Root canal fillings must meet a number of requirements. Not only must they be biocompatible and removable, but they must also tightly seal the root canal system. The effectiveness of the seal depends on the anatomy of the root canal system and especially on the shape of the canal and the type of mechanical preparation. It is undisputed that an effective seal can be technically achieved if the root canal is tapered from crown to apex [
Many studies are available that have investigated the adaptation of root fillings to the root canal walls and the ability of filling materials to seal the root canal system. For analysis of the adaptation dye penetration tests, which are simple to perform and relatively easy to evaluate, are available for this purpose [
Pressure differences of the pressure chamber and the pulp cavity for different root filling techniques at 5.0 bar chamber pressure (significance *
Group |
|
SEM | |
---|---|---|---|
Cold lateral condensation |
|
1.33 | 0.9 |
Carrier-based gutta-percha obturation |
|
0.09 | 0.04 |
Carrier-based Resilon obturation |
|
1.94 | 1.32 |
Downpack/backfill (Gutta-percha) |
|
0.03 | 0.02 |
Eighty extracted single-rooted human teeth (premolar) were randomly assigned to one of eight groups, each consisting of ten teeth. None of the teeth showed signs of dental caries or had been treated endodontically. Only teeth with a root canal curvature of less than 20 degrees were included in the study.
Following standardized machine instrumentation to a minimum preparation size of ISO # 30.04 (VDW Gold, VDW, Munich, Germany) and irrigation with 2.25% sodium hypochlorite (NaOCl) activated by ultrasound and 0.2% chlorhexidine (CHX), the root canals were dried with paper points. A light coating of AH Plus sealer (AH Plus, Detrey, Konstanz, Germany) was then applied to the root canal. The canals were filled to a depth 1 mm short of the apical foramen using either cold lateral condensation (Table
Apical dye leakage penetration after simulated diving up to 5.0 bar for different root filling techniques.
Group | Mean [mm] | SEM | |
---|---|---|---|
Cold lateral condensation |
|
2.36 | 3.23 |
Carrier-based gutta-percha obturation |
|
1.32 | 1.39 |
Carrier-based Resilon obturation |
|
8.05 | 3.85 |
Downpack/backfill (Gutta-percha) |
|
1.29 | 0.65 |
Ten teeth of each group underwent intrapulpal pressure measurement and the other ten teeth a dye penetration test during simulated dives to an external pressure of 5.0 bar. Pressure differences in the pulp cavity and dye penetration depths from the apex were measured.
For pressure measurement the manometer at the diving chamber and the pressure sensor were calibrated against each other prior to the first measurement. The pressure inside the chamber was directly read from the manometer at the chamber. The pressure within the pulp cavity was measured at a frequency of 0.5 Hz using computer software (Measure Foundry Version 4.0, Data Translation, Inc., Marlboro, United States).
The difference between the pressure in the chamber and the pressure in the pulp cavity was calculated at predefined time points for every 0.5 bar using the formula
The simulated dives were performed in a specially equipped diving chamber (Haux, Draegerwerk, Luebeck, Germany) using compressed air. Inlet valves allowed us to variably adjust the pressure increase inside the chamber. A manometer indicated the pressure in the chamber.
For the measurement of pressure inside the pulp cavity, a circular hole with a diameter of 6.0 mm was drilled from the crown through the enamel and dentine to the pulp chamber using a diamond burr (S-5 mm, Saint-Gobain, Norderstedt, Germany) with constant water cooling. A pressure sensor (4005BA5, Kistler, Ostfildern, Germany) was inserted into the cavity and the measuring sensor was placed in the roof of the pulp cavity. The gap between the tooth and the threads of the pressure sensor was then tightly sealed using an acid etch technique and a low-viscosity dental composite. Finally, impression material (KNET NF, Pluradent, Offenbach, Germany) was used to fix the tooth in such a way that the entire surface of the root was covered with a 0.5-mm-thick layer of water from the root apex to the neck of the tooth.
In order to prepare the teeth for the dye penetration test with methylene blue, we applied two layers of white nail varnish to the teeth except for the apical 2 mm, which remained exposed. The teeth were inserted into a plastic container filled with 2% methylene blue in such a way that they were completely covered with dye. The container was then placed into the experimental pressure chamber.
A dive was simulated and consisted of a descent to 5.0 bar in 2.5 minutes. The pressure was maintained for two hours and the subsequent return to ambient pressure was undertaken again over a period of 2.5 minutes.
The teeth were cleaned under running water. Residual dye was removed and a scaler was used to remove nail varnish. After the teeth were decalcified and made transparent according to a standard procedure, the depth of penetration was measured from four sides under a microscope at 20x magnification. The measured values were averaged.
The normal distribution and homogeneity of variance were assessed. Results are expressed as means ± SEM. Differences between pressure chamber and pulp cavity pressure were evaluated with a one-way analysis of variance (ANOVA). A
Intrapulpal pressure measurements revealed considerable differences both between and within the various groups of teeth in the ability of the root fillings to achieve a hermetic seal.
