Introduction
The aims of this study were to survey current retention procedures applied by Dutch orthodontists and to examine their acquaintance with “unintentionally active retainers.”
Methods
A questionnaire was sent to all 306 Dutch orthodontists involved in patient treatment. Questions were clustered in 4 parts: (1) general information, (2) retention procedures, (3) characteristics of wire materials for bonded retainers, and (4) acquaintance with “unintentionally active retainers.”
Results
The response rate was 98%. The most applied retention modality in the maxillary arch was a combination of a removable and a bonded retainer (54%); in the mandibular arch, mainly a bonded retainer without a removable retainer was used (83%). Bonded retention was aimed to be lifelong for the maxillary arch (90%) and the mandibular arch (92%). Mean removable retention duration was 2 years. Vacuum-formed retainers were used more frequently and Hawley-type retainers less frequently. The wire materials used for bonded retainers were diverse. All orthodontists were familiar with unintentionally active retainers; 44% believed this phenomenon is caused by the properties of round multistrand wires. The opinion that unwanted changes in tooth position can arise due to the properties of round multistrand wire material was associated with changing the wire material ( P <0.005).
Conclusions
Lifelong retention with bonded retainers continues to increase. All orthodontists were acquainted with unintentionally active retainers and their impact. There is a need to identify all causative factors of inadvertent tooth movement in relation to bonded retainers and to prevent the onset of unintentionally active retainers.
Highlights
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In 10 years, bonded retainer use has increased, especially in the maxillary arch.
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Lifelong retention with bonded retainers continues to increase.
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Acquaintance with “unintentionally active retainers” was high; their cause remains unknown.
To maintain the result of orthodontic treatment, retention is applied in virtually every patient. This widespread use is caused by the likelihood of posttreatment changes and the increased demand to permanently maintain a perfect esthetic result. Unfortunately, there is still no agreement about which retention regimen should be recommended. Recently, Littlewood et al concluded in their Cochrane systematic review that there is insufficient evidence to make recommendations on orthodontic retention procedures.
During the past decade, interest in retention procedures has increased and has shown that retention procedures differ from country to country ( Table I ). A trend toward more fixed retention has been demonstrated. Also, currently, more invisible retainers are used instead of Hawley retainers, and more often lifelong retention is prescribed instead of retention for a limited time. The choice for orthodontic retainer type, however, seems to remain mainly experience-based because of the large variations observed.
| Study | Country | Response rate | Recommend lifetime/ permanent retention |
Removable retention | Bonded retainer | Notable results | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| UA H/Pl |
UA VFR |
LA H/Pl |
LA VFR |
UA | LA | |||||
| Wong and Freer 2004 |
AU and NZ | 217 of 370 total sent (59%) | 21% | 44% | 31% | 18% | 22% | 14% | 38% | Use of permanent retention was either very high or very low % of cases Permanent retention regarded as lifetime retention by only 70%. No consensus on factors influencing permanent retention. |
| Keim et al 2008 |
USA | 808 of 10,523 total sent (8%) | 36% | NA | NA | NA | NA | 11% | 41% | Less VFR and bonded retainer use compared with Keim 2014. Less lifetime retention compared with Keim 2014. |
| Singh et al 2009 |
UK | 240 of 301 total sent (80%) | 84% | 35% | 62% | 19% | 71% | 22% | 38% | More bonded retainers applied in private practice compared with other practice settings. |
| Renkema et al 2009 |
NL | 254 of 279 total sent (91%) | 84% | 41% | 16% | 5% | 7% | 62% | 90% | A divide in removable retainer use. Pretreatment situation most common factor for retainer choice. Indications removable retainer UA: Extractions and arch expansion. Contra indications for bonded retention: oral hygiene and deep bite. |
| Valiathan and Hughes 2010 |
