Comparisons of different debonding techniques for ceramic brackets: An in vitro study Part II. Findings and clinical implications Samir E. Bishara, DDS, BDS, D. Orth., MS,* and Timothy S. Trulove, DDS, MS** Iowa City, Iowa, and Montgomery, Ala.
A series of tests of three different debonding techniques applied to three different types of ceramic brackets revealed the following: (1) The incidence of bracket failure during debonding was significantly greater with conventional debonding recommended by the manufacturer (10-35%), as compared with the incidence associated with either the ultrasonic or the electrothermal methods (0%). (2) Bond failure at the bracket-adhesive interface occurred with significantly greater frequency for the Starfire brackets when debonding was performed with the electrothermal instrument and with significantly less frequency when the debonding pliers were used. Combination bond failures, in which part of the adhesive stayed on the enamel and part stayed on the bracket, occurred with significantly greater frequency when Transcend and Starfire brackets were debonded with debonding wrenches than when other methods were used. Combination-bond failures occurred with significantly less frequency when the brackets were removed with ultrasonic tips or with the electrothermal instrument. (3) The debonding times for the ultrasonic method were significantly greater than the times for either the conventional or the electrothermal methods. There were no significant differences among the debonding times for the three bracket types. There were no significant differences in the debonding times between the electrothermal method (~ = 3.0 seconds) and the conventional bracket-removal method ~ = 1.0 seconds). (4) Enamel loss as a result of adhesive removal was not significantly different among the three adhesive-removal techniques tested. Post-treatment roughness of the enamel surface was greater for the high-speed adhesive-removal technique than for either the low-speed or ultrasonic adhesive-removal methods. (AMJ ORTHODDENTOFACORTHOP 1990;98:263-73.)
T h r e e debonding techniques--conventional (i.e., according to manufacturer's directions), ultrasonic, and electrothermal--were used to remove three types of ceramic brackets--Transcend (Unitek/3M, St. Paul, Minn.), Allure (GAC International, Central Islip, N.Y.), and Starfire ("A" Company/Johnson & Johnson, San Diego, Calif.)--from 140 human incisors and molars. The removal techniques and brackets were evaluated with respect to a number of characteristics in an effort to ascertain which method is safest and most reliable on each bracket. Measurement reliability Results of the dependent t test revealed no significant differences in inter- or intrainvestigator measurements of enamel loss. Furthermore, there were no sta*Professor, Orthodontic Department, University of Iowa, College of Dentistry. **In private practice of orthodontics, Montgomery, Ala. 811115608
tistically significant differences in the comparisons of the measurements obtained from the incisor and molar subgroups tested. Amount of residual adhesive The Adhesive Remnant Index (ARI) was used to rate the various removal techniques with respect to the amount of residual adhesive on each tooth surface after bracket removal. Table I lists the frequency of ARI scores for each bracket type and debonding technique. Fig. 1 (A-C) shows examples of the different residual adhesive patterns observed. With the conventional debonding techniques, there were no significant differences in the ARI scores for the three bracket types tested. With ultrasonic bracket removal, ARI scores for the Transcend and Allure brackets indicated that the amount of adhesive remaining on the teeth was minimal, as indicated by the high frequency of ARI scores with a value of 5. 263
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Fig. 1. A, Example of bond failure at the bracket-adhesive interface. Most of the adhesive stays on the tooth. B, Example of bond failure at the enamel-adhesiveinterface. Most of the adhesive is removed with the bracket. C, Example of a combination bond failure. Part of the adhesive remains on the tooth surface and part is removed with the bracket.
When the electrothermal debracketing instrument was applied to the Starfire bracket, there was a significantly greater number of ARI scores with a value of 2, indicating that the bulk of the adhesive remained on the tooth when this instrument was used. Site of bond failure
The frequency and location of bond failure for each bracket type and debonding technique are listed in Table II. For the Transcend bracket, the X2 analysis used to compare the effects of the various debonding techniques indicated a significant difference in the sites of bond failure. Combination bond failures--i.e., those in which part of the bonding material remained on the enamel and part remained on the bracket--occurred significantly more often when the recommended conventional debonding technique was used. With the ultrasonic technique, bond failure occurred with a significantly greater frequency at the enamel-adhesive interface. For the Allure bracket, the X2 analysis indicated that there were no significant differences between the sites of bond failure when the conventional and ultrasonic debonding techniques were used. Yet the general trends
were similar to those resulting with the Transcend bracket. For the Starfire bracket, the X2 analysis indicated the presence of a significant difference with respect to the sites of bond failure between the conventional and electrothermal debonding techniques. There was significantly less bond failure at the bracket-adhesive interface when conventional debonding pliers were used to remove the bracket. On the other hand, when the ETD instrument was applied, a significantly greater number of bond failures occurred at the bracketadhesive interface. Bracket failure (fracture)
The incidence of bracket failure was recorded as a percentage of the total number of debondings for each bracket type. The percentage of bracket failure for each bracket type with respect to debonding technique is presented in Table III. Conventional debonding techniques that employed a debonding wrench or debonding pliers recommended by the manufacturers resulted in a significantly greater percentage of bracket failure, as compared with either the ultrasonic or the electrothermal debonding methods. The Starfire bracket showed the greatest incidence of
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Different debonding techniques for ceramic brackets 265
Table I. Residual adhesive ratings, according to the Adhesive Remnant Index (ARI) for three bracket types
and three debonding techniques
Adhesive RemnantIndex Rating tagl)
roc e, e Transcend Allure Starfire
Oe o n ,echniq ,e
,12131415
Conventional Ultrasonic Conventional Ultrasonic Conventional Ultrasonic Electrothermal
7 4 0 3 6 7 17
0 1 6 0 7 1 1
6 1 2 3 4 3 0
4 1 6 3 1 3 l
3 13 6 l1 2 6 l
X2 = 18.5; p ~ 0.005; df = 4; 1, All composite remains on the tooth; 2, more than 90% of the composite remains on the tooth; 3, more than 10% but less than 90% of the composite remains on the tooth; 4, less than 10% of the composite remains on the tooth; 5, no composite remains on the tooth.
Table II. Frequency and type of bond failures for three ceramic brackets tested
Bracket type a~utdebonding technique
]
[ Enamel-adhesive
Bondfailure site Bracket-adhesive
[ Combination
Transcend* Debonding wrench Ultrasonic technique
3 13
6 4
Il 3
6
1
13
11
3
6
6 6 1
1 7 17
13 7 2
Alluret ETM 346 Debonding pliers Ultrasonic technique
Starfire~ Debonding pliers Ultrasonic technique Electrothermal debonding *X2 = l l . 2 l , p -< 0.005, DF = 2. I"X2 = 5.0, not significant. :~X2 = 28, p -< 0.00l, DF = 4.
bracket failure (35%), followed by Allure (25%) and Transcend (10%) brackets. The predominant site of bracket failure with the Starfire bracket was at the tie wing. Six of the seven total failures observed for the Starfire bracket occurred at the tie wing, while only one bracket fractured within the bracket base. Fig. 2, A shows the typical fracture pattern of the Starfire bracket. All bracket failures observed with the Allure and Transcend brackets occurred within the bracket base. Fig. 2 (B, C) indicates the typical fracture pattern observed with the Allure and Transcend brackets. Of the two fractures observed for the Transcend bracket, one was complete, resulting in 100% removal of the bracket from the tooth surface, while the second was a partial fracture, which left approximately 40% of the bracket material adhering to the tooth surface.
