The Effects of Fixed Versus Removable Orthodontic Retainers on Stability and Periodontal Health: 4-Year Follow-Up of a Randomized Controlled Trial

ABSTRACT

Introduction:

Long-term or even indefinite retention is routinely prescribed after orthodontic treatment as a preventive safeguard against post-treatment changes induced by tooth movement, physiological healing, and the aging process. Though both fixed and removable versions of retainers may be equally effective in terms of results, sufficient research to support this assumption is missing at the moment.

Objectives:

Long-term effects of fixed and removable retention on the periodontium, and the compliance level when used for an extended period of time.

Methods:

For 4 years participants were given a supply of canine-to-canine retainers and vacuum-formed canine-to-canine retainers. The inter-canine, as well as inter-molar widths, the length, and the extraction space opening of the mandibular anterior portion, were measured. Gingival inflammation, calculus, and plaque were observed, as well as the attachment of clinical and the case of bleeding during probing. 42 members had returned in the follow-up period, with 21 from each of the two groups. Measurements of the modified gingival index and plaque scoring were performed on the 10 intra-oral photographs that were taken at 4-week intervals in this study to investigate the intra-examiner reliability.

Results:

After controlling for confounding variables, there was a 1.64 mm (95% confidence interval [CI], 0.30, 2.98 mm) median between-groups difference among patients who utilized vacuum-formed retainers (VFRs). The treatment groups did not vary in inter-canine and intermolar widths (P = 0.52; 95% CI, −1.07, 1.05), arch length (P = 0.99; 95% CI, −1.15, 1.14), or opening of extraction spaces (P = 0.84).

Conclusion:

A long-term study demonstrates that fixed retention can preserve the alignment of the mandibular anterior over time for the first time. Gingival discomfort and higher plaque scores were reported in both types of retainers.

INTRODUCTION

Long-term or even indefinite retention is routinely prescribed after orthodontic treatment as a preventive safeguard against post-treatment changes induced by tooth movement, physiological healing, and the aging process.[1,2] Though both fixed and removable versions of retainers may be equally effective in terms of results, sufficient research to support this assumption is missing at the moment.[3]

There has also been no research on the long-term effects of fixed and removable retention on the periodontium, and the compliance level is unknown with removable retention when used for an extended time.[4]

There are no randomized controlled trials that compare fixed retainers with vacuum-formed retainers (VFRs).[5,6] In none of these investigations, there has been more than a 2-year follow-up period. According to the results of the trials, the average lower anterior irregularity scores were less than 2.0 mm, indicating adequate stability. In addition, it is estimated that the absence of irregularity would increase with time and that major differences among these therapies will only become apparent over a longer duration of time. In the long term, post-treatment change is likely to occur as a result of decreased compliance with removable retainer wear and uncontrolled growth changes, which are difficult to control with removable retainers. The drawback of fixed retainers is another concern that could influence post-treatment outcomes.[4]

Because of the lack of a long-term, prospective examination, it is only feasible to hypothesize about the relative relevance of these events. Fixing retainers may make it more difficult for patients to maintain good oral hygiene in the short term, but it is not known if this will result in worse periodontal results in the long run.[7] During the retention phase 7–10, several research assessed periodontal integrity. People with poor oral hygiene may be more likely to be excluded from such studies due to the retrospective nature of the research. Retainer types should be randomly distributed in the next study to avoid any bias. As a result, greater research into the advantages and disadvantages of long-term orthodontic retainer use is required.

Aims

For a minimum of 4 years, the durability of fixed and removable retainers was studied to determine, which was more effective. The other goal of the study was to evaluate the long-term effects of permanent and removable retainers on the periodontium.

MATERIALS AND METHODS

Stability was assessed for 18 months after the start of retention in a follow-up after the randomized controlled trial.

After a minimum period of about 48 months following the end of active appliance use, participants from the previous clinical research were contacted to assess their chances of getting enrolled in the present trial, and an appointment was scheduled according to their choice.

In the previous RCT, 82 participants were assigned using the system-generated random allocation method. An opaque, sealed envelope approach was used to conceal the allocation. In this experiment, the allocation was kept a secret from the treating physician.

