Thermal analysis and stability of commercially available endodontic obturation materials

Use of micro-CT to examine effects of heat on coronal obturation

PURPOSE

The aim of this study was to categorize the effects of heat on coronal obturation with gutta-percha and sealer using X-ray micro-computed tomography (micro-CT).

METHODS

Ten single-rooted, extracted human teeth were shaped using ProTaper NEXT files to size X5 (#50/Taper 6%) with 2.5% NaOCl irrigation. A single ProTaper NEXT X5 gutta-percha point was then inserted with epoxy resin (AH Plus) or tricalcium silicate (EndoSequence BC) sealer (n = 5/group), and cut at the cemento-enamel junction. The teeth were scanned using micro-CT (SkyScan1272) to obtain 11 sagittal 2-D images. Three calibrated raters categorized the coronal 0.5 mm of the images into four categories: "swirled sealer and/or gutta-percha without voids" (I), "uniform voids and sealer/gutta-percha" (II), "non-uniform voids and sealer/gutta-percha" (III), and "swirled sealer and/or gutta-percha with voids" (IV). Intra-rater and inter-rater reliability were then calculated. Chi-square tests were conducted to determine the significance of differences in each category between sealers.

RESULTS

The intra-class correlation coefficient was 0.55 (same rater/two different times) and Fleiss' kappa (different raters/same image) was 0.34. Categories I, II, III, and IV accounted for 16.4%, 4.2%, 30.3%, and 49.1% for AH Plus, and 6.7%, 4.2%, 27.3%, and 61.8% for EndoSequence BC, respectively.

CONCLUSION

Category IV was most common and Category II the least common. Significant differences were evident between sealers for Category I (P < 0.01).

Effects of heat on seven endodontic sealers

PURPOSE

To examine the microscopic surface features, chemical composition, and thermodynamic profile of seven endodontic sealers (AH Plus, Adseal, MTA-Fillapex, RoekoSeal, GuttaFlow 2, GuttaFlow BioSeal, and EndoRez) exposed to high-temperature changes using an endodontic obturation device.

METHODS

The thermal properties were examined using scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Then, six disc-shaped specimens of each sealer were prepared and divided into two groups - a room temperature group and a heat exposure group - for analysis of surface and chemical changes using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).

RESULTS

DSC analysis showed that AH Plus had the highest exothermal signal (122.9°C), while TGA analysis showed that MTA-Fillapex was most affected by increased temperature (32.4% mass loss at 230ºC). SEM analysis showed that while AH Plus and GuttaFlow BioSeal maintained their surface integrity after heat exposure, the EDS profiles demonstrated changes in the chemical composition of the sealers after heat exposure for 5 s. High-temperature exposure had a negative impact on the properties of five of the sealers (Adseal, MTA-Fillapex, RoekoSeal, GuttaFlow 2, and EndoRez).

CONCLUSION

AH Plus and GuttaFlow BioSeal showed minimal changes upon high-temperature exposure, suggesting their suitability for thermal endodontic obturation techniques.

The investigation of thermal behaviour and physical properties of several types of contemporary gutta-percha points

Aim

To analyse the contents and thermal behaviour of several brands of contemporary gutta‐percha points due to the variable nature of the components of gutta‐percha, and the impact they can have on the physical properties of this unique material during canal filling.

Methodology

Six brands of gutta‐percha were investigated: Conform Fit ^TM Gutta‐Percha Points for ProTaper Gold® (PTG) (Dentsply Sirona), ProTaper® Universal Gutta‐Percha Points (PTU) (Dentsply Sirona), Autofit ^TM Feathered Tip Gutta Percha (Kerr), Mtwo® Gutta‐Percha (VDW), Gutta Percha Root Canal Points (GC, GC Corporation) and Gutta‐Percha Points ISO Color‐Coded (ISO; Dentsply Sirona). The organic and inorganic fractions of gutta‐percha points were separated by quantitative chemical analysis. Thermal conductivity was detected using a laser flash method. In addition, the thermal behaviour of gutta‐percha in response to temperature variations was analysed using differential scanning calorimetry (DSC). Kruskal–Wallis and Dunn tests were applied for comparisons amongst groups for chemical compositions and temperature obtained from DSC. The associations between compositions and thermal conductivity were determined using simple linear regression. A p value <.05 was considered to be statistically significant.

Results

There were significant difference in the inorganic fractions of the gutta‐percha points in percentage by weight amongst the groups (p < .05). PTG had the lowest thermal conductivity (0.42 W/m K). A positive correlation was observed between the percentage of inorganic fraction and thermal conductivity (r = 0.95). The initial phase changing temperature and peak temperature measured by DSC were significantly different when the β‐form transformed to α‐form (p < .05), whereas no significant difference was found during the α‐form to the amorphous‐phase transition (p > .05).

