Thermal debracketing of orthodontic resins Frederick A. Rueggeberg, DDS, MS* and Petra Lockwood** Augusta, Ga. Ten commercial brands of orthodontic bonding materials representing three modes of delivery systems (two-paste, no-mix, and powder/liquid) were used to bond stainless steel brackets to bovine teeth. Heat was applied to the bracket, and the temperature at debonding was noted for each type of resin. The two-paste systems required a higher temperature to debond than did the no-mix systems. The powder/liquid system required the lowest temperature. There is a direct relationship between filler content and debonding temperature. There is an inverse exponential relationship between debonding temperature and load needed to cause debracketing. Room-temperature debonding showed failure at the bracket/resin interface with evidence of cohesive enamel fracture. Thermal debonding showed no evidence of overt enamel fracture, and failure site shifted toward the tooth/resin interface. Ceramic brackets required almost twice the time to debracket than did stainless steel brackets. (AMJ ORTHODDENTOFACORTHROP1990;98:56-65.)
R e m o v a l of bonded orthodontic brackets on completion of therapy has routinely been performed with mechanical crimping instruments. The function of these instruments is either to deform an orthodontic bracket so that it will come free of the tooth leaving the bonding resin adhering to the enamel or to stress the composite to its ultimate" strength, causing resin fracture and bracket debonding. I As a result of deformation involved with mechanical removal, many of the metal brackets cannot be reconditioned for reuse.~ Of those brackets that are acceptable for reuse, a decreased bond strength is noted when compared with the strength at initial bracket placement. 24 The recently developed ceramic brackets do not mechanically deform to allow removal from the bonding resin. 1.5 Removal of these ceramic brackets is performed either through highspeed rotary abrasion with a diamond bur or by using special pliers designed to separate the bracket from the tooth with a minimum of stress to the enamel.I A problem that has been associated with mechanical removal of ceramic brackets is the loss of enamel along with the bracket base. 6 An innovative approach to bracket removal was introduced with the development of electrothermal debracketing (ETD). 7.s Electrothermal debracketing consists of the use of a rechargeable cordless heating device that is placed into the bracket slot and engages the bracket wing. The bracket is heated until the resin no From the Medical College of Georgia. Research was supported by NIH grant 2-507-RRO5795-09 and funds from the Medical College of Georgia Research Institute. *Assistant Professor, School of Dentistry. **Research Assistant, School of Dentistry. 811110449
56
longer adheres and is then pulled free from the tooth surface. Investigation has shown that ETD does not raise the pulpal wall temperature to a level that has the potential for causing histologic damage. 7.8 The work performed with ETD has been reported for only stainless steel brackets bonded with a single type of resin. Neither the differences in debonding temperatures among different brands and systems of orthodontic bonding resiias nor the relationship between resin temperature and debonding load have been studied. The purpose of this article is to examine the relative temperatures needed to thermally debond ten different brands of orthodontic bracket adhesive that represent the three delivery systems (two-paste, no-mix, and powder/liquid). In addition, the resin filler content and the load needed for bracket separation are examined for the influence on debonding temperatures. Finally, the thermal debonding characteristics of ceramic and stainless steel brackets are compared. MATERIALS AND METHODS The ten brands of orthodontic bonding resin that were chosen for thermal testing and a classification of each type of delivery system are listed in Table I. The substrate for bonding consisted of bovine anterior teeth that were obtained within 20 minutes after the animal was killed and were stored in a solution of 0.9% sodium chloride with 0.2% sodium azide to inhibit microbial growth, and were kept at room temperature. After the periodontal membrane and the attached gingiva were removed, the teeth were stored in a 1% solution of sodium hypochlorite at room temperature. Tooth preparation consisted of grinding a portion of the facial surface fiat with a 400-grit silicon carbide abrasive,
Volume98 Number 1
Thermal debracketing of orthodontic resins 5 7
Table I. Resins tested
Resin Achieve Achieve no-mix Concise Dynabond plus Instabond
Phase II Quasar Right-on TP 1-1 Unite
I
Manufacturer "A"-Company San Diego, Calif. "A"-Company San Diego, Calif. 3M Dental Division Irvine, Calif. Unitek Monrovia, Calif. Lee Pharmaceuticals So. El Monte, CaliL Reliance Ortho., INC. Itasca, II1. Rocky Mountain Ortho. Denver, Colo. TP Orthodontics La Porte, Ind. TP Orthodontics La Porte, Ind. Unitek Monrovia, Calif.
