ORIGINAL ARTICLE

Comparison of bond strength between a

conventional resin adhesive and a resin-
modified glass ionomer adhesive: An in vitro
and in vivo study
Andrew Summers, DDS, MS,a Elizabeth Kao, DMD, MS,b Jeffrey Gilmore, DDS, MS,c Erdogan Gunel, PhD,d
and Peter Ngan, DMDe
Sioux Falls, Utah, Morgantown, WVa, and Marietta, Ohio

The objectives of this study were (1) to compare the in vivo survival rates of orthodontic brackets bonded with a
resin-modified glass ionomer adhesive (Fuji Ortho LC; GC America, Alsip, Ill) after conditioning with 10%
polyacrylic acid and a conventional resin adhesive (Light Bond; Reliance Orthodontic Products, Itasca, Ill) bonded
with 37% phosphoric acid, (2) to compare the in vitro bond shear/peel bond strength between the 2 adhesives,
(3) to determine the mode of bracket failure in the in vivo and in vitro tests according to the adhesive remnant index
(ARI), and (4) to compare the changes in surface morphology of enamel surface after etching or conditioning with
10% polyacrylic acid, with scanning electron microscopy. In the in vitro study, 50 extracted premolars were
randomly divided into 4 groups: brackets bonded with Fuji Ortho LC or Light Bond adhesive that were debonded
after either 30 minutes or 24 hours. Bond strengths were determined with a testing machine at a crosshead speed
of 1 mm/min. Data were analyzed with analysis of variance and a paired Student t test. The in vivo study consisted
of 398 teeth that were randomly bonded with Fuji Ortho LC or Light Bond adhesive in 22 subjects with the
split-mouth technique. Bracket survival rates and distribution were followed for 1.3 years. Data were analyzed with
Kaplan-Meier product-limit estimates of survivorship function. The in vitro study results showed significant
differences (P ⬍ .05) among the adhesives and the debond times. Light Bond had significantly greater bond
strengths than Fuji Ortho LC at 24 hours (18.46 ⫾ 2.95 MPa vs 9.56 ⫾ 1.85 MPa) and 30 minutes (16.19 ⫾ 2.04
MPa vs 6.93 ⫾ 1.93 MPa). Mean ARI scores showed that Fuji Ortho LC had significantly greater incidences of
enamel/adhesive failure than Light Bond adhesive (4.9 vs 4.1). For the in vivo study, no significant differences in
failure rate, sex, or location in dental arch or ARI ratings were found between the 2 adhesives. These results
suggest that, compared with conventional resin, brackets bonded with resin-modified glass ionomer adhesive
had significantly less shear bond strength in vitro. However, similar survival rates of the 2 materials studied after
1.3 years indicate that resin-reinforced glass ionomers can provide adequate bond strengths clinically. The
weaker chemical bonding between the adhesive and the enamel might make it easier for clinicians to clean up
adhesives on the enamel surface after debonding. (Am J Orthod Dentofacial Orthop 2004;126:200-6)

E
tching enamel with 37% phosphoric acid is the necessity of strict adherence to a dry field, the
used routinely by orthodontists to bond ortho- multiple steps required, and the remaining resin residue
dontic brackets to enamel.1 The disadvantages that cannot be easily removed after debonding of the
of this procedure are the loss of enamel during etching,2 bracket. A resin-modified glass ionomer (RMGI) adhe-
sive (Fuji Ortho LC; GC America, Alsip, Ill) has been
a

b
Private practice, Sioux Falls, Utah. introduced that can be used for bonding brackets
Professor, Department of Restorative Dentistry, West Virginia University
School of Dentistry.
without acid etching.5-9 However, previous studies
c
Private practice, Marietta, Ohio. have shown that nonetched RMGI adhesives have
d
Professor, Department of Statistics, West Virginia University School of lower bond strength and a higher failure rate when
Dentistry.
e
Professor and chair, Department of Orthodontics, West Virginia University compared with conventional acid-etch resin bonding
School of Dentistry. agents. Conditioning the tooth surface with 10% poly-
Reprints requests to: Dr Peter Ngan, West Virginia University, School of
Dentistry, Department of Orthodontics, Health Science Center North, P.O. Box
acrylic acid does not cause as much damage to the
9480, Morgantown, WV 26506; e-mail, pngan@hsc.wvu.edu. enamel surface as etching with 37% phosphoric acid
Submitted, April 2003; revised and accepted, June 2003. but enhances the bond strength of RMGI adhesives, at
0889-5406/$30.00
Copyright © 2004 by the American Association of Orthodontists. least under in vitro condition.13-15 The purposes of this
doi:10.1016/j.ajodo.2003.06.013 study were (1) to determine the in vivo survival rate of
200
American Journal of Orthodontics and Dentofacial Orthopedics Summers et al 201
Volume 126, Number 2

