British Journal of Orthodontics
ISSN: 0301-228X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/yjor19
Ceramic Brackets David Birnie B.D.S., F.D.S, R.C.S., Edin., M.Orth. To cite this article: David Birnie B.D.S., F.D.S, R.C.S., Edin., M.Orth. (1990) Ceramic Brackets, British Journal of Orthodontics, 17:1, 71-75, DOI: 10.1179/bjo.17.1.71 To link to this article: http://dx.doi.org/10.1179/bjo.17.1.71
Published online: 21 Jun 2016.
Submit your article to this journal
View related articles
Citing articles: 32 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=yjor19 Download by: [Tufts University]
Date: 29 November 2016, At: 02:36
Briti.rh Journal of Orthodontics/Vol. 17/1990{71-75
Orthodontic Materials Update Ceramic Brackets DAVID BIRNIE, B.D.S., F.D.S, R.C.S., EDIN., M.ORTH. Queen Alexandra Hospital, Portsmouth P06 3L Y
Introduction The appearance of fixed orthodontic appliances has always been of particular concern to many patients. The development of appliances which would combine both acceptable aesthetics for the patient and adequate technical performance for the orthodontist has remained an elusive goal. Three methods of achieving these criteria have been attempted. I. Altering the appearance of or reducing the size of stainless steel brackets. 2. Repositioning the appliance onto the lingual surfaces of the teeth. 3. Changing the material from which brackets are made. Early attempts to coat metal brackets with a toothcoloured coating were unsuccessful due to failure of the coating to adhere and its translucence. There has recently been a firm trend towards the development of smaller stainless steel brackets but although these generally provide the technical performance required by the orthodontist, they offer little aesthetic advantage over conventionally sized appliances. Lingual orthodontics satisfies aesthetic criteria . by repositioning the fixed appliance on the lingual surfaces of the teeth, but in doing so produces a significant decrease in the performance of the appliance. Lingual orthodontics consequently has gained only a limited following. Early attempts to produce brackets of different Manufacturer/Supplier A Company American Orthodontics American Orthodontics Class One Orthodontics Dentaurum GAC Hudson Orthodontics Lancer Orthodontics Masel 0301-228Xf90/002000 + 00102.00
materials included the use ofpolycarbonate. These brackets, while aesthetically satisfactory in the early stages of treatment, deteriorated in appearance with time, and were insufficiently strong to withstand long treatments or transmit torque. More recently, ceramic reinforced plastic brackets have become available and while these seem more durable than polycarbonate brackets, their ability to maintain their integrity over long treatments remains suspect. In late 1986, the first brackets made of ceramic materials became widely available and by the time that the 87th Annual Session of the American Association of Orthodontists was held in Montreal in May 1987, almost all major orthodontic manufacturers had either announced, or were about to announce ranges of ceramic brackets. Ceramics Ceramics are materials which are first shaped and then hardened by heat. This includes clays, glasses, some precious stones, and metallic oxides. The ceramic material used in orthodontic brackets is alumina, either in its polycrystalline or monocrystalline form. The advantages of using alumina for orthodontic brackets is that its appearance is very good, its chemical resistance is excellent, and it is both hard and strong. The disadvantages are that it lacks ductility, and is difficult and expensive to manufacture. Ceramic brackets are now available from the following manufacturers or suppliers:
Bracket Starfire Silkon 20/20 Contour Fascination Allure Ill Harmony Intrigue Eclipse
Material MCA (monocrystalline alumina) Plastic/PCA PCA (polycrystalline alumina) PCA PCA PCA Not known PCA PCA ! · 1990 Brilish Sociely for lh< Sludy of Onhodonlics
72 D. Bimie
BJO Vol. 17 No. I
Manufacturer/SuppUer OIS Orthodontics Ormco Orthodontic Organisers Orthodontic Partners Rocky Mountain Orthodontics TOOC (The Other Orthodontic Company) Unitekf3M
Bracket Magic Touch Gem Illusion Ultra Quasar Crystal Transcend
Ceramic brackets come in a variety of edgewise morphologies including true siamese, semi-siamese, solid, and Lewis/Lang designs. Many brackets are made by specialist ceramic manufacturers and sold under proprietary names by manfacturers of orthodontic products or orthodontic supply companies. Some brackets from different manufacturers may, therefore, be almost identical products such as Intrigue, Illusion, and Quasar brackets. At the present time no ceramic Begg brackets are available. MonocrystaJUne versus polycrystalUne alumina
