A b stra c ts Caries Res 1992;26:209-238
Abstracts of Papers Presented at the 39th ORCA Congress
1 Antimicrobial Factors of Saliva in Relation to Dental Caries and Mutans Streptococci in Saliva J. Tenovuoa- *, H. Jenischh, T. Soitkka ", /.. Karhuvaara“ “ Institute of Dentistry, University o f Turku, Finland: b Dental Institute, University of Rostock, FRO The possible association between salivary nonimmunoglobulin (lysozyme, lactoferrin, hypothiocyanite, agglutinins) or immunoglo bulin (total IgA, anti -Streptococcus mutans IgA) antimicrobial fac tors, and the prevalence o f dental caries was studied in 59 young adults. These antimicrobial factors were also analysed in relation to the salivary levels of mutans streptococci (MS), quantified on mitissalivarius agar supplemented with 15% sucrose and bacitracin. The levels of MS correlated significantly (+0.31, p B > A > E . Linear correlation coefficient comparing F uptake to [Fu,„jc] (r = 0.938) indicates the enhanced benefit (F uptake) for MFP/Ca over MFP/silica is likely the result o f higher [Fil)nic] o f the calcium-based MFP dentifrice. Under the conditions o f this study, no MFP formula tion performed equivalent to NaF/silica.
16 The Effect of Chiorhexidine-Fluoride-Strontium Gel in Preventing Enamel Softening in vitro S. Spets-Happonen *, H. Luoma, L. Seppii Department of Preventive Dentistry and Cariology, University of Kuopio, Finland Previous results suggest that the addition of strontium (Sr) into a chlorhexidinc(CHX)-fluoride combination improves its caries-pre ventive effect. The aim of the present study was to compare the effect of different Sr concentrations in CHX-fluoridc gel in preventing the softening of the enamel during bacterial fermentation. Bovine ena mel slabs were covered with 10 pi gel as follows: (1) placebo gel. (2) gel with 0.20% CHX and 0.16% sodiumfluoridc (NaF), (3) gel with CHX. NaF and 15 ppm Sr. (4) gel with CHX, NaF and 50 ppm Sr, (5)
gel with CHX, NaF and 250 ppm Sr. A volume o f 0.2 ml o f Streptococ cus mt/M/w-buffer suspension, 0.2 ml 10% sucrose solution and 0.2 ml distilled water were centrifuged to get the cells as a plaque-like layer on the top o f the gel-covered enamel. After 24-hour incubation the pH fall o f the fluid was significantly smaller in all test groups than in the control group. The addition of Sr seemed to have a slight inhib itory effect on the pH fall. All test gels prevented significantly the softening of the enamel during bacterial fermentation measured as Vickers hardness. In all Sr groups the enamel softened significantly less than in the group with CHX and NaF. The softening was least in the group with 250 ppm Sr. Total calcium and phosphorus contents of the cells and fluid after incubation were the smallest in the group with 250 ppm Sr. These results suggest that the addition of Sr into CHXfluoride gel improves the ability of this combination to prevent ena mel softening.
17 Remineralization of Deep Enamel Subsurface Lesions in a Medium with Time-Dependent Saturation II.C. Klinger*, W. Wiedemann, R. Jahns Klinik und Poliklinik für Zahn-, Mund- und Kieferkrankheiten, Universität Würzburg. BRD Time-dependent variations of the Ca++ and PO^ saturation in the remineralization medium will supposedly influence the local and the total mineral balance in the diffusion reaction system, initial caries. We measured the total mineral uptake and its local distribution in rather deep artificial caries-like lesions (500 pm deep, bovine ena mel). Parameter o f the experimental groups was the rise time of the mineral saturation in the remineralization solution. Using a constant Ca concentration o f 4 mmol/l (Ca:P = 1 ,1 ppm F~), the pH was in creased from pH 4 to 7 with a slope o f * , 0.20,0.10,0.05, and 0.025 pH/ min. When pH 7 was reached it was kept constant at this level for such a time that the ratio of the period of under- and supersaturation equaled 1 :7. This regime was repeated until the total incubation time amounted to 2 times 12 h. Mineral content in the lesions of the 2-mmthick specimens was measured before each experimental step by quantitative radiography combined with digital image processing. The permeability of the lesion surface was determined by dye pene tration. Significant mineral uptake was observed only in the experi mental group with 0.2 pH/min. i.e. 30 min to cover the interval from pH 4 to 7. Even in the rear of the deep lesion a marked mineral in crease was found. Using the statistical method o f discriminant analy sis we found that the parameters'total mineral balance’, ‘mineral bal ance front-rear’ and ‘surface permeability’ contributed most to the separation o f the experimental groups. The results are interpreted by means of a mathematical two-component model in terms o f reaction and diffusion rates.
18 De- and Remineralizing Hydroxyapatite as Bioactive Filling Material W. Wiedemann*. H.G. Klinger Klinik und Poliklinik für Zahn-, Mund- und Kieferkrankheiten. Universität Würzburg, BRD Dental restorative materials commonly used often have consid erable shortcomings. Their physical and chemical properties vary from those o f dental enamel. In 1989 we presented a new material, a special kind of hydroxyapatite, some essential properties o f which are
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ppm F. but between 1,500 and 2,500 ppm no further increase oc curred. Microradiography revealed mineral uptake and loss to occur in the same specimens at different depths: e.g. specimens showing overall net mineral uptake were partly remineralised in the original lesion body while a new lesion body was formed at depths beyond the original lesion front. This resulted in laminated lesions. The study re vealed a dose-response behaviour of fluoride dentifrices in a pHcycling model, and some mechanistic aspects of the fluoride action.
19 The Video Camera Compared with the Densitometer as a Scanning Device for Microradiography M.D. Lagerweija- *, J.M. ten Cate*, E. deJosselin deJongh * Department of Cariology and Endodontology, Academic Centre for Dentistry (ACTA), and b Inspektor Research Systems, Amsterdam, The Netherlands Microradiography is the most accurate and widely used method to determine mineral content profiles in enamel specimens. Origi nally, microscopes equipped with a densitometer were used for quan titative microradiography. More recently image analysis systems, comprising video (CCD) cameras and dedicated software, have been introduced. With the CCD camera scans can be made instantane ously, and scanning areas can easily be selected on a video screen (in pseudo-colours). In densitometry the most prominent system re quirements are a precision cross table and an accurate measuring slit. For the CCD camera the specifications for homogeneity of specimen illumination and accuracy must be high. It should be considered that the number of grey levels is limited to 255, which theoretically could jeopardise the accuracy of the measurement. With both systems working at optimal performance in our laboratory, we have com pared the enamel lesion profiles produced with the two techniques. No differences were found in the sensitivity and reproducibility of the polynomial regression analysis of the aluminium stepwedge data. Also the mineral profiles and the relevant lesion characteristics were found to match. Therefore it is concluded that both systems can pro vide equally reliable information on enamel lesions. The two systems are now being combined to make the best use of their respective ad vantages.