When the cold lateral condensation technique was used, pressure in the chamber and pressure inside the pulp cavity were completely equalized in two teeth. A minor intrapulpal pressure increase was observed in five teeth. No pressure equalization occurred in the three remaining teeth.
When the warm carrier-based gutta-percha obturation technique was used, a minor intrapulpal pressure increase by not more than 0.2 bar was observed in only one tooth. Equalization of pressure did not occur in any of these teeth at 5.0 bar chamber pressure.
By contrast, almost complete pressure equalization took place in half of the teeth when the carrier-based Resilon obturation technique was used. Minor pressure increases ranging between 0.3 and 0.7 bar were observed in the other teeth of this group.
When root canals were filled with warm vertical gutta-percha (Downpack/backfill), there was no significant change in intrapulpal pressure in response to an increase in external pressure.
The cold lateral condensation technique showed moderate dye penetration from the apex.
When the warm carrier-based gutta-percha obturation technique was used only minor dye penetration was observed. By contrast, significantly deeper dye penetration was observed for the warm carrier-based Resilon obturation technique. Half of the examined teeth showed total dye penetration in the entire root canal system. The warm vertical and warm carrier-based gutta-percha obturation techniques showed the least dye penetration.
The obturation techniques that we studied in vitro showed significant differences in their ability to hermetically seal the root canal system. A safe hermetic seal was achieved only by warm carrier-based gutta-percha obturation technique and warm vertical gutta-percha compaction.
The quality of root fillings can be evaluated with a variety of methods such as microscopic evaluations, cross-sections, fluid transport tests, and dye penetration tests. In the study presented here, we used methylene blue in order to study marginal infiltration and to facilitate the comparison of our results with other studies. In addition, we used transparent teeth rather than cross-sections in order to be able to evaluate the teeth without further manipulation. Although a dye penetration test is a widely used and convenient technique for assessing leakage in vitro, it is still unclear whether the results reflect microbial leakage in vivo [
Furthermore, we used a piezo-sensor to measure intrapulpal pressure. This method allowed us to assess the hermetic sealing of root fillings and to assess the effectiveness of the seal at changing external pressure levels. We were thus able to control external pressure and internal pulp cavity pressure changes. In our tests, we increased pressure by 2.0 bar per minute in order to simulate an ascent without decompression stops. This method of pressure measurement, however, allowed us to assess the hermetic sealing of the entire root canal system but not to localize possible sites of permeability. These sites require additional tests such as a dye penetration test.
Simulated root canals in plastic blocks or extracted natural teeth have proved to be useful in systematically examining root fillings in vitro. In this context, natural teeth are superior to plastic blocks since they better reflect the dentin surface and the resulting mechanical properties at the interface between dentin and root filling material. Depending on the configuration of the root canal, natural teeth differ widely in the anatomy of the root canal system. In addition, root curvature plays an especially important role in the preparation and obturation of the root canal system. In our study, we therefore used only single-root extracted teeth with a root canal curvature of less than 20 degrees in order to facilitate comparability.
The root canals were prepared with nickel-titanium (Ni-Ti) files since these instruments can produce canals that are more uniform, better centered, and rounder than those created by hand files. In addition, we finally used ultrasonic irrigation to remove debris and the smear layer and thus to increase the adaptation of the fillings to the root canal walls [
One of the main objectives of root canal treatment is to completely seal the root canal system and thus to prevent bacterial recontamination. For this purpose, sealers should be used in order to achieve as effective a seal as possible [
A variety of systems are available for obturating root canals [
When the root canals were filled with Resilon, pressure in the chamber and pressure in the pulp cavity were completely equalized in half of the teeth. Since a warm carrier-based technique was used to insert Resilon, inhomogeneity of the root canal filling, which can be observed after cold lateral condensation, is improbable. It is more likely that there was no hermetic seal between filling and canal wall. For this reason, it appears doubtful that a pressure-tight seal can be achieved when the combination of AH Plus and Resilon is used. This is supported by the results published by Onay et al. and Pasqualini et al., who reported that the combination of Resilon and AH Plus exhibited greater leakage than a combination of sealer and gutta-percha [
By contrast, obturation with warm gutta-percha showed better results in both the pressure measurements and the dye penetration tests irrespective of the method of application. When the warm carrier-based gutta-percha obturation technique was used, a minor intrapulpal pressure increase of no more than 0.2 bar was observed. When warm vertical compaction was used, there was no pressure increase at all. In the dye penetration test, warm vertical compaction showed results similar to those obtained for the warm carrier-based obturation technique with less variance. These findings are in line with the results by Lea et al., who reported that warm gutta-percha obturation techniques achieved a better seal than cold lateral compaction [
In conclusion, warm gutta-percha obturation techniques should be preferred to cold lateral condensation or warm carrier-based Resilon obturation techniques in the endodontic treatment of patients such as professional divers or parachutists who are often exposed to changes in atmospheric pressure.
The study has been approved by the local ethical committee.
There are no commercial conflict of interests and relationship of each author in connection with the submitted paper.