Author's personal copy
journal of dentistry 37 (2009) 763–768

available at www.sciencedirect.com

journal homepage: www.intl.elsevierhealth.com/journals/jden

Remineralization of enamel subsurface lesions by chewing
gum with added calcium
Fan Cai, Peiyan Shen, Glenn D. Walker, Coralie Reynolds, Yi Yuan, Eric C. Reynolds *Cooperative Research Centre for Oral Health Science, Melbourne Dental School and The Bio21 Institute of Molecular Science and Biotechnology,
The University of Melbourne, 720 Swanson Street, Victoria, 3010, Australia

article info

abstract

Article history:

Objectives: Chewing sugar-free gum has been shown to promote enamel remineralization.

Received 16 April 2009

Manufacturers are now adding calcium to the gum in an approach to further promote

Received in revised form

enamel remineralization. The aim of this study was to compare the remineralization

2 June 2009

efficacy of four sugar-free chewing gums, two containing added calcium, utilizing a dou-

Accepted 5 June 2009

ble-blind, randomized, crossover in situ model.
Methods: The sugar-free gums were: Trident Xtra Care, Orbit Professional, Orbit and Extra. Ten
subjects wore removable palatal appliances with four human-enamel half-slab insets con-

Keywords:

taining subsurface demineralized lesions. For four times a day for 14 consecutive days subjects

Sugar-free chewing gum

chewed one of the chewing gums for 20 min. After each treatment the enamel slabs wereCalcium additives

removed, paired with their respective demineralized control slabs, embedded, sectioned andEnamel subsurface remineralization

mineral level determined by microradiography. After 1-week rest the subjects chewed anotherIn situof the four gums and this was repeated until each subject had used the four gum products.
Results: Chewing with Trident Xtra Care resulted in significantly higher remineralization(20.67  1.05%) than chewing with Orbit Professional (12.43  0.64%), Orbit (9.27  0.59%) or
Extra (9.32  0.35%). The form of added calcium in Trident Xtra Care was CPP–ACP and thatin Orbit Professional calcium carbonate with added citric acid/citrate for increased calcium
solubility.
Conclusions: Although saliva analysis confirmed release of the citrate and calcium from the
Orbit Professional gum the released calcium did not result in increased enamel remineralization over the normal sugar-free gums. These results highlight the importance of
calcium ion bioavailability in the remineralization of enamel subsurface lesions in situ.
Crown Copyright # 2009 Published by Elsevier Ltd. All rights
reserved.

1.

Introduction

The anticariogenic effect of sugar-free chewing gum has
been demonstrated in a number of caries clinical trials.1–7
The reduction in caries experience has been attributed
to the stimulation of saliva increasing the available
calcium and phosphate ion concentrations, limiting enamel
demineralization and promoting remineralization of early

caries lesions.8,9 Recently gum manufacturers have been
adding calcium in various forms to enhance the potential
anticariogenic action of the gum.10 The normal forms ofcalcium added to gum, calcium carbonate and/or calcium
phosphate have limited solubility in saliva and are notreleased from the gum bolus when chewed in high enoughconcentrations or in a bioavailable form to affect the caries
process.10* Corresponding author. Tel.: +61 3 9341 1547; fax: +61 3 9341 1596.
E-mail address: e.reynolds@unimelb.edu.au (E.C. Reynolds).
0300-5712/$ – see front matter . Crown Copyright # 2009 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.jdent.2009.06.003

