Limitations in the intraoral demineralization of bovine enamel.

A model system was used to examine the relation between the duration of plaque pH fall and enamel demineralization following the intake of dietary carbohydrate in humans. Subjects wore palatal appliances containing blocks of bovine enamel covered with Streptococcus mutans IB 1600, and rinsed with 5 or 10% sucrose. Changes in iodide penetrability (delta Ip) of the enamel, and the pH and extracellular calcium and inorganic phosphate (Pi) concentrations of the streptococcal plaque were determined. Following rinses with 5% sucrose, delta Ip increased with time and reached a maximum (11.2 +/- 2.2 units) at 45-60 min although the S. mutans plaque remained acidic (pH = 4.8 +/- 0.6). After 10% sucrose, the maximum (14.7 +/- 3.1 units) was reached while the plaque pH was 4.0 +/- 0.3. Second rinses with sucrose increased delta Ip at most by 30%. Thus, demineralization did not persist throughout the period of low plaque pH, but occurred primarily during the early phase of plaque acidogenesis. Enamel demineralization appeared to be limited by factors other than the pH of the streptococcal plaque. Calcium concentrations in the S. mutans plaque rose to a maximum of 10.9 +/- 2.8 mEq/l at 30 min after the 5% sucrose rinses, then fell; Pi reached a stable level of 12.2 +/- 2.3 mEq/l by 60 min. Calculations showed that conditions approached saturation with respect to enamel and dicalcium phosphate dihydrate as demineralization reached a maximum. Demineralization appeared to be limited at low plaque pH, therefore, by the accumulation of high levels of mineral ions in the streptococcal plaque.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased permeability of enamel to iodide ions following the ingestion of cookies varying in sucrose or fat content

Experiments showed that the intraoral iodide permeability (Ip) method can be used in a reproducible and sensitive manner with solid foods. Ingestion of 5-gram portions of cookies made with defined concentrations of sucrose or fat led to an increased Ip (due to demineralization) of Streptococcus mutans-covered bovine enamel blocks in vivo. Demineralization increased with time to a maximum of 45 min, and the pH of the plaque dropped accordingly. Continued exposure in the mouth beyond 45 min led to an elevation of the pH and a decrease in delta Ip consistent with remineralization of the enamel. Control blocks worn without ingestion of cookies exhibited negative delta Ip values. Demineralization increased with increasing sucrose content of the cookies and reached a plateau when cookies containing 1.08 g sucrose per morsel were administered. Cookies prepared without added sucrose gave a high delta Ip. High fat content raised the delta Ip when sucrose was low. These findings are consistent with clinical and other observations, and emphasize the complex relation between foods and enamel demineralization.     

Prevention of sucrose-induced demineralization of tooth enamel by chewing sorbitol gum

Measurements were made of the effect of chewing sorbitol gum on the intra-oral demineralization induced by rinsing with 10% sucrose solutions. Blocks of bovine enamel were covered with a layer of Streptococcus mutans IB1600, and mounted on palatal appliances that were worn by five subjects for defined periods of time. Enamel demineralization was determined by following changes in iodide penetrability (delta Ip) of the enamel surfaces. Delta Ip increased to a maximum of about 15 units between 30 and 45 min, while the pH of the S. mutans plaque dropped to below 4 by 15 min. Plaque pH returned to 4.9 by 60 min. Chewing sorbitol gum after the sucrose rinse minimized further increases in delta Ip and brought about a more rapid return of the S. mutans plaque pH toward neutrality. The effect of chewing gum was greater when chewing was initiated earlier so that, when gum was given at five min after the sucrose rinse, demineralization was only 37% of that obtained without gum. The findings confirm earlier reports on the effect of gum on plaque pH, and directly demonstrate the profound protective effects that chewing sorbitol gum can have on tooth enamel.     

In situ study of sucrose exposure, mutans streptococci in dental plaque and dental caries.

