Influence of cement type on the bond strength of orthodontic bands to zirconia crowns

Abstract

Background

This study evaluated the retentive strength and residual cement of orthodontic bands bonded to zirconia crowns using four cementation protocols: Glass-ionomer cement (GIC), Resin-modified glass ionomer cement (RMGIC), Transbond Plus Light Cure Band Adhesive without silane, and Transbond Plus with silane primer application.

Materials and methods

Sixty zirconia crowns were divided into four groups (15 each) and cemented with the respective cements. Each crown was mounted on a resin-based tooth-like structure and secured to a universal testing machine. Orthodontic bands were adapted to the crowns, and forces were applied to measure retentive strength. After debonding, the remaining cement was assessed using the Adhesive Remnant Index (ARI). Specimens underwent thermocycling (5,000 cycles between 5 °C and 55 °C) to simulate oral conditions.

Results

The mean retentive strength was 1.23 MPa. Group 4 (Transbond Plus with silane) exhibited the highest strength (1.44 MPa), while group 1 (GIC) demonstrated the lowest (0.85 MPa). Cementation protocol significantly influenced retentive strength, with groups 2 (RMGIC) and 4 showing superior results to groups 1 and 3 (Transbond Plus without silane).

Conclusion

The cement type and protocol employed significantly affect the shear-peel bond strength of orthodontic bands cemented to zirconia crowns. RMGIC and Transbond Plus, especially with silane, provide superior retention compared to GIC.

Introduction

Several studies have evaluated the shear-peel bond strength of orthodontic bands on natural teeth [1–4]. A systematic review of the literature indicates that the failure rate for molar bands bonded to natural teeth can reach as high as 35% within a 12-month follow-up period, as observed in older studies. However, this review also highlights that the majority of studies did not report detailed failure rates for orthodontic bands [5].

In clinical practice, particularly when treating adults, it is common to restore compromised molars—especially those that have undergone endodontic treatment—with crowns, often porcelain ones. Clinical guidelines specifically recommend this restorative approach for posterior teeth with root canal treatment to shield them from potential contamination and further damage. Moreover, there are functional and aesthetic reasons that favor the use of crowns for posterior teeth [6, 7]. Consequently, it is not uncommon for orthodontic treatment to commence in patients who have already undergone restoration with porcelain crowns. The demand for orthodontic treatment among adult patients has notably increased [8]. This trend has been accompanied by a significant rise in the number of practitioners offering orthodontic services to adults, with one survey reporting that the percentage of orthodontists treating adult patients increased from 51 to 98.6% [9]. As a result, orthodontic treatment now frequently involves patients who already have porcelain crown restorations. In such cases, orthodontists must modify their bonding and banding techniques to effectively adhere to the crowned surfaces.

The dental literature extensively explores various protocols for bonding orthodontic brackets to non-natural tooth structures, such as restorations, acrylic crowns, porcelain, and gold/metal crowns [10–16]. Several systematic reviews have comprehensively evaluated in vivo and in vitro studies, assessing the effectiveness of different methods for improving bracket retention on acrylic, porcelain, and gold crowns [17–21]. While these reviews have yielded varying conclusions regarding the most effective methods, there is a consensus among researchers that special protocols should be employed to enhance bracket retention on non-natural tooth structures. A critical factor in achieving strong bracket adhesion on crowns is effective surface treatment, which involves preparing the crown surface through either chemical or mechanical methods to increase its retentive capacity. The application of specific bonding agents can further reinforce bracket retention on crowns or restorations. For instance, surface roughening techniques can enhance the adhesive bond, while primers may be applied to create a stronger bonding interface [22, 23]. Together, these preparatory steps contribute to a more stable and long-lasting attachment of orthodontic brackets on restorative materials [18, 20, 21].

