Asian Pacific
Journal of Dentistry
Volume 23

Issue 2

2023

Official Publication
Japanese Dental Science Federation
Japanese Academy of Dental Technology
J-STAGE: https://www.jstage.jst.go.jp/browse/apjod/
Asian Pac J Dent

Print ISSN 2185-3479

Online ISSN 2185-3487

Asian Pacific Journal of Dentistry
Official Publication
Japanese Dental Science Federation
Japanese Academy of Dental Technology

Print ISSN 2185-3479, Online ISSN 2185-3487
J-STAGE: https://www.jstage.jst.go.jp/browse/apjod/

Table of Contents
Volume 23 Issue 2 2023
15 The effect of ions used in bioactive dental materials on proliferation and differentiation of MC3T3-E1 cells
Nami Tsuchiyama, Yukihiko Tamura, Tadamu Gondo, Masaomi Ikeda, Yasushi Shimada
20 Diagnosis of occlusal caries using optical coherence tomography in a real clinical situation
Tomoko Tabata, Hisaichi Nakagawa, Kota Kobayashi, Azusa Takeuchi, Ryohei Fujimori, Keitaro Dohi, Riko
Nakamura, Hirotoshi Iwabuchi, Tadamu Gondo, Yukiko Tsuji, Xuefei Chen, Takaaki Sato, Go Inoue,
Yasushi Shimada
24 Patient with dental metal allergy treated with zirconia ceramic restorations
Shoko Miura, Takafumi Fujita, Yasuko Kohashi, Masanori Fujisawa

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The aim of the Asian Pacific Journal of Dentistry (APJD) is to provide a forum for the publication and rapid dissemination ofarticles in dentistry and dental technology. It allows dentists, dental technicians, dental hygienists, and dental researchers topublish their initial findings, new ideas, clinical experiences, and techniques.
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October 2023

Asian Pacific Journal of Dentistry
Print ISSN 2185-3479, Online ISSN 2185-3487

Editorial Staff
Editor-in-Chief
Hideo Matsumura, Nihon University School of Dentistry, Tokyo, Japan
Associate Editor
Ji-Hua Chen, School of Stomatology, The Fourth Military Medical University, Xi’an, PR China
Jin-Keun Dong, College of Dentistry, Wonkwang University, Iksan, Republic of Korea
Mika Furuchi, Nihon University School of Dentistry, Tokyo, Japan
Guang Hong, Tohoku University Graduate School of Dentistry, Sendai, Japan
Hiroyasu Koizumi, Nihon University School of Dentistry, Tokyo, Japan
Hiroyuki Minami, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
Toru Nikaido, Asahi University School of Dentistry, Mizuho, Japan
Chikahiro Ohkubo, Tsurumi University School of Dental Medicine, Yokohama, Japan
Amal Abd El-Samad Sakrana, Faculty of Dentistry, Mansoura University, Mansoura, Egypt
Hiroshi Shimizu, Fukuoka Dental College, Fukuoka, Japan
Saiji Shimoe, Hiroshima University Graduate School of Biomedical and Health Sciences, Hiroshima, Japan
Yohsuke Taira, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
Osamu Takeichi, Nihon University School of Dentistry, Tokyo, Japan
Naomi Tanoue, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan
Yoshihiro Tsukiyama, Faculty of Dental Science, Kyushu University, Fukuoka, Japan
Takashi Yamashiro, Osaka University Graduate School of Dentistry, Suita, Japan
Takayuki Yoneyama, Nihon University School of Dentistry, Tokyo, Japan
Editorial Board
Hong-Jun Ai, School of Stomatology, China Medical University, Shenyang, PR China
Noriko Hisamatsu, Nagasaki University Hospital, Nagasaki, Japan
Hideyuki Imai, Dental Technician School, Nihon University School of Dentistry, Tokyo, Japan
Atsushi Kamimoto, Nihon University School of Dentistry, Tokyo, Japan
Khairul Matin, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
Atsushi Mine, Osaka University Graduate School of Dentistry, Suita, Japan
Yasuko Momoi, Tsurumi University, Yokohama, Japan
Yoichiro Ogino, Faculty of Dental Science, Kyushu University, Fukuoka, Japan
Masayuki Otsuki, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
Tzu-Yu Peng, College of Oral Medicine, Taipei Medical University, Taipei, Taiwan ROC
Koichi Shinkai, The Nippon Dental University School of Life Dentistry at Niigata, Niigata, Japan
Yuka I Sumita, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
Yoshimasa Takeuchi, Nihon University School of Dentistry, Tokyo, Japan
Yukimichi Tamaki, Asahi University School of Dentistry, Mizuho, Japan
Xiao-Jing Wang, School of Stomatology, The Fourth Military Medical University, Xi’an, PR China
Hiroaki Yanagida, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan
Aki Yoshida, Gnathos Dental Studio, Weston MA, USA
Takako Yoshikawa, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
Assistant to the Editor
Junichi Honda, Nihon University School of Dentistry, Tokyo, Japan
Akihisa Kodaira, Kodaira Dental Clinic, Fujimino, Japan
Hiroshi Nogawa, PAPA Dental Clinic, Ageo, Japan
Advisory Board
Yi-Ru Fang, Osaka Dental University, Hirakata, Japan
Jianping Geng, Xi’an International Medical Center Hospital, Xi’an, PR China
Takayoshi Kawazoe, Osaka Dental University, Hirakata, Japan
Futoshi Komine, Nihon University School of Dentistry, Tokyo, Japan
Clive S. Langham, Nihon University School of Dentistry, Tokyo, Japan
Kazuhiko Suese, Nara Dental Association, Nara, Japan
Masahito Sumitomo, Japanese Dental Science Federation, Tokyo, Japan
Shiro Suzuki, School of Dentistry, The University of Alabama at Birmingham, Birmingham AL, USA
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Original Article

The effect of ions used in bioactive dental materials on proliferation anddifferentiation of MC3T3-E1 cells
Nami Tsuchiyama*1), Yukihiko Tamura2), Tadamu Gondo1), Masaomi Ikeda3), Yasushi Shimada1)
1) Department of Cariology and Operative Dentistry, Division of Oral Health Sciences, Graduate School of Medical and Dental Science, Tokyo Medical and Dental
University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan. *Corresponding author: tak2ope@tmd.ac.jp
2) Department of Pharmacology, Division of Bio-Matrix, Graduate School of Medical and Dental Science, Tokyo Medical and Dental University, 1-5-45 Yushima,
Bunkyo-ku, Tokyo 113-8549, Japan3) Oral Biomedical Engineering, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
Received July 11, 2023, Revised August 10, 2023, Accepted August 23, 2023

Abstract

Purpose: This study investigated the effects of the main ions thought to be released from bioactive dental materials on the proliferation anddifferentiation of MC3T3-E1 murine osteoblasts.
Methods: Cell proliferation was assessed in a control group (minimum essential medium α) and in several ion groups (control group medium +aluminum, boron, sodium fluoride, or strontium ions) to determine which ions affect the osteogenic response to MC3T3-E1. Three groups of MC3T3E1 cells, namely, a control group, a lipopolysaccharide (LPS) group (control + 5 μg/mL LPS), and a strontium group (control + 1 mM strontium ions)were cultured for 7 days.
Results: Significant differences in cell proliferation were observed in the strontium group (P < 0.05) but not in the aluminum, boron, or sodium fluoride
ion groups. Cell proliferation was enhanced in the strontium group compared with the control group (P < 0.05). Cytotoxicity was not observed in anyof the groups (P < 0.05). The strontium group had the highest alkaline phosphatase (ALP) activity (P < 0.05) and the greatest degree of ALP staining,
indicating that strontium affected cell differentiation. Collagen production was the highest in the control group and the lowest in the LPS group (P <0.05).
Conclusion: Media containing 1 mM strontium ions promoted osteoblastic differentiation in MC3T3-E1 cells without causing cytotoxicity. Further
research is needed to determine the influence of culture time and the minimum concentration for each ion.
Keywords: bioactive dental materials, cytotoxicity, differentiation, MC3T3E-1, osteoblast, strontium

Introduction

osteoblasts, were provided by the RIKEN BioResource Research Center(Tsukuba, Japan). The cells were maintained in minimum essential
medium α (MEM α) + L-glutamine + ribonucleosides + deoxyribonucleosides (Gibco, Thermo Fisher Scientific Inc., Waltham, MA,
USA), containing 1% (v/v) penicillin-streptomycin solution (100 U/mL
penicillin and 100 μg/mL streptomycin) and 10% (v/v) fetal bovine serum(FBS; Ireland origin, Biowest SAS, Nuaillé, France). The cells wereincubated at 37°C under a humidified atmosphere composed of 95% air
and 5% CO2. The medium was changed every other day until the cells
had reached 70%-80% confluence, after which the cells were seeded in
96-well plates at 4.0 × 104 cells/well for use in the subsequent cellproliferation, cytotoxicity, alkaline phosphatase (ALP) activity, andcollagen quantification experiments.
First, cell proliferation was assessed in the control group (n = 6, MEM
α + 10% FBS) and in the several ion (Fujifilm Wako Pure Chemical
Corp.) groups (n = 6, control group medium + each ion concentration
shown in Table 1) to determine which ions affect MC3T3-E1.
After the cells were treated with the selected ion solution, the cells
were seeded again in three groups (n = 6 per group for each experiment):
a control group (MEM α + 10% FBS), a lipopolysaccharide (LPS) group(control group medium + 5 μg/mL LPS), and strontium (Fujifilm Wako
Pure Chemical Corp.) group (control group medium + 1 mM strontium).
The amount of 1 mM strontium was selected because it is thought to be
the concentration at which the S-PRG filler releases ions. LPS(Escherichia coli 0111: B4; Sigma-Aldrich Corp., St. Louis, MO, USA)was used to induce inflammation in cells. The concentration of LPS wasdecided with reference to a previous study [15]. The medium waschanged every other day for 7 days prior to assessing the cell proliferation,
cytotoxicity, ALP activity, and collagen production.