An Essix Ace Plastic 120 mm diameter retainer (DENTSPLY) was given to six participants, whereas a fixed ortho-care retainer was given to six other participants. Shipley, United Kingdom: Ortho-Care Retainer” (0.0175” coaxial archwire; Transbond LR composite material). This is the retainer (0.0175) for Ortho-Care, Shipley, UK “trans bond LR composite with coaxial archwire (3M Unitek, UK). Participants were instructed that retainers should be worn full-time for the first 6 months, then just at night, followed by once a week for the following 12 to 18 months. A maintenance schedule of 1 to 2 nights per week has been suggested after that to keep it in good working order. Only 48 out of the 82 participants in the previous RCT had participated in the 18-month follow-up, which reflects a statistically significant shift.[6]

Participant information sheets were given to those patients who agreed to participate in a study at least after 48 months after the removal of their active appliances. The participants had to provide verbal and written consent. The periodontal examination in this study required that the participants should refrain for 1 month from seeing their dentist for scaling and root planning, and those taking drugs known to compromise gingival health were not included in the study. The distribution of the study population has been given in [Table 1].

Table 1.

Sample distribution

		Overall samplen =42	Fixed retainer groupn =21	Vacuum- formedretainer groupn=21
Meanageinyears(SD)		21.15(2.41)	21.54years(3.06)	20.77years(1.49)
Gender	Males	n=10	n=3	n»7
	Females	n=32	n=18	n=14
Meanyearsinretention(SD)		4.16(0.35)	4.09(0.25)	4.23(0.42)
Treatmentprotocol	Extraction	n=19	n=9	n=10
	Non-extraction	n=23	n=12	n=ll
Type oftooth-brush	Manual	n=37	n=18	nsl9
	Electric	n=5	n=3	n=2
Daily tooth- brushingfrequency	IX	n=7	n=6	n=l
	2X	n=35	n=15	n=20
Timespentintooth-brushing	<1 minute	n=l	n=0	n=l
	l-2minutes	n=29	n=14	n=15
	>2minutes	n=12	n=7	n=5
Use of otheroral hygienemeasures	None	n=23	n=13	n=10
	Dentalfloss	n=10	n=4	n=6
	Interdentalbrush	n=3	n=2	n=l
	Toothpick	n=9	n=4	n=5

Study flow diagram

Little’s Irregularity Index was used to assess mandibular inter-canine contact point displacement to determine orthodontic stability in the mandible. Inter-canines and intermolar widths, as well as the length of the arch and the size of the aperture of the extraction area, were all measured.

For the purpose of detecting any symptoms of periodontal breakdown, the labial and lingual surfaces of mandibular canines, as well as the central and lateral incisors, were inspected. To demarcate the surfaces of each tooth, vertical lines were drawn on the surface of each tooth based on the form and attachment position of the dental papilla. The clinical periodontal measurements were graded as follows.

• According to the patient’s report, the retainers were worn by following the manufacturer’s recommendations for use.

• Noncompliance: Retainers were not worn according to the manufacturer’s recommendations.

• Resistant means that you were not wearing the retainers.

To keep track of the fixed retainer maintenance and history of breakage, all relevant information was gathered and documented in the group. By comparing the findings of the two separate tests, the repeatability of clinical and research model measurements was assessed. At 4 weeks following the first five stability measures, 15 inter-examiner dependability was tested upon 10 randomly selected research models. A hat-trick was used to pick the models. For inter-examiner reliability, researchers used 10 randomly selected study models and found that intra-examiner (0.97) and inter-examiner (0.97) agreement was excellent (0.92). An online course on periodontal outcomes measurement must be completed before a periodontologist applies for the post of examiner to be considered. Measurements of the modified gingival index and plaque scoring were performed on the 10 intra-oral photographs that were taken at 4-week intervals in this study to investigate the intra-examiner reliability [Table 2]. A total of 10 healthy participants had their calculus scores, and clinical attachment level (CAL) measurements were taken twice, at 30 min duration apart, to test the repeatability of the results. There was a high degree of agreement (0.94–0.97) among the examiners during this testing procedure.

Table 2.

Measurement of periodontal parameters

Outcome measures	Statistical measures	Fixed retainer group (n=21)	Vacuum- formed retainer group (n=21)	P
Modified gingival index	Median	2.5	3	0.76(NS)
	IQR	3	3
Plaque index	Median	3.5	3	0.27(S)
	IQR	1	2
Calculus index	Median	0	0	0.19(S)
	IQR	1	1
Clinical attachment level	Median	2	1.5	0.23(S)
	IQR	1	1
Bleeding on Probing	Median	1	1	0.87(NS)
	IQR	2	2

S = significant, NS = not significant

Sample size

According to the previous research, the initial sample size was set although a larger degree of attrition should be expected with long-term follow-ups. It was possible to detect a difference in height of just 0.5 mm with 90% power and a 0.05 threshold of statistical significance with only 72 subjects altogether (with 36 participants in each group). To compensate for the dropout rate of 15%, 82 more participants were added to the first experiment sample.[6]

Statistical analysis

Bleeding on probing, the data were sent to median regression analysis to be examined. A similar approach was used to investigate the relationship between the kind of retainer and the attachment degree. In all studies, regardless of the technique employed, a 0.05 level of statistical significance was used as a cutoff point. The software used was the Stata statistical software package (version 14.1; StataCorp, College Station, Tex).