Since 1987, both monocrystalline and polycrystalline ceramic brackets have been available, and varied arguments put forward in favour of one or other material. Monocrystalline brackets are machined from extrusions of synthetic sapphire. Polycrystalline alumina brackets, on the other hand, are made by injection moulding submicron-sized particles of alumina suspended in a resin, sintering them to fuse the alumina and finally machining the bracket as necessary to produce the finished article. The physical properties of the raw materials (as opposed to brackets) compared with stainless steel are as follows: Property Hardness (Rockwell) Tensile strength (psi x 1000) Fracture toughness (MPa Pa) The figures for hardness show that both monocrystalline and polycrystalline a1umina have a significant advantage over stainless steel, and that for tensile strength monocrystalline alumina is much stronger than polycrystalline alumina, which in turn is significantly stronger than steel. This is reflected in the fact that the only true siamese brackets made from a ceramic material have been made from monocrystalline alumina. Scott (1988) has pointed out that the tensile strength of ceramics is dependent on the surface condition of the ceramic, and this can make tests on bulk samples misleading and irrelevant. In addition, an important physical property related to the behaviour of
Material PCA MCA (no longer manufactured) PCA PCA PCA PCA PCA
ceramics is fracture toughness, the ability of a material to resist fracture. This is determined by stressing the material by impact and measuring the size of crack produced. The units of measurement are metres pascals per square root metre. It can be seen that both types of alumina perform poorly compared with steel and this reflects their lack of ductility. Kusy (1988) examined the morphology of polycrystalline brackets under a scanning electron microscope and demonstrated defects, predominantly intergranular fractures which might have a detrimental effect on bracket performance. COnical AppUcation Introduction
Anecdotal reports of bracket breakage and tooth damage associated with the use of ceramic brackets have occurred over the past 18 months. In December 1988, the American Association of Orthodontists carried out a survey of members' experience with ceramic brackets. As a result of the survey, the President of the American Association of Orthodontists, Or John Lindquist, wrote to all AAO members suggesting that both health and MCA 97·5 260 2-4·5
PCA 82·5 55 3-5
Stainless steel 5-35 30--40 80-95
safety concerns existed on the part of the orthodontic specialty regarding ceramic brackets and prudent practitioners might wish to discuss the potential risks at an informed consent meeting with the patient and/or parent (Lindquist, 1989). Bonding
Ceramic brackets derive their bond strength either from the use of a silane coupling agent in the bracket base or mechanical retention. Some early designs used both these methods within the one bracket. All ceramic brackets can be bonded satisfactorily without the use of a special adhesive.
Ceramic Brackets 73
BJO February /99(1
Odegaard and Segner (1988) have shown that for one make of ceramic bracket, both mix and no-mix adhesives produced bond strengths that were slightly higher than for mesh backed brackets although the differences were not statistically significant. Patient selection and mechanical considerations
Ceramic brackets are not aesthetic versions of metal brackets and they require additional care from both orthodontist and patient if the best is to be obtained from them. Difficulties in the use of ceramic brackets arise from their brittleness and their hardness. The brittleness of ceramic brackets and their low fracture toughness make them liable to fracture either from external trauma or from occlusal trauma. Patients with deep overbites where occlusal contact may occur between lower ceramic brackets and, upper teeth may fracture bracket tiewings. Ceramic brackets are radiolucent, and remnants of fractured brackets may be harmful to the patient and difficult to detect. Every effort should, therefore, be made to prevent occlusal interferences either by bonding the upper arch before the lower, the use of a removable appliance to disclude the incisors or the use of rapid bite opening techniques with sectional mechanics initially in the upper arch. The problem of bracket fracture may also occur when placing or removing rectangular archwires which almost completely fill the slot and the risk of this can be reduced by using a more resilient full size wire before placing the stainless steel finishing archwire. Placement of additional torque in archwires may cause tiewing fracture on insertion with ceramic brackets and consideration should be given to increasing the amount of torque by inverting the bracket or even by using a torquing auxiliary rather than by incorporating torque in the archwire. · Care should be taken not to scratch the surface of the bra~ket during treatment. Careful ligation is necessary and elastomeric rings or coated ligatures (both conventional and Kobayashi) are recommended to prevent tie wing fracture. Monocrystalline ceramic brackets have a true siamese configuration which allows the use of ligation methods as used for metal brackets whereas most polycrystalline brackets have a semi-siamese tiewing design. Semi-siamese tiewing designs may make it difficult to place both elastomeric chain and ligating modules on the same bracket due to the reduced depth of the tiewing. Ceramic is much harder than enamel and may cause serious wear of the enamel on the upper incisors or canines where occlusal interferences and parafunctional habits are present (Douglass, 1989).
