Endo esthetics


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Endo esthetics

  1. 1. EndoEsthetics: The Rehabilitation of the Endodontically Treated Tooth Kenneth S. Serota, DDS, MMSc Structural engineering integrates competing stress-related vectors into a cohesive dynamic for thefabrication of an interactive framework. The fundamental precepts of engineering apply to restructuring thedentition as well; foundation, infrastructure, and superstructure must coalesce seamlessly to effect afunctional complex. The biodynamics of endodontic therapy necessitates elimination of pathologicallyconflicting variables in order to facilitate predictable clinical success. Predictable success will occur in approximately 95% of teeth treated endodontically. It is thereforeessential to rise to the challenge and develop protocols, which will facilitate the treatment of the root canalsystem, producing a stable foundation, thereby diminishing the variables that prevent the attainment of100% success. Removal of microbial contaminants and organic substrate from the root canal system in conjunction withthe total closure of that system is the primary biologic objective of root canal therapy. It is paramount thatthe shaping of the root canal space be defined in such a way that this objective is achieved. In the last few years, a dramatic paradigm shift has altered the protocol for cleaning and shaping the rootcanal system. The principle of “treating the apex last” has diminished the possibility of iatrogenic error whichresulted in stripping of furcal walls, ellipticizing, tearing, or zipping of the apical constriction, and the creationof false apical termini. The primary focus of “apex last” is the attainment of the terminal apical position bycontrolled passive insertion rather than aggressive acquisition through force. By relying upon repetition ofthe instrument series in sequence, incremental removal of the interior of the canal space is effected in acoronal-apical direction without spatial or dimensional alteration of the apical constriction. This approachpertains to the use of any instrument introduced into the root canal space and has proven to predictablyproduce a continuously tapering canal preparation incorporating a series of decreasing diameters whereinthe smallest diameter is located at the apical constriction. Keeping the constriction in its original spatialposition and retaining its native size obviates untoward alteration of the root canal space. Once thorough chemo-mechanical debridement and disinfection of the root canal system has beenachieved and the desired shape previously described has been produced, the next biologic consideration insequence is the sealing of all portals of exit within that system. By eliminating the continuum between theoral cavity and the periodontium wherein the root canal system is the biologic vector, healing ofpathologically altered periradicular tissues is ensured. Gutta-percha is a unique, naturally occurring thermoplastic polymer. Numerous investigators haverecommended utilizing the rheologic (flow) potential of gutta-percha by means of heat and manual pressure.As reported by Schilder, the “wavelike” condensation of gutta-percha towards the apex, using alternateapplications of heat and vertical pressure, results in an obturation of accessory canals and foramena morefrequently than other available techniques. Buchanan expanded on Schilder’s Vertical CondensationTechnique by introducing “The Continuous Wave of Condensation”. This technique enabled a single-tapered electric heat plugger to capture a wave of condensed gutta-percha at the orifice of a canal and rideit, without release, to the apical extent of down packing in a single, continuous movement. The duality ofheating and compacting gutta-percha through three to five interrupted waves of condensation as describedin the Vertical Condensation Technique was thereby eliminated. Having now established a predictably stable foundation for the endodontically treated tooth, the blueprintfor success continues by assembling an infrastructure for the final prosthesis. The use of the post/coreassembly as the infrastructure for the final prosthesis for an endodontically treated tooth has historicallybeen a well-established modality. It had long been thought that placing a post into a root canal actuallystrengthened the tooth. The presence of a post neither reinforces nor strengthens the root of anendodontically treated tooth. To the contrary, it has been shown that posts make these teeth moresusceptible to fracture. Current thinking suggests that post/cores should be avoided wherever possible 1
  2. 2. except in those situations where it is the only means of providing retention for a core due to excessive lossof coronal tooth structure. However; in retrospect, the design parameters for this assembly seem to have been derived from self-perpetuating anecdote. This is not to discount the science that has been directed towards the analysis,evaluation, and sanction of the protocol for this technique. Rather, it is to effect another paradigm shift, andview post channel preparation from an alternative perspective grounded in the dynamics of material andtechnical sophistication. Post length and diameter is inherently defined by the root canal space morphology uncovered during thecleaning and shaping sculpting phase of canal preparation, not by formalistic and product centeredparameters. It is essential that the operator view the root canal space as a three-dimensional configuration.In addition to the X and Y axes viewed radiographically, a Z axis exists; the dimensions of which must befactored into post channel design. To whit, if a three dimensional perspective on the cross-sectionalcoronal-apical