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In vitro evaluation of indigenously developed cyanoacrylates as bonding agents in comparison to a conventional bonding agent.

The most widely adopted bonding systems use composite materials based on acrylic or diacrylate resins bonded largely by mechanical interlock with enamel, which has been pretreated with acid. Alternative bonding agents such as cyanoacrylates have been reported in literature. The aims of this study were to compare the bond strength of two indigenously developed cyanoacrylates with a conventional self-cured composite and to study the nature of the failure. The bond strengths` of Begg brackets bonded onto 90 freshly extracted premolar teeth was tested using an universal testing machine. Later ARI scoring was done to study the nature of the bond failure. The results showed that although the initial bond strength of N-Butyl cyanoacrylate was higher than the control composite, it deteriorated when stored in physiologic saline for 48 hours. Isoamyl-2-cyanoacrylate had significantly lower bond strength when compared to the other samples in all the three groups under study. ARI scores indicate that for both the composite and N-Butyl cyanoacrylate groups, the bond failure was adhesive (between the bracket and adhesive) where as for the Isoamyl-2-cyanoacrylate group, the bond failure was cohesive (between the adhesive itself). This study shows that further work needs to be done with cyanoacrylates to decrease their bio-degradability, so that they can be clinically useful in orthodontics.

INTRODUCTION

The most widely adopted bonding systems in orthodontics use composite materials based on acrylic or diacrylate resins bonded largely by mechanical interlock with enamel, which has been pre-etched with acid. During the last of fifteen years, significant progress has been made in the development of alternative dental adhesive systems. Some of the more promising systems are based on multifunctional structures that contain polymerizable vinyl double bonds and reactive isocyanate groups. These materials are grouped under the term "cyanoacrylates". Among the unique properties of cyanoacrylates that attracted attention in orthodontics was their ability to polymerize, or harden at room temperature without the need for any bonding agent or a catalyst. Although cyanoacrylate is considered to be toxic and mutagenic in it's properties, it is considered safe for medical and dental use (C.C.Searle1986) [1]. Cyanoacrylates in the form of commercial "super glue" have been experimented with, as bonding agents. As reported by Herert Ivan Cueto [2], it was in 1966 that the first direct bonding using a cyanoacrylate was done. In a study done by Prashanth VK and Valiathan A et al (1996) [3], commercially available cyanoacrylate (Superglue- Locite Corp) was compared with "Right On" composite for shear bond strength. It was found that initial bond strength of cyanoacrylates was greater than composite, but after 48 hours in artificial saliva,it's bond strength deteriorated significantly making it unfit for clinical bonding.David. J. Howell(1989) [4] tried Ethyl cyanoacrylate as an alternative bonding agent, the manufacturers claimed that it was biocompatible, there was no tooth damage and that it had the ability to bond to wet teeth without any need for drying. Ortendahl and Ortengren [5] compared a new ethyl cyanoacrylate adhesive (Smartbond, Gestenco Int, Germany) to a conventional composite based bonding agent (Rely-a-bond). Their results showed that although Rely-a-bond has an adequate bond strength (9Mpa-11Mpa), the Smartbond`s strength was significantly higher (18Mpa-26Mpa) for the brackets tested. Several other studies [6] show that although the initial bond strength of cyanoacrylates is high, there is a deterioration of bond strength in the presence of moisture later.

The aims and objectives of the present study were: to find out the effectiveness of two Indigenously developed cyanoacrylates (N-Butyl cyanoacrylate and IsoAmyl-2-cyanoacrylate) as orthodontic bonding agents, by an in vitro comparison of its bond strength with a conventional composite; to test whether the cyanoacrylate bond strength is maintained after putting it in physiologic saline for 48 hours; to study the nature of bond failure with Adhesive Remnant Index [7,8].

MATERIAL AND METHODS

This study was done at the College of Dental Surgery, Manipal for bonding the brackets on the teeth and at Karnataka Regional Engineering College, Surathkal for bond strength testing. Ninety freshly extracted mandibular and maxillary non-carious first and second premolars without any cracks or fractures and which were extracted for orthodontic reasons were used for this study. All the teeth were cleared of blood and saliva and stored in 0.40% saliva. No pre-treatment with chemical agents like hydrogen peroxide, alcohol, formalin etc was done. Commercially available Begg brackets with a bracket surface area of 7.494[mm.sup.2] were used. Two varieties of cyanoacrylates, Isoamyl-2-Cyanoacrylate and N-Butyl Cyanoacrylate, which were indigenously developed at Indian Institute Of Chemical Technology (IICT), Hyderabad, were used as bonding agents. Commercially available self-cure composite resin (Right-On, TP Orthodontics, USA) was used as the control adhesive. The 90 teeth were divided into three groups of 30 teeth as follows;

Group-1 Shear bond strength tested after 1 hour.