Methods of avoiding this problem include the use of elastomeric rings with covers for the occlusal part of the bracket on lower incisors (Aiastigards, Unitek/ 3M), and the techniques for eliminating occlusal interferences mentioned in the previous paragraph. The hardness of the bracket also creates difficu'ity in space closure as the bracket may 'dig into' the relatively softer archwire. If sliding mechanics are being used then consideration may be given to using metal brackets on the premolars to make space closure easier. De bonding
Removal of ceramic brackets has been an area of significant concern. It is probable that manufacturers initially overestimated the bond strength required to retain the bracket throughout treatment and did not take account of the differences necessary in debonding technique between ductile metal and brittle ceramic brackets. Two manufacturers (A Company and Unitek/3M) have produced special instruments or pliers for debonding their own ceramic brackets, although the A Company Starfire debonding pliers may be used to remove any bracket. General purpose ceramic bracket debonding pliers are made by a number of companies. The brittleness of ceramic brackets has caused the development of enamel cracks, or the loss of sections of enamel when brackets have failed during treatment (Swartz, 1989, personal communication) or during debonding at the end of treatment. This problem seems to affect certain types of brackets more than others and is presumably related to bond strength. Ceramic brackets should, therefore, be removed with the greatest care in accordance with the manufacturer's instructions. Ceramic brackets that seem particularly difficult to debond should be removed with a diamond bur. Alternative methods of debonding are being explored and one promising avenue is that of electrothermal debracketing (Sheridan et al., l986a, b). This involves heating the bracket with a rechargeable heating gun while applying a tensile force to the bracket which then separates from the tooth once sufficient heat has penetrated the bracket/ adhesive interface. The rise in intrapulpal temperature that occurs both during and subsequent to bracket removal appears to be within the limits suggested by Zach and Cohen ( 1965). Prototype electrothermal debracketing instruments are at present undergoing clinical trials. Summary
Ceramic brackets have been understandably wel-
74 D. Birnie corned by patients; they are the best attempt so far at producing an orthodontic appliance which combines the aesthetic needs of the patient with the technical performance required by the orthodontist. Nevertheless, the only advantage that ceramic brackets have over stainless steel brackets is one of appearance and serious questions about bracket fracture and tooth damage during bracket removal remain unanswered at the present time. There is considerable interest throughout the world in the industrial development and use of ceramics and it may be that future generations of ceramic brackets solve some or all of the problems that currently exist. At the present time, however, ceramic brackets should be used cautiously within the limitations of the material and not simply as an alternative to metal brackets. Any adverse incidents concerned with their use should be reported promptly to the supplier.
References Douai-. J. B. (1989)
BJO Vol. 17 No. I
KIBy, R. P. (1988)
Morphology of polycrystalline alumina brackets and its relationship to fracture toughness and strength, Angle Orthodontist, 58, 197-203. Undqulst, J. T. (1989)
Letter to members gives results of AAO survey on ceramic brackets, The Bulletin, 7, 3. Odqaard, J. and Segner, D. (1988)
Shear bond strength of metal brackets compared with a new ceramic bracket, American Journal of Orthodontics, 9, 201-206.
Scott, G. (1988)
Fracture toughness and surface cracks-the key to understanding ceramic brackets, Angle Orthodontist, !!8, 5-8. Sbericlaa, J. J., Brawley, G. and Hastings, J. (1986) Electrothermal debracketing-Part 1: An in vitro study, American Journal of Orthodontics, 89, 21-27. Sberldaa, J. J., Brawley, G. and Hastings, J. (1986) Electrothermal debracketing-Part 2: An in vit•o study, American Journal of Orthodontics, 89, 141-145. Zach, L. and Cohen, G. (1965)
Pulp response to externally applied heat, Oral Surgery, Oral Medicine and Oral Pathology, 19, 515-530.
Enamel wear caused by ceramic brackets, American Journal of Orthodontics, 9!1, 96-98.
Product News Hawley Russell & Baker Ltd., Leighton House, 35 Darkes Lane. Potters Bar, Herts .. EN6 IBH. Tel: (0707) 55579
Fascination brackets are available in both standard Edgewise and Roth Straight-wire with torque in the base. They are made of polycrystalline alumina which is sintered allowing for smooth geometry design of the bracket and no machining. This patented process reduces the stress concentrations associated with machined ceramics which weaken the bracket and can cause fracturing. The bases of the brackets are coated with Silane allowing any adhesive to be used. The Silane strength has recently been increased from 30 to 90 Newtons. Fascination Roth Straight Wire brackets are pre-loaded onto colour-coded jigs allowing for easier identification and placement. Brackets are available either in boxes of 10 pes or in kits; straight-wire brackets are also available individually.