20 Reliability Investigation of an Intraoral Model H.M. Proskin *, D.T. Zero Eastman Dental Center. Rochester, N.Y., USA There has been much recent activity toward the investigation of the validity and reliability o f intraoral models for use as possible sur rogates for clinical trials for providing comparative information re garding the therapeutic effect o f anticaries agents, as is often re quired in submissions to regulatory agencies. This is particularly crit ical in the current environment, since long-term clinical trials, which can no longer use placebo groups, must now generally involve ex tremely large sample sizes when performed for this purpose. The
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present project is a component of ongoing work for which the long term goal is to characterize and document the reliability o f the model described by Zero et al. (1992 AADR Abstract], Five subjects used each of three dentifrices (table), during which time an appliance was worn bearing bovine enamel blocks (situated on either side of the mouth). On each block, ten replicate observations o f percent mineral recovered following intraoral exposure were obtained. Reliability was quantified through the calculation o f intraclass correlation coef ficients (ICCs) and their associated 90% lower confidence bounds (LCBs). as well as estimates of the reliability o f the blockwise means, obtained using the Spearman-Brown prediction formula. The results were as follows: Dentifrice
Side of mouth
ICC
90% LCB
Reliability of block means
Placebo
left right left right left right
0.60 0.44 0.70 0.86 0.84 0.63
0.41 0.25 0.52 0.74 0.72 0.44
0.94 0.89 0.96 0.98 0.98 0.95
250 ppm F 1,100 ppm F
These data suggest that blockwise mean scores possess excellent reliability for characterizing the percent of mineral recovered follow ing intraoral exposure.
21 Importance of Experimental Time during in situ De-/Remineralisation Studies F.A. Damato a *, D.R. Stirrups", K.W. Stephen*, A. Cummings', R. Strang' Departments of “ Oral Medicine and Pathology; b Orthodontics, and ‘ Clinical Physics and Bioengineering, University of Glasgow, Scotland. UK When testing P products with in situ model systems, the results may depend on the duration of the experiment. This time effect was investigated using an in situ single-section model which allows min eral content of enamel sections to be measured longitudinally. Thir teen volunteers were recruited in a cross-over study using two pastes with concentrations of 1,000 and 2,500 ppm P , respectively. Microradiography/microdensitometry were performed prior to the study and at 2 and 4 weeks. Changes in mineral content between 0 and 2 weeks, 2 and 4 weeks, and 0 and 4 weeks were calculated. Analysis o f var iance for Az mineralisation change for the two time periods (0-2 and 2-4 weeks) showed a significant fluoride dose effect (p = 0.0012) as well as a significant time period response (p = 0.0446) for the two pastes. In addition there was a significant intersubject difference (p = 0.0001). The rate of change o f Az for the two pastes for the second time period (2-4 weeks) was highly significant (p = 0.0006) but not for the first time period. The change that occurred during the second time period accounted for the significant dose effect seen over the 4 weeks (p = 0.0001). In situ studies may miss true differences between P products because of insufficient experimental duration.
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similar to those of dental enamel. Unlike the hydroxyapatite used for surgical purposes this special material takes part in the de- and re mineralization process in the mouth. During acid attack the surface softens like that of enamel giving rise to a large specific pore surface area. This phenomenon enables the hydroxyapatite to remineralize as fast as enamel does. Because of these properties we investigated whether this bioactive hydroxyapatite is suitable as a restorative ma terial. In a preliminary clinical test the material proved to be mouthresistant for 3 years. This encouraged us to start larger clinical trials. Before placing the new hydroxyapatite inlay it has to be milled from the bulk material w'ith high precision. To this end we developed a new copy milling machine which duplicates a master model with a preci sion o f about 10 ¡xm including the occlusal surface. The material and the milling machine will be presented and first clinical observations wall be reported.
22 Effect of Sugar-Free Chewing Gum on in situ Enamel Lesion Remineralization S.L. Creanor*. W.H. Gilmour, R. Sunni’. R.H. Faye, D.A.M. Geddes. A.F. Hull University of Glasgow, Scotland, UK Chewing gum after eating can raise lowered plaque pH [Jensen and Wefel: Br Dent J 1989;167:207-208] and increase salivary flow [Dawes and MacPherson: Caries Res 1991:25:225], The aim o f this study was to investigate whether remineralization by a fluoridated dentifrice could be enhanced in conjunction with the use of a sugarfree gum. Enamel lesions were mounted onto in situ appliances worn by 12 subjects [Creanor et al: Caries Res 1986;20:385-391] using an 1,100 ppm NaF dentifrice 2 x a day (test and control) and gum 5 x a day (test). A cross-over design was used. Mineral content was as sessed at baseline and after 7 weeks using microradiography. For Az (n = 264). linear regressions were made for test and control for each volunteer of the difference between baseline and final Az values of each lesion against baseline Az value. Predicted differences between test and control were calculated for a fixed baseline Az value. Five subjects had significantly greater remineralization with chewing gum. 1 subject showed significantly greater remineralization on control and 6 subjects gave inconclusive results. For the Az values, there was 18.2% remineralization for the test phase (p = 0.0006) compared to 12.1% (p = 0.003, both 1 tailed) for the control. Weighted analysis of variance showed this trend was almost statistically significant (p = 0.07, onc-tailcd). Although there was a trend towards greater remineralization in both the surface layer and lesion body during the test phase, these differences were not statistically significant. Results sug gest chewing sugar-free gum after eating may enhance enamel lesion remineralization beyond that obtained with fluoridated dentifrice alone. Supported by a grant from Wm. Wrigley Jr. Company, Chicago, USA.
23 Effect of Varying Dentifrice Formulation on in situ Enamel De-and Remineralisation P.W. Smith*. S.M. Higham, W.M. Edgar
same subjects following a 2-min rinse with a 10% (w/w) slurry of each dentifrice followed 10 min later by a 2-min 10% (w/v) sucrose rinse. Mean cH areas ± S D (pmol min) and mean pH ± S D were: 0 ppm F: 6.17± 8.9 and 6.11 ±0.32: 250 ppm F: 2 .6 5 ± 6 .9 4 and 6.13±0.19; 1,000 ppm F: 2.87 ±5.36 and 6.35 ±0.27; 1.500 ppm F: 0.70 ±2.57 and 6.59±0.60. The differences observed were not significant at the 5% level. Preliminary results suggest that significant reductions in lesion extent are observed when the dentifrice contains fluoride although this did not significantly affect cH area or minimum pH, indicating that fluoride may promote in situ remineralisation without a demon strable inhibitory effect on plaque acid challenge.
24 Development of an in situ Model for Studying Mineral Changes in Dentin W. Zlitmg. A.J. Dunipace. S.A. Kelly. G.K. Stookey* Indiana University School of Dentistry. Indianapolis, Ind. USA Two double-blind, crossover studies were conducted to develop an in situ model for studying fluoride uptake (D FU ), mineral chang es (MC) and lesion depth (L) in dentin. A sound dentin specimen (for D FU ) and a carrier containing 100-urn sections of sound and soft ened dentin (for MC) were mounted in partial dentures and subjects were randomly assigned to use a fluoride (F) or placebo (P) denti frice for a designated test period. After the test period, the specimens were removed and analyzed for DFU and MC by a microdrill biopsy method and microradiography (MR), respectively. Using new speci mens the test period was repeated with subjects using the second den tifrice. In the first study in which 20 subjects brushed their teeth 2x a day for 4 weeks, F was numerically more effective than P in promot ing DFU and reducing demineralization o f sound dentin and was sig nificantly more effective in softened dentin (p >0.05). In the second study, 15 of the most reliable subjects brushed for 1 min, 3x a day for 2 weeks. Data showed significantly different DFU o f 3.84 ±0.65 and 18.49±4.9 ug F/cm2 after P and F. respectively. MR analyses indi cated F significantly reduced sound dentin demineralization (AZ = 354 ± 99 for F and 1,201 ± 320 for P). and in carious dentin. F and P re sulted in numerically different AZ values o f 796 ±296 and 1,897 ± 624, respectively. Lesion depths were similar. As modified, this in situ model can detect significant differences in DFU, MC and L o f dentin.
