ENDO CROWN: AN APPROACH FOR RESTORING ENDODONTICALLY TREATED RIGHT MANDIBULAR FIRST MOLARS WITH LARGE CORONAL DESTRUCTION- A CASE REPORT

Rehabilitation of endodontically treated molar stilla challenge. After endodontic management of extensively carious molars, theyhave decreased mechanical characteristics. They became fragile and that is in relation with the removal of pulp and adjacent dentin tissues. Endocrown which is a single partial restoration could be measured as a good alternative for restoring molars having large coronal destruction and presenting endodontic treatment complications. We discuss the indication and use of endocrown to substitute single crowns with intraradicular retention and to present a clinical case report of an endocrown-type restoration, made-up from lithium disilicate ceramic (IPS e.Max CAD) in a mandibular first molar with widespread coronal destruction.


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Endo Crown is a one-piece ceramic structure fixed to the internal walls of the pulp chamber and on the cavity margins to advance macro mechanical retention and the use of adhesive cementation would also improve micro retention [4].
The aim of the present paper is topresent a clinical case, in which an aesthetic and conservative posterior endocrown was used to restore a right mandibular first molar that presented endodontic treatment and extensive coronal destruction. We will deliberate through this work the indication and the use of endocrown [5].

Case Report
A 23-year-old male patient reported to the Department of Conservative Dentistry and Endodontics, NPDCH, Visnagar, Gujarat, India, for treatment of tooth #46. He suffered from major coronal destruction and needed to have his first molar restored. Medical history was non-contributory. Radiographic and clinical examinations were performed initially anda nonvital tooth (46) was identified with caries (Figures 1). Tooth was treated endodontically. The patient had a satisfactory oral hygiene and a favourable occlusion.  The prosthetic decision was to restore tooth (46) with an endo crown made-up from lithium disilicate ceramic (IPS e.Max CAD). The preparation for the endocrown is different from the conservativewhole crown. Monolithic, ceramic adhesive restoration requires specific preparation techniques to be appropriate for biomechanical needs. This is achieved by an overall reduction in the height of the occlusal surface of tooth by at least 2 mm in the axial direction and to get a cervical margin or "cervical sidewalk" in the form of a butt joint. The cervical 80 margin has to be supragingival and enamel walls less than 2 mm have to be removed. Differences in levels between the various parts of the cervical margin should be linked by a slope of no more than 60° to seepage a staircase effect. We used a cylindrical-conical diamond bur apprehended parallel to the occlusal plane, to decrease the occlusal surface. Then we used a diamond wheel bur to control the orientation of the reduction and to assurance a flat surface thanks to its shape. We used a cylindrical-conical diamond bur with a total occlusal convergence of 8° to create continuity between the coronal pulp chamber and endodontic access cavity. The bur was positioned along the long axis of the tooth; the preparation was done without too much pressure and without moving the pulpal floor. The molar after preparation ( Figure 3). We ended the preparation with lining the root canal entrances with glass ionomer cement to protect the orifice of the canal ( Figure 4). Then we completed a try-in of the endo crown and tested occlusion, internal, and proximal adjustments. The internal surface of the endo crown was etched with 9 percent hydrofluoric acid, washed with water, and dried with an air syringe. A coat of a silane coupling agent was applied for 2 minute and dried. Rubber dam was used to attain proper isolationand then phosphoric acid was applied onto the tooth surface for 15 sec on dentin and 30 sec on enamel, then profusely washed and dried, applied with adhesive, and polymerized for 20 sec with light curing. A thin layer of a dual polymerizing resin was applied to the prosthetic endocrown and then was introduced into the tooth and polymerized at intervals of 5 seconds, making it easy to eliminate cement excesses. It was polymerized for 50 seconds on all surfaces. The crown was examined for any occlusal interfering using ceramic finishing instruments.

Discussion:-
Therestorative treatment of molars with a large coronal destruction is a clinical challenge, requires careful planning [6].
That is why the dentist has to choose for the best treatment option to ensure an efficient treatment providing clinical longevity of molars. The endo crown is suitable for all molars, chiefly those with clinically little crowns, calcified root canals, or narrow canals. But it is not suggested if adhesion cannot be assured, if the pulpal chamber is less than 2 mm deep, or if the cervical margin is less than 2 mm wide for most of its circumference [7].

