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 Table of Contents  
Year : 2021  |  Volume : 13  |  Issue : 6  |  Page : 564-570

Short-term comparative evaluation of BioHPP and cast cobalt–chromium as framework for implant supported prostheses: A split mouth clinical randomized trial

1 Department of Prosthodontic, Tanta University, Tanta, Egypt
2 Department of Oral Medicine, Periodontology, Diagnosis and Radiology, Faculty of Dentistry, Tanta University, Tanta, Egypt

Date of Submission20-Jul-2021
Date of Decision07-Oct-2021
Date of Acceptance14-Oct-2021
Date of Web Publication30-Nov-2021

Correspondence Address:
Dr. Marwa M Amer
Department of Prosthodontics, Faculty of Dentistry, Tanta University, El-Geish Street, Tanta.
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JIOH.JIOH_181_21

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Aim: The purpose of this parallel randomized clinical trial was to evaluate the effects of BioHPP versus cobalt–chromium (Co–Cr) frameworks in screw-retained implant-supported fixed dental prostheses (FDPs) on peri-implant soft and hard tissues clinically and radiographically. Materials and Methods: Fifteen patients with bilateral partial edentulism in the posterior mandible received two implants at the positions of the second premolar and second molar on both sides: one side was restored with BioHpp-based screw-retained FDP (test group) and the other side was restored with Co–Cr-based screw-retained FDP (control group). All patients were clinically examined at the time of prosthesis insertion, and 6 and 12 months later for fracture of implant or framework, fracture, or looseness of the screw, veneer chipping, and fractures, modified bleeding index, modified plaque index, peri-implant probing depth, as well as radiographically for marginal bone loss. Results: At 12 months, both groups showed no statistically significant differences in the modified bleeding index (P = 1.00), modified plaque index (P = 0.383), probing depth (P = 0.925), and marginal bone loss (P = 0.222). No technical complications occurred during the evaluation period in either group. Conclusion: BioHPP framework represents a viable nonmetallic alternative to cast Co–Cr framework, shown by good soft and hard tissue responses.

Keywords: BioHPP, Framework, Implant, PEEK, Screw-Retained

How to cite this article:
Amer MM, Elsheikh MM, Haleem MM, Ghoraba SF, Salem AA. Short-term comparative evaluation of BioHPP and cast cobalt–chromium as framework for implant supported prostheses: A split mouth clinical randomized trial. J Int Oral Health 2021;13:564-70

How to cite this URL:
Amer MM, Elsheikh MM, Haleem MM, Ghoraba SF, Salem AA. Short-term comparative evaluation of BioHPP and cast cobalt–chromium as framework for implant supported prostheses: A split mouth clinical randomized trial. J Int Oral Health [serial online] 2021 [cited 2022 Jan 27];13:564-70. Available from:

  Introduction Top

The type of the prosthetic material is one of the main factors that affect the long-term clinical success of any dental prosthesis. Various materials, such as titanium, cobalt–chromium (Co–Cr), and zirconium, are used in the production of abutments and frameworks.[1] Titanium and Co–Cr alloys have been used for many years in implant-supported frameworks because of their superior mechanical properties; however, they can undergo surface degradation, corrosion, and may induce metal allergy.[2],[3] The metallic appearance may also be problematic especially where there is limited bone or soft tissue support at the fixture platform.[4] Zirconium is a metal-free alternative that has high biocompatibility, favorable mechanical properties, and has the potential to overcome the esthetic problems encountered with metals in implant-supported FDPs.[5]

The elastic moduli of metallic and zirconium materials are higher than that of the human bone, so they transfer all the occlusal load to the bone without absorbing any type of shock from the chewing loads; thus, they do not assure protection to the bone–fixture interface.[6] PEEK was introduced recently as a nonmetallic replacement in different implant prosthetic applications.[7],[8],[9],[10],[11],[12] The main advantage of PEEK that its elastic modulus (4 GPa) is comparable to that of bone (4.2 GPa). Thus, it could allow bone stimulation that enables remodeling without overloading.[13] However, PEEK can be used mainly as temporary abutment and framework because its fracture resistance is lower than that of titanium.[14]

