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ABSTRACT

Every clinician tries their best to restore teeth with history of root canal filling with various ways which range from amalgam filling or composite with or without prefabricated post, other dental practitioners try to restore the teeth with a crown with or without the use of custom core. Lastly, the third group attempt restoring using inlay or onlay from metal or composite or glass ceramic. The uprising generation have been mixing conventional crowns and inlays, onlays, along with introducing endo-crown; which provides larger surface area between natural tooth and restoration with bonding and luting cement.

Nowadays, it’s a daily challenge for a dental health care professional to preserve maximal amount of tooth structure; especially the enamel which is the golden portion for bonding of restoration; which is a vital factor for the success of restoration; it guarantees mechanical stability of tooth, restoration integrity, increase surfaces for adhesion and greatly affect the durability success.

Endodontically treated teeth are directly affected by the amount of tooth structure area remaining; therefore, we need to increase biomechanical and chemical bonding between the two parts (tooth and restoration). Although the postcore and crown remains the treatment of choice for many years. However, there has been many reported cases with fracture of tooth or root therefore, this results in the removal of the tooth especially in the case of teeth consisting of multi-roots.

Since the bonding agent improved in quality within the last few years which made it widespread and efficient in the dental field along with adhesion and cohesion which has also been improving allowing dental practitioners to provide various treatment options in the aspect of teeth with root filling. Improving the strength of glass ceramic material resulted in a revolution and expansion of its uses in various ways.

Endo-crown has been used as a suitable alternative option, as it has superior result in esthetics, better mechanical performance, less clinical time in addition to less cost, because it covers larger surface area and can compensate different types of loss of tooth structure which benefits from the pulp chamber space to gain force distribution to the whole tooth structure not only the finish line of the normal crown. Therefore, the force will be distributed evenly on the tooth structure which all results in the reduction of the incident of cracks and fractures.

KEYWORDS

Endocrown, Endodontically treated teeth, Adhesvive restoration, Conservative dentistry, Minimally invasive.

Endo-crown: Viable Option for Restoration of Endodontically Treated Teeth

Niran Al- Gobori - BDS, MScMaster Degree; La Sapienza University | Private practice; Bright Dental Polyclinic | Abu Dhabi, UAE | neran.hassan@gmail.com

Gianluca Gambarini - MD, DDSProfessor of Endodontics, University of Rome, La Sapienza, Dental School | Official Italian member of ANSI/ADA and ISO Committees for

Endodontic Materials | Private practice limited to Endodontics, Rome, Italy | ggambarini@tin.it

INTRODUCTION

Rebuilding with endo-crown has been recommended as a sound newly developed method as it is a conservative, efficient technique for root filled tooth especially in the posterior region where the forces of mastication are high. This technique is based on reconstruction of missing tooth structure by merging both coronal and core restoration in a one- piece crown which will be anchored into the pulp chamber by making benefiting from the hallow space in the pulp chamber.

The walls of the pulp chamber provide macro-mechanical retention without requiring the use intra

canal retention, unlike the post build up which increases the stress along the root canal. The adhesive material (etching, bonding and luting cement) providing micro-retention and generates a media to link the endo-crown material (glass ceramic) to the tooth structure.

Although, endo-crown has showed proper stability, retention and good mechanical performance including even distribution of stress on resin cement and dental structure.

Endo-crown has been elucidated first by Bindle and Mörmann as a one-piece ceramic construction based on

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concepts developed by Pissis. This technique depends on preserving enamel structure instead of enamel amputation in conventional crown. Furthermore, prefabricated or custom-made core will increase strain and demolition of the radicular dentine and increase the risk of root fracture during or after delivery of crown.

CONCEPT OF ENDO-CROWN

• The idea to engage maximum pulp chamber area of root canal treated tooth with one-piece lithium disilicate restorative material which will provide wider cuspal coverage.

• To take advantage of bonding lithium disilicate material with sound remaining enamel structure, which is the major key of bonding success.

• The new bonding generations allow us to adhere enamel margin, dentine and the pulpal chamber space to lithium dislicialte material.

• Avoiding root preparation to insert pre-fabricate post (metal of fiber post), which will lead to compromising the root structure.

• Avoid impression for custom post, multiple visits and time loss. Also, we will end by root crack and loss of cementation.

