The Ideal Restoration of Endodontically Treated Teeth Structural and Esthetic Considerations a Review of the Literature and Clinical Guidelines for the Restorative Clinician Copia

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238THE EUROPEAN JOURNAL OF ESTHETIC DENTISTRY

The ideal restoration of endodonti-

cally treated teeth – structural and

esthetic considerations: a review of

the literature and clinical guidelines

for the restorative clinician

Konrad Meyenberg, DMD

Private Office for Reconstructive Dentistry

Zürich, Switzerland

Correspondence to: Konrad Meyenberg

Private Office for Reconstructive Dentistry, Rennweg 58 / Eingang Oetenbachgasse 26, 8001 Zürich, Switzerland;

E-mail: [email protected]; Web: www.zahnaerzte-rennweg.ch

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One of the most challenging dilemmas faced by today’s clinician is the manage-ment of the structurally and esthetically compromised endodontically treated tooth. Certainly, in recent years there has been a tendency to take the simplified approach of “extraction and implant” but this does not always prove to be as simple as we would like to think. Has the popularity of dental implantology made the restorative dentist complacent in regards to the possibilities that good endodontic, periodontal and restorative treatments can achieve? Without doubt the dental implant option has its place, and rightly so, but in many cases, I sus-pect, the endodontic/restorative option does not always receive its due merits.

Whenever we are faced with such a compromised tooth, we have to con-sider the following question: is the tooth maintainable? If so, then this is surely our primary goal. However, the question is complicated by the context – ie, is this a young patient? Is this a bridge abut-ment? Is there an esthetic challenge, ie, a dark tooth? In the younger patient, it may be desirable to maintain a poten-tially hopeless tooth for as long as pos-sible in order to “buy time” and delay the day of implant placement and its subse-quent eventual failure. Retreatment of a tooth is, more often than not, simpler with a broader range of options than retreat-ment of a failed implant, particularly in the esthetic zone. If this can be done


for the younger patient, then why can’t it be done for the older patient? On the other hand, perhaps it is more predict-able in a given case to remove the tooth and restore it with a dental implant res-toration. These and other issues are real concerns we have as practitioners and it is important to have objective as well as the subjective criteria on which to base our decision for the choice of restorative protocol.

Are all endodontically treated teeth really less predictable than a dental implant-supported restoration? Are they really more likely to fail? Do they really have a poor prognosis? Do implants re-ally have fewer complications? Is retreat-ment as easy? Do anterior and posterior teeth behave the same? When is the prognosis of the tooth unfavorable and at what point is extraction and an im-plant the best option? These and many other relevant questions are eloquently addressed below by our essayist and EAED Active Member, Dr Konrad Mey-enberg. My hope is that this paper will serve to help us to question our treat-ment choices more critically in this area, suggest useful answers to many of the questions in this dilemma, provide us with objective criteria on which to base our judgements and finally offer solu-tions so that we can make better choices for the treatment of our patients.

Dr Tidu Mankoo, BDS

Moderator/Editor’s Introduction

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Abstract

In restorative dentistry, the non-vital tooth and its restoration have been extensively studied from both its structural and es-thetic aspects.

The restoration of endodontically treated teeth has much in common with modern implantology: both must include multifaceted biological, biomechanical and esthetic considerations with a pro-found understanding of materials and techniques; both are technique sensitive and both require a multidisciplinary ap-proach. And for both, two fundamental principles from team sports apply well: firstly, the weakest link determines the limits, and secondly, it is a very long way to the top, but a very short way to failure.

Nevertheless, there is one major dif-ference: if the tooth fails, there is the op-tion of the implant, but if the implant fails, there is only another implant or nothing.

The aim of this essay is to try to an-swer some clinically relevant concep-tual questions and to give some clinical guidelines regarding the reconstructive aspects, based on scientific evidence and clinical expertise.

Rebuilding the ideal tooth from an endodontically treated tooth – what does this mean?Essentially, the goal is to restore the ap-pearance and biomechanical properties comparable to those of a vital, complete-ly intact tooth. In addition, the coronal restoration should prevent bacterial re-colonisation of the endodontically treat-ed root canal system.1

Clinically, most of non-vital teeth must be considered as structurally and es-thetically compromised.2 The fracture rate and as a consequence the risk for tooth loss is considerably higher com-pared to vital teeth.

Part 1: Structural considerations

What are the causes of fractures?

There are several causes for the in-creased risk of cracks in endodontically treated teeth to be considered. Cracks predispose the tooth immediately or af-ter some time to fracture. The following four factors contribute to this predisposi-

!" Structural loss of tooth substance due to pre-endodontic restorative proce-dures or the endodontically induces access cavity preparation and root canal enlargements.5,6

!" Increased brittleness by age induces changes in the dentin and the loss of free unbound water from the root ca-nal lumen and the dentinal tubules in pulpless teeth.7-11

!" Weakening effects by endodontic ir--

tions (CaOH2

bacterial interactions with the dentin substrates, corrosive effects of restor-ative materials, and negative mechan-ical effects through crack inducing or crack propagating endodontic and restorative methods and instruments, including endodontic files.12-16

!" The reduced level of proprioception of non-vital teeth causes a reduced level of control of forces by the normal

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protective neuromuscular inhibition mechanism.17

Some of these factors may be influ-enced or modified to improve the prog-nosis, however the most important factor for success is to avoid any unnecessary loss of tooth substance in general and to preserve as much as possible after removal of all decayed material.

Recent research shows that dentin has some very effective inherent proper-ties to inhibit crack progression (fracture

distribute local stresses and to partially repair defects, as long as a tooth is vi-tal.8,9 However, a non-vital tooth will lose some of these properties over time. A key consideration is that the amount of collagen fibers in endodontically treated

Fig 2 Fracture of first upper premolar due to deep cavity with endodontic treatment.

Fig 1 Cracks in lower first molar due to deep cavity.

Fig 4 Fracture originating from the apex of a canine due to the use of inadequate endodontic techniques.

Fig 3 Fracture of palatal root of upper first molar due to endodontic treatment.

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teeth decreases, which means that this dentin is much less fatigue resistant.17

In addition, even vital dentin loses some of its initial strength over its lifetime: it shows a different fracture behavior as the mineral content increases over time and causes a less favorable fracture be-havior because of the increased brittle-ness.18,19

Restorative options: what is the ideal concept?

