|Year : 2013 | Volume
| Issue : 6 | Page : 713-718
|Comparison of shear bond strengths of conventional orthodontic composite and nano-ceramic restorative composite: An in vitro study
Namit Nagar1, Anna C Vaz2
1 Department of Orthodontics, Pacific Dental College and Hospital, Debari, Udaipur, Rajasthan, India
2 Department of Orthodontics, PMNM Dental College and Hospital, Bagalkot, Karnataka, India
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|Date of Submission||28-Sep-2013|
|Date of Decision||22-Aug-2013|
|Date of Acceptance||11-Nov-2013|
|Date of Web Publication||20-Feb-2014|
| Abstract|| |
Objectives: To compare the shear bond strength of a nano-ceramic restorative composite Ceram-X MonoTM♦, a restorative resin with the traditional orthodontic composite Transbond XTTM† and to evaluate the site of bond failure using Adhesive Remnant Index.
Materials and Methods: Sixty extracted human premolars were divided into two groups of 30 each. Stainless steel brackets were bonded using Transbond XTTM† (Group I) and Ceram-X MonoTM♦ (Group II) according to manufacturer's protocol. Shear bond strength was measured on Universal testing machine at crosshead speed of 1 mm/minute. Adhesive Remnant Index scores were assigned to debonded brackets of each group. Data was analyzed using unpaired 't' test and Chi square test.
Results: The mean shear bond strength of Group I (Transbond XTTM†) was 12.89 MPa ± 2.19 and that of Group II (Ceram-X MonoTM) was 7.29 MPa ± 1.76. Unpaired 't' test revealed statistically significant differences amongst the shear bond strength of the samples measured. Chi-square test revealed statistically insignificant differences amongst the ARI scores of the samples measured.
Conclusions: Ceram-X MonoTM♦ had a lesser mean shear bond strength when compared to Transbond XTTM† which was statistically significant difference. However, the mean shear bond of Ceram X Mono was within the clinically acceptable range for bonding. Ceram-X MonoTM† and Transbond XTTM† showed cohesive fracture of adhesive in 72.6% and 66.6% of the specimens, respectively.
Keywords: Adhesive remnant index, Ceram-X MonoTM♦, shear bond strength, Transbond XTTM†
|How to cite this article:|
Nagar N, Vaz AC. Comparison of shear bond strengths of conventional orthodontic composite and nano-ceramic restorative composite: An in vitro study. Indian J Dent Res 2013;24:713-8
Orthodontic adhesives have evolved from the epoxy resins that were first used by G. V. Newman in 1965.  As an organic material, BisGMA developed by Bowen in 1956 revealed high viscosity due to hydrogen bonding interactions,  BisGMA is diluted with a more fluid resin, that is, triethylene glycol dimethacrylate for orthodontic use. Urethane dimethacrylate offers lower viscosity, more effective light curing, lower water sorption, greater toughness than BisGMA. The bond strength of UDMA adhesives depends on the filler content. 
|How to cite this URL:|
Nagar N, Vaz AC. Comparison of shear bond strengths of conventional orthodontic composite and nano-ceramic restorative composite: An in vitro study. Indian J Dent Res [serial online] 2013 [cited 2019 Mar 25];24:713-8. Available from: http://www.ijdr.in/text.asp?2013/24/6/713/127619
Nanotechnology, also known as molecular nanotechnology or molecular engineering, is the production of functional materials and structures in the range of 0.1 to 100 nanometers-the nanoscale-by various physical and chemical methods. 
Polymer nanocomposites are a new class of materials with unique internal structure and properties and contain nano fillers that are 0.005-0.01 microns in size. To make filler particles of the mechanically strong composites of today (such as macrofills, hybrids and microhybrids), one starts from dense, large particles (mined quartz, melt glasses, ceramics) and comminute them to small particle size. 
Orthodontics however, has not seen the application of nanotechnology with regard to bonding materials, and literature in orthodontics is scarce with regard to its applications in this area. Bishara and Ajlouni  compared the shear bond strength of a nano-hybrid restorative material, Grandio (Voco, Germany), and traditional adhesive material (Transbond XT; 3M Unitek) when bonding orthodontic brackets and concluded that nano-filled composite materials can potentially be used to bond orthodontic brackets to teeth if its consistency can be more flowable to readily adhere to the bracket base. Uysal and Yagai  evaluated shear bond strength (SBS) and failure site locations of nano-composite (Filtek Supreme Plus Universal) and a nano-ionomer (Ketac N100 Light Curing Nano-Ionomer) restorative in comparison with a conventional light-cure orthodontic bonding adhesive (Transbond XT). The authors concluded that the nano-composites and nano-ionomers may be suitable for bonding orthodontic brackets since they fulfill the previously suggested shear bond strengths ranges for clinical acceptability, but they are inferior to a conventional orthodontic composite.
