Material Properties of a Tricalcium Silicate–containing, a Mineral Trioxide Aggregate–containing, and an Epoxy Resin–based Root Canal Sealer

Material Properties of a Tricalcium Silicate–containing, a Mineral Trioxide Aggregate–containing, and an Epoxy Resin–based Root Canal Sealer

Basic Research—Technology Material Properties of a Tricalcium Silicate–containing, a Mineral Trioxide Aggregate–containing, and an Epoxy Resin–based ...

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Basic Research—Technology

Material Properties of a Tricalcium Silicate–containing, a Mineral Trioxide Aggregate–containing, and an Epoxy Resin–based Root Canal Sealer Raquel-Kathrin Pr€ ullage,* Kent Urban, ZA,* Edgar Sch€ afer, DMD,† and Till Dammaschke, DMD* Abstract Introduction: The aim was to compare the solubility, radiopacity, and setting times of a tricalcium silicate– containing (BioRoot RCS; Septodont, St Maur-desFosses, France) and a mineral trioxide aggregate–containing sealer (MTA Fillapex; Angelus, Londrina, Brazil) with an epoxy resin–based sealer (AH Plus; Dentsply DeTrey, Konstanz, Germany). Methods: Solubility in distilled water, radiopacity, and setting time were evaluated in accordance with ISO-6876:2012. The solubility was also measured after soaking the materials in phosphate-buffered saline buffer (PBS). All data were analyzed using 1-way analysis of variance and the Student-Newman-Keuls test. Results: After immersion for 1 minute in distilled water, BioRoot RCS was significantly less soluble than AH Plus and MTA Fillapex (P < .05). At all other exposure times, AH Plus was significantly less soluble than BioRoot RCS, whereas BioRoot RCS was significantly more soluble than the other 2 sealers (P < .05).All sealers had the same solubility in PBS and distilled water, except for BioRoot RCS after 28 days. At this exposure time, BioRoot RCS was significantly less soluble in PBS than in distilled water and less soluble than MTA Fillapex (P < .05). All BioRoot RCS specimens immersed in PBS had a surface precipitate after 14 and 28 days. The radiopacity of all sealers was greater than 3 mm aluminum with no statistical significant difference between the sealers (P > .05). The final setting time was 324 (1) minutes for BioRoot RCS and 612 (4) minutes for AH Plus. The difference was statistically significant (P < .05). MTA Fillapex did not set completely even after 1 week. Conclusions: The solubility and radiopacity of the sealers were in accordance with ISO 6876:2012. PBS decreased the solubility of BioRoot RCS. (J Endod 2016;-:1–5)

Key Words AH Plus, BioRoot RCS, MTA Fillapex, radiopacity, setting time, solubility

D

i- and tricalcium siliSignificance cate cements (eg, minThe solubility and radiopacity of the tricalcium silieral trioxide aggregate cate–containing sealer BioRoot RCS were in [MTA]) were introduced accordance with ISO 6876:2012. MTA Fillapex in dentistry for the repair required humidity for setting. of lateral root perforations and retrograde root-end fillings (1). These cements are highly biocompatible and bioactive; hence, tri- or, respectively, di- and tricalcium silicate–based root canal sealers were developed. The first MTAcontaining sealer was MTA Fillapex (Angelus, Londrina, Brazil). MTA Fillapex is a salicylate resin material that contains 13.2% set MTA particles with di- and tricalcium silicate, silica (as filler), and bismuth(III) oxide (as contrast medium). A new bioactive tricalcium silicate–based sealer is BioRoot RCS (Septodont, St Maur-des-Fosses, France), which consists of powder and liquid. According to the manufacturer, the powder mainly consists of tricalcium silicate, povidone as the stickiness agent, and zirconium dioxide as the contrast medium. The liquid is an aqueous solution of calcium chloride (curing accelerator) with polycarboxylate (superplasticizers). Obturation of the root canal system usually requires a sealer along with a core material whereby the sealer should act like a binding agent between the core material and the root canal dentin. Therefore, sealers should be dimensionally stable, radiopaque, and insoluble (2). Endodontic materials should provide a long-term seal and avoid coronal and apical leakage. The long-lasting bacteria-tight seal of the root canal depends mostly on the integrity of the sealer, not the core material (2, 3). Consequently, a low solubility of sealers in distilled water as laid down in the ISO standard 6876:2012 (4) is required. Another relevant property is the radiopacity of sealers to be able to evaluate the quality of the root canal obturation (5, 6). One millimeter of dentin has a radiopacity equal to that of 1 mm aluminum (7). Therefore, according to ISO 6876:2012 (4), a radiopacity of 3 mm aluminum minimum is required for root canal sealers. Furthermore, the setting time of a sealer must be sufficiently long enough to ensure easy handling even when using time-consuming obturation techniques (8).

