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Introduction
Direct bonding of orthodontic attachments to enamel surface has a significant impact on clinical
orthodontic treatment.1 Conservation of arch length, ease of placement and esthetic superiority
are some of the advantages of direct bonding. Direct bonding procedure requires de-bonding at
the termination of active treatment. Great consideration should be given to de-bonding
procedures and the effect that these procedures have on the enamel surface underlying the
bonded attachments. The primary consideration lies in returning the enamel surface to as near its
original state as possible following removal of bonded orthodontic attachments.2
The term debonding refers to removal of orthodontic attachments and all the residual adhesive
from the enamel surfaces and restore as closely as possible to its pretreatment condition without
inducing iatrogenic damage. The color similarity between present adhesives and enamel does not
allow for complete removal of remaining adhesive which discolors with time and creates an
esthetic problem.3 A variety of mechanical methods have been designed to achieve satisfactory
composite removal with minimal damage to the enamel surface. With the advent of ceramic
brackets, debonding of these brackets have caused enamel fractures and cracks.4
Although new techniques including thermal, electro-thermal and chemical aids to mechanical debonding, ultrasonic, lasers and intra-oral sandblasting have been advocated, mechanical debonding of both stainless steel and ceramic brackets remain the technique of choice.5 The
amount of resin left and up-to which extent enamel surface is restored to its original texture is
not known. Scanning electron microscopic evaluation permits a better understanding of what
happens to treated enamel. Also till date there are no studies comparing the different de-bonding
techniques in Bangalore urban population.
Thus the purpose of the present study was to examine microscopically the enamel surface
structure subjected to different de-bonding techniques using the Scanning Electron Microscope
(SEM) and to develop a technique for residual adhesive removal that restores the enamel surface
as closely as possible to natural enamel surface.
MATERIALS AND METHOD
Forty premolar teeth were collected from patients undergoing extractions for orthodontic
treatment purpose. All the teeth were divided at random into four groups of 10 teeth each. The
teeth were dried and mounted in improved plaster in color coded metal cups to ensure firm
support during the de-bonding procedures.
The buccal surfaces of all the forty premolars were cleaned with pumice, rubber wheel and cup.
Etchant, primer and resin used were light cure composite (TRANSBOND XT, 3M Unitek) The
straight wire twin brackets (Gemini,3M Unitek ) were bonded to the teeth. All the teeth were
bench cured for 10 minutes and later stored in distilled water for 24 hours.
The brackets were removed with direct bonding bracket remover (Balaji dental
products,Chennai) and the remaining resin on the enamel surfaces was removed by one of the
four de-bonding procedures described below.
Procedure1: Remaining resin on enamel of 10 teeth was removed with hand scaler (SU15/80-HuFriedy, USA)
Procedure2: Remaining resin on enamel of 10 teeth was removed with ultrasonic scaler
(Cavitron,09306 Dentsply Ltd,UK)
Procedure3: Remaining resin on enamel of 10 teeth was removed with plain fluted tungstun
carbide bur at high speed (NO.7803, SS White, Lakewood NJ)
Procedure4: Remaining resin on enamel of 10 teeth was removed with green stone (Shofu
Composite kit, California)
All the teeth from each procedure were finally polished with rubber wheel, cup and slurry of
pumice and water. After finishing, it was completely satisfied that the enamel surface appeared
clean and free of resin remnants by visual inspection as well as tactile sensation under operating
light and dental probe.
Enamel surface of each specimen was studied using scanning electron microscope(JOEL
JSM840 JAPAN). Photographs were obtained at x200 magnification for all the specimens treated
with the four procedures after polishing.The photomicrographs were studied for the nature of the
enamel surface and graded according to the modified surface roughness index (table 1) originally
proposed by Howell and Weekes in the form of grades and modified by Hong and Lew7 to
numerical form to facilitate statistical analysis.
TABLE 1
MODIFIED SURFACE ROUGHNESS INDEX
SCORE
1
2
3
4
CONDITION OF ENAMEL SURFACE.
Acceptable surface, fine scattered scratches
Mildly rough surface, denser fine scratches with some coarser scratches.
Rough surface, numerous coarse scratches over the entire surface.
Very rough, deep, very coarse scratches over the entire surface
RESULTS:
An acceptable clinical appearance of all the tooth surfaces was achieved with all the four debonding procedures. The scanning electron photomicrographs taken were qualitatively examined
for the nature of the enamel surface. All the four procedures failed to remove the adhesive resin
completely. Most surfaces showed the characteristic perichymata. Though no detectable resin
remnants were seen clinically the photomicrographs showed resin remnants scattered here and
there. All treatments left occasional scratches, depressions or a few gouges on the enamel
surfaces. Final polishing left the surfaces considerably smoother though it did not completely
remove the resin remnants which were true with all the four procedures.