Unlike the bonding of brackets to non-human tooth structures, which has been extensively studied [10–15, 17, 24–35], the retentive strength of orthodontic bands to non-human tooth structures has received relatively little attention. Previous research has primarily focused on the cementation of bands to porcelain denture teeth and gold crowns [36, 37], employing a range of protocols that varied in terms of surface treatment and cement type. Research on bands cemented to porcelain denture teeth has revealed no significant differences in mean shear-peel bond strengths across various protocols. However, bands cemented to gold alloy crowns using resin-modified glass ionomer cement demonstrated the strongest retention. Glass Ionomer Cement (GIC) and Resin-Modified GIC (RMGIC) have both been recommended for cementing molar bands [10]. RMGIC demonstrates an extended working time and enhanced resistance to moisture during setting compared to traditional GIC [38]. However, research has shown no significant difference in bond failure rates between GIC and RMGIC when used for molar bands [2, 39, 40]. The retentive strength of composite resin-based cements has shown mixed results; while some studies found that compomers perform comparably to GIC and RMGIC, others have observed that compomers have lower retentive strength than either GIC or RMGIC [41, 42].

The present study aimed to investigate the retentive strength of orthodontic bands cemented to zirconia crowns using four different cementation protocols: Glass Ionomer Cement (Medicem MC), Resin-Modified Glass Ionomer Cement (Fuji II LC), Transbond Plus Light Cure Band Adhesive without silane, and Transbond Plus Light Cure Band Adhesive with silane primer application. This study addresses a critical gap in the literature, as no previous research has comprehensively compared the retentive strength of these cements for bonding orthodontic bands to zirconia crowns. The null hypothesis was that there would be no significant difference in retentive strength among the four cementation protocols.

Materials and methods

This study is presented in accordance with the Risk of Bias (RoB) assessment tool specifically designed for laboratory studies on dental materials (RoBDEMAT) [43]. To ensure adequate statistical power, a priori sample size calculation was conducted, which determined that a minimum of 52 crowns, divided into four groups of 13 crowns each, would be required to achieve statistically significant results. This calculation was based on a statistical power of 0.8, an effect size of 0.485, and a significance level of 0.05, ensuring a high degree of precision and reliability in the study’s findings. A total of 60 porcelain crowns, specifically designed and fabricated to fit the maxillary right first molars, were utilized in the experiment. The sample was randomly allocated to four groups using Research Randomizer (www.randomizer.org), ensuring a high level of randomness and minimizing bias. A flow chart illustrating the study design and methodology is provided in Fig. 1.

Fig. 1.

Flow diagram of the experimental methodology for evaluating orthodontic band retention on zirconia crowns using different cementation protocols (n = 60)

Sample preparation

Each porcelain crown was filled with Ortho-Jet orthodontic resin to fabricate a prepared tooth-like structure (ORTOpoli, Polident, Slovenia). Additionally, a resin block made from the same orthodontic resin was fabricated to serve as a pedestal for the crown, facilitating a secure attachment to the universal testing machine (Instron Universal Testing Machine type 3366, 10 kN– Instron Corporation, Canton, MA).

Band adaptation

Orthodontic bands with microetched fitting surfaces (size 36, DTC bands, surface area, Zhejiang Province, China) were precisely adapted to each maxillary right first molar made of zirconia. The zirconia crowns were fabricated from 3Y-TZP (3 mol% yttria-stabilized zirconia) using CAD-CAM technology (Ceramill CAD/CAM, Amann Girrbach, Germany). The glaze was applied uniformly to the crown surface and fired in a ceramic furnace (Programat P510, Ivoclar Vivadent, Liechtenstein) at a temperature of 770 °C for 2 min. This process was performed to simulate clinical conditions and ensure a smooth, polished surface.These crowns were subsequently cemented to the prepared tooth-like structure made of resin using a permanent adhesive (Total Cram, Itena, Paris, France). The selected bands were carefully chosen to ensure a snug and secure fit to the crowns, thereby minimizing any potential for movement or slippage. Orthodontic wires (SS 0.9 mm) were then welded to the buccal and lingual surfaces of the bands, providing a secure attachment point for connecting the testing machine.

Band cementation

The materials used in this study, along with their composition and manufacturers, are detailed in Table 1. A total of 60 Zirconia crowns were allocated into four experimental groups, determined by the cementation protocol used to attach orthodontic bands to the Zirconia crowns.

Table 1.

