Enamel Protective Factors in Food

G. NEIL JENKINSDepartment of Oral Physiology, University of Newcastle upon Tyne, Markham Labora-tories, Newcastle upon Tyne, England

There is almost universal agreement thatcaries is a disease of westernized condi-tions,1 although many of the data are un-critical or were collected inexpertly byarcheologists and anthropologists. Althoughit is reasonable to assume that the chemicalchanges of the diet explain this effect ofwesternization, other aspects of feeding,such as, the timing of meals or the tough-ness of food or even nondietary differences,are difficult to exclude completely. There isno reason to believe that the same factorsoperate in all instances; eg, the traditionaldiet of the Eskimo contained no sugar andindeed virtually no carbohydrate, whereasthe native diet of the African Bantu is highin carbohydrate, consisting largely of un-refined mealie meal.

Clinical Data on the Effect ofWesternization

The clinical data of Osborn and Noriskin2on caries in the Bantus on native or Euro-pean diets were carefully collected but donot show a really dramatic difference inincidence, eg, 43% of 143 who stated thatthey never had European food had caries,compared with 57% of 44 who ate Euro-pean bread regularly. The data suffer fromseveral defects, such as the ignorance of theBantus about their own ages and relianceon their own testimony about the nature oftheir diet.

Turner and Vickery3 reported an attemptto study the effects of white and whole mealflour on caries. The DMF scores among agroup of 94 British children between 1 and18 years old who had always eaten wholemeal bread were compared with those fromseveral typical British groups (eg, the con-trols in the fluoridation studies). The resultsdid show considerably less caries in thewhole meal group: DMF scores for the 5-,6-, and 7-year-old children were below three

1318

in the whole meal group and between fiveand seven in the control groups. Unfortu-nately, these results cannot be taken at theirface value, because 64 of the children wereattending a "food reform school" at whichthe diet presumably differed from that eatenby the controls in several respects other thancontaining whole meal bread. The parentsalso stated that they "enforced significantcontrol over the intake of sugar," whichwould obviously confuse the issue.The effect of raw sugar cane on caries is

even less substantiated. Most of the clinicaldata are impossible to interpret, because nocomparisons were made between caries in-cidence in workers in sugar-cane planta-tions who ate much raw sugar and subjectswho ate the same quantities of refined sugarwith the same frequency during the day. Itis not disputed that a high caries incidencecan occur in sugar-cane eaters4,5 so thatcrude cane cannot exert dramatic over allprotection but, in the absence of a suitablecontrol, it is simply not known whethercrude cane exerts any protective influencesat all.

Animal Experiments on ProtectiveFactors in Unrefined Foods

Earlier animal experiments in which re-fined or unrefined cereals or sugars weretested for cariogenicity were contradic-tory'"' but tended to support the presenceof protective factors in the unrefined foods.These experiments were indecisive, however,because no evidence was presented onwhether the diets were adequately matchedfor such factors as viscosity and taste or forthe size and hardness of the particles, pointswhich, it is now realized, could have had acrucial influence on cariogenicity.The same criticism applies to some of the

more recent work of StraIlfors, which, onface value, suggested that cocoa'2 and "crys-

ENAMEL PROTECTIVE FACTORS IN FOODS 1319

tallised brown sugar's3 obtained from beetcontained protective factors. Kbnig andMUhlemannI4 repeated these tests with ratsfed on a feeding machine; they used thesame sugars used by StrAlfors,'3 in which theunrefined particles were coarser than the re-fined, and both sugars were ground to thesame particle size. When the unrefined sugarwas coarse, the reduction in caries score wassimilar to that found by Stralfors,'3 butwhen both sugars were ground to the sameparticle size, no difference in score wasfound. The result was the same whether thediet was fed ad libitum or with the numberof meals restricted (ie, a reduced food intakedid not influence the results). They con-sidered that the particle size of the unre-fined sugar had affected the result. Sincefood intake had not been lower in the groupon unrefined sugar, presumably the taste hadnot influenced the result. Stralfors'3 didshow, however, that when the sugars weredissolved in the drinking water, or includedin cakes, the rats that received the unre-fined sugar sustained a lower caries score.Since feeding cubes of the raw sugar beetdid not reduce caries but tended to increaseit, Stralfors'3 concluded that cariostaticfactors not present in the original beet areformed during the refining process.

