Introduction
Our objective was to determine and compare microleakage patterns of conventional glass ionomer cement (GIC), resin modified GIC (RMGIC), and polyacid-modified composite for band cementation.
Methods
Sixty freshly extracted third molars were randomly divided into 3 groups of 20 teeth each. Microetched molar bands in the 3 groups were cemented to enamel with one of three orthodontic cements: Ketac-Cem (3M ESPE, Gmbh, Seefeld, Germany), Multi-Cure (3M Unitek, Monrovia, Calif), and Transbond Plus (3M Unitek). A dye penetration method was used for microleakage evaluation. Microleakage was determined by a stereomicroscope for the cement-band and cement-enamel interfaces from both the buccal and lingual margins. Statistical analysis was performed with Kruskal-Wallis and Mann-Whitney U tests.
Results
The buccal sides had similar microleakage values compared with the lingual sides for the cement-enamel and cement-band interfaces with all cements. Statistical comparisons showed statistically significant differences among the band cements between both interfaces ( P <0.001). When the cement systems were compared, conventional GIC showed the highest leakage scores between cement-band (median, 3.50 mm) and cement-enamel (median, 2.88 mm) interfaces. Teeth banded with RMGIC and modified composite showed similar microleakage scores, and both had less leakage (<1 mm) than conventional GIC.
Conclusions
Conventional GIC is associated with more microleakage than RMGIC and modified composite at both the cement-band and cement-enamel interfaces.
Orthodontic bands are usually cemented with thin layers of adhesive; bulky materials that favor chemical-cure systems are lacking. Orthodontic bands, however, are susceptible to areas of variable cement thickness and they present a physically larger barrier to irradiation than brackets. Orthodontic cements lend themselves differently to specific applications, and it is important to note the differences in polymerization kinetics and how this might relate to their use. Because band retention is affected mechanically by its close adaptation to the tooth aided by the cement, various properties of cements have been tested and developed to improve retention.
In the past 2 decades, glass ionomer cements (GICs) have become popular for band cementation. They adhere to enamel and metal, release and uptake fluoride, and inhibit microbial activity. Resin addition to the cement formulation has facilitated light-curing, allowing snap set and rapid strength development.
There are a number of possible advantages of light-polymerized materials over conventional glass poly(alkenoate) cements. Due to variations in chemical composition and setting reaction among resin-ionomer hybrids, products have been categorized as resin-modified GICs (RMGICs) or modified composites, and these were used for cementing orthodontic bands. The ability of these cements to release fluoride and inhibit microbial growth appears to relate to the constituents of each product ; studies of such materials in orthodontic applications have shown favorable properties for band cementation. Laboratory studies of modified composites and RMGICs used for band cementation have indicated significantly greater bond strengths with these cements compared with conventional GICs.
A particular property of GICs is the formation of a complete seal against microleakage. Although there are no evidence-based results, Fricker suggested that RMGIC and conventional GIC are preferred adhesives over modified composite for the cementation of orthodontic molar bands because of the protection against microleakage at the enamel-cement interface. This author thought that adhesion of GICs to enamel is through an ion-enriched layer that prevents microleakage. Gillgrass et al indicated that, with the acid-modified composite, there might be a path of microleakage between cement and enamel with the potential for microbial ingress and consequent enamel demineralization beneath the band.
Recently, a new polyacid-modified composite resin was introduced as an orthodontic cement for banding. This light-cured cement, Transbond Plus (3M Unitek, Monrovia, Calif), contains hydroxy-1, 3-dimethacryloxypropane with another resin, carboxylate dimethacrylate, an oligomeric carboxylic acid with methacrylate groups. Carboxylate dimethacrylate is thought to provide a greater ratio of methacrylate groups, thus allowing greater cross-linking in the resin matrix and perhaps greater mechanical properties.
It would appear, however, that no previous studies have assessed the microleakage patterns of RMGICs and acid-modified composite and compared them to conventional GIC used for banding. Moreover, in the orthodontic literature, it appears that microleakage at the cement-enamel and cement-band interfaces was not assessed in relation to banded teeth.
