Comparison of orthodontic adverse effects: braces versus clear aligners

1. Introduction

The aim of the modern orthodontics has been summarized as achieving acceptable facial aesthetics and appropriate occlusal relationships. Since Dr. Andrews developed the straight-wire appliance system, the fixed orthodontic treatment technique (FOT) has been the most preferred method for orthodontic treatment [1]. Compared to-conventional braces used in conventional orthodontic treatments, the clear aligner therapy (CAT) was developed to find aesthetic solutions for orthodontic patients [2]. Orthodontic treatment with braces or clear aligners may have several adverse effects such as pain, root resorption and periodontal problems. Furthermore, the treatment may also affect the patient’s chewing and speech functions, leading to changes in their quality of life [3].

Brandon et al. [4] and Jianru Yi et al. [5] reported less root resorption with clear aligners therapy. On the other hand, Al Zainal et al.[6] stated that clear aligners were not effective in preventing orthodontically-induced root resorption.

Issa et al. [7] and Jiang et al. [8] compared periodontal parameters between patients treated with braces and clear aligners and showed that patients treated with clear aligners presented better periodontal results. However, Pango et al. [9] found no significant difference in terms of periodontal health between these two orthodontic methods.

Although many studies have evaluated the potential side effects of FOT and CAT, there is no consensus on the superiority or certain advantages of these techniques in terms of their adverse effects in comparison to each other in the literature. Therefore, this study aimed to compare the effects of FOT and CAT on root resorption, periodontal status, pain experience and chewing performance. The null hypothesis states that there would be no difference between the two orthodontic treatment methods in these parameters.

2. Materials and methods

The study was conducted at Bezmialem Vakif University between April 2020 and August 2022.

The inclusion and exclusion criteria are listed below:

Inclusion criteria: (1) patients treated with fixed braces or clear aligners, (2) patients with mild to moderate crowding, (3) patients without root canal treatment or resorption in anterior teeth, (4) patients with completed root development, (5) patients with good periodontal health at the beginning of the treatment, and (6) patients with no congenitally missing or impacted tooth.

Exclusion criteria: (1) history of orthodontic therapy, (2) poor patient compliance, (3) presence of any craniofacial syndrome or systemic disease, (4) presence of cleft lip and palate, (5) trauma history, (6) mental retardation, (7) use of oral antiseptic solutions during orthodontic treatment, (8) need for scaling and root planning during treatment, or (9) clear aligner patients with delayed movement of the anterior teeth.

The power analysis performed at the beginning of the study showed that at least 18 patients was necessary in each group to provide more than 85% power to detect significant differences with an effect size of 0.80 and a significance level of α = 0.05.

A total of 58 patients were included in this study based on the inclusion criteria. The patients were randomly divided into two groups according to the method of orthodontic treatment using the coin toss technique: the fixed orthodontic treatment and the clear aligner therapy groups.

7 patients from the FOT group and 2 patients from the CAT group were excluded from the study due to bracket or attachment failure, poor oral hygiene, interruption of treatment, poor cooperation, or the patient’s failure to keep orthodontic appointments. Finally, 22 patients (14 females, 8 males; mean age: 17.05 ± 4.51 years) who underwent fixed orthodontic therapy were included in the FOT group and 27 patients (20 females, 7 males; mean age: 22.57 ± 7.37 years) who underwent clear aligner therapy were included in the CAT group.

The patients were treated by senior assistants in the orthodontics department, and the analyses of the data were performed by the same researcher (I.E.M). All patients received the same oral hygiene instructions before and during the orthodontic treatment.

In both groups, leveling and alignment was performed without extractions and nor inter proximal reduction (IPR).

The patients in the CAT group had mean anterior crowding of 1.73 mm and 1.95 mm for the upper and lower arches, respectively. In the FOT group, the patients had mean anterior crowding of 1.54 mm and 2.03 mm for the upper and lower arches, respectively. There was no significant difference between the two groups in terms of the amount of crowding for the upper and lower arches (p > 0.05).

