Bonded orthodontic retainers have gained in popularity during recent years to maintain tooth positions upon completion of active tooth movement. This article aims to give an overview of the use of bonded retainers, discuss the different techniques for placement and review the different types of bonded retainers that are available.
The aim of orthodontic retention is to maintain teeth in their new positions after active treatment has ceased. Almost all treated malocclusions require some form of retention post-treatment and relapse of orthodontic treatment may be unpredictable.1 Histological studies in dogs have shown that supracrestal fibres can take at least seven months to adapt to their new positions.2,3 Hence, the most common period of retention within the UK is 12 months,4 however, teeth can still move from their corrected positions after this period due to continued skeletal growth and soft tissue maturation. Therefore, some clinicians advocate indefinite retention to minimize relapse.1,5
A wide number of appliances have been used as retainers and these can be divided into two main subgroups:
There is a variety of retention regimes used by orthodontists and currently there is insufficient evidence on which to base the clinical practice of orthodontic retention.1 The pre-treatment records and tooth movements during treatment should be considered prior to prescribing the appropriate retention regime (Table 1).6
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This article will review the use of bonded retainers in maintaining tooth position.
Kneirim 1973 published the first paper describing the use of fixed bonded retainers and described the use of a retainer made from 0.028” stainless steel bonded to the lower cuspids only.7
The advantages of bonded retainers are:
The disadvantages of bonded retainers include:
The main contemporary designs are retainers which are:
This design of retainer bonds the orthodontic wire to the lingual aspect of each individual tooth in the labial segment. The wire utilized usually has some flexibility so that teeth are not held rigidly in position, which allows physiological movement of the teeth even when several adjacent teeth are bonded; this may result in reduced bond failure since teeth can move independently of each other.6,8 The wire used is usually multistranded (3–6 strands)6,8 stainless steel varying in diameter from 0.0175” to 0.0215”. The thicker the wire or the more strands there are, the less chance of wire fracture; however, the wire becomes less flexible. Five- and six-strand stainless steel wire has been recommended owing to its adaptability and ability to retain adhesive material, eg composites.6,9 This design is indicated when individual tooth movements are prone to relapse.
This design of bonded retainer attaches a stiff orthodontic wire between the canine teeth and is not bonded to the incisors. Multistrand stainless steel wire or, more usually, plain stainless steel wire, 0.032”, may be used.6,10 This design is indicated when there is alteration of the antero-posterior or lateral position of the lower labial segment during treatment and maintenance of the post-treatment intercanine width is essential.
It has been suggested that this type of bonded retainer is easier to place, safer and more hygienic than retainers bonded to all six anterior teeth. In addition, if the retainer debonds from one of the canines, the patient is immediately aware and can seek assistance, therefore preventing any unnecessary relapse.6 However, there is some evidence to suggest that these retainers may be less effective at maintaining incisor alignment, particularly rotations, and long-term studies do not provide evidence that they are significantly more hygienic.10,11
| Type of Retainer | Advantages | Disadvantages |
|---|---|---|
| Multistrand stainless steel wire | Flexible, allowing physiological tooth movement |
Possibility of distortion |
| Plain stainless steel wire | Rigid, less chance of distortion |
Not usually bonded to all teeth in the labial segment |
| Glass-fibre reinforced retainers (Stick Tech Ltd) | Aesthetic |
Significantly higher failure rates compared to stainless steel wire retainers20,21 |
| Nickel titanium retainers | Can be used to correct relapse of mandibular anterior crowding and be left in situ for permanent retention | No long-term data on performance |
| Ortho-Flextech® (Reliance Orthodontic Products, Itasca, Ill) | Easily placed using a direct bonding technique | No long-term data on performance |
| V-loop design | Facilitates oral hygiene |
Technically demanding to produce |
| LingLock retainer (LingLock®) | Reduced laboratory time |
No long-term data on performance |
| Labial-bonded retainers | Good for use in posterior regions where bonding lingually is difficult | Poor aesthetics |
Zachrisson introduced the multistrand bonded lingual retainer12 and this type of bonded retainer has become the gold standard, despite variations in wire types, diameters and bonding procedures.8
Multistrand stainless steel wire can be used when bonding to all teeth in the labial segments or just canine to canine.8 In the former type, a smaller diameter multistrand wire, usually ranging from 0.0175” to 0.0215” is bonded to each tooth in the labial segment. In the latter, a relatively rigid large diameter multistrand wire, usually 0.032”, is bonded to the canines only. Multistrand wire has the ability to be adapted to the lingual surfaces of the incisors and the flexibility of the wire allows for physiological movement of the teeth, even when several adjacent teeth are bonded.13 Their irregular surface also offers increased mechanical retention for the composite without the need for placement of retentive loops.12
Multistrand wires may be round or rectangular in cross-section and are usually formed from 3–6 fine strands of wire6,8,14,15 that are either braided or arranged co-axially. An adhesive may be used to prevent the unravelling of cut ends16 and some wires are prepared with a coating to provide a smoother surface.