As a consequence, any attempts to restore a non-vital tooth must include not only the use of restorative materi-als with properties similar to the dental components, but also the use of clinical concepts that allow to compensate the inherent reduction of the mechanical re-sistance of endodontically treated teeth.

A true so-called biomimetic con-cept20 therefore does not only implicate the use of particular materials similar in their properties to dentin and enamel, but also sometimes the use of particular materials with different properties to re-store the incomplete tooth as a whole in all its mechanical, biological and esthet-ical aspects,21 above all if the remaining tooth structure is compromised.

Post or no post – are posts destructive?

In the past, fractures of teeth often have simply been attributed to inadequate re-storative procedures, be it by the use of inadequate core materials or the use of posts and screws. The introduction of ad-hesive techniques and their successful integration in almost all current restora-tive procedures has allowed the clinician

to dispense with posts in many indica-tions, as they are no longer required for the retention of a core build-up.

However, mindful clinicians can still observe a relatively high rate of vertical root fractures despite the absence of posts and even with the use of adhe-sive techniques – above all in curved and small roots; indeed some authors report up to 20% of vertical fractures of endodontically treated teeth. Man-dibular molars and maxillary premolars are most often affected.25,26 Provided there is enough coronal dentin structure

that there is no difference between teeth restored with or without posts in this re-spect.27 Interestingly in this article, 86% of molars with vertical root fractures had the fracture in a root without a post.

Therefore, as long as no active posts or screws are used, which may produce detrimental lateral forces on the den-tin walls,28 and as long as inadequate placement techniques with risk of per-forations are not used, posts per se may not be considered as destructive.

When is a post indicated?

The main reason to use a post today is no longer to increase the retention and resistance of a core build-up, since there are very effective adhesive tech-niques available. As discussed, provid-ed there is sufficient tooth structure avail-able, there is no longer a need to place a post. In premolars with limited amount of tooth destruction and molars where, in general, more dentin walls with greater surface area can be engaged to be bonded as compared to anterior teeth, a direct bonded core build-up is

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not be compensated simply by adhe-sive techniques using fiber posts and composite cores. In a recent long-term study over 7 to 11 years, the mechani-cal failures reached 7 to 11% and were always related to a lack of coronal tooth structure.

If anterior teeth and premolars pre-sent with large defects that require crowning, however, adequate transfer of forces from the crown into the core build-up and from there into the root is not possible without a post. Importantly, the function of the post is not only the increase of the retention of the core, but also the optimization of the resistance form. In addition, the mechanical prop-erties of a composite core alone may also not be sufficient in the case of a narrow abutment diameter and cannot reduce high stresses in the critical cervi-cal area, which in such a case, is prone to horizontal fractures. A clinical study

directly to a reduced macroretention ge-ometry without posts clearly showed that the concept can work for molars (87–95% success, depending from the

not work for premolars, if there were no cavity walls at all and the crown was just bonded directly into the residual pulp

Therefore, the purpose of a post and core as a unit is primarily to transfer the loads into the root and secondly, the post is used as a reinforcing element of the core build-up.

The downside of this concept is the weakening effect on the root itself; to compensate for this, the ferrule effect must be incorporated into the restoration design.

clinically the concept of choice; it can be regarded clinically as well established, reliable and perhaps preferable to con-ventional post-core concepts. In addi-tion, by avoiding posts, the risk of cracks due to thin residual root walls or perfora-tions can be eliminated.

For anterior teeth and heavily compro-mised premolars, however, this state-ment is limited to teeth that present with small to moderate defects and that will later not be crowned.

For posterior teeth, the best prognosis is achieved if – in addition to a bonded core foundation – a ferrule effect is cre-ated by the final restoration. This means that full cuspal coverage is used, be it a partial or full crown. Adhesive tech-niques alone without cuspal coverage may still lead to catastrophic failures over time (ie, untreatable long axis frac-

-cally safe.

It must be stated at this point that the ferrule effect is the most effective way of mechanical stabilization, ie, of optimiz-ing the resistance form, of any endodon-tically treated teeth. Given the weaker structure, as previously discussed, the effect of the better load distribution into the cervical zone and the avoidance of any wedging effect by the post or core build-up into the coronal part of the root cannot be overemphasized. Therefore, in order to provide a ferrule in situa-tions without sufficient tooth structure above the zone of the biological width, orthodontic extrusion or surgical crown lengthening should be considered. A ferrule length of 1.5 to 2 mm is recom-mended.

It must also be stated that, obviously, the lack of coronal tooth structure can-

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The ferrule effect may also compen-sate unexpected breakdown of adhe-sion after bonding and luting proce-dures in unqualified dentin conditions. A safe clinical concept always implies the incorporation of a ‘belt and braces’ approach to offset routes of potential failure.

A special indication for a post is the immature root, presenting with a large root canal.

Obviously neither gutta-percha nor MTA nor composite have a significant reinforcing effect. In this instance, the only significant reinforcing effect is achieved with a post. This is in line with the clinical observation of increased risk of fracture in immature teeth left without post and core-build up after endodontic treatment.

If a post is indicated: what post concept should be used: stiff or flexible?

“If something can break, it will break, and it will always break at the weakest point” – this basic finding and classic rule for construction is also true for this applica-tion and may explain the significant con-troversies regarding what would be the best of all the available concepts. The question may be not whether something will break, but rather where it will break.

Almost all dental materials have been used clinically for posts. Still clinically relevant today are gold-alloys, chrome-cobalt, titanium, zirconia and glass fib-er posts. Carbon fiber posts have no clinical significance due to poor clinical performance and disastrous potential; therefore they will not be discussed in this article.

-sues causing some disagreements on the ideal material of a post.2 From a me-chanical standpoint, it is evident that a post stiffer than dentin can take up more load but induces more stress in some api-cal parts of the root, which can increase the risk of a vertical root fracture. Con-versely, a post that has an elastic modu-lus closer to dentin will, in fact, induce less stress concentration apically in the root, but more in the cervical region.