Department o f Clinical Dental Sciences, University of Liverpool, UK
Caries Diagnosis 25 Prediction of Caries Experience at Age 15 by the State of Primary Teeth at Age 6 N. An*. M. Vehkalahti. S. Helminen Institute of Dentistry, University of Helsinki. Finland Two groups of children were selected in the present study accord ing to the DMFT index at age 15. The low-risk group (n = 159) con sisted o f children with DMF teeth no greater than 2. Those with 5 or more DMFT were assigned to the high-risk group (n = 187). All the children were followed from 6 to 15 years of age. Data were collected from the patients’ charts with annual dental recordings for each indi vidual. Prediction was made according to three indicators: (1) the number of df teeth in primary molars: (2) dfs in the proximal surfaces of primary molars, and (3) the experience of caries in any primary teeth before age 6. Sixty-eight percent of children with dft = 0 in pri
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Both plaque pH profiles and in situ enamel de- and remineral isation models can be used to provide information on potential car ies-related phenomena. This study was carried out to investigate the responses to dentifrices having a range o f fluoride levels. Artificial le sions were produced in vitro in sound extracted human premolars and divided to give three sections. One section was used as a control and the other two mounted onto brackets, covered with gauze and etch retained to the lower right first molar. During the first 3 weeks of the trial. 8 subjects used a dentifrice (3 x daily) with a fluoride con centration o f either 0 or 250 ppm and during the second part o f the trial with either 1,000 or 1,500 ppm. The lesions were removed, sec tioned and ground pianoparallcl to 80 pm and examined by polarized light microscopy, microradiography and image analysis. Mean lesion widths (u m ± S D ) were: control: 69.03 ± 12.99: 0 ppm F: 102.97± 10.95; 250 ppm F: 58.5 ± 21.24 with significant differences (p - *, C. Dawes'' Departments of a Anatomy, and b Oral Biology. University of Manitoba, Winnipeg, Canada When gum containing sucrose is chewed, there is the potential for promotion o f caries by the sucrose but also anticariogcnic effects from the stimulation o f salivary' flow. This study, on 5 male and 5 fe male subjects, investigated the change in the flow rate and bicarbo nate concentration in whole saliva stimulated by chewing Trident Peppermint® (1.8 g) and Doublemint® (3.0 g) chewing gums over a 20-min time period. For 15 subjects, salivary film velocity was also es timated on the buccal surfaces of the upper anterior teeth (where the velocity is normally lowest) by the method o f Dawes et al. [J Dent Res 1989;68:1479-1482]. In the first minute of chewing gum stimulation, salivary flow rate peaked at 4.3 ml/min and then fell gradually over the 20 min to a value of 1.4 ml/min. After 3 min of stimulation, salivary bicarbonate concentration peaked at 15 mmol/l and then fell gradu ally to 12 mmol/l over the 20 min o f chewing gum stimulation. There was little difference with respect to salivary flow rate or bicarbonate concentration between the two gums. The estimated mean salivary film velocity on the buccal surfaces o f the upper anterior teeth when salivary flow was unstimulated was 0.75 mm/min. With stimulation of salivary flow by the consumption o f sour lemon drops and use of chewing gum, the film velocity increased to 1.05 and 4.5 mm/min, re spectively, although the flow rate o f whole saliva was greater with the lemon drops than with the chewing gum. These data will be o f value in modelling the cariogcnic potential o f chewing gum containing fer mentable carbohydrate.
56 The Effect of Acupuncture on Salivary Secretion Rates in Patients with Radiation-Induced Xerostomia: A Preliminary Report M. Blom, I. Dawidson*, B. Angmar-Mânsson, G. Johnson Department of Cariology. Karolinska Institutct, Stockholm, Sweden The aim o f this study was to investigate the effect of acupuncture on xerostomia caused by irradiation treatment o f tumors in the head and neck region. The material comprised 40 subjects, all suffering from xerostomia after full dose (64 Gy) irradiation of the head and neck. Salivary flow rates for resting and paraffin-stimulated saliva were determined prior to the commencement of the acupuncture treatment. The patients were randomly assigned to an experimental group or to a control group. Two series o f acupuncture treatment (24 treatments) were given to the experimental group, and the control group received superficial acupuncture (placebo), also in two scries.
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between the two groups o f subjects. However, in subjects with low sa livary flow rates, recovery' was significantly slower than in subjects with good flow rates. The initial level had not been regained after 20 min. At the sublingual site, pH recovery was fastest. The initial level was reached in 1 min in the group with good salivary flow rates. It is concluded that consumption o f a low-pH drink increased salivary flow rates causing rapid pH increases, but that when the stimulus is over, pH recovery depends on the resting salivary flow rate. A longlasting decrease in pH is therefore observed in low flow rate subjects, especially at sites where oral clearance is slow.
57 Inhibition of Calcium Phosphate Crystal Growth by Lipoteichoic Acid J.J.M. Damen*. J.M. ten Cate Department o f Cariology and Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), The Netherlands The accumulation of organic matter in natural enamel and denti nal lesions is thought to be a major impediment for their remineral ization. A substantial part o f this matter consists o f compounds o f bacterial origin. Among these may be lipoteichoic acids (LTA), which because o f their polyanionic nature could be powerful inhibitors of crystal growth. We have purified LTA from a freshly isolated Strepto coccus sanguis strain and determined its effects on the crystal growth of two calcium phosphate salts, hydroxyapatite and dicalcium-phosphate-dihydrate (brushitc), in supersaturated solutions. The growth rate o f seeded crystals (0.1 mg/ml) in solutions of 1 mM CaCl2, 7.5 mM KfLPO.. 50 mM Hepes, pH 7.2, was found to be reduced in the pres ence o f both native LTA and its dclipidated derivative, which was ob tained by mild alkaline hydrolysis. LTA at concentrations (deter mined and expressed as P 0 4 units) over 200 uM inhibited growth completely, but at very low concentrations (10-40 pM P 0 4) the growth o f hydroxyapatite was slightly stimulated. It was concluded that LTA is a strong inhibitor o f crystal growth, and the inhibitory ef fect is almost entirely accounted for by its polyglyccrophosphate backbone.
