Scanning electron microscopic examination of root canal filling materials

A critical analysis of research methods and experimental models to study root canal fillings

Canal filling materials and techniques have been one of the most studied topics in Endodontics. A simple search using the mesh term "root canal filling" in PubMed revealed more than 11,000 articles, an impressive number that is much higher than "root canal disinfection" (5,544 articles) or even the popular "root canal preparation" (8,527 articles). The overriding importance attributed to root filling procedures is not merely intuitive. It derived from the appealing relevance given by the appearance of the white lines in common radiographs grounded on retrospective clinical data that had identified the quality of a root filling as one of the major causes of treatment failure (lack of healing). Since the publication of the Washington study, impressive efforts have been made for the release of new materials and techniques, as well as, for the development of a plethora of laboratory methods to assess the quality of root filling procedures. This narrative review aims to address and discuss the most relevant laboratory methods to assess the root canal filling. Since filling quality improvements have not translated into higher success rates, as reported in longitudinal clinical studies, more than to deliver a simple methodology-based review, this paper aims to present an in-depth critical view on the assessment of laboratory methods used to study the filling materials and techniques. Recent data indicate that the long-term dimensional stability/degradation over time of endodontic sealers plays a central role in the treatment outcome. In this context, laboratory methods should be developed focusing on predicting, at least to some degree, the long-term clinical behaviour of root canal fillings, rather than simply ranking different materials or techniques.

Comparative evaluation of a novel smart-seal obturating system and its homogeneity of using cone beam computed tomography: In vitro simulated lateral canal study

Aim:

The aim was to evaluate and compare a novel polyamide polymer based obturating system and Gutta-percha and sealer in filling simulated lateral canals and their homogeneity when used for obturating the root canals.

Materials and Methods:

A total of 60 freshly extracted human single rooted teeth with fully formed apices were selected for this study. Teeth were de-coronated, and roots were standardized to a working length of 15 mm. Root canal preparation was carried out with rotary Protaper file system in all groups. The specimens were then randomly divided into three groups A, B, and C (n = 20). Ten samples from each group were decalcified and simulated lateral canals were made at 2, 4, and 6 mm from the root apex. Remaining ten samples from each group were maintained calcified. Group A was obturated with SmartSeal system (Prosmart-DRFP Ltd., Stamford, UK). Group B was obturated with sectional backfill method. Group C was obutrated with cold lateral compaction method (control). Decalcified samples from the respective groups were analyzed with digital radiography and photography and the measurement of the linear extension and area of lateral canal filling was done using UTHSCSA (UTHSCSA Image Tool for Windows version 3.0, San Antonio, TX, USA) software. Calcified samples were subjected to cone beam computed tomography image analysis sectioned axially.

Results:

Group A 92.46 ± 19.45 showed greatest extent of filling in lateral canals and denser homogeneity of oburation, followed by Group B 78.43 ± 26.45 and Group C 52.12 ± 36.67.

Conclusions:

Polyamide polymer obturation proved to have greater efficiency when compared with Gutta-percha system, when used for obturation with regards to adaptation of the sealer and penetration into the simulated lateral canals.

Comparison of laterally condensed, vertically compacted thermoplasticized, cold free-flow GP obturations - A volumetric analysis using spiral CT

AIM/OBJECTIVE

To compare the laterally condensed gutta-percha, vertically compacted thermoplastized gutta-percha (E and Q Plus system) and cold free-flow gutta-percha (GuttaFlow). This is a volumetric analysis using spiral CT, an in vitro study.

MATERIALS AND METHODS

Access cavities were prepared in 60 single rooted anterior teeth; cleaning and shaping was done and obturated with three of the different techniques: group A: cold lateral; group B: vertically compacted thermoplasticized and group C: cold free-flow obturation techniques. Volume analysis was done using spiral computed tomography (CT). The percentage difference was calculated and statistically analyzed using one-way ANOVA and post hoc multiple comparison Tukey HSD tests.

RESULTS

There were statistical significant differences between group A (0.183cm(3)) and group B (0.136cm(3)); group A (0.183cm(3)) and group C (0.128cm(3)). But there was no statistical significance between group B (0.136cm(3)) and group C (0.128cm(3)).