diametrical changes in mesial roots of mandibular molars and mesial/distal buccal roots ofmaxillary molars was readily accessible, it is unlikely that these roots would ever be considered for postinsertion. The perception that post length and diametrical size are strategic variables contributing to rootreinforcement and reduced fracture potential has been discounted. It has been demonstrated thatunreinforced pulpless teeth may show a higher resistance to fracture than teeth restored with posts.Furthermore, numerous investigations have indicated that the availability of a substantial collar (ferrule) ofcoronal tooth structure for the marginal finish of the permanent restoration is of greater importance in crownretention than dowel length and diameter. Given that the vast majority of dowel/core assemblies are prefabricated, it is logical and reasonable toutilize intrachamber retention, and the coronal 2 - 3 mm of the non-posted root canal spaces for coreretention. Posts should be passively placed in the largest, straightest, and most circular canal asdetermined during the cleaning and shaping procedure. Once established the post channel may be refined,but never resized. The resultant step at the interface of the artificially created channel and the true canalspace is a potential fracture site. The treatment timing sequence for post-endodontic rehabilitation is a seriously under appreciated variable.A study at Loma Linda University demonstrated that teeth obturated with lateral and/or vertical condensationand left in saliva, would demonstrate apical microflora contamination within 30 days or less. Given the factthat the traditional endodontic access cavity seal of cotton and Cavit is usually placed in a tooth with apotentially leaking restoration, or one where considerable coronal tooth structure is missing, the failure toimmediately rehabilitate the endodontically treated tooth can have disastrous consequences. Rehabilitation is a function of the tooth type, its future function, its location in the arch, and its location inthe planned prosthesis. The decision to place a post in a prepared channel or to restore the tooth in analternative manner is contingent upon the amount of tooth structure remaining in all dimensions.Recommendations have been presented that indicate if less that one-half of the coronal tooth structureremains, then a post is necessary for core retention, whereas if more that one-half of the coronal toothstructure remains, a post may not be necessary. The use of bonded amalgam or composite inside the pulpchamber and remaining tooth structure should suffice. Furthermore, it was indicated that when all coronaltooth structure is missing additional anti-rotational features are necessary in at least 2 locations around thepost. The mythology associated with dowel/core design has included the fantasy that cast gold dowels shouldbe as long as possible, be designed with a lingual apron, and that the dowel should extend to beyond one-half the residual bone support. In addition, it has been presumed that large posts reinforce and prevent rootfracture, that the post channel preparation should extend to 4 mm from the apical terminus and that thelength of the dowel should be 1 to 1 1/2 the length of the clinical crown. Fortunately, the myths have beendebunked and we now recognize that teeth with custom-fit, tapered cast posts are less resistant to stress as 2
  3. 3. the post transmits forces like a wedge. The concern about brittleness of dentin after root canal treatmenthas been disproved; root strength is a function of the amount of residual dentin. It is essential to remove the organic smear layer from the post channel to ensure adhesive of the lutingagent. Ideally a passive prefabricated post is fit and cemented with a low viscosity resin. Even if castingsare to be used, it is best to retain the highest degree of parallelism possible with a minimized wedging effectand maximize surface contact area with the dentin walls. In order to ensure the prevention of post/corefailure the focus must shift to the elimination of the following variables; a) cement-dentin interface failure, b)cement-dowel interface failure, c) cohesive failure of the cement, d) failure of the dowel (bending orbreaking), and e) root failure as result of function or preparation. The methodology for post channel preparation needs to be reassessed and updated. Aggressive toothstructure removal i.e. corrugation, that disregards natural root anatomy and morphology will weaken the rootand predispose it to stress fracture. In the apex last approach to intracanal treatment procedures, thephysical parameters of a post channel preparation are defined during the cleaning and shaping phase. Noadjustment to these parameters is justified or warranted. Gutta-percha removal from the obturated canal space is effected initially by solvent i.e. rectified turpentineor chloroform and completed using a heated. Once the optimal depth of removal has been reached, thewalls of the post channel preparation are refined with side cutting gates glidden drills. The final post channeldesign is completed with a drill mated to the post from the system being used for dowel/core fabrication. The flared canal, whether due to age, carious extension, pulpal pathology, or endodontic access presentsa restorative management problem. Intra-radicular rehabilitation, prior to post fabrication and/orcementation, increases the chance for operative success. When fabricating a post/core, it is important toascertain that the remaining dentinal structure has sufficient strength to support the post/core/crowncomplex that will eventually restore the tooth to form and function. Excessive tooth structure removal canlead to a fracture of