58 Surface Interactions between Na-Lauryl Sulphate and Triclosan Measured by Ellipsometry Th. EricsorT *, G. Holla''. H. ArwiiT, R. Bjorklundc “ Department of Cariology, University of UmeS, Sweden; b Pedodontics, University o f Oslo. Norway; c Physics and Measurement Techniques, University of Linköping, Sweden Sodium lauryl sulphate (SLS), a surfactant, and the antibacterial compound Triclosan are components o f some toothpastes. Clinical experiments have indicated a synergistic effect resulting in more ef fective removal o f dental plaque. We have used ellipsometry to study the uptake on a methylated and thus hydrophobic silicon surface of each compound singly and in combination. Ellipsometry is an optical technique which allows quantitative measurement of thickness of monolayers at a solid/liquid interface. We found that SLS was rapidly adsorbed from a 0.03% solution on the hydrophobic surface in a 10to 15-A thick layer. Complete desorption was found when the liquid phase was substituted by a phosphate buffer (PBS). Triclosan was taken up from a 0.006% solution in a much thicker layer, 40-50 A. The final thickness was obtained after 5 min. Triclosan was rapidly
and also completely desorbed by PBS. When a combination of the two test compounds was studied a different pattern was obtained. In the initial phase a rapid uptake o f material to the surface was ob served resembling the reaction observed with Triclosan alone. The initial phase, which lasted for 2 min, was followed by a short period of desorption of approximately 20% o f the thickness. This second phase was followed by a third phase in which the building up o f a succes sively thicker layer was observed. Equilibrium was reached after ap proximately 20 min at a thickness of 100-110 A. Desorption was com plete and rapid when PBS was introduced in the system. These exper imental data show a synergistic interaction between the two compounds in support for the biological synergism observed clini cally.
59 Studies on the Nature of the Interaction between Salivary Proteins and Dental Enamel M. Hykke*. G. Holla Dental Faculty, University of Oslo, Norway Salivary proteins are rapidly adsorbed to enamel surfaces forming the acquired pellicle, which is assumed to provide protective func tions for the enamel surfaces. The mechanisms by which proteins ad sorb to solid surfaces are not completely known. Electrostatic inter actions involving charged groups of the proteins and calcium and phosphate ions on the enamel surfaces are assumed to be o f impor tance in pellicle formation as well as hydrophobic interactions. The aim of the present study was to examine the nature of protein interac tion with enamel surfaces. In vitro experiments comprised albumin adsorption to hydroxyapatite or to hydroxyapatite treated with py rophosphate. phosphonate, sodium lauryl sulphate or polydimethylsiloxane. In vivo experiments comprised scanning electron micros copy on enamel fragments which were untreated or pretreated with the same agents and then carried in the mouth to allow pellicle for mation. Amino acid analyses were performed to examine the chem ical nature o f the acquired pellicle formed on the enamel surfaces. The results indicated that the agents described reduced or blocked protein adsorption to hydroxyapatite as well as pellicle formation. Pyrophosphate rinsing of enamel surfaces with acquired pellicle showed furthermore that the pyrophosphate desorbed the pellicle from the enamel surfaces. The data indicated that pellicle formation may involve a multilayer adsorption of salivary proteins and that elec trostatic interaction may be one of the major mechanisms. Hydrophobic interactions may involve rigid protein interactions to polydimethylsiloxane-trcated surfaces. Amino acid analyses indicated that the same proteins were involved in pellicle formation to differently treated surfaces.
61 Enzymic Hydroloysis of Monofluorophosphate by Mixed Oral Organisms E.I.F. Pearce“• *, G.H. Dlbdlrb * Dental Unit, MRC o f New Zealand, Wellington, New Zealand; b MRC Dental Group, University of Bristol. UK To enable computer simulations o f diffusion plus reaction of monofluorophosphate (MFP) in dental plaque, fundamental infor mation on the enzymic hydrolysis o f this ion by oral bacteria has been obtained. Microcosm plaque, grown in an artificial mouth apparatus
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Salivary flow rates were monitored between the two acupuncture se ries, immediately after the end of the acupuncture treatment and then at 3,6 and 12 months. The preliminary results showed that some patients in the experimental group showed an increase in salivary flow rates, which persisted during the observation period. There were no significant changes in the control group subjects. The results in dicate that acupuncture may be a valuable adjunct in alleviating irra diation-induced xerostomia. Supported by grants from the Swedish Patent Revenue Research Fund.
62 Computer Model of Enzymatic Degradation of Monofluorophosphate by Dental Plaque Bacteria in a Diffusion Cell G.H. Dibdin "• *. E.l.F. Pearce" “ MRC Dental Group, University of Bristol, UK; h Dental Unit. MRC o f New Zealand. Wellington. New Zealand The long-term aim of the study [see also Pearce and Dibdin, ab stract 61 this meeting] was to investigate the degree to which mono fluorophosphate (MFP). released from toothpaste during toothbrushing, is hydrolysed to ionic fluoride and orthophosphate by den tal plaque enzymes before reaching an underlying tooth surface. The particular aim here was to model diffusion/reaction characteristics of MFP in an in vitro diffusion experiment being set up in Wellington. The simulation used a computer model [Caries Res 1990;24:231-238] originally designed to model a cariogcnic challenge but here mod ified to model a diffusion cell. F and the MFP/MFPase system were added, and simple Michaelis-Menten enzyme kinetics were assumed for MFP hydroloysis. based on V milx and KMvalues from Pearce and Dibdin [this meeting], HMFP/MFP buffer reactions (pK =4.8) and pH-dependent hydrolysis were also included. Diffusion coefficients assumed were D(MFP) = 2 x 10"* and D (P ) = 8 x 10'* cm ’ s'1based on earlier work. Initial simulations with 25 m.M MFP diffusing showed the expected strong dependence o f percentage breakdown on plaque thickness, ranging at pH 8 from 100% at 1 mm through 97% at 0.5 mm to only 7% at 0.1 mm thickness. Equivalent values at pH 6 were 93,38 and 1.6% due to the lower Vm;lx. These will be com pared with the diffusion cell results. In so far as the situation in vivo can be represented by such in vitro models, it seems possible that MFP from toothbrushing may be degraded before reaching tooth surfaces underlying thick plaques, but not under thin open-surface plaques.
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63 Human Lactoferrin Agglutinates Streptococcus mutans Cells but Inhibits Porphyromonas gingivalis Autoaggregation T. Soukka “• *, J. T enovuoJ. Rundegren" :l Institute of Dentistry, University of Turku, Finland; b Department of Biology, Biosurfacc AB, Malmö. Sweden Lactoferrin. a non-immunoglobulin defense factor, is known to be bactericidal and bacteriostatic against a variety of oral microor ganisms, but its possible role in bacterial agglutination is not known. In this study we have analysed the ability of various forms of human lactoferrin (LF) to agglutinate cells o f Streptococcus mutans. Strepto
coccus sanguis, Porphyromonas gingivalis undActinobacUlus actinomycetemcomitans using a spectrophotometric method. Partly and totally Fe'^-saturatcd LF were unable to agglutinate the bacteria studied whereas iron-free LF (apo-LF) effectively and dosc-dcpendcntly ag glutinated S. mutans cells but not the other bacteria. The efficiency and rate o f agglutination o f S. mutans were slightly lower by apo-LF than by human whole saliva. Secretory' IgA, phosphate and whole sa liva, but not scrum albumin, almost totally blocked the apo-LF-mediated agglutination of 5. mutans, indicating binding to the same recep tors on bacterial cell surfaces, or to each other. Exogenous iron (Fc2+, Fe
Abstracts of Papers Presented at the 39th ORCA Congress
1 Antimicrobial Factors of Saliva in Relation to Dental Caries and Mutans Streptococci in Saliva J. Tenovuoa- *, H. Jenischh, T. Soitkka ", /.. Karhuvaara“ “ Institute of Dentistry, University o f Turku, Finland: b Dental Institute, University of Rostock, FRO The possible association between salivary nonimmunoglobulin (lysozyme, lactoferrin, hypothiocyanite, agglutinins) or immunoglo bulin (total IgA, anti -Streptococcus mutans IgA) antimicrobial fac tors, and the prevalence o f dental caries was studied in 59 young adults. These antimicrobial factors were also analysed in relation to the salivary levels of mutans streptococci (MS), quantified on mitissalivarius agar supplemented with 15% sucrose and bacitracin. The levels of MS correlated significantly (+0.31, p B > A > E . Linear correlation coefficient comparing F uptake to [Fu,„jc] (r = 0.938) indicates the enhanced benefit (F uptake) for MFP/Ca over MFP/silica is likely the result o f higher [Fil)nic] o f the calcium-based MFP dentifrice. Under the conditions o f this study, no MFP formula tion performed equivalent to NaF/silica.
