CA1209050A - Dental rinse - Google Patents

Abstract

ABSTRACT
The specification describes a dry composition and aqueous solution useful in the mineralisation of dental pla-que. The solution contains 0.01 to 50% W/V of a substance metabolised by bacteria in plaque (urea is exemplified) to raise the pH of said solution, a physiologically acceptable source of calcium ions and a physiologically acceptable source of phosphate ions, both in concentrations to form a stable solution with respect to a calcium phosphate salt, and optionally a fluoride ion generating compound metabo-lised by bacteria in plaque to release fluoride ions and/or a water soluble fluoride salt, the pH of the solution being from 1 to 9, and the pH and calcium and phosphate ion con-centrations being such that the solution remains stable and with respect to the calcium phosphate salt until the substance is metabolised by bacteria in plaque. Results of some dental trials are presented.

Description

BACKGROUND OF THE INVENTION
Field of Invention This invention relates to artificial mineralization of dental plaque, a composition and an aqueous solution for carrying out such mineralization.
Description of the Prior Art It is known that calcium and phosphate concentrations in dental plaque vary from person to person and from site to site within the mouth. However plaque calcium and phosphate variations appear to be confined within certain limits.

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Fluoride concentrations within plaque are less closely controlled.
There is good evidence to suggest that these natural variations in plaque minerals are associated with variations in caries susceptibility. Theoretical considerations indi-cate that high plaque Ca and inorganic phosphate (Pi) levels will lower the 'critical pH', the pH which plaque must reach before it becomes unsaturated with respect to biological apatite, and enamel dissolution commences (Dawes et al., Archs Oral Biol. 7: 161-172 (1962)). In addition, higher concentrations of Pi may increase the buffering action of plaque and may inhibit acid production by certain plaque bacteria (Brown et al., Archs Oral Biol. 22: 521-524 - (1977)). Increasing concentrations of plaque F may also be expected to have an increasing caries-protective effect because of this ion's inhibition of microbial glycolysis (Jenkins, Archs Oral Biol. 1: 33-41 (1959)). Thus, it is likely that the higher the concentration of Ca, Pi and F in plaque, the greater will be the protection afforded.
Apart from these theoretical aspects, a protective role for plaque mineral ions is supported by a variety of clini-cal and experimental observations. Dental calculus, which may be regarded as plaque having a very high concentration of mineral, has long been associated with irnmunity to caries (Gottlieb: Dental Caries p.l00 (Lea & Febiger, Philadelphia 1947))-In plaque having insufficient mineral to be regarded as calculus, increased levels of calcium and phosphate have 5C~
also been associated with increased resistance to caries.
Ashley and Wilson ( _. Dent. J. 142: 85-91 (1977)) have found an inverse relationship between the levels of Ca, Pi and organic phosphate (PO) in plaque and the number of tooth surfaces becoming decayed or filled over the first 2 ~ears of a 3-year longitudinal study.
Likewise, clinical studies show that F in plaque -tends to protect the enamel against dental caries. The plaque F
concentration of children has been inversely related to their individual caries experience (Agus et al, Community Dent. Oral Epidemiol. 4: 210-214 (1976)) and to their number of carles-free teeth (Dental Plaque, p.p. 171-17B
(Livingstone, Edinburgh, 1970)).
I-t is an object of this invention to go some way towards achieving higher concentrations of Ca, Pi and F in plaque or at least to provide the publi~ with a useul choice.
Summary of the Invention .
Accordingly in one aspect the invention may be said broadly to consist in a dry mix composition containing the j 20 following components expressed in parts by weight:

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COMPONENT PARTS BY WEIGHT
Urea or other substance metabolised to alkali 1-500 Source of calcium ions 0.1-100~ Prefera~ly l~lQ0 Source of phosphate ions 0.01-20.0, preferably 0.1--20.0, and, optionally, Source of fluorophosphate ions 0.01-20, prefe~ably .1 to 20.0 Source of fluoride ions .001-40.0 Preferably the com^position comprises the following:

COMPONENT PARTS BY WEIGHT
Urea 5-100 Calcium salt 1-25, preferably 5-25 Phosphate salt 0.3-2.0 Monofluorophosphate salt 0.1-4.0, preferably 0.4-4.0 Fluoride salt .006-1.0, preferably .006-.030 More preferably the composition comprises the following:

COMPONENTS PARTS BY WEIGHT
Urea 60 Calcium-chloride 11.1 Sodium dihydrogen phosphate 0.60 Sodium monofluorophosphate 0.68 Sodium fluoride 0.0117 Alternatively the composition also contains up to 5 parts by weight of a salt such as KCl, preferably 3 parts by weight.