Bioactive dental materials that release ions are widely used in dentistry.
These materials release ions such as aluminum (Al), boron (B), fluorine(F), sodium (Na), silicon (Si), and strontium (Sr) and are used innumerous dental materials, including resin composites [1], fissuresealants [2], dentin bonding agents [3], root canal sealers [4], and toothcoating materials [5]. These ions are thought to have a variety of effects,
including caries prevention [6], inhibition of bacterial adhesion [2],suppression of decalcified lesions [7], antibacterial activity, anti-plaqueformation activity [1], and acid-buffering capacity [1,8].
Ions released by bioactive dental material can affect various biologicalphenomena. For example, fluoride ions exert an antimicrobial effect [9]and induce the remineralization of enamel [10], strontium ions are known
to enhance bone formation [11], silicate ions are believed to haveantioxidant effects and promote bone formation [12], and boron ionsstimulate osteogenic and odontogenic differentiation [13]. Consequently,
the release of these multiple ions may have a positive effect on the
proliferation and differentiation of osteoblasts.
This study investigated the effects of the main ions thought to bereleased from bioactive dental materials on the proliferation anddifferentiation of MC3T3-E1 cells.

Materials and Methods
Ions
In this study, experimental ion solutions (Fujifilm Wako Pure Chemical
Corp., Osaka, Japan) are prepared following the type and amount of ionsreleased from surface pre-reacted glass-ionomer (S-PRG) filler eluate
reported previously [14]. Ions at various concentrations are listed in Table
1.

Cell proliferation
Cell proliferation in the control group, ion group with a different
concentration as shown in Table 1, strontium group, and LPS group
was assessed using the Cell Counting Kit-8 (CCK-8) assay (Dojin

Cell culture
Mouse calvaria-derived MC3T3-E1 cells, which differentiate into

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
creativecommons.org/licenses/by-nc-nd/4.0/©2023 Asian Pacific Journal of Dentistry15

Table 1

Ions in various concentrations with reference to the dilution of surface pre-reacted glass-ionomer filler eluate
S-PRG dilute

1/25,000

1/5,000

1/1,000

Aluminum (mM)

0.02

0.1

0.5

1/200
2.5

Boron (mM)

4.00

20.0

100.0

500.0

Strontium (mM)

0.08

0.4

2.0

10.0

Fluoride (mM)

0.20

1.0

5.0

25.0

Laboratories, Kamimashiki, Japan), a well-established method forevaluating cell viability. The cells were incubated for 1 h and the opticaldensity of each well was measured at a wavelength of 450 nm on aniMark microplate reader (Bio-Rad Laboratories Inc., Hercules, CA,
USA).
Cytotoxicity
Lactate dehydrogenase (LDH) is a useful marker for detecting damage tocell membranes. Cytotoxicity was evaluated using the LDH-Cytotoxicity
Test (Fujifilm Wako Pure Chemical Corp.). After adding 100 μL of thetest reagent to each well, the samples were incubated at 37°C for 90 min.
The optical density of each well was then measured at 570 nm on a
microplate reader.
ALP activity
ALP activity can be used to assess cell differentiation. ALP activity wasdetermined using LabAssay ALP kits (Fujifilm Wako Pure Chemical
Corp.). After adding 100 μL of the test reagent to each well, the samples
were incubated at 37°C for 15 min. The optical density of each well wasthen measured at 405 nm on a microplate reader.
Collagen quantification
The cultured cells were washed with phosphate-buffered saline (SigmaAldrich Corp.) and fixed in Bouin solution (Fujifilm Wako Pure
Chemical Corp.), then washed again and stained for 1 hr in Sirius Red(Fujifilm Wako Pure Chemical Corp.) dissolved in picric acid solution(Fujifilm Wako Pure Chemical Corp.). Each well was measured at 550
nm on a microplate reader to determine the collagen content.
Statistical analysis
All data are presented as the mean ± standard deviation (n = 6). The
distribution and variance of the data were analyzed by the Shapiro-Wilk
test and Levene’s test. The cell proliferation and collagen quantification
data indicated normal distribution and homogeneity of variance, thenboth data were analyzed by Tukey’s honestly significant difference test.
The ALP activity indicated normal distribution and non-homogeneity ofvariance, then data was analyzed by Dunnett’s T3 test. Differences in cellproliferation at different concentrations of strontium were analyzed by at-test with Bonferroni correction, since data indicated normal distribution
and homogeneity of variance. A P-value of <0.05 was considered toindicate statistical significance and all analyses were performed using
SPSS version 26.0 for Windows, (IBM Corp., Armonk, NY, USA).

Results
Cell proliferation
Cell proliferation in the ion groups was measured by performing CCK-8
assays after 7 days of incubation. As shown in Fig. 1, a significant
difference was observed in only the strontium group (P < 0.05, t-test with
Bonferroni correction).
Cell proliferation in the control group, LPS group, and 1-mM
strontium group was measured by performing CCK-8 assays after 7 daysof incubation. As shown in Fig. 2, cell proliferation was enhanced in theexperimental groups (5 μg/mL LPS, 1 mM strontium ions) compared withthe control group. Cell proliferation was highest in the strontium group,with a significant difference compared with the control group (P < 0.05,
Tukey’s honestly significant difference test).

Fig. 1 Cell proliferation of the ions groups at different concentrations
There was a significant difference in only the strontium group (n = 6, *P < 0.05,
t-test with Bonferroni correction)(P > 0.05, t-test with Bonferroni correction). In addition, no differencesin the cell morphology were observed (data not shown). Taken together,
these results indicate that none of the treatments exerted cytotoxic effects
on the MC3T3-E1 cells.

Cytotoxicity
LDH was used to monitor the occurrence of cell membrane damage
after 7 days of incubation. As shown in Fig. 3, there were no significant
differences between the control group, LPS group, and strontium group

ALP activity
ALP activity was measured using LabAssay ALP kits after 7 days of
incubation. As shown in Fig. 4a, significant differences were observed
16

Fig. 2 Cell proliferation in the three experimental groups
There was a significant difference between the control group and the strontium
group (n = 6, *P < 0.05, Tukey’s honestly significant difference test).

Fig. 3 Cytotoxicity in the three experimental groups
There were no significant differences between any of the groups (n = 6, P >0.05, t-test with Bonferroni correction).

Fig. 4a ALP activity results for the three experimental groups
There were significant differences between all of the groups (n = 6, *P < 0.05,
Dunnett’s T3 test).

Fig. 4b Representative ALP staining images
The lowest and highest degrees of staining were observed for the LPS andstrontium groups, respectively.

Fig. 5 Collagen quantification results for the three experimental groups
Collagen production was highest in the control group and lowest in the LPS
group (n = 6).

Fig. 6 Representative collagen staining images after 14 days
The lowest degree of staining was observed for the LPS group.

between all groups (P < 0.05, Dunnett’s T3 test). The LPS groupdisplayed the lowest ALP activity, indicating that the cells cultured in thepresence of LPS had reduced calcification. As seen from the ALP staining
in Fig. 4b, the strontium group stained more deeply than the other groups,
showing that the strontium affected cell differentiation.

collagen staining images are presented in Fig. 6.

