DEBONDING

BY DR TONY PIOUS

INTRODUCTION In orthodontic field its often necessary to break an adhesive

bond between two dental structures which includes procedures such as the removing of orthodontic bands or brackets from the teeth at the completion of treatment.

Typically, orthodontic brackets are removed by mechanical devices with application of force.

There are many types of devices used for bracket removal, such as pliers, mechanical arms etc.

Orthodontic tool and method for fracturing the bond between two dental structures should be quick and should not cause significant trauma to the patient.

Buonocore (1955): Demonstrated the increased adhesion of attachments to tooth surface by conditioning the enamel surface with 85% phosphoric acid for 30 seconds.

Sadler (1958): Attempts to cement orthodontic attachments directly to enamel without etching have been recorded. Sadler tested nine materials (four dental cements, one rubber base cement, two metal adhesives and two general purpose adhesives) but these were all unsuccessful.

Bowen (1962) developed a new resin system, Bisphenol-A-Glycidyl dimethacrylate commonly known as BIS-GMA and is often referred to as “Bowen’s Resin”.

Newman (1965) was the first to bond orthodontic attachments to teeth by means of an epoxy resin. He used a mixture consisting of equal parts of low molecular weight epoxy liquid and a high molecular weight solid epoxy with a polyamide curing agent.

Cueto (1966), his experiment was done to see if it was feasible to attach a bracket directly to tooth enamel without the use of orthodontic bands. The adhesive consisted of a liquid monomer, methyl-2-cyanoacrylate, and a silicate filler.

Mitchel (1967) had failures with an epoxy resin but described a successful, although limited, clinical trial using black copper cement and gold direct attachments.

Buonocore et al (1968) showed that enhanced bonding to acid conditioned surfaces were due to the presence of “prism like” tags and also observed poor bonding with unconditioned enamel surfaces.

Smith (1968) introduced Zinc polyacrylate and bracket bonding with cement was reported.

Miura et al (1971) experimented with a new catalyst (a modified trialkyl borane) and introduced orthomite. This proved to be particularly successful for bonding plastic brackets and for enhanced adhesion in the presence of moisture.

Retief (1973) described the importance of preconditioning with 50% phosphoric acid.

Reynolds (1975) reported that a maximum tensile bond strength of 5.9 to 7.9 Mpa would be a adequate to resist treatment forces but added that, in vitro tensile strength levels of 4.9 Mpa have proved clinically acceptable.

Keizer et al (1976) evaluated direct bonding adhesives for orthodontic metal brackets. Their study showed large standard deviation of bond strength giving rise to speculation on reliability.

Zachrisson (1978) stated that the objective of bonding was to get as good as mechanical as possible between enamel and adhesive and evenly distributed etching pattern with marked surface roughness, but little actual loss of enamel is most desirable to achieve mechanical interlock.

Tavas et al (1979) introduced the concept of light activated composites. They demonstrated that the bond strength of brackets bonded with this was comparable with two chemically cured adhesives.

Although important improvements in bonding have been made in the last 30 years, the requirements of an ideal bonding system are quite similar to those indicated by Buonocore. Apparently, the future has a sound background in the past.

THE OBJECTIVES OF DEBONDING to remove the attachment and all the adhesive resin from the tooth and restore the surface as closely as possible to its pretreatment condition without inducing iatrogenic damage.

To obtain these objectives, a correct technique is of fundamental importance.

Debonding may be unnecessarily time consuming and damaging to the enamel if performed with improper technique or in a careless manner.

Debonding is discussed as follows:

• Clinical procedure• Influence of different debonding instruments on surface

enamel• Amount of enamel lost in debonding• Enamel tearouts• Enamel cracks• Adhesive remanant wear• Reversal of decalcifications

CLINICAL PROCEDURES

Bracket removal Removal of residual adhesives

Bracket Removal

DEBONDING STEEL BRACKETS

Several different procedures for debracketing with pliers are available.

An original method was to place the tips of a twin-beaked pliers against the mesial and distal edges of the bonding base and cut the brackets off between the tooth and the base.

A gentler technique is to squeeze the bracket wings mesiodistaly and lift the bracket off with a peel force. This is particularly useful on brittle, mobile, or endodontically treated teeth.

The recommended technique

Use of Debonding pliers: Recommended technique in which the chisel shaped beaks are placed as close to the base of the bracket as possible and a peeling type force is applied.

Because metal brackets are ductile, this force is transmitted to the adhesive bond, breaking it

Lift-off Debonding Instrument: This a design of pliers in which a tensile force is placed on the adhesive bond through a wire loop hooked over the bracket tie wings, pulling the wings of the bracket directly away from the tooth surface. This method distorts the brackets the least and is preferred if recycling is a consideration.

