Table 1 Characteristics of included studies

Bovali et al. 2014 [24]

RCCT

Comparison of the bonding time and number of failures between direct and indirect bonding procedure

64 patients (35 W, 29 M)32 patients per group

Direct and indirect bonding technique using a round 0.0215 in multistrand stainless steel wire (Penta One; Masel, Philadelphia, Pa

The time needed for bonding mandibular lingual retainers and the number of failures at any time within 200 days time (checked 1st,2nd,4th and 6th month)

The indirect bonding technique resulted in a significantly shorter chairtime (321 ± 31 s) than the direct technique (401 ± 40 s). The log-rank test showed no statistically significant difference between the survival rates of the indirect and direct bonding techniques (P = 0.35). The learning curve applied both to chairtime and failures.

Gunay et al. 2016 [25]

RCCT

Comparison of the failure rate of fixed orthodontic retention between 2 different wires

120 patients60 patients per group(83 W, 37 M)

0.0175-in 6-strand stainless steel wire (Ortho Technology, Lutz, Fla)Vs.0.0195-in dead-soft coaxial wire (Respond; Ormco, Orange, Calif)

Debonding rate within 12 month period (every 3 months)

The bond failure rates were 13.2% for the 0.0175-in 6-strand stainless steel wire and 18.9% for the 0.0195-in dead-soft wire. Mandibular irregularity index increased with time in both groups.

Bolla et al. 2011 [26]

RCCT

Comparison of the failure rate and breakage rate of fixed orthodontic retention between 2 different wires

85 patients (56 W 29 M) with 98 retainers (32 maxillary, 66 mandibular)

Glass fiberVs.0.0175 multistranded stainless steel wire

Debonding rate and breakage rate within 6 years period (every 3 months in 1st year, 6 months in following years)

The failure rates were comparable in the GFR and 0.0175 multistranded groups in terms of detachment and breakage. However, the overall failure rate is quite high. Detachment in the maxillary arch occurred in 3/14 glass fiber retainers (21.42%) and 4/18 SS wire retainers (22.22%); in the mandibular arch detachment was recorded 4/34 glass fiber retainers (11.76%) and in 5/32 SS wire retainers (15.62%).Interproximal wire breakage in the maxillary arch was observed in only 1/14 glass fiber retainer (7.14%) and in 3/14 MST retainers (16.66%); in the mandibular arch, in 3/34 glass fiber retainers (8.82%) and in 5/32 SS wire retainers (15.62%). It can be concluded that in both groups, detachment happens equally often, and that statistically it is a more frequent cause of failure. Wire breakage was less common in the glass fiber group, but the differences are not significant.

Årtun et al. 1997 [27]

RCCT

Comparison of failure rate and the ability of maintain alignment in the anterior segment of the jaw.

49 patients in irregular groups

Thick plain wire bonded only to canines VsThick spiral wire bonded only to canines VsThin spiral wire bonded to incisors and canines VsRemovable retainers

Failure rate, level of plaque and calculus accumulation (Gingival Index, Calculus Index, Plaque Index, Loss of attachment) within 3 years period

A total of 8/35 (22,9%) failed, one during the first year, one during the second year, and six during the third year. Failures occurred in 4/13 retainers made of thick spiral wire bonded only to the canines (30.8%), 1/11 made of thick plain wire bonded only to the canines and 3/11 made of thin, flexible spiral wire bonded to each tooth (27.3%). Two of the 14 removable retainers (14.3%) were lost, what was also considered as failure. Plaque was observed more frequently gingivally to the wire. No significant differences in plaque nor calculus accumulation were found between the wires.The smallest differences in the mandibular irregularity index were observed in patients with thin spiral wire bonded to all teeth, and the largest in patients with thick plain wire bonded only to canines and in patients with removable retainers.

Nagani et al. 2020 [28]

RCT

Comparison of failure rate and evaluation of failure pattern in 2 types of mandibular canine-canine bonded retainers.

52 patients (8 W, 44 M), 26 patients per group The adhesion to single dental element was considered separately

Fiber reinforced composite retainers (INOD, U.P. Fiber Splint, 2 mm)Vs.Multistranded stainless steel wire retainers (All Star Orthodontics, 0.0175 in.)

Failure rate within 12 months (checked monthly)

The bond failure rates were 42.94% for patients with fiber reinforced composite retainer and 31.41% for multistranded SS wire. Hence, total number of bond failures in both groups were 37.17%. The difference between those groups were statistically significant. Adhesive failure (no retained resin on enamel surface) is the most common type of bond failure observed with both groups of fixed lingual retainers. (23% of all failures). According to their finding, multistranded SS wire is superior option to fiber splin.