CONCLUSION

Within the limitations of this in vitro study it can be concluded that cold free-flow obturation technique showed the highest volume of obturation, followed by the vertically condensed thermoplasticized technique. The least volume of obturation was observed in cold lateral condensation technique.

Comparison of the obturation density of cold lateral compaction versus warm vertical compaction using the continuous wave of condensation technique

The purpose of this in vitro study was to compare quantitatively the density of standard cold lateral gutta-percha compaction and warm vertical compaction by using the continuous wave of condensation technique. Forty transparent acrylic blocks with 30-degree, curved root canals were instrumented using Gates Glidden burs and Profile 0.06 taper rotary nickel-titanium files in a crown-down manner. The blocks were weighed and randomly assigned to two evenly distributed groups. Group A was obturated with the cold lateral-compaction technique using medium-fine, gutta-percha accessory points until the canal was completely filled. Group B was obturated with the continuous wave of condensation technique until the canal was completely filled. The blocks were weighed again after obturation. Data were analyzed using a two-sample t test at the 5% significance level. Results demonstrated that the continuous wave of condensation technique resulted in a significantly greater density compared with cold lateral compaction. Warm vertical compaction using the continuous wave of condensation technique in acrylic blocks resulted in a greater gutta-percha fill by weight compared with standard cold lateral compaction.

A comparison of fill density obtained by supplementing cold lateral condensation with ultrasonic condensation

The purpose of this study was to compare quantitatively the density of gutta-percha root canal fillings produced by cold lateral condensation with those produced by an ultrasonically energized spreader in a warm lateral condensation technique in artificial root canals. Thirty-degree simulated root canals in 30 transparent acrylic blocks were instrumented by using rotary files. The blocks were weighed. The canals were obturated with gutta-percha using cold lateral condensation without sealer and then weighed again. Two applications of warm lateral condensation were then performed on the same 30 canals using the UES. The blocks were weighed once more after each additional UES obturation treatment. The first heat application produced a 26.92% increase in weight over lateral condensation, and the second heat application produced an additional 5.95% increase. A one-way repeated measures ANOVA followed by the Tukey-Kramer test revealed that both applications of warm lateral condensation produced significant (p < 0.001) increases in weight. Results indicate that warm lateral condensation using a ultrasonically energized spreader results in denser gutta-percha fills by weight than cold lateral condensation.

Increased density of gutta-percha using a controlled heat instrument with lateral condensation

The purpose of this study was to compare quantitatively the density of standard cold lateral gutta-percha condensation and warm lateral gutta-percha condensation using the System B heating instrument in a low-heat warm lateral condensation technique in an artificial root canal in vitro. Thirty-degree simulated root canals in 30 transparent acrylic blocks were instrumented using Gates-Glidden burs and Quantec (NT Company, Chattanooga, TN) rotary files. The canals were then obturated with gutta-percha using standard cold lateral condensation without sealer. Warm lateral condensation without sealer using the System B instrument at 101 degrees C was then performed on the same 30 canals. A second treatment of warm lateral condensation was then applied to these same canals. The blocks were weighed after the initial canal preparation and after each obturation treatment. Results showed warm lateral condensation of gutta-percha using the System B resulted in a significant increase in density by weight when compared with standard cold lateral condensation. A 23.97% increase in weight was realized after the first heat application, compared with standard lateral condensation. A second heat application produced an additional 2.59% increase in weight over that produced by the first heat application. Data were analyzed using a t test for repeated measures. Both increases were statistically significant (p < 0.001). Warm lateral condensation using the System B instrument results in denser gutta-percha fills by weight when compared with standard cold lateral condensation.

The effect of root canal preparation on microleakage within endodontically treated teeth: an in vitro study

AIM

The purpose of this study was to evaluate the effects of smear layer and canal instrumentation on leakage in root-filled teeth.