RESULTS

There were a total of 82 participants in the original RCT study. 48 of these patients appeared for their follow-up sessions at the end of the 18 months (T3). After 4 years of the follow-up period (T4), 42 members had returned, with 21 individuals from each of both the retainer groups. Both the fixed and removable retainer groups were matched in terms of demographics and treatment procedures, with a great majority of the former group consisting of females and the latter group consisting mainly of extraction-based therapy”. Despite the fact that three (14%) were partially detachable and two (10%) had a history of retainer repair, all (100%) were in place at the time of the recall visit. According to the removable retainer group, the number of reports of non-compliance increased from 0% to 19% over the first 6 months, and then to 52% throughout the second year and 67% after that.

Fixed orthodontic retention versus removable orthodontic retention:

Using data from 42 individuals, researchers investigated the irregularity of the mandible’s front part [Table 3]. After a4-year follow-up period, both fixed retainer and detachable retainer groups saw a median increase in the irregularity of 0.85 mm, and 1.47 mm, respectively, indicating some relapse.

Table 3.

Clinical parameters evaluated

Use of otheroral hYgienemeasures	Dentalfloss	n=10	n=4	n=6
	Interdentalbrush	n=3	n=2	n=l
	Toothpick	n=9	n=4	n=5
Lastvisittothedentist	<6months	n=10	n=5	n=5
	6months-<l year	n=5	n=3	n=2
	1-2 years	n=12	n=9	n=3
	>2 years	n=15	n=4	n=ll
Smokers		n=4	n=3	n=l
Gingivalbiotype	Thick	n=17	n=7	n=10
	Thin	n=24	n=14	n=10
Fraenalattachment	Low	n=41	n=21	n=20
	High	n=l	n=0	n=l

Individuals who wore VFRs had a median difference of 1.64 mm across groups (P = 0.02; 95% confidence interval [CI]: 0.30, 2.98 mm) according to the findings.

There was no statistically significant difference between the two treatment groups in the inter-canine and inter-molar widths (P = 0.52; 95% CI).

DISCUSSION

Retention is an inevitable and a very crucial part of orthodontic treatment to control post-treatment changes due to unstable tooth positioning at the end of active orthodontic treatment or due to non-adaptation of periodontal and gingival tissues to the new tooth position, which normally takes a few months to years to complete. Orthodontic relapse is also partly physiological and associated with natural age-related changes or growth. Although there are numerous varieties of retainers available to date, each suitable for specific case scenarios, the search continues for an ideal retainer with desired clinical properties that can cater to all case types. Retention is a very important part of orthodontic treatment that needs to be included in the original orthodontic treatment plan right at the beginning.

It has been found no significant differences in the stability of the mandibular anterior area. An RCT employing fixed retainers and VFRs demonstrated that the maxillary arch relapsed at the same rate as the mandibular arch (LII: 0.92 mm).[8] The results of this study imply that permanent retention may be beneficial in preventing changes in tooth positions and relapse, whereas removable retention may predispose to the recurrence of malalignment. It follows that the removable retainer group will likely experience further changes in alignment in the future, perhaps expanding the distance between the two. Such retention degradation with time is not surprising as the current study sample’s poor compliance with removable retention protocol tends to prove that degradation of occlusal and alignment results that were achieved over a period of time with orthodontic treatment in the retention phase is likely a result of patients’ non-compliance with the prescribed retention protocol.[9-16]

Even after 2 years of retention, 67% of patients were still non-compliant with retention protocol, showing an overestimation of collaboration. During the active orthodontic treatment phase, many patients fail to comply with the required duration of wear of any prescribed removable orthodontic components such as intra-oral elastics.[17] The idea that patients would wear removable retainers for many years following treatment may be an extremely optimistic assumption, especially if the treating practitioner does not regularly follow up with the cases.[18] New methods for boosting patient compliance with retention, especially those who do not require direct patient–clinician contact, may be helpful. This includes providing high-quality online patient awareness content, using social media platforms to spread awareness, and employing technological reminders via emails or mobile apps. Creating social media groups for patients where they can interact and observe each other may be a very useful tool to boost their morale and improve compliance with retention protocol. Despite their extensive usage as orthodontic retainers, there has been one randomized controlled study on VFRs’ effect on periodontal health.[5] After a year, fixed retainers had higher calculus index values than VFRs[5,19] despite the fact that periodontal assessment was confined to the calculus scores alone. The fixed retainer group in the aforementioned study was required to wear a proper “removable retainer” at night, making this difficult to compare the results. Therefore, to make the comparison between groups more reliable, in the current study, the participants of the fixed-retainer group were not required to wear any additional removable retainers. This protocol helps to strictly demarcate the two different groups being studied.