Table III. Incidence of bracket failure for three
bracket types and three debonding techniques
Debonding technique Manufacturer's recommendation Ultrasonic Electrothermal
TranscendAllure Starfire 10% 0 N/A
25% 0 N/A
35% 0 0
N / A = Not applicable.
There was no incidence of bracket failure when the ultrasonic or ETD instruments were used.
Debonding time Tables IV and V provide an analysis of variance summary and the results of Duncan's multiple range
266 Bishara and Trulove
Fig. 2. A, Example of fracture of the Starfire bracket. B, Example of fracture of the Allure bracket. C, Example of fracture of the Transcend bracket.
Table IV. Analysis of variance summary of
debonding times for three debonding techniques and three ceramic brackets
IDegrees°fSum°fl Sourceof variation freedom squares Bracket type Debonding technique Combination
2 2 2
F
3816.48 5.37 6 0 7 1 0 . 1 1 85.48 731.24 1.03
P 0.0057* 0.0001" 0.3600
*p -- 0.05 is significant.
test used in the comparison of debonding times for the various debonding techniques. The mean debonding time for the ultrasonic method was significantly greater than the times for either the conventional or the electrothermal methods (p = 0.001). There were no significant differences in debonding times for the conventional and electrothermal methods. The debonding times for conventional bracket removal on all three types of ceramic bracket were in the l-second range. With the ultrasonic technique, the mean debonding time for the Allure brackets was the greatest (49.9 sec-
onds), followed by Transcend (45.9 seconds) and Starfire (38.0 seconds). The average debonding time for the Starfire brackets when the ETD instrument was used was 3.0 seconds (Table V).
Enamel damage The second phase of this investigation evaluated various aspects of enamel loss. Enamel damage in the form of cracks in the enamel surface or missing enamel fragments was not observed for any bracket type or debonding technique. Although the average amount of enamel loss (Table VI) was greatest with the high-speed removal technique (2 = 68.77 ~m), it was not significantly greater than the loss that occurred with either slow-speed removal (2 = 62.63 i_tm) or with ultrasonic removals (2 = 49.97 Ixm). These findings indicate that significant amounts of enamel were lost between the pretreatment and posttreatment evaluations when either the high-speed bur, the low-speed bur, or an ultrasonic technique was used to remove the residual adhesive from the enamel surface after debracketing. Scanning electron microscopy (SEM) was used to evaluate surface roughness after the removal of residual adhesive. Typical SEM photographs of pretreatment
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Different debonding techniques for ceramic brackets 267
Table V. Comparison (by Duncan's multiple range test) of three types of debonding methods applied to
different types of bracket
Debonding technique Conventional*
Ultrasonic
Electrothermalt
I
Bracket type Transcend Allure Starfire Transcend Allure Starfire Starfire
I
No. 20 20 20 20 20 20 20
I
Debondingtime (seconds)
SD (seconds)
Duncan grouping
1.0 1.0 1.0 45.9 49.9 38.0 3.0
0 0 0 32.6 33.2 17.9 1.2
A A A B B B --
*Conventional debonding was defined as debonding performed according to the manufacturer's instructions. tBecause the heating element of the electrothermal debonding instrument could not be inserted into the slots on the Transcend and Allure brackets, this tool was not tested on those brackets.
and posttreatment impressions of the enamel surface taken at 40 x magnification for the three techniques are shown in Figs. 3, 4, and 5. The roughest surface was observed when the residual adhesive was removed with a high-speed finishing bur (Fig. 3 ) - - a finding that was consistent with the extent of the mean enamel loss observed by direct measurement. Surface roughness was similar after low-speed bur (Fig. 4) and ultrasonic adhesive removal (Fig. 5).
Table VI. Duncan's multiple range test for enamel loss with three adhesive-removal techniques
Meanloss Adhesive removal I enamel technique No. (llm) High-speed with bur Slow-speed with bur Ultrasonic with tip
10 10 10
68.77 62.63 49.97
SD
Duncan's group
85.53 50.54 27.77
A A A
DISCUSSION
Early introduction of ceramic orthodontic brackets into the marketplace without adequate clinical research to evaluate their performance has created a pressing problem in the orthodontic specialty. A report describing enamel wear as a result of occlusal interferences from ceramic brackets is one example. 1 A recent letter from the past president of the American Association of Orthodontists further articulates a number of concerns.2 As a result, it is hoped that the present investigation will help explain, at least in part, the bases of some of the problems encountered by the clinician who uses ceramic brackets. Furthermore, the present investigation explores the feasibility of using alternative techniques that could be better suited for debonding of ceramic brackets with greater safety and less trauma to the patient. Site of bond failure
The results of this study indicate that the site of bond failure during debonding varies significantly according to the technique of bracket removal. Conventional debonding techniques. A combination bond failure was defined as a mixed phenomenon of bond failures occurring at the enamel-adhesive interface, at the bracket-adhesive interface, and within the
adhesive resin. It is believed that a combination bond failure that involves the enamel-adhesive interface increases the likelihood of enamel damage. In this study combination bond failures occurred with significantly greater frequency for the Transcend and the Starfire brackets debonded by the recommended conventional techniques. These results are consistent with other studies of tensile and shear bond strengths of various ceramic brackets 3"4and point to the need for a careful approach to bracket removal by the clinician, to minimize the potential for enamel damage. Although there was no evidence of enamel damage in this study, the sites of bond failure observed with all conventional debonding techniques could increase the possibility of such an occurrence. This risk is even more critical when the bracket is affixed to the adhesive, both mechanically and chemically, and when the integrity of the tooth structure is compromised as a result of enamel cracks, restorations, or devitalizated teeth. Swartz, 5 on the other hand, concluded that ceramic bracket removal with debonding pliers, which apply a squeezing pressure at the bracket-adhesive interface, results in a tensile bond failure and is the safest and the most effective technique of bracket removal with respect to potential enamel damage. Swartz, however,
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Am. J. Orthod. Dentofac. Orthop. September 1990
Fig. 3. SEM analysis of adhesive removal with higher speed and carbide bur. A, Enamel surface before treatment. B, Enamel surface after removal of residual adhesive. Notice the rough surface morphology after the removal of a ~ = 68.77 I.tm of enamel.
used a ceramic bracket that relies totally on mechanical retention. Ultrasonic debonding technique. With the ultrasonic KJS tips, a significantly greater number of bond failures occurred at the enamel-adhesive interface. The increased incidence of enamel-adhesive bond failures observed in this study with the ultrasonic approach is consistent with the results obtained by Krell, Courey, and Bishara, 6 who observed that the bulk of composite material was frequently removed along with the bracket when metal brackets were removed ultrasonically.
