Abstract
Objective
To compare the levels of functional impairments, discomfort and satisfaction experienced by those treated with full-mouth customized lingual appliances (Lingual appliances), full-mouth self-ligating bracket (Labial appliances), or upper lingual and lower labial appliances (Mixed appliances) using questionnaires.
Materials and methods
Patients within one year of the end of treatment were included in the survey and given a questionnaire concerning different kinds of discomfort and difficulties during the treatment process. The questionnaires focused on the following aspects including speech difficulty, pain (lip, cheek or tongue), difficulty in chewing, difficulty in tooth brushing and overall aesthetics and comfortability. Ordinary one-way ANOVA Tukey’s multiple comparison tests and Kruskal–Wallis tests were employed to analyze the data.
Results
A total of 115 patients participated in the study. In terms of functional impairments and discomfort, the rate and degree of speech difficulty was significantly higher in the Lingual appliances Group than that in the Labial appliances Group. But there was no difference among the three groups for difficulty in chewing and tooth brushing. Both lingual and labial appliances caused a similar level of overall pain, however, those treated with lingual appliances experienced more tongue pain, and those treated with labial appliances experienced more cheek and lip pain. The most common sites of irritation were the tongue lateral and tongue tip in the Lingual appliances Group, tongue lateral and cheek in the Mixed appliances Group, and cheek and lower lip in the Labial appliances Group. In total, patients gave highest scores to mixed appliances for comfortability and lowest scores to labial appliances for aesthetics when it came to satisfaction.
Conclusions
Lingual and labial appliances caused similar level of overall pain. Taking into account the overall comfortability, aesthetics and cost, the mixed appliances may be suitable for some patients who have aesthetic and comfort pursuits.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12903-024-05041-8.
Keywords: Lingual appliances, Labial appliances, Pain, Satisfaction
Background
Malocclusion has a high prevalence around the world and fixed labial orthodontic appliance has been used in clinic for a long time since the introduction of orthodontics. As a traditional orthodontic appliance, a large number of clinical practices and studies have proved its effectiveness [1, 2]. However, labial appliance has some obvious disadvantages including aesthetics and mucosal irritation, which makes it difficult to be accepted for increasing number of adult patients [3].
Since the introduction of lingual appliances by FUJITA [4], there has been significant progress in their design, manufacturing, and clinical application. The advantages of lingual appliances include lower noticeability, fewer white spot lesions and caries on the buccal surface of teeth, smaller anchorage loss ensuring more stable and predictable treatment outcomes, and increased comfort [5]. However, several surveys reported increasing plaque index, tongue soreness and speech difficulty after the bonding of lingual orthodontic appliances [6, 7]. With the diversification of people's needs and the development of orthodontic technology, some clinicians choose upper lingual appliance and lower labial appliance due to the comprehensive consideration of aesthetics, comfortability, and cost.
However, there still lack of surveys on the discomfort and satisfaction of fixed labial orthodontic appliance, lingual appliance and upper lingual-lower labial appliance. Since this mainly involves patients' subjective feelings, we designed questionnaires to investigate the discomfort and satisfaction of patients wearing these three different appliances, aiming to compare the levels of functional impairments, discomfort and satisfaction experienced by those treated with full-mouth customized lingual appliances, full-mouth self-ligating bracket, or Mixed appliances.
Methods
Subjects and inclusion criteria
Patients within one year of the end of treatment (17 males and 98 females, total 115 patients) who visited Shanghai Ninth People's Hospital were included in the survey. All the subjects had already been treated with full-mouth customized lingual appliances (Lingual appliances, n = 36), full-mouth customized self-ligating bracket (Labial appliances, n = 38), or upper lingual and lower labial appliances (Mixed appliances, n = 41) (Fig. 1). All patients' orthodontic appliances are crafted using CAD/CAM technology. Initially, a digital setup is performed in accordance with the treatment plan. Subsequently, based on the outcomes of the setup, the brackets are customized using CAM technology. The lingual bracket is fabricated using 3D printing technology, whereas the labial bracket is created through a combination of CNC machining and 3D printing. All archwires are customized and processed by a bending robot.
Fig. 1.
