May 1, 2005
by Kenneth S. Serota, DDS, MMSc, Len Boksman, BSc, DDS and Gregg Tousignant, CDT
Numerous studies on endodontic treatment outcomes demonstrate a significant degree of predictable clinical success,1,2 however, cross-sectional, retrospective population studies have demonstrated “post-treatment disease” in 30 to 50 percent of cases.3 While recent studies have introduced significant predictors of outcome which may impact upon future treatment protocols, at present, continued sophistication of contemporary clinical treatments (debridement, disinfection and root filling) and/or materials are required.4-6
Adhesive technologies have innovated cosmetic and restorative dentistry, however, very little research has been dedicated to their application in endodontic procedures, particularly in the area of obturation of the root canal system.7 Obturation theoretically entombs residual microflora resident within morphologic canal vagueries. The ideal root filling material should seal the root canal space preventing re-infection from the oral cavity (coronal leakage) and from apical penetration of tissue fluids.8 Unfortunately, neither gutta-percha nor conventional sealers can be relied upon to obviate the effects of coronal leakage.9-10 In fact, the quality of the coronal seal has been shown to be significant in the periradicular status of root filled teeth in several studies.11-13
The microleakage potential of many current restorative materials used in mainstream clinical practice is well documented.14,15 To reduce leakage around endodontic temporary stopping materials, a variety of methods have been suggested; alternating heat-carriers with condensation (Schilder technique) has been shown to enhance the quality of the coronal seal16 as has the placement of restorative materials over the pulp chamber floor and orifices at the time of obturation.17,18 The variability in the results of studies used to determine the optimal technique has been attributed to the different techniques and materials used for bacterial and radioisotope penetration over different periods of time.19-21 No consistent standard has emerged.
Operative and endodontic procedures should incorporate the use of either laser fluorescence and/or caries detection solutions to distinguish between affected and infected dentin.22,23 While there are concerns about the impact of caries detection agents on bond strength, their efficacy and their specificity to stain either bacteria in infected dentine and/or the carious degradation products of the dentin matrix place them in the vanguard of comprehensive care.
Recently, innovative adhesive materials have become available for obturation [microstructural replication] of the root canal space; 1) Real Seal (SybronEndo, Orange CA) consists of a self-etch primer, a dual-curing, resin-based composite sealer and a thermoplastic synthetic polymer-based (polyester) root canal core material that contains bioactive glass, bismuth oxychloride and barium sulphate, 2) EndoREZ (UDP, South Jordan UT) a urethane dimethacrylate resin-based, root canal sealer with hydrophilic properties and Endo REZ resin coated gutta-percha points. The intracanal monobloc, adhesion of the core material to the sealer, which adheres and penetrates into dentinal tubuli, addresses many of the shortcoming of the traditional gutta-percha/sealer combinations currently used as the “gold standard” of obturation.
Authors’ note: The teeth restored for this paper were not endodontically treated. The intent was to provide in vitro examples of procedures that use adhesive technologies for the elimination of coronal leakage in conjunction with an optimal aesthetic result.
MB2 canals are present in the mesial buccal roots of 93.0 percent of maxillary first molars and 60.4 percent of maxillary second molars.24 Seek Caries Indicator (UDP, South Jordan UT) was used to assist in the identification of the orifice of the MB2 canal. Seek caries indicator contains D&C dyes in a glycol base that stain carious dentin red and assist in locating calcified canal orifices. The concept of “chroma-topography” in mapping the pulpal floor is paramount in all endodontic procedures (Fig 1).
Given that the orifices occlude calcifically with irregular secondary and tertiary dentin formation, the use of caries detection agents in conjunction with magnification and illumination provides a significant assist in the identification of all entry portals to the root canal space. In addition, the dentin of the floor is always darker than the axial walls and if the floor is burnished with a multi-fluted finishing bur after ultrasonics, the glossy appearance particularly if moist, creates a highly distinctive visual outline of the canal orifice locations.