Although the incidence of bond failure at the enamel-adhesive interface is high when the ultrasonic technique is used, the likelihood of enamel damage with this technique is relatively minimal because the force levels required to achieve bond failure are significantly reduced with the ultrasonic tips compared with the force needed for the conventional removal methods tested. Furthermore, the same ultrasonic tip can also be used to remove the residual composite material. The Allure ceramic bracket, which uses a combination of chemical and mechanical retention, showed
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Different debonding techniquesfor ceramic brackets 269
Fig. 4. SEM analysis of adhesive removal with low-speed and carbide bur. A, Enamel surface before treatment. B, Enamel surface after removal of residual adhesive. Notice the relatively smooth enamel surface after the removal of an ~ = 62.63 p.m of enamel.
no predominant site of bond failure with either the conventional debonding pliers or the ultrasonic debonding method. Electrothermal debondhzg technique. Bond failure at the bracket-adhesive interface was observed mainly when the Starfire brackets were debonded with the ETD instrument. Interestingly, this is the only debonding technique that yielded a significantly greater number of bond failures at this site. The disadvantage of such a bond failure is that too much residual adhesive needs to be removed. On the other hand, the obvious advan-
tage is a reduction in the probability of enamel damage during debonding, since all of the adhesive remains on the tooth surface. One explanation for the increased incidence of bond failure at the bracket-adhesive interface with the ETD technique revolves around the heat applied to the bracket. Sheridan ~ proposed the hypothesis that deformation of the resin material at the metal bracket base resulted in bond failure when the ETD instrument is used. A similar hypothesis could also be suggested for ceramic brackets, i.e., that the heat transferred to the
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Fig. 5. SEM analysis of adhesive removal with the ultrasonic method. A, Enamel surface before treatment. B, Enamel surface after removal of residual adhesive. Notice relatively smooth enamel surface after removal of an ~ = 49.47 i-tm of enamel.
bracket base and the composite resin results in the deformation of a layer of adhesive material closest to the bracket. Since the thermal expansion properties of the adhesive material differ from those of the aluminum oxide bracket material, the resulting difference in contraction and expansion at this interface, accompanied with a light twist by the clinician, are sufficient to break the chemical bond between the polymers of the adhesive and the silane coupling agent of the bracket base.
Bracket failure (fracture) A number of factors influence the failure of ceramic brackets during removal. These factors include the amount of force applied during removal, the condition of the bracket before debonding, and the bracket design. It is interesting to note that, in this study, the greatest percentage of bracket failure during debonding occurred when the manufacturers' recommended conventional bracket-removal methods were used. It is also inter-
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esting to note that the site of failure was not consistent among the three bracket types tested. The majority of failures with Starfire brackets involved fracture of the tie wing and occurred at the time the plier blades collapsed onto the bracket. The explanation .for this type of fracture is related to the force applied, as well as to the design of the bracket and, more specifically, to the tie wing itself. The junction between the bracket body and the tie wing is relatively narrow and reduces the bulk of ceramic material supporting the tie wing extension. In all instances, Allure bracket failure was observed at the bracket base--probably because the bracket body and tie wings were considerably more bulky and hence better supported. The findings further indicate that bracket failure occurred when the bracket was squeezed. The force applied during removal of the Transcend bracket with the wrench is different in direction from that used with the Starfire and Allure bracket-removing pliers. With the Transcend bracket-debonding wrench, force is applied in a torsional shear direction. However, the design of the base of the Transcend bracket provides bulk, which reduces the likelihood of bracket failure at the base during removal with the debonding wrench. This increased bulk at the site of application of force with the conventional techniques seems to be an important factor in minimizing bracket failure. The ultrasonic and electrothermal debonding methods did not result in any bracket failure, probably because the mode of action and the force used during bracket removal were significantly less than those needed for the conventional debonding methods.
Debonding time The mean debonding times recorded in this study varied according to debonding technique. However, bracket type had no discernible influence on the efficiency of bracket removal with any of the techniques. As expected, debonding times with the ultrasonic KJS tips were significantly longer than for either the conventional or the electrothermal debonding methods. Several factors influenced the increased debonding times for the ultrasonic bracket-removal method. First among these factors was the need to remove composite flash from the bracket periphery before debonding. This layer of composite is frequently difficult to see and even more difficult to remove at the time of bonding without disturbing bracket placement. Second was the requirement that a purchase point be created. The relatively "soft" stainless steel ultrasonic tip, applied to the rel-
Different debonding techniques for ceramic brackets
271
Fig. 6. Example of partial bracket failure. The part of the bracket that remains on the tooth can be removed ultrasonically to minimize patient discomfort and maximize protection of the enamel surface.
atively "hard" ceramic bracket material, results in a considerable loss of tip length during removal. Finally, a reduction in the cutting efficiency of the tips occurred over time as a result of the vibration of the tip against the ceramic material.
Enamel damage Three approaches for adhesive removal were evaluated and compared in this study: a technique involving a high-speed bur, one with a low-speed bur, and one employing ultrasonic KJS tips. The mean amounts of enamel loss for the high-speed, low-speed, and ultrasonic techniques were 68.8 I.tm, 62.63 Ixm, and 49.97 I-tm, respectively. Althoug h the mean enamel loss observed with the high-speed bur was greater, there was no statistically significant difference between the various techniques. The amount of enamel loss observed in this study is comparable to that reported by Fitzpatrick and Way, 8 of 55.6 ~m with a high-speed finishing bur. Pus and Way9 also evaluated enamel loss with similar adhesiveremoval techniques and observed lesser amounts of enamel loss, ranging from 29.5 to 41.2 I-tm, depending on the technique used for enamel clean-up. Scanning electron microscopic analysis showed a significantly rougher surface with the high-speed technique than with either the low-speed or ultrasonic techniques. However, it should be remembered that this relative roughness is microscopic and will most likely blend into the surrounding tooth structure with time as a result of the normal mechanical influences of toothbrushing and mastication.
