The aim of this study was to analyze the behavior of different bioactive glass fillers (BAGs) embedded in a polydimethylsiloxane matrix of an endodontic sealer.
Three different endodontic sealers were fabricated using S53P4, 45S5 and 18−06 glass fillers. Endodontic sealer Guttaflow Bioseal consisting of polydimethylsiloxane (PDMS) matrix was used as base of the experimental sealers. Behaviors of different glass fillers leaching from polymer matrix was studied in vitro for 14 days by measuring static ion dissolution profiles of Si, Na, Ca and P -ions. In addition, pH of the simulated bodyfluid (SBF) was monitored during the 14 days and all the sealer samples was examined with SEM/EDX analysis on the surface. Identical but non-glass filler containing polydimethylsiloxane-based sealer was used as a control material.
By the time point of 24 h sealer with 45S5 had released twice as much of Si-ions compared to sealer with S53P4. No statistical differences of Na, Ca and P -ions dissolution were observed in the first 168 h for any groups whereas concentrations of Ca and P -ions decreased with 45S5 significantly after 336 h. Highest pH was measured for sealers with glass filler 45S5 and S53P4 (7.64–7.65). Visible mineral precipitation was observed only on sealer surfaces after 336 h’ time period with groups of 45S5 and S53P4. However, presence of calcium and phosphorus oxides was confirmed only with 45S5.
Bioactive glass type 45S5 outperforms S53P4 and 18−06 by acting more dynamically in vitro set-up
Successful endodontic treatment relies on several key parameters; complete removal of caries infected tissue, mechanical elimination of micro-organisms thorough from root canal area combined with adequate 3-step chemical rinsing with sodium hypochlorite, ethylenediaminetetraacetic acid and chlorhexidine gluconate [ , ]. Undoubtedly impervious seal of the root canal and restoring the lost coronal hard-tissue defect with close-fitting restoration has also proven influence the treatment outcome in long term [ ].
Guttaflow Bioseal is one of the new generation endodontic sealers, which was originally launched in 2015. It contains approximately 20–40 micrometer sized fillers of bioactive glass 45S5 (BAG) which are embedded in the sealer’s polydimethylsiloxane matrix. BAG fillers are intended to promote sealer’s biocompatibility and biomineralization in the periapical area of the root [ ]. Physicochemical and sealing properties of the sealer has been studied and recently it was shown that the sealer induced only limited inflammatory reactions in subcutaneous tissue of Wistar rats after 30 days of implantation indicating its biocompatibility and safety of use [ , ]. It was also reported that Guttaflow Bioseal incorporated promotes human periodontal stem cell differentiation which may have a role in healing of periapical periodontitis by mechanism of cementogenesis [ , ].
Use of BAG fillers in endodontic sealers have clearly shown new interest of use in dental restoratives and conditioning materials although it’s not novel idea [ ]. BAG`s renowned antimicrobial and bioactive properties have been its main arguments to incorporate it in wide range of applications [ ]. For example, it has been used successfully to induce osteogenesis and neovascularization of cranial implants and periodontal bone defect repairs although in the latter indication xenogenic enamel derivatives is regarded as golden standard [ ].
Antimicrobial activity of different BAGs against 29 clinically important species of microbes has been studied and clearly shown to have growth-inhibitory effect against aerobic bacteria and moderate evidence against anaerobic bacteria [ ]. However, the beneficial properties of BAGs have shown to be dependent on actual elemental composition of the glass type and dissolution rate of the glass in the adequate water containing environment. BAG S53P4 seems to have the strong antimicrobial effect even with lower concentrations against several species of microbes [ ]. It is known that fast rate of dissolution of BAGs increase pH and osmotic pressure in surrounding fluidic microenvironment and this is one of the factors contributing to antimicrobial properties.
Antimicrobial effect of BAG 45S5 wasn’t actually studied in the same set up has however shown faster and higher pH increase in dissolution studies compared to BAG S53P4 which clinically used in surgical indications [ ]. Correlation of antimicrobial activity by release of Zn 2+ from Zn-doped BAG against Streptococcus mutans has also been reported [ ]. However, the correlation of actual glass components, namely silicon, sodium, phosphorus and calcium in terms of ion release for the antibacterial properties remains still more or less controversial in the literature [ ].
Surface reactions of BAGs, where gradual dissolution of ions leads to formation of SiO 2 rich layer on the surface of the glass acts as a nucleation site for calcium and phosphate which are the fundamental ions for the biomineralization and tissue bonding function of BAGs [ ]. The formed calcium-phosphate layer acts as an intermediate layer of BAG to surrounding hard tissues. During dissolution of BAG the released ions may also induce osteogenesis and neovascularization which could have an impact to the healing process of periapical infections [ , ].