being careful that no dentin was exposed. Access to the pulp was made on the lingual surface, and the tissue was removed. The dentin on the facial tooth wall was thinned from the lingual side and, with a No. l/a bur, a hole was drilled through in the center of the flattened enamel from the pulpal side to the facial side. A type K thermocouple (Part TT-K-30SLE, Omega Engineering Inc., Stamford, Conn.) was prepared and positioned in this hole from the lingual side so that it was flush with the flattened enamel surface. The thermocouple was stabilized from the lingual aspect by the addition of light-cured composite. The facial surface was ground once again with a 400-grit silicon carbide to ensure that the thermocouple and enamel surfaces were flush. The facial enamel was then acid etched with the material supplied with the specific brand of bonding resin for the times recommended. After a 30-second water spray and clean air drying, the facial surface was examined for the presence of frosted enamel. The bonding material was mixed according to the manufacturer's directions, and an anterior stainless steel bracket (type A5701/02500, Rocky Mountain Orthodontics, Denver, Co.) was bonded to the facial surface and allowed to cure for 5 minutes. After this setting time, the tooth was placed in water and stored at 37 ° C for 24 hours before thermal debonding. After 24 hours, the tooth was placed in a brass holding jig by means of a positioning fork that oriented both the facial enamel surface perpendicular to the po-
Lot number
Delivery system
L0020
Two-paste
L0021
No-mix
7AE2
Two-paste
061087 091687 051287 7128/ BIDS None
Two-paste
71001
Powder/liquid
1617000
No-mix
2297024
Two-paste
061287
No-mix
No-mix
Two-paste
sitioning jig base and the upper bracket surface parallel to the jig base. Fig. 1 shows the tooth and bracket positioning. Once oriented, the tooth was stabilized in this position by the addition of mounting stone along the root. After the stone had hardened, the mounting jig with tooth was placed in a testing device that was capable of applying a known load to the upper surface on the bracket. The load was transferred to the bracket by means of a knife-edge positioned on the bracket base as close to the resin interface as possible. This load resulted in a shear stress at the resin/tooth interface. The vertical position of the bracket was monitored with a linear variable differential transformer, and the output was traced on an X-Y recorder. Heat was applied to the bracket by means of the flat blade of a soldering gun (Craftsman 200, Sears, Roebuck & Co., Chicago, I11.) oriented within the bracket slot. The temperature at the tooth/resin interface was monitored by the type K thermocouple, and the output was fed to an electronic cold-junction compensator (Omega Engineering, Inc., Stamford, Conn.) and was displayed on the same X-Y recorder. Fig. 2 is a diagrammatic close-up of the thermal debonding apparatus. The temperature at failure was noted by a sharp drop in the vertical position of the bracket. Five replications of the ten brands of resin were tested under a load of 22.2 N (5 pounds), and the mean debonding temperature of each brand was determined. The resin brands were grouped according to each delivery' system type, and the mean debonding
58
Am. J. Orthod. Dentofac. Orthop. July 1990
Rueggeberg and Lock, rood KNIFE BLADE FLATTENED ENAHEL
SOLDERING GUN
BRACKET POSITIONING FORK MOUNTING STONE
"11
TIP
THERMOCOUPLE
BRASS HOLDING JIG
.--'STONE BASE HOLDING JIG ~ 1
Fig. 2. Close-up of testing apparatus.
