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Characterization of Ca3SiO5/CaCl2 Composite Cement for Dental Applications ARTICLE in DENTAL MATERIALS · JANUARY 2008 Impact Factor: 3.77 · DOI: 10.1016/j.dental.2007.02.006 · Source: PubMed
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Jiang Chang
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Chinese Academy of Sciences
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d e n t a l m a t e r i a l s 2 4 ( 2 0 0 8 ) 74–82
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Characterization of Ca3 SiO5 /CaCl2 composite cement for dental application Xiaohong Wang a,b , Hongchen Sun a,∗ , Jiang Chang b,∗∗ a
Department of Oral Pathology, Stomatological College, JiLin University, 418 Ziqiang Street, Changchun City, Jilin Province 130041, PR China b Biomaterials & Tissue Engineering Research Center, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, PR China
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Article history:
Objectives. The purpose of this study was to investigate the effect of CaCl2 on the setting time,
Received 23 September 2006
pH values and compressive strength of tricalcium silicate, and the in vitro bioactivity and
Received in revised form
compatibility of Ca3 SiO5 /CaCl2 composite paste was also studied to explore the possibility
19 January 2007
for using as a root canal filling material.
Accepted 7 February 2007
Methods. Composite cements were obtained by mixing Ca3 SiO5 and different amounts of CaCl2 (0, 5%, 10% and 15%) with deionized water as liquid phase. The composite cement and pure tricalcium silicate were compared for setting time, pH value, compressive strength, in
Keywords:
vitro bioactivity and compatibility.
Tricalcium silicate
Results. With the addition of CaCl2 from 0% to 15%, the initial setting time and final setting
Calcium chloride
time decreased obviously from 90 to 50 min and from 180 to 90 min, respectively. The com-
Bioactivity
pressive strength of the Ca3 SiO5 /CaCl2 composite cement after setting for 7 days increased
Root canal
obviously from 5.28 to 23.46 MPa when the content of CaCl2 increased from 0% to 10%. Furthermore, the paste with up to 15% of CaCl2 showed good ability to induce the formation of hydroxyapatite (HA), and the dissolution extracts of the Ca3 SiO5 /CaCl2 composite paste also have a stimulatory effect on L929 cell proliferation in a certain concentration range. Significance. The results indicated that the Ca3 SiO5 /CaCl2 composite cement had good selfsetting properties, bioactivity and compatibility, and may be used as a novel root canal filling material. © 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
Teeth with severe pulpal or periapical inflammation can be successfully treated with the established techniques of cleaning and shaping the root canals, followed by obturation of the root canal system. Choosing an appropriate root canal filling material is the key to the success of the therapy. Zinc oxide eugenol cement (ZOE) was the first root canal filling mate-
∗
rial to be recommended for permanent teeth, as described by Sweet in 1930. However, later studies showed some shortcomings of this cement such as the slow rate of resorption in the canals, limited antibacterial action and cytotoxic effects, which are possibly due to release of eugenol and formaldehyde [1–5]. In recent years, the introduction of calcium hydroxide in dental therapy has received attention, and the main advantage of calcium hydroxide is its biological activity.It has
Corresponding author. Tel.: +86 431 88913506. Corresponding author. Tel.: +86 21 52412804; fax: +86 21 52413903. E-mail addresses:
[email protected] (H. Sun),
[email protected] (J. Chang). 0109-5641/$ – see front matter © 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2007.02.006 ∗∗
d e n t a l m a t e r i a l s 2 4 ( 2 0 0 8 ) 74–82
antibacterial and anti-inflammatory properties primarily due to the high pH value of the surrounding environment (approximately 12.5) after its dissolution [6,7]. In addition, calcium hydroxide can induce mineralization, which results in repair of damaged dentin matrix [8,9]. Although calcium hydroxide has some advantages as compared with ZnO–eugenol cement and has been used in filling the root canal system, it has also shown disadvantages such as the low hardening and dissolution which results in a loose filling [10]. So it can only be used as a temporary filling material in indications for which hermeticity is a priority. An ideal root canal filling material should have several properties, such as being harmless to the periapical tissues and permanent tooth germ, resorbing readily if pressed beyond the apex, easily filling the root canals, adhering to the walls of the canal, not being susceptible to shrinkage, being easily removed if necessary, being radiopaque and not discoloring the tooth [11,12]. At present, no root canal filling materials is able to meet all the above requirements [13,14]. A new class of restorative material called mineral trioxide aggregate (MTA) was recently introduced as a dental material, which is a derivative of Portland cement [15,16] and was developed for many clinical applications such as capping of dental pulp tissues, root-end closure, repairing of root perforation as well as root-end filling [17,18]. Several in vitro and in vivo studies have demonstrated that the sealing ability and biocompatibility of MTA are superior to that of traditional materials [19–21]. But the main disadvantage of its long setting time of approximately 2 h [22] limits its application as a root canal filling material because it is easily washed away by the body fluid before setting. In addition, the complexity of its composition makes it difficult to prepare, which in turn leads to high cost. Tricalcium silicate is the main constituent of MTA, which can be prepared by the sol–gel method as previously described and has been reported to have good bioactivity, degradability and compatibility [23,24]. But its initial setting time of 1.5 h seems too long to meet the need of clinical applications. Calcium chloride is one of the most effective accelerators of hydration and setting in Portland cement pastes. The accelerative power of this salt increases with the increase in its concentration [25], but the addition of CaCl2 into Ca3 SiO5 for use as a root canal filling material has not been investigated before. Therefore, the purpose of this study was to investigate the effect of CaCl2 on the setting time, pH values and compressive strength of tricalcium silicate, and the in vitro bioactivity and compatibility of Ca3 SiO5 /CaCl2 composite paste was also studied to explore its possibility for use as a root canal filling material.
