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Endocrowns: A clinical report Erika Lander, DDS1/Didier Dietschi, DMD, PhD, PD2 The endocrown is a restorative option for endodontically treated teeth. It consists of a circular butt-joint margin and a central retention cavity inside the pulp chamber and lacks intraradicular anchorage. This article describes the rationale and clinical guidelines for the placement of endocrowns. In the case presented, 2 old amalgam restorations on mandibular molars were replaced with endocrowns made of pressed ceramics (Empress 2, Ivoclar) following endodontic and periodontal therapy. A composite resin base was also used to fill undercuts and ensure a correct design of the preparations, contributing to significant tissue preservation. The postoperative situation shows the potential of this restorative approach to provide adequate function and esthetics, as well as biomechanical integrity of structurally compromised posterior nonvital teeth. It also prevents interferences with periodontal tissues, thanks to a supragingival position of the restoration margins. The foundation of this technique is to use the surface available in the pulpal chamber to assume the stability and retention of the restoration through adhesive procedures. Guidelines for the preparation, as well as the decision for omitting a post, are dictated by the amount of remaining coronal substance. This technique represents a promising and conservative alternative to full crowns for the treatment of posterior nonvital teeth that require long-term protection and stability. (Quintessence Int 2008;39:99–106)

Key words: adhesive posterior restoration, Empress 2, endocrown, nonvital teeth, pressed ceramics

The restoration of endodontically treated teeth is a topic that has been widely and controversially discussed in the dental literature.1 Clinical concepts regarding the restoration of nonvital teeth have long been based on rather empirical philosophies due to the

1

Department of Aesthetic Dentistry, Private Educational Center Somos Salud y Educacion, Caracas, Venezuela; Adjunct Professor, Universidad Nacional Experimental Politecnica de la Fuerza Armada of Caracas, Venezuela; Adjunct Professor, Department of Operative and Esthetic Dentistry, Universidad Santa Maria of Caracas, Venezuela.

2

Senior Lecturer, Department of Cariology and Endodontics, School of Dentistry, University of Geneva, Geneva, Switzerland; Adjunct Professor, Department of Comprehensive Care, Case Western University, Cleveland, Ohio.

Correspondence: Dr Erika Lander, Anexo Hospital de Clinicas Caracas, Piso 6—Oficina 609, 1010 San Bernardino, Caracas, Venezuela. Fax: +58 212 5747976. E-mail: [email protected]

weak link between available scientific data and the large number of rather inconclusive clinical studies.2,3 In fact, this profuse literature can be confusing, which is only aggravated by the large choice of restorative materials used for restoring nonvital teeth. Biomechanical principles indicate that the structural strength of a tooth depends on the quantity and intrinsic strength of hard tissues and the integrity of the anatomic form. Tooth integrity can be significantly disrupted by caries or procedures such as cavity preparation, coronal access to the pulp, canal enlargement, and chemomechanical preparation.4–9 Clinicians have long assumed that dentin strength would be adversely affected by pulp removal, presumably decreasing dentin moisture, elasticity, and tensile strength, but these assumptions could not be scientifically confirmed. In fact, varia-

COPYRIGHT © 2008 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF THIS ARTICLE MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER

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tions in tissue quality following endodontic treatment proved to have a negligible influence on tooth biomechanical behavior.10–14 From a mere mechanical aspect, it could also be demonstrated that a conservative endodontic access cavity alters to a minimal extent the fracture resistance of a tooth.8,9 Another issue is the impairment of neurosensory feedback related to the loss of pulpal tissue, which might reduce the protection of the endodontically treated tooth during mastication.15,16 The purpose of a post-and-core foundation is to stabilize the remaining coronal tooth structure and to replace missing coronal tissue.1–3,17–19 Although some finite element analysis (FEM) studies indicate that a rigid post can strengthen a tooth in its cervical part by way of totally cohesive interfaces,20,21 most studies suggest that posts have no strengthening effect.3 Many authors even discourage the use of posts, in consideration of various risks such root perforation, root weakness, and a more dramatic failure pattern of teeth restored with posts.3 In fact, when present restorative techniques and materials are used, a post is to be considered only as a retentive feature in well-selected situations. Other in vitro experiments have also shown that there is no difference in retention, marginal adaptation, and fracture resistance between a vital tooth configuration and a nonvital tooth covered with an onlay restoration,22 favoring the way of conservative partial crown coverage for endodontically treated teeth. Nayyar et al23 described the amalcore or coronal-radicular restoration. Amalgam was placed into the pulpal chamber, entering 2 to 4 mm into the canal. The following criteria were considered for the application of this technique: (1) The remaining pulp chamber should be of sufficient width and depth to provide adequate bulk and retention of the amalgam restoration, and (2) an adequate dentin thickness around the pulp chamber was required for the tooth-restoration continuum rigidity and strength. This restoration has been successful in both laboratory24,25 and clinical studies.1 But the true breakthrough in the restoration of endodontically treated teeth was the introduction of adhesion, propelled by the