Table 2 shows the scores obtained from photomicrographs for each removal procedure for
surface roughness Index. Statistically significant differences were detected between different
finishing procedures using chi-square test. Because calculated value of X2 is 30.857 which is
greater than table value of X2= 16.919, we reject the hypothesis of the four procedures being
homogeneous with respect to SRI scores. It concludes that there is significant difference between
the four procedures. The tungsten carbide bur was superior in terms of enamel smoothness to all
other finishing procedures showing greater score 1(photomicrograph1). Ultrasonic scaler came
next with larger proportion of score 2(photomicrograph2) which was slightly superior to hand
scaler (photomicrograph3) which showed equal proportion of scores 2and 3.Green Stone had a
larger proportion of score 3(photomicrograph4). None of the finishing procedures showed score
4 although all the four procedures left some amount of resin remnants with scratches and gouges
even on final pumicing. The teeth surfaces finished with tungsten carbide bur came closest to
resemble natural enamel (photomicrograph5).
TABLE 2
Scores of different de-bonding procedures obtained from Scanning Electron
Microscopic photomicrographs
DEBONDING
PROCEDURES
SCORE 1
SCORE 2
SCORE 3
SCORE 4
Hand scaler
Green stone
Ultrasconic scaler
0
0
2
5
3
6
5
8
2
0
0
0
Tungsten carbide bur
8
2
0
0
DISCUSSION
Post de-bonding scarring of enamel is a disadvantage of orthodontic
bonding. However, there is no doubt that the advantages outweigh the
disadvantages. The clinician therefore must accept enamel scarring and then
methodically attempt to return the enamel surface to as near its original condition
as possible. 7-9 There is a wide range of opinion as to the best method of debonding. Restoration to a relatively smooth surface while preserving the
topographic qualities of enamel is the key to a successful debonding procedure.
For all practical purposes the final enamel appearance after debonding should be
comparable to the adjacent enamel surface, dry as well as wet. A variety of
debonding techniques have been introduced in order to achieve a satisfactory
finishing of the enamel surface.
Seong-Sik et al10 found that intra- oral sand blasting technique of de-bonding
to be similar to that after resin removal with a low-speed hand-piece. There were
significant greater temperature changes in the low-speed hand-piece than in the
sand blasting group. Sandblasting for resin removal did not cause pulpal damage.
In terms of time taken for resin removal sandblasting group was significantly
slower than low-speed group but the vibration of low-speed hand-piece caused
discomfort for the patient.However the disadvantages of intra-oral sand blasting
are it is a highly complex procedure and various factors including sandblasting
pressure, duration of sandblasting, particle size, type of particle and protection for
operator and patient should be considered.
At bracket removal bond failure can occur at the resin-enamel interface
(adhesive failure) or resin-bracket interface (cohesive failure). Cohesive failure is
safer than adhesive failure but with adhesive failure less adhesive is left on the
enamel and less time is spent on clean-up. It can also lead to enamel loss and
depend largely on the bracket material, type of resin used and the method of
bracket removal. The preferred site of failure is controversial.6 Previous studies
have reported undesirable enamel cracks and bracket fracture with ceramic
brackets.4,11-14 It can lead to poor esthetics and costly treatment and even
compromise the long –term prognosis of the affected tooth. Also conventional debonding techniques have reported bracket fractures occurring 10%-35% of the
time. Because metal brackets are routinely used, the risk is reduced. Because
ceramic material do not bond chemically with resin, they derive their bond strength
from the use of silane coupling agent on the base of the bracket through
mechanical retention or both. Mechanically retained brackets have adequate bond
strength and and cause minimal enamel damage. Chemical retention results in an
extremely strong bond that stresses the enamel-adhesive interface during
debonding.5, 15
In order to overcome the drawbacks in debonding ceramic brackets,
lasers came to be used to debond the ceramic brackets without risk of enamel
fractures eg. C02 and YAG Lasers. Ezz Azzeh and Paul J. Feldon18 in their review
article highlight the advantages of laser debonding of ceramic brackets. These
cause debonding of the brackets by thermal softening of the adhesive and resin
contraction. Debonding occurs at the resin-bracket interface, where much of the
resin remains on the enamel surface. Light microscope and scanning electron
microscope showed no enamel or bracket damage in any sample. The term
DEBONDING refers to removal of bracket and the residual adhesive from the
enamel surface and restore the surface as closely as possible to its pretreatment
condition. Lasers bring about only removal of the brackets and much of the resin
remains on the surface of the enamel .The risk of enamel damage and bracket
fracture is significantly reduced with lasers but necessitates the removal of more
residual adhesive after bracket removal.
It is always better to get a cohesive failure where most of the resin
remains on the enamel surface and damage to the enamel is also less during
bracket removal. Various studies on the type of bond failure of metal and ceramic
brackets have reported a cohesive failure.5,15,16 In one of the study to determine the
amount of resin remnants on the enamel surface with three kinds of adhesives, a
smaller portion of resin-modified glass ionomer was left behind than the resin
based adhesives. They also concluded that it was during final enamel clean-up that
most enamel surface loss occurred.16
The purpose of this study was to evaluate four different techniques of debonding
for restoring the enamel to a superior quality after removal of directly bonded
metal brackets. Residual resin was removed using tungsten carbide bur, ultrasonic
scaler, greenstone and hand scaler and finally polishing the enamel surfaces.
