Bonding in orthodontics

•Introduction

•Bonding over banding

•Basic bonding procedure

•Materials used in bonding

•Bonding to crowns&restorations

•Bonding various brackets

•Indirect bonding•Lingual bonding•Rebonding

•Debonding

•Factors affecting bond strength

•Conclusion

Introduction

In 1995 BUNOCORE introduced acid etching technique.He demonstrated increased adhesion produced by acid pretreatment of enamel.This led to dramatic changes in practice of orthodontics . 1965-with the advent of epoxy resin bonding NEWMAN began to apply these findings to direct bonding of orthodontic attachments In early 1970s considerable no, of preliminary reports were published on different commercially available direct &indirect bonding system.

A survey conducted by LEONARD GOERLICK in 1979 JCO revealed almost 93% of orthodontists started bonding brackets (at least in anteriors )instead of banding.

BONDING OVER BANDING

1. Esthetically superior.2. Faster & Simpler.3. Less discomfort for the patient4. Arch length is not increased by band material.5. Allows more precise bracket placement even in tooth with

aberrant shape.6. Improved gingival health.7. Better access for cleaning .8. Mesiodistal enamel reduction possible during treatment.9. Interproximal areas are accessible for composite buildup.10.Caries risk under loose bands is eliminated.Interproximal caries

can be deducted & treated.11. No band spaces to close at end of treatment.12.No large supply of bands are needed.

Advantages

13. Brackets can be recycled further reducing the cost.14. Invisible lingual brackets can be used when esthetic is important.15. Attachments can be bonded to fixed bridgeworks.

Disadvantages

1. Bonded brackets have weaker attachments than cemented band.2. If excess adhesive extends beyond bracket base increases risk of

plaque accumulation3. Protection against interproximal caries of well contoured

cemented brackets is absent.4. Bonding generally not indicated when lingual auxillaries or

headgear required.5. Rebonding loose brackets require more preparation than

rebanding loose bands.6. Debonding- more time consuming due to more difficult removal

of adhesives.7. Evidence based decalcification& white spot lesion occurs more

following bonding than banding.

BASIC BONDING PROCEDURE

1. CLEANING

2. ENAMEL CONDITIONING.

3. SEALING

4. BONDING

CLEANING

• Thorough cleaning of teeth to remove plaque &organic pellicle that normally forms on teeth is mandatory.

• Materials used are water slurry of pumice or prophylaxis paste with rotary instruments like rubber cup or small polishing brush.

ENAMEL CONDITIONING

1. MOISTURE CONTROL

2. ENAMEL PRETREATMENT

MOISTURE CONTROL

Completely dry working field is absolutely necessary .

Devices like

•Lip expanders &cheek retractors•Saliva ejectors•Tongue guards with bite blocks•Salivary duct obstructers•Cotton or gauze rolls•Antisialogogues can be used.

ANTISIALOGOGUES

They help to decrease salivary release from glands & ducts unlike other devices that control released saliva.

Ex: • Atropine sulphate- In JCO-1981 Sidney brant Showed this is a safe drug with complication & can be used as an sublingual injection Dose-0.4 mg

reported that 50 mg per100 lb in a sugar free drink 15 min before bonding is adequate.

• Banthine tablets –In JCO 1981 Richard .N. Carter

ENAMEL PREATREATMENT

PROCEDURE:

After drying the tooth apply a conditioning solution or gel ( usually 37% to 50% phosphoric acid ) lightly over enamel surface with a pellet or brush for 15-60 sec.

Enchant Is rinsed off with abundant water spray for about 15 sec. If salivary contamination occurs rinse with water spray & re etch for another 30 sec .

Dry the tooth thoroughly to obtain dull frosty white appearance. If not re etch

Etching is also done by 10% polyacrylic acid 10% maleic acid or

HISTOLOGY:

Lehman & Davidson AJO 1981

When enamel is etched with phosphoric acid of high %age like 50% it forms monocalcium phosphate monohydrate on the surface which is highly soluble in water & can be completely washed away leaving a roughness of larger surface area.

Type -2

Cobblestone appearance with prism edges lost.

Type 1

Honey comb appearance with loss of enamel prism centers.

There are 4 types of enamel appearance after various pre treatment

Type -4

Granulation of enamel with numerous holes

Type -3

Pitted enamel with map like appearance.

Enamel after 15% phosphoric acid etching

15 secs, 30 secs,

60 secs,

Enamel after 37 % phosphoric acid etching

15 secs, 30 secs,

60 secs,

Enamel after 37 % phosphoric acid etching

Enamel after 10 % polyacrylic acid etching

Air abrasion:

Its a older technique of enamel pretreatment introduced as early as 1940 by Dr. Robert black..It uses abrading with 50 um or 90 um particles of aluminium oxide for 3 sec at 10mm distance..AJO-DO 1997 Marc .E. Olsen et al reported that air abrasion significantly decreases bond strength & on debonding leaves no adhesive on enamel surface. So it is not recommended.

