Introduction
Rootcanal obturation involves the three-dimensional filling of the entire rootcanal system and is a critical step in endodontic therapy. There are twopurposes to obturation: the elimination of all avenues of leakage from the oralcavity or the periradicular tissues into the root canal system; and the sealingwithin the root canal system of any irritants that remain after appropriateshaping and cleaning of the canals, thereby isolating these irritants. Pulpaldemise and subsequent periradicular infection result from the presence ofmicroorganisms, microbial toxins and metabolites, and the products of pulptissue degradation. Failure to eliminate these etiologic factors and to preventfurther irritation as a result of continued contamination of the root canalsystem are the prime reasons for failure of nonsurgical and surgical root canaltherapy.
Theimportance of three-dimensional obturation of the root canal system cannot beoverstated, with the ability to achieve this goal primarily dependent on thequality of canal cleaning and shaping as well as clinical skill. Other factorsthat influence the ultimate success or failure of each case include thematerials used and how they are used. The ultimate coronal restoration of thetooth following canal obturation may loom as the most important goal, for thereis reasonable evidence thatcoronal leakage through improperlyplaced restorations after rootcanal treatment andfailure of the restorativetreatment or lack of health of thesupporting periodontium are thefinal determinants of successor failure in treatment.
Factors influencingcomplete obturation
- Quality ofthe cleaning and shaping of the canal system
- Skill andexperience of the clinician
- Materialsand their usage
- Restorationof the tooth
- Health ofthe supporting periodontium
Characteristics ofan Ideal Root Canal Filling
Anideal root canal filling three-dimensionally fills the entire root canal systemas close to the cemento-dentinal junction as possible. Minimal amounts of rootcanal sealers, most of which have been shown to be biocompatible or toleratedby the tissues in their set state, are used in conjunction with the corefilling material to establish an adequate seal. Radiographically, the rootcanal filling should have the appearance of a dense, three-dimensional fillingthat extends as close as possible to the cemento-dentinal junction. Thesestandards should serve as the benchmark for all clinicians performing rootcanal therapy, and it is only through a knowledgeable approach to root canaltreatment that quality assurance can be continually demonstrated in theobturation of root canal systems.
The ideal rootcanal filling
3-D filling ofthe entire root canal space as close as possible to the cemento-dentinaljunction
Radiographicallydense fill with absence of voids
Shape reflecting acontinuously tapered funnel that is approximately the same as the external rootmorphology
While a plethora ofmaterials has been advocated over the last 150 years for root canal obturation,historically, gutta-percha has proven to be the material of choice forsuccessful filling of root canals from their coronal to apical extent. Althoughit is not the ideal filling material, gutta-percha has satisfied the majorityof criteria for an ideal root filling material. The disadvantages ofgutta-percha – specifically, its adhesiveness, lack of rigidity, and ease ofdisplacement under pressure – do not overshadow its advantages. In light of itsshortcomings, a sealer/cement is always used with gutta-percha. However, regardlessof the delivery system or technique used, neither gutta-percha nor sealer/cementalone enables standard-ofcare canal obturation. In addition, the availablematerials and techniques do not routinely provide for an impervious seal of thecanal system; all canals leak to a greater or lesser extent.
It is recommended thatclinicians master multiple obturation techniques and become competent withvarious root canal sealers/cements, to be able to manage the diversity ofanatomical scenarios that may be encountered.
ContemporarySealers/Cements
The use of a sealerduring root canal obturation is essential for success. Not only does it enhancethe possible attainment of an impervious seal, it also serves as a filler forcanal irregularities and minor discrepancies between the root canal wall andcore filling material. Sealers are often expressed through lateral or accessorycanals and can assist in microbial control should there be microorganisms lefton the root canal walls or in the tubules.Sealers can also serve as lubricants,enabling thorough seating of the core filling material during compaction. Incanals in which the smear layer has been removed, many sealers demonstrateincreased adhesive properties to dentin in addition to flowing into the patenttubules. A good sealer should be biocompatibleand well tolerated by the periradicular tissues, and although all sealers exhibittoxicity when freshly mixed, their toxicity is greatly reduced on setting andall are absorbable when exposed to tissues and tissue fluids. Subsequent tissuehealing or repair generally appears unaffected by most sealers, provided thereare no adverse breakdown products of the sealer over time. In particular, thebreakdown products may have an adverse action on the proliferative capabilityof periradicular cell populations. Some clinicians consider that a small puffof root canal filler extending beyond the working length is indicative of a fullyobturated canal space with a well-sealed apical constriction. Excessive sealershould not be routinely placed in the periradicular tissues as part of an obturationtechnique.
