Construction of an In Vivo Debonding Device and Comparison of Bracket Failure Rate and Debonding Force for Indirect Orthodontic Bonding

BACKGROUND

Bracket bonding is an integral part of fixed orthodontic treatment. The correct position of the brackets bonded to teeth determines the prognosis of the treatment. Orthodontic bonding can either be direct or indirect.¹

In 1972, Silverman and Cohen introduced indirect orthodontic bonding,² in which brackets were positioned and stuck on a diagnostic cast and a transfer tray was constructed over it in the laboratory. Teeth were etched, rinsed, dried, bonding agent was applied and light-cured, composite was placed on the brackets, then transfer tray with the brackets was placed onto the dentition and light-cured, clinically.

Techniques developed over the years for indirect bonding include sugar daddy technique that was introduced by Swartz in 1974, in which he used caramel candy, a water-soluble material, as the adhesive for placement of brackets onto the model.³ Moin and Dogon introduced a technique in which brackets were positioned on the model using drops of sticky wax. Impressions were recorded using polyether material, and this tray was separated while the brackets remained attached to the cast. The brackets were then retrieved from the cast, heated to remove residual wax, which is then embedded into the impression.⁴ Thomas proposed a technique in which the brackets were bonded directly onto the cast with composite resin and a thermoplastic sheet was adapted over it using a vacuum former.⁵ Transparent material was used to fabricate transfer trays by Read and O’Brien⁶ and Read and Pearson⁷ so that light-cure resin could be used instead of self-cure resin. A “dual-tray” transfer system with chemically cured composite was developed by Hickham in 1993.⁸ Cooper and Sorenson⁹ in 1993 and Kalange¹⁰ and Sondhi¹¹ in 1999 developed the adhesive precoated brackets (APC) which made the placement of brackets easy and reduced chair time significantly. Sinha et al. used the thermally cured, fluoride-releasing indirect bonding system in which the mixed sealants contained hydrogen fluoride. Moskowitz et al. modified the technique of Thomas and advocated the use of a thermal-cured adhesive system and reprosil vinyl polysiloxane impression material.¹² Kasrovi et al. in 1997 used light-cure composite for indirect bonding. He used opaque transfer trays which provided direct access and visualization to the brackets during laboratory as well as clinical procedures.¹³ Tacky Glue was used by White in 1999, to place brackets on the cast. He used hot glue to make the matrix around the brackets.¹⁴ Vashi and Vashi used thermoplastic glue as advocated by White in 1999 and thermoplastic impression compound was used along with thermoplastic glue to increase the rigidity of transfer trays. This indirect bonding technique was economical and also required less laboratory time.¹⁵ Bhardwaj et al. used a double-sided sticky tape to place brackets on the working cast and then used a soft transfer tray made up of vacuum-formed thermoplastic material.¹⁶ Madhusudhan et al. used micropore adhesive tape along with cyanoacrylate glue to attach the brackets to the working model and gelatin jigs were prepared over brackets for additional retention. A 2 mm thick bioplast was used to fabricate transfer trays.¹⁷

Incorrect appliance placement leads to a compromised orthodontic treatment, which occurs in the majority of patients. A minimal number of errors in bracket placement are the prime advantage of indirect bonding.¹⁰ The additional advantages include reduced chairside time, enhanced comfort for the patient, and the clinician.

Incomplete curing of the composite due to partial light penetration through the transfer tray¹⁸ is one of the major limitations of indirect bonding. Other drawbacks include additional laboratory time,¹⁹ the need for an additional set of impression, and technique sensitivity.³

After searching the literature databases (Google, PubMed, and EBSCO) till date February 12, 2019, there was no in-vivo study conducted on the comparative evaluation of dual-cure composite and light-cure composite in indirect bonding of orthodontic brackets. Hence an attempt was made to assess bracket failure rate and clinical bond strength using dual-cure composite and light-cure composite for indirect orthodontic bonding.

The null hypothesis that was devised stated that there was no difference in bracket failure rate and clinical bond strength between dual-cure composite and light-cure composite in indirect orthodontic bonding. The aim and objectives of this study were to evaluate and compare bracket failure rate and clinical bond strength between dual-cure composite and light-cure composite for indirect orthodontic bonding of brackets.