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CLINICAL IMPLICATIONS Conventional techniques for bracket removal
All of the bracket-removal techniques recommended by the manufacturers were effective, required little expenditure of time, and did not result in significant enamel damage under the conditions employed in this study. On the other hand, the degree of force required to achieve bond failure and the sudden nature of the bracket failure could cause enamel fracture or cracks and raise the risk of aspiration of bracket fragments by the patient. The probability of damage to tooth structure would be even higher if the integrity of the tooth structure was already compromised by the presence of developmental defects, enamel cracks, large restorations, or non-vital teeth. In addition, the need for relatively strong forces to obtain bond failure may result in various degrees of patient discomfort. In the clinical setting, such a force would be transmitted to teeth that are often mobile and sometimes sensitive to pressure at the end of the active phase of orthodontic treatment. To minimize such an episode, the teeth should be well supported during bracket removal. It has been suggested that the orthodontist have the patient bite firmly into a cotton roll to help stabilize these sensitive and relatively mobile teeth. ~° It needs to be pointed out to the clinician that the likelihood of bracket failure can be minimized if the debonding instrument is fully seated to the base of the bracket and to the tooth surface. This firm seating allows the forces used for bracket removal to be transmitted through the strongest and bulkiest part of the bracket--namely, the bracket base. Failure to adhere to this requirement as a result of hastiness by the clinician or the presence of large amounts of composite flash on the surface of the tooth and around the bracket periphery could result in a greater incidence of bracket failure than that observed in this study. Since bracket failure is usually quick and sudden, it could result in injury to the pericoronal soft tissue, the oral mucosa, the tooth, or the clinician if debracketing is performed carelessly. Another significant precaution concerns projectiles of either brackets or bracket fragments that are created as a result of sudden bond and bracket failure. Whole or fractured bracket particles can become dislodged into the field of operation and ingested or aspirated by the patient, creating a significant medical emergency. Furthermore, the "flying" bracket particles subject both the patient and the clinician to possible eye injury if protective eyewear is not available or not worn by both individuals. The pliers designed for removal of the Starfire bracket have a protective sheath that covers the
working end of the instrument. This sheath decreases the probability that bracket fragments will become dislodged in the patient's mouth or in the field of operation. It also became evident from this study that the plier blades progressively lose their sharpness because of the interaction between the stainless steel blade and the much harder and more abrasive ceramic material. As the plier blades become dull, debonding efficiency is reduced. Ultrasonic bracket removal
Although bracket removal is not as fast with the ultrasonic debonding method as with the conventional or electrothermal debracketing methods, effective bracket removal can be achieved with this technique. The advantages of the ultrasonic debonding approach include a decreased chance of enamel damage and a decreased likelihood of bracket failure. In addition, adhesive removal after debonding can be accomplished with the same ultrasonic tip. Another advantage of the ultrasonic debonding method includes the ability for the removal of the residual adhesive with the same instrument after debracketing. The amount of force needed for the ultrasonic approach was low compared with that needed for the conventional methods of bracket removal; hence there was no incidence of bracket failure. There are a number of disadvantages associated with the ultrasonic technique, including (1) a significantly increased debonding time compared with the other techniques tested, (2) excessive wear of the expensive ultrasonic tips, (3) the need to apply moderate force levels, which could create some discomfort to sensitive teeth, (4) the potential for soft tissue injury by a careless operator, and (5) the need for a water spray to reduce the heat build-up and to minimize any possibility of pulpal damage. Since the ultrasonic method is effective but timeconsuming, its use might be indicated when a ceramic bracket fractures while the conventional method is being used and part of it remains attached to the tooth (Fig. 6). The ultrasonic approach would be a useful alternative, compared with the removal of the bracket remnant by means of a high-speed instrument and a diamond stone. The orthodontist should balance the relative safety of the ultrasonic method with the additional time (3-5 minutes for the removal of six brackets) and the additional expense for the ultrasonic instrument and tips. Electrothermal debonding
The electrothermal debracketing instrument is a relatively new development that is being considered for
Volume98 Number 3
clinical use. In its present form, this instrument is compatible only with the Starfire bracket series, but it is an effective means for removing these ceramic brackets. The advantages of the ETD method include a reduction in the incidence of bracket failure compared with the conventional bracket-removal methods and a relatively short debonding time, which does not differ significantly from that observed with the debonding pliers. The reduced incidence of bracket failure is attributable to the small amount of force required to break the bond after the heat-inducing tip has promoted bond failure. The minimal potential for enamel damage with this removal method is directly related to the type of bond failure that occurs during d e b o n d i n g - - i . e . , failure at the bracket-adhesive interface. The disadvantages of electrothermal bonding inelude the following: I. Limited applicability in the clinical setting, since it can be used only with the Starfire ceramic bracket series that incorporates a vertical saddle in its design. Unlike the slots on the Transcend and Allure brackets, this saddle allows for the proper fit of the heating tip. Since the size of the slots on most brackets is more universal, an instrument with a tip that can be introduced into the bracket slot, rather than into the bracket saddle, will be of much wider use in a clinical setting. 2. A potential for pulpal damage that still needs to be definitively assessed. 3. An increase in the temperature of the cone part o f the handpiece, which has the potential to cause patient discomfort or mucosal irritation if carelessly used. 4. The still-bulky handpiece design, which makes its intraoral use difficult in the premolar region. 5. The possibility o f deformation during debonding of the small wire loops that hold the bracket. Deformation of these wires could result in the release of a hot bracket into the patient's mouth. To reduce the likelihood of pulpal damage, the manufacturer suggests that the tip not be engaged in the bracket saddle for periods extending beyond 5 seconds. In addition, the possibility o f mucosal bums can be eliminated if cheek retractors are used during bracket removal. It should be remembered that the instrument used in this study is a prototype that is still being refined.
Different debonding techniques for ceramic brackets
273
Concurrent research efforts are being conducted to provide clinical and histologic evaluation of any possible pulpal sequelae o f the ETD debonding technique, in vivo, on human teeth. CONCLUSIONS
The evidence presented in this study suggests that a safe, simple, and efficient method for removing the three ceramic brackets tested has yet to be designed. All of the debonding techniques used to remove the ceramic brackets were effective, but each had its limitations. The advantages and disadvantages of each debonding technique have been discussed in detail. This report suggests that clinicians contemplating the use of ceramic brackets should consider the information presented on the advantages and limitations of the presently available brackets and bracket-removal techniques. REFERENCES 1. Douglas JB. Enamel wear caused by ceramic brackets. AM J OR'rHODDEr~rOFACORTHOP1989;95:96-8. 2. Linquist JT. President's letter of AAO members regarding ceramic brackets. Bull Am Assoc Orthod 1989;7(2):3. 3. Gwinnett AJ. A comparison of shear bond strengths of metal and ceramic brackets. Ar,1J ORTHODDZ,~rOFACORTItOP1988;93: 346-8. 4. Odegaard J, Segner D. Shear bond strength of metal brackets compared with a new ceramic bracket. AMJ ORTHODDENTOFAC OR'mOP1988;94:201-6. 5. Swartz ML. Ceramic brackets. J Clin Orthod 1988;22:82-8. 6. Krell KV, Courey JM, Bishara SE. Orthodonticbracket removal using conventional and ultrasonic debondingtechniques: enamel loss and time requirements. Submitted for publication. 7. Sheridan J J, Brawley G, Hastings J. Electrothermal debracketing. Part I. An in vitro study. AM J OR'rHOD1986;89:21-7. 8. FitzpatrickDA, Way DC. The effects of wear, acid etching, and bond removal on human enamel. AM J ORTHOD1977;72:67181. 9. PUSWD, Way DC. Enamel loss due to orthodonticbonding with filled and unfilled resins using various clean-up techniques. AM J ORTHOD1980;77:269-83. 10. TranscendInstructionManual, Unitek/3M Corporation:No. 11447-2, 1988. 11. Trulove TS. An in vitro comparative study of debonding three ceramic brackets with three debonding techniques [MS Thesis]. Iowa City: University of Iowa, May 1989. Reprint requests to:
Dr. Samir Bishara University of Iowa Department of Orthodontics College of Dentistry Iowa City, IA 52242
A series of tests of three different debonding techniques applied to three different types of ceramic brackets revealed the following: (1) The incidence of bracket failure during debonding was significantly greater with conventional debonding recommended by the manufacturer (10-35%), as compared with the incidence associated with either the ultrasonic or the electrothermal methods (0%). (2) Bond failure at the bracket-adhesive interface occurred with significantly greater frequency for the Starfire brackets when debonding was performed with the electrothermal instrument and with significantly less frequency when the debonding pliers were used. Combination bond failures, in which part of the adhesive stayed on the enamel and part stayed on the bracket, occurred with significantly greater frequency when Transcend and Starfire brackets were debonded with debonding wrenches than when other methods were used. Combination-bond failures occurred with significantly less frequency when the brackets were removed with ultrasonic tips or with the electrothermal instrument. (3) The debonding times for the ultrasonic method were significantly greater than the times for either the conventional or the electrothermal methods. There were no significant differences among the debonding times for the three bracket types. There were no significant differences in the debonding times between the electrothermal method (~ = 3.0 seconds) and the conventional bracket-removal method ~ = 1.0 seconds). (4) Enamel loss as a result of adhesive removal was not significantly different among the three adhesive-removal techniques tested. Post-treatment roughness of the enamel surface was greater for the high-speed adhesive-removal technique than for either the low-speed or ultrasonic adhesive-removal methods. (AMJ ORTHODDENTOFACORTHOP 1990;98:263-73.)