METHODOLOGY

Six groups (n = 12) of freshly extracted human canines and premolars with closed apices and single roots were used. Groups A, B, C, and D were instrumented with engine-driven rotary nickel-titanium MCXIM files and Groups E and F were instrumented with conventional stainless steel hand files. Groups A, C, and E were flushed with 3.0 mL of 17.0% REDTA to remove the smear layer prior to obturation. All teeth were flushed with 5.25% NaOCl, then obturated with AH-26 sealer and either the lateral condensation (Groups C-E) or thermomechanical compaction technique (Groups A and B). Copper wire was placed coronally in contact with the gutta-percha in each tooth and, after immersion in 0.9% NaCl solution, a 10 volt dc voltage was connected between each tooth and a stainless steel electrode. The current flow in the circuit was observed for 45 days. One way ANOVA and Duncan's Multiple Range Test were used to compare Groups A-F at time intervals of 10, 20, 30 and 45 days and identify statistically significant differences.

RESULTS

Significantly less microleakage occurred when the smear layer was removed and when the canals were obturated with thermoplasticized gutta-percha. Canals instrumented with engine-driven NiTi files exhibited less leakage than hand-instrumented canals irrespective of obturation method.

CONCLUSIONS

Smear layer removal is beneficial to root canal sealing. Obturation with thermoplasticized gutta-percha provides a superior seal whilst canal instrumentation with engine-driven NiTi files reduces the extent of microleakage in root canals.

Testing of sealing ability of endodontic filling materials

Incomplete obturation of the root canal system is the major cause of endodontic failure. Endodontic filling materials with ability to seal the root canal are, therefore, essential for successful endodontic therapy. However, assessment of sealing ability is not included in the requirements specified in the current international standard covering root canal sealers. A number of different in vitro methods have been used to evaluate the sealing quality of endodontic filling materials. The tests have usually been leakage tests, i.e. based on assessment of penetration of a tracer along the obturated root canal. Leakage tests have poor reproducibility and are, therefore, not suited for standardized test programs. By selecting the properties necessary for sealing ability and testing them separately, it might be possible to find a number of tests, which individually are suitable for a standardized test program, and which combined will give information on the sealing ability of the test material.

A critical reevaluation of stresses generated during vertical and lateral condensation of gutta-percha in the root canal

The finite element method was used to calculate the stresses in a maxillary canine tooth produced during lateral and vertical condensation. Description of the biological domain to be analyzed, and conversion of the manual operations of the endodontist to realistic load representation are intricate problems which must be overcome before stresses are recovered and plotted. The stresses in dentin are in general of comparable magnitudes during lateral or vertical condensation, but these magnitudes generally remain much below those presented in a previous study. From these calculations it appears that root fractures reported by some investigators may be explained in terms of stress concentrations and local irregularities of the samples tested.

Dentinal wall adaptation of thermoplasticized gutta-percha in the absence or presence of smear layer: a scanning electron microscopic study

The dentinal adaptation of injected thermoplasticized gutta-percha and thermoplasticized gutta-percha resulting from Ultrafil and Thermafil systems was evaluated by scanning electron microscopy and compared with adaptation obtained with the lateral condensation of gutta-percha. Each method was evaluated with and without the smear layer removed. Scanning electron microscopic observations showed the thermoplasticized gutta-percha resulting from either system to have better dentinal wall adaptation than lateral condensation of gutta-percha in either the absence or presence of the smear layer. In the absence of smear layer, the adaptation of gutta-percha was improved in all groups. Although sealer was used, removing the smear layer was found to enhance the ability of the thermoplasticized gutta-percha to enter the patent tubules.

Improved density of gutta-percha after warm lateral condensation

Simulated straight root canals in 30 transparent acrylic blocks were instrumented and obturated with gutta-percha without sealer using standard lateral condensation (group A). The "zap and tap" method of warm lateral condensation was then used on the same 30 canals (group B). A second treatment of warm lateral condensation was then applied to these same canals (group C). The acrylic blocks were weighed after initial canal preparation and after each subsequent obturation. A 14.63% increase in weight of the gutta-percha occurred in group B compared with group A, and a 2.43% increase in weight occurred in group C compared with group B. Both differences were statistically significant (p < 0.001).

