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Biomedical subjects

E I Pearce

Publications and source records attributed to E I Pearce.

At least 19 recordsLinked to original sources
PubMed2001

An improved fluorophotometric method for tear turnover assessment.

PURPOSE: Scanning fluorophotometry is considered the "gold standard" to determine tear turnover rates (TTR). In this study, we attempted to improve the precision of basal TTR by fluorophotometry through a number of methodological changes. METHODS: By means of a timer program that produces audio cues, a new methodology that ensures confluence and a constant thickness of the tear film and minimization of reflex lacrimation as a result of the inhibition of the blink reflex was developed. This was compared with the standard protocol, both in a paired study and by a review of unpaired data. The minimum length of time required to monitor TTR measurements was also investigated. RESULTS: A significant improvement in correlation coefficient (r) of the log decay curve was observed as a result of changes in the protocol in both the paired (p = 0.016) and unpaired study (p < 0.0001). We determined that it was sufficient to monitor TTR for 10 min to obtain accurate results. CONCLUSIONS: We advocate that the changes be adopted as widely as possible for the precise and rapid measurement of basal tear turnover rates.

Adult↗
PubMed2001

What does the phenol red thread test actually measure?

PURPOSE: This study attempts to resolve whether the phenol red thread test (PRT) is a test of tear volume or tear production through comparisons with other techniques. METHODS: Twenty asymptomatic subjects (10 men and 10 women; average age 30.6 +/- 10.8 years) had PRT (Zone Quick, Menicon) results compared with tear turnover rate (by fluorophotometry; Fluorotron Master, OcuMetrics) and tear volumes (from tear meniscus height and back extrapolation from fluorometric data). RESULTS: PRT wetting was not correlated with either tear turnover or volume (by fluorophotometry or tear meniscus height) on a Pearson product moment correlation test (p > 0.05). CONCLUSIONS: No clear experimental evidence in favor of the PRT being a measure of tear production or volume was found. It is probable that the PRT measures uptake of a (small) amount of fluid residing in the eye, stimulates a low degree of reflex tearing, and reflects the absorption characteristics of the thread dependent on the biophysics or composition of tears.

Adolescent↗
PubMed2001

Effect of oral contraceptives on tear physiology.

Variations in sex hormones due to the menstrual cycle (and oral contraceptives) were evaluated for their effect on tear physiology. Subjects were 18 females taking oral contraceptives or their age matched controls (no medication), aged 21-33 years. Symptoms of ocular discomfort (visual analog scale), tear film structure (TearScope), non-invasive tear thinning time (HirCal grid), evaporation rate (ServoMed evaporimeter), osmolality (Nanolitre Osmometer), tear turnover rate, tear volume (Fluorotron Master), and tear protein levels (HPLC) were measured around day 2 (D2), actually day 1-4 and day 19 (D19) actually day 18-21 of the cycle. No significant differences were found for any tear parameters between D2 and D19 for either pill users or controls alone, or in the comparison of pill users with controls. No effect on tear physiology was found for serum hormone changes induced by oral contraceptive use or by normal cyclic variations in healthy young females.

Adult↗
PubMed2001

Plaque mineral induction and inhibition properties in the formation of supragingival calculus.

Several individual species of dental plaque bacteria have the ability to initiate the precipitation of calcium phosphate minerals in vitro; other plaque components have been shown to inhibit mineralisation. We have examined subjects' overall plaque mineralisation promoter and inhibitor properties, and have attempted to correlate them with supragingival calculus development over 6 months. Three-day-old plaque was collected from 22 adult subjects at the start and end of the study. To detect promoter activity, the plaque was placed in a suspension of brushite, the liquid phase of which was supersaturated with respect to hydroxyapatite. The extent of mineralisation was determined by the rise in phosphate concentration over 4 days. To detect inhibitor activity, plaque was placed in a similar suspension, which also contained hydroxyapatite. Promoter activity was compared with that hydroxyapatite, and inhibitor activity was compared with polyaspartate. The subjects' teeth were scaled at the start of the study, and calculus deposition was measured at the end using the Volpe Manhold method. Most plaque samples showed some promoter or inhibitor activity, or both, but no significant correlation existed between these activities and a subject's development of calculus. A significant inverse correlation existed between plaque mineralisation promoter activity and its inhibitor activity at the start of the study. Our results suggest that the nucleating and mineralisation inhibitory properties of young plaque will probably not be a useful target for a practical preventive methodology for supragingival calculus.

