The Effectiveness and Predictability of BioHPP (Biocompatible High-Performance Polymer) Superstructures in Toronto-Branemark Implant-Prosthetic Rehabilitations: A Case Report

Abstract

Objectives: To evaluate the clinical performance of BioHPP^® (Biocompatible High-Performance Polymer) superstructures in full-arch implant-prosthetic rehabilitations following the Toronto-Branemark protocol, focusing on biomechanical and biological outcomes. Methods: A 70-year-old edentulous male patient underwent full-arch implant-prosthetic rehabilitation using BioHPP^® superstructures fabricated through a CAD-CAM workflow. Radiological and clinical evaluations were conducted to plan implant placement and assess outcomes after one-year of follow-up. The primary endpoints included prosthetic stability, peri-implant bone resorption, and patient-reported satisfaction. Results: The BioHPP^® superstructure demonstrated effective stress distribution, leading to minimal peri-implant bone resorption and improved implant stability. Clinical evaluations showed excellent prosthetic fit and functionality, with no complications during the observation period. Radiological analyses confirmed the absence of prosthetic misfits, while patient-reported outcomes indicated high levels of comfort and aesthetic satisfaction. Conclusions: BioHPP^® superstructures offer a promising alternative to traditional materials for full-arch implant-prosthetic rehabilitations, providing significant biomechanical and aesthetic advantages. These findings suggest that BioHPP^® may enhance clinical outcomes, though further research with larger cohorts and longer follow-up periods is required to validate its long-term reliability.

1. Introduction

Implant-supported prostheses represent the optimal approach for the functional and aesthetic repair of edentulous arches in the rehabilitation of edentulous patients [1].

The ’Toronto Bridge’ surgical and prosthetic protocol, introduced by Brånemark at the 1982 Consensus Conference in Toronto, remains one of the most prevalent and reliable techniques for the rehabilitation of edentulous arches in the field of osseointegrated implantology.

The ‘Toronto bridge’ surgical protocol necessitated the insertion of 4 or 6 implants in the intraforaminal region, which must be subjected to delayed loading. The prosthetic protocol entails the creation of a metallic framework featuring a screwed or glued metal ferrule, along with distal extensions generally comprising two components: either two premolars or a premolar and a molar [2]. The pink resin covering of the framework aims to substitute and regenerate the soft tissue lost over time, with the objective of re-establishing the vertical dimension and restoring appropriate inter-arch relationships.

In 1995, Branemark et al. examined the survival rates of Toronto-Branemark rehabilitations with a 10-year follow-up [3]. This study suggested that the rehabilitations with the highest success rate (93.2%) were those in the mandible, supported by six implants [3]. Despite subsequent enhancements and alterations, the original Branemark protocol (OT) continues to exemplify an exemplary technique for the comprehensive rehabilitation of edentulous patients. As the population of edentulous patients seeking implant-supported prostheses rises, there is a necessity to establish more efficient, precise, and reliable advancements and treatment processes. Consequently, over the years, many clinicians and scientists have concentrated on researching new materials that can enhance the mechanical and biological properties of implant-retained prosthetic restorations [4,5]. BioHPP^® (Biocompatible High-Performance Polymer), a product based on PEEK (polyether-ether-ketone), is one of the most innovative materials utilized in the construction of implant superstructures.

Prostheses constructed from BioHPP^®, including extensive bridges or individual single-unit abutments, can be produced utilizing either the thermoplastic injection method or a CAM system workflow. The finishing and polishing processes are swift and uncomplicated, without compromising the material’s quality in comparison to zirconium dioxide. This case report aims to illustrate the therapeutic benefits of BioHPP^® prostheses, which improve workflow efficiency while maintaining optimal functionality and aesthetics.

2. Materials and Methods

BioHPP (Bredent group GMBH&Co. KG, Senden, Germany) is a fiber-reinforced polymer derived from PEEK (polyether-ether-ketone) that has lately garnered interest for its application in the fabrication of superstructures for dental implants [6]. BioHPP^® is a high-performance, partly crystalline PEEK-based polymer that is thermoplastic and has exceptional stability at extreme temperatures, as per the manufacturer’s specifications [7]. The incorporation of PEEK and inorganic ceramic microparticles, each under 0.5 μm in diameter, is the essential structural characteristic that supports the clinical benefits of this prosthetic superstructure [8,9]. This increase maintains the material’s inherent physiological flexibility, while the ceramic particles provide an optimal equilibrium of rigidity and superior polishing characteristics. Through appropriate finishing and polishing procedures, the material can be safely subjected to saliva, attaining a surface roughness of 4 µm. This surface feature can be employed in instances where BioHPP^® is utilized for transmucosal segments, guaranteeing optimal fibroblast adherence for an impeccable seal. The material’s structural properties and surface texture provide unique mechanical, biological, and prosthetic advantages, clinically resulting in an optimal equilibrium between elasticity and stiffness, weight, and fracture resistance, as well as biocompatibility and plaque resistance [10,11]. Moreover, the compositional characteristics mimic the elastic modulus of bone tissue and accommodate mandibular bone torsions, ensuring the superior preservation of peri-implant bone and optimal absorption of occlusal pressures [12].