MATERIALS AND METHODS

The study was started after obtaining ethical approval from the Sumandeep Vidyapeeth Institutional Ethics Committee (SVIEC/ON/Dent/BNPG19/D20003). Sample size estimation was done using G Power Software and the estimated sample size was found to be 42. The effect size and power of the study were set at 0.80 with an alpha error of 0.05. The level of significance was also set at 5% and a p-value of ≤0.05 was considered to be significant. Considering 20% dropout during follow-up suggested an increase of 8.4 participants. Hence, a total of 51 participants were included in the study.

OBSERVATIONS AND RESULTS

The present study was carried out to evaluate and compare bracket failure rate and clinical bond strength using light-cure composite and dual-cure composite for indirect orthodontic bonding. The results are based on an analysis of 51 patients subjected for evaluation and comparison of the bracket failure rate and bond strength in split-mouth design.

Figure 6 shows the demographic characteristics of study participants. A major proportion of the study participants were females (58.8%). The mean age of the male and female participants was found to be 21.0476 ± 3.38 and 20.9667 ± 2.41 years, respectively.

Table 1 shows the bracket failure rates in the maxillary and mandibular arch. A comparative evaluation revealed no significant differences in failures rates between the two composites for both maxillary (p-value 0.350) and mandibular (p-value 0.828) arch. Insignificantly, higher bracket failure was seen in the dual-cure composite for both the arches, and higher overall bracket failure was seen in the mandibular arch. Table 2 shows the evaluation of bracket failure by adhesive and tooth type in maxillary and mandibular arches with more bracket failure rate in the dual-cure group, central incisor bracket showing maximum bracket failure rate (8), followed by second premolar (6) for the maxillary arch. In the light-cure group, maximum bracket failure was seen with the second premolar bracket (7). No bracket failure was seen in canine brackets in the dual-cure group and with canine and first premolar brackets in the light-cure group.

For the mandibular arch, it was observed that maximum bracket failure was observed in the dual-cure group, the second premolar bracket being the most common to fail (17), followed by central incisor (10) and first premolar (4). In the light-cure group also, the second premolar showed maximum bracket failure (11).

Table 2 shows the evaluation of bracket failure by adhesive and tooth types. A comparative evaluation revealed no failures in canine and first premolar by light-cure composite and in canines by dual-cure composite in the maxillary arch. Maximum failure was reported in the second premolar for both the composites in the mandibular arch.

Table 3 shows the evaluation of the ARI scores among the two groups. A comparative evaluation revealed no significant difference (p-value 0.795) between the two groups. Although insignificantly, a greater proportion of score 2 (60%) was seen with light-cure composite. Similarly, score 2 (55.55%) was highest with the dual-cure composite.

Figure 7 shows the reasons for bracket failure among the two groups. A comparative evaluation of the reasons for bracket failure among the two groups revealed no significant difference between the two groups (p-value 0.993). Eating/chewing and biting were the reasons for bracket failure reported in major proportion in both the groups; biting is the most common reason in dual-cure composite (19) and light-cure composite (11) followed by chewing (18 in dual-cure composite and 10 in light-cure composite) Flowchart 1.

Table 4 shows the comparative evaluation of the debonding force among the two groups which revealed no significant difference in debonding force between dual-cure composite and light-cure composite (p-value 0.722).

Table 5 shows the tooth-wise evaluation and comparison of debonding force among the two groups. A comparative evaluation revealed no significant difference in debonding force between the two groups for any tooth. The highest clinical bond strength in the dual-cure group was seen for the mandibular canine bracket (8.09 + 1.36 N) and the lowest for maxillary second premolar (7.03 + 1.24 N). Whereas, in the light-cure group, the highest clinical bond strength was seen for the maxillary canine bracket (7.98 + 1.25 N) and lowest for the mandibular second premolar (7.04 + 1.22 N).

DISCUSSION

Indirect bonding is the process of positioning the brackets on a cast outside the mouth, fabricating a transfer tray over it, and then bonding those brackets on the teeth through this transfer tray which is convenient for both patient and the clinician.

Various authors have introduced different adhesive systems to bond brackets to teeth and a variety of materials to fabricate the transfer tray for the same. The “Gum and Gun” method was introduced by Aileni et al.²⁰ to stick brackets to the casts using Erkogum and glue to fabricate a customized transfer tray over the casts. The Erkogum, glue, and glue gun are readily available in the market and economical. Additionally, the weaker strength of Erkogum provided optimal strength for the bracket to stick to the cast, but also facilitate easy removal of transfer tray and brackets from the cast. The flexibility of the glue transfer tray provided the ease of removal of the tray from the oral cavity without causing any bracket failure. The authors of this technique claimed the requirement of attention in detailing but reduced the complexity of the indirect bonding procedure. Hence this technique of bonding was selected in our study.