• To reduce patient cost and chairside time. Changes occurring in Endodontically Treated Teeth:

The main idea is improving fracture resistance of endodontically treated teeth and reduce the loss of structural integrity due to trauma from occlusal forces or occurrence of caries and reduction micro spaces between tooth and restoration by using conservative cavity preparation rather than physical changes in dentine or enamel caused by dehydration or over reduction of tooth structure throughout the preparation of normal crown.

Studies shows a prove that marginal ridge loss is the main cause of reduction and durability of endodontically treated teeth; some researchers have reported that the approach of cavity and root canal preparation causes an increase in the loss of tooth structure which leads to variation in brittleness of dentine.

There are two important factors which directly impact the longevity of endodontic treatment which include:

1. Suitable restoration that conserve tooth structure and it has similar resilience of tooth structure.

2. Type of restorative material used.

The integrity and quality of the remaining tooth structure is preferably to be maintained carefully, in order to ensure a solid base which is essential for restoration and optimizing the structural strength of tooth restoration. Biomechanical principles specify that structural strength of a tooth depends on the quality, strength of hard

tissue and the integrity of the anatomical structure. Following endodontic treatment distinction in tissue quality has been proved to have a negligible influence on biomechanical tooth behavior.

Mechanically conservative access cavity has been found to be minimally affecting the fracture resistance of tooth, another important factor is the disability of neurosensory feedback related to the loss of pulp tissue which might decrease the protection of the endodontically treated teeth during mastication.

A study has been done on healthy human teeth comparing the influence of endodontics and restorative procedure on cusp durability which proved that endo- procedures, occlusal cavity and MOD cavity preparation reduce strength by 5%, 20% and 63% respectively.1

RESTORATION OF ENDODONTICALLY TREATED TEETH

The optimal way to reinstate teeth after endo-treatment proceeds to remain a debatable topic of heated discussion to this day. Some criteria must be taken into consideration; such as, the functional requisite and quantity of remaining tooth structures are important factors to be reviewed throughout treatment planning.

Ferrule thickness influence: on fracture resistance of Endodontically Treated Teeth:

- When the ferrule is present in an amount which is more than 2mm along with intra- root post placement it might lead reduce the incidence of fatal fracture, disabling dental remnant. Since it permits the transmission of occlusal forces to the cemento-enamel junction (if fracture occurs its horizontal).

- In the absence of ferrule, the occlusal forces are directed towards the root, resulting in root fracture. Consequently, the ferrule allows the stress to be distributed to different tooth surfaces.

- It has been proven that 1.5-2.0mm long ferrule can increase the fracture resistance of endodontically treated tooth. Thickness is usually related to the remaining tooth structure after endo-treatment along with the amount of dentine that needs to be removed during crown preparation, which depends on the cervical end design and on the type of crown that has been used. So, the presence of ferrule can increase the fracture resistance of endodontically treated teeth.

(Fig. 1)2

Classification of fracture modes; repairable fracture includes fractures above CEJ or core-tooth fracture, non-repairable fracture includes fractures below CEJ, apical third fractures or vertical root fracture

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ENDO-CROWN

The authentic breakthrough in endodontically treated teeth restoration was the initiation of adhesion and development of dentine adhesive material.

The main advantage of adhesive restoration is the micro-retentive component is no longer obligatory as long as enough surface area is present. The use of intra-radicular post has been proven to cause more root cracks and vertical fracture, therefore, its use has been restricted to root filled tooth.

Nowadays, the golden standard in restoration of endodontically treated teeth is to minimize tissue preparation and maximum tissue conservation. By following this rule, endo-crowns are easily applied as prosthetic option in restoration endodontically treated teeth incisors, premolars and molars with excessive tissue loss.

Pissis was the precursor of the infamous endo-crown technique described as “mono-block porcelain technique” in 1999. Endo-crown was referred to for the first time by “bindle & mörmann” as adhesive endo-crown and indicated as a full porcelain crown fixed to endo-treated posterior teeth. Endocrown is illustrated as “mono lithic one-piece” full composite or full ceramic overlays which restore partially or totally the coronal portion of a deviated tooth. classified by a supra cervical butt joint, retaining maximum enamel to improve adhesion and extend inside pulp chamber and partially inside root canal with a short endo-core. This represents viable alternative option to restore endo treated teeth.3

These restorations have micromechanical retention by being anchored to the innermost portion of the pulp chamber and the cavity margins and micromechanical by adhesive cementation. The demonstration of this method is used in cases with excessive loss of coronal tooth structure, diminished intermaxillary space, and short critical crowns with poor stability and retention for teeth with acutely curved root canal, which circumvents the insertion of intra canal retainers.