16 The Effect of Chiorhexidine-Fluoride-Strontium Gel in Preventing Enamel Softening in vitro S. Spets-Happonen *, H. Luoma, L. Seppii Department of Preventive Dentistry and Cariology, University of Kuopio, Finland Previous results suggest that the addition of strontium (Sr) into a chlorhexidinc(CHX)-fluoride combination improves its caries-pre ventive effect. The aim of the present study was to compare the effect of different Sr concentrations in CHX-fluoridc gel in preventing the softening of the enamel during bacterial fermentation. Bovine ena mel slabs were covered with 10 pi gel as follows: (1) placebo gel. (2) gel with 0.20% CHX and 0.16% sodiumfluoridc (NaF), (3) gel with CHX. NaF and 15 ppm Sr. (4) gel with CHX, NaF and 50 ppm Sr, (5)
gel with CHX, NaF and 250 ppm Sr. A volume o f 0.2 ml o f Streptococ cus mt/M/w-buffer suspension, 0.2 ml 10% sucrose solution and 0.2 ml distilled water were centrifuged to get the cells as a plaque-like layer on the top o f the gel-covered enamel. After 24-hour incubation the pH fall o f the fluid was significantly smaller in all test groups than in the control group. The addition of Sr seemed to have a slight inhib itory effect on the pH fall. All test gels prevented significantly the softening of the enamel during bacterial fermentation measured as Vickers hardness. In all Sr groups the enamel softened significantly less than in the group with CHX and NaF. The softening was least in the group with 250 ppm Sr. Total calcium and phosphorus contents of the cells and fluid after incubation were the smallest in the group with 250 ppm Sr. These results suggest that the addition of Sr into CHXfluoride gel improves the ability of this combination to prevent ena mel softening.
17 Remineralization of Deep Enamel Subsurface Lesions in a Medium with Time-Dependent Saturation II.C. Klinger*, W. Wiedemann, R. Jahns Klinik und Poliklinik für Zahn-, Mund- und Kieferkrankheiten, Universität Würzburg. BRD Time-dependent variations of the Ca++ and PO^ saturation in the remineralization medium will supposedly influence the local and the total mineral balance in the diffusion reaction system, initial caries. We measured the total mineral uptake and its local distribution in rather deep artificial caries-like lesions (500 pm deep, bovine ena mel). Parameter o f the experimental groups was the rise time of the mineral saturation in the remineralization solution. Using a constant Ca concentration o f 4 mmol/l (Ca:P = 1 ,1 ppm F~), the pH was in creased from pH 4 to 7 with a slope o f * , 0.20,0.10,0.05, and 0.025 pH/ min. When pH 7 was reached it was kept constant at this level for such a time that the ratio of the period of under- and supersaturation equaled 1 :7. This regime was repeated until the total incubation time amounted to 2 times 12 h. Mineral content in the lesions of the 2-mmthick specimens was measured before each experimental step by quantitative radiography combined with digital image processing. The permeability of the lesion surface was determined by dye pene tration. Significant mineral uptake was observed only in the experi mental group with 0.2 pH/min. i.e. 30 min to cover the interval from pH 4 to 7. Even in the rear of the deep lesion a marked mineral in crease was found. Using the statistical method o f discriminant analy sis we found that the parameters'total mineral balance’, ‘mineral bal ance front-rear’ and ‘surface permeability’ contributed most to the separation o f the experimental groups. The results are interpreted by means of a mathematical two-component model in terms o f reaction and diffusion rates.
18 De- and Remineralizing Hydroxyapatite as Bioactive Filling Material W. Wiedemann*. H.G. Klinger Klinik und Poliklinik für Zahn-, Mund- und Kieferkrankheiten. Universität Würzburg, BRD Dental restorative materials commonly used often have consid erable shortcomings. Their physical and chemical properties vary from those o f dental enamel. In 1989 we presented a new material, a special kind of hydroxyapatite, some essential properties o f which are
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ppm F. but between 1,500 and 2,500 ppm no further increase oc curred. Microradiography revealed mineral uptake and loss to occur in the same specimens at different depths: e.g. specimens showing overall net mineral uptake were partly remineralised in the original lesion body while a new lesion body was formed at depths beyond the original lesion front. This resulted in laminated lesions. The study re vealed a dose-response behaviour of fluoride dentifrices in a pHcycling model, and some mechanistic aspects of the fluoride action.
19 The Video Camera Compared with the Densitometer as a Scanning Device for Microradiography M.D. Lagerweija- *, J.M. ten Cate*, E. deJosselin deJongh * Department of Cariology and Endodontology, Academic Centre for Dentistry (ACTA), and b Inspektor Research Systems, Amsterdam, The Netherlands Microradiography is the most accurate and widely used method to determine mineral content profiles in enamel specimens. Origi nally, microscopes equipped with a densitometer were used for quan titative microradiography. More recently image analysis systems, comprising video (CCD) cameras and dedicated software, have been introduced. With the CCD camera scans can be made instantane ously, and scanning areas can easily be selected on a video screen (in pseudo-colours). In densitometry the most prominent system re quirements are a precision cross table and an accurate measuring slit. For the CCD camera the specifications for homogeneity of specimen illumination and accuracy must be high. It should be considered that the number of grey levels is limited to 255, which theoretically could jeopardise the accuracy of the measurement. With both systems working at optimal performance in our laboratory, we have com pared the enamel lesion profiles produced with the two techniques. No differences were found in the sensitivity and reproducibility of the polynomial regression analysis of the aluminium stepwedge data. Also the mineral profiles and the relevant lesion characteristics were found to match. Therefore it is concluded that both systems can pro vide equally reliable information on enamel lesions. The two systems are now being combined to make the best use of their respective ad vantages.
