From Volume 4, Issue 4, October 2011 | Pages 112-117
Fixed retainers are a popular method of maintaining incisor position following orthodontic treatment. This paper reviews the complications reported with fixed retainers and reports a case in which suspected activation in a multistrand bonded retainer had caused severe unwanted movement of two teeth in the upper labial segment.
Retention of orthodontic treatment is an important aspect to consider when treating any orthodontic patient. Relapse is defined as movement of teeth into any position other than that achieved after orthodontic movement.1
There are different ways to achieve retention after orthodontic tooth movement. The choice of retention type depends on several factors, such as:
Two types of orthodontic retention method exist. The first method involves utilizing occlusion in maintaining teeth in their final position, eg the use of a positive overbite in retaining teeth after correction of crossbite cases. The second method involves the use of appliances, either removable or fixed, in order to maintain the teeth in their final position.
Fixed or bonded retainers are usually used in the labial segment. They are long-term retainers used for cases in which the teeth are moved into an unstable position and likely to relapse, such as:
Fixed retainers offer several advantages over removable retainers with patient compliance being the most important.2 Another advantage is aesthetics, as removable retainers (except for the vacuum-formed retainers) usually have a visible wire running on the labial surfaces of the anterior segment. Comfort is another factor as no bulky acrylic-containing device is needed.
Currently, there is insufficient evidence on which to base the clinical practice of orthodontic retention.3 Since this review3 was published a new randomized controlled study comparing bonded retainers in the lower arch with vacuum-formed retainers had been identified.4,5,6 In this study, patients preferred the bonded retainers to the vacuum-formed retainers, because they found them more acceptable to wear. Interestingly, the clinicians preferred the vacuum-formed retainers, as they were easier to fit. More incisor irregularity recurred with the patients wearing vacuum-formed retainers, and this related to reported wear. Although some bonded retainers were broken, more patients lost or broke their removable retainers. The fact that patients did not need to remember to wear their bonded retainers meant that they were more effective at reducing relapse. One disadvantage was that the bonded retainers caused slightly more gingival inflammation and periodontal pockets >4mm. The long-term clinical significance for this is unclear, but certainly it would seem that good initial care instructions are indicated for bonded retainer patients, and the need for long-term maintenance may be important.
Several types of fixed retainers are reported in the literature with the wire containing fixed retainers being the most widely used type. The wires used are different in thickness, cross-section (round versus rectangular), design (plain versus multistrand), and shape (straight and v-shaped).2,3,4,5,6,7 Other types of fixed retainers include mesh pads,8 and resin fibreglass strips.9
Despite the advantages of using fixed retainers, these are not complication free. Several complications to the use of fixed retainers are reported in the literature, such as:
This paper will focus on discussing complications with fixed retainers and report a case in which severe relapse had occurred despite the use of a fixed retainer.
Although there is a lack of high quality evidence to support the current practice of orthodontic retention,3 the general consensus is that fixed retainers may have an important role in maintaining incisor position following orthodontic treatment.2,4,5,6,10,11
It had been reported that overall failure rates of fixed retainers range between 10.3% and 47.0%, over a period of 38 months and 41 months, respectively,12 with detachment at the wire/bond interface being the type of failure most commonly observed. The survival rate of fixed retainers decreases with time with the highest number of failures being reported within the first 3–6 months.13,14
The following factors have been suggested as affecting the success of fixed retainers.
In a study involving 103 patients with fixed retainers placed a minimum of 5 years, more incisal position of the retainers tended to cause less failure than a cervical position.15 The authors suggested that a more incisal position of the retainer reduces the spans of interdental wires offering less flexibility of the wire and hence less failure.
The choice of bonding material could be a factor for bond failure. Composite is usually the material of choice for bonding fixed retainers, with several brands being reported in the literature.12Concise (3M Unitek Corp, Monrovia, Calif) is the composite material mostly used.12 Other composite materials, such as light cured composites, micro-filled composite, hybrid composite and orthodontic bonding resins, have been used. In a study comparing Concise (auto cure composite) and Heliosit (light cure composite with a lower proportion of filling particles), a statistical significant difference in favour of the Concise group was found.14
Different bonding techniques ranging from chairside fixed retainer fabrication, using pre-contoured lab fabricated fixed retainers (Figure 1), and cutting grooves into the lingual side of the teeth to accommodate the wire were used.
Cutting grooves into the lingual side of the teeth to accommodate the wire was found to reduce failure rates.15 This technique was used in 12 out of 67 maxillary retainers in the sample, with only 25% failure rate compared to 40% in the remaining fixed retainers without a groove.15 However, the authors mentioned that the figures represented only 10% of the whole sample and advised that the data be considered with caution.
In the same study, 54% of retainers were laboratory made and 46% were done chairside. Bonding or fracture failure occurred in 27% of the pre-fabricated laboratory made retainers and 42% of the chairside fabricated ones.