USA | 658 of 2000 total sent (33%) | 76% | 58% | 30% | 37% | 18% | <11% | 40% | Orthodontists who have practiced less than 16 years use significantly more bonded retainers. Significant differences were found in retention protocols between orthodontists from different regions in the USA. |
| Pratt et al 2011 |
USA | 1,632 of 9,143 total sent (18%) | 82% | 54% | 48% | 33% | 33% | 13% | 48% | A positive correlation was found between incidence of extraction cases and use of removable retainers. Orthodontists’ self-observed trends: almost half reported a decrease in Hawley/plate retention and an increase in bonded retention. |
| Miles 2013 | AU | 156 of 433 total sent (36%) | 68% | 47% | 80% | 27% | 47% | 53% | 81% | An increase in VFR and bonded retainer use compared with Wong and Freer. The most common research questions clinicians would like to have answered were related to retention. |
| Vandevska-Radunovic et al 2013 |
NO | 150 of 193 total sent (78%) | 10% | NA | NA | NA | NA | 50% | 89% | Contrary to other studies, only 10% recommended lifetime retention. Pretreatment situation was most common factor for retention choice. Retention protocols largely based on clinical experience (57%) and specialty training (28%). (Presentation of results impeded interpretation.) |
| Lai et al 2013 |
CH | 145 of 223 total sent (65%) | 87% | 37% | 7% | 3% | 5% | 73% | 78% | Indications removable retention UA: extractions and arch expansion. Contra indications for bonded retention: oral hygiene and deepbite. Side effects occur in bonded retainers according to 57% of orthodontists. |
| Meade and Millet 2013 |
IRL | 101 of 123 total sent (82%) | 67% | 18% | 69% | 13% | 61% | 19% | 47% | Contrary to most other studies, most common retainers were maxillary and mandibular VFRs (either used singly or combined with bonded retainer). |
| Keim et al 2014 |
USA | 209 of 10,688 total sent (2%) | 65% | NA | NA | NA | NA | 23% | 56% | Trend toward more VFR and more bonded retainer use. Trend toward more lifetime retention. |
Also, several reports regarding complications after long-term use of bonded retainers have been published. In severe situations, an “unintentionally active retainer” can almost completely move the root out of the alveolar process ( Fig 1 ).
In 2005, a survey of retention procedures was carried out in the Netherlands. It was possible to accurately determine how Dutch orthodontists used retention after orthodontic treatment. However, questions regarding wire material used for bonded retainers and unintentionally active retainers were not included. This is an important subject, since specific wire materials are partially responsible for posttreatment complications.
Therefore, the aims of this study were to survey current retention procedures applied by Dutch orthodontists and to examine their acquaintance with unintentionally active retainers.
Material and methods
The questionnaire designed by Renkema et al was adjusted to include additional aspects to be addressed. In July 2015, a pilot study was performed to determine the reliability of the additional questions, and some questions were adjusted. In September 2015, the questionnaire was sent to all orthodontists working in The Netherlands, registered in the Dutch register of specialists in orthodontics and involved in patient treatment. Nonresponding orthodontists were reminded after 1 month. Those who still did not reply were contacted by phone after another month. If an orthodontist was not willing to participate, his or her reasons were recorded. In case of incomplete questionnaires, respondents were contacted by phone to complete the questionnaire. In December 2015, the survey was completed, and the replies were entered in a Filemaker database.
The questionnaire consisted of 4 parts. Part A addressed background information about the orthodontist. Part B consisted of questions on the use of different retainer types, duration of retention with removable and bonded retainers, and number of retention checkups. In part C, information regarding type and size of the wires for bonded retainers was assessed, and in part D, questions asked about unintentionally active retainers. Respondents could add comments and additional information at the end of the survey.
Statistical analysis
All statistical analyses were performed using the Statistical Package for Social Sciences (version 22.0; IBM, Armonk, NY). Background information on each orthodontist was described in frequencies and percentages, with the other results in percentages. Chi-square tests were used for 2-by-2 cross tables; when necessary, the Fisher exact test was applied.