Kbnigl5 compared caries development inrats on white and brown bread and foundconsistently that brown bread producedslightly more caries than white bread, al-though the caries score on both was lowcompared with the score of rats on sugardiets. He explained this result on the basisthat starch had a low cariogenicity and thatthe higher vitamin content of the brownbread slightly stimulated bacterial activity.

As a follow-up of some indecisive sug-gestions in the Vipeholm experiment's of ananticaries effect of chocolate, StrAlfors re-ported experiments in which 20, 10, 5, and2% of cocoa12 and 20% of milk or darkchocolate'7 were included in the diet of ham-sters. Large reductions in caries were found(of 84, 75, 60 and 42%, respectively, withthe cocoa and 35 and 73% with the choco-late). The effect was not caused by the fat inthe cocoa, since it was still present with de-fatted cocoa; furthermore, 15% cocoa but-ter added to the diet had no protective effectbut increased caries. Aqueous extracts ofcocoa and the extracted residue were both

active, which indicates the probable presenceof two factors, some properties of whichwere studied. Food consumptions were notmeasured in most of these experiments, butbody weights showed no difference, exceptin the group that received 20% cocoa, whichindicates that there was no gross interferencewith the amount of food consumed. How-ever, the possible effects of a different eatingpattern or differences in the extent to whichthe diet was held in the mouth were noteliminated.

StrAlfors'8 also showed that several con-stituents of cocoa (0.2% theobromine,0.2% xanthine, 0.05% vanillin, and 0.01 to0.05 tannic acid) all reduced caries at theindicated concentrations, which did not af-fect food intake (higher concentrations ofsome of them did reduce food consump-tion). Aqueous extracts of cocoa have adefinite effect on the solubility of apatitebut negligible antibacterial activity, and anapparent small effect on acid productionwas for the most part accounted for bythe buffering power of the extract.'9A number of investigators have reported

that the inclusion of hulls from oats, rice,cottonseed, peanuts, and pecan all reducedcaries in rats.9,20-22 The effect of the oathulls was believed to be chemical ratherthan mechanical, because the anticaries ac-tion was increased, rather than reduced, bygrinding the hulls finely. Nor could it beaccounted for by a mere dilution of thesugar, because the addition of an equiva-lent amount of an inert diluent, celluflour,had no effect. Autoclaved rice hulls hadlost much of their cariostatic activity,which again suggests a chemical rather thanphysical effect.

Nature of the Protective Factorsin Foodstuffs

After clinical observations, Osborn, Noris-kin, and Staz23 demonstrated that unrefinedcereals and sugar-cane juice contained sub-stances that reduced the solubility rate ofwhole teeth when incubated -with salivawithout altering acid production. This hasbeen confirmed by others,24-27 who havealso shown that phytate, like other organicphosphates, possesses this property and canaccount for the in vitro effect of unrefinedcereals, which are known to contain thissubstance. Osborn23 suggested that organicphosphates might account for the protec-

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tive effect that he observed, but he con-cluded (at least at one stage of his work)that these substances were broken down byenzymes of the salivary bacteria and that theinorganic phosphate released was the activesubstance. Andlaw25 also concluded thatinorganic phosphate explained the reducedsolubility of the blocks of enamel that hetested in unrefined flour-saliva mixtures.This conclusion was based on the fact thatextracts of wheat bran and wheat germ pos-sessed activity after ashing, but this resultmay be an artifact. Not only would ashingconvert organic phosphate to the inorganicform (thus raising the inorganic phosphateto much higher levels than the original ex-

tract), but some of the inorganic phos-phates would be converted to pyrophos-phate. Both the orthophosphate and pyro-phosphate would, by different mechanisms,reduce enamel solubility (orthophosphateby a common ion effect and pyrophosphateby binding to the enamel crystals). Thisconversion of orthophosphate to pyrophos-phate by ashing is an important potentialsource of error in dietary research and

may have confused the results of some

experiments on caries (eg, that of Nizel andHarris28).

Since uncooked flour was used byAndlaw,25 the enzymes of the cereal (in-cluding phytases) would be active, andthe concentration of phytate would be fall-ing and that of phosphate rising throughoutthe experiment. The reduction in solubilityrate is about the same in experiments ofthis type in which cooked cereals are used,as it is when buffers are used as a solventin place of saliva with its bacterial enzymes.