Author's personal copy764

journal of dentistry 37 (2009) 763–768

One form of soluble, bioavailable calcium that has been
added to sugar-free gum is casein phosphopeptide–amorphous calcium phosphate (CPP–ACP) [RecaldentTM CASRN
691364-49-5]. The calcium in CPP–ACP is present as bioavailable ions together with phosphate ions stabilized by casein
phosphopeptides containing the cluster sequence -Ser(P)Ser(P)-Ser(P)-Glu-Glu- as water soluble nanocomplexes.11 The
CPP–ACP in sugar-free gum has been shown to remineralize
enamel subsurface lesions in situ and to reduce the progression of approximal lesions in a randomized, controlled caries
clinical trial10,12–14
Recently, Hass and Greenberg15 have proposed adding foodacids (e.g. citric acid/citrate) to sugar-free gum containing
insoluble calcium phosphate/calcium carbonate in an
approach to increase the solubility and hence bioavailabilityof the added calcium. However, to our knowledge these sugarfree gum formulations containing calcium phosphate/calcium
carbonate together with food acids have not been tested fortheir ability to remineralize enamel subsurface lesions in situ
even though they have been shown to increase the release of
calcium from the gum.15 The aim of this study was to compare
the ability of four commercially available sugar-free chewing
gums, two containing added calcium, to remineralize enamel
subsurface lesions in an in situ model. One of the gums
contained added calcium as CPP–ACP (Trident Xtra Care), andthe other as calcium carbonate with added citric acid/citrate(Orbit Professional). The other two gums (Orbit and Extra) werenormal sugar-free chewing gums.

2.

Materials and methods

2.1.

Study design and subject recruitment

The study was a double-blind, randomized, crossover in situ
design with four treatments. Approval for the study was
obtained from The University of Melbourne Human Research
Ethics Committee and the study was conducted in accordancewith Australia’s National Statement on Ethical Conduct in
Human Research (2007). After providing informed consent 10
healthy adult subjects (seven males and three females) wererecruited from the staff and postgraduate students (age 25–55
years) of the Melbourne Dental School. All subjects had at least
22 natural teeth with no current caries activity, periodontal
disease or other oral pathology. None of the subjects wereusing antibiotics or medications, which could have affectedsaliva flow rate. For each subject, the unstimulated saliva flowrate was higher than 0.2 ml/min, and the stimulated saliva
flow rate, measured whilst chewing two pellets of sugar-freegum, was >1.0 ml/min.
Subjects were sequentially allocated a subject ID by theexaminer on recruitment. Each subject ID had a corresponding
product allocation sequence that had been generated by abiostatistician using standard randomization tables for crossover studies. Subjects and those personnel dispensing, supervising or performing analysis did not have access to thetreatment codes and were unaware of which treatment had
been administered. The code was not released by the sponsor
until data collection and analysis were complete. Subjects
were monitored for adverse events using health updatequestionnaires during each treatment and at the completionof the study.

2.2.

Intraoral appliances

Removable mid-palatal acrylic appliances covering the firstpremolars to the last tooth in the arch, were fabricated foreach subject as described previously.14 The appliances wereretained by four stainless steel circumferential clasps andeach had two bilateral troughs to house four enamel slabs aspreviously described.16

2.3.

Preparation of enamel subsurface lesions

Extracted human third molars were obtained from the Royal
Dental Hospital of Melbourne. The outer enamel surface waspolished wet to a mirror finish using SoftexTM disks (3M, St.
Paul, MN, USA) on a slow-speed contra-angle dental handpiece. Each polished surface was then sawn from the tooth as a
10 mm  4 mm slab and the whole slab covered with acidresistant nail varnish except for two (occlusal and gingival)
mesiodistal windows (9 mm  1 mm) separated from eachother by 1 mm of varnish. Subsurface lesions were createdusing a demineralization buffer containing 20 g/l Carbopol 907(BF Goodrich, Cleveland, OH, USA), 500 mg/l hydroxyapatite(Bio-Rad, Richmond, CA, USA) and 0.1 mol/l lactic acid, pH 4.8
for 96 h at 37 8C as described previously.16 After demineralization each enamel slab was sawn through the midline of eachwindow into two 4 mm  4 mm half-slabs and the cut surfaceof each half-slab covered with nail varnish. One half-slab ofeach pair was retained as the demineralization control. The
other enamel half-slab of the pair was inset into an intraoral
appliance and retained using dental wax for the remineralization protocol. Care was taken to keep the windows free of wax.
Four enamel half-slabs were inset into each appliance, two on
each side in bilateral troughs.14 The enamel slabs wererecessed into the bilateral trays to produce a 1 mm space
above the enamel surface to allow plaque to establish and beretained.16

2.4.