Sealers/cements can begrouped based on their prime constituent or structure, such as zincoxide-eugenol, polyketone, epoxy, calcium hydroxide, silicone, resin, glassionomer, or resin-modified glass ionomer. However, many of the sealers/ cementsare combinations of components, such as zinc oxideeugenol and calciumhydroxide,43 with the addition ofcalcium hydroxide claimed to create a therapeutic material that can beinductive of hard tissue formation.Epoxy-based and methacrylate-based resinsealers that can be bonded to the root canal dentin (but not to gutta-percha)are also now available.
Sealers should bemixed to a creamy consistency, allowing them to adhere to the master cone andnot ball up at the shaft of the cone, leaving the gutta-percha exposed. Thesealer should adhere to the cone evenly along its length and at the end of the cone.Clinicians should read the product insert and material safety data sheet foreach product chosen before using it.
Contemporary CoreFilling Materials
Gutta-percha is thestandard material of choice as a solid core filling material for canalobturation. It demonstrates minimal toxicity and minimal tissue irritability,is the least allergenic material available when retained within the canal system,andin cases of inadvertent gutta-percha cone overextension into the periradiculartissues, is well tolerated provided the canal is clean and sealed. Chemicalsolvents have been used for almost 100 years to soften gutta-percha, with methodsranging from merely dipping the gutta-percha cones into the solvent for onesecond for better canal adaptation, to creating a completely softened paste ofgutta-percha with the solvent. Solvents used have included chloroform,halothane, rectified white turpentine, and eucalyptol. Periradicular tissuesmay be irritated if the solvent is expressed beyond the canal or significantamounts of softened gutta-percha are inadvertently placed into theperiradicular tissues. Failure to allow for dissipation of chemical solvents,if volatile, or the removal of excess solvent with alcohol can result insignificant shrinkage and possible loss of the apical seal. The use of chemicalsolvents has been both praised and questioned, but with the advent of thermoplasticizedgutta-percha, the need to consider the use of solvents at any time must bequestioned. The use of solvents, however, may still be considered for a numberof challenges the clinician may face in daily practice, such as the customfitting of master cones in irregular apical preparations or followingapexification.
Gutta-percha Cones
The composition ofgutta-percha cones is approximately 19% to 22% Balata and 59% to 75% zincoxide, with the remainder a combination of various waxes, coloring agents, antioxidants,and metallic salts.58 Thespecific percentages for components varies by manufacturer, with resultingvariations in the brittleness, stiffness, tensile strength, and radiopacity ofthe individual cones attributable primarily to the percentages of gutta-perchaand zinc oxide. The antimicrobial activity of gutta-percha is also primarilydue to the zinc oxide.
The cones aremanufactured in both standardized and nonstandardized sizes. The standardizedsizes coordinate with the ISO root canal files sizes 15 through 140 and areused primarily as the main core material for obturation. They generally have a2% taper, but can have a 4 or 6% taper or more. The non-standardized sizes aremore tapered from the tip or point to the top. With some obturation techniques thesecones have been used primarily as accessory or auxiliary cones duringcompaction, being matched with the shape of the prepared canal space or thecompaction instrument.
Non-standardized conesbegan to assume a greater role as the primary core material in the morecontemporary obturation techniques, and with the development of morepredictable shapes with current nickel titanium (NiTi) rotary and hand instruments,cones tapered from 4% to 10% have gained use.
Tapered gutta-perchacones
In particular, fortechniques that use vertical compaction of heat-softened gutta-percha, both thenon-standardized and more tapered cones have become quite acceptable. Custom conescan also be developed for canals with irregular or large apical anatomy, Over time,numerous methods have been advocated for obturating the prepared root canalsystem, each with their own claims of ease, efficiency, or superiority. Most contemporarytechniques still rely on gutta-percha and sealer to achieve their goal. Fourbasic techniques exist for the obturation of the root canal system withgutta-percha and sealer
(1) the coldcompaction of gutta-percha; (2) the compaction of heat-softened gutta-perchawith cold instruments
Cold compaction carrier Heated compaction Presoftened core
until it has cooled;(3) the compaction of gutta-percha that has been thermoplasticized, injectedinto the system, and compacted with cold instruments; and (4) the compaction ofgutta-percha that has been placed in the canal and softened through thecontinuous wave technique (Calamus). A multitude of variations on these fourbasic themes exists. For injectable thermoplastic obturation techniques,gutta-percha may come in either pellet forms or in cannulae.
Cold compactioncarrier Heated compaction Presoftened core
No single techniquehas proven to have statistically significant superiority when considering both in vitro and invivo studies, as the successof all techniques is highly dependent on the cleaning and shaping of the canalsand the clinician’s expertise in the use of a particular technique.While manyhave advocated the use of the lateral compaction technique or a single conefill (monocone) to achieve a quality apical seal, the technique in itself doesnot necessarily favor the filling of canal irregularities.63 Recognizing this, use of a softenedgutta-percha technique with heat or chemical softening is required to achieve athorough obturation.
