Effect of a bioactive glass-based root canal sealer on root fracture resistance ability

Abstract

Background/purpose: The root fracture resistance of endodontically treated teeth is decreased significantly, and it is more likely to fracture. This study aimed to evaluate the effect of a novel root canal sealer based on bioactive glass (BG) on root fracture resistance and explore its mechanism.

Materials and methods: The BG-based root canal sealer (BG Sealer) was prepared by mixing a kind of bioactive glass (10.8% P₂O₅, 54.2% SiO₂, 35% CaO, mol.%, named PSC), zirconia (ZrO₂) powder, sodium alginate (SA) and phosphate solution (PS). A pH meter was used to measure the pH of simulated body fluid (SBF) after immersion with BG Sealer at different time. After preparing the samples of BG sealer with a diameter of 4 mm and a height of 6 mm, the compressive strength was tested by a universal testing machine. The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to detect and analyze the mineral status of root canal systems filled with BG Sealer. The push out test was used to measure the push out bond strength of BG Sealer. The fracture resistance of root canals filled with BG Sealer was detected by the compressive loading test. Bioceramic root canal sealer iRoot SP was set as the control group.

Results: (1) Physicochemical properties: The pH value of SBF immersed with BG Sealer increased slightly up to 7.68, while the pH of SBF immersed with iRoot SP increased to 12.08. The compressive strength of the novel BG Sealer was 4.62 ± 1.70 MPa, which was lower than that of iRoot SP (P < 0.05). (2) Mineralization: The hydroxyapatite layers were observed on the surface of BG Sealer and iRoot SP after being immersed in SBF for 4 weeks. BG Sealer and iRoot SP were both able to penetrate into the dentin tubules, duplicate the morphology of root canals well, and form a layer of hydroxyapatite. (3) Adhesion to dentin: There was no significant difference between the push out bond strength of the novel BG Sealer and iRoot SP (P > 0.05). (4) Fracture resistance: After immersion in SBF for 4 weeks, the fracture resistance of roots filled with BG Sealer and iRoot SP was 454.16 ± 155.39 N and 445.50 ± 164.73 N, respectively, both of which were not statistically different from that of the roots unprepared and unfilled (394.07 ± 62.12 N) (P > 0.05), whereas higher than that of the roots prepared and unfilled (235.36 ± 83.80 N) (P < 0.05).

Conclusion: The novel BG Sealer has good adhesion to the root dentin, can penetrate into the dentin tubules to generate minerals, and meanwhile can improve the fracture resistance of the roots after root canal treatment. It is expected to be a bioactive root canal sealer with good clinical application prospects.

Keywords: Bioactive glass; Fracture resistance; Mineralization; Push out bond strength; Root canal sealer.

Figure 1

pH value change of SBF immersed with root canal sealers at different time.

Figure 2

Photomicrographs of penetration and mineral formation in dentin tubules by SEM. The second column was the enlargement of the red box in the first column, and the third column was the enlargement of the red box in the second column. The yellow arrow showed the exposure of collagen fiber (b, c). The red arrow showed that sealers penetrated into the dentin tubule, replicating the morphology of the root canal, and mineral deposits were formed on the surface (e, f, i, j). EDS showed that the minerals are deposited (g, k). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Figure 3

Loads to fracture of roots with or without being filled with sealers (n = 9). ∗ represented statistically significant difference compared with the negative control group, P < 0.05. # represented statistically significant difference compared with the positive control group, P < 0.05.