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Although urea is the favoured compound for the dry mix to be used in a plaque mineralising aqueous solution any physiologically acceptable soluble substance which is meta-bolised by bacteria to produce alkali in plaque can be employed. Typically amino acids such as peptides having 2-4 amino acids, one of which is an arginine unit may be used.
Aspartame is another compound that may be substituted for urea.
The source of calcium ions is typically a calcium salt such as calcium chloride, but other physiologically accep-table salts such as calcium lactate, calcium acetate or calcium borate may be selected.
The source of phosphate ions is typically sodium phosphate but any other soluble phosphate may be selected.
In the solution embodiment described below phosphoric acid may be used provided the pH is maintained at a level to keep the solution supersaturated.
The fluorophosphate salt is typically a sodium or potassium mono- or hexa- fluorophosphate.
The source of fluoride ions is typically potassium or sodium fluoride.
When the dry mix is to be put into aqueous solution the pH has to be Xept sufficiently low to avoid precipitation of calcium phosphate~ This may be achieved by controlling the pH during mixing of the dry mix, or alternatively by making a first solution with the first two components and a second solution with the last three componen-ts and subsequently combining the first and second solutions.

o In another embodiment the invention may be said broadly to consist in a plaque mineralizing aqueous solution comprising 0.01 to 50~ W/V of a physiologically acceptable substance metabolised by bacteria in plaque to raise the pH
of said solution, a physiologically acceptable source of calcium ions and a physiologically acceptable source of phosphate ions, both in concentrations to form a stable solution with respect to a calcium phosphate salt, and, optionally, a physiologically acceptable fluoride ion generating compound metabolised by bacteria in plaque to release fluoride ions or other physiologically acceptable source o~ fluoride ions, the pH of said solution being from 1 to 9, with the pro-viso that th~ pH and calcium and phosphate ion con-centrations are such that the solution remains stable and with respect to said calcium phosphate salt until said substance is metabolised by bacteria in plaque.
Preferably said substance metabolised by bacteria i5 urea.
Preferably said urea is present in from 3 to 6% W/~.
More preferably said urea is present in 6% W/V.
Preferably said calcium salt is calcium chloride.
Preferably said calcium chloride is present in a concen-tration of 100 mM.
Preferably said phosphate salt is NaH2PO4.
Preferably said NaH2PO4 salt is present in a con-centration of 5 mM.

Preferably said fluoride ion generating compound is also a phosphate ion generating compound.
More preferably said fluoride ion generating compound is Na2PO3F.
Preferably said ~a2PO3F is present in a concentration such that the total 1uoride concentration to be generated within the solution is 5 mM.
Preferably the pH of said solution is from 4 to 5.
More preferably the pH o~ said solution is 5.
In another alternative an additional salt is present.
Preferably said additional salt is KCl.
Preferably said KCl is present in a concentration of 0.04 M.
In another preferred embodiment the invention may be said broadly to consist in a mouth rinse which comprises an aqueous solution containing:

urea 3% (w/v) calcium chlori~de 20 mM
sodium dihydrogen phosphate 12 mM
sodium monofluorophosphate 4.72 mM
sodium fluoride 0.28 mM