Discussion
It is said that bioactive dental material such as S-PRG filler eluate
releases ions (Na+, F−, Al3+, BO33−, Sr2+, and SiO32−) [8], some of which
promote hard tissue formation or remineralization [16]. S-PRG filler
eluate has also been shown to promote the osteoblastic differentiation ofhuman MSCs [17]. Human MSCs and MC3T3-E1 cells are commonlyused as model systems to study osteogenic differentiation, and they
undergo a similar mineralization process. MC3T3-E1 cells are non-Collagen quantification
Collagen production was measured after 7 days of incubation. As shownin Fig. 5, significant differences were observed between all groups (P <0.05, Tukey’s honestly significant difference test). Collagen production
was the highest in the control group and the lowest in the LPS group. The
17

Like calcium, strontium occurs naturally in bone and teeth, albeit intrace amounts. Strontium ions have been reported to promote boneformation, where a low concentration was most effective in inducing
bone formation [31]. Previous studies have also reported that strontium
was able to positively modulate osteogenic differentiation atconcentrations ranging from 1 to 10 mM in osteoblast cells [32]. The
effects of strontium on cell proliferation have been investigated. The
addition of 1.5 mM of SrCl2 promoted chondrocyte differentiation of
dedifferentiated fat cells, while 3 mM of SrCl2 promoted thedifferentiation of MC3T3-E1 cells [33].
Previous studies demonstrated that strontium at 12.5 μM (i.e.,
approximately 1.1 μg/mL) did not affect the proliferation of the murine
cementoblast cell line OCCM-30 but significantly promoted theexpression of osteogenic genes in these cells. High concentrations ofstrontium ranging from 25 to 200 μM (i.e., approximately 2.2-17.6μg/mL) significantly decreased the viability of OCCM-30 cells, whereas
a concentration of 12.5 μM (1.1 ppm) had no effect. S-PRG filler eluate
which was diluted to obtain final strontium ion concentrations of 0.79 or
1.6 μg/mL, was found to be osteoinductive with the ability to promoteosteoblastic differentiation in UE7T-13 cells [17]. S-PRG filler eluate
diluted to afford final strontium ion concentrations of 0.7928-7.928 ppm
was not cytotoxic to human gingival fibroblasts [21].
With respect to MC3T3-E1 cells, 1 mM of strontium ions was foundto stimulate proliferation and increase the mRNA levels of osteocalcin
and bone morphogenetic protein 2 [34]. In accordance with the previous
results, a strontium ion concentration of 1 mM also led to osteoblastic
differentiation in this study. The concentration of strontium in S-PRG
filler [14] is close to this amount. An LDH assay was used to evaluate theoccurrence of cytotoxicity. The results indicated that strontium ions were
not cytotoxic to MC3T3-E1 cells and did not adversely affect osteoblastic
differentiation at the concentrations used. The boron ions alone could becytotoxic to the cells, but the combination of ions together may interact
in a manner that suppresses this effect.
In conclusion, media containing 1 mM strontium ions promoted
osteoblastic differentiation in MC3T3-E1 cells without displaying
cytotoxicity. Future research is warranted to determine the minimum
concentration and the culturing time for each ion released by S-PRG
fillers.

transformed murine osteoblasts that can differentiate into premature andmature osteoblasts [18]. Osteoblastic differentiation is characterized bycell proliferation, differentiation, and mineralization. ALP activity is a
widely used marker for early osteoblastic differentiation [19]. The aim of
this study was to investigate which ions affect the osteogenic response of
MC3T3-E1 cells in vitro. Strontium ions can activate osteoblast activity
and inhibit osteoclast activity.
Boron, silicon, and strontium are considered to promote boneformation by inducing osteoblastic differentiation of undifferentiatedmesenchymal cells [20]. Meanwhile, sodium fluoride promotes theproliferation of osteoblasts in a dose-dependent manner and aluminum
ions at high concentrations contribute to cell death in cell proliferation
experiments [21].
Aluminum ions at concentrations of 10-40 ppm were reported tosignificantly decrease the expression of osteogenic genes in cultured
primary rat osteoblasts and suppress mineralization in a dose-dependent
manner [22]. In another work, aluminum ions at concentrations of 2.828.4 ppm were found to significantly reduce the viability of cultured
primary rat osteoblasts and suppress the expression of osteogenic marker
genes [23]. These findings suggest that high concentrations of aluminum
ions contribute to cell death in cell proliferation experiments [21].
Furthermore, 2 mM AlCl3 was reported to induce ultrastructural damage,oxidative stress, mitophagy, apoptosis, and cellular dysfunction in
MC3T3-E1 cells [24].
S-PRG filler eluate diluted to contain 0.012-0.12 ppm of aluminum
ions was reported to be compatible with human gingival fibroblasts
without displaying cytotoxicity [21]. In addition, S-PRG filler eluate
diluted to contain 0.013-0.025 ppm of aluminum ions did not affectosteoblastic differentiation in UE7T-13 human bone marrow-derived
MSCs [17].
Boron promotes the expression of bone differentiation markers and isreported to have potential osteoinductive effects. Inhibition of cellproliferation was observed when human dental-pulp-derived stem cells(hDPSCs) were cultured in S-PRG filler eluate containing ≥1 mM boron[25]. However, media containing boron concentrations of 230, 247, and280 μM but almost no other components, had no effect on the
proliferation of hDPSCs after culturing for 2 days. The ALP activity inthe presence of 247 μM boron was higher than that of the control althoughproliferation was significantly suppressed, and at 280 μM the ALP
activity increased remarkably. These results suggest that the release ofboron from S-PRG fillers could increase the ALP activity of hDPSCs.
Boron plays a crucial role in osteogenesis and bone maintenance andhas important effects on the mineralization and morphogenesis of
MC3T3-E1 cells. The addition of 0.1-10 ng/mL of boron was reported topromote calcification without affecting viability in MC3T3-E1 cells [26].
Furthermore, the addition of diluted S-PRG filler eluate to obtain amedium containing 1.31 ppm (121 μM) of boron promoted thecalcification of UE7T-13 human bone-marrow-derived MSCs [17]. In
addition, primary rat bone-marrow-derived MSCs cultured in thepresence of boron concentrations ranging from 6 ng/mL to 6 μg/mL
displayed significantly induced ALP activity after the 10th day [20].
These findings suggest that boron ions at concentrations of 0.0001-6 ppm
may have the ability to induce osteogenic differentiation of preosteoblasts or MSCs, although high doses of boron ions (1 ppm) may
cause cytotoxicity against undifferentiated MSCs [26, 20].
There have been no studies reporting that fluoride promoted boneformation. At the same time, fluoride may exert dose-dependent toxic
effects [27]. Sodium fluoride at 50-100 μM (i.e., approximately 2.1-4.2
μg/mL) releases 1.0-1.9 μg/mL (ppm) of fluoride ions, which has beenreported to enhance cell proliferation and promote osteogenic
differentiation of human dental pulp cells [28]. Fluoride ion
concentrations of 10-50 ppm inhibit human dental pulp cell proliferation,
and a fluoride ion concentration of 50 ppm was reported to be a lethal
dose for human pulp cells [29], such that high concentrations of fluoride
ions may cause cell death in proliferation experiments [21]. Fluoride ionsare considered a multifunctional growth factor with diverse effects on the
proliferation and differentiation of osteoblasts. For example, sodium
fluoride promotes the osteoblastic differentiation of MC3T3-E1 cells andenhances ALP activity and matrix mineralization in a dose-dependent (50or 500 μM) manner. However, at high doses (5 mM), sodium fluoride led
to apoptosis and autophagy and affected the proliferation and survival of
MC3T3-E1 cells [30].

Author Contributions
NT: conceptualization, investigation, methodology, data curation, formal
analysis, visualization, and writing. YT: conceptualization, methodology,
formal analysis, writing, review, editing, and supervision. TG:
investigation. MI: formal analysis, writing, review, editing, andsupervision. YS: conceptualization, methodology, formal analysis,
writing, review, editing, and supervision. All authors read and approved
the final version of the manuscript.
Conflicts of Interest
The authors declare no potential conflicts of interest with respect to theauthorship and/or publication of this article.
Data Availability Statement
The data supporting the findings of this study are available from thecorresponding author, NT, upon reasonable request.
Funding
This research was supported by a Grant-in-Aid for Scientific Research(No. 20KK0209) from the Japan Society for the Promotion of Science.
Acknowledgment
The authors thank Dr. Mahmoud Sayed at the Oral Health Science Center,
Tokyo Dental College for assistance in figure preparation.
ORCID iD

1) NT*: tak2ope@tmd.ac.jp, https://orcid.org/0000-0002-3359-6942
2) YT: tamu.hpha@tmd.ac.jp, https://orcid.org/0000-0002-4287-5927
1) TG: tadamu.g.0131@gmail.com, https://orcid.org/0000-0003-4933-3394
3) MI: ikeda.csoe@tmd.ac.jp, https://orcid.org/0000-0003-2214-4980
1) YS: shimada.ope@tmd.ac.jp, https://orcid.org/ 0000-0002-0751-4819