development of effective dentin adhesives.26 The chief advantage of adhesive restorations is that macroretentive elements are no longer mandatory as long as enough surface is available. With this approach, the insertion of radicular posts has become the exception rather than the rule when applying conventional nonadhesive restorative techniques. In fact, minimally invasive preparations, with maximal tissue conservation, are now considered the gold standard for restoring endodontically treated teeth.3 The endocrown strictly follows this rationale; the preparation consists of a circular equigingival buttjoint margin and central retention cavity into the entire pulp chamber instead of employing intracanalicular posts.27 Bindl and coworkers28 examined 208 partial Cerec (Sirona) ceramic restorations placed on nonvital teeth and concluded that this restoration modality was satisfactory for molars and premolars, following an average observation period of 55 months. Gohring and Peters29 and Gohring and Roos30 described the application of glass-fiber–reinforced composite endocrowns on premolars and molars, as a single restoration or as an abutment for fixed partial dentures. The problem with some fiber-reinforced restorations, however, is the delaminating of the veneering material30; use of a nonreinforced polymerbased restoration appears to be a more feasible alternative to ceramic endocrowns on either anterior or posterior teeth.20–22

CASE PRESENTATION A 32-year-old woman with old amalgam restorations on the mandibular right molars, both having caries lesions, requested their replacement. The first molar had an insufficient root canal treatment and its distal root was periodontally compromised, while the second molar had a caries lesion invading the pulp (Figs 1a and 1b). Because of the quantity of remaining tissue in both teeth, which could be appreciated during clinical evaluation (Figs 1b and 1c), endocrowns were considered as a feasible conservative restorative approach.

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Fig 1a Initial radiographic view with radiolucent images corresponding to caries, marginal gaps, and periodontal lesions. Fig 1b Preoperative occlusal view showing the 2 old amalgam restorations, which needed to be removed. Fig 1c Lateral view showing recurrent caries and marginal gaps.

Fig 1d Initial diagnostic waxup. Fig 1e Radiographic view after endodontic treatment and retreatment. Fig 1f Occlusal view with provisional restorations in place, following surgical crown lengthening and third molar extraction.

A waxup was made (Fig 1d) before removing the old restorations and proceeding with endodontic treatments and surgical crown lengthening (Figs 1e and 1f). After removal of the provisional restorations, preparation for endocrowns was initiated on both teeth; the pulpal chamber floor was exposed, and appropriate leveling of residual buccal and lingual walls was achieved (Figs 1g and 1h). Interocclusal space was carefully evaluated, and it was observed that enough space was present to use IPS Empress 2 ceramic (Ivoclar Vivadent) (Fig 1i). Shade was recorded with the specific Eris (Ivoclar Vivadent) shade samples (Figs 1j and 1k). Then, retraction cords were placed and an impression made with a polyvinyl siloxane material (President light body and heavy body, Coltène Whaledent) (Fig 1l). After the impression was poured with hard stone, dies

were cut and prepared for the fabrication of models (Figs 1m to 1o). A second full waxup was made (Fig 1p) before reduction to obtain the core shape. Interocclusal space was checked carefully to guarantee the restoration strength (minimal core thickness ≥ 0.8 mm and veneering porcelain ≥ 0.7 mm) (Figs 1q and 1r). The waxes were then invested and ceramic cores pressed (Figs 1s and 1t). Buccal shoulders were reduced to provide more translucency and a better esthetic integration of the restorations. The ceramics were layered to achieve optimal occlusal anatomy and esthetics (Figs 1u to 1x). Restorations were adhesively cemented using a dual-cured material (Variolink II, Vivadent), according to the manufacturer’s instructions (Fig 1y). The 3-year recall findings are illustrated in Figs 2a to 2c.