When initially introduced, composite resins, the BisGMA, was introduced into restorative dentistry and applied to orthodontics with modifications. Hence, the application of the newly introduced technology in conservative dentistry, that is, nano-composites into orthodontics was considered to be relevant; therefore, this study attempted to evaluate the performance of a restorative nano-composite, Ceram-X Mono TM♦ with traditional orthodontic composite, Transbond XT TM† with respect to
- Shear bond strength
- Adhesive remna bnt index.
| Materials and Methods|| |
Sixty human maxillary and mandibular premolars extracted for orthodontic purpose with intact crown, unattrited and free from hypoplastic areas, cracks, gross irregularities, decays, and fractures were collected.
Teeth were scaled and polished with pumice and stored in normal saline at 37 0 C for no longer than three months.
Each tooth was then placed in a mould and embedded in self-curing acrylic resin. The block was standardized to the diameter of 30 mm and height of 15 mm, and the long axis of the tooth was kept parallel to the long axis of the acrylic block [Figure 1].
Stainless steel premolar brackets with 0.022" × 0.028" slot, (MBT prescription, 3M Unitek) with 9.00 mm 2 of average bracket base surface area. [Figure 2].
| Bonding Procedure|| |
The 60 teeth were divided randomly into two equal groups of 30. The buccal crown surface of each tooth was rinsed and dried after a 15-second polish with fluoride-free pumice slurry.
Group I: Brackets bonded with conventional orthodontic composite resin, Transbond XT TM† [Figure 3].
The buccal enamel surface was etched with 37% phosphoric acid for 30 seconds, rinsed for 15 seconds, and dried with oil and moisture-free air until the enamel had a faint white appearance. Transbond XT TM† primer was applied as a thin film to the etched surface and light-cured for 10 seconds.
Transbond XT TM† adhesive paste was applied to the bracket base, and the bracket was positioned on the tooth and light-cured as per the protocol of Wang and Meng  that is, 20 seconds from incisal and 20 seconds from gingival end.
Group II: Brackets bonded with nanoceramic composite resin, Ceram-X Mono TM♦ [Figure 4].
Ceram-X Mono TM♦ adhesive paste was applied to the bracket base, and the bracket was positioned on the etched and primed buccal surface and light-cured for 20 seconds according to the Ceram-X Mono TM♦ protocol.
| Debonding Procedure|| |
The shear bond strength tests were measured using Universal Testing Machine (HOUNSFIELD H5KS-0195) at cross head speed of 1 mm/minute[Figure 5].
A custom-made rod was locally fabricated for exerting a force parallel to the tooth surface in an occlusal-apical direction during bracket debonding [Figure 6].
The force applied at failure was recorded in Kilograms and then converted to Newtons (N), and the stress was calculated in Mega Pascals by dividing the force in N by the bracket base area of 9 mm 2 (1 MPa = 1 N/mm 2 ).
| Bond Failure Assessment|| |
The debonded enamel surfaces were examined under stereomicroscope (Lawrence and Mayo) using 10× magnification[Figure 7].
The percentage of the area still occupied by adhesive remaining on the tooth after debonding was obtained by subtracting the area of adhesive covering the bracket base from 100%. Later, each tooth was assigned an Adhesive Remnant Index (ARI) value according to Artun and Bergland  [Figure 8].
Score 0: No adhesive remained on the tooth
Score 1: Less than 50% of the adhesive remained on the tooth
Score 2: More than 50% of the adhesive remained on the tooth
Score 3: All adhesive remained on the tooth.
The ARI scores were used to assess the sites of bond failure on the enamel-adhesive interface and the adhesive-bracket interface.
Descriptive statistics including the mean, standard deviation, and minimum and maximum values were calculated for each of the various groups of teeth tested.
Unpaired "T" test was used to determine whether significant differences existed between the two groups of the bond strength values calculated.
Chi square test was used to determine significant differences in the adhesive remnant scores between the comparative groups.
