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Clear aligner vs fixed self-ligating appliances: Orthodontic emergency during the 2020 coronavirus disease 2019 pandemic

Clear aligner vs fixed self-ligating appliances: Orthodontic emergency during the 2020 coronavirus disease 2019 pandemic

American Journal of Orthodontics and Dentofacial Orthopedics, 2022-04-01, Volume 161, Issue 4, Pages e400-e406, Copyright © 2021 American Association of Orthodontists


The aim was to investigate the type, incidence, and degree of orthodontic-related emergencies in orthodontic patients during the 2020 coronavirus disease 2019 pandemic and compare the different effects of clear aligner (CA) and fixed self-ligating appliances on the orthodontic emergency.


The questionnaire was based on emergencies in orthodontics. The responses of 428 patients between the ages of 12 and 38 years (20.4 ± 7.03) in orthodontic treatment during 2020 were examined.


The gender, age, and the type of orthodontic appliance affect the incidence of orthodontic-related emergencies. Female or adolescent patients treated by self-ligating appliances showed a higher incidence of emergencies. The patients treated by CA exhibited a much lower incidence of emergency. Appliance detachment and mucosa injury were very common in respondents, whereas accidental ingestion and other rare emergencies were less common. The most common reason leading to appliance detachment was chewing hard food. Interestingly, the fixed self-ligating appliances group was also affected by the accidental detachment of appliances to a large extent. The CA and self-ligating groups showed an almost equal incidence of accidental ingestion. The most common foreign body was elastics in both groups. However, the self-ligating group could accidentally ingest dangerous foreign bodies, such as archwires, miniscrews, and welded attachments.


Orthodontic-related emergencies were very common in patients. The CA could effectively reduce orthodontic-related emergencies. Dentists should raise patients’ awareness of proper appliance care. A proper and standard protocol should be developed.


  • The incidence of orthodontic-related emergencies was very high.

  • The gender, age, appliance type affect incidence of orthodontic-related emergencies.

  • The clear aligner could effectively reduce orthodontic-related emergencies.

It has been reported that emergencies are common in dental practice. Although less than other oral specialties, orthodontic emergencies should not be overlooked because more and more children, adolescents, and adults seek orthodontic treatment nowadays. , Sometimes, dental practices lead to dental emergencies, prolonged courses, and complicated treatment methods, increasing the medical cost and sometimes leading to medical accidents and disputes. To strengthen dental-medical safety, the design and use of effective methods to prevent dental and medical mistakes should receive attention.

Orthodontic treatment is slightly different from the treatment of other oral diseases. Several appliances have been used in orthodontic treatment. The types of devices could be one of the most complex appliances among dental therapy. Orthodontic treatment usually lasts for >1 year and the appliances, such as wires, mini-implant, transpalatal arch (TPA), Nance palate pad, and so on, are under patients’ control outside the dental clinic. Oral functions such as chewing, swallowing, and speech could also have unavoidable effects on the appliances, leading to damage or detachment of the appliances.

It has been reported that the number of patients with a dental emergency has increased annually. The most common cause of dental emergency visits was pain due to caries, pulpitis, periapical periodontitis, and dental injury of either soft tissue, such as oral mucosa, or hard tissue, such as primary or permanent teeth. Though it was not common for an orthodontic emergency to occur, broken or detached orthodontic appliances or attachments could lead to severe adverse events outside the dental clinic or hospital.

Orthodontic emergencies include mucosal injury because of displaced archwire or protruded orthodontic ligation wire, accidental appliance or attachments ingestion and aspiration, discomfort because of the detachment of appliances or bands, etc. Reasonable and effective decision-making was very important for the prevention, early diagnosis, and appropriate treatment of foreign body inhalation and ingestion in orthodontic practice to avoid severe consequences.

The coronavirus disease 2019 (COVID-19) pandemic altered the visit pattern of the orthodontic patients, and this could cause anxiety and tension in patients and lead to more accidents or emergencies. This study aimed to investigate the types and incidence proportion of orthodontic emergencies in orthodontic patients, based on a questionnaire completed by the patients during the pandemic prevention and control period in 2020. This study also compared the different effects of the clear aligner (CA) and fixed self-ligating appliance (FS) on the incidence proportion of orthodontic emergencies. These results might provide orthodontists with appropriate measures to reduce the probability of orthodontic emergencies and patients to avoid potential risks during orthodontic treatment.