This restoration alternative is counter-indicated when bonding cannot be achieved and also for teeth with pulp chamber less than 3mm in depth or with cervical margins thinner than 2mm. Contrasted to conventional crown, endo crowns are low cost, short clinical time, short preparation time, minimal chair time, ease of application and good esthetic result. Furthermore, endo-crowns are alternative in teeth with atresia clinical crown, calcified, curved root canal.

Endo-crown Classification

There are three various types of endo-crowns which were demonstrated in the dental field which is used on the basis of remnant tooth tissue amount after preparing the tooth. Determining of endo-crown classes was based on the

inspection of clinical pictures and/or master casts by two different dental practitioners. In case deviation in opinions, a fair settlement is established between the two.

CLASS I: shows a tooth structure where a minimum of two cuspal walls have a height greater than half of their original height.

CLASS II: demonstrates a prepared tooth where a maximum of one cuspal wall has a height more of the half of its original height.

CLASS III: describes a tooth preparation where all cuspal walls are less than the half of the original height. Moreover, the existance of a buccal chamber or an extension in the pulp chamber were made clear.

INDICATION AND CONTRAINDICATION

• Successfully root treated teeth • Supra-gingival margins inter-proximally• Adequate thickness of buccal and palatal cusp • Adequate height of buccal and palatal cusp (this is not

to be administrated in the case of the height being less than 50% height. The endo-crown is contraindicated if, adhesion cannot be insured, if the pulpal chamber is less than 3mm in depth or if the cervical margin is less than 2mm in width for most of its circumference)

PREPARATION

Endo crown preparation is made up of circumferential supra cervical 1.0-1.2mm deep butt joint, in order to allow maximum conservation of enamel structure which improves adhesion. The endo-crown invades the pulp chamber however, not the root canal. The central retentive cavity inside the pulp chamber builds up both the crown and the core as a single mono-block unit structure which doesn’t require the support of the root canal.

The recommended dimensions: a cylindrical pivot which is 3mm in diameter and 5mm in depth for the first maxillary premolars. 5mm in depth for molars. However, the exact dimensions are not set for the central cavity.

The thickness of endo-crown of the occlusal ceramic portion usually ranges from 3-7mm. In an in vitro study, it has been proved that as occlusal thickness increases fracture resistance increases of ceramic potion.

(Fig. 2)4 Classification of Endo-crown

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Mormann etel demonstrated that fracture resistance with occlusal thickness 5.5mm was two times higher than ceramic crown with occlusal thickness 1.5mm.

Bindle and Mormann assessed the performance of 208 endo-crown cemented to molars and premolars and reported that premolars had more cases of fractures than molars.5

The adhesion loss of endo-crown on premolars occurs due to less surface area for adhesive bonding in compression with molars, along with a high ratio of the prepared tooth surface to overall crown which may cause higher leverage for premolar than molar.

CHOICE OF MATERIAL

With the evolution of ceramics that had high mechanical strength, bio-combability and biomimicry. Its wear coefficient is nearly close to that of natural human teeth. They also were capable of being acid etched such as reinforced with Lucile or lithium disilicate allied with the adhesive system + resinous cement made it possible to restore posterior teeth without need of core + intra-radicular posts.

Indirect composites and porcelain lab systems are the best option for restoration of wide cavities in the posterior teeth region. manufactured in laboratory, indirect porcelain or composite resin inlays offer optimal esthetic with the least tooth preparation with rehabilitation mechanical and biological functions, both indirect resin and porcelain ensure eminent marginal fit, best proximal shrinkage, high wear resistance and optimal esthetics with feldspathic ceramic used in CAD/CAM in compression with dental ceramic material done in laboratory, they demonstrated higher fracture strength and structural homogeneity, this preparation is best for conservative + modern preparation design. In addition to that, the restoration is completed in single visit with: good esthetic and good marginal fitness.