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glycerol 5% (v/v) saccharine ) to increase spearmint ) palatability vanilla food colour adjusted to pH 5Ø
The invention consists in the foregoing and also envisa-ges constructions of which the following gives examples.
EXAMPLE 1:
Removable intra-oral appliances were constructed for 2 female and 3 male adults tPearce et al., ~.~. Dent. J. 75:
8-14 (1979)), after a design of Koulourides. The applicances carrled two 3 x 4 mm slabs of bovine enamel mounted in the buccal sulcus adjacent to the lower first permanent molar, one on the left side of the mouth and one on the right. Each - pair of enamel slabs was cut from the same bovine incisor crown after it had been sterilised in e-thylene oxide and the enamel surface ground flat with 600 mesh carborundum and smoothed with 5 ~m alumina. The enamel surface was covered with 2 layers of a fine "Dacron" (a trade mark~ gauze to accelerate plaque formation.
The appliances were worn continuously for 2 days to establish a plaque and then, for the next 5 days, perioai-cally remo~ed from the mouth for exposure to the minera-lizing solution. Plaque was treated either for 10-min periods 3 times per day, or for 15-min periods 4 times per day, with a minimum of 2 h between treatments. Plaque on ~2~5~
only one side was treated, the contralateral side acting as a control. The whole appliance was rinsed in tap water -before being replaced in the mouth. The appliances were always worn overnight and during meal-times.
The plaque mineralizing solution contained 6% urea, 0.04 M KCl, 100 mM CaC12, 5 mM NaH2PO4, 4.72 mM sodium~
monofluorophosphate (MFP~, 0.2~ mM F and was adjusted to pH
5Ø All chemicals were Analar grade except sodium mono-fluoro~ho~phate which was a commercial sample. The solution was stored at 5. For use, a 10-ml sample was preheated to 37C and the appropriate flange of the applicance dipped into the solution while the temperature was held constant at 37C.

0~ the morning following the final treatment day, at least 16 hours after the last plaque treatment, the appliance was removed from the mouth, e~cess saliva removed by blotting with filter paper, and-the 3 x 4 mm "Dacron"
'plaque gauzes' excised. Remaining plaque was scraped from the enamel surface with a chisel-shaped piece of soft polythene, and both gauzes and scrapings extracted in 0.5 ml of 0.5 N HC104 for 12 hours in a capped l-ml polystyrene vial. The acid extract was analysed for Pi by a phosphomo-lybdate method (Chen et al., Analyt. Chem. 28: 1756-1758 (1956)) and for Ca by flame photometry, using 1% lanthanum to overcome phosphate interference. F was estimated with a specific ion electrode (Orion model 96-09) after the neutra-lization of 100 ~1 aliquots with 10 ~1 of 5 N NaOH and the addition of TISAB (Orion) containing sufficient F to ensure a minimum final concentration of 0.02 ppm. The plaque resi-due was heated in 0.5 ml of 1.7-1.9 ~ NaOH at 80-90C for 45 min and the protein content determined (Lowry et al., J.
B _ . Chem. 193: 265-275 (1951)) using bovine serum albumin as a standard.
Plaque gauzes from one experiment utilising the longer and more frequent exposure periods were dried in air and subjected to X-ray diffraction analysis (Philips model PW
1050/25 using Ni filtered Cu K~ radiation).
The effects on dental plaque of treatment with the mineraliziny solution for 10-min periods, 3 times per day for 5 days are shown in table I. In this series of experi-ments each subject used the solution for two 5-day periods;
once to treat plaque on the left side of the mouth and once to treat plaque on the right. The contralateral side always served as a control. The results are expressed as ~g of Ca, P or F/mg protein since the unknown amount of "Dacron" pre-sent in each gauze made dry weights impossible to obtainO