T h r e e debonding techniques--conventional (i.e., according to manufacturer's directions), ultrasonic, and electrothermal--were used to remove three types of ceramic brackets--Transcend (Unitek/3M, St. Paul, Minn.), Allure (GAC International, Central Islip, N.Y.), and Starfire ("A" Company/Johnson & Johnson, San Diego, Calif.)--from 140 human incisors and molars. The removal techniques and brackets were evaluated with respect to a number of characteristics in an effort to ascertain which method is safest and most reliable on each bracket. Measurement reliability Results of the dependent t test revealed no significant differences in inter- or intrainvestigator measurements of enamel loss. Furthermore, there were no sta*Professor, Orthodontic Department, University of Iowa, College of Dentistry. **In private practice of orthodontics, Montgomery, Ala. 811115608
tistically significant differences in the comparisons of the measurements obtained from the incisor and molar subgroups tested. Amount of residual adhesive The Adhesive Remnant Index (ARI) was used to rate the various removal techniques with respect to the amount of residual adhesive on each tooth surface after bracket removal. Table I lists the frequency of ARI scores for each bracket type and debonding technique. Fig. 1 (A-C) shows examples of the different residual adhesive patterns observed. With the conventional debonding techniques, there were no significant differences in the ARI scores for the three bracket types tested. With ultrasonic bracket removal, ARI scores for the Transcend and Allure brackets indicated that the amount of adhesive remaining on the teeth was minimal, as indicated by the high frequency of ARI scores with a value of 5. 263
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Fig. 1. A, Example of bond failure at the bracket-adhesive interface. Most of the adhesive stays on the tooth. B, Example of bond failure at the enamel-adhesiveinterface. Most of the adhesive is removed with the bracket. C, Example of a combination bond failure. Part of the adhesive remains on the tooth surface and part is removed with the bracket.
When the electrothermal debracketing instrument was applied to the Starfire bracket, there was a significantly greater number of ARI scores with a value of 2, indicating that the bulk of the adhesive remained on the tooth when this instrument was used. Site of bond failure
The frequency and location of bond failure for each bracket type and debonding technique are listed in Table II. For the Transcend bracket, the X2 analysis used to compare the effects of the various debonding techniques indicated a significant difference in the sites of bond failure. Combination bond failures--i.e., those in which part of the bonding material remained on the enamel and part remained on the bracket--occurred significantly more often when the recommended conventional debonding technique was used. With the ultrasonic technique, bond failure occurred with a significantly greater frequency at the enamel-adhesive interface. For the Allure bracket, the X2 analysis indicated that there were no significant differences between the sites of bond failure when the conventional and ultrasonic debonding techniques were used. Yet the general trends
were similar to those resulting with the Transcend bracket. For the Starfire bracket, the X2 analysis indicated the presence of a significant difference with respect to the sites of bond failure between the conventional and electrothermal debonding techniques. There was significantly less bond failure at the bracket-adhesive interface when conventional debonding pliers were used to remove the bracket. On the other hand, when the ETD instrument was applied, a significantly greater number of bond failures occurred at the bracketadhesive interface. Bracket failure (fracture)
The incidence of bracket failure was recorded as a percentage of the total number of debondings for each bracket type. The percentage of bracket failure for each bracket type with respect to debonding technique is presented in Table III. Conventional debonding techniques that employed a debonding wrench or debonding pliers recommended by the manufacturers resulted in a significantly greater percentage of bracket failure, as compared with either the ultrasonic or the electrothermal debonding methods. The Starfire bracket showed the greatest incidence of
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Different debonding techniques for ceramic brackets 265
Table I. Residual adhesive ratings, according to the Adhesive Remnant Index (ARI) for three bracket types
and three debonding techniques
Adhesive RemnantIndex Rating tagl)
roc e, e Transcend Allure Starfire
Oe o n ,echniq ,e
,12131415
Conventional Ultrasonic Conventional Ultrasonic Conventional Ultrasonic Electrothermal
7 4 0 3 6 7 17
0 1 6 0 7 1 1
6 1 2 3 4 3 0
4 1 6 3 1 3 l
3 13 6 l1 2 6 l
X2 = 18.5; p ~ 0.005; df = 4; 1, All composite remains on the tooth; 2, more than 90% of the composite remains on the tooth; 3, more than 10% but less than 90% of the composite remains on the tooth; 4, less than 10% of the composite remains on the tooth; 5, no composite remains on the tooth.
Table II. Frequency and type of bond failures for three ceramic brackets tested
Bracket type a~utdebonding technique
]
[ Enamel-adhesive
Bondfailure site Bracket-adhesive
[ Combination
Transcend* Debonding wrench Ultrasonic technique
3 13
6 4
Il 3
6
1
13
11
3
6
6 6 1
1 7 17
13 7 2
Alluret ETM 346 Debonding pliers Ultrasonic technique
Starfire~ Debonding pliers Ultrasonic technique Electrothermal debonding *X2 = l l . 2 l , p -< 0.005, DF = 2. I"X2 = 5.0, not significant. :~X2 = 28, p -< 0.00l, DF = 4.
bracket failure (35%), followed by Allure (25%) and Transcend (10%) brackets. The predominant site of bracket failure with the Starfire bracket was at the tie wing. Six of the seven total failures observed for the Starfire bracket occurred at the tie wing, while only one bracket fractured within the bracket base. Fig. 2, A shows the typical fracture pattern of the Starfire bracket. All bracket failures observed with the Allure and Transcend brackets occurred within the bracket base. Fig. 2 (B, C) indicates the typical fracture pattern observed with the Allure and Transcend brackets. Of the two fractures observed for the Transcend bracket, one was complete, resulting in 100% removal of the bracket from the tooth surface, while the second was a partial fracture, which left approximately 40% of the bracket material adhering to the tooth surface.