Materials characteristics according to Trade Name

Trade Name	Cement Type	Composition	Manufacturer
Medicem	Conventional glass inomer	Powder: Fluoroaluminosilicate glass Liquid: Polyacrylic acid, tartaric acid, water	Promedica, Neumünster, Germany
Fuji II LC	Resin modfied glass inomer	Powder: Fluoroaluminosilicate glass Liquid: Polyacrylic acid, HEMA (2-hydroxyethyl methacrylate), water, photoinitiators	GC Corporation, Tokyo, Japan
Ultradent	Silane prime	Ethanol, 3-methacryloxypropyltrimethoxysilane (functional silane coupling agent)	Ultradent, South Jordan, UT, USA
Transbond plus	Lignt cure band Adhseive	Bisphenol A diglycidyl ether dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA), silane-treated quartz, photoinitiators, stabilizers	3 M Unitek, Monrovia, California, USA
Ultradent	Etchant	9.5% hydrofluoric acid	Ultradent, South Jordan, UT, USA

Group 1

Glass-ionomer cement (Medicem MC; Promedica Dental Material GmbH, Neumuenste, Germany) was applied following the manufacturer’s instructions, using a powder-liquid ratio of 3:1.

Group 2

The resin-modified glass ionomer cement (Fuji II LC; GC Corporation, Tokyo, Japan) was mixed for 10 s using an amalgamator (Ultramat 2; SDI, Bayswater, VIC, Australia) and then placed into a gun applicator for application to the band. After application, the cement was polymerized with a LED curing light unit (Bluephase Style; Ivoclar Vivadent, Mississauga, ON, Canada) operating in high-power mode at 1200 mW/cm² for 20 s.

Group 3

Transbond Plus Light Cure Band Adhesive (Transbond Plus; 3 M Unitek Ortho Products) was utilized. Each crown was etched with 9.5% hydrofluoric acid gel (Ultradent; South Jordan, UT, USA) for 90 s, followed by thorough rinsing with water and drying. An adhesive primer (Transbond XT Light Cure Adhesive Primer; 3 M Unitek) was applied to the crown, and the band was seated. Excess adhesive was carefully removed with a sharp scaler, and light-curing was conducted for 30 s using the LED curing light unit.

Group 4

The same procedure as in Group 3 was followed, with the addition of silane primer (Ultradent Porcelain Etch and Silane; Ultradent Products, South Jordan, Utah) applied after etching. The cement was mixed according to the manufacturer’s guidelines, and the band was seated with any excess cement removed.

Curing and storage

The specimens were placed in a water bath maintained at 37 °C for 24 h after the cementation procedure, simulating the oral environment. Following this, they underwent thermocycling, which involved 5000 cycles of temperature changes between 5 °C and 55 °C, conducted using a thermocycling machine (THE1400 SD Mechatrnik Thermocycler, Germany) [10, 30, 34].

Retentive strength testing

A blinded assessor from the allocated groups measured the retentive load of the bands using a universal testing machine (Instron model 5965, USA) in tensile mode (Fig. 2). A crosshead speed of 1 mm per minute and a 5 kilonewton load cell were utilized. Testing continued until the band separated from the crown. The force required to detach the band from the crown was calculated and then converted into a measure of retentive strength, expressed in MPa, by dividing the force by the band’s surface area. The bonding area was calculated based on the band’s mesial-distal and buccal-lingual dimensions, as well as its height.

Fig. 2.

Photograph of the retentive strength testing setup. The zirconia crown, mounted on a resin block, is secured to the base of the testing machine. The orthodontic band is attached to the load cell via a wire, allowing for tensile force application in a vertical direction

After debonding, the specimens were visually inspected using a 2.5X magnifying glass to determine the location of cement failure. The Adhesive Remnant Index (ARI) scoring system, which was initially developed for evaluating bonded brackets and subsequently modified for use with cemented bands, was employed to categorize the specimens in this study [42, 44]. The ARI scores ranged from 0, indicating no residual cement on the crown surface, to 3, indicating complete coverage, with intermediate scores representing increasing levels of cement coverage [36].

Statistical analysis

A two-way analysis of variance (ANOVA) was performed to assess the impact of the cementation method on the retentive strength of orthodontic bands. To identify significant differences between groups, post-hoc comparisons were made using the Bonferroni method. The statistical analysis was conducted using SPSS version 29.0 (SPSS, Chicago, Ill) with a significance level of 0.05.

