Radiopacity evaluation of calcium silicate sealers using digital radiography

doi:10.21203/rs.3.rs-2121866/v1

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Radiopacity evaluation of calcium silicate sealers using digital radiography

https://doi.org/10.21203/rs.3.rs-2121866/v1

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published 14 Jul, 2023

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Background

The aim of this study was to compare the radiopacity of calcium silicate sealers using a digital imaging method.

Methods

Four calcium silicate-containing sealers, NeoMTA2, BioMTA, ProRoot MTA, and Biodentine, were used in this study. Standard disk-shaped samples were prepared from each root canal filling material and placed on a plexiglass plate. An aluminum penetrometer was placed on a digital radiograph to obtain the irradiation parameters of 70 kVp, 8 mA, and 0.32 seconds. The object-beam distance was adjusted to 30 cm. The grayness values of the tested materials were measured digitally with the system software and compared with a penetrometer to determine the equivalent aluminum thickness.

Results

The radiopacity values of the studied materials in decreasing order, expressed in millimeters of aluminum equivalent, were ProRoot MTA (4.32), Biodentine (2.29), Bio MTA (3.92), and NeoMTA2 (3.83). Statistically significant differences were found between the mean radiographic density values of the tested materials (p < 0.005).

Conclusion

ProRoot MTA was the most radiopaque root canal filling material among the tested materials in this study. All materials, except Biodentine, are compliant with the minimum radiopacity standard recommended by the International Organization for Standardization and the American National Standards Institute/American Dental Association.

Biodentine

Calcium silicate sealers

MTA

Radiopacity

Radiopacity is an essential property of endodontic sealers, and it is a desired feature of the obturation material that it is more radiopaque than dentin. The International Organization for Standardization (ISO) and the American National Standards Institute/American Dental Association (ANSI/ADA) procedures are used to determine radiopacity. The radiopacity of an ideal root canal filling material should be sufficient for its physical and chemical properties [1, 2].

To determine the radiopacity of a particular material, a disk of specified thickness is made and radiographed, with steps of the increasing thickness of aluminum as a reference. Expressing radiopacity as the equivalent thickness of the material minimizes the illusions that may arise from exposure time. For example, if the material appears brighter on an underexposed radiograph, it will appear brighter on an aluminum plate. Therefore, the procedure suggests this comparative setup. Modern digital systems use slightly different methods to measure X-ray radiation, so it is possible that the radiopacity recorded on conventional film is not indicative of the radiopacity recorded by a digital sensor. As the clinical use of conventional film radiography has decreased with the adoption of digital systems, it is essential to consider the radiopacity of an object using clinically relevant techniques [3].

According to the ISO standard, root canal filling materials should have at least 3 mm of aluminum radiopacity. According to the ANSI/ADA, endodontic filling materials should show a radiopacity difference of at least 2 mm aluminum equivalent compared to bone or dentin [2, 4]. Previous studies have reported that, according to the standardized protocol, an occlusal film should be irradiated with an aluminum stepped wedge at 65 ± 5 kVp at a target distance of 30 cm [5].

Calcium silicate cement types are indicated for many endodontic applications, including perforation repair, pulp capping, apexification, root canal filling, retrofilling, and resorption repair. Mineral Trioksit Agregat (MTA) (ProRoot MTA, Dentsply Tulsa Dental Specialties, Johnson City, TN) was the first commercial MTA product released in 1999. It is mainly obtained from portland cement. Its cytotoxicity is low, and it is biocompatible. MTA has good sealing properties, is not affected by blood, and is effective in a moist environment, making MTA application a preferred material [6].

Recently, alternatives to MTA and new MTA types have been developed [7]. Zirconium oxide has also been used in calcium silicate-containing cement due to its radiopacifying properties. One of these innovative materials is Biodentine (Septodont, France). Biodentine contains tricalcium silicate, which includes a radiopacifier, such as zirconium oxide. In addition to endodontic indications, Biodentine is frequently preferred as a restorative indication because it forms fast reparative dentin on the pulp [8].

