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BONDING IN ORTHODONTICSPresented By, Dr. Girish G. Sarada 1ST year P.G. Department Of Orthodontics & Dentofacial Orthopedics K.L.E. society`s Institute of dental sciences, Bangalore
EVOLUTION OF BONDING For the orthodontic treatment to carry out, force is to be applied to the teeth, to apply force we need some form of attachment over the teeth, so this can be done in two ways 1. Banding 2. Bonding BANDS - Bandless dentistry had been dream of orthodontists for many years. These bands were introduced by W.E. Magill in 1871 & have been in existence for more than 100 years.
DISADVANTAGES OF BANDING
Laborious, time-consuming Skilled work is required Difficulty in banding partially erupted teeth Decalcification /discoloration with loose or un-contoured bands Gingival irritation Unaesthetic Need of separators Closure of band spaces after completion of treatment
For the patient to whom esthetics being prime consideration even during treatment ,metallic look of fixed orthodontic appliance , has always been the bone of contention. A survey of the developments in the field of orthodontics over last 50 years would indicate that successful bonding of brackets to teeth, replacing conventional system of cementing stainless steel bands with welded attachments is most significant achievement. Since breakthrough of bandless dentistry in 1955, when buonocore described acid technique to achieve to achieve micromechanical retention of resin to enamel, bonding had come to stay.
3 major developments that made bonding of attachments to teeth possible 1. BUONOCORE 1955 improved retention of methyl methacrylate to enamel 85% phosphoric acid for 30 seconds 2. BOWEN 1962 bis Glycidyl methacrylate more stable and greater strength 3. NEWMAN 1965 first to acid etch and bond orthodontic brackets with epoxy resin
ACID ETCHING -Michael Buonocore in 1955 The first bonding agent for restorative dentistry, Sevriton Cavity Seal introduced in 1949 by Oskar Hagger, a Swiss chemist working in London, using glycerophosphoric acid dimethacrylate, an unfilled acrylic resin. In 1955, Buonocore, borrowing the techniques of industrial bonding, enhanced the adhesion with the phosphoric acid etch. Micahel Buonocore was first to demonstrate that bonding of acrylic material was substantially increased by conditioning enamel surface with 85% phosphoric acid for 30 seconds. Monomer of acrylic wet etched surface, flowed into each pits aided by capillary action & generated retentive resin tags. Mainly used to seal pits & fissures. This procedure has expanded the use of resin bonded restorative materials as it provides a strong bond between resin & enamel, forming basis for many innovative dental procedures like resin bonded metal retainers, porcelain laminates & bonded orthodontic brackets.
Newmann in 1965Was first to apply these findings & bonded plastic brackets with an epoxy resin after etching with 40% phosphoric acid for 60 seconds. Mitchell in 1967 Described a successful although limited, clinical trial using black copper cement & gold copper attachment. Smith in 1968Introduced zinc polycarboxylate cement & bracket bonding with this cement. Miura et al in 1971Described an acrylic resin ORTHOMITE using a modified trialkyl borane catalyst, that proved to be particularly successful for bonding plastic brackets & for enhanced adhesion in presence of moisture. In 1975, Silverstone Three patterns of enamel etching.
