The present study analysed the influence of sexual dimorphism on long-term stability (10 years) of skeletal Class III malocclusion treatment with RME combined with face mask protraction followed by fixed appliances. As far as we know, this is the first study that analyses differences between sex in the evolution of the treated Class III patients in such a long period of time (10 years post-treatment). In the Class III group, changes in the maxillomandibular relationship after treatment were favourable. Overjet and overbite relapse were observed in both females and males. In the long term, significant differences are observed between males and females, mainly in the ANB angle and Wits appraisal, which developed more negatively in males. The treatment success rate ten years later is 73.3% in males and 80% in females. Many cephalometric measurements have been analysed (n=34) and some of them are closely correlated. Therefore, it could be that some statistically significant differences may be found by chance, especially those with higher p values (*p < 0.05). Results for these comparisons should be taken with caution.
During treatment (T0–T1), very favourable skeletal changes were observed in the Class III group, both in males and females. This improvement in the intermaxillary relationship has been extensively described previously [11, 18, 21, 22, 24, 29,30,31]. These skeletal effects were due to significant changes in the maxilla and mandible. On the maxilla, advancement, increase in maxillary length, the advancement of point A, and increase in maxillary depth were observed, similar to what has been reported in other studies [22, 32, 33]. In contrast, in the Class I group, point A is retruded, more so in males. The effects on the mandible in the Class III group include retarded growth while the SNB angle remains stable, as reported in other studies [18, 21]; however, some authors even describe a decrease in the SNB angle during treatment [2, 22, 33]. The ANB angle and Wits appraisal increase during treatment, becoming more positive, both in males and females, unlike in the Class I group, in which the values of both variables decrease in both sexes. In the Class III group, the angle of the occlusal plane relative to the Frankfurt plane is reduced in females, with an anterior rotation of the maxilla; and also interdental relationships improve in both sexes, correcting overjet, overbite, and molar relationship. The upper incisor is buccally displaced during Class III treatment, to a greater extent in females, reflecting the dentoalveolar compensation of the upper incisor during treatment, while the lower incisor is less protruded in Class III than in Class I, both in females and males. Therefore, it is clear how buccal displacement of the lower incisor is prevented during treatment. These dental effects are similar to those described by other authors [18, 22, 29, 32], although some [7] describe a lingualization of the lower incisor during treatment that was not present in our study, as we only observed that the lower incisor remains in its lingualized position.
During treatment, the only variable differing between males and females is overjet. Overjet change from T0 to T1 is much more favourable in females, achieving an improvement of 4 mm on average during treatment, but only 2 mm in males. Therefore, it should be noted the better prognosis in females for Class III malocclusion treatment.
Analysis of the T1–T2 interval allowed us to observe long-term changes after Class III treatment. In the Class III group, substantial differences are observed between males and females, mainly in the ANB angle and Wits appraisal, which develop more negatively in males, indicating a worse prognosis in the stability of long-term outcomes and a greater tendency to relapse in males than in females. Furthermore, in males with Class III, the SNB angle increases, while it decreases in males with Class I. This increased SNB angle can be attributed to the remaining mandibular growth. The ANB angle and Wits appraisal become more negative, not reaching initial values (T0) but, as noted in the literature, mandibular growth distinctive of Class III continues, and skeletal and interdental relationship worsen again after the end of treatment [5, 18, 22, 24, 33].
Overjet and overbite relapse 10 years after Class III treatment, in both females and males. In females, they are the only two variables showing significant differences between Class III and Class I groups during this T1–T2 period. This post-treatment development in overjet and overbite is also observed in Class I but in the opposite direction. Overbite decreases in Class III and increases in Class I. In both class III and class I patients, overjet and overbite had a post-treatment development in a direction that was the opposite to their correction. Our study found that the interdental relationship relapse is higher in males than in females, which could be due to a larger overjet of the lower incisor in males during this period. Since, as mentioned in other studies [33], interdental relationship relapse can be expected, the possibility of applying overcorrection during treatment could be considered.
Our study found no maxillary relapse, like other authors, who also consider maxillary changes to be stable during treatment [7]; however, other studies have described a tendency to relapse in the anteroposterior position of the maxilla [22, 33].
The most common criteria for long-term class III relapse reported in different studies are class III molar relationship and anterior crossbite [1, 21, 22, 27, 28]. In our Class III patients, the success rate is 73.3% in males and 80% in females, similar to what has been described in previous studies. In the meta-analysis conducted by Lin et al. [33], the success rate in the studies reviewed ranges from 67 to 95%. Massucci et al. [22] observed 73%, Wells et al. [34] 75%, Westwood et al. [18] 76%, and Ngan et al. 75% [35]. In a previous study that only included females, we found a success rate of 81.8% [12]. A reason for the high percentage of stable cases in our sample could be due to the fact that the mandibular plane remained unchanged during treatment. According to various authors [21, 25], there is greater stability if the mandibular plane does not change during treatment.
It is important to tell the patients and their parents that prepuberal class III treatment is a very long treatment that requires overcorrection and a long retention period, especially in males. Long-term follow-up is crucial, even when the active growth period has finished.