Table I.Four test groups with number of samples, test Table II. Modified ARI scale and corresponding
material, and time of testing definitions
Group n Bonding material Time of testing Score Definition

I 13 RMGI (Fuji Ortho LC) 30 min 5 All of adhesive remained on bracket

II 12 RMGI (Fuji Ortho LC) 24 h 4 More than 90% of adhesive remained on bracket
III 13 Resin (Light Bond) 30 min 3 More than 10% but less than 90% of adhesive remained
IV 12 Resin (Light Bond) 24 h on bracket
2 Less than 10% of adhesive remained on bracket
1 No adhesive remained on bracket

orthodontic brackets bonded with an RMGI adhesive

after conditioning with 10% polyacrylic acid with a consisted of pumicing the tooth surface for 10 seconds,
conventional resin adhesive bonded with 37% phos- followed by a rinse for 10 seconds with water. The
phoric acid used as the control group, (2) to determine enamel was etched for 30 seconds with 37% phosphoric
the in vitro shear/peel bond strength of the 2 adhesives, acid and then rinsed for 10 seconds. The tooth was
(3) to determine the mode of failure in the in vivo and dried with a stream of air until a chalky white appear-
in vitro tests, and (4) to compare the changes in surface ance was observed. A thin layer of Light Bond sealant
morphology of enamel surface after etching or condi- was applied with a brush and light-cured for 10
tioning with 10% polyacrylic acid, with scanning elec- seconds. A bracket was applied to the tooth with a
tron microscopy (SEM). constant force with the Light Bond adhesive. Flash was
carefully removed, and the adhesive was light-cured for
MATERIAL AND METHODS a total of 40 seconds, with 20-second curing on the
In vitro bond strength study mesial and distal aspects.
Two bonding materials were tested: Fuji Ortho LC, The teeth were mounted in a testing ring with the
an RMGI, and Light Bond (Reliance Orthodontic facial enamel surface perpendicular to the base of the
Products, Itasca, Ill), a light-cured resin. Fifty ex- mounting ring, with a dental surveyor. Epoxide resin
tracted, noncarious premolars were randomly divided was used to secure the tooth in the mounting ring. Teeth
into 4 groups, as shown in Table I. The teeth were from all groups were stored in an incubator with 100%
cleaned, steam autoclaved, and stored in distilled water humidity immediately after bonding. Debonding force
and 0.9% thymol. The teeth were mounted in epoxide (in newtons) was determined within 30 minutes after
resin (Buehler, Lake Bluff, Ill), with a surveyor used to bonding in Groups I and III and 24 hours after bonding
ensure that the bonding surface was parallel to the in Groups II and IV, with a testing machine (Instron,
debonding force, pumiced, and stored in distilled water. Canton, Mass) with a cross-head speed of 1 mm/min.
For groups I and II, the bonding procedure con- The bracket failure interface was examined under
sisted of pumicing the tooth surface for 10 seconds with light microscopy to determine whether the failure
flour pumice, followed by a rinse of 10 seconds with occurred at the enamel-adhesive or the bracket-adhe-
water. The bonding surface was conditioned with 10% sive interface. The brackets were then assessed with a
polyacrylic acid for 20 seconds and rinsed for 10 modified adhesive remnant index (ARI) and scored for
seconds. Each tooth was then wiped with a moist cotton the amount of resin material adhering to the bracket.14
roll to ensure that the bonding surface was not desic- The criteria for the modified ARI scale are shown in
cated, and excess water was removed. Fuji Ortho LC Table II. Data were analyzed by analysis of variance
RMGI capsule was triturated for 10 seconds and then (ANOVA) and paired Student t test.
applied to a GAC micro-arch universal orthodontic The facial surfaces of 3 noncarious premolars were
premolar bracket (GAC International, Bohemia, NY) observed with SEM to compare the effects of 37%
with a base dimension of 3.12 ⫻ 3.40 mm, covering the phosphoric acid and 10% polyacrylic acid on dental
entire base of the bracket without bubbles or voids. The enamel. The first tooth was the control, with no enamel
bracket was applied to the tooth with a constant force, treatment. The second tooth had the facial surface
and the surrounding flash was carefully removed. The conditioned with 10% phosphoric acid for 20 seconds,
adhesive was light-cured with the Ortholux XT visible followed with a rinse for 10 seconds. The third tooth
light-curing unit (3M Unitek, Monrovia, Calif) for a had the facial surface etched with 37% phosphoric acid
total of 40 seconds, with 20-second curing intervals for 30 seconds and then rinsed for 10 seconds. The
from the mesial and distal aspects of the bracket. teeth were dehydrated in a series of alcohol concentra-
For Groups III and IV, the bonding procedure tions ranging from 40% to 95% and prepared for
202 Summers et al American Journal of Orthodontics and Dentofacial Orthopedics
August 2004

