Blanket or tailored prescription of retainers in orthodontics: a questionnaire-based study

While there is now a deeper understanding of the contributors to posttreatment change^1,2  and a broadening armamentarium of mechanical options for orthodontic retention, considerable uncertainty continues to surround the choice of optimal retention regimes. The susceptibility of specific features to change dictates the potential value of tailored retention protocols. In particular, the stability of orthodontic treatment outcomes varies depending on the pretreatment malocclusion and the nature of orthodontic changes with, for example, anterior open-bite correction related to the extrusion of the incisors thought to have a poor prognosis for stability.³  Additionally, favorable posttreatment dental changes are sometimes required to improve interdigitation following debond.⁴  As such, the universal prescription of homogeneous regimes may be inappropriate, with nuances related to retainer selection, design, protocols, the incorporation of active elements,⁵  and the use of adjunctive procedures being possible.⁶ 

Previous questionnaire-based studies^7–10  have focused on common retention practices rather than linking these to the nature of orthodontic correction. Alterations to retention protocols, however, have been explored in national surveys regarding the management of diastema, following maxillary expansion, and in relation to open bite and severe rotations.^11–13  It was observed that more than two-thirds of orthodontists prescribed fixed retention and clear plastic retainers following the closure of a maxillary midline diastema.^11–13  A Hawley appliance^12,13  or a clear plastic retainer¹¹  has been commonly prescribed following maxillary expansion. Clear plastic retainers, with or without fixed retention, may be more commonly prescribed following the correction of an anterior open bite than Hawley retainers.^11,12  Dual retention, using a clear plastic retainer and a fixed retainer (FR), has been commonly prescribed following the correction of severe rotation of the maxillary anterior teeth.^11–13  Previous questionnaires were centered primarily on orthodontist preferences in terms of fixed or removable retainers in different malocclusions, with little information being related to tailoring retainers in terms of their design, material selection, and prescription of adjunctive procedures.

Certain modifications of removable appliances have been described to mitigate different tooth movements or occlusal changes, for example, the incorporation of bite planes into removable retainers anteriorly and posteriorly following the correction of deep bite and open bite, respectively.⁵  Additionally, FRs can be altered to include the mandibular first premolars but may be confined to the upper central incisors only following midline diastema closure.¹⁴  However, the extent to which retention protocols, including the selection of retainer type and material and recall routines, are tailored on an individual basis has not been captured in previous survey-based studies. The aims of the current study, therefore, were to evaluate the prescription of different retainer protocols and surgical adjunctive procedures by orthodontists and to understand how this is influenced by the orthodontic presentation and the nature of the correction.

A questionnaire-based survey targeting orthodontists was designed on the SurveyMonkey platform following ethical approval (Queen Mary Ethics of Research Committee, QMERC22.109). The following aspects were considered: demographics and clinical experience, clinical preference in terms of types of retainer options and follow-up during retention, retainer fabrication, clinical indications for prescribing adjunctive surgical procedures or no retainers, and specific questions related to orthodontic retainer material choice and design for different types of malocclusions.

The questionnaire was piloted twice on each of five orthodontic specialists. The following aspects were assessed: clarity of the language and readability, style and formatting consistency, and feasibility. Amendments were made accordingly until a final version, including up to 45 items, was devised.

The online questionnaire was made available on orthodontic social media platforms, including multiple closed Facebook groups. A link to the questionnaire, along with accompanying explanatory information, was posted, and the survey remained open for 4 weeks after the final post.

Descriptive statistics were performed, and data were presented as frequencies and percentages. Responses to open-ended questions were also considered, coded, and reported.

A total of 206 responses were obtained from orthodontists with an almost equal gender distribution (Table 1). The majority of the participants (46.8%) were aged 30–40 years and had up to 10 years of experience (53.7%). Most participants were from Asia (56.3%), followed by Europe (26.8%). More than half of the participants were working in private practice (59.5%).

Overall, respondents reported the prescription of maxillary removable retention (63.6%) and mandibular fixed retention (45%) in isolation, in more than half of their treated cases (Table 2). FRs in isolation were rarely prescribed for the maxillary arch. Dual retention using fixed and removable retainers concomitantly was slightly more prevalent in the mandibular than in the maxillary arch.

The utilization of FRs was reported to have changed over the past 5–10 years in more than half of the sample (59%). Of these, more than half reported an increase in their use, mainly due to relapse observed with removable retainers and patient request/awareness (Table 2). The remainder reported the reduced use of FRs due to the associated breakage, research findings, inadvertent torque expression, and time implications.

In terms of monitoring retention, most respondents relied on face-to-face appointments (95.1%; Table 2). More than one-third of the participants (38.2%) reviewed patients for over 6 months to 1 year after the completion of active orthodontic treatment. A significant proportion (39.2%) arranged follow-up visits at 3, 6, and 12 months. Clear plastic retainers were the most commonly prescribed type of removable retainers, with 44.1% expecting these retainers to last only up to 1 year. Only 3.9% felt that clear plastic retainers could last lifelong.

