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Effect of glass ionomer cements on nanohardness of caries-affected
dentinChaiwat Maneenut, DDS, MDSc,a Toru Nikaido, DDS, PhD,b Richard M. Foxton,
BDS, PhD,c and Junji Tagami, DDS, PhDb,da

Department of Operative Dentistry, Faculty of Dentistry, Chulalongkorn
University, Bangkok, Thailand, bCariology and Operative Dentistry, Department ofRestorative Sciences, Graduate School, cDivision of Conservative Dentistry, GKT
Dental Institute, London, United Kingdom, and dCenter of Excellence Program for
Frontier Research on Molecular Destruction and Reconstruction of Tooth andBone, Tokyo Medical and Dental University, Tokyo, Japan
Purpose: To evaluate nanohardness of caries-affected dentin adjacent to conventional and resin-modified
glass ionomer cements.
Materials and Methods: Dentin caries was removed from the occlusal surfaces of human molars. Teeth
were cut mesio-distally through the middle of prepared cavities to get two halves. One half was filled withthe tested material, either Fuji IX GP or Fuji II LC, while the other half was unfilled and used as a negative
control (n=7). After 1, 7 and 30 days of restoration, nanohardness was measured on intertubular dentin at
20, 40, 60, 80 and 100 µm from the pulpal margin. Mean nanohardness` at each distance of each period
were compared using analysis of variance (ANOVA) and Fisher's least significant difference (LSD)
multiple comparison tests at significant level of 5%.
Results: Nanohardness of caries-affected dentin adjacent to both materials increased after restoration forseven days. Significant increases were observed after 30 days of restoration. Nanohardness change of
caries-affected dentin adjacent to Fuji IX GP was more than that adjacent to Fuji II LC.
Conclusion: The nanohardness of caries-affected dentin adjacent to conventional and resin-modified glassionomer cements increased after seven days of restoration. (Int Chin J Dent 2003; 3: 122-130.)
Clinical Significance: Application of glass ionomer cements on caries-affected dentin can increase
hardness of such dentin.
Key Words: caries-affected dentin, glass ionomer cement, nanohardness.

Introduction
Glass ionomer cements are frequently used as a restorative material, especially in highly caries-riskpatients.1 Chemical bonding to tooth structures is one of their advantageous properties.2-5 Cariostatic effectand remineralization promotion due to gradual release of fluoride are their other favorable properties.6-8
Several studies have reported demineralization inhibition of normal tooth structures9,10 and remineralizationof enamel lesions adjacent to glass ionomer cements.11,12

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Clinically, carious dentin is a common substrate to be dealt with when treating the patients. It isclassically described as consisting of two layers: the outer carious dentin or infected dentin and the innercarious dentin or affected dentin.13

The outer carious dentin, which is irreversibly denatured,

unremineralisable, infected, insensitive, and necrotic; should be completely removed.14,15 The inner carious
dentin, which is reversibly denatured, remineralisable, uninfected, sensitive, and vital; should bepreserved.16 Using a caries detector, which stains infected dentin, enables us to remove the outer carious
dentin while preserving the caries-affected dentin.17 Caries-affected dentin has a lower hardness value thannormal dentin since it is partially demineralized.18-20
In vitro studies using artificial dentin caries models have demonstrated remineralization andhyper-mineralization of dentinal lesions adjacent to glass ionomer cement restorations.21,22 In vivo studies,
physiological remineralization of caries-affected and artificial demineralized dentin, after restoring using
several kinds of materials, have also been reported.14,16,23-25 These studies were mostly done in dogs andmonkeys, and only one study has been performed on human teeth.16 The results showed that mineralcontent recovering of the lesions resulted in an increase of hardness. This type of remineralization wasstated to be the result of either normal biological processes or the process that was initiated by mineralreleased from restorative materials.14 However, the effect of glass ionomer restoration on hardness orremineralization of caries-affected dentin of human teeth has not been clarified. Therefore, the purpose ofthis study was to investigate the nanohardness of caries-affected dentin of human teeth adjacent to glassionomer restorative cements.