Another alternative, BioMTA (BioMTA, Seoul, Korea), is a calcium silicate material that was introduced in 2007 and is frequently preferred because it forms a hydroxyapatite layer between the canal wall and prevents microleakage [9]. NeoMTA2 (Avalon Biomed, Bradenton, FL) is a recently developed MTA containing tantalite oxide instead of bismuth oxide. The possibility of discoloration in the material is reduced due to the tantalite oxide. It is also frequently used due to its fast setting time and periapical tissue repair features [10].

In this study, three different MTA and Biodentine radiopacities were comparatively investigated. The first material used in our study was ProRoot MTA, which contains bismuth oxide as a radiopacifier. The second material was NeoMTA2, which contains tantalum oxide as a radiopacifier. The third was BioMTA, which includes a calcium-zirconia complex. Finally, the fourth was Biodentine with zirconium oxide as a radiopacifier [11]. Regarding the disadvantages of Biodentine, its radiopacity is significantly lower than MTA, despite the presence of zirconium oxide. Radiopacity decreases gradually over time, which can cause difficulties in long-term radiographic observations [12].

Preparation

Four calcium silicate materials were used in this study. The radiopacity of NeoMTA2, BioMTA, Biodentine, and ProRoot MTA was evaluated. The compositions and manufacturers of the materials are listed in Table 1.

Table 1

Compositions of the materials
Material	Composition	Manufacturer
ProRoot MTA	Powder: Tricalcium silicate, dicalcium silicate, tricalcium aluminate, bismuth oxide, and gypsum Liquid: Water	Dentsply Tulsa Dental Specialties, Johnson City, TN
BioMTA	Powder: Calcium carbonate, silicon dioxide, aluminum oxide, and calcium-zirconia complex Liquid: Distilled water	BioMTA, Seoul, Korea
NeoMTA2	Powder: Tricalcium silicate, dicalcium silicate, tantalum oxide (Ta2O5), and minor amounts of calcium sulfate and tricalcium aluminate Liquid: Water and polymers	Avalon Biomed, Bradenton, FL
Biodentine	Powder: Tricalcium silicate, calcium carbonate, zirconium oxide (radiopacifier), dicalcium silicate, calcium oxide, and iron oxide Liquid: Aqueous solution of a hydrosoluble polymer with calcium chloride	Septodont, France

Plexiglass plates measuring 1 mm in depth and 10 mm in internal diameter were fabricated. The calcium silicate materials were manipulated according to the manufacturer’s instructions. Each of the mixed calcium silicate materials was placed on a plexiglass plate. A glass plate was used to keep the surfaces flush. The samples placed in the molds were kept in an incubator at 37°C and 95% humidity until they were completely hardened. The samples were removed from the molds, and their thicknesses were checked with a digital caliper.

Radiographs

A 14-step wedge aluminum plate was made, the thickness of which increased by 1 mm with each step. According to ISO 6876, the aluminum content was Al 99.12%, Fe 0.47%, Mg 0.41%, and Cu < 0.1%. These specimens and an aluminum step wedge ladder were radiographed using an intraoral radiography device and image plate scanner (Vistascan Mini, Dürr Dental, Bietigheim-Bissingen, Germany). The X-ray plate was scanned immediately after exposure using an image plate scanner. The obtained intraoral radiography device was set at 70 kVp and 7 mA. The focal spot and object distance was set to 30 cm, and the exposure time was 0.32 seconds (Fig. 1).

To determine the average grayness of each aluminum step and the selected material, digital radiography (Vistascan Mini, Dürr Dental, Bietigheim-Bissingen, Germany) was loaded into the Mediadent (Morita-IC5-HD software) and measured by outlining the relevant area using the software’s equal-density area tool. The measurement was undertaken by one evaluator, who was not informed about the types of materials. The zones were chosen by avoiding areas with air bubbles in the materials (Fig. 2). This procedure was repeated five times for each material and aluminum step wedge, and then the averages were calculated. The level at which the average grayness value results obtained from the calcium silicate material were compared in the aluminum step-wedge was determined. The average gray value of each material was converted to the equivalent aluminum thickness using Curve Expert Professional software (www.curveexpert.net) as shown in Fig. 3.

