Manufacturers of self-ligating bracket systems claim that these systems have a number of advantages over conventional ligation, such as that treatment can be achieved more quickly and more effectively, and that the brackets in combination with the recommended archwires exert lower forces and there is consequently less risk of root resorption. Self-ligation is also thought to allow better oral hygiene and cause less discomfort during treatment. A number of these claims are discussed below in greater detail, focusing particularly on the following claims:
Chairside time is shorter for each appointment.
Overall treatment time is shorter.
Self-ligating brackets are more hygienic and easier to keep clean.
There are longer intervals between adjustments, so that fewer adjustments are necessary.
The dental practice is able to work with fewer staff.
Shorter Chairside Time
It is essential to have appropriate and well-established reference standards to test the theory that self-ligating brackets lead to reduced chairside time. The authors used the German health-insurance schedule (BEMA 2004), which standardizes the payments dentists receive for itemized dental services, as a basis for assessment. This assessment was based on the following procedures: bonding time for straight-wire brackets; teeth etched and primed separately; elastomeric elements used to li-gate the archwires. The time values used for the calculations assumed that the average operator needed the following amount of time per procedure:
Approximately 3 minutes for placement of a bracket
Approximately 9 minutes for placement and cementing of a band
Approximately 9 minutes for an archwire change (removal and placement of a new wire)
About 1 minute to remove a bracket or band (per bracket and band)
The times mentioned above do not include preparation time, such as time for cleaning surfaces or giving the patient instructions (on oral hygiene, etc.). The focus is therefore exclusively on the time the doctor spends with the patient.
Using the above data, the average chair times for orthodontic treatment were:
Bonding: 60 minutes (20 minutes × 3)
Band placement and cementing: 72 minutes (8 × 9 minutes)
Archwire change: 108 minutes (12 × 9 minutes; assuming that 12 visits are necessary)
Remove bands and brackets: 28 minutes (28 × 1 minute)
The average chairside time thus adds up to 268 minutes ( Fig. 3.39 ). Only an experienced operator would be able to achieve these times reliably. The above data are used for reference purposes only; no attempt is made here to discuss the validity of the data.
Bonding of Brackets
There is little scope for shortening the bonding time required for self-ligating brackets in comparison with a normal ligation system. It might in fact be argued that due to the physical characteristics of the brackets, as well as the ligation mechanism involved, the bonding time may actually increase rather than decrease. It is more likely that the chairside time could be reduced by using different primers and etching techniques (for example, using a self-etching primer), rather than self-ligating brackets. One could also consider using indirect bonding, which may be able to reduce the chairside time by up to 30 minutes. However, this requires complex and costly laboratory techniques. It is difficult to determine whether the 30 minutes saved during bonding are lost due to the time required for laboratory production of the model used to bond the brackets. Also, an additional impression may need to be taken. However, self-etching primers do reduce chairside time, as it is no longer necessary to remove the phosphoric acid and have a drying step before application of the bond, and the time reduction should be approximately 15 minutes per patient. It has to be taken into consideration, however, that slightly lower bond strengths are obtained with self-etching primers in comparison with the conventional phosphoric acid and bond technique.
Self-ligating brackets do not confer any advantage during the bonding procedure. Time savings could potentially be made using indirect bonding techniques and/or with self-etching primers.
Ligation of Archwires
A number of manufacturers claim that less chairside time is required for removing and ligating archwires. We are not aware of any study that confirms this. A direct comparison between self-ligation and standard brackets showed similar times for both methods.5 However, it is important to remember that changing the elastomeric modules has to be undertaken by an experienced operator. There may be one other potential advantage with self-ligating systems: the operator can open and close the self-ligating brackets easily without any assistance. For efficient and speedy archwire changes using conventional elastomeric modules, it is best to have an assistant handing the modules to the operator. Another advantage may be that self-ligating brackets usually ensure full engagement of the wire, as the locking mechanisms would otherwise not shut properly. This can be important if wire changes are done by less experienced operators who have yet to learn how to spot partially disengaged wires.