REMOVING BONDED BEGG BRACKET

James n, here the walls of the vertical slot are squeezed together.

This action causes the base of the bracket to peel away from the bonding material, lifting the edges of the base and breaking the adhesive bond.

The bracket and base then can be peeled off the tooth and any adhesive remaining on the tooth surface can be gently sanded and polished.

A plier with a sturdy tip should be used for this technique, to avoid breakage. The technique works best on minibased (3 – mm width) brackets. If the base is wider or curved then ‘base – squeezing” is very effective.

LINGUAL DEBONDING

DEBONDING CERAMIC BRACKETS

- First generation ceramic brackets depended on silane coating to ensure adhesion.

- The silane coupling led to excessively high bond strengths and a resultant damage to the enamel at the time of debonding.

This problem has been solved in second generation

by incorporating a polycarbonate base or base can be sprayed with atomized glass.

This ensured that at the time of debonding the failure occurred at the bracket adhesive interphase.

Ceramic brackets will not flex when squeezed with debonding pliers. The preferred mechanical debonding is to lift the brackets off with peripheral force application, much the same as for steel brackets.

Several tie-wings may still fracture, which in practice requires grinding away the rest of the bracket. Cutting the brackets off with gradual pressure from the tips of twin-beaked pliers oriented mesiodistally close to the bracket-adhesive interface is not recommended because it might introduce horizontal enamel cracks.

Vukovich ME etal (AJO 1991) Low – speed grinding of ceramic brackets with no watercoolant cause permanent damage or necrosis of dental pulps. Therefore water cooling of the grinding sites is necessary.

Bishara SE etal (AJO1997) More recent ceramic brackets have a mechanical lock base and a vertical slot, which will split the bracket by squeezing. Seperation is at the bracket adhesive interface, with little risk of enamel fracture.

THERMAL DEBONDING

Norman R. Gorback suggested that removal of ceramic brackets can be painful and harmful for the patient, and difficult to remove by the orthodontist. The use of heat makes bracket removal efficient and painless, although extreme care is required to avoid touching the teeth with a heated instrument.

Procedure: Tips of the utility plier are heated in the micro torch for ten seconds.

The bracket is gripped with the heated plier.

A light rotational force is applied after ten seconds.

If the bracket does not snap off easily the procedure is repeated after heating the plier for 15 seconds.

LASER DEBONDING Since the early 1990s, laser have been used experimentally

for debonding ceramic brackets.

Mechanism of laser debonding (Tocchio et al AJO 1993 )

Laser energy can degrade the adhesive resin by three methods :

1. Thermal softening 2. Thermal ablation 3. Photoablation

Thermal softening occurs when the laser heats the

bonding agent until it softens. Clinically, this results in the bracket’s surrendering to gravity and sliding off the tooth surface.

Thermal ablation occurs when heating is fast enough to raise the temperature of the resin into its vaporization range.

Photoablation It occurs when very high – energy laser light interacts with the adhesive material.

Time span for debonding with lasers

The super CO2 laser products have high energy pulses over a short time. The normal CO2 laser is made of continuos waves with millisecond – duration pulses.

Obata et al (Eur J 1999) reported that the super – pulse CO2 laser took less time for debonding than did the normal – pulse laser (less than 4 seconds).

Effects on the pulp When laser radiation is applied to a ceramic bracket, energy is absorbed and converted into heat.

This heat is then free to propagate by conduction to the base of the bracket to soften the adhesive. There is also potential for this heat to propagate to the tooth structure and eventually lead to pulp damage.

Obata (1995) reported that there was less increase in pulp cavity temperature compared with bracket surface temperature. Furthermore, lased and nonlased tooth pulps showed no histological difference.

Ma et al ( AJO 1997) showed that there is a linear relationship between lasing time and an increase in intrapulpal temperature. A mean intrapulpal temperature increase of 0.91º C after 1 second of lasing 1.74º C after 2 seconds 2.67ºC after 3 seconds

Obata (1995) reported that there was less increase in pulp cavity temperature compared with bracket surface temperature. Furthermore, lased and nonlased tooth pulps showed no histological difference.

Ma et al ( AJO 1997) showed that there is a linear relationship between lasing time and an increase in intrapulpal temperature. A mean intrapulpal temperature increase of

0.91º C after 1 second of lasing 1.74º C after 2 seconds 2.67ºC after 3 seconds

Time lag between lasing and debonding

Abdul – kader and Ibrahim(1999) reported that significantly higher force was required for debonding ceramic brackets when 1 minute elapsed after laser exposure compared with debonding immediately after laser exposure.