BioHPP is based on PEEK polymer and was presented to be used as a definitive superstructure prosthesis on dental implants to support single crowns to full-arch reconstructions. It is reinforced with 20% ceramic microparticles, which significantly improve the strength and abrasive properties of the material, and its ability to be veneered. BioHPP has excellent biocompatibility, exceptional physical properties regarding (toughness, hardness, lightweight, and elasticity) and high chemical resistance even at high temperatures. In addition, it has excellent mechanical properties.[12],[15],[16],[17] BioHPP frameworks can be processed either through CAD/CAM technique or using the conventional lost wax technique, and it can be veneered by composite material.[7]

In vitro studies have been performed to test the mechanical and biological behavior of PEEK as a prosthetic material. The results of these studies further suggest PEEK-based polymers as the material of choice for fixed-detachable hybrid implant FPDs.[18],[19],[20],[21],[22]

Nevertheless, clinical studies that evaluate the use of reinforced PEEK as definitive implant superstructure are lacking. Therefore, the purpose of this in vivo study was to assess the clinical and radiographic effects of using BioHPP on peri-implant tissues in comparison with cast Co–Cr in fixed-detachable implant-supported mandibular partial dentures. The null hypothesis was that no significant differences would be found between Co–Cr and BioHPP framework in terms of peri-implant hard and soft tissue parameters.

  Materials and Methods Top

Setting and design

A total of 60 implants were inserted in 15 healthy partially edentulous participants at the Faculty of Dentistry. The study was accepted by the Research Ethical Committee at the Faculty of Dentistry in our University. Determination of the sample size was based on the marginal bone loss data.[23]

All interventions and procedures were performed between 2017 and 2019 in the University clinic.

Sampling criteria

The inclusion criteria of the study involved partially edentulous patients with the mandibular first premolar as the last standing abutment tooth with sufficient bone width and height at the prospective implant site to allow placement of at least 10 mm implant length and 4 mm width. Opposing arch was almost dentulous, and any missing teeth were restored using fixed partial denture. Remaining teeth were in good periodontal condition. The exclusion criteria of the study were active infection, inflammation, or flabby tissue in the areas intended for implant placement, medical conditions that contraindicate implant placement, heavy smoking, and severe clenching or bruxism.


Cone beam computed tomography (CBCT) and scanning of mandibular casts were performed for all patients for accurate implant planning and preparation of surgical guides. Tooth-supported completely guided template was designed using 3shape software (3 shape implant studio software) and printed using Mogassam Dent2printer, (Mogassam Co., LLC, Egypt). Two implants (Dentium Co, Ltd, Korea) were inserted in each side at the sites of second premolar and second molar under local anesthesia in a flapless manner using the fully guided implant kit (Dentium Co, Ltd, Korea).

In a split mouth design, the fifteen participants were divided into two groups to receive three-unit implant supported screw-retained prostheses on both sides, one side was restored using BioHPP framework and the other side was restored using Co–Cr framework.

Randomization and group allocation

The selection of the side was done randomly through the permuted block randomization technique. The allocation sequence and the code were hidden from the person allocating the participants to the intervention arm by using sealed envelopes.

After a three-month healing period, an implant-level impression was made using open tray. Impression with the fixture mounts connected to the analogs, opposing impression, bite registration, and the shade of the restoration were sent to the dental laboratory. For BioHPP group, two nonengaging titanium bases were tightened into the implant analogs in one side of the cast using the hex driver. The framework wax pattern was constructed and sprued then invested in a special investment material (Brevest for2press investment material; Bredent GmbH and Co. KG, Senden, Germany). BioHPP (BioHPP Granular, Bredent, Senden, Germany) was pressed into the mold using (For2press vacuum press device; Bredent, Senden, Germany), then devested, and inspected carefully for defects. The BioHPP framework was polished on the lingual side.

