Histologic investigation of the human pulp after thermodebonding of metal and ceramic brackets PauI-Georg Jost-Brinkmann, Dr.med.dent.," Harald Stein, Dr.med., b Rainer-Reginald Miethke, Dr.med.dent., ~ and Minoru Nakata, DDS, DDSc d
Berlh~, Germany, and Fukuoka, Japan Twenty-five human permanent teeth scheduled for extraction for orthodontic reasons were used to study the effect of thermodebonding on the pulp tissue. One week before brackets were removed the teeth were bonded with either metal or ceramic brackets, with two alternative adhesives. For debonding, three different techniques were used: (1) debonding of ceramic brackets warmed up indirectly by resistance heating of a metallic bow applied to the bracket slot, (2) debonding of metal brackets warmed up directly by inductive heating of the bracket itself, and (3) debonding of ceramic brackets warmed up indirectly by inductive heating of metallic plier tips, applied to the mesial and distal bracket surfaces. Teeth with metal brackets removed without heat by squeezing the wings together served as a control group. The teeth were extracted 24 hours after debonding and subjected to a light microscopic study after histologic preparation and staining. In addition, the location of adhesive remnants was evaluated. While the thermodebonding of metal brackets worked properly and without any obvious pulp damage, there were problems related to the thermodebonding of ceramic brackets: (1) if more than one heating cycle was necessary, several teeth showed localized damage of the pulp with slight infiltration of inflammatory cells, (2) bracket fractures occurred frequently, and enamel damage could be shown, and (3) often with Transbond (Unitek/3M, Monrovia, Calif.) as the adhesive, more than one heating cycle was necessary for bracket removal, and thus patients complained about pain. (AMJ ORTHODDENTOFACORTHOP1992;102:410-7.)
T h e r e is no doubt that ceramic brackets represent a major esthetic improvement for our patients. However, when compared with metal brackets, they have a number of disadvantages: They are extremely hard and brittle, '3 expensive, and until now debonding was a severe problem. Therefore, since their introduction on the market, several articles have been published dealing with the fracture of ceramic brackets during treatment or at debonding, enamel wear, t,4'5 and even enamel fracture during the debonding procedure. 4'6 These partially unsolved problems provoked critical voices to claim that these brackets have been marketed without sufficient testing. Because of this, they called for strict rules concerning the security of new appliances for the sake of the patients' health. 7
Supported in part by Japan Society for the Promotion of Science, Dentaurum, Pforzheim, Germany, and Scheu-Dental, lserlohn, Germany. 'Assistant Professor, Department of Orthodontics and Pediatric Dentistry, Zahnklinik Nord, Freie Univcrsitht Berlin, Germany. At present with the Department of Pediatric Dentistry, Faculty of Dentistry, Kyushu University, Fukuoka, Japan (JSPS fellowship). bProfessor and Chairman, Department of Pathology, Klinikum Steglitz, Freie UniversitSt Berlin, Germany. 'Professor and Chairman, Department of Orthodontics and Pediatric Dentistiy, Zahnklinik Nord, Freie Universit~itBerlin, Germany. aProfessor and Chairman, Department of Pediatric Dentistry, Faculty of Dentistry, Kyushu University, Fukuoka, Japan. 811132342
410
In the meantime several attempts have been made to solve the debonding problem of ceramic brackets by investigating the etching time, 6 the type of adhesive in relation to bond strength, 6"8"9''~and the introduction of mechanical retention. Also, special debonding devices and procedures for almost every ceramic bracket system were developed. To avoid enamel fracture, it would be desirable that separation occurred between bracket base and adhesive or within the adhesive layer. If at the same time, brackets came off undamaged, recycling would be possible," which means a considerable financial improvement. In several instances, thermodebonding has been suggested as the ideal procedure for the debonding of brackets.t.tz't3 After the introduction of thermodebonding by electromagnetic induction, t4:5 an appliance has become available more recently that heats metal brackets by induced current. The heating time for this kind of appliance varies between 80 and 120 msec. In laboratory and clinical studies it has been shown that this kind of bracket removal is safe and simple, t3 Unfortunately, this procedure does not work with ceramic brackets because they are electronic and thermal insulators. Therefore, in the case of ceramic brackets, the heating has to be done indirectly. Although the thermal conductivity of aluminumoxide is poor, it could be shown by means of a finite element analysis that the
rob,me 102
Number 5
Thermodebonding of metal and ceramic brackets
411
Fig. 1. Dentaurum thermodebonding unit inserted into bracket slot. The missing bracket wing was broken during the first attempt to remove the bracket.
