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A comparative in vitro study with new generation ethyl cyanoacrylate (smartbond) and a composite bonding agent.

Orthodontics like any other science is constantly undergoing development and is evolving through the discovery of newer techniques, materials and improvement of older ones. The concept of "bonding in orthodontics" has been a monumental step in the progress of our science. One of the most daunting tasks for Orthodontists during the bonding procedures it the strict maintenance of a dry field, which is often very difficult. For nearly 20 years, cyanoacrylate glues have been widely used in Dentistry as well as in Medicine. Although toxic and mutagenic properties of cyanoacrylates, particularly lower cyanoacrylates, have been reported. they are generally considered safe for medical and dental use. The present study was undertaken to compare the shear bond strength of this new generation bonding adhesive (Smartbond) with a conventionally used dental composite (Right on) bonding agent (TP Orthodontics).

INTRODUCTION

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 pre-etched with acid. One of the most daunting tasks for Orthodontists during the bonding procedures is the strict maintenance of a dry field, which is often very difficult. Apart from that using a conventional technique, bracket placement, bracket removal and dean up is responsible for the loss of up to 55 microns of enamel (1). This sacrifice should provide a cause for concern (2): less destructive bonding techniques are to be desired.

For nearly 20 years, cyanoacrylate glues have been widely used in Dentistry as we 11 as in Medicine. Although toxic and mutagenic properties of cyanoacrylates, particularly lower cyanoacrylates, have been reported, they are generally considered safe for medical and dental use (1986) (Searle CE, Cancer Campaign Research Lab, Birmingham) (3).

In vitro studies have been conducted in our department by Valiathan et al. (4,5) using cyanoacrylates as bonding agent. Results showed that the cyanoacrylate initially showed bond strength greater than the composite but deteriorated significantly as time proceeded making it unfit for clinical bonding.

Gestenco International, manufacturer of a newer generation bonding adhesive (Cyanoacrylate based)--'Smartbond' calms to have overcome the foresaid drawbacks of routine adhesives. Smartbond is different from the other cyanoacrylates in that its viscosity has been altered with silica gel and the product has received FDA approval in the United States and CB mark for Europe. Because polymerization starts only in the presence of moisture and pressure, the clinical procedure for bonding with smartbond differs from that of composite.

It was felt that there was a need of an investigation to validate the above Balms of Smartbond adhesive. Hence the present In vitro study was undertaken to compare the shear bond strength of this new generation bonding adhesive (Smartbond) with a conventionally used composite (Right on) bonding agent (TP Orthodontics).

AIMS AND OBJECTIVES

The main alms of this study were to:

1. Find out the efficiency of the new generation product, ethyl cyanoacrylate (SMARTBOND) as an orthodontic bonding adhesive and to compare the bond strength with conventional composite (Right-on, no-mix).

2. Test whether the cyanoacrylate bond strength is maintained after storage in artificial saliva for 2A hours and 48 hours.

3. Compare the change in bond strength of this cyanoacrylate ,(SMARTBOND) with that of composite after 24 hours and 48 hours In artificial saliva.

4. Study the significance of the adhesive remnant index for both.

MATERIALS AND METHODS

This study was conducted 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.

Sixty freshly extracted mandibular and maxillary non-carious first and second premolar without any cracks or fractures and which were extracted from young patients for orthodontic reasons were used for this study. All the collected teeth were cleared of blood and saliva

and were stored in distilled water. The sixty extracted teeth were randomly divided into three groups of twenty each.

Group I--bond strength to be tested after 1 hour (Dry).

Group II--Bond strength to be tested after 24 hours in artificial saliva.

Group III--Bond strength to be tested after 48 hours in artificial saliva.

Criteria for tooth selection were perfect buccal enamel, no caries or cracks present, no pretreatment with chemical agents like alcohol, formalin or hydrogen peroxide. Commercially available Begg brackets with flat base (T.P. Orthodontics) were used In this study. By using a traveling microscope (least count 0.001cm) the area of the bracket base was found out as 8.965mm.