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The concentrations of acid-extractable Ca, Pi and F
increased markedly in each subject's plaque after treatment with the solution. There were considerable differences in amounts deposited in the 2 experiments in each subject as well as between subjects. However, the 2 highest values for treated plaque Ca and Pi concentrations were found in 1 sub-ject (A.W.), while the subject having the lowest amount deposited (A.M.) also had a low amount deposited when the contralateral plaque was treated. Rather more mineral appeared to be deposited in the outer plaque (represented by the material contained within the "Dacron" gauze) than in the inner plaque (represented by the material which could be scraped from the enamel surface after removal of the gauze), although this variation appeared to be less than the 'between subject' or 'between side' variations. The mean Ca concentration of the 10 treated plaques (outer a~d inner plaque material combined) was 307 + 176 ~g/mg protein (mean + 1 SD) compared with a value of 7.59 + 3.37 for the untreated plaque. The Pi concentration of treated plaque was 157 + 90.1 ~g/mg protein (untreated Plaque P~ concentration 4.02 + 1.90) and the F concentration 13.0 +
6.15 ~g/mg protein (untreated plaque F concentration 0.014 +
0.007)-The average amount of protein in plaque developing on the treated side was 0045 + 0.11 mg while a similar amount was found in plaques from the untreated side, 0.41 + 0.09 mg. The outer plaque samples (in the gauzes) contained an s~ ~
average of 0.33 + 0.09 mg protein ~hile the inner plaque samples (enamel scrapings) contained an average of only 0.09 + 0.04 mg.
After subtracting values for Ca and Pi found in plaque on the control side, the mineral deposited in the treated plaques had a Ca:P (rnolar) ratio of 1.55 + 0.14. There was a very high correlation between the increase in Ca and the increase in Pi in the plaques (r = +0.997), and al-though the F concen-tration also tended to increase with the Ca con-centration, this correlation was not as strong (r = +0.621).The Ca:F ratios varied from 6.5 to 20.3.
X-ray diffraction analysis of an outer plaque gauze sample which had been treated for 15-min periods, 4 times per day, clearly showed the presence of a well-crystallized apatite mineral phase. The main peaks of hydroxyapatite were clearly separated and most of the peaks having a rela-tive intensity >10 seen. There was no evidence of the pre-sence of octacalcium phosphate, brushite, calcium fluoride or whitlockite, although the most useful peak for iden-tifying this latter compound in the presence of hydroxyapa-tite (d = 3.21 A) would have been obscured by the 3 very large and broad peaks resulting from the "Dacron" (d = 3.44, 3.86 and 4.95 ~). Plaque from the untreated control side showed these "Dacron" peaks only.
The 40-fold increases in Ca and Pi and the 900-fold increase in F found in treated~plaque more than 16 h after the last treatment are greater than any previously reported in the literature following àttempts to mineralise plaque SC~ , artificially. Any high levels of Pi or F obtained pre-viously have declined ayain -to normal levels within 3 h of treatment (Tatevossian, Proc 20th ORCA Congr. Helv. Odont.
Acta _ : 51 (1973); Tatevossian et al., Archs Oral Biol. 24:
461-466 (1979)). Retaining one plaque as an untreated control while reversing treatment sides showed that the mineralisation was not an effect related to saliva, rather than the treatment (e.g. due to one plaque gauze lying close to the orifice of the parotid duct). ~owever, this does not exclude the possibility that the natual mineralising ability of the saliva increased the plaque mineral content once it had been nucleated by solution treatment.
The high correlation between the increase in Ca and the increase in Pi in treated plaque indicates that these ions were precipitated together as a mineral phase. Although X-ray diffraction revealed the presence of only apatite in the sample analyzed, it is possible in view of the low initial pH that small amounts of brushite were also precipitated (~ewesely, Caries Res. 2: 19-26 (196~)). This could account for the lower Ca:P ratios of 1.38 and 1.45 which were found in two of the samples. F can cause the conversion of brushite to apatite ~Chow, J. Dent. Res. 52: 1220-1227 (1973)) but it is not known if the small but variable amount of F present (about 5 ppm) would be sufficient to inhibit brushite forming in the plaque. Alternativelys the low Ca:P
ratios may be explained by the formation of a Ca-deficient apatite.
F uptake was less well correlated with Ca uptake but . -- . . . _ . _ . _ . _ . . _ _ . . .

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this would not exclude its co--precipitation in an apatite phase. F can be incorporated in a continuously variable amount (from none to the 3.77% in fluorapatite) - its inclu-sion depending on concentration and pH (Le Geros, IADR 58th General Session, Abstr No.344, J Dent. Res 59 special issue B p.973 (1980)). Both of these factors would have differed from run to run in the present series, depending on the ~FP-degrading and the ureolytic abilities of the particular pla-que. However, the Ca:F ration of 6.5 achieved in one sample indicated that maximum incorporation as fluorapatite was being approached.
EXAMPLE 2: -In another experiment an adult subject ceased tooth-brushing and other usual oral hygiene practices for 4 days in order to allow natural dental plaque to accumulate. On the final 3 days of this period, the subject mouthrinsed for

2 consecutive l-minute periods, 4 times per day, with a modified plaque-mineralizing mouth rinse solution. Fifteen ml of fresh solution, preheated to 37C, was used for each minute and then expectorated. The mouthrinse contained:

