Does microetching enamel reduce bracket failure when indirect bonding mandibular posterior teeth? Peter G. Miles Private practice, Caloundra, Queensland, Australia
Aim: To determine if microetching the mandibular premolars and first molars prior to acid-etching reduced bracket failures during the first six months of orthodontic treatment. Methods: Sixty four patients with 384 mandibular first molar and premolar brackets were used in a split-mouth study design. In each patient the teeth on one side were acid-etched and the contralateral teeth were microetched prior to acid-etching. The microetched side was alternated in successive patients. The brackets were indirect bonded to the teeth on both sides. First time bracket failures were recorded over a 6-month period. Results: Two brackets (1 per cent) came loose on the microetched enamel side and four brackets (2.1 per cent) failed on the conventionally acid-etched side. This difference was not clinically or statistically significant (p = 0.41). Conclusion: The addition of microetching prior to acid-etching does not result in fewer bracket failures during the first six months of treatment. (Aust Orthod J 2008; 24: 1–4) Received for publication: February 2008 Accepted: March 2008
Introduction Treatment efficiency in orthodontics relies on accurate bracket positioning and effective bonding of brackets to the enamel. The advent of direct bonding of orthodontic attachments to the etched enamel surface was a major advance in orthodontic treatment.1 Bracket debonding during treatment is inconvenient and costly to both the orthodontist and the patient. Bracket failure rates vary between studies and between different regions of the mouth with failures more common on the posterior teeth. Bracket failure rates are higher on the second premolars than the anterior teeth, and even higher rates have been reported on the molars.2,3 Pandis et al.4 reported a total failure rate for the posterior teeth of 14.8 per cent, with first and second molars failing 9.7 per cent and 20 per cent of the time respectively. They also reported that mandibular molars had a higher bracket failure rate (21 per cent) than maxillary molars (7.5 per cent). Similar bracket failure rates have been reported by others with more failures occurring on the mandibular molars than the maxillary molars.5,6 © Australian Society of Orthodontists Inc. 2008
Various theories have been proposed for the differences in bracket failure rates. Brackets on posterior teeth may fail if the bases are not evenly adapted to the tooth surfaces, resulting in uneven composite thicknesses.7 Furthermore, etched surfaces on posterior teeth are more prone to contamination with salivary proteins and moisture.8,9 The mandibular molars are also subjected to higher masticatory loads than the maxillary molars.6 Prismless enamel is more common and occurs to a greater depth on the posterior teeth: this might reduce the effectiveness of acid-etching resulting in reduced resin penetration and a weaker bond.10,11 Finally, the extent and definition of an etch decreases toward the distal end of each arch, particularly on the mandibular molars. Enamel can also be prepared for bonding by airabrading or microetching the surface. However, acidetched enamel surfaces have been found to result in higher bond strengths than air-abraded enamel surfaces.12–14 Although the bond strength was not affected by the abrasion particle size it was affected by the distance between air abrasion nozzle and the Australian Orthodontic Journal Volume 24 No. 1 May 2008
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enamel surface: greater distances resulted in lower bond strengths. Microetching alone is unsuitable for routine enamel conditioning, but if used prior to acid-etching it may result in higher bond strengths. At present there are no published reports of clinical studies evaluating the effect of microetching prior to acid-etching on bracket failure rates.
etched for 30 seconds, rinsed, dried for 10 seconds each and a moisture insensitive primer applied (MIP, 3M/Unitek, Monrovia, California). A small amount of Filtek Flow material (3M/Unitek, Monrovia, California) was applied to the gingival edges of the bracket bases and the tray seated on the teeth and light cured.15
The purpose of this investigation was to determine if microetching the mandibular premolars and first molars prior to acid-etching reduced bracket failures during the first six months of orthodontic treatment.
A 0.014 inch thermally active NiTi wire (G&H, Greenwood, USA) was then placed. The same instructions regarding care and diet were given to all patients. The normal archwire sequence used was: after 10 weeks a 0.018 x 0.018 inch thermally active NiTi wire (G&H, Greenwood, USA) was placed and after an additional 10 weeks a 0.016 x 0.022 inch stainless steel wire (G&H, Greenwood, USA) was used. Composite resin bite wedges were used when required to disclude the mandibular brackets during initial alignment and overjet correction. At each visit any loose brackets were recorded, but only the first time failures were included in the analysis. The study ran for six months from the time the brackets were placed. For the analysis, the data were paired from contralateral quadrants in each patient. As the data were not normally distributed the Wilcoxon signed ranks test was used.