Table III. Incidence of bracket failure for three
bracket types and three debonding techniques
Debonding technique Manufacturer's recommendation Ultrasonic Electrothermal
TranscendAllure Starfire 10% 0 N/A
25% 0 N/A
35% 0 0
N / A = Not applicable.
There was no incidence of bracket failure when the ultrasonic or ETD instruments were used.
Debonding time Tables IV and V provide an analysis of variance summary and the results of Duncan's multiple range
266 Bishara and Trulove
Fig. 2. A, Example of fracture of the Starfire bracket. B, Example of fracture of the Allure bracket. C, Example of fracture of the Transcend bracket.
Table IV. Analysis of variance summary of
debonding times for three debonding techniques and three ceramic brackets
IDegrees°fSum°fl Sourceof variation freedom squares Bracket type Debonding technique Combination
2 2 2
F
3816.48 5.37 6 0 7 1 0 . 1 1 85.48 731.24 1.03
P 0.0057* 0.0001" 0.3600
*p -- 0.05 is significant.
test used in the comparison of debonding times for the various debonding techniques. The mean debonding time for the ultrasonic method was significantly greater than the times for either the conventional or the electrothermal methods (p = 0.001). There were no significant differences in debonding times for the conventional and electrothermal methods. The debonding times for conventional bracket removal on all three types of ceramic bracket were in the l-second range. With the ultrasonic technique, the mean debonding time for the Allure brackets was the greatest (49.9 sec-
onds), followed by Transcend (45.9 seconds) and Starfire (38.0 seconds). The average debonding time for the Starfire brackets when the ETD instrument was used was 3.0 seconds (Table V).
Enamel damage The second phase of this investigation evaluated various aspects of enamel loss. Enamel damage in the form of cracks in the enamel surface or missing enamel fragments was not observed for any bracket type or debonding technique. Although the average amount of enamel loss (Table VI) was greatest with the high-speed removal technique (2 = 68.77 ~m), it was not significantly greater than the loss that occurred with either slow-speed removal (2 = 62.63 i_tm) or with ultrasonic removals (2 = 49.97 Ixm). These findings indicate that significant amounts of enamel were lost between the pretreatment and posttreatment evaluations when either the high-speed bur, the low-speed bur, or an ultrasonic technique was used to remove the residual adhesive from the enamel surface after debracketing. Scanning electron microscopy (SEM) was used to evaluate surface roughness after the removal of residual adhesive. Typical SEM photographs of pretreatment
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Different debonding techniques for ceramic brackets 267
Table V. Comparison (by Duncan's multiple range test) of three types of debonding methods applied to
different types of bracket
Debonding technique Conventional*
Ultrasonic
Electrothermalt
I
Bracket type Transcend Allure Starfire Transcend Allure Starfire Starfire
I
No. 20 20 20 20 20 20 20
I
Debondingtime (seconds)
SD (seconds)
Duncan grouping
1.0 1.0 1.0 45.9 49.9 38.0 3.0
0 0 0 32.6 33.2 17.9 1.2
A A A B B B --
*Conventional debonding was defined as debonding performed according to the manufacturer's instructions. tBecause the heating element of the electrothermal debonding instrument could not be inserted into the slots on the Transcend and Allure brackets, this tool was not tested on those brackets.
and posttreatment impressions of the enamel surface taken at 40 x magnification for the three techniques are shown in Figs. 3, 4, and 5. The roughest surface was observed when the residual adhesive was removed with a high-speed finishing bur (Fig. 3 ) - - a finding that was consistent with the extent of the mean enamel loss observed by direct measurement. Surface roughness was similar after low-speed bur (Fig. 4) and ultrasonic adhesive removal (Fig. 5).
Table VI. Duncan's multiple range test for enamel loss with three adhesive-removal techniques
Meanloss Adhesive removal I enamel technique No. (llm) High-speed with bur Slow-speed with bur Ultrasonic with tip
10 10 10
68.77 62.63 49.97
SD
Duncan's group
85.53 50.54 27.77
A A A
DISCUSSION
Early introduction of ceramic orthodontic brackets into the marketplace without adequate clinical research to evaluate their performance has created a pressing problem in the orthodontic specialty. A report describing enamel wear as a result of occlusal interferences from ceramic brackets is one example. 1 A recent letter from the past president of the American Association of Orthodontists further articulates a number of concerns.2 As a result, it is hoped that the present investigation will help explain, at least in part, the bases of some of the problems encountered by the clinician who uses ceramic brackets. Furthermore, the present investigation explores the feasibility of using alternative techniques that could be better suited for debonding of ceramic brackets with greater safety and less trauma to the patient. Site of bond failure
The results of this study indicate that the site of bond failure during debonding varies significantly according to the technique of bracket removal. Conventional debonding techniques. A combination bond failure was defined as a mixed phenomenon of bond failures occurring at the enamel-adhesive interface, at the bracket-adhesive interface, and within the
adhesive resin. It is believed that a combination bond failure that involves the enamel-adhesive interface increases the likelihood of enamel damage. In this study combination bond failures occurred with significantly greater frequency for the Transcend and the Starfire brackets debonded by the recommended conventional techniques. These results are consistent with other studies of tensile and shear bond strengths of various ceramic brackets 3"4and point to the need for a careful approach to bracket removal by the clinician, to minimize the potential for enamel damage. Although there was no evidence of enamel damage in this study, the sites of bond failure observed with all conventional debonding techniques could increase the possibility of such an occurrence. This risk is even more critical when the bracket is affixed to the adhesive, both mechanically and chemically, and when the integrity of the tooth structure is compromised as a result of enamel cracks, restorations, or devitalizated teeth. Swartz, 5 on the other hand, concluded that ceramic bracket removal with debonding pliers, which apply a squeezing pressure at the bracket-adhesive interface, results in a tensile bond failure and is the safest and the most effective technique of bracket removal with respect to potential enamel damage. Swartz, however,
268
Bisharaand Trulove
Am. J. Orthod. Dentofac. Orthop. September 1990
Fig. 3. SEM analysis of adhesive removal with higher speed and carbide bur. A, Enamel surface before treatment. B, Enamel surface after removal of residual adhesive. Notice the rough surface morphology after the removal of a ~ = 68.77 I.tm of enamel.
used a ceramic bracket that relies totally on mechanical retention. Ultrasonic debonding technique. With the ultrasonic KJS tips, a significantly greater number of bond failures occurred at the enamel-adhesive interface. The increased incidence of enamel-adhesive bond failures observed in this study with the ultrasonic approach is consistent with the results obtained by Krell, Courey, and Bishara, 6 who observed that the bulk of composite material was frequently removed along with the bracket when metal brackets were removed ultrasonically.