37% H3PO4 acid 90 um AlO2 air abrasion

In AJO-DO 1980 Nordenwall Reported that 15 sec etching is adequate for young permanent teeth ,whereas 60 sec are needed for permanent teeth. Same author in 1981 that there is no significant differences appear between etching solution or gel. But gel provides better control for restricting the etched area but requires more thorough rinsing afterward.

In AJO-DO 1986 Chris .D.Johnson's et al Recommended 60 sec etching of buccal surface of molars to produce optimal etch pattern .

.

Its best to avoid etching over acquired as well as developmental demineralizations. If its impossible a short etching time , application of sealant & the use of direct bonding with extra attention to not having areas of adhesive deficiency are important The presence of voids can lead to metal corrosion & indelible staining of underlying developmental white spots.

Tooth with exposed dentin should be coated with Ca(OH)2 paste before etching.

Though Zachrisson reports fluoride content of tooth has no effect on etching time R. Lehman& Davidson in AJO-DO 1981 reported that fluoride is important in decreasing enamel solubility. Fluoridated enamel has highly acid resistant layer of 2-4 um thickness which may sometimes resist even 3 min etch. So avoiding fluoride application shortly prior to bonding is recommended.

.But In AJO-DO Garcia Godey et al reported that addition of 0.5% NaF2 to 60% phosphoric acid gel produced significantly higher bond strength than 30% phosphoric acid without fluoride.

AMOUNT OF ENAMEL IOST DURING ETCHING:

Zachrisson- Routine etching with 37% phosphoric acid removes 3-10 um of surface enamel.

Gwinnett et al -50% Phosphoric acid removes 5 – 25 um of enamel.

Fitzpatrick & way and by Silverstone reported that 30% phosphoric acid for 90 sec removes enamel with a mean of 9.9 um

Leebrown & Way –37% phosphoric acid in 90 secs removes a mean of 3 u ( 0.2 +11.2 um)

Crystal growth theory:

Jon Arton in AJO-DO 1984 reported crystal growth conditioning after use of polyacrylic acid with residual sulphate provided retention areas in enamel similar to phosphoric acid etching with less risk enamel damage at debonding.

Phosphoric acid etched enamel surface

Crystal growth on enamel surface

Laser etching:

This new concept was proposed in 1993.Angle by J.A.Von Fraunhofer. He showed at 3 watts for 12 sec laser etching produced acceptable bond strength though significantly less than conventional acid etching. He used Nd/ YAG as laser source. Serder Usumuz et al in AJO-DO 2002 used ErCr ; YSGG as the hydrokinetic laser system for acid etching & came to the same conclusion.

But major disadvantage as reported by Fraunhofer is that high laser produces heat in sufficient magnitude to cause at least localized pulpal infection & possible irreversible damage to pulpal tissue immediately opposite the site of laser irradiation.

NEW CONCEPTS OF ETCHING:

SEM picture of enamel after 37% phosphoric acid etching.

SEM picture of enamel after laser etching of 2 W output.

SEALING

After etching a thin layer of sealant may be painted over entire enamel surface . Its best applied with a small foam pellet or brush &it should be thin & even.

Use of sealant led to many divergent conclusions.

1. They might be necessary to achieve proper bond strength .2. Its necessary to improve resistance to micro leakage.3. After sealant coating moisture control may not be

extremly important.4. It provides enamel cover in areas of adhesive voids.5. Gwinnet& Ceen found light polymerized sealant

protect enamel adjacent to brackets from dissolutions & subsurface lesions

6. Sealant might permit easier bracket removal & protect against enamel tear outs during debonding.

7. Study by Leonardo Foresti et al Angle 1994 showed sealant actually increases no, & length of resin tags. Also more fluid resin coupled with previously applied sealant penetrates deeper into enamel & forms longer tags.

BONDING

1. TRANSFER.

Bracket gripped with a pair of cotton pliers . Slight excess of adhesive is applied to bracket base .To mix adhesive the per tooth mixing is the best mtd , because it provides sufficient working time & can obtain optimal bond strength.The operator can work in a relaxed manner .Now the bracket is placed on tooth close to its correct position.

2. POSITIONING.

Placement scaler preferably with parallel edges is used to position the bracket both vertically & horizontally in correct position.

Use of bracket positioning gauge:

Using precision instrument:

3.FITTING

Using the scaler with one point contact with the bracket , its pushed firmly towards the tooth surface. This tight fit ensures good bond strength & reduces sliding of bracket.Remove the scaler & do not disturb the bracket.( totally undisturbed setting is essential for achieving adequate bond strength).

4.REMOVAL OF EXCESS

A slight bit of excess adhesive is essential to minimize possibility of voids.so using sufficient adhesive & buttering it into entire mesh backing of bracket is very helpful.But this leads to excess adhesive flush.Its better to remove excess adhesive with scaler before the adhesive sets without disturbing bracket position .We can also use oval(No 7006 No 2) or tapered (No 1172) tungsten carbide (TC) bur.