Most participants reported the use of clear plastic retainers (91.1%), with these being fabricated exclusively in external laboratories for 43.7%, although in-house fabrication (37.3%) and a combination of external and in-house fabrication (19%) were also prevalent (Table 3). More than two-thirds of participants reported that vacuum forming was the preferred manufacturing technique (69.6%). The thickness of clear retainer blanks commonly used was 1 mm (44.3%), with 0.75 mm being the next most commonly used thickness (20.9%). Over three-quarters of respondents provided patients with only one set of clear retainers (79.1%). Only 37.3% were aware of the type of material used to fabricate their clear plastic retainers, which included mainly polyethylene terephthalate glycol (PET-G) (39%), polyurethane (17%), polypropylene (15.3%), polyester (8.5%), and polyvinylchloride (8.5%).

Two-thirds of participants typically prescribed FRs (75.7%), with four incisors (38.8%) or six anterior teeth (51.9%) usually being bonded in the maxilla and six anterior teeth being bonded in the mandible (91.5%) (Table 3). A range of popular wire designs were reported, including twisted ligature wires (22.3%), stainless steel (SS) multistrand (flattened) (19.2%), and SS retainer chain (17.7%). Almost two-thirds of respondents (64.6%) were unaware of the dimensions of the FRs used.

Frenectomy prescription was dictated by the extent of frenal attachment observed clinically (71.3%) and radiographically (29.3%) (Table 4). Most respondents did not change their standard practice regarding the use of FRs in patients with midline diastema in terms of the number of teeth included. However, the most common FR type used in patients with midline diastema was SS multistrand (flattened) (20.7%), followed by twisted ligature wires (18%). Fewer also used chain-like designs, including FlexTech, in the presence of preexisting diastema than they did for general use (16% vs 22.3%).

Respondents commonly prescribed Hawley retainers (58.4%), followed by clear plastic retainers (43.6%), following nonsurgical maxillary expansion, with no modification to their standard protocol (Table 4). Clear plastic retainers were prescribed with palatal coverage in less than one-quarter of these cases (23.8%).

Following the correction of significant maxillary incisor rotations, fixed retention (76.8%) and/or circumferential supracrestal fiberotomy (CSF) (25.4%) were commonly prescribed (Table 4). Participants were more likely to prescribe clear plastic retainers (62.7%) than Hawley retainers (9.9%) to retain derotated teeth. CSF was commonly prescribed for rotations greater than 90° (61.1%).

Maxillary and mandibular clear plastic retainers and/or FRs were commonly prescribed in anterior open-bite cases (Table 4). Over half did not deviate from their standard protocol in these cases. Removable appliances, including clear plastic retainers (64.5%) or Hawley retainers (34.8%), were commonly prescribed following deep-bite correction, and respondents also commonly integrated anterior bite planes with the removable retainers following deep-bite correction (Table 4). Cases with poor interdigitation following orthodontic treatment were usually managed with the use of Hawley retainers (35%) and/or FRs (30%) (Table 4).

No retainer was rarely prescribed other than for patients who were either unwilling or unsuited to have retainers (Table 4). An exception was that no retainers were commonly prescribed following anterior crossbite correction (52.4%).

The present survey is the first to explore retention preferences based on the presenting malocclusion and treatment outcome and to evaluate the knowledge of orthodontists regarding the plethora of materials available. The findings highlighted that there is little tailoring of orthodontic retention and limited awareness of clear plastic retainer options and dimensions. Short durations of follow-up of patients in retention as well as the patchy adoption of monitoring software and mobile applications were also noted. The latter, in particular, may reflect the challenges associated with the uptake of newer technology within orthodontic offices.¹⁵ 

A preference for clear plastic retainers over other types of removable retainers was noted, most likely attributable to esthetics and patient experiences.¹⁶  The limited longevity of clear plastic retainers was a recognized drawback, however, with a mean life span of as little as 3.5 months being noted in one study.¹⁷  In the present study, the majority of participants expected these retainers to last up to 1 year. Previous qualitative studies highlighted that breakage and loss risk the termination of removable retainer wear.¹⁸  Notwithstanding this, only one set of retainers was typically provided, and most orthodontists did not schedule retainer review visits beyond 1 year into retention. Participants reported the nearly routine use of clear plastic retainers of 1-mm thickness, in line with previous research in which this was the most popular thickness in Canada,¹¹  Australia,¹³  and Ireland.¹²  Previous research highlighted lower failure rates with 1-mm-thick than with 0.75-mm-thick clear plastic retainers over a 12-month period.¹⁹  Notwithstanding that, the effects of increasing the retainer thickness further have been the subject of limited assessments. In the current study, 63% of the participants were unaware of the type of material used. Of those who reported the material used, PET-G copolymer, followed by polypropylene, was the most common. In the current study, more than 40% of the respondents relied on dental technician preferences rather than clinical experience despite known differences in durability and the advent of tougher polymers, including polyurethane, which have been associated with lower fracture rates than PET-G copolymer-based clear retainers at 6 months of follow-up.²⁰ 

