4.2. Treatment Changes Comparison
Both treated groups presented a restriction of the forward displacement of the maxilla, however with a significant difference only between JJ and control groups.
JJ group presented a smaller increase of the effective length of the maxilla during treatment when compared to the other groups. This means that the JJ promoted a greater restriction of the maxillary growth in relation to MPA and the normal growth in untreated subjects. MPA was not effective in producing a significant restriction of the forward displacement of the maxilla, since there was not a statistically significant difference with the control group.
The effect of restricting the anterior growth and displacement of the maxilla was already observed in some studies evaluating cases treated with the JJ [11, 16-23].
The lack of significant difference in the maxillary skeletal component between the groups MPA and control was already observed by other authors [8, 24].
Some studies described the decrease of SNA angle and the backward relocation of the A point with the use of JJ appliance as the “headgear effect”, with distalization and intrusion forces in the maxillary posterior region [18, 19, 22]. However, since MPA has the same mechanism of Class II correction as JJ, this effect was also expected in MPA group, but this was not observed. Therefore, the uprighting effect of both appliances on the maxillary incisors led to forward relocation of A-point because of appositional changes at that alveolar area. Since the MPA group had more palatal tipping of the maxillary incisors , this could have camouflaged the restrictive effect of the MPA on the maxilla. Other researchers also reported A-point relocation related to the incisor inclination [22, 25, 26].
MPA group demonstrated a significantly greater increase in mandibular effective length when compared to JJ and control groups. This corroborates other studies, however, they also found a significant mandibular protrusion [5-8, 24].
It is noticed that there was no significant mandibular protrusion neither a significant increase in mandibular effective length with the use of JJ. This is in agreement with previous studies [16, 17, 19-21, 27]. However, some authors reported mandibular protrusion with the use of the JJ [11, 23, 26, 28].
Another factor that can explain this difference, despite the similar pretreatment age of the groups, is that the MPA group presented a significantly smaller mandibular effective length in this stage than the other groups. Possibly these subjects still were at the beginning of the craniofacial growth spurt.
The two experimental groups treated with MPA and JJ showed a significant improvement of the maxillomandibular relationship when compared to the control group, also reported in the literature [8, 9, 16-18, 20-23, 26-29]. This improvement of the maxillomandibular relationship results mainly of the restriction of the forward displacement of the maxilla in the JJ group and the increase of the mandibular effective length in the MPA group and the mandibular normal growth in the JJ group.
The vertical component remained practically unchanged in all groups evaluated, indicating that treatment with MPA and JJ did not influence the craniofacial growth pattern. Some authors reported an increase of the vertical measurements, with a tendency of clockwise mandibular rotation in patients treated with the JJ appliance [16-19, 22, 26], while others did not verify significant vertical changes [20, 27].
MPA group presented a greater palatal tipping and a greater retraction of the maxillary incisors when compared to the JJ and control groups. This is probably because, at the beginning of treatment, the maxillary incisors in the MPA group were significantly more labially tipped, and consequently, during treatment, a greater retrusion was needed in order to correct the overjet. This palatal tipping corroborates some previous findings about MPA [5, 8, 24, 30].
Some studies found a significant retrusion of the maxillary incisors in cases treated with the JJ [16-19, 22, 26, 28]. The lack of significant retrusion of JJ group in the present study may be due to the greater maxillary retrusion observed during treatment .
MPA group presented greater labial tipping of the mandibular incisors with treatment, when compared to the control group, already mentioned in the literature [8, 24]. In JJ group, this side effect probably was minimized by the lingual crown torque applied to the mandibular anterior teeth [11, 16, 17].
JJ group presented greater protrusion of the mandibular incisors in relation to the control group, corroborating previous studies [16-19, 21-23, 26-28]. However, this significant protrusion was also reported by studies evaluating MPA [8, 24].
Both experimental groups presented significant decreases of the overjet and overbite and significant improvement in molar relationship with treatment, in relation to the control group. However, MPA group showed a greater decrease of overjet also significant when compared to JJ group.
The greater decrease of the overjet in MPA group in relation to JJ group can be explained by the pretreatment increased overjet presented by MPA group. This way, the overjet correction needed to be greater in MPA group.
The correction of overjet was several times previously reported in the literature [8, 16-24, 26, 28].
In MPA group, the overjet correction was due to the increase in mandibular effective length, the palatal tipping of the maxillary incisors and the protrusion and proclination of the mandibular incisors. In JJ group, the overjet correction was mainly due to the restriction of the forward displacement of the maxilla and the protrusion of mandibular incisors, associated with the normal mandibular growth.
The labial inclination of mandibular incisors in MPA group and the protrusion of these teeth in JJ group may have contributed to the relative “Intrusion Effect” of these teeth and correction of the overbite [20, 26, 28].
In general, MPA and JJ associated with fixed appliances corrected the Class II malocclusion, and this was due to some skeletal and mainly dentoalveolar changes [8-10, 18-22, 24, 27]. This way, both appliances can be used in growing patients as well as in adults, that do not present growth potential [9, 10, 16, 18].
However, these skeletal and dentoalveolar changes presented important differences between the two appliances, that must be remembered when planning an orthodontic treatment.
In MPA group, there was a significant increase in mandibular effective length and great dentoalveolar compensation, including palatal inclination and retrusion of the maxillary incisors and buccal inclination of mandibular incisors.
In JJ group, there was a significant restriction of the anterior displacement of the maxilla, and also important dentoalveolar compensations, as protrusion of mandibular incisors.
This way, JJ must be indicated mainly in cases with a maxillary protrusion, and MPA, especially in cases with mandibular deficiency.
Thus, the most important of the orthodontic treatment is the detailed planning and the correct determination of the treatment protocol. Further researches are needed in order to evaluate the long-term stability of treatment with MPA and JJ associated to fixed appliances.
Functional appliances can also be used in patients with juvenile idiopathic arthritis, to reduce the asymmetry of mandibular growth and TMJ disorder . Functional appliance can reduce the pain during jaw movement, maximal mouth opening, TMJ sounds and crepitations and TMJ click .