The adhesives introduced in the early 1970s were primarily those of the powder-liquid type of methyl methacrylate that did not incorporate a filler. During this period, all the adhesives introduced had to adhere to plastic brackets that were made of polycarbonate. As time passed, however, the weakness of plastic brackets became apparent and metal brackets began to be used.
From the mid 1970s, the paste type of adhesives emerged in which both the base material and the catalyst were dispensed as pastes to be mixed before being used for bonding. The reason for this change was mainly due to the change in the type of brackets used in bonding.
Most of the resins used in orthodontics presently are modifications of the Bowen’s resin. The modifications are mainly in the physical properties such as viscosity of the materials to achieve optimal penetration of the resin into the etched enamel spaces which enhanced the bond strength and increased the dimensional stability by cross-linking.
The future of bonding is promising. Product development in terms of adhesives, brackets, and technical details is continually occurring at a rapid rate. Also new avenues for bonding in orthodontics are opening up;
q Lingual bonding
q Various types of bonded retainers and splints
q Semi-permanent single-tooth replacements
q Resin build-ups addressing tooth shape & size problems and
q Bonded space maintainers.
Bracket Bonding
Optimal performance in bonding of orthodontic attachments offers many ADVANTAGES when compared with conventional banding.
1. It is esthetically superior
2. It is faster and simpler
3. It results in less discomfort for the patient (no band seating and separation)
4. Arch length is not increased by band material
5. It allows more precise bracket placement (aberrant tooth shape does not result in difficult banding and poor attachment position)
6. Bonds are more hygienic than bands, therefore an improved gingival and periodontal condition is possible and better access for cleaning is available
7. Partially erupted teeth can be controlled
8. Mesiodistal enamel reduction is possible during treatment
9. Attachments may be bonded to artificial tooth surfaces (e.g. amalgam, porcelain and gold) and to fixed bridge work
10. Interproximal areas are accessible for composite build ups
11. Caries risk under loose bands is eliminated. Interproximal caries can be detected and treated.
12. No band spaces are present to close at the end of treatment.
13. No large inventory of bands is needed.
14. Brackets may be recycled, further reducing the cost.
15. Lingual brackets, invisible braces, can be used when the patient rejects visible orthodontic appliances.
DISADVANTAGES of bonding are;
1. A bonded bracket has a weaker attachment than a cemented band. Therefore it is more likely that a bracket will come off rather than that a band will become loosened.
2. Some bonding adhesives are not sufficiently strong.
3. Better access for cleaning does not guarantee better oral hygiene and improved gingival condition, especially if excess adhesive extends beyond the bracket base.
4. The protection against interproximal caries provided by well-contoured cemented bands is absent.
5. Bonding is more complicated when lingual auxiliaries are required or if headgears are attached.
6. Rebonding a loose bracket requires more preparation than recementing a loose band.
7. Debonding is more time consuming than debanding because removal of adhesive is more difficult than removal of cement.
Classification of Bonding Materials
A. Based on the basic bonding type
1. Acrylic based system
2. Diacrylate system
3. Glass ionomer system
B. Based on the curing system
1. Self curing system
2. Light curing system
3. Dual curing system
4. Laser curing system
C. Based on fluoride content
1. Fluoride releasing system
2. Non-fluoride releasing system
D. Based on filler content
1. Low or unfilled bonding system
2. Highly filled bonding system
Types of Adhesives
There are 2 basic types of dental resins currently in use for orthodontic bracket bonding. Both are polymers and are classified as;
A) Acrylic resins and B) Diacrylate resins
A. ACRYLIC RESINS – are based on self curing acrylics and consists of methyl methacrylate monomer and ultrafine powder. They formed linear polymers only. E.g. Orthomite, Directon, Genie.
B. DIACRYLATE RESINS – are based on acrylic modified epoxy resin (Bis GMA or Bowen’s resin). They polymerize by cross-linking into a three dimensional network. This contributes to greater strength, lower water absorption and less polymerization shrinkage.
q Both types of adhesives exist in either filled or unfilled forms.
q Investigations indicate that filled diacrylate resins of the Bis GMA type have the best physical properties and are strongest adhesives for metal brackets.
q Acrylic or combination resins have been most successful with plastic brackets.
q Some composite resins (Concise, Solo-Tach, Nuva-Tach) contain large coarse quartz or silica glass particles of highly variable size (3 to 20 micrometer) impart abrasion resistance properties.
q Others (Endur, Dynabond) contain minute filler particles of uniform size (0.2 to 0.3 micrometer) which yield a smoother surface that retains less plaque, but more prone to abrasion.
q Failure rates are significantly less with adhesives containing large filler particles and are recommended for extra bond strength but careful removal of excess is mandatory since such adhesives accumulate more plaque than others.
There are several alternatives to chemically autopolymerizing paste – paste systems.