The aims of this in-vitro investigation were, therefore, to determine and compare microleakage patterns of conventional GIC (Ketac-Cem [3M ESPE, Gmbh, Seefeld, Germany]), RMGIC (Multi-Cure [3M Unitek]), and a polyacid-modified composite (Transbond Plus) for band cementation. Our null hypothesis assumed that there were no statistically significant differences in microleakage of these orthodontic band cements.
Material and methods
Sixty caries-free extracted mandibular third molars were collected and stored in distilled water in a refrigerator after decontamination in 0.5% chloramine. The teeth were randomly divided into 3 groups of 20 teeth each.
The teeth were then cleaned with pumice, rinsed in distilled water, and dried thoroughly in a stream of air. Because there are no bands for third molars, mandibular first permanent molar bands with microetched fitting surfaces (3M Unitek) were used. A band was selected and adapted optimally to the crown of each tooth. Twenty bands were cemented with each of the 3 cements. Summary characteristics of each cement are given in Table I . The manufacturers’ instructions were followed for each cement. To standardize specimen preparation, band selection and cementation were done by 1 operator (S.I.R.).
| Brand name | Manufacturer | Cement type | Curing mechanism |
|---|---|---|---|
| Ketac-Cem | 3M ESPE, Gmbh, Seefeld, Germany | Conventional glass ionomer cement | Chemically cured |
| Multi-cure | 3M Unitek, Monrovia, Calif | Resin-modified glass ionomer cement | Tri-cured (acid-base reaction, light cured, and self cured) |
| Transbond Plus | 3M Unitek, Monrovia, Calif | Polyacid modified composite | Light cured |
Group 1 had powder and liquid Ketac-Cem mixed and then applied directly to the fitting surface of each band. After band placement, the excess cement was removed with dry cotton rolls. The Ketac-Cem was allowed to bench cure for 5 minutes after band cementation.
In group 2, after the powder and liquid components of Multi-Cure were mixed, the bands were adapted to the molars the same as group 1 and light-cured.
In group 3, Transbond Plus was applied directly to the fitting surface of each band. After band placement, the excess cement was removed with dry cotton rolls and light-cured.
Multi-Cure and Transbond Plus were light-cured with a halogen dental curing light (Hilux 350, Express Dental Products, Toronto, Ontario, Canada) with a 10-mm diameter light tip for 60 seconds from the occlusal aspect of each band according to the manufacturer’s guidelines.
All specimens were then placed in distilled water for 24 hours before measuring microleakage.
Before dye penetration, the tooth apices were sealed with sticky wax. After that, the teeth were rinsed in tap water and air dried, and nail varnish was applied to the entire surface of the tooth except for approximately 1 mm from the bands. To minimize dehydration of the specimens, the teeth were replaced in water as soon as the nail polish dried. The teeth were immersed in 0.5% solution of basic fuchsin for 24 hours at room temperature. After removal from the solution, the teeth were rinsed in tap water, the superficial dye was removed with a brush, and the teeth were dried and embedded in self-curing acrylic up to the occlusal surface of the band. First, the molars were separated into 2 parts through the mesiodistal direction. Four parallel longitudinal sections from the middle part of each molar were made at the occluso-buccal and occluso-lingual surfaces with a low-speed diamond saw (Isomet, Buehler, Lake Bluff, Ill) in the buccolingual direction according to the method of Arhun et al for evaluation of microleakage under the orthodontic brackets.
The specimens were evaluated with a stereomicroscope (20 times magnification) (SZ 40, Olympus, Tokyo, Japan) for dye penetration along the cement-band interface. Then the band materials were gently removed from the cement, and dye penetration at the cement-enamel interface was also evaluated with the stereomicroscope.
Each section was scored from both buccal and lingual margins of the bands between the cement-band and cement-enamel interfaces. Microleakage was measured directly by an electronic digital caliper and the nearest recording 0.5 mm was recorded as microleakage value, in a range of 0.5 to 5 mm.