In addition, whilefilling the entire root canal system is the major goal of canal obturation, amajor controversy exists as to what constitutes the apical termination of theroot canal filling material. Working length determination guidelines often citethe cemento-dentinal junction or apical constriction as the ideal position forterminating canal cleaning and shaping procedures and placing the fillingmaterial. However, the cemento-dentinal junction is a histologic and not aclinical position in the root canal system and, in addition, the cemento-dentinal junction is not always the mostconstricted portion of the canal (yellow arrows) in the apical portion of theroot
Contemporary practicesof obturation favor material softening even this does not guarantee that animpervious seal of the root canal system will be established. Also, withsoftened gutta-percha obturation techniques there has been a greater incidenceof material extrusion beyond the confines of the canal. While softening ofgutta-percha may be viewed as routinely desirable, the selective use of thistechnique solely or in combination with a solid core of gutta-percha must be atthe discretion of the competent clinician when anatomy dictates this approach.
Apical constriction ofroot canal
Recent researchconducted at Nova Southeast University using micro CT scanning technology hasshown the effectiveness of scanning for imagery and the greater precision observedcompared to standard radiographs. In one example, a mesiobuccal canal wasfilled using GT® Series X™ obturator andthe mesiolingual canal was filled using a single cone technique (ActiV GP). Itappeared from one angle that all canals were equally filled.
Radiograph of filledcanals
However, closerexamination subsequent to filling showed voids using the single cone techniquethroughout the length of the root filled using this technique. The single conetechnique did not produce a monoblock obturation. The gutta-percha from the GTobturator flowed into the canal isthmus and filled it.
Voids using single cone technique
Cross-section withActiV GP and GT Series X obturation
Activ V GP GT Series X obturator
Canal isthmus filledwith GT obturator gutta-percha
Differences in obturationtechniques and results are also more observable using CT scanning than usingtraditional radiographs.Contemporary techniques include the use of bonded rootcanal filling materials. Recent developments in resin-bonding have led to theavailability of resin cones and pellets similar in shape and size togutta-percha materials.
Resin-based conescontaining methacrylate resin, fillers, bioactive glass, and polymers areavailable that can be handled similarly to gutta-percha and can be used with alateral or vertical compaction technique. Resin-based materials can also bedelivered via a heated syringe (Obtura gun, Spartan Obtura). Since resin-basedmaterials require a slightly moist environment, it is important to avoid usingany dessicating solutions, such as alcohol, during root canal preparation. Further,if sodium hypochlorite or peroxide was used during root canal preparation, thismust be thoroughly removed prior to using a resin-based material as it wouldreduce the ability of the resin material to bond. Similarly, the smear layermust also be thoroughly removed.
PrefabricatedObturators
Gutta-percha can alsobe formed on a plastic carrier or corecarrier. Prefabricated obturators werefirst described in 1978 by William Ben Johnson.79 The prototype for the obturator had beenprenotched K-files wrapped in gutta-percha (hand formed) that were then heatedover a flame until the surface glistened and expanded. These prenotched“obturators” were inserted into the canal and apical pressure applied while thehandle was twisted off.
Prototype obturator
Prefabricatedobturators were introduced in 1988 (Thermafil) using first a stainless steeland subsequently a titanium core, coated with gutta-percha. Plastic obturatorswere first offered in 1992. Since then, a number of prefabricated obturator systemshave been introduced, including one that does not involve thermosoftening ofthe gutta-percha (SimpliFil, Discus Dental) but instead is used cold with onlythe apical area coated in gutta-percha, and after placement the carrier itselfis removed.
A recently developedprefabricated obturator utilizes a resin-based system (RealSeal One, SybronEndo) and is used with, and bonded to, methacrylate resin-based sealer materialand is first held in its custom oven and thermosoftened. Other systems usethermosoftened gutta-percha, including Calamus® (Tulsa Dental, Dentsply) , Successfil®(Hygienic-Coltene-Whaledent, Inc.), Gutta- Flow®, System B Obturation System, Thermafil, Thermafil Plus, ProTaper® Universal and ProSystem GT® Obturators (Dentsply, Tulsa Dental), andSoft-Core® (Soft-Core® Texas, Inc.).
Current plasticobturators are available in a nonvented shape with a taper of around 0.04(Densfil) and a vented shape with the same taper (Thermafil Plus). Both arebiologically inert. Thecarrier is thick with a thinner outer coating of gutta-percha, which helps toreduce material shrinkage as the gutta-percha cools in the canal. A vented prefabricatedobturator helps the flow of gutta-percha during placement and also aids inretrieval of the obturator should retreatment be necessary.
For sizes 40 and belowin the Thermafil series, an insoluble liquid crystal plastic is used. For size45 and above soluble polysulfone polymer is used. All of these use a sizeverifier to help select the correct size obturator, as do ProTaper Universal carriers,which start at a .04 taper. Systems that do not use a size verifier include theProSystem GT carriers and GT Series X carriers, which are made in a variety oftapers between 0.04 and 0.12.
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