Material and methods

This study was approved by the Ethics Committee of Stomatological Hospital of Chongqing Medical University. The screening questionnaire was designed on the basis of emergencies in orthodontics. Besides age, sex, and the types of appliances used, additional questions intended to reveal types and incidence proportion of orthodontic emergency, including bracket, band or attachment detachment, mucosa injury because of orthodontic appliances, accidental appliance or attachment ingestion or aspiration, and other orthodontic emergencies. Although data were obtained through patient self-reports, the follow-up medical records of the patients were checked to complement the results. Recall bias was applied to evaluate the consistency of the self-report. Twenty patients with FS and 20 with clear appliances were randomly selected to finish the questionnaire a second time 1 month later.

Inclusion criteria consisted of people undergoing orthodontic treatment without systemic diseases at the orthodontic clinic of Stomatological Hospital of Chongqing Medical University during the pandemic prevention and control period in 2020. In the survey, the patients and their parents or guardians were informed about the aim of the study, its privacy policy, and their right to refuse to participate. The patients were asked to complete the questionnaire on the basis of the past 12-month situation in 2020 after giving their informed consent. The ages of respondents between were 12 and 38 years (20.4 ± 7.03).

Statistical analysis

The associations were considered statistically significant if P <0.05. The consistency of the subjects’ questionnaire was also analyzed. A regression model was done to compare the effect of appliance type while controlling for potential confounders such as age and gender. All analyses, including descriptive analysis, chi-square test, were performed using the SPSS (version 18.0; SPSS Inc, Chicago, Ill).


This survey received feedback from 428 respondents, including 81 patients treated by CA and 327 patients treated by FS ( Table I ). To evaluate the consistency, 40 patients were randomly selected for a second questionnaire survey. The self-reports were consistent. The study consisted of 137 males and 291 females. The male group showed a slightly higher incidence proportion of appliance detachment. The female group showed a higher incidence proportion of mucosa injury. However, both groups showed an equal incidence proportion of accidental ingestion. The adolescents exhibited a higher incidence proportion of emergency than the adults.

Table I
Incidence of orthodontic-related emergency
Variables Respondent Total emergency Appliance detachment Mucosa injury Accidental ingestion Other emergency
Male 137 96 (70.07%) 76 (55.47%) 61 (44.53%) 9 (6.57%) 1 (0.73%)
Female 291 218 (74.91%) 151 (51.89%) 150 (51.55%) 20 (6.87%) 6 (2.06%)
Adolescent 211 166 (78.67%) 134 (63.51%) 106 (50.24%) 9 (4.27%) 3 (1.42%)
Adult 217 148 (68.20%) 93 (42.86%) 105 (48.39%) 20 (9.22%) 4 (1.84%)
CA 81 29 (35.80%) 17 (21%) 12 (14.8%) 6 (7.4%) 0 (0.00%)
FS 347 285 (82.13%) 210 (60.5%) 199 (57.3%) 27 (7.8%) 7 (2.0%)
Total 428 314 (73.36%) 227 (53%) 211 (49.3%) 29 (6.8%) 7 (1.6%)

This study investigated the incidence proportion and degree of emergency in orthodontic patients in 2020 ( Table 1 , linear regression analysis in the Supplementary Table ). Orthodontic-related emergencies included 4 categories: mucosa injury because of displaced archwire or prolapsed orthodontic ligation wire, detached orthodontic appliances or attachments, ingestion and aspiration of appliances, attachments, or other accidental small accessories, and other emergencies. The incidence proportion of mucosa injury in the CA group was 14.8%, and in the FS group was 57.3%. The incidence proportion of detached clear attachments in the CA group was 21%; however, the incidence proportion of detached orthodontic appliances in the FS group was 60.5%. The incidence proportion of accidental ingestion was 7.4% and 7.8% in the CA and FS groups, respectively. There was no accidental aspiration in both groups. Other emergencies, such as the archwire breaking, occurred at a low incidence and only in the FS group. According to the above results, the incidence proportion of mucosa injury and orthodontic appliance detachment was much higher in the FS group than in the CA group. Although the 2 groups had a lower probability of appliances or attachments or accessories accidental ingestion, the FS group was slightly higher than those in the CA group.

The degree of orthodontic-related emergency was also analyzed ( Table II ). On average, mucosa injuries occurred 0.15 times in the CA group and 1.45 times in the FS group within 1 year. In the CA group, 0.37 attachments fell off, whereas 1.51 appliances fell off in the self-ligating group within 1 year. The CA and FS groups had a similar degree of accidental ingestion, respectively 0.14 and 0.15 foreign body. Other emergencies occurred only in the self-ligating bracket, on average, 0.02 times within 1 year.

