Abstract
Objective
Tricalcium silicate-based cements have been displayed as suitable root-end filling materials. The physical properties of prototype radiopacified tricalcium silicate cement, Bioaggregate and Biodentine were investigated. Intermediate restorative material was used as a control.
Methods
The physical properties of a prototype zirconium oxide replaced tricalcium silicate cement and two proprietary cements composed of tricalcium silicate namely Bioaggregate and Biodentine were investigated. Intermediate restorative material (IRM) was used as a control. Radiopacity assessment was undertaken and expressed in thickness of aluminum. In addition the anti-washout resistance was investigated using a novel basket-drop method and the fluid uptake, sorption and solubility were investigated using a gravimetric method. The setting time was assessed using an indentation technique and compressive strength and micro-hardness of the test materials were investigated. All the testing was performed with the test materials immersed in Hank’s balanced salt solution.
Results
All the materials tested had a radiopacity value higher than 3 mm thickness of aluminum. IRM exhibited the highest radiopacity. Biodentine demonstrated a high washout, low fluid uptake and sorption values, low setting time and superior mechanical properties. The fluid uptake and setting time was the highest for Bioaggregate.
Significance
The addition of admixtures to tricalcium silicate-based cements affects the physical properties of the materials.
1
Introduction
A variety of materials used routinely in dentistry as restorative materials have been utilized as root-end filling materials. Such materials include dental amalgam and intermediate restorative material (IRM). Mineral trioxide aggregate (MTA) has been developed specifically as a root-end filling material and for the repair of furcal perforations . It has been reported that the success rate for the clinical use of MTA and IRM is similar when assessed after 12 and 24 months . More recently materials based on tricalcium silicate cement have been introduced as root-end filling materials. Tricalcium silicate is the main component of MTA and it has demonstrated similar chemical characteristics . The use of tricalcium silicate avoids the presence of trace elements which are inadvertently incorporated in mineral trioxide aggregate from the raw materials and the secondary fuels used during manufacture . Heavy elements have been shown to be present in high amounts MTA and Portland cements . The leaching in solution was reported to be less but still is a matter of concern . Tricalcium silicate-based cements do not leach any contaminants thus are considered safer for use as root-end filling materials .
Tricalcium silicate cement has been used alone and with additives, as bone cement and as a posterior restorative material . It has been demonstrated that pure tricalcium silicate is a suitable replacement for the cementitious component in MTA due to their similar composition and bioactivity , the ability to form hydroxyapatite and maintenance of the bone–biomaterial interface once implanted . Tricalcium silicate cement has also proved to have sufficient physical properties to be suitable for use as a root-end filler . In addition, tricalcium silicate cement has been found to have a shorter setting time than MTA, good injectability, good bioactivity and acceptable in vitro degradability (the ability for the implanted cement to be replaced by natural tissue) . Additions of calcium carbonate and calcium sulphate both improve the setting time and the compressive strength of the material with calcium sulphate having the added advantage of being bioactive and degradable .
Tricalcium silicate is found as the main cementitious component in Biodentine and Bioaggregate. Biodentine has been developed and produced with the aim of bringing together the high biocompatibility and bioactivity of calcium silicates, with enhanced properties such as quick setting time (a function of the calcium chloride added to the Biodentine liquid) and high strength (result of the low water to cement ratio made possible by the addition of a water soluble polymer); properties not usually associated with said cements . Septodont claims to be able to maintain a balance between the two through its water reducing agent in Biodentine thus offering a homogeneous, dense product, with maximized strength. Biodentine uses zirconium oxide as a radiopacifying material. Most of the data available on Biodentine is forthcoming from the manufacturer with few independent researches being conducted.
Bioaggregate contains approximately 41% tricalcium silicate cement and no aluminum content . Bioaggregate is similar to white ProRoot MTA in terms of chemical composition, with the major difference being the radiopacifier (tantalum oxide in Bioaggregate as opposed to bismuth oxide in MTA) . The same study found calcium hydroxide in the set form of both materials, which may point to good bioactivity and biocompatibility of the material.
The aim of this study is to assess the physical properties of tricalcium silicate-based root-end filling materials. Prototype radiopacified tricalcium silicate cement, Biodentine and Bioaggregate are investigated and compared to intermediate restorative material.
2
Methodology
The materials used in this study included:
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Tricalcium silicate cement (Mineral Research Processing, Meyzieu, France) replaced with 20% zirconium oxide (ZrO 2 ; Sigma–Aldrich, Buchs, Germany) – TCS-20-Z;
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Biodentine™ (Septodont, Saint-Maur-des-fossés Cedex, France);
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Bioaggregate™ (Verio Dental Co. Ltd. Vancouver, Canada);
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Intermediate restorative material (Dentsply DeTrey, Konstanz, Germany) – IRM;
The TCS-20-Z was mixed at a water to cement ratio of 0.35 with an effective water to powder ratio of 0.28. The Biodentine, Bioaggregate and IRM were mixed according to manufacturer’s instructions. The materials were soaked in Hank’s balanced salt solution (HBSS; H6648, Sigma–Aldrich, St. Louis, MO, USA) for 28 days at 37 °C in an incubator.