In addition, the interface between post and core and between core and dentin is also subjected to stress, so one can expect to see more root fractures

made from metallic or ceramic materi-als, whereas more flexible posts would show more post fractures, debonding of core materials and loss of retention (pos-

-lems of leakage and caries. The latter may lead to endodontic reinfection and catastrophic coronal destruction of tooth substance, thus leveling out the poten-tial advantage of this latter concept over the first one.

The dilemma for the clinician is the meaningful interpretation of the litera-ture, as countless studies have been published in this field, most of them being in vitro studies with questionable clinical potential relevance. Numerous theoreti-cal studies using finite element analysis have also been performed, which would all need to be verified according to clas-sic engineering principles in a real mod-el, but only a minority of the in vitro stud-ies have been performed with dynamic or fatigue loading under a simulated oral environment. Another difficulty is that study results are also influenced by

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the structural condition, various types of natural teeth utilized and the respective loading pattern.

One of the more clinically relevant in vitro studies compared cast posts and

-ite cores, zirconia posts with composite cores and zirconia posts with ceramic cores, using, in all groups, adhesive techniques and a ferrule of 1 to 2 mm on central incisors where all teeth were crowned. The most favorable results

with the stiffest concept (zirconia posts -

vorable with the cast post and core sys-

In contrast to this study with ideal tooth substrate, another study compared dif-ferent degrees of tooth destruction, us-ing fiber posts and composite cores or composite cores alone on premolars. It was shown that posts had a significant positive effect on fracture strength if only 1 or 2 cavity walls were left, whereas no

walls were left. However, if a completely flat profile without any substance above the preparation line is used, most likely the post will debond as predominant mode of failure.

Two facts are of special importance in the judgment of studies comparing dif-ferent concepts:!" The results of these in vitro studies

largely depend on the presence or

Principally, differences in materials of posts and cores level out from the mo-ment where a crown is placed.!" If metal-free post and core concepts

are to be successfully used, the es-

tablishment of proper bonding be-tween all substrates is of paramount importance.51 If bonding fails, much less favorable stress patterns occur both in the root, above all in the critical cervical area, and in the post and core itself.52 As a clinical consequence, loss of retention of the core and post is still unfortunately the major compli-cation.

Most of the clinical studies are difficult to interpret in their outcome, since the amount of tooth loss and the condition of the remaining dentin (pre-existing cracks, aging, endodontic treatment

influenced the choice of the concept.The scientific dilemma is very nicely

expressed in a systematic review about the simple final question, whether a crown or a filling is more effective in the clinical performance for an endodonti-cally treated tooth. The authors con-clude “There is insufficient evidence to support or refute the effectiveness of conventional fillings over crowns for the restoration of root filled teeth. Until more evidence becomes available cli-nicians should continue to base deci-sions on how to restore root filled teeth on their own clinical experience, whilst taking into consideration the individual circumstances and preferences of their patients”.

This statement shows not only the complexity of the topic, but also that clinical multifactorial reality does not al-low clear definition of one simple gener-ally valid concept.

Nevertheless, there is still a need for clear clinical guidelines, based on scientific evidence paired with clinical

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expertise. Only this combination finally leads to clinical evidence.

As a conclusion from numerous clini-cal studies, it must be stated that there is

direct and indirect concepts and gold, Ti, fiber and zirconia posts work well if the respective concepts are properly ex-ecuted. The single most important point is to preserve as much remaining tooth structure as possible.

Two additional arguments may require consideration for the reconstructive cli-nician: a) fiber posts offer the highest potential for reintervention due to their relative ease of removal, however their successful use clinically is much more technique sensitive,58 and b) post and cores with a high modulus of elasticity

-ture resistance as a foundation of the crown,50 which may be of significance for the long-term success of all-ceramic crowns.59,60

What about bonding a post into the root canal space? Does bond-ing help in cases with extended amount of tooth destruction? What is the ideal surface condi-tioning of fiber posts?Looking at the results of a recent clini-cal 10-year fiber post study, a surpris-

reported and an overall failure rate of

11% post debondings.61 The highest probability of a failure was reported for anterior teeth with no cavity walls.

This is confirmed by another clini-cal study62 where premolars of varying degrees of destruction were restored

with different concepts of build-ups. All teeth were finally crowned with porcelain

failure rate in this 6-year survival study of

ferrule of 2 mm or less was left, the fail-ure rate increased to nearly 90 to 100%

prefabricated posts, and to around 70% for the customized post concept.

The results clearly suggest that pre-fabricated fiber posts are superior to customized fiber posts (glassfiber

cores without any posts, if there are only 2 walls or less remaining. However, even if in addition to the bonded core a pre-fabricated fiber post is used, the con-cept obviously fails to be convincingly successful in cases with extended tooth destruction.

rate over 6 years of non-metallic posts and build-ups, a 10-year report of pre-fabricated metal posts and cast metal

RetentionThe almost doubled overall failure rate of fiber posts and the surprisingly high debonding rate must raise the question about the effectiveness and efficiency of this concept in general practice. Per-haps it is unsurprising given the inher-ently more technique-sensitive concept of the required adhesive techniques and the lack of a simple clear user protocol.

A recent study compared the reten-tion of different fiber posts with different surface conditionings (performed ac-cording to the manufacturer‘s recom-

-

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tin Ti-posts luted with conventional zinc phosphate-cement served as the con-trol group. The control Ti-post showed, together with some combinations of the test group, the highest pull-out strength, whereas some combinations of the test group showed surprisingly low values. This is in line with another study, where adhesively luted fiber posts were not superior to gold posts either adhesively luted or conventionally cemented with glass ionomer cement.65

Adhesion to radicular dentinAdhesively luting a post into root den-tin is a controversial issue. Conflicting results have been published about the efficacy of bonding to radicular dentin. Probably due to the structural differenc-es in radicular dentin, bond strengths improve from the apical to the coronal section. Comparing the use of compli-cated separated dentin bonding and lut-ing procedures with simpler self-etching cements, it seems clinically more relia-ble to use self-etching and self priming cements taking into account the poten-tially somewhat lower bond strength to dentin.66-71 Inadequate ability to cure the luting agents precludes the use of light-curing materials. Dual-cure or chemically curing materials should be used instead, since different fiber posts indeed differ in their light transmitting properties, however posts with optimal mechanical properties do not allow enough light penetrating all over the whole length of the post to sufficiently polymerize light-cured materials.72

Adhesion to post surfaceTo improve bond strength to the pre-fabricated fiber posts, chemical (silane,

etching with hydrogen peroxide for

or micromechanical treatments (sand-

been proposed. Surprisingly, sand-blasting seems to not affect the mechan-ical properties of the fiber posts.75 Sand-blasting with silanization is, therefore, an efficient, simple and predictable way of surface conditioning a fiber post before bonding.77,78 However, fiber posts are susceptible to water degradation, and damaging the surface will increase this phenomenon. Thus, a predictable bond-ing procedure that completely seals the post surface and avoids any voids is of paramount importance to preserve frac-ture resistance.79 Some manufacturers now use a coating on their posts to fur-ther simplify and improve the bonding.80 Nevertheless, care should be taken to consider both the manufacturers’ rec-ommendations and their scientific basis.