A study comparing bonding the fixed retainers under either rubber dam (dry field condition) or without a rubber dam (relatively dry field condition) showed no significant differences in failure rate between absolute and relatively dry field conditions.14 The authors recommended the use of relative dry fields owing to the relative ease of the technique compared to the use of rubber dam.
In a study comparing the 0.0195″ and 0.0215″ multistrand wires, it was reported that the thicker the wire, the higher the chance of bond failure.14 These authors attributed their findings to the increased rigidity of the wire thereby increasing the chance of de-bonding. This was in agreement with the results of a prospective study which found that using 5-stranded wires reduced the failure rate cause by de-bonding, compared with that of the 3-stranded wires with the same overall thickness (7.8% versus 25%, respectively).11 This was attributed to the fact that each of the 5-stranded wires had smaller diameters than those of the 3-stranded wires, offering more flexibility to the overall wire.
Breakage can also be associated with wire fatigue or to excessive bite force (Figure 2). Wire breakage is thought to be related to wire thickness, as the thicker the wire the more rigid it is and the higher its chance of breakage. This was also demonstrated in the previous study, with the 5-stranded wires having only 3.1% breakage in comparison with 23.2% of the 3-stranded wires with the same overall diameter.11 However, bonded retainer wire needs to be sufficiently thick to prevent accidental fracture, but sufficiently flexible to allow physiological movement of the teeth.
In a prospective randomized controlled clinical study (RCT) comparing bonded retainers with thick plain and thick spiral wires, both bonded to the canines only; the fixed retainers made of thick plain wires appeared to have a lower failure rate (9.1%) than those made of thick spiral wires (30.8%).2 However, no significant difference was detected, possibly as a result of the low sample size.
Bond failures, with the detachment of the retainer from the composite, is often due to mechanical forces.14 For upper retainers this was attributed to the abrasion of composite caused by occlusal contact with the lower incisors. In a study assessing failure rate of fixed retainers in the maxilla and mandible, there was a higher failure rate in the maxilla (7.8% with 5-stranded wires and 25% in 3-stranded wires) than in the mandible (5.9% with 5-stranded wires and 10.3% in 3-stranded wires) over an average period of 3.2 years.11 These findings were in agreement with other work which found a failure rate of fixed retainers twice as high in the maxilla compared to the mandible.13 These authors also found that most of the patients with reduced overbite had no composite wear in the maxillary retainers.
In the mandible, on the other hand, abrasion of composite bond could be caused by mechanical forces such as toothbrushing and chewing.11
Maintaining oral hygiene can be a problem with fixed retainers that could also cause periodontal problems in the long term. In an RCT comparing bonded lower retainers with lower vacuum-formed retainers, there was more gingival inflammation noted with the bonded retainer patients after one year.6 Regardless of the wire used in the construction of the fixed retainers, plaque and calculus tend to accumulate along the retainer wires.16,17,18 However, the presence of plaque and calculus along the fixed retainer does not seem to prevent satisfactory hygiene along the gingival margin.2,3,4,5,6,7,8,9,10,11,12,13,14,15,16 It was recommended that professional plaque and calculus removal with oral hygiene instructions should be repeated every 6 months.19
The long-term effect of fixed retainers on the gingival and periodontal health seems to be controversial. Some researchers reported no negative effects on gingival and periodontal health after long-term use of fixed retainers.2,20 However, some of these studies reported that patients had professional cleaning at their general dental practitioners or at the orthodontic department throughout the study period.2 In a study involving 60 patients who had bonded retainers for a period of 20 years, the authors concluded that bonded retainers do not interfere with oral hygiene practice and do not have any adverse effect on periodontal health.20
Despite the lack of increased plaque and gingival indices after using fixed retainers, a tendency to promote calculus accumulation, marginal recession, and increased probing depth was reported after reviewing 32 patients treated with bonded fixed retainers for at least 9 years.21 Similar results were reported in another study where greater probing depth, bleeding on probing, plaque index, and gingival recession were found.22 These authors questioned the practice of providing fixed retainers without considering patient oral hygiene.21,22
The presence of a fixed retainer and the increased chance of plaque and calculus accumulation along the wire seems not to pose any risk of demineralization of the hard tissues.2,6
In a study investigating the demineralization effect of 549 retainers, it was reported that fixed retainers have not been responsible for inducing any new caries over a period of 3 years.13 Even after 20 years of using fixed retainers, there were no enamel lesions on the lingual aspect of the mandibular incisors and canines, even in those patients with poor oral hygiene.20
A case was reported in the literature in which a nickel-containing fixed retainer caused severe allergic contact dermatitis.23 The wire, however, did not cause any oral symptoms which, in the opinion of the authors, was related to early oral exposure to nickel by orthodontic appliances causing oral tolerance.
In the RCT comparing lower bonded retainers with lower vacuum-formed retainers,4,5,6 less relapse was observed with the bonded retainers after one year.