Multistrand wires which are thinner and have fewer strands may have the tendency to distort, however, thicker strands may be more stable, albeit with reduced flexibility. A number of designs of multistrand wire have been described,6,8,14,15 however, Zachrisson has published data regarding the use of gold-coated 0.0215” five-stranded spiral wire, quoting success rates up to 96.5% over a mean observation period of 4.2 years.6
This wire is bonded to the canines only. It has been suggested that the use of plain stainless steel wire reduces the possibility of distortion compared to multistrand wire. The recommended dimensions of this wire are 0.030” or 0.032” stainless steel,10,17 with some authors recommending the use of gold-coated stainless steel, to enhance aesthetics and biocompatibility6 (Gold n Braces Inc). The wire may need to be sandblasted at its terminal ends to improve retention of the bonding resin.
Some clinicians argue that one of the disadvantages of using stainless steel wire as a bonded retainer is that it is visible and unattractive.18 Glass-fibre reinforced bonded retainers have been developed to address this issue. They have the advantages of being tooth-coloured, can be easily repaired and can be used in patients with metal allergies.18,19 However, they also exhibit a number of disadvantages, including reduced flexibility and complex, technique-sensitive placement. Glass-fibre reinforced retainers have demonstrated a significantly higher failure rate (51% over 2 years) compared to stainless steel wire retainers (12% over 2 years), in the same study, and therefore their use has been discouraged in daily practice.20,21
Some authors have described the successful use of 0.018” nickel-titanium wire bonded lingually to each tooth from canine to canine. This wire could be used to correct relapse of mandibular anterior crowding and also be left in situ for permanent retention. However, there is no long-term data available on the performance of this type of retainer.22
Ortho-Flextech® (Reliance Orthodontic Products, Itasca, Ill) is a type of bonded retainer which may be fitted at the chairside. Ortho Flextech® is a chain made of white gold with small amounts of copper, zinc, silver and a trace of nickel that can be bonded directly on to the lingual of tooth surfaces. Users report that a significant advantage of this method is the ease of adaptability of the links in the chain (Figure 1).23
One of the disadvantages of bonded retainers cited is the difficulty in facilitating oral hygiene.10 To address this issue, different retainer designs have been suggested. Lew published a design for a flossable bonded retainer, which involved adapting a length of 0.0195” multistrand wire to the lingual surfaces of the teeth with V-portions across the interdental papilla.24 This design has the advantage of facilitating oral hygiene and, owing to the V-loops, allows physiological movement of the bonded teeth. However, this retainer would need to be fabricated on a model and is more technically demanding than the conventional bonded retainer. In addition, there may be concerns that the wire actually crosses the gingival margin. There is also the possible concern that the increased wire length introduces greater flexibility, if not compensated for by increased wire thickness, that may allow tooth movement. The V-loop retainer, however, has been reported to be well tolerated by patients and has similar success rates to conventional bonded retainers (Figure 2).25
Another design of bonded retainer, which allows the patient to floss, is the LingLock retainer.26 This retainer consists of pairs of retention elements each with female and male interlocking components. Retention is gained by the close contact of these female and male parts, but also allows access to floss interdentally. The designers of this retainer have suggested that the advantages are improved aesthetics, reduced laboratory and chairside time, reduced risk of breakage, easy repair and facilitation of oral hygiene procedures (Figure 3).26
