The Class II Carriere Motion appliance:A 3D CBCT evaluation of the effects on the dentition

Class II correction appliances have received careful review in the orthodontic literature. Among them, Class II elastics were shown to be effective in correcting Class II malocclusion.^1,2  Other frequently used Class II appliances include, but are not limited to, extraoral appliances such as headgear,^3–5  intramaxillary appliances,^6–8  and intermaxillary appliances.^2,9–13 However, most of these methods procline mandibular incisors.^{6,8–11,13,14} 

The introduction of the Class II Carriere Motion appliance (CMA) has raised many questions from the orthodontic community about its treatment effects. The appliance was designed to be an intermaxillary, nonextraction, Class II corrector.¹⁵  It consists of mold-injected, nickel-free stainless steel that runs from the maxillary canine to the first molar. It has a ball-and-socket design on the molar pad to allow tipping and rotation of the molar and a hook on the canine pad for elastic wear to the mandibular first molar, where anchorage is required.¹⁵  A “shorty” model is also available, which runs from the maxillary first premolar instead of the maxillary canine.¹⁵ 

Carriere claimed that the appliance produced “distal rotational movement of the maxillary first molars around their palatal roots.”¹⁵  Distal movement was demonstrated through photos displayed in case reports.^16,17  Rodriguez¹⁷  demonstrated unilateral usage of a shorty model of the CMA, which showed distal movement of the entire maxillary posterior segment. However, without any measurements, there can only be speculation as to the effects of the appliance.

No study has specifically examined whether distal molar rotations were the reason behind the distal movements previously observed. Thus, this study aimed to determine the three-dimensional (3D) treatment changes of the CMA, including distal rotation of maxillary molars, in Class II adolescent patients.

The study protocol was approved by the Saint Louis University Institutional Review Board. The sample comprised 59 adolescents (16 boys and 43 girls) who were treated at three private orthodontic offices. Records were collected retrospectively based on the following inclusion criteria: adolescent patients age 10–17 years, unilateral or bilateral Class II molar relationship, bilateral Class II canine relationship, bilateral use of the CMA for Class II correction, availability of pretreatment (T1) and post-CMA use (T2) cone beam computed tomography (CBCT) measurements, nonextraction treatment, Essix retainer in the mandibular arch for anchorage, and permanent or late mixed dentition. The sample excluded those with the following: posterior crossbite and syndromes or skeletal deformities.

Based on skeletal classification, two groups were formed, group 1 with skeletal Class I (N = 27; ANB 2.90° ± 1.40°; 13.30 ± 1.53 years) and group 2 with skeletal Class II (N = 32; ANB 6.06° ± 1.64°; 13.26 ± 1.76 years), to examine whether skeletal Class II patients (ANB >4°) had different treatment changes compared to skeletal Class I patients (ANB 0°–4°). The demographic characteristics and molar relationships in each group are described in Table 1.

Treatment protocol with the CMA was the same at all three offices. A CBCT was taken within 1–3 months before treatment (T1). Then, the CMA was placed (regular or shorty model) bilaterally along with a hook or molar bracket on the mandibular first molar (Figure 1A). An Essix retainer was used as anchorage on the mandibular dentition (Figure 1A). In addition, 1/4” 6 oz elastics were used for the first month followed by 3/16” 8 oz elastics after the first month until both Class I molar and canine relationships were achieved bilaterally (Figure 1B). A CBCT image was taken at the completion of CMA usage after the achievement of bilateral Class I molar and canine relationships (T2).

If a patient had a unilateral Class I molar and Class II canine on the Class I molar side, the CMA was still bonded and used until a Class I canine relationship was achieved on that side. However, the elastic protocol was to use 1/4” 6 oz elastics for the Class I molar side.

Pretreatment and post-CMA CBCTs were taken with the iCAT FLX (Kavo Kerr, Brea, Calif) at a field of view size of 16 cm × 13 cm or 23 cm × 17 cm, and traced by the principal investigator (Dr Areepong) with use of Invivo 6.0 and 3D Analysis software (Anatomage, San Jose, Calif). Accuracy of landmark identification was noted, and no clinical significance between CBCT tracings and lateral cephalometric tracings was found.¹⁸  Bilateral structures were traced separately to identify 16 landmarks (Table 2) and averaged for comparison between groups. Frankfort horizontal was created by using SN-7 to represent the X-axis and a perpendicular to represent the Y-axis in order to measure distal and mesial movement of the maxillary molar, maxillary canine, and mandibular molar (Figure 2). The rotational movements of the maxillary canine and molar were measured from the SN line (Figure 3). Thirty-six linear and angular measurements were generated through the 3D Analysis software from the traced points (Table 3).

