| Abstract|| |
Introduction: After fixed orthodontic treatment, following bracket removal, the debonding procedure should lead to restitutio ad integrum of the enamel or, at least, restore the enamel surface as closely as possible to its pretreatment condition. Adhesion of brackets in orthodontics is that they should be strong enough to prevent failure during all treatment but also low enough, so that enamel damage would be minimal during bracket removal after treatment. Material and Methods: A total of 60 premolars were collected and stored in distilled water. The extracted teeth were divided into two groups of 30 each, group A was to be bonded with self-cure adhesive while group B light cure adhesive was to be used. A standardised protocol was followed for adhering the brackets to the tooth surfaces. All the teeth were bonded with metal brackets (3M Unitek, Gemini Twin Brackets 0.022 slot). In group A, bonding adhesive (3M Unitek self cure adhesive primer) was applied. In group B, the bonding adhesive (3M Unitek light cure adhesive primer) was photopolymerized for 10 seconds after application. Results: Surface roughness of enamel as assessed by profilometry shows that light cure adhesive creates more roughness as compared to self cure adhesive. To conclude, self cure adhesive is clinically better than light cure adhesive. Discussion: In the present study enamel surface roughness were compared after debonding. Enamel surface roughness after bracket debonding depends on a host of factors, which include – brackets, adhesive used and method of remnant removal.
Keywords: Bonding, enamel surface, light cure adhesive, orthodontic brackets, profilometry, self-cure adhesive
|How to cite this article:|
Chandrasekharan D, Sourabh C, Deenadayalan, Praveen K. Enamel surface roughness evaluation after bracket debonding: Comparison between light cure and self cure adhesive resin 3-Dimensional profilometric study. Indian J Dent Res 2022;33:80-4
|How to cite this URL:|
Chandrasekharan D, Sourabh C, Deenadayalan, Praveen K. Enamel surface roughness evaluation after bracket debonding: Comparison between light cure and self cure adhesive resin 3-Dimensional profilometric study. Indian J Dent Res [serial online] 2022 [cited 2022 Oct 4];33:80-4. Available from: https://www.ijdr.in/text.asp?2022/33/1/80/353529
| Introduction|| |
After fixed orthodontic treatment, following bracket removal, the debonding procedure should lead to restitutio ad integrum of the enamel or, at least, restore the enamel surface as closely as possible to its pretreatment condition.
Adhesion of brackets in orthodontics is that they should be strong enough to prevent failure during all treatment but also low enough, so that enamel damage would be minimal during bracket removal after treatment. During bracket removal, bond failure can occur at the adhesive-enamel interface or at the adhesive-bracket interface (adhesive failure), or within the adhesive (cohesive failure). Generally, bracket failure is a combination of adhesive and cohesive failures, the latter resulting in the retention of material on the enamel and bracket surfaces (mixed failure).
When adhesive failure between the adhesive resin and the enamel surface occurs, a certain amount of enamel loss is almost inevitable because of the micromechanical bond between the composite resin bonding agent and the acid-etched enamel.
Bonding onto and removal of brackets from the enamel surfaces are potential risks for topographic changes in the form of cracks, scarring, scratches, or loss of enamel. The loss of surface enamel and associated exposure of enamel prism endings to the oral environment can result in decreased resistance of the enamel to the organic acids in plaque and make it more prone to decalcification.
Adhesive enamel interface failures can lead to enamel loss and depend largely on the bracket material and the method of debonding. Debonding forces can be influenced by many factors: type of enamel conditioning agents, adhesive resin, cement, polymerisation methods, bracket type, or bracket base architecture. Usually, an increase in debonding force causes an increased risk of enamel damage. Although subjective information on enamel surface morphology after bracket debonding has been the topic of some in-vitro studies, quantitative information relevant to enamel damage after bracket debonding evaluation using 3 Dimensional Profilometry is limited.
Profilometer is a measuring instrument used to measure a surface's profile, in order to quantify its roughness. Contact profilometers have a diamond stylus which is moved vertically in contact with a sample and then moved laterally across the sample for a specified distance and specified contact force. A profilometer can measure small surface variations in vertical stylus displacement as a function of position. A typical profilometer can measure small vertical features ranging in height from 10 nm to 1 mm. The height position of the diamond stylus generates an analog signal which is converted into a digital signal stored, analysed and displayed. The radius of the diamond stylus ranges from 20 nm to 50 μm, and the horizontal resolution is controlled by the scan speed and data signal sampling rate. The stylus tracking force can range from less than 1 to 50 mg.