Customarily, orthodontists used single or double paste chemically cured systems for indirect orthodontic bonding. These resins provided adequate strength to withstand orthodontic forces but provided the clinician with limited working time, due to which the clinician had to quickly position the bracket in the desired position and wait for it to set for any further process to be carried out. The introduction of resins that are cured by visible light and ultraviolet light has helped the clinicians overcome this problem by allowing them to control the setting time as per their requirements. The major drawback with light-cured resin for orthodontic bonding was incomplete curing of metal brackets due to improper light penetration, resulting in partial curing of the composite under the bracket base. Also, light penetration through transfer trays decreased when the indirect method for orthodontic bonding is used. This situation demanded a type of resin that would use the feature of light cure to initiate the process of curing and continue to set chemically after the initiation of photocuring. This property of material was observed in the dual-cure composite. Li et al.²¹ and Smith et al. conducted an in vitro study on dual-cure composite and suggested that shear bond strengths were adequate to withstand normal orthodontic forces, increased control of the setting time, and complete polymerization with its dual property facilitate its use in orthodontics.

Adhesive remnant index is one of the most common and reliable methods used to evaluate adhesive left on the tooth surface in orthodontics.²² Hence ARI was used to appraise the amount of adhesive remaining on the tooth surface.

No in vivo study was observed in the pretext of evaluation of dual-cure composite resins for orthodontic bonding. Hence, an in vivo study was conducted to evaluate and compare conventional light-cure and dual-cure resin considering its bracket failure rate and clinical bond strength. To compare both materials in the oral cavity, a uniform environment was required; hence, a split-mouth design was implemented in the study, which also allowed participants to become their own controls. Elimination of the selection bias, balancing the groups concerning many known, and unknown confounding variables were taken care of by the randomization process. Microsoft Excel had the advantages of ease of operation and wide acceptance; therefore, this method was employed in this study. This also provided equal inclusion of adhesive systems for each quadrant.

In the present study, 51 participants (21 males and 30 females) were included to compare both adhesive systems. Group I was allocated to dual-cure composite resin and light-cure composite resin was allocated to group II.

Orthodontic treatment is a long-term treatment that requires the brackets to stay in the oral cavity for a minimum of 12–15 months during which the brackets are exposed to orthodontic and masticatory forces. Bond strength plays a vital role to overcome these forces. However, the bond strength should not be so high that it damages the teeth during its removal; therefore, orthodontists strive to achieve optimal bond strength. Since no in vivo study was conducted to evaluate the dual-cure bond strength, an attempt was made to appraise it.

When the literature was appraised, intraoral bond strength was evaluated either with a customized force gauge or a force-sensing resistor. It was observed that the force-sensing resistor evaluated the bond strength in an indirect method wherein the amount of force exerted by the operator on the handles of the devices significantly affected the results. Hence the bond strength was evaluated with the customized force gauge which could measure the force in Newton from 0.01 to 50 N. Pressure measured in megapascal signifies the amount of force applied per unit area. Pressure measured in MPa denotes the average stress that debonds the bracket but not the average force, whereas Katona²³ advocated that average force in Newton is a better indicator to determine the bond strength of the bracket through a finite element approach. Therefore, the customized force gauge was selected to measure the bond strength of brackets in this study.

When the gender was appraised in the study, majority of the patients were observed to be females. The average age of males and females did not differ much (Fig. 6).

The bracket failure was evaluated for maxillary and mandibular arch, light-cure and dual-cure resin individually, and tooth type. Bracket failure was observed in maxillary and mandibular arches. On average, the mandibular arch had higher overall bracket failure in comparison to the maxillary arch. When bracket failure was appraised for both the adhesive system, the dual-cure resin had a higher bracket failure rate in both maxillary and mandibular arches; (Table 1) these results are similar to a study by Linklater and Gordon,²⁴ and Khan et al.²⁵ for conventional light-cure adhesive. However, no literature was observed that compared the bracket failure between dual-cure and conventional light-cure composite systems in an in vivo setting.

The only maxillary canine did not show any bracket failure in both the adhesive system and maxillary first premolar did not show any bracket failure in the conventional light-cure adhesive. Maximum overall bracket failure was observed with mandibular second premolar bracket, followed by mandibular central incisor, maxillary central incisor, and maxillary second premolar brackets. Dual-cure resin showed more bracket failure in each of these when compared with their light-cure counterpart (Table 2). This observation was concordant with the observations made by Linklater and Gordon²⁴ for the conventional light-cure adhesive system.

