Warm vertical compaction of gutta-percha is a technique that is used by most specialists for root canal obturation. The sealers currently available exhibit irriversible chemical changes when heated. New biologically active sealers that do not sustain irreversible changes when heated are an attractive alternative to be used with warm vertical compaction obturation technique. The aim of this study was to measure the heat generated by warm vertical compactors inside the root canal, characterize a newly developed root canal sealer at different temperatures and verify its suitability at the actual temperature window used clinically.
The typical temperatures generated by two heat carriers in a root canal were assessed by thermocouples. Two premixed root canal sealers TotalFill BC and HiFlow BC (FKG, Switzerland) were allowed to set and they were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD) immediately after setting and by XRD after 28 days in physiological solution. The ion leaching in solution was assessed by inductively coupled plasma (ICP). The organic component was extracted in acetone and assessed by Fourier transform infrared spectroscopy (FT-IR) for both the unset sealer and sealer subjected to different temperatures. The heat profiles of both sealers were investigated by FT-IR and thermographic analysis.
None of the devices tested achieved the temperatures set on the dial. The highest temperatures were coronal followed by apical for both devices. The sealers were identical except for the vehicle. The inorganic components included tricalcium silicate, dicalcium silicate and zirconium oxide. No calcium hydroxide was produced by any of the sealers after immersion in physiological solution but calcium was released in solution. The chemistry of both sealers was modified when heated but both recovered when cooled.
The heat carriers were unreliable and the heat generated inside the canal was not the same as the temperature set on the dial. Since both sealers had identical chemistry save for minimal modifications to the organic component and were both resistant to heat, TotalFill BC sealer is recommended for use with warm vertical compaction technique as it is cheaper and as effective as the HiFlow.
The warm vertical compaction of gutta-percha is a very popular obturation technique where the gutta-percha is heated until it changes phase and softens, then it is compacted vertically to take the shape of the prepared root canal . With this technique the obturation is composed mostly of gutta-percha with minimal amounts of sealer. There is no specific sealer that is suggested for use with this technique so all sealer types are believed to be suitable.
The temperature of phase changes to gutta-percha have been reported to be 60 °C to convert from the β form to completely amorphous . Regardless of this, all the heat carriers indicate the use of temperature settings ranging from 180 to 230 °C. There seems to be no scientific reason for the use of such temperatures which are unsafe. Increases in temperature of bone has been shown to lead to necrosis as the bone can only tolerate an increase by few degrees . Regardless of the reading on the dial, the temperature of the heat carriers is less and the temperature is further dissipated when the heat carrier is placed in a tooth and sealer is used in the root canal . As a result of this, the temperature rise on the external surface of the root is minimal .
A rise in temperature in the root canal has deleterious effects on the root canal sealers particularly the epoxy resin-based sealers such as AH Plus (Dentsply). At higher temperatures the AH Plus showed irreversible changes in chemistry and its physical properties were modified with a reduction in the setting time and flow and increase in film thickness . Zinc oxide eugenol-based sealers sustained an increase in setting time when exposed to heat but the flow was unaffected while BioRoot RCS showed changes in its chemistry due to the water evaporation at high temperature and iRoot SP had reduced flow . Heating of AH Plus also resulted in an increase in void volume while BioRoot RCS and Gutta-flow were unaffected .
Recently a new hydraulic calcium silicate-based sealer which can be used with warm vertical compaction of gutta-percha has been developed. This sealer is claimed to have a similar chemistry to the premixed hydraulic sealers (BC sealers) manufactured by Brasseler/FKG Dentaire but is resistant to heat thus is recommended for use with warm vertical compaction obturation technique. The aim of this research was to determine the temperature generated by two heat carriers inside the root canal in a simulated clinical environment and to characterize both the classical BC sealer and the HiFlow and assess their heat profiles and chemical changes when subjected to high temperatures.
Materials and methods
In this study two premixed hydraulic calcium silicate sealers are tested. These included TotalFill and HiFlow BC sealers. Both sealers are manufactured by FKG Dentaire (Chaux-de-Fonds, Switzerland). The HiFlow was developed as an alternative to the BC sealer to be used together with gutta-percha for warm vertical compaction of gutta-percha obturation technique. All analysis was undertaken in triplicate.
Assessment of heat profiles of the endodontic heat carriers
The heat profiles of two heat carriers used in clincial practice was assessed using a method described in the literature . A single rooted tooth was accessed and chemo-mechanically prepared with ProTaper Gold to a size F2 using sodium hypochlorite irrigation. Three holes 0.8 mm in diameter were drilled along the root face, 2 mm, 8 mm and 12 mm from the apex. K-type thermocouples (0.3 mm diameter, Maplins, UK) were inserted into the root canal through these holes and were held in place by unfilled resin. The thermocouples were connected to a multi-channel data logger (PicoData Logger, TC-08, UK). The whole assembly was placed in alginate to simulate the clinical environment. Temperature was recorded in real-time at a rate of 1 s −1 for 30 s using the PicoData logging software. The heat profiles generated by each device were composed of a 10 s pre-heating phase, 4-s heating phase followed by a 10-s cooling phase. Two endodontic heat carriers were tested; E&Q Master (Meta Biomed, Chalfont, PA, USA) and System-B (Orange, CA, USA) both using a fine tip inserted 3 mm short of the apex. The E&Q Master was operated at 180 °C and 230 °C with automatic cut-out after 4 s. System-B was set at 200 °C and a heating cycle of 4 s heating and 10 s cooling was recorded. Each cycle was repeated three times for each heat carrier and set temperature to check for repeatability and the data expressed as mean and standard deviation to the mean.