Hence the purpose of this study was to evaluate the surface morphology after bracket debonding and comparing two orthodontic adhesive resins –light cure and self cure using profilometry.
| Material and Methods|| |
Ethical clearance for the study was obtained vide SBDC ref 05/2014. Sixty human premolars extracted for orthodontic purposes were collected and stored in distilled water at room temperature. The criteria for tooth selection included intact buccal enamel not subjected to any bracket bonding procedures, no damage caused by the extraction forceps, and no caries. The teeth were cleaned to remove debris, rinsed in water spray for 5 second, and air-dried.
The extracted teeth were divided into two groups of 30 each, group A was to be bonded with self cure adhesive while in group B light cure adhesive was to be used. The self cure group was embedded in type III dental stone plaster (Gold StoneR) while the light cure group was embedded in type I dental plaster (White GoldR). The buccal surface of each tooth was oriented upward from the bottom of the block so that its buccal surface would be perpendicular to the cantilever tip of the surface profilometer.
A standardized protocol was followed for adhering the brackets to the tooth surfaces. All the teeth were bonded with metal brackets (3M Unitek, Gemini Twin Brackets 0.022 slot). Enamel surfaces were rinsed with water and dried with an air syringe. Each tooth surface was etched with 37% ortho-phosphoric acid (d-TECH dental technologies) for 30 seconds, rinsed thoroughly with an oil-free air-water spray for 20 seconds, and air dried until they appeared frosty. In group A, bonding adhesive (3M Unitek self cure adhesive primer) was applied with a microbrush, and air thinned. In group B, bonding adhesive (3M Unitek light cure adhesive primer) was photopolymerized for 10 seconds after application with a microbrush.
The brackets were bonded by using adhesive cement. Self cure adhesive (3M Unitek) was used for group A. In group B, light cure adhesive (3M Unitek) was used. After removal of the excess around the bracket margins with the tip of a probe, they were photo-polymerized from five directions: above the bracket, cervico-incisal, inciso-cervical, mesial and distal for 20 seconds each (Ortholux, 3M Unitek - light output, 430-480 nm).
As reported by Eliades et al., and to ensure maximum bond strength, 7 days after bonding, the brackets were debonded by placing debonding pliers (Skodi) at the outer wings of the bracket. After the teeth had been debonded with pliers the adhesive remnant index (ARI) scores were recorded for both the group. The ARI of Artun and Bergland was used to define the quantity of resin remaining on the tooth surfaces. The ARI scores ranged from 0 to 3: 0, no adhesive remaining on the tooth; 1, less than half of the enamel bonding site covered with adhesive; 2, more than half of the enamel bonding site covered with adhesive; and 3, the enamel bonding site entirely covered with adhesive. One clinician performed all tests, including bonding, debonding, and adhesive removal. Visual inspection of the enamel surfaces was useful in the resin removal process. The adhesive remnants were carefully removed from the teeth by using a tungsten carbide bur driven on a low speed hand piece at 20000 rpm with water cooling. Complete removal of the composite resin was verified by visual inspection of the teeth under a dental operating light, after which the teeth were cleaned with water spray.
The cleaned enamel surfaces were subjected to a test with a surface roughness profilometer (Mitutogo Surftest SJ-210). The profilometer has a tip that is placed on the enamel surfaces and scans the surface to measure the surface roughness. Two recordings were made in contact with the enamel for each specimen, and the mean values were recorded. Average roughness (Ra) indicates the overall roughness of the enamel surface. It is the arithmetic mean of all absolute distances of the surface roughness from the center line within the measuring length. Root mean square roughness (Rq) describes the height distribution relative to the mean line. Maximum roughness depth (Rt) reflects isolated features on the enamel surface.
The ARI scores were evaluated with the Chi-square test. The comparison of surface roughness for both groups was done using an unpaired t-test.
Descriptive analysis was done for measuring the surface roughness in two groups. Unpaired t-test was used for comparison of the surface roughness between the self cure group and the light cure group. A Chi-square test was performed for comparative evaluation of ARI scores of both the groups.
| Results|| |
[Table 1] shows a descriptive analysis of surface roughness variation among the two groups. In self cure group, the surface roughness was 15.28 ± 1.37 mu.m. Whereas in light cure group the surface roughness was found to be 24.27 ± 5.05 mu.m.
[Table 2] and [Figure 1] show the unpaired t-test values for comparative evaluation of surface roughness between the two groups A and B. surface roughness for self cure was 15.282 ± 1.367 while for light cure it was found to be 24.271 ± 5.048. The comparison of surface roughness between self cure and light cure was statistically highly significant.