In the earlier work, tungsten carbide bur clean-up was considered the gold standard
for residual resin removal against which other methods could be compared. 17,18 In
our study, of the four instruments used, tungsten carbide bur at high speed proved
to be the fastest and most efficient method of residual resin removal. It received
score of 1 for the surface roughness index. Most of the surfaces exhibited a cobble
stone effect, which is a reflection of the prisms exposed during etching of enamel
prior to bonding. This infers that the tungsten carbide bur clean up did not remove
enamel beyond that penetrated by the etchant. Fitzpatrick and Way19 in an SEM
study of the effects of wear, acid etching and resin removal on human enamel
showed that tungsten carbide bur at high speed removed an average of 55 microns
of surface enamel or approximately the entire thickness of the etch. This was in
agreement with studies done by Retief and Denys,17 Campbell,2 Hong and Lew,8
Bertrand Marshall and Cooley. 7 The time required for residual resin removal was
also less with tungsten carbide bur at high speed .But studies by Zachrisson and
Arthun,20 Hannah and Smith 21and Ingrid et all 22 found that tungsten carbide bur at
low speed was most effective in removal of residual resin. Ingrid et al22 found that
using self-etching primer rather than conventional acid-etching technique caused
less enamel loss.
The ultrasonic scaler clean up in our study also produced a considerable
smooth surface which was in accordance with Burapavong,20 Krell,Courey and
Bishara.23 But time taken for resin removal was long. The enamel surface appeared
superior to that of green stone finishing. This finding is of particular interest since
the task of this procedure can be thought in terms of delegating to the hygienist.
With additional training a hygienist can be transformed into an expanded dental
auxiliary. The ultrasonic cleanup received a large number of scores of 2 for the
surface roughness index which comes nearest to being acceptable. Ingrid Hosein et
al 22 found that ultrasonic finishing caused a great degree of enamel loss.
The other two instruments tested i.e the hand scaler and the green
stone left surfaces which were rough and left rougher and deep cuts which were
not removed with pumicing which was in agreement with Gwinnet and Gorelick.24
Even Retief and Denys17 and Oliver and Griffiths25 do not advocate the use of hand
scaler. Even though the hand instrument could pop adhesive almost entirely in
many instances and should be tried first, they must be used cautiously if the
adhesive offers resistance. Burapavong20 found a satisfactory enamel surface after
resin removal by hand scaler and was superior to that achieved after finishing the
enamel with green stone. Green stone left unnecessary roughness which could not
be removed even with polishing. He found hand scaler and ultrasonic scaler to be
useful for initial resin removal.
Irrespective of the procedure, however, small amounts of resin are bound to
remain on the enamel as seen in this study and others. Casperson26 found that SEM
could disclose presence of acrylic islands, flakes or diffuse membranes. The
finding in this study and those of others indicated that all rotating instruments
effective in removing resin remnants, introduced some abrasion to enamel surface.
Enamel surface is a heterogeneous tissue, composed of sub- microscopic
crystallites embedded in a sparse organic matrix. Its microscopic characteristics
predisposes it to many and varied abrasion anomalies. It is necessary to be cautious
in using de-bonding instruments when approaching enamel.
Another problem associated with cleanup is heat. Retief and Denys17
recommend air cooling whereas Campbell 2 and Rouleau et al 7 and Torun et al6
insisted on water cooling. In this study water cooling was preferred with highspeed hand-piece, even though it has the disadvantage of masking the resin
remaining on the enamel surface making it difficult for the operator to differentiate
between the resin and enamel. Perhaps the enamel surfaces after de-bracketing can
be subjected to a disclosing medium, which allows better contrast of the tooth
coloured adhesive remnants and the enamel making resin clean up easy.
Burapavong,20 Hong and Lew,8 Zarrinnia ,Eid and Kehoe9 and many others
found that final pumicing bettered the appearance of enamel surface. Even though
Casperson 26 found that pumicing was ineffective in removing the remnants of
adhesive, it was effective in smoothening the rough enamel surfaces. Although
pumice is a mild abrasive, it apparently is capable of smoothening most of the
roughened areas left by different procedures. Only the deep gouges, cuts and
depressions are not removed by pumice prophylaxis. In addition enamel surface is
subjected to normal wear with age that reduces these artificial marks together with
other factors such as tooth brushing and nature of diet. Final pumicing is a
necessary step in debonding.
CONCLUSION
The results of this study indicates that removing resin during de-bonding
using a high speed tungsten carbide bur followed by pumice polishing produced
significantly more acceptable surfaces than the other procedures, coming closest to
resemble untreated natural enamel.
With additional training a hygienist can be delegated the task of ultrasonic
clean-up of enamel surfaces since the procedure produced surfaces which come
nearest to being acceptable.
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LEGENDS OF FIGIRES
photomicrograph 1: Enamel surface debonded with tungsten carbide bur.
photomicrograph 2: Enamel surface debonded with ultrasonic scaler.
photomicrograph 3: Enamel surface debonded with hand scaler.
photomicrograph 4: Enamel surface debonded with green stone.
photomicrograph 5: Normal Enamel surface.