日大歯学 ，98（1），18-24，2024

Original Article

Influence of ion-releasing filler-containing gel application
on dentin remineralizationby using ultrasonic velocity measurement
Miho Suzuki 1 , Hiroyasu Kurokawa 2 , Taketo Okuwaki 2 , Toshiki Takamizawa 2 ,Atsushi Kamimoto 3 , Koji Komoriya 2 , Ryo Ishii 2 , Masashi Miyazaki 2
1

Kichijoji Orthodontic Clinic
Department of Operative Dentistry, Nihon University School of Dentistry3
Department of Comprehensive Dentistry and Clinical Education, Nihon University School of Dentistry2

Abstract: Purpose: The main objective of this study was to investigate the efficacy of S-PRG filler-containing gel
application in promoting dentin remineralization using ultrasonic velocimetry.
Methods: Root dentin slabs of bovine teeth were sliced and formed into rectangles, treated with 0.1 M lactate
buffer (pH 4.75) for 10 min, and then immersed in artificial saliva (pH 7.0). This treatment was repeated three times
a day for 28 days. S-PRG filler-containing gel (PRG) and high-fluorine concentration silver diamine fluoride (SDF)
solution were used. The treatment methods were: 1) untreated group, 2) PRG one-off application group, 3) SDF oneoff application group, 4) PRG frequent-time application group, and 5) SDF frequent-time application group. After
treatment, dentin slabs were soaked in 0.1 M lactate buffer solution and dipped in artificial saliva. This treatment
was repeated 3 times a day for 28 days.
Results: The ultrasonic velocity of the untreated samples decreased slightly during the experimental period. In the
one-off application group, ultrasonic velocities of SDF and PRG increased rapidly on day 7 and then decreasedslightly during the experimental period. In the frequent-time application group, ultrasonic velocities of SDF and PRG
increased during the experimental period; specimens treated with SDF had significantly higher ultrasonic velocities
on each measurement day compared to specimens treated with PRG.
Conclusion: From the results of this experiment, it was concluded that the S-PRG filler-containing gel and silver
diamine fluoride solution appear to promote remineralization and inhibit dentin demineralization.
Keywords: S-PRG filler, dentin, remineralization, ultrasonic measurement

イオン徐放性フィラー含有ゲルが象牙質の再石灰化に及ぼす影響に関する
超音波測定による検討
鈴
紙

木
本

美

穂1
篤3

黒 川 弘 康2
小森谷 康 司 2
2

奥
石

脇
井

岳

人2
亮2

髙見澤
宮 崎

俊
真

樹2
至2

1
吉祥寺矯正歯科クリニック
日本大学歯学部保存学教室修復学講座
3
日本大学歯学部総合歯科学分野

要旨：目的：S-PRG フィラー含有ゲル塗布による象牙質の再石灰化促進効果を超音波流速計を用いて検討した。
方法：ウシ歯根部象牙質板を長方形にスライスし，0.1 M 乳酸緩衝液（pH 4.75）で10分間処理した後，人工唾液（pH 7.0）に浸漬した。この処理を 1 日 3 回，28日間繰り返した。試片の処理は，S-PRG フィラー含有ゲル（PRG）とフッ化ジアンミン銀（SDF）溶液を用い，1）未処理群，2）PRG 単回塗布群，3）SDF 単回塗布群，4）PRG 頻回塗布群および 5）SDF 頻回塗布群とした。処理後，象牙質板を0.1M 乳酸緩衝液に浸漬し，人工唾液に保管した。この処
置を 1 日 3 回，28日間繰り返した。
成績：未処理試料の超音波速度は，実験期間中にわずかに低下した。単回塗布群では，SDF と PRG の超音波速度は 7 日目に急激に上昇し，その後実験期間中にわずかに低下した。頻回塗布群では，SDF と PRG の超音波速度は実験期間中に増加した。SDF で処理した試料は，PRG で処理した試料と比較して各測定日の超音波速度が有意に高かった。
結論：本実験の結果から，S-PRG フィラー含有ゲルおよびフッ化ジアンミン銀溶液は再石灰化を促進し，象牙質の脱灰を抑制することが示された。
キーワード：S-PRG フィラー，象牙質，再石灰化，超音波測定（受付：令和 5 年 11 月 20 日）
Corresponding author. Hiroyasu Kurokawa
Department of Operative Dentistry, Nihon University School of
Dentistry
1-8-13, Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan