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~LZ~C3 5~1 urea 3% (w/v) calcium chloride 20 mM
sodium dihydrogen phosphate 12 mM
sodium monofluorophoshate 4.72 mM
sodium fluoride 0.28 mM

glycerol 5~ (v/v) saccharine ) sufficent to spearmint ) increase vanilla ) palatability food colour adjusted to pH 5.0 At the end of -the 4-day experiment period, natual plaque was collected from the buccal surfaces of upper premolar, canine and incisor teeth with a plastic dental instrument, palced in-a platinum dish and the dry weight obtained.
Plaque was then analysed for acid-extractable calcium, phosphate, fluoride and protein content as described pre-viously. For comparison, untreated control plaque wascollected after a similar 4-day period when the rinsing solution was not used. The effect of in vivo use of the modified plaque mineralizing solution is seen in table II.
The solution increased the concentration of Ca, Pi and F
markedly~ to levels comparable to those achieved with the original formulation used in vitro! even though the total plaque exposure time was only 24 min compared to 150 min in the experiments using the appliances. The result of this experiment indicates that -the dental plaque which grows natually on teeth in the mouth can be mineralized by repeated short treatments with the urea and MFP-containing mineralizing solution as readily as plaque which grows on removable appliances.

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TAsLE II: In vivo mineralization of natural dental plaque Plaque minerals ~g/mg protein Ca].cium phosphate fluoride treated control treated control treated control 337 12.0 185 11.1 3.34 0.071 ~g phosphorus/mg protein It is to be understood that the subject ceased usual oral hygiene practices for ease of analytical technique. Plaque was allowed to accumulate to allow a sufficient amount to be collected for straight forward analyses. This not to suggest that there not sufficent plaque remaining after toothbrushing to allow the treatment to have benefi-cial effects on persons carrying out normal oral hygiene practices.

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~L2~6)5Gt EXAMPLE 3:
Effect of Plaque Mineralisation on Experimental Dental Caries Removable lower arch appliances were constructed for 5 adult subjects. Extensions into the right and left buccal sulci, adjacent to the 1st permanent molars, held two plaque gauze-enamel units each. A unit consisted of a 3 ~ 4 mm piece of bovine enamel covered with two layers of fine tery-lene gauze and was mounted in a recess in the acrylic buccal extension with an epimine resin. Two enamel pieces were cut from the same permanent ~ovine incisor crown and these werealways used as a matched pair - one being mounted on the left and one on the right side of the applianceO Two such pairs were used in each appliance.
Following sterilisation of the -tooth pieces in ethylene oxide, the original surface was removed with 600 mesh car-borundum and the underlying enamel polished to a high gloss with alumina and diarnond abrasives~ Initial hardness testing was then carried out, gauze layers were added, and ~ the dry units stored.
For the first 2 days of the 14-day experimental period the appliance was worn continuously to establish a plaque growth within the terylene gauze. During the next 5 days the appliance was removed from the mouth three times per day and the plaque-enamel units on the right (test) side exposed to a plaque-mineralising solution for 10 min. The plaque-enamel units on the le~t (control) side were kept in a humid s~