Although the incidence of bond failure at the enamel-adhesive interface is high when the ultrasonic technique is used, the likelihood of enamel damage with this technique is relatively minimal because the force levels required to achieve bond failure are significantly reduced with the ultrasonic tips compared with the force needed for the conventional removal methods tested. Furthermore, the same ultrasonic tip can also be used to remove the residual composite material. The Allure ceramic bracket, which uses a combination of chemical and mechanical retention, showed
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Different debonding techniquesfor ceramic brackets 269
Fig. 4. SEM analysis of adhesive removal with low-speed and carbide bur. A, Enamel surface before treatment. B, Enamel surface after removal of residual adhesive. Notice the relatively smooth enamel surface after the removal of an ~ = 62.63 p.m of enamel.
no predominant site of bond failure with either the conventional debonding pliers or the ultrasonic debonding method. Electrothermal debondhzg technique. Bond failure at the bracket-adhesive interface was observed mainly when the Starfire brackets were debonded with the ETD instrument. Interestingly, this is the only debonding technique that yielded a significantly greater number of bond failures at this site. The disadvantage of such a bond failure is that too much residual adhesive needs to be removed. On the other hand, the obvious advan-
tage is a reduction in the probability of enamel damage during debonding, since all of the adhesive remains on the tooth surface. One explanation for the increased incidence of bond failure at the bracket-adhesive interface with the ETD technique revolves around the heat applied to the bracket. Sheridan ~ proposed the hypothesis that deformation of the resin material at the metal bracket base resulted in bond failure when the ETD instrument is used. A similar hypothesis could also be suggested for ceramic brackets, i.e., that the heat transferred to the
270
Am. J. Orthod. Dentofac. Orthop. September 1990
Bishara and Trulove
Fig. 5. SEM analysis of adhesive removal with the ultrasonic method. A, Enamel surface before treatment. B, Enamel surface after removal of residual adhesive. Notice relatively smooth enamel surface after removal of an ~ = 49.47 i-tm of enamel.
bracket base and the composite resin results in the deformation of a layer of adhesive material closest to the bracket. Since the thermal expansion properties of the adhesive material differ from those of the aluminum oxide bracket material, the resulting difference in contraction and expansion at this interface, accompanied with a light twist by the clinician, are sufficient to break the chemical bond between the polymers of the adhesive and the silane coupling agent of the bracket base.
Bracket failure (fracture) A number of factors influence the failure of ceramic brackets during removal. These factors include the amount of force applied during removal, the condition of the bracket before debonding, and the bracket design. It is interesting to note that, in this study, the greatest percentage of bracket failure during debonding occurred when the manufacturers' recommended conventional bracket-removal methods were used. It is also inter-
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esting to note that the site of failure was not consistent among the three bracket types tested. The majority of failures with Starfire brackets involved fracture of the tie wing and occurred at the time the plier blades collapsed onto the bracket. The explanation .for this type of fracture is related to the force applied, as well as to the design of the bracket and, more specifically, to the tie wing itself. The junction between the bracket body and the tie wing is relatively narrow and reduces the bulk of ceramic material supporting the tie wing extension. In all instances, Allure bracket failure was observed at the bracket base--probably because the bracket body and tie wings were considerably more bulky and hence better supported. The findings further indicate that bracket failure occurred when the bracket was squeezed. The force applied during removal of the Transcend bracket with the wrench is different in direction from that used with the Starfire and Allure bracket-removing pliers. With the Transcend bracket-debonding wrench, force is applied in a torsional shear direction. However, the design of the base of the Transcend bracket provides bulk, which reduces the likelihood of bracket failure at the base during removal with the debonding wrench. This increased bulk at the site of application of force with the conventional techniques seems to be an important factor in minimizing bracket failure. The ultrasonic and electrothermal debonding methods did not result in any bracket failure, probably because the mode of action and the force used during bracket removal were significantly less than those needed for the conventional debonding methods.
Debonding time The mean debonding times recorded in this study varied according to debonding technique. However, bracket type had no discernible influence on the efficiency of bracket removal with any of the techniques. As expected, debonding times with the ultrasonic KJS tips were significantly longer than for either the conventional or the electrothermal debonding methods. Several factors influenced the increased debonding times for the ultrasonic bracket-removal method. First among these factors was the need to remove composite flash from the bracket periphery before debonding. This layer of composite is frequently difficult to see and even more difficult to remove at the time of bonding without disturbing bracket placement. Second was the requirement that a purchase point be created. The relatively "soft" stainless steel ultrasonic tip, applied to the rel-
Different debonding techniques for ceramic brackets
271
Fig. 6. Example of partial bracket failure. The part of the bracket that remains on the tooth can be removed ultrasonically to minimize patient discomfort and maximize protection of the enamel surface.
atively "hard" ceramic bracket material, results in a considerable loss of tip length during removal. Finally, a reduction in the cutting efficiency of the tips occurred over time as a result of the vibration of the tip against the ceramic material.
Enamel damage Three approaches for adhesive removal were evaluated and compared in this study: a technique involving a high-speed bur, one with a low-speed bur, and one employing ultrasonic KJS tips. The mean amounts of enamel loss for the high-speed, low-speed, and ultrasonic techniques were 68.8 I.tm, 62.63 Ixm, and 49.97 I-tm, respectively. Althoug h the mean enamel loss observed with the high-speed bur was greater, there was no statistically significant difference between the various techniques. The amount of enamel loss observed in this study is comparable to that reported by Fitzpatrick and Way, 8 of 55.6 ~m with a high-speed finishing bur. Pus and Way9 also evaluated enamel loss with similar adhesiveremoval techniques and observed lesser amounts of enamel loss, ranging from 29.5 to 41.2 I-tm, depending on the technique used for enamel clean-up. Scanning electron microscopic analysis showed a significantly rougher surface with the high-speed technique than with either the low-speed or ultrasonic techniques. However, it should be remembered that this relative roughness is microscopic and will most likely blend into the surrounding tooth structure with time as a result of the normal mechanical influences of toothbrushing and mastication.