Study protocol

The study utilized a double-blind, randomized, crossoverprotocol as previously described16 with four sugar-free gums
(Table 1). Two of the gums were normal sugar-free chewing
gums (Orbit and Extra) and the other two had added calciumwith Trident Xtra Care containing CPP–ACP and Orbit Professional containing calcium carbonate/citrate. The chewing
gums were provided as coded products by the Clinical andConsumer Group, Cadbury-Adams Worldwide Research andDevelopment (NJ, USA) in sealed packages and were stored atroom temperature. The code was not released until all
remineralization data had been acquired.
One of the chewing gum products was randomly assigned
to each of the subjects for each of four 2-week treatment
periods. Four times a day at specified times (10.00 am,
11.30 am, 2.00 pm and 3.30 pm) subjects with appliances
inserted chewed two pellets or one slab of gum for 20 min.
This was repeated for 14 consecutive days (treatment period).
At the end of each treatment period, subjects rested for 7 days

Author's personal copy
765

journal of dentistry 37 (2009) 763–768

Table 1 – Details of sugar-free chewing gum used for the study.
Gum

Type
TM

ColourDose

Weight/dose (g)Trident Xtra Care(with RecaldentTM)

Slab

Blue

1 slab

1.96  0.02

Orbit Professional(with calcium)

PelletWhite

2 pellets

3.13  0.08

Orbit

Slab

White

1 slab

1.96  0.02

Extra

Slab

White

1 slab

2.69  0.05aaIngredients
Sorbitol, gum base, xylitol, glycerine, mannitol,
natural and artificial flavours, acesulfame K,
aspartame, BHT, blue 1 lake, calcium casein
peptone calcium phosphate, soy lecithin,titanium dioxide and yellow 5 lake.
Xylitol, sorbitol, maltitol syrup, mannitol, aspartame,acesulfame-K, gum base, calcium carbonate, bulk agent
dicalcium phosphate, thickening agent gum Arabic,
flavour, humectant agent glycerol, colour E171
(titanium dioxide), emulsifier soy lecithin, glazing
agent, carnauba wax, antioxidant BHA,
colour E133 (FD&C blue 1).
Sorbitol, gum base, glycerol, mannitol, natural andartificial flavours; less than 2% of: xylitol,
acesulfame K, aspartame, soy lecithin, BHT(to maintain freshness). phenylketonurics;
contains phenylalanine.
Sorbitol, gum base, glycerol, mannitol, natural andartificial flavours, hydrogenated starch hydrolysate,
aspartame, acesulfame K, soy lecithin,
BHT (to maintain freshness).

Mean  SD.

during which time new demineralized enamel slabs wereinserted into the appliances. Subjects then crossed over toanother gum product. This was repeated until each subject
used each of the four products. Subjects were instructed toremove the intraoral appliances when they ate or drank andwhen they conducted their normal oral hygiene procedures.
The times of wearing the appliances and gum chewing wererecorded in a diary, collected together with used gum
wrappers after each treatment period. On removing theappliances, subjects were instructed to rinse them briefly
with distilled/deionised water and then to store them in asealed, humidified containers at 37 8C until re-insertion.
Subjects were also instructed to clean the appliances, avoiding
the enamel slabs, with a toothbrush and fluoride-free toothpaste provided by the sponsor. Subjects maintained normal
oral hygiene and dietary habits throughout the study except
during the times they wore the appliances when they were
instructed not to eat or drink. At the commencement of thestudy all subjects were provided with standard 1000 ppm
fluoride toothpaste, which they used morning and night forthe duration of the study. The appliances were inserted 30 min
after oral hygiene procedures. The subjects lived in metropolitan Melbourne where the reticulated water supply is
fluoridated at 1 ppm. After completion of each treatment
period, the enamel slabs were removed from the appliances,
rinsed with distilled/deionised water and stored in moist,labeled microcentrifuge tubes for further processing.

2.5.