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Fig 1g Occlusal view after removal of provisional restorations, showing the amount of residual tooth structure. Fig 1h Completed preparations. Fig 1i Lateral view of the preparations, showing the interocclusal space.

Figs 1j and 1k Shade selection is performed with the samples of the Eris ceramic system (dentin and enamel) used in combination with Empress 2. Fig 1l Thanks to the crown lengthening, impression can be simply taken after placement of retraction cords.

Fig 1m Cutting the model to obtain the dies. Fig 1n View of 2 dies prepared for placement in the model. Fig 1o View of finished Geller model.

Fig 1p Occlusal view of finished waxup before cutback. Fig 1q Lateral view of waxup of cores in model, checking interocclusal space. Fig 1r Calibration of wax before investing, confirming that it is no less than 0.8 mm.

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Fig 1s View of the aspect of cores after pressing ceramic. Fig 1t Lateral view of finished cores placed in the model. Fig 1u Finished cores tested in the mouth.

Fig 1v Occlusal view of 2 restorations in the model with ceramic buildup. Fig 1w Finished ceramics placed in the model. Fig 1x Occlusal view of the 2 molars with finished restorations in the mouth after cementation.

Fig 1y

Lateral view of 2 restorations model before cementation.

Figs 2a to 2c The 3-year follow-up radiograph (a) and clinical views (b, c) show the satisfactory behavior of the restorations and their limited impact on marginal tissue health. In addition, one can appreciate the positive influence of adhesion on restoration stability and tissue preservation. The placement of conventional post and core on these teeth would lead to greater weakness and impaired biomechanical behavior. COPYRIGHT © 2008 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART OF THIS ARTICLE MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER

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DISCUSSION AND CLINICAL RECOMMENDATIONS The literature asserts that the need for a post is determined by 2 main factors, the amount and quality of remaining coronal and radicular structure, which determine the potential strength, and the retention of core materials and prosthetic restoration.3 Factors such as trauma and caries, as well as endodontic procedures, can lead to the creation of large flared root canals. Flared canals are then more susceptible to fracture because of thin remaining walls, thereby requiring restorative techniques that will not further compromise the integrity of remaining tooth structure.27 As clinical experience has been gained, guidelines for the application of endocrowns and other restorative techniques for nonvital posterior teeth have evolved and logically been refined; indications actually relate to the integrity of residual tooth structure.

Minimal loss of coronal structure Minimal loss of coronal structure usually relates to teeth that have had little or no restoration but require root canal therapy. The remaining tooth structure, despite endodontic treatment, should present only minimal strength loss compared to a vital tooth, providing no horizontal or vertical crack is present; actually, the endodontic access cavity and minimal enlargement of the pulp chamber are considered not to significantly affect tooth biomechanics.8,9,11 The authors suggest that such teeth be treated with only adhesive restoration filling the access cavity and pulpal chamber. The choice of material should be limited to composite resins, in combination with an effective adhesive system, following the total bonding concept.31 The only potential contraindication to such a highly conservative approach is the case of patients with parafunctions, group guidance, and steep cuspal inclination, which also suggest complete occlusal coverage.