The purpose of this study was to investigate the relationship among frequency of sucrose exposure, mutans streptococci levels and dental caries. Adult volunteers took part in this crossover study performed in 4 phases of 28 days each. The volunteers wore intra-oral palatal appliances containing blocks of human dental enamel and dripped 20% sucrose solution onto the dental blocks from 0 to 8 times/day. After each phase, the colony forming units (CFU) were determined in dental plaque and enamel dental caries was evaluated using cross-sectional hardness. Sucrose frequency had no statistically significant effect on mutans streptococci levels. In the enamel cross-sectional hardness tests, significant differences (p < 0.05) in relation to area of mineral loss were observed only when sucrose exposure was 8 times/day. Similar results were obtained when cross-sectional hardness was assessed at each distance from enamel surface.     

菌斑固相、变形链球菌及葡聚糖对酸的缓冲作用

目的研究糖代谢后菌斑固相缓冲力的变化及影响因素。方法采集40名18~21岁的大学生的饥饿牙菌斑,体外10%蔗糖孵育1h。体外制备无糖培养和2%蔗糖培养的变链菌团。以25mmol/L KCl制备菌斑固相、变链菌团和不溶性葡聚糖混悬液及可溶性葡聚糖溶液,用1mmol/LHCl滴定并计数细菌密度,统计学分析。结果变链菌团代谢蔗糖后的缓冲容量为(0·099±0·047)mmol/L,比无蔗糖培养的变链菌团的缓冲容量(0·609±0·202)mmol/L低,且缓冲力随细菌密度降低直线下降,葡聚糖几乎没有缓冲作用[(0·028~0·032)mmol/L]。人牙菌斑固相缓冲力的变化规律与体外纯菌培养研究结果一致。结论菌斑固相缓冲力与所含细菌密度密切相关。     

Composition of dental plaque formed in the presence of sucrose and after its interruption

Since dental plaque reservoirs of fluoride (F), calcium (Ca) and inorganic phosphorus (Pi) are susceptible to decreases in pH, this in situ crossover study was conducted to test the hypothesis that the low concentration of these ions in plaque, formed in the presence of sucrose, could be attributed merely to the fermentation of this sugar. Eleven volunteers wore palatal appliances containing 6 human enamel blocks during two stages. In each stage, the treatments were either 20% sucrose solution or distilled deionized water, which were dripped onto the blocks 8 times a day. After 28 days, in each stage, the dental plaque formed on two blocks was collected, the treatment was inverted and after a further 24 and 48 h, the biofilm formed was collected from the other blocks. The concentration of acid-soluble F, Ca and Pi, and the concentration of insoluble polysaccharide (IP) were determined in the dental plaque. Statistically lower concentrations of F, Ca and Pi, and a higher concentration of IP were found in the 28-day biofilm formed in the presence of sucrose than in its absence; after the treatment inversion the change in F, Ca and Pi was not statistically significant, but the IP concentration changed significantly. The hypothesis was rejected because change in concentration of F, Ca and Pi is not due to fermentation of the sucrose.     

Effect of sucrose containing iron (II) on dental biofilm and enamel demineralization in situ

Since the effect of iron (Fe) on the cariogenicity of sucrose in humans is unexplored, this study assessed in situ the effect of Fe co-crystallized with sucrose (Fe-sucrose) topically applied in vitro on the acidogenicity, biochemical and microbiological composition of the dental biofilm formed in vivo and on the demineralization of the enamel. During two phases of 14 days each, 16 volunteers wore palatal appliances containing blocks of human enamel, which were submitted to four groups of separate treatments: (1) water; (2) 20% sucrose; (3) 20% (w/v) sucrose plus 18 microg Fe/ml, and (4) 20% (w/v) sucrose plus 70 microg Fe/ml. The solutions were dripped onto the blocks 8 times per day. The biofilms formed on the blocks were analyzed with respect to acidogenicity, biochemical and microbiological composition. Mineral loss was determined on enamel by surface and cross-sectional microhardness. Lower demineralization was found in the blocks subjected to Fe-sucrose (70 microg Fe/ml) than in those treated with sucrose (p < 0.05). This concentration of Fe also reduced significantly the populations of mutans streptococci in the biofilm formed on the blocks. In conclusion, our data suggest that Fe may reduce in situ the cariogenic potential of sucrose and the effect seems to be related to the reduction in the populations of mutans streptococci in the dental biofilm formed.     