Bazargani et al. 2012 [29]

RCT

Evaluation of the use the effect of liquid resin on the survival of fixed lingual retainers and to evaluate the incidence of calculus accumulation and discoloration adjacent to the lingual retainers.

52 patients (26 W, 26 M) dived into 2 equal groups

0.0195-in. multistranded Penta-one wire (Masel Orthodontics, Bristol, Penn) bonded with the use of Optibond FL resign and Tetric Evo flow composite Vs.Wire + Tetric Evo flow composite only

Failure rate, calculus accumulation and eventual discoloration due to retainers presence within 2 years (checked monthly)

In the resin group, the failure within 2 years occurred once in one patient only (4%), while at the composite-wire interface. In the nonresin group, the incidence of retainer failure occurred once in seven different patients (27%), from one or several teeth, and all at the enamel-composite interface. The incidence of calculus accumulation (4 to 31%) and discoloration adjacent to the composite pads (0 to 69%) was much more higher in the nonresin group.

Salehi et al. 2013 [30]

RCT

Comparison of failure rate and survival rate of two types of fixed orthodontic retainer

142 patients (83 W, 59 M) divided into unequal groups (68–74)

Polyethylene woven ribbon (Ribbond, Seattle, WA, USA) Vs.0.0175-in flexible spiral wire (Respond, Ormco, Glendora, CA, USA).

Survival and rate within 18 month period (checked monthly)

There was no statistically significant differencebetween the two types of retainers in the maxillary or the mandibular arches in terms of survival rate. One-tooth failure was the most frequent failure of the two retainer types. Among all the retainers in all experimental groups, only in one case the multi-stranded retainer was completely detached in the maxilla. The most frequent type of failure in the multi-stranded group was retainer loosening, both in the maxilla (22/27 (81.48%)) and in the mandible (27/28 (96.42%)). In the ribbon retainer group, the most frequent type of failure was retainer fracture in the maxilla (30/34 (88.23%)) and retainer loosening in the mandible (19/29 (65.51%)). This study showed that the mean survival time and the rates of broken or detached ribbon retainers and multistranded retainers are comparable. Ribbon were more prone to breakage, while spiral wires debonded more often.

Arash et al. 2020 [31]

RCT

Comparison of failure rate of two types of fixed orthodontic retainer

260 patients (161 W, 99 M) divided into unequal groups (138–122)

0.0175 stainless steel twisted wire (G&H Orthodontics, USA)Vs.single-strand ribbon titanium lingual retainer wire (Retainium, Reliance orthodontics, USA)

Failure rate and timing of failure within 2 years (checked monthly)

Failure rates in terms of detachments in all groups seemto have occurred at the enamel junction which is clinicallyobserved the bulk of detached composite, and it was25 in twisted retainer group (18.1%) and was 10 in ribbonretainer group (8.9%), what points out ribbon titanium retainer as more reliable. The average duration of success was ca. 23,5 months for both twisted wire and ribbon wire, what shows, that failure of retention was not frequent phenomenon.

Scribante et al. 2011 [32]

RCT

Comparison of failure rate of two types of fixed orthodontic retainer in mandibular arch

34 patients (9 W, 25 M)

A multistrand stainless steel wire (Ortosmail Krugg, Milan, Italy)Vs.a polyethylene ribbon-reinforced resin composite (InFibra TPItalia, Gorle, Italy)

Survival rate, patients satisfaction measured with VAS scale within 12 months (30, 60, 120, 180, 360 days to evaluate detachments)

The percentage of detachment was 22,54% for stainless steel wire teeth to 14,45% for polyethylene ribbon-reinforced resin retainer. The patients with multistrandedstainless steel wire expressed a mean value of satisfaction of 8.24, whereas patients with polyethylene fiber reinforced resin retainer for lingual retention expressed a mean value of satisfaction of 9.73. The failure rate did not statistically differ between two types of reteiners, however polyethylene ribbon-reinforced resin composite is considered as more aesthetic for patients.

Rose et al. 2002 [33]

RCT

Comparison of survival of multistranded stainless steel wire and a direct-bonded polyethylene ribbon-reinforced resin composite

20 patients (8 W, 12 M)

The polyethylene woven ribbon (Ribbond) Vs. the multistranded steel wire (Respond, 0.0175 in., Ormco)

Survival rate, distribution of failures in time within 24 months period (checked monthly)

The median survival time of the Ribbond reteiners was 15.8 months (standard error = 3.6 months). Fifty percent of the retainers were still in place after 24 months. The most frequent kind of failure was a loosening between the Ribbond and theComposite. The rate of retainer loosening was lower in the multistranded retainer group. The median survival time was 23.9 months. Among those 10 retainers, only one became loose within the study period; the remaining ones were still in place at 24 months.