Three different appliances involved in this study. A Full-mouth customized lingual appliances (Lingual appliances). B Customized upper lingual and lower labial appliances (Mixed appliances). C Customized full-mouth self-ligating bracket (Labial appliances)
The inclusion criteria included the following: 1) first orthodontic treatment; 2) older than 18 years of age; 3) no use of transpalatal arch (TPA), expansion and occlusal pad; 4) non-surgical treatment. All patients had been given instructions on the on teeth brushing, diet and orthodontic protective wax. All patients received comprehensive orthodontic treatment of at least one year of active treatment time by orthodontists with more than 10 years of experience.
This study was approved by the Institutional Review Board of Shanghai Ninth People’s Hospital affiliated to Shanghai Jiao Tong University, School of Medicine (SH9H-2023-T71-1). This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement [8].
Contents of questionnaire survey
All patients were given a questionnaire concerning different kinds of discomfort and difficulties during the treatment process. Sex, age information and treatment time was collected first. The contents of the questionnaire mainly included the following aspects:
Speech difficulty
Pain (lip, cheek or tongue)
Difficulty in chewing and tooth brushing
Overall aesthetics and comfortability
The questions covered the period of the speech difficulty and appliance adaption, the main site of pain stimulation and the most obvious site of irritation. Likert scales were employed to describe the levels of pain and difficulty. Visual analogue scales (VAS) were used to describe the overall aesthetic and comfortability of the appliance. An additional movie file shows this in more detail (see Additional file 1).
Statistical analysis
Rate of occurrence of each form of discomfort in each group was calculated in this study. Data were analyzed with the use of GraphPad Prism 9.0.0 software (GraphPad, La Jolla, CA, USA). Ordinary one-way ANOVA Tukey’s multiple comparison test was applied to compare continuous data in three groups. Percentages were statistically compared using the Chi-square test and Likert scales were analyzed with Kruskal–Wallis tests. P < 0.05 indicated a significant difference between groups.
Results
Description of subjects and study
Demographics of subjects were shown in Table 1. A total of 115 people took part in the survey. There was no significant difference in gender ratio among the three groups with Chi-square tests. The mean age was lower in Labial appliance Group than that in the other two groups. The mean treatment time was also listed in the table.
Table 1.
Subjects demographics
| Group | Gender (Male: Female) | Age | N | Treatment time |
|---|---|---|---|---|
| Lingual appliances | 3:33 | 27.6 | 36 | 25.5 ± 5.6 |
| Mixed appliances | 5:36 | 28.2 | 41 | 24.9 ± 6.3 |
| Labial appliance | 9:29 | 24.3 | 38 | 23.7 ± 5.4 |
| Total | 17:98 | 26.7 | 115 | / |
The rate and level of each form of discomfort in each group were described in Tables 2 and 3.
Table 2.
Rate (%) of occurrence of each form of discomfort in each group
| Discomfort | Group | ||
|---|---|---|---|
| Lingual appliances | Mixed appliances | Labial appliance | |
| Speech difficulty | 91.67 | 87.80 | 71.05 |
| Pain | 97.22 | 82.93 | 94.74 |
| Lip | 52.75 | 65.85 | 76.32 |
| Cheek | 50.00 | 70.73 | 86.84 |
| Tongue | 94.44 | 73.17 | 50.00 |
| Difficulty in chewing | 86.11 | 85.37 | 94.74 |
| Difficulty in tooth brushing | 97.22 | 95.12 | 97.37 |
Table 3.
