###### Abstract  
Temporary restorations play a fundamental role in oral rehabilitation. They can be used to teeth or implants for a variable period of time during the period prior to rehabilitation with definitive restorations. Temporary or provisional restorations manufactured via CAD/CAM methods are becoming increasingly used in the intermediate phase of the treatment of complex cases. The main objective of this study was to compare the fracture resistance of three materials used in the creation of provisional crowns on implants: polymethyl methacrylate (PMMA), composite resin, and polyether ether ketone (PEEK). Fracture resistance in PMMA (Zirkonzahn Temp Basic(r), Gais, South Tyrol, Italy) ranged from 1216.0 N to 1461.2 N, with a mean of 1300.4 N (SD = 97.09). In the composite material (3M Lava Ultimate(r), St. Paul, MN, USA), fracture resistance varied between 1343.5 N and 1490.6 N, with a mean of 1425.9 N (SD = 49.03). Lastly, in PEEK (Tecno Med Mineral(r), Zirkonzahn(r), Gais, South Tyrol, Italy), fracture resistance ranged from 2294.8 N to 2451.7 N, with a mean of 2359.5 (SD = 50.01). The crowns made with the PEEK Tecno Med Mineral(r) (Zirkonzahn(r), Tyrol, Italy) material presented the best fracture resistance, followed by the crowns made with the Lava Ultimate(r) (3M) ESPE, Minnesota, USA) composite resin material and, finally, those made with the PMMA Temp Basic(r) (Zirkonzahn(r), Tyrol, Italy) material. provisional restorations; fracture resistance; PMMA; composite resin; PEEK +
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The material has good polishability, but its abrasion resistance is low, and patients who exhibit parafunctional habits may show wear of the material over time [2,3]. Additional disadvantages include a high volumetric shrinkage during setting, with a high exothermic reaction; the degree of heat generated by the exothermic reaction is related to the volume of material being cured [5]. When this may be an issue either because of pulpal health or patient comfort, fabricating the majority of the provisional restoration extraorally on a model and relining intraorally will reduce the volume of material being cured on the teeth and lower the heat generated during the exothermic setting [6,7]. As another consideration with regard to the pulp, it has been shown that free monomer may be toxic to the pulp and this material may not be the material of choice when pulpal health is questionable or when the material will be in close approximation to the pulp [8]. Furthermore, these materials may be objectionable to the patient because of odor, and there have been some reported tissue reactions to the monomer [9]. Composite resins are typically presented in a self-mixing paste/paste form, with chemical or dual polymerization. Typically, the composite resins are reinforced to a provisional polymer matrix reinforced with fibers. The fibers are usually glass, carbon, or aramid. Most composites have strong, stiff fibers in a matrix which is weaker and less stiff. The objective is usually to make a component which is strong and stiff, often with a low density. Commercial material commonly has glass or carbon fibers in matrices based on thermosetting polymers, such as epoxy or polyester resins. Sometimes, thermoplastic polymers may be preferred [6,7]. In addition to these forms, PMMA and composite resin are also available in CAD/CAM (computer-aided design/computer-aided manufacturing) blocks, with PEEK available only in this form [1,2,4]. CAD/CAM blocks are manufactured under controlled industrial conditions involving high temperatures and pressures, resulting in better conversion and a decrease in residual monomers. In this process, the physical properties of the materials are improved compared to those formed with the use of traditional methods, allowing for the use of CAD/CAM systems in the intermediate phase of the treatment of complex cases (e.g., involving adjustment of the occlusal plane). On the other hand, the high monomer conversion rate decreases the adhesion capacity of adhesive resins [1,6,7].