Results

The retentive strength values for all 60 orthodontic bands are summarized in Table 2, revealing a mean retentive strength of 1.23 MPa (95% CI: 1.16 to 1.29) across all experimental groups. Notably, Group 4 exhibited the highest mean retentive strength, recorded at 1.44 MPa (95% CI: 1.36 to 1.52), which was closely followed by Group 2, which demonstrated a mean retentive strength of 1.39 MPa (95% CI: 1.33 to 1.45). In contrast, Groups 1 and 3 exhibited lower mean retentive strength values, with Group 1 showing a mean of 0.85 MPa (95% CI: 0.80 to 0.91) and Group 3 presenting a mean of 1.22 MPa (95% CI: 1.14 to 1.31), respectively. These findings highlight the variability in retentive strength among the different cementation protocols employed, emphasizing the importance of selecting appropriate materials for optimal clinical outcomes.

Table 2.

Retentive strength values for SM bands with different adhesive cements

Cement	N	Mean	SD	95% CI		Minimum	Maximum
				Lower Bound	Upper Bound
Medicem	15	0.85	0.10	0.80	0.91	0.70	1.02
Fuji II LC	15	1.39	0.11	1.33	1.45	1.24	1.55
Transbond	15	1.22	0.15	1.14	1.31	1.00	1.51
Transbond + Silane	15	1.44	0.14	1.36	1.52	1.27	1.68
Total	60	1.23	0.26	1.16	1.29	0.70	1.68

The minimum and maximum retentive strength values were recorded in Groups 1 and 4, with corresponding values of 0.70 MPa and 1.68 MPa, respectively. The cementation protocol employed had a significant impact on the retentive strength of the orthodontic bands, as demonstrated by the one-way ANOVA analysis, which yielded a significance level of P < 0.05. Post-hoc analysis further revealed that Group 1 exhibited significantly lower retentive strength compared to the other experimental groups. In contrast, Groups 2 and 4 demonstrated significantly higher retentive strength than both Groups 1 and 3. Notably, no significant differences were observed between Groups 2 and 4. Additionally, while Group 3 showed a significantly higher retentive strength than Group 1, it remained significantly lower than both Groups 2 and 4. A comprehensive comparison of the retentive strength values among the different groups is presented in Table 3, highlighting the influence of the cementation protocols on the performance of the bands.

Table 3.

Comparison of the mean values of shear peel bond strength using ANOVA

		Mean Difference	Sig.	95% CI
				Lower Bound	Upper Bound
Medicem	Fuji II LC	− 0.53*	< 0.001	-0.66	0
	Transbond	− 0.37*	< 0.001	-0.49	0
	Transbond + Silane	− 0.59*	< 0.001	-0.71	0
Fuji II LC	Medicem	0.53*	< 0.001	0.41	1
	Transbond	0.17*	0	0.04	0
	Transbond + Silane	-0.05	1	-0.18	0
Transbond	Medicem	0.37*	< 0.001	0.24	0
	Fuji II LC	− 0.17*	0	-0.29	0
	Transbond + Silane	− 0.22*	< 0.001	-0.35	0
Transbond+ Silane	Medicem	0.59*	< 0.001	0.46	1
	Fuji II LC	0.05	1	-0.07	0
	Transbond	0.22*	< 0.001	0.09	0

The Adhesive Remnant Index (ARI) scores for the study groups are presented in Table 4. The most common site of failure was at the crown-cement interface, which occurred in 49 out of the 60 crowns (81.6%). Notably, crowns cemented with Transbond (group 3) showed the lowest prevalence of ARI score “0”, while crowns cemented with Fuji II LC and Transbond after application of Silane showed similar numbers of crowns with ARI score “0”.

Table 4.