Materials and Methods
Specimen Preparation
Fourteen extracted human molars having occlusal carious lesions involving middle dentin, which were
kept frozen less than one month, were randomly divided into two groups. Caries was removed with slow
speed steel round burs (Meisinger ISO #016, 014, 012, and 010, Hager & Meisinger GmbH, Dusseldorf,
Germany) using caries detector solution (Caries Detector, Kuraray Medical, Tokyo, Japan) as an indicator.
Each tooth was mesio-distally sectioned through the middle of the prepared cavity into two halves using a
low speed diamond saw (Isomet, Buehler Ltd., Lake Bluff, IL, USA). The cavities on one half of the teeth
in the first group were filled with Fuji IX GP (GC Corp., Tokyo, Japan) and those in the second group werefilled with Fuji II LC (GC Corp.) according to the manufacturer’s recommendations. The cavities on theother half of the teeth in both groups were unfilled and used as a negative control. Each specimen wasembedded in epoxy resin (Epon 815, Nisshin EM, Tokyo, Japan). After 24 hours, the surface of thespecimen was polished with consecutive 600, 800, 1,000, and 1,200 grit waterproof silicon-carbide papers(Struers A/S, Copenhagen, Denmark) under tap water, followed by diamond paste particle sizes 6, 3, and 1µm (DP- Paste, P, Struers A/S). Marks were made by a razor blade under a light microscope (x20) at bothends of the pulpal cavity wall (Fig. 1). Each specimen was kept separately in deionized water at 37˚Cthroughout the 30-day experimental period. Storage water was changed weekly to refresh the environment.

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13
Fig. 1. Marks (arrows) were made at both ends of pulpal margin as a reference for nanohardness
indentation on caries-affected dentin (x35).
Fig. 3. Indentation marks on intertubular dentin, T = dentinal tubule. (x7,500).

Fig. 2.
A. Nanohardness measurements were made at six
specific areas. Five areas were on caries-affected
dentin and one area was on normal dentin.
B. Each measurement area consists of threecolumns of indentation marks.
Each column
represents the indentation at each period of testing(1, 7 and 30 days). Five indentations per column
were performed on caries-affected dentin and two
indentations per column were performed on normal
dentin. Distance between each indentation was 20µm.

Hardness Measurements
Nanohardness of caries-affected and normal dentin of all specimens was measured at 1, 7 and 30 days
after restoration using a nanoindentation tester (ENT-1100, Elionix Corp., Tokyo, Japan). Fig. 2 illustrates
simulated indentation areas of restored specimens. Fig. 3 shows an SEM picture of the indentation marks
on intertubular dentin (x7,500). At day 1, the indentation positions were set on intertubular dentin ofcaries-affected dentin at distances of 20, 40, 60, 80 and 100 µm from the pulpal cavity margin. Fiveindentations at each distance, a total of 25 indentations, were performed between the marks.

Fornormal-dentin hardness measurement, the indentation positions were set on the intertubular dentin besidecaries-affected dentin, and two indentations were performed. Positions of indentation at day 7 and day 30
were set along side those of day 1. Indentations in the control specimens were done using the sameprocedure as that of the restored specimen. After indentation performing, nanohardness values were124

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calculated.
Statistical Analysis
Mean nanohardness at each distance and each period was calculated. The data were compared by
one-way analysis of variance (ANOVA) and Fisher's least significant difference (LSD) multiple
comparison tests (p=0.05). Statistical tests were performed using a computerized statistical program (SPSSfor Windows release 8.0.0, SPSS Inc., USA).

Results
Mean nanohardness of caries-affected and normal dentin of the Fuji IX GP and Fuji II LC groups areshown in Tables 1 and 2, respectively. Nanohardness of caries-affected dentin increased when measured
from cavity wall toward deep dentin. During the 30 days of this study, there was no significant change of
nanohardness in the control specimens of both groups. Increases in nanohardness of caries-affected dentinof the restored specimens in both groups were observed after 7 and 30 days. Fig. 4 shows the nanohardnessof caries-affected dentin adjacent to Fuji IX GP at 1, 7 and 30 days. After restoration for seven days,
nanohardness at all measured distances increased but were not significantly different from those of day 1(p>0.05).
Table 1. Mean nanohardness of caries-affected and normal dentin of Fuji IX GP group.
Distance(µm)

Controlled
Day 1

Restored
Day 1

Controlled
Day 7

RestoredDay 7

Controlled
Day 30

RestoredDay 302030.27 (4.69)

30.38 (4.47) a

30.10 (4.91)

34.61 (4.97)

30.66 (4.77)

37.42 (3.88) a40

31.95 (5.12)

31.69 (4.85) b

31.58 (5.22)

35.43 (5.48)

32.63 (4.95)

37.99 (4.82) b

60

33.01 (4.35)

32.92 (4.68) c

33.37 (4.79)

35.89 (4.52)

33.58 (5.16)

39.69 (4.89) c

80

34.88 (4.19)

34.73 (4.29) d

34.05 (4.48)

36.14 (4.93)

34.35 (5.29)

39.22 (3.54) d

100

34.60 (4.37)

34.84 (4.17)e34.50 (4.46)

37.22 (4.73)

34.52 (5.06)

39.70 (4.40) e

Normal Dentin

59.89 (5.07)

59.36 (5.24)

59.93 (5.51)

59.33 (5.06)

60.23 (5.72)

60.05 (5.44)

Data having the same letter are significantly different (p<0.05).

