Evaluation of the Shear Peel Bond Strength of the Computer-aided Design/Computer-aided Manufacturing Polyetheretherketone Band for Space Maintainer: An In Vitro Study

Abstract

Background and aim

Computer-aided design/computer-aided manufacturing (CAD/CAM)-fabricated space maintainers offer a reliable alternative to traditionally fabricated stainless steel (SST) appliances, avoiding their commonly encountered drawbacks. The aim of this study is to evaluate the shear peel bond strength of the CAD/CAM polyetheretherketone (PEEK) space maintainer in comparison with an SST one.

Materials and methods

The study was conducted on 50 molars, divided into two groups: a customized PEEK band (study group) and a prefabricated SST orthodontic molar band (control group). The crowns of the study group were scanned using a lab scanner, the bands were designed using ExoCAD software, and the PEEK disks were milled. The inner surfaces of the PEEK bands were sandblasted, etched, rinsed, and dried. Both bands were cemented to the teeth using self-etch dual-cure resin cement. The sheer peel bond of the bands was tested twice, both before and after cementation, using an electromechanical tensile universal testing machine. The data were analyzed using Statistical Package for the Social Sciences (SPSS) software.

Results

Prior to cementation, the peel bond strength of the PEEK band (0.02 ± 0.01) was significantly higher than the SST band (0.01 ± 0.00) (p = 0.000). Additionally, the PEEK band's shear peel bond strength (0.58 ± 0.18) following cementation with self-etch dual-cure dental resin cement was considerably higher than the SST band's shear peel bond strength (0.49 ± 0.24) (p = 0.04).

Conclusion

PEEK bands designed with CAD/CAM technology showed a better shear peel bond than SST bands, both before and following cementation, which imply that PEEK might provide a dependable alternative for traditional SST bands used in pediatric dentistry.

How to cite this article

Mohamed OS, Karawia I, Gaber AH, et al. Evaluation of the Shear Peel Bond Strength of the Computer-aided Design/Computer-aided Manufacturing Polyetheretherketone Band for Space Maintainer: An In Vitro Study. Int J Clin Pediatr Dent 2025;18(1):75–79.

Introduction

The primary dentition plays a pivotal role in oral growth and development. One of its importance is preserving the arch length since it serves as the best space maintainer and best guidance to the permanent successors to erupt into the arch in the proper position.¹ The loss of the primary tooth before the indicated time of exfoliation and within 6 months might lead to unfavorable mesial or distal shifting movements of the neighboring teeth, ectopic eruption, crowding, or even impaction of the successors, which in turn negatively affect the neutral occlusion of permanent dentition. Thus, maintaining the space after tooth extraction is imperative until the permanent successor begins to pierce the gingiva.²

Space maintainers are the most effective way to prevent future malocclusion from premature loss of the primary tooth.³ The conventional stainless steel (SST) band and loop is the most widely used fixed space maintainer, especially for unilateral premature loss of a single primary molar. However, its fabrication requires alginate elastic impression material, which cannot be endurable for some pediatric patients. Moreover, potential drawbacks such as plaque retention and caries formation around the band's margin may occur.⁴

The conventional fabrication process of an SST space maintainer is soldering wire to an SST band or crown may be prone to inaccuracies during fabrication that leads to appliance failure later, which could be in the form of loop slipping, abutment tipping, or even appliance dislodgment from band decementation. The digital space maintainer not only helps to address these problems but also aids in the fabrication of precise, convenient, and rapid designs since the material used for computer-aided design/computer-aided manufacturing (CAD/CAM) demonstrates superior stability and durability.⁵