Labial-bonded retainers may be indicated in specific situations, eg prevention of space re-opening in a closed extraction site in adults. These retainers tend to be used on posterior teeth, owing to the difficulty of bonding lingually in this region. Labial-bonded retainers have a better survival rate if they are short (eg two teeth) and gold-plated wire is more acceptable to patients than stainless steel. A 4% failure rate over 2 years has been quoted.6,27
Composites are the preferred material for bonding orthodontic fixed retainers.9 A wide range of composite materials have been used for bonding orthodontic retainers, ranging from macro-filled, hybrid and micro-filled.9 More recently, nano-filled composites have been developed which contain filler particles 5–100 nm in diameter, however, no work has been carried out in relation to bonded retainers.28
Failure of bonding can occur in two ways:
Evidence has suggested that composites with higher filler content have higher shear strength than composites with low filler content, when bonded to enamel.29 The most frequent site of failure is the wire-composite interface and this is usually associated with previous loss of composite because of abrasion.9 Therefore, a composite with higher filler content has been shown to be more desirable. The use of multistrand wire and/or sandblasting the terminal ends of the retainer should assist the bond between the wire and composite interface. In vitro studies have suggested that the combination of a six-stranded wire (increasing the surface area for the composite to interlock) and macro-filled composite may provide optimum performance in fixed bonded retainers.9 Other studies have suggested that diluting macro-filled composites with unfilled resin would improve handling properties, however, may deteriorate abrasion resistance.30
A light-cured, colour-reactivating composite has been proposed which facilitates visual monitoring for removal of excess adhesive, thus avoiding undue thickness, which can cause plaque retention and gingival inflammation.19
Glass ionomer cements may be used for bonded retainers. They have the advantages of fluoride release which would decrease the risk of decalcification and also have the ability to bond to wet enamel surfaces. Even though they have a decreased bond strength and abrasion resistance compared to composites, they may have sufficient bond strength for use in bonded retainers, as demonstrated in vitro.31,32
The placement of bonded retainers is time consuming and technique sensitive. To avoid unwanted tooth movement or failure:
There are two main techniques for placement of lingual bonded retainers.
The indirect technique involves fabrication of the bonded retainer on a cast of the patient's dentition. There have been a number of methods developed to fabricate orthodontic bonded retainers indirectly, however, they all essentially follow similar processes (Table 3).
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The indirect method of bonding retainers has the advantages that it allows for accurate positioning, passive placement and minimal disturbance during bonding. The use of a transfer mechanism allows the operator and assistant to have both hands free for bonding.40 In addition, the wire can be easily designed to avoid occlusal interferences (Figure 4).
The direct technique involves placement of the bonded retainer in the mouth without the need for an intermediate laboratory step. The retainer wire must be kept in the proper position, be passive and must not move during bonding.41 A number of techniques have been developed to assist wire placement in direct bonding. These include using fingers, dental floss, orthodontic elastics or ligature wires.42,43,44,45,46,47,48,49 However, these methods may be unreliable.39 Any shift in wire position can lead to bond failure and affect the stability of the treatment results. The use of elastics may mean that the wire is not passive when being placed (Figure 5 and 6).
