Effect of Fabrication Monolithic Zirconia Endocrown on Marginal Integrity

The successful restoration of endodontically treated teeth is dependent on the type and quality of the coronal restoration. Endodontically treated teeth restored with crowns have a 5-year survival rate similar to vital teeth restored with crowns (94.2% versus 95%).(1,2) However, in the absence of cuspal coverage (restored with composite resin), endodontically treated teeth have a lower success rate, with a 5-year survival rate of 63%. The improved survival of teeth treated endodontically with satisfactory coronal cuspal coverage has been attributed to a reduction in microleakages and the preservation and protection of the remaining tooth structure.(3) Immediate placement of a satisfactory coronal restoration has been reported to reduce microleakage and subsequently decrease the risk of endodontic treatment failure, while cuspal coverage and preservation of the remaining coronal tooth structure have been reported to improve fracture resistance and the outcome of the endodontically treated tooth.(4) Despite the clinical success of intraradicular posts for the restoration of endodontically treated teeth, they require removal of additional sound tooth structure for optimal adaptation of the post in the root canal system, affecting the biomechanical behavior of the restored tooth.(5) Endocrowns are 1-piece restorations comprising a coronal part and a cavity part in the pulp chamber that were introduced following advances in adhesive bonding techniques. Endocrowns are indicated for molar teeth with short roots, severely curved roots, fragile or resorbed roots, and limited interarch space.(6) Marginal adaptation is the most important criterion determining the long-term functional success of a restoration. Marginal discrepancy increases the plaque retention and inflammation of periodontal tissue and secondary caries, leading to eventual failure of the restoration. A consensus regarding the maximum clinically acceptable marginal gap is lacking, but values between 50 and 200 mm have been reported. Nonetheless, most authors use the threshold mentioned by McLean and von Fraunhofer, who evaluated over 1000 crowns and reported that the maximum acceptable marginal gap was0 120 mm.(7,8,9) All-ceramic endocrowns are bonded to the tooth using adhesive resins creating strong bonds to the tooth structure resulting in strengthening effect and reducing the need for post and core. various CAD/CAM materials can be used for the fabrication of endocrowns including lithium-disilicate reinforced glassceramics, monolithic zirconia, feldspathic ceramics, in ceram alumina and in ceram spinell as well as hybrid ceramics and composites.(10)

1. a.2 Description of research question P: Participants: Patients having endodontically treated molars indicated for endocrown. I: Intervention: Endocrown fabricated using intra oral scan. C: Comparator : Endocrown fabricated using traditional impressions. O: Outcome name, measuring device \& measuring unit Outcome name: Marginal integrity Clinical performance. Measuring Device : Modified USPHS criteria. (11,12,13) Measuring Unit : Categorical. S: Randomized clinical trial (RCT) T: one year 6.a. 3 Formulated question: In patients with endodontically treated teeth requiring endocrown restorations, will impression techniques of endocrowns could affect the clinical performance and patient satisfaction? 6. a. 4 The justification for undertaking the study: One of the conservative approaches that has been developed with the advances of adhesive and bonding techniques is the endocrown restoration, which is a monoblock restoration that has the ability to restore a severely destructed endodontically posterior teeth. It follows the concept of minimal invasive preparation as it gains its retention and stability from anchoring to the internal part of the pulp chamber and the cavity margins.(14,15) Endocrown restorations may be fabricated either by intra oral scanning or by traditional impressions. Endocrown restoration approach has gained more popularity, due to its advantages in providing better aesthetics, better mechanical performance, less removing of sound tooth tissues, and less clinical time.(16,17) Endocrown restoration has been considered as a reliable alternative to the conventional restoration of severely damaged posterior teeth.(18,19) Along with the surface treatment of tooth structure by acid etching and application of bonding agents. It also has adequate mechanical and sufficient strength to be used in single and short span bridges up to the premolar areas combined with having acceptable clinical margins and internal adaptation. (20,21)

6.a.5 Rationale: Elastomeric impression materials have been successfully used for the fabrication of restorations for many years.(22) However, despite the advances in impression material technology, a number of factors such as the impression technique, impression material, transfer to and from the dental laboratory, disinfection techniques, impression trays, and mixing techniques can significantly affect the accuracy of impressions. Moreover, the conventional impression technique may be associated with patient discomfort, nausea, and the unpleasant taste of the impression material. (23)

Benefits of the research to the patient:

Patient will receive a restoration with superior marginal integrity and quality.

It will provide the patient with long-term predictable prosthetic outcome.

Benefits of the research to the clinician:

Practitioner will have the advantage to assess a different fabrication techniques that can be used in different situations for better marginal integrity outcomes. It will improve patient's confidence with the dentist. 6.b. Explanation for choice of comparators: The (CAD-CAM) technique includes intraoral digital scanning, designing and fabrication of definitive endocrowns with high marginal integrity, fewer fabrication steps than the conventional technique, faster processing time, lower cost and some limitations of the conventional technique are avoided. (CAD-CAM) technology also allows access to novel biomaterials such as monolithic zirconia.(24,25)