the entire complex. A post that does not fit the canal well, whether due to an inappropriate natural shape or ill-consideredover-preparation, will result in a decreased retention of the prosthetic restoration and, possibly, fracture ofthe remaining dentinal structure. All too often, cements are used as displacement materials to overcome theloss of adequate tooth structure. This is particularly true of the popular prefabricated post systems where, atbest, the shape of the post is a distant approximation of the post endodontic canal space. Cementing materials remain the weakest aspects of fixed prosthodontic procedures. The lack of strongadhesion to tooth structure and metal demonstrated by such traditional luting agents as glass ionomer,polycarboxylate, and zinc phosphate cements, has dictated the characteristics necessary for full and partialcoverage preparations. Furthermore, the tendency was to make the diametrical width of the dowel as greatas possible to ensure retention. In fact, the gains in retention diminish with the increasing diameter. In an era of microetchers (Danville Engineering, Danville CA) and exponential development of adhesionmaterials, it would seem that a new protocol for cementation using posts of lesser diameter, with exquisiteintimacy of fit, could be developed. This would ensure that decreased possibility of fracture, enhancedresistance to displacement, and improved esthetics due to the use of dentin shaded composites as corematerials. The value of cementation of prefabricated posts using composite resin as a luting agent has beenestablished. The rationale for the use of dentin bonded composite for intra-radicular rehabilitation is alsowell established. Bonding, tensile, and shear strengths of composite to dentin indicate its potential clinicalperformance. An intra-radicular rehabilitation matrixed within dentin is less susceptible to microleakage. Inaddition, this type of restoration is not likely to be exposed to the corrosive nature of the oral cavity providedthat all margins of the full coverage restoration are placed beyond the marginal areas of the post/corecomplex. The inherent problem of light curing composite down a post space to a depth greater than five tosix mm was solved by the introduction of the Luminex 2001, the light transmitting post [LTP] (WeissmanTechnology International Inc., NY). 3
  4. 4. Protocol Step 1: The post channel preparation is etched and rinsed. A dentin-bonding agent (unfilled resin) isused for the preliminary layer of the rehabilitation. Primers are applied, the adhesive painted on the internalanatomy, and after a brief spray of oil-free air using a Stropko irrigator (Roydent, Romulus MI) to thin out thematerial, a light transmitting post [LTP] is loosely fit in the channel preparation and the dentin bondingmaterial cured. Step 2: The bonded canal is filled with a hybrid composite and compacted with a ThompsonFR #3 or FR #2 instrument (Thompson Dental Manufacturing Co., Missoula, Montana). A pre-selected LTPmated to the size of the post determined to optimally fit the channel preparation is inserted within the centreof the composite mass. The pressure of placement on the uncured composite will force it into the voids andmicro-fissures of the intra-radicular walls. The composite is cured according to manufacturer’s instructions.The LTP will trans-illuminate throughout its length, curing the surrounding material. Step 3: The plastic post (LTP) is removed with a slight rotational pressure. The newly defined postchannel is re-prepared using the mated drill from the post system chosen. The selected post is verified forfit and micro-etched. A thin layer of dentin bonding agent is painted on the post and light cured. Step 4: As the composite will undergo polymerization shrinkage towards the bonded surface and awayfrom the LTP, the dowel is cemented using a dual cure resin cement to compensate for volumetric increasein the post channel space. The choice of resin cement over conventional cementation materials ispredicated on its ability to chemically bond with the dentin-bonding adhesive of the post, the resin core, andthe tooth structure. 4
  5. 5. Drill DiametersReferencesFreedman G, Glassman GD, Serota KS. EndoEsthetics: Part I: Intraradicular rehabilitation.Ontario Dentist, November 1992, 28-31.Glassman GD, Serota KS. In Search of Excellence in Endodontics.Oral Health, April 1993;83(4):35-42.Freedman G, Klaiman H, Serota KS, Glassman GD. EndoEsthetics:Part II: Castable ceramic post/core restorations. Ontario Dentist, June 1993;70(5):21-24.Freedman G, Novak IM, Serota KS, Glassman GD. Intra-Radicular Rehabilitation:A Clinical Approach; Practical Periodontics and Aesthetic Dentistry, June/July 1994; 6(5), 33-39.Serota KS, Glassman GD, McCutcheon-Jones E. The Endodontic Restorative Continuum:Genesis, Synthesis, and Hypothesis. Oral Health, July 1994;84(7):53-65.Serota KS, Glassman GD, McCutcheon-Jones E. The Endodontic Restorative Convergence:Genesis, Synthesis, and Hypothesis. Dentistry Today, December, 1994Blitz N, Serota KS. Rehabilitation of the Endodontically Treated Tooth:Exploding the Myths, Defining the Future. Oral Health December, 1995Blitz N, Serota KS. Endodontic-Restorative Interconnection:Interdisciplinary Integration Oral Health Vol 86(12) December 1996Serota KS, Glassman GD, McCutcheon-Jones E, Freedman G.Il continuum dell’Endodonizia restaurativa: genesi, sintesi ed ipotesi.Volume 1, Numero 2, Anno 1997. 5
  6. 6. Glassman GD, Serota KS. Endodontic Lexicon for a New Millennium:Precepts, Concepts and Perspective. Oral Health, December 1998.Glassman GD, Serota KS, Soll J. A New Method for the Restoration of the Endodontically Treated Tooth:The Luscent Anchor™ System. Oral Heath, December 1999. 6