Thus neither enzymic release of phosphatenor reductions in acid production are an

essential part of the in vitro effect.24 Mostorganic phosphates have been found to re-

duce solubility, but of those tested phytateis the most active, in the sense that it can

work at greatest dilution because its effectis detectable at concentrations as low as

0.01 mM (ie, about 1% of the concentra-tion of inorganic phosphorus with a similareffect). Organic phosphates appear to act bybecoming adsorbed on to the enamel sur-face and perhaps acting as a "kink poison."After exposure to phytate. a tooth can beshown to have retained a lower solubilityafter thorough washing: phytate is also de-tectable chemically on calcium phosphate

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after it has been shaken with phytate solu-tion and washed in water. Several animalexperiments have confirmed that I to 2%of phytate added to the diet can have aconsiderable effect in reducing caries,29 32although a negative result has also beenreported.33

Support is given to the concept that or-ganic phosphates have protective propertiesby the promising reductions in caries ob-tained in the Australian clinical trial of cal-cium sucrose phosphate34-36 as an additiveto sugar and the findings that calciumglycerophosphate has anticaries propertiesin rats37 and monkeys.38

It is, of course, not proved that in theseclinical and animal experiments calcium su-crose phosphate or phytate reduced cariesby lowering solubility, although this seemsthe most likely explanation, since no otherproperty of these substances is known thatcould account for an anticaries effect. Innone of these animal experiments were un-specific effects, such as reduced food in-take, eliminated. Two reports do cast doubton this mode of action of organic phos-phates, however. McClure30 found that 1 :6fructose diphosphate was the most highlyeffective organic phosphate in reducingcaries, whereas this substance has low solu-bility-reducing powers in vitro, except inhigh concentrations. The second reason fordoubting the mechanism of action of thesesubstances arises from results of Tatevos-sian and Jenkins39 on the entry of the sub-stances into the plaque when used as addi-tives to sugar. Subjects with 24 houraccumulation of plaque sucked sugar lumpsthat contained 1% of calcium or sodiumorthophosphate, calcium sucrose phosphate.phytate or calcium glycerophosphate, or noadditive (in the controls). Inorganic, andorganic phosphates in plaque were analyzedbefore and two minutes after sucking thesugar. The results showed that only calciumphosphate or calcium sucrose phosphateappeared to enter the plaque in detectableconcentrations under the conditions of theexperiment. However, when the sugarswith additives are present during plaqueformation, it is possible that they may be-come incorporated into a developing plaquebut cannot readily diffuse into a preformedplaque. With sodium phosphate, the prob-able reason for its failure to enter plaqueis that by the time the saliva has dissolved

ENAMEL PROTECTIVE FACTORS IN FOODS 1321

the sugar, it has so diluted the phosphateadditive (and the phosphate of the salivaalso falls with increasing rate of flow) thatits concentration outside the plaque is be-low the already rather high concentrationin plaque.How may the positive results of phytate

in animal experiments be reconciled withKbnig's15 negative findings with animalsthat received brown flour? A likely explana-tion is that the phytate added to diets wasin a soluble and available form, whereas thephytate in flour is present inside insolubleparticles of bran. It is doubtful whetherthe food would stimulate a sufficiently briskflow of saliva to extract the phytate andmake it available to contact the tooth sur-face within the few seconds that it remainsin the mouth. An implication of this is thatphytate trapped in unrefined foods may notplay a part in the low caries incidence ofprimitive communities but, as a soluble ad-ditive to carbohydrate, might have an ap-plication in modem caries control. Morework on these substances is needed.

Thanik and Bibby40 tested the decalcifi-cation of radioactive enamel blocks in whiteflour extracts and saliva with or withoutthe addition of extracts of wheat germ orbran. The results showed that the extractsof unrefined materials reduced solubility,but there was no exact proportionality be-tween the concentrations of calcium andphosphorus in the cereals and the reductionin solubility. This was not surprising, sincethe extracts would be expected to containprotective factors other than inorganic ions;although, as in Andlaw's25 experiments, theuncertainties were introduced by enzymicrelease of phosphate and correspondingreduction of organic phosphate concentra-tion.Khanna and Bibby4' found that cereal

products from different geographic regionsdiffered in their powers of reducing decal-cification, but the effects did not correspondwith known variations in regional cariesprevalence.