Results
Questionnaires were sent to 306 orthodontists, of whom 300 (98.0%) responded. Four orthodontists were not willing to participate, and it was impossible to contact 2 of the 22 orthodontists who did not fill in the questionnaire completely; they were therefore excluded. Table II gives an overview of the sample size, age, professional experience, days per week involved in patient treatment, and professional setting of the orthodontists. Days involved in patient treatment showed a negative correlation with age (−0.24; P <0.001). The male-female ratio for working as a practice owner or associate was 4:3, and the male-female ratio for working as a locum tenant was 1:3. Orthodontists working as a locum tenant had significantly less experience than did the other orthodontists (6.2 years; P <0.001). The most often combined professional setting was working in private practice and at the university (n = 19; 6.3%). Of the 300 orthodontists, 92 (30.7%) received their postgraduate training abroad.
| Study sample, n = 300 | Male, n = 175 (58.3%) | Female, n = 125 (41.7%) | ||||||
|---|---|---|---|---|---|---|---|---|
| Mean | SD | Minimum | Maximum | Mean | SD | Minimum | Maximum | |
| Age (y) ∗ | 50.7 | 10.4 | 29.0 | 69.8 | 44.9 | 9.9 | 29.0 | 69.5 |
| Experience (y) ∗ | 18.2 | 10.4 | 0.7 | 41.3 | 14.3 | 9.8 | 0.8 | 38.4 |
| Patient treatment (d/wk) ∗ | 4.0 | 0.9 | 1.5 | 5.0 | 3.5 | 0.8 | 1.0 | 5.0 |
| Professional setting | Male, n (%) | Female, n (%) |
|---|---|---|
| Private practice | ||
| Solo owner † | 68 (38.9%) | 30 (24.0%) |
| Associated † | 70 (40.0%) | 43 (34.4%) |
| Staff member † | 31 (17.7%) | 22 (17.6%) |
| Locum † | 15 (8.6%) | 32 (25.6%) |
| Academic † | 17 (9.7%) | 20 (16%) |
The most often applied retention modality in the maxillary arch was the combination of removable and bonded retainers (53.6%); in the mandibular arch, mainly a bonded retainer without a removable retainer was applied (82.6%) ( Table III ). Almost a third (n = 95) applied this retention modality in 80% or more of their patients.
| Retention modality | Maxillary arch | Mandibular arch | ||||
|---|---|---|---|---|---|---|
| Mean % | SD | n | Mean % | SD | n | |
| Hawley-type retainer | 7.3 | 19.3 | 22 | 0.5 | 2.3 | 108 |
| Vacuum-formed retainer (VFR) | 4.1 | 13.3 | 108 | 1.8 | 7.6 | 74 |
| Bonded retainer I 2 -I 1 -I 1 -I 2 | 5.6 | 16.7 | 72 | – | – | – |
| Bonded retainer C-I 2 -I 1 -I 1 -I 2 -C | 29.1 | 35.4 | 177 | 77.5 | 34.1 | 273 |
| Bonded C-C (canines only) | – | – | – | 5.1 | 20.2 | 28 |
| Hawley-type + bonded I 2 -I 1 -I 1 -I 2 | 12.2 | 26.4 | 120 | – | – | – |
| Hawley-type + bonded C-I 2 -I 1 -I 1 -I 2 -C | 15.5 | 27.6 | 158 | 1.8 | 11.2 | 25 |
| Hawley-type + bonded C-C (canines only) | – | – | – | 0.4 | 5.2 | 3 |
| VFR and bonded I 2 -I 1 -I 1 -I 2 | 9.3 | 23.4 | 91 | – | – | – |
| VFR and bonded C-I 2 -I 1 -I 1 -I 2 -C | 16.6 | 29.9 | 145 | 11.5 | 25.1 | 139 |
| VFR and bonded C-C (canines only) | – | – | – | 0.7 | 8.2 | 3 |
| Other | 0.3 | 1.6 | 16 | 0.8 | 7.1 | 18 |
| Total | 100% | 100% | ||||
Use of a Hawley-type retainer in the maxillary arch (without a bonded retainer) showed a positive correlation with the orthodontists’ experience (0.28; P <0.01) and an association with location of postgraduate training ( P <0.05). Reasons for using removable retainers were retention of arch width and extraction sites.