Removing excess adhesive is a must because

•To minimize gingival irritation by preventing plaque accumulation around the periphery of bracket base.

•Facilitate debonding.

•Improves esthetics.

•It avoids bridging when tooth are crowded

•To prevent possibility of decalcifications.

•To reduce periodontal damage.

Glass ionomer cements (GIC)

IT was introduced in 1972 by Wilson & Kent as a new translucent cement for dentistry. It’s a hybrid of silicate & polycarbonate cement. :

First generation

Used as luting agent & direct restorative material with unique properties for bonding chemically to enamel , dentin,& stainless steel.IT also releases fluoride that prevents caries formation. But it has high susceptibility to water while setting leading to weaker bond.

Second generation

Water hardening cements with same acids in freeze – dried form or an alternative powdered co-polymer of acrylic & maleic acid.

MATERIALS USED IN BONDING

ADHESIVES

Basically 2 types.

1. Acrylic resins:

• These are self curing resins • Composed of methylmethacrylate monomer & ultra fine powder• They produce linear polymer so has less bond strength

2. Diacrylic resins:

• These are acrylic modified epoxy resin (bis –GMA or Bowen's resin)•They polymerize by forming cross linking •So increase strength •Decrease water absorption•Decrease polymerization shrinkage

Can also be classified as

1. Unfilled resins:

• Has minute filler particles of uniform size ( 0.2 & 0.3 millimicron)• Yield smoother surface• Retains less plaque• More prone to abrasion

2.Filled resins:

• Has coarse filler particles of quartz or silica of variable size. • Increase abrasion resistance.• Increase plaque accumulation.

No mix adhesives

• Here one paste is applied to bracket base & a primer is applied to etched enamel. When both come in contact under slight pressure its cured chemically.• Simplicity.• Unpolymerized monomer might retain causing toxicity & allergy.

Visible light cured adhesive

• These adhesives are cured when exposed to light.They contain CAMPHOROQUINONE as photo initiator which is absorbed at the wave length of 470 nm & thus gets activated.

•Light cured composite resins used with metal brackets are usually dual cured having both light initiators & chemical catalyst.

Depth of curing usually depends on

• Composition of resin

• Light source

• Exposure time

Light sources used are :

• Xenon or plasma arc lamp from 1998

• Light emitting diode (LED) introduced by mills et al

• Halogen is the conventional light source used.

• Argon laser curing

Halogen

• Light is generated using two hot filaments.• It uses about 400 mW / cm 2 power.• It has a broad wave length of 400 – 520 nm .This results in decreased intensity of light .

In EJO 2004 Nendl & droshl et al reported halogen light achieved highest bond strength with 40 sec curing time .

Tarle et al EJO 2002 found halogen light achieved highest conversion rate of about 60+ 55 in 20 sec & 73.5+ 1.4% in 40 sec

Argon laser

• It produces 60% conversion in 5-10 sec.Advantages

Disadvantages

• Superior to conventional light cure regarding bond strength. As supported by Nazir Lalahl et al ANGLE 2000.They also found it causes less than half the frequency of enamel # during debonding.• It saves chair time.

• Requires shielding appliance over teeth which are not bonded.• Cost.

• Its introduced in late 1980s to increase output light energy to 800 mW / cm2 • It has narrow wave length of 470 nm which corresponds to the peak area of absorption of camphoroquinone.

Xenon produced 53.8+ 2.7 in 1 & 2 sec & 69.7+5.5 in 3 sec. It uses 1370 mw/ cm2. IT saves chair side time as supported by Vittoriocacciofesta et al AJO-DO 2004 Aug .

Plasma arc or xenon arc lamp

• Introduced in 1990s .• Light source is xenon gas that is ionized by 2 electrodes.• The large white light is filtered to width of 450-500 nm.• Power density can reach more than 2000 mW/cm2 which is about 5 times more intense than halogen.

Advantages

• Has high lifetime of 10000 with little degradation.• Requires little power to operate.• Requires no filter to produce blue light.• It is resistant to shock & vibration.•

• LED produces 54.9+ 3% in 20 sec & 65.4+ 2.4 in 40

sec

Light emitting diode ( LED )

• Introduced since 2000. • It uses doped semi conducters to generate light instead of hot filaments.

• It has the wavelength of 468 nm.

TYPES OF BRACKETS

METAL BRACKETS

Usually made of SS , Gold coated or Titanium based .

Advantages

•Higher strength.•Small & less noticeable bases helps avoiding gingival irritation.

Disadvantages

•Less esthetics •Increased corrosion susceptibility as reported by Tsui Hsein Huang et al in EJO 2004 Feb SS brackets has increased amount of ions released & this increases with time over 48 week period. ( Nickel being the most predominant metal released causing Ni skin allergy)

PLASTIC BRACKETS

.Its introduced in 1969 by Newman as an esthetic alternative.They are made of polycarbonate.

Advantages

•Esthetically superior.

