Clinical SOME TIPS TO HELP THE DEBONDING PROCEDURE


Bond strength is greatest at the bracket- composite interface and therefore enamel frac- ture is highly likely. A “plane of cleavage” can act as a stress breaker for comfortable debonding Silane coupling is not


required for bonding brackets due to the quality of mechanical retention inherent in quality bracket bases. Mechanical retention reduces enamel detachment but maintains high strength, durability and retention similar to metal brackets8 Use a weaker orthodontic-


specific unfilled resin bonding agent (not a restorative bonding agent) as the brackets are supposed to be removed at a later date and a permanent bond is not required Use ceramic bracket with a notched pre- stressed base and plane of cleavage for debond9


Bond with resin modified glass ionomer cement


Remove composite flash around the brackets before debonding10


Use the manufacturer’s debonding instruments11


Fig 1 Continued »


simple cases that may run into diffi- culty and necessitate transfer or referral, using an established bracket system enables the receiving orthodontist to pick up the case with a knowledge of where the teeth have been pre-programmed to move. It is unlikely therefore that spurious brackets will have to be removed and then re-bonded with known and proven ones. This will save time, money and discomfort/ potential enamel damage to the patient.


Ideal properties of an aesthetic bracket These can be broadly divided into: • optimum aesthetics • optimal clinical performance. The first point is rather obvious


but there are discernible differences according to quality. The second point requires further understanding and elabo- rating upon. We will discuss each type of aesthetic bracket in turn.


Plastic brackets Plastic brackets were introduced in the ı970s. Initially, they were made from acrylic or polycarbonate. Problems were quickly identified, including staining and odoursı


. More importantly, their lack of


strength and stiffness resulted in bonding problems, tie wing fractures and perma- nent deformation2


. Their success, as a


viable alternative to metal brackets was understandably short lived. Plastic bracket slots distort with time under a constant stress, rendering them insufficiently strong3


Composite (thermoplastic polyurethane)


To compensate for the lack of


strength and rigidity of the original poly- carbonate brackets, high-grade medical polyurethane brackets reinforced with ceramic or fibreglass fillers and/or metal slots were introducedı


Diagram of (a) 1st Order (in-out), (b) 2nd Order (tip) and (c) 3rd Order (torque) movements


. Brackets with


metal reinforced slots demonstrated less enamel wear than ceramic and signifi- cantly less creep than conventional plastic polycarbonate brackets, although initial problems still existed (Fig 3).


Ceramic brackets Ceramic brackets were introduced in the ı980s, offering several advantages over the aforementioned aesthetic brackets: • higher strength • greater resistance to wear and defor- mation


• better colour stability • superior aesthetics. All currently available ceramic brackets are composed of aluminium oxide (alumina) in either polycrystalline or monocrystalline form, depending on their method of fabrication. The first brackets were each milled from


a single crystal of sapphire and were more translucent. More recent monocrystalline brackets are machined from extrusions of synthetic sapphire and are virtually clear4 Polycrystalline alumina brackets are


. . Also, and importantly, much of the


energy stored in the aligning archwire was expended in distorting the brackets due to the poor integrity of the bracket slot and therefore archwire forces were not trans- mitted effectively for tooth movement. A comparison with stainless steel brackets illustrated that plastic brackets are only suited for clinical application if they have a metal slotı


(Fig 2).


made by injection moulding of submicron- sized particles of alumina suspended in a resin, sintering them to fuse the alumina and produce a bracket that is finally machined to shape5


. Polycrystal-


line ceramics, due to their rougher more porous surface, have a high coefficient of friction. This problem has largely been overcome by the use of metal reinforced archwire slots and improvement in modern ceramic technology. These disadvantages are not associated


with simple alignment cases and non- extraction cases, where sliding mechanics


Fig 3 Composite brackets


is less of a requirement. More recent injec- tion moulded microcrystalline brackets (e.g. Gemini Clear) demonstrate excel- lent aesthetics and are smoother, smaller, better contoured (thus more comfortable and better adapted to tooth surfaces) and stronger than conventional ceramic brackets (Fig 4).


Bond strength The majority of currently available


Continued » Ireland’s Dental magazine 25 Fig 2 Plastic bracket


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