Statistical Method

The data were analyzed using IBM SPSS version 23. Conformity to the normal distribution was evaluated using the Shapiro–Wilk test. Radiopacity density values for the materials were compared with a one-way analysis of variance, and multiple comparisons were analyzed with Tukey’s honestly significant difference test (Tukey’s HSD test). The results of the study were presented as means ± standard deviations. The significance level was p < 0.050.

Table 2

Expressing the radiopacity values of root canal filling materials as millimeter aluminum equivalents
Filling Materials	Radiopacity Density	Radiopacity al(mm)	p*
	Mean ± SD	Mean	p*
NeoMTA2	32165.60 ± 644.07	3.83	< 0.001
BioMTA	33177.40 ± 747.43	3.92
Biodentine	20638.60 ± 442.34	2.29
ProRoot MTA	35314.60 ± 941.17	4.32
* One-way analysis of variance (ANOVA)

The average grayness value of the samples was measured from five different points. There was a difference between the mean radiopacity values according to the materials (p < 0.001). The NeoMTA2 average was 32165.60, the BioMTA average was 33177.40, the Biodentine average was 20638.60, and the ProRoot MTA average was 35314.60. These values were calculated in terms of equivalent aluminum thickness values with Curve Expert 2.3 (Table 2). The aluminum stepwedge values of the materials were analyzed through multiple comparisons (Table 3).

Table 3

Multiple comparison results of materials
Multiple Comparison	P
NeoMTA2 – BioMTA	0.157
NeoMTA2 – Biodentine	< 0.001
NeoMTA2 – ProRoot MTA	< 0.001
BioMTA – Biodentine	< 0.001
BioMTA – ProRoot MTA	< 0.001
Biodentine – ProRoot MTA	< 0.001

*Tukey's HSD test

As shown in Table 3, there was no statistically significant difference between NeoMTA2 and BioMTA (p = 0.157). A statistically significant difference was observed between NeoMTA2 and Biodentine (p < 0.001), as well as between NeoMTA2 and ProRoot MTA (p < 0.001), and BioMTA and Biodentine (p < 0.001). A statistically significant difference was also observed between BioMTA and ProRoot MTA (p = 0.001), and Biodentine and ProRoot MTA (p < 0.001). ProRoot MTA showed significantly higher radiopacity than NeoMTA2, BioMTA, and Biodentine. Both BioMTA and NeoMTA2 showed significantly higher radiopacity than Biodentine.

The aim of this study was to compare the radiopacity of currently used calcium silicate-containing materials by converting the average grayness value to the aluminum value through comparative radiography.

Root canal filling materials should be observed on radiography. The radiopacity of an endodontic material should exhibit a contrast difference between the surrounding dental tissues and the filling material. A material's molecular structure and thickness have a significant effect on its radiopacity, and endodontic filling materials should present a difference in radiopacity equivalent to at least 2 mm Al compared with bone or dentine [13, 14]. Therefore, in past studies, international standards regarding the radiopacity of root canal filling materials were recommended using test specimens prepared in molds on standard disks. In this study, we prepared an equal-sized plexiglass plate to measure the radiopacity of the materials.

Eliasson and Haasken [15] were the first researchers to establish an equivalent aluminum thickness capable of producing similar radiographic density using optical radiographic density values as a standard of comparison for radiopacity studies. Beyer-Olsen and Ørstavik [16] modified this model. They measured the amount of light transmitted from the sample with an optical densitometer. They converted it to an equivalent aluminum thickness by comparing it with an aluminum ladder radiographed on the same film. An aluminum step wedge with varying thicknesses was chosen as the standard for measuring radiopacity in the present study, and radiography was performed on the materials with the aluminum step wedge, similar to Beyer-Olsen and Ørstavik’s method.