20 Reliability Investigation of an Intraoral Model H.M. Proskin *, D.T. Zero Eastman Dental Center. Rochester, N.Y., USA There has been much recent activity toward the investigation of the validity and reliability o f intraoral models for use as possible sur rogates for clinical trials for providing comparative information re garding the therapeutic effect o f anticaries agents, as is often re quired in submissions to regulatory agencies. This is particularly crit ical in the current environment, since long-term clinical trials, which can no longer use placebo groups, must now generally involve ex tremely large sample sizes when performed for this purpose. The
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present project is a component of ongoing work for which the long term goal is to characterize and document the reliability o f the model described by Zero et al. (1992 AADR Abstract], Five subjects used each of three dentifrices (table), during which time an appliance was worn bearing bovine enamel blocks (situated on either side of the mouth). On each block, ten replicate observations o f percent mineral recovered following intraoral exposure were obtained. Reliability was quantified through the calculation o f intraclass correlation coef ficients (ICCs) and their associated 90% lower confidence bounds (LCBs). as well as estimates of the reliability o f the blockwise means, obtained using the Spearman-Brown prediction formula. The results were as follows: Dentifrice
Side of mouth
ICC
90% LCB
Reliability of block means
Placebo
left right left right left right
0.60 0.44 0.70 0.86 0.84 0.63
0.41 0.25 0.52 0.74 0.72 0.44
0.94 0.89 0.96 0.98 0.98 0.95
250 ppm F 1,100 ppm F
These data suggest that blockwise mean scores possess excellent reliability for characterizing the percent of mineral recovered follow ing intraoral exposure.
21 Importance of Experimental Time during in situ De-/Remineralisation Studies F.A. Damato a *, D.R. Stirrups", K.W. Stephen*, A. Cummings', R. Strang' Departments of “ Oral Medicine and Pathology; b Orthodontics, and ‘ Clinical Physics and Bioengineering, University of Glasgow, Scotland. UK When testing P products with in situ model systems, the results may depend on the duration of the experiment. This time effect was investigated using an in situ single-section model which allows min eral content of enamel sections to be measured longitudinally. Thir teen volunteers were recruited in a cross-over study using two pastes with concentrations of 1,000 and 2,500 ppm P , respectively. Microradiography/microdensitometry were performed prior to the study and at 2 and 4 weeks. Changes in mineral content between 0 and 2 weeks, 2 and 4 weeks, and 0 and 4 weeks were calculated. Analysis o f var iance for Az mineralisation change for the two time periods (0-2 and 2-4 weeks) showed a significant fluoride dose effect (p = 0.0012) as well as a significant time period response (p = 0.0446) for the two pastes. In addition there was a significant intersubject difference (p = 0.0001). The rate of change o f Az for the two pastes for the second time period (2-4 weeks) was highly significant (p = 0.0006) but not for the first time period. The change that occurred during the second time period accounted for the significant dose effect seen over the 4 weeks (p = 0.0001). In situ studies may miss true differences between P products because of insufficient experimental duration.
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similar to those of dental enamel. Unlike the hydroxyapatite used for surgical purposes this special material takes part in the de- and re mineralization process in the mouth. During acid attack the surface softens like that of enamel giving rise to a large specific pore surface area. This phenomenon enables the hydroxyapatite to remineralize as fast as enamel does. Because of these properties we investigated whether this bioactive hydroxyapatite is suitable as a restorative ma terial. In a preliminary clinical test the material proved to be mouthresistant for 3 years. This encouraged us to start larger clinical trials. Before placing the new hydroxyapatite inlay it has to be milled from the bulk material w'ith high precision. To this end we developed a new copy milling machine which duplicates a master model with a preci sion o f about 10 ¡xm including the occlusal surface. The material and the milling machine will be presented and first clinical observations wall be reported.
22 Effect of Sugar-Free Chewing Gum on in situ Enamel Lesion Remineralization S.L. Creanor*. W.H. Gilmour, R. Sunni’. R.H. Faye, D.A.M. Geddes. A.F. Hull University of Glasgow, Scotland, UK Chewing gum after eating can raise lowered plaque pH [Jensen and Wefel: Br Dent J 1989;167:207-208] and increase salivary flow [Dawes and MacPherson: Caries Res 1991:25:225], The aim o f this study was to investigate whether remineralization by a fluoridated dentifrice could be enhanced in conjunction with the use of a sugarfree gum. Enamel lesions were mounted onto in situ appliances worn by 12 subjects [Creanor et al: Caries Res 1986;20:385-391] using an 1,100 ppm NaF dentifrice 2 x a day (test and control) and gum 5 x a day (test). A cross-over design was used. Mineral content was as sessed at baseline and after 7 weeks using microradiography. For Az (n = 264). linear regressions were made for test and control for each volunteer of the difference between baseline and final Az values of each lesion against baseline Az value. Predicted differences between test and control were calculated for a fixed baseline Az value. Five subjects had significantly greater remineralization with chewing gum. 1 subject showed significantly greater remineralization on control and 6 subjects gave inconclusive results. For the Az values, there was 18.2% remineralization for the test phase (p = 0.0006) compared to 12.1% (p = 0.003, both 1 tailed) for the control. Weighted analysis of variance showed this trend was almost statistically significant (p = 0.07, onc-tailcd). Although there was a trend towards greater remineralization in both the surface layer and lesion body during the test phase, these differences were not statistically significant. Results sug gest chewing sugar-free gum after eating may enhance enamel lesion remineralization beyond that obtained with fluoridated dentifrice alone. Supported by a grant from Wm. Wrigley Jr. Company, Chicago, USA.
23 Effect of Varying Dentifrice Formulation on in situ Enamel De-and Remineralisation P.W. Smith*. S.M. Higham, W.M. Edgar
same subjects following a 2-min rinse with a 10% (w/w) slurry of each dentifrice followed 10 min later by a 2-min 10% (w/v) sucrose rinse. Mean cH areas ± S D (pmol min) and mean pH ± S D were: 0 ppm F: 6.17± 8.9 and 6.11 ±0.32: 250 ppm F: 2 .6 5 ± 6 .9 4 and 6.13±0.19; 1,000 ppm F: 2.87 ±5.36 and 6.35 ±0.27; 1.500 ppm F: 0.70 ±2.57 and 6.59±0.60. The differences observed were not significant at the 5% level. Preliminary results suggest that significant reductions in lesion extent are observed when the dentifrice contains fluoride although this did not significantly affect cH area or minimum pH, indicating that fluoride may promote in situ remineralisation without a demon strable inhibitory effect on plaque acid challenge.
24 Development of an in situ Model for Studying Mineral Changes in Dentin W. Zlitmg. A.J. Dunipace. S.A. Kelly. G.K. Stookey* Indiana University School of Dentistry. Indianapolis, Ind. USA Two double-blind, crossover studies were conducted to develop an in situ model for studying fluoride uptake (D FU ), mineral chang es (MC) and lesion depth (L) in dentin. A sound dentin specimen (for D FU ) and a carrier containing 100-urn sections of sound and soft ened dentin (for MC) were mounted in partial dentures and subjects were randomly assigned to use a fluoride (F) or placebo (P) denti frice for a designated test period. After the test period, the specimens were removed and analyzed for DFU and MC by a microdrill biopsy method and microradiography (MR), respectively. Using new speci mens the test period was repeated with subjects using the second den tifrice. In the first study in which 20 subjects brushed their teeth 2x a day for 4 weeks, F was numerically more effective than P in promot ing DFU and reducing demineralization o f sound dentin and was sig nificantly more effective in softened dentin (p >0.05). In the second study, 15 of the most reliable subjects brushed for 1 min, 3x a day for 2 weeks. Data showed significantly different DFU o f 3.84 ±0.65 and 18.49±4.9 ug F/cm2 after P and F. respectively. MR analyses indi cated F significantly reduced sound dentin demineralization (AZ = 354 ± 99 for F and 1,201 ± 320 for P). and in carious dentin. F and P re sulted in numerically different AZ values o f 796 ±296 and 1,897 ± 624, respectively. Lesion depths were similar. As modified, this in situ model can detect significant differences in DFU, MC and L o f dentin.