Mechanical propertiesMajor differences in the mechanical properties of different brands of posts is another critical point. Since there are now countless brands of posts on the market with a sometimes-unknown origin, a proper selection based on in-dependent scientific investigations is imperative to avoid basic mechanical failures.81,82 Using a fatigue resistance test, a difference of roughly 7,000 cy-cles until fracture for the worst and up to 2,000,000 cycles for the best post in

could be shown. The quality of the man-ufacturing processes including type of fiber and matrix, pre-tensioning of fibers, bond between fibers and matrix, among other factors, play an important role.

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Fig 5 Case 1: initial radiograph of non-vital cen-tral incisors with different degree of remaining tooth substance, final radiograph of build-ups with short

Fig 6 Case 1: initial clinical situation, large com-posite build-ups, discolorations.

Fig 7 Case 1: abutment teeth after removal of ex-isting composite cores.

Therefore, both a sensitive indication and technique is mandatory for the suc-cessful use of the concept of fiber posts combined with composite cores (Figs 5

Fig 8 Case 1: abutment teeth after internal bleach-ing.

Fig 9 Case 1: build-ups of abutment teeth com-pleted with fiber posts and composite core, buccal view.

Fig 10 Case 1: build-ups of abutment teeth com-pleted with fiber posts and composite core, occlusal view.

Fig 11 Case 1: final clinical result.

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Concluding remarks regarding the structural aspects

The following statements regarding the structural aspects may be made:!" Where a crown is fabricated and a

proper ferrule effect is created, neither the material (Ti, gold alloys, zirconia,

of the post are a significant influence, as long as clinically reasonable con-cepts are used.!" Conversely, insufficient coronal tooth

structure will always lead to an in-creased failure rate independent of the concept of restoration.!" Increasing the coronal diameter of the

post helps to reduce the fracture risk of all posts, however the residual den-tin wall thickness needs to be consid-ered.!" Huge differences in the quality of fib-

er posts require a careful selection to avoid post fractures.

!" Materials with potential of corrosion

fractures of materials and dentin and therefore should not be used.!" Adhesive cementation of fiber posts

is mandatory.!" Adhesive cementation of metallic

posts is not mandatory.!" Core build-ups should always be

bonded, even if a metal post is not bonded.

Regarding the clinical reality, the fol-lowing additional statements must be made:!"

removed after luting, offer no potential for reintervention and should therefore be used in selected cases only.!" For abutment teeth presenting large

defects and requiring crowning, or longer span bridges, or in general heavy loads, metallic posts are pref-

Fig 12 Case 2: initial radiograph of second lower premolar with fiber post and PFM crown. Fig 13 showing post fracture, composite core debonding and crown dislodgement.

Fig 14 Case 2: clinical view showing fractured fiber post and extensive caries destruction under-neath debonded composite core.

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57. Jung RE, Kalkstein O, Sailer I, Roos M, Hämmerle CH. A comparison of composite post buildups and cast gold post-and-core buildups for the restoration of nonvital teeth after 5 to 10 years. Int J

-dini S. Fiber posts and endodontically treated teeth: a compendium of scientific and clinical perspectives, ed 1. Wendywood, South Africe: Modern Dentist Media. Wendywood, 2006.

59. Malament KA, Socransky SS. Survival of Dicor glass-ceramic dental restorations over 20 years: Part IV. The effects of combinations of variables. Int J Prosthodont

60. Malament KA, Socransky SS, Thompson V, Rekow D. Survival of glass-ceramic materials and involved clinical risk: variables affecting long-term survival. Pract Proced Aesthet Dent

61. Naumann M, Koelpin M,

10-year survival evaluation for glass-fiber-supported postendodontic restoration: a prospective observa-tional clinical study. J Endod

62. Ferrari M, Vichi A, Fadda GM, Cagidiaco MC, Tay

Goracci C. A randomized controlled trial of endodonti-cally treated and restored premolars. J Dent Res 2012;91:72S–78S.

Rivero A, Del Río J, Celemín A. A 10-year retrospective study of the survival rate of teeth restored with metal prefabricated posts versus cast metal posts and cores.

Schirrmeister JF, Altenburg-er MJ, Hellwig E. Retention of fiber posts dependent on different resin cements. Schweiz Monatsschr Zahn-

65. Kremeier K, Fasen L, Klaib-

of endodontic post type (glass fiber, quartz fiber or

push-out bond strength to dentin in vitro. Dent Mater

66. Ferrari M, Mannocci F, Vichi

structural characteristics of the substrate. Am J Dent

Clavijo V, Andrade MF, Vaz LG, Campos EA. Effect of resin cement system and root region on the push-out bond strength of a translu-cent fiber post. Oper Dent

68. Huber L, Cattani-Lorente M,

S. Push-out bond strengths of endodontic posts bonded with different resin-based luting cements. Am J Dent 2007;20:167–172.