TEL：+81-3-3219-8141
FAX：+81-3-3219-8347
E-mail：kurokawa.hiroyasu@nihon-u.ac.jp

18

日大歯学

第 98 巻第 1 号

solutions 9). However, one of the main drawbacks of SDF

Introductionis that it discolors the tooth surface. The use of biofunctional

Evidence-based root surface caries prevention

materials, especially those containing calcium andguidelines have been proposed for the management ofphosphate ions, has been introduced as a strategy toroot surface caries, including control of dietary

facilitate remineralization and improve fluoride uptake incarbohydrate intake, improvement of oral hygiene,

dental substrates 10). Surface-reaction prereacted glass

antibacterial agents, fluoride-containing dentifrice, caseinionomer (S-PRG) filler is prepared by acid-base reaction ofphosphopeptide-stabilized amorphous calcium phosphate,

fluoroboronaluminosilicate glass with polyacrylic acid inand application of bioactive glasses . It is believed thatthe presence of water, the preliminary product being a

the use of fluoride is a noninvasive and effective

stable glass ionomer phase within the glass particles. It is1)

treatment to control root surface caries . Mechanicalreported that the S-PRG inhibits tooth demineralization

tooth cleaning with the use of fluoridated gels is a cost-and plaque formation by releasing fluoride (F‒), borate

effective means of cleaning the tooth surface because it(BO33‒), strontium (Sr2+), silica (SiO32‒) sodium (Na+), andcombines the mechanical destruction of dental biofilm

aluminum (Al3+) ions. As a matter of fact, compared towith the addition of fluoride. Root surfaces have a higher

fluoroaluminosilicate glass fillers, resin composites withaffinity for fluoride uptake than enamel, but dentin is

SPRG fillers were shown to release F‒ at a higher rate 11).

more easily dissolved in the acidic environment ofIn the previous report 12), S-PRG filler also has the effectcariogenic plaque than enamel, with the critical pH ofof modulating the acidity of the oral cavity, making thecementum and dentin being 6.0 to 6.8 rather than 5.2 for

pH of the surrounding environment slightly alkaline uponenamel .

contact with water or acidic solutions. It is thought that2)

3)

this effect is mediated by ions released from the S-PRG

Root surface caries can occur in young adults but isfiller 13).

more frequent in the populations . This is the result of a4)longer lifespan that presents favorable conditions for the

There are individual reports of effects on tooth

maintenance of natural teeth. Furthermore, root surface

remineralization using fluoride-containing agents, but few

caries is often related to gingival recession. Due to thereports have compared them. The principal purpose ofrough, retentive anatomy of the root surface and thethis study was to demonstrate the efficacy of S-PRG

difficulty of adequate cleaning, biofilm can easily

filler–containing gel application on the prevention of

accumulate, which may increase the risk of root surface

dentin remineralization by using ultrasonic measurement

caries development and progression . Fluoride plays an

method. The null hypothesis tested was that there were

essential role in preventing demineralization, and fluoride-

no differences among the samples treated with the S-PRG

containing products such as dentifrice, gels, mouthwashes,

filler containing gel and the SDF solution.

5)

coatings, and sealants are widely used.