The patients in FOT were treated with 0.018-inch slot metal Roth brackets (Mini Master Series, American Orthodontics, USA). The arch wire sequence involved conventional 0.014-inch Ni-Ti, 0.016-inch Ni-Ti, and 0.016 × 0.022-inch Ni-Ti wires according to the patients’ needs. The patients in CAT were treated with the Invisalign® system and anterior teeth movement started from the first pair of aligners. Microfill (Filtek A110 (AO), (3M-ESPE)), and brace paste primers were used for bonding the attachments. The patients changed their aligners every 2 weeks.

2.1 Radiographic evaluation

Pretreatment (T0) digital lateral cephalometric radiographs were taken from the patients to compare pretreatment characteristics between the groups. All cephalograms were traced by the same researcher using the NemoCeph software version 10.4.2 (Software Nemotec, SL, Madrid, Spain).

The digital periapical radiographs taken with the paralleling technique were obtained from the maxillary and mandibular incisors at the beginning of the treatment (T0) and after 6 months (T2) by the same dental radiologist for root resorption assessments. Linear measurements to evaluate root resorption were performed using the method which was reported by Lago et al. [10]. Digital periapical X-rays were imported into the ImageJ software (ImageJ software1.37, Maryland, USA). The calibration was performed using the Set Scale function on the ImageJ toolbar. When the setting procedure was completed, the program automatically calculated the distance based on the registered parameters. The closest linear distance from the center of the incisal edge to the root apex was used for tooth length measurements (Fig. 1).

Fig. 1.Root length measurement method.

3. Results

The comparison of the demographic characteristics of the groups at T0 are demonstrated in Table 1. The patients’ cephalometric and occlusal characteristics were similar at the baseline. There was no difference in the amount of crowding for the maxilla and mandible between groups (p > 0.05). The mean age was found higher in CAT than FOT group.

4. Discussion

The objective of this study was to assess and compare the potential adverse effects of FOT and CAT on root resorption, periodontal status, pain experience, and chewing performance.

Periapical radiographs taken using the paralleling cone technique were used to optimize magnification errors and eliminate false negative or false positive changes in measured root lengths. Gupta et al. [17] reported that periapical radiographs provide accurate data for actual tooth dimensions regardless of the patient’s head position. Similarly to our study, Lago et al. [10] evaluated root resorption using cone-beam computed tomography (CBCT) and periapical X-rays after 6 months of orthodontic treatment on maxillary incisors. They revealed that both radiographic methods are suitable and reliable in the assessment of external root resorption. They concluded that the difference in magnitude between the measurements obtained using these radiographic methods does not justify requesting CBCT merely to assess external root resorption.

Among radiographic techniques, the accuracy of CBCT is higher than that of periapical radiography, and the accuracy of periapical radiography is higher than that of panoramic radiography in the detection of root resorption [18, 19]. On the other hand, Parrales-Bravo et al. [20] highlighted that both CBCT and periapical radiographs are good diagnostic methods for external root resorption. Furthermore, Zamani et al. [21] aimed to compare the absorbed dose and lifetime cancer risk between CBCT and panoramic X-rays on 332 patients and reported that CBCT had a significantly higher level of radiation risk.

The concept of “as low as reasonably achievable” (ALARA) should be adopted in dental imaging both for the patient and the clinician [22]. Therefore, to limit the harmful effects of ionizing radiation on patients, periapical X-ray imaging procedures using the paralleling cone technique were used to evaluate root resorption in this study.

Leveling and alignment generally constitute the first stage of orthodontic treatment. A previous study showed that the mean duration of the leveling and alignment of mild to moderate crowding without extraction was 6 months [23]. Therefore, in our study, the groups were compared following a 6-month observation period.

The root lengths of maxillary and mandibular anterior teeth were evaluated at the beginning of the treatment and at the end of the 6-month observation period. Accordingly, the degree of root resorption was markedly higher in FOT than in CAT (p < 0.05) (Table 2).