Significance for all statistical tests was predetermined at P ≤ 0.05.
| Results|| |
The descriptive statistics, including the mean, standard deviation, range, minimum and maximum values of shear bond strength for each of the two groups are presented in [Table 1].
|Table 1: Descriptive statistics of shear bond strength (MPa) of two groups tested |
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Comparison of shear bond strengths of two groups
Unpaired 't' test revealed value = 10.89 with 58 0 of freedom and mean difference of -5.59. The two-tailed P value was 0.0001, which revealed statistical significant differences between two groups. Group I (Transbond XT TM† ) showed higher mean SBS values of 12.89 ± 2.19 in comparison with 7.29 ± 1.76 SBS values of Group II (Ceram-X Mono TM [Table 2].
Comparisons of adhesive remnant index scores
Chi-square test was used to analyze the statistical differences in ARI scores of two groups. [Table 3].
|Table 3: Frequency distribution and results of chi squared analyses of the ARI scores of two groups evaluated |
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Group I showed ARI scores 1 in 20 samples, which revealed that the bond failure occurred at adhesive enamel interface with less than 50% adhesive remaining on tooth surface. Eight out of remaining 10 samples showed scores of 2, revealing that more than 50% adhesive remaining on tooth surface on debonding. This indicated that there was cohesive failure in the adhesive.
In contrary, Group II showed ARI scores of 2 in 22 samples, which revealed that more than 50% adhesive remaining on tooth surface on debonding. The ARI scores indicated more of cohesive fracture of the adhesive. Six out of remaining 8 samples showed scores of 3, revealing that all adhesive left on tooth on debonding depicting adhesive failure. None of the samples bonded with Ceram-X Mono TM♦ have shown the ARI score of 0, indicating that the bond strength at the enamel adhesive interface is higher than that of at the bracket adhesive interface.
Chi-Square value, X 2 = 4.94 and P = 1.0000, which revealed statistical insignificant differences among the ARI scores of two groups (P > 0.05).
| Discussion|| |
Comparison of shear bond strength of Transbond XT TM† with Ceram-X Mono TM♦
Ceram-X Mono TM♦ adhesive was cured for 20 seconds, that is, 10 seconds from incisal and 10 seconds from gingival according to manufacturer's protocol for curing.
The shear bond strength tests were measured using Universal Testing Machine at cross head speed of 1 mm/minute as proposed by D'Attilio,  Tecco T,  and Ryou. 
The bond strength for the control composite Transbond XT TM† was 12.89 MPa ± 2.19. These values were in accordance to those values observed in study done by Vicente A and Bravo LA.  However, the shear bond strength values of Transbond XT TM† were less than that obtained by D'AttilioM,  Tecco,  Uysal,  Northrup,  Machado,  and Isber;  and were higher than those obtained by Owen,  Ajlouni, , and Ryou.  These variations could suggest the importance of other factors, such as study design, bracket base design, and enamel pre-treatment in determining the shear bond strength. However, Poosti  added Titanium oxide nano-particles in conventional orthodontic composite (Transbond XT) and concluded that no significant differences in shear bond strengths were observed.
The values obtained in this study are higher than that recommended by Reynolds  (5.9 MPa). However, as this is an in-vitro study, according to Hajrassie M and Kheir,  the in-vivo bond strength could be lower than the in-vitro values.
The shear bond strength value for Ceram-X Mono TM♦ measured was 7.29 MPa ± 1.76. When the shear bond strength values of Ceram-X Mono TM♦ were compared with the studies carried out on other nanocomposites, it was higher than Grandio TMx as studied by Bishara and Ajlouni  and was less than Filtek Supreme Plus Universal TM≤ , Filtek Z350, and Tetric Ceram TM as measured by Uysal  Machado,  and Isber ,[ respectively.
Hence, it could be concluded that Ceram-X Mono TM♦ could potentially be used to bond orthodontic brackets.
Analysis of adhesive remnant index
The Adhesive Remnant Index (ARI)  scores were assigned to each specimen. A Chi-square test was used to find out if there is any significant association between the materials and the adhesive remnant index scores. No significant differences were seen between the two groups in the Adhesive Remnant Index scores with the P value of 1.00 (P > 0.05).