Materials and methods This prospective clinical trial was performed in the author’s private practice, and informed consent was obtained from all patients. One hundred and six subjects were prospectively selected from the author’s orthodontic practice. Forty patients failed to meet the selection criteria: 20 patients had restorations on the teeth to be bonded; 14 patients had missing or extracted lower premolars or first molars; three patients had severe rotations or unerupted teeth; and three patients had the indirect bonding trays sectioned in the laboratory. Of the 66 patients in the trial, two transferred during the study leaving a final sample of 64 patients (44 females, 20 males) with a median age of 13.7 years, range 11.0–43.1 years. Each patient was consecutively assigned to one of two alternating groups. In Group 1 the right mandibular first molar, first and second premolars were microetched, acid-etched and indirect bonded as previously described (experimental side).15 The corresponding teeth on the contralateral side were acidetched and indirect bonded (control side). In Group 2 the left side was the experimental side and the right side the control side. The teeth were not pumiced, but if plaque was visible they were brushed and rinsed thoroughly. Three hundred and eighty four brackets were bonded with 192 brackets on each side. The mandibular teeth (first molar and both premolars) on the experimental side were microetched for approximately two seconds per tooth with 110 µm aluminium oxide particles (Korox 110, BEGO, Bremen, Germany) using a microetcher (Danville Engineering, San Ramon, USA). The corresponding teeth on the control side were not microetched. The teeth on both sides were isolated with a dry field system saliva evacuator/retraction device (NOLA Specialties, Inc., New Orleans, Louisiana, USA) and 2
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Results A total of six brackets was dislodged giving an overall bracket failure rate of 1.6 per cent. The bracket failures were evenly distributed over the study with the earliest breakage occurring two weeks after bonding and the last breakage occurring at six months. Considering the low number of bracket failures survival curves were not plotted. Of the brackets placed on the microetched (experimental) side, two molar brackets were dislodged (1.0 per cent failure rate) while four brackets (three molar, one second premolar) were dislodged on the conventionally bonded (control) side (2.1 per cent failure rate). The difference between the experimental and control sides was not statistically significant (p = 0.41), and was not considered to be clinically significant.
Discussion The overall bracket failure rate of 1.6 per cent over six months is in agreement with similar studies on indirect bonding failure rates reported by the author.15,16 However, this failure rate is noticeably less than the rates reported in other studies of indirect
DOES MICROETCHING ENAMEL REDUCE BRACKET FAILURE?
bonding. For example, Aguirre and coworkers reported a failure rate of 4.5 per cent over three months,17 and others have reported failure rates between 6.5 and 13.9 per cent over six months.18,19 In the present study the difference in the bracket failure rates between conventional etching (2.1 per cent) and microetching prior to acid-etching (1 per cent) was not statistically or clinically significant. However, if the failure rates had been higher or had the patients been followed for a longer period of time microetching may have had a significant impact on the findings. Pandis et al. reported an overall failure rate of 14.8 per cent over 26 months on the posterior mandibular teeth when a self-etching primer was used, and a lesser failure rate of 8 per cent when all teeth were sandblasted prior to etching, but the observation period was shorter in the more recent study: 15 months versus 26 months.4,20 It is impossible to say which factor was more influential: microetching or time. Others have reported also that the bracket failure rate increased over time: 3.0, 5.3 and 14.8 per cent at 1, 6 and 12-months respectively.21 The clinical technique and adhesives used may have contributed to the different results. In the present study composite resin bite wedges or ramps were used to protect the brackets during initial alignment and overjet correction. This precaution may have improved the overall bracket success rate as compared with other studies. It is not clear if other investigators used these or similar aids to avoid occlusal loads on the brackets. Of the six brackets that debonded during the study, four were lower right first molars, one was a lower right second premolar, and the other a lower left first molar. This pattern of more breakages on the right side is in agreement with Pandis et al.,4 who reported that mandibular right side first molar tubes were almost three times more likely to fail than left side tubes. This failure pattern is possibly due to the right side being the preferred chewing side, better operator access and visualisation during bonding on the patient’s left side, or because adhesive curing was commenced on the left side (as in this study). Pandis et al. also noted that mandibular tubes on first molars were twice as likely as maxillary tubes to fail. In their later study Pandis and coworkers microetched every tooth for 3-seconds prior to conditioning and reported a failure rate on lower first
molars of 6 per cent over the 15 month observation period (Range: 12–18 months).20 In the present study five first molar brackets failed giving a 3.9 per cent lower first molar bracket failure rate over six months, which is comparable to the failure rate reported by Pandis et al.20 Finally, the findings of the present study are supported by a recent split-mouth study of bonding orthodontic attachments to severely fluorosed enamel, which reported that there was no advantage in microetching when using an adhesion promoter.22 One difficulty in comparing bonding studies is the lack of uniformity in the observation period. It would, therefore, be useful if investigators used the same time frame or related bracket failures to the length of treatment.
Conclusions 1. The additional procedure of microetching prior to acid-etching lower posterior teeth did not significantly improve bracket failure rates in the first six months of treatment. 2. Further research is required to determine if microetching prior to acid-etching reduces the bracket failure rates over longer periods of time and on the first and second molars.
Corresponding author Dr Peter Miles 10 Mayes Avenue Caloundra Qld 4551 Tel: (+61 7) 5491 9077 Fax: (+61 7) 5491 9477 Email:
[email protected]
References 1. 2.
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16. Miles PG. A comparison of retention rates of brackets with thermally-cured and light-cured custom bases in indirect bonding procedures. Aust Orthod J 2000;16:115–17. 17 Aguirre MJ, King GJ, Waldron JM. Assessment of bracket placement and bond strength when comparing direct bonding to indirect bonding techniques. Am J Orthod 1982;82: 269–76. 18. 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;98:259–62. 19. Zachrisson BU, Brobakken BO. Clinical comparison of direct versus indirect bonding with different bracket types and adhesives. Am J Orthod 1978;74:62–78. 20. Pandis N, Polychronopoulou A, Eliades T. A comparative assessment of the failure rate of molar tubes bonded with a self-etching primer and conventional acid-etching. World J Orthod 2006;7:41–4. 21. House K, Ireland AJ, Sherriff M. An investigation into the use of a single component self-etching primer adhesive system for orthodontic bonding: a randomized controlled clinical trial. J Orthod 2006;33:38–44. 22. Noble J, Karaiskos NE, Wiltshire WA. In vivo bonding of orthodontic brackets to fluorosed enamel using an adhesion promotor. Angle Orthod. 2008;78:357–60.