Hudson Ltd., 243 Crookesmoor Road, Sheffield S6 3FQ. Tel: (0742) 666170/683175
Quasar Polycrystalline Siamese Brackets are avail-
able with torque in the base to Andrews or Roth values, and canines are available with a traction hook. Being a siamese bracket they are easy to ligate. The bracket is bonded via a Silane coupling interface. Miura plastic brackets are a very robust solid bracket made in clear acrylic, 0·018 or 0·022 slot, with well rounded contours for maximum patient comfort. Miura brackets are available with a vertical slot as per Brussard. Also available are Harmony ceramic brackets. Constructed in zirconia, they are said to have four times the strength of polycrystalline brackets. This feature makes debonding much easier, reducing the chance of damage.
Oradent Ltd., Eton Square, Eton, Windsor, Berks SL4 6BQ. Tel: (0753) 857714
Since GAC first introduced Allure ceramic brackets in 1986 they have undergone a number of essentially cosmetic changes. Constructed from polycrystalline aluminium oxide, Allure have a low profile and are a translucent enamel shade to blend with most tooth
BJO February /9911
colours. Allure brackets are available with 0·018" or 0·022" archwire slots and in either standard Edgewise or pre-torqued and angulated with Roth values. Most types of bonding adhesives can be used due to the manufacturer's use of a Silane coupling agent. In addition, the bracket bases have small recesses which serve to aid bonding and bracket release at the debonding stage. To aid bracket positioning, a plastic height and alignment gauge is incorporated which is particularly helpful when using straight-wire techniques. The design of plastic brackets has changed considerably since their introduction in the early sixties. GAC and TP are two companies which produce a range of plastic brackets from high dens.ity polycarbonate plastic. TP who specialize in the Begg system have plastic brackets available in either clear or tooth enamel shades. Similarly, GAC have a range of clear plastic brackets to meet Edgewise requirements. Both manufacturers advocate an acrylic based adhesive for bonding.
Ortho-Care UK Ltd, 5 Oxford Place, Bradford B03 OEF. Tel: (0274) 392017
Lancer Orthodontics have engineered the Intrigue bracket to help compensate for the brittleness present in all alumina brackets. The Intrigue is designed with a rounded slot base, smooth contours, and rounded hooks. The round base of the bracket slot leaves torque unaffected, yet the common fracture points resulting from sharp angles has been eliminated, reducing tie-wing breakage. Available in Roth specifications, with torque in the base, in Straight Wire twin brackets, 0·0 18" or 0·022" including 1st and 2nd premolars. Ortho-Care also have plastic Edgwewise brackets with a round 0·0 18" vertical slot. They are made of clear durable Lexan to the true Edgewise design for rotational control. They have contoured textured bases for maximum retention and rounded edges for maximum patient comfort. They offer an inexpensive alternative for aesthetic orthodontics.
Ceramic Brackets 75
Ortbomax Dental Ltd., Bankfield House, Carrbottom Road, Bradford B05 9BJ. Tel: (0274) 733842
The Transcend bracket is produced from polycrystalline alumina, which ensures a product of consistent strength and predictability. The translucent properties of Transcend diffuse light, rather than deflect it, thus, disguising the edges of the bracket rather than defining them and allowing the natural colour of the patient's teeth to show through. Transcend have a unique bonding surface which assures a superior chemical bond with all normal bonding adhesives; however, a light activated new material called Transbond, is now recommended for ease of positioning and correct bond strength. Several design changes to Transcend have been made since this product was first launched. The main changes are cuspids and bicuspids with or without hooks and an improved lower anterior bracket. Unitek also guarantee Transcend against material breakage or staining during the course of normal treatment (for single use only). Transcend is available in the Roth prescription 0·018" and 0·22" slot and is also available for the standard Edgewise technique. Transcend brackets are supplied with removable colour coded indicators which provide positive identification for each tooth and allow for accurate bracket placement. Two videos are available which demonstrate the correct debonding technique of ceramic brackets and the clinical use of Transcend (updated).
American Orthodontics (UK), Syma Building, Wellington Road, Cressex Industrial Estate, High Wyeombe, Bucks HPI2 3PR. Tel: (0494) 465364
Si/kon polycarbonate brackets are filled with a fibre reinforcing material which adds to their strength. Silkon brackets are not as hard as ceramics, a fact which may be an advantage rather than a disadvantage. These brackets will not wear or chip enamel if occluded upon. Debonding without problems is assured. While one may break, they will not shatter. Cosmetically, they are unsurpassed and the price is less than half of most ceramics. Use of 'Nomix 30-Si/kon Formula' eliminates the need of a plastic bracket primer although other adhesives may be used with a primer.