1819. Gallea S, Lallemand F, Atfi A, Rawadi G, Ramez V, Spinella-Jaegle S, et al. Activationof mitogen-activated protein kinase cascades is involved in regulation of bonemorphogenetic protein-2-induced osteoblast differentiation in pluripotent C2C12 cells.
Bone 2001; 28: 491-8. doi: 10.1016/s8756-3282(01)00415-x
20. Movahedi Najafabadi BA, Abnosi MH. Boron induces early matrix mineralization
via calcium deposition and elevation of alkaline phosphatase activity indifferentiated rat bone marrow mesenchymal stem cells. Cell J 2016; 18: 62-73. doi:
10.22074/cellj.2016.3988
21. Kashiwagi K, Inoue H, Komasa R, Hosoyama Y, Yamashita K, Morisaki A, et al.
Optimal dilutions of S-PRG filler elute for experiments on human gingival fibroblasts
in vitro. Dent Mater J 2021; 40: 136-42. doi: 10.4012/dmj.2019-380
22. Sun X, Cao Z, Zhang Q, Li M, Han L, Li Y. Aluminum trichloride inhibits osteoblast
mineralization via TGF-β1/Smad signaling pathway. Chem Biol Interact 2016; 244: 915. doi: 10.1016/j.cbi.2015.11.027
23. Zhu Y, Xu F, Yan X, Miao L, Li H, Hu C, et al. The suppressive effects of aluminium
chloride on the osteoblasts function. Environ Toxicol Pharmacol 2016; 48: 125-9. doi:
10.1016/j.etap.2016.10.009
24. Liu M, Wu X, Cui Y, Liu P, Xiao B, Zhang X, et al. Mitophagy and apoptosis mediatedby ROS participate in AlCl3-induced MC3T3-E1 cell dysfunction. Food Chem Toxicol
2021; 155: 112388. doi: 10.1016/j.fct.2021.112388
25. Ishigure H, Kawaki H, Shintani K, Ueno K, Mizuno-Kamiya M, Takayama E, et al.
Effects of multi-components released from S-PRG filler on the activities of humandental pulp-derived stem cells. Dent Mater J 2021; 40: 1329-37. doi:
10.4012/dmj.2020-390
26. Hakki SS, Bozcurt BS, Hakki EE. Boron regulates mineralized tissue-associatedproteins in osteoblasts (MC3T3E-1). J Trace Elem Med Biol 2010; 24: 243-50. doi:
10.1016/j.jtemb.2010.03.003
27. Song GH, Wang RL, Chen ZY, Zhang B, Wang HL, Liu ML, et al. Toxic effects of
sodium fluoride on cell proliferation and apoptosis of Leydig cells from young mice. J
Physiol Biochem 2014; 70: 761-8. doi: 10.1007/s13105-014-0344-1
28. Nakade O, Koyama H, Arai J, Ariji H, Takada J, Kaku T. Stimulation by low
concentrations of fluoride of the proliferation and alkaline phosphatase activity ofhuman dental pulp cells in vivo. Arch Oral Biol 1999; 44: 89-92. doi: 10.1016/s00039969(98)00099-5
29. Veron MH, Couble ML, Magloire H. Selective inhibition of collagen synthesis byfluoride in human pulp fibroblasts in vitro. Calcif tissue Int 1993; 53: 38-44. doi:
10.1007/BF01352013
30. Li X, Meng L, Wang F, Hu X, Yu Y. Sodium fluoride induces apoptosis and autophagy
via the endoplasmic reticulum stress pathway in MC3T3-E1 osteoblastic cells. Mol
Cell Biochem 2019; 454: 77-85. doi: 10.1007/s11010-018-3454-1
31. Kaygili O, Keser S, Kom M, Eroksuz Y, Dorozhkin SV, Ates T, et al. Strontium
substituted hydroxyapatites: synthesis and determination of their structural properties,
in vitro and in vivo performance. Mater Sci Eng C Mater Biol Appl 2015; 55: 538-46.
doi: 10.1016/j.msec.2015.05.081
32. Querido W, Farina M, Anselme K. Strontium ranelate improves the interaction of
osteoblastic cells with titanium substrates: Increase in cell proliferation,differentiation and matrix mineralization. Biomater 2015; 5: e1027847. doi:
10.1080/21592535.2015.1027847
33. Cheng Y, Huang L, Wang Y, Huo Q, Shao Y, Bao H, et al. Strontium promotes
osteogenic differentiation by activating autophagy via the the AMPK/mTOR
signaling pathway in MC3T3-E1 cells. Int J Mol Med 2019; 44: 652-60. doi:
10.3892/ijmm.2019.4216
34. Peng S, Liu XS, Huang S, Li Z, Pan H, Zhen W, et al. The cross-talk between
osteoclasts and osteoblasts in response to strontium treatment: involvement of
osteoprotegerin. Bone 2011; 49: 1290-8. doi: 10.1016/j.bone.2011.08.031

References
1. Saku S, Kotake H, Scougall-Vilchis RJ, Ohashi S, Hotta M, Horiuchi S, et al.
Antibacterial activity of composite resin with glass-ionomer filler particles. Dent Mater
J 2010; 29: 193-8. doi: 10.4012/dmj.2009-050
2. Shimazu K, Ogata K, Karibe H. Evaluation of the ion releasing and recharging abilities
of a resin-based fissure sealant containing S-PRG filler. Dent Mater J 2011; 30: 923-7.
doi: 10.4012/dmj.2011-124
3. Iida Y, Nikaido T, Kitayama S, Takagaki T, Inoue G, Ikeda M, et al. Evaluation ofdentin bonding performance and acid-base resistance of the interface of two-step selfetching adhesive systems. Dent Mater J 2009; 28: 493-500. doi: 10.4012/dmj.28.493
4. Han L, Okiji T. Evaluation of the ion release / incorporation of the prototype SPRG filler-containing endodontic sealer. Dent Mater J 2011; 30; 898-903. doi:
10.4012/dmj.2011-101
5. Hosoya Y, Ando S, Otani H, Yukinari T, Miyazaki M, Garcia-Godoy F. Ability ofbarrier coat S-PRG coating to arrest artificial enamel lesions in primary teeth. Am J
Dent 2013; 26: 286-90.
6. Ito S, Iijima M, Hashimoto M, Tsukamoto N, Mizoguchi I, Saito T. Effects of surface
pre-reacted glass-ionomer fillers on mineral induction by phosphoprotein. J Dent 2011;
39: 72-9. doi: 10.1016/j.jdent.2010.10.011
7. Siiya T, Tomiyama K, Iizuka J, Hasegawa H, Kuramochi E, Fujino F, et al. Effect of
the coating material on root dentin remineralization in vitro. Am J Dent 2014; 27: 25862.
8. Fujimoto Y, Iwasa M, Murayama R, Miyazaki M, Nagafuji A, Nakatsuka T. Detectionof ions released from S-PRG fillers and their modulation effect. Dent Mater J 2010;
29: 392-7. doi: 10.4012/dmj.2010-015
9. Miki S, Kitagawa H, Kitagawa R, Kiba W, Hayashi M, Imazato S. Antibacterial
activity of resin composites containing surface pre-reacted glass-ionomer (S-PRG)
filler. Dent Mater 2016; 32: 1095-102. doi: 10.1016/j.dental.2016.06.018
10. Manarelli MM, Delbem AC, Binhardi TD, Pessan JP. In situ remineralizing effect offluoride varnishes containing sodium trimetaphosphate. Clin Oral Investig 2015; 19:2141-6. doi: 10.1007/s00784-015-1492-6
11. Kuang GM, Yau WP, Wu J, Yeung KW, Pan H, Lam WM, et al. Strontium exerts dual
effects on calcium phosphate cement: accelerating the degradation and enhancing theosteoconductivity both in vitro and in vivo. J Biomed Mater Res A 2015; 103: 161321. doi: 10.1002/jbm.a.35298
12. Ilyas A, Odatsu T, Shah A, Monte F, Kim HK, Kramer P, et al. Amorphous silica: a new
antioxidant role for rapid critical-sized bone defect healing. Adv Healthc Mater 2016;
5: 2199-213. doi: 10.1002/adhm.201600203
13. Taṣli PN, Doğan A, Demirici S, Ṣahin F. Boron enhances odontogenic and osteogenic
differentiation of human tooth germ stem cells (hTGSCs) in vitro. Biol Trace Elem Res
2013; 153: 419-27. doi: 10.1007/s12011-013-9657-0
14. Nishimaki M, Nassar M, Tamura Y, Hiraishi N, Dargham A, Nikaido T, et al. The
effect of surface pre-reacted glass-ionomer filler eluate on dental pulp cells andmineral deposition on dentin: in vitro study. Eur J Oral Sci 2021; 129: e12777. doi:
10.1111/eos.12777
15. Lin SK, Kok SH, Kuo MY, Lee MS, Wang CC, Lan WH, et al. Nitric oxide promotes
infectious bone resorption by enhancing cytokine ‐ stimulated interstitialcollagenase synthesis in osteoblasts. J Bone Miner Res 2003; 18: 39-46. doi:
10.1359/jbmr.2003.18.1.39
16. Ammann P. Strontium ranelate: a physiological approach for an improved bone quality.
Bone 2006; 38: 15-8. doi: 10.1016/j.bone.2005.09.023
17. Nemoto A, Chosa N, Kyakumoto S, Yokota S, Kamo M, Noda M, et al. Water-soluable
factors eluated from surface pre-reacted glass-ionomer filler promote osteoblastic
differentiation of human mesenchymal stem cells. Mol Med Rep 2018; 17: 3448-54.
doi: 10.3892/mmr.2017.8287
18. Yang L, Meng H, Yang M. Autophagy protects osteoblasts from advanced glycation
end products-induced apoptosis through intracellular reactive oxygen species. J Mol
Endocrinol 2016; 56: 291-300. doi: 10.1530/JME-15-0267

19

Asian Pac J Dent 2023; 23: 20-23. doi: 10.47416/apjod.23-0004

Original Article

Diagnosis of occlusal caries using optical coherence tomography in a realclinical situation
Tomoko Tabata1), Hisaichi Nakagawa2), Kota Kobayashi1), Azusa Takeuchi1), Ryohei Fujimori1),
Keitaro Dohi1), Riko Nakamura1), Hirotoshi Iwabuchi1), Tadamu Gondo1), Yukiko Tsuji1),
Xuefei Chen1), Takaaki Sato2), Go Inoue1), Yasushi Shimada*1)
1) Department of Cariology and Operative Dentistry, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima,
Bunkyo-ku, Tokyo 113-8549, Japan. *Corresponding author: shimada.ope@tmd.ac.jp
2) Department of Oral Biomedical Engineering, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima,
Bunkyo-ku, Tokyo 113-8549, Japan
Received August 24, 2023, Revised September 21, 2023, Accepted September 24, 2023

