Abstract
Aim and background
The retention of the band and loop space maintainer over the stainless steel crowns (SSCs) dictates the success of the space maintainer. Using two widely used luting agents, this study assesses the binding strength between SS bands and the most popular SSCs as well as the recently released Bioflx crowns.
Materials and methods
This in vitro study consisted of 48 samples divided into four groups. Type I glass ionomer cement (GIC) and resin-modified glass ionomer cement (RMGIC) were used to cement stainless steel (SS) bands over SSCs and Bioflx crowns. The shear bond strength was tested using a universal testing apparatus. To determine the degree of significance, one-way analysis of variance (ANOVA), post-hoc Tukey's test, and a p-value maintained at ≤0.05 were utilized.
Results
The shear bond strength between the SSC and RMGIC (0.908 ± 0.20 MPa) was statistically significant and higher than between the SSC and GIC (0.362 ± 0.21 MPa). Though not statistically significant, the binding strength between Bioflx crowns and GIC was stronger than between Bioflx crowns and RMGIC.
Conclusion
The SS bands bonded well to the SSCs with RMGIC, and there was no significant difference between the SSCs and Bioflx crowns with GIC as the luting agent. Cohesive failures were common with GIC, and adhesive failures were common with RMGIC in both crowns.
Clinical significance
The present study's findings can help clinicians make informed decisions when choosing crowns and luting agents for teeth with SSCs.
How to cite this article
Singh D, Rao A, Shenoy R, et al. Comparative Evaluation of the Bond Strength Between Bioflx, Stainless Steel Crowns, and Stainless Steel Bands Using Type 1 Glass Ionomer Cement and Resin-modified Glass Ionomer Cement as Luting Agents: An In Vitro Study. Int J Clin Pediatr Dent 2025;18(1):70–74.
Keywords: Band, Bioflx crowns, Shear bond strength, Stainless steel crowns
Introduction
Stainless steel (SS) crowns are among the most common restorations preferred for primary dentition. Recently, many tooth-colored crowns have been introduced, including Bioflx (BF) crowns. These crowns have excellent strength and flexibility.1,3
Early loss of primary teeth in children is one of the most common reasons for severe occlusal discrepancies in permanent dentition. A fixed space maintainer is one of the most commonly chosen space maintainers and requires the cementation of a band over the tooth. If the abutment tooth has or needs a crown, then one of the choices is to cement the band over the crown.4,5
The band material, crown material, and luting agent all have an impact on the strength of the bond between the SS bands and crowns.6 The most popular luting materials in pediatric dentistry for the cementation of bands are type 1 glass ionomer cement (GIC) and luting resin-modified glass ionomer cement (RMGIC).7
The current study uses two commonly types of luting cement, GIC and RMGIC, to evaluate and compare the bond strength between SS bands and the most popular SS crowns and the recently released BF crowns.
The null hypothesis was that there is no difference in the shear bond strength between the SS band and either the SS crowns or BF crowns when using GIC or RMGIC.
Materials and Methods
Study Design and Study Setting
This was an in vitro experimental study conducted at the Department of Pediatric and Preventive Dentistry and Dental Material Laboratory. It was organized in accordance with the modified Consolidated Standards of Reporting Trials (CONSORT).
Ethical Considerations
Every procedure was completed in compliance with the institutional ethics committee's ethical guidelines. The Institutional Ethics Committee granted ethical approval for the present study (ref: 22078 dated 28th July 2022) before the study.
Sample Size Calculation
The study's sample size was determined using a power analysis based on mean and standard deviation data taken from a study by Kalaskar et al.2 using the following formula:
(Zα + Zβ) 2 × S2/∆2 that is 1–β = 80% → β = 20% → Zβ = 0.84
where n = sample size of groups, Δ = difference in group means, Z1 – α/2 = two-sided Z value (e.g., Z = 0.96 for 95% confidence interval) and Z1 – β = power = 80%..
Using the above formula in OpenEpi software and two additional samples added to the sample size, assuming a 20% sample loss, a final sample size of 48 was determined.2
Outcomes
Primary Outcome
To evaluate the maximum force needed to dislodge the SS bands from BF crowns and SS crowns while using RMGIC and GIC as luting materials.
Secondary Outcome
To observe the modes of failure (adhesive, cohesive, mixed) that each material displayed following debonding.
Grouping and Randomization
The 48 reference models were then split into four groups, each with 12 samples (Fig. 1). Group I consisted of SS crowns, and group II consisted of BF crowns. Each group was further divided into A and B, where the SS bands were cemented using GIC and RMGIC, respectively.
