BONDING IN ORTHODONTICSGuided By: Dr Falguni MehtaProfessor & HOD Of Dept of OrthodontiaGDCH Ahmedabad.

CONTENTS

1. Introduction2. History & Pioneers3. Bonding Materials(Types) -Self-cure -Light-cure -Dual-cure

4. Preparation for Bonding

5. Bonding techniques a) Direct b) Indirect -Labial & Lingual

6. Failures in Bonding

7. Microscopic structure of a good bond 8. Bonding procedures for-

-Hypo plastic teeth -Porcelain crown -Metal crown 9. Conclusion.

Bonding of attachments, eliminating the need for bands, was a dream for many years before rather abruptly becoming a routine clinical procedure in the 1980s. Banding is based on the mechanical/ chemical locking of an adhesive to irregularities in the enamel surface, and to mechanical locks formed in the base of orthodontic attachment.

Successful bonding in orthodontic, therefore, requires careful attention of three components of the system: the tooth surface and its preparation,the design of the attachment base and the bonding material itself.

Advantages of bonding over banding

Optimal performance in bonding of orthodontic attachments offers many advantages when compared conventional banding.

1. It is esthetically superior 2. It is faster and simpler. 3. Less discomfort for the patient 4. Arch length is not increased 5. Bonds are more hygienic than band, improved gingival and periodontal condition 6. Partially erupted teeth can be controlled

7. Mesio-distal enamel reduction (proximal stripping) is possible during treatment.8. Attachments may be bonded to artificial tooth surfaces and to fixed bridgework 9. Interproximal areas are accessible for complete buildups.10.Caries risk under loose bands is eliminated. 11. No band spaces are present to close at the end of treatment.12. Brackets may be recycled, further reducing the cost .

History & Pioneers

The development of the bonding procedure has revolutionized the use of fixed orthodontic appliances.

Although the molars are the only teeth that are commonly banded, many practitioners today exclusively bond all fixed appliances including the molar using bondable molar tubes.

Over the years, refinements have taken place both in the bonding techniques as well as in the materials that are used for bonding.

The history of Bonding goes back all the way to the 1950s and the acid-etch bonding technique has led to dramatic changes in the practice of orthodontics

Buonocore in 1955 demonstrated increased adhesion by acid pretreatment, using 85% Phosphoric acid.

Newman began to apply this finding to direct bonding of orthodontic attachments.

Retief also described an epoxy resin system to withstand orthodontic forces.

Smith in 1968 introduced zinc polyacrylate cement and bracket bonding with this cement.

In 1971, Miura et al described an acrylic resin (ORTHOMITE), using a modified trialkyl borane catalyst that proved successful for bonding plastic brackets and in presence of moisture

* ClassificationI. According to Sturdevant : 1.Based on matrix composition - Bis GMA based - UDMA based

2.Based on polymerization method - Self curing - Ultra violet light curing - Visible light curing - Dual curing - Staged curing

3.Based on filler content - Weight % - Volume %

* 4.Based on filler particle size

- Mega fill contains mega fillers (very large individual filler particles).

- Macrofill contains macrofillers (10-100m)

- Midifill contains midifillers (1-10 m)

*- Minifill contains minifillers (0.1-1m)

- Micro fill- contains micro fillers (0.01 - 0.1 m)

- Nanofill contains nanofillers (0.005-0.01m)

* Hybrids composites with mixed ranges of particle sizes ( largest particle size range is used to define the hybrid type e.g.. Minifill hybrid contains mini micro fillers).

Homogeneous contain fillers, uncured matrix material.

*Heterogeneous it includes precured composites or other unusual fillers.

Modified if it includes novel filler modifications in addition to conventional fillers (e.g.. Filler modified homogeneous minifill)

* 5) Based on Specific Handling Characteristics -Packable composites -Flowable

II According to Anusavice (Phillips) : (Based on particle size of major filler).-Traditional composites 8-12m -Microfilled composites 0.04-0.4m -Small particle filled composites 1-5m -Hybrid composites 0.6 - 1m

III According to Craig :

Type 1 : Polymer based materials suitable for restorations involving occlusal surfaces.

