experimental formulations to have low comparative erosivity. However, the methodologies in vitro and in situ somewhat unusually do not correlate in ranking the erosivity of drinks. The results of this study should therefore be viewed with caution, further research being clearly warranted.

Adolescent↗
PubMed2003

Development of low erosive carbonated fruit drinks 2. Evaluation of an experimental carbonated blackcurrant drink compared to a conventional carbonated drink.

OBJECTIVE: Previous studies demonstrated that a non-carbonated blackcurrant juice drink with added calcium produced little erosion of enamel in vitro and in situ by comparison with other low pH fruit drinks. The aim of this study is to evaluate the erosive effects in situ of an experimental formulation carbonated drink with added calcium, compared to a conventional carbonated drink over a 20 day period using a similar design as in previous studies. METHOD: The study was a single centre, single blind, randomised placebo controlled three cell crossover design involving 15 volunteers. The test drinks were an experimental carbonated ready-to-drink (RTD) blackcurrant drink, a conventional carbonated RTD orange drink and water. Two enamel samples were retained in situ, in the midline of the hard palate on an upper removable acrylic appliance. Drinks were 250 ml volumes consumed four times per day during 20 working days. Measurements of enamel loss were made on enamel samples after days 2, 5, 10, 15 and 20 by profilometry. RESULTS: The experimental carbonated blackcurrant drink caused significantly less enamel loss than the conventional carbonated orange drink at all time points measured, but was not significantly different from water at days 2, 5 and 20. CONCLUSIONS: This study has shown that it is possible to modify carbonated soft drinks in a manner similarly shown with non-carbonated soft drinks, to minimise dental erosion.

Adult↗
PubMed2000

Effects of pH and concentration of citric, malic and lactic acids on enamel, in vitro.

OBJECTIVE: Dental erosion associated with soft drink consumption probably results from the contained dietary acids in the formulations. The pH value of any formulation is an important variable in acid erosion but not necessarily the only important factor. The aim of this study was to measure enamel erosion by citric, malic and lactic acids at pH values and acid concentrations representative of a range found in soft drink formulations and to determine the effect of adding calcium to citric acid. METHODS: Flat ground enamel samples were prepared from unerupted human third molar teeth. Groups of five specimens were placed in citric, malic and lactic acid solutions of different pH and acid concentration for three by 10 min exposures at 35 degrees C. Enamel loss was measured by profilometry. Enamel specimens were also exposed to citric acid solutions containing calcium at different pH values and at the same pH with different concentrations of calcium. RESULTS: Numerical data and contour plots for each acid showed a similar pattern for increasing erosion with decreasing pH and increasing acid concentration and vice versa for decreasing erosion. Increasing the concentration of calcium in a fixed pH citric acid solution resulted in decreased erosion. This effect was most marked at higher pH. CONCLUSIONS: This study has shown that under highly controlled conditions the erosion of enamel by solutions of dietary acids is influenced by the interplay of pH, acid concentration and presence of calcium. These variables and in particular the concentration of calcium could be manipulated to produce soft drinks with reduced erosivity to enamel.

Beverages↗
PubMed1999

Development and evaluation of a low erosive blackcurrant juice drink. 3. Final drink and concentrate, formulae comparisons in situ and overview of the concept.

OBJECTIVE: Two previous studies demonstrated that a blackcurrant juice drink with added calcium produced little erosion of enamel in vitro and in situ by comparison with other low pH fruit drinks. The primary aim of this study was to demonstrate that the final formulation drink and concentrate were of similar low erosivity. Secondary aims were to provide more data on the erosivity of other fruit drink concentrates and whether erosion was influenced by anterior and posterior palate siting of enamel specimens. METHOD: The study was a single centre, single blind, randomised placebo controlled 5 cell crossover design involving 15 volunteers. The test drinks were blackcurrant juice/calcium concentrate, blackcurrant juice/calcium drink, proprietary apple & blackcurrant juice concentrate, proprietary orange drink concentrate and water. Four enamel samples were retained in situ, 2 anterior palate and 2 mid/posterior palate, on upper removable acrylic appliances. Drinks were 250 ml volumes consumed 4 times per day during 15 working days. Concentrates were diluted 50 ml in 200 ml water. Measurements of enamel loss were made on one anterior and one posterior sample on days 2, 5, 10 and 15 by profilometry. RESULTS: One subject approached the 20 microns erosion limit by day 10 on the orange drink and was withdrawn from that cell. Differences in mean erosion between anterior and posterior sites were variable and small. By day 15 the mean losses of enamel averaged over anterior and posterior were blackcurrant/calcium concentrate 0.28 micron, blackcurrant/calcium drink 0.35 micron, apple & blackcurrant concentrate 2.04 microns. orange concentrate 8.29 microns and water 0.08 micron. Except at day 15 for the blackcurrant/calcium drink the erosion by the blackcurrant/calcium formulations was not significantly different from water at any time point. Erosion by the apple & blackcurrant and orange concentrate drinks was highly significantly greater than the blackcurrant/calcium drinks at all but the 2 day time point for the apple & blackcurrant concentrate drink compared to the blackcurrant/calcium drink. CONCLUSIONS: All data thus far indicate that dependant on tooth site susceptibility and the specific drink, the consumption of standard low pH fruit drinks could result in 1 mm loss of enamel in periods ranging from as little as 2 years to 20 years. Similar erosion by the low pH blackcurrant drinks with added calcium would take in excess of 100 years.