69. Monticelli F, Ferrari M, Toledano M. Cement system and surface treatment selection for fiber post lut-ing. Med Oral Patol Oral Cir

Krokidis A, Acquaviva PA, Cerutti F, Cerutti A. Polymerization degree and cementation methods of two different self-adhesive lut-ing cements used for glass fiber post cementation. Minerva Stomatol 2012;61:

71. Sterzenbach G, Karajouli G,

K. Fiber post placement with core build-up materials or resin cements – An evalu-ation of different adhesive approaches. Acta Odontol

72. Radovic I, Corciolani G, Magni E, Krstanovic G, Pavlovic V, Vulicevic ZR, Ferrari M. Light transmission through fiber post: the effect on adhesion, elastic modu-lus and hardness of dual-cure resin cements. Dent

FT, Radovic I, Toledano M, Ferrari M. Surface treatments for improving bond strength to prefabri-cated fiber posts: a lit-erature review. Oper Dent

Effects of chemical sur-face treatments of quartz and glass fiber posts on the retention of a compos-ite resin. J Prosthet Dent

75. Radovic I, Monticelli F, Goracci C, Cury AH, Coniglio I, Vulicevic ZR, Garcia-Godoy F, Ferrari M. The effect of sandblasting on adhesion of a dual-cured resin composite to methacrylic fiber posts: microtensile bond strength and SEM evaluation. J Dent

76. Soares CJ, Santana FR, Pereira JC, Araujo TS, Menezes MS. Influence of airborne-particle abrasion on mechanical proper-ties and bond strength of carbon/epoxy and glass/bis-GMA fiber-reinforced resin posts. J Prosthet Dent

77. Valandro LF, Yoshiga S, de Melo RM, Galhano GA, Mallmann A, Marinho CP,

bond strength between a quartz fiber post and a resin cement: effect of post sur-

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face conditioning. J Adhes Dent 2006;8:105–111.

78. Zicari F, De Munck J, Scotti R, Naert I, Van Meerbeek

cement-post interface. Dent Mater 2012;28:287–297.

79. Vano M, Carvalho C, Sedda M, Gabriele M, García-Godoy F, Ferrari M. The influ-ence of storage condition and duration on the resist-ance to fracture of different fiber post systems. Am J

80. Schmage P, Nergiz I, Marko-poulou S, Pfeiffer P. Resist-ance against pull-out force of prefabricated coated FRC posts. J Adhes Dent

81. Cheleux N, Sharrock PJ. Mechanical properties of glass fiber-reinforced endo-

82. Grandini S, Goracci C, Monticelli F, Tay FR, Ferrari M. Fatigue resistance and structural characteristics

of fiber posts: three-point bending test and SEM evaluation. Dent Mater 2005;21:75–82.

Cagidiaco MC, Goracci C, Ferrari M. Fatigue resistance and structural integrity of different types of fiber posts. Dent Mater J 2008;27:687–

Part 2: Esthetic considerations

Introduction

In addition to the numerous issues dis-cussed in part 1 of this paper, non-vital teeth are frequently esthetically com-promised. This frequently presents sig-nificant and special challenges when it comes to meeting the demand for nat-ural-looking, esthetically pleasing teeth sought by our patients today.

The aim of the second part of this pa-per is to try to answer several clinically relevant conceptual questions and to provide some clinical guidelines regard-ing the management of the esthetic as-pects, based on scientific evidence and clinical expertise.

Why are most endodontically treated teeth dark?

The discoloration of endodontically treated teeth is a common observation. In the posterior region, this phenom-enon is seldom esthetically disturbing

or is largely addressed with full crowns, since endodontically treated posterior teeth present mostly with large recon-structions that require optimal stabiliza-tion by full or partial crowns.

In the anterior zone, however, esthet--

tive effects:!" Discolouration of the clinical crown.!" Discolouration of the cervical region.!" Discolouration of the gingiva and mu-

cosa.

There are various causes of these en-dodontically induced intrinsic discolora-tions:!" Intrapulpal haemorrhage.!" Pulpal necrosis.!" Incomplete removal of pulp tissue

during the endodontic treatment.!" Endodontic irrigants, medications

and root canal filling material (root

!" Restorative materials (cervical zone

!" Coronal leakage.!" Dentin sclerosis.

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Unfortunately almost all root canal seal-ers including Zinc Oxide-Eugenol and

-

Also the use of MTA, be it grey or white, will ultimately lead to a greyish appear-ance or darkening of the root.5,6

Furthermore, the calcification pro-cess in the dentin through obliteration of the dentinal tubules and changes in the free water content before and after endodontic treatment and through ag-ing processes, contributes to an altered optical appearance in addition to the in-creased brittleness.7-10

How can we improve the color of

or replacing discoloured coronal dentin?

Although some of the above mentioned negative factors can be clinically modi-fied, it is evident that a non-vital tooth inevitably loses some esthetic qualities in terms of the color. As a matter of prin-ciple, replacing discolored dentin to cor-rect the color is not the preferable op-tion from a structural viewpoint. In part 1, the mechanical aspects to support this axiom have already been extensively discussed.

Therefore, bleaching the existing substance is always the better option, if we agree on the principle that “hav-ing a discolored tooth is preferable to having no tooth”. Most discolorations are bleachable except those caused by metal ions (amalgam, or silver and other

2 So the only indication to remove discolored dentin may be if small spots that do not contribute to the structural resistance of

the tooth are heavily discolored and do not respond to the bleaching procedure.

Do bleaching procedures lead to external resorption?

Cervical root resorption is a serious complication that is difficult to treat11,12

and ultimately can lead to tooth loss. There are various reasons for this phe-nomenon. Orthodontic treatment and tooth trauma are the most common pre-disposing factor. Internal bleaching may increase the combinatory risk, however it seems to be limited to cases where extensive concentrations of H2O2 com-bined with heat (the thermo-catalytic

The presence of defects at the cemento-enamel junc-tion seem to play a major role, allowing the bleaching agent to penetrate into the periodontal space.15

The recommendations today are therefore not to heat the bleaching agent in the access cavity, to seal the residual root filling well before application of the bleaching agent and to generally use less aggressive bleaching chemicals instead of high concentrations of H2O2.

The best clinical compromise of ef-fect, side-effects, risks and long-term experience is in the use of the so called “walking bleach technique”16 where, classically, sodium perborate is mixed with water.