Fig. 1. Bracket-positioning device.
Table II. Debonding temperature with 22.2 N (5-pound) applied load Debonding temperature centrigrade* Resin
Mean
TP h i Phase II Achieve mix Concise Unite Achieve no-mix Right-on Dynabond plus lnstabond Quasar
228 ° 190 ° 187 ° 173" 167 ° 150 ° 139 ° 121" 61"
28 ° 42 ° 6° 21" 17" 12° 30 o 13° 8°
44*
6°
I
SD
*Mean of 5 replications.
temperatures of the system types were compared by means of a one-way analysis of variance to determine the presence of significant differences. Fisher's PLSD test at the 95% level of confidence was used to determine specific mean debonding temperature differences among the delivery system types. A record of the location of bond failures was kept, categorizing the failure at the tooth/resin interface (T/R), the cohesive failure within the resin bulk (C), or the separation at the bracket/resin interface (B/R). Inorganic filler content was determined gravimetrically in a manner similar to I S * specification 4049, s e c t i o n 5 . 7 . 9 Three replications were performed for each brand and the mean percent of filler loading was determined. Filler content was examined as a function of delivery system type, and a one-way analysis of variance was performed to determine the presence of significant differences. Specific mean differences in
filler content among delivery systems was identified by means of the Fisher's PLSD test at the 95% level of confidence. Regression analysis of the relationship between filler content and debonding temperature was also performed. One brand of bonding resin, Achieve, was chosen for a study of the effect of temperature on the load needed to cause debonding. Four replications of debonding the adhesive at loads of 89 N (20 pounds) and 178 N (40 pounds) were performed, and the temperatures were determined. To test the load required to cause debonding at room temperature (23 ° C), a dental surveyor table served as a positioning device for the toothholding jig. Five replications of debonding were made at room temperature with a Universal testing machine (model TT-B, Instron Corporation, Canton, Mass.) that applied a shear force in a manner similar to the device used for thermal debonding. The crosshead speed was 1.27 mm per minute. The load required to debond the bracket at room temperature was determined from a calibrated strip-chart recording. A record was kept of the site of bracket failure at the tooth/resin (T/R) interface, separation at the bracket/resin (B/R) interface, or fracture within the enamel (E). Five stainless steel and five single crystal sapphire (Starfire, "A"-Company, San Diego, Calif.) brackets were bonded to bovine teeth with Achieve bonding resin in the manner previously described. The same amount and type of brackets were bonded with Achieve NoMix. The brackets were debonded electrothermally under a load of 22.2 N (5 pounds) and the failure temperatures were noted. An analysis of variance was used at the 95% level of confidence to observe significant differences in debonding characteristics (temperature and time until bracket failure) between ceramic and stainless steel brackets with resins of different delivery systems. By means of the Fisher PLSD test, specific mean value differences were examined. The location
Volume 98 Number 1
Thermal debracketing of orthodontic resins 5 9
TP I:1
,-]
~ A - - t
PHASE II ACHIEVE MIX
2 PASTE SYSTEMS (*)
CONCISE
I
UNITE
SSSSSSSSSSSSSSS
ACHIEVE NO-MIX
I
RIGHT-ON
NO-MIX SYSTEMS
DYNABOND INSTABOND QUASAR
• POWDER & LIQUID SYSTEM I
I
I
I
0
100
200
300
TEMPERATURE (°C)
Fig. 3. Mean debonding temperature of resins and systems with 22.2 N load (horizontal bar = standard deviation).
of the fracture site was catalogued as previously described.