Percentage of patients reporting discomfort according to the level in each group (Likert scale)
| Discomfort | Level | ||||
|---|---|---|---|---|---|
| 1(None) | 2(Mild) | 3(Moderate) | 4(Obvious) | 5(Severe) | |
| Speech difficulty | |||||
| Lingual appliances | 8.33 | 27.78 | 30.56 | 30.56 | 2.78 |
| Mixed appliances | 12.20 | 56.10 | 19.51 | 12.20 | 0 |
| Labial appliance | 28.95 | 28.95 | 21.05 | 18.42 | 2.63 |
| Pain | |||||
| Lingual appliances | 2.78 | 13.89 | 47.22 | 36.11 | 0 |
| Mixed appliances | 17.07 | 41.46 | 39.02 | 2.44 | 0 |
| Labial appliance | 5.26 | 36.84 | 34.21 | 15.79 | 7.89 |
| Lip pain | |||||
| Lingual appliances | 47.22 | 44.44 | 2.78 | 5.56 | 0 |
| Mixed appliances | 34.15 | 43.90 | 12.20 | 9.76 | 0 |
| Labial appliance | 23.68 | 31.58 | 26.32 | 18.42 | 0 |
| Cheek pain | |||||
| Lingual appliances | 50 | 33.33 | 11.11 | 5.56 | 0 |
| Mixed appliances | 29.27 | 36.59 | 26.83 | 7.32 | 0 |
| Labial appliance | 13.16 | 36.84 | 23.68 | 26.32 | 0 |
| Tongue pain | |||||
| Lingual appliances | 5.56 | 11.11 | 44.44 | 27.78 | 11.11 |
| Mixed appliances | 26.83 | 26.83 | 29.27 | 17.07 | 0 |
| Labial appliance | 50.00 | 28.95 | 13.16 | 5.26 | 2.63 |
| Difficulty in chewing | |||||
| Lingual appliances | 13.89 | 13.89 | 38.59 | 33.33 | 0 |
| Mixed appliances | 14.63 | 34.15 | 34.15 | 17.07 | 0 |
| Labial appliance | 5.26 | 36.84 | 18.42 | 28.95 | 10.53 |
| Difficulty in tooth brushing | |||||
| Lingual appliances | 2.78 | 11.11 | 41.67 | 38.89 | 5.56 |
| Mixed appliances | 4.88 | 29.27 | 36.59 | 29.27 | 0 |
| Labial appliance | 2.63 | 18.42 | 39.47 | 39.47 | 0 |
Speech difficulty
91.67% of the patients in the Lingual appliances Group, 87.8% of the patients in Mixed appliances Group and 71.05% of the patients in Labial appliances Group reported speech difficulty. Rate of speech difficulty was much higher in the Lingual appliances Group than that in Labial appliances Group (P = 0.036). There was also a significant difference in the level of speech difficulty between the two groups (P = 0.0369), with 63.9% of patients in Lingual appliances Group reporting moderate to severe difficulty, while 57.9% of patients in Labial appliances Group reporting none to mild difficulty.
The duration of speech difficulty was also investigated in this survey and the results showed that duration of speech difficulty in the Lingual appliances Group lasted longer than that in the Labial appliances Group (P = 0.0406) (Fig. 2). 42.42% of the patients in the Lingual appliances Group and 33% of the patients in Labial appliances Group reflected speech difficulty for more than 3 months, but only 22.22% of the patients in Mixed appliances Group claimed speech difficulty for more than 3 months. While the rate, level, and duration of speech difficulty reported by Mixed appliances Group showed no statistical difference from the other two groups.
Fig. 2.
Duration of speech difficulty
Pain
Nearly all subjects in Lingual appliances Group reported tongue pain (94.44%), but only half reported pain of lip (52.75%) and cheek (50.00%). 65.85% of the subjects in Mixed appliances Group reflected lip pain and similar subjects reflected cheek pain (70.73%) and tongue pain (73.17%). While only half of subjects in Labial appliances Group reported tongue pain, but more reported pain of lip (76.32%) and cheek (86.84%).
Patients in Lingual appliances Group (P < 0.0001) and Labial appliances Group (P = 0.0441) described higher level of pain than Mixed appliances Group as a whole. To be specific, 91.66% and 83.88% of the subjects in Lingual appliances Group had none to mild lip or cheek pain. The level of lip and cheek pain was much lower than that in Labial appliances Group (P = 0.0044 and P = 0.0003, respectively). However, the level of tongue pain in Lingual appliances Group was more obvious than that in Mixed appliances Group (P = 0.0033) and Labial appliances Group (P < 0.0001). 83.33% of the subjects in Lingual appliances Group, 46.34% of the subjects in Mixed appliances Group and 21.05% of the subjects in Labial appliances Group claimed moderate to severe tongue pain.