Sectioning, microradiography and microdensitometry

After each treatment, the enamel half-slabs were paired with
their respective control half-slabs and dehydrated in absolute
alcohol. Each pair of half-slabs was embedded in freshly
poured transparent cold curing methacrylate resin (Paladur,
Heraeus Kulzer, Germany), with lesion windows parallel.
Approximately 200 mm thick sections perpendicular to thelesion surfaces through the midline of both half lesions using
an internal annulus saw microtome (Leica 160, Leica,
Germany). The sections were then lapped down to85  5 mm using a RotoPol-21/RotoForce4 lapping instrument(Struers, Denmark) using 1200 grit lapping paper. Microradiography and computer-assisted microdensitometry were conducted on each section as described in detail previously.12
Each section contained two remineralized lesions and theirpaired demineralized control lesions. Lesion depth (Ld) of eachscanned lesion was measured and densitometric profiles(vol%min versus mm) determined for each demineralized andremineralized lesion as well as for the median sound enamel.
The difference between the area under the densitometricprofile of the demineralized lesion and the median soundenamel, calculated by trapezoidal integration, is represented
by DZd. The difference between the area under the densitometric profile of the remineralized lesion and the medium
sound enamel is represented by DZr. These parameters werethen converted to percentage change values after remineralization with respect to each control untreated demineralized
lesion. As such percentage remineralization (%R) represents
the change in DZ values:
%R ¼

2.6.

DZd  DZr
 100
DZd

Saliva flow rate and ion analyses

Subjects were instructed to swallow all saliva present in themouth before collection started. Unstimulated saliva wascollected by leaning forward with head tilted downwards andallowing saliva to flow into a pre-weighed 15 ml centrifuge
tube for 2 min. Saliva stimulated by chewing sugar-free gum
was collected using the same procedure.
Unstimulated and stimulated saliva samples were centrifuged (1000  g, 15 min) and supernatants diluted, acidified

Author's personal copy
766

journal of dentistry 37 (2009) 763–768

with 0.01N HNO3, thoroughly mixed and transferred into a
10 ml syringe fitted with a 0.2 mm filter (Minisart, Sartorius,
VIC, Australia). Filtrates were injected into a labeled Dionex
sampling vial (Dionex Corporation, CA, USA). Levels of
inorganic ions were determined using an automatic ion
chromatography system, equipped with two columns forboth cation (IonPac CS12) and anion (IonPac AS18) and two
separated conductivity detectors (ICS3000, Dionex Corporation, CA, USA). A combined seven anion standard (#56933) anda combined six cation standard (#046070) were diluted 20, 50
and 100 times with distilled/deionised water to calibrate andquantify the conductivity reading.

2.7.

Gum analyses

One dose (2 pellets or 1 slab) of each gum type was thinly sliced
with a scalpel and extracted with either 40 ml of distilled
deionised water or 40 ml of 0.01N HNO3 overnight. Extracted
samples were centrifuged (1000  g, 15 min) to remove gum
debris. Supernatants were collected, diluted and analyzed for
pH (water extract only) and for ions using the Dionex system
as described above. An extra series of sodium carbonate (Ajax
Finechem, NSW, Australia) and tri-sodium citrate (BDH
chemicals, VIC, Australia) standards were also included forcarbonate and citrate ion analyses.

2.8.

Data analysis

Data were statistically analyzed using repeated measures
analysis of variance with contrasts.17 Homogeneity of variance was tested using Levene’s test and normality of the data
was tested using normal probability plots and the Kolmogorov–Smirnov test. All statistical analyses were performed
using SPSS version 12.0 software.18

The highest amount of added calcium was found in Orbit
Professional with 320 mmol of calcium in two pellets (single
dose/serve) added as calcium carbonate with a small amountof calcium phosphate (Tables 1 and 2). However, most of thiscalcium was not extractable in water and required acid forsolubilization. Only 69.70  1.51 mmol of calcium ion was
extracted into water from two pellets (3.13 g) of Orbit
Professional, therefore the majority of the calcium added
was unavailable. The analysis of this gum also confirmed the
addition of citric acid/citrate which would account for some(69.70  1.51 mmol, 22%) of the calcium phosphate/calcium
carbonate being soluble (extracted) in water. The gum with thehighest level of water-extractable calcium was the Trident
Xtra Care with added calcium as CPP–ACP. This gum released
88.73  2.59 mmol of calcium from one slab (1.96 g) into water.

3.2.