The cyanoacrylate used was the new generation ethyl cyanoacrylate, SMARTBOND (Manufacturer--Gentenco International and marketed by GAC).

Commercially available chemically cured composite resin (Right-on, no-mix, TP orthodontics) was used to also bond brackets and served as control to the experiment.

All the teeth were bonded by one operator and all materials were handled as per the manufacturers instructions. Samples to be tested for bond strength after 24 hours and 48 hours were stored in artificial saliva. This artificial saliva was obtained from the Kasturba Medical College Pharmacy, Manipal, and consisted of a mixture of 3% viscous methylcellulose solution and glycerine.

BONDING PROCEDURE

Group I: Testing after ONE HOUR (Dry Strength)

Twenty teeth were rinsed with tap water by using an air/water syringe for twenty. seconds, cleaned with a prophylaxis cup in a slow hand piece with non-fluoridated pumice for 30 seconds and then rinsed.

The twenty teeth were then divided into two sub groups of 10 teeth each.

Group IA: Control group--Composite (Right-on).

Group IB: Test group--Ethyl Cyanoacrylate (SMARTBOND).

For Group IA (composite group) the teeth were dried well and etched with 3796 phosphoric acid applied buccally for a period of 50 seconds. The teeth were then rinsed for twenty seconds in water and air dried for twenty seconds. The composite (no-mix) was spread on the base of the Begg brackets, which were placed on the mid buccal crown, and seating pressure was applied until the bracket to tooth contact was achieved.

For Group IB (SMARTBOND) the dried surface of each tooth was etched with a phosphoric acid etchent gel supplied by the manufacturer (SMARTBOND KIT) for 10 seconds. The etched surface was rinsed with water and was not dried. A small amount of adhesive was applied on to the bracket base directly from the Luer Lock tip supplied in the SMARTBOND kit and was bonded to the mid buccal crown.

Both these samples were tested for bond strength after and hour (Dry).

Group II: Testing after 24 hours in artificial saliva

Twenty teeth were rinsed with tap water by using an air/water syringe for twenty seconds, cleaned with a prophylaxis cup in a slow hand piece with non-fluoridated pumice for 30 seconds and then rinsed.

The twenty teeth were then divided into two subgroup of 10 teeth each.

Group IIA: Control group--Composite (Right-on).

Group HS: Test group--Ethyl cyanoacrylate (SMARTSOND).

Brackets were bonded using these materials according to their bonding Instructions specified.

Shear bond strength testing was done after 24 hours of immersion in artificial saliva.

Group III: Testing after 48 hours In artificial saliva

Twenty teeth were rinsed with tap water by using an air/water syringe for twenty seconds, cleaned with a prophylaxis cup in a slow hand piece with non-fluoridated pumice for 30 seconds and then rinsed.

The twenty teeth were then divided into two subgroups of 10 teeth each.

Group IIIA: Control group--Composite (Right-on).

Group IIIB: Test group--Ethyl cyanoacrylate (SMARTBOND).

Brackets were bonded to these teeth with those materials as per their bonding instructions.

Shear bond strength testing was done after 48 hours of immersion in artificial saliva.

Mounting

A suitable mould of a diameter 12mm and height 20mm was placed on a platform to embed the root portion up to the level usually covered by the alveolar bone in the dental arch, designed to fit the universal testing machine. This procedure was repeated for all the sixty specimens. After setting they were kept in water for storage at' room temperature for 24 hours.

Determination of Shear bond strength:

The shear bond strength of the bonded teeth was tested using the Universal Testing Machine (Hounsfield Tensometer, United kingdom, 1 ton capacity) at the Metallurgy Department, Karnataka Regional Engineering College, Surathkal.

After storage in artificial saliva at room temperature the specimens were dried and transferred to the Universal testing machine individually and subjected to the shear strength study. A steel loop, which exactly fitted, the gingival slot of the bracket was constructed and used so that the forces during the bond strength test would be uniformly distributed.

Load was applied till the point of fracture; that is till the bracket detached from the tooth surface. The peak force that was required to debond the bracket in Newton was monitored and was subsequently . calculated in mega Pascal using the formula.

