An in-vitro study to compare efficacy of lingual retainer bonder with different adhesive system
Dr. SachinShaji M1, Dr. Glodwin Antony2,Dr. Shetty Suhani Sudhakar3*, Dr. PrachiGaonkar4, Dr. Aparna K5, Dr. Anand Abraham6
1,2Consultant orthodontist, Ernakulam, Kerala, India
3Srinivas Institute of Dental Sciences, Mangalore, Karnataka, India
4Terna Dental college and Hospital, Navi Mumbai, Maharashtra, India
5Consultant orthodontist, Bangalore, Karnataka, India
6Consultant orthodontist, Kottayam, Kerala, India
ABSTRACT
Objective: To compare detachment force, wire deflection and adhesive remnant index (ARI) after debonding between different lingual retainers with two adhesive system
Methods: 80 extracted teeth were mounted on acrylic blocks in pair and divided into 4 groups of 10 sample in each. Group 1 was coaxial wire bonded with packable composite, Group 2 was co axial wire bonded with flowable composite, Group 3 was braided wire bonded with packable composite and group 4 was braided wire bonded with flowable composite. Wire deformation was recorded using a Universal Testing Machine during debonding procedure. The amount of adhesive remaining in tooth after wire debonded was assessed using ARI index.
Results: Mean force for debonding was found to be higher in group 4 followed by Group 3, 2 and 1 respectively. Braided wire required force for dislodgement. Higher mean deformation was recorded in Group 2 followed by group 1, 3 and 4 respectively.
The difference in mean deformation among the groups was found to be statistically significant (P<0.001). The association between ARI scores and the groups were not statistically significant.
Conclusion: .The difference in mean deformation among the groups was found to be statistically significant (P<0.001). Coaxial wire bonded with flowable composite showed the greatest deformation when compared to other groups. The association between ARI scores and the groups were not statistically significant.
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Keywords
lingual retainers, bond strength, deformation
Introduction
Retention is the most important part of any orthodontic treatment. Retention helps to overcome periodontal fibre recoil and help in alveolar bone remodelling.1 Various methods have been used for retention. Removable appliance were most commonly used but they have several disadvantages like patient compliance, bulky and poor esthetics.
Lingual retainer is another type of retainer used for retention2.
Numerous designs and techniques for placement of lingual retainers have been proposed in recent literature. Flexible spiral wire retainer is one of the methods described by Zachirsson in which they use multistranded wire on the lingual surface of anterior teeth. The flexibility of the wire reduces the concentration of stress within the bonding composite, thus minimizing the risk of subsequent failure.3
Composite is used to bond the lingual retainer to lingual surface of teeth. Typically, failure of composite occurs due to internal crack propagation or thinning of composite by abrasion which occurs due to food habits and brushing.4 Traditional packable composite is used widely as it has good filler property which resist abrasion. The disadvantage is that isolation is critical in this method thus it is a time consuming process. Flowable composite has numerous advantage over packable as they are non-sticky, no trimming or polishing required after placement and direct placement of wire. This leads to reduced chair side time. Flowable composites with nano-sized filler particles has a good filler content per unit volume, higher abrasive resistance compared to the traditional micro filled flowable composites.5
Failure rate of lingual retainers is a problem of great concern as frequent debonding of these retainers can lead to relapse. Hence, this study is undertaken to evaluate detachment force, wire deflection and adhesive remnant index (ARI) between different lingual retainers during debonding with packable and flowable composite on extracted teeth.
Methodology
The study was conducted on 80 extracted human incisor teeth collected from Department of Oral and Maxillofacial Surgery. Teeth with caries, cracks or abnormalities were excluded. Soft tissue remnants were removed with ultrasonic scaler and teeth were stored in preservative solution. Pairs of teeth were matched to form a contact area that mimics the intraoral situation. Chemically cured acrylic resin was placed into molds and the roots of the teeth were embedded in the acrylic. The tooth were mounted so that the long axis were perpendicular to the base of the molds. In total, 40 blocks were constructed. The teeth were polished with pumice, the blocks were divided in 4 groups of 10 sample each. Group 1 was Coaxial wire bonded with packable composite, Group 2 was Co axial wire bonded with flowable composite, Group 3 was Braided wire bonded with packable composite and group 4 was Braided wire bonded with flowable composite.