3. Case Presentation

A 70-year-old edentulous male, a nonsmoker with no important medical history, presented to our department with complaints of prosthetic instability during mastication and phonation, along with pain and discomfort in the mandibular arch. A preliminary radiographic examination (Rx panorax) indicated the presence of a solitary implant supporting the mandibular prosthesis (Figure 1). This configuration is suboptimal, as masticatory forces may result in prosthetic instability, potential fracture of the prosthesis, and, in severe instances, failure of the implant, consistent with the existing literature [13].

To evaluate the feasibility of prosthetically guided implant rehabilitation, a second-level RX CBCT scan was performed to assess bone thickness (Figure 2a,b). As supported by the literature, this approach facilitates optimal implant positioning and enhances prosthetic stability [14,15].

Using local anesthesia with an articaine hydrochloride/adrenaline solution at a concentration of 1:100,000 (Septanest, Saint-Maur-des-Fossés, Cedex, France), the prosthesis was removed, revealing the condition of the underlying keratinized tissue and the presence of a single implant (Figure 3a). A mid-crestal incision was performed to establish an envelope flap, facilitating the complete visualization of the mental foramen region and ensuring the optimal exposure of the surgical field during the implant placement procedure (Figure 3b).

Consequently, a full-thickness flap was made and the alveolar crestal bone was exposed (Figure 4a). An ostectomy was performed to address the defect. An osteotomy was then performed to reduce the most coronal part of the alveolar process to an adequate thickness in order to prepare a correct size for implant placement (Figure 4b). Five implants were inserted (3.6 × 9 and 4.2 × 9, Astra Dentsply Sirona B, Piazza dell’Indipendenza, 11, 00185 Roma, Italy), following the Toronto-Branemark technique (Figure 4c) [16]. After securing the cover screws, the flap was repositioned to cover the implants and was stabilized with 5/0 nonabsorbable monofilament sutures (Monomyd^®, Butterfly, Cavenago di Brianza (MB), Italy) using interrupted sutures. To allow for implant osseointegration and proper tissue healing, the temporary phase was managed with a passive-fit resin-made complete removable prosthesis.

Following a six month recovery period, the prosthetic procedure was started. First of all, a second surgical stage was performed in order to place the healing abutments. A crestal incision was made, and the correct abutment was positioned, based off the tissue thickness. A simple suture was made to ensure a correct-healing wound. One month later, a dental impression was taken in order to produce a particular framework in a resin base; consequently, an aesthetic evaluation was conducted using resin teeth mounted to a wax base adapted to the framework. Additionally, phonetic tests were performed, occlusion parameters were evaluated, and patient satisfaction was assessed. Finally, the correct positioning and proper shape of the dental elements were found (Figure 5a,b).

Upon concluding the intraoral assessments, the laboratory phase advanced with the CAD-CAM project for the framework and titanium-link connection to the BioHPP structure. The procedure involved a CAD-CAM-type procedure with the design of a BioHPP structure passivated to the implants. The structure was obtained through CAD design (Cad 3 Shape, Copenhagen, Denmark) and subsequent milling, (DCS Dental Concept Systems, Wesertal, Germany). After milling the structure, the sandblasting process was performed using 110 μm aluminum oxide on both the structure and the links, followed by the application of a thin layer of Visiolink bonding glue (Bredent group GMBH&Co. KG, Germany) to the structure.

The linkages were activated using the MKZ primer (Bredent group GMBH&Co. KG, Senden, Germany) and affixed to the BioHPP structure with a self-curing adhesive cement (Bredent group GMBH&Co. KG, Senden, Germany). Similarly, the resin teeth, following sandblasting, were coated with adhesive and affixed to the framework using Combo Lign dual resin cement (Bredent group GMBH&Co. KG, Senden, Germany).

The gingival portion was shaped and layered with gingival composite resin Crea Lign (Bredent group GMBH&Co. KG, Senden, Germany) to achieve a natural shape and color. As the last step, the definitive resin prosthesis was finished with layering and polishing. From a procedural perspective, the CAD-CAM workflow allowed for an improved operational process and ensured the passivity of the prosthetic framework. Following the CAD design project (3SHAPE, Copenhagen, Denmark), the structure was obtained in modified PEEK, such as BioHPP^®, through CAM milling (DCS Dental Concept Systems DC1 milling machine) (Figure 6a–d).