Abstract

Purpose: Optical coherence tomography (OCT) is an imaging device that can create cross-sectional images of tooth structure. This study evaluated the
diagnostic performance of dental OCT system for occlusal caries in a real clinical situation.
Methods: Twenty-four occlusal locations on 20 teeth were selected from 12 patients (mean age: 39.6 years). Swept-source OCT (SS-OCT) images
were taken from the occlusal surfaces to diagnose occlusal enamel caries using the international caries detection and assessment system (ICDAS)
grading. Indices of sensitivity and specificity for the detection of superficial enamel demineralization (code 1), distinct enamel demineralization (code2), and enamel caries (code 3) were calculated from the results of visual inspection and SS-OCT obtained by three dentists with less than 2 years clinicalexperience.
Results: The sensitivity of visual inspection and SS-OCT for enamel demineralization (code 1) were 0.22 and 0.55; for enamel demineralization (code2) were 0.50 and 0.61; and for enamel caries (code 3) were 0.22 and 0.44, respectively. The specificity of visual inspection and SS-OCT were 0.52 and
0.78, respectively.
Conclusion: SS-OCT can provide excellent diagnostic performance for occlusal enamel caries in a real clinical situation.
Keywords: enamel caries, ICDAS, occlusal caries, optical coherence tomography

Introduction

in real clinical situations [12]. Therefore, this study was designed toinvestigate the intraoral diagnostic accuracy of dental OCT for early
caries in molar occlusal surfaces.

Dental caries is a dynamic disease process that involves demineralization
and remineralization, for which the imbalance of equilibrium decline
during demineralization can cause advanced lesions [1,2]. The
application of bioavailable calcium, phosphate and fluoride ions in anoral environment is recognized as an efficient therapy for theremineralization of demineralized enamel [2-4]. As for the recent
development of a minimally invasive option for the treatment of caries,
an accurate diagnosis is essential to select the optimal therapy for the
caries.
For the diagnosis of caries, intraoral radiography is widely usedespecially for occlusal caries and interproximal caries, where visualinspection is difficult to access. However, dental radiographs exhibit alow sensitivity in early caries because of the superimposition of
anatomical structures and artifacts [5,6].
The International Caries Detection and Assessment System (ICDAS)
was recently developed to detect the severity and activity of the caries as
early as possible by visual inspection. The ICDAS determines opticalchanges in enamel demineralization after air drying. Thus far, the ICDAS
has demonstrated a high accuracy and reproducibility for detecting early
enamel caries in permanent teeth [7], and for diagnosis of caries invarious stages [8].
Optical coherence tomography (OCT) is a non-invasive imaging
method using light to visualize the internal biological structure. Sweptsource OCT (SS-OCT) is one of the latest versions of OCT, which
demonstrates excellent scanning speed and image resolution for clinicalapplications. Since OCT does not require any radiation dose and cansafely be used on pregnant woman, it is recognized as a sustainable
imaging technology for the diagnosis of caries in dentistry. Previous
studies showed that a dental OCT system based on SS-OCT has a highdiagnostic accuracy for occlusal and proximal surface caries from in vitro
experiments using extracted teeth [9-11]. Nevertheless, only a small
number of studies have been conducted on OCT used to diagnose caries

Materials and Methods
Subjects
This study included 12 adults without any systemic diseases aged
between 23 and 77 years (mean age: 39.6 years). Twenty-four occlusal
surfaces of 20 molars were selected from patients for this study. After
tooth surface cleaning using prophylaxis paste (Pressage, Shofu Inc.,
Kyoto, Japan) and brush cone (Merssage Brush No.1, Shofu Inc.)
attached to a low-speed handpiece at a rotating speed below 2,000 rpm,
digital camera photographs of the occlusal surfaces were taken bothunder moist and dry conditions. SS-OCT scanning was then performed
to obtain a three-dimensional (3D) dataset of the occlusal surface. Using
digital camera photographs and SS-OCT images, ICDAS grading ofenamel caries at occlusal surfaces was carried out by the examiners.
Dental OCT system and imaging
Figure 1 shows the Dental OCT System (Octina, the Yoshida Dental Mfg.
Co., Ltd., Tokyo, Japan), which was used in the present study. Thissystem is a SS-OCT, which employs a high-speed frequency-swept laser
light with a center wavelength of 1,310 nm and a scan range of 140 nm
at 50 KHz. The z-axis resolution of the system is 11 µm in air. A handheld
probe for intraoral imaging attached to the system was used to obtain 3D
dataset for the occlusal surfaces (Fig. 1).
Scoring of occlusal surfaces using ICDAS and dental OCT
Before scoring by the examiners, the occlusal surfaces were carefully
observed by four calibrated dentists with over 8 years of experience incariology at Tokyo Medical and Dental University (NH, TT, TS, and YS)
using both digital camera photographs and SS-OCT images. Using digital
camera photographs, taken under both moist and dry conditions, together

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
creativecommons.org/licenses/by-nc-nd/4.0/©2023 Asian Pacific Journal of Dentistry20

Fig. 1 Clinical image using a dental OCT system
OCT imaging of molar occlusal surface was performed using an intraoral probe
attached to the OCT system (red arrow). Obtained 3D preview image wasdisplayed on the monitor.

Fig. 2 Representative images of intact enamel (red arrows, ICDAS code 0)
a: occlusal view under dry condition. b: occlusal view under moist condition. No
visible changes of occlusal fissure were observed before and after the air
drying. c: en face intensity image generated by 3D OCT. d: extracted 2D imageof the area along the red line in c. Whole thickness of enamel was identified
with the location of DEJ (white open arrow).

Table 1 Sensitivity, specificity and diagnostic accuracy for visual inspection and SSOCT using ICDAS code
SP
SE

κ

Visual inspection

SS-OCT

0.52

0.78

code 1

0.22

0.55

code 20.50

0.61

code 3

0.22

0.44

0.33

0.61

SE, sensitivity; SP, specificity; κ, diagnostic accuracy

with SS-OCT images, the calibrated dentists performed ICDAS grading
for the 24 occlusal surfaces as follows: Code 0, Sound surface; Code 1,
First visual change in enamel seen only after prolonged air drying or
restricted to the confines of a pit or fissure; Code 2, Distinct visual change
in enamel that is within or wider than the confines of a pit or fissure andseen on a wet or dry surface; Code 3, Localized enamel breakdown
without visual signs on dentin exposure; and Code 4, Underlying dark
shadow from dentin.
The findings obtained from the investigated sites were then comparedby the calibrated dentists to achieve a consensus score for each site. The
scoring results by the calibrated dentists were employed as the definitive
diagnosis and used for the following experiment.
Three dentists who had less than two years of clinical experience
participated in this study, carrying out the ICDAS grading of occlusal
surface blind to each other. The same criteria as for the definitive
diagnosis was employed for the diagnosis by the three dentists, but using
either digital camera photographs for visual inspection or SS-OCT
images. For visual inspection, digital camera photographs both under the
moist and dry conditions were used. For SS-OCT imaging, 2D image ofocclusal surface was selected from the 3D dataset and displayed in themonitor, where the three dentists evaluate the presence of enamel caries.

Fig. 3 Representative images of first enamel change by demineralization (redarrows, ICDAS code 1)
a: occlusal view under dry condition. Central pit of occlusal surface was stained
dark (red arrow). b: occlusal view under moist condition. Staining of central pit
was not obvious under the moist condition (red arrow). c: en face intensity
image generated by 3D OCT. d: extracted 2D image of the area along the redline in c. The brightness of occlusal fissure was increased and imaged white(red arrow). The depth of bright zone was confined within the half thickness ofenamel. Location of DEJ was identified (white open arrow).

Statistical analysis
The results obtained by the three dentists were statistically analyzed using
a statistical software package (Dr SPSS-2 for Windows, SPSS Inc.,
Chicago, IL, USA). The results of ICDAS grading for visual inspectionand SS-OCT image by three dentists were compared with the results ofdefinitive diagnosis performed by the calibrated dentist, and indices ofsensitivity and specificity for visual inspection and SS-OCT were
calculated. The diagnostic accuracy as the agreement of visual inspection
or SS-OCT imaging with the definitive diagnosis was calculated using
weighted kappa.

visual inspection and SS-OCT for code 1 enamel demineralization were0.22 and 0.55, whereas code 2 enamel demineralization values were 0.50
and 0.61, respectively. The sensitivity values of visual inspection and SSOCT for code 3 enamel caries were 0.22 and 0.44, respectively. The
specificity values of visual inspection and SS-OCT were 0.52 and 0.78,
respectively. The diagnostic agreement for visual inspection and SS-OCT
were 0.33 and 0.61, respectively.
Representative images of visual inspection and SS-OCT obtained
from in vivo occlusal surfaces are shown in Figs. 2-5.