From the *Department of Periodontology and Operative Dentistry, Westphalian Wilhelms University, and †Central Interdisciplinary Ambulance in the School of Dentistry, M€unster, Germany. Address requests for reprints to Dr Till Dammaschke, Westphalian Wilhelms University, Department of Operative Dentistry, Albert-Schweitzer-Campus 1, Building W 30, 48149 M€unster, Germany. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2016 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2016.09.018

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Properties of Root Canal Sealers

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Basic Research—Technology The aim of the present study was to measure the solubility, radiopacity, and setting time of a tricalcium silicate–containing (BioRoot RCS), an MTA-containing (MTA Fillapex), and an epoxy resin–based root canal sealer (AH Plus; Dentsply DeTrey, Konstanz, Germany). The null hypothesis was that with regard to the 3 properties evaluated, no significant differences exist.

Radiopacity Stainless steel ring molds having an internal diameter of 10.0 mm (0.1 mm) and a height of 1.0 mm (0.1 mm) were used according to ISO 6876:2012 (4). Five samples made of each material were left to set in an incubator (Heraeus) at 37 C and 95% relative humidity for 24 hours. From each sealer, 1 sample was placed on a dental x-ray film (Kodak Insight Dental Film, film speed E, lot 3110641; Carestream Dental, Rochester, NY) together with an aluminum step wedge (1– 9 mm, 99 % Al). The aluminum step wedge met all requirements given in ISO 13116:2014 (9). The x-ray exposures were made using a Sirona Heliodent DS x-ray unit (Sirona, Bensheim, Germany) with a Sirona tube and a 2.5-mm aluminum filter (Sirona) added. The tube voltage was 60 kV and the current 7 mA. The exposure time was 120 milliseconds with a constant source-to-film distance of 21 cm. The films were developed, fixed, and dried in an automatic processor (XR-24-Nova; D€urr Dental, Bietigheim-Bissingen, Germany). The densities (D = density) were measured with a densitometer (Darklight duo ref; Medset, Hamburg, Germany) with a measuring range of D = 0 up to D >4.5 and accuracy for D <3 (0.01).

Materials and Methods BioRoot RCS was obtained from Septodont (lot powder B 06929, liquid B 109299A) and MTA Fillapex from Angelus (lot 30362). AH Plus (lot compound A 1504000267, compound B 1504000319) served as a control. All sealers were mixed according to the manufacturers’ instructions.

Solubility Test Solubility was determined based on the results obtained after immersion of the samples in double distilled water and phosphatebuffered saline (PBS) buffer (pH = 7.4) (AppliChem, Darmstadt, Germany). The specimens’ change in weight was recorded. For all sample preparations, stainless steel ring molds with a height of 1.6 mm (0.1 mm) and an internal diameter of 20.0 mm (0.1 mm) were used. All molds were cleaned in an ultrasound bath with acetone for 15 minutes. Thereafter, a copper wire was fixed at each mold in order to hang the specimens in a glass dish in such a way that the surfaces did not touch and the materials remained undisturbed in the dish. Before use, all molds were weighed 3 times (accuracy  0.0001 g), and the mean was calculated. The ring molds were placed on a glass plate and filled to slight excess with the mixed material avoiding air entrapment. After setting of the sealers, excess material was trimmed to the surface level of the mold using silicon carbide paper (600 grit). From each material, 70 samples were prepared for immersion in water and 70 samples for immersion in PBS buffer. In each case, the 70 samples were divided into 7 groups of 10 for immersion in water or PBS buffer for 1 minute, 20 minutes, 2 hours, 24 hours, 72 hours, 14 days, and 28 days. Before testing, all samples were left to set in an incubator (Heraeus, Hanau, Germany) at 37 C and 95% relative humidity for 24 hours. The materials in the ring molds were weighed (accuracy  0.0001; Sartorius 1801MPS, G€ottingen, Germany) 3 times before the immersion of the samples. The average reading was recorded. After immersion, the samples were weighed again 3 times, and the mass of the cements was determined to the nearest 0.0001 g. The difference between the original weight of the material and its final weight was recorded to the nearest 0.0001 g. This difference in mass was calculated as a percentage of the original weight of the material recorded to the nearest 0.001%. The solubility test is a modification of the methodology laid down in ISO 6876:2012 (4) (eg, solubility testing in PBS buffer). A detailed experimental setup has been described previously (3, 8).