Disadvantages

•Less strength to resist distortion & breakage •Wire slot wear leads to loss of tooth control •Low bond strength (3-6 Mpa )•Water intake & Discolorations•Need for compatible bonding resins

CERAMIC BRACKETS

They are machined from monocrystalline or polycrystalline aluminium oxide .

They bond to enamel by

•Mechanical retention•Chemically by means of silane coupling agents

Advantages

•Its rigid•Esthetic•Achieves higher bond strength especially chemically curing brackets when used with composite resins.

Disadvantages

•Increased bond strength also causes increased debonding stress causing bond failure to occur at enamel/adhesive interface in EJO 1998

•Mechanically retentive base has higher bond strength when cured with RMGIC•Failure occurred at enamel/adhesive interface-60%and at bracket / adhesive interface –40%•Increase frictional resistance between wire & brackets causes difficult force & anchorage control by Bishara AJO-DO 2000•Less durable & brittle•Harder than steel causing opposing enamel wear.Bowens& Rodrigal et al reported mean linear tensile strength of enamel is 14.5 MPa & enamel #occurs as low as 13.5 MPa

But ceramic brackets gain bond strength of 16-22MPa

•Because of rougher & porous surface it attracts more plaque

GOLD COATED BRACKETS

Recently introducedAdvantages

1. Esthetic improved over metal brackets2. Neater & Hygienic3. Good patient acceptance4. No significant side effects in form of corrosion or other

adverse effects has been observed yet

Hybrid or Resin modified GIC ( RMGIC )

Its recently introduced.It has composite resin component that gives increased strength.& with the added advantage if fluoride releasing property.

But as per Fricker RMGIC is not recommended in case of occlusal interference due to its decreased strength & brittleness.

EJO 2004 April according to S.B. Oliveria et al there is no significant bond strength difference occurred when compared to composite resin when used with light and medium arched wires. So RMGIC is a viable alternative when used with light & medium arch wires.

In Aug 2004 AJO-DO by Andrew Summerset al concluded that regarding bond strength highest is achieved by conventional chemically cured composite followed by RMGIC & least by GIC

NEWER MATERIALS IN BONDING

SHEIF ETCHING PRIMERS ( SEP)

Bonding usually contains 4 steps.

1. Cleaning..2. Conditioning..3. Primer application.4. Adhesive application prior to bracket placement.

Use of self etching primers combines the conditioning & priming into single step.

Composition:

It contains methacrylated phosphoric acid ester formed when phosphoric acid& methacrylate groups are combined into a molecule that etches & primes simultaneously.

Advantages

1. Decreases chair time

2 . Decreases technique sensitivity.

3. Bishara in AJO-DO 2001 reported that there are more adhesive remaining on tooth surface after debonding when self etching primer is used than with conventional etching

Disadvantages

1. It has significantly less bond strength when compared conventional etching & priming 2 step procedure. Supported by Aljibouri et al EJO 2003

2. Bishara in AJO-DO 2002 also concluded that SEP produces less bond strength with are without saliva contamination.

His study showed that SEP Without saliva contamination – 6 Mpa Contamination before primer – 4.8 Mpa Contamination after primer – 4.8 Mpa Contamination before & after primer – 1.7 MPa

Rielco yamada et al in ANGLE 2002 reported that composite resin with SEP has less bond strength than when used with conventional 2 step etching . But its comparable with that of RMGIC after polyacrylic acid

RamKumar Gandhi et al in AJO-DO 2001 reported SEP produce more bond strength with used light activated composite than with chemically cured resin.

IN ANGLE 2002 SEP produces less enamel dissolutions than phosphoric acid or polyacrylic acid . This might have led to decrease in bond strength.

IN AJO-DO 2003 Ryan .W. Arnold et al showed no significant diff, in bond strength occurred between SEP & conventional etching..

MOISTURE INSENSITIVE PRIMERS (MIP)

These are hydrophilic methacrylate monomer which acts even in the presence of moisture contaminated enamel.

Bond strength is less than conventional phosphoric acid etchant.

MOISTURE RESISTANT ADHESIVES

They act even in the presence of moisture. The main reactive component is a methacrylate functionalised poly alkenoic acid copolymer originally used as dentin bonding system.

Mechanism:

Excess interfacial water ionizes carboxylic group forming hydrogen bonded dimers A reversible breaking & reforming of calcium –poly alkenoic acid complexes with enamel providing some stress relaxation capacity. Thus a dynamic equilibrium occurs at the interface incorporating water in the process & thereby minimizes the detrimental plasticizing effect of water.

MOISTURE ACTIVE ADHESIVES

These products requires rather than tolerate moisture for proper polymerization A recent product based on cynoacrylate formulation has demonstrated superior properties.

Mechanism: First step- the iso cynate groups react with water forming an unstable carbamic acid component which rapidly decomposes to CO2 & corresponding amine.

Second step- Amine reacts with residual iso cynate groups cross linking the adhesive through substituted urea groups.