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This has been shown to be a beneficial technique as the procedure is easy.It facilitates the steps of impression taking and protects the periodontium. The use of ceramic has the advantages of biocompatibility and biomimicry and its wear coefficient is close to that of the natural tooth [8].
The single interface of a one-piece restoration makes cohesion better. The objective of the preparation is to get anextensive and stable surface resisting the compressive stresses that are frequent in molars [9].
The prepared surface is parallel to the occlusal plane thusdeliver stress resistance along the major axis of the tooth. The stress levels in teeth with endocrowns were lower than in teeth withcrowns. Because of the development of adhesive cementation systems, the need for macroretentive preparation for crowns has decreased [10].
The pulpal chamber cavity also deliversretention and stability. Its trapezoidal shape in mandibular molars and triangular shape in maxillary molars increase the restoration's stabilityand additional preparation is not desirable. The saddle form of the pulpal floor increases solidity. The adhesive qualities of the bonding material, makes it nonessential to attempt further use of post-involving root canals. The root canals do not need any exactshape.They are not fragilized by the drilling and they will not obtain the stresses associated with the use of post [11].
The compressive stresses are concentrated, being spread over the cervical butt joint and the walls of the pulp chamber. Dartora et al. haveevaluated the biomechanical behaviour of endodontically treated teeth restored using different extensions of endocrowns inside the pulp chamber and concluded that the greater extension of endocrowns provided improved mechanical performance. A 6 mm extension presented lower intensity and a better stress distribution pattern than a 2 mm extension which offered a low fracture resistance and a high possibility of rotating the piece when in function [12].
An in vitro study performed by Taha et al. was done to evaluate the effect of varying the margin designs on the fracture resistance of endodontically treated teeth restored with polymer-infiltrated ceramic endocrown restorationsThe results presented that endocrowns with axial reduction and a shoulder finish line had higher mean fracture resistance values than endocrowns with butt margin design. [13]. It has been also shown that butt joint designs providing a stable surface that resists the compressive stresses because it is prepared parallel to the occlusal plane [14].
Biacchi and Basting compared the fracture strength of two types of full ceramic crowns: indirect conservative crowns retained by glass fibre posts and endocrowns. They came to the conclusion that endocrowns were more resistant to compressive forces than the first ones. Finite element study highlighted the role of endocrowns in stress distribution [15].
According to Schultheis et al., endocrown seems to be a more reliable other for posterior loadbearing teeth, a bilayer configuration is more susceptible to reduce load fracture failure [16].
As stated by Biacchi et al., endocrowns procure acceptable function and aesthetics and reserve the biomechanical integrity of nonvital posterior teeth. The restoration is described to be less exposed to the adverse effects of degradation of the hybrid layer [17].
Researchlinking equivalent stresses in molars restored with endocrowns as well as posts and cores during masticatory simulation using finite element analysis revealed that teeth restored by endocrowns are potentially more resilient to failure than those with FRC posts. This study also showed that under physiological loads, ceramic endocrowns ideally cemented in molars should not be deboned [18].
A systematic review done by Sedrez-Porto et al. has compared clinical (survival) and in vitro (fracture-strength) studies of endocrown restorations associated to conventional treatments using intraradicular posts, direct composite resin, or inlay/onlay restorations; it has been shown that endocrowns may perform similarly or better than the conservative treatments [19].
Altier et al. evaluated the fracture resistance of three different endocrowns made of lithium disilicate ceramic and two different indirect resin composites and concluded that lithium disilicate ceramic endocrowns exhibited higher fracture strength than the indirect composite groups. It has been shown that endocrowns made of lithium disilicate-83 based ceramics are measured among the best restorative materials because of their adhesive properties;they promoted micromechanical interlocking with resin cement [20].
In vitro study accomplished by Gresnigt et al. evaluated the consequence of axial and lateral forces on the strength of endocrowns made of Metastable Lithium Disilicate and multiphase resin composite. It has been concluded that under axial loading, both Metastable Lithium Disilicate and multiphase resin composite used as endocrown material existing similar fracture strength but under lateral forces, the latter exhibited suggestively lower results. Tribst et al. evaluated the effect of a restorative material type on the biomechanical behaviour of endocrown restorations and concluded that Leucite presents a well stress distribution and it can be anauspicious alternative to lithium disilicate for the manufacture of endo crown restorations. Study conducted by Skalskyi et al. compared the fracture resistance of different restorative materials used in dental endocrown restorations. It has demonstrated that the mechanical behaviour of Zirconium dioxide in the tooth restorations altered [21].
The zirconium dioxide endocrowns cracked subsequent to crack propagation in the tooth. It has been also shown that the use of metal ceramic as endocrown material may deliver the lowest risk of failure during clinical use and had the highest fracture strength [22].
A study done by Darwish et al. showed that endodontically treated maxillary premolars restored with resin nanoceramic endocrowns obtainable better internal adaptation associated to those restored with lithium disilicate endocrowns and that endocrown preparation with smaller axial wall divergence ("6"degree) if better internal fit [23].
In a recent study, Zoidis et al. proposed polyetheretherketone (PEEK) as a substitute framework material for endocrown restorations. They demonstrated that the elastic modulus of the polyetheretherketone framework (5 GPa) veneered with indirect composite resin could dampen the occlusal forces defensive tooth structures better than ceramic materials. But further long-term clinical indication is required. CAD-CAM system, with aprojected success of 90.5% for molars and 75% for premolars in 58 patients [24].
According to Belleflamme et al., even in the presence of widespread coronal tissue loss or occlusal risk factors, for example bruxism or unfavourable occlusal relationships, endo crowns could be a dependable approach to restore severely damaged molars and premolars [25].

Conclusion:-
The preparation for endocrowns is modest and can be achieved quickly. Root canals are not engaged in the processand the procedure is not as much of traumatic as other preparations. The supragingival position of the cervical margin protects the marginal periodontium, enables impression taking, and conserves the solid substance of the remaining tooth. Forces are discrete over the cervical butt jointand axial walls, thus governing the load on the pulpal floor. The endocrown signifies a very hopeful treatment alternative for endodontically treated molars, it allows preserving of tooth structure, it is compatible with goal slightly invasive dentistry, and it is satisfactory for the concept of biointegration. It is a conservative method for mechanical and aesthetic restoration of nonvital posterior teeth. This type of reconstruction, which is still unusual, should be more extensively known and practised.

Conflicts Of Interest
The authorshave no conflicts of interest.