Even though overall dental hygiene was lacking in the current study sample, participants were randomly assigned to the two retainer groups, thus ensuring that all groups were anticipated to be equal in terms of probable confounding factors. The latest follow-up research verified this. Randomization should further lessen the selection bias as fixed retainers are often reserved for use in individuals with reasonably good oral hygiene. Observer bias was reduced by masking the lingual surfaces of the mandibular teeth; however, it was not practicable because periodontal results had to be clinically examined. Because frontal instability is more common due to both the treatment-induced changes and the physiological changes due to aging, the mandibular arch was investigated.[20] As a result, the lower arch may vary considerably amongst populations.

Although fixed retainers are preferred by many practitioners because these retainers are less demanding with regard to patient compliance in terms of maintaining the orthodontic treatment results achieved, a well-known disadvantage with these retainers is the possibility of debonding. Many times, the patients are unaware of the retainer being debonded due to masticatory forces or other reasons and they are left unattended for a very long time. This may cause a relapse of malalignment in the long run.

Maxillary fixed retainers are stable as dental retainers. Despite this, maxillary retainers tend to fail more frequently due to occlusal along with masticatory forces,[21] diminishing any kind of associated benefit. Little’s irregularity index[22] was employed on the study models to determine stability with each retainer type. The drawback of this index is that it mainly ignores the “vertical displacements, reciprocal rotations, angulation, and inclination changes.” This has been shown in Little’s evaluations, where both plain and professional observers valued horizontal displacements at 22. Unintentional issues, such as localized torque variations, are more prevalent with fixed retainers over time.[23,24] However, due to the limited study sample size, these concerns were not evident in the current study.

The periodontal examination included a thorough inspection of both the buccal and lingual aspects of the teeth. This was done to prevent diminishing the impact of plaque development on the lingual surfaces. Following the use of Hawley retainers for up to 6 months,[25] minor changes were detected in gingival index scores on the buccal aspects of maxillary and mandibular front teeth. The plaque index scores for both groups were 3 to 3.5 after 6 months, which was nearly 0.5 units higher than for mandibular incisor teeth with fixed and Hawley retainers.[25] Fixed and VFRs had similar gingival and plaque indices in the mandibular labial region, whereas fixed retainers had higher plaque scores.[25]

A study by Fareena et al.[26] reported enhanced plaque and calculus accumulation with a fixed retainer when compared with a removable retainer. On the basis of the Al-Moghrabi et al.’s study, it appears that fixed retainers may be the approach of choice to maintain alignment of the mandibular anterior teeth in the long term; however, there is a clear need for optimal oral hygiene before, during, and after orthodontics to prevent increased levels of gingival inflammation.[27]

Eroglu et al.[28] reported that oral hygiene improved after orthodontic treatment with fixed appliances, regardless of retainer type. They also showed that fixed and removable orthodontic retainers did not differ in terms of salivary Streptococcus mutans and Lactobacillus casei levels and periodontal status. A study by Han et al. reported that the calculus index of the lower anterior teeth was significantly greater than that of the upper anterior teeth after the bonding of fixed retainers.[29]

VFRs were found to be significantly more cost-effective than Hawley retainers within the National Health Service over a 6-month retention period.[30]

Using a retainer was significantly associated with plaque accumulation in the maxilla and calculus accumulation in the mandible. More pronounced calculus formation has been shown in patients with fixed retainers when compared to removable, or no retainers.[31]

In the case of fixed retainers, the type of wire used and the finish of the adhesive used to bond the retainer may also play a role in plaque retention. Braided retainer wire bonded with a composite resin that has a rough finish may tend to accumulate more plaque than a well-finished adhesive.

Limitations of the study include a small sample size and a short follow-up period. Also, it is possible that the study’s massive number of statistical tests produced false-positive results; however, they were all pre-specified.

CONCLUSIONS

Based on the above evaluation, it can be concluded that at 4 years of follow-up evaluation, fixed retainers can be more successful than VFRs in maintaining the mandibular anterior segment alignment, though some alignment alterations occurred in both the retainer groups. Gingival irritation and poor dental hygiene were connected to both permanent and removable retainers. Fixed retention appears to be the best option for maintaining the lower anterior segment alignment in the long term, according to the findings of this study. However, good dental hygiene is essential before and after orthodontic treatment to prevent gingival irritation from worsening.

Financial support and sponsorship

Department of Dentistry, Pramukh Swami Medical College, Bhaikaka University, Karamsad, Gujarat.

Conflicts of interest

There are no conflicts of interest.