Advantages

•Particularly useful in conditions where moisture control is difficult like in Lingual bonding or while bonding surgically exposed impacted tooth,.

Disadvantages

• Presence of excess water produce only the first step resulting in formation of deleteriously brittle polymer films.

•CO2 released has only limited diffusion through the adhesive films as polymerization proceeds & become entrapped forming gap or voids with detrimental effects on interfacial strength

ADHESIVE PRECATED BRACKETS( APC)

To save chairside time there are brackets with precoated adhesive.The adhesive differ in their composition by %age of various ingredients incorporated

Bishara in ANGLE 2002 conducted a study where he found no significant difference occur in shear bond strength with precoated and uncoated brackets .APC brackets provide clinically acceptable bond strength within first 30 min uncoated brackets – 5.7+2.4MPaAPC brackets - 5.1+1.7MPa

BONDING TO CROWNS & RESTORATIONS

AMALGAM RESTORATIONS & CROWNS

Methods used are1. Modifying metal surface2. Use of intermediate resin3. New adhesive resins that bond chemically to non-precious as

well as precious metals

Recommended procedure

By Zachrisson in ANGLE 98 & AJO-DO 20001. Intra oral sandblasting amalgam alloy with 50 micron

aluminium oxide for 3 sec as supported by Sperder In AJO-DO 1999

2. If small restorations, then condition the surrounding enamel with 37% phosphoric acid for 30 sec

3. If large restoration or in crowns create a window & restore it with composite resin & continue the same process

4. Apply reliance or any metal primer that has 4-META & wait for 30 sec

5. Bond with concise resin.

BONDING TO PORCELIN

Many in vitro studies has been conducted by Zachrisson & many others which gave controversial results in clinical practice.

Procedure

1. Surface is to be roughened with sandpaper discs 2. 8-9.6%HF acid gel applied for 2 min( HF is not effective

when bonding to high alumina porcelins & glass ceramics)

3. Silane coupling agent is optional.In vitro studies shows increased bond strength with silane addition.But clinically silane produce insignificant support to bond strength

4. Use concise resin for bonding

AJO-DO 1998 Zachrisson showed HF produce extensive in depth penetrating pattern .But diamond roughening & microetching produce only surface peeling.AJO –DO 2004 Mutlu Ozean et al superior bond strength is obtained when ceramic surface is pretreated with silica coating & silanization giving about 13.6 MPa particularly with polycarbonate brackets. Bond failure site is at bracket / adhesive interface.

BONDING TO GOLD

In vitro studies showed sandblasting & special primers with 4-META containing resin bonding provides good adhesion.

Tin plating improved bond strength only marginally

But clinically is still difficult to achieve good bond strength when bonding to gold

Gloria Nollie et al in ANGLE 1997 reported that Type –1V gold treated with adlloy has increased bond strength & gives twice as strong as those found in microetched gold.

INDIRECT BONDING

It was first introduced by Silverman& Cohen in 1974.They used methylmethacrylate adhesive to attach to plastic brackets to model cast in laboratory.An unfilled bis-GMA resin was used as an adhesive between etched enamel & previously placed adhesive.

Advantages

1. More accurate bracket positioning

AJO-DO 1999 by Bonchankoo et al concluded that indirect technique has better bracket placement in vertical position,but no significant difference occurred in angulation or mesiodistal position.

2. Decreased chairtime

AJO-DO 1982 by Michael Aquirre et al showed that avg, time needed for direct technique – 42.18 mins & for indirect technique – 53.73 mins with only 23.91 mins representing actual clinical time

3. Increased patient control

4. Its superior in lingual bonding where visualization is difficult

Disadvantages

1. Technique sensitive2. Increased lab time3. Risk of adhesive leakage to gingival embrasure could

lead to difficult oral hygiene management.ANGLE 2004 by Polatkaramen et al.

4. Removing adhesive is difficult to achieve & time consuming

5. Achieving consistent & predictable adhesion is difficult.6. Accidental removal of brackets with tray is not unusual.7. Adequate bond strength shortly after sealant application

is mandatory.(To withstand force during tray removal ) 8. Failure rates are slightly higher – Zachrisson &

Brobakken

9. Less disturbance during adhesive polymerization is difficult to achieve

10. Closer fitting of bracket base is better achieved by one point contact of scaler in direct bonding than when transfer tray should be held in place by finger pressure in indirect bonding.

BOTTOM LINE – WHEN CORRECT TECHNIQUE IS USED WITH EXPERIENCE FAILURE RATES WITH DIRECT & INDIRECT TECHNIQUE ARE WITHIN CLINICALLY ACCEPTEBLE RANGE

Clinical procedure

Many techniques are available which differ by

•The way brackets are attached temporarily to models•Type of transfer tray•Adhesive or sealant employed

Indirect bonding using silicone transfer tray :

• Patients stone model is marked for long axis & vertical height

•Water soluble adhesive is placed on bracket base or model & bracket is positioned accurately

Procedure:

•Mixed silicone putty material is pressed onto the cemented brackets & tray is formed with sufficient thickness for strength• •After silicone sets model & tray are immersed in hot water to separate brackets from model.Remaining adhesive is removed under water

•Patient s teeth are prepared as per direct technique.