1. No-mix adhesives – (Rely-A-Bond, System 1+) - These materials set when one paste under light pressure is brought together with a primer fluid on the etched enamel and bracket backing, or another paste on the tooth to be bonded.
Thus one adhesive component is applied to bracket base while another is applied to the dried etched tooth. As soon as it is precisely positioned, the bracket is pressed firmly into place and curing occurs usually within 30 to 60 seconds.
Little long term information is available on their bond strengths compared with those of the conventionally mixed paste – paste systems.
Furthermore, little is known about how much unpolymerized rest monomer remains in the cured adhesives, and its eventual toxicity. Invitro tests have shown that the liquid activators of the no-mix systems are definitely toxic, allergic reactions have been reported in patients, dental assistance and doctors when such adhesives are used.
2. Visible – Light polymerized adhesives (Transbond) - These materials are cured by transmitting light through tooth structure and ceramic brackets. Argon laser may also be used for polymerization. Light cured resins used with metal brackets are usually dual cure resins, incorporating light initiators as well as chemical catalysts. Maximum curing depth of light activated resins depends on the composition of the composite, the light source and the exposure time.
Light cured composites are useful in situations in which quick set is required, such as when placing an attachment on a palatally impacted maxillary canine after surgical uncovering, with the risk for bleeding.
But they are also advantageous when extra long working time is desirable. This may be the case when difficult premolar bracket positions need to be checked and rechecked with a mouth mirror, before the bracket placement is considered optimal.
Metallic and ceramic brackets pre-coated with light cure composite and stored in suitable containers have consistent quality of adhesive, reduced flash, reduced waste and improved cross-infection control, and appear to have adequate bond strength.
3. Glass Ionomer Cements - GIC were introduced in 1972 primarily as luting agents and direct restorative material with unique properties for bonding chemically to enamel and dentin, as well as to stainless steel, being able to release fluoride ions for caries protection.
Such cements are now used routinely for cementing bands, because they are stronger than zinc phosphate and polycarboxylate cements, with less demineralization at the end of treatment.
Larry White in 1986 described a method of bonding orthodontic brackets with GIC. The earlier chemically cured GIC typically took 24 hours to reach optimal bond strengths. Therefore arch wires use had to be deterred or else very light force generating arch wires could only be placed.
Silverman et al (1995) introduced a light curing GIC for orthodontic bonding (Fuji Ortho LC). They have recommended a no-etch technique for bonding and claims it to bond satisfactorily in the presence of moisture. They reported failure rate of approximately 3% comparable to that of bonding resins which indicates it is clinically satisfactory.
From the mid 1970s, the paste type of adhesives emerged in which both the base material and the catalyst were dispensed as pastes to be mixed before being used for bonding. The reason for this change was mainly due to the change in the type of brackets used in bonding.
Most of the resins used in orthodontics presently are modifications of the Bowen’s resin. The modifications are mainly in the physical properties such as viscosity of the materials to achieve optimal penetration of the resin into the etched enamel spaces which enhanced the bond strength and increased the dimensional stability by cross-linking.
The future of bonding is promising. Product development in terms of adhesives, brackets, and technical details is continually occurring at a rapid rate. Also new avenues for bonding in orthodontics are opening up;
q Lingual bonding
q Various types of bonded retainers and splints
q Semi-permanent single-tooth replacements
q Resin build-ups addressing tooth shape & size problems and
q Bonded space maintainers.
Bracket Bonding
Optimal performance in bonding of orthodontic attachments offers many ADVANTAGES when compared with conventional banding.
1. It is esthetically superior
2. It is faster and simpler
3. It results in less discomfort for the patient (no band seating and separation)
4. Arch length is not increased by band material
5. It allows more precise bracket placement (aberrant tooth shape does not result in difficult banding and poor attachment position)
6. Bonds are more hygienic than bands, therefore an improved gingival and periodontal condition is possible and better access for cleaning is available
7. Partially erupted teeth can be controlled
8. Mesiodistal enamel reduction is possible during treatment
9. Attachments may be bonded to artificial tooth surfaces (e.g. amalgam, porcelain and gold) and to fixed bridge work
10. Interproximal areas are accessible for composite build ups
11. Caries risk under loose bands is eliminated. Interproximal caries can be detected and treated.
12. No band spaces are present to close at the end of treatment.
13. No large inventory of bands is needed.
14. Brackets may be recycled, further reducing the cost.
15. Lingual brackets, invisible braces, can be used when the patient rejects visible orthodontic appliances.
DISADVANTAGES of bonding are;
1. A bonded bracket has a weaker attachment than a cemented band. Therefore it is more likely that a bracket will come off rather than that a band will become loosened.
2. Some bonding adhesives are not sufficiently strong.
3. Better access for cleaning does not guarantee better oral hygiene and improved gingival condition, especially if excess adhesive extends beyond the bracket base.
