Advanced computer-aided design/computer-aided manufacturing (CAD/CAM) technology has led to the introduction of polyaryletherketone (PAEK), a new restorative material [1]. It is a semicrystalline high-performance thermoplastic polymer with linear chain structure [1].

Polyetheretherketone (PEEK) is a popular member of the PAEK family and has been in use in the medical field more than three decades [1]. PEEK has been used as an implant material as well as a framework material in dentistry [2]. Recently, Zoidis [3] and Kasem et al. [4] reported a custom PEEK post-and-core fabricated using a heat-pressing unit and CAD/CAM technology

Meanwhile, newly introduced polyetherketoneketone (PEKK) is another member of the PAEK family, which has a wide range of potential uses in dentistry [1,5]. In addition to being biocompatible, PEKK has high compressive, flexural, and tensile strengths, manufacturing versatility, and low cost [5]. Owing to the presence of titanium dioxide particles and the second ketone group in this polymer, it has a high fatigue limit and compressive strength (246 MPa), which is 80% more than that of PEEK [1,5]. Compared with PEEK, PEKK shows less bacterial adhesion (<37%) on its surface [2]. PEKK has been employed as a framework for implant-supported fixed restorations, tooth-supported fixed restorations, removable complete dentures, speech bulb prosthesis, and implant overdentures [1,5-8].

An ideal post material should have physical properties similar to those of dentin, can bond to the tooth structure, is biocompatible, and can act as a shock absorber by transmitting a limited amount of stress to the residual tooth structure [9]. PEKK has high potential as a post-and-core material due to its machinability, biocompatibility, and mechanical properties that are similar to dentin [1,5]. This clinical report describes the treatment of a severely damaged tooth with a custom PEKK post-and-core using digital and adhesive bonding technologies.

A 57-year-old female with no underlying systemic disease was referred by an oral and maxillofacial surgeon to our clinic for evaluation of the maxillary right first molar. The patient shared that the tooth had a crown restoration 15 years ago and the restoration had dislodged 5 days ago.

The maxillary right first molar had extensive coronal destruction caused by caries and fracture (Fig. 1). The mandibular left second premolar, left first molar, and second molars were missing, so a high occlusal force might be exerted on the fractured tooth.

Figure 1. Preoperative condition. Extensive coronal destruction of the maxillary right first molar because of caries and fracture is observed.

The treatment plan was discussed with the patient. She hoped not to use a maxillary fixed partial denture or an implant after removal of the damaged tooth and a mandibular interim removable partial denture. She desired to restore the damaged tooth at a lower cost.

As the loss of coronal structure was more than 50%, a post was also necessary to augment the core retention [9]. Although a fiber-reinforced composite (FRC) resin post allowed favorable stress distribution within the root, reducing the possibility of root fracture, it was not chosen because of the high cost and possibility of post debonding caused by an irregular cement layer thickness [10,11]. As an alternative to a FRC post, a custom PEKK post-and-core was selected because it could provide intimate adaptation to the wide palatal root canal and has adequate mechanical properties, biocompatibility, wide range of fabrication processes, retrievability, and moderate cost [5]. Consent for publication of the patient’s clinical details and clinical images was obtained from the patient.

After the post space was prepared, the remaining coronal tooth structure was reduced for a crown restoration conventionally. A definitive impression was made with polyvinyl siloxane material (Aquasil Ultra LV, Aquasil Ultra XLV; Dentsply Sirona), reinforcing wire (Remanium laboratory coils; Dentaurum), and a dual-arch tray (Lion bite tray; Asia Dental) (Fig. 2).

Figure 2. Conventional impression with polyvinyl siloxane material.

An antireflection substance (Easy Scan; Dental Story) was applied to the impression, and it was digitized with a blue-light scanner (Identica Blue; Medit) (Fig. 3) [12,13]. An anatomically corrected post-and-core was designed using an inlay module in the CAD software (Dental System; 3Shape) (Fig. 4) [13]. The design data were saved and exported to a 5-axis milling machine (Arum 5X-200; Arum Dentistry). A PEKK disk (Pekkton ivory Milling blank; Cendres+M_étaux) was milled (Fig. 5).

