A clinical trial of an indirect bonding technique with a visible light-cured adhesive M. J. F. Read, BDS, FDS, D. Orth., and K. D. O'Brien, BDS, FDS, MSc, D. Orth.

Manchester, England A trial was carried out to evaluate the clinical performance of a visible light-cured adhesive when used with a foil mesh base in an indirect bonding technique. Thirty-seven patients entered the trial, and a total of 407 brackets were placed. The incidence and site of bond failure were recorded. The overall failure rate was 6.5%. There were no significant differences detected between the failure rates for either the upper or the lower arches or for the anterior and the posterior segments of the arches (p < 0.01). (AMJ ORTHOO DENTOFAC ORTHOP 1990;98:259-62.)

T h e bonding of orthodontic attachments to the etched enamel surface of teeth is a well-established clinical procedure. There are at present two techniques for the placement of orthodontic attachments. The first is called the direct technique in which the brackets are placed directly on the enamel surface by the operator, as was initially described by Newman) The second method of bracket placement is the indirect technique, which was first described by Silverman et al. 2 This is a two-stage procedure: the first stage is carded out in the laboratory, where the brackets are located and attached to a plaster model of the patient's teeth, and in the second stage the brackets in their positions are transferred by means of a tray to the patient's mouth, where they are attached to the etched enamel surface of the teeth. In an investigation that examined the preference of 2000 operators for either the direct or the indirect technique of bonding, Gorelicka found that the ratio of direct to indirect as the preferred method was 13:1. It has been suggested that, as the use of preadjusted and pretorqued appliances is increasing, greater emphasis is being placed on the importance of the exact positioning of brackets, and therefore the indirect technique may become more popular. 4 In a clinical trial s in which direct and indirect methods were compared, failure rates of 2% for the direct method and 13% for the indirect method were reported. It was suggested that, apart from this difference in failure rates, the indirect technique was inferior because of the increased time required for bracket placement. In addition, there was excess adhesive around the *Consultant Orthodontist. **Lecturer in Orthodontics/MRC Research Fellow. 8/I/14463

bracket bases, which was both difficult and time consuming to remove. The use of visible light-cured adhesives for direct bonding was first described in 1980. 6 In the clinical situation the adhesive material is cured by transilluruination through the tooth structure. 7 The results of laboratory investigations have suggested that the in vitro properties of light-cured adhesives are similar to those of chemically cured adhesives? The major advantage of the light-cured materials is the command set that gives the operator complete control of adhesive polymerization. In addition, it has been suggested that there is less residual material adherent to the enamel surface after removal of the attachment at the conclusion of treatment. 9 In recent clinical trials of light-cured and chemically cured adhesives, in which a direct technique was used, investigators found that the clinical properties of both kinds of adhesives were similar. Failure rates of 4.7% for the light-cured adhesives and 6.0% for the chemically cured materials were reported) ° It is suggested that visible light-cured materials with the property of command set and a consequently extended working time are ideal for use with an indirect technique. The aim of this investigation was to evaluate the clinical performance of an experimental visible lightcured adhesive when it was used in an indirect bonding technique.

MATERIALS AND METHODS The adhesive used in the trial was an experimental light-cured adhesive (Opalux, I.C.I. Dental, Macclesfield, U.K.) composed o f a urethan dimethacrylate resin that contained filler particles of an average size of 13 p.m; 50% of the particles were less than 2 i_tm in size, which result in a filler loading of 62.8% by volume 259

Am. J. Orthod.Dentofac. Orthop. September 1990

260 Read and O'Brien Table I. The position of brackets and site of failure

Upper arch Anterior Posterior Total

Lower arch Anterior Posterior Total Overall failure rates Anterior Posterior

196 98 294

13 6 19

6.6 6.1 6.4

66 37 103

5 2 7

7.5 5.4 6.7

262 135

18 8

6.8 5.9

Table II. Detailed breakdown of the site of bond failure

Position

[ lncisor

[

Canine

l

Premotar

Upper arch

10

3

6

Lower arch

0

5

2

(similar to Opulex). The catalyst system consisted of an ¢x-diketone and an amine, and polymerization occurred on exposure to a visible light source with a wavelength of 470 nm. The bracket base (Mini Mono, GAC International, Inc., Commack, N.Y.) was of a foil mesh design, and retention was provided by a mesh of stainless steel wire, 0.12 mm in diameter, woven to create openings of 0.20 mm 2. The method of indirect bonding used in this trial is similar to that first described by T h o m a s ) ~ in which the brackets are attached to the plaster model by the clinical bonding material. (This technique will be described in some detail.) The technique may be divided into two stages, the laboratory stage and the clinical stage, both of which are common to all indirect bonding procedures. LABORATORY PROCEDURE

A stone model was cast from an accurate impression of the patient's teeth. The time between the taking of the impression and the placement of the brackets was kept to a minimum. The bracket positions were marked on the model, and the contour of the bracket bases was checked against the tooth surface and was redone if necessary. The brackets were then attached to the stone model with the visible light-cured bonding material. Any excess material around the bracket was carefully removed.