Effect of iron on bovine enamel and on the composition of the dental biofilm formed "in situ"

OBJECTIVES: This study investigated in situ the effect of iron (Fe) on the reduction of demineralization of bovine enamel, as well as on the composition of dental biofilm. DESIGN AND METHODS: Twelve volunteers were included in this blind crossover study, which was conducted in two stages of 14 days each. For each stage, the volunteers received palatal appliances containing four blocks of bovine enamel (4 mm x4 mm x 2.5 mm). Six volunteers dripped a solution of 15 mmol L(-1) ferrous sulphate onto the fragments and the remaining six dripped deionized water (eight times per day). After five minutes, a fresh 20% (w/v) sucrose solution was dripped onto all enamel blocks. During the experimental period the volunteers brushed their teeth with non-fluoridated dentifrice. After each stage, the percentage of surface microhardness change (%SMHC) and area of mineral loss (DeltaZ) were determined on enamel and the dental biofilm formed on the blocks was collected and analysed for F, P, Ca, Fe and alkali-soluble carbohydrates. The concentrations of F, Ca and Fe in enamel were also analysed after acid biopsies. RESULTS: There was a statistically significant increase in the P and Fe concentrations in the biofilms treated with ferrous sulphate (p<0.05), which was not observed for F, Ca and alkali-soluble carbohydrates. The group treated with ferrous sulphate had significantly lower %SMHC and DeltaZ when compared to control (p<0.05). CONCLUSIONS: These results showed that ferrous sulphate reduced the demineralization of enamel blocks and altered the ionic composition of the dental biofilm formed in situ.     

In situ effect of frequent sucrose exposure on enamel demineralization and on plaque composition after APF application and F dentifrice use

Since the effect of the combination of methods of fluoride use on enamel demineralization and on plaque composition is not clearly established, this study examined the effect of the combination of acidulated phosphate fluoride (APF) application and F dentifrice on enamel demineralization and on plaque composition. In this crossover study, 16 volunteers, wearing a palatal appliance containing bovine enamel blocks, were subjected to 4 treatment groups: non-fluoridated dentifrice (PD), FD, APF+PD, and APF+FD. The APF was applied to the enamel before the 14-day experimental period. During the experimental period, test dentifrices were applied 3x/day, and a 20% sucrose solution was applied 4x and 8x/day by being dripped on the blocks. Although APF application was able either to increase F concentration in plaque or to reduce the % of mutans streptococci, its combination with F dentifrice use neither reduced enamel mineral loss nor changed any other measured plaque variable with respect to the FD group alone.     

Influence of extraoral xylitol and sucrose dippings on enamel demineralization in vivo

This paper describes the effect of xylitol on demineralized enamel in plaque-free and plaque-covered conditions in vivo. Fissure-like plaque retention grooves were created in 66 human enamel blocks and demineralized in vitro. The blocks were mounted in a prosthesis of 11 participants, who used a 2.5% xylitol, a 2.5% sucrose solution or water extraorally in a randomized cross-over design, for three periods of 16 days. The participants submerged the prosthesis twice a day in the solution during 5 min. Mineral loss and lesion depth were measured before and after the in vivo experiment, using quantitative microradiography and polarized light microscopy. Lesion depth at the surface enamel was +/- 45 microns, at the wall of the grooves +/- 30 microns and at the bottom of the grooves +/- 50 microns before the experiment. After 16 days the lesion depth at the wall of the grooves was +/- 40 microns and at the bottom of the grooves +/- 75 microns. In the grooves no differences were found between the xylitol, the sucrose and the water treatment. At the surface enamel a significant reduction of enamel demineralization was found after the xylitol dippings. The lesion depth at the surface enamel increased 17 microns after the sucrose treatment and 7 microns after the xylitol treatment. The mineral loss after the sucrose and the water treatment were both approximately three times higher than the mineral loss after the xylitol treatment.     