Once the root filling is completed, the pulp chamber is air-abraded, washed and dried prior to etching in preparation for bonding. The depth of the etch is critical in attaining full penetration of the bonding resin into the dentinal tubules to create a non-porous hybrid layer. UltraEtch 35 percent (UDP, South Jordan Utah) has proven to be uniquely self-limiting in its depth with an average penetration of 1.9 microns using a 15 second etch (Fig 2). Liquid phosphoric acid (37 percent) shows an average penetration of 5 microns at 15 seconds, and a polymer thickened etchant a 4.8 micron depth penetration.25 Clinical experience and FE-SEM evaluations show 15 seconds etch time on both dentin and enamel provides optimal conditioning of both tissues. It is important to blot off excess water after the air/water rinse, but to leave the dentin surface visibly wet.
The smear layer must be removed as it will otherwise dissolve beneath the restoration material through hydrolytic action. This will facilitate bacterial penetration and will result in failure of the restoration. The majority of long-term clinical studies continue to support multiple step smear layer removal systems.26,27
PQ CLEAR is dispensed through the Inspiral brush tip, agitated and rubbed onto the dentin, air thinned and cured (Figs. 3A & 3B). This bonding agent bonds to dentin/enamel, cast metal, porcelain, amalgam and composite.28 Alternatively, PQ1 (UDP, South Jordan UT), a 40 percent filled radiopaque bonding system with an ethyl alcohol solvent carrier can be used. The ability to bond to various substrates is critical in creating an impervious seal when restoring crowned teeth that have had root canal treatment.
Currently, there are a number of bonding systems available to the clinician, which are self-etching or self-priming. These systems are either a single step or two-step applications in which the smear layer is dissolved and incorporated into the adhesive layer. Hybridized smear layers (dissolved smear layers reinforced by impregnated resin) may be intrinsically too weak to provide hydrolytically stable, strong and durable mechanical properties.29 In a study by Oliveira et al, the results demonstrated a demineralized dentin zone below the hybrid layer formed by the self-etching primer, not fully protected by the adhesive, which could jeopardize bond strength.30
The self-etching and priming systems using one-coat application have the increased risk of forming too thin a layer with the possibility of dry spots and recently, drawbacks have been demonstrated when self-etching using very low pH adhesives. The acidity appears to block the polymerization, not only of the adhesive, but also of the composite material on top, especially for the tertiary amine-based self or dual-curing composites.31 This is particularly critical when placing cores or restoring lost dentin with a self or dual-curing composite material.
Their poor bonding quality to enamel with the resultant leakage at enamel margins is also a concern. Transmission electron microscopy has shown a thin hybridized complex of resin in enamel produced by the self-etch primers without the usual micrometer-sized resin tags seen in resin-enamel bonds produced using a total etch adhesive.32 It has been recommended that a solution to the problem of degradation of resin-dentin bond strength over time
is to cover these hydrophilic adhesives with a thin layer of flowable composite. This allows the convenience of dry bonding, simplified packing of the composite material and simplified bonding procedures without sacrificing bond strength or quality.
When a thin layer of intermediate low viscosity composite with an intermediate modulus of elasticity is placed on top of a low modulus adhesive layer, which rests over a resin infiltrated hybrid layer that itself has a low modulus of elasticity, it is very likely that there will be a much different stress concentration across the interface than occurs when stiff resin composites are placed on a thin adhesive layer.33
On the basis of the lower elastic modulus, a so-called “stress breaker” function is also attributed to this layer of free flowing composites, i.e. this layer is meant to effect elastic compensation for polymerization stresses in the restoration composite.34 Whenever using light intensities of 800m W/cm2 or greater it is very important to use a flowable composite as a liner since this material serves to absorb any shrinkage or contraction of the curing composite resin at its surface which may result from the high light intensity.
In the example of Tooth #1, Permaflo Purple (UDP, South Jordan UT), a flowable composite, was placed as the initial restorative layer over the chamber floor and canal orfices and cured for 20 seconds. The advantage of this material is that in the off-chance retreatment is necessary; the colour obviates the possibility of iatrogenic misadventure during the re-entry procedure. The layer should be no more than 2 mm in depth as it could impact on the colour of the final restoration (Fig. 4).