A definitive Toronto BioHPP^® prosthesis was inserted, and the subsequent clinical and radiological images demonstrate a satisfactory aesthetic outcome and an absence of prosthetic misfit, confirming acceptable framework passivation. Rx panorax (OPT) and clinical images at a 1-year follow-up confirm the long-term clinical reliability of the prosthetic material (Figure 7a–d).

4. Discussion

Currently, there are two types of retaining methods for superstructures: screw retention and cement retention [17,18]. Screw retention offers a significant advantage in terms of ease of maintenance and repair. The possibility of easily removing the superstructure makes it particularly useful for addressing mechanical complications [19]. However, the manufacturing process is highly technique-sensitive and distortions in the impression material or deformations in the model can occur, avoiding a passive fit between implants and superstructures [20]. On the other hand, cement retention is often favored for its simplicity and cost-effectiveness in the manufacturing process. The aesthetic appeal of cement-retained superstructures is another significant advantage, as they generally provide a more natural-looking result without the visible access holes that screw-retained systems may have [21]. However, removing a cement-retained superstructure is notably more difficult, and any residual cement left around the implant can lead to the inflammation of the surrounding tissues, potentially causing biological complications such as peri-implantitis [22]. Each approach requires careful consideration of the potential complications and the best strategy for achieving a successful and durable implant-supported restoration. Therefore, thanks to the advantages in maintenance and long-term care, along with the precision provided by computer-aided design–computer-aided manufacturing (CAD-CAM) technology in the production of implant superstructures, we opted for a screw-retained solution for the management of the following clinical case [23]. Nevertheless, if the connection between the abutment and the superstructure is not properly secured, it can result in increased stress on the patient’s bone. This additional stress may negatively affect the implant’s prognosis, underscoring the importance of precise fitting and secure connections in screw-retained systems. According to a literature review by Kihara et al. [24], the main complications of superstructures in implant-prosthetic rehabilitations are the misfitting of the superstructure, abutment screw loosening, and the fracturing of the abutments. Based on these considerations and in accordance with the determinants of proper occlusion, the microstructural qualities of the BioHPP^® prosthetic superstructure, along with its resulting elasticity, may ensure the adequate dissipation of masticatory forces even in the case of an imperfect fit between the abutment and the implant. In fact, the elastic modulus of BioHPP, which closely matches the average value of natural bone tissue, sets it apart from the more rigid materials typically used in implant-prosthetic rehabilitations. Nevertheless, BioHPP^® is derived from PEEK with the addition of ceramic microfillers to enhance its physical properties. PEEK is a bioinert and biocompatible material that has been used in medicine for over 35 years as a material for prostheses in finger joints, intervertebral disks, and hip joint replacements [25].

According to a recent literature review [26], the limited evidence on the viability of PEEK as an implant-prosthodontic material has hindered its adoption in clinical practice. However, a narrative review suggests that PEEK may be well-suited for CAD-CAM-fabricated fixed and removable dental prostheses, thanks to its advantageous mechanical, chemical, and physical properties [9].

Furthermore, according to the bibliographic references [27], our clinical experience suggests that BioHPP^® abutments may offer a superior biological seal between the abutments and soft tissues. As reported by a recent experimental study [28], BioHPP^® implant superstructures seem to biologically enhance fibroblast proliferation and attachment, stimulate increased neovascularization, and promote extracellular matrix deposition on the biomaterial. The clinical implication of these findings would be an improvement in both the quantity and quality of soft tissue adhesion on the transmucosal side of the abutments, thereby providing a more effective protective seal between the oral environment and the implant.

Finally, BioHPP^®’s lightweight nature, coupled with its favorable mechanical properties, enhances force distribution and reduces the risk of implant overload, thereby contributing to the overall stability of the prosthetic rehabilitation. However, the success of BioHPP^® in such demanding clinical applications relies heavily on meticulous planning, precise design, and careful execution. While our results are promising, further research involving larger patient cohorts and extended follow-up periods is necessary to fully establish the long-term survival and benefits of BioHPP^® superstructures in these scenarios.

5. Conclusions

This case report underscores the effectiveness and predictability of BioHPP^® superstructures in managing delayed loading in full-arch implant-prosthetic rehabilitations using the Toronto-Branemark protocol. The findings suggest that BioHPP^® is a viable alternative to traditional materials, offering significant advantages in terms of comfort, aesthetics, and implant stability. Ongoing research is essential to validate these findings and to better understand the long-term implications of using BioHPP^® in complex clinical settings.