Clear aligners generate intermittent forces as they are occasionally removed during food consumption and hygiene maintenance [24]. Sawicka et al. [25] evaluated root resorption variations using continuous and discontinuous forces during orthodontic treatment and observed less resorption with intermittent forces because the intermittent force provided cementum the time to heal. If clear aligner treatment plans are designed well by orthodontists, they can help providing predictable tooth movement and avoid jiggling to reduce root resorption compared to fixed orthodontic treatments [26].

Brandon et al. [4] reported higher amounts of root resorption in the upper and lower incisors in the fixed treatment group than in the clear aligner group. Jianru et al. [5] also found that clear aligner therapy induced less risk for apical root resorption compared to fixed orthodontic treatment in the upper and lower incisors in non-extraction patients. Li et al. [27] reported that, the prevalence of apical root resorption in patients with clear aligners were lower than those in patients with fixed appliances.

The highest pain scores were recorded at the 24th hour of the treatment in both groups. Diddige et al. [28] also found the highest pain levels at 24th hours in both methods, and these pain levels gradually dropped to the baseline levels by the 7th day. It was reported that clear aligners apply lower forces on the 7th and 14th days compared to the initial levels [24].

The secretion of neuropeptides such as Calcitonin Gene-Related Peptide and Substance P, which stimulate the secretion of proinflammatory cytokines increases after the application of orthodontic forces during the first 2 days of treatment [29]. These biochemicals reduce the pain threshold by disrupting the mechanism in the nerve endings going into the periodontal ligament during the first two days after the initiation of orthodontic forces [30]. In this study, the decline in the perceived pain levels of the patients occurred in a shorter time in CAT compared to FOT (Table 3).

As stated in the literature, aligners can be removed by patients when they feel pain to relieve this pain, and the decrease in the perceived pain levels of patients was faster in CAT [31].

Almasoud et al. [32] and reported less pain in the clear aligner group in the first week of orthodontic treatment compared to the fixed orthodontic treatment group. Gao et al. [33] found that patients treated with clear aligners experienced lower pain levels in comparison to those receiving fixed orthodontic treatment. These findings were similar to those of our study.

The maximum discomfort scores in chewing performance in our study were also recorded at the 24th hour for both groups. This finding can be explained by the high pain levels at the 24th hour of treatment. Moreover, while the chewing function of the patients in the FOT group improved after the 1st week, it improved after the 2nd week in the CAT group.

Gameiro et al. [34] reported that a significant increase in pain was observed during chewing at 24 hours after the activation of the appliances, and this was significantly correlated with a decrease in their masticatory performance of the patients. The findings of their study were consistent with our findings.

Computerized analysis methods such as T-Scan® can provide accurate and repeatable occlusion recordings [35]. The number of contact points, occlusal force parameters during centric occlusion and lateral movements, occlusion and disocclusion times, and temporomandibular joint diseases can also be evaluated using various methods [36]. Moreover, a correlation was reported between surveys and VAS, which are more inexpensive, more practical, and objective methods [37]. The studies mentioned above suggested that subjective methods can be used to evaluate masticatory functions. In our study, the survey used in the study by Stamm et al. [15] was used to evaluate the chewing performance.

In support of our finding, Lou et al. [38] reported that CAT was associated with a transient increase in masticatory muscle activity, possibly because of an increase in wake-time parafunctional tooth clenching. They reported that patients without temporomandibular disorders adapted well to CAT as the masticatory muscle activity decreased toward the baseline levels after 2 weeks.

A current study also reported that the activation and/or installation of fixed labial appliances temporarily reduces masticatory performance and bite forces (for 24 to 48 hours) [39].

Ngan et al. [40] observed no significant difference on the 7th day, while discomfort reached its maximum levels at the 24th hour after fixed orthodontic treatment. Compared to fixed labial appliances, clear aligner wearers reported less chewing discomfort which might be related to the temporary removal of the aligners during meals [41].