•Adhesive applied to bracket bases

•Tray seated on patient s arch & held firmly with steady pressure for 3 mins

•After 10 mins tray is cut & removed

•Any excess adhesive is removed

Indirect bonding with double sealant technique :

• Here adhesive is placed on bracket base to fix temporarily to models.Excess removed.• After 10 mins a placement tray is vacuum formed & placed with models in water until thoroughly saturated.• Trays are separated & trimmed so its gingival edge is within 2 mm of brackets• The bracket bases are lightly abraded with a stone point.• Patient s teeth are prepared • Brackets are painted with catalyst sealant resin& enamel surfaces are painted with universal sealant resin.• Tray is inserted , seated & held for 3 mins• Tray is peeled off from lingual to buccal• Excess Flash removed

The above technique is called Thomas technique& introduced in1979.Many criticism arrived stating that curing of sealant might be incomplete.

So later arrived a modified Thomas technique which uses a sealant that is mixed just before placing transfer tray on to the tooth that ensures complete mixing of the 2 components of the sealant..

.In ANGLE 1993 Jing-Yi- Shiac et al reported that Thomas technique creates an interface between the old (aged) composite& sealant which is not present in other techniques.This might create marginal voids which when not covered by sealant might result in 50% reduction in bond strength.

JCO 1996 M.Moskowitz et al using Light vinyl polysiloxone impression material

JCO Michael Read & Pearson using Memosil CD

LINGUAL BONDING

This is a recently invented technique introduced for patients particularly adults who are highly esthetic consiousFujita of Japan was a pioneer in lingual bonding

Advantages

• Esthetic

• Enamel demineralization is better controlled & of less consequence

• Precise detailing of tooth position can be made without the distractions of wires & brackets.

• Lip posture seen correctly instead of being artificially determined in front of incisors

Disadvantages

•Technique sensitive

•Time consuming

•Awkward working position

•More precision necessary for adjustment of arch wires

•Decreased interbracket distances

•Good active ligation us difficult

•Ariane hohoff et al in AJO-DO 2003 concluded that lingual orthodontics induces significant speech performance impairment & oral discomfort.Smaller the appliance lesser the impairment & so customized brackets are recommended.

REBONDING

More time consuming & uncomfortable for orthodontists is loose brackets during treatment.

The loose bracket is removed from arch wire.Ligatures of 2 neighboring brackets are cut & arch wire is placed on top of these brackets.

Clinical procedure

. The adhesive remaining on tooth surface is removed

Adhesive on bracket is removed with bur or slightly roughened .Do not burnish mesh backing

Tooth is etched for 60 secs sealed & bracket rebonded.

Total time should not exceed 3 mins

Unetched & etched enamel

Re etched enamel with adhesive remnant

Effect on enamel by various rebonding procedure

After scaling as a rebonding procedure

After scaling and re etching as a rebonding procedure

After scaling ,prophylaxis & re etching

After finishing bur & re etching

After green stone & re etching

After green rubber wheel & re etching

RECYCLING

Main goal of recycling process is to remove the adhesive from bracket base without damaging or weakening the delicate foil mesh or distorting the dimensions of bracket slot.

Some methods used are:

•Applying heat about 450 c to burn off the resin followed by electro polishing ( to remove tarnish & oxide)

•Solvent stripping followed by high frequency vibrations with only flash electro polishing

•Recycling with sandblasting

•Recycling with microetching

Advantages

• Cost effective

•EJO 2004 by Victoria Cacciafesta et al reported after 12 month in vivo trial that there is no significant difference in bond failure rate occurred between recycled& new SS brackets.•In ANGLE 1995 Peter .G.Gaffey et al reported electro thermal recycling resulted in bond strength greater than 9 MPa which is clinically acceptable

Disadvantages

1. It results in decreased bond strength.

Supported by Chan Hsi Chung et al in AJO-DO 2002. They also concluded that sandblasting debonded brackets gave acceptable bond strength .Silane does not improve & HF acid actually decreases bond strength.

In AJO-DO 1998 by James.K.Grubouski et al reported significant decrease in bond strength occurred when microetching is used

Bishara also concluded shear bond strength considerably decreases with repeated bonding

2. Decreases corrosion resistance

EJO 2004 Feb. by TsuiHsein Huang et al reported that recycled SS brackets release more ions than new ones.

DEBONDINGAim:To remove the attachments & all adhesive resin from the tooth & to restore the surface as closely as possible to its pretreatment condition without inducing iatrogenic damage

Procedure:

First method with pliers:Squeezing the bracket wings mesiodistally using tips of weingart pliers& bracket removed with applying peel force.

Advantages

•Gentler technique•Useful on brittle, mobile or endodontically treated tooth

1. Bracket removal ( SS )

Disadvantages

•Bracket deformed & so can not be reused•Break likely to occur at adhesive / bracket interface leaving more adhesive remnant- By Bishara AJO –DO 1999Second method with band remover.

