|Year : 2013 | Volume
| Issue : 2 | Page : 59-63
Evaluation of the effect of a self-etching primer on the shear bond strength of a conventional light cure composite resin in the dry state: An in vitro study
Sanjay Jacob, Anila Charles, RS Senkutvan
Department of Orthodontia, Madha Dental College, Dr. MGR Medical University, Kundrathur, Chennai, Tamil Nadu, India
|Date of Web Publication||22-Oct-2013|
Department of Orthodontia, Madha Dental College, Dr. MGR Medical University, Madha Nagar, Kundrathur, Chennai - 600 069, Tamil Nadu
Aim: The aim of this study is to evaluate the effect of a self-etching primer (SEP Adper Prompt L-pop; 3M ESPE) on the shear bond strength of a conventional light cure composite resin (Transbond XT primer) in the dry state. Materials and Methods: Forty Freshly extracted human premolar teeth extracted for orthodontic purpose were collected and divided into two groups and mounted on colour coded acrylic blocks. Premolar brackets were bonded using a conventional light cure composite resin and primer in Group I and a self-etch primer was used in Group II. The shear bond strength was evaluated using Instron Universal Testing Machine with an occlusal shear force applied directly onto the enamel-bracket interface with a crosshead speed of 0.5 mm/min. Results: No statistically significant difference were observed in the bond strengths of the two groups evaluated. Conclusion: These results indicated the SEP evaluated showed satisfactory bond strength and is potentially adequate for orthodontic bonding needs.
Keywords: Bonding, shear bond strength, self-etching primer
|How to cite this article:|
Jacob S, Charles A, Senkutvan R S. Evaluation of the effect of a self-etching primer on the shear bond strength of a conventional light cure composite resin in the dry state: An in vitro study. SRM J Res Dent Sci 2013;4:59-63
|How to cite this URL:|
Jacob S, Charles A, Senkutvan R S. Evaluation of the effect of a self-etching primer on the shear bond strength of a conventional light cure composite resin in the dry state: An in vitro study. SRM J Res Dent Sci [serial online] 2013 [cited 2019 Nov 17];4:59-63. Available from: http://www.srmjrds.in/text.asp?2013/4/2/59/120179
| Introduction|| |
Bonding of orthodontic brackets to the enamel surface with a conventional light cure composite resin involves three steps; acid etching of enamel, applying a primer and composite resin followed by curing with visible light.  Buonocore in 1955 demonstrated that a methacrylic resin could be strongly bonded to acid-etched enamel.  Acid etching produces micro porosities in the enamel surface into which the primer penetrates and form resin tags resulting in micromechanical retention with long-term durability. , Several generations of such bonding agents or primers are available. The Self-etching primers (SEP) are sixth generation bonding agents with a simple application technique combining etching and priming thus saving chair side time and eliminating the risk of moisture contamination, which usually occurs during the etching and rinsing procedure. , The SEP is supplied as two liquid systems in which before applying to the tooth has to be mixed b Liquid 1 (red blister): Methacrylated phosphoric esters, bisphenol A-glycidyl-methacrylate Initiators based on camphorquinone, Stabilizers. Liquid 2 (yellow blister): Water, 2-hydroxyethyl methacrylate polyalkenoic acid, stabilizers.
The aim of the present study is to evaluate the effect of a SEP in the shear bond strength and adhesive remnant index (ARI) scores of a conventional light cure composite resin used for orthodontic bonding and to compare it with that of a conventional primer.
| Materials and Methods|| |
Preparation of tooth specimen
Freshly extracted human premolars both maxillary and mandibular first and second premolars extracted for orthodontics purpose were collected, washed in running water to remove blood and tissue debris and stored in normal saline at room temperature in sterile plastic containers. Tooth with caries, fillings, hypoplastic spots, anatomical defects and enamel cracks produced from extraction forces were excluded from the study. Forty premolars with intact buccal surface were selected and divided randomly into two groups. The premolars were embedded in colour coded acrylic blocks of standard size (35 mm × 9 mm × 9 mm) formed from a standard mould.
The teeth were mounted on acrylic blocks such that the roots were completely embedded into the acrylic up to the cement-enamel junction leaving the crown and the long axis of the root is kept perpendicular to the surface of the block [Figure 1]. The buccal surface of the premolars were cleaned and polished with slurry of non-fluoridated flour of pumice (Moyco Industries, Philadelphia, PA, USA) for 10 s using a rubber prophylactic cup and then rinsed with a stream of water for 10 s.
Stainless steel premolar brackets (Generous Roth Brackets, GAC International Inc., Islandia, NY, USA), with an average bracket base surface area of 12.13 mm 2 , were used for all teeth.