[Table 3] and [Figure 2] show the comparison of ARI scores for self cure and light cure. In the self cure group, 19 of 30 samples (63.3%) had an ARI score of 0 while 11 of 30 samples (36.7%) had an ARI score of 1. Similarly, in the light cure group majority of the sample i.e 13 of 30 or 43.3% of the sample had an ARI score of 3, while score 2 and 1 were found in equal no. of samples i.e 8 of 30 samples each. Only 1 of 30 samples (3.3%) had a score of 0. This difference in the distribution of specimens with respect to ARI scores was statistically highly significant between self cure and light cure.
| Discussion|| |
It was previously emphasised that the outermost layer of enamel should be left as intact as possible since it has greater micro hardness and contains more minerals and fluoride than the deeper zones. Consequently, the loss of surface enamel and associated exposure of the enamel prism endings to the oral environment might cause a decrease in the resistance of enamel to the organic acids in plaque. This eventually makes enamel more prone to demineralisation. Nonetheless, enamel scarring after debonding is inevitable. However, the advantages of bonding orthodontic attachments unquestionably outweigh the disadvantages.
In the present study enamel surface roughness was compared after debonding and remnant removal, among two groups i.e light cure group and self cure group. Remnant removal was done with TC bur with a low speed handpiece. Optical profilometry was used for a precise quantitative measurement of the surface roughness.
Enamel surface roughness after bracket debonding depends on a host of factors, which include – brackets, adhesive used and method of remnant removal. Surface roughness caused by metal and ceramic brackets was not of much difference. So, in the present study metal brackets were used.
Of the various methods available for remnant removal after bracket debonding, Retief and Denys proposed the use of a tungsten carbide bur to remove bulk and residual resin from teeth and to finish the underlying enamel using graded discs or ceramic wheels. Zachrisson and Arthun reported that a tungsten carbide bur used at low speed produces a fine scratch pattern and less enamel loss, whereas Rouleau et al. recommended a tungsten carbide bur operated at high speed. Similar to Retief and Denys, Zarrinia et al.,,,,,, suggested using a 12-bladed tungsten carbide bur to remove resin, followed by polishing with Sof-Lex discs to produce a smoother enamel surface. Contrary to the results of Howell and Weekes Ozer et al. recently found that Sof-Lex discs restored the enamel closer to its original smoothness. In this present in-vitro study tungsten carbide bur was used at low speed with water spray.
After ascertaining these two variables, a comparative study was planned to compare surface roughness characteristics between self cure adhesive and light cure adhesive.
Adhesion has two aspects – one to the tooth surface and the other to the bracket base – evaluation of ARI scores provides information on the site of bond failure as either adhesive at the bracket – adhesive resin interface or the adhesive at the enamel – adhesive resin interface. Macroscopic evaluation could also show cohesive failures in the enamel or in the resin.
In the self cure group, 63.3% of samples i.e 19 out of 30 had an ARI score of 0 whereas the rest of 11 samples (36.7%) had a score of 1. It indicated that most of the adhesive was on the bracket base and very little was left over on the tooth surface. Hence clean-up procedure was minimally required for this group. While in the light cure group, most of the samples had score 2 and 3. It indicates that most of the adhesive was left over on the tooth surface. Hence it required an exhaustive clean-up procedure with the help of tungsten carbide bur. This leads to the surface roughness observed in the light cure group, which is higher as compared to the self cure group. Debonding and cleanup are operator-dependent procedures, so the results might vary between operators. Since this could be a serious limitation, in this study, only 1 operator carried out all clinical procedures.
Scanning electron microscope (SEM) evaluation of an enamel surface shows its topography only; it is not quantitative and cannot be used for comparative purposes. Profilometric examination of a surface permits an objective determination, and profilometry was the main testing instrument used in this study, although the SEM evaluation helps to make a visual comparison of the cleanup procedures.,,
| Conclusion|| |
ARI for light cure adhesive is higher in comparison to self cure adhesive. Samples with more ARI values cause more surface roughness as more time and effort are needed to remove the remnant adhesive. So, the surface roughness of enamel as assessed by profilometry shows that light cure adhesive creates more roughness as compared to self cure adhesive. To conclude, self cure adhesive is clinically better than light cure adhesive.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Prof. Deepak Chandrasekharan
Department of Orthodontics, SRM Kattankulathur Dental College and Hospital, Chennai - 603 203, Tamil Nadu
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]