Fig. 1.
Grouping of the samples based on the type of crown and luting agent used
Stainless steel crowns with a size of 4 (Hu-Friedy Stainless Steel, Rockwell St, Chicago, IL, USA) and BF crowns with a size of 4 (Kids-e-Crown, India) were used in this investigation. Both the crowns used were mandibular right second primary molars. Prefabricated SS band sizes of 32 and 33 (Liberal Traders Pvt. Ltd., Okhla, New Delhi, India) were chosen and modified to obtain the best fit for the SS crowns and BF crowns, respectively.
Type I GIC (Gc Fuji Type I, Gc Corporation, Tokyo, Japan) and RMGIC (GC FujiCEM 2, Gc Corporation, Tokyo, Japan) were used as luting agents.
Blinding
A nonparticipant in the study completed the random assignment process and sample enrollment using the lottery method. The statistician who performed the analysis and the person who tested and assessed the shear bond strength were blinded to the sample allocation. However, it was not possible to blind the person who cemented the bands.
Procedure
Fabrication of Reference Blocks
The models were fabricated according to the methods and techniques used by Kalaskar et al.2 Twenty-four primary right mandibular second molar SS crowns and an equal number of BF crowns were embedded in resin blocks.
Prefabricated silicon molds with dimensions of 3.5 × 3.5 × 2.5 cm were used to create the acrylic blocks. A polyvinyl siloxane impression material was placed in the mold, the crown was reverse dipped into the impression material exposing the inner side of the crown, and the material was allowed to set (Fig. 2A). Self-curing acrylic was then poured to fill the entire inverted crown and mold and left to polymerize. The same procedure was repeated to create 48 blocks with SS crowns and BF crowns. After the acrylic was set, the blocks were removed from the mold.
Figs 2A and B.
Reference blocks. (A) Crown reversed and placed in the polyvinyl siloxane impression material in a silicone mold; (B) Prepared samples, with a U-shaped loop soldered to the band
Band Adaptation and Preparation
Preformed SS bands were adapted on the SS crowns and BF crowns. A “U”-shaped loop 2.5 cm in length made from 20-gauge stainless steel wire was soldered on either side of the band in the midbuccal and midlingual portions (Fig. 2B). The bands were then cemented on the crowns using either of the luting materials, following which each sample was kept at a steady 37°C for 24 hours in a water bath.
Cementation of the Stainless Steel Band Over the Stainless Steel Crowns and Bioflx Crowns
The cements were manipulated as per the manufacturer's recommendations. The SS bands on the inside surfaces were then loaded with the mixed cement, and a band pusher was used to seat the band over the crown. The extra cement was then removed from the band edge, and the samples from groups IA and IIA were left to cure for 10 minutes. Group IB and IIB samples were light cured for 5 minutes covering all the sides of the crown. The models were then stored in a water bath for 24 hours at a constant temperature of 37°C to prevent dehydration at longer aging times.
Bond Strength Estimation
A universal testing machine (INSTRON 3366—10 kN) was used to evaluate the shear bond strength utilizing the amount of force necessary to debond the SS bands from the crowns. Each sample was placed on the lower jaw of the machine, and a U-shaped soldered wire was fixed to the upper jaw (Fig. 3A). Tensile mode was used to assess the bond strength at a cross spread of 1 mm/minute. The band was forced to fully separate from the crown by applying tensile tension (Fig. 3B). The debonding force maximum was measured in Newtons (N).
Figs 3A and B.
The universal testing machine. (A) The samples placed on the lower jaw and upper jaw engage the U loop; (B) The stainless steel band completely dislodged from the crown
The following formula was used to calculate the shear bond strength:
Shear bond strength (MPa) = The maximum force needed to completely separate the band from the crown (N) / Circumferential area of band (mm2) × band length (mm)
The circumferential area of the band was calculated using the formula πr2 (r = radius of the band).
Estimation of the Mode of Failure
A stereomicroscope with a 10× magnification was used to examine the specimens from each group in order to determine the location of the bond failure.8 The results were classified given as follows:
Adhesive failure: Exclusively occurring at the band or crown contact
Cohesive failure: This kind of failure only happens inside the luting substance
Mixed failure: When cohesive and adhesive failures coexist.
Statistical Analysis
The Statistical Package for Social Sciences (SPSS v17.0, IBM SPSS®)-Java (TM) Platform SE binary-IBM Corp, London, UK was used to statistically analyze the collected data. There was tabulation of the descriptive statistics. The information was put through a normalcy test for further analysis. Intergroup comparisons (<two groups) were performed using one-way analysis of variance (ANOVA), and post-hoc Tukey's test was applied depending on the normality of the data. The p-value was kept at ≤0.05 to assess the level of significance.
