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Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

https://doi.org/10.62574/mh32ds76

Stability of dental position post-orthodontics with the use of thermoplastic

retainers vs fixed retainers. Systematic review

Estabilidad de posición dental post ortodoncia con el uso de retenedores

termoplásticos vs retenedores fijos. Revisión sistemática

Karina Elizabeth Solano-Palacios

karina.solano.70@est.ucacue.edu.ec

Catholic University of Cuenca, Cuenca, Azuay, Ecuador

https://orcid.org/0000-0003-3717-4445

Cristian Hernán Campoverde-Torres

ccampoverdet@ucacue.edu.ec

Catholic University of Cuenca, Cuenca, Azuay, Ecuador

https://orcid.org/0000-0003-0908-1049

ABSTRACT

Objective: to establish the best retainer for maintaining orthodontic post-treatment results. based on

this information. Method: PRISMA systematic review. 23 articles were processed, the PICO question

was applied. Results and conclusion: Fixed retainers: They are effective, especially those placed

from 13-23, as they show fewer changes in stability parameters compared to those from 12-22.

However, both are effective if good adhesion to the lingual surfaces of the teeth is ensured. Vacuum-

formed retainers (VFR) are also an excellent option, but their effectiveness depends on patient

compliance in their regular use. Lack of use can lead to relapse.

Descriptors: orthodontics; orthodontics corrective; orthodontic appliances;

orthodontic appliances fixed. (Source, DeCS).

RESUMEN

Objetivo: establecer cuál es el mejor retenedor para mantener los resultados postratamiento de

ortodoncia. a partir de esta información. Método: Revisión sistemática PRISMA. Se procesaron 23

articulos, se aplicó la pregunta PICO. Resultados y conclusión: Retenedores fijos: Son eficaces,

especialmente aquellos colocados de 13-23, ya que muestran menores cambios en los parámetros

de estabilidad en comparación con los de 12-22. Sin embargo, ambos son efectivos si se asegura

una buena adherencia en las caras linguales de los dientes. Retenedores removibles al vacío (VFR):

También son una excelente opción, pero su eficacia depende del cumplimiento del paciente en su

uso regular. La falta de uso puede llevar a recidiva.

Descriptores: ortodoncia; ortodoncia correctiva; aparatos ortodóncicos; aparatos ortodóncicos fijos.

(Fuente, DeCS).

Received: 07/02/2025. Revised: 16/02/2025. Approved: 26/02/2025. Published: 18/03/2025.

Original short

Sanitas

Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

INTRODUCTION

Orthodontic treatment aims to improve aesthetics, function and maintain long-term

stability of the teeth. This last parameter represents a major challenge for the

orthodontist, which can be addressed by the placement of fixed retainers or the use

of removable retainers (1-8). If the fixed appliance is not properly retained after

removal, this can lead to a relapse of the results, i.e. the teeth tend to return to their

pre-treatment position.

This phenomenon can be caused by tension of the periodontal tissue fibres, natural

tooth movement, ageing, occlusion and pressure exerted by soft tissues such as the

tongue and lips (1,5-12). Relapse is not predictable; about 70% of patients who have

had any orthodontic treatment may present alterations in tooth position after some

years (5). Therefore, retention must be continued after the use of fixed appliances

to obtain good future results (7,11,13).

Already in the 19th century, it was proposed that retention procedures were

necessary to maintain treatment results. It was mentioned that teeth "could only be

retained in the new position by the constant use of appliances" (14,15). In 1908, a

removable retainer for the upper jaw, made of platinum and gold, was suggested. In

1914, the Hawley retainer appeared, initially made of vulcanite, which is still in use

today, but with other materials such as acrylic and wire. In 1950, vacuum-formed

retainers (VFR), transparent thermoplastics, were developed in a dental vacum prior

to obtaining the patient's plaster model. Subsequently, bonded fixed retainers

appeared, hand in hand with the advent of adhesive systems (10,15).

Fixed retainers are placed on the lingual surfaces of the teeth, have good aesthetics

as they are not visible on the vestibular surfaces and ensure retention because they

Sanitas

Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

do not depend on the patient's cooperation. However, they have some

disadvantages, such as the detachment of the retainer, tartar accumulation that can

affect periodontal health, and limitation of functional tooth movement (1,2,5,6,9).