The main site of pain stimulation in the three groups displayed obvious differences (Fig. 3) and 75% of subjects in the Lingual appliances Group chose lingual as main site of pain stimulation. The most obvious sites of the irritation were tongue lateral (80.56%) and tongue tip (27.78%) in Lingual appliances Group, tongue lateral (60.98%) and cheek (31.71%) in Mixed appliances Group, cheek (60.53%) and lower lip (36.84%) in Labial appliances Group (Fig. 4).
Fig. 3.
The main site of pain stimulation
Fig. 4.
Most obvious site of the wear irritation
Difficulty in chewing, tooth brushing and adaptation time
There was no difference among the three groups for difficulty in chewing and tooth brushing (Tables 2 and 3). There was also no statistical difference in the time it took to adjust to the appliance among the three groups as well (Fig. 5). 41.67% of the subjects in Lingual appliances Group, 68.29% of the subjects in Mixed appliances Group and 65.79% of the subjects in Labial appliances Group could adjust to the appliances within one month.
Fig. 5.
Time required to adjust to the appliances
Satisfaction of comfortability and aesthetics
Subjects in Mixed appliances Group and Lingual appliances Group gave higher scores for aesthetics of appliances than Labial appliances Group with VAS scores. There was no difference between Mixed appliances Group and Lingual appliances Group on aesthetics. For comfortability of appliances, subjects in Mixed appliances Group gave the highest scores, Labial appliances Group the second, and Lingual appliances Group the lowest (Fig. 6).
Fig. 6.
VAS scores for comfortability and aesthetic of appliance. A VAS scores for comfortability of appliance. B VAS scores for aesthetic of appliance
Discussion
Today's society is a humanistic society. At present, there are many studies focusing on the treatment effect of appliance, focusing on the measurement and analysis before and after treatment, but there are few studies focusing on the subjective feeling of patients. Understanding the patient's subjective feelings including pain when using different appliances and understanding the patient's treatment needs is helpful to the selection and improvement of appliances.
In our study, we found that 91.6% and 87.8% of women chose lingual or mixed appliances, respectively. According to previous research, the patients receiving customized lingual appliances are mainly in the age range of 20–40 years old. Compared to labial appliances, women under 40 years old prefer lingual appliances, and patients mainly seek orthodontics treatment based on aesthetic needs [9]. The mean age was lower in the Labial appliances Groups than the other two, which is consistent with the current clinical situation as older persons tend to prefer invisible appliances. However, there is another issue that needs our attention, anxious patients tend to prefer invisible appliances [10].
Based on the information gathered from the questionnaires, lingual appliances are more likely to cause speech difficulty. Multiple studies have shown that lingual appliances are associated with increased speech difficulty [11]. A systematic literature review included 13 studies and found that lingual fixed appliances had an evident influence on speech and the /i/, /s/, /t/, and /d/ sounds were the primarily affected ones [12]. The tongue is the most flexible articulatory organ in the mouth. Its prominent function is to change the shape of the oral resonator through its activity to produce different sounds. Lingual fixed appliances limit the activity of the tongue to a certain extent, so it is easy to understand why they are more likely to cause speech difficulty compared with labial fixed appliances. According to the research, the phonetic-functional adaptation period was 1–3 weeks in lingual patients [9]. However, aligner appliances can also cause speech interference. These speech difficulties were temporary and most patients recovered in 7–14 days in aligner patients [13].
Pain is common in orthodontic treatment regardless of the type of appliance used. The most obvious sites of the irritation were tongue lateral with lingual appliances and cheek with labial appliances. A prospective longitudinal study compared pain experiences among Chinese adult patients treated with labial and lingual orthodontic appliances and draw the same conclusions with us that labial and lingual appliances caused similar level of overall pain [7]. Research has shown that tongue pain from lingual appliance was similar to buccal and lip irritation brought by the labial appliance [6, 14]. However, there are also studies that suggest that patients treated with lingual appliances reported more oral pain [15], and some other studies found that patients treated with lingual appliances experienced less pain compared with those with labial appliances [16], which is controversial. Since many previous studies were conducted 20 years ago, lingual appliances were standard brackets and resin base at that time, and the volume of braces was generally large. Now, lingual appliances are customized manufactured with 3D printing, reducing the volume of brackets by 35%, thus improving the comfortability of lingual appliance [17]. Therefore, compared to traditional lingual appliances, the comfort of contemporary customized lingual appliances has significantly improved, with 87% of patients willing to recommend lingual appliances to their relatives and friends [9].