Distribution of Adhesive Remnant Index (ARI) scores for groups

	Group
Ari Score	Medicem	Fuji II LC	Transbond	Transbond + Silane
0	14(93%)	12 (80%)	11(73%)	12(80%)
1	1 (7%)	3(20%)	4(17%)	3(20%)
2	0	0	0	0
3	0	0	0	0

*ARI Score Meanings: 0 = No adhesive left on the crown surface; 1 = Less than 50% of adhesive left on the crown surface; 2 = More than 50% of adhesive left on the crown surface; 3 = All adhesive left on the crown surface

Discussion

Attaining sufficient clinical retentive strength of cemented bands is crucial in orthodontics, as frequent band loosening can lead to inefficiencies, prolonged treatment durations, and increased emergency visits [5, 20]. The attachment of orthodontic fixed appliances to restoration surfaces poses a significant challenge due to the higher failure rate [5]. While a considerable body of research has investigated the bond strength of brackets to various surfaces, including natural teeth and non-natural tooth structures such as acrylic, porcelain, and gold [11, 18, 39, 40, 42, 45–48], relatively fewer studies have examined the retentive strength of cemented bands to non-natural tooth structures [36, 37]. This knowledge gap is particularly relevant, as the use of non-natural tooth structures, such as Zirconia crowns, is becoming increasingly common in orthodontic practice. To address this knowledge gap, this study investigated the shear-peel bond of orthodontic bands cemented to Zirconia crowns in a laboratory setting. The findings of this study indicate significant differences in retentive strength among the various cement types and protocols, leading to the rejection of the null hypothesis.

The results of this study indicate that the retentive strength of cemented orthodontic bands exhibited a range from 0.70 MPa to 1.68 MPa, highlighting the significant variability in bond strength across different cementation techniques. Notably, bands cemented with Glass Ionomer Cement (GIC) demonstrated the lowest retentive strength when compared to the other types of cements utilized in this study. These findings are in agreement with previous research that has shown that the retentive strength of bands cemented to various types of crowns, such as natural teeth and stainless steel crowns, can exhibit considerable variation [47, 49]. For example, the retentive strength of GIC in this study was observed to be higher than the value reported in a previous study that assessed the retentive strength of bands cemented to porcelain crowns (0.63 MPa) [36]. Similarly, bands cemented to stainless steel crowns were found to exhibit slightly lower retentive strength (0.79 MPa) [49].

Likewise, the results of this study demonstrate that bands cemented with Resin-modified Glass Ionomer Cement (RMGIC) exhibited significantly greater retentive strength compared to previous findings. Notably, the retentive strength values obtained in this investigation were considerably higher than those recorded in a study that assessed the retention of bands on porcelain crowns and stainless steel, which reported values of 0.59 MPa for both materials [36, 49]. Furthermore, the retentive strength of RMGIC on gold alloy crowns was found to be 1.26 MPa, while on natural teeth, it was 1.53 Mpa [37, 47]. These findings suggest that the utilization of RMGIC can provide a strong and reliable bond between the orthodontic band and the crown, regardless of the specific type of crown material employed.

Furthermore, the results of this study indicate that bands cemented with Transbond Plus Light Cure Band Adhesive demonstrated higher retentive strength values, both with and without silane application, compared to previous studies. Specifically, the retentive strength values obtained in this study were 1.22 MPa without silane application and 1.44 MPa with silane application, which are significantly higher than the values reported in previous studies on porcelain (0.76 MPa) [36], gold ( 0.29 MPa) [37], and natural teeth (2.63 MPa) [47], where the bands were cemented with resin cement. These findings suggest that the use of Transbond Plus Light Cure Band Adhesive, particularly with silane application, can provide a strong and reliable bond between the band and the crown.

The variability in retentive strength observed in this study and in previous research can be attributed to several factors. Variations in tooth shape, the tightness of orthodontic bands, and the surface characteristics of the materials used likely contribute to the differences noted. A close-fitting orthodontic band was employed in this study, which may have enhanced mechanical retention in addition to the retentive properties provided by the various cements. Moreover, the use of CAD-CAM zirconia crowns, as opposed to materials such as denture teeth, alloys, or natural teeth, may have significantly influenced the results obtained. Zirconia’s unique surface characteristics, such as its high crystalline content, low surface energy, and absence of enamel rods, make it inherently less receptive to chemical bonding compared to natural teeth. Additionally, the specific experimental conditions can impact the outcomes. For instance, we conducted thermocycling prior to testing, while other studies may not have implemented this procedure, potentially leading to notable differences in results [45]. It’s worth noting that many previous studies have used bands with varying surface areas [30, 36, 37, 42, 46, 49]. This lack of standardization in methodology can influence the calculated retentive strength, particularly when forces are measured in Newtons and converted to megapascals. Such variations in methodology may limit the direct comparability of results across different studies.

