Comparative Stress Analysis of Polyetherketoneketone (PEKK) Telescope Crowns Supported by Different Primary Crown Materials  
[PERSON]  
1 Department of Dental Materials, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam, 1081 LA Amsterdam, The Netherlands; [EMAIL_ADDRESS] (P.J.T.J. ); [EMAIL_ADDRESS] (A.M.d.O.D.P)  
2 Department of Prosthodtatics, College of Dentistry, University of Science and Technology of Fujiarah, Fujiarah P.O. Box 2202, United Arab Emirates 2  
2 Department of Prosthodtatics, College of Dentistry, King Saud University, Fujiarah P.  
the restoration of missing dental elements in the arch such as telescopic overdenture on natural teeth [8]. The telescopic prosthesis overdenture is a prosthetic rehabilitation with the particular advantage of being indicated in severe cases of horizontal and vertical soft tissues loss [9]. This restorative approach allows obtaining good esthetics by recovering the naso-labial angle obtained with the prosthesis flange, a feature that is not present with fixed prosthesis even with osseo-densification techniques [8; 9; 10]. Regarding chewing load dissipation, it is important to note that there are differences between implant-assisted overdenture rehabilitation and telescopic-crowns overdenture on natural teeth [11]. Since the periodontal ligament is conserved as well as the anatomic roots, the overdenture on natural teeth will dissipate the masticatory forces lighter and consequently with less stress on the prosthetic components. Therefore, it can justify the orofacial system with a lower incidence of orofacial pain and temporomandibular disorders for this prosthetic modality [8; 9; 10; 11; 12; 13; 14; 15; 16; 17]. Despite the reported benefits, the double crown retention system can be affected by the manufacturing method and design parameters. In cylindrical crowns, the retention is performed mostly due to the friction between the primary crown's external surface and the secondary crown's intaglio surfaces [2; 18]. Cylindrical crowns have technique sensitivity, difficulty in manufacturing, increased misfit, and progressive wear; therefore, conical crown design is preferred as it may reduce these undesired effects. The conical design system promotes a wedging action strong enough to assist the prosthesis retention. In addition, the conicity between primary and secondary crowns allows a manufacturing process less sensitive to the technique and wear between the contacting surfaces [2; 18; 19]. Conventionally, casting and electroforming techniques are applied to manufacture telescopic crowns. When using the conventional casting method, the lost-wax technique should be applied using precious alloys. Nonetheless, since their high cost, time consumption, and difficulty in using the paralleling device, telescopic prostheses are not considered as the primary treatment option for dental prostheses [1; 2]. However, with the aid of digital dentistry, telescopic dentures can be reliably manufactured with stable retentive forces using customized design features while reducing the processing time and technical errors [1; 2; 3]. Furthermore, the modeling software allows for design adjustments prior to crown manufacturing [2; 20] and with a wide range of materials. The most common dental materials used in the double crown-retained systems for removable dentures are titanium, non-precious metal alloys, precious metal alloys, zirconia, and high-density polymers [polyaryletherketone (PAEK) family]. The use of high-performance thermoplastic polymers is indicated since they present high strength, rigidity, excellent biocompatibility, and fast processing [21]. In the dental field, Polyetherketoneketone (PEKK), a member of the PAEK family, has already been used in removable dentures [22], temporary prostheses, intrarradicular posts [21], crowns [23] implant-supported frameworks [24], and fixed dental bridges [25; 26].