Materials and Methods

Silver diamine fluoride (SDF) has been employed in
dentistry for more than 50 years, and studies on its

1 ．Specimen preparation

efficacy are promising; SDF solutions have been reported

In this study, oral gel containing S-PRG filler (PRG;

to be an effective treatment to arrest dental caries and

PRG Pro-Care Gel; Shofu, Kyoto, Japan) and a highare usually recommended for children at high risk offluoride concentration SDF solution (Saforide; Toyodeveloping caries

Pharmaceutical, Osaka, Japan) were used (Table 1).

6). According to a recent systemic

review, annual application of 38% SDF in aged patients

Incisor of freshly extracted bovine teeth were cleaned

reduced incidences of new caries on exposed rootand stored in physiological saline solution for up to 2

surfaces by at least 50%, and longer-term interventions

weeks. About two-thirds of the root apex structure of

were more effective . In clinical trials, various concentrations

each tooth was removed using a diamond-impregnatedwere applied and it was found that the 38% solution was

disk in a low-speed saw (IsoMet 1000 Precision Sectioning

significantly more effective in arresting caries than the

Saw; Buehler, Lake Bluff, IL, USA). Surfaces of root

12% SDF or no application 8). It was found that when

dentin were polished with wet #240-grit silicon carbide

SDF was applied to teeth, it penetrated the enamel and(SiC) paper (Fuji Star Type DDC; Sankyo Rikagaku,

dentin and provided two to three times more fluoride

Saitama, Japan) to expose flat dentin surfaces. Dentin

storage under the tooth surface than with other fluoride

blocks were shaped carefully into rectangles (4×4×7)

19

Influence of S-PRG filler containing gel application on dentin remineralization

令和 6 年 6 月

Table 1 Materials used in this study and their compositions
Table 1

Materials used in this study and their compositions

Material(Lot No.)

Code

Saforide(808RA)SDF

38% silver diamine fluoride

PRG Pro-Care Gel(4G0011)PRG

hydrated silica, S-PRG filler, glycerol, carboxymethylcellulose
sodium, sorbitol, sodium dodecyl sulfate, mint flavoring

Composition

Create a root surface lesion

Manufacture
Toyo Pharmaceutical,
Osaka, Japan
Shofu,
Kyoto, Japan

Treatment steps of root surface lesion

Bovine root dentin(4×4×1 mm)

Root surface lesion
Application

Untreated

3 times / day (28 days)

Applied SDF for 3 min

Applied PRG for 10 s

One-off application :→ Perform the processing
before the treatment period

Frequent-time application :→ Perform the processing
every week until 21 days

Rinse and dry
Immersed inlactic acid buffer solution(10 min)

Immersed in
artificial saliva

3 times / day (28 days)

Root surface lesion

Immersed inlactic acid buffer
solution (10 min)

Immersed in
artificial saliva

Fig 1. Specimen preparation and study design of the experiment.

Fig. 1. Specimen preparation and study design of the experiment.

1mm) using a super-fine diamond point (SF106RD; ISOand 0.10 g/100 mL sodium carboxymethyl cellulose) at#021a, Shofu). The surfaces of the specimens were

37℃. These procedures were conducted three times daily

successively polished with #600, #1,200, and #2,000 grit(with an 8 h interval time) over 28 days. The specimens

size wet SiC paper. The thickness and size of thewere then divided into five different treatment groups ofspecimens were measured using a dial gauge micrometer10 specimens each (Fig. 1).

(CPM15-25DM; Mitutoyo, Tokyo, Japan) and covered with

1）Untreated: The cells were treated with 0.1 M lactate

wax except for the labial side of the dentin slab on thebuffer for 10 min and then immersed in artificial

treated surface.

saliva. This procedure was repeated three times. The

All specimens were treated with undersaturated 0.1 M

specimens were then subjected to acid challenge for

lactic acid buffer solution (pH 4.75, 0.75 mM CaCl2 · 2H2O,

the duration of the experiment.

and 0.45 mM KH 2PO 4) for 10 min and then placed in2）One-off application with PRG: PRG was applied with aartificial saliva (pH 7.0, 14.4 mM NaCl, 16.1 mM KCl, 0.3

soft brush for 10 s, rinsed with tap water, and dippedmM MgCl2 · 6H2O, 2.0 mM K2HPO4, 1.0 mM CaCl2 · 2H2O,

in artificial saliva. The specimens were then subjected

20

日大歯学

第 98 巻第 1 号

whereto acid challenge for the duration of the experiment.