*Type 2 : Other polymer based material -Class 1 : self cured materials.-Class 2 : light cured materials. Group 1 energy applied intra orally. Group 2 energy applied extra orally.-Class 3 : dual cured materials.

According to Marzouk : (Based on chronological development) 1) First generation composites : Consist of macro ceramic reinforcing phases Exhibits highest mechanical properties except for high proportion of destructive wear and high surface roughness

*2) Second generation composites. Consist of colloidal micro ceramic phases in a continuous resin phase. Exhibits best surface texture of all composite resin. Wear resistance better than 1st generation

3) Third generation composites : Hybrid composite which is a combination of macro and micro (colloidal) ceramic as reinforces (75:25 ratio) Properties compromise between 1st and 2nd generation.

*4) Fourth generation composites : Are also hybrid type, but instead of macro ceramic fillers,these contains heat-cured, irregularly shaped, highly reinforced composite macro particles with reinforcing phase of micro (colloidal) ceramics. Produce superior restorations. Exhibits maximum shrinkage of all composites.

*5) Fifth generation composites : A hybrid composite in which the continuous resin phase is reinforced with micro ceramics (colloidal), macro ceramics, spherical, highly reinforced heat cured composite particles. Spherical shape of the macro composite particles will improve their wettability, and consequently, their chemical bonding to the continuous phase of the final composite. Surface texture and wear comparable to 2nd generation. Physical and mechanical properties similar to those of 4th generation

*6) Sixth generation composites : Hybrid types in which the continuous phase is reinforced with a combination of micro (colloidal) ceramics and agglomerates of sintered micro (colloidal) ceramics. Exhibits highest % of reinforcing particles of all composites. Has best mechanical properties Wear and surface texture similar to 4th generation. Least shrinkage, due to minimum amount of continuous phase, and also due to condemnable nature of their materials.

* Based on mode of supply :i.Chemically cured paste paste system.ii.Chemically cured or photo cured powder / liquid system.iii.Chemically cured or photo cured paste liquid system.iv. Photo cured one- paste system.v. Photo cured one liquid system.vi.Chemically cured three or four part system.

BONDING TECHNIQUESDIRECT BONDINGINDIRECT BONDING LINGUAL BONDINGFACIAL BONDING

BONDING ADHESIVESComposite resins Chemical cure Light cure Dual cure Glass Ionomer CementsAcrylic ResinCompomerHybrid Ionomer

Chemical cure adhesives are the ones in which two components of adhesives interact.

The light-cure system is polymerized via exposure of a high intensity visible light.

The dual cure system utilizes both chemical & light system.

The choice depends upon personal performances keeping in mind, however that orthodontic adhesives are low film thickness, meaning that they have a higher strength in a thin layer than in a thick

GICGlass-ionomer dental cements were invented in the late 1960s by replacing the phosphoric acid solution

Recently introduced resin-modified glass ionomer cement s (both chemical and light cured)

Bond to saliva-contaminated enamel surfaces without phosphoric acid etching.

The liquid contains polyarcylic and maleic acid which remove contaminants and change the enamel surface mechanically but it will not create micromechanical retentions

The advantages of glass-ionomer cements are: * Self-adhesion to both enamel and dentin. * Fluoride release and re-release , without dis-integration. * Thermal expansion co-efficient similar to dentin. * No appreciable setting exotherm. * Biocompatibility in appropriate host environments

Resin composite does not bond well to unetched enamel: however. Hybrid Glass ionomer orthodontic cement does not require etching and has bond strength ranging from 8 to 25MPa.

BONDING PROCEDURE

Bonding Procedure :

The steps involved in direct and indirect bracket bonding on facial or lingual surfaces are as follows,

Cleaning

Enamel conditioning

Sealing

Bonding

CLEANING

Cleaning is carried out with pumice in order to remove plaque & organic pellicle.