SUGAR PRODUCTS.-The existence of fac-tors that reduce solubility rate in cane juiceand molasses has been confirmed,42 al-though the results with molasses are con-fused by the presence of about 0.5% cal-cium, which arises from the lime addedduring refinement and not from the originalplant. The position with crude sugar and

honey is more complicated. In buffers,honey reduces the solubility rate of enamel,but the active constituent (probably an or-ganic phosphate) is destroyed during incu-bation with saliva. The powerful effect ofcrude sugars on enamel solubility in buffersis observed after four hours' incubationwith saliva but is much reduced or abol-ished after 24 hours. The active constituentsare probably calcium and traces of copperand iron, which are present in the crudesugar and which can simulate its action inbuffers. These are less effective in saliva,especially after 24 hour incubations, becausethe different conditions found during pro-longed incubation-lower pH and the chem-ical nature of the acids produced-tend tocounteract the effects of these solubility-reducing actions. In addition, the greaterbuffer strength of the incubations contain-ing crude sugars, compared with controls,may tend to nullify the solubility-reducingaction.

ANTIBACTERIAL FACTORS IN UNREFINEDCEREALS.-Taketa and Phillips20 reportedthat alcoholic extracts of oat hulls con-tained antibacterial factors, partly identifiedas polyphenols, and assumed that they wereresponsible fQr the action against caries inanimals. Neither they or others who hadstudied various seed hulls on animal cariesinvestigated their action on enamel solu-bility, but Jenkins and Smales19 demon-strated that they all possessed water-solubleconstituents that reduced the solubility rate.These authors suggested that these sub-stances were more likely to be effective invivo than antibacterial factors, which areinsoluble in water or require an extractionprocedure far more drastic than is likely tooccur to food in the mouth. Of the ma-terials tested in animals, only pecan nuthulls contain water-soluble antibacterialfactors.Madsen and Edmonds43 found that feed-

ing a diet containing 25% rice hulls toweaning cotton rats for as short a time asten days reduced caries as effectively asfeeding the diet throughout the whole ex-perimental period. This high dose of what,in any case, cannot be regarded as a food,makes this a somewhat academic experi-ment but suggests a possible systemic effect.Could an antibacterial effect exerted over ashort time have a prolonged action oncaries? This is possible, since Jay44 has

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shown that drastic reduction in carbohydrateeating for two weeks can alter the oral florafor some time. It is even possible that sub-stances that reduce solubility bind to thetooth surface and exert a prolonged reduc-tion in solubility, a process that may or maynot resemble an increase in the normal post-eruptive maturation.

Action of Major Food ConstituentsROUGHAGE.-The cellulose roughage of

plant foods probably has some mechanicaleffect in removing plaque, and eating rawvegetable matter (eg apple, carrot, or cel-ery) has long been recomended as a cariespreventive measure. Although it is easy toobserve that plaque on the smooth surfacesis removed by these procedures, personalobservations agree with Lindhe45 in show-ing that the procedures have little effect oncervical or interstitial plaque, which is pre-sumably most relevant to caries. Only oneclinical trial on caries appears to have beencarried out, that of Slack and Martin46 onapple rings. The results gave indications ofreduced caries but were not entirely con-vincing, because of initial variations betweenthe caries score of the apple and controlgroup. Apples are a srtongly acidic food(which led Stephan"1 to suggest that theymight be a cause of erosion) and evenwhen mixed with rapidly flowing, and there-fore alkaline, saliva, the pH of the mouthcontents is usually around 3.9 to 4.2 (Jen-kins, unpublished results). Other toughfoods (such as raw celery or carrots) havea similar mechanical effect and, althoughnot such a powerful saliva stimulant, obser-vations show that the pH of mouth fluidswhen these foods are chewed is much higher(from 6.1 to 6.50). This result suggeststhat celery and carrots might be more valu-able in caries control than apples.*PROTEINS.-Milk and proteins from milk

and other foods have been found to re-duce enamel solubility even after the teethtreated with these proteins were thoroughlywashed.47-50 Presumably, the protein be-comes adsorbed on to the surface and actsas a barrier between acid and apatite. Bothenamel powder and blocks of enamel withthe outer layer removed have been used,4849

* Since this was written, Reece and Swallow (BritDent J 128:55, 1970) have shown that eating carrotsafter the midday meal did not produce a statisticallysignificant reduction of caries in schoolchildren.