When all the brackets had been placed, the material was cured with the visible light source (Coe-lite, Coe Dental, Chicago, I11.). The light was directed down the long axis of each tooth so that the center of the beam was directed at the composite material between the bracket and the model. This part of the procedure was carried out behind a protective shield (Premier Dental Products, Norristown, Penn.). Each bracket required an individual cure of 30 seconds' duration. Complete polymerization could then be confirmed by touching the material with a sharp probe at the farthest point away from the light source. A vacuum-formed transfer tray, made from a 2 mm thick soft, clear plastic sheet (Drusoft, Dreve, West Germany) was then molded over the brackets. The model was soaked in water for 15 minutes before removal of the tray. The tray was then trimmed to a horseshoe shape so that the border extended only to the gingival margin; this prevented any moisture on the gingivae from running under the close-fitting tray through capillary action. CLINICAL PROCEDURE

The teeth were dried, and the fit of the tray was checked. The teeth were thoroughly cleaned with pumice, the enamel surfaces were etched with 37% phosphoric acid for 60 seconds, and the teeth were then washed with copious amounts of water and dried with compressed air from an oil-free air supply. While the teeth were being etched, the composite on the bracket bases was cleaned and lightly abraded with a green alpine stone. The dried etched enamel surfaces and the composite on each bracket base were then painted with unfilled resin. This was carried out immediately before the tray was placed on the teeth because any delay at this stage would result in polymerization of the material, since it was exposed to visible light. The tray was placed in the mouth and firmly seated. The adhesive under each bracket was then exposed, through the clear plastic tray, to the visible light source for 10 seconds. The light source was directed down the long axis of each tooth. (During this procedure the operator wore a protective shield or glasses.) The tray was then peeled from the palatal or lirigual side to remove it from the teeth, and any flash of unfilled resin was also removed. As the adhesive material was fully polymerized, an arch wire could be immediately engaged in the brackets. All teeth were bonded except for molars, and all brackets were placed by one operator. Patients who were undergoing lingual orthodontic treatment were not included in the study. A record of incidence and time

Volume 98

Number3

Indirect bonding technique with a visible light-cured adhesive

of bracket failure for each patient was kept. Each patient was followed up until the completion of treatment. The study was carried out over a 30-month period. Statistical analysis was carried out with the ×2 test.

RESULTS Thirty-seven patients entered the study; the sample comprised 13 men and 24 women. Of the total sample 13 patients were fitted with mandibular and maxillary appliances, and in 24 patients were restricted to upper arch treatment alone. The length of treatment ranged from 4 to 28 months, with mean and median lengths of 12.94 months and 14 months, respectively. Thirteen patients (35%) had bond failures. Of the 407 brackets that were placed, 29 failed; and all failures occurred during the first 12 months of treatment. Thirteen per cent (4) of the failures occurred within the first month, and 94% (27) occurred within the first 6 months. Because there was considerable variation in the length of treatment, the investigators decided to examine the outcome of bracket success or failure after a fixed period of time. Only those patients whose treatment had extended to this time point would be included in any further analysis. For comparability with other investigations, 5'~° we decided to note the success or failure of each attachment at the 6°month time point. As a consequence, two patients who had completed treatment in less than 6 months were excluded from further data analysis. This resulted in a total of 26 bond failures at the 6-month cutoff point. The distribution of the various adhesive/base combinations and recorded bond failures after t.his 6-month period are shown in Tables I and II. The overall failure rate was 6.5%, and the failure rates for the upper and lower arches were 6.4% and 6.7%, respectively. For the anterior and posterior teeth in the upper arch, the failure rates were 6.6% and 6. 1%. Those for the lower arch were 7.5% and 5.4%, respectively. The overall failure rates for anterior and posterior teeth for both arches were 6.8% and 5.9%. Data analysis with the X2 test revealed the following: 1. No significant differences were detected between the failure rates of the attachments for both the upper and lower arches (p > 0.01). 2. Similarly, no significant differences were detected between the anterior and posterior failure rates when the data for both arches were analyzed either separately or in combination (p > 0.05).

