ORIGINAL ARTICLES
Shear peel bond strengths of esthetic orthodontic brackets A. M. P. Harris, BChD, Hons-BSc, DTE, MChD, FFD(SA), ~ V. P. Joseph, BDS, MSc (Dent), b and P. E. Rossouw, BSc, BChD, Hons-BChD, MChD ~
Tygerberg, Republic of South Africa Anecdotal reports of bracket fracture and tooth damage associated with the use of certain esthetic orthodontic brackets have been reported in the literature. With the advent of new esthetic orthodontic brackets, the need has arisen to test the claims of the manufacturers. The objectives of this study were to determine: (1) shear peel bond strengths (SPBS) of various debonded orthodontic brackets, (2) SPBS of these rebonded esthetic brackets with and without use of silane, and (3) fracture sites of all groups examined. Seventy-five noncarious human premolar teeth were randomly divided into five groups (A through E). The teeth were cleaned, stored in 70% ethyl alcohol, and mounted for testing in the Instron machine. The following brackets were bonded to the teeth with Ortho-Concise bonding resin: (A) metal brackets, (B) Silkon brackets, (C) Transcend 2000 brackets, (D) debonded Transcend 2000 brackets, and (E) debonded silanized Transcend 2000 brackets. After wet storage at 37 ~ C for 7 days, the SPBS of brackets were recorded, and fracture sites observed. There were statistically significant differences between the SPBS of metal brackets when compared with the Transcend 2000 and the Silkon brackets. These groups exhibited clinically acceptable SPBS. Debonded silanized Transcend 2000 brackets showed clinically unacceptable SPBS. Fracture sites of metal and Transcend 2000 brackets were resin-bracket, whereas Silkon brackets fracture sites were predominantly resin-enamel. (AMJ OR'rHODDENTOFACORTHOP1992;102:215-9.)
In
late 1986 the first brackets made of ceramic material became widely available. Subsequently, anecdotal reports of bracket breakage and tooth damage associated with the use of ceramic brackets have been published. ~-3These problems have led to a very cautious approach by some orthodontists on the use of ceramic brackets. As new ranges of ceramic brackets are launched on the market, it is important to be able to evaluate certain characteristics of these brackets. Manufacturers' claims regarding shear peel bond strengths and fracture sites may be tested for their application to the clinical situation. One of the problems associated with the chemically bonded variety of some cosmetic brackets is the situation of the preferred fracture plane on debonding. Ideally fracture sites should be consistently at the resin/enamel interface, but as enamel damage is often associated with these fracture sites, a fracture site at the interface between resin and bracket is clinically acceptable. Joseph and Rossouw 4 demonstrated mainly resin/enamel fracture sites when a primary coating of fissure sealant was applied to the enamel surface before
stainless steel brackets were bonded. Some esthetic brackets do not demonstrate mainly resin-bracket fractures but rather resin-enamel fractures and even enamel fractures. Realizing these negative characteristics, a major orthodontic supply company has changed from chemically bonding to mechanically retentive brackets (Transcend 2000 brackets, Unitek/3M, Monrovia, Calif.) Recently plastic brackets employing a chemically retentive mechanism for adhesion to enamel have appeared on the market (Silkon brackets, American Orthodontics, Sheboygan, Wis.). Another important aspect is the clinical behavior of rebonded esthetic brackets. Articles describing the use of silane coupling agents with ceramic brackets to create a chemical bond between resin and bracket base have indicated varying rates of successY ~~ The objectives of this study were to determine: (1) shear peel bond strengths (SPBS) of stainless steel, ceramic, and plastic orthodontic brackets, (2) SPBS of debonded esthetic brackets with and without the use of silane, and (3) fracture sites of all groups examined. MATERIALS AND METHODS
From the University of Stellenbosch, Tygerberg, Republic of South Africa. 'Specialist, Department of Orthodontics. ~Registrar, Department of Orthodontics. 'Head of Department, Department of Orthodontics. 811129950
Seventy-five nonearious human premolar teeth were collected for the purpose of this study. After extraction the teeth were cleaned on a dental lathe with pumice and stored in 70% ethyl alcohol as reported in the literature." The teeth were 215
216
llarris, Joseph, and Rossouw
Am. J. Orthod. Dentofac. Orthop. September 1992
SHEAR PEEL BOND STRENGTH BOND STRENGTHS {N/re.m2) 25 20
18.10
15
12.83
/----d,
/
10
I I I
"
[
0
METAL
SILKON
12.g4
12.94
/
7
1.81
T 2000
T REBOND
T S[LANE
GROUPS Fig. 1. Bar graph indicating significant differences between median shear peel bond strengths for metal, ceramic, debonded ceramic and plastic, and debonded silanJzed ceramic brackets.