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as well as thoroughly brushed whole teethin which pellicles were presumably intact.YBoth groups observed a 20% reduction insolubility rate. It is not surprising that pro-tein should become attached to the exposedapatite of ground enamel but it is unex-pected that whole teeth, which must havebeen exposed to proteins for years in vivo,should still be influenced by in vitro treat-ment. Either the protein is not bound underin vivo conditions or it is readily removedeven by toothbrushing. In any case, it wouldseem that protein can be adsorbed by pel-licle as well as by apatite. Pearce andBibby48'49 suggested that the higher nitro-gen of early caries and possibly the greaterdecalcification in early caries of the deeperlayers of enamel (less accessible to proteinsin the oral fluids) may arise from this ad-sorption of protein by enamel. Whetherquantitative or qualitative variations inprotein intake could influence caries by theformation of these layers is unknown.FAT.-Dietary fat reduces caries in ani-

mal experiments, but there is no clear evi-dence of this in man. Nevertheless, thispossibility leads to a complication in inter-preting certain experiments in man (eg, theVipeholm experiment16): if carbohydrateis restricted, fat is increased to maintainthe calories, thus introducing another vari-able. The mechanism of action of lipids isunknown, but it is speculated that they maysurround bacteria and carbohydrate food,thus keeping them apart, or form an im-permeable barrier on the enamel surface.Foods with a high fat content are retainedin the mouth in smaller amounts than simi-lar foods low in fat.5' Certain fatty acids(eg, palmitic) inhibit some oral bacteria,although it is unlikely that the weak lipasesin saliva would be able to hydrolyze fat inthe food (although the lipase activity ofplaque has not been studied).

FRUIT JUICES.-Gross decalcification,usually of the maxillary incisors, that leadsto rampant caries has been reported afterthe consumption of acid fruit juices in com-forters, in "dinkie feeders," or wheneverallowed to remain in contact with enamelfor long periods or move over it slowly.52The exact course of events is not knownbut it might be speculated as follows: thehigh acidity of the juice (pH 3 is common)dissolves the outer surface of the enamel,plaque accumulation is favored and allowed

ENAMEL PROTECTIVE FACTORS IN FOODS 1323

to penetrate more deeply than usual into theenamel, and, perhaps supplemented by acidproduced bacterially from the sugar in thejuices, gradually forms the penetrating le-sion characteristic of caries.

Blackwell and Fosdickm3 found that su-gar tended to reduce the amount of enameldissolving in acid buffer solutions and thatthe effect was much greater with sucrosethan with the other sugars tested. It is pos-sible, therefore, that the sucrose in fruitjuices may have two contradictory effects:to reduce the action of the acid in the juicesand to provide a substrate for the bacterialactivity, which may be necessary to converta superficial erosion into a penetrating cari-ous lesion.

It must be emphasized that this conditionarises only from the misuse of these fruitjuices; when consumed in the normal wayor as directed by the manufacturers theyhave no adverse effect on the teeth.

There are cases on record of damage toteeth by habitual eaters of fruit, such aslemons, especially when sucked or eaten insuch a way as to prolong contact with theteeth, but this is chemical erosion, inducedpresumably by the combined acid and che-lating effects of the citrate in the fruitsrather than caries.4 55 Stephan" found ero-sion from apples in rat caries and consid-ered that any fruit with a pH below 4.5was potentially harmful.

Interactions Between Sucrose and Enamel

It has been suggested by several investi-gators that sucrose may have a direct effectin dissolving enamel and thus lead to carieswithout the intervention of bacteria.5657After one inadequately described experi-ment, Blackwell, McMillan, and Fosdick58published electron micrographs that showedetching on replicas of the enamel surfaceby sucrose solutions at a pH of 11.0, whichgives some support to this possibility. It iswell established that compounds known assaccharates can be formed between sucroseand calcium. Tatevossian and Jenkins39have confirmed previous work in showingthat sucrose readily combines with Ca(OH)2at pH 11.0 but have found no conditionsunder which it solubilizes Ca3(PO4)2 orenamel. They concluded that direct inter-action of sucrose in favoring caries is mostunlikely and that the one reported result

of Blackwell, McMillan, and Fosdick58 re-mains unexplained.