The tooth were etched for 30 seconds with 37% orthophosphoric acid, then rinsed with water for 30 seconds using a three-way syringe, and dried for 20 seconds. Then the Primer was applied, in accordance with the manufacturer’s instructions and cured. To provide best fit of the wire over the tooth, a gentle curve was given. A 10 mm length of test wire was cut and the midpoint of the wire was marked with a pencil. The test wire was then placed on the primed tooth surface. The adhesive was applied with mini mold which was 4 mm in diameter with a 1.5 mm depth which provided a 12.6 mm2 bond area on each tooth and cured in accordance with the manufacturer’s instructions using a light curing unit. The same procedure was repeated for all the other blocks.
Debonding procedure was carried out in the following manner-Specimens were secured in a jig attached to the base plate of Universal Testing Machine. A chisel-edge plunger was mounted in the movable crosshead of the testing machine and positioned so that the leading edge aims at the marked midpoint of the wire. The chisel-edge was carefully placed so that it should not contact any part of the specimen. The crosshead speed was set to 1 mm/ min and the maximum load necessary to debond the wire was recorded for each specimen. Wire deformation was recorded using a Universal Testing Machine during debonding procedure for all the specimens.
The amount of composite left on the surface of each specimen was recorded using ARI index to find out the interface where the fracture is happening. In this system, fractures are ranked from 0 to 3, based on amount of adhesive remaining in tooth after wire debonded.
0-No adhesive remaining on the enamel surface 1-Less than 50% adhesive remaining on tooth surface.
2-More than 50% adhesive remaining on tooth surface.
3-All adhesive remaining on tooth surface.
Statistical analysis- For this study the null hypothesis was stated that there is no significant difference in the mean force (max force) recorded in the four groups i.e. µ1 = µ2= µ3 = µ4 .The alternate hypothesis was stated that there is a significant difference in the mean force (max force) recorded in the four groups i.e. µ1 ≠ µ2≠ µ3 ≠ µ4 ≠ . The level of significance was taken as α=0.05. The statistical technique which was used is analysis of variance (ANOVA). An ANOVA test is a way to find out if survey or experiment results aresignificant. In other words, they help to figure out if you need torejectthenullhypothesisor accept thealternatehypothesis. It is a test for groups to see if there’s a difference between them. Decision criterion is to reject the null hypothesis if the p-value is less than 0.05. Otherwise we accept the null hypothesis. If there is a significant difference between the groups, we carry out multiple comparisons (posthoc test) using bonferroni test to find out between which group the difference exist.
Result
Table 1: Mean force (max force) recorded in the groups
Group Mean StdDev
SE of Mean
95% CI for Mean
Min Max
Lower Bound
Upper Bound
1 45.04 11.52 3.64 36.80 53.28 28.37 63.12
2 49.47 14.01 4.43 39.44 59.49 32.19 66.90
3 50.36 12.14 3.84 41.67 59.04 27.55 71.14
4 50.87 12.81 4.05 41.70 60.03 37.89 75.83
Table 2: Mean force (max force) recorded in between groups and within group using ANOVA
Source of
Variation
Df
Sum of
Squares
Mean Square
F P-Value
Between Groups 3 212.087 70.696 0.441 0.725
Within Groups 36 5764.775 160.133 --- ---
Total 39 5976.863 --- --- ---
Wire deformation that occurred on debonding in different groups are shown in Table 3.It was seen that the mean deformation was least in group 4 followed by group 3, group 1 and the highest deformation was recorded in group 2.
The results of wire deformation obtained on debonding in different groups were subjected to ANOVA and the results are shown in Table 4 The results of the table 4 suggested that there was statistically significant difference in mean deformation on debonding present among the groups with the p value of < 0.001.
Table 3: Mean deformation (mm) recorded in the groups
Group Mean StdDev
SE of Mean
95% CI for Mean
Min Max
Lower Bound
Upper Bound
1 0.800 0.367 0.116 0.538 1.063 0.173 1.352
2 0.819 0.251 0.079 0.640 0.999 0.382 1.336
3 0.471 0.248 0.078 0.293 0.648 0.108 1.035
4 0.310 0.142 0.045 0.208 0.411 0.095 0.477
Table 4: Mean deformation (mm) recorded in between groups and within group
Source of Variation Df
Sum of
Squares
Mean Square
F P-Value
Between Groups 3 1.892 0.631 9.029 <0.001*
Within Groups 36 2.515 0.070 --- ---
Total 39 4.408 --- --- ---
The results were then subjected to multiple comparisons using Bonferroni test in order to find out among which pair of groups there exist a significant difference,the results of which are given in table 5. The difference in mean deformation (mm) was found to be statistically significant between Group 1 & Group 4 (P<0.01), Group 2 and 3 (P<0.05) as well as between Group 2 & Group 4 (P<0.01) as shown in table 5.