Conclusions

Chemical compositions and initial phase changing temperature by DSC varied according to the various brands of gutta‐percha points. Conform Fit ^TM gutta‐percha had the lowest percentage of inorganic fraction and thermal conductivity amongst these six brands of gutta‐percha. Thermal conductivity had the strongest positive correlation with the percentage of inorganic components and zinc, whilst there was a negative correlation to the amount (ratio) of gutta‐percha.

Efficacy of Removing Thermafil and GuttaCore from Straight Root Canal Systems Using a Novel Non-Surgical Root Canal Re-Treatment System: A Micro-Computed Tomography Analysis

The present study aims to evaluate the effectiveness of an XP-endo non-surgical root canal re-treatment system in removing both GuttaCore and Thermafil gutta-percha carrier-based root canal filling materials from straight root canal systems using micro-computed tomography (micro-CT) analysis. The study was performed on 20 single-rooted upper teeth, which were randomly allocated into the following study groups: Group A, Thermafil and AH Plus sealer (n = 10); Group B, GuttaCore and AH Plus sealer (n = 10). Before and after the non-surgical root canal re-treatment procedure, the samples were submitted for a micro-CT analysis. The volume of the root canal filling material (mm³), the volume of the remaining root canal filling material (mm³) and the time (minutes) needed to remove the root canal filling material were also recorded. Student's t-test was used to analyze the results. No statistically significant differences were found between the volume of the remaining root canal filling material in the GuttaCore and Thermafil root canal filling systems at the coronal third (p = 0.782), middle third (p = 0.838) or apical third (p = 0.882) of the straight root canal systems; however, the GuttaCore required a statistically significant (p = 0.037) shorter amount of time (4.72 ± 0.76 min) to be removed than the Thermafil carrier-based root canal filling material (5.92 ± 1.42 min). The XP-endo Finisher non-surgical endodontic re-treatment system removes both GuttaCore and Thermafil gutta-percha carrier-based root canal filling materials from straight root canal systems, although removal of the GuttaCore gutta-percha carrier-based root canal filling material required less time.

Thermal behavior and viscoelastic properties of gutta-percha used for back-filling the root canal

BACKGROUND/PURPOSE

In clinical operations, qualitative differences in the texture and operational feeling of the regular type and soft type back-filled gutta-percha are readily discernible. This study aimed to investigate and compare the thermal behavior and physical properties of the two gutta-percha materials.

MATERIALS AND METHODS

The chemical compositions of regular and soft type Gutta-Percha Obturator® pellets were examined via energy dispersive X-ray spectroscopy. The thermal behaviors of the pellets during heating and cooling were evaluated using a differential scanning calorimeter. Finally, the viscoelastic properties of the two materials during cooling were assessed using a modular compact rheometer.

RESULTS

The soft type gutta-percha contained a greater atomic percentage of zinc than the regular type material. In addition, the soft type gutta-percha exhibited exothermic peaks during cooling, whereas the regular type gutta-percha did not. The two materials exhibited different viscoelastic behaviors under cooling. In particular, the rate of change of the loss factor for the soft type gutta-percha was more than that of the regular type gutta-percha at temperature lower than 80°C.

CONCLUSION

The soft type gutta-percha underwent significant crystallization during cooling, and therefore exhibited pronounced volume shrinkage. Furthermore, the soft type gutta-percha underwent a greater rate of change in viscoelasticity under cooling than the regular type gutta-percha, and exhibited poorer physical stability. Consequently, in the back-packing procedure, soft type gutta-percha must be compacted more often over time than regular type gutta-percha to ensure the same quality of root canal obturation.

Experimental Resin-Based Monoblock Endodontic Obturation System

Objective. The aim of the present study was to characterize a novel resin-based monoblock endodontic obturation system consisting of a polymeric cone and a resin-based endodontic sealer. Methods. The preliminary tests performed for the experimental cone were as follows: cohesive strength, dimensional stability, standardization of the diameter and taper, calcium ion release, and radiopacity, for the characterization of the experimental sealer, film thickness and flow tests were performed. Tests were performed according to the American National Standards Institute/American Dental Association (ANSI/ADA) Standards Nos. 57 and 78. The experimental cone was compared to gutta-percha, whereas the experimental sealer was compared to AH Plus. Data were analyzed by Student’s t-test (α = 0.05). Results. The experimental cone had superior values for cohesive strength and dimensional stability compared to gutta-percha. Regarding calcium ion release, the experimental system continued to release calcium ions after 30 days. Film thickness was similar for both endodontic sealers; conversely, the experimental resin-based sealer achieved higher values for flow compared to AH Plus. Conclusion. The experimental resin-based monoblock obturation system fully met the requirements of the ANSI/ADA Standard No. 78 and the ANSI/ADA Standard No. 57, except for radiopacity. Considering this, further studies are still needed to evaluate other radiopacifiers and the effect of their incorporation on the physicochemical properties of this novel resin-based monoblock endodontic obturation system.