Fig. 2. Scheu-Dental ceramic thermodebonding plier with ceramic bracket inserted. Through closing the plier, the metal bars above the bracket come into contact and start the induced current, which heats the plier tips.
adhesive layer can be softened without raising the temperature at the enamel-dentine border to 42 ~ C if the temperature of the heating device is at least 450 ~ C . " To make further clinical experiments with ceramic brackets after the introduction of additional equipment on the market unnecessary, the following study was initiated.
B in combination with heating-plier prototype (Fig. 2) (heating time 120 msec). Before thermodebonding, the brackets were dried with compressed air to avoid evaporation during the debonding procedure. During the heating time, all ceramic brackets were loaded with a couple. If the brackets could not be removed during the first heating cycle, the next one was started as soon as the built-in safety mechanism of the thcrmodebonding appliances allowed, and the number of necessary heating cycles was registered. Also registered was the time during which the patients had unpleasant sensations or even slight pain. To define the location of fracture, the bracket base and tooth were examined with an optical magnifier. If more than two thirds of the adhesive remained on the tooth, this condition was classified as tooth, whereas it was classified as bracket if more than two thirds was left on the bracket base. Every other adhesive distribution was labeled toothlbracket (see Table I). Finally, any bracket damage that occurred was recorded. Twenty-four hours after thermodebonding all respective teeth were extracted after local anesthesia was induced. To achieve a complete fixation of the crown pulp immediately after extraction, the roots of the teeth were cut off with a diamond disk. To avoid false histologic findings, any heat development was suppressed by cooling the whole system with physiologic solution of sodium chloride. Subsequently, the crowns were transferred for at least 14 days into a fixing solution (0.2 mol/L solution of cacodylate buffer [pH 7.2] plus an equal amount of 4% glutaraldehyde) and stored at 4 ~ C. After complete fixation, the teeth were embedded in methacrylate, and semithin sections (30 to 50 I.tm) were cut. These were superficially stained ahcrnatively with Giemsa or yon Kossa/fuchsin for histopathologic examination. First, the sections were observed at random without
MATERIAL AND METHODS Two different prototypes of thermodebonding appliances were tested in this investigation. One appliance, A (Dentaurum, Pfor-zheim, Germany), uses a heating resistance that fits in the bracket slot (Fig. 1), whereas the other appliance, B (DeBond 200, Scheu-Dental, lserlohn, Germany), heats the brackets at the mesial and distal surface with plier tips that are heated by electromagnetic induction (Fig. 2). After replacing these pliers, the latter appliance can also be used for the debonding of metal brackets. Twenty-five permanent human premolars and incisors were used for this investigation. As can be seen in Table I, the teeth were bonded with either metal (American Orthodontics, Lemgo, Germany) or polycrystalline ceramic brackets (Dentaurum, Pforzheim, Germany). Etching time was 60 seconds, and 37% phosphoric acid served as the etching agent. As the bonding adhesive, two light-curing materials (Heliosit Orthodontic, Vivadent, Liechtenstein, and Transbond, Unitek/3M, Monrovia, Calif.) were used alternatively. The time of light exposure was respectively 20 seconds from occlusal and gingival. One week after bonding all brackets were removed with different techniques (see Table 1): removal of metal brackets without heat by squeezing the bracket wings, thermodcbond-" ing of metal brackets with appliance B (heating time 80 msec), thcrmodebonding of ceramic brackets with appliance A (Fig. I), and thermodebonding of ceramic brackets with appliance
Jost-Brinkntann et al.