2.
Materials and methods
2.1.
Preparation of paste
Tricalcium silicate powders were prepared by the sol–gel method as previously described [23]. The resultant powders were ground and sieved to 300-mesh for further experiments. To prepare the pastes, Ca3 SiO5 and CaCl2 (AR, Lingfeng Co., PR) powders were weighted and dry mixed in a vibrator for 6 h. Then, the Ca3 SiO5 /CaCl2 powders with different contents of CaCl2 were mixed with deionized water so that the liq-
75
uid to powder ratio (L/P ratio) was 0.8 mL g−1 . The mixtures were stirred to form homogeneous pastes within 1 min, transferred to stainless steel molds with a diameter of 6 mm, and then stored in a 37◦ , 100% humidity water bath for various times.
2.2.
pH measurement procedure
To determine the pH variation of the Ca3 SiO5 /CaCl2 composite cement paste in the simulated body environment, the composite materials of Ca3 SiO5 and CaCl2 powders with different weight ratios were mixed with deionized water so that the L/P ratio was 0.8 mL g−1 and 3 mL paste was poured into a container. Then, the paste was covered with 6 mL SBF and stored in a 37◦ , 100% humidity water bath, and the solution changed once after 24 h. The pH value was recorded every hour over a period of 48 h. The test was repeated three times for each sample at each time point and the results were expressed as mean (±standard deviation) (mean ± S.D.).
2.3.
Setting times
Initial (I) and final (F) setting times were measured with a Vicat needle according to ISO9597-1989E. The initial setting time is defined as the time necessary so that the light needle (280 g, Ø1.13 mm) plunges into the paste and has a span of 5 ± 1 mm to the tube bottom. The final setting time is defined as the time necessary so that the heavy needle (350 g, Ø2.0 mm) no longer leaves a visible print on the surface of the paste.
2.4.
Characterization of the paste
After the pastes were set for given intervals, they were transferred into acetone (100%) to stop hydration and then air-dried. The phase composition was characterized by X-ray diffraction (XRD; Geigerflex, Rigaku Co., Japan) using monochromated Cu K␣ radiation. The surface and cross-section of the samples was observed by scanning electron microscopy (SEM; JSM-6700F, JEOL, Tokyo, Japan). The compressive strength was measured on the samples with diameter of 6 mm and height of 10 mm at a loading rate of 0.5 mm min−1 using a universal testing machine (Instron-1195, USA) according to ASTM D695-91. Six replicates were tested for each group and the results were expressed as mean (±standard deviation) (mean ± S.D.).
2.5.
Soaking in SBF
The simulated body fluid (SBF) was prepared according to the procedure described by Kokubo [26]. The composition of the SBF is shown in Table 1. The ion concentrations of the SBF are similar to those in human blood plasma. The 7-day-set paste disks (6 mm in diameter and 2 mm in height) were soaked in the SBF solution at 37◦ in a shaking water bath for 7 days with a surface area-to-volume ratio of 0.1 cm−1 [27]. Then the disks were gently rinsed with deionized water to remove SBF solutions followed by drying at room temperature. The structural and morphological variations of the disks were characterized by XRD (Geigerflex, Rigaku Co., Japan) and SEM (JSM-6700F, JEOL, Tokyo, Japan) after soaking in SBF.
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d e n t a l m a t e r i a l s 2 4 ( 2 0 0 8 ) 74–82
Table 1 – Ion concentrations of SBF and human blood plasma Type
Ion concentrations (mmol/L) Na+
SBF Blood plasma
2.6.
142.0 142.0
K+ 5.0 5.0
Mg2+
Ca2+
Cl−
1.5 1.5
2.5 2.5
148.8 103.0
Cell proliferation
The investigation of cell proliferation was conducted using the extraction method with mouse fibroblast cell line L929, according to the methods reported in ISO 10993-5 [28]. The 7-day-set paste was crushed to powders and sieved to 300mesh for further experiments. The dissolution extracts were prepared by adding paste powders to Roswell Park Memorial Institute 1640 (RPMI 1640; Gibco, USA) cell culture medium for 1 day at 37◦ in humidified atmosphere of 5% CO2 and 95% air, without agitation. Ratios between the sample weight (mg) and the medium volume (mL) were 0.000625, 0.00625, 0.0625, 0.625, 6.25, 12.5, 25, 50, 100 and 200 mg mL−1 . After incubation, the mixture was centrifuged and the supernatant was collected. The cell suspension was adjusted to a density of 1 × 104 cell mL−1 , and 100 L cell suspension was added to each well of a 96-well plate and incubated for 24 h. The culture medium was then removed and replaced by 50 L of extracts and 50 L of RPMI 1640 medium supplemented with 20% FCS. The medium supplemented with 10% FCS without addition of extracts was used as a positive control. The medium supplemented with 0.2% Trion-X100 was used as a negative control. The MTT method was used to assess the cell proliferation levels [29]. This assay relies upon the ability of living cells to reduce a tetrazolium salt into a soluble colored formazan product. After incubating at 37◦ and 5% CO2 for 6 days, 100 L of 0.5 mg mL−1 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) solution was added and incubated for 4 h at 37◦ . Then 100 l dimethyl sulfoxide (DMSO) was added to each well, the plate was shaken for 5 min, and the optical density (OD) at 590 nm was measured with an enzyme-linked immunoadsorbent assay (ELISA) plate reader (ELX800, Bio-TEK, USA). Six samples per group were tested in the experiment: the values were expressed as mean ± standard deviation (S.D.) and were analyzed using two-way analysis of variance (ANOVA). A p-value