Results
The results of sensitivity, specificity and diagnostic agreement for visualinspection and SS-OCT are shown in Table 1. The sensitivity values of21

using a prototype OCT system [13]. In this study, 1 of the 14 patients,
who had a history of temporomandibular joint disorder, found the SSOCT imaging of the lower second molar uncomfortable because ofdifficulties keeping their mouth open. However, the lower first molar of
this patient could be safely scanned using SS-OCT. The acquisition timeof the 3D dataset in the SS-OCT system was approximately 4 s. Whilepatients were required to keep their mouth open during the 3D scanning,
the extension of acquisition time to take several images should be avoided
in patients with temporomandibular joint disorder. As a result, one
premolar and 19 molars of 10 first molars and 9 second molars from 12
healthy volunteer patients were used in this study.
In SS-OCT, the entire enamel layer of the molar occlusal surface, as
well as dentinoenamel junction (DEJ) with underlying dentin, wasdisplayed on the monitor (Fig. 1). It has been reported that thedemineralization of enamel increases the scattering coefficient of thestructure, which in turn increases the brightness of OCT image [14-16].
The results of this study also show that OCT images of enamel
demineralization for ICDAS codes 1 and 2 are associated with an increasein brightness and are significantly different from the surrounding healthy
enamel (Figs. 3, 4). Due to the increased brightness of OCT, there werealso variations in depth and area images between ICDAS code 1 and code
2 fissures (Figs. 3, 4). In code 3, due to the distinct changes in occlusal
fissure in the enamel, image alterations of SS-OCT were also evident,
demonstrating the morphological deterioration and increased scatteringof the roughened enamel (Fig. 5).
Although ICDAS is based on visual evaluation, initial enamel
demineralization is differentiated into code 1 and code 2 since moistureaffects the optical appearance of teeth [17,18]. In enamel
demineralization, water usually clogs the pores of demineralization andobscures the appearance of lesions in a similar refractive index. Code 1
is the enamel demineralization that can only be found when enamel isdehydrated, where demineralization is confined to the superficial enamel(Fig. 3). Code 2 is the enamel demineralization that can be identified evenunder the presence of moisture, where demineralization penetrates into
deeper enamel (Fig. 4). In this experiment, the results of SS-OCT fromthe examiners with less than two years clinical experience showed
excellent agreement with the results of definitive diagnosis performed bycalibrated dentists.
In this experiment, there are several limitations. If caries havedemineralized enamel with no cavitation, they can be treatednoninvasively using appropriate remineralization therapy; caries-relatedchanges in enamel with ICDAS codes from 1 to 3 can be treated by
specific teeth brushing and remineralization therapy. Therefore, in thisstudy, the patient's teeth were not cut histologically to validate the real
penetration depth of caries.
Moreover, only enamel caries were diagnosed in this study since
ICDAS can outperform the diagnostic accuracy of enamel caries via
optical changes in enamel [17,19]. However, it is necessary to evaluate
the diagnostic accuracy of SS-OCT for caries, including dentin caries. In
a previous experiment carried out by the authors using extracted teeth,
the accuracy of OCT diagnosis by dentists with over 9 years of clinicalexperience was higher than that carried out by dentists with less than 3
years of experience [10]. Therefore, it is highly probable that dentists canimprove the diagnostic accuracy of caries using SS-OCT system throughclinical experience. Moreover, dental OCT has the potential to provide
caries management and monitoring, determining the remineralization
state of enamel demineralization using tomographic images [16]. Further
evidence is necessary to evaluate enamel demineralization andremineralization in order to develop an accurate diagnosis for occlusal
enamel caries.

Fig. 4 Representative images of distinct enamel change by demineralization(red arrows, ICDAS code 2)
a: occlusal view under dry condition. Distal pit of occlusal surface was stained
dark (red arrow). b: occlusal view under moist condition. Distal pit was staining
dark even under the moist condition (red arrow). c: en face intensity image
generated by 3D OCT. d: extracted 2D image of the area along the red line in c.
The brightness of occlusal fissure was increased and imaged white (red arrow).
The depth of bright zone was confined within the half thickness of enamel.
However, the area was increased more than Fig. 3d. Location of DEJ was
identified (white open arrow).

Fig. 5 Representative images of localized enamel breakdown without visualsigns on dentin exposure (red arrows, ICDAS code 3)
a: occlusal view under dry condition. Almost the whole occlusal fissure wasstained dark suspicious of enamel caries. Distal pit was visibly concave andbecame chalky (red arrow). b: occlusal view under moist condition. Almost
whole occlusal fissure was stained dark. The chalky appearance observed
under the dry condition was not obvious under the moist (red arrow). c: en faceintensity image generated by 3D OCT. d: Extracted 2D image of the area along
the red line in c. The contour of occlusal fissure was concave (red arrow). The
brightness of occlusal fissure was increased and imaged white. The depth ofbright zone was confined within the enamel. Location of DEJ was identified(white open arrow).

Ethical Approval
This study design was approved by the Institutional Review Board ofTokyo Medical and Dental University (approval number D2013-013 andD2013-0014) and conducted on the patients who visited the university
hospital at Tokyo Medical and Dental University. The study protocol had
been explained to the subjects before the involvement in the study andwritten informed consent for the participation in the study was obtained.

Discussion
The SS-OCT system used in this study involves intraoral scanning using
an oral probe, for which the imaging of molar occlusal surfaces showedno adverse events in this study. This result was in accordance withprevious studies performed on populations with special health care needs

Consent to Participate
The subjects in this clinical study gave their informed consent by signinga written consent form for participation in the research project.
22

3. Takagi S, Liao H, Chow LC. Effect of tooth-bound fluoride on enamel
demineralization/ remineralization in vitro. Caries Res 2000; 34: 281-8. doi:
10.1159/000016603
4. Chow LC, Takagi S, Carey CM, Sieck BA. Remineralization effects of a twosolution fluoride mouthrinse: an in situ study. J Dent Res 2000; 79: 991-5. doi:
10.1177/00220345000790041601
5. Wenzel A, Fejerskov O. Validity of diagnosis of questionable caries lesions in
occlusal surfaces of extracted third molars. Caries Res 1992; 26: 188-94. doi:
10.1159/000261441
6. Bader JD, Shugars DA, Bonito AJ. Systematic reviews of selected dental caries
diagnostic and management methods. J Dent Educ 2001; 65: 960-8.
7. Rodrigues JA, Hug I, Diniz MB, Lussi A. Performance of fluorescence methods,
radiographic examination and ICDAS II on occlusal surfaces in vitro. Caries Res 2008;
42: 297-304. doi: 10.1159/000148162
8. Jablonski-Momeni A, Stucke J, Steinberg T, Heinzel-Gutenbrunner M. Use of ICDASII, fluorescence-based methods, and radiography in detection and treatment decisionof occlusal caries lesions: an in vitro study. Int J Dent 2012; 2012: 371595. doi:
10.1155/2012/371595
9. Shimada Y, Sadr A, Burrow MF, Tagami J, Ozawa N, Sumi Y. Validation of sweptsource optical coherence tomography (SS-OCT) for the diagnosis of occlusal caries. J
Dent 2010; 38: 655-65. doi: 10.1016/j.jdent.2010.05.004
10. Nakagawa H, Sadr A, Shimada Y, Tagami J, Sumi Y. Validation of swept source opticalcoherence tomography (SS-OCT) for the diagnosis of smooth surface caries in vitro. J
Dent 2013; 41: 80-9. doi: 10.1016/j.jdent.2012.10.007
11. Nakajima Y, Shimada Y, Sadr A, Wada I, Miyashin M, Takagi Y, et al. Detection of
occlusal caries in primary teeth using swept source optical coherence tomography. J
Biomed Opt 2014; 19: 16020. doi: 10.1117/1.JBO.19.1.016020
12. Shimada Y, Nakagawa H, Sadr A, Wada I, Nakajima M, Nikaido T, et al.
Noninvasive cross-sectional imaging of proximal caries using swept-source opticalcoherence tomography (SS-OCT) in vivo. J Biophotonics 2014; 7: 506-13. doi:
10.1002/jbio.201200210
13. Espinoza K, Hayashi J, Shimada Y, Tagami J, Sadr A. Optical coherence tomography
for patients with developmental disabilities: a preliminary study. Sensors (Basel) 2021;
21: 7940. doi: 10.3390/s21237940
14. Jones RS, Darling CL, Featherstone JD, Fried D. Imaging artificial caries on theocclusal surfaces with polarization-sensitive optical coherence tomography. Caries Res
2006; 40: 81-9. doi: 10.1159/000091052
15. Jones RS, Fried D. Remineralization of enamel caries can decrease optical reflectivity.
J Dent Res 2006; 85: 804-8. doi: 10.1177/154405910608500905
16. Hariri I, Sadr A, Nakashima S, Shimada Y, Tagami J, Sumi Y. Estimation of the enameland dentin mineral content from the refractive index. Caries Res 2013; 47: 18-26. doi:
10.1159/000342416
17. Gugnani N, Pandit IK, Srivastava N, Gupta M, Sharma M. International caries
detection and assessment system (ICDAS): a new concept. Int J Clin Pediatr Dent
2011; 4: 93-100. doi: 10.5005/jp-journals-10005-1089
18. Pitts NB, Ekstrand KR. International caries detection and assessment system (ICDAS)
and its international caries classification and management system (ICCMS) - methods
for staging of the caries process and enabling dentists to manage caries. Community
Dent Oral Epidemiol 2013; 41: e41-52. doi: 10.1111/cdoe.12025
19. Carvalho RN, Letieri ADS, Vieira TI, Santos TMPD, Lopes RT, Neves AA, et al.
Accuracy of visual and image-based ICDAS criteria compared with a micro-CT gold
standard for caries detection on occlusal surfaces. Braz Oral Res 2018; 32: e60. doi:
10.1590/1807-3107bor-2018.vol32.0060

