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Ten-month in vitro leakage study of a single-cone obturation system.

BACKGROUND AND LITERATURE REVIEW

Even before Kakehashi et al proved in their landmark 1965 germ-free rat study that bacterial contamination of the root canal system is the cause of apical periodontitis, (1) endodontists have sought the most effective means to seal the root canal space. Although successful endodontic therapy is a multifactorial process of bacterial elimination, the apical to coronal seal is well accepted as a key element of preventing reinfection and refractory disease. (2) Once pathogenic microorganisms have been reduced below a patient's threshold to cause disease, the goal is to 3-dimensionally fill and seal the complex root canal system. (3-5) However, the manner in which this goal is achieved has fueled a great deal of research and innovation.

Currently, there are many obturation systems available. For the purposes of this study, 3 obturation techniques are described: lateral compaction, continuous wave of condensation, and a less common single-cone technique. The first, lateral compaction, uses a master cone of gutta-percha supplemented by accessory cones. To this day, it is likely to be the first technique taught in dental school. (6) In 1967, Schilder described a warm vertical compaction technique that hydraulically pushes thermoplasticized gutta-percha into the most apical parts of the canal system with a series of custom fitted pluggers. (5) Another warm vertical compaction technique incorporates thermoplasticized gutta-percha dispensers and standardized master cones that precisely match the taper of nickel titanium rotary files and is known as the continuous wave of condensation technique. (7) Once mastered, this technique can reduce the time required to complete obturation and is the technique of choice of many practitioners today. (6) The third technique, the single-cone technique, has been used for years in various forms. In 1984, Cohen and Burns described a technique using a single, uncondensed but fitted gutta-percha master cone for obturation. (8) The appeal of the single-cone technique is simplicity and speed of obturation. (9)

Regardless of the technique implemented, the type and composition of sealer is a key component in achieving the goal of a sealed root canal system. Today, a popular epoxy resin based sealer, AH Plus (E/T Endodontic Technologies Ltd, Halifax, Nova Scotia, Canada), has performed well in in vitro leakage studies. (10-12) Recently, glass-ionomer-based sealers have been reintroduced because of their chemical bond to dental hard tissues, (13,14) fluoride release, antimicrobial activity and biocompatibility. (15) One such recently introduced glass-ionomer sealer is the Activ GP Precision Obturation System (Brasseler USA, Savannah, GA).

The Activ GP System combines a single-cone technique with a glass-ionomer-based sealer that the manufacturer claims will create a "monoblock" between the tooth, sealer, and core material. The term "monoblock" has been used in many of the methacrylate based obturation systems not examined here. Monoblock generally refers to a gap-free, solid mass of different materials that simultaneously improves the seal and fracture resistance of the filled canals. (16) The Activ GP System uses a gutta-percha master cone that has been coated and impregnated with glass ionomer particles. The rationale is the glass-ionomer-based sealer will bond to the dentinal walls of the canal as well as the glass ionomer particles in and on the master cone. The manufacturer recommends a heatless single-cone technique that relies on tapered cones that match prepared canals, as well as a glass-ionomer-based sealer to fill canal irregularities and seal the apical canal space. Unfortunately, single-cone techniques have not historically met the challenges of providing a 3-dimensionally filled and sealed root canal system. (17) The unfavorable geometry of the canal space (18) and a preponderance of sclerotic radicular dentin in the canal's apical third (19) prevents a true, gap-free seal as suggested by the monoblock moniker used in many advertisements.

The purpose of this study is to compare the newly introduced Activ GP obturation system to the continuous wave of condensation technique with a resin based sealer over a 10-month period.

MATERIALS AND METHODS

All procedures were completed by one investigator.

Fifty extracted, single-canal, human anterior teeth with at least 15 mm of root length were collected and stored in 0.9% saline. Calculus and soft tissue remnants were removed by mechanical means. All teeth were examined for cracks or fractures, as well as to confirm a single apical foramen using transillumination (Microlux Transilluminator, Adent Inc, Danbury, CT) and a dental operating microscope (Global Surgical Corporation, St Louis, MO). Teeth with canal curvatures greater than 10[degrees] or canal patency greater than an International Standards Organization (ISO) size 15 K-type file (Henry Schein Inc, Melville, NY) were discarded.