ISSN: 0301-228X (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/yjor19
Ceramic Brackets David Birnie B.D.S., F.D.S, R.C.S., Edin., M.Orth. To cite this article: David Birnie B.D.S., F.D.S, R.C.S., Edin., M.Orth. (1990) Ceramic Brackets, British Journal of Orthodontics, 17:1, 71-75, DOI: 10.1179/bjo.17.1.71 To link to this article: http://dx.doi.org/10.1179/bjo.17.1.71
Published online: 21 Jun 2016.
Submit your article to this journal
View related articles
Citing articles: 32 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=yjor19 Download by: [Tufts University]
Date: 29 November 2016, At: 02:36
Briti.rh Journal of Orthodontics/Vol. 17/1990{71-75
Orthodontic Materials Update Ceramic Brackets DAVID BIRNIE, B.D.S., F.D.S, R.C.S., EDIN., M.ORTH. Queen Alexandra Hospital, Portsmouth P06 3L Y
Introduction The appearance of fixed orthodontic appliances has always been of particular concern to many patients. The development of appliances which would combine both acceptable aesthetics for the patient and adequate technical performance for the orthodontist has remained an elusive goal. Three methods of achieving these criteria have been attempted. I. Altering the appearance of or reducing the size of stainless steel brackets. 2. Repositioning the appliance onto the lingual surfaces of the teeth. 3. Changing the material from which brackets are made. Early attempts to coat metal brackets with a toothcoloured coating were unsuccessful due to failure of the coating to adhere and its translucence. There has recently been a firm trend towards the development of smaller stainless steel brackets but although these generally provide the technical performance required by the orthodontist, they offer little aesthetic advantage over conventionally sized appliances. Lingual orthodontics satisfies aesthetic criteria . by repositioning the fixed appliance on the lingual surfaces of the teeth, but in doing so produces a significant decrease in the performance of the appliance. Lingual orthodontics consequently has gained only a limited following. Early attempts to produce brackets of different Manufacturer/Supplier A Company American Orthodontics American Orthodontics Class One Orthodontics Dentaurum GAC Hudson Orthodontics Lancer Orthodontics Masel 0301-228Xf90/002000 + 00102.00
materials included the use ofpolycarbonate. These brackets, while aesthetically satisfactory in the early stages of treatment, deteriorated in appearance with time, and were insufficiently strong to withstand long treatments or transmit torque. More recently, ceramic reinforced plastic brackets have become available and while these seem more durable than polycarbonate brackets, their ability to maintain their integrity over long treatments remains suspect. In late 1986, the first brackets made of ceramic materials became widely available and by the time that the 87th Annual Session of the American Association of Orthodontists was held in Montreal in May 1987, almost all major orthodontic manufacturers had either announced, or were about to announce ranges of ceramic brackets. Ceramics Ceramics are materials which are first shaped and then hardened by heat. This includes clays, glasses, some precious stones, and metallic oxides. The ceramic material used in orthodontic brackets is alumina, either in its polycrystalline or monocrystalline form. The advantages of using alumina for orthodontic brackets is that its appearance is very good, its chemical resistance is excellent, and it is both hard and strong. The disadvantages are that it lacks ductility, and is difficult and expensive to manufacture. Ceramic brackets are now available from the following manufacturers or suppliers:
Bracket Starfire Silkon 20/20 Contour Fascination Allure Ill Harmony Intrigue Eclipse
Material MCA (monocrystalline alumina) Plastic/PCA PCA (polycrystalline alumina) PCA PCA PCA Not known PCA PCA ! · 1990 Brilish Sociely for lh< Sludy of Onhodonlics
72 D. Bimie
BJO Vol. 17 No. I
Manufacturer/SuppUer OIS Orthodontics Ormco Orthodontic Organisers Orthodontic Partners Rocky Mountain Orthodontics TOOC (The Other Orthodontic Company) Unitekf3M
Bracket Magic Touch Gem Illusion Ultra Quasar Crystal Transcend
Ceramic brackets come in a variety of edgewise morphologies including true siamese, semi-siamese, solid, and Lewis/Lang designs. Many brackets are made by specialist ceramic manufacturers and sold under proprietary names by manfacturers of orthodontic products or orthodontic supply companies. Some brackets from different manufacturers may, therefore, be almost identical products such as Intrigue, Illusion, and Quasar brackets. At the present time no ceramic Begg brackets are available. MonocrystaJUne versus polycrystalUne alumina