Table Ill. Delivery system and mean debonding temperature using 22.2 N (5-pound) load Debonding temperature centrigrade*
RESULTS Table II lists the mean debonding temperatures of the ten brands of resin tested when a load of 22.2 N was applied. The highest mean debonding temperature of 228 ° C was observed with TP 1" I, and the lowest mean debonding value temperature of 44 ° C was observed with Quasar. Fig. 3 displays the mean debonding temperatures in graph form and categorizes the materials according to delivery system. It is apparent from this figure that the two-paste systems have a higher debonding temperature than the no-mix systems. The powder/liquid system demonstrated the lowest debonding temperature. Table III lists the mean debonding temperatures of each system type and shows that the two-paste materials had significantly higher debonding temperatures than did the no-mix systems. The powder/liquid system required the lowest heat to cause bracket removal with a 22.2 N (5 pound) load and differed significantly from the other two systems. Table IV reports the incidence of failure sites of thermal debonding of the ten test resins with a load of 22.2 N (5 pounds). There does not appear to be any trend associated with failure site and type of delivery system. Table IV also reports the mean filler content of the resins. There was quite a range of filler levels from 0% to 75% by weight. The two-paste systems showed the highest values of filler load.
DeliveR" system
Mean
I
SD
Two-paste
180"
42°]]
No-mix
129°
45 ° -,
44 °
6° ]
Powder/liquid
*Mean of five replications. Bars connect systems significantly different (p < 0.05).
Table V indicates that there is no significant difference between the filler level of the two-paste and nomix systems, although the no-mix values were generally lower. However, the powder/liquid system differs significantly from the other two types. Fig. 4 indicates that as filler content is increased, mean debonding temperature increases in a linear manner (R 2 = 0.88). Fig. 5 presents the relationship between temperature at debonding and the load needed to cause failure when using Achieve resin. The relationship demonstrates that as the temperature of debonding increases, the load needed for debracketing decreases. The regression curve fits the characteristics of an inverse exponential relationship very well (R 2 = 0.99). Table VI shows
Am.J. Orthod.Dentofac.Orthop. July 1990
60 Rueggeberg and Lockavood 300 y = 54.301 + 1.798X R 2 = 0.88 lrl W rr
200
I'-w n
~1.11 I.-.
100
I
0
•
20
I
I
|
40 60 MEAN % FILLER (w/w)
80
Fig. 4. Filler content and debracketing temperature.
Table IV. Debonding failure site and mean filler content
t Brand TP I : 1 Phase II Achieve Concise Unite Achieve no-mix Right-on Dynabond plus Instabond Quasar
I
Delivery system
Failuresite (%)* 60 B I R 50 BIR 30 B / R 20 B / R 50 B / R 30 B / R 100 B / R 100 B / R 100 Cohesive I00 B / R
* BIR, Bracket-resin interface failure and **Mean of three replications.
40 50 70 80 50 70 0 0
TtR T/R T/R T/R T/R T/R T/R T/R
Two-paste Two-paste Two-paste Two-paste No-mix No-mix No-mix Two-paste No-mix Powder/liquid
0 T/R
Filler • Mean 73 71 73 75 62 71 54 31 0 0
¢jv/w)** SD 2 1 2 1 2 1 2 1 2 4
T/R, tooth-resin interface failure.
the incidence of bond failure site for each mean load used. As the mean load is increased (as the debonding temperature is lowered), the site of fracture tends to become associated more with the bracket/resin surface than with the tooth/resin interface in the stainless steel brackets tested. Fig. 6 indicates the relationship between type of bracket used (stainless steel or single crystal sapphire) and delivery system (two-paste or no-mix). There is a greater difference in debonding temperatures between the two-paste and no-mix systems when stainless steel brackets were used than when the ceramic brackets were used. There is a significant difference between the debonding temperatures of stainless steel and ceramic brackets when the no-mix system was used
(p = 0.015) but not when the two-paste material was used (p = 0.069). There was a significant difference in debonding temperature when the different systems were used with stainless steel brackets (p < 0.001) but not when the ceramic brackets were used (p = 0.393). When the debonding failure sites of ceramic brackets are compared with the different delivery systems and a 22.2 N load, Table VII shows that the two-paste system demonstrates all possible combinations of fracture. However, the use of a no-mix system with the ceramic brackets indicates that the primary failure site is at the tooth/resin interface. The difference in mean debonding time of ceramic and stainless steel brackets with a load of 22.2 N is shown in Table VIII. The mean time needed to de-
Volume98 Number I
Thermal debracketing of orthodontic resins 61
400
^(-0.007x) R = 0.99
z
300
173 < O ._d
200
A
u.I ..J 13.. 13..