Gelin et al. 2020 [34]

RCT

Comparison of effectiveness of CAD/CAM customized nitinol retainers with standard stainless-steel fixed retainers

61 patients (43 W 18 M) Groups were designed as equal – one patient dropped out

Rectangular 0.014 × 0.014 in memory shape customized CAD/CAM nitinol retainer (Memotain™; CA Digital GmbH, Mettmann, Germany)Vs.Round 0.0175′ 6-strand twisted stainless-steel wire retainer (Supra-FlexTM; RMO Europe, Illkirch-Graffenstaden, France)

Failure rate, changes in intercanine width, interpremolar width, anterior arch length, total arch length, Gingival index, Plaque Index with other periodontal measurements within 12 months period. (checked monthly)VAS Scale was used to measure patients satisfaction.Little Index measured at the beginning, after 6 and 12 months and IMP angle were measured at the begging and in the end of treatment

The average number of debonding per patientshowed no significant difference from during the study between the two groups. The type ofdebonding (adhesive-enamel interface or wire-compositeinterface) was found also similar. The level of satisfaction in terms of the final result was the same in the two groups. Similar to the level of discomfort for the tongue. The changes of value of Little Index did not significantly differ between the two groups. Dental stability parameter measurements in the control and test groups also did not show any significant difference. The overall periodontal parameters also remained unchanged from baseline until the end of the study in each group, with exception of Gingival Index, which was higher in test group. From begging to the end of the study, theIMPA and inter-incisor angles remained stable betweenthe two groups.

Kartal et al. 2020 [35]

RCT

Comparison of effectiveness of CAD/CAM customized nitinol retainers with standard five-stranded steel retainers

52 patients (32 W, 20 M) divided in 2 groups of 26 patients

Rectangular 0.014 × 0.014 in memory shape customized CAD/CAM nitinol retainer (MemotainTM; CA Digital GmbH, Mettmann, Germany)Vs.0.0215′ five-stranded retainers (GC Orthodontics Inc., Alsip, IL, USA)

Failure rate, survival rate plaque index, gingival index, BoP, Probing depth, marginal recession within 6 months period (checked monthly)

No significant difference was observed for plaque index, gingival index scores, marginal recession, blooding on probing and probing depth between the groups on any visit during the follow - up. On the other hand, significant differences were observed within both groups for plaque index scores and probing depth obtained at different appointments during the 6-month follow-up period. No difference was observed for failure rate per tooth scores between the groups during any evaluation. All failures occurred due to debonding between the adhesive–enamel and none of the retainer wires were completely detached, deformed or broken. The survival rates of the retainer wires were 77% for the Memotain and 73% for the five-stranded group.

Scribante et al. 2020 [36]

RCT

Comparison of failure rate of multistrand stainless steel wire attached with different composites

100 patients divided into equal groups

Use of composite resin Transbond XT (3 M, St. Paul, MN, USA)VsUse of Filtek Supreme XTE flowable nanocomposite (3 M, St. Paul, MN, USA),

Failure rate and survival failure rate within 24 months (checked monthly)

For both the upper and lower arch, as well as if considering them overall, higher total failures were found in retainers attached with flowable nanocomposite. The lower teeth reported a higher failure rate to the upper ones (13.33% vs. 10.67%). The detachment was not location- specific (none of the teeth come loose more often).

Sfondrini et al. 2014 [37]

RCT

Comparison of failure rate of a resin composite retainer reinforced with glass fibers with a multistranded stainless steel wire

87 patients (52 W,35 M) 47 flexible spiral wire and 40 FRCs splints

Silanised-treated glass fibers (Everstick Ortho, Stick Tech ltd, Turku, Finland)Vs0,0175″ flexible spiral wire (Ortosmail, Krugg spa, Milan, Italy)

Failure rate and survival failure rate within 12 months(checked monthly)

17.73% (N of teeth = 47) for flexible spiral wires and 11.25% (N of teeth = 27) for glass fiber-reinforced resin retainers. No significant differences were found.

Sobouti et al. 2016 [38]

RCT

Comparison of effectiveness of twisted wire fixed retainer versus spiral wire and fiber-reinforced composite retainers

128 patients (68 W, 60 M) in unequal groups due to expulsion from examination by exclusion criteria

0,0175″ flexible spiral wire (Ortosmail, Krugg spa, Milan, Italy)VsSilanised-treated glass fibers (Everstick Ortho, Stick Tech ltd, Turku, Finland)VsManually fabricated two twisted 0.009-in dead soft wires [6 rounds per 10 mm] (3 M Unitek, Monrovia, CA, USA)

Failure rate, Survival rate within 24 months

The average duration of success was approximately 21 months. Marginally significant difference was detected in the survival rates between the Silanised-treated glass fibers and manually fabricated two twisted soft wire retainers. A hazard ratio of retainer detachment was two times smaller in case of use of new kind of retention. The risk of failure was approximately 50% less for TDW retainers compared to FSW retainers, though it was not statistically significant.