Removable retainers are also effective in maintaining dental stability; however, their

effectiveness depends on patient compliance (6,9,16).

Post orthodontic stability can be assessed by the following parameters: Little's

Irregularity Index (LII), which analyses the movement of the horizontal contact points

of six anterior teeth (12); the arch length, which is measured from the attachment

point of the central incisors to the mesial attachment point of the right and left first

permanent molar, respectively; the intercanine width, which is measured across the

cusps of the canines; the intercanine width, which is measured across the

mesiovestibular cusps of the first permanent molars, and the intercanine width,

which is measured across the mesiovestibular cusps of the first permanent molars;

the intermolar width, which is measured at the level of the mesiovestibular cusps of

the left and right first permanent molars; the overjet, which corresponds to the space

between the vestibular face of the lower incisor and the incisal edge of the upper

incisor; and the overbite, which refers to the overbite between the maxillary incisors

and the mandible (7-9).

Given the great need to maintain the results obtained in orthodontic treatment, it was

decided to carry out a systematic review with the aim of establishing which is the

best retainer for maintaining post-treatment orthodontic results.

METHOD

This review was carried out according to the Preferred Reporting Items for

Systematic Reviews and Meta-Analyses (PRISMA) statement (17) and was

registered with INPLASY under registration number INPLASY202490010. The aim

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Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

of the study was to establish the best retainer for maintaining orthodontic post-

treatment results.

The selection of the studies was based on the PICO question: "Which retainer

maintains stability of tooth position after orthodontic treatment?

In May 2023, the search for information began in the digital databases PubMed,

Scopus and LILACS. The Boolean operator AND was used. The Mesh Terms used

were: orthodontic, orthodontic retainers, orthodontic appliances, fixed. The keywords

used were: orthodontics, orthodontic retainers, orthodontic appliances, fixed.

In order to select the articles, the first step was to read the title and abstract of each

article found. In the studies that matched the search criteria, the full text was read.

Only randomised clinical trial articles were included, in English and Spanish, which

analysed the stability of teeth after orthodontic treatment with the use of removable

(thermoplastic) retainers and fixed retainers in the last 5 years. Systematic reviews,

meta-analyses and case reports were excluded. For the selection, collection and

cleaning of the data, a data table was created in Excel.

The variables analysed in the studies were: irregularity index, overbite, overjet, arch

length, intermolar width and intercanine width, in bonded fixed retainers and vacuum

removable retainers. For data analysis, risk-of-bias assessment of the articles was

performed using Version 2 of the Cochrane Risk-of-Bias Tool for Randomised Trials

(RoB 2) (18,19) for randomised clinical trials.

RESULTS

Figure 1 shows the flow diagram of the information obtained through the different

phases of a systematic review (PRISMA) (17). The preliminary search for information

in the digital databases PubMed, Scopus and LILACS showed a total of 2146

Sanitas

Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

articles. Then, a filter was applied to identify articles from the last 5 years in order to

obtain more up-to-date information, obtaining 1076 articles.

The search was continued by adding the randomised clinical trials filter, obtaining a

total of 218. After reading the title and abstract in relation to the research topic, 17

articles were selected. Subsequently, the articles were read in full and only 8 met the

inclusion criteria, of which 4 were duplicates. As a result, 4 articles were obtained

with a total of 388 participants in the selected studies.

Figure 1. PRISMA search strategy schematic flow diagram

Elaboration: The authors.

Key words

Pub med: ((orthodontic retainer)

AND (orthodontic)) AND

(Orthodontic Appliances, Fixed)

Scopus: ((orthodontic retainer)

AND (orthodontic)) AND

(Orthodontic Appliances, Fixed)

LiLacs: ((orthodontic retainer) AND

(orthodontic))

Items identified:

(n=2146)

Identified articles from

the last 5 years:

(n=1076)

Articles identified as

clinical trials:

(n=218)

Articles in relation to

the topic after reading

the title and abstract:

(n=17)

Duplicate

articles:

(n=4)

Articles that met the

inclusion criteria:

(n= 8)

Total:

(n=4)

IDENTIFICATION

INCLUSION AND EXCLUSION

SELECTION

Excluded items:

(n= 213)

Number of records identified in the

search of digital databases:

Pub med: (n=390)

Scopus: (n=1562)

LiLacs: (n=194)

Sanitas

Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

The investigators of the different studies evaluated the variables by obtaining plaster

models that were digitised, which were performed at different time periods: at

completion, at 6, 12, 12, 18 and 24 months, and 5 years after removal of orthodontic

treatment (2,3,11,16). One study evaluated treatment stability 1 year after removal

of the retention appliances (9). Table 1 describes the results of the studies evaluated

(2,3,8,11).