Therefore, debonding ceramic brackets one by one immediately after exposure, before the adhesive resin material resolidifies, requires less debonding force.

According to comprehensive review done on Laser debonding of ceramic brackets by Ezz Azzeh and Paul J. Feldon (AJO 2003) they concluded that:

The time spent to debond ceramic brackets is less when using lasers.

Debonding forces are significantly reduced with lasers.

The risk of enamel damage and bracket fracture is significantly reduced with lasers.

The CO2 super – pulse laser is superior to normal pulse CO2 and YAG lasers.

The use of monocrystalline brackets is suggested over polycrystalline brackets.

Ceramic brackets should be irradiated and debonded one by one immediately after laser exposure.

The risk of pulpal damage is significantly reduced if the following are used: Super – pulse CO2 laser at 2 W for less than 4 seconds. CO2 laser for 3 seconds at 3 W. CO2 laser ( normal pulse ) at 18 W for 2 seconds.

REMOVAL OF RESIDUAL ADHESIVE

Because of the color similarity between present adhesives and enamel, complete removal of all remaining adhesive is not easily achieved.

Many patients may be left with incomplete resin removal, which is not acceptable.

Abrasive wear of present bonding resins is limited and remnants are likely to become unesthetically discolored with time.

The removal of excess adhesive may be accomplished by

1. Scraping with a very sharp band or bond-removing pliers or with scaler.

2. Using a suitable bur and contra –angle.-- Dome shaped TC bur

-- Ultrafine diamond bur -- White stone finishing bur

Although the first method is fast and frequently successful on curved teeth it is less useful on flat anterior teeth. Also, a risk exists of creating significant scratch marks.

The preferred alternative is to use a suitable dome tapered TC bur in a contra-angle handpiece.

Clinical experience and laboratory studies indicate that approximately 30,000 rpm is optimal for rapid adhesive removal without enamel damage.

Light painting movements of the bur should be used so as not to scratch the enamel. Water cooling should not be employed when the last remnants are removed because water lessens the contrast with enamel.

When all adhesive has been removed, the tooth surface may be polished with pumice.

Adhesive remnant index (ARI) -Artun

Used to evaluate the amount of adhesive left on the tooth after debonding.

Score 0 : No adhesive left on the toothScore 1 : Less than half of the adhesive leftScore 2 : More than half of the adhesive leftScore 3 : All adhesive left on the tooth, with distinct impression of the bracket mesh.

Presence of perichymata and imbrications.

Change in microstructure of enamel surface with age. Gradual wear of enamel with age 0-2 µm per year

Characteristics of normal enamel

INFLUENCE ON ENAMEL BY DIFFERENT DEBONDING INSTRUMENTS Zachrisson and Artun were able to compare different instruments commonly used in debonding procedures and rank their degrees of surface marking on young permanent teeth.

The study demonstrated that 1. diamond instruments were unacceptable; even

fine diamond burs produced coarse scratches and gave a deeply rough appearance.

2. medium sandpaper disks and a green rubber wheel produced similar scratches that could not be polished away

3. fine sandpaper disks produced several marked and some even deeper scratches and a surface appearance largely resembling that of adult teeth.

4. plain cut and spiral fluted TC burs operated at about 25,000 rpm were the only instruments that provided the satisfactory surface appearance.

5.none of the instruments tested left the virgin tooth surface with its perikymata intact.

The clinical implication of the study is that TC burs produced the finest scratch pattern with the least enamel loss and are superior in their ability to reach difficult areas-pits, fissures,, and along the gingival margin

AMOUNT OF ENAMEL LOST IN DEBONDING 10 to 25 μm. Pus and Way(AJO 1980) found a high-speed bur and

green rubber wheel removes approximately 20μm and a low-speed TC bur removes around 10μm of enamel.

Van Waes etal(1997) recently confirmed observations of a more limited loss of enamel when TC burs are used cautiously. They found an average enamel loss of only 7.4 μm and concluded that minimal enamel damage is associated with careful use of a TC bur for removal of residual composite.

ENAMEL TEAROUTS

Redd TB(Jco1991) suggested localized enamel tearouts have been reported to occur associated with bonding and debonding both metal and ceramic brackets.

They may be related to the type of filler particles in the adhesive resin used for bonding and to the location of bond breakage.

When comparisons were made between tooth surface appearances after debonding metal brackets attached with either macrofilled (10 to 30μm) or microfilled (0.2 to 0.3μm) adhesives, a difference occurred when the resin was scrapped off with pliers.