4. The protection against interproximal caries provided by well-contoured cemented bands is absent.
5. Bonding is more complicated when lingual auxiliaries are required or if headgears are attached.
6. Rebonding a loose bracket requires more preparation than recementing a loose band.
7. Debonding is more time consuming than debanding because removal of adhesive is more difficult than removal of cement.
Classification of Bonding Materials
A. Based on the basic bonding type
1. Acrylic based system
2. Diacrylate system
3. Glass ionomer system
B. Based on the curing system
1. Self curing system
2. Light curing system
3. Dual curing system
4. Laser curing system
C. Based on fluoride content
1. Fluoride releasing system
2. Non-fluoride releasing system
D. Based on filler content
1. Low or unfilled bonding system
2. Highly filled bonding system
Types of Adhesives
There are 2 basic types of dental resins currently in use for orthodontic bracket bonding. Both are polymers and are classified as;
A) Acrylic resins and B) Diacrylate resins
A. ACRYLIC RESINS – are based on self curing acrylics and consists of methyl methacrylate monomer and ultrafine powder. They formed linear polymers only. E.g. Orthomite, Directon, Genie.
B. DIACRYLATE RESINS – are based on acrylic modified epoxy resin (Bis GMA or Bowen’s resin). They polymerize by cross-linking into a three dimensional network. This contributes to greater strength, lower water absorption and less polymerization shrinkage.
q Both types of adhesives exist in either filled or unfilled forms.
q Investigations indicate that filled diacrylate resins of the Bis GMA type have the best physical properties and are strongest adhesives for metal brackets.
q Acrylic or combination resins have been most successful with plastic brackets.
q Some composite resins (Concise, Solo-Tach, Nuva-Tach) contain large coarse quartz or silica glass particles of highly variable size (3 to 20 micrometer) impart abrasion resistance properties.
q Others (Endur, Dynabond) contain minute filler particles of uniform size (0.2 to 0.3 micrometer) which yield a smoother surface that retains less plaque, but more prone to abrasion.
q Failure rates are significantly less with adhesives containing large filler particles and are recommended for extra bond strength but careful removal of excess is mandatory since such adhesives accumulate more plaque than others.
There are several alternatives to chemically autopolymerizing paste – paste systems.
1. No-mix adhesives – (Rely-A-Bond, System 1+) - These materials set when one paste under light pressure is brought together with a primer fluid on the etched enamel and bracket backing, or another paste on the tooth to be bonded.
Thus one adhesive component is applied to bracket base while another is applied to the dried etched tooth. As soon as it is precisely positioned, the bracket is pressed firmly into place and curing occurs usually within 30 to 60 seconds.
Little long term information is available on their bond strengths compared with those of the conventionally mixed paste – paste systems.
Furthermore, little is known about how much unpolymerized rest monomer remains in the cured adhesives, and its eventual toxicity. Invitro tests have shown that the liquid activators of the no-mix systems are definitely toxic, allergic reactions have been reported in patients, dental assistance and doctors when such adhesives are used.
2. Visible – Light polymerized adhesives (Transbond) - These materials are cured by transmitting light through tooth structure and ceramic brackets. Argon laser may also be used for polymerization. Light cured resins used with metal brackets are usually dual cure resins, incorporating light initiators as well as chemical catalysts. Maximum curing depth of light activated resins depends on the composition of the composite, the light source and the exposure time.
Light cured composites are useful in situations in which quick set is required, such as when placing an attachment on a palatally impacted maxillary canine after surgical uncovering, with the risk for bleeding.
But they are also advantageous when extra long working time is desirable. This may be the case when difficult premolar bracket positions need to be checked and rechecked with a mouth mirror, before the bracket placement is considered optimal.
Metallic and ceramic brackets pre-coated with light cure composite and stored in suitable containers have consistent quality of adhesive, reduced flash, reduced waste and improved cross-infection control, and appear to have adequate bond strength.
3. Glass Ionomer Cements - GIC were introduced in 1972 primarily as luting agents and direct restorative material with unique properties for bonding chemically to enamel and dentin, as well as to stainless steel, being able to release fluoride ions for caries protection.
Such cements are now used routinely for cementing bands, because they are stronger than zinc phosphate and polycarboxylate cements, with less demineralization at the end of treatment.
Larry White in 1986 described a method of bonding orthodontic brackets with GIC. The earlier chemically cured GIC typically took 24 hours to reach optimal bond strengths. Therefore arch wires use had to be deterred or else very light force generating arch wires could only be placed.
Silverman et al (1995) introduced a light curing GIC for orthodontic bonding (Fuji Ortho LC). They have recommended a no-etch technique for bonding and claims it to bond satisfactorily in the presence of moisture. They reported failure rate of approximately 3% comparable to that of bonding resins which indicates it is clinically satisfactory.
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