C: acoustic velocity
T: thickness of the specimen3）One-off application with SDF: SDF was applied with aΔt: round trip transit time

microbrush, allowed to stand for 3 min, rinsed withThree measurement points were selected for eachtap water. The specimens were then subjected to acidsample, and the average value was used as the specimen's

challenge for the duration of the experiment.

ultrasonic velocity.

4）Frequent-time application with PRG: PRG was appliedwith a soft brush for 10 s, rinsed with tap water,

3 ．Statistical analysis

This procedure was repeated once a week during theData were analyzed using commercially availableacid challenge experiment.
5）Frequent-time application with SDF: SDF was applied

statistical software (Sigma Plot Ver. 13; Systat Software,with a microbrush, allowed to stand for 3 min, rinsed

Chicago, IL, USA). Data for each group were first tested

with tap water.This procedure was repeated once afor homogeneity of variance using the Bartlett test,

week during the acid challenge experiment.

tested for normal distribution using the KolmogorovSmirnov test, and then analyzed using repeated measures

PRG was applied using a micromotor handpiece (Torqanalysis of variance and the Tukey-Kramer post hoc

tech CA-DC; J. Morita Mfg. Co., Ltd., Kyoto, Japan) and amultiple comparison test. The significance level was set

soft brush (Merssage Brush Soft; Shofu) with a digitalat α = 0.05.

balance (AT200; Mettler-Toledo, Greifensee, Switzerland).

Results

The process was performed at 1,000 rpm and a constantpressure of 0.1 N while monitoring. These operations

The average ultrasonic velocities in different treatment

were performed by a single operator to ensure accuracy.

groups are shown in Figs. 2, 3. During the initialdemineralization period, the ultrasonic velocities of all

2 ．Ultrasonic velocity measurement

groups decreased. The differences in storage periods

Ultrasonic velocity measurements were performed

were greater than expected by chance after allowing forusing a system comprising a pulse receiver (5900PR;

the effects of storage conditions, so multiple comparisonsPanametrics, Waltham, MA, USA), a longitudinal wave

were done on the data. The average ultrasonic velocities

transducer (V112; Panametrics), and an oscilloscopeof all groups in the initial deminerarization period(Waverunner LT584; LeCroy, Chestnut Ridge, NY, USA)decreased from 3938 to 3000 m/s. During the experimental(Figure 2). The instruments were initially calibrated byperiod, ultrasonic velocity of untreated group gradually

standard procedures using a 304 stainless steel calibration

decreased from 2971 to 2934 m/s. In the one-off application

block (2211M; Panametrics, Inc.). Measurements were

specimens, the ultrasonic velocities of SDF and PRG

taken before the start of the study and on days 1, 7, 14,

increased dramatically on day 7 and then slightly decreased

21, and 28. All measurements were performed at 23 ℃±

during the experimental period. For the frequent-time

1 ℃ and 50% ± 5% relative humidity.

application specimens, the ultrasonic velocities of SDF

Ultrasonic waves travel through the transducer intoand PRG increased during the experimental period.

the sample and are either reflected at the surface orSpecimens treated with SDF had a significantly higher

transmitted through the sample. The reflected wave thatultrasonic velocity on each measurement day whenreaches the probe is termed the surface echo (S echo),compared with those treated with PRG.

while the transmitted wave reflected at the interface

Discussion

between the air and the back surface of the sample istermed the back surface echo (B echo). The time