R e m o v a l of bonded orthodontic brackets on completion of therapy has routinely been performed with mechanical crimping instruments. The function of these instruments is either to deform an orthodontic bracket so that it will come free of the tooth leaving the bonding resin adhering to the enamel or to stress the composite to its ultimate" strength, causing resin fracture and bracket debonding. I As a result of deformation involved with mechanical removal, many of the metal brackets cannot be reconditioned for reuse.~ Of those brackets that are acceptable for reuse, a decreased bond strength is noted when compared with the strength at initial bracket placement. 24 The recently developed ceramic brackets do not mechanically deform to allow removal from the bonding resin. 1.5 Removal of these ceramic brackets is performed either through highspeed rotary abrasion with a diamond bur or by using special pliers designed to separate the bracket from the tooth with a minimum of stress to the enamel.I A problem that has been associated with mechanical removal of ceramic brackets is the loss of enamel along with the bracket base. 6 An innovative approach to bracket removal was introduced with the development of electrothermal debracketing (ETD). 7.s Electrothermal debracketing consists of the use of a rechargeable cordless heating device that is placed into the bracket slot and engages the bracket wing. The bracket is heated until the resin no From the Medical College of Georgia. Research was supported by NIH grant 2-507-RRO5795-09 and funds from the Medical College of Georgia Research Institute. *Assistant Professor, School of Dentistry. **Research Assistant, School of Dentistry. 811110449
56
longer adheres and is then pulled free from the tooth surface. Investigation has shown that ETD does not raise the pulpal wall temperature to a level that has the potential for causing histologic damage. 7.8 The work performed with ETD has been reported for only stainless steel brackets bonded with a single type of resin. Neither the differences in debonding temperatures among different brands and systems of orthodontic bonding resiias nor the relationship between resin temperature and debonding load have been studied. The purpose of this article is to examine the relative temperatures needed to thermally debond ten different brands of orthodontic bracket adhesive that represent the three delivery systems (two-paste, no-mix, and powder/liquid). In addition, the resin filler content and the load needed for bracket separation are examined for the influence on debonding temperatures. Finally, the thermal debonding characteristics of ceramic and stainless steel brackets are compared. MATERIALS AND METHODS The ten brands of orthodontic bonding resin that were chosen for thermal testing and a classification of each type of delivery system are listed in Table I. The substrate for bonding consisted of bovine anterior teeth that were obtained within 20 minutes after the animal was killed and were stored in a solution of 0.9% sodium chloride with 0.2% sodium azide to inhibit microbial growth, and were kept at room temperature. After the periodontal membrane and the attached gingiva were removed, the teeth were stored in a 1% solution of sodium hypochlorite at room temperature. Tooth preparation consisted of grinding a portion of the facial surface fiat with a 400-grit silicon carbide abrasive,
Volume98 Number 1
Thermal debracketing of orthodontic resins 5 7
Table I. Resins tested
Resin Achieve Achieve no-mix Concise Dynabond plus Instabond
Phase II Quasar Right-on TP 1-1 Unite
I
Manufacturer "A"-Company San Diego, Calif. "A"-Company San Diego, Calif. 3M Dental Division Irvine, Calif. Unitek Monrovia, Calif. Lee Pharmaceuticals So. El Monte, CaliL Reliance Ortho., INC. Itasca, II1. Rocky Mountain Ortho. Denver, Colo. TP Orthodontics La Porte, Ind. TP Orthodontics La Porte, Ind. Unitek Monrovia, Calif.