Reliability was judged using Cronbach alpha (Table 3). Descriptive statistics were calculated for 36 measurements in both groups at T1 and T2. The Wilcoxon signed-rank test was performed to test significance between T1 and T2 in each group, as the population was not assumed to be normally distributed. A Welch t-test was performed to compare groups 1 and 2 after left and right measurements were combined into averages. Treatment time was compared between groups 1 and 2 with a paired t-test. All analyses were performed using the software R (version 3.4.2).

Groups 1 and 2 had mean treatment durations of 150 days (4.9 months) and 129 days (4.2 months), respectively, which were not significantly different. The 36 measurements at T1 and T2 are described in Table 4 for group 1 and Table 5 for group 2.

Group 1 showed statistically significant changes in all 36 variables except for U1-SN, Right U3 rotation, and MP-SN (Table 4). The maxillary canines underwent statistically significant distal movement of 2.34 ± 1.07 mm (right: 2.57 ± 1.28 mm; left: 2.12 ± 1.19 mm), as they tipped distally by 6.34 ± 3.22° (right: 7.50 ± 3.74°; left: 5.18 ± 3.74°), rotated distally by 3.19 ± 6.98° (right: 3.46 ± 10.04°; left: 2.92 ± 6.94°), and extruded by 1.54 ± 1.17 mm (right: 1.65 ± 1.30 mm; left: 1.42 ± 1.26 mm). Similarly, the maxillary first molars underwent statistically significant distal movement by 1.92 ± 0.80 mm (right: 2.01 ± 1.05 mm; left: 1.83 ± 0.84 mm), as they tipped distally by 4.59 ± 2.46° (right: 4.86 ± 2.95°; left: 4.32 ± 3.18°) and rotated distally by 3.58 ± 8.44° (right: 3.93 ± 6.77°; left: 3.22 ± 6.98°).

The mandibular first molars underwent statistically significant mesial movement by 1.37 ± 1.23 mm (right: 1.57 ± 1.44 mm; left: 1.17 ± 1.14 mm), as they tipped mesially by 3.68 ± 3.21° (right: 4.07 ± 3.31°; left: 3.29 ± 3.74°) and extruded by 1.69 ± 0.96 mm (right: 1.55 ± 1.04 mm; left: 1.84 ± 1.08 mm). The mean IMPA significantly increased by 3.50 ± 2.62°.

As shown in Table 5, all variables except MP-SN were statistically significantly changed. The maxillary canines underwent statistically significant distal movement by 2.24 ± 1.91 mm (right: 2.25 ± 2.15 mm; left: 2.24 ± 1.80 mm), as they tipped distally by 7.44 ± 5.56° (right: 7.46 ± 5.96°; left: 7.41 ± 5.85°), rotated distally by 6.47 ± 5.27° (right: 4.87 ± 6.65°; left: 8.07 ± 7.23°), and extruded by 1.87 ± 1.36 mm (right: 2.03 ± 1.55 mm; left: 1.71 ± 1.28 mm). Similarly, the maxillary first molars underwent statistically significant distal movement by 1.67 ± 1.56 mm (right: 1.81 ± 1.77 mm; left: 1.53 ± 1.63 mm), as they tipped distally by 6.45 ± 4.75° (right: 6.98 ± 5.56°; left: 5.91 ± 4.50°) and rotated distally by 4.64 ± 5.72° (right: 4.17 ± 6.65°; left: 5.12 ± 7.23°).

The mandibular first molars underwent statistically significant mesial movement by 2.51 ± 1.51 mm (right: 2.55 ± 1.44 mm; left: 2.46 ± 1.76 mm), as they tipped mesially by 2.51 ± 1.51° (right: 2.55 ± 1.44°; left: 2.46 ± 1.76°) and extruded by 1.79 ± 1.26 mm (right: 1.82 ± 1.40 mm; left: 1.76 ± 1.22 mm). The mean IMPA significantly increased by 4.06 ± 3.28°.