Masticatory Stress and CariesNeumann and DiSalvo59 state that the

one factor common to populations with alow caries incidence is major tooth com-pressions, produced either in eating or useof teeth as tools. They have speculated aboutthe ways in which stress might build up aresistance and suggest reorientation ofenamel crystals60 or changes in hydrationof the organic matter analogous to thethickening of the epidermis caused by ha-bitually walking barefoot.6' Neither ofthese effects would seem to be obviouslyrelated to caries prevention, although thepossibility cannot be dismissed. Two clin-ical trials did show that chewing sugar caneor a hard gum was associated with a reduc-tion in caries,6263 but several interpreta-tions are possible in addition to those sug-gested by Neumann's group.59-63

Although of considerable theoreticalvalue, this effect, even if fully confirmed,would have limited application in view ofthe reluctance of most contemporary youngpeople to chew vigorously.

References1. JENKINS, G.N.: The refinement of Foods

in Relation to Dental Caries, in Advancesin Oral Biology, Vol 2, New York: Aca-demic Press Inc., 1966, p 67.

2. OSBORN, T.W.B., and NORIsKIN, J.N.: TheRelation between Diet and Caries in theSouth African Bantu, J Dent Res 16:431,1937.

3. TURNER, E., and VICKERY, K.O.A.: TheWholemeal Bread Family, Vitalstofle-Zivilisationskrankheiten 53:(No. 3), 1966.

4. OTTESEN, I.: Kosten kostvaner og tennene,Munnpleien 29:(No. 3), 1946.

5. DREIZEN, S., and SPIES, T.D.: The Inci-dence of Dental Caries in Habitual SugarCane Chewers, JADA 45:193, 1952.

6. KING, J.D.: Dental Cavities in the GoldenHamster, Brit Med J 1:876, 1950.

7. CONSTANT, M.A.; PHILLIPS, P.H.; andELVEHJEM, C.A.: Dental Caries in theCotton Rat: XIII. The Effect of WholeGrain and Processed Cereals on DentalCaries Production, J Nutr 46:271, 1952.

8. CONSTANT, M.A.; SIEVERT, H.W.; PHILLIPS,P.H.; and ELVEHJEM, C.A.: Dental Cariesin the Cotton Rat. XIV. Further Studiesof Caries Production by Natural Dietswith Especial Reference to the Role of

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Minerals, Fat, and the Stage of Refine-ment of Cereals, J Nutr 53:17, 1954.

9. MCCLURE, F.J.: Inhibition of ExperimentalCaries by Oat Hulls, A rch Oral Biol 9:219, 1964.

10. SHAW, J.H.: Nutrition and Dental Caries.Fed Proc 8:536, 1949.

11. STEPHAN, R.M.: Effects of Different Typesof Human Foods on Dental Health in Ex-perimental Animals, J Dent Res 45:1551,1966.

12. STRXLFORS, A.: Inhibition of HamsterCaries by Cocoa, Arch Oral Biol 11:149,1966.

13. STRXLFORS, A.: Inhibition of HamsterCaries by Substances in Brown Sugar,Arch Oral Biol 11:617, 1966.

14. K6NIG, K.G., and MUHLEMANN, H.R.:The Cariogenicity of Refined and Unre-fined Sugar in Animal Experiments, ArchOral Biol 12:1297, 1967.

15. K6NIG, K.G.: Caries Induced in Labora-tory Rats, Brit Dent J 123:585, 1967.

16. GUSTAFSSON, B.E.; QUENSEL, C.-E.; SWEN-ANDER LANKE, L.; LUNDQVIST, C.; GRAH-NEN, H.; BONOW, B.E.; and KRASSE, B.:The Effect of Different Levels of Carbo-hydrate Intake on Caries Activity in 436Individuals Observed for Five Years, ActaOdont Scand 11:232, 1954.

17. STRXLFORS, A.: Inhibition of Hamster Car-ies by Substances in Chocolate, A rch OralBiol 12:959, 1967.

18. STRXLFORS, A.: Effect on Hamster Cariesby Purine Derivatives. Vanillin and SomeTannin Containing Materials. Caries inRelation to Food Consumption and Ani-mal Growth. Arch Oral Biol 12:321, 1967.