Vit-l-escence shade A3.5 (UDP, South Jordan UT), two shades darker than the final shade chosen for the restoration, was used to create a depth of colour that would block the purple shade of the flowable composite layer (Figs. 5A & B). Vit-l-esence A2, chosen as the main body shade of the restoration, was used to build the internal anatomy. The body shade is feathered up to the margins of the access preparation in order to ensure that the margins will not be visible. This might occur should a more translucent shade be used (Fig. 6).
Vit-l-esence Pearl Natural (PN) was chosen as the best enamel shade match (Fig. 7). Vit-l-esence Opaque Snow (OS) was placed along the ridges of the occlusal surface as the natural tooth displayed a highly decalcified surface.
Authors’ Note: The most effective way of choosing an enamel shade is to place a small amount of the composite on an unetched, unbonded portion of the tooth and light cure. In vivo, this test should be done on the tooth prior to placement of the rubber dam. In all cases of shade selection, the colour should be chosen before the teeth have a chance to dehydrate.
To create a more natural look, Vit-l-escence Colour Light Brown was added through a 31 gauge nano tip into the fossae and fissures (Fig. 8). These modifiers are highly filled and their characterization can last on the surface of the restoration without the need to cover them with sealers. The surface of the restoration was smoothed with Jiffy Polishers (UDP, South Jordan UT) and PermaSeal (UDP, South Jordan UT) applied, air-thinned and light-cured (Fig. 9). The PermaSeal material fills micro-cracks caused from polymerization shrinkage as well as the stress cracks caused by polishing.
The endodontic access preparation was etched with Uni-Etch(r) (Bisco Inc., Schaumburg IL), a 32 percent phosphoric acid semi-gel utilizing a polymer to create thixotropic properties which enhance handling characteristics and leave no residue on rinsing (Fig. 10). The tooth was rinsed with water and lightly air dried for 2 seconds, leaving a visible moist surface (Fig. 11).
It is advisable to have a separate dedicated air line for drying and evaporating solvent from dentin bonding agents, as triplex syringes may leak water when air only is used.
One-Step Plus (Bisco Inc., Schaumburg IL), was applied in two coats to seal the dentin (Fig. 12). This bonding agent bonds to all substrates, bonds to self, dual and light-cured composites and cements, and is thin enough to use with indirect systems. It is filled 8.5 percent with 0.93 particle size filler and has an acetone solvent. The One-Step Plus is air dispersed to evaporate the solvent and then light-cured (Fig. 13).
Figure 14 shows an adequate post-cure glossy surface. In this example, the Ultra-Lume 5 (UDP, South Jordan UT), a broadband LED curing light was used. This low profile, high intensity light has a 10 x 13 mm footprint and intensity range of 375 to 500 nanometers, providing an equivalent depth of cure to that of quality halogen lights.
De-Mark (Cosmedent Inc., Chicago IL) was applied in a thin layer to line the access preparation. Its filler particles are more radiopaque than enamel thereby notably demarcating the composite restoration on an x-ray (Figs. 15 & 16). The De-Mark is light-cured and the chamber floor reconstructed by using AELITEFLO A3.5 (Bisco Inc. Schaumburg IL), a low modulus micro-hybrid composite that acts as a stress breaker beneath the restoration (Fig. 17).
After this layer was light-cured, Renamel Universal Microhybrid A3 (Cosmedent Inc., Chicago IL) was adapted over the lining material to mimic the dentin shade of the tooth (Fig. 18). This microhybrid has excellent wetting properties and mimics the opacity, translucency and luminescence of the natural tooth structure.
Next, a layer of Renamel Universal Microhybrid A2 was placed to blend in the occlusal shade and build up the character of the marginal ridges. This material was sculpted to mimic the occlusal ridges as closely as possible (Fig. 19). In order to create a subsurface tinting and characterization of the fissure anatomy, Renamel Creative Colour Tint Dark Brown was placed with a fine sable hairbrush and light cured (Fig. 20).
A layer of Renamel Universal Microhybrid Occlusal Clear was then placed over the tint. This material demonstrates a translucency consistent with enamel and enables the underlying material to show through (Fig. 21).
