Types of bonding materials in orthodontics and bonding techniques

 

if you are intersted in this article please follow for more readings

https://myorthodonticsblogg.blogspot.com/      👈🏻

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. 

 

BASIC BONDING PROCEDURE

 1. CLEANING

2. ENAMEL CONDITIONING.

 3. SEALING

4. BONDING

 

1-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.

2-ENAMEL CONDITIONING

 I. MOISTURE CONTROL

II. ENAMEL PRETREATMENT

I- 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.

 

II-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

·        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

·        There are 4 types of enamel appearance after various pre treatment :

Type -1 Honey comb appearance with loss of enamel prism centers.

Type -2 Cobblestone appearance with prism edges lost.

Type -3 Pitted enamel with map like appearance.

Type -4 Granulation of enamel with numerous holes

 

·        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.

 

3- 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.

I) They might be necessary to achieve proper bond strength .

II) Its necessary to improve resistance to micro leakage.

III) After sealant coating moisture control may not be extremly important.

 IV) It provides enamel cover in areas of adhesive voids.

V) Gwinnet& Ceen found light polymerized sealant protect enamel adjacent to brackets from dissolutions & subsurface lesions

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

 VII) 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

 

 4- BONDING

a-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.

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

c-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).

d-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. 

 

 

 MATERIALS USED IN BONDING

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.

 

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.

 

 BONDING TO CROWNS & RESTORATIONS AMALGAM RESTORATIONS & CROWNS

Methods used are

 1. Modifying metal surface

 2. Use of intermediate resin

3. New adhesive resins that bond chemically to non-precious as well as precious metals .

Recommended procedure :By Zachrisson in ANGLE 98 & AJO-DO 2000

1.     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. 

 

 NEWER MATERIALS IN BONDING

Ø 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.

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

Ø 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.

Ø 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 .