observation with SEM by gold sputtering of the enamel Table III. In vitro shear bond strength for the 4 test
surfaces. groups
Bonding Debond Mean SD Minimum Maximum
Group material time n (MPa) (MPa) (MPa) (MPa)
In vivo survival distribution study
I Fuji Ortho LC 30 min 13 6.93 1.93 3.43 9.83
The in vivo portion of the experiment included 22
II Fuji Ortho LC 24 h 12 9.56 1.85 7.10 12.42
patients who received comprehensive orthodontic treat- III Light Bond 30 min 13 16.19 2.04 12.65 19.14
ment in the Department of Orthodontics, West Virginia IV Light Bond 24 h 12 18.46 2.95 15.44 23.47
University School of Dentistry. The selection criteria SD, standard deviation.
included no decalcification on teeth, good oral hygiene,
and permanent dentition. A split-arch technique was
used, in which the maxillary right quadrant and the
Data analysis
mandibular left quadrant were bonded with either Fuji
Ortho LC RMGI or Light Bond resin adhesive. This Data in the in vitro study were analyzed by
was determined randomly by a coin toss. The remain- ANOVA and paired Student t test. For the in vivo data,
ing 2 quadrants were bonded with the material that was significant differences in the bracket survival rate
not chosen for the other 2 quadrants. Each tooth was among the 2 materials, patient sex, location in the oral
pumiced for 10 seconds and rinsed for 10 seconds. The cavity, and ARI scores were determined with the
quadrants bonded with Fuji Ortho LC had the bonding Kaplan-Meier product limit survival estimates and the
surfaces conditioned with 10% polyacrylic acid for 20 log-rank test at P ⱕ .05.
seconds and rinsed for 10 seconds. The teeth were RESULTS
wiped with a moist cotton roll to ensure that the In vitro bond strength study
bonding surface was not desiccated, and excess water
The shear force recorded in newtons on the testing
was removed. Fuji Ortho LC RMGI capsule was
machine was converted to megapascals by dividing the
triturated for 10 seconds and applied to the base of an
force by the area of the bracket base (3.12 mm ⫻ 3.40
orthodontic bracket covering the entire base of the
mm ⫽ 10.608 mm2). The shear bond strengths of all
bracket, without bubbles or voids. The bracket was
test groups are shown in Table III. The control group
applied to the tooth with a constant force, and any flash
(Light Bond debonded at 24 hours) was found to have
was carefully removed. The adhesive was light-cured
the highest mean shear bond strength (18.46 ⫾ 2.95
with the Ortholux XT visible light-curing unit for a
MPa). This was followed by the Light Bond group
total of 40 seconds, with 20-second curing intervals
debonded at 30 minutes (16.19 ⫾ 2.04 MPa). The Fuji
from the mesial and distal aspects of the bracket. Ortho LC group debonded at 24 hours had a mean shear
The quadrants bonded with Light Bond resin adhe- bond strength of 9.56 ⫾ 1.85 MPa, and the Fuji Ortho
sive had the bonding surfaces prepared with acid LC group debonded at 30 minutes had the lowest mean
etching of the enamel for 30 seconds with 37% phos- shear bond strength (6.93 ⫾ 1.93 MPa).
phoric acid and then rinsed for 10 seconds. Each tooth Analysis of variance showed significant differences
was dried with a stream of air until a chalky white in the shear bond strengths among the 4 groups (P ⬍
appearance was observed. A thin layer of Light Bond .05). Paired Student t tests showed a significant differ-
sealant was applied with a brush and light-cured for 10 ence between the control group (Light Bond at 24
seconds. Light Bond adhesive was placed on the hours) and the 3 experimental groups: Fuji Ortho LC,
bracket and applied to the tooth with a constant force. 24 hours (P ⬍ .0001), Fuji Ortho LC, 30 minutes (P ⬍
Flash was carefully removed, and the adhesive was .0001), and Light Bond, 30 minutes (P ⬍ .03). Signif-
light-cured with the Ortholux XT visible light-curing icant differences were found between the Light Bond,
unit for a total of 40 seconds, with a 20-second cure 30 minutes, and the Fuji Ortho LC groups (P ⬍ .0001).
interval from the mesial and distal aspects. Significant differences were also found between the
Bracket failures were noted during the study. Any Fuji Ortho LC, 24 hours, and Fuji Ortho LC, 30
failed bracket was saved, and the tooth was no longer minutes, groups (P ⬍ .001).
followed in the study. The bracket failure interface was
observed with light microscopy to determine the failure Bracket failure interface study
interface. The failed brackets were then assessed with The average ARI scores for the 4 test groups are
the modified ARI and scored with respect to the amount shown in Table IV. Fuji Ortho LC, 30 minutes, and Fuji
of resin material adhering to the bracket.16 Ortho LC, 24 hours, had the highest mean ARI scores
American Journal of Orthodontics and Dentofacial Orthopedics Summers et al 203
Volume 126, Number 2