In this study, four different calcium silicate-containing materials were used for radiopacity comparisons. Four different material and aluminum step wedge images were collated using computer radiography software to perform the radiographic image analysis. The radiographic software displayed the radiographic image on the computer screen, and the average grayness value was calculated using Morita-IC5-HD software [17]. Digital X-ray systems have been used in past studies to determine radiopacity [14, 16, 17]. This study used an intraoral radiography device and an image plate scanner.

Previous studies used software to convert radiopacity values obtained in materials to equivalent aluminum thickness [13, 18]. Likewise, our study converted the radiopacity values of calcium silicate cement to equivalent aluminum thickness using Curve Expert 2.3.

In a previous study comparing ProRoot MTA and Biodentine, ProRoot MTA was found to be significantly more radiopaque than Biodentine and thus not compliant with ISO standards [19]. These results support the findings in this study, in which ProRoot MTA showed significantly higher radiopacity than all the sealers and did not comply with ISO 6876:2001 standards. While ProRoot MTA contains about 2% bismuth oxide, Biodentine contains 5% zirconium oxide (according to the manufacturer’s information). Zirconium oxide is a more biocompatible material than bismuth oxide [20]. However, the radiopacity of Biodentine has been considered low for clinical use in similar studies [19, 20], and in this study, its radiopacity made it difficult to distinguish it from dental tissues.

In another study in which four different root canal filling materials were compared with other radiopacity measurement methods, BioMTA showed significantly higher radiopacity than Biodentine [21, 22]. In one study, the radiopacity of MTA Angelus BioMTA and Biodentine were compared, and MTA Angelus with bismuth oxide showed the highest radiopacity. This was due to the high radiopacity content of bismuth oxide. Since Biodentine includes more biocompatible zirconium oxide as a radiopacifying material, it remained below the radiopacity value specified in ISO 6876:2001. For BioMTA, the 20–30% calcium-zirconium oxide complex eliminated the disadvantage of Biodentine and showed results above the radiopacity value specified in ISO 6876:2001 [23]. In this study, BioMTA showed significantly higher radiopacity than Biodentine, which can be attributed to using a calcium-zirconium oxide complex in BioMTA.

In a study by Souza et al. [24], ProRoot MTA and Retro MTA (BioMTA, Seoul, Korea) were compared, and ProRoot MTA showed significantly higher radiopacity than Retro MTA. In this study, ProRoot MTA showed significantly higher radiopacity than BioMTA. Our study is similar to Souza’s [24] results.

Another study was conducted on the radiopacity of NeoMTA Plus and MTA Plus. MTA Plus contains bismuth oxide in the powder as a radiopacifer, which plays an active role in cement hydration. However, it has been reported to discolor in contact with sodium hypochlorite. NeoMTA Plus contains tantalum oxide as a radiopacifer [25], but its influence on hydration is unknown, and a comparative study of the radiopacity of NeoMTA2 has not been encountered in the literature.

The use of calcium silicate cement with low radiopacity may cause misdiagnosis on radiography. Knowing the radiographic properties of calcium silicate materials is essential for root canal treatment. Except for Biodentine, the other calcium silicate cement had values in accordance with ANSI/ADA standards for root canal materials. Only Biodentin showed results that did not comply with ANSI/ADA standards. This difference is due to the material that gives the cement its radiopacity.

ProRoot MTA was the most radiopaque material. All materials, except Biodentine, were found to be compliant with the radiopacity standards.

ISO: The International Organization for Standardization ANSI/ADA: American National Standards Institute/American Dental Association MTA: Mineral Trioksit Agregat

Acknowledgments

Not applicable.

Authors’ contributions

HGS: Conceptualization, Methodology, Investigation, Writing - Original Draft

AY: Methodology Conceptualization, Resources, Supervision, Software

DHY: Visualization, Writing - Review & Editing

All authors have read and approved the article.

Funding

Not applicable

Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request.

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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No competing interests reported.

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Journal Publication

published 14 Jul, 2023

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Editorial decision: Major revision
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You are reading this latest preprint version

Radiopacity evaluation of calcium silicate sealers using digital radiography

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