When it comes to teeth brushing, there was no significant difference in perceived difficulty among the three types of appliances. Labial appliances have been found to lead to demineralization of the tooth surface [18], while lingual appliances do not usually cause enamel demineralization due to the thicker lingual enamel and increased saliva production [19]. However, the lingual appliances are more likely to cause swelling of the gingiva. Oral hygiene guidance is essential during orthodontic treatment.
Patients reported more trouble with chewing in the Labial appliances Group, though no significant difference was observed. Only a few studies on masticatory problems of patients undergoing orthodontic treatment have been constructed. According to a meta-analysis, lingual appliances had a greater impact on chewing than labial appliances, although the evidence was low to very low [20]. It could be inferred that lingual appliances can often lead to occlusal interference in the anterior teeth after braces are bonded, so the proportion of occlusal raise may be higher when lingual appliances are initially bonded. For labial appliances, the occlusal interference mainly occurs when the buccal cusp of maxillary posterior teeth bites into the mandibular posterior brackets. The functional cusp of maxillary posterior teeth is the lingual cusp, so labial appliances have little effect on chewing as long as there is no interference from the buccal cusp. Other possible causes of disturbed chewing include pain, dietary restriction and food impaction, resulting in a decrease in subjective food intake ability [21, 22].
There are also some shortcomings in our research. We only compared three sets of fixed appliances in this study and did not compare aligner appliances. According to previous research, patients undergoing aligner therapy reported the overall highest quality of life (QoL) scores, followed by lingual and labial groups [23]. Compared to fixed appliances, invisible appliances have better comfort and oral hygiene [24, 25]. On the other hand, the small sample size, lack of sample homogeneity (in terms of sex, DOD, type of malocclusion, etc.), absence of prior questionnaire validation, inconsistent active treatment durations, and the challenge of recalling pain and discomfort after a year could limit the generalizability of these findings to the broader orthodontic population.
Mixed appliance may be a balanced choice due to its higher comfortability and aesthetics. It combines the advantages of labial and lingual appliances. The maxillary lingual orthodontic ensures aesthetics, while the use of a labial orthodontic in the mandible reduces irritation to the tongue and speech difficulty. Moreover, mixed appliance is cheaper than lingual appliance and offers relatively higher cost performance. However, there are limited studies on labial appliance at present, so more evidence is needed to confirm its optimal efficiency.
Conclusions
Based on the information gathered, lingual appliances are more likely to cause speech difficulty. Lingual and labial appliances caused similar level of overall pain, while patients treated with lingual appliances experienced more tongue pain and patients treated with labial appliances experienced more cheek and lip pain. Patients treated with mixed appliance reported the lowest level of pain in general.
Supplementary Information
Acknowledgements
Not applicable.
Availability of data and material
Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.
Authors’ contributions
YLJ and DT analyzed the data and was a major contributor in writing the manuscript. LL and OYLJ contributed to the collection and analysis of the data. YNS revised the manuscript. FB was the major contributor in the conception of the study. All authors read and approved the final manuscript.
Funding
This study was supported by the Clinical Research Plan of SHDC (No. SHDC2020CR3009A), the National Natural Science Foundation of China (Grants Nos. 82301075) and Fundamental research program funding of Ninth People's Hospital affiliated to Shanghai Jiao Tong University School of Medicine (JYZZ178).
Data availability
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
This study was approved by the Institutional Review Board of Shanghai Ninth People’s Hospital affiliated to Shanghai Jiao Tong University, School of Medicine (SH9H-2023-T71-1) and informed consent was obtained from all subjects and/or their legal guardian(s).
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Lingjun Yuan and Ting Dong share first authorship.
Contributor Information
Niansong Ye, Email: yns119@126.com.
Bing Fang, Email: fangbing@sjtu.edu.cn.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.