Up to one-half of the coronal tooth structure missing Teeth with existing medium-sized restorations that require root canal therapy obviously do not need a post-and-core restoration since enough coronal structure is present to provide restoration stability, retention, and strength. Complete occlusal coverage such as an endocrown or indirect tooth-colored overlay is, however, suggested,3,9 overlying a bonded composite resin liner-base to create an even cavity geometry and fill undercuts.32

More than half of the coronal tooth structure is missing When more tissue is missing, limiting to a significant extent the surfaces available for adhesion and possibly also coronal structure integrity, a post-and-core restoration is mandatory to ensure tooth-restoration continuum strength and resistance to fracture. With proper preparation design (maintaining walls with sufficient intrinsic strength, ≥ 1.0 to 1.5 mm thickness), the remaining coronal tooth structure should assume antirotational stability. A ferrule effect should also be attained by extending future restoration margins 1.5 to 2.0 mm below the foundation limits.33,34 Present scientific knowledge and literature are definitely in favor of adhesive techniques for the post and core fabrication.3 Occlusal anatomy and function are usually restored with a full crown. This restorative option, however, presents a higher inherent biomechanical risk of failure, related directly to the amount of missing tooth structure.

Most of the coronal tooth structure is missing This represents the least favorable biomechanical situation and cannot be satisfactorily or safely approached in the long term. Since orthodontic extrusion is rarely performed on pluriradicular teeth and because extensive crown lengthening to assume a ferrule effect and restoration stability is no longer considered as a feasible option, extraction and implant therapy can be considered an alternative to the conventional treatment of severely compromised posterior teeth.35,36

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CONCLUSIONS

6. Chiba M, Itoh K, Wakumoto S. Effect of dentin

The ideal treatment of endodontically treated teeth has been widely and controversially discussed in the literature. The only consensus is the need to conserve remaining and healthy dental structures, which can help to mechanically stabilize the tooth-restoration complex and increases surfaces available for adhesion, therefore impacting positively the treatment long-term success. In this perspective, endocrowns can be considered as a feasible alternative to full crowns or composite overlays for the restoration of nonvital posterior teeth, in particular, those with minimal crown height and sufficient tissue available for stable and durable adhesive cementation.

cleansers on the bonding efficacy of dentin adhesive. Dent Mater 1989;8:76–85. 7. Saleh AA, Ettman WM. Effect of endodontic irrigation solutions on microhardness of root canal dentin. J Dent 1999;27:43–46. 8. Trope M, Ray HL. Resistance to fracture of endodontically treated roots. Oral Surg Oral Med Oral Pathol 1992;73:99–102. 9. Reeh ES, Messer HH, Douglas WH. Reduction in tooth stiffness as a result of endodontic and restorative procedures. J Endod 1989;15:512–516. 10. Helfer AR, Melnick S, Shilder H. Determination of the moisture content of vital and pulpless teeth. Oral Surg Oral Med Oral Pathol 1972;34:661–670. 11. Papa J, Cain C, Messer HH. Moisture content of vital vs endontically treated teeth. Endod Dent Traumatol 1994;10:91–93. 12. Gutmann JL. The dentin root complex: Anatomic and biologic considerations in restoring endodontically treated teeth. J Prosthet Dent 1992;67:458–467.

ACKNOWLEDGMENTS

13. Huang TJ, Shilder H, Nathanson D. Effect of moisture content and endodontic treatment on some mechanical properties of human dentin. J Endod

The authors wish to express their gratitude to Dr Juan

1992;18:209–215.

Saavedra and Dr Ricardo Almón of the Universidad

14. Rivera EM, Yamauchi M. Site comparisons of dentine

Central de Venezuela for their unconditional support of

collagen cross-links from extracted human teeth.

this work. The authors especially wish to thank Prof Rafael Laplana from Universidad Nacional Experimental Politecnica de la Fuerza Armada, also director of the

Arch Oral Biol 1993;38:541–546. 15. Paphangkorakit J, Osborn JW. The effect of pressure on a maximum incisal bite force in man. Arch Oral

Private Educational Center Somos Salud y Educacion in

Biol 1997;42:11–17.

Caracas, Venezuela, for his precious support and guidance, as well as for providing the appropriate environ-

16. Paphangkorakit J, Osborn JW. The effect of normal occlusal forces on fluid movement through human

ment to complete the treatment presented.

dentine in vitro. Arch Oral Biol 2000;45:1033–1041. 17. Guzy GE, Nicholls JI. In vitro comparison of intact endodontically treated teeth with and without endo-post reinforcement. J Prosthet Dent 1979;42:

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