ARI and Transbond XT TM†
In Group I, 6.6% of the samples showed an ARI score of 0, which showed that no adhesive was left on tooth surface. Studies by D'Attilio  and Tecco  showed 5% of the samples to have an ARI score of 0. These percentages of the total sample studied were less than that observed in this study, and Northrup  (8%) and Ryou  (10%) showed higher percentages of samples showing an ARI score of 0. Around, 66.6% and 26.6% of the sample showed an ARI score of 1 and 2, respectively. This indicated that there was cohesive failure in the adhesive. These percentages were in accordance to those evaluated by Ryou. 
Groups I did not exhibit an ARI score of 3. However, studies done by Northrup,  Lee and Lim  have shown ARI score of 3 in 90% and 40% of the total samples evaluated, respectively. These differences in the ARI scores could suggest the influence of other variables such as study design, bracket base, and enamel pre-treatment in determining the type of bond failures.
ARI and Ceram-X Mono TM♦
76.26% and 19.98% of brackets bonded with Ceram-X Mono TM♦ showed ARI scores of 2 and 3, respectively. This percentage was seen to be more when compared with the study by Nandlal and Khatri.  The ARI scores indicated more of cohesive fracture of the adhesive. None of the samples bonded with Ceram-X Mono TM♦ have shown the ARI score of 0, indicating that the bond strength at the enamel adhesive interface is higher than that of at the bracket adhesive interface. The poor bond strength at the bracket adhesive interface could be assigned to poor penetration of the adhesive owing to the viscosity of the adhesive. 
The present findings indicate that the consistency of Ceram-X Mono TM♦ is fairly viscous and does not flow readily into the retentive mesh of the bracket base. As indicated by Bowen in 1956, the BisGMA resin reveals a high viscosity owing to the hydrogen bonding interactions. Ceram-X Mono TM♦ is a BisGMA resin.
As a result, it is suggested that, for orthodontic purposes, the manufacturer should consider reformulating the composition of Ceram-X Mono TM♦ to produce a paste with more flowable consistency that can readily penetrate the mesh of the bracket base. Ferracane  suggested that BisGMA resin could be diluted with a more fluid such as triethylene glycol dimethacrylate for orthodontic purpose.
Alternatively, it is suggested that urethane dimethacrylate resin, which offers lower viscosity, more effective light-curing, lower water sorption, and greater toughness, could be substituted for the BisGMA resin. Faltermeier and Rosentritt  recommend a highly filled urethane dimethacrylate resin to be appropriate for orthodontic use. Utilizing organically modified fillers in an UDMA resin could be a more biocompatible alternative, particularly with regard to the toxicity reported for BisGMA resins.
Majority of ARI scores for Ceram-X Mono TM♦ were 2 and 3, which revealed that more adhesive was left on tooth surface after debonding. Therefore, it can be concluded that less enamel fracture during debonding could be expected when brackets are bonded using Ceram-X Mono TM♦ in comparison with that of Transbond XT TM† .
An orthodontic composite resin displayed significantly greater shear bond strength values than that of nanoceramic restorative composite, although the shear bond strength of both composites were clinically acceptable. Clinical conditions may significantly differ from an in-vitro setting. Moreover, heat and humidity conditions of the oral cavity are highly variable. Because of the probable differences in in-vivo and in-vitro conditions, further clinical research is suggested.
| Conclusion|| |
From the results of this study, the following conclusions can be drawn:
- Ceram-X Mono TM♦ had a lesser mean shear bond strength when compared to Transbond XT TM† , which was statistically significant difference. However, the mean shear bond of Ceram X Mono was within the clinically acceptable range for bonding
- Ceram-X Mono TM♦ and Transbond XT TM† showed cohesive fracture of adhesive in 72.6% and 66.6% of the specimens, respectively. Around 19.8% of the Ceram-X Mono TM♦ specimens tested showed failure site at adhesive-bracket interface, indicating poor penetration of the viscous bonding material into the retentive mesh of the bracket base.
As a consequence to this study, it is suggested that, for orthodontic purposes, the manufacturer could consider reformulating the composition of Ceram-X Mono TM♦ to produce a paste with more flowable consistency that can readily penetrate the mesh of the bracket base.
The highly viscous BisGMA resin could be substituted by a less viscous, biocompatible UDMA resin filled with the organically modified ceramics.
| Note|| |
TM†= 3M UNITEK, TM♦ = DENTSPLY, TMx = VOCO, TM≤ = 3M UNITEK
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Department of Orthodontics, Pacific Dental College and Hospital, Debari, Udaipur, Rajasthan
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3]
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