Adult↗
PubMed1999

Development and evaluation of a low erosive blackcurrant juice drink in vitro and in situ. 1. Comparison with orange juice.

OBJECTIVE: The aim of this study was to determine whether an experimental blackcurrant juice drink with added calcium was less erosive to enamel both in vitro and in situ compared with a proprietary orange juice product. METHODS: The study was a single centre, blind, randomised, placebo controlled three cell crossover design. An intra oral appliance capable of retaining one enamel sample in situ was constructed and worn by 12 volunteers. The drinks under test were orange juice, the experimental blackcurrant juice drink with calcium and water. Drinks were consumed as 250 ml volumes four times during the working day under supervision for 15 days. The same methodology was modelled in vitro. Measurements of enamel loss were made by profilometry. RESULTS: Water, the experimental blackcurrant juice drink and orange juice produced 0.19, 0.41 and 2.54 microns loss of enamel respectively in situ and 0.0, 5.2 and 22.18 microns loss of enamel respectively in vitro. All differences between pairs of drinks in situ and in vitro were statistically significant. CONCLUSIONS: Data using this model in situ were only available for orange juice and this was therefore considered as a positive control with water a placebo control. The results have demonstrated that the experimental blackcurrant juice drink with calcium is markedly less erosive than orange juice, particularly and importantly in situ. The experimental blackcurrant juice drink has limited erosive potential to teeth and deserves further comparative investigation and development as a low pH fruit drink for public consumption.

Adult↗
PubMed1999

Development and evaluation of a low erosive blackcurrant juice drink. 2. Comparison with a conventional blackcurrant juice drink and orange juice.

OBJECTIVE: A previous study demonstrated that an experimental low pH blackcurrant juice drink with calcium was markedly less erosive to enamel both in situ and in vitro than orange juice. Further development of the experimental blackcurrant juice drink formula has occurred and the aims of the present studies were two fold. Firstly, to confirm the low erosivity of the modified formulation and secondly, to provide more comparative data with other acidic fruit drink products. METHOD: The study was a single centre, single blind, randomised placebo controlled 4 cell crossover design involving 12 healthy volunteers. The test drinks were orange juice, water, experimental blackcurrant juice drink with calcium and a proprietary blackcurrant juice drink. Enamel samples were retained in situ at the mid palatal regions using intraoral appliances and exposed to 250 ml volumes of the drinks 4 times per day during 15 working days. Measurements of enamel loss were made by profilometry. The same method was modelled in vitro. RESULTS: By day 15 the mean losses of enamel in situ for orange juice, water, experimental blackcurrant juice drink with calcium and blackcurrant juice drink were 1.70, 0.05, 0.44 and 2.75 microns respectively. At all bar one measurement, the loss of enamel was significantly greater for all fruit drinks compared to water. Losses caused by the blackcurrant juice drink with calcium were significantly less than the other two fruit drinks at all time points. Losses of enamel by day 15 in the study in vitro were 13.02, 0.00, 1.78 and 39.02 microns respectively. The blackcurrant juice drink with calcium was not significantly different from water at days 3 and 6, otherwise all pairwise comparisons for differences between the 4 drinks at each time period were significant. CONCLUSIONS: The methodologies in situ and in vitro again appear to correlate in ranking the order of erosivity of drinks. The data particularly from the study in situ allude to the very low comparative erosivity of the further modified experimental blackcurrant juice drink with calcium and support the further development of such drinks for public consumption.

Adult↗
PubMed1998

A method to measure clinical erosion: the effect of orange juice consumption on erosion of enamel.

OBJECTIVE: Acidic soft drinks are frequently implicated in dental erosion, but there are limited supporting data. Research is problematic due to the insidious nature of erosion and accuracy in assessing tissue loss. The aim of this study was to develop and validate, using a negative control, a model to accurately measure erosion in situ due to a single aetiological agent over a relatively short time period. METHODS: An intra-oral appliance capable of retaining an enamel sample was designed in order to assess the effect of orange juice consumption on enamel. The study was a single centre, randomized, placebo controlled, blind, crossover design. RESULTS: Ten subjects, each consuming 11 of orange juice per day for 15 days, showed significantly more erosion on the enamel specimens than the same subjects consuming 11 of water per day over the same time period, measurements undertaken with surfometry. The same investigation was performed in vitro. Again, orange juice was significantly more erosive; indeed, it was in the order of 10 times that produced in situ. Surface microhardness testing in situ and in vitro demonstrated statistically significant differences between exposed and unexposed areas after orange juice treatment. CONCLUSIONS: Changes produced by water either in situ or in vitro were always well within the baseline measurement parameters (+/- 0.3 micron) set down for the method and hence validated the clinical model in terms of reproducibility and accuracy in measurement. It is concluded that this method has confirmed the erosive potential of orange juice in situ. The method could have many applications to study dental erosion under highly controlled conditions and over realistic time periods.