Table 1. Characteristics of the studies included in the systematic review.

Author

Year

Evaluation

time

Sample

Age

Type of

retainer

assessed

Evaluation

Site

Conclusions

Krämer et al.

2020

6 and 18

months after the

removal of

orthodontic

treatment

104

17.1

years

Fixed (13-

23), VFR

Max Sup.,

Max Inf.

VFR and 13-23 fixed

retainers have the same

retention capacity in the

mandible at 6 and 18

months.

Naraghi et al.

2021

2 years after

orthodontic

treatment

13.9

years

Fixed (13-

23), Fixed

(12-22),

VFR

Max Sup.,

Max Inf.

All 3 retention methods

showed effective retention

capacity and all changes

were small and clinically

insignificant.

Naraghi et al.

2023

1 year after

withholding is

removed

(-)

Fixed (13-

23), Fixed

(12-22),

VFR

Max Sup.,

Max Inf.

The changes were

clinically insignificant

during and after the

retention period. Therefore,

all three methods showed

equal retention capacity.

Krämer et al.

2023

5 years after

orthodontic

removal

104

(-)

Fixed (14-

24), VFR

Max Sup.,

Max Inf.

Post-treatment changes in

both jaws were small. The

anterior alignment in the

mandible was more stable

with a bonded CTC retainer

compared to a removable

VFR after 5 years of

retention.

Elaboration: The authors.

Post-treatment orthodontic retention stability was evaluated in 104 adolescent

patients: 52 VFR and 52 fixed canine-to-canine (CTC) retainers were delivered and

both types of retainers were evaluated in the lower jaw. The variables analysed were:

Sanitas

Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

LII, overbite, overjet, arch length, intermolar width and intercanine width. Records

were obtained in models after removal (T1), at 6 months (T2) and at 18 months (T3).

In the CTC group, at T1 and T2 there were significant increases in LII and overbite,

as well as at T1 and T3 in the VFR group. There were no significant differences

between the groups. There were minimal variations in protrusion. In both groups,

after 6 and 18 months, arch length decreased, while intermolar and intercanine

widths remained unchanged (8).

In another study, IIL and single-tooth contact point discrepancy (CPD) were

evaluated in 90 adolescent patients. Two types of fixed retainers were used: a 13-

23 and a 12-22 retainer; in addition, a maxillary VFR covering all teeth up to the

second molars was evaluated. For the measurement of the variables, models were

obtained before and after two years of retention. There was a slight increase in LII

and CPD in all groups evaluated, but no statistically significant differences were

found in each group. A minimal increase in intercanine width and some canine

rotations were also evident in the group of patients using VFR (3).

In a comparative study, VFRs and CTCs were analysed after 5 years of retention.

The study included 104 adolescent patients with previous fixed orthodontic treatment

in both the upper and lower jaw. All patients received a VFR for the upper jaw, while

52 patients received a VFR for the mandible and 52 patients received a CTC in the

mandible. The plaster casts were obtained at different stages: at orthodontic removal

(T1), at 6 months (T2), at 18 months (T3) and finally after 5 years (T4). The variables

evaluated were LII, protrusion, overbite, arch length, and intercanine and intermolar

width. There were small changes in both jaws between T1 and T4. The LII was

significantly increased equally in both groups. In both the CTC and VFR groups, the

protrusion remained stable, the overbite increased, the arch lengths decreased, and

the intercanine and intermolar widths in the lower jaw remained the same. In the

Sanitas

Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

upper jaw, the intermolar width decreased significantly. No differences were found

between the groups (11).

Single-tooth IIL and CPD were evaluated 1 year after retention removal in two

bonded and one removable retention methods. Ninety adolescent patients

participated and were divided into three groups: A) adhesive retainer 13-23; B)

adhesive retainer 12-22; and C) vacuum-formed removable retainer. Models were

obtained before retention (T1), after 2 years of retention (T2) and 1 year after

retention removal (T3). The changes in LII during retention were: in group A, 0.3 mm;

in group B, 0.6 mm; and in group C, 1 mm. Changes after removal of retention were:

in group A, 1.1 mm; in group B, 0.5 mm; and in group C, 0.4 mm. CPD did not show

significant changes in any of the groups (2).