Although clear aligners can be removed while eating and allow normal mastication function during orthodontic treatment, the doubled thickness of the aligner material increases the interocclusal distance, and their intrusive effect induced on posterior teeth may prevent optimal mastication [42].

Ramfjord teeth were included in this study to make the outcomes related to data on periodontal parameters simpler and more comprehensible [43]. Probing depth was found higher in the FOT group than in the CAT group in this study. Plaque accumulation is the most significant etiological factor of gingival inflammation, and it causes gingival enlargement by increasing the flow of gingival groove fluids that feed plasma proteins required for the growth of proteolytic anaerobes [44]. Previous systematic review and meta-analysis studies reported similar findings to those in our study regarding probing depth [8, 45]. Moreover, the general biodiversity and salivary microbial community structure did not change significantly during the first six months of clear aligner treatment [46].

The plaque index scores, which is another parameter providing information about the periodontal status, were significantly lower in the CAT group at all time points in our study. Since clear aligners are removable, they allow flossing resulting in better oral hygiene [9, 47]. Furthermore, since this technique does not involve braces bonded on teeth that create retentive areas for dental plaque, a more effective mechanical cleaning occurs with masticatory function during clear aligner treatment. Moreover, braces can make toothbrushing more difficult and reduce natural self-cleansing by the saliva and the tongue [48]. Cantekin et al. [49] demonstrated high levels of dental plaque accumulation, gingival swelling, and gingival bleeding during orthodontic treatment with fixed appliances. In our study, the presence of bleeding on probing showed probably no significant difference between the groups for maxillary and mandibular molars and mandibular incisors due to their proximity to the salivary glands and the physical washing effect of saliva. On the other hand, FOT provoked significantly more bleeding than CAT for maxillary incisors and maxillary and mandibular premolars at T1 and T2. The factors leading to the accumulation of more dental plaque in the FOT group also increased bleeding on probing as a secondary outcome. Another explanation for this finding may be that patients treated with braces avoid brushing their teeth vigorously with the fear of damaging their appliances.

In contrast to our finding, Lanteri et al. [50] showed that clear aligner system did not demonstrate a significantly superior “periodontal performance” compared to traditional equipment, as opposed to what was expected. This was probably because the coverage, almost all day, of dental surfaces, can lead to the accumulation of various substances resulting in inflammation, especially in patients who consume snacks or drinks with high sugar content. According to Karkhanechi et al. [51], the CAT group had less bleeding on probing and less probing depth at 6 months of treatment compared to the FOT group. Our results were similar to those presented by Karkhanechi et al. [51] and Haili Lu et al. [45].

Our study had some limitations. The first limitation of our study was the short-term observation period. Additionally, we included patients with only mild to moderate crowding and the patients were monitored in terms of adverse effects for a limited time of 6 months, within the greatest amount of tooth movement occur. We recommend that further studies with longer observation periods to be performed on patients with more severe orthodontic malocclusions.

5. Conclusions

- Patients treated with clear aligners had better periodontal health during orthodontic treatment compared to patients treated with conventional fixed appliances.

- Although root resorption occurred in both groups, the FOT group developed more root resorption than the CAT group.

- Patients in both groups experienced the highest pain levels and chewing difficulty levels at the 24th hour. While pain decreased to the baseline levels earlier in the CAT group, chewing performance improved more rapidly in the FOT group.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Author contributions

IEM and EDS—designed the research study and performed the literature search and data analysis. IEM—wrote the manuscripts. DS and EDS—help and advice on the write, drafted and/or critically revised the work. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript.

Ethics approval and consent to participate

This prospective study was approved by the Ethics Committee of Bezmialem Vakif University with 17/2 file number. Informed consent was received from the patients.

Acknowledgment

Thank you to Bezmialem Vakif University Scientific Research Projects Coordination Unit.

Funding

This study was supported by the Bezmialem Vakif University Scientific Research Projects Coordination Unit (20211212).

Conflict of interest

The authors declare no conflict of interest.