Setting Time The setting time was evaluated according to ISO 6876:2012 (4). For each sealer, 5 stainless steel ring molds having an internal diameter of 10 mm (0.1 mm) and a height of 2 mm (0.1 mm) were filled and stored at 37 C and 95% relative humidity. Shortly before the setting time indicated by the manufacturer, a Gilmore-type needle was carefully lowered onto the surface of the sealer without exerting any further pressure. The Gilmore-type needle had a diameter of 2 mm (0.1 mm), a flat cylindrical end, a height of 5 mm, and a weight of 100 g (5 g). This testing was repeated every minute until an impression was no longer visible on the sealer surface. According to the Kolmogorov-Smirnov test, all data were distributed normally and analyzed using 1-way analysis of variance and post hoc Student-Newman-Keuls test for all pair-wise comparisons (P < .05).

Results Solubility BioRoot RCS was significantly less soluble than AH Plus and MTA Fillapex after immersion in distilled water for 1 minute (P < .05) (Table 1) but was significantly more soluble than the 2 other sealers at all times longer than 1 minute (P < .05). The control samples of empty molds did not change weight after immersion in water or PBS buffer, respectively, after 28 days. AH Plus and MTA Fillapex had the same solubility in PBS buffer and distilled water, whereas BioRoot RCS was significantly less soluble in PBS buffer than in distilled water after 28 days (P < .05) (Table 2). On the surface of all BioRoot RCS specimens immersed in PBS buffer for 14 and 28 days, a white precipitate was visible. The deposits adhered onto the surfaces even after drying and were hard to remove.

TABLE 1. Solubility of BioRoot RCS, MTA Fillapex, and AH Plus in Distilled Water 1 min

20 min

2h

24 h

72 h

14 d

28 d

Material

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

BioRoot RCS MTA Fillapex AH Plus

0.068b (0.026) 0.113a (0.159) 0.108a (0.026)

0.559a (0.088) 0.164b (0.018) 0.109c (0.013)

1.051a (0.098) 0.122c (0.010) 0.179b (0.015)

1.174a (0.184) 0.452b (0.062) 0.221c (0.019)

1.337a (0.149) 0.762b (0.092) 0.203c (0.009)

1.763a (0.151) 1.383b (0.198) 0.236c (0.017)

1.785a (0.214) 1.531b (0.253) 0.352c (0.303)

SD, standard deviation. The mean percentages with SD of weight loss for each material and for each immersion period are provided. Values with different superscript letters were statistically different at P = .05 (analysis of variance and Student-Newman-Keuls test).

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Basic Research—Technology TABLE 2. Solubility of BioRoot RCS, MTA Fillapex, and AH Plus in Phosphate-buffered Saline Buffer 1 min

20 min

2h

24 h

72 h

14 d

28 d

Material

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

Mean (SD)

BioRoot RCS MTA Fillapex AH Plus

0.035c (0.016) 0.111a (0.020) 0.072b (0.023)

0.310a (0.095) 0.106b (0.011) 0.107b (0.028)

0.754a (0.076) 0.098c (0.016) 0.177b (0.036)

0.958a (0.168) 0.242b (0.045) 0.221b (0.014)

1.028a (0.117) 0.317b (0.070) 0.223c (0.011)

1.142a (0.114) 0.718b (0.076) 0.264c (0.015)

0.885b (0.086) 1.225a (0.122) 0.352c (0.030)

SD, standard deviation. The mean percentages with SD of weight loss for each material and for each immersion period are provided. Values with different superscript letters were statistically different at P = .05 (analysis of variance and Student-Newman-Keuls test).