Results
Debonding Force
The initial debonding force (Table 1) needed to partially dislodge the band was a maximum of 58.24 ± 12.98 N between the SS crowns and RMGIC as a luting agent. The least force needed for initial debonding was observed in group IIB between the BF crowns and RMGIC as a luting agent. The maximum debonding force needed to completely dislodge the band was observed in group IB between the SS crowns and RMGIC as a luting agent (109.93 ± 22.94 N) compared to the other groups, and this difference was statistically significant with a p-value of 0.0000. The least force needed to completely debond the band was observed in group IIB (41.04 ± 23.55 N) between the BF crowns and RMGIC as a luting agent. Better results were observed when RMGIC was used as a luting agent with SS crowns than with BF crowns, and this was statistically significant with a p-value of 0.000. GIC exhibited better results with SS crowns, but the difference was not statistically significant.
Table 1.
Force (in Newtons) for initial and complete debonding of the band
| Type of crowns | Initial debonding force (N) | Complete debonding force (N) | ||||
|---|---|---|---|---|---|---|
| GIC (mean ± SD) | RMGIC (mean ± SD) | Significance | GIC (mean ± SD) | RMGIC (mean ± SD) | Significance | |
| SS crowns | 26.26 ± 15.07 | 58.24 ± 12.98 | p-value = 0.000 | 102.925 ± 22.94 | 109.93 ± 22.94 | p-value = 0.000 |
| Bioflx crowns | 32.48 ± 16.00 | 23.22 ± 13.33 | p-value = 0.592 | 57.39 ± 28.28 | 41.04 ± 23.55 | p-value = 0.592 |
| p-value = 0.916 | p-value = 0.000 | p-value = 0.916 | p-value = 0.000 | |||
Shear Bond Strength
The maximum shear bond strength (Table 2) was observed in group IB between the SS crowns and RMGIC as a luting agent (0.908 ± 0.20 MPa) compared to the other groups. The least shear bond strength was observed in group IIB (0.362 ± 0.21 MPa) between the BF crowns and RMGIC as a luting agent.
Table 2.
Shear bond strength values (MPa)
| Type of crowns | GIC (mean ± SD) | RMGIC (mean ± SD) | Significance |
|---|---|---|---|
| SS crowns | 0.405 ± 0.24 | 0.908 ± 0.20 | p-value = 0.000 |
| BF crowns | 0.506 ± 0.25 | 0.362 ± 0.21 | p-value = 0.592 |
| p-value = 0.916 | p-value = 0.000 |
The shear bond strength between the SS crowns and RMGIC was greater than between the SS crowns and GIC and was statistically significant, with a p-value of 0.0000. The shear bond strength between BF crowns and GIC was greater than between BF crowns and RMGIC but was not statistically significant.
The shear bond strength between SS crowns luted with RMGIC was greater than between BF crowns luted with RMGIC, and this difference was statistically significant (p-value of 0.0000). Compared with that of RMGIC, the bond between the SS band and BF crowns was better when GIC was used for luting, but this difference was not statistically significant.
Mode of Failure
All the samples exhibited mixed types of failure with the presence of cohesive and adhesive failures, as observed under a stereomicroscope. Group IA and group IIA had predominantly cohesive types of failure (n = 7 each).
The group IB and group IIB samples exhibited predominantly adhesive failure. Group IB had seven adhesive failures, and group IIB had eight adhesive failures.
Discussion
Crowns have been traditionally used for deciduous teeth when indicated due to their longevity and need for minimum tooth reduction compared to multisurface amalgam.9
Because of their high impact hybrid resin polymer composition, BF crowns are the first flexible, strong, self-adapting, and esthetically pleasing preformed pediatric crowns that offer qualities of both zirconia and SS crowns.3
The interface between a band and a crown is unique, as both sides are smooth, and the success of their retention dictates the overall performance of the banded space maintainer placed over the existing crowns.6
Glass ionomer cement and RMGIC are the most commonly used materials for luting.7,10 The bond between the luting material and enamel is chemical, while that between the band and crown is mechanical. This difference can be crucial in the retention of the band over the crown. The question, thus, arises whether the luting cement used to bond the SS bands over the SS crowns has the same bond strength as BF crowns.