Table IV. Average ARI scores for the 4 in vitro test In vivo bracket survival distribution
groups
Twenty-two patients participated in this study (9
Mean Minimum Maximum male, 13 female). The mean observation time at final
Bonding Debond ARI ARI ARI data collection was 481.4 days (1.32 years), with a
Group material time n score SD score score
maximum of 664 days (1.82 years) and a minimum of
I Fuji Ortho LC 30 min 13 4.92 0.28 4 5 217 days (0.59 years). A total of 199 teeth were bonded
II Fuji Ortho LC 24 h 12 4.67 0.65 3 5 with Light Bond, and 199 teeth were bonded with Fuji
III Light Bond 30 min 13 4.31 0.75 3 5 Ortho LC. During the observation period, 10 brackets
IV Light Bond 24 h 12 4.08 0.67 3 5
bonded with Light Bond adhesive failed, resulting in a
failure rate of 5%. Thirteen brackets bonded with Fuji
Ortho LC failed, giving a slightly higher failure rate of
(4.92 ⫾ 0.28 and 4.67 ⫾ 0.65, respectively). Light 6.5%. However, the Kaplan- Meier survival distribu-
Bond, 30 minutes, and Light Bond, 24 hours, had ARI tion test showed no statistically significant correlation
scores of 4.31 ⫾ 0.75 and 4.08 ⫾ 0.67, respectively. between the type of bonding material and bracket
Significant differences in ARI scores were found be- failure rates (P ⬍ .41) (Fig 2). There was no statisti-
cally significant correlation between sex and bracket
tween Light Bond, 24 hours, and Fuji Ortho LC, 30
failure rates. The male subjects had a 5.2% bracket
minutes (P ⬍ .05), and also between Light Bond, 24
failure rate, and the female subjects had a failure rate of
hours, and Fuji Ortho LC, 24 hours (P ⬍ .04). No
6.2%.
significant differences were found between Light Bond,
There was no statistically significant correlation
24 hours, and Light Bond, 30 minutes (P ⬍ .44). between the quadrant in which the teeth were bonded
Significant differences were found between Fuji Ortho and the bracket failure rate (P ⬍ .99). The failure rates
LC, 30 minutes, Fuji Ortho LC, 24 hours, and Light were 6.0% for the maxillary right quadrant, 6.0% for
Bond, 30 minutes (P ⬍ .01). No differences were found the maxillary left quadrant, 5.0% for the mandibular
between Fuji Ortho LC, 30 minutes, and Fuji Ortho LC, right quadrant, and 5.0% for the mandibular left quad-
24 hours (P ⬍ .21). rant.
The distribution of ARI scores for the test brackets The ARI scores for all failed brackets (Table VI)
is shown in Table V. Most of the brackets bonded with showed that Light Bond had a slightly higher mean ARI
Fuji Ortho LC had an ARI score of 5 (Table V). Most value (3.7) than Fuji Ortho LC (3.5). There were no
of the brackets bonded with Light Bond had an ARI statistically significant differences in the ARI scores
score of 4. Light Bond had 4 brackets with a score of 3, between the 2 bonding materials (P ⬍ .52). Most
whereas Fuji Ortho LC had 1 bracket in this category. brackets that were bonded with Light Bond had an ARI
No sample tested received a score of less than 3. score of 5 (Table VII). There were more brackets with
ARI scores of 3 and 4 in the Fuji Ortho LC groups than
in the Light Bond groups.
SEM study of enamel morphology
Three extracted premolars were examined with DISCUSSION
SEM at ⫻1000 magnification. The untreated enamel In vitro study
showed a smooth surface (Fig 1, A). After application
The shear/peel bond strengths of the 2 bonding
of 37% phosphoric acid for 30 seconds, the enamel
materials were measured at 30 minutes and at 24 hours.
showed surface irregularities typical of a Type I enamel This was designed to more fully simulate a clinical
etching pattern; etching of prism cores was predomi- situation, because archwires are typically placed at the
nant17 (Fig 1, B). Figure 1, C, shows the enamel surface bonding appointment, when light-cured resins or ce-
after application of 10% polyacrylic acid for 20 sec- ments might not have been completely polymerized.2
onds. The enamel surface exhibits minimal surface The bond strengths of both the composite resin and the
irregularities and smooth precipitate in some areas. RMGI were significantly higher at 24 hours than at 30
Comparison of the enamel surfaces shows that enamel minutes. The reduced shear/peel bond strength imme-
conditioned with 37% phosphoric acid produced a diately after bonding agrees with the findings of
qualitatively rougher enamel surface than the enamel Bishara et al15 and is probably related to incomplete
conditioned with 10% polyacrylic acid, indicating a polymerization of light-cured materials.18,19
greater loss of enamel from conditioning with 37% The bond strengths of the composite resin with 37%
phosphoric acid. phosphoric acid at both 24 hours and 30 minutes were
204 Summers et al American Journal of Orthodontics and Dentofacial Orthopedics
August 2004