In vivo effects of fluoride, chlorhexidine and zinc ions on acid formation by dental plaque and salivary mutans streptococcus counts in patients with irradiation-induced xerostomia

Irradiation therapy including major salivary glands may result in xerostomia and enhanced susceptibility to dental caries. The present aim was to assess the ability of mouthrinses with F-, Zn2+, and chlorhexidine (CH), in various combinations, to reduce acidogenic potential of dental plaque and salivary mutans streptococcus counts (SMSC) in 7 patients with xerostomia secondary to irradiation. The patients rinsed twice daily for 3 weeks with the following test solutions: (1) 12 mmol/l NaF (F; control), (2) NaF + 20 mmol/l ZnCl2 (F-Zn), and (3) NaF + 1.1 mmol/l CH (F-CH). Resting periods (F) of varying lengths were incorporated. Acid formation by dental plaque was monitored as plaque pH response to a sucrose mouthrinse, at the end of each test period, 4 h after mouthrinsing with test solution. Plaque pH was measured repeatedly at 2-8 sites in each patient before, and up to 60 min after the sucrose mouthrinse using touch microelectrodes. SMSC were determined using Dentocult SM-Strip mutans. Compared with F, F-CH significantly (P < or = 0.02) reduced acid formation by plaque and SMSC, whereas F-Zn did not affect acid formation or SMSC significantly. Pilot experiments in 4 patients showed mouthrinses with NaF + 0.55 mmol/l CH + 10 mmol/l Zn2+ to be ineffective, whereas NaF + 2.2 mmol/l CH was highly effective, but no better than F-CH. Twice daily mouthrinses with 12 mmol/l NaF in combination with 1.1 mmol/l CH may be an effective regimen to prevent post-irradiation caries.     

Association of caries activity with the composition of dental plaque fluid

This study tests the hypothesis that caries activity is associated with lower degrees of saturation with respect to enamel mineral in dental plaque fluid following sucrose exposure. Plaque fluids were obtained from caries-free, caries-positive, and caries-active subjects. Samples were collected before and at 3 and 7 min after a sucrose rinse on consecutive weeks and analyzed for organic acids, inorganic ions, pH, calcium activity, and, in selected samples, total protein. After sucrose, pH values were significantly lower in the caries-active group in comparison with the caries-free and caries-positive groups. Total and free calcium concentrations increased with decreasing pH, with free calcium being about one-third of total calcium. The caries-active group exhibited significantly lower degrees of saturation with respect to enamel mineral, after sucrose, and had significantly higher mutans streptococci levels in plaque than did the caries-free samples. Thus, saturation levels in post-sucrose plaque fluids reflect the cariogenic potential of dental plaque.     

Effect of some salts of calcium, sodium, potassium, and strontium on intra-oral enamel demineralization

A newly-developed intra-oral enamel demineralization test was used to evaluate the effect of supplementation of a 10% sucrose solution with various components on enamel demineralization induced by the sucrose. Five human subjects wore a palatal prosthesis holding eight blocks of subsurface bovine enamel covered with a layer of S. mutans cells. The test involved rinsing with sucrose solution or with sucrose solution supplemented with 0.162 mol/l of different calcium salts or equivalent concentrations of Na-, K-, and Sr salts; rinsing was for one min at times zero and 45 min of the 90-minute test period. Ca-propionate, Ca-acetate, and Ca-levulinate completely inhibited sucrose-induced enamel demineralization; Ca-chloride, Ca-lactate, and Ca-ascorbate gave from 65-75%, and K-acetate, Na-lactate, and Sr-lactate 39, 25, and 18% inhibition, respectively. Consideration of the anion dissociation constants and the Ca-anion association constants of the salts suggests that the observed inhibition is caused mainly by common ion effects and, to a lesser extent, by buffer effects.     

Calcium phosphate deposition in human dental plaque microcosm biofilms induced by a ureolytic pH-rise procedure