2.1
Evaluation of radiopacity
Radiopacity evaluation was performed using ISO 6876 recommendations. Three specimens 10 ± 1 mm in diameter and 1 ± 0.1 mm thick were used. Specimens were prepared and immediately immersed in gelatinized HBSS. They were radiographed after one day and 28 days. At each time point the specimens were placed directly on a photo-stimulable phosphor (PSP) plate adjacent to a calibrated aluminum step wedge (Everything X-ray, High Wycombe, UK) with 3 mm increments. A standard X-ray machine (GEC Medical Equipment Ltd., Middlesex, UK) was used to irradiate X-rays onto the specimens using an exposure time of 0.80 s at 10 mA, tube voltage at 65 ± 5 kV and a cathode–target film distance of 300 ± 10 mm. The radiographs were processed (Clarimat 300, Gendex Dental Systems, Medivance Instruments Ltd., London, UK) and a digital image of the radiograph was obtained. The gray pixel value on the radiograph, of each step in the step-wedge was determined using an imaging program, Microsoft Paint (Microsoft Corp., Redmond, WA, USA) as a number between 0 and 255 with 0 representing pure black and 255 pure white. A graph of thickness of aluminum vs. gray pixel value on the radiograph was then plotted and the best-fit logarithmic trend line was plotted through the points. The equation of the trend line gave the gray pixel value of an object on the image as a function of the object’s thickness in mm of aluminum. This equation was inverted so as to express the object’s thickness as a function of its gray pixel value on the radiograph. The gray pixel values of the cement specimens were then determined using the imaging program, and plugged into this equation to calculate the equivalent radiopacity of the cement sample, expressed in mm of aluminum.
2.2
Determination of washout resistance
Resistance to washout was determined using the basket drop method . The test set-up ( Fig. 1 ) consisted of a standard-sized test tube with an internal diameter of 14.5 mm which was filled to a height of 120 mm with distilled water and a woven brass mesh cylinder (60 wires per inch with a wire diameter of 0.18 mm) 9.0 mm diameter and a height of 17 mm. The empty mesh cylinder was weighed on an analytic balance with an accuracy of ±0.0001 g (Sartorius AG, Gottingen, Germany) after which it was filled with approximately 1 g of test material and reweighed. The cylinder was released just above the surface of the fluid in the test tube and allowed to sink unhindered. The cylinder was left at the bottom of the tube for 15 s, then brought out of the water in 5 ± 1 s and allowed to drip for 2 min. The cylinder was patted dry with absorbent paper to remove any remaining water, and weighed. The complete procedure was repeated to give a total of three drop cycles per specimen. Two replicate tests per material were conducted using fresh solution for each replicate. Washout (or loss of mass of the sample) was expressed as a percentage of the initial mass of the sample and calculated using Eq. (1) :
D = 100 × M i − M f M i
where D = washout (%), M i = mass of sample before initial drop, M f = mass of sample after each drop.
2.3
Evaluation of fluid uptake, sorption and solubility
Specimens for these tests were prepared using disc shaped rubber molds of internal diameter 15 ± 1 mm and a thickness of 1 ± 0.1 mm as specified in ISO 4049; 2009 . The materials were mixed, placed in the molds and allowed to cure for 24 h at 37 ± 1 °C. The specimens were then demolded and weighed in order to record their mass ‘ m 1 ’ to an accuracy of ±0.1 μg. The mean diameter of each specimen and the thickness of each specimen were measured to an accuracy of 0.01 mm and the volume ‘ V ’ of each specimen was calculated. The specimens were then immersed upright in 10 ml of HBSS. The specimens were then removed after 1 day and dried using filter paper. These were then weighed 1 min after being removed from the storage solution to an accuracy of 0.1 μg. Their mass was recorded as ‘ m ’. The fluid uptake of each specimen could be recorded using Eq. (2) :
F u p t a k e ( % ) = m − m 1 V × 100
This process was repeated to measure the fluid uptake of the specimens after 1, 7, 14, 21 and 28 days. After 28 days, the mass of the specimens (fully saturated) was recorded as ‘ m 2 ’. The specimens were stored in a desiccator maintained at 23 ± 1 °C for 24 h using silica gel as desiccant until a constant mass could be recorded. This constant mass was recorded as ‘ m 3 ’. Fluid sorption ( F sp ) for each sample was calculated using Eq. (3) .
F sp ( % ) = m 2 − m 3 V × 100
Fluid solubility ( F sl ) for each sample was calculated using Eq. (4) :
F sl ( % ) = m 1 − m 3 V × 100
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