The use of magnets has also been advocated for the placement of lingual-bonded retainers and has been shown to be adequate at supporting and positioning a multistrand canine to canine retainer during bonding.50,51
Bonded retainers may fail in a number of ways:
A bonded retainer may fail at the wire-composite interface as previously discussed. The use of 1 mm thickness high filler composite with a six strand multistrand wire may decrease the risk of failure of this type.9 To ensure good enamel adhesion, a good bonding technique must be employed, including sandblasting of enamel, and there must not be any wire movement during bonding.10 The thicker the retainer wire, the higher the detachment rate due to increased rigidity.11,52 However, thinner wires may become more easily distorted and suffer stress fractures.6
Bonded retainers have been shown to have a variable survival rate, ranging from over 90%, over a 10-year period,7 to 30%, over a 3-year period (Table 4).53 It has been suggested that survival rates are heavily dependant on the operator skill and extent of the retainer. Where over 90% survival over a 10-year period has been reported, there was a single operator placing bonded retainers in a prescribed manner ranging from 4–6 teeth. Where a survival rate of 30% over 3 years was reported, this study included multiple operators with a wide range of prescriptions, ranging from 2–8 teeth. Higher failure rates were recorded when the upper canines or the lower first premolars were included in the retainer. Table 4 demonstrates the various survival rates quoted in the literature for different designs of retainer. Bonded retainers in the upper arch tend to have higher failure rates, especially if the upper canines are included.6,53 This may be due to the fact that bonded retainers in the upper arch may be subjected to greater occlusal forces and there may be a kink in the wire to allow for the morphology of the canine.
| Paper | Type of Retainer | Bonded to which Teeth | Period of Time | Survival Rate |
|---|---|---|---|---|
| Dahl and Zachrisson 199160 | Multistrand 3-stranded 0.0195” and 0.0215” stainless steel wire | Bonded to all teeth in labial segment | 5 years | Maxilla = 75% |
| Dahl and Zachrisson 199160 | Multistrand 5-stranded 0.0215” stainless steel wire | Bonded to all teeth in labial segment | 5 years | Maxilla = 92.2% |
| Foek et al 200861 | Flexible, braided, rectangular 0.022” × 0.016” bonded stainless steel lingual retainers | Bonded to all teeth in labial segment | 3.4 years | Mandible = 68.4% |
| Stormann and Ehmer 200211 | 0.0195” Respond wire retainer | Bonded to all teeth in in labial segment | 2 years | Maxilla and Mandible = 67% |
| Stormann and Ehmer 200211 | 0.0215” Respond wire retainer | Bonded to all teeth in labial segment | 2 years | Maxilla and Mandible = 50% |
| Stormann and Ehmer 200211 | Pre-fabricated canine and canine retainer | Bonded to canines only | 2 years | Maxilla and Mandible 82% (but frequent relapse of incisors) |
| Segner and Heinrici 200053 | 0.0175” Respond wire | Bonded on all teeth ranging from 4–4 and 1–1 | 3 years | Maxilla and Mandible = 30% |
| Årtun et al 199710 | Thin flexible 0.025” spiral wire | Bonded to all teeth in labial segment | 3 years | Mandible = 72.8% |
| Årtun et al 199710 | Thick wire 0.032” spiral/plain | Bonded to canines only | 3 years | Mandible = 79.2% |
| Zachrisson 20076 | 0.030” Gold–coated wire | Bonded to canines only | 4 years mean observation time (range 1–10 years) | Mandible = 96.5% |
| Zachrisson 20076 | 0.0215” Gold–coated five–stranded spiral wire | Bonded to all teeth in labial segment | 4 years mean observation time (range 1–10 years) | Mandible = 94.7% Maxilla = 78.5% |
| Zachrisson 20076 | 0.0215” Gold–coated five–stranded spiral wire | Bonded to incisors in the maxilla | 4 years mean observation time (range 1–10 years) | Maxilla = 93.8% |
| Booth et al 200817 | 0.025” or 0.032” steel wire | Bonded to canines only | 20 years | Maxilla and Mandible = 47% |
| Lee and Mills 200925 | 0.0160” Australian black wire in a V–loop design | Bonded to all teeth in labial segment | 6 months | Maxilla and Mandible = 85.7% |
| Lee and Mills 200925 | 0.0175” Pentacat multistrand stainless steel wire | Bonded to all teeth in labial segment | 6 months | Maxilla and Mandible = 87.6% |
| Tacken et al 200920 | Glass fibre–reinforced retainers containing 500 unidirectional glass fibres | Bonded to all teeth in labial segment | 2 years | Maxilla = 48.9% Mandible = 53% |
| Tacken et al 200920 | Glass fibre–reinforced retainers containing 1000 unidirectional glass fibres | Bonded to all teeth in labial segment | 2 years | Maxilla = 47.9% |
| Tacken et al 200920 | Six-stranded 0.0215” co-axial wire | Bonded to all teeth in labial segment | 2 years | Maxilla = 85.7% |
| Lumsden et al 199962 | 0.018” co-axial wire | Bonded to all teeth in labial segment | 5-year period | Maxilla = 25-61.2% |
Respond wire is a stainless steel co-axial wire from Ormco Int.