On debonding the small fillers reinforce the adhesive tags. The macrofillers, on the other hand, create a more natural breakup-point in the enamel-adhesive interface. Similarly, with unfilled resins there is no natural breakpoint.

The clinical implications is 1. To use brackets that have mechanical

retention and debonding instruments and techniques that primarily leave all or the majority of composite on the tooth.

To avoid scraping away adhesive remnants with

hand instrument.

ENAMEL CRACKS Zachrisson BU et al (AJO 1980) The prevalance of cracks,

their distribution per tooth, their location on the tooth surface and the type were described;

1. Vertical cracks are common, but great individual variation.

2. Few horizontal and oblique cracks are observed normally.

3. No significant difference exists between the three groups with regard to prevalance and location of cracks.

4. The most notable cracks are on the maxillary central incisors and canines.

The clinical implication of these findings

1. observes several distinct enamel cracks on the patients teeth after debonding, particularly on teeth other than maxillary canines and central incisors

2. detects cracks in horizontal direction, this is an indication that the bonding or debonding technique used may need improvement.

With ceramic brackets, the risk for creating enamel cracks is greater than for metal brackets. The lack of ductility may generate stress build-up in the adhesive-enamel interface that may produce enamel cracks at debonding.

ADHESIVE REMNANT WEAR

Adhesive has been found on the tooth surface, even after attempts to remove it with mechanical instruments.

Because of color resemblance to the teeth, particularly when wet, residual adhesive may easily remain undetected.

Brobakken and Zachrisson (AJO 1981) Abrasive wear depends on the size, type and

amount of reinforcing fillers in the adhesive. At the time of debonding, varying amounts of adhesive were purposely left on the teeth assumed to be the most exposed to tooth brushing forces. Only thin films of residual adhesive showed any reduction in size.

Gwinnett and Ceen (AJO 1978) reported that small remanants of unfilled sealant did not predispose to plaque accumulation and did begin to wear away with time. However, this finding can not automatically be transferred to different types of filled adhesives, some of which have much greater wear resistance and accumulate plaque more readily.

Brobakken and Zachrissons( AJO 1981) findings showed that residual filled adhesive will quickly disappear by itself after debonding; it appears irresponsible to leave large accumulations of adhesive.

REVERSAL OF DECALCIFICATION

White spots or areas of demineralization are carious lesions of varying extent.

The general conclusion was that individual teeth, banded or bonded, may exhibit significantly more white spot formation than untreated control teeth.

In a multibonded technique Gorelick et al (AJO 1982) found that 50% of the patients experienced an increase in whitespots.

The highest incidence was in the maxillary incisors, particularly the laterals.

This obvious degree of iatrogenic damage suggests the need for preventive programs using fluoride associated with fixed appliance orthodontic treatment.

Zachrisson BU (AJO 1975) suggested daily rinsing with dilute (0.05%) sodium fluoride solution throughout the periods of treatment and retention, plus regular use of a fluoride dentifrice, is recommended as a routine procedure for all orthodontic patients.

Artun and Thylstrup(1986) after debonding, arrest of further demineralization, and a gradual regression of the lesion at the clinical level takes place primarily because of surface abrasion with some redeposition of minerals.

Ogaard et al (AJO 1981) observed that remineralization of surface softened enamel and subsurface lesions are completely different processes.

The surface – softened lesions remineralize faster and more completely than subsurface lesions which remineralize extremely slowly, probably because of lesion arrest by widespread use of fluoride.

Visible white spots that develop during orthodontic therapy should therefore not treated with concentrated fluoride agents immediately after debonding because this procedure will arrest the lesions and prevent complete repair.

At present it seems advisable to recommend a period of 2 to 3 months of good oral hygiene but without fluoride supplementation associated with the debonding session. This should reduce the clinical visibility of the white spots.

More fluoride may tend to precipitate calcium phosphate onto the enamel surface and block the surface pores. This limits remineralization to the superficial part of the lesion, and the optical appearance of the white spot is not reduced.

Microabrasion Done when remineralizing capacity of oral fluids is exhausted and white spots established. Microabrasion: A gel prepared from 18% HCl, pumice and glycerine is applied professionally with a modified toothbrush tip for 3-5 mins; followed by rinsing. This is effective for removing white spots and brownyellow enamel discolorations. In case of more extensive mineral loss, grinding with diamond burs or composite restorations may be required

White spot lesions After micro- abrations

CONCLUSION Orthodontic bonding has found to be more practical, and

beneficial than the circumferential bonding for many reasons.

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

The future of bonding is promising. Product development in terms of adhesives, brackets, and technical details is continually occurring at a rapid rate. It is necessary for the orthodontist to update and stay oriented.