The emergence of a novel biomaterial, polyetheretherketone (PEEK), has garnered attention in the biomedical field.⁶ PEEK is a semicrystalline thermoplastic composite polymer type.⁷ It has been the most popular polymer in the polyaryletherketone (PAEK) family by exhibiting outstanding mechanical and chemical properties such as a low elastic modulus (approximately 3:4 GPa), which closely resembles that of human bone (11.5 GPa), as well as lower compressive strength compared to alveolar and cortical bones.⁸ Moreover, PEEK offers dimensional stability, shock absorption, rigidity at high temperatures, a high level of biocompatibility, and is more hygienic since it has a low plaque affinity in comparison to other dental materials.^9,10 The aromatic chemical structure of ketone and other components of the PEEK creates an inert surface with suboptimal bonding. Surface conditioning, such as roughening by etching or abrasive techniques as well as surface activation with plasma treatment or laser, may be necessary to achieve optimized bonding.^11,12 Tensile or shear bond tests are appropriate methods for evaluating the bonding quality of dental materials.¹³

Shear bond strength is the resistance of the restorative material to lateral forces that may cause the material to displace from the tooth structure. This parameter quantifies the maximum stress that can be withstood at the interface between the tooth and restorative material. Thus, it is a critical factor for a successful restoration, as the primary forces dislodging the tooth restoration have a shearing effect at the interface. Although the shear strength measurement of a material may not fully indicate its longevity, the heightened shear bond strength values typically signify superior adhesion of the material to the tooth structure.¹⁴

Polyetheretherketone presents alternatives that can be used in diverse clinical situations, including pediatric appliances. However, very limited studies compare the mechanical advantages of PEEK as a band for space maintainers to those of other materials, including traditional SST bands. The aim of the study is to investigate shear bond strength, one of PEEK's mechanical properties, as an alternative space maintainer material. The null hypothesis was that there are no differences in the shear peel bond strength of the PEEK and metal band.

Materials and Methods

Study Design and Sample Size

The current study had an in vitro clinical design. The ethical approval was obtained from the ethics committee at Pharos University (number PUA-UREAC-01-3-223). G*Power software version 3.1.9.4 was used to calculate the minimum required sample size. Sample size determination was based on the effect size of different intervention groups (0.84) retrieved from previous research¹⁵ using a two-tailed t-test, α error = 0.05, and power of 80.0%; the total calculated sample size was 48 rounded to 50 teeth. The current study was written according to the Checklist for Reporting In vitro Studies (CRIS) guidelines.¹⁶

Teeth Selection and Grouping

Intact extracted permanent molars were collected from university and governmental and private dental clinics in Alexandria, Egypt. Teeth were disinfected with a 1:10 sodium hypochlorite solution, mounted in acrylic blocks allowing the appearance of the full crown of the molars to ease their manipulation, and stored in saline solution until use.

The 50 permanent molars were randomly divided into two groups, each consisting of 25 molars given as follows:

• Group 1: Customized PEEK band (study group)

• Group 2: Prefabricated SST orthodontic molar band with a tube on the buccal surface and cleats on the lingual one (3M style-Yahong, China) (control group).

Fabrication of the Polyetheretherketone Band

The crowns of the teeth of group 1 were scanned using an extraoral scanner (EDGE HD, DOF, Seoul, Korea) to produce virtual dies. The bands were designed using ExoCAD (DentalCAD 2.2 Valletta) design software according to previous literature.¹⁷ Two horizontal bars were added on the buccal and lingual surfaces to allow the engagement of SST wires in the pullout test, and then the PEEK disks (Green DenTech Co., Ltd., Taiwan) were milled by a five-axis milling machine for band fabrication (Fig. 1).

Fig. 1.

PEEK band

The inner surfaces of the PEEK bands were sandblasted with alumina 110 µ under two bars at a distance of 10 mm, etched with 98% sulfuric acid for 60 seconds, rinsed for 60 seconds under running water, and then dried with oil-free air. A thin layer of primer (visio-link, Bredent GmbH & Co. KG, Germany) was applied to the etchant surface of the band.

The teeth of the two groups were rinsed with water, followed by drying with oil-free air. Both bands (SST and PEEK) were cemented to the teeth according to their group using self-etch dual-cure dental resin cement (Hande Chemicals, Korea) and cured for 20 seconds.