DISCUSSION The overall failure rate recorded in this investigation is similar to that obtained in a previous trial in which

261

light-cured adhesive was used in a direct technique, l° However, in the previous investigation a higher posterior failure rate for posterior teeth was detected. One of the possible explanations for a high posterior failure rate is the increased difficulty of moisture isolation for the posterior segments of the dentition. It could be that the coverage afforded by the close-fitting transfer tray results in a degree of additional moisture isolation in the posterior segments. It is also interesting to note that the failure rate is considerably lower than that resulting from a clinical trial of an indirect method in which a chemically cured material is used. 5 It could be that this resulted because of differences in both the material and the technique used. In the technique used in this study the adhesive material was loaded onto the individual bracket bases, which were then pressed onto the tooth surface and cured in the laboratory. Because this procedure was carried out under ideal conditions, it resulted in a thin, well-adapted layer of adhesive material. Whereas in the method described earlier, the material was placed on the brackets in the transfer tray immediately before the tray was seated in the mouth. Consequently, any poor adaptation or uneven pressure application could result in an unequal thickness of adhesive material. This could also result in a decreased bond strength and thus in an increased failure rate. 12 When the differences in materials are appraised, the factor of most importance is the command set of the light-cured material. When a chemically cured material is used with either bonding technique, polymerization begins as soon as the two components of the material come into contact. This is of minor importance when the direct technique is used. However, with the indirect technique, it is inevitable that the material on the bracket bases that were loaded first will be at a more advanced state of polymerization than the material on the bases that were loaded at the end of the procedure. This uneven rate of polymerization could result in an increase in air inclusions. In addition, adaptation and penetration of the adhesive into the etched enamel will not be ideal. In contrast, when the light-cured material is used, the adhesive material does not begin rapid polymerization until it is exposed to the visible light source. This light is not applied until the transfer tray is fully seated. Therefore, it is possible that this results in optimum adaptation and penetration of the adhesive material to the etched enamel, resulting in a higher bond strength and a lower failure rate. There are some further advantages of the indirect technique when light-cured adhesive material is used, which may result in a reduction of clinical time. After exposure to the visible light source, the material is

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Am. J. Orthod. Dentofac. Orthop. September 1990

Read and O'Brien

completely polymerized, and the transfer tray can then be removed immediately. The aligning arch wire can be fully tied into the brackets. However, when chemically cured materials are used, it is necessary to delay tray removal and arch wire engagement until the adhesive material has set. Again, because all o f the decisions regarding the positioning of the bonded attachments are made before the clinical procedure, accuracy is enhanced, and the positions o f the bonds can be examined intraorally before exposure to the light source. The technique is particularly amenable for use with trained auxiliary staff. This will, o f course, result in a reduction o f the orthodontist's clinical time. Arguably, adoption of indirect bonding procedures in combination with the controlled polymerization o f light-cured materials could result in increased cost-effectiveness o f treatment, with no reduction in the quality o f service provided.

CONCLUSIONS 1. A n indirect method o f bond placement, in which a visible light-cured adhesive material is used, was evaluated in a clinical trial and found to result in an adequate clinical performance, with failure rates comparable to other well-documented clinical trials of bonding adhesives and methods. 2. Statistical analysis revealed that the failure rates for any one segment o f the dentition were not significantly different from those for another. Interestingly, the high rate o f posterior bracket failure reported in other clinical studies was not evident in this trial. This may have been due to the improved moisture isolation afforded b y the use o f the transfer tray in the indirect technique.

REFERENCES 1. Newman GV. Epoxy adhesives for orthodontic attachments: A progress report. AM J OaTHOD 1965;51:901-12. 2. Silverman E, Cohen M, Gianelly AA, Dietz VS. A universal direct bonding system for both metal and plastic brackets. AM J ORTHOD1972;62:226-44. 3. Gorelick L. Bonding: the state of the art. J Clin Orthod 1979;13:39-53. 4. Read MJF. The bonding of orthodontic attachments using a visible light cured adhesive. Br J Orthod 1984;11:16-20. 5. Zachrisson BU, Brobakken BO. Clinical comparison of direct versus indirect bonding with different bracket types and adhesives. AM J ORrHOD 1978;74:62-78. 6. Tavas A. Studies into orthodontic adhesives. Manchester, England: Manchester University; 1980. Thesis. 7. Read MJF. The bonding of orthodontic attachments using a visible light cured adhesive. Br J Orthod 1984;11:16-20. 8. Tavas A, Watts De. A visible light activated direct bonding material: an in vitro comparative study. Br J Orthod 1984; 11:33-7. 9. O'Brien KD, Watts De, Read MJF. Residual debris and bond strength--is there a relationship? AM J ORTHODDENTOFACORa'noP 1988;94:222-30. 10. O'Brien KD, Read MJF, Sandison RJ, Roberts CT. A visible light-activated direct bonding material: an in vivo comparative study. AM J OR~XODDENIOrACORrHOP 1989;95:348-51. 11. Thomas RG. Indirect bonding: simplicity in action. J Clin Orthod 1979;13:93-106. 12. Evans LB, Powers JM. Factors affecting in vitro bond strength of no-mix orthodontic cements. AM J ORTHOD1985;87:508-12. Reprint requests to:

Dr. M. J. F. Read and Dr. K. D. O'Brien Department of Orthodontics Dental Hospital of Manchester and Turner Dental School Higher Cambridge St. Manchester MI5 6FH England.

A clinical trial of an indirect bonding technique with a visible light-cured adhesive.

A trial was carried out to evaluate the clinical performance of a visible light-cured adhesive when used with a foil mesh base in an indirect bonding ...
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