Bond Strength = Breaking load (Newton) / Normal surface area of bracket base ([mm.sup.2])

(The surface area of the bracket base was determined using a traveling microscope.)

The residual adhesive was graded for each tooth debonded as per Artun and Bergland Index (6) as under

5 = 0% adhesive remained on the tooth.

4 = 1-9% (<10%) of adhesive remained on tooth.

3 = 10-90%, more than 10% but less than 90% of adhesive remained on the tooth.

2 = 91-99%, more than 90% of adhesive remained on the tooth.

1 = 100%: all adhesive remained on the tooth.

Data was entered in computer in FoxBASE and analyzed using the statistical package SPSS/PCT version 6.0 for Microsoft Windows in a Pentium computer. Mean force (Bond strength) and its standard deviation (SD) were calculated for each group.

RESULTS

60 samples were tested for shear bond strength on a universal testing machine. The breaking load at which bond failures occurred for the cyanoacrylate and the right-on composite were recorded and the bond strength calculated for all the three groups. The mean values with standard deviation were calculated and compared. The bond strength was calculated using above formula.

The nominal area of bracket base was found to be 8.97 [mm.sup.2]. The mean value of bond strength for composite and cyanoacrylate at various time intervals were as follows.

The significance of difference between pairs of mean was assessed using student 't' test, and appropriate analysis of variance were applied to groups of mean. Probability greater than 0.05 were treated as not significant, whereas those less than 0.001 were highly significant.

Overall there was a highly significant difference between the performances of the two materials (Table 2-5). For the cyanoacrylate group the mean bond strength initially at 1 hour was low but Increased: after 24 hour showing significant difference from the initial value (3.32 Mpa to 5.07 Mpa). However at 48 hours the strength of cyanoacrylate declined gradually to 5.03 Mpa (Table 3).

However for the composite group there was a steady increase in bond strength from 1 hour to 48 hours (4.87 Mpa to 6.01 Mpa) (Table 2).

The Adhesive Remnant Index was recorded for each sample showing no significant difference between the two groups at various time intervals (Table 6).

DISCUSSION

Initial debonding (after 1 hour) showed lesser bond strength for smartbond when compared to right-on composite (3.32 Mpa and 4.87 Mpa) (Tables 2 & 3). However debonding 24 hours after storage in artificial saliva showed that the bond strength of cyanoacrylate did rise significantly attaining a value closer to that of composite (5.07 and 5.70) (Tables 2 & 3). This increase in bond strength for cyanoacrylate was in accordance to study by Ortendahl et al (7) where they found that smartbond did not achieve its maximum strength until after 24 hours.

It was needed to know the effect of strength as time progressed. Hence the samples were again tested for bond strengths after 48 hours (in saliva). Results showed that there was no statistically significant difference in the bond strength for both cyanoacrylate and composite groups. However, clinically the bond strength did gradually decline for cyanoacrylate and increase for composite (5.03 and 6.01 Mpa).

For cyanoacrylate, the reduction in bond strength could be due to the biodegradability of cyanoacrylate in an aqueous environment. These findings are in accordance with the, study conducted by Daniel J Howells and Peter Jones in 1989 (8).

Assessment of residual adhesive on debonding during the test as per Artun and 8ergland's adhesive remnant index (ARI) scores showed no significant difference between the two groups (Table 6).

Thomas W Ortendahl et al (7) compared smartbond with established composite material regarding shear bond strength, debonding properties and ARI index. The mean shear bond strength of smartbond came within the range of 20 Mpa and was higher than the composite (Rely-a-bond). However in the present study done using contoured Begg brackets, smartbond achieved- maximum bond strength of only 5.07 Mpa at 24 hours in presence of artificial saliva, which declined after 48 hours. This bond strength was comparatively lower than the composite (control) tested.

Earlier studies done in our department by Valiathan et of in 1996 (4) and 2000 (5) also showed that as time progressed cyanoacrylate had deterioration in bond strength making it unfit for clinical bonding.