Adult↗
PubMed2000

Spatial location studies on the chemical composition of human tear ferns.

Tear ferns are the patterns formed when tears are allowed to dry on a clean smooth surface. The patterns have been categorised according to confluence of pattern, with less confluent ferns indicative of tear film abnormalities. Little is known about the mechanism that gives rise to this phenomenon. Previous work has concentrated on correlation of alterations in tear film composition on the ferning phenomenon. The present study takes a new approach by analysing the locations of chemical elements in the fern to understand how the ferns form. By means of SEM coupled with EDXA, Na, K and Cl were detected within the fern. Sulphur, indicative of the presence of macromolecules such as mucins and proteins, was only found at the very periphery of the dry tear drop. The results suggest that macromolecules do not play a direct role in the formation of the ferns. A model is put forward to explain the observation whereby proteins and mucins are precipitated selectively by increasing salt concentration at the drop margin.

Adult↗
PubMed1999

Individual variations of pH, buffer capacity, and concentrations of calcium and phosphate in unstimulated whole saliva.

In order to evaluate the risk of development of dental caries and/or of formation of dental calculus, salivary variables have often been used, but not with particular success. A reason for the apparent lack of association could be that the individual temporal variation of a characteristic was so substantial relative to the overall variation that it is not possible to characterize an individual by a single salivary measurement. The aim here was to examine the individual variation of pH, buffer capacity, and concentrations of calcium and phosphate and to compare it with the overall variation of the characteristics in order to shed light on the above problem. Eight weekly samples of up to 4 ml of unstimulated whole saliva were collected from 11 dental students before tooth brushing on their arrival at 8 a.m. in the dental school. Calcium was determined by atomic absorption spectroscopy, phosphate colorimetrically, and pH electrometrically. The buffer capacity was assessed by titration of the saliva sample from the pH initially observed to pH 3. It was found that within each individual the concentration of calcium and of phosphate, pH, the hydroxyapatite ion product and the buffer capacity varied considerably over the 7 weeks. The individual range frequently covered more than a third of the total range. Further, within each of the variables, single individuals could be found whose samples covered 60% or more of the overall range, whilst others covered less than 10% of the range. It was therefore concluded that, although collected at the same time of the day, pH, buffer capacity and concentrations of calcium and phosphate in unstimulated whole saliva in the single individual vary so much that characterization of individuals and of their saliva based on a single salivary analysis is unreliable and hazardous.

Buffers↗
PubMed1999

Effect of in situ plaque mineral supplementation on the state of saturation of plaque fluid during sugar-induced acidogenesis.

Dental plaque fluid is normally supersaturated with respect to enamel mineral but this may change to a state of undersaturation when plaque pH falls following sugar exposure, placing the adjacent enamel at risk of caries. We have determined the saturation status of the fluid in both resting and fermenting plaque following mineral supplementation. Eleven subjects abstained from oral hygiene and rinsed their mouth 3 times/d for 3 d with a placebo solution or with test solutions designed to enrich plaque with hydroxyapatite or fluorhydroxyapatite. On the morning of day 4, plaque samples were collected before and after exposure to 10% sucrose. Compared to the placebo, use of the test rinses resulted in significantly higher concentrations of Ca, P and F in plaque residue. In plaque fluid, higher post-sucrose Ca2+ free concentrations and saturation levels with respect to enamel mineral and fluorapatite were found after use of the hydroxyapatite rinse compared to the placebo, effects that probably resulted from the release of cell-bound Ca2+ as well as from the dissolution of apatite. Thus, some evidence was obtained that the test mouthrinses can counteract the fall in saturation level found when plaque is exposed briefly to sucrose. Potential long-term benefits of the test mouthrinses deserve further study.

Acetates↗
PubMed1999

Prophylactic mineral enrichment of approximal dental plaque.

