The aim of the present study was to evaluate the skeletal, dental, and soft tissue changes produced by PowerScope and AdvanSync2 compared with untreated controls. This study was conducted because of the limited literature available on AdvanSync2, and no study has compared its effects with those of PowerScope. Therefore, this study can be considered as a useful addition to the current literature. Current evidence on fixed functional appliances revealed varying treatment effects with a lack of standardization of age, sex, skeletal age, and initial sagittal and vertical parameters between the groups [7]. In the present study, confounding factors such as chronological and skeletal age, sex, and initial sagittal and vertical parameters were closely matched between groups. Skeletal age was assessed at T0, pre-functional for PowerScope, and T1 by CVMI staging. In our study, significant dentoskeletal and soft tissue changes were observed in both the PowerScope and AdvanSync2 groups compared with the untreated controls.
Skeletal changes
AdvanSync2 produced better skeletal effects than PowerScope did. The PowerScope did not have any significant effects on maxillary growth. This result was consistent with the findings of Antony et al. [3]. AdvanSync2 has a restraining effect on maxillary growth known as the headgear effect [14]. This result was consistent with the findings of AI-Jewair et al. [8] and Raghav et al. [10], contradicted the findings of Hemanth et al. [15] who noticed non-significant effects of AdvanSync on the maxilla. The reason for these conflicting results might be due to differences in the methodology. They conducted a study on postpubertal patients. According to Raghav et al. [10], better skeletal changes were observed in patients at the peak of puberty than in post-pubertal patients. Although both appliances produced mandibular advancement, AdvanSync2 displayed greater mandibular advancement (2.360 increase in SNB values) than PowerScope (1.40 increase in SNB). This is supported by the findings of Shahi et al. [16] and Raghav et al. [10]. This contrasts with the findings of AI-Jewair [8] and Jayachandran et al. [17]. According to them, AdvanSync2 has a greater restriction effect on the maxilla than on mandibular advancement. However, these studies compared AdvanSync2 with MARA and Class II elastics. The probable reason for the better skeletal effects produced by AdvanSync2 might be its early placement in the treatment at the time of initial bonding, better utilizing the growth of the subjects, whereas PowerScope required placement of heavy stainless steel wires, that needed 5-6months of fixed appliance treatment, leading to loss of effective utilization of growth in patients [7, 10]. This was confirmed by the different growth statuses of the patients in the treatment groups at T1. At the time of placement of PowerScope, most patients were in CVMI stage 4 (deceleration phase of growth) and stage 5 (post-pubertal) at T1. Due to the early placement of AdvancSync2 at the time of initial bonding, the patients were at stage 3 (peak of puberty) and stage 4 at T1.
Both groups showed significant improvements in the intermaxillary skeletal relationship compared to the control group. Changes in ANB angle were attributed to maxillary and mandibular advancement. This is in agreement with the study conducted by Panigrahi and Vineeth [18], who stated that fixed functional appliances correct Class II malocclusion by posterosuperior displacement of the maxillary dentition and pterygoid plate while simultaneously advancing the mandible and creating a forward and downward pull on the mandibular dentition.
Dental Changes
Both appliances showed significant dentoalveolar changes compared with the control group. PowerScope resulted in more dentoalveolar changes than AdvanSync2, which might be due to the differences in the growth status of the subjects. PowerScope portrayed more reduction of overjet of 5.6mm compared to AdvanSync2 of 4.6mm due to better retraction of upper incisors with PowerScope (-3.760 and − 4.58 mm) compared to AdvanSync2 (-3.040 and − 1.84 mm). This was due to the more distally directed forces on the maxilla by PowerScope compared to AdvanSync2 [2]. Molar correction in both groups was due to mandibular skeletal effects, and partly due to distalization of the upper molars and forward movement of the lower molars. These findings are in agreement with those of previous studies that have evaluated the dental effects of fixed functional appliances [3, 16, 19]. AdvanSync2 leads to greater intrusion and distalization of the upper molars, which might be due to its placement [8]. Similar findings have been reported in previous studies [8, 17]. The vertical force vector might have resulted in intrusion of the upper molars, and therefore can be used in high-angle patients.
Significant overbite reduction due to intrusion and proclination of the lower incisors was noticed with PowerScope. This finding was in agreement with previous studies [2, 5, 6]. AdvanSync2 did not lead to significant overbite correction. Hemanth et al. [15] reported similar results. The reason for this finding could be the difference in the mode of the appliance placement. PowerScope has an anterior attachment, leading to intrusive and forward forces on the lower incisors, whereas AdvanSync2 is placed on the molars. Our findings contradict those of Shahi et al. [16], who reported a significant reduction in overbite with AdvanSync. The variation in the observations could be attributed to differences in the patient’s skeletal age. The negative torque in the lower brackets and lingual crown torque in the arch wires could not prevent the proclination of lower incisors, therefore, FFA supported with mini-plates can be used to prevent this side effect. [20].
Soft tissue changes
Statistically significant changes were observed in the soft-tissue relationship and facial profile after treatment with both appliances. Upper lip retrusion, lower lip protrusion, increased Z angle, and chin prominence together led to significant improvement in the convex profile of a skeletal class II patient. This could be attributed to the forward position of the mandible along with proclination of the lower incisors and headgear effects in the maxilla brought about by fixed functional appliances. This is supported by the findings of previous studies [21]. In contrast, these findings disagree with those reported by Mofty et al. [12, 17, 22], who found no significant soft tissue changes after AdvanSync2 treatment. A probable reason for such differences could be differences in the growth status of the patients.
Treatment time
PowerScope group took 1.3 years of functional phase (5-6months before placement of appliance and 6-7months of functional phase), compared to 8months in AdvanSync2 group (appliance placed at the time of bonding).
Thus, the null hypothesis was rejected in this study.
Limitations of the study
Long-term treatment changes were not evaluated in the present study; therefore, multicenter prospective studies with long-term follow-ups are crucial.
Clinical implications of the study
In growing skeletal Class II patients, AdvanSync2 is the appliance of choice because of its early placement at the time of initial bonding, efficiently utilizing the growth of the patients and producing better skeletal effects.