Thus, bone-bonding is based on cellular activity of osteogenetic cell lines and biomineralization whereas bonding to dentin is based on purely chemical biomineralization where amorphous calcium-phosphate can turn to crystallized hydroxylapatite mineral between the BAG as such or BAG containing composite and dentin. In the case of BAG containing composites, it is still unclear to what extent the polymer matrix of the composite such as polydimethylsiloxane sealer affects the dissolution processes and diffusion of the ions through the polymer matrix.
In this study the behavior and kinetics of two rapidly and one slowly reacting BAG fillers (S53P4, 45S5 and 18−06) in polydimethylsiloxane (PDMS) sealer matrix were examined in aqueous environment. Aim of the study was to evaluate the performance of the endodontic sealer in terms of ion release, pH change and bioactivity.
Materials and methods
Polydimethylsiloxane based endodontic sealer Guttaflow Bioseal was used as base of test materials. Three different experimental sealers (Group A, B and C) containing three different BAG fillers ( Table 1 ) were fabricated by Coltene Whaledent (Altstätten Switzerland) on authors request. Total volume of BAG fillers in the product is declared by the manufacturer to range between 5–30% in weight. All of the sealers were tested for ion release, changes of the pH in the simulated body fluid (SBF) solution and mineral precipitation on the sealer surface by SEM/EDX analysis. Identical sealer without any bioglass fillers (Group D) was used as a control material.
|Glass filler||SiO 2||CaO||Na 2 O||P 2 O 5||B 2 O 3||MgO||Group|
Test specimen preparation
Disc shaped specimens (N=6) for each group were prepared by filling circular stainless-steel molds (thickness 1.0 mm ± 0.1 diameter 5.0 mm ± 0.1) with slight excess of the sealer material on inert glass plates and covered with 50 μm thick Mylar sheet. The molds were then covered with another Mylar sheet and pressed together with glass plates to remove the excess sealer material. The molds between the glass plates were transferred for curing at 37.0 °C for 60 min.
The disc formed test specimens were then removed from molds and excess material from the periphery of the specimens was removed with surgical knife and silicon carbide grinding paper (FEPA #1000) and grinding machine (Struers LaboPol 21, Struers A/S, Rodovre, Denmark). The surfaces of the discs were not otherwise ground.
Dissolution studies and biomineralization
SBF was prepared as the dissolution medium according to the protocol of Kokubo [ ]. The pH of the solution was adjusted with HCl to 7.4 at 37 °C. Firstly, the specimens were immersed in 20 mL of SBF and kept for 1, 3, 7 and 14 days in orbital incubator under a shaking speed of 100 rpm at 37 °C. After desired immersion times, the pH of the SBF was determined at 35−37 °C and the specimens were collected and washed with ethanol. Thereafter specimens were kept in an oven at 40 °C for approx. 24 h of time in excicator until examined with scanning electron microscope. The ion concentrations in the SBF solution after immersion were analyzed with an inductively coupled plasma optical emission spectrometry (ICP-OES, PerkinElmer Optima 5300 DV). Analyzes were carried on diluted media (1 mL of SBF and 9 mL of purified ELGA-water).
Carbon coated specimens were studied using SEM (Gemini 1530, LEO Oberkochen/Carl Zeiss, Germany) coupled with energy-dispersive X-ray spectroscopy (EDX, UltraDry Silicon Drift Detector, Thermo Scientific, Madison, WI, US). The EDX analysis was used to determine elemental content of mineralized layer in oxide form using an accelerating voltage of 15 kV.
The data of ion release and pH change were both normally distributed with equal variance and therefore Tukey’s honestly significant difference test was used to compare means between the tested groups.
Dissolution and pH change
By the time of 24 h Group C, Guttaflow Bioseal with BAG 45S5 had released twice as much of Si ions compared to Group A; Guttaflow Bioseal with BAG S53P4 ( Fig. 1 ). More rapid and prominent release was continued until 168 h’ time period. Group A continued to release more Si ions slowly reaching almost the level of release of group C in 336 h. The ion release of Ca and P ions was relatively stable with all of the groups whereas release of Na ions exhibited slight alteration during the investigation period. No statistical differences on Na, Ca and P ions dissolution was observed in the first 168 h between the groups. Thereafter Ca ion and P ion concentration in the medium decreased significantly on Guttaflow Bioseal with BAG 45S5 (Group C) after 168 h until 336 h (p < 0.05).