In the author‘s long-term experience, this is clinically as efficient as other more aggressive chemicals, provided a cor-rect cervical and coronal seal of the bleaching cavity have been realized. The cervical seal is preferably achieved with a modified glass ionomer cement, classically applied at the level of the con-

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nective tissue attachment, whereas the coronal seal is achieved with adhesively luted composite to ensure an optimal penetration of the bleaching agent into the dentin. Hence, leaving the access cavity open and using at-home tech-niques with open trays is not advisable.17

Success largely depends from the ap-plication duration of the bleaching agent

-forms alternative quick in-office tech-niques in the long run.18 In a recent study it could also be shown that this concept compares very favorably to more ag-gressive mixtures of chemicals in terms of H2O2 leakage at different root locations with and without external defects.19,20

Since cervical defects are difficult to detect with conventional radiographs and require cone beam computed to-

21 the use of this less-aggressive concept makes additional sense in avoiding added un-known risks while producing good es-thetic results.

Do bleaching procedures weaken the tooth – or may dark roots also be bleached?

Recent research clearly shows that bleaching chemicals weaken tooth sub-stance.

Since the endodontic treatment itself already weakens the dentin consider-ably through chemical and mechanical effects 25 additional care must be taken if a bleach-ing procedure is being considered.

First of all, internal removal of dis-colored dentin should be avoided. It does not lead to better results with the described bleaching technique and will

further compromise the strength of the residual tooth structure. This is an im-portant consideration particularly if ad-ditional reconstructive measures are to be executed26 and if the potential for re-intervention is taken into account.

Second, as mentioned, bleaching agents themselves lead to a weakening of the tooth structure through the chemi-cal modification of the dentin.27,28 A re-cent publication supported the use of sodium perborate mixed with water in this respect, since this combination led to a significantly smaller additional open-ing of the dentinal tubules compared to all other bleaching agents. Interestingly

worst effect.29

Another important consideration is the influence of bleaching on dentin bonding. As emphasized in part 1, the quality of the internal reconstruction af-ter endodontic therapy is of key impor-tance in reconstituting the resistance to fracture. Using an adhesive approach is advisable but technique sensitive and, in general, all bleaching agents lead to reduced bond strengths and increased microleakage. Consequently, the use of antioxidants has been advocated to counteract this effect (eg, sodium ascor-

-cedure for at least 10 days after washing out the bleaching agent The antioxi-dant is especially necessary and should be mandatory if bonding with simplified single bond dentin adhesives, or if de-layed bonding is not warranted or pos-sible.

However, good dentin adhesion can be achieved if: a) sodium perborate mixed with water is used to bleach, b) the tooth is left with saline solution for 7 days after

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removal of the bleaching agent, and c) a scientifically and clinically well estab-lished self-etching 2-step dentin bonding

For enamel, the same principle of waiting after washing off the bleaching agent is a simple and successful strategy. Recent proposals for new resin formulations that are supposed to allow immediate bond-ing after bleaching have not proved as effective.

Since adhesion within the root remains a challenge even in ideal experimental

Fig 15incisor with PFM crown, initial clinical situation.

Fig 16 -tial radiographic situ-ation. A carbon com-posite post had been placed.

Fig 17post removal.

Fig 18 -nal bleaching of coronal part of the abutment tooth.

conditions – owing to unfavorable ovoid root canal configurations and dentin mi-crostructure in the deeper parts of the root canal – the root should not be further compromised by using bleach-ing techniques inside the root canal. As long as the intracoronal bleaching is performed within the access cavity reaching to the level where the connec-tive tissue attachment ends coronally, the results constitute a sufficient com-promise esthetically,26 even in the criti-

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Fig 19tooth with bonded fiber post and core, after internal bleaching with sodium perborate and water.

Fig 20technique.

Fig 21 Fig 22showing good adaptation of the short fiber post and bonded core to the den-

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What about the predictability and stability of bleaching procedures?

There has been some debate about the predictability and long-term effective-ness of internal bleaching, with de-scribed esthetic success rates of around 90% after 2 years, 75% after 5 years and 60% after 16 years. The potential causes for the recurrence of discoloration have been suggested as: a) the same sub-stances as those having caused the ini-tial discoloration, or b) penetration of pig-ments from the oral cavity, or c) bacterial reinfection of the root canal system with subsequent infiltration into the cervical and coronal dentin.1

From long-term studies and clinical observations, the following can be con-cluded:

!" Internal bleaching is a technique-sensitive approach. Potential rea-sons for failures are numerous, with coronal or apical leakage being the most frequent, and “short-cut” treat-ment protocols are more likely to have

apical-cervical seal, along with the optical quality of the access restora-tion, account for success or failure.!" The prognosis of the bleaching pro-

cedure is more prone to recurrence of discoloration if the tooth became rapidly discolored after the endodon-tic treatment.!" Subjective and objective satisfaction

of the dentist or the patient may differ substantially.!" The potential for intervention and the

concept of a progressive (conserva-

a discolored tooth are essential. Ag-gressive reconstructive concepts based just on esthetic considerations and early crowning can lead to prema-ture tooth loss. Therefore, bleaching instead of removing tooth substance is the preferable treatment, both for non-reconstructive and reconstruc-tive cases.26

May crowns or veneers compensate darkened coronal tooth structure?

First of all it is important to understand the concept of illumination of the oral tis-sues. The tooth with its clinical crown and root, the gingiva, the bone and the periodontium form an optical unit. Light is transmitted by diffuse reflection into the tissues. It is therefore critical not to disturb this delicate system with discol-

Fig 23 Limited light conducting properties of fib-er posts with good mechanical properties preclude the use of long posts, if light-cured materials are to be used.

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orations or by the introduction of inad-equate opaque or dark restorative ma-terials. Of particular importance in this respect is a soft color transition from the cervical third of the clinical crown into the adjacent gingival tissues.

Since the mid 1960s, dental techni-cians and prosthodontists tried to imple-ment this concept in order to improve the esthetics of full crown margins. In the 1980s, PFM crowns without metal collars were introduced, using shoulder and ve-neering porcelains with better light con-ducting properties to illuminate the adja-cent tissues. Despite these efforts, the results were never completely sat-isfying when the underlying tooth struc-ture was dark, or if there were vital and rather translucent teeth to be matched. Hence the search and development of true light conducting materials as frame-works with lower opacity than metal or the pre-existing all-ceramic cores.