The reasons for the failure of brackets were also evaluated. Reasons like eating/chewing, biting, brushing, external trauma, and lack of isolation were prevalent for the participants included in the study. Maximum bracket failure was observed due to eating/chewing, followed by biting and brushing in both dual-cure and light-cure resin groups. A study by Khan et al.²⁵ concluded that bracket failure was maximum in cases with an increased overbite, which results in interferences in the mandibular brackets while eating/chewing and biting (Fig. 7).

Our study also shows that the ARI score of 2 and 3 is predominant among both the adhesive systems (Table 3). The observation of this study correlated to the observations made by Ahmed et al.²⁶ for conventional light-cure adhesive.

The debonding forces recorded in our study were similar to those recorded by them ranging from 5.5 to 9.5 N, the average being 7.60 N for dual-cure resin, and 7.57 N for light-cure resin (Table 4) which correlates to the observations made by Pickett et al.²⁷ Highest clinical bond strength in the dual-cure group was seen for the mandibular canine bracket (8.09 + 1.36 N) and lowest for maxillary second premolar (7.03 + 1.24 N). The highest bracket failure in this group was seen with mandibular second premolar and the lowest bracket failure was seen with maxillary canine bracket. Whereas in the light-cure group, the highest clinical bond strength was seen for the maxillary canine bracket (7.98 + 1.25 N) and lowest for mandibular second premolar (7.04 + 1.22 N). Maxillary canine brackets in the light-cure group showed the lowest bracket failure and highest bond strength, and mandibular second premolar brackets in the same group showed the highest bracket failure and lowest bond strength which indicates that a high bond strength aids in a low bracket failure rate. Bond strength and bracket failure showed a mutual relationship in conventional light-cure adhesive. No such mutual relationship was observed in the dual-cure resin adhesive, probable cause for such an observation could be attributed to the decreased working time of dual-cure resin adhesive and lack of isolation. Hence, to achieve a minimal bracket failure, factors like bond strength, isolation, amount of masticatory forces, and type of malocclusion have a predominant influence (Table 5).

Some of the limitations in this study included decreased working time of dual-cure composite, problems maintaining isolation when transfer tray had to be inserted in the mouth, and dislodging the transfer tray that sometimes got stuck in undercuts.

Further studies are required with a higher sample size to establish and verify a mutual relationship between bond strength and bracket failure for dual-cure composite adhesive and technological advances in the indirect bonding procedures.

CONCLUSION

This study evaluated the bracket failure rate and clinical bond strength when dual-cure and light-cure composite resins are used in the indirect orthodontic bonding technique. The following conclusions can be drawn:

The study brought to light that Gum and Gun is an easy and feasible method to carry out indirect bonding procedure. Bracket failure in mandibular arch is more than maxillary arch in both the groups. Bracket failure rate of brackets bonded with dual-cure composite is more than those bonded using light-cure composite, especially in the mandibular second premolar. Most common reason for bracket failure was chewing and biting, which suggests that bracket failure occurred due to undue masticatory forces. Even though dual-cure composite showed higher bracket failure, it is statistically and clinically insignificant. Most common ARI score was 2, followed by 3, which interprets to minimal damage to the enamel of teeth. Average clinical bond strength of the dual-cure composite is slightly more than that of the light-cure composite but it is not statistically significant.

REFERENCES

1. Silverman E, Cohen M, Gianelly AA, et al. A universal direct bonding system for both metal and plastic brackets. Am J Orthod 1972;62(3):236–244. DOI: 10.1016/s0002-9416(72)90264-3.

2. Silverman E, Cohen M. A report on a major improvement in the indirect bonding technique. J Clin Orthod 1975;9:270–276. PMID: 1097465.

3. Swartz M. About orthodontic bonding, an interview with Dr. Michael Swartz. Ortho Cyber J 2003. DOI: 10.31021/jnn.20181120.

4. Moin K, Dogon IL. Indirect bonding of orthodontic attachments. Am J Orthod 1977;72:261–275. DOI: 10.1016/0002-9416(77)90212-3.