Evaluation

Testing the sheer peel bond of the bands was done in the Faculty of Engineering, Alexandria University, using an electromechanical tensile universal testing machine with a 5 KN load cell. The two horizontal bars of the PEEK bands and tubes and cleats of the SST bands were hanging from the upper movable chamber of the testing machine by a double 0.7 mm orthodontic wire. The machine was submitted to increase the vertical load slowly by 1 mm/min until band dislodgment. The required load for dislodgment was registered in Newton using computer software (Fig. 2).

Figs 2A and B.

Testing the sheer peel bond of the bands. (A) PEEK band; (B) SST band

The band length and width were measured. The width was measured by wrapping the band with string and marking the point of meeting of the two ends, and then the string length was measured. The area was determined in mm², and then shear peel bond strength was calculated by dividing the debonding force (N) by the band area (mm²) and represented in megapascals (MPa).

The evaluation was done twice, once before the cementation of the bands of both groups and then after cementation. Before the second evaluation, all teeth after 10 minutes of band cementation were stored in synthetic saliva at 37°C for 24 hours in a hot air oven.

Statistical Analysis

The data were tabulated and analyzed using Statistical Package for the Social Sciences (SPSS) software version 25. Data were analyzed for normal distribution using the Kolmogorov–Smirnov test and then submitted to the Mann–Whitney U test, where the significant level was calculated at 0.05.

Results

It was found, as shown in Table 1, that the peel bond strength of the PEEK band (0.02 ± 0.01) was significantly higher than the SST band (0.01 ± 0.00) before cementation (p = 0.000). Also, after cementation with self-etch dual-cure dental resin cement, the shear peel bond strength of the PEEK band (0.58 ± 0.18) was significantly higher than the SST band (0.49 ± 0.24) (p = 0.04).

Table 1.

Shear peel bond strength before and after cementation of PEEK and SST bands

	Group 1 (PEEK band)		Group 2 (SST band)		p-value
	Mean ± SD	Median (IQR)	Mean ± SD	Median (IQR)
Before cementation	0.02 ± 0.01	0.02 (0.00–0.04)	0.01 ± 0.00	0.01 (0.00–0.02)	0.000*
After cementation	0.58 ± 0.18	0.52 (0.46–0.67)	0.49 ± 0.24	0.45 (0.36–0.65)	0.04*

*Significance level at p-value ≤ 0.05

Discussion

Computer-aided design/computer-aided manufacturing PEEK material has been recently explored for use in orthodontic and space maintenance applications. PEEK retainers with optimized designs showed superior clinical performance over 12 months,¹⁸ maintaining color match, anatomic contour, and marginal integrity, suggesting their use as a better alternative to conventional SST space maintainers, avoiding commonly encountered drawbacks such as band decementation, fracture, plaque retention, and caries formation around the band's margin.⁴

The purpose of this study is to evaluate the shear peel bond strength of the PEEK band. Fifty permanent molar teeth were used in this study, divided into two groups of 25 each. In the study group, CAD/CAM-fabricated PEEK bands were used, while conventional prefabricated SST bands were used in the control group. Both bands (SST and PEEK) were cemented to the teeth according to their group using self-etch dual-cure resin cement and cured for 20 seconds as per the recommendation of previous literature, which demonstrated the highest resistance to decementation when self-adhesive resin cement was used in comparison to conventional or resin-modified glass ionomer cements.¹⁹ The results of this study showed that the peel bond strength of the PEEK band was significantly higher than the SST band before and after cementation. Therefore, the null hypothesis of the study was rejected.