Table 5: Mean deformation (mm) recorded to find out among which pair of group there exist a significant difference
(I-J) Lower Bound Upper Bound
1
2 -0.019 1.000 -0.349 0.311
3 0.330 0.050 0.000 0.660
4 0.491 0.001* 0.161 0.821
2
1 0.019 1.000 -0.311 0.349
3 0.349 0.033* 0.019 0.679
4 0.510 0.001* 0.180 0.840
3
1 -0.330 0.050 -0.660 0.000
2 -0.349 0.033* -0.679 -0.019
4 0.161 1.000 -0.169 0.491
4
1 -0.491 0.001* -0.821 -0.161
2 -0.510 0.001* -0.840 -0.180
3 -0.161 1.000 -0.491 0.169
Test was conducted to find out the amount of adhesive remaining on the tooth surface after debonding using ARI score and the results were subjected to chi square test as shown in table 6. The results of table 6, shows that even though high ARI scores were found in group 4 and low ARI scores were seen group 1, the results didn’t show statistical significance.
Table 6: Analysis of ARI Scores: (Chi-squared test)
Group
Score 0 Score 1 Score 2
χ2 P-
Value
N % N % N %
1 4 57% 3 14% 3 27%
12.727 0.050
2 0 0% 6 27% 4 36%
3 1 14% 9 41% 0 0%
4 2 29% 4 18% 4 36%
Total 7 100% 22 100% 11 100%
According to the results explained in table 2, table 4, table 5 and table 6, the null hypothesis was accepted in the case of mean force required for debonding the lingual retainer, which was not statistically significant between the groups suggesting there is no difference in debonding force between coaxial and braided wire when used along with different composite combination. The null hypothesis was accepted in relation to the ARI scores between the group which was also not statistically different suggesting that the mode of fracture between wire and composite was similar between groups having almost similar amount of composite remaining on tooth surface after dedonding. The null hypothesis was rejected and the alternate hypothesis was accepted in the case of wire deformation caused on debonding of lingual retainer, as there was statistically significant difference between the groups.
Discussion
Structural stability is an important aspect in orthodontics which should retain in retention phase. Proper occlusion within the limits of normal muscle balance along with proper relation with apical bases important for attaining stability after orthodontic treatment.6 During retention phase, stability is achieved by gingival and periodontal fibers reorganisation to the new teeth position. Both these mechanisms help to prevent relapse.7 lack of stability can lead to loss of function or esthetics which as achieved during active period. Treatment mechanics and growth also affect retention. For this reason, orthodontic forces are gradually withdrawn. 1,8,9 long term retention of aligned anterior teeth is thus essential.
Fixed lingual retainers have been used to maintain orthodontic treatment. It was reported in a study that 81% of orthodontists use fixed retainer out of which 37% use them frequently and 44% use them rarely.10 thus in our study we have tested different types of fixed retainers.
Bond strength of 6-8 Mpa for orthodontic brackets was sufficient for orthodontic forces but very little information is available on the minimum clinically acceptable bond strength in relation to bonded retainer wires.11,12
Retainer failure using either different composite or wire combination using variables either debonding force and deformation caused was tested in our study. There are very few studies which have compared different wire combination with different composite and bonding agent combination together, in relation to debonding force and deformation caused and type of failure caused at tooth and retainer interface.
Also while most of the published studies tested materials by loading method applied directly at the bonding site of the orthodontic attachment, very few authors have examined the wire’s interdental segment.13
In the present study we simulated the clinical bite situation by applying a vertical force on the retainer. Reynolds et al found that a vertical force yields the highest values of bond strength compared to a tensile force in horizontal or vertical orientation. However, bond strength not only depends on the direction, but also on the location of the applied force.11
Several authors have demonstrated that the lowest values of bond strength occur when the force is applied to the interdental segment. Therefore we chose this most fragile segment to determine the lowest strength required for debonding.14
Recently use of flowable composites has been suggested for bonding lingual retainers, when compared to conventional composite and almost every dental manufacturer now has its own flowable composite. So in the present study both packable and flowable composite were used along with different wire combination. This study aimed at identifying the most reliable wire-and-composite combination thus has considerable clinical implications.