FujiCEM 2, a second-generation RMGIC, was developed with enhanced properties that incorporate cross-linking monomers and has the benefits of both conventional glass ionomers and resins. These cross-linking monomers improve the strength and provide a high release of fluorides. Additionally, it also provides a low film thickness and offers remarkable marginal integrity. This cement has a wide range of applications, such as inlays, onlays, crowns, and bridges made of metal, resin, and zirconia.11,12
The samples were prepared as described by Kalaskar et al.2 The mold technique was used to secure the crown in the acrylic block and prevent it from becoming dislodged during shear bond testing. The self-curing acrylic filled into the crown ensured that the crown was stable in its core.
Stainless steel wire was made into a loop and soldered on the band before mounting the sample on the testing machine to allow uniform stress distribution.13
The force at which the band first partially dislodges is denoted as the initial debonding force, and the force at which the band is completely dislodged is referred to as the complete debonding force. The initial debonding force was the lowest between the BF crowns and SS bands with RMGIC as the luting material, followed by the SS crowns with GIC as the luting material. The complete debonding force needed for complete dislodgement was least between the BF crowns and the SS bands with RMGIC followed by the BF crowns with GIC.
The current study found that when RMGIC was used as a luting cement, SS bands and SS crowns bonded more strongly. The bond strength between the BF crowns and SS bands did not significantly differ whether GIC or RMGIC was used as the luting agent.
Most of the existing literature14,17 is based on the estimation of the bond strength between bands placed over natural teeth,16,17 and this cannot be used for comparison with the present study results. RMGIC is a good luting material of choice for the cementation of SS crowns over natural teeth.1
Few existing studies recommend GIC for the cementation of SS bands on SS crowns due to the better bond strength compared to that of RMGIC.2,7 However, there has been no published research evaluating the bond strength between SS bands and BF crowns.
The reason behind cohesive failure in groups IA and IIA may be attributed to the low fracture toughness and lower modulus of elasticity, leading to elastic deformation of the GIC.15
The manufacturers of BF crowns recommend FujiCEM 2 for cementation over the natural tooth. In the present study, similar results were also obtained when SS bands were cemented over the BF crowns using either GIC or RMGIC; thus, both luting materials can be recommended for cementation of SS bands over BF crowns. RMGIC was found to be more suitable than GIC for cementation of SS bands over the SS crowns. The null hypothesis was rejected based on the present outcomes.
This observation is beneficial for clinicians who can make informed decisions while cementing SS bands over the new BF crowns or the SS crowns and minimize luting failures.
Limitations and Strengths of the Study
Bioflx crowns are new, and this study will aid clinicians in making an informed decision while choosing a luting agent for the cementation of SS bands over BF crowns. The current study focused on estimating the bond strength but could not provide the solution for band failures and improve the bond strength.
Conclusion
Based on the results of this study, the following conclusions can be made:
The SS bands bonded well to the SS crowns with RMGIC as the luting agent.
There was no significant difference between SS crowns and BF crowns with type 1 GIC as the luting agent.
Cohesive failures were common with type 1 GIC, and adhesive failures were common with RMGIC in both crowns.
Clinical Significance
The retention of the band and loop space maintainer over the existing crowns dictates its success. The present study's findings can help clinicians make informed decisions when choosing crowns and luting agents for teeth with existing SS crowns to minimize luting failure.
Declarations
Ethics Approval
All procedures were carried out in accordance with the ethical guidelines of the Institutional Ethics Committee. The Institutional Ethics Committee granted ethical approval for the present study (ref: 22078 dated 28th July 2022) before the study.
Author Contributions
DS, AR, GK, and RS made substantial contributions to the conception or design of the study.
DS, AR, and RS contributed to the acquisition, analysis, and interpretation of the data.
DS drafted the manuscript, and AR, RS, GK, and SBS critically revised the manuscript for important intellectual content.
All authors approved the version to be published and agreed to be accountable for all aspects of the work, ensuring that questions related to the accuracy or integrity of any part of the work were appropriately investigated and resolved.
Availability of data and materials: Data can be provided upon reasonable request.
Orcid
Divya Singh https://orcid.org/0009-0007-6276-3061
Arathi Rao https://orcid.org/0000-0001-6440-1274
Ramya Shenoy https://orcid.org/0000-0003-3126-4415
Gurvinder Kaur https://orcid.org/0000-0002-6646-7127
Baranya Shrikrishna Suprabha https://orcid.org/0000-0001-7003-3121
Footnotes
Source of support: A total of Rs 20,000 funding was received from the Wings NGO, Lucknow, India on 30th July 2022.
Conflict of interest: Dr Gurvinder Kaur is associated as the International Editorial and Advisory Board of this journal and this manuscript was subjected to this journal's standard review procedures, with this peer review handled independently of this editorial board member and his research group.
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