Most of the randomised clinical trials showed a low risk of bias in almost all domains,

with the exception of one study in which the patients, operator and outcome assessor

could not be blinded due to the study design. In addition, follow-up was lost to follow-

up and there were withdrawals from the trial. Missing data were compensated with

median values for the remaining subjects in each group (8).

Table 2. Rob2 risk of bias assessment.

Title of the study

Author

Year

Vacuum-formed retainer versus bonded retainer for dental stabilization

in the mandible-a randomized controlled trial. Part I: retentive capacity

6 and 18 months after orthodontic treatment.

Krämer et

al.

2020

●

Stability of maxillary anterior teeth after 2 years of retention in

adolescents: a randomised controlled trial comparing two bonded and a

vacuum-formed retainer

Naraghi

et al.

2021

●

Post-treatment stability after 5 years of retention with vacuum-formed

and bonded retainers-a randomized controlled trial

Krämer et

al.

2023

●

Stability of maxillary anterior teeth during retention and 1 year after

removal of retention-an RCT on adolescents retained with two different

bonded retainers and a vacuum-formed retainer

Naraghi

et al.

2023

●

Source: Authors.

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Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

Legend of the domains:

D1: Bias due to the randomisation process

D2: Biases arising from deviation from planned interventions

D3: Biases arising from loss of results

D4: Biases in the measurement of results

D5: Biases in the selection of the described outcomes

Colours:

🟢: Low risk of bias.

🟡: Moderate risk of bias.

🔴: High risk of bias.

DISCUSSION

There are some considerations when choosing a post orthodontic treatment retainer,

among which we can mention: the position of the teeth before orthodontic treatment,

the completion of the cases, whether or not there is potential for growth, especially

in young patients, aesthetic requirements, patient responsibility, whether or not there

were dental extractions, and skeletal class (20-23). Although some variables were

analysed in the studies evaluated to determine dental stability, the final outcome of

the treatment, i.e. how stable the occlusion was after completion, was not taken into

account, nor was the growth potential analysed. All studies considered the age of

the patients, where all participants were adolescents (2,3,8,11).

In the case of skeletal class, only one study mentioned the skeletal class that

patients had before starting orthodontic treatment (11). Tooth rotations were not

analysed in all the articles, only two of them did, this being an important parameter

to analyse in dental stability (2,3). Not all studies were performed on both jaws; some

were only on the maxilla and some only on the mandible. Consequently, all studies

used plaster models at different stages of the evaluation, which were subsequently

digitised (2,3,8,11).

Sanitas

Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

CONCLUSION

Post-treatment retention in orthodontic treatment has so far been considered a

challenge for successful orthodontic treatment. After reviewing the literature, studies

determined that both fixed and removable retainers are effective in maintaining

results. With regard to fixed retainers, those that were placed at 13-23 showed fewer

changes in the different parameters for evaluating stability, compared to retainers of

12-22; however, the latter did not generate statistically significant changes, the

important thing in this type of retention is good adherence of the retainer to the lingual

surfaces of the teeth.

Vacuum removable retainers (VFR) continue to be a very good option, as long as

the patient complies with their use, otherwise there may be a relapse. Although the

existing studies provided us with valuable and useful information for decision-making

on the retainer to be used, this research could not be conclusive in its results, due

to the different methods and times for measuring the variables, which generated

conflicts in interpreting and comparing the results. It would be good if future clinical

studies could have a standardisation in the methodologies used, the analysis of the

same variables, as well as the maxillary or mandibular study sites, thus benefiting

future systematic reviews.

FUNDING

Non-monetary

CONFLICT OF INTEREST

There is no conflict of interest with persons or institutions involved in research.

ACKNOWLEDGEMENTS

To the UCACUE Postgraduate Department.

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Revista arbitrada de ciencias de la salud

Vol. 4(1), 1-13, 2025

Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

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Estabilidad de posición dental post ortodoncia con el uso de retenedores termoplásticos vs

retenedores fijos. Revisión sistemática

Stability of dental position post-orthodontics with the use of thermoplastic retainers vs fixed retainers.

Systematic review

Karina Elizabeth Solano-Palacios

Cristian Hernán Campoverde-Torres

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