412
T
a
b
l
e
Am.J. Orthod.Dentofac.Orthop. November1992
I. M a t e r i a l s a n d d e t a i l e d results
Name I.W. S.K. R.P. S.K. R.P. R.P. R.P. D.B. N.K. N.K. A.S. D.B. D.B. A.S. D.B. A.R. A.R. L.P. A.C. A.C. B.P. B.P. A.R. A.R. L.P.
Debonding
Age ] Gender I Tooth [ Bracket [ Adhesive 10 12 12 12 12 12 12 12 13 13 24 12 12 24 12 20 20 17 16 16 18 18 20 20 17
Female Female Male Female Male Male Male Male Female Female Female Male Male Female Male Female Female Male Male Male Female Female Female Female Male
44 35 45 45 14 24 35 44 24 14 24 24 14 14 34 45 14 24 lI 21 45 14 35 23 14
Metal Metal Metal Metal Metal Metal Metal Metal Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic
Transb. Transb. Transb. Transb. Transb. Transb. Transb. Transb. Heliosit Heliosit Heliosit Heliosit Heliosit tteliosit Heliosit Heliosit Heliosit Traasb. Transb. Transb. Transb. Transb. Transb. Transb. -Transb.
Plier Plier Plier Scheu 80 msec Scheu 80 msec Scheu 80 msec Scheu 80 msec Scheu 80 msec Scheu 120 msec Scheu 120 msec Scheu 120 msec Scheu 120 msec Scheu 120 msee Scheu 120 msec Dentaurum l)entaurum Dentaurum Dentaurum Dentaurum Dentaurum Dentaurum Dentaurum Dentaumm Dentaurum Dentaurum
No. of heating I Bracket [ Complaint I cycles fracture duration Odontoblasts Yes Yes Yes ------Yes -
-
-
-
Yes Yes -
-
--Yes -
-
Yes Yes -
-
-
-
-Yes
-----------------15 min -< 1 min
Berlh~, Germany, and Fukuoka, Japan Twenty-five human permanent teeth scheduled for extraction for orthodontic reasons were used to study the effect of thermodebonding on the pulp tissue. One week before brackets were removed the teeth were bonded with either metal or ceramic brackets, with two alternative adhesives. For debonding, three different techniques were used: (1) debonding of ceramic brackets warmed up indirectly by resistance heating of a metallic bow applied to the bracket slot, (2) debonding of metal brackets warmed up directly by inductive heating of the bracket itself, and (3) debonding of ceramic brackets warmed up indirectly by inductive heating of metallic plier tips, applied to the mesial and distal bracket surfaces. Teeth with metal brackets removed without heat by squeezing the wings together served as a control group. The teeth were extracted 24 hours after debonding and subjected to a light microscopic study after histologic preparation and staining. In addition, the location of adhesive remnants was evaluated. While the thermodebonding of metal brackets worked properly and without any obvious pulp damage, there were problems related to the thermodebonding of ceramic brackets: (1) if more than one heating cycle was necessary, several teeth showed localized damage of the pulp with slight infiltration of inflammatory cells, (2) bracket fractures occurred frequently, and enamel damage could be shown, and (3) often with Transbond (Unitek/3M, Monrovia, Calif.) as the adhesive, more than one heating cycle was necessary for bracket removal, and thus patients complained about pain. (AMJ ORTHODDENTOFACORTHOP1992;102:410-7.)