being careful that no dentin was exposed. Access to the pulp was made on the lingual surface, and the tissue was removed. The dentin on the facial tooth wall was thinned from the lingual side and, with a No. l/a bur, a hole was drilled through in the center of the flattened enamel from the pulpal side to the facial side. A type K thermocouple (Part TT-K-30SLE, Omega Engineering Inc., Stamford, Conn.) was prepared and positioned in this hole from the lingual side so that it was flush with the flattened enamel surface. The thermocouple was stabilized from the lingual aspect by the addition of light-cured composite. The facial surface was ground once again with a 400-grit silicon carbide to ensure that the thermocouple and enamel surfaces were flush. The facial enamel was then acid etched with the material supplied with the specific brand of bonding resin for the times recommended. After a 30-second water spray and clean air drying, the facial surface was examined for the presence of frosted enamel. The bonding material was mixed according to the manufacturer's directions, and an anterior stainless steel bracket (type A5701/02500, Rocky Mountain Orthodontics, Denver, Co.) was bonded to the facial surface and allowed to cure for 5 minutes. After this setting time, the tooth was placed in water and stored at 37 ° C for 24 hours before thermal debonding. After 24 hours, the tooth was placed in a brass holding jig by means of a positioning fork that oriented both the facial enamel surface perpendicular to the po-
Lot number
Delivery system
L0020
Two-paste
L0021
No-mix
7AE2
Two-paste
061087 091687 051287 7128/ BIDS None
Two-paste
71001
Powder/liquid
1617000
No-mix
2297024
Two-paste
061287
No-mix
No-mix
Two-paste
sitioning jig base and the upper bracket surface parallel to the jig base. Fig. 1 shows the tooth and bracket positioning. Once oriented, the tooth was stabilized in this position by the addition of mounting stone along the root. After the stone had hardened, the mounting jig with tooth was placed in a testing device that was capable of applying a known load to the upper surface on the bracket. The load was transferred to the bracket by means of a knife-edge positioned on the bracket base as close to the resin interface as possible. This load resulted in a shear stress at the resin/tooth interface. The vertical position of the bracket was monitored with a linear variable differential transformer, and the output was traced on an X-Y recorder. Heat was applied to the bracket by means of the flat blade of a soldering gun (Craftsman 200, Sears, Roebuck & Co., Chicago, I11.) oriented within the bracket slot. The temperature at the tooth/resin interface was monitored by the type K thermocouple, and the output was fed to an electronic cold-junction compensator (Omega Engineering, Inc., Stamford, Conn.) and was displayed on the same X-Y recorder. Fig. 2 is a diagrammatic close-up of the thermal debonding apparatus. The temperature at failure was noted by a sharp drop in the vertical position of the bracket. Five replications of the ten brands of resin were tested under a load of 22.2 N (5 pounds), and the mean debonding temperature of each brand was determined. The resin brands were grouped according to each delivery' system type, and the mean debonding
58
Am. J. Orthod. Dentofac. Orthop. July 1990
Rueggeberg and Lock, rood KNIFE BLADE FLATTENED ENAHEL
SOLDERING GUN
BRACKET POSITIONING FORK MOUNTING STONE
"11
TIP
THERMOCOUPLE
BRASS HOLDING JIG
.--'STONE BASE HOLDING JIG ~ 1
Fig. 2. Close-up of testing apparatus.
Fig. 1. Bracket-positioning device.