Since 1987, both monocrystalline and polycrystalline ceramic brackets have been available, and varied arguments put forward in favour of one or other material. Monocrystalline brackets are machined from extrusions of synthetic sapphire. Polycrystalline alumina brackets, on the other hand, are made by injection moulding submicron-sized particles of alumina suspended in a resin, sintering them to fuse the alumina and finally machining the bracket as necessary to produce the finished article. The physical properties of the raw materials (as opposed to brackets) compared with stainless steel are as follows: Property Hardness (Rockwell) Tensile strength (psi x 1000) Fracture toughness (MPa Pa) The figures for hardness show that both monocrystalline and polycrystalline a1umina have a significant advantage over stainless steel, and that for tensile strength monocrystalline alumina is much stronger than polycrystalline alumina, which in turn is significantly stronger than steel. This is reflected in the fact that the only true siamese brackets made from a ceramic material have been made from monocrystalline alumina. Scott (1988) has pointed out that the tensile strength of ceramics is dependent on the surface condition of the ceramic, and this can make tests on bulk samples misleading and irrelevant. In addition, an important physical property related to the behaviour of
Material PCA MCA (no longer manufactured) PCA PCA PCA PCA PCA
ceramics is fracture toughness, the ability of a material to resist fracture. This is determined by stressing the material by impact and measuring the size of crack produced. The units of measurement are metres pascals per square root metre. It can be seen that both types of alumina perform poorly compared with steel and this reflects their lack of ductility. Kusy (1988) examined the morphology of polycrystalline brackets under a scanning electron microscope and demonstrated defects, predominantly intergranular fractures which might have a detrimental effect on bracket performance. COnical AppUcation Introduction
Anecdotal reports of bracket breakage and tooth damage associated with the use of ceramic brackets have occurred over the past 18 months. In December 1988, the American Association of Orthodontists carried out a survey of members' experience with ceramic brackets. As a result of the survey, the President of the American Association of Orthodontists, Or John Lindquist, wrote to all AAO members suggesting that both health and MCA 97·5 260 2-4·5
PCA 82·5 55 3-5
Stainless steel 5-35 30--40 80-95
safety concerns existed on the part of the orthodontic specialty regarding ceramic brackets and prudent practitioners might wish to discuss the potential risks at an informed consent meeting with the patient and/or parent (Lindquist, 1989). Bonding
Ceramic brackets derive their bond strength either from the use of a silane coupling agent in the bracket base or mechanical retention. Some early designs used both these methods within the one bracket. All ceramic brackets can be bonded satisfactorily without the use of a special adhesive.
Ceramic Brackets 73
BJO February /99(1
Odegaard and Segner (1988) have shown that for one make of ceramic bracket, both mix and no-mix adhesives produced bond strengths that were slightly higher than for mesh backed brackets although the differences were not statistically significant. Patient selection and mechanical considerations
Ceramic brackets are not aesthetic versions of metal brackets and they require additional care from both orthodontist and patient if the best is to be obtained from them. Difficulties in the use of ceramic brackets arise from their brittleness and their hardness. The brittleness of ceramic brackets and their low fracture toughness make them liable to fracture either from external trauma or from occlusal trauma. Patients with deep overbites where occlusal contact may occur between lower ceramic brackets and, upper teeth may fracture bracket tiewings. Ceramic brackets are radiolucent, and remnants of fractured brackets may be harmful to the patient and difficult to detect. Every effort should, therefore, be made to prevent occlusal interferences either by bonding the upper arch before the lower, the use of a removable appliance to disclude the incisors or the use of rapid bite opening techniques with sectional mechanics initially in the upper arch. The problem of bracket fracture may also occur when placing or removing rectangular archwires which almost completely fill the slot and the risk of this can be reduced by using a more resilient full size wire before placing the stainless steel finishing archwire. Placement of additional torque in archwires may cause tiewing fracture on insertion with ceramic brackets and consideration should be given to increasing the amount of torque by inverting the bracket or even by using a torquing auxiliary rather than by incorporating torque in the archwire. · Care should be taken not to scratch the surface of the bra~ket during treatment. Careful ligation is necessary and elastomeric rings or coated ligatures (both conventional and Kobayashi) are recommended to prevent tie wing fracture. Monocrystalline ceramic brackets have a true siamese configuration which allows the use of ligation methods as used for metal brackets whereas most polycrystalline brackets have a semi-siamese tiewing design. Semi-siamese tiewing designs may make it difficult to place both elastomeric chain and ligating modules on the same bracket due to the reduced depth of the tiewing. Ceramic is much harder than enamel and may cause serious wear of the enamel on the upper incisors or canines where occlusal interferences and parafunctional habits are present (Douglass, 1989).