Department o f Clinical Dental Sciences, University of Liverpool, UK
Caries Diagnosis 25 Prediction of Caries Experience at Age 15 by the State of Primary Teeth at Age 6 N. An*. M. Vehkalahti. S. Helminen Institute of Dentistry, University of Helsinki. Finland Two groups of children were selected in the present study accord ing to the DMFT index at age 15. The low-risk group (n = 159) con sisted o f children with DMF teeth no greater than 2. Those with 5 or more DMFT were assigned to the high-risk group (n = 187). All the children were followed from 6 to 15 years of age. Data were collected from the patients’ charts with annual dental recordings for each indi vidual. Prediction was made according to three indicators: (1) the number of df teeth in primary molars: (2) dfs in the proximal surfaces of primary molars, and (3) the experience of caries in any primary teeth before age 6. Sixty-eight percent of children with dft = 0 in pri
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Both plaque pH profiles and in situ enamel de- and remineral isation models can be used to provide information on potential car ies-related phenomena. This study was carried out to investigate the responses to dentifrices having a range o f fluoride levels. Artificial le sions were produced in vitro in sound extracted human premolars and divided to give three sections. One section was used as a control and the other two mounted onto brackets, covered with gauze and etch retained to the lower right first molar. During the first 3 weeks of the trial. 8 subjects used a dentifrice (3 x daily) with a fluoride con centration o f either 0 or 250 ppm and during the second part o f the trial with either 1,000 or 1,500 ppm. The lesions were removed, sec tioned and ground pianoparallcl to 80 pm and examined by polarized light microscopy, microradiography and image analysis. Mean lesion widths (u m ± S D ) were: control: 69.03 ± 12.99: 0 ppm F: 102.97± 10.95; 250 ppm F: 58.5 ± 21.24 with significant differences (p - *, C. Dawes'' Departments of a Anatomy, and b Oral Biology. University of Manitoba, Winnipeg, Canada When gum containing sucrose is chewed, there is the potential for promotion o f caries by the sucrose but also anticariogcnic effects from the stimulation o f salivary' flow. This study, on 5 male and 5 fe male subjects, investigated the change in the flow rate and bicarbo nate concentration in whole saliva stimulated by chewing Trident Peppermint® (1.8 g) and Doublemint® (3.0 g) chewing gums over a 20-min time period. For 15 subjects, salivary film velocity was also es timated on the buccal surfaces of the upper anterior teeth (where the velocity is normally lowest) by the method o f Dawes et al. [J Dent Res 1989;68:1479-1482]. In the first minute of chewing gum stimulation, salivary flow rate peaked at 4.3 ml/min and then fell gradually over the 20 min to a value of 1.4 ml/min. After 3 min of stimulation, salivary bicarbonate concentration peaked at 15 mmol/l and then fell gradu ally to 12 mmol/l over the 20 min o f chewing gum stimulation. There was little difference with respect to salivary flow rate or bicarbonate concentration between the two gums. The estimated mean salivary film velocity on the buccal surfaces o f the upper anterior teeth when salivary flow was unstimulated was 0.75 mm/min. With stimulation of salivary flow by the consumption o f sour lemon drops and use of chewing gum, the film velocity increased to 1.05 and 4.5 mm/min, re spectively, although the flow rate o f whole saliva was greater with the lemon drops than with the chewing gum. These data will be o f value in modelling the cariogcnic potential o f chewing gum containing fer mentable carbohydrate.
56 The Effect of Acupuncture on Salivary Secretion Rates in Patients with Radiation-Induced Xerostomia: A Preliminary Report M. Blom, I. Dawidson*, B. Angmar-Mânsson, G. Johnson Department of Cariology. Karolinska Institutct, Stockholm, Sweden The aim o f this study was to investigate the effect of acupuncture on xerostomia caused by irradiation treatment o f tumors in the head and neck region. The material comprised 40 subjects, all suffering from xerostomia after full dose (64 Gy) irradiation of the head and neck. Salivary flow rates for resting and paraffin-stimulated saliva were determined prior to the commencement of the acupuncture treatment. The patients were randomly assigned to an experimental group or to a control group. Two series o f acupuncture treatment (24 treatments) were given to the experimental group, and the control group received superficial acupuncture (placebo), also in two scries.
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between the two groups o f subjects. However, in subjects with low sa livary flow rates, recovery' was significantly slower than in subjects with good flow rates. The initial level had not been regained after 20 min. At the sublingual site, pH recovery was fastest. The initial level was reached in 1 min in the group with good salivary flow rates. It is concluded that consumption o f a low-pH drink increased salivary flow rates causing rapid pH increases, but that when the stimulus is over, pH recovery depends on the resting salivary flow rate. A longlasting decrease in pH is therefore observed in low flow rate subjects, especially at sites where oral clearance is slow.
57 Inhibition of Calcium Phosphate Crystal Growth by Lipoteichoic Acid J.J.M. Damen*. J.M. ten Cate Department o f Cariology and Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), The Netherlands The accumulation of organic matter in natural enamel and denti nal lesions is thought to be a major impediment for their remineral ization. A substantial part o f this matter consists o f compounds o f bacterial origin. Among these may be lipoteichoic acids (LTA), which because o f their polyanionic nature could be powerful inhibitors of crystal growth. We have purified LTA from a freshly isolated Strepto coccus sanguis strain and determined its effects on the crystal growth of two calcium phosphate salts, hydroxyapatite and dicalcium-phosphate-dihydrate (brushitc), in supersaturated solutions. The growth rate o f seeded crystals (0.1 mg/ml) in solutions of 1 mM CaCl2, 7.5 mM KfLPO.. 50 mM Hepes, pH 7.2, was found to be reduced in the pres ence o f both native LTA and its dclipidated derivative, which was ob tained by mild alkaline hydrolysis. LTA at concentrations (deter mined and expressed as P 0 4 units) over 200 uM inhibited growth completely, but at very low concentrations (10-40 pM P 0 4) the growth o f hydroxyapatite was slightly stimulated. It was concluded that LTA is a strong inhibitor o f crystal growth, and the inhibitory ef fect is almost entirely accounted for by its polyglyccrophosphate backbone.