atmosphere during this period. The whole appliance was then rinsed in tap water and replaced in the mouth. After the first 7 days, i.e., halfway through -the experiment, one pair of matched plaque-enamel units was removed for analysis (a unit from each side) and the appliance worn continuously for a further 2 days. On the last 5 days of the e~periment the appliance was again removed from the mouth for 10-min periods, -three times per day, but this time both left and right sides were exposed to a cariogenic solution. Finally, the remalning matched pair of plaque-enamel units was removed for analysis. Appliances were always worn overnight and during meals, bu~ were removed at normal toothbrushing times when the acrylic surfaces were cleaned, a non-fluoride toothpaste being used.
The plaque-mineralising solu-tion contained 6% urea O.04 M KCl, 100 mM CaC12, 5 mM NaH2P04, 4.72 mM Na2P03F, 0.28 mM NaF, and was adjusted to pH 5Ø The cariogenic solution contained 5% glucose and 0~04 M KCl, pH 7. All chemicals were Analar grade except sodium monofluoro-phosphate which was a commercial sample. Both solutions were stored at 5C, but were preheated to 37C and held at this temperature during use.
The gauzes (outer plaque) were excised from the enamel pieces, the remaining (inner~ plaque was scraped from the enamel surface with a chisel-shaped piece of soft polythene, and both gauzes and scrapings extracted in 0.5 ml of 0.5 N
HC104 or 12 h in a capped l-ml polystyrene vial. The supernatant acid extract was analysed for Pi by a molybdate method [Chen et al., Analyt. Chem. 28: 1756-1758, (1956)]
and for calcium by flame photometry, using 1% lanthanum to overcome phosphate interference. Fluoride was estimated with a specific ion electrode (model 96-09, Orion Research, Cambridge, Mass., USA) after neutralisation of 100 ~1 ali-quots with 10 ~1 of 5 N NaO~ and the addition of 100 ~1 of Tisab (Orion). The plaque residue was heated in 0.5 ml of 1.8 N NaOH at 80-90 C for 45 min and the protein content determined according to the method of [Lowry et al J. Biol.
Chem. 193:265-275 (1951)], using bo~ine serum albumin as a standard.
Hardness testing of the enamel was carried out with a Knoop diamond and a 50-gram load (Leitz miniload; Leitz, Wetzlar, FRG). Each piece was initially tested with a pre-determined pattern of 12 indentations ana then retestedafter an experiment with a further 12 indentations, again following a predetermined pattern. Oceasionally during retesting a mineral deposit partly obscured the polished enamel surface and then the indentations were placed 20- wherever possible. The difference in average length of the diamond indentations before and after an experiment served as a measure of enamel softening. The significance of the difference (i.e., of the softening) was tested by the method of [Welch Biometra 34:28-35 (1947)].
Finally, each enamel piece was sectioned with a water-cooled diamond saw and the sections ground to 50-60 ~m thickness [Sundstrom, Acta Odont. Scand. 24:159-178, (1966)]. Radiography was performed with a Softex CMR X-ray ~ 9~5~1 generator (Hosoda, Tokyo, Japan) on Kodak 649-0 spectrosco-pic film. The X-ray wave length was approximately 2.5 ~ and the exposure time 15-25 min.
Results Changes in Plaque Mineral Ion Concentrations Trea-tment of plaque with the urea-MFP mineralising solu-tion from day 3 to day 7 increased its average calcium con-centration from 7.6 + 1.7 ~g/mg protein (the value on the ; control side) to 219 + 111 ~g/mg protein (mean of combined, i.e., outer + inner, plaque material from 5 subjects + 1 SD). During this period, when normal dietary conditions were maintained, acid-extrable Pi also rose from 5.4 ~ 0.6 to 107 f 52.7 ~Ig/mg protein and fluoride from 0.008 + 0.004 to 7.62 + 1.43 ,Ig/mg protein. The final concentrations were more often higher in outer plaque contained within the tery-lene gauze than in inner plaque scraped from the enarnel sur-face. Increases in calcium were closely related to increases in Pi and fluoride. The calcium/phosphate molar ratio of the increases for combined plaque material was 1.60 j 20 + 0.08 while the calcium/fluoride molar ratio was 7.29 +
1~40.
- The cariogenic conditions subsequently prevailing from days 10-14 caused marked reductions in all three ions in the treated plaques. Nevertheless, they were, with few 25 exceptions, still higher than in untreated (control) pla- -ques. The average calcium concentration of combined plaque material was now 59.6 + 39.4 ~g/mg protein ~compared to 6.5 + 1.8 in the control), Pi 32.7 + 20.0 (compared to 7~5 +