A laboratory investigation of a composite resin/dentine bonding agent mixture used as a root canal sealer

The objective of this project was to determine the effectiveness of a dentine bonding agent, in conjunction with a composite resin, to act as an endodontic sealing material. The effectiveness was compared with that provided by a conventional sealer (AH26) by measuring dye penetration into the root canal. Two obturation techniques were used with each sealer; the single gutta-percha point technique, and lateral condensation with multiple gutta-percha points. Lateral condensation with the conventional sealer was found to be the superior procedure, by producing the least amount of linear leakage (coronally from the apex) on average. However, the single point technique with the composite resin/dentine bonding agent sealer provided the greatest number of 'no leakage' samples. Scanning electron microscope investigation of obturated roots revealed the presence of resin tags in dentine tubules only in those samples where the composite resin/dentine bonding agent sealer was used. The short working time provided by the composite resin/dentine bonding agent sealer prevented successful obturation using lateral condensation. The provision of an extended working time composition for this sealer may produce more favourable results in obturation with lateral condensation.

Photoelastic stress comparison of warm (Endotec) versus cold lateral condensation techniques

Stress generated during gutta-percha obturation of root canals can create microcracks and ultimately lead to failure. A new thermosoftening device, the Endotec, which develops a warm lateral condensation technique, was tested against the traditional lateral condensation procedure. The results indicated that the warm lateral condensation technique created less stress during obturation than did cold lateral condensation.

Effectiveness of a brush in removing postinstrumentation canal debris

The purpose of this study was to evaluate the effectiveness of a brush in removing debris in the root canal after endodontic instrumentation. Seventeen extracted human maxillary first molars with mesiobuccal canal curvatures of 25 to 35 degrees were divided into two groups. After endodontic access and determination of working length, one group was hand instrumented to a #45 file and the other group to a #35 file at the working length. After the teeth were sectioned at the working length and at 2, 4, and 6 mm from the working length, they were evaluated for debris remaining in the canal space. The specimens were reassembled, brushed with an Endobrush, and reevaluated. The scores for instrumentation alone (controls) and instrumentation plus brushing were compared with paired t tests. Instrumentation with brushing was significantly better than instrumentation alone in debriding the root canal.

An evaluation of sealing ability of calcium hydroxide sealers

Solid core filling material such as gutta-percha has been used to fill the root canal in conjunction with a sealer to prevent apical leakage. The purpose of this study was to compare apical seal of five different root canal sealers. Sixty roots of maxillary central incisors were cleansed and shaped and randomly assigned to one of six groups of ten roots each. The root canals were obturated with gutta-percha and one of the sealers by the lateral-vertical condensation technique. Groups I, II, III, IV, and V consisted of roots in which the canal was filled with gutta-percha along with either Roth's sealer, AH26, Sealapex, CRCS, or Nogenol sealer, respectively. Group VI was filled with gutta-percha and without sealer to serve as a control. The access opening was filled with amalgam. Each tooth was then placed in a capped vial containing 2 X 2 inch gauze pads saturated with distilled water, and the sealer was allowed to set at 37 degrees C in the humidor for 48 hours. The roots, except for the apical 2 mm, were coated with two layers of nail polish. The roots were stained with india ink, decalcified, dehydrated, and then placed in methylsalicylate to make them transparent. The leakage was measured with a filar micrometer eyepiece under a dissecting microscope. The mean apical leakage of six groups was as follows: I = 0.45 mm, II = 0.277 mm, III = 0.343 mm, IV = 0.263 mm, V = 0.336 mm, and VI = 2.310 mm. Results showed no significant difference in the apical seal produced by gutta-percha and the tested root canal sealers.(ABSTRACT TRUNCATED AT 250 WORDS)

Spectrophotometric analysis of microleakage in the fine curved canals found in the mesial roots of mandibular molars

Mesial roots from forty human mandibular first and second molar teeth were randomly assigned to two groups and obturated with laterally condensed gutta-percha or silver cones. Each group was divided into two subgroups. The first subgroup for each group consisted of specimens that had two canals with a common foramen. The second subgroup consisted of specimens with two canals and separate foramina. All specimens were obturated and exposed to 2 percent methylene blue dye at 37 degrees C. for a period of 30 days. A dye-recovery, spectrophotometric method was used to evaluate the apical microleakage. Results indicated no statistically significant difference in leakage between the groups or subgroups.