T h e r e is no doubt that ceramic brackets represent a major esthetic improvement for our patients. However, when compared with metal brackets, they have a number of disadvantages: They are extremely hard and brittle, '3 expensive, and until now debonding was a severe problem. Therefore, since their introduction on the market, several articles have been published dealing with the fracture of ceramic brackets during treatment or at debonding, enamel wear, t,4'5 and even enamel fracture during the debonding procedure. 4'6 These partially unsolved problems provoked critical voices to claim that these brackets have been marketed without sufficient testing. Because of this, they called for strict rules concerning the security of new appliances for the sake of the patients' health. 7
Supported in part by Japan Society for the Promotion of Science, Dentaurum, Pforzheim, Germany, and Scheu-Dental, lserlohn, Germany. 'Assistant Professor, Department of Orthodontics and Pediatric Dentistry, Zahnklinik Nord, Freie Univcrsitht Berlin, Germany. At present with the Department of Pediatric Dentistry, Faculty of Dentistry, Kyushu University, Fukuoka, Japan (JSPS fellowship). bProfessor and Chairman, Department of Pathology, Klinikum Steglitz, Freie UniversitSt Berlin, Germany. 'Professor and Chairman, Department of Orthodontics and Pediatric Dentistiy, Zahnklinik Nord, Freie Universit~itBerlin, Germany. aProfessor and Chairman, Department of Pediatric Dentistry, Faculty of Dentistry, Kyushu University, Fukuoka, Japan. 811132342
410
In the meantime several attempts have been made to solve the debonding problem of ceramic brackets by investigating the etching time, 6 the type of adhesive in relation to bond strength, 6"8"9''~and the introduction of mechanical retention. Also, special debonding devices and procedures for almost every ceramic bracket system were developed. To avoid enamel fracture, it would be desirable that separation occurred between bracket base and adhesive or within the adhesive layer. If at the same time, brackets came off undamaged, recycling would be possible," which means a considerable financial improvement. In several instances, thermodebonding has been suggested as the ideal procedure for the debonding of brackets.t.tz't3 After the introduction of thermodebonding by electromagnetic induction, t4:5 an appliance has become available more recently that heats metal brackets by induced current. The heating time for this kind of appliance varies between 80 and 120 msec. In laboratory and clinical studies it has been shown that this kind of bracket removal is safe and simple, t3 Unfortunately, this procedure does not work with ceramic brackets because they are electronic and thermal insulators. Therefore, in the case of ceramic brackets, the heating has to be done indirectly. Although the thermal conductivity of aluminumoxide is poor, it could be shown by means of a finite element analysis that the
rob,me 102
Number 5
Thermodebonding of metal and ceramic brackets
411
Fig. 1. Dentaurum thermodebonding unit inserted into bracket slot. The missing bracket wing was broken during the first attempt to remove the bracket.
Fig. 2. Scheu-Dental ceramic thermodebonding plier with ceramic bracket inserted. Through closing the plier, the metal bars above the bracket come into contact and start the induced current, which heats the plier tips.
adhesive layer can be softened without raising the temperature at the enamel-dentine border to 42 ~ C if the temperature of the heating device is at least 450 ~ C . " To make further clinical experiments with ceramic brackets after the introduction of additional equipment on the market unnecessary, the following study was initiated.