5. Thomas RG. Indirect bonding: simplicity in action. J Clin Orthod 1979;13(2):93–106. PMID: 397232.

6. Read MJ, O’Brien KD. A clinical trial of an indirect bonding technique with a visible light-cured adhesive. Am J Orthod Dentofacial Orthop 1990;98(3):259–262. DOI: 10.1016/S0889-5406(05)81603-8.

7. Read MJF, Pearson AL. A method for light-cured indirect bonding. J Clin Orthod 1998;32(8):502–503.

8. Hickham JH. Predictable indirect bonding. J Clin Orthod 1993;27(4):215–218. PMID: 8360338.

9. Cooper RB, Sorenson NA. Indirect bonding with adhesive precoated brackets. J Clin Orthod 1993;27(3):164–167. PMID: 8496356.

10. Kalange JT. Ideal appliance placement with APC brackets and indirect bonding. J Clin Orthod 1999;33(9):516–526. PMID: 10895657.

11. Sondhi A. Efficient and effective indirect bonding. Am J Orthod Dentofacial Orthop 1999;115(4):352–359. DOI: 10.1016/s0889-5406(99)70252-0.

12. Moskowitz EM, Knight LD, Sheridan JJ, et al. A new look at indirect bonding. J Clin Orthod 1996;30(5):277–281. PMID: 10356506.

13. Kasrovi PM, Timmins S, Shen A. A new approach to indirect bonding using light-cure composite. Am J Orthod Dentofacial Orthop 1997;111(6):652–656. DOI: 10.1016/s0889-5406(97)70319-6.

14. White LW. A new and improved indirect bonding technique. J Clin Orthod 1999;33(1):17–23. PMID: 10535005.

15. Vashi N, Vashi B. An improved indirect bonding tray and technique. J Indian Orthod Soc 2008;42:19–23. DOI: 10.1177/0974909820080105.

16. Bhardwaj A, Belludi A, Gupta A, et al. Indirect bonding technique–a simplified novel technique. J Asian Pacific Orthod Soc 2011;2(3):1. DOI: 10.4103/2321-1407.118172.

17. Madhusudhan S, Laxmikanth SM, Shetty PC. A newly simplified indirect bonding technique. Indian J Dent Sci 2012;4(4):81–83.

18. Smith RT, Shivapuja PK. The evaluation of dual cement resins in orthodontic bonding. Am J Orthod Dentofacial Orthop 1993;103(5):448–451. DOI: 10.1016/S0889-5406(05)81795-0.

19. Aksakalli S, Demir A. Indirect bonding: a literature review. Eur J General Dent 2012;1(1):6. DOI: 10.5152/turkjorthod.2016.16023.

20. Aileni KR, Rachala MR, Mallikarjun V, et al. Gum and gun: a new indirect bonding technique. J Indian Orthod Soc 2012;46(4_suppl1):287–291. DOI: 10.5005/jp-journals-10021-1107.

21. Li J, Shibuya I, Teshima I, et al. Development of dual-curing type experimental composite resin cement for orthodontic bonding–effect of additional amount of accelerators on the mechanical properties. Dent Mater J 2009;28(4):401–408. DOI: 10.4012/dmj.28.401.

22. Montasser MA, Drummond JL. Reliability of the adhesive remnant index score system with different magnifications. Angle Orthod 2009;79(4):773–776. DOI: 10.2319/080108-398.1.

23. Katona TR. A comparison of the stresses developed in tension, shear peel, and torsion strength testing of direct bonded orthodontic brackets. Am J Orthod Dentofacial Orthop 1997;112(3):244–251. DOI: 10.1016/s0889-5406(97)70251-8.

24. Linklater RA, Gordon PH. Bond failure patterns in vivo. Am J Orthod Dentofacial Orthop 2003;123(5):534–539. DOI: 10.1067/mod.2003.s0889540602000252.

25. Khan H, Mheissen S, Iqbal A, et al. Bracket failure in orthodontic patients: the incidence and the influence of different factors. BioMed Res Int 2022;2022. DOI: 10.1155/2022/5128870.

26. Ahmed T, Rahman NA, Alam MK. Comparison of orthodontic bracket debonding force and bracket failure pattern on different teeth in vivo by a prototype debonding device. BioMed Res Int 2021;2021. DOI: 10.1155/2021/6663683.

27. Pickett KL, Lionel Sadowsky P, Jacobson A, et al. Orthodontic in vivo bond strength: comparison with in vitro results. Angle Orthod 2001;71(2):141–148. DOI: 10.1043/0003-3219(2001)071%3C0141:oivbsc%3E2.0.co;2.