Figure 3. Impression scan. (A) Virtual image of post space, occlusal view. (B) Virtual image of post space, apical view.

Figure 4. Computer-aided design of a custom post-and-core.

Figure 5. Milled custom PEKK post-and-core. PEKK: polyetherketoneketone.

The fit of the post-and-core was evaluated with an elastomeric detection paste (Tokuyama Fit Tester; Tokuyama Dental) (Fig. 6). The surface of the post-and-core was airborne-particle abraded with 110-μm alumina particles (Cobra 110 μm; Renfert) for 15 seconds at a pressure of 0.25 Mpa [1,14]. The restorations were cleaned with distilled water in an ultrasonic cleaner for 60 seconds [1,14]. After drying the restorations with air, a methylmethacrylate primer (Luxatemp-Glaze & Bond; DMG Dental) was applied to the post-and-core for 20 seconds and light-polymerized [1,14].

Figure 6. Evaluation of milled post and core with polyvinyl siloxane material.

A cotton roll was placed on the buccal side of the tooth for isolation. Compressed air and endodontic paper points (Pro-Endo; Yamahachi Dental) were used to dry the tooth structure. A self-adhesive resin cement (RelyX U200; 3M ESPE) was applied to the post and palatal root canal [1,14,15]. The post-and-core was gently placed on the tooth and polymerized (Fig. 7). After digitizing the intraoral environment, a definitive crown was designed, and a cobalt-chromium alloy block (M4; Medipion) was milled with the milling machine (Arum 5X-200). The crown restoration was luted with the resin cement (Fig. 8).

Figure 7. Custom PEKK post-and-core in place. PEKK: polyetherketoneketone.

Figure 8. Milled definitive crown in place.

The fabrication of a custom PEKK post-and-core was described. The amount of the remaining coronal tooth structure is a critical factor in selecting post systems [9]. In the case of moderate-to-severe tooth loss, custom posts are recommended, as FRC resin posts are prone to debonding because of an irregular gap between the dentin and FRC posts, which may result in increased polymerization shrinkage stress on the resin cement [9,11]. Custom posts are required in this case because of its intimate adaptation to the root canal walls, uniform cement layer thickness, improved retention of coronal restorations, and more conservative root canal preparation. However, the high elastic modulus of metal and zirconia, which is between 4 and 11 times, respectively, that of dentin, lead to unfavorable stress distribution, which may result in root fractures [9].

To overcome the limitation, a custom PEKK post-and-core is fabricated as the elastic modulus of PEKK is similar to that of dentin and its intimate adaptation to the root canal can be achieved [1,5,15]. Custom PEKK posts can act as a shock absorber and be compatible with the natural flexing movements of the tooth structure that cannot be achieved by rigid post systems [5,15]. Finite element analysis of PEKK post-and-core systems have shown reduced risk of root fractures because of favorable stress distribution [5]. Furthermore, the custom PEKK post-and-core can be efficiently fabricated with less human errors by using impression scan and CAD/CAM technology. This is supported by in vitro studies showing that the half-digital workflow is accurate and time efficient [12,13].

To achieved appropriate and durable adhesion of the PEKK post to resin cement, airborne-particle abrasion and an adhesive system were applied in the presented case [1,14,15]. Fuhrmann et al. [1] described that airborne-particle abrasion in combination with an adhesive primer was as effective as tribochemical silica coating and silane containing universal primer. Tosun and Yan_ıko_ğlu [14] reported similar bond strength values between airborne-particle abrasion and tribochemical silica coating when used in conjunction with a universal primer. According to Labriaga et al. [16] airborne-particle abrasion in combination with plasma and adhesive application enhanced the bond strength caused by increased surface roughness and wettability. Surface etching with 98% sulfuric acid resulted in the high bond strength of PEKK to dentin [17]. However, chairside application of sulfuric acid is dangerous, and the stability of PEKK bonding to dentin is unknown [16,17].

The disadvantage is its low translucency and grayish color, which may limit its use in the anterior teeth [16]. Further in vitro and clinical studies are needed to evaluate the long-term performance of PEKK post-and-core [15].

None to declare.

None.

No potential conflict of interest relevant to this article was reported.