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1.8), and fluoride 4.27 + 3.49 ~g/mg (compared to 0.007 +
0.004 !Ig/mg protein). In absolute terms, greater losses were associated with greater amounts deposited initially.
The mineral-depleting e~fect of the glucose exposures was most pronounced in outer plaque material and in 1 subject (A.M.), deposited calcium and Pi was almost completely lost.
Similar percen-tages of calcium and Pi were lost from plaque, but in 3 subjects relatively less fluoride was lost.
Overall, in 5 subjects and for combined plaques, the mineral remaining after glucose exposures (control values subtracted~ had a calcium¦phosphate ratio of 1.68 + 0.43 and a calcium/fluoride ratio of 6.28 + 1.20O
Changes in Enarnel Hardness and Radiopacity Enamel beneath untreated plaque (control), exposed to a normal diet for 7 days, always showed a small but variable degree of softening. The increase in Knoop diamond inden-tation length averaged for the 5 subjects was 3.7 ~m. Under mineralised plaque, matched enamel exposed to similar dietary conditions showed much less softening, an average 1.3 ~m increase, representing a 65% reduction. In 2 sub-jects there was no significant change in hardness and in another the softening was of marginal significance. These small decreases in enamel hardness could not be detected by microradiography.
Enamel beneath untreated plaque exposed to a cariogenic challenge during a further 7 days in the mouth showed mar~ed softening. The average increase in indentation length was 25.0 ~m. Except in the subject showing the smallest reduc-- 2~ -5~3 tion in hardness, the enamel showed distinct subsurface radiolucent areas on microradiography. By contrast, under mineralised plaque, matched enamel exposed to the same cariogenic challenge showed much less softening. The average increase in indentation length was only 4.3 ~m, representing an 83% reduction over the control enamel samples. No radiolucent areas were detected in enamel beneath mineralised plaque.
Pla~ue Minerals and Enamel Softening There was no apparent association between the con-centrations of calcium, Pi and fluoride in plaque and the degree of softening of the underlying enamel on the control side of the appliance. However, a distinct inverse asso-ciation appeared on the experimental side. During both the initial 7 days of normal dietary conditions and the sub-sequent period of cariogenic challenges, greater amounts of mineral in plaque were associated with less enamel sof-tening. In the latter period, softening was negligible when a large amount of mineral was retained in plaque.
Conversely softening was greatest w~ere outer plaque calcium and Pi had been reduced to near control levels.
EXAMPLE 4: I~ VIV0 STUDIES
Fifteen student school dental nurses, mean age 18 years 6 months, volunteered to take part in the trial. A control phase in which normal oral hygiene was withheld for 4 days was followed 3 weeks later by ~-day experimental phase when, in addition to withholding oral hygiene, the mouthrinse solution was used. Plaque samples were collected at the end - 2~ -~z~
of each phase.
The subjects were examined on the morning of the first day of both control and experimental periods and areas of gingivitis and supragingival calculus recorded. The clini-cal crowns of all teeth were then cleaned of soft deposits using a rubber cup and non-fluoride toothpaste. The sub-jects were again examined on the morning of the 5th day when all available supragingival plaque was collected from the buccal and lingual surfaces of teeth 15-25, 34-37, and 44-47 (FDI notation), using a soft plastic instrument ("Delrin", DuPont). Remaining plaque was then disclosed with erythro-sine and removed with a prophyla~is paste (Nupro fine grit).
Finally, the subjects rinsed for 30 secs with a 0.2%
chlorhexidine solution ("Savacol", I.C.I.).
During the experimental phase the plaque mineralising mouthrinse was used 4 times per day on days 2, 3 and 4, at 2-hourly or longer-intervals. At each rinsing period approximately 15 ml of solution was swished around the mouth or 1 min, spat out and the process repeated once.
The mouthrinse was the same as that of Example 2. The solution was stored at 5C but was warmed to 37~C for use.
Plaque samples were placed in small tared platinum dishes and, after 16 h in a vacuum at 40C over P205, dry weights were obtained. The samples were extracted in 0.5 ml of 0.5 N HC104 overnight and phosphate determined in the superna~ant by a molybdate method, calcium by flame photo-metry using 1% La to overcome phosphate interference, and fluoride by a speci~ic ion electrode (Orion model 94-09).
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~ - 26 -The samples were -then heated in 2N NaOH at 80-90C for 45 min and the protein content determined. Bovine serum albu-min was used as a standard.
Results Rinsing with the mineralising solution over 3 days resulted in an 80-fold increase in the average concentration of acid-extractable fluoride in plaque, a 13-fold increase in calcium and a 6-fold increase in phosphate. While plaque of every sub]ect showed some effect, there was a large indi-vidual variation in response. Increases in fluoride ranged from 32 to 1535 ~g/mg dry wt, increas~s in calcium from 1.0 to 97.7 ~g/mg and increases in phosphate from 0.4 to 44.6 ~IgP/mg.
- Increase in plaque calcium was very strongl~ related to increase in phosphate (r = +0.99, P<0.01) and the Ca/P molar ratios of the increases averaged 1.64.- Increase in calcium - was less strongly related to increase in fluoride (r =
- +0.70, P~0.01) and the Ca/F molar ratios of the increases averaged 34.2 trange 16.2 to 68.9).
The magnitude of the increases in calcium and phosphate tended to be related to the initial concentrations of these ions (i.e. in the control plaque); r = +0.71, P<0.01 in both cases. However there was no corresponding trend with respect to increases in fluoride. A number of subjects had small amounts of supragingival calculus on lingual surfaces of lower anterior teeth at the initial examination but there was no apparent association between ~his and subsequent increases in calcium, phosphate or fluoride.