Due to the extreme white opaque character of the surface of this molar, Renamel Microhybrid White Opaque was added to mimic the appearance of the natural tooth structure (Fig. 22). The flash was removed with a Brasseler #7803 finishing bur (Brasseler USA, Savannah GA) (Fig. 23) and the surface then polished with GROOVY Diamond Polishing Brushes (Clinical Research Dental, London ON). These brushes are constructed of diamond impregnated bristles which enable access to the grooves without flattening the anatomy created.
Renamel Creative Colour Opaque White was added for characterization creating an undetectable final restoration. The restoration was covered with Renamel Creative Colour Clear (Fig. 24) as all finishing procedures on composite resin restorations create surface cracks.
In the third example of the restorative possibilities for creating the endodontic monobloc, the access preparation was opened and treated up to the level of the flowable composite in the manner previously described. The first layer of composite resin placed in the endodontic access preparation after the flowable composite was Renamel Posterior Body A1, a two-part hybrid system (Cosmedent Inc., Chicago IL) (Fig. 25).
Renamel Posterior Body is very dense and can be compacted like amalgam and its large filler particles give it an added compressive strength. When condensing or molding the composite to the interior walls of the preparation, it is critical to use an instrument that does not penetrate the composite resin. It this occurs, tugback created while removing the instrument will create voids at the cavo-surface margins. It is best to use a round condenser of an appropriate size to butter and sculpt the material to the edges.
Renamel Occlusal Clear (Cosmedent Inc., Chicago IL), a sculptable translucent hybrid was placed as the next layer (Fig. 26). A
fter teasing Renamel Creative Colour Tint Light Brown into the fissure areas with an explorer (Fig. 27), Renamel Creative Colour Opaque White was again used to simulate the white opaque areas of the tooth structure (Fig. 28).
When applying the Renamel Colour Clear it is important to air-thin the material prior to light-curing. This will create an imperceptible coating to give a long-lasting, smooth, wear-resistant surface to the restoration (Fig. 29). Figure 30 shows the final restoration in place after polishing and sealing.
Dentists have traditionally been taught to fill a restoration to an excess contour and then cut back to the marginal finish line. This approach will work well, if you are using a single composite and a single colour to obtain the end result. However, in the examples herein, the approach taken has been the opposite; fill from the inside out. This is analogous to the technique used by ceramists in order to provide a lifelike vibrancy to the final restoration. Whether applied to posterior or anterior teeth, this particular method will truly produce optimal cosmetic results with current and future composite resin systems.
Gutta-percha and sealer have “defined” root canal obturation for over a century. The concept of comprehensive care has only recently evolved. The integration of diagnosis, prevention, restoration, health of the attachment apparatus and the creation of harmonious function is logical, but not seamless in the mainstream. Far too often the treatment baton was passed to the next team to complete the task at hand rather than by the creation of a nexus of procedures.
New materials and techniques must be developed through the application of basic, applied and clinical sciences and perhaps then predictable clinical success will be an omnipresent reality. Understanding the dimensions of inner space may present a cornucopia of answers and resolution. This article was designed to further demonstrate the intersection and convergence of both the science and the artistry. Far too often one is subjugated to facilitate the dominance of the other.
Gerhard Staguhn wrote, “Whenever man tries to probe into the universe’s dimension of time, he will finally be confronted with eternity. Where he tries to understand the dimension of space, he will be finally confronted with infinity.” It’s time for dentistry to explore the infinite connections in both its fundamental tenets and the myriad of additions to its service mix with all the renewed vigour comprehensive dental care mandates.
Dr. Serota is a contributing consultant to Oral Health and maintains an endodontic specialty practice in Mississauga, ON.
Dr. Boksman is in Private Practice 1987 to present; FICD International College of Dentists fellowship, 2003; Director of Clinical Affairs, Clinical Research Dental 2004 – present.
Mr. Tousignant graduated Dental Technology from George Brown College in 1992, Certified Dental Technician since 1994 from the The National Board For Certification in the USA. Currently provides lectures and hands on esthetic composite courses for both general dentists and dental schools across Canada.
Oral Health welcomes this original article.
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