then prepared for mounting in brass cups by sectioning their roots and undercutting their pulp chambers according to a well-publicized method, u All the teeth protruded I mm above the lip of the cup and were secured in the cup with an acrylic resin. To produce fiat enamel surfaces, the teeth were ground wet with a grinding and polishing machine with 200 grit, followed by 600 grit, silicon carbide paper. These ground surfaces were all visually verified to be in enamel and wide enough to allow the brackets to be completely seated. The teeth were randomly divided into five groups (A through E), and the brackets bonded with Ortho-Concise (3M/Dental Products, St. Paul, Minn.) as follows: A. Metal brackets (ORMCO Ormesh, Ormco Corp., Glendora, Calif.) B. Silkon brackets C. Transcend 2000 brackets D. Debonded Transcend 2000 brackets (thoroughly washed after debonding, and rebonded) E. Debonded Transcend 2000 (silanized and rebonded) Lower anterior brackets were used because of the fiat base curvature and relatively small surface area, which made the laboratory enamel surfacing easier. Any curvature in the bracket base would induce weaker bond strengths on this fiat surface because of the uneven composite layer, as well as lack of intimacy,u All teeth were subjected to a 60-second etch ~,ith 37% orthophosphoric acid. They were washed for 20 seconds under running tap water to remove the acid and blown dry with uncontaminated air (chip syringe). The bonding material was applied strictly following the manufacturer's recommendations. The two pastes of Ortho-Concise were mixed for 20 seconds and applied to the bracket bases before placement. Silkon brackets were coated with a primer before bonding. All samples were allowed 5 minutes to bench cure. Silanization procedure. Freshly mixed silane was applied to debonded bracket bases and allowed to air dry before the bonding resin was applied. The teeth were wet stored in distilled water at 37~ C in an incubator for 7 days. The teeth were secured in a clamp device of the Instron Universal testing
machine (lnstron Corp., Canton, Mass.). A 0.020-inch gauge wire was placed under the wings of the bracket with its ends clamped to a self-centering device. The specimens were then stressed in a gingivoincisal direction to failure employing a shear bond test on the Instron machine, according to a similar procedure described in the literature. 2'u All the recordings were calculatcd as force measured in Newtons, which was subsequently converted to stress per unit area (N/mm ~) by dividing the force by the unit area of the base of the bracket. Mean bonding surface area (bracket) was determined with a reflex microscope and a computer program: area of metal bracket: 9.2 mm'area of Silkon bracket: 9.9 mm2 area of Transcend 2000 bracket: 8.5 mm2 The sites of fracture of all the teeth were examined by a light optical stereoscopic microscope and recorded. Fracture sites were defined as occurring in predominately resin-bracket (RB) or resin-enamel (RE) areas when 50% or more of the surfaces were involved (RB =
Shear peel bond strengths of esthetic orthodontic brackets A. M. P. Harris, BChD, Hons-BSc, DTE, MChD, FFD(SA), ~ V. P. Joseph, BDS, MSc (Dent), b and P. E. Rossouw, BSc, BChD, Hons-BChD, MChD ~
Tygerberg, Republic of South Africa Anecdotal reports of bracket fracture and tooth damage associated with the use of certain esthetic orthodontic brackets have been reported in the literature. With the advent of new esthetic orthodontic brackets, the need has arisen to test the claims of the manufacturers. The objectives of this study were to determine: (1) shear peel bond strengths (SPBS) of various debonded orthodontic brackets, (2) SPBS of these rebonded esthetic brackets with and without use of silane, and (3) fracture sites of all groups examined. Seventy-five noncarious human premolar teeth were randomly divided into five groups (A through E). The teeth were cleaned, stored in 70% ethyl alcohol, and mounted for testing in the Instron machine. The following brackets were bonded to the teeth with Ortho-Concise bonding resin: (A) metal brackets, (B) Silkon brackets, (C) Transcend 2000 brackets, (D) debonded Transcend 2000 brackets, and (E) debonded silanized Transcend 2000 brackets. After wet storage at 37 ~ C for 7 days, the SPBS of brackets were recorded, and fracture sites observed. There were statistically significant differences between the SPBS of metal brackets when compared with the Transcend 2000 and the Silkon brackets. These groups exhibited clinically acceptable SPBS. Debonded silanized Transcend 2000 brackets showed clinically unacceptable SPBS. Fracture sites of metal and Transcend 2000 brackets were resin-bracket, whereas Silkon brackets fracture sites were predominantly resin-enamel. (AMJ OR'rHODDENTOFACORTHOP1992;102:215-9.)