Moisture control Enamel conditioningEnamel Pretreatment

Moisture controlLip expanders and/or cheek retractors saliva ejectors Tongue guards with bite blocks salivary duct obstructersCotton or gauze rolls Antisailalogues

Regarding antisailagogues both tablets and injectable solutions of different preparations, for example Banthine, Pro-Banthine , atropine,surfate etc.) are used

Generally not needed for most patients. When indicated, Banthine tablets (50 mg per 100 lb [45kg] body weight in a sugar-free drink 15 minutes before bonding may providing adequate results

Enamel pretreatment ( Etching ) After isolation, the conditioning solution or gel (usually 37% phosphoric acid) is applied over the enamel surface for 15 to 30 sec. The etchants is rinsed off the teeth with abundant water spray. Next the teeth are thoroughly dried with a moisture-and-oil-free air source to obtain the well-known dull, frosty appearanceCare should to avoid salivary contamination.

Type and concentration of Acid

A. LiquidB. Gel

Etching with 10% to 37% phosphoric acid produces the highest bond strengths (28MPa) to enamel.The use of 10% Maleic Acid results in a lower bond strength (18MPa).

DURATION OF ETCHING

Normally 15-30 sec etching time is preferred in normal teeth, however shorter etching time causes less enamel damage on debonding.Hypominieralised tooth require 30-69 sec whereas in flurosis etching time should be 60-90 sec

Clinically, the etching of enamel creates

1. Microporosity within the enamel and

2. Reduces surface tension and allows the resin to penetrae and polymerize within the etched enamel rods.

Standard etchant dissolves about 5-10m of enamel surface and creates a zone of etched enamel rods for about 15-25m.

Etching process creates calcium monophosphate and calcium sulfate by-products that must be removed by a vigorous water rinse

Fracture and cracking of enamel upon debonding .

2. Increased surface porosity - possible staining

Loss of acquired fluoride in outer 10 m of enamel surface.

Loss of enamel during etching .

Resin tags retained in enamel - causing discoloration of resin.

Rougher surface if over - etched.

SEALINGAfter etching a thin layer of primer is coated over the etched enamel surface.This make the surface more amenable to accept a bond.Mainly hydrophilic monomers,carried in solvent-Acetone, ethanol-waterHydrophilic molecules HEMA (Hydroxy ethylmethacrylate)This wet the surface for better penetration of monomer

Moisture -Resistant primers

Moisture resistant primer (Transbond) have been used to bond tooth where moisture control is difficult.This primer is a hydrophilic methacrylate monomer. Can be used even if enamel is contaminated with saliva or moisture. Bond strength is similar to resin composite adhesive

The recommended bracket bonding procedure (with any adhesive) consists of the following steps:

Transfer

2. Positioning

3. Fitting

4. Removal of excess.

BONDING PROCEDURE

TRANSFERThe bracket is gripped with bracket holder

Adhesive is applied to the base of the bracket

Then the bracket is placed on the tooth closed to its correct position

POSITIONINGThe correct position is determined by Boones gauge which is kept perpendicular to long axis of tooth.

The bracket is now correctly positioned mesio-distally & inciso-gingivally, to its final predetermine position.

FITTINGThe bracket is firmly pushed against the tooth surface.

The tight fit will result inGood bond strengthLittle material to remove on debondingOptimal adhesive penetration into bracket backing Reduce slide when excess material extrudes peripherally

REMOVAL OF EXCESSExcess adhesive is removed with the help of scaler to minimize or prevent gingival irritation or plaque build up

Indirect Bonding with Silicone Transfer Trays. Take an impression and pour a stone model. The model must be dry. It may be marked on each tooth.

2. Select brackets for each tooth.

3. Apply water-soluble adhesive on each base or tooth.

4. Position the brackets on the model. Reposition if needed

5.Mix material according to the manufacturers instructions. Press the putty onto the cemented brackets. Form the tray allowing sufficient thickness for strength.