Lee and Mills 2009 [39]

Case – Control Clinical Trial

Comparison of the failure rate of fixed orthodontic retention between 2 different wires (stand. SS multistranded wire to innovative SS black Australian wire in V-loop design)

300 patients153 SSW (9–60 yrs. Old; 65% W, 35% M)147 VL (9–58 yrs. Old; 68%W, 32% M)

.0175-in stainless steel multi-stranded wire placed as a straightVs..016-in stainless steel black Australian wire placed in a V-loop design

Debonding rate within 6 months observation period (checked monthly)

The detachment rates were 14.3% for the V-loop design and 12.4% for the straight wire retainer. However, the differences remain statistically insignificant. No wire fracture of deformation was observed.

Taner and Aksu 2012 [40]

Case – Control Study

Comparison of failure rate of flexible, braided rectangular bonded lingual retainers, discover differences in directly and indirectly bonded patients and the distribution of failures in time

66 patients (52 W, 14 M) divided in unequal groups

An eight-braided, flattened, stainless steel dead soft wire (Bond-a-Braid, 0.016 × 0.022 in.; Reliance Orthodontic Products, Itasca, Illinois, USA) bonded directly Vs.Bonded indirectly

Survival rate, distribution of failures in time within 2 years period (checked every 6 months)

Through the whole follow-up period, 25/66 had experienced failures. The failure rate was 46.9% with retainers bonded with the direct method and 29.4% with the indirect method. The highest failure rate was seen in the first month, a total of 24 failures occurred in 13 patients. The highest rate was 33.3% for the lower right central incisor. The lowest failure rate was observed in the fifth month, a total of three failures in two patients. From the total of 25 patients who had failures, 7 had repeated bond failures. The method of bonding does not affect the success of retention.

Renkema et al. 2011 [41]

Retrospective cohort study

Assessment of the long-term effectiveness of FSW canine-to-canine lingual retainers in maintaining the alignment of the mandibular anterior teeth after orthodontic treatment

221 patients (75 W, 146 M)

Position of tooth before treatment Vs. Position of tooth after treatment Vs. 2 years after treatment Vs. 5 years after treatment obtained with FSW retainer (0.0195-in, 3-strand, heat-treated twist wire, Wildcat, GAC International, Bohemia, NY)

Little’s index within 5 years period (checked every year)

At T2, the irregularity index was stable in 93.7% of the patients; at T5, it was stable in 90.5%. According to Little’s index, at T0 the alignment of the mandibular front teeth was very good (irregularity index\1.00 mm) in 97.7% of the patients; at T2 and T5 the percentages were 95.0 and 93.7%, respectively. 32.2% of our patients experienced retainer failures. In only 1 patient, the retainer was broken. The bonding failure rate (ie, bonding failures per year) was higher during the first 2 years after treatment (32.0% from T0 to T2 and 17.6% from T0 to T5). Retainer failures were obtained from the patient files.

Farronato et al. 2014 [42]

Retrospective cohort study

Evaluation of the long term results of fixed retention with FRC lingual retainers

119 patients, 15 with retainers in both arches (134 retainers)

Influence of gender, patient age and retainer location on survival.

Survival rate within ca. 39.9 months (median 40.7 months, SD 13.3 months) (checked every 6 months)

In total, fracture or delamination of the composite was recorded in 25 FRC retainers (18.7%). The incidence of relative failures was lower for the mandibular than for the maxillary retainers. The researchers found no correlation between any of the personal characteristics and survivial rate. Regrettably, however, the article lacks a summary table of the personal characteristics and their possible impact.

Kocher et al. 2019 [43]

Retrospective cohort study

Comparison of failure rate of two types of fixed orthodontic retainer

88 patients

.016″ × .022″ braided SS (ORMCO) bonded to all six mandibular anterior teeth in mandible and four incisors in maxillaVs..027″ round TMA wire bonded to canines only (ORMCO)

Failure rate and type of failure within 10 to 15 years afterorthodontic treatment

The original retainer was still in situ 10–15 years after debonding for 87 patients (98.9%) in the mandible and for 80 patients (97.6%) in the maxilla. No failure of any type was observed in the mandible for 19 (40.4%) patients fitted with the .016″ × .022″ braided SS retainers and 25 (61%) with the .027″ round TMA retainers. The only significant predictor for survival was the type of retainer. (higher in SS group) In bothjaws, the most frequent first failure was composite damage(mandible 22.7%; maxilla 13.4%) followed by detachment(mandible 19.3%; maxilla 7.3%). Six events 6.8% ofloss of the whole retainer with need for replacement in the mandible were observed. No retainer fractured.