B in combination with heating-plier prototype (Fig. 2) (heating time 120 msec). Before thermodebonding, the brackets were dried with compressed air to avoid evaporation during the debonding procedure. During the heating time, all ceramic brackets were loaded with a couple. If the brackets could not be removed during the first heating cycle, the next one was started as soon as the built-in safety mechanism of the thcrmodebonding appliances allowed, and the number of necessary heating cycles was registered. Also registered was the time during which the patients had unpleasant sensations or even slight pain. To define the location of fracture, the bracket base and tooth were examined with an optical magnifier. If more than two thirds of the adhesive remained on the tooth, this condition was classified as tooth, whereas it was classified as bracket if more than two thirds was left on the bracket base. Every other adhesive distribution was labeled toothlbracket (see Table I). Finally, any bracket damage that occurred was recorded. Twenty-four hours after thermodebonding all respective teeth were extracted after local anesthesia was induced. To achieve a complete fixation of the crown pulp immediately after extraction, the roots of the teeth were cut off with a diamond disk. To avoid false histologic findings, any heat development was suppressed by cooling the whole system with physiologic solution of sodium chloride. Subsequently, the crowns were transferred for at least 14 days into a fixing solution (0.2 mol/L solution of cacodylate buffer [pH 7.2] plus an equal amount of 4% glutaraldehyde) and stored at 4 ~ C. After complete fixation, the teeth were embedded in methacrylate, and semithin sections (30 to 50 I.tm) were cut. These were superficially stained ahcrnatively with Giemsa or yon Kossa/fuchsin for histopathologic examination. First, the sections were observed at random without
MATERIAL AND METHODS Two different prototypes of thermodebonding appliances were tested in this investigation. One appliance, A (Dentaurum, Pfor-zheim, Germany), uses a heating resistance that fits in the bracket slot (Fig. 1), whereas the other appliance, B (DeBond 200, Scheu-Dental, lserlohn, Germany), heats the brackets at the mesial and distal surface with plier tips that are heated by electromagnetic induction (Fig. 2). After replacing these pliers, the latter appliance can also be used for the debonding of metal brackets. Twenty-five permanent human premolars and incisors were used for this investigation. As can be seen in Table I, the teeth were bonded with either metal (American Orthodontics, Lemgo, Germany) or polycrystalline ceramic brackets (Dentaurum, Pforzheim, Germany). Etching time was 60 seconds, and 37% phosphoric acid served as the etching agent. As the bonding adhesive, two light-curing materials (Heliosit Orthodontic, Vivadent, Liechtenstein, and Transbond, Unitek/3M, Monrovia, Calif.) were used alternatively. The time of light exposure was respectively 20 seconds from occlusal and gingival. One week after bonding all brackets were removed with different techniques (see Table 1): removal of metal brackets without heat by squeezing the bracket wings, thermodcbond-" ing of metal brackets with appliance B (heating time 80 msec), thcrmodebonding of ceramic brackets with appliance A (Fig. I), and thermodebonding of ceramic brackets with appliance
Jost-Brinkntann et al.
412
T
a
b
l
e
Am.J. Orthod.Dentofac.Orthop. November1992
I. M a t e r i a l s a n d d e t a i l e d results
Name I.W. S.K. R.P. S.K. R.P. R.P. R.P. D.B. N.K. N.K. A.S. D.B. D.B. A.S. D.B. A.R. A.R. L.P. A.C. A.C. B.P. B.P. A.R. A.R. L.P.
Debonding
Age ] Gender I Tooth [ Bracket [ Adhesive 10 12 12 12 12 12 12 12 13 13 24 12 12 24 12 20 20 17 16 16 18 18 20 20 17
Female Female Male Female Male Male Male Male Female Female Female Male Male Female Male Female Female Male Male Male Female Female Female Female Male
44 35 45 45 14 24 35 44 24 14 24 24 14 14 34 45 14 24 lI 21 45 14 35 23 14
Metal Metal Metal Metal Metal Metal Metal Metal Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic Ceramic
Transb. Transb. Transb. Transb. Transb. Transb. Transb. Transb. Heliosit Heliosit Heliosit Heliosit Heliosit tteliosit Heliosit Heliosit Heliosit Traasb. Transb. Transb. Transb. Transb. Transb. Transb. -Transb.
Plier Plier Plier Scheu 80 msec Scheu 80 msec Scheu 80 msec Scheu 80 msec Scheu 80 msec Scheu 120 msec Scheu 120 msec Scheu 120 msec Scheu 120 msec Scheu 120 msee Scheu 120 msec Dentaurum l)entaurum Dentaurum Dentaurum Dentaurum Dentaurum Dentaurum Dentaurum Dentaumm Dentaurum Dentaurum
No. of heating I Bracket [ Complaint I cycles fracture duration Odontoblasts Yes Yes Yes ------Yes -
-
-
-
Yes Yes -
-
--Yes -
-
Yes Yes -
-
-
-
-Yes
-----------------15 min -< 1 min