19. JENKINS, G.N., and SMALES, F.C.: ThePotential Importance in Caries Preventionof Solubility Reducing and AntibacterialFactors in Unrefined Plant Products, Arc/hOral Biol 11:599, 1966.

20. TAKETA. F., and PHILLIPS, P.H.: Oat HullFractions and the Development of DentalCaries, J Amer Diet Assn 33:575, 1957.

21. BUTTNER, W.; and MUHLER, J.C.: The Ef-fect of Oat Hulls on the Dental CariesExperience in Rats, J Dent Res 38:823.1959.

22. MADSEN, K.O., and EDMUNDS, E.J.: Effectof Rice Hulls and Other Seed Hulls onDental Caries Production in the CottonRat, J Dent Res 41:405, 1962.

23. OSBORN, T.W.B.; NORISKIN, J.N.; and STAZ.J.: A Comparison of Crude and RefinedSugar and Cereals in Their Ability ToProduce In Vitro Decalcification of Teeth.J Dent Res 16:165, 1937.

24. JENKINS, G.N.; FORSTER, M.G.; SPEIRS,R.L.; and KLEINBERG, I.: The Influenceof the Refinement of Carbohydrates on

Their Cariogenicity. In Vitro Experimentson White and Brown Flour, Brit Dent J106:195, 1959.

25. ANDLAW, R.J.: The Relationship BetweenAcid Production and Enamel Decalcifica-tion in Salivary Fermentations of Carbo-hydrate Foodstuffs, I Dent Res 39:1200,1960.

26. GRENBY, T.H.: Wheat Bran Factors inDecalcification Tests, Arch Oral Biol 12:523, 1967.

27. GRENBY, T.H.: Phytates in DecalcificationTests In Vitro, Arch Oral Biol 12:531,1967.

28. NIZEL, A.E.; and HARRIS, R.S.: Effects ofAshed Foodstuffs on Dental Decay inHamsters, J Dent Res 34:513, 1955.

29. MCCLURE, F.J.: The Cariostatic Effect inWhite Rats of Phosphorus and CalciumSupplements Added to the Flour of BreadFormulas and to Bread Diets, J Nutr 72:131, 1960.

30. MCCLURE, F.J.: Further Studies on theCariostatic Effects of Organic and Inor-ganic Phosphates, J Dent Res 42:693, 1963.

31. DAWES, C., and SHAW, J.H.: DietaryPhosphate Supplementation and Its Effectson Dental Caries and Salivary and SerumConcentrations of Calcium and InorganicPhosphate in the Rat, Arch Oral Biol 10:567, 1965.

32. ENGLANDER, H.R., and KEYES, P.H.: Ef-fect of Phosphate Supplements on Cavita-tion in Hamsters Infected with Caries-conducive Streptococci. J Dent Res 49:140.1970.

33. LIMBASUTA, S.; SINGH, B.; and JOHANSEN,E.: The Effect of Sodium Phytate and So-dium Acid Pyrophosphate on Rat Caries,J Dent Res 40:658, 1961.

34. HARRIS, R., SCHAMSCHULA, R.G.; GREGORY,G.; ROOTS, M.; and BEVERIDGE, J.: Obser-vations on the Cariostatic Effect of Cal-cium Sucrose Phosphate in a Group ofChildren Aged 5-17 Years. Aust Dent J12:105, 1967.

35. HARRIS, R.; SCHAMSCHULA, R.G.; BEVER-IDGE, J.; and GREGORY, G.: The Cario-static Effect of Calcium Sucrose Phosphatein a Group of Children Aged 5-17 years,Aust Dent J 13:32, 1968.

36. HARRIS, R.; ROOTS, M.; GREGORY, M.; andBEVERIDGE, J.: Calcium Sucrose Phosphateas a Cariostatic Agent in Children Aged5-17 Years, Aust Dent J 13:345, 1968.

37. FEDEROV, T.A.: Studies on Local Effectsof Calcium Glycerophosphate and SodiumFluoride in Experimental Dental Caries inWhite Rats, Dokl Akad Nauk USSR 161:244, 1965.

38. BOWEN, W.H.: The Cariostatic Effect ofCalcium Glycerophosphate in Monkeys

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ENAMEL PROTECTIVE FACTORS IN FOODS 1325

(M irus), abstracted, J Dent Res, in press.39. TATEVOSSIAN, A., and JENKINS, G.N.: Un-

published results.40. THANIK, D.D., and BIBBY. B.G.: Enamel

Dissolution in Saliva and the Calcium andPhosphorus Content of Some Foodstuffs,J Dent Res 45:204, 1966.