For Co–Cr group, two plastic nonengaging cylinder abutments with prefabricated metallic bases were tightened to the implants on the other side of the cast and shortened using diamond disc. The wax pattern for three-unit framework was made and sprued. The framework pattern assembly was invested in phosphate-bonded investment material (Bellavest SH, Bego Gmbh and Co. KG, Bremen, Germany (, then casted with Co–Cr alloy (Wirobond 280, Cr–Co alloy, Bego, Bremen, Germany). The casting was devested carefully, inspected for defects, and finished.

The frameworks were screwed to the implants [Figure 1] and checked for passive fit and complete seating using periapical and panoramic radiographs. Both frameworks were tested for enough clearance for the composite facing, then returned to the lab. The BioHPP framework was conditioned with primer (, Bredent, Senden, Germany); the Co–Cr framework was sandblasted, conditioned and opaqued to hide the metal shadow. Composite facing (Visiolign, Bredent, Senden, Germany) was added to both frameworks (Co–Cr and BioHPP) according to the selected shade, cured, and polished using special tools. The finished prostheses were inserted onto the implants and tightened with a manual screwdriver. Complete seating of the prostheses on the implants was confirmed radiographically [Figure 2]. Ten minutes after the initial torque applications, a calibrated torque wrench was used to retighten the abutment screws to the recommended torque value of 30 N. The occlusion was evaluated and adjusted if needed. The patients were given appropriate oral hygiene instructions before being discharged.
Figure 1: Framework try in step

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Figure 2: Panoramic radiograph showing that the superstructures were seated completely on the implants

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Each case was evaluated clinically and radiographically at time of prosthesis insertion, 6 and 12 months after insertion for technical complications such as (framework fracture, screw loosening, screw fracture, and chipping, or fracture of veneer layer), and for modified bleeding index,[24] modified plaque index,[24] and probing depth. All readings were taken around each fixture at four locations: lingual, mesial, buccal, and distal surfaces by an independent trained examiner blindly. Marginal bone level was measured from the implant shoulder to the first bone to implant contact on the mesial and distal sides of the implant on digital standardized periapical radiograph using the long cone paralleling technique using SIDEXIS XG 2.52 software package (Sirona Dentsply).

Statistical analysis

The data were collected and statistically analyzed by using SPSS statistics 22 (SPSS Inc., Chicago, Illinois) with a significance level of 0.05. Nonparametric data (bleeding and plaque scores) were presented as median (minimum–maximum) and parametric data (probing depth, marginal bone level) was presented as mean ± standard deviations. For nonparametric data, Mann–Whitney U test was used to compare the two groups, the Friedman test was used to compare data at the various observation periods within each group, followed by Wilcoxon signed-rank test was used to compare each two observation periods within the same group. For probing depth, Independent t test was used to compare between the groups. Within-group comparison was performed with repeated measure analysis of variance (ANOVA), followed by the Tukey test to compare between each two observation periods within the same group. For marginal bone loss, comparisons between the groups and between the different observation periods within the group were performed by independent t test. A value of P was significant at 0.05 or less, using 95% confidence intervals.

  Results Top

In this study, all participants attended all follow-up visits, and their results were analyzed. No implant failure occurred throughout the study period. No implant or framework fracture, no screw loosening or fracture, and no chipping or fracture of veneer layer occurred in either group; thus, the success rates for both types of prosthesis were 100%.

The median of bleeding and plaque scores, the mean values ± standard deviations for probing depth over the evaluation period are listed in [Table 1] and [Table 2]. No statistically significant differences were found between both groups in bleeding, plaque index, or probing at either the 6- or 12-month follow-up observations (P > 0.05). However, statistically significant differences were observed within each group at both follow-up observations.
Table 1: Comparison between studied groups throughout evaluation period in relation to modified bleeding index and modified plaque index

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Table 2: Comparison between studied groups throughout evaluation period in relation to probing depth

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Non-significant differences were found for the mean values of the marginal bone loss between the test groups at the different follow-up periods and within each group in the different follow-up periods as shown in [Table 3].
Table 3: Comparison between the studied groups in relation to the marginal bone level at different follow-up periods

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  Discussion Top

In vitro studies and clinical case reports of PEEK superstructure have been published, but only limited controlled clinical assessments of the soft and hard tissues responses to PEEK-based superstructures are available. For these reasons, the effects of BioHpp versus Co–Cr framework on peri-implant hard and soft tissues were investigated clinically and radiographically in this study. At the end of this study because there was no statistically significant difference between both types of framework materials, so the null hypothesis of this study was accepted.