Saliva ion analysis

Saliva samples were collected from the subjects while chewing
the four sugar-free gums for the first 2 min of chewing. These
saliva samples were analyzed for calcium and phosphate ionsusing the Dionex ion analyzer and the results are presented inTable 3. Chewing Orbit and Extra did not significantly increase
saliva calcium and phosphate ion concentrations. However,chewing Trident Xtra Care and Orbit Professional did significantly increase salivary calcium concentration to 3.63  1.73
and 3.95  1.08 mmol/ml, respectively, and there was no
significant difference between the gums in this respect.
The unstimulated and stimulated saliva flow rates for eachof the 10 subjects ranged from 0.42 to 1.14 ml/min and 2.31 to
5.77 ml/min, respectively. The mean stimulated flow rate
(4.22  0.88) was approximately fourfold higher than the mean
unstimulated flow rate (0.87  0.21 ml/min) (Table 4). The
mean stimulated saliva flow rates for the four sugar-free gums
are presented in Table 4 and were not significantly different.

3.

Results

3.3.

3.1.

Gum ion analysis

All randomized subjects completed the in situ study without
significant protocol violations and were included in theanalysis. No adverse events were reported and no subjects
withdrew. There was no correlation between stimulated saliva
flow rates or saliva calcium levels and measurements ofenamel remineralization (DZd  DZr or %R) (Table 4). Chewing
Trident Xtra Care resulted in significantly ( p < 0.001) greater

Ion analyses of water and acid extracts of the four gums usedin the clinical study confirmed that Trident Xtra Care and Orbit
Professional contained added calcium (Table 2). Orbit andExtra are normal sugar-free gums without added calcium andthe small amounts of soluble calcium were from the gum base.

Enamel remineralization

Table 2 – Ion analysis of water extracts of the four sugar-free gums.
Ion
2+

Ca
PO43
CitrateCO32
aTrident Xtra Care, mmol/dose
88.7  2.6
37.5  0.9
ND
15.0  1.2

a,c,d

Orbit Professional, mmol/dosecb

69.7  1.5 (320 )0.38  0.01
24.0  0.1
28.7  5.1 (104e)

Mean  SD.
Total calcium, mmol/dose measured using 0.01N HNO3 extraction.
c
Significantly different ( p < 0.01) to all other Ca values in row.
d
Calcium added as CPP–ACP.
eTotal carbonate, mmol/dose measured using 0.01N HNO3 extraction; ND = not detected.
bOrbit, mmol/dosecb

8.8  0.3 (211 )ND
ND
9.0  0.5 (82e)Extra, mmol/dose
24.0  1.2c (266b)
ND
ND
11.5  0.1 (78e)Author's personal copy
767

journal of dentistry 37 (2009) 763–768

Table 3 – Calcium and phosphate ion analyses of saliva stimulated by chewing sugar-free gum.
Ion

Unstimulated
saliva, mmol/ml

Trident Xtra Caresaliva, mmol/ml

Orbit Professional
saliva, mmol/ml

Orbit saliva, mmol/ml

Extra saliva, mmol/ml

Ca2+
PO43

1.83  0.47a
5.11  1.68

3.62  1.73b
4.83  2.19

3.95  1.08b
2.82  0.75

1.69  0.26
3.49  1.29

1.99  0.39
3.46  1.49

abMean  SD.
Calcium concentration in saliva significantly higher ( p < 0.01) for Trident Xtra Care and Orbit Professional.

Table 4 – Saliva flow rates and enamel subsurface lesion remineralization by four sugar-free gums.
Gum

Gum stimulated salivary DZd, vol%min mm
flow ratea, ml/min

Trident Xtra Care
Orbit Professional (with calcium)
Orbit
Extra

3.85  0.65b4.72  0.74
3.83  0.92
4.48  0.91

2006.89  561.50
1792.73  496.09
2039.15  305.94
2013.41  418.32

Ldd, mm

DZd  DZr,
vol%min mm%R

99.47  9.08
95.54  8.50
96.55  5.53
97.63  5.74

414.87  122.36c
222.86  61.26
189.13  27.10
187.59  34.83

20.67  1.05c
12.43  0.64
9.27  0.59
9.32  0.35aUnstimulated saliva flow rate was 0.87  0.21 ml/min.
Mean  SD.
c
Significantly higher ( p < 0.01) than other values in same column.
dInitial depth of the subsurface lesion.
b

enamel remineralization than that produced by chewing theother three gums (Table 4).

4.