Today, in the case of vital teeth with adequate tooth substance, more con-servative bonded porcelain restorations, such as veneers and anterior partial all-ceramic crowns, are increasingly the treatment of choice as compared to full crowns, due to esthetic, technical and biological advantages. It is impor-tant to understand that the success of these restorations is largely based on the esthetic and mechanical advantag-es of the natural uncompromised tooth substrate as the foundation of the resto-ration rather than an artificial substrate. As a consequence of this success, the concept has been extended to endo-dontically treated teeth, with the idea be-hind to convert darkened tooth structure into vital looking tissues. Naturally this is not only relevant to bonded lami-

nates and all-ceramic partial crowns, as a wide variety of all-ceramic crown systems exist today with excellent opti-cal properties and long-term survival, in particular, the new generation of glass-ceramic materials. In addition, these materials allow the provision of bonded full coverage “veneer type” crowns with

-

Consequently, the management of discolored tooth substrate becomes increasingly important. It should be re-membered that all attempts to ‘mask out’ discolored tooth substance will invari-ably end up with increased opacity and therefore unnatural reflection of the light instead of a diffuse reflection inside the materials. This is of particular importance when veneering a tooth with a discolored cervical zone, as the fine veneer margins cannot create the appropriate color tran-sition from the tooth crown into the gin-giva. If a full crown is provided in such a case, a pleasing result can be achieved by using opaque all-ceramic framework materials, provided that adjacent struc-tures are also more opaque and the gin-gival tissue is thick, but this is rather the exception than the rule.57,58 The same is true if opaque cements are used to cover dark underlying substance.

Above all, trying to mask out dis-colored teeth should not result in over-preparation:59 the mission statement of Hippocrates primum nihil nocere (first

Thus the clinical concept for man-agement of discolored tooth substance should always consider internal bleach-ing as first option, even if the result will not be absolutely perfect.

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If the tooth needs an additional indi-rect restoration, a veneer or full cover-age veneer-crown is an attractive and less invasive solution. In the author’s own experience over the last 15 years from when the concept first was used, long-term results for esthetics and sur-vival rates in both types of restorations are comparable to all-ceramic crowns. However, in the literature there are only studies with vital teeth available at the moment, which show a survival rate of

100% for extended veneers over 5 years.60,61 The observation of small su-perficial cracks not influencing survival

is similar to what can be observed within the enamel of natural teeth.

One drawback certainly is if the dis-colored tooth has already been restored with a post. If removal of the post without risk of damage to the root is viable, then the internal bleaching can be performed before a new post and core is fabricat-ed. If this is considered too risky, metallic posts and cores can at least be masked with a tooth-colored opaquer and com-posite to avoid to improve the substrate color for an all-ceramic framework.

This leads to the next question: Can tooth-colored posts enhance the color of dark roots?

Tooth-colored posts have long been advocated in esthetic dentistry. Since early trials around 1965 by John McLean with Alumina posts, the concept has been further developed to mechanically more reliable posts, with the introduc-tion of the first Zirconia posts in 1995and the first fiber posts in 1990.

The proposed reasons for tooth-color-ed posts for esthetics in root treated teeth are:!" To illuminate the root and cervical re-

gion and thus brighten up darkened tooth substance.

Fig 24cast post and cores, leading to a disturbance in the illumination of the adjacent tissues.

Fig 25to the symmetry of the case, the suboptimal color transition from the abutment margins into the gin-gival tissues fortunately does not disturb too much in this case.

Fig 26 Case 5: left central incisor with polished cast post and core, right lateral incisor with tooth-colored post and core.

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!" To prevent any darkening effect of a post on non-discolored tooth substance.!" To create a tooth-colored basis for the

core and the crown.

While the first reason has already been disputed early on by experienced cli-nicians not being able to see any dif-ference in the color between a metallic post and a tooth-colored post put into the same dark root under natural light conditions, the second two points are good arguments for tooth-colored posts. In fact a recent study showed that there is no difference in the cervical color of abutment teeth between white and me-tallic posts, however tooth-colored posts and cores were beneficial for the overall color of the all-ceramic crowns.65 This is in line with observations of clinicians aware of these subtle differences.66

Some care must be taken when trying to translate in vitro studies about color influences into clinical practice. Some subtle components of the color, such as the quality of the internal diffuse reflec-tion depending on the intensity of light and the softness of the transition into the marginal gingiva cannot be measured

Fig 27 Case 5: final picture showing the good reflection properties of the polished metal part of the left central abutment tooth.

Fig 28 Case 6: abutment teeth with various de-grees of discolorations.

by photospectroscopic studies67 and may lead to incorrect clinical recom-mendations in specific cases.

However, given the clinical and sci-entific evidence, there is actually little reason to take out existing well adapted and luted cast post and cores if the re-maining dentin itself is not discolored and does not require bleaching. It is clinically sufficient to mask the buccal part of the metal with a tooth-colored opaquer. If space and residual thick-ness of a gold alloy post and core do not allow to do this, another smart ap-proach is to polish the buccal part of the exposed metal to a high gloss, thus creating total reflection of the light at the core surface.68 This concept has been widely used by the author for years with no adverse effects regarding the reten-

In conclusion, it can be stated that the color of the remaining tooth sub-strate is of much greater importance than the color of the post and cannot be influenced positively by the post in the cervical and apical region, however having a tooth-colored post is beneficial for the core.

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Can soft tissue thickening compensate darkened cervical root structure?

A soft color transition from the crown into the soft tissue is essential for an esthetically pleasing result. In the pre-ceding pages, the focus was placed on the root and crown of the tooth and how negative effects can be managed. However, if discolorations are still pre-sent in the critical cervical supra- and subgingival zone, it makes sense to consider influencing the soft tissue characteristics.

The margin of the soft tissue cover-ing the cervical part of the root plays an important role as a “curtain” to hide unpleasing structures. In addition, the buccal bone plate has also some mask-ing effect over a discolored root. A thick bone plate can virtually completely mask out the root discoloration. In periodontol-ogy, there is little information available about the masking effect of the soft tis-

sue. In oral implantology, however, some studies have been performed looking at the influence of various abutment ma-terials on the color of the existing soft tissues, and how variations in the soft tissue thickness can modify the overall color resulting from abutment and cov-ering soft tissue. Since these abutments all have a subgingival component and a titanium implant base, this would appear to offer a situation well in line with a dis-colored root. Comparing zirconia, pol-ished gold alloys and machined titanium in a pig model, a visible difference was always present if the tissue thickness

in thickness, only zirconia (regardless of

material itself had no influence.69 In a human study, comparing metal abut-ments and PFM crowns with all-ceramic abutments and crowns, the latter be-haved better, but there was still a visible difference for both groups compared to the adjacent teeth.70 Another study presented similar results,71 although no correlation between the thickness of the mucosa and the respective amount of discoloration could be found.