The main components of the precipitate were analyzed by X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis, and the minor constituents were identified with inductively coupled plasma optical emission spectroscopy. Moreover, the chemical composition of the precipitate was investigated by X-ray photoelectron spectroscopy and the surface morphology by scanning electron microscopy (Fig. 1) as described previously (10). The precipitation was calcium hydroxyapatite (Ca10[PO4]6[OH]2  n H2O).

Radiopacity The radiopacity of AH Plus was 6.85 mm (0.11 mm) Al, BioRoot RCS was 6.85 mm (0.12 mm) Al, and MTA Fillapex was 6.73 mm (0.08 mm) Al, respectively. No statistical significant difference was measured among the 3 sealers (P > .05). Setting Time The final setting time of BioRoot RCS (324  1 minutes) was significantly shorter than that of AH Plus (612  4 minutes) (P < .05). MTA Fillapex did not set completely even after 1 week.

Discussion The solubility tests performed in the present study followed the methodology of ISO 6876:2012 to a great extent (4). However, although weight loss of the test specimens was recorded by determining the decline in mass of the sealer samples after storage in the different liquids, as already described by some authors (11–14), ISO 6876:2012 (4) requires that the increase in weight of the dish in which the samples

Figure 1. A scanning electron microscopic micrograph of the white precipitate on the BioRoot RCS surface after 28 days of storage in PBS buffer. Original magnification: 1,400. The bar represents 10 mm.

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have been placed (residue method) should be ascertained as the amount of material removed from the specimens (4, 15, 16). The specimens were weighed to avoid an underestimation of the material going into solution. For instance, it is well-known that when the residue method is applied to zinc oxide–eugenol cements, eugenol, the major consistent of the eluate, is lost by volatilization during the course of evaporation and hence is not estimated (17). Moreover, it has been shown that the best indication of the extent of the disintegration can be obtained by weighing the specimens before and after the test (17). To enhance the accuracy of the measurements, 1 sample was used for only 1 immersion period; thus, undesirable weight loss of the sealer caused by repeated drying and immersion was excluded. After the immersion period, all samples were washed with double distilled water in order to remove loose debris of decomposition (17). The standard deviation obtained was low for all sealers and ranged from 0.009 %–0.159 % (in distilled water) and 0.011%–0.168% (in PBS buffer); it was lower than those described by Ørstavik (12) under nearly identical experimental conditions for distilled water. Moreover, sealers differing by less than 0.5% in solubility could be separated with statistical significance. Furthermore, copper wire has, unlike threads, no weight changes after storage in water or PBS buffer, respectively. Based on these findings, the experimental method seemed appropriate. It has to be kept in mind that with regard to the strict definition of the physicochemical term solubility, the test used in the present study measured the elution of water-soluble material but not the solubility. Moreover, measuring weight differences of the specimens may also record disintegration processes that may not be the result of dissolution (12, 17). Furthermore, water uptake may compensate for dissolved material (12, 13). In previous studies, the solubility of AH Plus was determined to range between 0.11% and 0.36% (3, 8, 18, 19). Thus, the results of the present study are in accordance with previous findings. However, considerably higher values of about 15% after 7 days were reported for MTA Fillapex recently (18, 19). To the best of our knowledge, no data concerning the solubility of BioRoot RCS are available yet. The null hypothesis of this study has to be rejected because BioRoot RCS was significantly more soluble than MTA Fillapex after immersion times longer than 1 minute and AH Plus for all time periods. Solubility is considered deleterious for a sealer, but di- and tricalcium silicate cements form calcium hydroxide during setting (20). BioRoot RCS has exhibited the formation of calcium hydroxide early in the setting process, whereas MTA Fillapex has not (21). Thus, BioRoot RCS probably promotes bioactivity (21), and, hence, the release of OH and Ca2+ ions is necessary and related to the solubility of these materials. It has been shown for calcium silicate cements that materials with a higher solubility had a higher OH and Ca2+ release (20). Thus, the higher solubility of BioRoot RCS may be explained by the leaching of calcium ions. In a physiological solution (HBSS), leaching of calcium was significantly higher for BioRoot RCS (30 mg/g) than MTA Fillapex (3 mg/g) within