Zain et al. (2004) found that force application directly to the adhesive pad of a wire/bond combination yielded a higher mean force for failure of 64.3N among all the groups which included wires Dentaflex co-axial 0.018", Dentaflexmultistranded 0.018", and Respond Dead Soft straight, length 0.0175"; composites: Tetric Flow and Heliosit Orthodontic.14 However, the difference in mean force among the groups was not found to be statistically significant similar to study done by Baysal et al, Foek et al14,15
Some studies showed statistically significant difference among groups like studies done by Aldrees et al. In that study, the wire was taken was flexible coaxial wire and solid wire and this can be the reason in difference in the results.16
To accurately score the ARI is important because it is an important factor to be considered in the selection of orthodontic adhesive. Studies have debated whether the differences in ARI scores reflect a difference in bond strength between the enamel and the adhesive for the different adhesive systems, but adhesive systems that show less adhesive remnant on the tooth has been advocated for easier and safer removal of residual resin after debonding.
17
Artun et al favoured use of a 0.0205 inch diameter five stranded twisted wire and postulated that the use of five rather three strands reduced the tendency of stress fracture of the wire, whilst Rose et al. (2002) used a 0.0175 inch multi-stranded wire. 17
A study done by Cooke et al measured deflections in conjunction with the ARI scores. It was suggested that the force experienced by these flexible interdental wires dragged the wire and deformed the interdental segment, leading to propagation of cracks within the composite, most likely along the wire–composite interface, and subsequent bond failure at the wire–composite interface i.e. cohesive failure.13
In the present study, more than 50% of sample shows ARI index score 1. ie, less than 50% adhesive remained on the tooth surface which advocated easy removal of lingual retainer on debonding. In the present study the association between ARI scores and the groups was not statistically significant which states that lingual retainer when used with flowable or packable have similar ARI scores which suggest that we can select adhesive according to clinical preferences.17
A study showed that, breakage appears unrelated to materials used or to the age and sex of patients. The upper retainers break more often than the lower retainers and that the early breakage is more likely to occur at the adhesive pad than at the wire.14 But on the contrary a study was done by Paolone to assess the retention forces and mechanical behavior of different types of wires matched with different kinds of composites in lingual retainers. The results showed that the bonding between wires and composites in lingual fixed retainers seemed to be lowest for rectangular smooth wires and increased in round twisted and rectangular twisted wires where the bonding was so strong that the maximum tension/bond strength was greater than the ultimate tensile strength of the wire. The highest values were in rectangular twisted wires. Concerning the composites, hybrid composites had the lowest interface bonding values and broke very quickly, while the nano- and micro-composites tolerated stronger forces and displayed higher bonding values. The results of this study show that, when selecting a lingual retainer in daily clinical practice, not only must the patient’s compliance and dependability be considered but also the mechanical properties and composition of different combinations of composites and wires.18
In the present study wire deformation that occurred on debonding in different groups. It was seen that the mean deformation was least in group 4 followed by group 3, group 1 and the highest deformation was recorded in group 2(mean=0.819mm).The difference in mean deformation (mm) was found to be statistically significant between group 1& Group 4 (P<0.01), Group 2 & 3 (P<0.05) as well as between Group 2 & Group 4 (P<0.01)
Lingual bonded retainer bonded with co axial shows more deformation as compared to braided retainer wire.
However co axial bonded with packable composite (group 1) showed a wire deformation which was similar to lingual bonded retainer fabricated with braided rectangular wire and packable composite (group 4). This may be attributed to packable composite which was used to bond in both groups.It is may still be recommended to use braided rectangular wire for fabricating lingual bonded retainer as it shows less deformation. Whenever co axial wire is used, it may be better to use along with packable composite as the deformation is comparatively lesser than the flowable composite. According to Cooke et al deformation of two multi-stranded wires bonded to the lingual enamel of lower incisor teeth shows similar mean degrees of deflection of 1.30 and 1.51 mm for the 0.0175 inch and 0.016 × 0.022 inch wires, respectively.13 According to Baysal et al greater deformations were seen in dead-soft wires and five stranded coaxial wires exhibited less deformation and concluded five-stranded coaxial wires are suggested for use in bonded lingual retainers.14
According to Lie Sam Foek et al, the results of in vitro studies can relate to in vivo conditions. This inability to mimic in vivo conditions can be considered as a limitation of the present study.15 Clinical studies may be needed to
assess the effect of saliva, physiologic movement of teeth, functional forces of tongue, and mastication as well as the presence of plaque and calculus.
In this study although there is no difference in mean bond strengths and ARI among the groups, Wire deformation, an important parameter to assess clinical outcome, showed variation among the groups. It can be recommended that braded rectangular wire bonded with flowable composite (Group 4) may be used as the wire of choice while bonding lingual bonded retainers as it showed maximum bond strength, less ARI and minimum deformation.