The organic component of the sealers was extracted in acetone by centrifugation from the unset sealer and analysed by Fourier transform infrared (FT-IR) spectroscopy. The set sealers were characterized by scanning electron microscopy, and X-ray diffraction (XRD) analysis immediately after setting and by XRD after 28 days immersed in Hank’s balanced salt solution (HBSS) at 37 °C. The leachate was tested by inductively coupled plasma mass spectroscopy (ICP-OES). All experiments were carried out in triplicate.
The sealers were syringed and specimens 10 mm in diameter and 2 mm thick were made. The specimens were covered by a wet gauze and were placed in an incubator at 37 °C and 100% humidity for 24 h. Setting was verified by indenting the specimen surfaces. One group were tested immediately after setting and the rest were placed in 5 mL of HBSS for 28 days.
For scanning electron microscopy, the specimens were embedded in a cold cure epoxy resin (Epoxy-fix, Struers, Ballerup, Denmark) and the surfaces were polished with an automatic polishing machine (Buhler, Lake Buff, USA) using 250, 500 and 1200 grit diamond discs under water coolant (Struers, Ballerup, Denmark) and polishing cloths (Struers) with ascending grades of diamond-impregnated polishing pastes (Struers). Once polished the embedded specimens were mounted on aluminum stubs and held in place with carbon tape and were sputter coated with gold. The specimens were then viewed under the SEM (Zeiss). The sealers were assessed in back scatter mode to obtain elemental contrast. Images at different magnifications were obtained. Energy dispersive spectroscopy was performed to assess the elemental distribution.
For the XRD the aged specimens were retrieved from solution and dried in desiccator. For both ages, the sealers were then ground using a mortar and pestle to a fine powder. XRD was performed with a diffractometer (Bruker D8 Advance, Bruker Corp., Billerica, MA, USA) with a CuKa radiation at 40 mA and 45 kV was set to rotate between 10° and 60° with a 0.02° 2 θ step and a step time of 0.6 s. Phase identification was undertaken using a search-match software using the ICDD database (International Center for Diffraction Data, Newtown Square, PA, USA). The leachates were assessed for calcium, silicon, zirconium and phosphorus with inductively coupled plasma-optical emission spectrometry (Optima 8000, Perkin Elmer, Waltham, USA). Calculation of results was performed in parts per million (ppm).
Investigation of the chemical changes in the sealers
The sealers were dispensed on a heated diamond plate (MIRacle) attached to a control module (Pike Technologies, USA). The chemical changes to the sealers exposed to a heating and cooling cycle were assessed by FT-IR in ATR mode as described for the sealer characterization. A baseline measurement was taken immediately after sample placement at room temperature (21 ± 1 °C) and then the heating module was activated to heat the samples at a rate of 12.5 °C/min. Measurements were taken from 25 °C to either 50, 100 or 200 °C at increments of 25 °C and then air-cooled to 25 °C and re-measured. All spectra were baseline corrected between 650 and 4000 cm −1 and an average ( n = 3) was taken. The testing assembly was kept at high relative humidity.
Changes in weight sustained at different temperatures were recorded by thermogravimetric analysis/differential scanning calorimetry, (TGA/DSC; Mettler-Toledo, Beaumont Leys, Leicester, UK). Twenty milligram of set sealers were tested at a temperature range of 50–200 °C at a heating rate of 10 °C min −1 and O 2 flow rate of 40 mL min −1 . The experiment was repeated three times to ensure repeatability.
The organic component was also extracted after setting at room temperature and after subjecting the sealers to temperatures of 50, 100 and 200 °C and this was tested by FT-IR ( n = 3).
The statistical analysis was performed using Predictive Analytics Software (PASW) version 18. One-way ANOVA was used to determine whether there were significant differences between data sets. The data was tested to ensure it was normally distributed and then with analysis of variance with P = 0.05 the turkey post hoc test was used.
Assessment of heat profiles of endodontic heat carriers
The heat generated by the endodontic heat carriers is shown in Table 1 . The higher setting of the E & Q Master heat carrier led to a higher temperature mostly coronally with minimal changes mid-root and apically. None of the heating devices achieved the temperature set on the dial. All devices exhibited the highest temperature at the coronal portion followed by the apical region with the mid-root exhibiting the lowest temperature. The highest temperature was recorded coronally for the E&Q Master set at 230 °C.