Properties of Root Canal Sealers

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Basic Research—Technology 14 days (22). Furthermore, the high solubility of calcium silicate–containing sealers correlated with their antimicrobial efficiency (19). All 3 sealers fulfilled the requirements of ISO 6876:2012 (4) and showed a solubility of less than 3% after immersion in water for 24 hours using our modified method of suspending the samples (Table 1). The solubility tests in PBS buffer were performed to provide a better understanding of the advantages of biocompatibility and bioactivity by components to be released from di- and tricalcium silicate–containing materials (23). Di- and tricalcium silicate cements may form hydroxyapatite crystals on their surface after contact with phosphatecontaining liquids like body fluid or PBS buffer (23–25). Calcium ions, the dominant ion released from calcium silicate sealers, may react with the phosphate in the PBS buffer to precipitate hydroxyapatite (24). The release of ions and the formation of hydroxyapatite on the surface of di- and tricalcium silicate–containing materials are related to their biocompatibility and bioactivity (1). Recently, bioactivity was not proven for MTA Fillapex in vivo (26), which may be explained by the present findings. The solubility of BioRoot RCS was lower after immersion for 28 days than after 14 days in PBS. BioRoot RCS does not include a calcium phosphate phase; however, this phase was identified when the material was immersed in a physiological solution (HBSS) (22). This deposit seems to impede a further increase of solubility. The scanning electron microscopic micrographs showed the precipitated crystals on the surface of BioRoot RCS (Fig. 1). Radiopacity greater than 3 mm aluminum is required by ISO 6876:2012 (4), and all of the sealers tested met this criterion. Differences among the 3 sealers were not statistically significant. The radiopacity given by the manufacturer for BioRoot RCS is about 5 mm Al, whereas Xuereb et al (22) determined a value of 8.9 mm Al. The value obtained in the present study was 6.85 mm Al and thus in between these 2 values. Reports of radiopacity of MTA Fillapex ranged between 3.9 and 8.9 mm Al (22, 27– 29), and the value determined here was 6.73 mm Al, which is within this range. The radiopacity of AH Plus was measured to be 6.85 mm Al, which is in accordance with a value of 6.30 mm Al reported previously (8) but clearly lower than the radiopacity given in other reports ranging from 11.2 mm Al to 18.4 mm Al (6, 28, 29). The setting time of sealers depends on their constituent components, particle size, the ambient temperature, and relative humidity (30, 31). According to the manufacturer, the setting time of BioRoot RCS is less than 4 hours, but the setting time determined in the present study was more than 5 hours. The setting time of AH Plus was in good accordance with previous findings (8). MTA Fillapex did not set within 1 week, which has been observed by others (22). This sealer was unable to set in a dry environment, whereas a setting time of over 19 hours was measured for samples immersed in HBSS (22). BioRoot RCS set in a relatively short period of time (78 minutes) in a dry environment but required nearly 16 hours when immersed in HBSS (22).

Conclusion The solubility and radiopacity of BioRoot RCS met the requirements of ISO 6876:2012 using our modified solubility method. However, in double distilled water, BioRoot RCS was significantly more soluble than MTA Fillapex or AH Plus, which both contain resins. In contrast, the solubility of BioRoot RCS in PBS buffer was notably less. 4

Pr€ullage et al.

Acknowledgments The authors thank Priv Doz Dr Gunther Brunklaus, Institute for Physical Chemistry, Westphalian Wilhelms-University, M€unster, Germany, for kindly analyzing the white precipitation of BioRoot RCS after storage in PBS buffer by X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis, inductively coupled plasma optical emission spectroscopy, and scanning electron microscopy. The authors deny any conflicts of interest related to this study.

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Properties of Root Canal Sealers

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