Most research on the chemical modification of dental plaque has used material from buccal and lingual smooth surfaces of teeth--plaque that is readily accessible to treatment solutions. The aim of this study was to test, on the more sheltered approximal plaque, the effect of a mouthrinse previously found to be effective in raising calcium, phosphate, and fluoride concentrations in accessible plaque. Five young adults participated in a blind, cross-over trial to compare a Ca-P-MFP-urea test rinse and a NaCl placebo rinse. For 6 days, subjects rinsed twice per day after their normal toothbrushing, using 10 ml of rinse solution for 30 seconds and a fresh 10 ml for a further 30 seconds. A non-fluoride toothpaste was used and normal flossing was withheld. Plaque was collected before rinsing and again 16 hours after the final rinse from all approximal sites except those between the lower anterior teeth. Pre- and post-rinse calcium values were 291 +/- 100 and 511 +/- 107 nmol/mg protein (mean +/- SD) respectively for the test rinse, and 368 +/- 223 and 306 +/- 125 nmol/mg protein respectively for the placebo. Analysis of variance showed that the test rinse had a significant effect on plaque calcium but not on phosphate or fluoride. Mean calcium values of about 2,400 nmol/mg protein have been obtained previously in smooth-surface plaque after use of the test rinse. The reduced effect here is probably due to restricted access of the rinse solution.

Adult↗
PubMed1998

Fluoride distribution in sound and carious root tissues of human teeth.

Proton probe analysis has been used to provide for the first time quantitative F concentration data in carious root tissues from subjects consuming water containing 1 ppm F. In small lesions at the neck of the tooth with minimal tissue loss the F concentration was significantly higher at the outer lesion edge than at the outer edge of adjacent sound root tissue. In one sample with high F values the lesion edge had 19,000 ppm F and the adjacent sound root surface 5,400 ppm F microg F/g apatite). In large lesions with extensive cavitation F was again concentrated in the outer edge of the lesion and was significantly higher (1,800-4,100 ppm) than in adjacent sound inner dentine (190-290 ppm). Fluoride concentrations varied markedly along the outer edge of both normal and carious root tissues. Fluoride increase at the lesion edge is not an effect of tissue shrinkage but probably a result of remineralisation events during caries. This additional F may be expected to increase tissue resistance to further acid attacks.

Acids↗
PubMed1997

Dissolution of powdered human enamel suspended in acid solutions at a high solid/solution ratio under a 5% CO2 atmosphere at 20 degrees C.

The aim was to examine the nature of enamel dissolution in aqueous suspensions with a high solid/solution ratio and in a CO2-rich atmosphere. Before experimentation, a water-saturated mixture of 95% N2-5% CO2 was passed through the acid solutions for 24 hr. Samples of 2 g of powdered enamel were suspended in 7 ml of either 5 or 10 mmol/l HClO4, with or without 2 parts/10(6) fluoride and kept gently agitated for 24 hr in the above atmosphere. The same enamel samples were repeatedly exposed to fresh acid for 26 runs. All experiments were duplicated. The aqueous phase was analysed after 20 min and 24 hr for calcium, phosphate, fluoride, chloride, sodium and magnesium. It was found that after 20 min the fluoride was invariably taken up in the enamel and the solution was supersaturated with respect to hydroxyapatite with pH ranging 6.7-5.6. During the following 24 hr pH increased further, the supersaturation remained unchanged and the concentrations of calcium and phosphate in solution decreased. In contrast, sodium, magnesium and chloride were released from enamel during the entire period. In the later runs, the supersaturation with respect to hydroxyapatite was only modest and the decrease of calcium and phosphate concentrations limited, as were the release of sodium, magnesium and chloride. It is concluded that despite a CO2-rich atmosphere, calcium, phosphate and carbonate were released from enamel and quickly established a supersaturation with respect to hydroxyapatite with a secondary reprecipitation of mineral. It indicates that within the dental caries lesion in vivo, lesion fluid cannot exist undersaturated with respect to enamel apatite.

Acids↗
PubMed1997

A computer program for correlating dental plaque pH values, cH+, plaque titration, critical pH, resting pH and the solubility of enamel apatite.