A conventional light Cure Composite resin (Transbond XT, 3M Unitek, Monrovia, CA, USA) was used to bond the brackets in all the premolars. In Group I, a conventional primer (Transbond XT, 3M Unitek, Monrovia, CA, USA) was used after etching while a (SEP Adper Prompt L-pop; 3M ESPE) was used in Group II. Materials used in the study are given in [Table 1].
Group I: (phosphoric acid etching and bonding with Transbond XT)
The buccal surface of the premolars were etched with 65% by weight phosphoric acid gel for 30 s rinsed with water for 20 s and air-dried. A thin layer of Transbond XT primer was applied to the etched enamel surface and gently thinned with air. The primer was then light cured for 10 s and the brackets were bonded with Transbond XT adhesive. The bracket is light cured for 20 s on the mesial and 20 s on distal as per manufacturer's instruction. Light curing was performed with a halogen curing light (Optilux 501, Kerr Corp., Orange, CA, USA).
Group II: (SEP and bonding with Transbond XT)
In this group the material evaluated was Adper Prompt L-pop [Figure 2]. An acidic SEP, was placed on the enamel for 30 s. Excessive primer solution was evaporated using compressed air. Then orthodontic metal brackets were bonded to the enamel using Transbond XT resin cement according to the above procedures.
After bonding, all the samples were stored in 37°C deionized water for 24 h.
Shear bond strength testing
Shear bond strength was measured with Instron universal testing machine (Lloyd Universal testing machine-Model No. L.R 100K) The specimen mounted in the acrylic block is secured to the lower grip of the Instron machine. A loop was embedded in a similar acrylic block was fixed to the movable head of the Instron universal testing machine. The loop was positioned in such a way that it applies a shear force in the bracket adhesive interface during the experiment [Figure 3]. The A cross-head speed of 1 mm/min was used. The computer recorded the force to debond the bracket in Newtons (N) and converted into megapascals as a ratio of force to debond to the surface area of the bracket bond strength MPa = force (N)/surface area 2 of bracket (mm).
After debonding, the teeth and brackets were examined under ×10 magnification. The debonding characteristics for each specimen were determined using the ARI. 
ARI scores were scored as 0-3:
All statistical analyses were performed with the software the results were then subjected to statistical analysis using the SPSS package (IBM corporation, USA) for Windows Graph Pad Software at the 5% level of significance. The statistical analysis of the results included descriptive statistics for each group tested. The data of bond strength were tested for normality with the Shapiro-Wilk method. The Student's t-test was used to determine whether significant differences were present in the bond strength between the two groups. The Chi-square test was used to evaluate differences in the ARI scores between groups.
- No adhesive remained on the enamel;
- Less than half of the adhesive remained on the tooth surface;
- More than half of the adhesive remained on the tooth;
- The entire adhesive remained on the tooth with a distinct impression of the bracket base.
| Results|| |
The results of this study indicate that the use of SEP had a mean bond strength of 8.422 ± 1.1401 MPa, whereas the control group with conventional etch/priming system had a mean of 9.611 ± 1.1672 MPa. The Student's t-test did not show significant differences (t = 3.376, 1.868, P = 0.003, 0.069) between the groups evaluated. The descriptive statistics comparing the shear strength of the two groups is shown in [Table 2].
The ARI scores for the two groups were concluded with the results of Chi-square comparisons, which indicated that there was a significant difference (P = 0.0003) between the group that was bonded with Adper Prompt L-pop as compared with the control group. With the use of the SEP, there was a higher frequency of ARI scores of 0 and 1, which indicated that less composite remained on the teeth.
| Discussion|| |
The direct bonding of orthodontic brackets has revolutionized and improved the clinical practice of orthodontic procedures. However, there is a need to further improve the bonding procedure to save time and to minimize enamel loss without jeopardizing the ability to maintain clinically useful bond strength.  Traditionally, the use of acid etchants followed by a primer has been an essential part of the bonding procedure of composite adhesives to allow good wetting and penetration of the sealant into the enamel surface. However, the bond strength required to withstand normal orthodontic forces is believed to be between eight and nine MPa. 
Advances in adhesive technology have led orthodontists to incorporate new adhesives, composite resins and bonding techniques into clinical practice. SEP products, which combine acid and primer, simplify the bonding procedure, reduce chair time and avoid the side-effects of acid etching. ,,
SEPs are considered as bicomponent hydrophilic adhesives containing hydrofluoric complexes, deionized water, stabilizer in one compartment and activator, orthophosphoric ester methacrylate and stabilizers in a separate compartment Bishara et al.  and, Velo et al. evaluated the effectiveness of using Prompt L-pop (ESPE, See field, Germany) to bond orthodontic brackets with composite resin. According to the results, this SEP provided significantly lower (but clinically acceptable) shear bond strength when compared with conventional etch/priming techinique before bonding brackets with Transbond XT adhesive paste (3M Unitek, Monovia, California, USA).