The objectives were to develop and characterize a procedure based on a ureolytic pH rise to deposit calcium phosphate into microcosm dental plaque biofilms and to test the importance of the plaque pH range. Plaque biofilms were cultured in a multiplaque culture system ('artificial mouth') with a continuous supply of a simulated oral fluid (basal medium mucin; BMM) with 146 mmol/l (5% w/v) sucrose periodically applied over 6 min every 8h. After initial plaque growth, the biofilms were periodically exposed for up to 16 days to 6-min applications of calcium phosphate monofluorophosphate urea (CPMU) solution containing 20 mmol/l CaCl(2), 12 mmol/l NaH(2)PO(4), 5 mmol/l monofluorophosphate and 500 mmol/l urea (pH 5.0). Three application regimes were examined, one included a sucrose-induced acidic pH fluctuation. Plaque hydrolysis of the urea in CPMU caused the pH to rise to between 8.2 and 8.8, depositing fluoridated and carbonated calcium phosphates, and possibly some calcium carbonate, into the plaque. Calcium, phosphate and fluoride deposition was rapid for about 4 days and then slowed. After 10 days' treatment under standard conditions (BMM containing 1 mmol/l urea and 1 mmol/l arginine), plaque calcium and phosphate concentrations had increased up to 50-fold and 10-fold to approximately 2-4 and 1-2 mmol/g plaque protein, respectively. The calcium, phosphate and fluoride content increased steadily. Calcium phosphate deposition was proportional to the plaque resting pH, increasing over four-fold when the BMM urea concentration was increased from 0 to 20 mmol/l, which raised the resting pH from 6.4 to 7.2 and yielded a mean plaque calcium concentration of 14.3 mmol/g protein, one subsample reaching 20.8 mmol/g protein. Supplementation of BMM with 20% human serum inhibited deposition. These results support the hypothesis that an alkaline pH in plaque is critical in promoting plaque mineralization and that mineral deposition is modulated by serum. These factors are likely to be important in regulating calculus formation.     

Effect of tooth-bound fluoride on enamel demineralization/ remineralization in vitro

The effect of tooth-bound fluoride (F) on enamel caries formation was investigated under the condition that loosely bound F was essentially absent. Eighteen thin enamel sections, prepared from the lingual or buccal surfaces of extracted human molars, were embedded in acrylic resin with the enamel surfaces exposed. The sections were placed in a pH 7 remineralizing solution (RS; 1.2 mmol/l Ca, 0.72 mmol/l P, 30 mmol/l KCl, 50 mmol/l HEPES) for 5 days, and were randomly divided into 3 groups: (1) control group that received no treatment, (2) acidulated phosphate fluoride (APF) group that received 5 cycles of a 4 min treatment with APF gel followed by immersion in the RS for 2 days (RS changed daily) and (3) dicalcium phosphate dihydrate (DCPD) - APF group that received 5 cycles of a 4-min pH 2.1 DCPD-forming solution followed by 4 min APF gel and then placed in the RS for 2 days. After the treatment cycles, the sections were washed in a constant composition F titration system to remove loosely bound F. An in vitro model, which consisted of cycles of de- (6 h) and remineralization (18 h) each day for 5 days, was used to produce caries-like lesions in the specimens. The DeltaZ (mineral loss) values, measured by quantitative microradiography, of the lesions formed in the three groups were (mean +/- standard deviation; n = 6) 91.2+/-12.3 microm for the control group, 41.3+/-10.1 microm for the APF group and 21.2+/-4.8 microm for the DCPD-APF group. The same system produced lesions in untreated shark enamel with a mean DeltaZ of 4.4+/-0.3 microm (n = 12). One-way fixed-effects ANOVA indicated that mineral loss was significantly different among the different groups (p<0.05). The results showed that enamel resistance to lesion formation increased with increasing tooth-bound F content. Shark enamel was much more resistant to demineralization than human enamel.     

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

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

Release of mineral ions in dental plaque following acid production

The release of appreciable amounts of calcium, phosphate and fluoride found in whole plaque into the plaque-fluid phase, following bacterial acid production, can potentially reduce the driving force for tooth demineralization. However, limited information is available on this topic, particularly on the release of fluoride. This study sought to determine the change in calcium, phosphate and fluoride concentrations in plaque fluid after sucrose exposure. 48 h overnight-fasted supragingival plaque samples were collected from all tooth surfaces (with the exception of the lower lingual anterior teeth) of one half of an individual mouth, following a 1 min water rinse. Plaque samples were then collected from the other half of the same mouth, following a 292 mM sucrose rinse. Plaque fluid was isolated by centrifugation and analysed for total calcium and phosphate (ion chromatography) and for free fluoride (ion-specific electrode). Samples were collected from seven individuals. Following sucrose exposure, plaque-fluid pH decreased significantly from 6.5+/- 0.3 to 5.4+/-0.2; calcium concentrations (mmol/l) also increased significantly (p < 0.01) from 1.9+/-0.5 to 5.0+/-2.1. Fluoride and phosphate concentrations in plaque fluid, however, did not increase significantly after sucrose exposure: mean concentrations (mmol/l) of fluoride after the water and sucrose rinses were 0.006+/-0.003 and 0.005+/-0.002, respectively, and mean phosphate concentrations (mmol/l) were 11.0+/-2.0 and 12.0+/-3.0, respectively. When results were expressed per wet plaque weight, phosphate concentrations were also found to increase significantly. The same trends were observed when additional plaque samples were treated in vitro with sucrose: fluoride-ion activity did not increase in plaque under in vivo-like conditions.     

