Pre-surgical orthodontics plays a crucial role in the success of orthodontic-orthognathic treatment, including the occlusal function, surgery stability, and facial esthetics. In the recent years, clear aligners (CAs) have been increasingly used in complex cases, including pre-surgical treatment. Therefore, it is essential to validate the effectiveness and efficiency of CA used for pre-surgical orthodontics. Thus, the aim of our study was to compare the effectiveness and efficiency of CAs with fixed appliances (FAs) in the pre-surgical orthodontic treatment for skeletal class III patients. To ensure reliable results, we employed well-established measurement indexes based on previous studies known for practical convenience and accuracy [23-28].
In comparison with fixed appliances, the CAs are usually used in relatively simpler cases, which might affect the authenticity of the results. Therefore, we conducted baseline characteristics assessments, age, gender, PAR index evaluations, and incisal compensation analysis to ensure comparability in difficulty, required tooth movement, and treatment outcomes between the two groups. All measurements were performed twice by two blinded professional orthodontists (Wei and Gao) in this study. In addition, we used ICC tests to evaluate the intra- and inter-examiner’s reliability, which resulted in excellent repeatability and reproducibility.
Treatment effectiveness
In this study, we evaluated the effectiveness of CAs in pre-surgical orthodontic treatment for skeletal class III patients compared to FAs. Our evaluation was based on post-PAR scores, arch width discrepancy, incisor up-righting, root parallelism rate, root resorption rate, and alveolar bone dehiscence rate. As shown in Table 2 and 3, the results indicated no statistical differences between CA and FA groups in most parameters, except for upper incisor up-righting in non-extraction patients (1.46 ±5.57 vs. -2.52±6.11 degrees, P=0.023). This discrepancy may be attributed to CA's proficiency in molar distalization [29], which better facilitates the correction of anterior teeth compensation. Overall, our findings suggest that CA can achieve teeth alignment and decompensation equivalent to FAs [30].
Several previous studies have evaluated the effectiveness of clear aligners in orthodontic treatment. According to Gaffuri et al., both CAs and FAs techniques showed significant improvement in the total mean scores of the OGS categories after treatment, with no statistically significant differences observed between the two groups [31]. Jaber et al. found no significant differences in the LII for the upper and lower jaws between the CA and FA groups. Also, the two groups had no significant differences in PAR index [32]. One study in 2020 reported that CA were just as effective as FA for treating mild malocclusions in adolescents [33], which are in agreement with our current study.
We also investigated width discrepancies and found no significant differences between the two groups as orthognathic surgery requires good coordination of dental arch width. It indicated that CAs are as effective as FAs in achieving width coordination. Interestingly, we also found that the width discrepancies between the first and second molars were reduced in the CA group, regardless of whether teeth were extracted or not. This is in line with a previous study, which found that CA have a low expansion rate in the molar areas [34]. Previous research has shown that CA as effective in correcting dentoalveolar crossbite and achieving inter-arch transverse coordination [14, 35]. In contrast to FA, which achieve maxillary expansion by tipping teeth in a buccal direction [36]. CA achieve expansion through limited buccal inclination of the posterior teeth [37]. This may explain our finding that CAs are just as effective as FA in achieving width coordination, as the efficiency of expansion declines from premolars to second molars.
Root resorption occurs mainly in the anterior teeth [38], in this study, our measured the anterior teeth of upper and lower, and calculated the root resorption rate in CAs and FAs. Notably, our study found that there no significant differences at root resorption rate between CA and FA groups. It has been reported that patients treated with CAs was less than those in patients treated with FAs in severity and prevalence of root resorption [15]. Several factors may contribute to our different results, such as shorter pre-orthodontic treatment duration and different criteria for determining root resorption (2mm or greater length difference).
For root parallelism rate and bone dehiscence rate, no significant differences were found between CA and FA groups. While a study has indicated that non-extraction with CAs was associated with an increased presence of bone dehiscence [39]. These variations may arise from different treatment mechanics and forces applied. It is important to consider factors like treatment duration, tooth movement complexity, patient characteristics, and orthodontic techniques when comparing bone dehiscence incidence between CA and FA. To some extent, pre-surgical orthodontic treatment has reduced the duration and simplified the complexity of orthodontic treatment. Interestingly, our found that extraction patients have lower incidence of bone dehiscence than no-extraction patients, which indicated that treatment modalities such as expansion and proclination that tend to move teeth labially have higher risks for alveolar dehiscence, which was supported by previous studies [40, 41].
Treatment efficiency
Our study revealed that CAs were an effective alternative to FAs for pre-surgical orthodontic treatment in skeletal class III patients. Importantly, we found that CAs resulted in shorter treatment duration and fewer follow-up visits compared to FAs, in both extraction and non-extraction cases. The treatment duration of CAs was reduced by 25.4% and 30.2% in non-extraction and extraction patients, respectively, while the number of follow-up visits decreased by 52.9% and 58.2%, respectively, which is consistent with the results obtained from other studies [14, 33].
These findings have significant benefits for both orthodontists and patients. For orthodontists, the use of clear aligners can increase chair utilization and enhance clinical efficiency, particularly when practice capacity is limited. For patients, the reduction in follow-up visits results in increased convenience, reduced travel costs, and less time away from work or school. In addition, the shorter treatment duration of pre-surgery orthodontics helps to alleviate patients’ anxiety, a common concern among orthognathic patients [42]. A different conclusion were reported by Li et al. in 2015, which showed that the treatment duration of clear aligners was 44% longer than that of fixed appliances [18]. However, discrepancies in treatment duration reported by different studies may be attributed to advancements in clear aligner technology and the clinical experience of orthodontists [43]. Our study highlights the importance of a good experience in computer-aided design of aligners to ensure success in clear aligners orthodontics.
While this study provides valuable insights into the effectiveness and efficiency of clear aligners compared to traditional fixed appliances in pre-surgical orthodontic treatment of skeletal class III patients. there are some limitations to consider. Firstly, the study has a retrospective design which may introduce some bias into the results. Secondly, as noted earlier, there may be variations in treatment outcomes depending on the experience and skills of individual dentists, which could be a crucial factor influencing the results.
To conclude, our study demonstrates that clear aligners can provide a similar therapeutic effect as fixed appliances in pre-surgical orthodontic treatment for skeletal class III patients, with the added benefits of shorter treatment duration and fewer follow-up visits. These findings support the use of clear aligners as a viable alternative to fixed appliances in orthodontic practice.