Discussion

This study utilized an intraoral enamel remineralization
model to assess the remineralization efficacy of four sugarfree chewing gums, two with added calcium. The sugar-freegum Trident Xtra Care with added calcium as CPP–ACP wassuperior to the other three gums producing approximately
double the level of remineralization. The gum Orbit Professional containing high levels (320 mmol calcium per twopellets) of calcium phosphate/calcium carbonate with citricacid released similar amounts of calcium to the Trident Xtra
Care gum, however this did not result in increased enamel
remineralization. Citrate anions bind calcium ions with the
fully dissociated citrate anion exhibiting the strongest calcium
binding [log K (CaH2 Cit+), 1.04; log K (CaH Cit0), 2.03 and log K(CaCit), 3.64].19 The binding of calcium ions by citrate will
lower the calcium ion activity and therefore its remineralization potential. This suggests that even though the Orbit
Professional gum released calcium, the ion was not bioavailable and hence did not promote enamel remineralization.
Calcium in the form of CPP–ACP has been shown to bebioavailable.10,11,16 CPP containing the sequence -Ser(P)-Ser(P)Ser(P)-Glu-Glu- have been shown to stabilize calcium, phosphate and hydroxide ions and to localize those ions onto theenamel surface.10,11 The high solubility of the CPP–ACP in the
Trident Xtra Care gum is shown in this study with the Trident
Xtra Care gum releasing 88.73 mmol calcium/dose into waterwhereas the Orbit Professional gum, even with the very highlevel of calcium carbonate/calcium phosphate (320 mmol
calcium/dose) and citric acid/citrate, only released 69.70 mmolof calcium/dose into water in vitro (Table 2). It should be notedthat the dose (amount chewed per serve) of the Orbit

Professional gum was significantly greater than the Trident
gum dose hence the solubility differential is even greater when
expressed per gram of gum. For example, the Trident Xtra Caregum released 45.3 mmol of Ca/g of gum whereas the Orbit
Professional gum released only 22.3 mmol of Ca/g of gum
into water in vitro. Interestingly, it appeared that thesaliva calcium concentrations achieved on chewing the
Trident Xtra Care (3.62  1.73 mmol Ca/ml) and Orbit Professional (3.95  1.08 mmol Ca/ml) gums were similar (Table 3)even though the Trident Xtra Care gum released more calcium
into water in vitro. However, it should be noted that the saliva
was collected while chewing the gum in vivo and it has beenshown previously that CPP–ACP released by gum chewing
binds to tooth surfaces.10,16 Hence, it should be expected thatthe level of calcium from the CPP–ACP in saliva would be anunderestimate of the CPP–ACP released due to the significant
binding of the CPP–ACP onto tooth surfaces. These results
highlight the important role of the CPP not only in markedly
increasing the solubility of calcium and phosphate ions but
also in binding and localising the ions at the tooth surface tofacilitate subsurface enamel lesion remineralization.
The CPP–ACP nanocomplexes bind on contact with theenamel surface releasing the associated calcium, phosphateand hydroxide ions that are then available to diffuse down
concentration gradients into the subsurface enamel to promote
remineralization.10,20 The bioavailability of calcium and phosphate ions of the CPP–ACP nanocomplexes and the promotionof subsurface enamel remineralization by the Trident Xtra Caregum in this in situ study are consistent with the recent caries
clinical trial of Morgan et al.13 This clinical trial demonstrated
that chewing sugar-free gum containing CPP–ACP (Recaldent)
relative to a control sugar-free gum over a period of 24 months
resulted in a significant reduction in progression and enhancement of regression of approximal dental caries in school
children. The control sugar-free gum was equivalent to thenormal sugar-free gums used in the current study.

Author's personal copy
768
5.

journal of dentistry 37 (2009) 763–768

Conclusions

In conclusion, this in situ study demonstrates that Trident Xtra
Care containing CPP–ACP was superior in remineralizationof enamel subsurface lesions when compared with Orbit
Professional, Orbit and Extra sugar-free gums. The study
highlights the importance of calcium ion bioavailability in theremineralization of enamel subsurface lesions.