A computer program was written in Visual Basic (Microsoft) to calculate (a) the area between a plaque pH curve (as seen after a sucrose rinse) and either a resting pH (around pH 7) or a critical pH value (around 5.5) above at least parts of the pH curve; (b) the solubility of apatite at the pH values in plaque; (c) the area between the plaque pH solubility curve and the apatite solubility at the resting pH/critical pH; (d) the area between plaque cH+ curve and the cH+ value at resting pH/ critical pH; and (e) the area between a plaque pH curve and a cut-off pH value below the curve, e.g. pH 3. It was found that because both the cH+ and the solubility of apatite increased logarithmically with a pH drop, the two latter area functions (d, e) were basically different from those based directly on pH curves. Thus, pH changes around the resting pH value had little effect on areas calculated from concentrations of H+ and solubility. In contrast, a small pH change around pH 4 had a strong impact on both demineralization potential and areas based on cH+. Also, because of the logarithmic nature, demineralization potentials were generally large in comparison to remineralization potentials, a point that has hitherto received little attention.

Apatites↗
PubMed1996

Characterization of rat HSA/CD24 protein bearing the B lineage-restricted epitope recognized by MAb HIS50.

HIS50 MAb recognizes a GPI-linked molecule on the surface of rat cells committed to the B lineage but is absent from cells of other hematopoietic lineages. Eukaryotic expression cloning of the cDNA has revealed that HIS50 recognizes a rat homologue of human CD24 and murine HSA. CD24/HSA exists in multiple glycoforms and plays an important role in hematopoietic and neural cell development. HIS50 is significant in that it is the only, presently available, anti-rat CD24/HSA MAb. Furthermore it is the only reported MAb with specificity restricted to B cell forms of CD24. Here we report Western blot analysis of HIS50 antigen (ag). In rat bone marrow HIS50 MAb recognized MW species in the range of 35-70 kDa. These species were shown by immunomagnetic cell sorting to be all derived from the HIS50+ cell subset. In other tissues with varying HIS50 levels as judged by immunostaining, apparent levels of HIS50 ag in the 35-70 kDa range varied accordingly. Thus, Western blot data corresponded to the immunostaining data of HIS50 ag, and the size distribution of B-restricted forms of rat CD24 appeared as wide as that reported for the more extensively expressed forms of human and murine CD24. N-Deglycosylation of cell lysates from lymphoid organs reduced the signal in the 35-70 kDa range, without appearance of lower MW HIS50-reactive species. Thus, unlike certain epitopes on human and murine CD24, HIS50 epitopes appeared (partially) N-linked carbohydrate dependent. The data reported here provide a basis for the further use of HIS50 MAb in studying the role of the highly heterogeneous CD24 molecules in cell development.

Amidohydrolases↗
PubMed1996

Fluoride content of the enamel and dentine of human premolars prior to and following the introduction of fluoridation in New Zealand.

The fluoride content of the enamel and dentine of premolars was used as a determinant of the availability of ingested fluoride in New Zealand prior to and following the introduction of water fluoridation 40 years ago. Premolar teeth, which developed during the periods (PRE and POST respectively) under study, were selected from teeth extracted from 12 to 14-year-old children resident in different geographic areas in the country. The fluoride content, determined by multiple proton microprobe analyses, of surface enamel, deep enamel, and dentine, were for PRE teeth 440, 65 and 115, respectively. For POST teeth the mean values were significantly (p<0.001) higher, by 69, 29 and 102% respectively. The relevance of the change in fluoride content was assessed by comparison with published reports on the fluoride content of teeth developed in communities exposed to low (<0.5 ppm), optimal (1-2 ppm) and high (>3 ppm) naturally occurring fluoride levels in drinking water. The PRE teeth had a fluoride content associated with a low fluoride exposure and POST teeth with optimal fluoride exposure during tooth development. It was concluded that fluoride availability in New Zealand teeth had increased over the past 30 years but this increase is compatible with exposure of the community to optimal rather than excessive levels of ingested fluoride.