In the oral cavity, bonded brackets are subjected to a combination of shear, tensile and torsional forces. Wheeler and Ackerman (9) hold the opinion that the orthodontic forces never exceeded 1 pound per tooth. Newmann (10) indicated that a load of 200 psi (1.38 Mpa) per tooth is probably the maximum that occurs in clinical situation. Similarly, Keizer et al (11) indicated that shear stresses exerted on attachment during orthodontic treatment ranges from 1 to 3 Mpa.

The mean bond strength required of an adhesive is difficult to determine, since occlusal loads vary considerably and an assessment of the forces transmitted to an individual tooth is difficult to obtain. Reynolds (12) suggested that a maximum bond strength of 60-80 kg/[cm.sup.2] {5.88 to 7.85 Mpa} would appear reasonable although successful clinical bonding has been reported with an adhesive giving an in vitro bond strength of 50 kg/[cm.sup.2] (4.9 Mpa). Both the groups tested for our study did show the minimum required bond strength (>4.9).

In this study the overall values in bond strength were comparatively lower (<10 Mpa). It appears that the difference In opinion regarding adequate bond strength may be related to variations in experimental design of different investigations (13).

SUMMARY

This study was to compare bond strengths of composite (right-on) and a recently marketed cyanoacrylate (smartbond) at various time intervals--1 hour (dry), 24 hours and 48 hours (in artificial saliva). The following conclusions of the study were:

1. Composite did show progressively higher bond strength than cyanoacrylate at all time intervals.

2. Cyanoacrylate attained a maximum strength only after 24 hours and then gradually declined after a period of 48 hours in artificial saliva.

3. Debonding effects of both composite and cyanoacrylate were found to be similar.

It may be reasonably concluded that since the shear bond strength of cyanoacrylate (smartbond) was lesser than composite (right-on), it might not be a better option as an orthodontic bonding adhesive. But because the cyanoacrylate group of adhesives has a number of desirable properties, it is felt that further research and modification should be done, so as to obtain a cyanoacrylate adhesive having all the required properties essential for an ideal orthodontic bonding adhesive.

REFERENCES

(1.) Fltzpatric D.A. and Way D.C.: The effect of wear on acid etching and bond removal of human enamel. Am. J. Orthodont., 1977; 71:671-881.

(2.) Thurow R.C.: Editorial--The skin of our teeth. The Angle. Orthodontist, 1985; 55:179-180.

(3.) Searle C.E.: How safe is cyanoacrylate. Cancer Campaign Research Laboratories. Birmingham Medical School Publication, 1986.

(4.) Prashanth V.K. and Valiathan A.: In vitro evaluation of cyanoacrylate as a bonding agent. TIB & AO, 1998; 12(1).

(5.) Amit Kumar Srivastav, Vatlathan Ashima: In vitro evaluation of Indigenously developed cyanoscrylates as a bonding agent in comparison to conventional bonding agent. Thesis submitted to Manipal Academy of Higher Education. Manipal (2000 December).

(6.) Artun J., Bergland 5.: Clinical trials with crystal growth conditioning as an alternative to acid etch enamel pretreatment. Am. J. Orthodont. 1984; 85: 333-40.

(7.) Thomas W. Ortendahl O.D., ULF Ortengren: A new orthodontic bonding adhesive--SMARTBOND. J. Clin. Ortho. 2000; 34(1):50-54.

(8). David J. Howells and Peter Jones: In vitro evaluation of a cyanoacrylate-bonding agent. Br. J. Orthodont., 1989; 16: 75-78.

(9.) Wheeler J.J. and Ackerman R.J.: Bond strength of thermally recycled metal brackets. Am. J. Orthodont. 1983; 88: 181-88.

(10.) Newman V. George: Epoxy adhesives for orthodontic attachments: Progress report. Am. J. Orthodont. 1985; 51: 900-12.

(11.) Keizer S., Tencate J.M. and Arends J.: Direct bonding of orthodontic brackets. Am. J. Orthodont. 1978; 69: 318-27.

(12.) Reynolds I.R.: A review of direct orthodontic bonding. Br. J. Orthodont. 1975; 2:171-180.