Four orthodontists (1.3%) indicated that they used only removable retainers in the maxillary arch, whereas 14 orthodontists (4.3%) used this modality in 80% to 99% of their patients. On the other hand, 6 orthodontists (2.0%) stated that they only used bonded retainers in all patients. Twenty-four respondents (16.0%) indicated that they did so in 90% or more of their patients. Twelve orthodontists (8.0%) always used the combination of bonded and removable retainers in both arches in all patients, and 54 (18.0%) indicated that they used this modality only in the maxillary arch for all patients. Several orthodontists commented that it is difficult to obtain sufficient cooperation for wearing removable retainers.
Prescribed initial duration of removable retention is presented in Table IV . When more hours of removable wear per day were prescribed, respondents indicated a shorter duration of the initial phase and vice versa. Orthodontists who prescribed 24 hours of initial retainer wear per day in the maxillary arch had a mean initial phase of almost 3 months (SD, 0.15), whereas those who prescribed 8 hours of initial retainer wear per day had a mean initial phase of 0.99 year (SD, 0.82).
| Initial wearing time per day (h) | Duration of initial phase of removable retention (y) | |||||||
|---|---|---|---|---|---|---|---|---|
| Maxillary arch (n = 294) | Mandibular arch (n = 191) | |||||||
| n | Mean (SD) | Minimum | Maximum | n | Mean (SD) | Minimum | Maximum | |
| Day and night | 88 | 0.23 (0.15) | 0.08 | 0.75 | 54 | 0.22 (0.14) | 0.08 | 0.75 |
| After school, evening and night | 15 | 0.27 (0.13) | 0.08 | 0.50 | 11 | 0.23 (0.11) | 0.08 | 0.50 |
| Evening and night | 43 | 0.58 (0.44) | 0.08 | 2.00 | 30 | 0.60 (0.43) | 0.08 | 2.00 |
| Nighttime only | 148 | 0.99 (0.82) | 0.08 | 5.00 | 96 | 1.04 (0.86) | 0.08 | 5.00 |
Total duration of removable and bonded retention is described in Table V . Almost half of the clinicians who indicated that removable retention should be temporary recommended that their patients should check the retainer’s fit every now and then: 44.7% (n = 102) for the maxillary arch and 46.8% (n = 65) for the mandibular arch. When duration of removable retainer wear was “individually determined,” the following indications were given: distinction between adults and adolescents, until growth has ended, dependent upon fixed retention, and until the placement of a fixed dental prosthesis. Respondents who indicated “individually determined” for the duration of bonded retention mentioned a distinction between adults and adolescents, until growth has ended, after eruption of the third molars. Lifetime retention with bonded retainers was recommended by almost 90% of orthodontists for the maxillary arch and 92% for the mandibular arch. Several respondents mentioned that today’s patients are more demanding, and even minor irregularities are no longer accepted.
| Total duration of removable retention | ||||||||
|---|---|---|---|---|---|---|---|---|
| Maxillary arch (n = 294) | Mandibular arch (n = 191) | |||||||
| n | % | Mean (SD) | Min-max | n | % | Mean (SD) | Min-max | |
| Temporarily | 228 | 77.6% | 2.0 (1.6) | 0.25-12.0 | 136 | 71.2% | 2.0 (1.5) | 0.25-10.0 |
| Permanently (lifetime) | 16 | 5.4% | – | – | 25 | 13.1% | – | – |
| Individually determined | 50 | 17.0% | – | – | 30 | 15.7% | – | – |
| Total duration of bonded retention | ||||||||
|---|---|---|---|---|---|---|---|---|
| Maxillary arch (n = 296) | Mandibular arch (n = 300) | |||||||
| n | % | Mean (SD) | Min-max | n | % | Mean (SD) | Min-max | |
| Temporarily | 21 | 7.1% | 9.7 (7.7) | 2-30 | 16 | 5.3% | 9.6 (6.6) | 3-25 |
| Permanently (lifetime) | 265 | 89.5% | – | – | 276 | 92.0% | – | – |
| Individually determined | 10 | 3.4% | – | – | 8 | 2.7% | – | – |
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