Table 2. Mean nanohardness of caries-affected and normal dentin of Fuji II LC group.
Distance(µm)

Controlled
Day 1

Restored
Day 1

Controlled
Day 7

RestoredDay 7

Controlled
Day 30

RestoredDay 3020

32.08 (4.11)

32.66 (4.04) a

32.34 (4.17)

35.41 (6.78)

32.75 (4.19)

38.69 (4.76) a

40

34.57 (4.06)

34.22 (4.71)

34.90 (3.16)

35.76 (5.32)

34.76 (4.16)

37.62 (2.84)

60

35.67 (4.49)

35.89 (3.98)

36.28 (3.19)

35.97 (5.40)

36.48 (4.83)

38.20 (2.87)

80

37.35 (4.26)

37.32 (4.95)

37.29 (3.06)

37.25 (5.11)

37.77 (4.45)

38.74 (3.33)

100

38.93 (3.95)

39.02 (5.03)

38.78 (3.81)

39.22 (5.29)

39.29 (6.08)

41.45 (3.10)

Normal Dentin

61.06 (5.07)

61.46 (5.51)

61.87 (5.59)

61.30 (5.27)

61.58 (5.46)

61.18 (5.42)

Data having the same letter are significantly different (p<0.05).

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After restoration for 30 days, nanohardness values at every measured distance were significantly higher
than those of day 1 (p<0.05), but not significantly different from those of day 7 (p>0.05). Fig. 5 shows theresults of nanohardness of caries-affected dentin adjacent to Fuji II LC. Nanohardness at all measured
distances increased after restoration for seven days but were not significantly different from those of day 1(p>0.05). After restoration for 30 days, nanohardness of only the 20 µm distance was significantly higher
than that of day 1 (p<0.05) but was not significantly different from that of day 7 (p>0.05). After 30 days,
nanohardness of caries-affected dentin adjacent to restorations was lower than that of normal dentin.

45Fig. 4. Nanohardness of caries-affected dentin adjacent to Fuji IX GP.
Fig. 5. Nanohardness of caries-affected dentin adjacent to Fuji II LC.
∗ : Significantly different (p<0.05) for comparison between nanohardness at day 30 andday 1 for both figures.

Discussion
To investigate demineralization and remineralization of teeth in vitro and in vivo studies, several methods
have been used including hardness test,10 microradiography,26 contact microradiography,22 energy
dispersive spectroscopy (EDS),24 and electron-probe microanalysis (EMPA).25 Hardness of enamel anddentin is associated with mineral change. Demineralization decreases hardness while remineralization
increases hardness.10,24,25,27
caries-affected dentin.

Our study used the nanohardness test for evaluation of nanohardness of

The nanoindentation tester allows measurements in small areas such as thedentin-enamel junction, inter- and intra-tubular dentin with ultra light loads,28,29 and provided useful datathat could not be obtained using the classical type of hardness tester.30 Measured areas in this study was
focused and set on intertubular dentin (Fig. 3). Recent works27,31,32 indicated that dentin properties arelargely dependent on the properties of intertubular dentin. Mineralization appears to increase substantiallyin caries-affected dentin, and such an increase can be accounted for only if intertubular dentin becomes
hypermineralized. The result of this study showed that nanohardness of caries-affected dentin was about
half that of normal dentin. This finding is in agreement with other previous studies and clarified thesubstrate that we wanted to study.20,33 This substrate was partially demineralized and can be remineralized
under suitable conditions. The hardness of the studied area in all groups increased when measured toward
deep dentin. This data indicated an approaching to normal dentin that lies under caries-affected dentin.18

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Nanohardness of the control specimens in both groups did not show any significant change during theperiod of this study (p>0.05). This demonstrates non-effectiveness on remineralization of the storage
solution (deionized water), which was used in this study. Nanohardness of caries-affected dentin adjacentto the tested materials tended to increase after seven days of restoration, however, no significant increasing
was shown (p>0.05). After 30 days of restoration, a significant increase of nanohardness was observed atevery measured distance for Fuji IX GP group and at 20 µm from pulpal margin for Fuji II LC group(p<0.05). The increase of nanohardness showed signs of remineralization, which needed a period of timeto occur. The increasing nanohardness or remineralization that took place in the restored specimens seems
to be due to the effectiveness of the filling materials, when compare to the hardness of the controlled
specimens in the same environment. Several in vivo studies demonstrated physiological remineralization of
artificial and normal demineralized tooth structures.14,23-25 These authors proposed that in the closed
environment, minerals (mainly calcium) were delivered from pulp tissue under odontoblastic-process
initiation. The data of their studies showed that full re-calcification of the lesion in vivo could take place
within several months.