Microleakage of four root canal sealer cements as determined by an electrochemical technique

Eighty-eight teeth were used to determine the sealing quality of four root canal sealer cements--Kerr, Diaket, AH-26, and ProcoSol--via the vertical condensation of warm gutta-percha technique. In addition, limited studies were carried out to determine the sealing quality of injected Hydron and thermoplasticized gutta-percha. A comparison was also made between the lateral condensation of gutta-percha and vertical condensation of warm gutta-percha when Kerr sealer was used. Teeth filled with vertical condensation of warm gutta-percha and AH-26 sealer cement showed lower leakage in one experiment but higher leakage in another. Hydron showed the highest leakage of any material. Teeth filled via vertical condensation of warm gutta-percha and Diaket showed less leakage than the other groups. A statistically significant difference was also found between lateral condensation of gutta-percha and vertical condensation of warm gutta-percha using Kerr sealer cement.

Evaluation of the apical seal obtained with endodontic implant stabilizers and different cementing materials

Preliminary research was conducted to evaluate in vitro the apical seal obtained with endodontic implant stabilizers in conjunction with four different cement sealers. Standard laterally condensed gutta-percha cones and sealer were used as a control. Apical leakage was measured with the use of methylene blue dye solution. Gross leakage patterns resulted from endodontic implants cemented with both zinc phosphate and polycarboxylate. However, leakage appeared notably reduced when the implants were cemented with cyanoacrylate and Kerr Tubli-Seal. Statistical analysis showed that the lateral condensation of gutta-percha cones and sealer yielded the largest proportion of favorable results. Even so, none of the techniques employed was totally effective for obtaining a hermetic sealing of the root canal.

New chemotherapeutic agent for root canal treatment. A preliminary electron microscopic study on an in vivo and in vitro endodontically treated tooth

A preliminary in vivo and in vitro electron microscopic study of root canals treated endodontically with EDTA-C and Salvizol proved the latter to be superior as a chemomechanical and irrigation solution, especially in the apical third of the roots. A further virtue of Salvizol, as has been demonstrated, is its capability to dissolve the organic matrix of dentin, thus exposing the mineralizing front and the patent tubules even in the apical third of the canal. The combined properties of Salvizol which introduce it as a chemotherapeutic agent for endodontics are: (1) broad spectrum of bactericidal activity, (2) ability to dissolve calcium, (3) neutral pH, (4) cleansing potency, and (5) biologic compatibility.

Scanning electron microscopic examination of root after apicoectomy

The scanning electron microscope was used to examine resected areas of eight roots of human teeth extracted after long intervals following surgical procedures. Some resorption lacunae were observed in the areas with protuberances of newly formed cementum. In the lacunae, honeycomb-like structures were found. On the resected surface, residues of ligaments and periodontal fibers, and in one of the specimens dentinal tubules with odontoblastic processes protruding above the surface were present.

Effect of aging on the mechanical properties of hand-rolled gutta-percha endodontic cones

This study examined the effect of storage, for periods varying up to 24 weeks and at temperatures from -12 degrees C. to 50 degrees C., on the compression, tension, torsion, and bend properties of size 100 hand-rolled gutta-percha cones. All of the properties changed during storage, with the largest changes occurring at the highest temperatures, the smallest changes occurring at the lowest temperatures, and the greatest rate of change occurring during the initial 40- to 60-day storage period. All of the cones tested were subjectively found to be clinically usable. Since ideal characteristics or standards for mechanical properties are nonexistent, assessment of the changes is speculative and arbitrary. The condition of cones at which clinicians decide they are unusuable also varies widely. Continual study of this problem is indicated and important.

Silver points and gutta-percha and the role of root canal fillings

Both gutta-percha and silver points can be used as root canal fillings with a high success rate although it is unlikely that either produces a "hermetic" seal. In the cases cited here, the canals remained dry even though they were not obturated for a considerable length of time (in one instance, for two years); this indicates that tissue fluids did not accumulate in the canals. Moreover, my findings indicate that root canal fillings are not necessary for healing. These observations indicate the need for investigation of the validity of the current concept of the role of the root canal filling in treatment.