Conclusion
Mean force required to separate bonded wire was found to be higher in was Braided wire bonded with flowable composite followed by was Braided wire bonded with packed composite, co axial wire bonded with flowable composite and coaxial wire bonded with packable composite respectively.
Higher mean deformation (max deformation) was recorded in co axial wire bonded with flowable composite followed by coaxial wire bonded with packable composite, Braided wire bonded with packable composite and was Braided wire bonded with flowable composite respectively. The difference in mean deformation among the groups was found to be statistically significant (P<0.001).
The ARI score is important because it is an important factor to be considered in the selection of orthodontic adhesive. Studies have debated whether the differences in ARI scores reflect a difference in bond strength between the enamel and the adhesive for the different adhesive systems, but adhesive systems that show less adhesive remnant on the tooth has been advocated for easier and safer removal of residual resin after debonding. In this study ARI scores was not statistically significant among all the 4 group which states that lingual retainer when used with flowable or packable have similar ARI scores, which suggests that we can select adhesive according to clinical preferences.
Results of present study recommended to use braided rectangular wire for fabricating lingual bonded retainer as it shows less deformation. Whenever co axial wire is used, it is better to use along with packable composite as the deformation is comparatively lesser than the flowable composite.
In this study although there is no difference in mean bond strengths and ARI among the groups; wire deformation, an important parameter to assess clinical outcome, showed variation among the groups. It can be recommended that braided rectangular wire bonded with flowable composite (Group 4) may be used as the wire of choice while bonding lingual bonded retainers as it showed maximum bond strength, less ARI and minimum deformation.
References
[1]. Proffit WR. Contemporary orthodontics. 5th ed. St. Louis, Mo.: Elsevier/Mosby; 2013:754.
[2]. Case CS. Principles of retention in orthodontia. 1920. Am J OrthodDentofacialOrthop. 2003;124(4):352-361.
[3]. Knierim RW. Invisible lower cuspid to cuspid retainer. Angle Orthod. 1973;43(2):218-220.
[4]. Hegde N, Reddy GY. Bonded retainers in Orthodontics: A review.InternationalJourn Of Dental Clinics.
[5]. Littlewood SJ, Millett DT, Doubleday B, Bearn DR, Worthington HV. Orthodontic retention: A systematic review.JOrthod. 2006;33(3):205-212.
[6]. Lundstrom AF. Malocclusion of the teeth regarded as a problem in connection with the apical base.
International Journal of Orthodontia, Oral Surgery and Radiography.
[7]. Salzmann JA. Factors in successful orthodontic therapy before and after using appliances. Am J Orthod. 1963 [8]. Moyers EM. Force systems and tissue responses to forces in orthodontics and facial orthopedics (Chapter 13) In Moyers EM. Hand Book of Orthodontics Year Book Medical Publishers. 1988:309-11.
[9]. Graber TM, Vanarsdall RL. Orthodontics: current principles and techniques. CV Mosby; 1994.
[10]. Reicheneder C, Hofrichter B, Faltermeier A, Proff P, Lippold C, Kirschneck C. Shear bond strength of different retainer wires and bonding adhesives in consideration of the pre-treatment process. Head Face Med. 2014;
10:51.
[11]. Reynolds IR. A review of direct orthodontic bonding. British journal of orthodontics. 1975 Jul 1;2(3):171-8.
[12]. Waters NE. Some mechanical and physical properties of teeth. The mechanical properties of biological materials. SympSocExpBiol 1980:99-134.
[15]. Lie Sam Foek DJ, Ozcan M, Verkerke GJ, Sandham A, Dijkstra PU. Survival of flexible, braided, bonded stainless steel lingual retainers: a historic cohort study. Eur J Orthod 2008;30:199-204.
[16]. Aldrees AM, Al-Mutairi TK, Hakami ZW, Al-Malki MM. Bonded orthodontic retainers: a comparison of initial bond strength of different wire-and-composite combinations .J OrofacOrthop.. 2010;71(4):290-9.
[17]. Artun J, Bergland S. Clinical trials with crystal growth conditioning as an alternative to acid-etch enamel pretreatment. Am J Orthod. 1984 ;85(4):333-40.
[18]. Paolone MG, Kaitsas R, Obach P, Kaitsas V, Benedicenti S, Sorrenti E, Barberi F. Tensile test and interface retention forces between wires and composites in lingual fixed retainers. IntOrthod. 2015;13(2):2