In
late 1986 the first brackets made of ceramic material became widely available. Subsequently, anecdotal reports of bracket breakage and tooth damage associated with the use of ceramic brackets have been published. ~-3These problems have led to a very cautious approach by some orthodontists on the use of ceramic brackets. As new ranges of ceramic brackets are launched on the market, it is important to be able to evaluate certain characteristics of these brackets. Manufacturers' claims regarding shear peel bond strengths and fracture sites may be tested for their application to the clinical situation. One of the problems associated with the chemically bonded variety of some cosmetic brackets is the situation of the preferred fracture plane on debonding. Ideally fracture sites should be consistently at the resin/enamel interface, but as enamel damage is often associated with these fracture sites, a fracture site at the interface between resin and bracket is clinically acceptable. Joseph and Rossouw 4 demonstrated mainly resin/enamel fracture sites when a primary coating of fissure sealant was applied to the enamel surface before
stainless steel brackets were bonded. Some esthetic brackets do not demonstrate mainly resin-bracket fractures but rather resin-enamel fractures and even enamel fractures. Realizing these negative characteristics, a major orthodontic supply company has changed from chemically bonding to mechanically retentive brackets (Transcend 2000 brackets, Unitek/3M, Monrovia, Calif.) Recently plastic brackets employing a chemically retentive mechanism for adhesion to enamel have appeared on the market (Silkon brackets, American Orthodontics, Sheboygan, Wis.). Another important aspect is the clinical behavior of rebonded esthetic brackets. Articles describing the use of silane coupling agents with ceramic brackets to create a chemical bond between resin and bracket base have indicated varying rates of successY ~~ The objectives of this study were to determine: (1) shear peel bond strengths (SPBS) of stainless steel, ceramic, and plastic orthodontic brackets, (2) SPBS of debonded esthetic brackets with and without the use of silane, and (3) fracture sites of all groups examined. MATERIALS AND METHODS
From the University of Stellenbosch, Tygerberg, Republic of South Africa. 'Specialist, Department of Orthodontics. ~Registrar, Department of Orthodontics. 'Head of Department, Department of Orthodontics. 811129950
Seventy-five nonearious human premolar teeth were collected for the purpose of this study. After extraction the teeth were cleaned on a dental lathe with pumice and stored in 70% ethyl alcohol as reported in the literature." The teeth were 215
216
llarris, Joseph, and Rossouw
Am. J. Orthod. Dentofac. Orthop. September 1992
SHEAR PEEL BOND STRENGTH BOND STRENGTHS {N/re.m2) 25 20
18.10
15
12.83
/----d,
/
10
I I I
"
[
0
METAL
SILKON
12.g4
12.94
/
7
1.81
T 2000
T REBOND
T S[LANE
GROUPS Fig. 1. Bar graph indicating significant differences between median shear peel bond strengths for metal, ceramic, debonded ceramic and plastic, and debonded silanJzed ceramic brackets.
then prepared for mounting in brass cups by sectioning their roots and undercutting their pulp chambers according to a well-publicized method, u All the teeth protruded I mm above the lip of the cup and were secured in the cup with an acrylic resin. To produce fiat enamel surfaces, the teeth were ground wet with a grinding and polishing machine with 200 grit, followed by 600 grit, silicon carbide paper. These ground surfaces were all visually verified to be in enamel and wide enough to allow the brackets to be completely seated. The teeth were randomly divided into five groups (A through E), and the brackets bonded with Ortho-Concise (3M/Dental Products, St. Paul, Minn.) as follows: A. Metal brackets (ORMCO Ormesh, Ormco Corp., Glendora, Calif.) B. Silkon brackets C. Transcend 2000 brackets D. Debonded Transcend 2000 brackets (thoroughly washed after debonding, and rebonded) E. Debonded Transcend 2000 (silanized and rebonded) Lower anterior brackets were used because of the fiat base curvature and relatively small surface area, which made the laboratory enamel surfacing easier. Any curvature in the bracket base would induce weaker bond strengths on this fiat surface because of the uneven composite layer, as well as lack of intimacy,u All teeth were subjected to a 60-second etch ~,ith 37% orthophosphoric acid. They were washed for 20 seconds under running tap water to remove the acid and blown dry with uncontaminated air (chip syringe). The bonding material was applied strictly following the manufacturer's recommendations. The two pastes of Ortho-Concise were mixed for 20 seconds and applied to the bracket bases before placement. Silkon brackets were coated with a primer before bonding. All samples were allowed 5 minutes to bench cure. Silanization procedure. Freshly mixed silane was applied to debonded bracket bases and allowed to air dry before the bonding resin was applied. The teeth were wet stored in distilled water at 37~ C in an incubator for 7 days. The teeth were secured in a clamp device of the Instron Universal testing
machine (lnstron Corp., Canton, Mass.). A 0.020-inch gauge wire was placed under the wings of the bracket with its ends clamped to a self-centering device. The specimens were then stressed in a gingivoincisal direction to failure employing a shear bond test on the Instron machine, according to a similar procedure described in the literature. 2'u All the recordings were calculatcd as force measured in Newtons, which was subsequently converted to stress per unit area (N/mm ~) by dividing the force by the unit area of the base of the bracket. Mean bonding surface area (bracket) was determined with a reflex microscope and a computer program: area of metal bracket: 9.2 mm'area of Silkon bracket: 9.9 mm2 area of Transcend 2000 bracket: 8.5 mm2 The sites of fracture of all the teeth were examined by a light optical stereoscopic microscope and recorded. Fracture sites were defined as occurring in predominately resin-bracket (RB) or resin-enamel (RE) areas when 50% or more of the surfaces were involved (RB =