. , .. . ._ _ . , . ., ., , ..... , ... ~

The protein concentration in the control plaque was 484 + 46 ~g/mg (mean + s.d.) and in the experimental plaque 437 + 40 ~g/mg dry wt. The average dry weight of control plaque collected was 1.78 + 0.97 mg and experimental plaque, 2.50 1.15 mg.
EXAMPLE 5: NON-FLUORIDATED CALCIUM PHOSPHATE
In the previous examples the mouth rinses described all contained a source of fluoride ions. A satisfactory rinse solution could also be prepared without a source of fluoride ions. Such a mouth rinse would deposit mineralising calcium phosphate salt. This would not provide as much caries pro-tection as would the solution which did have a Eluoride source but it would be an improvement over no treatment at all.

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~ - 28 -i

Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A dry mix composition containing the following components in parts by weight:

2. A dry mix composition according to claim 1 which also contains:
A source of fluorophosphate ions 0.1-20.0 A source of fluoride ions .001-40Ø

3. A composition according to claim 2 comprising the following:

4. A composition according to claim 2 comprising the following:

5. A composition according to claim 3 which also contains up to 5 parts by weight of a further water soluble physiolo-gically acceptable salt.

6. A composition according to claim 4 which also contains up to 5 parts by weight KCl.

7. A plaque mineralizing aqueous solution comprising 0.01 to 50% W/V of a substance metabolised by bacteria in plaque to raise the pH of said solution, a physiologically acceptable source of calcium ions and a physiologically acceptable source of phosphate ions, both in concentrations to form a stable solution with respect to a calcium phosphate salt, the pH of said solution being from 1 to 9, with the pro-viso that the pH and calcium and phosphate ion con-centrations are such that the solution remains stable and with respect to the calcium phosphate salt until said substance is metabolised by bacteria in plaque.

8. A solution according to claim 7 which in addition con-tains a physiologically acceptable fluoride ion generating compound metabolised by bacteria in plaque to release fluoride ions or other physiologically acceptable source of fluoride ions.

9. A solution according to claim 7 wherein said substance metabolised by bacteria is urea present in a concentration of from 3 to 6% W/V.

10. A solution according to claim 7 wherein said source of calcium ions is calcium chloride present in a concentration of about 100 mM.

11. A solution according to claim 7 wherein said source of phosphate ions is NaH2PO4 present in a concentration of about 5 mM.

12. A solution according to claim 8 wherein said fluoride ion generating compound is also a phosphate ion generating compound.

13. A solution according to claim 12 wherein said fluoride ion generating compound is Na2PO3F present in a con-centration such that the total fluoride concentration to be generated within the solution is about 5 mM.

14. A solution according to claim 12 or 13 wherein the pH of said solution is from 4 to 5.

15. A solution according to claim 7 in which KCl is present in a concentration of about 0.04 M.

16. A solution according to claim 7 in the form of a mouth rinse which comprises an aqueous solution containing:

urea 3% (w/v) calcium chloride 20 mM
sodium dihydrogen phosphate 12 mM
sodium monofluorophosphate 4.72 mM
sodium fluoride 0.28 mM
glycerol 5% (v/v) saccharine ) sufficent to spearmint ) increase vanilla ) palatability food colour ) adjusted to pH 5Ø