One study reported no change in incisor irregularity using retainers bonded to each tooth in the labial segment, while minor changes in alignment were observed among the patients with retainers bonded only to the canines after three years.2
This was in agreement with another study where the irregularity index was used to compare post-treatment relapse after using three types of retainers [0.0195″ Respond® (canine to canine), 0.0215″ Respond® (canine to canine), and canine and canine retainer (prefabricated and bonded to two teeth)].14 These authors found that canine and canine retainer had the highest incidence of change in the irregularity index (80%), followed by the 0.0215″ retainer at 20% and finally no relapse with the 0.0195″ retainer after 24 months.
In a retrospective study, comparing relapse occurring after using canine to canine multistrand retainers and Hawley-type retainers (with acrylic labial to the incisors) which was measured using Little's index,24 these authors found that the relapse was statistically significant in both groups. However, no statistically significant difference in relapse was found between the two groups. They concluded that, even with bonded retainers in place, relapse still occurs.
Another study reported 21 cases with post-treatment changes,25 the author reported two types of post-treatment changes, namely torque difference between two adjacent mandibular incisors causing increased buccolingual inclination (18 patients) and movement of single mandibular canine (3 patients). These patients had flexible spiral wire-bonded retainers attached to all six teeth in the mandibular segment. Retainers were fabricated on dental casts for the retainer to be passive.
A 21-year-old Caucasian female, who was a dental student at the Leeds Dental Institute, was referred by her General Dental Practitioner to the Orthodontic Department at the same Institute. The patient had completed a course of non-extraction, fixed appliance treatment five years previously and had a fixed retainer bonded to all the teeth from canine to canine in both the upper and lower arches. Her complaint was a worsening displacement of the UR3 and UR2 (Figure 3). There was no history of trauma to the dentition.
The patient presented with a mild Class II skeletal pattern with average vertical proportions and competent lips.
The patient presented with all adult teeth present apart from the permanent third molars. The incisor relationship was Class I, with the upper centreline being 0.5 mm to the left-hand side. The molar and canine relationships were Class I bilaterally. There was an open bite between the UR3 and the lower dentition, with the UR3 root being excessively torqued palatally and the UR2 root excessively torqued buccally and palpable in the buccal sulcus. Oral hygiene was good and there was a fixed multistrand retainer, bonded from canine to canine, in the upper and lower arches. The upper right central incisor was found to have increased mesio-distal width in comparison with the upper left central incisor.
An orthopantomogram and long cone periapical of the UR3 and UR2 revealed the presence of all permanent teeth and showed no pathology or altered root morphology. Electronic pulp testing was positive for all maxillary incisor teeth.
Records at the end of orthodontic treatment clearly showed well aligned teeth. The patient reported that the displaced position of her teeth did not reflect her initial malocclusion, so the change did not seem to reflect normal orthodontic relapse. It is possible that either the multistrand wire was distorted after placement by occlusal trauma, or the initial wire was not placed passively.
The aims of treatment were to correct the torque of the UR3 and UR2 and to maintain the buccal segment relationships. The minor centreline discrepancy was to be accepted.
At the initial appointment the upper fixed retainer was removed in order to prevent a worsening of the malocclusion prior to the placement of the upper fixed appliances. Treatment progressed conventionally, with an archwire sequence of 0.014″ NiTi, 0.020″ × 0.020″ Cu NiTi, 0.019″ × 0.025″ SS followed by 0.021″ × 0.025″ TMA. The sequence was followed in order to try and efficiently correct the torque in the UR3 and UR2. Vitality testing was completed at 3-monthly intervals with all teeth giving positive results (Figure 5). The 0.0195″ twistflex fixed retainer was contoured to a cast model and placed with the use of a passive jig.
The complication of torque difference between two adjacent teeth in relation to a fixed retainer has been described previously,25 but only in relation to mandibular incisors. This previous case, presented at 2 years following placement of the fixed retainer and involved a 0.0195″ 3-strand heat-treated twistflex wire cemented on all upper anterior teeth. The authors stated that the torque difference was seen in 18 patients in total over a 3-year observation period. Two cases of relapse in the inclination of maxillary incisors 16 months following the placement of a fixed retainer had been previously presented,26 although this was attributed to relapse, rather than non-passive placement of the fixed retainer. It was suggested that the use of a 5-strand 0.0215″ gold-coated spiral wire, placed passively, reduces the side-effects due to wire distortion that are seen when using thinner wires (0.0174″ or 0.0195″).27 In the case illustrated, it is impossible to rule out wire distortion, secondary to trauma, as the cause of the torque difference between the adjacent teeth. This is clearly a factor that is out of the control of the clinician, although the passive placement of the fixed retainer is not. There is currently no universally accepted method of the passive placement of a fixed retainer with the following techniques being previously described:28
With the level of evidence being only at the case series level and retrospective studies, it would not be appropriate to recommend one wire type over another or one technique of placing the retainer over another. The case illustrated, and the others described, indicate that the clinician can minimize unwanted post placement side-effects, by the use of a passive technique. It also suggests the need for long-term review of patients wearing bonded retainers, as problems can develop years after placement, even when the bonded retainer is still intact.