The crowns were removed with a #557 carbide bur (Henry Schein, Melville, NY), leaving no less than 15 mm root sections. Working length was determined by subtracting 1.0 mm from the length that a 10 K type file was first visible at the apical foramen. All canals were hand filed to a 20 K type file using full-strength sodium hypochlorite (Clorox, Oakland, CA) as a lubricant. The 50 root canals were randomly divided into 2 experimental groups (n=20) and 2 control groups (n=5).

EXPERIMENTAL GROUP 1: CONTINUOUS WAVE OF CONDENSATION

Canal preparation was completed using a crown down technique with 0.04 tapered nickel-titanium rotary instruments to a size 40 rotary file. The root canals were irrigated with sodium hypochlorite using a 28gauge side port syringe (Max-i-Probe, Dentsply Rinn, Elgin, IL). Patency and apical stops were confirmed with a 10 K type file and a 40 K type file respectively. A final rinse of 5 ml of 17% ethylenediamine tetraacetic acid (Pulpdent Corp., Watertown, MA) was followed by 5 ml of sodium hypochlorite rinse. All canals were then dried using paper points (Henry Schein, Melville, NY).

An epoxy resin-based sealer, AH Plus, was mixed according to the manufacturer's instructions and applied to the root canal walls while placing a size 40/0.04 taper master gutta-percha cone (DiaISO GT .04; DiaDent, Burnaby, BC, Canada) to working length. Once seated, a 0.08 tapered System B heat source plugger (SybronEndo, Orange, CA) set at 200[degrees] C was introduced into the canal. The System B was activated and slowly pushed into the canal within 4 mm of working length. The plugger was then held in position for 10 seconds, reactivated for 1 second, and withdrawn. A 5/7 plugger (Hu-Friedy Mfg Inc, Chicago, IL) was immediately introduced into the canal to assure seating of the apical plug. The coronal canal walls were coated with the epoxy resin-based sealer and backfilled with warm gutta-percha from an Obtura II (Spartan, Fenton, MO) set at 185[degrees]C. The warm gutta-percha was immediately down-packed with a 5/7 plugger.

Since the obturated canals were to be stored for 10 months, the coronal 2 to 3 mm of gutta-percha was removed with the System B, sealed with a 2 to 3 mm amalgam restoration (Tytin amalgam, Kerr Corporation, Orange, CA), and stored in 100% relative humidity at 37[degrees]C for 10 months.

EXPERIMENTAL GROUP 2: SINGLE-CONE TECHNIQUE (ACTIV GP)

Experimental Group 2 was prepared the same as Group 1 in regards to working length, hand filing, and smear layer removal. The final canal preparation was completed using a crown down technique with 0.04 tapered nickel-titanium rotary instruments to a size 40 rotary file.

Per the manufacturer's recommendations, the Activ GP glass-ionomer sealer was mixed and placed in the canal with a clean 40 K type file using a circular motion to the working length. An Activ GP 0.04 taper gutta-percha master cone was coated with sealer and slowly inserted to working length, allowing the sealer to escape coronally. The coronal 2 to 3 mm of gutta-percha was removed with the System B, and the canal orifice was sealed with an amalgam and stored in 100% relative humidity at 37[degrees]C for 10 months.

EXPERIMENTAL GROUPS 3 AND 4: POSITIVE AND NEGATIVE CONTROLS

Five roots were treated the same as Group 1 with the exception that no sealer was used. These 5 roots served as the positive controls to test the maximum fluid flow through the fluid transport device. The last 5 roots were treated the same as Group 1 with the exception that the root surfaces were sealed with cyanoacrylate to act as the negative controls. All roots were sealed with amalgam and stored in 100% relative humidity at 37[degrees]C for 10 months.

LEAKAGE TESTS

Using a fluid transport model (Figure 1) as described by Maloney et al, (20) Koagel et al, (21) and Stratton et al, (22) Plexiglass blocks were penetrated by an 18-gauge stainless steel tube (SafetyGlide Needle, Franklin Lakes, NJ) so that 1.0 mm of tubing protruded from the root side of the Plexiglass. The 2.0 to 3.0 mm deep amalgam restorations were removed from each root with a 330 carbide bur. The roots were mounted with viscous cyanoacrylate cement to the Plexiglass blocks with the orifices located over the steel tubing. The negative controls were re-treated with cyanoacrylate prior to testing.

