Chemical-Physical Properties and Bioactivity of New Premixed Calcium Silicate-Bioceramic Root Canal Sealers

Abstract

The aim of the study was to analyze the chemical−physical properties and bioactivity (apatite-forming ability) of three recently introduced premixed bioceramic root canal sealers containing varied amounts of different calcium silicates (CaSi): a dicalcium and tricalcium silicate (1−10% and 20−30%)-containing sealer with zirconium dioxide and tricalcium aluminate (CERASEAL); a tricalcium silicate (5−15%)-containing sealer with zirconium dioxide, dimethyl sulfoxide and lithium carbonate (AH PLUS BIOCERAMIC) and a dicalcium and tricalcium silicate (10% and 25%)-containing sealer with calcium aluminate, tricalcium aluminate and tantalite (NEOSEALER FLO). An epoxy resin-based sealer (AH PLUS) was used as control. The initial and final setting times, radiopacity, flowability, film thickness, open pore volume, water absorption, solubility, calcium release and alkalizing activity were tested. The nucleation of calcium phosphates and/or apatite after 28 days aging in Hanks balanced salt solution (HBSS) was evaluated by ESEM-EDX, vibrational IR and micro-Raman spectroscopy. The analyses showed for NeoSealer Flo and AH Plus the longest final setting times (1344 ± 60 and 1300 ± 60 min, respectively), while shorter times for AH Plus Bioceramic and Ceraseal (660 ± 60 and 720 ± 60 min, respectively). Radiopacity, flowability and film thickness complied with ISO 6876/12 for all tested materials. A significantly higher open pore volume was observed for NeoSealer Flo, AH Plus Bioceramic and Ceraseal when compared to AH Plus (p < 0.05), significantly higher values were observed for NeoSealer Flo and AH Plus Bioceramic (p < 0.05). Ceraseal and AH Plus revealed the lowest solubility. All CaSi-containing sealers released calcium and alkalized the soaking water. After 28 days immersion in HBSS, ESEM-EDX analyses revealed the formation of a mineral layer that covered the surface of all bioceramic sealers, with a lower detection of radiopacifiers (Zirconium for Ceraseal and AH Plus Bioceramic, Tantalum for NeoSealer Flo) and an increase in calcium, phosphorous and carbon. The calcium phosphate (CaP) layer was more evident on NeoSealer Flo and AH Plus Bioceramic. IR and micro-Raman revealed the formation of calcium carbonate on the surface of all set materials. A thin layer of a CaP phase was detected only on AH Plus Bioceramic and NeoSealer Flo. Ceraseal did not show CaP deposit despite its highest calcium release among all the tested CaSi-containing sealers. In conclusion, CaSi-containing sealers met the required chemical and physical standards and released biologically relevant ions. Slight/limited apatite nucleation was observed in relation to the high carbonation processes.

Keywords: apatite nucleation; bioactivity; bioceramics; calcium phosphate nucleation; calcium silicates; calcium silicates cements; endodontic sealers; root canal sealers.

Figure 1

ESEM images at 3000× of Ceraseal before and after immersion in HBSS. Set Ceraseal sample was characterized by a regular surface with small granules widely spread. EDX revealed the constitutional elements of the materials, namely Zr, Ca, Si and Al. After 28 days immersion, an irregular surface was observed. Numerous globular structures covering the sealer surface were detected. EDX revealed an increase in Ca and a decrease in Zr and Si. No P was detected.

Figure 2

Average IR spectra recorded on just extruded Ceraseal (black) as well as on the surface of set disks before (blue) and after aging in HBSS for 28 days (red). The bands assignable to polyethylene glycol (PEG), alite (tricalcium silicate) (A), belite (dicalcium silicate) (B), monoclinic zirconia (Z), calcite (C), hydrated tricalcium aluminate (HyAl), CSH and CASH phases are indicated.

Figure 3

Average micro-Raman spectra recorded on just extruded Ceraseal (black) as well as on the surface of set disks before (blue) and after aging in HBSS for 28 days (red). The bands assignable to polyethylene glycol (PEG), tricalcium silicate (alite) (A), dicalcium silicate (belite) (B), tricalcium aluminate (Al), monoclinic zirconia (Z) and calcite (C) are indicated. PEG component was not indicated in the Material Safety Data Sheet.

Figure 4

ESEM images at 3000× of NeoSealer Flo before and after immersion in HBSS. The set sample was characterized by a homogeneous surface with granules of different sizes and shapes. EDX analyses revealed the constitutional elements of the sealer, namely Ta, Ca, Si and Al. After 28 days immersion in HBSS, ESEM images revealed a less uniform surface with an irregular layer, characterized by needle-like structures and granules that were agglomerated in larger irregular structures. EDX microanalysis revealed an increase in Ca and Al, stability of Si and Ta and the appearance of P.

Figure 5

Average IR spectra recorded on just extruded NeoSealer Flo (black) as well as on the surface of set disks before (blue) and after aging in HBSS for 28 days (red). The bands assignable to polyethylene glycol (PEG), tantalite (Ta), calcite (C), aragonite (Ar), hydrated tricalcium aluminate (HyAl), amorphous calcium phosphate (ACP), CSH and CASH phases are indicated. With regard to the 950–400 cm⁻¹ range, band assignments to calcium silicates and aluminates are reported in Table S1, Supplementary Material. PEG and grossite were not reported by the manufacturer in the Material Safety Data Sheet.

Figure 6

Average micro-Raman spectra recorded on just extruded NeoSealer Flo (black) as well as on the surface of set disks before (blue) and after aging in HBSS for 28 days (red). The bands assignable polyethylene glycol (PEG), tricalcium silicate (alite) (A), dicalcium silicate (belite) (B), tricalcium aluminate (Al), calcium monoaluminate (CA), calcite (C), aragonite (Ar) and tantalite (Ta) are indicated.

Figure 7

ESEM images at 3000× of AH Plus Bioceramic before and after immersion in HBSS. ESEM on the set sample showed a uniform surface with few irregularities. EDX revealed constitutional elements of the sealer, namely Zr (the radiopacifier) Ca, Si and traces of Al. The surface was covered by a vast layer after 28 days in HBSS. The layer was composed of globular and cubic-shaped structures. EDX analysis revealed a slight increase in Si, a marked increase in Ca, the decrease in Zr, the appearance of P, Na, Cl and Mg.

Figure 8

Average IR spectra recorded on just extruded AH Plus Bioceramic (black) as well as on the surface of set disks before (blue) and after aging in HBSS for 28 days (red). The inset shows the 3700–2800 cm⁻¹ spectral range of the just extruded sealer. The bands assignable to portlandite (P), dimethyl sulfoxide (D), tricalcium silicate (alite) (A), monoclinic zirconia (Z), CSH phase, calcite (C), aragonite (Ar) and calcium phosphate (CaP) are indicated. Band assignable to water (1656 cm⁻¹) was also detected in the just extruded sealer.

Figure 9

Average micro-Raman spectra recorded on just extruded AH Plus Bioceramic (black) as well as on the surface of set disks before (blue) and after aging in HBSS for 28 days (red). The bands assignable to dimethyl sulfoxide (D), tricalcium silicate (alite) (A), monoclinic zirconia (Z), calcite (C) and aragonite (Ar) are indicated.