41. KHANNA, S.L., and BIBBY, B.G.: EnamelDecalcification by Cereals of DifferentGeographic Origin, J Dent Res 45:927,1966.

42. EDGAR, W.M., and JENKINS, G.N.: TheEffects of Honey and Barbados Sugar uponthe Rate of Calcium Phosphate Solubilityin Different Media, J Dent Res 46:1296,1967.

43. MADSEN, K.O., and EDMONDS, E.J.: Pro-longed Effect on Caries of Short-termFeeding of Rice Hulls to Cotton Rats,J Dent Res 42:137, 1963.

44. JAY, P.: The Reduction of Oral Lactobacil-hIs acidophilus Counts by the PeriodicRestriction of Carbohydrate, Amer J Orth33:162, 1947.

45. LINDHE, J., and WICEIN, P-O.: The Effectson the Gingiva of Chewing Fibrous Food.J Periodont Res 4:193, 1969.

46. SLACK, G.L., and MARTIN, W.J.: Applesand Dental Health, Brit Dent J 105:3 66,1958.

47. WEISS, M.E., and BIBBY, B.G.: Effects ofMilk on Enamel Solubility, Arc/ OralBiol 11:49, 1966.

48. PEARCE, E.I.F., and BIBBY, B.G.: ProteinAdsorption on Bovine Enamel, Arch OralBiol 11:329, 1966.

49. PEARCE, E.I.F., and BIBBY, B.G.: Effectsof Time, Surface Area, pH and Some Ionson Protein Adsorption by Bovine Enamel,Ar/ch Oral Biol 11:825, 1966.

50. JENKINS, G.N., and FERGUSON, D.B.: Milkand Dental Caries, Brit Dent J 120:472,1966.

51. BIBBY, B.G.: GOLDBERG, H.J.V.: and CHEN.

E.: Evaluation of Caries-producing Poten-tialities of Various Foods, JADA 42:491,1951.

52. WINTER, G.B.; HAMILTON, M.C.; andJAMES, P.M.C.: Role of the Comforter asan Aetiological Factor in Rampant Cariesof the Deciduous Dentition, A rc/i DisChild 41:207, 1966.

53. BLACKWELL, R.Q., and FOSDICK, L.S.:Studies on the Physio-chemical PhenomenaRelated to Dental Caries: III. The Effectof Sucrose upon the Solubility of HumanDental Enamel, J Dent Res 35:210, 1956.

54. PICKERILL, H.P.: The Prevention of Den-tal Caries and Oral Sepsis, London: Bail-liere, Tindall and Cox, 1912.

55. ALLAN, D.N.: Enamel Erosion with LemonJLiice, Brit Dent J 122:300, 1967.

56. SPRAWSON, E.: Diet in Relation to theTeeth and Jaws, Brit Dent J 64:245, 1938.

57. EGGERS-LURA, H.: The Non-Acid Coin-plexing Theory of Dental Caries, Holbaek:H. Eggers-Lura, 1967.

58. BLACKWELL, R.Q.; MCMILLAN, L.; andFOSD!CK, L.S.: Sucrose Retardation ofAcid Etching in Dental Enamel: AnElectron-Microscopic Study, J Dent Res40:16, 1961.

59. NEUMANN, H.H, and DISALVO, N.A.:Caries in Indians of the Mexican Cordil-lera, the Peruvian Andes and at the Ama-zon Headwaters, Brit Dent J 104:13, 1958.

60. NEUMANN, H.H., and DISALVO, N.A.: Com-pression of Teeth under the Load of Chew-ing, J Dent Res 36:286, 1957.

61. NEUMANN, H.H., and DISALVO, N.A.:Dental Caries in Aymara Indians of Peru,Odont T 67:473, 1959.

62. NEUMANN, H.H.; LEFKOWITZ, W.; andDISALVO, H.A.: Relation of Function toCaries Rate, J Dent Res 31:200, 1952.

63. NEUMANN, H.H., and DISALVO, N.A.:Does Functional Effort Affect Caries Ac-tivity? J Dent Child 22:151. 1955.

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