The majority of failures tend to occur in the first year. If a bonded retainer survives the first year then the probability of failure dramatically decreases. Early failure may be due to technique deficiencies, ie insufficient enamel/composite bond strength or poor isolation. Late failure is associated with wire fatigue, abrasion of the composite over the wire or excessive bite force.11,53
When bonded retainers are attached to all teeth in the labial segment they appear to be effective at maintaining incisor alignment. However, when a canine to canine only retainer is used this may not be the case.10,11,54 There have been case reports published demonstrating that bonded retainers may fail, occasionally, either to prevent relapse of torque correction, or they may be the cause of a developing torque discrepancy within the teeth retained.55 This may be prevented by utilizing a rectangular wire as a bonded retainer or using two wires which are bonded occluso-gingivally to each other and also ensuring that the wire is passive before bonding.55,56
Although bonded retainers are generally effective at maintaining alignment, they have the disadvantage of compromising oral hygiene. Patients with bonded retainers have been shown to have increased plaque accumulation around the retainer. This may predispose the patient to risks of decalcification, dental caries and periodontal disease.11 Even though there is an accumulation of plaque and calculus around the retainer, there may not be any long-term damage to hard or soft tissues.10,17 There also appears to be no difference in the periodontal implications for patients who wear removable retainers or have bonded retainers, even though patients with bonded retainers tend to have slightly more plaque and calculus build-up.57 The design of the bonded retainer does not have a significant effect on plaque or calculus accumulation, however, the length of time that the appliance is in the mouth and the oral hygiene of the patient do have an effect.17,57 The saliva pooling in the lingual region of the lower incisors may decrease the risk of decalcification.
The use of bonded retainers in multidisciplinary cases, which require the use of crown and bridgework, is problematic. There is very little evidence on the use of bonded retainers in conjunction with crown and bridgework. The use of silane coupling agents has been recommended to bond brackets on to feldspathic porcelain, but no evidence exists on bonding of retainers.58Panavia adhesive cements (Kuraray Dental, New York, USA) have been used in restorative dentistry to cement crown and bridgework constructed from nickel-chromium. Hypothetically, a similar cement could be used as a bonded retainer specifically if:
However, this has never been tested.
Crown and bridgework has been designed with a slot or tunnel for placement of a fixed bonded retainer. This is a very technique sensitive procedure and may require extra tooth removal or may compromise the structural integrity of the prosthesis.
Another option would be either to use splinted crowns or double abutted bridgework. These options may not be conducive to the maintenance of oral health. In addition, double-abutted, resin-retained bridges are twice as likely to fail compared to cantilever designs.59
Bonded retainers are an effective way of maintaining orthodontic tooth positions. There are various situations where their use is indicated, though placement may be time consuming and technically challenging. Bonded retainers should be bonded passively, with a good bonding technique. Following this review, suggestions to assist bonded retention include:
There are many different types of bonded retainers, techniques of fabrication and methods of fitting bonded retainers, with many different materials used to bond the retainers. If a bonded retainer is indicated, the design of the retainer should be carefully considered and the execution on fitting the retainer should be excellent to ensure long-term survival and retention.