In our study, without a physiological environment, remineralization ofcaries-affected dentin adjacent to filling materials could take place in a short period of time. This may be
due to the effect of the tested glass ionomer materials that may provide some mineral ions, which become
involved in the remineralization of caries-affected dentin. Several mineral ions are released from glassionomer cements including fluoride, sodium, silicon, calcium strontium, aluminum, and magnesium.34-36
High concentrations of fluoride and other ions have been detected in dentin adjacent to glass ionomer
restorations.8,37 Initial burst and long-term releases of fluoride from conventional and resin-modified glassionomer cements have been reported.7,38,39

Such fluoride demonstrated effectiveness has been

demonstrated through the remineralization of caries lesion.40,41 Sennou et al.42 reported the diffusion ofminerals, mainly fluoride, from glass ionomer cements into contacted dentin. They also reported thedecalcifying effect of pre-treated cavity conditioner on dentin; result in having decalcified minerals(calcium and phosphate) in lesion. In our study, some released mineral ions from demineralization andfrom cavity conditioner pre-treatment, may remain in caries-affected dentin lesion and favor
re-calcification. Re-growth of residual minerals enhanced by fluoride may contribute to remineralizationand increasing of hardness in the lesion.43
Rate of remineralization depends not only on residual minerals in lesion but also on concentration offluoride in that area.43,44 The amount of fluoride that is required for remineralization of caries-affected
dentin has not been reported. The content of fluoride in restorative materials should, however, be as highas possible and the release should be as great as possible. In our study, nanohardness changes at day 7 inFuji IX GP group, and at every measured distance, were more than that of Fuji II LC group. This may be
the result of higher fluoride and other mineral ions released from Fuji IX GP than Fuji II LC in this study
condition. Comparative study data of fluoride release between these two cements were not clarified.45,46
Regarding composition, setting reaction and physical properties, conventional glass ionomer cements were
expected to have a higher potential for mineral release than resin-modified glass ionomer cements.47,48

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Several previous studies reported higher fluoride release from convention glass ionomer cements thanresin-modified glass ionomer cements, especially in the first week.39,41,49 In our study, apart from fluoride,other mineral ions and environmental condition might initiate and promote remineralization ofcaries-affected dentin.
Significant increases of nanohardness of caries-affected dentin was observed in restored specimens ofboth groups, after 30 days of restoration. Nanohardness of caries-affected dentin adjacent to Fuji IX GP
was significant higher than that of day 1, but was not significant higher than that of day 7. However, thenanohardness values at day 30 have not close to that of normal dentin. In the Fuji II LC group, only
nanohardness at 20 µm from the cavity was significant higher than that of day 1. These data suggest theeffectiveness of both materials on increasing hardness or remineralization of caries-affected dentin. Fuji IX
GP seems to have more effectiveness than Fuji II LC due to the evident of more hardness-changed.
However, differences between both groups regarding carious condition and mineral content of teeth thatwere used should be considered for the comparison. Further in vitro and in vivo studies should be designed
to directly compare the effectiveness of both materials.
As for clinical implications, physiological remineralization of caries-affected dentin combines withphysico-chemical remineralization that was generated by fluoride-releasing materials may provide benefits
to this type of dentin.

Hardness of caries-affected dentin under the combination of both types ofremineralization may approach the level of normal dentin faster than having only one enhancer. In addition,
the results of this study support the strategy of conservative intervention in preserving caries-affected
dentin for restorative treatments.

Conclusion
Conventional and resin-modified glass ionomer cements could promote some level of re-hardening on
human caries-affected dentin.

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Reprint request to:
Dr. Chaiwat Maneenut
Department of Operative Dentistry, Faculty of Dentistry, Chulalongkorn University
Henry-Dunant Road, Pathumwan, Bangkok 10330, Thailand
Fax: +66-2-218-8791 E-mail: mchaiwat@chula.ac.th
Received on November 19, 2003. Revised on December 9, 2003. Accepted on December 24, 2003.
Copyright ©2003 by the Editorial Council of the International Chinese Journal of Dentistry.

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