Table II. Debonding temperature with 22.2 N (5-pound) applied load Debonding temperature centrigrade* Resin
Mean
TP h i Phase II Achieve mix Concise Unite Achieve no-mix Right-on Dynabond plus lnstabond Quasar
228 ° 190 ° 187 ° 173" 167 ° 150 ° 139 ° 121" 61"
28 ° 42 ° 6° 21" 17" 12° 30 o 13° 8°
44*
6°
I
SD
*Mean of 5 replications.
temperatures of the system types were compared by means of a one-way analysis of variance to determine the presence of significant differences. Fisher's PLSD test at the 95% level of confidence was used to determine specific mean debonding temperature differences among the delivery system types. A record of the location of bond failures was kept, categorizing the failure at the tooth/resin interface (T/R), the cohesive failure within the resin bulk (C), or the separation at the bracket/resin interface (B/R). Inorganic filler content was determined gravimetrically in a manner similar to I S * specification 4049, s e c t i o n 5 . 7 . 9 Three replications were performed for each brand and the mean percent of filler loading was determined. Filler content was examined as a function of delivery system type, and a one-way analysis of variance was performed to determine the presence of significant differences. Specific mean differences in
filler content among delivery systems was identified by means of the Fisher's PLSD test at the 95% level of confidence. Regression analysis of the relationship between filler content and debonding temperature was also performed. One brand of bonding resin, Achieve, was chosen for a study of the effect of temperature on the load needed to cause debonding. Four replications of debonding the adhesive at loads of 89 N (20 pounds) and 178 N (40 pounds) were performed, and the temperatures were determined. To test the load required to cause debonding at room temperature (23 ° C), a dental surveyor table served as a positioning device for the toothholding jig. Five replications of debonding were made at room temperature with a Universal testing machine (model TT-B, Instron Corporation, Canton, Mass.) that applied a shear force in a manner similar to the device used for thermal debonding. The crosshead speed was 1.27 mm per minute. The load required to debond the bracket at room temperature was determined from a calibrated strip-chart recording. A record was kept of the site of bracket failure at the tooth/resin (T/R) interface, separation at the bracket/resin (B/R) interface, or fracture within the enamel (E). Five stainless steel and five single crystal sapphire (Starfire, "A"-Company, San Diego, Calif.) brackets were bonded to bovine teeth with Achieve bonding resin in the manner previously described. The same amount and type of brackets were bonded with Achieve NoMix. The brackets were debonded electrothermally under a load of 22.2 N (5 pounds) and the failure temperatures were noted. An analysis of variance was used at the 95% level of confidence to observe significant differences in debonding characteristics (temperature and time until bracket failure) between ceramic and stainless steel brackets with resins of different delivery systems. By means of the Fisher PLSD test, specific mean value differences were examined. The location
Volume 98 Number 1
Thermal debracketing of orthodontic resins 5 9
TP I:1
,-]
~ A - - t
PHASE II ACHIEVE MIX
2 PASTE SYSTEMS (*)
CONCISE
I
UNITE
SSSSSSSSSSSSSSS
ACHIEVE NO-MIX
I
RIGHT-ON
NO-MIX SYSTEMS
DYNABOND INSTABOND QUASAR
• POWDER & LIQUID SYSTEM I
I
I
I
0
100
200
300
TEMPERATURE (°C)
Fig. 3. Mean debonding temperature of resins and systems with 22.2 N load (horizontal bar = standard deviation).
of the fracture site was catalogued as previously described.
Table Ill. Delivery system and mean debonding temperature using 22.2 N (5-pound) load Debonding temperature centrigrade*
RESULTS Table II lists the mean debonding temperatures of the ten brands of resin tested when a load of 22.2 N was applied. The highest mean debonding temperature of 228 ° C was observed with TP 1" I, and the lowest mean debonding value temperature of 44 ° C was observed with Quasar. Fig. 3 displays the mean debonding temperatures in graph form and categorizes the materials according to delivery system. It is apparent from this figure that the two-paste systems have a higher debonding temperature than the no-mix systems. The powder/liquid system demonstrated the lowest debonding temperature. Table III lists the mean debonding temperatures of each system type and shows that the two-paste materials had significantly higher debonding temperatures than did the no-mix systems. The powder/liquid system required the lowest heat to cause bracket removal with a 22.2 N (5 pound) load and differed significantly from the other two systems. Table IV reports the incidence of failure sites of thermal debonding of the ten test resins with a load of 22.2 N (5 pounds). There does not appear to be any trend associated with failure site and type of delivery system. Table IV also reports the mean filler content of the resins. There was quite a range of filler levels from 0% to 75% by weight. The two-paste systems showed the highest values of filler load.