[FIGURE 1 OMITTED]

Each Plexiglass-root assembly (Figure 2) was attached to the fluid transport-measuring device. The fluid transport device used compressed nitrogen gas and a pressure pot to push a solution of 0.02% sodium azide at 10 psi through the stainless steel tube of the Plexiglass-root assembly and ultimately the root being tested. The fluid rates through the tested specimens were quantified by measuring the progress of a tiny air bubble as it traveled within the polyethylene tubing along a 150 mm Fisher Scientific ruler. Each specimen was tested 3 times for 3 minutes and the bubble's movement was recorded to the tenth of a millimeter. A Mann-Whitney Rank Sum test (SigmaStat 3.5, Point Richmond, CA) was calculated to determine the existence of a statistically significant difference between the two groups. Values of P<.05 were considered significant.

[FIGURE 2 OMITTED]

RESULTS

The leakage of the negative controls was uniformly zero and the leakage of the positive controls was immeasurably high. The leakage results of 14 of the 20 teeth (70%) in Group 2 (Activ GP) were immeasurably high using a fluid transport system with a 150 mm ruler. The 6 teeth that registered measurable levels in Group 2 (Activ GP) had a median leakage of 18.865 mm, and the median leakage for Group 1 (GP) was 0.500 mm.

A Mann-Whitney Rank Sum test indicated the differences in the median values is greater than would be expected by chance. The results showed a statistically significant difference between the test groups (P=<.001).

COMMENT

Although obturation techniques and materials continue to improve, the results of this study remind one that no current obturation technique or material can completely seal a complex root canal space. (23-25) The advantage of testing leakage with a fluid transport model is its unique ability to quantify leakage. Under the conditions of this study, the magnitude of difference between the two test groups is statistically significant.

The high leakage rates of the Activ GP obturation system may be due to the potential for gapping along the sealer/dentin interface. (26) Additionally, the contribution of glass ionomer's adhesive properties in the apical third of a canal has been theorized but not demonstrated in the literature.21-30 Also, some researchers have expressed concern over glassionomer cement/sealer's propensity for disintegration and leakage. (31,32)

In vitro studies of another glass-ionomer sealer, Ketac-Endo (3M/ESPE, Minneapolis, MN), found lower leakage rates than traditional zinc oxide-eugenol sealers. (25,33,34) However, this is not conclusive and some studies have found more leakage with glass-ionomer-based sealers. (10,35) An English-language literature search for glass-ionomer sealer studies failed to reveal any studies for a period greater than 90 days. It appears that time may be correlated to the Activ GP obturation system's high leakage rates and the concern for disintegration of glass-ionomer-based sealers merits further research.

One consistent finding of fluid transport model studies is that sealers have lower leakage rates when the sealer is the thinnest. (36) A single-cone technique is often considered inferior to continuous wave of condensation because the volume of sealer is high relative to the volume of the cone. (37) The Activ GP obturation system is no exception, especially when ovoid shaped canals are obturated. The imbalance in sealer-to-cone ratio promotes void formation and likely reduces the quality of the seal. (38) Currently, the goal is to maximize the amount of solid core material and minimize the amount of sealer (39) to best seal the root canal system, entomb remaining bacteria and fill irregularities of the prepared canal. (40)

Under the conditions of this study, the incorporation of glass ionomer in the sealer and master cone of the Activ GP obturation system does not appear to solve the historically poor in vitro leakage rates often associated with single-cone techniques. However, any correlation between fluid transport leakage rates and bacterial leakage is currently unknown. (33)

CONCLUSION

Within the parameters of this study, a complete seal did not occur for any test group. Using a fluid transport system, the Activ GP glass-ionomer-based single-cone obturation technique demonstrated significantly higher leakage rates than a continuous wave of condensation and gutta-percha technique (P=<.001).

[ILLUSTRATION OMITTED]

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LTC A. John McKissock, DC, USA

COL Pete Mines, DC, USA

COL Mark B. Sweet, DC, USA

Col Steven L. Klyn, DC, USAF

LTC McKissock is Chief, Endodontic Services, US Army Dental Activity, and Officer in Charge, Smith Dental Clinic, Fort Carson, Colorado.

COL Mines is Chief, Endodontic Services, US Army Dental Activity, and Officer in Charge, Rohde Dental Clinic, Fort Bragg, North Carolina.

COL Sweet is Commander, Vicenza Dental Clinic Command, US Army Garrison, Vicenza, Italy.

Col Klyn is Chief of Endodontics, 10th Dental Squadron, United States Air Force Academy, Colorado.
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Author:McKissock, A. John; Mines, Pete; Sweet, Mark B.; Klyn, Steven L.
Publication:U.S. Army Medical Department Journal
Article Type:Report
Geographic Code:1USA
Date:Jan 1, 2011
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