(13.) Owens Jr. S.E.. Miller B.H.: A comparison of shear bond strengths of three visible light-cured orthodontic adhesives. Angle Orthod, 2000; 70(5): 352-356.

James Sunny P *

Ashima Vallathan **

* Assistant Professor

** Professor and Head, Director of Postgraduate Studies

Department of Orthodontics and Dentofacial Orthopaedics

College of Dental Surgery

Manipal 576 119, Kamataka

Correspondence to Prof. (Dr.) A. Vallathan
Table 1: Bond strength of bonding agents

Composite Cyanoacrylate

Right-on (1 hr) [right arrow] 4.87 Smartbond (1 hr) [right arrow]
Mpa 3.32 Mpa
Right-on (24 hrs) [right arrow] 5.70 Smartbond (24 hrs) [right arrow]
Mpa 5.07 Mpa
Right-on (48 hrs) [right arrow] 6.01 Smartbond (48 hrs) [right arrow]
Mpa 5.03 Mpa

Table 2: Bond strengths of composite at various time intervals

Period
(hrs) n Mean (Mpa) SD

 1 Composite 10 4.87 0.39
 (Right-on)
 24 Composite 10 5.70 0.47
 (Right-on)
 48 Composite 10 6.01 0.52
 (Right-on)

Table 3: Mean bond strength of cyanoacrylate (Smartbond) at
various time intervals

Period
 (hrs n Mean(Mpa) SD

 1 Cyanoacrylate 10 3.32 0.32
 (Smartbond)
 24 Cyanoacrylate 10 5.07 0.46
 (Smartbond)
 48 Cyanoacrylate 10 5.03 0.41
 (Smartbond)

Table 4: Analysis of variance test between composite
(Right-on) and cyanoacrylate (Smartbond) at various time
intervals

 F Significance

Composite (Right-on) 16.358 0.000 vhs
Cyanoacrylate
(Smartbond) 81.618 0.000 vhs

Table 5: Comparison of mean bond strength among samples
composite/cyanoacrylate

Period Group Mean SD 't'

(hrs) Composite 4.87 0.39 9.78
 1 Cyanoacrylate 3.32 0.32 p=.000 vhs

 24 Composite 5.70 0.47 3.07
 Cyanoacrylate 5.07 0.46 p=.007 vhs

 48 Composite 8.01 0.52 4.70
 Cyanoacrylate 5.03 0.41 p=.000 vhs

Table 6: Adhesive Remnant Index (ARI) Score

 1 2 3 4 5
Groups (100%) (91-99%) (90-10%) (10-0%) (0%)

 1 HOUR TESTING (Dry)

Composite 2 (20) 8 (80) 0 0 0
(Right-on)
Cyanoacrylate 1 (10) 5 (50) 3 (30) 1 (10) 0
[Smartbond]

 24 HOURS TESTING (In Artificial Saliva)

Composite 0 9 (90) 1 (10) 0 0
(Right-on)
Cyanoacrylate 0 6 (60) 4 (40) 0 0
(Smartbond)

 48 HOURS TESTING (In Artificial Saliva)

Composite 3 (30) 7 (70) 0 0 0
(Right-on)
Cyanoacrylate 3 (30) 5 (50) 2 (20) 0 0
(Smartbond)

 Chi-square
Groups test

 1 HOUR TESTING (Dry)

Composite [chi square] = 5.028
(Right-on)
Cyanoacrylate p=0.1699 NS
[Smartbond]

 24 HOURS TESTING (In Artificial Saliva)

Composite [chi square] = 1.067
(Right-on)
Cyanoacrylate p=0.3017 NS
(Smartbond)

 48 HOURS TESTING (In Artificial Saliva)

Composite [chi square] = 2.333
(Right-on)
Cyanoacrylate p=0.3114 NS
(Smartbond)
COPYRIGHT 2003 Society for Biomaterials and Artificial Organs
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Author:Sunny P., James; Vallathan, Ashima
Publication:Trends in Biomaterials and Artificial Organs
Geographic Code:9INDI
Date:Jan 1, 2003
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