DeliveR" system
Mean
I
SD
Two-paste
180"
42°]]
No-mix
129°
45 ° -,
44 °
6° ]
Powder/liquid
*Mean of five replications. Bars connect systems significantly different (p < 0.05).
Table V indicates that there is no significant difference between the filler level of the two-paste and nomix systems, although the no-mix values were generally lower. However, the powder/liquid system differs significantly from the other two types. Fig. 4 indicates that as filler content is increased, mean debonding temperature increases in a linear manner (R 2 = 0.88). Fig. 5 presents the relationship between temperature at debonding and the load needed to cause failure when using Achieve resin. The relationship demonstrates that as the temperature of debonding increases, the load needed for debracketing decreases. The regression curve fits the characteristics of an inverse exponential relationship very well (R 2 = 0.99). Table VI shows
Am.J. Orthod.Dentofac.Orthop. July 1990
60 Rueggeberg and Lockavood 300 y = 54.301 + 1.798X R 2 = 0.88 lrl W rr
200
I'-w n
~1.11 I.-.
100
I
0
•
20
I
I
|
40 60 MEAN % FILLER (w/w)
80
Fig. 4. Filler content and debracketing temperature.
Table IV. Debonding failure site and mean filler content
t Brand TP I : 1 Phase II Achieve Concise Unite Achieve no-mix Right-on Dynabond plus Instabond Quasar
I
Delivery system
Failuresite (%)* 60 B I R 50 BIR 30 B / R 20 B / R 50 B / R 30 B / R 100 B / R 100 B / R 100 Cohesive I00 B / R
* BIR, Bracket-resin interface failure and **Mean of three replications.
40 50 70 80 50 70 0 0
TtR T/R T/R T/R T/R T/R T/R T/R
Two-paste Two-paste Two-paste Two-paste No-mix No-mix No-mix Two-paste No-mix Powder/liquid
0 T/R
Filler • Mean 73 71 73 75 62 71 54 31 0 0
¢jv/w)** SD 2 1 2 1 2 1 2 1 2 4
T/R, tooth-resin interface failure.
the incidence of bond failure site for each mean load used. As the mean load is increased (as the debonding temperature is lowered), the site of fracture tends to become associated more with the bracket/resin surface than with the tooth/resin interface in the stainless steel brackets tested. Fig. 6 indicates the relationship between type of bracket used (stainless steel or single crystal sapphire) and delivery system (two-paste or no-mix). There is a greater difference in debonding temperatures between the two-paste and no-mix systems when stainless steel brackets were used than when the ceramic brackets were used. There is a significant difference between the debonding temperatures of stainless steel and ceramic brackets when the no-mix system was used
(p = 0.015) but not when the two-paste material was used (p = 0.069). There was a significant difference in debonding temperature when the different systems were used with stainless steel brackets (p < 0.001) but not when the ceramic brackets were used (p = 0.393). When the debonding failure sites of ceramic brackets are compared with the different delivery systems and a 22.2 N load, Table VII shows that the two-paste system demonstrates all possible combinations of fracture. However, the use of a no-mix system with the ceramic brackets indicates that the primary failure site is at the tooth/resin interface. The difference in mean debonding time of ceramic and stainless steel brackets with a load of 22.2 N is shown in Table VIII. The mean time needed to de-
Volume98 Number I
Thermal debracketing of orthodontic resins 61
400
^(-0.007x) R = 0.99
z
300
173 < O ._d
200
A
u.I ..J 13.. 13..