Adolescent↗
PubMed1995

Stoichiometry of fluoride release from fluorhydroxyapatite during acid dissolution.

Release of F from fluorhydroxyapatite (FHAp) during acid dissolution was studied to validate the use of this mineral as a plaque reservoir of F. FHAp minerals having a wide range of F concentrations were synthesised by aqueous precipitation, and samples repeatedly exposed to 50 mM lactic acid solution, pH 4.5, or similar lactic/acetic/formic acid mixtures, until dissolution was complete. While the Ca/P ratio in solution remained relatively constant and close to the ratio in the solid, the solution F/Ca ratio invariably changed during dissolution. During initial stages the F/Ca solution ratio was lower than in the solid but rose to reach a plateau higher than in the solid as dissolution progressed, an effect that was more pronounced with low-F FHAp. With these minerals the plateau F/Ca level never reached 0.2, suggesting that a F-enriched FHAp rather than pure fluorapatite precipitates during dissolution. It is concluded that a high-F FHAp mineral would best serve as an apatitic plaque reservoir of F.

Acetates↗
PubMed1995

Studies on the influence of fluoride on the equilibrating calcium phosphate phase at a high enamel/acid ratio.

Data obtained in a previous study suggested that brushite is the solubility-determining phase when enamel is first exposed to acid solution in a series of repeated equilibrations. Fluoride in solution might be expected to inhibit brushite formation, and experimental studies at low solid/solution ratio support this. We have now re-examined the effect at a very high ratio, in an attempt to mimic what happens in an enamel caries lesion. Powdered enamel was repeatedly exposed to HCl solution, 10-70 mmol/l, containing 2 ppm F, for 24 h, initially in a ratio of 1 g/3 ml. Ion activities were determined after 20 min and 24 h and potential plot diagrams constructed. In early repetitions the -log (Ca2+) (OH-)2 vs. -log (H+)3(PO4(3-)) points tended to follow the brushite line, rather than the hydroxyapatite (HAp) line which one would expect if enamel behaved as pure HAp. Solution F was below measurable limits after 20 min and F then had little influence on the brushite equilibrating phase. In later (> 13) repetitions, points fell closer to the HAp line, with or without F added to the acid solution. However, added F, which was not then completely removed from solution, caused the slope of the regression line through the points to approach the Ca/P ratio of HAp, and therefore may have had a small effect in reducing the brushite phase. It is concluded that high solid/solution ratio, a previously neglected factor in enamel dissolution studies, has a profound effect in increasing the manifestation of a brushite surface phase and reducing the inhibitory effect of F on this phase.

Apatites↗
PubMed1995

The diffusion and enzymic hydrolysis of monofluorophosphate in dental plaque.

Although the ability of dental plaque to hydrolyze sodium monofluorophosphate (MFP) has been known for some time, its effect on the F- concentration at the plaque-enamel interface is undefined. We have determined enzyme kinetic values for MFP hydrolysis and diffusion coefficients so that the penetration and degradation of MFP in plaque can be modeled by computer. The KM and Vmax values for natural human plaque were 1.77 mmol/L and 41.4 nmol/min/mg protein, respectively, at pH 8.0. At pH 6.0, the Vmax was lower, 15.6 nmol/min/mg, but KM was not significantly different. Competitive inhibition by orthophosphate gave a Ki of 4.55 mmol/L. The diffusion coefficient for MFP in artificial plaque was 1.91 x 10(-6) cm2/sec. When these data were used for mathematical modeling of the effects of rinsing with MFP and F- solutions, compared with an equivalent NaF application, the concentration of F- from MFP was lower at the inner surface of plaque, and the peak occurred later. Both pH and plaque thickness had a marked effect on the amount of MFP that could penetrate: At pH 8.0, almost none reached the inner surface of a 1-mm-thick plaque intact. At pH 6.0, however, more MFP was able to penetrate, due to lower MFPase activity. While MFP diffusion is inherently slower than that of F-, enzymic degradation increases the gradient for inward diffusion. If the conventional view that MFP in toothpaste acts as a source of F- is true, then MFP toothpaste should be formulated to optimize MFPase activity in dental plaque.

Adult↗