Chang YT in compression to the failure mode and fracture resistance of CEREC endo-crown with post-core support crowns on maxillary premolars, it has been showed that CEREC endo-crowns have higher fracture resistance than typical crowns, however, failure; no major difference has been found in between the two types.6

Lately, fiber-reinforced composite system relocated from intra-coronal restoration into crown and bridge restoration by intensifying the:

1. Esthetic2. Physical 3. Mechanical properties

In order for them to become extremely a good option to ceramic & resin material. On the other hand, CADCAM crowns made from malleable composite resin block to

insure a better alternative to all ceramic crowns from the aspect of marginal adaptation.

In a study on adhesive restoration of endodontically treated anterior teeth treated with an endo-crown using a composite or ceramic block was assessed with no significant variations in fracture resistance and failure mode were demonstrated between two groups. The similar flexural strength values of composite and ceramic CAD/CAM blocks and ferrule effect were emphasized as it might have been important in achieving those results.

Zirconia et al. has introduced 3D FE mode of maxillary central incisor with various restoring material and configuration composite, sintered alumina, field spathic ceramic endo-crown and centered alumina, field spathic ceramic glass fiber post supported crowns were put to test in the study. The analysis, was that high stiffness material cause stress, in the interfaces and high negative effect on bio mechanical properties of restoration, in contrast to, low stiffness material, E.g.: composite resin, were found to co-exist the natural flexural properties of tooth and decrease stresses arising at the interface.

CEMENTATION

To this day, the most accepted type of cement is resin cement which consists of BISGMA or ODMA resin matrix along with inorganic filler particles. Resin cement is the most commonly used in cementation of ceramic, metal and composite indirect restoration.

The major issue with eugenol containing root canal seeder in which inhibits the polymerization has been vanquished by cleaning the root canal walls and acid-etching. Cleaning all of the gutta percha and eugenol suppressed sealer is tough without removing dental tissue debris on the rugged surface of root canal which averts the adequate roughens of dentine + polymerization of resin cement.

Yet, in an in vitro study, it has been brought to attention that eugenol-containing paste doesn’t have negative effect on the bond durability and stability of the resin.7

PERSONAL OPINION

I would like to share my personal observation on what I feel is a sound, conservative efficient technique that preserve sound tooth structure. In which it avoids:

1. Total enamel amputation 2. Further stress and destruction of the radicular dentine 3. Reduces the chances of root fracture along with

iatrogenic damage during preparation

CONSIST OF:

1. Circular butt margin of the angle of 902. Central retention cavity inside the pulp chamber • Without intra-radicular preparation

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• It is a viable option, simple and efficient concept compatible with the philosophy of bio-integrated prothesis

DISCUSSION

Now the gold standard for restoring endodontically treated teeth is minimally invasive preparation with maximal tissue conservation. The endo-crown is precisely following this principle. The preparation consists of a circular butt joint margin and central retention cavity.8

In endo-crown we have two types of mechanical retention:

1. Macromechanical retention by internal portion. 2. Micromechanical retention is achieved by adhesive

cementation.

The choice of prothesis to restore endodontically treated teeth is directly dependent on the amount of remaining tooth structure after R.E treatment. The best and long-term maintainable restoration can be obtained from reinforcement of remaining healthy tooth structure which can contribute in the harmony of a tooth restoration complex.

In the modern time of esthetic and adhesive dentistry, endo-crown aids as a feasible and conservative alternative option to conventional post and core crowns as it preserves root tissue, in addition to limiting internal preparation of pulp chamber to its anatomic shape.Endo-crown- post endodontic restoration is possible in all teeth but it should be restricted only on molars since masticatory forces on premolars has not been the same as that achieved in molars. It is assumed that small pulp chambers of premolars restrain the bonding strength of the adhesive system and resin cement.9

The arrangement of premolar crowns in which the height of the piece is larger than the width which may create a long lever arm, intensifies the risk of adhesive fracture and displacement.10

However, when restricted to molars endo-crown shows excellent accomplishment in relation to operation of occlusal forces, bond strength and esthetic recovery.11,12

Various materials are proposed for production of endo-crown such as, field spathic porcelain, glass ceramic, hybrid composite resin and current computer aided design/computer aided producing all ceramic blocks. The settlement of tooth preparation for all types of restoration are the same applied, the preparation is conservative as when compared to the traditional crowns with minimal involvement of biological width. In comparison to the post and core restoration, bonding surface provided by the pulpal chamber of the endo-crown is frequently equal or leveled superior to that acquired from the bonding of a radicular post of 8mm depth.