58 Surface Interactions between Na-Lauryl Sulphate and Triclosan Measured by Ellipsometry Th. EricsorT *, G. Holla''. H. ArwiiT, R. Bjorklundc “ Department of Cariology, University of UmeS, Sweden; b Pedodontics, University o f Oslo. Norway; c Physics and Measurement Techniques, University of Linköping, Sweden Sodium lauryl sulphate (SLS), a surfactant, and the antibacterial compound Triclosan are components o f some toothpastes. Clinical experiments have indicated a synergistic effect resulting in more ef fective removal o f dental plaque. We have used ellipsometry to study the uptake on a methylated and thus hydrophobic silicon surface of each compound singly and in combination. Ellipsometry is an optical technique which allows quantitative measurement of thickness of monolayers at a solid/liquid interface. We found that SLS was rapidly adsorbed from a 0.03% solution on the hydrophobic surface in a 10to 15-A thick layer. Complete desorption was found when the liquid phase was substituted by a phosphate buffer (PBS). Triclosan was taken up from a 0.006% solution in a much thicker layer, 40-50 A. The final thickness was obtained after 5 min. Triclosan was rapidly
and also completely desorbed by PBS. When a combination of the two test compounds was studied a different pattern was obtained. In the initial phase a rapid uptake o f material to the surface was ob served resembling the reaction observed with Triclosan alone. The initial phase, which lasted for 2 min, was followed by a short period of desorption of approximately 20% o f the thickness. This second phase was followed by a third phase in which the building up o f a succes sively thicker layer was observed. Equilibrium was reached after ap proximately 20 min at a thickness of 100-110 A. Desorption was com plete and rapid when PBS was introduced in the system. These exper imental data show a synergistic interaction between the two compounds in support for the biological synergism observed clini cally.
59 Studies on the Nature of the Interaction between Salivary Proteins and Dental Enamel M. Hykke*. G. Holla Dental Faculty, University of Oslo, Norway Salivary proteins are rapidly adsorbed to enamel surfaces forming the acquired pellicle, which is assumed to provide protective func tions for the enamel surfaces. The mechanisms by which proteins ad sorb to solid surfaces are not completely known. Electrostatic inter actions involving charged groups of the proteins and calcium and phosphate ions on the enamel surfaces are assumed to be o f impor tance in pellicle formation as well as hydrophobic interactions. The aim of the present study was to examine the nature of protein interac tion with enamel surfaces. In vitro experiments comprised albumin adsorption to hydroxyapatite or to hydroxyapatite treated with py rophosphate. phosphonate, sodium lauryl sulphate or polydimethylsiloxane. In vivo experiments comprised scanning electron micros copy on enamel fragments which were untreated or pretreated with the same agents and then carried in the mouth to allow pellicle for mation. Amino acid analyses were performed to examine the chem ical nature o f the acquired pellicle formed on the enamel surfaces. The results indicated that the agents described reduced or blocked protein adsorption to hydroxyapatite as well as pellicle formation. Pyrophosphate rinsing of enamel surfaces with acquired pellicle showed furthermore that the pyrophosphate desorbed the pellicle from the enamel surfaces. The data indicated that pellicle formation may involve a multilayer adsorption of salivary proteins and that elec trostatic interaction may be one of the major mechanisms. Hydrophobic interactions may involve rigid protein interactions to polydimethylsiloxane-trcated surfaces. Amino acid analyses indicated that the same proteins were involved in pellicle formation to differently treated surfaces.
61 Enzymic Hydroloysis of Monofluorophosphate by Mixed Oral Organisms E.I.F. Pearce“• *, G.H. Dlbdlrb * Dental Unit, MRC o f New Zealand, Wellington, New Zealand; b MRC Dental Group, University of Bristol. UK To enable computer simulations o f diffusion plus reaction of monofluorophosphate (MFP) in dental plaque, fundamental infor mation on the enzymic hydrolysis o f this ion by oral bacteria has been obtained. Microcosm plaque, grown in an artificial mouth apparatus
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Salivary flow rates were monitored between the two acupuncture se ries, immediately after the end of the acupuncture treatment and then at 3,6 and 12 months. The preliminary results showed that some patients in the experimental group showed an increase in salivary flow rates, which persisted during the observation period. There were no significant changes in the control group subjects. The results in dicate that acupuncture may be a valuable adjunct in alleviating irra diation-induced xerostomia. Supported by grants from the Swedish Patent Revenue Research Fund.
62 Computer Model of Enzymatic Degradation of Monofluorophosphate by Dental Plaque Bacteria in a Diffusion Cell G.H. Dibdin "• *. E.l.F. Pearce" “ MRC Dental Group, University of Bristol, UK; h Dental Unit. MRC o f New Zealand. Wellington. New Zealand The long-term aim of the study [see also Pearce and Dibdin, ab stract 61 this meeting] was to investigate the degree to which mono fluorophosphate (MFP). released from toothpaste during toothbrushing, is hydrolysed to ionic fluoride and orthophosphate by den tal plaque enzymes before reaching an underlying tooth surface. The particular aim here was to model diffusion/reaction characteristics of MFP in an in vitro diffusion experiment being set up in Wellington. The simulation used a computer model [Caries Res 1990;24:231-238] originally designed to model a cariogcnic challenge but here mod ified to model a diffusion cell. F and the MFP/MFPase system were added, and simple Michaelis-Menten enzyme kinetics were assumed for MFP hydroloysis. based on V milx and KMvalues from Pearce and Dibdin [this meeting], HMFP/MFP buffer reactions (pK =4.8) and pH-dependent hydrolysis were also included. Diffusion coefficients assumed were D(MFP) = 2 x 10"* and D (P ) = 8 x 10'* cm ’ s'1based on earlier work. Initial simulations with 25 m.M MFP diffusing showed the expected strong dependence o f percentage breakdown on plaque thickness, ranging at pH 8 from 100% at 1 mm through 97% at 0.5 mm to only 7% at 0.1 mm thickness. Equivalent values at pH 6 were 93,38 and 1.6% due to the lower Vm;lx. These will be com pared with the diffusion cell results. In so far as the situation in vivo can be represented by such in vitro models, it seems possible that MFP from toothbrushing may be degraded before reaching tooth surfaces underlying thick plaques, but not under thin open-surface plaques.
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63 Human Lactoferrin Agglutinates Streptococcus mutans Cells but Inhibits Porphyromonas gingivalis Autoaggregation T. Soukka “• *, J. T enovuoJ. Rundegren" :l Institute of Dentistry, University of Turku, Finland; b Department of Biology, Biosurfacc AB, Malmö. Sweden Lactoferrin. a non-immunoglobulin defense factor, is known to be bactericidal and bacteriostatic against a variety of oral microor ganisms, but its possible role in bacterial agglutination is not known. In this study we have analysed the ability of various forms of human lactoferrin (LF) to agglutinate cells o f Streptococcus mutans. Strepto
coccus sanguis, Porphyromonas gingivalis undActinobacUlus actinomycetemcomitans using a spectrophotometric method. Partly and totally Fe'^-saturatcd LF were unable to agglutinate the bacteria studied whereas iron-free LF (apo-LF) effectively and dosc-dcpendcntly ag glutinated S. mutans cells but not the other bacteria. The efficiency and rate o f agglutination o f S. mutans were slightly lower by apo-LF than by human whole saliva. Secretory' IgA, phosphate and whole sa liva, but not scrum albumin, almost totally blocked the apo-LF-mediated agglutination of 5. mutans, indicating binding to the same recep tors on bacterial cell surfaces, or to each other. Exogenous iron (Fc2+, Fe
