In this study, we analyzed the VAS scores not only in the first week after the appliance delivery but also after 3 and 5 weeks of appliance adjustments. At the first stage, the peak VAS score was observed 1 day after and gradually decreased in all three groups. Generally, the pain increases few hours after placement of the initial arch wire, peaks at 24 h, and decreases to almost baseline levels at 7 days ,. Ngan et al. report that on surveying pain levels 4 h, 24 h, and 7 days after the insertion of arch wires and separators, pain was greatest when using both devices after 24 h . Harazaki and Isshiki implemented a questionnaire survey regarding the time during which pain was felt by patients having the initial wire inserted to an attachment device fitted to all their teeth and reported that pain occurred after between 3.4 and 3.5 h, peaked at around 24 h, and disappeared a week later . In each of these cases, the pain threshold was at its lowest around 24 h after the application of orthodontic force, after which gradual recovery was noted. In this study, the pain disappeared 5 days after in EIG and IG but not until 6 days after in EG. All VAS scores decreased while the stage progressed.
In stage 1, more pain was observed 3 and 4 days after, but there was also more pain after 1 day in stage 2 and after 2 and 3 days in stage 3 in EG compared to EIG and IG. This indicates that the intensity of pain may not be different before 24 h of appliance adjustment, but after 2 to 3 days, the edgewise appliance may produce more pain than Invisalign. Also, the edgewise appliance may cause prolonged pain compared to Invisalign. This is consistent with a similar past study which indicated that fixed appliance subjects reported more pain than Invisalign subjects . Others also indicated that fixed appliances caused more pain or discomfort to patients than removable appliances ,.
One of the unique data of this study is that we were able to compare the pain level between the edgewise appliance and Invisalign in the same patient (EIG). During the initial stages of treatment, EIG resulted in a similar VAS score to that of IG. The combination approach by initial alignment with the edgewise appliance and later with Invisalign tends to have less pain than just with edgewise treatment. The overall VAS scores for EIG resulted in significantly less pain, duration, and discomfort during the Invisalign treatment period than during the initial edgewise treatment. Therefore, patients who experienced both appliances prefer Invisalign than edgewise treatment from a pain and discomfort point of view. However, the limitation of this result is that since all EIG patients experienced the edgewise appliance prior to Invisalign, the initial edgewise treatment may have masked the intensity of pain by the use of Invisalign. Thus, comparison of VAS between the group that has the edgewise appliance initially and the group that started with Invisalign must be performed to clarify this problem.
Our overall results collected after the treatment also showed significantly more and long-lasting pain in EG than in IG. However, there was no significant difference in pain duration and discomfort between EG and EIG. Thus, patients may feel less pain with Invisalign, but the duration of pain and discomfort level seems to be the same. Since several patients complained of pain or discomfort, we further identified the problems with Invisalign trays. As a result, most of the reasons for pain or discomfort in the Invisalign cases were deformation of trays. Some patients experienced pain other than the four categories such as pain related to the change in the gingival morphology due to the eruption of third molars, swelling of the gingiva due to inefficient oral hygiene, and inefficient use of aligner (bad cooperation) which were not included in the present analysis. Recently, since there was a change in the material of the tray from EX30 to LE30, which is softer and has more flexibility, this problem should be greatly improved.
One of the limitations of this study was the different extraction ratios among groups. The extraction ratio was quite similar between IG and EIG; however, EG has a higher extraction rate (approximately 5% higher) compared to the other two groups. Since extraction requires a surgical procedure, it might have resulted in higher VAS scores compared to non-extraction therapy. However, we suggest that a 5% difference would not have a significant impact on the results of our study. Future studies such as randomized clinical trials with more controlled selection of the sample are required to elucidate this problem.
Brown and Moerenhout indicated that adolescents, pre-adolescents, and adults varied in their pain reports during orthodontic treatment, with adolescents reporting the most pain. In this study, the average age was very similar among the three groups; thus, there should not be any influence on our results on age among groups. On the other hand, the male:female ratio was 20:35, 10:28, and 19:33 for EG, IG, and EIG, respectively. IG had a higher female ratio (73.7%) compared to EG (63.6%) and EIG (63.5%). However, since a lower VAS score was observed in IG (with a higher female ratio), we indicate that there was no significant impact on the results of our study.