Dentin has a complex structure and comprised two

difference between the S and B echoes represents the

major components, namely, collagen-based organic matrix

time it takes for the wave to propagate through theand hydroxyapatite crystal. Collagen fibrils are woven

sample (Figure 3). When the specimen thickness (T) isand lie perpendicular to the tubules, whereas apatite

known, the acoustic velocity (C) can be calculated by

crystals tend to be parallel to the long axis of the collagenmeasuring the difference time (Δt) between the S and B

fibrils. Regarding root surface lesions, it has been suggested

echoes using the following equation:that the anticaries effect of combining with fluoride isC = 2T/Δt

related to the intrinsic mineral and organic composition21

Influence of S-PRG filler containing gel application on dentin remineralization

令和 6 年 6 月

One-off application
4500

Experimental period

Ultrasonic velocity

4000
3500
3000
2500
2000
Untreated
SDF treated
PRG treatedInitialdemineralization
period03938 aA
3828 aA
3865 aA

28/0
3000 bA
3034 bA
3005 bA

7
2971 bA
3816 aB
3475 cC

142942 bA
3719 acB
3389 cdC

212938 bA
3678 cB
3368 cdC282934 bA
3593 cB
3351 dC

Unit: m/s, n = 10 teeth per group.
Within groups, means with the same lower-case letter are not significantly different (p ≧ 0.05).
Between groups at the same periods, means with the same upper-case letter are not significantly different (p ≧ 0.05).
Fig 2. Changes in the ultrasonic velocity of one-off application groups.

Fig. 2 Changes in the ultrasonic velocity of one-off application groups.
Frequent-time application
4500

Experimental period

Ultrasonic velocity

4000
3500
3000
2500 Initialdemineralization
period20000
28/0
Untreated
3938 aA
3000 bA
SDF treated3898 aA
3038 bA
PRG treated3963 aA
2979 bA

7
2971 bA
3881 aB
3569 cC

142942 bA
4080 cB
3737 dC

212938 bA
4100 cB
3848 adC

282934 bA
4121 cB
3922 aC

Unit: m/s, n = 10 teeth per group.
Within groups, means with the same lower-case letter are not significantly different (p ≧ 0.05).
Between groups at the same periods, means with the same upper-case letter are not significantly different (p ≧ 0.05).
Fig 3. Changes in the ultrasonic velocity of frequent-time application groups.

Fig. 3 Changes in the ultrasonic velocity of frequent-time application groups.

comprising the root surface. Both clinical and laboratory

Ultrasonic imaging is a non-invasive technique thatstudies have shown the role of fluoride in enhancing theoffers considerable potential for diagnosis, as well as

resistance to or preventing cervical lesions 1). Fluoride

being a valuable research tool. Ultrasonic devices are also

suppresses mineral loss from dentin during the acidused to detect dentin demineralization 15), and to measure

dissolution process and enhances remineralization in adentin thickness between the tooth surface and the pulp

similar physicochemical manner as occurs in enamel. The

chamber 16). Because the speed of sound (V) is sensitive toavailability of fluoride in saliva and plaque fluid isthe viscoelastic properties of materials 17), ultrasonicessential, even at low levels, to maintain the surface

devices can be used to monitor the setting process of

integrity of teeth and avoid the formation of subsurface

resin cements. This method might also result in lesscariesvariation than the visual-examination method, depending

.