It is also worthwhile mentioning that not all bracket-archwire combinations are advisable or indeed possible.6 The Damon system, for example, works with a rigid locking mechanism. This can make it difficult to ligate thicker rectangular wires, and occasionally it is difficult to open or close the clip. The manufacturer recommends specific archwire sequences to avoid these potential issues ( Fig. 3.40 ).
The same also applies for 3M’s SLBs. For example, it is not possible to engage a 0.017 × 0.025 Turbo-NiTi (Ormco) in a SmartClip or Clarity SL bracket ( Fig. 3.41 ). In general, it is uncomfortable for patients who are being treated with these brackets to use wires that are larger than 0.021 × 0.021 (NiTi or stainless steel).
A shorter procedure time with SLBs is only evident in comparison with ligating an entire arch using steel ligatures.7
Even an experienced operator may find it challenging to complete an archwire change in both upper and lower arches in less than 9 minutes, the basic value established by health insurance companies in Germany for reimbursement to dentists (BEMA).
Another important aspect of the treatment is often not mentioned by the manufacturers-i.e., the possibility of using elastomeric chains. There are significant differences between self-ligating bracket systems in this respect. Some systems do not even allow silicone or elastomeric chains to be used under or over the archwire. Bracket systems with a very rounded design may make it very challenging for elastic chains to be used at all ( Fig. 3.42 ). Elastomeric chains interfere with the locking mechanism of some self-ligating systems. This applies in particular to the Discovery SL bracket (Dentaurum), the Time 2 and Time 3 brackets (American Orthodontics), and the Flare bracket (Adenta). Other self-ligating brackets make it difficult, if not impossible, to ligate silicone elastomeric chains on top of the archwire. The Speed bracket, for example, has no retention for attaching a chain on top of the archwire. Some composite-based materials with poor abrasion characteristics (e.g., Damon 3) may lose their capacity to engage an elastomeric chain ( Fig. 3.43 ). Removing the archwires can also be difficult in patients with significant calculus accumulation, which is often more pronounced in adult patients. Passive brackets (such as Damon) can be particularly difficult to open and close ( Fig. 3.44 ) in such cases. Some manufacturers recommend using vinegar or 37% phosphoric acid to overcome the blockage of the system. “Airflow” and “sandblasting” have also been recommended. Any of the above methods would certainly eliminate any potential advantages of self-ligation over conventional ligation.
Ultrasound cleaning devices can be used to reestablish the mechanism used in self-ligating brackets, particularly in patients with increased calculus accumulation ( Fig. 3.45 ). Ceramic brackets may fracture when using ultrasound cleaning devices.
It is unlikely that there is any time-saving in comparison with conventional ligation during ligation or removal of archwires using a self-ligation system. However, fewer staff may be needed, as the ligation and removal of archwires can be carried out by a single operator rather than with a four-handed technique, which requires two operators. It needs to be borne in mind that chairside time may occasionally be prolonged due to mechanical problems associated with the opening and closing of self-ligating brackets.
Debonding of the Fixed Appliances
There are significant differences when debonding brackets, because manufacturers pursue one of two goals: brackets such as Damon 3 and Opal usually leave a large amount of composite on the tooth on debonding ( Fig. 3.46 ). The advantage claimed for this is that it reduces the vulnerability of the enamel on debonding, which occurs at the bracket-adhesive interface, with no risk to the enamel. However, the operator needs to remember that removing any residual composite is time-consuming and may also be traumatic to the tooth.
Additional time may have to be spent to remove residual composite when using some of the self-ligating systems.
In an ideal situation, the operator would like the bonding agent to be completely attached to the bracket after de-bonding, so that the cleaning-up process is shortened or even eliminated ( Fig. 3.47 ). However, this type of approach could lead to enamel fractures in rare cases, as the debonding would occur at the adhesive-enamel interface.
Using self-ligating brackets does not reduce the treatment time on debonding in comparison with normal ligation. In fact, some self-ligating brackets create a significant disadvantage if all the composite is left on the tooth surface at debonding.