Still ligated in place brackets are gripped with anterior band removed & lifted off outwardly at 45 degree angle.

Bracket removal - ceramic brackets:

Bishara et al in 1994 ANGLE proposed that Modified diametrial compression using debonding pliers requires the application of 30 % less force to enamel than when using shear force to remove ceramic brackets .

Thermal debracketing is another method which contains application of controlled heat to resin that bonds the brackets.

• Powder – liquid material has significantly lower debonding temperature of about 45 degree C

• No mix paste requires 60-170 degree C

Brackets using mechanical retention can be safely removed with a peripheral force applied to gingival tie wings using an ETM 346 RT or similar plier.

But brackets using chemical retention requires a wrench type instrument & using a torquing force.

2. Removal of residual adhesive

Accomplished by

1. Scraping with super sharp band or bond removing pliers or with a scaler – produces significant scratch marks

2. Using TC bur at 30,000 rpm with contraangle hand piece

3. Brain.W. Thomas et al in ANGLE 1996 proposed a new technique to remove residual resin using laser aided degradation .When resin is lased with Nd :YAG laser energy at 100 Hz showed 75 % decrease in compressive strength of the resin.

Enamel surface at 1200x magnification without being lased.

Enamel surface at 1200x magnification after 3 sec lasing

INFLUENCE ON ENAMEL

By proposing ESI ( Enamel Surface Index ) with scores 0 to 4 Under SEM Zachrisson & Artun compared influence on enamel by different debonding instruments.

• Hand scaler produces highest roughness( By Double Rix et al in AJO-DO 2001 )

Score - 3

By medium sand paper disk By green rubber wheel

Score 4 – diamond instruments

Score 2- Fine sand paper disk

Score 1-Oval plain cut & or Spiral fluted TC bur. Final pumicing treatment found to be beneficial

Although it did not remove any deep scratches.

Amount of enamel loss during Debonding :

Depends on

• Types of instruments used

• Type of primer & resin used

• Bond failure interface.

For prophylaxis-With bristle brush – 10 millimicron enamel is lost With rubber cup – 5 millimicron enamel is removed.

Resins - Unfilled – 5 to 8 millimicron lost with hand instruments Total loss of enamel is 20 to 40 millimicron . Filled – 10 millimicron with low speed TC bur. 20millimicron with high speed bur & green rubber wheel. Total of 10 to 25 millimicron with rotary instrument

ANGLE 2004 by Rangasamy Rajagopal showed that MIP & SEP under moisture contamination produce bond failure at bracket / adhesive interface which results in les enamel damage . But conventional etchant under moisture contamination resulted in bond failure at enamel/ adhesive interface leading to more enamel damage.

EJO 2004 Elliets et al proposed diamond bur is better than bladed bur in view of debonded enamel surface.

Additional deep reaching enamel tearouts down to a depth of 100 millimicron & localized enamel loss of 150 to 160 millimicron have also been reported.

Enamel tearouts.

It is likely to occur with resins having small filler particles.Might be due to greater penetration depth with small particles. Upon debonding small fillers would reinforce the adhesive tags. & bond failure occurs at bracket adhesive interface.

Enamel cracks.

They occur as split lines in enamel.A shap sound sometimes heard upon removal of bonded brackets could be reflected in the creation of enamel cracks.

• Vertical cracks are more common .• Few horizontal & oblique cracks are observed.• More noticeable cracks are in upper central incisors & canines0

BOND STRENGTH

Definition : It’s the force obtained at bond failure divided by superficial surface area

FACTORS AFFECTING BOND STRENGTH :1.Improper procedure:

•Pumicing has no effect on composite resin but decreases bond strength significantly with the use of RMGIC

2. Moisture control: •Presence of water or saliva or blood contamination significantly decreases bond strength. Possible mechanism is presence of high mucous protein content & enzymes in saliva would likely result in increased degradation of reactions in the adhesive & this affect bond strength

ANGLE 1999 by Talconi et al reported water contamination decreases bond strength to etched & unetched enamel using RMGIC for short aging times . For unetched enamel saliva was less deleterious than water regarding bond strength .

AJO-DO by Ross & Hobson reported that though moisture &blood contamination decreases bond strength Transbond MIP is a suitable adhesive for bonding conditions of poor moisture control.

•Bond strength at dry condition: 15.69 MPa After contamination : 12.89 MpaAfter blood contamination : 11.6 MPa

EJO 2000 for RMGIC etched surfaces Contaminated with saliva actually increases bond strength & plasma still increase s it.But it is not significant .So RMGIC has acceptable bond strength regardless of enamel surface.

ANGLE 2004 Somsak Kayo et al showed saliva contamination of SEP did not cause any significant decrease in bond strength AJO –DO 2004 Aug by Vittorio Cacciafesta et al showed blood contamination decreases bond strength with conventional as well as moisture insensitive primer & produces clinically inadequate bond strength .Even time of moisture contamination affects bond strength differently.If it occurred before primer application bond strength decreases considerably than when when it occurs after primer application.