The findings of this study demonstrated that resin-modified glass ionomer cement (RMGIC) and Transbond Plus with silane primer provided significantly higher retentive strength compared to conventional glass ionomer cement (GIC). These results are consistent with previous studies reporting superior bond strength for RMGIC and resin-based cements in orthodontic band cementation [39, 42]. The improved performance of RMGIC can be attributed to its resin component, which enhances moisture resistance and mechanical properties compared to conventional GIC. Similarly, the superior performance of Transbond Plus, particularly when used with silane, is likely due to the silane coupling agent’s ability to form chemical bonds with the zirconia surface, thereby improving adhesion. In contrast, the lower retentive strength of GIC may result from its sensitivity to moisture and relatively lower mechanical strength, as supported by previous studies [21, 41].

When bands were cemented to porcelain crowns, the bond failure typically occurred at the interface between the porcelain and the cement, leading to a greater amount of cement remaining on the band (ARI score 0). This finding aligns with some previous studies, which reported similar failure patterns [46, 48]. It is reasonable to expect a lower amount of cement retention on Zirconia crowns due to the use of microetched bands and the lack of chemical adhesion and adhesive rod formation, compared to normal enamel structure [22, 23, 36, 50].

The thermocycling protocol of 5000 cycles (5 °C to 55 °C) was selected based on its widespread use in dental research to simulate long-term clinical aging and stress on dental materials. This protocol is consistent with previous studies that have demonstrated its effectiveness in evaluating the durability of orthodontic cements and adhesives [10, 30, 34, 45]. By incorporating thermocycling, this study aimed to replicate the thermal stresses experienced in the oral environment, thereby providing a more accurate assessment of the long-term retentive strength of orthodontic bands cemented to zirconia crowns.

The conclusions drawn from this study are constrained by several factors, including the laboratory-based nature of the investigation, which may not fully capture the complexities inherent in a clinical setting. Although the study made efforts to simulate oral conditions by incorporating a thermocycling phase—thereby providing valuable insights into the research question—the implementation of dynamic testing using specialized apparatus in the presence of saliva would have significantly enhanced the study’s validity. Furthermore, this study focused on cementation protocols currently recommended for orthodontic bands and did not evaluate advanced zirconia-bonding strategies such as sandblasting or MDP-containing primers, which may further optimize retention. These advanced protocols, while well-established for bracket bonding, require separate investigation to assess their efficacy in band cementation. Additionally, conducting a clinical investigation to assess the failure rate of orthodontic bands in a real-world setting would yield more reliable and generalizable information, ultimately contributing to a deeper understanding of the performance of these materials in practical applications.

Conclusion

The present study investigated the retentive strength of orthodontic bands that were cemented to zirconia crowns, with a specific focus on evaluating the performance of various types of cement. The results indicated significant variability in retentive strength, ranging from 0.70 to 1.68 MPa, which was influenced by the type of cement used. Notably, bands cemented with resin-modified glass ionomer cement (RMGIC) and Transbond Plus exhibited superior retentive strength when compared to those cemented with conventional glass ionomer cement (GIC). Additionally, the cementation protocol had a significant impact on retentive strength, with the application of silane showing an enhancement in bond strength specifically for Transbond. Future studies should consider the implementation of clinical trials and incorporate dynamic testing in the presence of saliva to achieve a more accurate and comprehensive evaluation of the retentive properties in a real-world context.

Author contributions

FA contributed to conceptualization, study design, analysis and drafting the manuscript.

Funding

The article was self-funded by the author.

Data availability

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

Declarations

Ethics approval and consent to participate

The research did not involve any human or animal subjects, and therefore, ethical approval or consent forms were not required.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Clinical trial number

Not applicable.