According to Perdigão et al.  the fourth generation or the total etch multi-bottle adhesives (Transbond XT) has the highest dentin bond strength among all adhesives. In general contain a dual-cure option for indirect bonding. However, multiple bottles make their utilization cumbersome; some bottles in the kit may never be used. It was also found that there was a possibility of running out of Primer A before Primer B (or vice versa). Since primer and adhesive resin are dispensed into the same plastic container, their sequential application may be inverted.
Adper Prompt L-pop (3M ESPE, ST Paul, Minn) was introduced to improve enamel and dentin bond strength for more consistent performance. SEP contains a methacrylated phosphoric acid ester active component that etches and primes simultaneously. Unlike conventional acid etch methods, the self-etch primer is not rinsed away after application; the calcium dissolved from the hydroxyapatite forms a complex with the phosphate group and this is then incorporated into the resin network when the primer is polymerized. The obvious potential advantages of the primers include improved patient comfort as there is no need to rinse, a reduction in chairside time and therefore, improved cost-effectiveness. However, to be considered truly cost-effective not only must these SEP reduce the number of procedural steps and be easy to use, but they must also produce a reliable clinical bond for the duration of treatment and then leave the enamel unblemished at the end of treatment when the appliance is removed. 
This purpose of this study was to determine the effects of this newly introduced SEP on the shear bond strength of orthodontic brackets bonded to enamel.
The present study was therefore carried out to evaluate and compare the shear bond strength of the orthodontic brackets to the dry conditioned enamel between the conventional 3M Unitek Transbond XT primer and the SEP 3M ESPE Adper Prompt L-pop. When comparing the shear bond strength of the primer carried out to the dry enamel surface showed maximum bond strength of 9.611 ± 1.1672 Mpa for the conventional primer followed by bond strength of 8.422 ± 1.1401 Mpa for the SEP. [Graph 1] illustrates the Comparison of mean difference between Transbond and L-pop.
The groups were also subjected to a Student's t-test to validate their level of significance. This study revealed that there was a statistically significant difference in their shear bond strength when they were tested 24 h from the time of bonding.
Maintaining a sound unblemished enamel surface after debonding orthodontic brackets is a primary concern of the clinician. As a result, bond failure at the bracket adhesive interface or within the adhesive is more desirable (safer) than failure at the adhesive-enamel inter-face because enamel fracture and crazing have been reported. 
Uysal et al. studies have demonstrated that when SEPs is used it significantly decreases shear bond strength values when compared with conventional acid etching for bonding ceramic brackets there by the damage to enamel was reduced as the degree of penetration by the adhesive to the etched enamel is less when compared with that of conventional acid etching. 
The study conducted by Scougall-Vilchis et al. found the shear bond strength of enamel conditioning with different SEP had clinically acceptable values for bonding orthodontic brackets. 
The present study shows that though the SEP has significantly lower shear bond strength than the conventional primer, but has clinically acceptable shear bond strength when compared with conventional etch/priming technique before bonding brackets with Transbond XT adhesive paste (3M Unitek, Monovia, California, USA). There is not universally accepted minimum clinical bond strength. However, the bond strength required withstanding normal orthodontic forces is believed to be between 8 and 9 Mpa. In this study, bracket failures occurred at 9.611 ± 1.1672 and 8.422 ± 1.1401 Mpa for the conventional primer and the SEP respectively. These results are in agreement with other study, which suggests that adequate bond strengths can be achieved with SEP when bonding is carried out to a dry enamel surface.
Adper Prompt L-pop contains different percentages of the same components as the original Prompt L-pop. The manufacturer claim that maximizing bond strength has been achieved, in part, by optimizing the relatives amounts of non-acid functional methacrylated phosphates esters. Afterward, Adper Prompt also introduces better activation control and other chemical modifications enhancing a uniform adhesive film, improving the quality of hybridization between the adhesive and the enamel surface.
| Summary and Conclusion|| |
Bonding is a technique sensitive procedure this study reveals that SEP provides adequate bond strength within the clinically acceptable limits. By reducing the number of steps during the bonding, clinicians are able to save time and reduce the potential for moisture, saliva, blood or plasma contamination and technique sensitivity during the bonding procedure. Combining conditioning and priming into a single treatment step results in improvement in both time and cost-effectiveness to the clinician and the patient. Although still unpredictable, SEP systems have undergone a rapid evolution over the past few years, possibly, in future, dental adhesion will involve only one step procedure for optimum bonding.
Analysis of the results of the study showed that the shear bond strength of primers was acceptable, though that of conventional primer was the highest. This study was supported by Cacciafesta et al., Rajagopal et al., and Ravi et al. ,,
Under the conditions of this investigation, the results suggest no difference in bond strength whether a conventional etching and primer or Adper Prompt L-pop is used.
The amount of adhesive on enamel after debonding was significantly less when using Adper Prompt than when using the phosphoric acid.
These results indicated that Adper Prompt is potentially adequate for orthodontic bonding needs.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]