Acknowledgement
The support of Cadbury-Adams USA LLC Science andTechnology is gratefully acknowledged.

references[1] Alanen P, Isokangas P, Gutmann K. Xylitol candies incaries prevention: results of a field study in Estonian
children. Community Dentistry and Oral Epidemiology
2000;28:218–24.
[2] Peng B, Petersen PE, Bian Z, Tai B, Jiang H. Can school-based
oral health education and a sugar-free chewing gum
program improve oral health? Results from a two-year
study in PR China. Acta Odontologica Scandanivica
2004;62:328–32.
[3] Beiswanger BB, Boneta AE, Mau MS, Katz BP, Proskin HM,
Stookey GK. The effect of chewing sugar-free gum after
meals on clinical caries incidence. Journal of the American
Dental Association 1998;129:1623–6.
[4] Kandelman D, Gagnon G. A 24-month clinical study of theincidence and progression of dental caries in relation to
consumption of chewing gum containing xylitol in school
preventive programs. Journal of Dental Research
1990;69:1771–5.
[5] Machiulskiene V, Nyvad B, Baelum V. Caries preventive
effect of sugar-substituted chewing gum. Community
Dentistry and Oral Epidemiology 2001;29:278–88.
[6] Makinen KK, Bennett CA, Hujoel PP, Isokangas PJ, Isotupa
KP, Pape HR, et al. Xylitol chewing gums and caries rates: a
40-month cohort study. Journal of Dental Research
1995;74:1904–13.
[7] Szoke J, Banoczy J, Proskin H. Effect of after-meal sucrosefree gum-chewing on clinical caries. Journal of Dental
Research 2001;80:1725–9.

[8] Dawes C, Dong C. The flow rate and electrolyte compositionof whole saliva elicited by the use of sucrose-containing
and sugar-free chewing-gums. Archives of Oral Biology
1995;40:699–705.
[9] Dawes C, Kubieniec K. The effects of prolonged gum
chewing on salivary flow rate and composition. Archives ofOral Biology 2004;49:665–9.
[10] Reynolds EC, Cai F, Shen P, Walker GD. Retention in plaqueand remineralization of enamel lesions by various forms ofcalcium in a mouthrinse or sugar-free chewing gum. Journalof Dental Research 2003;82:206–11.
[11] Cross KJ, Huq NL, Palamara JE, Perich JW, Reynolds EC.
Physicochemical characterization of casein
phosphopeptide–amorphous calcium phosphate
nanocomplexes. The Journal of Biological Chemistry2005;280:15362–9.
[12] Iijima Y, Cai F, Shen P, Walker G, Reynolds C, Reynolds EC.
Acid resistance of enamel subsurface lesions remineralized
by a sugar-free chewing gum containing casein
phosphopeptide–amorphous calcium phosphate. Caries
Research 2004;38:551–6.
[13] Morgan MV, Adams GG, Bailey DL, Tsao CE, Fischman SL,
Reynolds EC. The anticariogenic effect of sugar-free gum
containing CPP–ACP nanocomplexes on approximal caries
determined using digital bitewing radiography. Caries
Research 2008;42:171–84.
[14] Shen P, Cai F, Nowicki A, Vincent J, Reynolds EC.
Remineralization of enamel subsurface lesions by sugarfree chewing gum containing casein phosphopeptide–
amorphous calcium phosphate. Journal of Dental Research
2001;80:2066–70.
[15] Haas MS, Greenberg MJ, inventors. Calcium Phosphate salts
in oral compositions suitable as a tooth remineralizing agent.
International Patent Application WO 2007/092763 A2, 2007.
[16] Cai F, Manton DJ, Shen P, Walker GD, Cross KJ, Yuan Y, et al.
Effect of addition of citric acid and casein phosphopeptide–morphous calcium phosphate to a sugar-free chewing gum
on enamel remineralization in situ. Caries Research
2007;41:377–83.
[17] Sokal R, Rohlf F. Biometry. San Francisco: Freeman; 1969.
[18] Norusis M. SPSS for windows: base system user’s guide,
Release 6. 0. IL, USA: SPSS Inc.; 1993.
[19] Pearce KN. Formation constants for magnesium andcalcium citrate complexes. Australian Journal of Chemistry
1980;33:1511–7.
[20] Cochrane NJ, Saranathan S, Cai F, Cross KJ, Reynolds EC.
Enamel subsurface lesion remineralisation with casein
phosphopeptide stabilised solutions of calcium, phosphateand fluoride. Caries Research 2008;42:88–97.