It has been reported that flexible spiral wires are associated with unwanted torque changes in the long term in up to 1% of cases.²¹  Chain-like retainer materials may be less likely to introduce these changes, although further research on this would be helpful.²²  In addition, the use of computer-aided design and computer-aided manufacturing (CAD-CAM) designs was infrequent, perhaps related to high breakage rates and associated costs.²³  Evolving FR prescription rates were commonly reported, with 34.7% using more, and 24.2% using less, fixed retention than in the past. According to Pratt et al, 36% of orthodontists in the United States reported that their prescription of FRs increased in the last 5 years, compared to only 11% of orthodontists who reported that their prescription decreased.⁸  It is interesting to note that research findings were reported as being instrumental in accounting for both increased and reduced use. Previous research has alluded to the limited interaction with and understanding of orthodontic research,²⁴  likely explaining this discrepancy.

Fewer than one-third of the respondents referred to follow-up for more than 2 years after the completion of orthodontic treatment, and just over one-half dismissed patients within the first year. The 1-year follow-up duration may be favored due to the high proportion of detachments of FRs at the enamel-composite interface occurring within the first 6 months.^23,25  Additionally, breakage of removable retainers is common in the first year; over half of thermoplastic retainers of a 0.75-mm thickness and Hawley retainers were fractured at 1 year of follow-up.²⁶  Nevertheless, it is accepted that retention requires long-term monitoring, and the delegation of the review of retention to general dentists may be problematic.^11,13,27 

The use of fixed retention in cases with preexisting maxillary diastema is well established. The most common type of FR used by respondents to preserve midline diastema correction was SS multistrand wire (flattened) (20.7%), followed by twisted ligature wires (18%). In general, 17.7% of the respondents prescribed an SS retainer chain; however, this was reduced to 10.7% following the closure of midline diastema. This may have been due to the risk of stretching of passive chains leading to the reopening of space. A recent systematic review found that there was a dearth of research evaluating the effectiveness of frenectomy following the closure of midline diastema.⁶  In the current study, frenectomy prescription was dictated primarily by the extent of frenal attachment clinically (71.3%). It is therefore likely that functional and esthetic concerns may influence the decision to undertake frenectomy.

Following nonsurgical maxillary expansion, participants preferred the prescription of Hawley retainers over clear plastic retainers, with no modifications to their standard protocol. Regarding the use of clear plastic retainers, palatal coverage was rarely prescribed. In a recent randomized controlled trial, no difference in transverse stability was observed with 1-mm clear plastic retainers, including palatal coverage, compared to Hawley retainers.²⁸  Additionally, the relative impact of newer, tougher polyurethane-based clear plastic retainers has not been assessed in clinical research. Up to one-quarter of respondents prescribed CSF, in keeping with previous research in Iraq²⁹  and Turkey.³⁰  A recent systematic review concluded that there was weak evidence supporting the prescription of CSF.⁶  As such, a discrepancy between research findings and clinical practice may again exist.

Following open-bite correction, clear plastic retainers were preferred over Hawley retainers. This may be attributable to the intrusion effect of clear plastic retainers.³¹  The use of fixed retention in these cases was particularly prevalent. While the benefit of fixed retention would appear intuitive in terms of overbite preservation, this has not been uniformly demonstrated in prospective research.³²  Furthermore, modification to removable retainers with preferential posterior coverage can be considered to limit the risk of unwanted molar extrusion,⁵  although long-term evidence to support this practice is unavailable. Either way, almost one-quarter of the respondents reported the use of this approach following molar intrusion during treatment.

The findings of the current study were based on self-reported practice, which may be subject to recall bias. The prescription of different types of FRs and modification of removable retainers may also be influenced by the availability of materials and access to technical skills; however, the responses are likely to reflect real-world practice. A limitation of the current study included the relatively small sample size, which is a common issue associated with surveys in general. However, the sample size was considered sufficient to provide plausible results. Additionally, there was no evidence to suggest that the low response rate was associated with bias in relation to retainer prescription. In addition, while respondents were limited to those who were active on social media, a broad international cross-section, comprising those based in both private practice and university practice, was included.

• The findings highlight the surprising lack of tailoring of orthodontic retention regimes based on individual patient characteristics, relatively short follow-up of patients during retention, and limited application of remote monitoring software to augment in-person evaluation.

• The prescription of surgical adjunctive procedures was limited, although the use of CSF was common for severe rotations.

• Prospective research evaluating the effectiveness of nuanced approaches to retainer prescription based on the presenting malocclusion would be welcome.

The project was funded by the Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2023R88), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.