No technical complications, such as framework fracture, screw loosening or fracture or veneer chipping or fracture, were observed with either framework types. The use of a mechanical torque instrument to tighten the screws to the recommended torque level contributes to reducing the risk of screw loosening.[25],[26] Retightening the abutment screws 10 min after the initial torque application was performed routinely to increase stability and decrease screw loosening,[27] also the application of implant protective occlusal concept guidelines helped reduce the offset loads on the implants.[28] These factors may have contributed to the excellent technical outcome of both framework types in this study. These findings agree with Zoidis,[12] who reported that ceramic reinforced peek covered with high strength polymethyl methacrylate veneer did not display any screw loosening at the end of 2 years.

The fact that no veneer chipping or fracture was found in either group throughout the follow-up period can be attributed to the use of adequate uniform thickness of the visio.lign veneer layer, proper bonding, and good preparation of the framework surface before bonding according to the manufacture recommendations. The cushioning effect of the composite veneer layer may contribute to the absence of veneer chipping and screw loosening.[9] This result corroborated that of Elshahawy et al.,[29] who found that visio.lign to be durable and to have comparable fracture resistance to other veneering materials such as porcelain.

In both groups, the plaque index and bleeding index increased significantly during the first 6 months but did not increase significantly over the next 6 months. This can be related to the plaque control by the patient and the repeated motivation of oral hygiene care given to the patient. Intergroup comparison revealed no statistically significant differences at different follow-up periods.

The BioHpp group showed better probing depth compared with the cast Co–Cr group, although the difference was not statistically significant. Watchet et al.[30] found absolute protection against bacterial leakage under cyclic masticatory loading in case of using PEEK superstructure on conventional titanium implants unlike other conventional abutment material. They attributed this finding to the high elasticity and self-deformation of the PEEK superstructure that led to prevention of micromovements along the implant-abutment interface.

Few studies examined the reaction of oral mucosa to implant components made of different materials. Abrahamsson et al.,[31] reported that the abutment material could affect the quality of the attachment that formed between the mucosa and the implant abutment in an experimental study. Several studies have shown optimal soft tissue healing around abutments made from titanium, aluminum-based ceramic, and zirconium.[31],[32] On the contrary, abutments made from polymer materials have not been studied extensively.

Outcomes in the two groups did not differ significantly. These results matched those of previous studies, in which the change in superstructure material did not affect the amount of marginal bone loss,[33] as well as those of experimental in vivo studies, in which different materials resulted in similar histological outcomes by means of histomorphometric evaluation of the peri-implant hard tissues.[34]


Based on the limitations of this study (limited number of patients, short follow-up time) it was concluded that using BioHPP as framework material in fixed-detachable prosthesis gives predictable results comparable to those of cast Co–Cr alloy.

  1. Both types of frameworks showed very good technical outcomes

  2. Statistically non-significant differences were found between both types of frameworks in soft and hard tissue response.

  3. BioHPP can replace metallic implant superstructure with good soft and hard tissue response.


The authors acknowledge all the staff members and colleagues at Department of Prosthodontics, Faculty of dentistry, Tanta University for their support and encouragement.

Financial support and sponsorship

This study was self-funded.

Conflicts of interest

There are no conflicts of interest.

Author contributions

MA: conceptualization, methodology, writing––review and editing. ME: supervision, review and editing. MH: writing––original draft preparation. SG: visualization, investigation. AS: writing––reviewing and editing. All the authors approved the final version of the article for publication.

Ethical policy and Institutional Review board statement

Ethical approval was obtained from the Institutional Research Ethical Committee at Faculty of Dentistry, Tanta University on June 1, 2016.

Patient declaration of consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Data availability statement

Data are available on reasonable request with the corresponding author’s mail.

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3]


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