A new microsample grinding technique for quantitative determination of calcium and phosphorus in dental enamel

A new microsampling method is described for measuring variations in calcium and phosphorus distribution in dental enamel. Ten successive layers, 10 micron thick, from five human enamel posts with previously abraded flat upper surfaces were ground and analyzed. Mean Ca and P values were, respectively, 1116 +/- 110 and 527 +/- 47 micrograms/mm3, and mean Ca/P w/w and molar ratios, 2.11 +/- 0.10 and 1.63 +/- 0.08, respectively. Despite its limitations, the present method allows for accurate investigation of the mineral content in sound, experimentally-treated enamel.     

An intra-oral appliance study of the plaque microflora associated with early enamel demineralization

An intra-oral appliance model was used to investigate the composition of the plaque microflora associated with early enamel demineralization. Enamel sections, with exposed windows, were mounted on lower removable appliances, and the devices were worn by volunteers for three-week periods under three experimental conditions. These were: (1) "normal" plaque conditions, (2) extra-oral sucrose applications nine times daily, and (3) inoculation of each volunteer's own mutans streptococci onto the test sites and sucrose applications as described for (2). After 21 days, the plaque overlying each window was removed, and the bacterial composition was determined. Changes in mineral content of the associated enamel were measured by microradiography and microdensitometry, and the total mineral loss (delta z) that had occurred at each site was calculated. The 144 sites studied were divided into four demineralization groups by delta z value, with an increase in mineral loss from group 1 to group 4. A progressive and significant increase in the isolation frequency of mutans streptococci occurred from delta z group 1 to group 4 sites. These organisms were isolated from the plaque of every location with enamel mineral loss of over 1000 delta z units, but were not detected in 27% of the group 3 sites. Lactobacilli comprised 2% to 3% of the total cultivable microflora in groups 1-3 sites, but were found in significantly higher proportions (18%) at those enamel sites experiencing the most extensive mineral loss (group 4). No significant relationship was found between demineralization and the levels of Actinomyces species or Veillonella.(ABSTRACT TRUNCATED AT 250 WORDS)     

Colonization of rat molar teeth by mutans streptococci with different salivary agglutination characteristics

The oral implantation of salivary agglutination-positive and -negative mutans streptococci was studied using streptomycin resistant (StrR) organisms. StrR Streptococcus mutans strains Ingbritt and NCTC 10449 are agglutinated by rat saliva and the StrR strains Streptococcus sobrinus 6715-13 and Strep. mutans GS5 are not. Four groups of Sprague-Dawley rats were inoculated orally with each organism (one per group) and fed a sucrose diet. A further two groups of animals were similarly inoculated with either the agglutination-positive Strep. mutans Ingbritt or the agglutination-negative Strep. sobrinus 6715-13 and fed a glucose diet. StrR streptococci were recovered from smooth-surface dental plaque of all animals on the sucrose diet with no significant difference in the recovery of agglutination-positive Strep. mutans strains Ingbritt and NCTC 10449 and agglutination-negative Strep. mutans GS5. However, the recovery of agglutination-negative Strep. sobrinus 6715-13 from smooth-surface plaque of animals on either the sucrose or the glucose diets was significantly lower than that of the other strains. Agglutination-positive Strep. mutans Ingbritt colonized smooth enamel surfaces of animals on the sucrose and the glucose diets in numbers that were not significantly different. However, the colonization of such surfaces by agglutination-negative Strep. sobrinus 6715-13 was significantly enhanced by the sucrose diet. Agglutination-positive and -negative StrR mutans streptococci were recovered from fissure plaque of all inoculated sucrose-fed animals in numbers that were not significantly different. Successful colonization of smooth enamel surfaces by the StrR streptococci resulted in increased smooth-surface caries.(ABSTRACT TRUNCATED AT 250 WORDS)