272
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Bishara and Trulove
CLINICAL IMPLICATIONS Conventional techniques for bracket removal
All of the bracket-removal techniques recommended by the manufacturers were effective, required little expenditure of time, and did not result in significant enamel damage under the conditions employed in this study. On the other hand, the degree of force required to achieve bond failure and the sudden nature of the bracket failure could cause enamel fracture or cracks and raise the risk of aspiration of bracket fragments by the patient. The probability of damage to tooth structure would be even higher if the integrity of the tooth structure was already compromised by the presence of developmental defects, enamel cracks, large restorations, or non-vital teeth. In addition, the need for relatively strong forces to obtain bond failure may result in various degrees of patient discomfort. In the clinical setting, such a force would be transmitted to teeth that are often mobile and sometimes sensitive to pressure at the end of the active phase of orthodontic treatment. To minimize such an episode, the teeth should be well supported during bracket removal. It has been suggested that the orthodontist have the patient bite firmly into a cotton roll to help stabilize these sensitive and relatively mobile teeth. ~° It needs to be pointed out to the clinician that the likelihood of bracket failure can be minimized if the debonding instrument is fully seated to the base of the bracket and to the tooth surface. This firm seating allows the forces used for bracket removal to be transmitted through the strongest and bulkiest part of the bracket--namely, the bracket base. Failure to adhere to this requirement as a result of hastiness by the clinician or the presence of large amounts of composite flash on the surface of the tooth and around the bracket periphery could result in a greater incidence of bracket failure than that observed in this study. Since bracket failure is usually quick and sudden, it could result in injury to the pericoronal soft tissue, the oral mucosa, the tooth, or the clinician if debracketing is performed carelessly. Another significant precaution concerns projectiles of either brackets or bracket fragments that are created as a result of sudden bond and bracket failure. Whole or fractured bracket particles can become dislodged into the field of operation and ingested or aspirated by the patient, creating a significant medical emergency. Furthermore, the "flying" bracket particles subject both the patient and the clinician to possible eye injury if protective eyewear is not available or not worn by both individuals. The pliers designed for removal of the Starfire bracket have a protective sheath that covers the
working end of the instrument. This sheath decreases the probability that bracket fragments will become dislodged in the patient's mouth or in the field of operation. It also became evident from this study that the plier blades progressively lose their sharpness because of the interaction between the stainless steel blade and the much harder and more abrasive ceramic material. As the plier blades become dull, debonding efficiency is reduced. Ultrasonic bracket removal
Although bracket removal is not as fast with the ultrasonic debonding method as with the conventional or electrothermal debracketing methods, effective bracket removal can be achieved with this technique. The advantages of the ultrasonic debonding approach include a decreased chance of enamel damage and a decreased likelihood of bracket failure. In addition, adhesive removal after debonding can be accomplished with the same ultrasonic tip. Another advantage of the ultrasonic debonding method includes the ability for the removal of the residual adhesive with the same instrument after debracketing. The amount of force needed for the ultrasonic approach was low compared with that needed for the conventional methods of bracket removal; hence there was no incidence of bracket failure. There are a number of disadvantages associated with the ultrasonic technique, including (1) a significantly increased debonding time compared with the other techniques tested, (2) excessive wear of the expensive ultrasonic tips, (3) the need to apply moderate force levels, which could create some discomfort to sensitive teeth, (4) the potential for soft tissue injury by a careless operator, and (5) the need for a water spray to reduce the heat build-up and to minimize any possibility of pulpal damage. Since the ultrasonic method is effective but timeconsuming, its use might be indicated when a ceramic bracket fractures while the conventional method is being used and part of it remains attached to the tooth (Fig. 6). The ultrasonic approach would be a useful alternative, compared with the removal of the bracket remnant by means of a high-speed instrument and a diamond stone. The orthodontist should balance the relative safety of the ultrasonic method with the additional time (3-5 minutes for the removal of six brackets) and the additional expense for the ultrasonic instrument and tips. Electrothermal debonding
The electrothermal debracketing instrument is a relatively new development that is being considered for
Volume98 Number 3
clinical use. In its present form, this instrument is compatible only with the Starfire bracket series, but it is an effective means for removing these ceramic brackets. The advantages of the ETD method include a reduction in the incidence of bracket failure compared with the conventional bracket-removal methods and a relatively short debonding time, which does not differ significantly from that observed with the debonding pliers. The reduced incidence of bracket failure is attributable to the small amount of force required to break the bond after the heat-inducing tip has promoted bond failure. The minimal potential for enamel damage with this removal method is directly related to the type of bond failure that occurs during d e b o n d i n g - - i . e . , failure at the bracket-adhesive interface. The disadvantages of electrothermal bonding inelude the following: I. Limited applicability in the clinical setting, since it can be used only with the Starfire ceramic bracket series that incorporates a vertical saddle in its design. Unlike the slots on the Transcend and Allure brackets, this saddle allows for the proper fit of the heating tip. Since the size of the slots on most brackets is more universal, an instrument with a tip that can be introduced into the bracket slot, rather than into the bracket saddle, will be of much wider use in a clinical setting. 2. A potential for pulpal damage that still needs to be definitively assessed. 3. An increase in the temperature of the cone part o f the handpiece, which has the potential to cause patient discomfort or mucosal irritation if carelessly used. 4. The still-bulky handpiece design, which makes its intraoral use difficult in the premolar region. 5. The possibility o f deformation during debonding of the small wire loops that hold the bracket. Deformation of these wires could result in the release of a hot bracket into the patient's mouth. To reduce the likelihood of pulpal damage, the manufacturer suggests that the tip not be engaged in the bracket saddle for periods extending beyond 5 seconds. In addition, the possibility o f mucosal bums can be eliminated if cheek retractors are used during bracket removal. It should be remembered that the instrument used in this study is a prototype that is still being refined.
Different debonding techniques for ceramic brackets
273
Concurrent research efforts are being conducted to provide clinical and histologic evaluation of any possible pulpal sequelae o f the ETD debonding technique, in vivo, on human teeth. CONCLUSIONS
The evidence presented in this study suggests that a safe, simple, and efficient method for removing the three ceramic brackets tested has yet to be designed. All of the debonding techniques used to remove the ceramic brackets were effective, but each had its limitations. The advantages and disadvantages of each debonding technique have been discussed in detail. This report suggests that clinicians contemplating the use of ceramic brackets should consider the information presented on the advantages and limitations of the presently available brackets and bracket-removal techniques. REFERENCES 1. Douglas JB. Enamel wear caused by ceramic brackets. AM J OR'rHODDEr~rOFACORTHOP1989;95:96-8. 2. Linquist JT. President's letter of AAO members regarding ceramic brackets. Bull Am Assoc Orthod 1989;7(2):3. 3. Gwinnett AJ. A comparison of shear bond strengths of metal and ceramic brackets. Ar,1J ORTHODDZ,~rOFACORTItOP1988;93: 346-8. 4. Odegaard J, Segner D. Shear bond strength of metal brackets compared with a new ceramic bracket. AMJ ORTHODDENTOFAC OR'mOP1988;94:201-6. 5. Swartz ML. Ceramic brackets. J Clin Orthod 1988;22:82-8. 6. Krell KV, Courey JM, Bishara SE. Orthodonticbracket removal using conventional and ultrasonic debondingtechniques: enamel loss and time requirements. Submitted for publication. 7. Sheridan J J, Brawley G, Hastings J. Electrothermal debracketing. Part I. An in vitro study. AM J OR'rHOD1986;89:21-7. 8. FitzpatrickDA, Way DC. The effects of wear, acid etching, and bond removal on human enamel. AM J ORTHOD1977;72:67181. 9. PUSWD, Way DC. Enamel loss due to orthodonticbonding with filled and unfilled resins using various clean-up techniques. AM J ORTHOD1980;77:269-83. 10. TranscendInstructionManual, Unitek/3M Corporation:No. 11447-2, 1988. 11. Trulove TS. An in vitro comparative study of debonding three ceramic brackets with three debonding techniques [MS Thesis]. Iowa City: University of Iowa, May 1989. Reprint requests to:
Dr. Samir Bishara University of Iowa Department of Orthodontics College of Dentistry Iowa City, IA 52242