Author Contributions
Conceptualization: TT, NH, TS, YS; Methodology: TT, NH, TS, KK, AT,
RF, KD, RN, HI, TG, YT, XC, GI; Validation: TT, NH, YS; Formal
analysis, TT, NH; Investigation: TT, NH, KK, AT, RF, KD, RN, HI, TG,
YT, XC, GI; Data curation: TT, NH; Writing—original draft preparation:
TT, NH, YS; Writing—review and editing: TT, NH, TS, YS; Supervision:
TS, YS; Project administration: TS, GI, YS; Funding acquisition: YS
Conflict of Interest
Yasushi Shimada received a research grant from the Yoshida Dental Mfg.
Co., Ltd. The other authors declare that they have no conflicts of interest
to disclose.
Data Availability Statement
All data generated during this study are available from the corresponding
author on reasonable request.
Funding
This research received no external funding.
Acknowledgments
The authors are grateful to the Yoshida Dental Mfg. Co., Ltd. for theirsupport in using the dental OCT system.
ORCID iD

1) YS*: shimada.ope@tmd.ac.jp, https://orcid.org/0000-0002-0751-4819
1) TT: tabope@tmd.ac.jp, https://orcid.org/0000-0001-9423-2424
2) HN: vastinager@gmail.com, https://orcid.org/0000-0003-3364-0031
1) KK: koba.ope@tmd.ac.jp, NA
1) AT: azusa.takeuchi.0715@gmail.com, NA
1) RF: fujimori0111@gmail.com, NA
1) KD: kunosuke_super@yahoo.co.jp, NA
1) RN: rico.na0722@gmail.com, NA
1) HI: rockpool18@gmail.com, NA
1) TG: gondope@tmd.ac.jp, NA
1) YT: yukiko0601.tsuji@gmail.com, NA
1) XC: chenxuefei0510@gmail.com, https://orcid.org/0000-0002-8357-0863
2) TS: tsatope@tmd.ac.jp, https://orcid.org/0000-0001-5515-7345
1) GI: inoue.ope@tmd.ac.jp, https://orcid.org/0000-0002-7933-0832

References
1. Featherstone JD. The continuum of dental caries - evidence for a dynamic disease
process. J Dent Res 2004; 83(Spec C): C39-42. doi: 10.1177/154405910408301s08
2. FDI World Dental Federation. FDI policy statement on minimal intervention dentistry(MID) for managing dental caries: adopted by the general assembly: September 2016,
Poznan, Poland. Int Dent J 2017; 67: 6-7. doi: 10.1111/idj.12308

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Asian Pac J Dent 2023; 23: 24-27. doi: 10.47416/apjod.23-0003

Case Report

Patient with dental metal allergy treated with zirconia ceramic restorations
Shoko Miura*1), Takafumi Fujita1), Yasuko Kohashi2), Masanori Fujisawa1)
1) Division of Fixed Prosthodontics, Department of Restorative & Biomaterials Sciences, Meikai University School of Dentistry, 1-1 Keyakidai, Sakado 350-0283,
Japan. *Corresponding author: miuras@dent.meikai.ac.jp
2) Hi-Tech Dental Studio Co., Ltd., 12-8 Nakacho, Sakado 350-0227, Japan
Received August 22, 2023, Revised September 13, 2023, Accepted September 16, 2023

Abstract

This report describes the case of a 52-year-old woman with oral lichen planus due to a dental metal allergy, who was treated successfully by removing
metal restorations and replacing them with a zirconia centered non-metal based fixed partial denture (FPD). Following basic periodontal treatment, allintraoral metal restorations were removed, and provisional restorations were placed. After approximately 3 months of follow-up, allergic symptoms
had resolved, and the patient received the definitive prosthetic treatment. A monolithic zirconia FPD was selected for the molars, and a porcelain layered
zirconia FPD was selected for the anterior dentition. The patient wished to improve the form of the contralateral maxillary anterior tooth, for which alaminate veneer restoration was planned. For the placement of the zirconia FPDs, alumina blasting was applied to the inner surface of the FPDs, andthe placement operation was performed according to the instruction manual for the adhesive resin luting agent used. After completion of prosthetic
treatment, maintenance was performed every 4 months, and 4 years and 4 months have passed. The periodontium was in good condition, and there was
no evidence of secondary caries, debonding, fracture of the FPDs, or abnormal jaw function. Allergic symptoms are in remission, and the FPDs are ingood condition based on patient satisfaction.
Keywords: adhesive dentistry, laminate veneer, lithium disilicate, palmoplantar pustulosis, porcelain, zirconia

Introduction

treatment was performed using zirconia. Since the patient wished to
improve the crown form and color of the left maxillary anterior tooth, alaminate veneer restoration was planned as an esthetic solution, andconsent was obtained accordingly. Restorative and prosthodontic
treatments are shown in Table 1.

Dental metal allergy is a type of contact dermatitis brought on by a known
or suspected allergic reaction to metallic materials used in dental
procedures that are placed in the oral cavity. Since it was first reported in
1928, the prevalence and etiology of this allergy have been investigatedin several clinical, in vitro, and animal studies [1]. However, the causesof dental metal allergies remain poorly understood despite a recent
increase in the number of affected individuals [1]. The basis of dental
metal allergy treatment is the identification and removal of suspected
metals and modification of the environment to avoid contact with theallergen (removal and replacement therapy). This report describes thecase of a patient with oral lichen planus due to a dental metal allergy, who
was treated successfully by removing the suspected metal allergens andreplacing them with a zirconia centered non-metal based fixed partial
denture (FPD).

Clinical Procedure
At the start of the treatment, the patient was given a thorough explanationof the treatment method and precautions to be taken in cases of suspected
metal allergies. Informed consent was obtained from the patient. Afterbasic periodontal treatment, all intraoral metal restorations were removed,
and provisional restorations (Unifast III, GC Corp., Tokyo, Japan) wereplaced using provisional cement (Hybond Temporary Cement Hard,
Shofu Inc., Kyoto, Japan). Subsequently, tooth #37 was restored with acomposite resin material (Gracefil LoFlo, Putty, GC Corp.).
After approximately 3 months of follow-up, the patient received thedefinitive prosthetic treatment, as the allergic symptoms had resolved.
Owing to the presence of vital teeth in the planned treatment area, theamount of tooth preparation was considered. For the subjective
symptoms of clenching, monolithic zirconia FPDs were selected as thematerials (Luxen Multi A2, Geomedi Co., Ltd., Fukuoka, Japan) for themolars, as the tooth structure of the abutment tooth was compromised andthe possibility of FPD fracture was low. A porcelain layering zirconia
FPD (Luxen Multi A2, Geomedi Co., Ltd., Vintage ZR, Shofu Inc.) was
selected for the FPDs, including the maxillary right anterior tooth,because of its esthetic color reproduction. In addition, the patient wishedto improve the form of the contralateral maxillary anterior tooth;therefore, laminate veneer restoration using lithium disilicate glass
ceramics (IPS e.max Press HT A2, Ivoclar Vivadent AG, Schaan,
Liechtenstein) was selected. During the fabrication of the maxillary rightanterior FPDs and maxillary left anterior laminate veneer, a diagnostic
wax-up was performed. The final tooth form was confirmed by thepatient, dental technician, and dentist (Fig. 2a-c). Airborne-particle
abrasion (50 µm aluminum oxide, Zest Dental Solutions, San Diego, CA,
USA) was performed on the inner surface of the FPD, and it was placed
successfully according to the manufacturer’s instructions for the adhesive
resin luting agent used (ResiCem EX, Shofu Inc.). Airborne-particle
abrasion was not performed on the laminate veneers due to the possibilityof cracking in the thin layer shell of the lithium disilicate glass ceramic.