Statistical analysis
For the cement-band and cement-enamel interfaces, the microleakage scores were obtained by calculating the buccal and lingual microleakage scores. After the statistical evaluation of leakage for each specimen, the score for each group was obtained by calculating the means of the buccal and lingual microleakage scores.
The Shapiro-Wilks normality test and the Levene variance homogeneity test were applied to the microleakage data. The data showed nonnormal distribution, and there was no homogeneity of variances among the groups. Thus, the statistical evaluation of microleakage values between the groups was performed with nonparametric tests (Kruskal-Wallis and Mann-Whitney U tests). Intraexaminer and interexaminer method errors were evaluated by kappa test. The level of significance was set at P <0.05.
Results
The intraexaminer and interexaminer kappa scores for assessment of microleakage were high, with all values greater than 0.70 ( Table II ).
| Buccal side | Lingual side | ||||||
|---|---|---|---|---|---|---|---|
| Interface | Evaluation type | Ketac-Cem | Multi-Cure | Transbond Plus | Ketac-Cem | Multi-Cure | Transbond Plus |
| Cement-band | Intraexaminer | 0.79 | 0.71 | 0.85 | 0.95 | 0.99 | 0.90 |
| Interexaminer | 0.72 | 0.89 | 0.77 | 0.75 | 0.83 | 0.91 | |
| Cement-enamel | Intraexaminer | 0.87 | 0.80 | 0.88 | 0.95 | 0.98 | 0.89 |
| Interexaminer | 0.71 | 0.89 | 0.93 | 0.73 | 0.80 | 0.90 | |
Descriptive statistical values and buccal and lingual microleakage comparisons between the cement-band and cement-enamel interfaces are shown in Table III . Comparisons of the buccal and lingual microleakage scores for all specimens had no statistically significant differences for the side ( P >0.05). Thus, the buccal and lingual microleakage scores for each specimen were pooled, and the microleakage values for each band cement and interface were obtained by calculating the mean of the buccal and lingual microleakage scores.
| Interface | Group | Side | n | Median (mm) | Interquartile range | Sig |
|---|---|---|---|---|---|---|
| Cement-band | Ketac-Cem | Buccal | 20 | 2.00 | 1.75-2.75 | 0.778 |
| Lingual | 20 | 2.18 | 1.50-2.25 | |||
| Multi-Cure | Buccal | 20 | 0.25 | 0.00-0.75 | 0.181 | |
| Lingual | 20 | 0.38 | 0.25-0.75 | |||
| Transbond Plus | Buccal | 20 | 0.00 | 0.00-0.25 | 0.191 | |
| Lingual | 20 | 0.25 | 0.00-0.75 | |||
| Cement-enamel | Ketac-Cem | Buccal | 20 | 2.00 | 1.75-2.50 | 0.622 |
| Lingual | 20 | 1.50 | 1.25-1.75 | |||
| Multi-Cure | Buccal | 20 | 0.13 | 0.00-0.25 | 0.196 | |
| Lingual | 20 | 0.25 | 0.25-0.50 | |||
| Transbond Plus | Buccal | 20 | 0.00 | 0.00-0.25 | 0.123 | |
| Lingual | 20 | 0.13 | 0.00-0.50 |
Descriptive statistics and the results of the statistical tests for microleakage between the cement-band and cement-enamel interfaces are shown in Table IV . Statistical comparisons showed significant differences among the band cements at the cement-band and cement-enamel interfaces ( P <0.001). Therefore, the null hypothesis of no statistically significant differences in microleakage of these orthodontic band cements was rejected. Multiple comparisons showed statistically significant microleakage differences between Ketac-Cem and Multi-Cure, and Ketac-Cem and Transbond Plus ( P <0.001). However, no statistically significant difference was found between Multi-Cure and Transbond Plus ( P >0.05). Ketac-Cem had the highest leakage scores between the cement-band (median, 3.50 mm) and cement-enamel (median, 2.88 mm) interfaces.
