Splinting the teeth after orthodontic treatment is a common clinical procedure. Multi-strand wires appear to be the most popular for direct-bonded retainers, and its retentive efficacy and reliability have been proved [13]. In this study, splinting the teeth with ribbon metal wire that has gained popularity in the last years was compared. The results showed that the reliability with the multi-stranded wire retainer was comparable to the ribbon retainer, and there was no significant overall difference between the treatments of old (twisted wire) and new (ribbon wire) retainers (p = 0.13).
The duration of the success for the multi-strand wire was about 23 months that was not significantly different from the ribbon wire. Rose et al. showed a similar survival time for multi-strand wire. They concluded that in terms of reliability, the direct-bonded multi-strand wire is superior to the plasma-treated polyethylene woven ribbon and resin retainer [12]. Similar findings have been described for glass fiber reinforced retainers [15]. In contrast with these studies, Scribante et al. showed no statistically significant differences in survival time after 12 months for the multi-strand wire and FRC. They described that the use of different materials and different bonding techniques could be the reason for different results [11].
The study of Sobouti et al. was about a 2-year survival analysis of twisted wire-fixed retainer versus spiral wire and fiber-reinforced composite retainers [14]. Although the failure rate of the twisted wire retainer was two times lower than that of the FRC retainer, the differences between the survival rates were not significant. FRC retainers might have a higher failure rate because of their lower flexibility, which results in higher strain in the inter-dental areas under loading. Among different FRC retainers, the ribbon type displayed the highest bond strength. Salehi et al. showed that the mean survival time and the rate of broken or detached ribbon retainers and multi-strand retainers are comparable [4].
Against this result, the present study showed that the failure rate of the ribbon metal wire was more than two times lower than that of the twisted wire. The failure rates in the present study were considered in terms of detachments; but it is better to consider that the failure should be evaluated with regard to not only the adhesion quality but also the clinical reversibility, with the least damage to enamel during removal or repair of the failed retainer. So, the results based on the method of the study might vary in different studies. In the study of Foek et al., the ribbon retainers presented adhesive failure and material breakage in 50% and 40% of the specimens, respectively [16].
Foek and his colleagues evaluated fatigue resistance, debonding force, and failure type of fiber-reinforced composite, polyethylene ribbon-reinforced, and braided stainless steel wire lingual retainers and stated that the retainers presented similar debonding forces, but different failure types and braided stainless steel wire retainers presented the most repairable failure type [16]. The difference might be related to types of studies because we performed a clinical trial but the study of Foek et al. was in vitro.
In a systematic review that was conducted by Iliadi et al., the failure of fixed orthodontic retainers was evaluated. The random-effects meta-analysis between two studies that compared polyethylene woven ribbon vs multi-stranded wire retainers indicated no statistically significant difference in the risk of failure between the treatment groups [17].
Finally, it should be noted that although fixed orthodontic retainers have been used in clinical practice for many years, the best protocol for post orthodontic treatment still remains an important issue. Iliadi et al. also mentioned in their systematic review that the available studies and their hypothesis cannot provide reliable evidence about fixed orthodontic retainers. They concluded that despite the numerous studies dealing with parameters of fixed retention, there is a lack of evidence on the selection of the optimal protocol and materials for that [17].