3. Types of primer used

•Conventional etching & priming 2 step procedure highest bond strength . Its followed by SEP. MIP gives the least bond strength.

• Bishara in ANGLE 2002 concluded that fluoride releasing SEP has significantly lower shear bond strength than conventional 2 step procedure.

4. Types of adhesives used

• Composite resin gives highest bond strength . Its followed by RMGIC . 1st & 2nd generation GIC gives least bond strength.

• Cook in 1990 reported up to 12 % failure rate observed with GICs when used in upper anteriors which has least occlusal interference

5. Time of curing:

• AJO-DO 1999 By Akra Kumori et al : Delayed exposure decrease bond strength. Its affects LCC more than RMGIC• AJO-DO 2000 By Bishara et al :Increasing curing time for additional 5 – 10 sec increases bond strength of RMGIC

6.Location of brackets:

• Bracket failure is more common in lower arch than in upper arch• Posteriors are more susceptible than anteriors• Premolars has highest prevalence for bond failure.• Upper incisors are least affected.• Bond failures are more in crowded teeth with complex design than spaced teeth with simpler design.

7. Types of brackets used:

• Ceramic brackets yield highest bond strength .• Metal brackets has comparable bond strength.• Plastic brackets yield lowest bond strength.

8. Types of brackets bases:

AJO-DO 2004 by Wang et al :

TOMY bracket base with circular concave discs showed highest bond strength

Bracket base with horizontal retention grooves concave moderate bond strength

Conventional bracket base with larger mesh spacing produce better bond strength

Bishara In ANGLE 2004 June:

Single mesh bracket base gives 5.2 + 3.9 MPa bond strength.

Double mesh bracket base gives 5.8 + 2.8 MPa bond strength.

The difference is not significant.

Oliver Sorrel et al in AJO-DO 2002:Reported laser structured bracket base provides 2 times higher bond strength than simple foil mesh. Also bond failure likely to occur at enamel / Adhesive interface but with acceptable enamel damage.

Major & smith et al in AJO-DO 1981:

• Weld spots could decrease retentive areas.• Weld spurs could decrease bond strength with foil mesh bases• Weld spurs at edges should be avoided to increase resin mesh seal• Best resin penetration is obtained with a fine mesh of woven type.

Matasha in Orthodontic materials : He suggested to increase bracket performance use of proper primer would help to wet the surface of the base & invite the adhesive to pass through mesh .It also decreases air trapping.

9.Recycled brackets:

Recycled brackets has decreased bond strength.

10.Other products application

• Todd kimura et al in AJO –DO 2004reported application of fluoride varnish did not affect bond strength significantly when etched either with conventional or SEP.

• Ching Liang Meng in AJO – DO 1998 reported APF application after itching to prevent enamel demineralization decreases bond strength.

11. Miscellaneous

• Bishara in ANGLE 2000 : Removing excess adhesive after 5 sec of light curing to initially secure the brackets decreases bond strength significantly.

• Newman in Angle 2001 reported that micro etching bracket base and use of adhesion promotors to enamel like Pyromellitic glycerol dimethacrylate increase bond strength

EFFECTS OF BONDING ON TEETH

& PERIODONTIUM

White spot lesions (WSL )

They are early carious lesions first seen as white spots in caries susceptible region usually around bracket margin especially in gingival 3rd of teeth.

Treatment with fixed appliance makes conventional oral hygiene for plaque removal more difficult & thus increases cariogenic challenge on surfaces that normally show low prevalence for caries.

ANGLE 2000WSL – In non treated patients: 3% to 82% In treated patients : 8.5% to 44% in anteriors. 7.7 % to 81% in posteriors.

Zachrisson – enamel etching removes outer surface which is better in absorbing fluorides.Also it exposes more susceptible subsurface to oral environment.

AJO 1998 by Bronwen et al reported RMGIC adhesives minimize enamel demineralization.

EJO 1997 by Agneta Marasson et al reported WSL are less when GIC is used than with diacrylate.

AJO-DO 1999 by Alex .T.H. Hang et al reported that polymerization of bonding resins is compromised at atmospheric oxygen, giving rise to a layer of low molecular wt, chemical species known as oxygen inhibited layer which was found to be cytotoxic to human fibroblast.

Effect on Periodontium;

Excess adhesive especially in gingival 3rd of tooth causes inflammation of periodontium & remains throughout treatment.

AJO-DO 1999 by Kent.L, Knoernschild et al demonstrated P.gingivalis, E.coli lipopolysaccharides exhibit a high affinity for orthodontic brackets especially SS when compared with ceramic , plastic or gold brackets.This increases inflammation of tissues adjacent to brackets.

Simplicity of bonding can be misleading . Success in bonding requires understanding of and adherence to accepted orthodontic and preventive dentistry principles.