Endo-crown preparation principles follows the same path as for indirect inlay and onlay restoration: slightly banished axial wall (10-12) and flat floor of pulp chamber.

Supra gingival termination eases the steps of impression, adjustment and cementation.

In fabrication of endo-crown, was used monolithic, lithium disilicate based ceramic, IPS e.max (ivoclar vivadent, schan, Liechtenstein) which has appropriate physical properties and considerable translucence, according to manufacturer, there are two types of ceramic IPS e-max system; monolithic type with an occlusal dimension of 1.5mm thickness, without the need for a follow-up porcelain coating, and the lithium disilicate coping (minimum: 0.7mm) covered with a porcelain coating (maximum: 0.7mm).

Both, have an adequate strength for restoration of posterior teeth (=/-400uPa), in addition to not advancing of excessive wear of the antagonist teeth.13

There is also the possibility to use CAD/CAM for the production of restoration in single block. However, considering that preparation walls were very thin, the choice was to use ceramic injection by the lost wax technique.14

Yet, the resin cement is made of BiS-GMA or UDMA resin matrix and m-organic filler particles are the most approved type of cements. When differentiated to conventional cements, resin cements have superior esthetic and mechanical properties, so it has increasing use in cementation of ceramic and composite indirect restoration.15

CONCLUSION

Endo-crown have been a viable and feasible alternative option to conventional post-core and fixed partial dentures in restoration of endodontically treated teeth with extensive loss of coronal tissue structure. Compared to traditional techniques, better mechanical performance, low cost, better esthetic and short clinical time are the benefits of endo-crown and can be successfully used for teeth restoration with short clinical crown.

REFERENCES1. Reeh ES, Douglas WH, Messer HH. Stiffness of endodontically-

treated teeth related to restoration technique. J Dent Res. 1989;68(11):1540–4.

2. Vivek Aggarwal, Mamta Singla, Suman Yadav et al. The effect of ferrule presence and type of dowel on fracture resistance of endodontically treated teeth restored with metal-ceramic crowns. JCD. 2014;17(2):183-7.

3. Robbins JW. Restoration of the endodontically treated tooth. Dent Clin North Am. 2002;46(2):367–84.

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4. G.R. Biacchi, B. Mello, R.T. basting, et al. The endocrown: analternative approach for restoring extensively damaged molars,JERD. 2013;25(6):383-90.

5. Bindl A, Mörmann WH. Clinical evaluation of adhesively placedCerec endo-crowns after 2 years—preliminary results. J Adhes Dent.1999;1(3):255–65.

6. Chang CY, Kuo JS, Lin YS, Chang YH. Fracture resistance andfailure modes of CEREC endo-crowns and conventional post andcore-supported CEREC crowns. J Dent Sci. 2009;4(3):110–7.

7. Reeh ES, Douglas WH, Messer HH. Stiffness of endodontically-treated teeth related to restoration technique. J Dent Res.1989;68(11):1540–4.

8. Van Meerbeek B, Perdigão J, Lambrechts P, Vanherle G. The clinicalperformance of adhesives. J Dent. 1998;26:1-20.

9. Bindl A, Richter B, Mörmann WH. Survival of ceramic-computer- aided/manufacturing crowns bonded to preparations with reducedmacroretention geometry. Int J Prosthodont. 2005;18:219–24.

10. Lander E, Dietschi D. Endocrown: a clinical report. QuintessenceInt. 2008;39:99–106.

11. Biacchi GR, Basting RT. Comparison of fracture strength ofendocrowns and glass fiber post-retained conventional crowns.Oper Dent. 2012;37:130–3.

12. Valentina V, Aleksandar T, Dejan L, et al. Restoring endodonticallytreated teeth with all-ceramic endo-crowns—case report. SerbianDent J. 2008;55:54–64.

13. Stappert CF, Att W, Gerds T, Strub JR. Fracture resistance ofdifferent partial coverage ceramic molar restorations: an in vitroinvestigation. J Am Dent Assoc. 2006;137(4):514-22.

14. Esquivel-Upshaw JF, Rose WF Jr, Barrett AA, Oliveira ER, Yang MC,Clark AE, et al. Three years in vivo wear: core-ceramic, veneers,and enamel antagonists. Dent Mater. 2012;28(6):615- 21.

15. McCabe JF, Walls AWG. Application of dental materials. 8th Ed.,Madlen: Blackwell Science. 1998;189-201.

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