Group-2 Shear bond strength tested after 48 hours.

Group-3 Shear bond strength tested after 48 hours in saline.

One operator did the bonding of all the teeth. Standard bonding protocol was followed. All the 90 teeth were mounted and the shear bond strength was tested using an universal testing machine (Hounsfield Tensometer, UK) at the metallurgy department of KREC, Surathkal. The ARI for each tooth debonded was recorded as follows;5, 0% adhesive on the tooth.4, 1%-9% adhesive on the tooth.3, 10%-90% adhesive on the tooth.2, 91%-99% adhesive on the tooth.1, 100% adhesive on the tooth.

RESULTS

Bond strength comparison

90 teeth were tested for bond strength. The breaking load at which the bond failure occurred for the two cyanoacrylate groups and composite groups were recorded.

Group-1. The initial bond strength measured 1 hour after bonding was highest for N-Butyl cyanoacrylate(6.18MPa) compared to the Right On composite(4.77MPa), followed by Isoamyl-2-cyanoacrylate(2.36MPa).

Group-2. The bond strength tested after 48 hours was the highest for Right On composite (7.46MPa) followed by N-Butyl cyanoacrylate (6.20MPa). Isoamyl-2-cyanoacrylate had the least bond strength (3.03MPa).

Group-3. The final bond strength testing for the three groups was done after immersing them in saline for 48 hours, 10 minutes after bonding. Both the cyanoacrylate groups showed a significant decrease in bond strength as compared to control. Right-on had a mean bond strength of 4.75MPa, followed by N-Butyl cyanoacrylate(2.51MPa) and Isoamy-2-cyanoacrylate(1.98MPa).

Nature of bond failure

Adhesive remnant index scoring showed that debonding of the composite and N-butyl cyanoacrylate group occurred at the bracket resin interface, but for the Isoamyl-2-cyanoacrylate group, majority of the failures were within the material itself.

CONCLUSION

N-Butyl cyanoacrylate bond strength was higher than Right On immediately after bonding. Isoamyl-2-cyanoacrylate showed lower bond strength in comparison.

The bond strengths of both the cyanoacrylates deteriorated sharply after 48 hours in physiologic saline solution when compared to Right On composite.

The nature of bond failure in the Right On group and N-Butyl cyanoacrylate group is mainly adhesive (failure between the bracket base and adhesive) where as in the Isoamy-2-cyanoacrylate group, it was cohesive (failure between the adhesive itself).

Further work needs to be done with cyanoacrylates to ensure the non-biodegradability and improvement in physical characteristics like viscosity, but the present results indicate that they cannot be used clinically for orthodontic bonding.

REFERENCES

[1.] Searle C.E. How safe are cyanoacrylates? Cancer campaign research laboratories, Birmingham Medical School Publication (1986).

[2.] Herbert Ivan Cueto. A little bit of history, The first direct bonding in orthodontics. American journal of Orthod and Dentofacial Orthopedics.;98:276-277 (1990).

[3.] Prashanth V.K, Valiathan A. In vitro evaluation of cyanoacrylates as a bonding agent. TIB and AO;12:1 (1998).

[4.] David J. Howells, Peter Jones. In vitro evaluation of a cyanoacrylate as a bonding agent. Brit Jour of Orthod;16:75-78 (1989).

[5.] Ortendahl T.W, Ortengren U. Smartbond: A new orthodontic bonding adhesive. Journal of Clinical Orthodontics; 34(1):50-54 (2000).

[6.] Darmon j.C. Cemented brackets and cyanoacrylate. Rev Ortho Dento facilate;9(4):424-438 (1975).

[7.] Artun J, Bergland S. Clinical trials with crystal growth conditioning as an alternative to acid-etch enamel pretreatment. AJO-DO;85:333-340 (1984).

[8.] Farquar R.B. Direct bonding comparing polyacrylic acid and phosphoric acid technique. AJO-DO;90:187-194 (1986).

Amit Srivastava, Suresh Gorantla and Ashima Valiathan

Dept Of Orthodontics

College of Dental Surgery

Manipal 576 119
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Author:Srivastava, Amit; Gorantla, Suresh; Valiathan, Ashima
Publication:Trends in Biomaterials and Artificial Organs
Geographic Code:9INDI
Date:Jul 1, 2002
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