19 September 2022

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Failure of lingual retainer, a RCT

Davide Elsido

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The objective of a RCT published on AJODO on oct 2021 issue was to compare the survival rates and periodontal health in patients with 3-strand round twisted (RT) vs 8-strand rectangular braided (RB) fixed retainers bonded to all 6 anterior teeth in the mandible. A total of 133 patients completing orthodontic treatment were randomly allocated in a 1:1 ratio to receive either an RT or RB wire retainer.

FRs bonded to all 6 anterior mandibular teeth come in variable cross-sectional dimensions, the number of strands, type of alloy or structure (twisted vs braided), and are widely used by orthodontists.

FRs in the mandible are maintained for prolonged periods, even for life.

Growing popularity and extended use can be associated with unwanted sequelae such as the development of decalcification or caries or the presence of gingival or periodontal inflammation. Both phenomena result directly from the increased capacity to retain dental plaque and the difficulty to clean.

Findings in this study do not confirm concerns that the presence of the mandibular retainer bonded to 6 anterior teeth leads to periodontal problems. In contrast, they seem to agree that orthodontic fixed retainers seem to be a retention strategy rather compatible with periodontal health, or at least not related to severe detrimental effects on the periodontium.

There is evidence that in patients with mandibular FRs, unwanted tooth movements, even without bond failure or wire breakage, can occur. Those side effects have been attributed to unexpected torque changes between the adjacent mandibular incisors or opposite inclinations of contralateral mandibular canines.

Although the exact cause of this phenomenon is not clear, it was suggested that the retainer could become active and move the retained teeth to unwanted positions.

The risk for the retainer to become active seems to be associated with retainers made from several single stainless-steel filaments twisted into a round wire. After mechanical deformation during biting, the wire could untwist and lead to complications. The increasing popularity of rectangular wire for the fabrication of mandibular retainers implies that the strategy to use non-twisted, non-round wires for retainer fabrication was meant to prevent such complications.

The overall risk for first-time failure was high and amounted to 52.3% (56.1% in the RT group and 48.5% in the RB group). There was no difference in terms of survival or periodontal health between the examined retainers.

Thirty-seven out of 66 participants (56.1%) from the RT group and 32 out of 66 participants (48.5%) from the RB group had at least 1 retainer failure during 2 years after retainer placement. The majority of failures were retainer detachments, whereas retainer breakages and complete retainer loss were infrequent.

No bond on the tooth surface suggests that the adhesive-enamel interface was weakened, possibly by moisture contamination during the bonding procedure, whereas the presence of the bond remnants at the debonding site implies that other factors (eg, mechanical, inadequate bond polymerization, or inadequate bond quality) led to detachment.