Clinical Report
A 52-year-old woman presented to the Prosthodontic Department, Meikai
University Hospital, in October 2018. The patient’s chief complaint wasthat she wished to have all intraoral metal elements removed. The
patient’s medical history included a blister on the central part of the palate
in August 2018, which led to a visit to a nearby dentist. The patient wasprescribed a mouthwash, but had contact pain on the palate and difficultyeating; thus, the patient visited the oral surgery department of Meikai
University Hospital for a thorough examination. After a thoroughexamination, a metal allergy was suspected, and the patient was referredto the Prosthodontic Department for removal of metal restorations in theoral cavity. The patient presented with a slightly erythematous central
palate with mild ulceration. The patient’s mouth had several metallic
restorations (Fig. 1). Histopathological examination and the results of apatch test led to the diagnosis of a masticatory disorder due to oral lichen
planus caused by gold, palladium, and tin metal allergies.
Periodontal histology revealed periodontal pockets of 2-4 mm, withno signs of tooth mobility. Examination revealed secondary dental caries
in inlays at teeth #24 and #37. The palate exhibited gingival erythema,
blistering, and contact pain. The treatment strategy involved removing
the metals from the tooth and replacing them with provisional
restorations. As the FPDs were seated on the molars, prosthodontic

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
creativecommons.org/licenses/by-nc-nd/4.0/©2023 Asian Pacific Journal of Dentistry24

Fig. 1 Intraoral photographs of initial examination
a: frontal view, b: maxillary occlusal view, c: mandibular occlusal view, d: right lateral view, e: left lateral view

Table 1

Restorative and prosthodontic treatments

Tooth

Treatment detail

Material

Manufacturer#37

composite resin filling

Gracefil Loflo, Putty

GC (Tokyo, Japan)#36

monolithic zirconia crown

Luxen Multi A2

Geomedi (Fukuoka, Japan)#45-47, pontic: #46

monolithic zirconia 3-unit fixed partial denture

Luxen Multi A2

Geomedi#16, 17monolithic zirconia crown

Luxen Multi A2

Geomedi#24, 25, 26, 27

monolithic zirconia crown

Luxen Multi A2

Geomedi#11-15, pontic: #12

porcelain layering zirconia 4-unit fixed partial
dentureLuxen Multi A2

GeomediVintage ZR

Shofu (Kyoto, Japan)

laminate veneer

IPS e.max Press HT A2

Ivoclar (Schaan, Liechtenstein)#21, 22, 23#14, missing at the first visit

Fig. 2 a: diagnostic wax-up of laminate veneer on maxillary left anterior teeth, b: frontal view of laminate veneer on maxillaryleft anterior teeth, c: lingual view of laminate veneer on maxillary left anterior teeth, d: frontal view of intraoral photographs at
the end of treatment, e: maxillary occlusal view of intraoral photographs at the end of treatment, f: mandibular occlusal view of
intraoral photographs at the end of treatment, g: right lateral view of intraoral photographs at the end of treatment, h: left lateralview of intraoral photographs at the end of treatment

performed every 4 months, and 4 years and 4 months have passed (Fig.
2d-h). Due to the high strength of zirconia, there was concern about thewear of the antagonist teeth; however, the occlusal contact area of theinterocclusal record taken at the time of maintenance showed no obvious

Therefore, an adhesive resin cement with a self-etching glass ceramic
primer was used (Variolink Esthetic LC, Ivoclar Vivadent AG). Allabutment teeth were cleaned with a brush cone before luting.
After completion of the prosthetic treatment, maintenance was25

Fig. 3 a: interocclusal record at the end of treatment, b: interocclusal record 3.5 years after completion of treatment, c:plantar photograph of the initial examination, d: plantar photograph during final prosthetic treatment, e: plantar photograph 3
years after completion of treatment

long-term prognosis remains unknown and should be continuously
monitored in the future. Furthermore, the labial and incisal surfaces ofthe maxillary left anterior teeth were reduced by 0.2-1.0 mm to improve
the tooth form, and the laminate veneer covered the incisal edge of the
tooth. Therefore, some of the dentin was partially exposed. Accordingly,
there is more concern about debonding of laminate veneers in such cases
than in those where the abutment bonding surface is enamel only. It has
been reported that porcelain laminate veneers without incisal coverage
have a higher failure rate than porcelain laminate veneers with incisal
coverage [9]; however, it is necessary to observe progress to ensure that
there is no debonding or breakage.
In the present case, zirconia centered non-metal based FPDs wereconsidered useful prostheses after metal removal for lichen planus due todental metal allergy. For a good long-term prognosis, material selection
according to the case, appropriate bonding, and continuous maintenanceaccording to the material selected are important.

wear (Fig. 3a, b). At the end of treatment, blisters were still present on
the plantar; however, they disappeared by the time of maintenance (Fig.
3c-e). The periodontium was in good condition, and there was noevidence of secondary caries, debonding, fracture of the FPDs, orabnormal jaw function. Allergic symptoms are currently in remission, andthe FPDs are in good condition based on patient satisfaction. Furthermore,
the patient was instructed to wear a night guard at bedtime due to thesubjective symptoms of clenching. The long-term prognosis ofmonolithic zirconia restorations remains unknown and will continue tobe carefully monitored.

Discussion
In this case, a monolithic zirconia FPD with a single zirconia material
was selected due to all maxillary molar restorations being vital teeth, thelimited amount of tooth material removed, the subjective symptoms ofclenching, and the need to select a material with a high fracture resistance.
As per the interocclusal record over a period of 3.5 years after placement,
the occlusal contact areas of the entire dentition showed no change. A
monolithic zirconia restoration finished with glazing was reported toshow wear in all occlusal contact areas after 1 year, with a wear volumeof less than 15 μm [2]. Furthermore, the average wear of natural teeth wasreported to be 16.3 µm at 1 year [3], smaller than that produced byfeldspar porcelain and lithium disilicate glass ceramics [3]. In addition,
glazed monolithic zirconia restorations cause more wear to the antagonist
enamel than polished monolithic zirconia restorations after 1 year ofclinical use [4]. Therefore, in the present case, the occlusal contact
surfaces of the FPD on the maxillary anterior teeth that occluded with thenatural teeth were polish finished. However, since the left sided molars
were finished with glazing in consideration of esthetics, it is necessary toobserve the presence or absence of wear. The smooth surface of mirrorpolished zirconia has been reported to have the least influence on thewear of the tooth among other computer-aided design/computer-aided
manufacturing materials [5], whereas it was observed that the monolithic
zirconia restoration caused around twice as much damage on the tooth
enamel after two years of use when compared with that of the natural
tooth [6]. Therefore, although good progress has been achieved, further
long-term observations are required to determine changes in occlusal
contacts.
To test for metal allergy, a patch test is performed in a specialized
setting, such as by a dermatologist. After a metal allergy has been
diagnosed, it is desirable to conduct a metal elemental analysis to confirm
the possibility that an allergenic metal is present in the oral cavity. In thiscase, a patch test result led to the diagnosis of gold, palladium, and tin
metal allergies. However, a metal elemental analysis was not performedat the patient's request.
Although the short-term prognosis of monolithic zirconia restorations
has been reported and the success and survival rates were high [7,8], theConsent for Publication
Written informed consent was obtained from the patient for publicationof this case report and accompanying images.
Author Contributions
SM: conceptualization, investigation, methodology, validation,
investigation, resources, data curation, writing original draft, review, andediting. TF: review and editing. YK: FPDs fabrication, review, andediting. MF: supervision, formal analysis, review, and editing. All authors
read and approved the final version of the manuscript.
Conflicts of Interest
The authors declared no potential conflicts of interest with respect to thisreport, authorship, and/or publication of this article.
ORCID iD

1) SM*: miuras@dent.meikai.ac.jp, https://orcid.org/0000-0002-5564-9670
1) TF: t-fujita@dent.meikai.ac.jp, NA
2) YK: boss@e-job.co.jp, NA
1) MF: m-fujisawa@dent.meikai.ac.jp, https://orcid.org/0000-0001-9507-769X

References
1. Takaoka Y, Akiba Y, Nagasawa M, Ito A, Masui Y, Akiba N, et al. The
relationship between dental metal allergy, periodontitis, and palmoplantar
pustulosis: an observational study. J Prosthodont Res 2022; 66: 438-44. doi:
10.2186/jpr.JPR_D_20_00307
2. Koenig V, Wulfman C, Bekaert S, Dupont N, Le Goff S, Eldafrawy M, et al. Clinicalbehavior of second-generation zirconia monolithic posterior restorations: two-year
results of a prospective study with Ex vivo analyses including patients with clinicalsigns of bruxism. J Dent 2019; 91: 103229. doi: 10.1016/j.jdent. 2019.103229
3. Pathan MS, Kheur MG, Patankar AH, Kheur SM. Assessment of antagonist enamel
wear and clinical performance of full-contour monolithic zirconia crowns: one-year
results of a prospective study. J Prosthodont 2019; 28: e411-6. doi: 10.1111/jopr.12960

26

8. Waldecker M, Behnisch R, Rammelsberg P, Bömicke W. Five-year clinicalperformance of monolithic and partially veneered zirconia single crowns-a
prospective observational study. J Prosthodont Res 2022; 66: 339-45. doi:
10.2186/jpr.JPR_D_21_00024
9. Alenezi A, Alsweed M, Alsidrani S, Chrcanovic BR. Long-term survival andcomplication rates of porcelain laminate veneers in clinical studies: a systematic review.
J Clin Med 2021; 10: 1074. doi: 10.3390/jcm10051074

4. Dondani JR, Pardeshi V, Gangurde A, Shaikh A, Mahule A, Deval P. Comparativeevaluation of wear of natural enamel antagonist against glazed monolithic zirconia
crowns: an in vivo study. Int J Prosthodont 2023; 36: 273-81. doi: 10.11607/ijp.7798
5. Ban S. Chemical durability of high translucent dental zirconia. Dent Mater J 2020; 39:
12-23. doi: 10.4012/dmj.2019-109
6. Storber T, Bermejo JL, Schwindling FS, Schmitter M. Clinical assessment of enamel
wear caused by monolithic zirconia crowns. J Oral Rehabil 2016; 43: 621-9. doi:
10.1111/joor.12409
7. Miura S, Yamauchi S, Kasahara S, Katsuda Y, Fujisawa M, Egusa H. Clinicalevaluation of monolithic zirconia crowns: a failure analysis of clinically obtainedcases from a 3.5-year study. J Prosthodont Res 2021; 65: 148-54. doi:
10.2186/jpr.JPOR_2019_643

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