1979 Maijer R. and Smith D.C. introduced an alternative to acid etching.The crystal growth on the enamel surface.
Bonding materials strong enough for clinical use did not become routinely available until mid 1970s before that experimental bonding system based on epoxy & acrylic resin had been proposed & evaluated clinically with success. The greatest difficulty with epoxy resin was slow development of full strength, so it was not possible to place arch wires at same visit the bonded attachments were placed. The early resin materials suffered from their different thermal coefficient of expansion relative to enamel extended to weaken bonds. The adhesives used introduced in early 1970s were primarily those of powder-liquid type of methyl methacrylate that did not incorporate a filler. During this period, all adhesives introduced had to adhere to plastic brackets that were made up of polycarbonate. As time passed however the weakness of plastic brackets became apparent & metal brackets begin to be used. From mid 1970s the paste type of adhesives emerged in which both base materials & catalyst were dispensed as pastes to be to be mixed before being used for bonding. The reason for change from powder & liquid type to paste was mainly due to change in type of brackets used in bonding. It was in 1977, first detailed post-treatment evaluation of direct bonding over a full period orthodontic treatment was published. In survey by Gorlick in 1979 in U.S. it was seen that 93% of orthodontist preferred bonding for bracket placement
First commercially available orthodontic adhesives1. OIS Adhesive system OIS company in 1969. => Masuhara introduced -- called direct bonding system for enamel. It was one of the first dental adhesive commercially introduced after Buonocore proposed the concept of acid-etching enamel. 2. Bracket Bond GAC in 1970 3. Fujio Miura and associates in 1971 Introduced ORTHOMITE MMA - TriNButyl Borane (catalyst) Increased adhesive strength Coupling agent silane methacryloxypropyltrimethoxysilane Increased adhesive penetration Chemically bonded to adhesive Affinity to enamel
Methyl Methacrylate 1st used adhesiveCatalyst - BPO (Benzoyl peroxide) Difficulty in adhesion Polymerization shrinkage Pulpal irritation Merits of MMA adhesives: 1. Plastic brackets 2. Good storage stability 3. Increased working time brush-on / dip-in 4. Elimination of sealant - good penetration into enamel surface 5. Less damage during debonding Demerits of MMA adhesives: 1. Fluctuating proportion of powder-liquid depending on operator 2. Poor mechanical interlocking to metal bracket bases
BOWEN 1962 :Bisphenol Glycidyl Dimethacrylate (Bis-GMA)
Greater strength Lower water absorption Less polymerization shrinkage 2-paste system Strongest adhesives for metal brackets
MERIT AND DEMERIT OF BIS-GMA Poor penetration due to increased viscosity dilution reqd. Plastic brackets could not be used primer for partially dissolving added Active life less than powder liquid system
In 1974 ORTHOMITE II 20% more HNPM hydroxy napthoxy propyl methacrylate Eliminated silane ORTHOMITE SUPER BOND 4 - META methacryloxyethyl trimellitate anhydride
4 - META Bonds to Plastic & metal PRE-PRIMED brackets Base was primed with adhesive Bracket base covered with PMMA powder Base dipped in monomer and pressed onto etched surface. Bond strength less than manual application
Nanotechnologyhas led to the development of a new composite resin characterised by containing nanoparticles measuring approximately 25 nm and nanoaggregates of approximately 75 nm, which are made up of zirconium/silica or nanosilica particles.
Advantages of bonding1. Esthetically superior. 2. Faster & simpler. 3. There is less discomfort for patient 4. Arch length not increased by band material 5. Allows more precise bracket placement 6. Improved gingival condition is possible & there is better access for cleaning. 7. Partially erupted or fractured teeth can be controlled. 8. Mesiodistal enamel reduction is possible during treatment. 9. Interproximal areas are accessible for composite buildup. 10. Caries under loose bands is eliminated. Interproximal caries can be detected & treated. 11. No band spaces to close at end of treatment. 12. No large supply of bands needed. 13. Brackets may be recycled further reducing the cost. 14. Lingual brackets Invisible Braces may be used when esthetics important. 15. Improved appearance, deceased discomfort for patient & ease of application for clinician.
Improved appearance Hygiene Ease of application Decreased discomfort for the patient
Disadvantages1. A bonded bracket has weaker attachment than a cemented band. 2. Few bracket adhesives are not strong. 3. Better access for cleaning does not necessarily guarantee better oral hygiene & improved gingival condition, specially if excess adhesive extends beyond bracket base. 4. Protection against interproximal caries of well contoured cemented band is absent. 5. Bonding in not indicated on teeth where lingual auxillaries are required or where headgear are attached. 6. Rebonding a loose bracket requires more preparation than rebanding a loose band. 7. Debonding is more consuming than debanding since removal of adhesive is more time consuming.
TERMINOLOGYBonding Process of joining 2 materials by means of an adhesive agent that solidifies during bonding process. Types1. Physical bonding Involves Vander wall / electrostatic interactions that are relatively weak. It is the type of bonding seen when surfaces smooth & chemically dissimilar. 2. Chemical bonding Involves bonds between atoms are formed across the interface from adhesive & adherand. Since materials are dissimilar,the extent to which bonding is possible is limited, overall contribution to bond strength low. Mechanical bonding Result of an interface that involves undercuts & other irregularities that produce interlocking of the material. Almost every case of dental adhesion is based primarily on mechanical bonding.
A molecular attraction between 2 contacting surfaces promoted by interfacial force of attraction between molecules or atoms of two different species. Can be chemical, mechanical or combination.