Table V. Number of the in vitro brackets in each score category of ARI

Group Material Debonded ARI ⫽ 1 ARI ⫽ 2 ARI ⫽ 3 ARI ⫽ 4 ARI ⫽ 5

I Fuji Ortho LC 30 min 0 0 0 1 12

II Fuji Ortho LC 24 h 0 0 1 2 9
III Light Bond 30 min 0 0 2 5 6
IV Light Bond 24 h 0 0 2 7 3

Fig 1. A, SEM of untreated enamel surface. B, SEM of enamel conditioned with 37% phosphoric
acid for 30 seconds. C, SEM of enamel conditioned with 10% polyacrylic acid for 20 seconds. For
all panels, original magnification ⫻1000.

Table VII. Number of in vivo brackets in each ARI

score category
Group ARI ⫽ 1 ARI ⫽ 2 ARI ⫽ 3 ARI ⫽ 4 ARI ⫽ 5

Fuji Ortho LC 1 1 4 4 3
Light Bond 0 1 2 0 7

by surface conditioning with 10% polyacrylic acid.22

The acid removes contaminants and pellicles from the
substrate surface and serves as a cleaning and wetting
agent to improve the bonding of cement to enamel.
Shammaa et al7 reported adequate bond strength when
glass ionomer (Fry Ortho LC) was bonded to enamel
clinically without acid etching. However, the bond
Fig 2. Bracket survival distribution over time with Fuji strength was less compared with the values reported in
Ortho LC and Light Bond. this study with 10% polyacrylic acid. Etching of
enamel with 37% phosphoric acid produces resin tags
Table VI. Descriptive statistics of all in vivo ARI to a depth of 80 ␮m that greatly increase the mechan-
scores ical retention of composite resin to the enamel.23
Tavas and Watt24 recommended that adhesive bond
Adhesive n Mean Minimum Maximum
strength greater than 58 N is necessary for clinical use.
Fuji Ortho LC 13 3.5 1 5 According to this recommendation, Fuji Ortho LC
Light Bond 10 3.7 1 5 adhesive, with a shear bond strength of 73.5 N (6.9
MPa) at 30 minutes, has the potential to resist forces
during orthodontic treatment. However, the average
significantly greater than those of the RMGI with 10% force transmitted to a bracket during mastication has
polyacrylic acid. These findings agree with those of been reported to be between 40 and 120 N.25,26 The use
Jobalia et al,6 Meehan et al,20 Bishara et al,15 and of Fuji Ortho LC in areas of traumatic or heavy
Owens et al.21 Bonding of glass ionomers is enhanced occlusion might be guarded.
American Journal of Orthodontics and Dentofacial Orthopedics Summers et al 205
Volume 126, Number 2

The SEM results showed that the enamel surface cured composite materials.35 Clinically, it is the au-
conditioned with 37% phosphoric acid was qualita- thors’ experience that, during debonding, the resin
tively rougher than when 10% polyacrylic acid was adhesive remaining on the tooth is more difficult to