7. Trim the silicone tray and mark the midline.

8. Prepare the patients teeth as for a direct application. 9. Mix adhesive load it in a syringe and apply a sufficient portion to the bonding bases.

11. Remove the tray after 10 minutes. The tray may be cut longitudinally or transversely to reduce the risk of bracket debonding when it is peeled off.

12. Complete the bonding carefully, remove excess adhesive . Use oval or tapered TC bur,clean around each bracket. Also inspect around the bracket pad for adhesive voids (from too little adhesive, tray slide on the teeth or delayed seating) and fill with a small mix of adhesive if needed.

CURING

Based upon the polymerization initiation mechanism.

* Chemically activated (Also termed chemically cured, autocured or self-cured): two-paste or one-paste * Light-cured (also termed photocured) * Dual-cured (Chemically activated and light cured)

Classification of orthodontic adhesive systems:

The most widely used resin commonly referred to as Bowens resin or bis GMA (bisphenol A glycidyl dimethacrylate), was designed to improve bond strength and increase dimensional stability by cross-linking.

LIGHT CUREDLight-cure is used to initiate polymerization and this depends upon several factors-

-the exposure time,

-the photoinitiator concentration

-the light intensity emitted by the curing unit and the filler volume

DUAL CUREThis approach combines the advantages of rapid initiation for photo polymerizing resins and high conversion rates for chemically cured resins.

Here polymerization is induced through surface exposure by visible light, and in bulk material occurs by a chemical process.

Hence, both improved surface and bulk material properties would be expected.In a study, this has significantly higher bond strength then chemical or light cure.

Bonding on plastic bracketsThis are typically polycarbonate,although some are reinforced fiber-glass or metal.

Bonding is typically mechanical

Disadvantage-1) Lack of strength to resist distortion and breakage2) Wire slot wear3)Uptake of water and discoloration

The filler content of resin composite affects the bond strength .

Highly filled resin composite bond better to metal bracket. Hybrid GIC have bond strengths lower than resin composite

Retention of adhesives to ceramic brackets can be mechanical or chemical or both. Mechanical bonding requires indentations or roughness caused by chemical etching with a 9.6% hydrofluoric

Chemical bonding requires treatment with silane. One end of the silane molecule bonds to the ceramic, while the other end bonds to the carbon -carbon double bonds available from the resin composite adhesive.

Harder then steel, causes enamel wear of the opposing tooth Difficult to debond Surface is rougher, attracts plaque and stain more easily. Brittle in nature.

Coupling AgentThe coupling agent Gamma-methacryloxypropyl trimethoxysilane (MPTS) is widely used for promoting chemical adhesionBonding arises from two mechanism- 1.Silanol groups of the hydrolyzed silane adhere to the hydration layer of the inorganic surface, 2.Methacrylate groups of silane copolymerize with the methacrylate resin matrix, possibly forming covalent bonds.

Bonding to porcelain.

For optimal bonding of orthodontic brackets and retainer wires to porcelain surfaces, the following technique is recommended Isolate the working field

2. Deglaze an area by sandblasting with 50 m aluminum oxide for 3 seconds.

3. Etch the porcelain with 9.6% HF acid gel for 2 minutes.

4. Carefully remove the gel with Cotton roll then rinse.

5.Immediately dry and bond with highly filled bisGMA resin

BOND FAILURES

Possible causes of adhesive -enamel bond failure

* Contamination. * Insufficient rinsing of etchant . * Inadequate drying of enamel surface precludes penetration of resin. * Over -etching demineralizes enamel, reduces depth of resin tags penetration,* Excessive force exerted on bracket from occlusion or appliance.

* Movement of bracket during initial setting .

* Contaminated bracket mesh

* Adhesive not buttered into base firmly

* Activator not placed on bracket in paste-primer system.

* Inadequate cure of light-cured resin composite

* special primer required (plastic brackets)

References:

1. Graber Varnasdall Xubair2. Proffit

THANK YOU

************