Methods of avoiding this problem include the use of elastomeric rings with covers for the occlusal part of the bracket on lower incisors (Aiastigards, Unitek/ 3M), and the techniques for eliminating occlusal interferences mentioned in the previous paragraph. The hardness of the bracket also creates difficu'ity in space closure as the bracket may 'dig into' the relatively softer archwire. If sliding mechanics are being used then consideration may be given to using metal brackets on the premolars to make space closure easier. De bonding
Removal of ceramic brackets has been an area of significant concern. It is probable that manufacturers initially overestimated the bond strength required to retain the bracket throughout treatment and did not take account of the differences necessary in debonding technique between ductile metal and brittle ceramic brackets. Two manufacturers (A Company and Unitek/3M) have produced special instruments or pliers for debonding their own ceramic brackets, although the A Company Starfire debonding pliers may be used to remove any bracket. General purpose ceramic bracket debonding pliers are made by a number of companies. The brittleness of ceramic brackets has caused the development of enamel cracks, or the loss of sections of enamel when brackets have failed during treatment (Swartz, 1989, personal communication) or during debonding at the end of treatment. This problem seems to affect certain types of brackets more than others and is presumably related to bond strength. Ceramic brackets should, therefore, be removed with the greatest care in accordance with the manufacturer's instructions. Ceramic brackets that seem particularly difficult to debond should be removed with a diamond bur. Alternative methods of debonding are being explored and one promising avenue is that of electrothermal debracketing (Sheridan et al., l986a, b). This involves heating the bracket with a rechargeable heating gun while applying a tensile force to the bracket which then separates from the tooth once sufficient heat has penetrated the bracket/ adhesive interface. The rise in intrapulpal temperature that occurs both during and subsequent to bracket removal appears to be within the limits suggested by Zach and Cohen ( 1965). Prototype electrothermal debracketing instruments are at present undergoing clinical trials. Summary
Ceramic brackets have been understandably wel-
74 D. Birnie corned by patients; they are the best attempt so far at producing an orthodontic appliance which combines the aesthetic needs of the patient with the technical performance required by the orthodontist. Nevertheless, the only advantage that ceramic brackets have over stainless steel brackets is one of appearance and serious questions about bracket fracture and tooth damage during bracket removal remain unanswered at the present time. There is considerable interest throughout the world in the industrial development and use of ceramics and it may be that future generations of ceramic brackets solve some or all of the problems that currently exist. At the present time, however, ceramic brackets should be used cautiously within the limitations of the material and not simply as an alternative to metal brackets. Any adverse incidents concerned with their use should be reported promptly to the supplier.
References Douai-. J. B. (1989)
BJO Vol. 17 No. I
KIBy, R. P. (1988)
Morphology of polycrystalline alumina brackets and its relationship to fracture toughness and strength, Angle Orthodontist, 58, 197-203. Undqulst, J. T. (1989)
Letter to members gives results of AAO survey on ceramic brackets, The Bulletin, 7, 3. Odqaard, J. and Segner, D. (1988)
Shear bond strength of metal brackets compared with a new ceramic bracket, American Journal of Orthodontics, 9, 201-206.
Scott, G. (1988)
Fracture toughness and surface cracks-the key to understanding ceramic brackets, Angle Orthodontist, !!8, 5-8. Sbericlaa, J. J., Brawley, G. and Hastings, J. (1986) Electrothermal debracketing-Part 1: An in vitro study, American Journal of Orthodontics, 89, 21-27. Sberldaa, J. J., Brawley, G. and Hastings, J. (1986) Electrothermal debracketing-Part 2: An in vit•o study, American Journal of Orthodontics, 89, 141-145. Zach, L. and Cohen, G. (1965)
Pulp response to externally applied heat, Oral Surgery, Oral Medicine and Oral Pathology, 19, 515-530.
Enamel wear caused by ceramic brackets, American Journal of Orthodontics, 9!1, 96-98.
Product News Hawley Russell & Baker Ltd., Leighton House, 35 Darkes Lane. Potters Bar, Herts .. EN6 IBH. Tel: (0707) 55579
Fascination brackets are available in both standard Edgewise and Roth Straight-wire with torque in the base. They are made of polycrystalline alumina which is sintered allowing for smooth geometry design of the bracket and no machining. This patented process reduces the stress concentrations associated with machined ceramics which weaken the bracket and can cause fracturing. The bases of the brackets are coated with Silane allowing any adhesive to be used. The Silane strength has recently been increased from 30 to 90 Newtons. Fascination Roth Straight Wire brackets are pre-loaded onto colour-coded jigs allowing for easier identification and placement. Brackets are available either in boxes of 10 pes or in kits; straight-wire brackets are also available individually.