In essence, the fiber content and the degree of keratinization may play a more important role for the masking ability than the soft tissue thickness alone. In this respect, the use of a connective tis-sue graft taken from the palate with its higher content of collagen fibers is the most promising approach using an en-velope technique to improve the esthetic integration of the augmented tissue. Some modifications in the technique, in-cluding a microsurgical approach, have been introduced to further decrease

Fig 29 Case 6: layered glass ceramic crowns with internal opaquer and varying opacities of frameworks.

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healing complications and unesthetic tissue scars.

An additional benefit of this approach is the easier tissue handling during the reconstructive phase and the preven-tion of post-reconstructive recessions over time, which may expose further dis-colored root parts. Indeed, since many of the discolored teeth exhibit some cer-vical tissue loss over time anyway, this procedure can also be considered as a preventive treatment of a cervical reces-sion,76 dealing not primarily with health, but with stable, esthetic tissue levels. It may also serve to counteract the loss in cervical tissue height that occurs by tis-sue modeling during the aging process, which is more noticed around discolor-ed roots and is independent of the pres-ence or absence of dental restorations.

As a conclusion, soft tissue thicken-ing may not completely solve the prob-lem of the discolored cervical hard and soft tissue zone, but it can improve the overall result by at least stabilizing soft

tissue contours and preventing further exposure of discolored root surfaces.

Final consideration: at what point should we give up and extract?It is fair to state that a tooth should be saved as long as there is a predictable way to functionally and biologically do so with a reasonable prognosis. This 2-part article has shown various possi-bilities to overcome classic biomechani-cal and esthetic problems with respect to minimizing reconstructive risks. The basis for reconstructive survival in the context of this article, however, is the quality of the endodontic treatment as the starting point.

It can also be stated that today too many teeth are extracted in favor of im-plants, with insufficient regard for the extensive reconstructive options avail-able to maintain them. Furthermore, the

Fig 30 Case 6: final picture of the four anterior teeth, showing an acceptable color transition be-

abutment teeth.

Fig 31 Case 6: final picture of the right side, showing an acceptable color transition between the

vital discolored central incisor.

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short- and long-term biologic, esthetic and technical complications of implants are not fully appreciated.77 Unfortu-nately, poor endodontic treatment is still a major factor in premature tooth loss. However, if performed correctly, results are at least as good as replacement with implants for single units.77 It is striking that despite this fact, today a tendency towards a more extraction-oriented re-constructive concept can be observed in practice. There are two main reasons for this.

The first reason is that in clinical de-cision-making, the predictability of the whole procedure is of primary impor-tance in respect of complications and cost. Obviously there is some pessimism among clinicians regarding the progno-sis of endodontic treatments in general and this is not completely unfounded. The combined failure rate of endodonti-cally treated teeth in general practice is higher than described in earlier reports:

up to 20% is documented.78 In general, the outcome of endodontic treatments may have been overestimated in previ-ously published reviews because of the general lack of correct apical diagnosis.

the endodontic status cannot correctly be analyzed. The authors of a current review state: “In conclusion, the serious limitations of longitudinal clinical studies restrict the correct interpretation of root canal treatment outcomes. Systematic reviews reporting the success rates of root canal treatment without referring to these limitations may mislead read-ers”.79 Therefore, the trend towards sim-plified endodontic protocols may also be based on incorrect interpretations of

previous studies and may produce less successful results than expected or than achieved with the classic concepts of experienced endodontic specialists. A

-ed in a private practice by a specialist, documented an overall success rate of 91.5%.80 Initial endodontic treatments

-pared to the non-surgical retreatment

how important the quality of the first en-dodontic treatment is for the long-term success. In addition, the coronal resto-ration has a significant influence in the success of the endodontic treatment. Thus, to strive in every respect for an optimal restoration is as essential as an optimal endodontic treatment alone.81

The second reason is that measures to potentially save a compromised tooth can later preclude the placement of an implant or make it very demanding. Therefore, if an endodontic retreatment due to recurrent apical pathology is considered, above all, careful diagnos-tic steps including soft and hard tissue probing and radiographs are required. Conventional radiographs do not allow proper analysis and interpretation of the root and remaining bone housing around the root. The possible causes for the endodontic failure (eg, crack, fracture, perforation, insufficient root filling or ac-

established without a high-resolution

and appropriate treatment approach can only be determined based on an accurate diagnosis.

Periapical microsurgery should be performed exclusively if non-surgical endodontic retreatment is not viable,

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and if the remaining bone housing is suf-ficient. The surgical approach seems to be more successful in the short term, but

6 years for the non-surgical approach,

the surgical approach.82 In addition, the added bone loss caused by the surgical access osteotomy and incomplete heal-ing can make the placement of an im-plant after a potential failure and eventful extraction very difficult.

Ultimately, when we examine the treat-ment outcome of implant versus non-vi-

tal tooth-supported restorations, there is no clear winner in terms of sustainabil-

solutions require a perfect synergy of all the fields of specialties involved and the treatment steps to achieve the optimal result for the individual patient.

AcknowledgementsThe author would like to thank Dr Tidu Mankoo for the systematic and thorough editing of the whole es-

of the endodontic aspects, and Walter Gebhard and Nic Pietrobon for their contribution in creating the dental ceramics.

References, Part 2

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Lambrianidis T. Ex vivo study of the efficiency of two techniques for the removal of mineral trioxide aggre-gate used as a root canal filling material. J Endod

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16. Spasser HA . A simple bleaching technique using sodium perborate. New York

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1997;28:771–777.18. Dietschi D. Nonvital bleach-

ing: general considerations and report of two failure cases. Eur J Esthet Dent 2006;1:52–61.

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Documents

The Ideal Restoration of Endodontically Treated Teeth Structural and Esthetic Considerations a Review of the Literature and Clinical Guidelines for the Restorative Clinician Copia