14)

22

日大歯学

第 98 巻第 1 号

filler in the gel may have contributed to the promotion of

upon the examiner 18).
The results of this study indicated that the ultrasonicdentin remineralization. To promote tooth remineralization

velocities of the SDF- and PRG-applied samples wereand prevent acid attack, fluoride uptake from the outerfaster than those measured in the untreated group.

surface of the tooth is essential. Silica, among other ions

These changes might be due to the presence of SDF-

released from S-PRG filler, may play an important role inderived F- and PRG filler-derived ions in the gels, which

dentin mineralization by promoting hydroxyapatite

strengthened the eroded dentin surface and enhanced

formation via induction of hydroxyapatite nucleation 22).

calcification. Although both PRG and SDF were

In aqueous environments, sodium ions (Na + ) witheffective in increasing sound velocity, SDF had ahydrogen cations (H+ or H3O+) are exchanged rapidly

predominantly greater effect. Thus, the null hypothesis

from the solution. The migration of Ca2+ and PO4‒3 groups

12)

tested was that there was no difference between theto the S-PRG fillers formed a CaO–P2O5-rich layer on the

PRG and SD treated samples was rejected.

dentin surface that crystallized into hydroxycarbonate

It has been shown that SDF confers remineralizing

apatite 23) . Chemical reactions that promote apatite

properties to dentin through preservation and protection

formation have been suggested to stimulate remineralizationof the collagen matrix. SDF showed a greater protective

and possibly prevent demineralization of dentin 24). Hence,

effect against dentin demineralization compared tothe combination of fluoride and silica ions can inhibit theuntreated samples, as detected by ultrasonic velocimetry,

dissolution of dental minerals by acids produced by cariogenic

which further support the findings. Because SDF contains

bacteria. In addition, strontium acts as a substitute forhigh concentrations of fluoride and silver, it is expectedcalcium during precipitation and is thought to have ato be highly effective in preventing caries in root surface

synergistic caries-inhibiting effect with fluoride 25) .

dentin. In addition to its anti-decalcification effect on the

Furthermore, reportedly, BO33‒ and F ‒ released frommineral phase, SDF has been reported to have a significant

resin composite containing S-PRG fillers exhibit inhibitory

effect on dentin collagen fibers and may inhibit theireffects on the metabolic activities of Streptococcus mutans

degradation in an acidic environment . SDF also exhibits

at concentrations lower than those that inhibit S. mutans

very effective antimicrobial activity against cariogenic

growth 11).

13)

1)

biofilms

14). A systematic review consistently supports theConclusions

effectiveness of SDF in preventing coronal caries in thedeciduous dentition and in preventing and arresting root
surface caries in the elderly

Under the current experimental condition, using. In contrast, because

dentifrices containing PRG and SDF solution appear to

dentistry is concerned with esthetics, the potential

promote remineralization of the dentin. For people with adrawbacks of SDF need to be taken into account. Among

low risk of caries, avoiding preventative effects may be

its main drawbacks is that it causes discoloration, whichmost cost-effective, daily use of gel containing S-PRG filler

occurs when silver ions in the composition of SDF aremight be suitable. Application of SDF is indicated fortransformed into metallic silver in the presence of lightpatients with extremely higher caries risk, those whoand spread deep into the tooth19). A report evaluating

cannot tolerate conventional dental treatment, patients

how dental staining associated with SDF affects acceptance

who are medically compromised, and those in disparityof this treatment among parents with young children

populations with little access to care.

20)

21)

.

The results suggest that many parents are willing to

Acknowledgements

compromise esthetics in favor of less invasive treatment
options when patients are not cooperating with conventional

This work was supported in part by JSPS KAKENHI

treatment methods. In adult patients, dentists and dental

through grant numbers 21K09900, 22K17047, andhygienists may be concerned about the esthetic consequences

22K10006. This project was also supported in part by theof stained lesions because dentin unaffected by caries

Sato Fund and by a grant from the Dental Researchdoes not stain.

Center of the Nihon University School of Dentistry,

The S-PRG filler behaves as a fluoride-releasing

Japan.

substance, and the combination of strontium and fluoride

Conflict of Interest

ions enhances the crystallinity of carbonated hydroxyapatite.
The fluoride ions and silica ions released from the S-PRG

The authors of this manuscript certify that they have23Influence of S-PRG filler containing gel application on dentin remineralizationno proprietary, financial, or other personal interest of any

令和 6 年 6 月

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