used. The preferential etching of prism cones is typical remove than the RMGI adhesive.
of a type I enamel etching pattern.17 Polyacrylic acid
has a larger molecular size than phosphoric acid. The CONCLUSIONS
smaller molecule of 37% phosphoric acid was able to 1. In vitro results showed significantly greater shear
penetrate to a greater depth; thus, potentially more bond strengths when brackets were bonded with
enamel can be lost during conditioning and debonding. 37% phosphoric acid and composite resin (Light
SEM studies show that enamel surfaces after debonding Bond) compared with RMGI (Fuji Ortho LC)
of brackets are more porous with acid etching com- bonded with 10% polyacrylic acid.
pared with clean and smooth enamel surface without 2. Significantly greater shear bond strengths can be
etching.3 Repumicing of the bonded surface could obtained 24 hours after bonding brackets for both
restore the tooth surface to its original appearance.27 materials.
In vivo investigation 3. The in vivo results showed no significant difference
in bracket failure rates between Fuji Ortho LC and
Bracket survival distribution was used to analyze Light Bond after 1.3 years. Clinically, Fuji Ortho LC
the in vivo data. This gives the clinician a better adhesive has adequate bond strength to withstand
perspective on when failure occurred compared with the occlusal forces of chewing and biting.
studying the failure rates only at the final data collec- 4. The ARI study showed that the predominant bracket
tion. failure interface for Fuji Ortho LC was at the
Our study showed no statistically significant differ- enamel-adhesive interface. The weaker chemical
ences between Light Bond and Fuji Ortho LC as bonding between RMGI and the enamel might make
bonding materials. The failure rates of Light Bond and it easier for clinicians to clean up the adhesive on the
Fuji Ortho LC were 5% and 6.5%, respectively. In enamel surface after debonding.
several studies, the failure rates for brackets bonded 5. The SEM study showed that etching with 37%
with glass ionomer cements varied from 3.2% to phosphoric acid on dental enamel for 30 seconds
50%.28-33 The lowest failure rates for Fuji Ortho LC produced a qualitatively rougher and more porous
were reported by Fricker29 in 1998 (3.2%) and Silver- surface than conditioning with 10% polyacrylic
man et al30 in 1995 (3.3%). In addition, several clini- acid.4,10,11,12,34
cians, after 3 years of using Fuji Ortho LC, experienced
bonding success rates comparable to those of conven-
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