Adult↗
PubMed1997

Evidence for the view that temporospatial integration in vision is temporally anisotropic.

In two experiments low-pass and high-pass spatially filtered versions of a base image were prepared and the effect of the order of delivery of sequences of filtered and base images investigated. A task that required subjects to discriminate 120 ms presentations of a full-bandwidth base image and degraded sequences that contained sets of three different spatially filtered versions, or mixtures of spatially filtered and full-bandwidth versions of the image, were used. Each set of images used in the degraded sequences was presented either so that within the 120 ms presentation window the spatial content swept from low to high spatial frequencies or from high to low. In experiment 1 twenty subjects discriminated between a base image and degraded sequences of an urban scene. Results showed both a significant overall effect of image order, with low-to-high spatial-frequency information delivery being mistaken more often for the full-bandwidth presentation than high-to-low, and that different sets of degraded image sequences varied significantly in the frequency with which they were mistaken for the full-bandwidth presentation. In experiment 2 a base and filtered versions of a human face were used in an identical task with twenty different subjects and a very similar pattern of significant results was obtained, although imposed on a lower overall error frequency than that obtained in experiment 1. It was concluded that the results of both experiments provide evidence for an anisotropic temporospatial integration mechanism in which availability of spatial information in a low-to-high spatial-frequency sequence results in more efficient integration than a high-to-low.

Adolescent↗
PubMed1996

Role of coarse and fine spatial information in face and object processing.

In 4 experiments the role of coarse (low-pass filtered) and fine (high-pass filtered) spatial information in guiding visual processing was studied in a same-different task. The second of a pair of sequential patterns was either a normal image or the first 100 ms was restricted either coarse or fine information before a normal image was shown for the rest of the presentation. This 100-ms cue could be from the immediately succeeding image (relevant) or from other images in the set (irrelevant). Analysis of response times and errors showed relevant coarse- and fine-scale cues were usually equally effective, but any differences favored fine-scale versions. Irrelevant fine-scale cuing was significantly more disruptive than coarse-scale cuing. No evidence of preferential cuing by coarse-scale information occurred in any experiment.

Adult↗
PubMed1996

The depiction of distance: a Bartelian analysis.

Work by Bartel has shown that observers make systematic errors when attempting to set a receding row of staves at equal intervals, and make even-more-pronounced errors in the same direction when drawing a similar row; consequently, the factors that contribute to this systematic distortion in spatial representation were examined. The results indicate that the tendency to overestimate nearer distances and underestimate further distances in pictorial space may be enhanced both by increasing the size ratio of the nearest and furthest pictorial elements and by increasing the angle of convergence of represented parallel contours. However, it is clear that size ratio is the more powerful independent variable. The reasons for this discrepancy are discussed and an explanation of the pattern of pictorial distortion, in terms of a compromise between an objective representation of the relative estimated distance of the depicted distances and an inaccurately anticipated optical projection, is proffered.

Depth Perception↗
PubMed1996

Effects of high-pass and low-pass spatial filtering on face identification.

If face images are degraded by block averaging, there is a nonlinear decline in recognition accuracy as block size increases, suggesting that identification requires a critical minimum range of object spatial frequencies. The identification of faces was measured with equivalent Fourier low-pass filtering and block averaging preserving the same information and with high-pass transformations. In Experiment 1, accuracy declined and response time increased in a significant nonlinear manner in all cases as the spatial-frequency range was reduced. However, it did so at a faster rate for the quantized and high-passed images. A second experiment controlled for the differences in the contrast of the high-pass faces and found a reduced but significant and nonlinear decline in performance as the spatial-frequency range was reduced. These data suggest that face identification is preferentially supported by a band of spatial frequencies of approximately 8-16 cycles per face; contrast or line-based explanations were found to be inadequate. The data are discussed in terms of current models of face identification.

Adult↗
PubMed1995

Viewing angle and the perceived orientation of pictorial elements: geometric or representational effects?

The role of geometric shape properties in determining the perceived orientation (heading) change of picture elements was investigated in four experiments. In experiment 1 the systematic change in perceived heading of each of a depicted team of horses which projected irregular geometric shapes was measured. In experiment 2, involving silhouettes, the perceptual axes of these same horse shapes, together with those of a pair of enantiomorphic deltoid shapes, were derived. These derived shape axes were used in experiment 3, along with single oblique contours, to determine the degree of heading shift as a function of the complexity and orientation of the shape. The degree of heading shift was remarkably similar for both silhouette shapes and the single contours when the axes were oblique but, whereas vertical orientation was predicted to abolish heading shift, this was only true for the deltoid shapes. In experiment 4 a possible explanation of the nonpredicted heading shift for the vertically oriented horse silhouettes was investigated. Subjects' individual estimates of the axes of the horse shapes, rather than a group mean value, were used to set the horse shapes to the vertical. When viewing was from two positions no significant heading change with view was found. Taken as a whole the data suggest that the geometric properties of patterns, rather than their representative nature, determine the very obvious heading shift when pictures are viewed from different angles.

Adolescent↗