In accordance with the findings of the present study, a clinical trial in 2023 studied the clinical effectiveness and patient's comfort of the CAD/CAM PEEK space maintainer in comparison with conventional band and loop space maintainers. The study revealed that the CAD/CAM PEEK space maintainer showed high clinical success rates and greater patient comfort during the 6-month follow-up period in comparison to the conventional band and loop space maintainer. Only one debonded CAD/CAM PEEK space maintainer at the enamel–resin interface, which the authors attributed to the prismless enamel nature of the primary tooth, which has poor bond strength with resins that had a negative effect on the resin retentions.¹⁷ Similarly, a clinical trial by Wang et al. concluded that the digital semirigid bridge space maintainers, fabricated with PEEK, were convenient and esthetically pleasing, and none of the 15 space maintainers or abutments became loose or fell off during the 6-month study period.²⁰

However, Alabbadi et al. in 2023 investigated the debonding force of CAD/CAM-fabricated PEEK and fiber glass reinforcement composites in comparison with metal lingual retainers. The study findings revealed that among the examined retainers, the highest debonding force values were registered for CAD/CAM fiber-reinforced composites, while the lowest for CAD/CAM PEEK. However, both the CAD/CAM-fabricated retainers were fitter, easier to bond, and had sufficient debonding force, but to maintain the function of the tooth, it needed to be fabricated in a small amount of deflection.²¹ Variations in surface treatments or testing conditions could be the cause of this study's inconsistent results.

When comparing the peel bond strength before the cementation process, the study revealed that CAD/CAM PEEK space maintainers had significantly higher values than conventional SST bands, which may be due to the use of the CAD/CAM technology with its customized precisive nature, which ensures consistent quality and fit of the band, thereby enhancing the bond strength in comparison to the conventional prefabricated one. This is consistent with the findings of a study conducted in 2016 comparing the marginal gap and internal fit of CAD/CAM PEEK provisional crowns with that of directly fabricated provisional crowns, revealing the superior fit and better strength of the CAD/CAM-fabricated crowns than direct provisional crowns.²² Furthermore, PEEK has inherent good mechanical properties,²³ including high tensile strength and resistance to wear, which might contribute to better adhesion and bonding compared to SST. This superiority of the CAD/CAM-fabricated bands even before the cementation process could translate into better clinical outcomes, such as a reduced risk of debonding or failure of the maintainers during use.

Strengths and Limitations

To the best of the authors' knowledge, this is the first study to evaluate the peel shear bond strength of CAD/CAM-designed PEEK band in comparison with traditional SST ones. The study was conducted under controlled experimental conditions such as temperature and the application of forces. Using a universal testing machine with a 5 kN load cell ensures consistent and reliable measurement of shear peel bond strength across all samples. However, the study has some limitations because it used an in vitro setting, which does not completely replicate the complex oral environment where factors such as saliva and oral hygiene practices exist. Furthermore, while a universal testing machine provides controlled load application, it may not fully replicate the dynamic loading conditions of the masticatory system, which could influence bond strength differently. Additionally, in vitro studies often simplify the cementation process compared to clinical practice, which may be compromised with blood or saliva, especially in the cases of uncooperative pediatric patients.

Conclusion

Within the limitations of this study, PEEK maintainers designed with CAD/CAM technology showed a better shear peel bond than SST maintainers, both before and following cementation. These results imply that PEEK might provide a dependable alternative for space maintenance in pediatric dentistry, possibly improving clinical results due to its better material characteristics, with optimized designs and appropriate adhesive systems enhancing their performance and longevity, avoiding the frequent debonding and failure of the traditionally fabricated ones. Future research should focus on verifying these results in clinical settings over extended periods as well as investigating other material production and bonding technique improvements.

Declaration

Ethics Approval and Consent to Participate

This research was approved by the research ethics committee at Pharos University under registration no. (PUA-UREAC-01-3-223). All methods were carried out in agreement with the Declaration of Helsinki. A written informed consent was obtained from patients at the time of extractions, declaring that these teeth would be used for research purposes instead of being discarded as waste.

Availability of Data and Materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Author Contributions

OSM: Performed the literature search, methodology, investigation, and writing–original draft. IK: Methodology, analyzed, and interpreted the data. AHG: Conceptualization and writing–review. MAH: Methodology, investigation, and writing original draft. All authors read and approved the final version of the manuscript.

Orcid

Osama S Mohamed https://orcid.org/0000-0002-8745-6179