Hudson Ltd., 243 Crookesmoor Road, Sheffield S6 3FQ. Tel: (0742) 666170/683175
Quasar Polycrystalline Siamese Brackets are avail-
able with torque in the base to Andrews or Roth values, and canines are available with a traction hook. Being a siamese bracket they are easy to ligate. The bracket is bonded via a Silane coupling interface. Miura plastic brackets are a very robust solid bracket made in clear acrylic, 0·018 or 0·022 slot, with well rounded contours for maximum patient comfort. Miura brackets are available with a vertical slot as per Brussard. Also available are Harmony ceramic brackets. Constructed in zirconia, they are said to have four times the strength of polycrystalline brackets. This feature makes debonding much easier, reducing the chance of damage.
Oradent Ltd., Eton Square, Eton, Windsor, Berks SL4 6BQ. Tel: (0753) 857714
Since GAC first introduced Allure ceramic brackets in 1986 they have undergone a number of essentially cosmetic changes. Constructed from polycrystalline aluminium oxide, Allure have a low profile and are a translucent enamel shade to blend with most tooth
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colours. Allure brackets are available with 0·018" or 0·022" archwire slots and in either standard Edgewise or pre-torqued and angulated with Roth values. Most types of bonding adhesives can be used due to the manufacturer's use of a Silane coupling agent. In addition, the bracket bases have small recesses which serve to aid bonding and bracket release at the debonding stage. To aid bracket positioning, a plastic height and alignment gauge is incorporated which is particularly helpful when using straight-wire techniques. The design of plastic brackets has changed considerably since their introduction in the early sixties. GAC and TP are two companies which produce a range of plastic brackets from high dens.ity polycarbonate plastic. TP who specialize in the Begg system have plastic brackets available in either clear or tooth enamel shades. Similarly, GAC have a range of clear plastic brackets to meet Edgewise requirements. Both manufacturers advocate an acrylic based adhesive for bonding.
Ortho-Care UK Ltd, 5 Oxford Place, Bradford B03 OEF. Tel: (0274) 392017
Lancer Orthodontics have engineered the Intrigue bracket to help compensate for the brittleness present in all alumina brackets. The Intrigue is designed with a rounded slot base, smooth contours, and rounded hooks. The round base of the bracket slot leaves torque unaffected, yet the common fracture points resulting from sharp angles has been eliminated, reducing tie-wing breakage. Available in Roth specifications, with torque in the base, in Straight Wire twin brackets, 0·0 18" or 0·022" including 1st and 2nd premolars. Ortho-Care also have plastic Edgwewise brackets with a round 0·0 18" vertical slot. They are made of clear durable Lexan to the true Edgewise design for rotational control. They have contoured textured bases for maximum retention and rounded edges for maximum patient comfort. They offer an inexpensive alternative for aesthetic orthodontics.
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Ortbomax Dental Ltd., Bankfield House, Carrbottom Road, Bradford B05 9BJ. Tel: (0274) 733842
The Transcend bracket is produced from polycrystalline alumina, which ensures a product of consistent strength and predictability. The translucent properties of Transcend diffuse light, rather than deflect it, thus, disguising the edges of the bracket rather than defining them and allowing the natural colour of the patient's teeth to show through. Transcend have a unique bonding surface which assures a superior chemical bond with all normal bonding adhesives; however, a light activated new material called Transbond, is now recommended for ease of positioning and correct bond strength. Several design changes to Transcend have been made since this product was first launched. The main changes are cuspids and bicuspids with or without hooks and an improved lower anterior bracket. Unitek also guarantee Transcend against material breakage or staining during the course of normal treatment (for single use only). Transcend is available in the Roth prescription 0·018" and 0·22" slot and is also available for the standard Edgewise technique. Transcend brackets are supplied with removable colour coded indicators which provide positive identification for each tooth and allow for accurate bracket placement. Two videos are available which demonstrate the correct debonding technique of ceramic brackets and the clinical use of Transcend (updated).
American Orthodontics (UK), Syma Building, Wellington Road, Cressex Industrial Estate, High Wyeombe, Bucks HPI2 3PR. Tel: (0494) 465364
Si/kon polycarbonate brackets are filled with a fibre reinforcing material which adds to their strength. Silkon brackets are not as hard as ceramics, a fact which may be an advantage rather than a disadvantage. These brackets will not wear or chip enamel if occluded upon. Debonding without problems is assured. While one may break, they will not shatter. Cosmetically, they are unsurpassed and the price is less than half of most ceramics. Use of 'Nomix 30-Si/kon Formula' eliminates the need of a plastic bracket primer although other adhesives may be used with a primer.