Table II
Analysis of the degree of orthodontic-related emergency
Respondents n No. AD Average No. AD No. MJ Average No. MJ No. AI Average No. AI No. OE Average No. OE
CA 81 30 0.37 12 0.15 11 0.14 0 0
FS 347 525 1.51 503 1.45 51 0.15 7 0.02
Total 428 555 1.3 515 1.21 62 0.14 7 0.016
AD, appliance detachment; MJ, mucosa injury; AI, accidental ingestion; OE, other emergency.

The causes of the detachment of appliances were divided into 5 categories ( Table III ), including chewing hard food, occlusal interference, the impact of external forces, accidental detachment, and other reasons. Chewing hard food was the main reason for attachment or appliance detachment, with an incidence of 14.81% in the CA group and 48.7% in the FS group. The incidence of appliance detachment in the FS group was 12.68%, which indicated that accidental detachment was the second important cause of appliance detachment. The incidence proportion of appliance detachment because of other reasons was low.

Table III
Analysis of the cause of appliance detachment
Respondents Hard food Occlusion Injury Accidental detachment Other reasons
CA 12 (14.81%) 4 (4.9%) 0 (0.0%) 3 (3.7%) 0 (0.0%)
FS 169 (48.7%) 30 (8.6%) 5 (1.4%) 44 (12.68%) 1 (0.3%)
Total 181 (42.28%) 34 (7.94%) 5 (1.17%) 47 (10.98%) 1 (0.23%)

Given the degree of appliance detachment, chewing hard food was still the main cause of the detachment of attachments or appliances ( Table IV ). In the CA group, 0.21 attachments fell off per person because of hard food, whereas 1.19 appliances fell off in the FS group because of hard food.

Table IV
Analysis of the degree of appliance detachment
Respondents Hard food Occlusion Injury Accidental detachment Other reasons
n Average n Average n Average n Average n Average
CA 17 0.21 6 0.074 0 0 6 0.074 0 0
FS 413 1.19 43 0.124 7 0.02 61 0.176 1 0.003
Total 430 1 49 0.114 7 0.164 67 0.157 1 0.002

The position of attachments or appliance detachment was also analyzed ( Table V ). The CA group showed a similar degree of detachment in the maxillary and mandibular dental arch. In contrast, the self-ligating group showed much higher detachment of appliances in the mandibular dental arch.

Table V
Analysis of the position of appliance detachment
Respondents Maxillary arch (no. of respondents) Mandibular arch (no. of respondents) Maxillary arch (no. of appliances) Mandibular arch (no. of appliances)
CA 12 11 15 15
FS 121 157 208 317
Total 133 168 223 332

Linear regression analysis was done. It was found that female patients were more likely to be uncomfortable because of mucosal injury than male patients ( P = 0.010 and P <0.05), and young patients were more likely to encounter appliance detachment than older ones ( P <0.001) ( Supplementary Table ).

Because no patients had accidental aspiration, we only show the data of accidental ingestion in Tables VI-VIII . Combined with the literature, the accidental aspiration caused by orthodontic treatment was rare. The CA and FS groups had a similar amount of accidental ingestion, 0.135 and 0.147 foreign bodies. The main foreign body by ingested in both groups was elastics, which are relatively safe. The self-ligating group could ingest broken metal archwire, miniscrews, and welding accessories. Although the probability was not high, these might cause more serious consequences.

Table VI
Analysis of accidental ingestion
Respondents n Respondents with accidental ingestion Accidental ingestion appliances
CA 81 6 7.4% 11 0.135
FS 347 27 7.8% 51 0.147
Total 428 33 7.71% 62 0.145
IAI, incidence of accidental ingestion; ANAI, average number of accidental ingestion.

Table VII
Type of appliance in accidental ingestion
Respondents Archwire Bracket Miniscrew Welded attachment Band Spring Elastic Other appliance Total
CA 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 0 (0.0%) 4 (4.94%) 2 (2.47%) 6 (7.4%)
FS 6 (1.73%) 2 (0.58%) 1 (0.29%) 1 (0.29%) 0 (0.0%) 0 (0.0%) 15 (4.32%) 2 (0.58%) 27 (7.8%)
Total 6 2 1 1 0 0 19 4 33

Table VIII
The degree of accidental ingestion
Appliances Archwire Bracket Miniscrew Welded attachment Band Spring Elastic Other appliance Total
CA 0 0 0 0 0 0 8 3 11
FS 7 3 1 1 0 0 37 2 51
Total 7 3 1 1 0 0 45 5 62

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