As shown in Table 6, the T1–T2 changes of 16 measurements were compared between groups 1 and 2. The lower first molars underwent statistically significantly more mesial movement in group 2 than group 1. Group 2 showed statistically significantly more proclination of the maxillary central incisors than group 1.

This research focused on the dentoalveolar treatment effects, which were mainly expected with the CMA.¹⁹  Class II correction was achieved in a mean treatment time of 4.9 and 4.2 months in group 1 and group 2, respectively, which was similar to the 4.4 months reported by Sandifer et al.,¹⁹  and shorter than 8.5 months when only Class II elastics were used.²⁰  As shown in Table 1, group 2 with skeletal Class II (ANB > 4°) had a more severely Class II molar relationship at T1. Interestingly, the results suggested that CMA can successfully correct these molar and canine relationships, similarly to the less severe presentation in patients in group 1 with skeletal Class I relationships (ANB 0–4°).

Previous reports available on CMA did not use CBCT to assess canine or molar movements.¹⁹  It is also worth noting the rotational changes can be observed with CBCT but not with conventional lateral cephalometric analysis. This report has also shown the similar treatment changes in the left and right canines and molars, as shown in Tables 4 and 5. This is probably because bilateral Class II molar relationships were more often observed than unilateral Class II in both groups, and a similar elastic protocol was used for both sides.

The distal movement of maxillary canines showed components of tipping and rotation in both groups. This data did not correlate directly with the manufacturer's claim of “distal movement of the canine along the alveolar ridge without tipping”¹⁵  as the data showed tipping of the maxillary canine in groups 1 and 2 (6.34 ± 3.22° and 7.44 ± 5.56°, respectively).

Extrusion of maxillary canines in both groups was similar (1.54 mm in group 1 and 1.87 mm in group 2), suggesting that CMA may be beneficial if maxillary canines require extrusion.

Both canine to molar (regular) CMA and premolar to molar (shorty) CMA were included in this study to increase the sample size. Group 1 included 4 bilateral shorty CMA patients and 23 bilateral regular CMA patients, while group 2 included 8 bilateral shorty CMA patients, 23 bilateral regular CMA patients, and one combination patient. If patients with shorty CMA were excluded in this study, more movement of the canines could have been expected.

On average, with the CMA, distal movement of the maxillary first molars was 1.80 mm (1.92 mm in group 1 and 1.67 mm in group 2), approximately the same as previously reported by Sandifer et al.,¹⁹  while only Class II elastics did not show any significant maxillary molar movements.²⁰  The CMA produced significant distal rotation and tipping of the maxillary first molars. This confirmed the manufacturer's claim that the appliance produces “distal rotation around the palatal root.”¹⁵ 

Although not statistically significant, the data suggested that, in skeletal Class II patients, the amount of tipping and rotation of maxillary molars may be greater than skeletal Class I patients (6.45° tipping and 4.64° rotation in group 2, and 4.59° tipping and 3.58° rotation in group 1).

In this study, when a patient had a unilateral Class II canine on the Class I molar side, the CMA was still bonded and used until a Class I canine relationship was achieved on that side. However, the elastic protocol was to use 1/4” 6 oz elastics for the Class I molar side, not 3/16” 8 oz elastics. As shown in Table 1, bilateral Class II molar relationships were found less often in group 1 than group 2. In addition, a full-step Class II molar relationship was found less often in group 1 than group 2. Thus, although not significant, the differences in distal tipping and rotation of the first molars between the groups may be related to these variations.

The amounts of mesial tipping, rotation, and extrusion of lower molars were almost identical between the groups. This suggested that the Essix retainers provided enough anchorage in group 2, which had more severe Class II molar relationships than group 1. Meanwhile, the correction of the Class II malocclusion in skeletal Class II patients came more from the mesial movement of the mandibular molars (2.51 mm in group 2 and 1.37 mm in group 1). The mesial movement shown in this study was more than the 1.2 mm found when only Class II elastics were used.²⁰  It is hard to conclude whether the whole dentition moved mesially in the mandible as lower incisor AP position was not measured.

The difference in change of the U1-SN in group 1 compared with group 2 was statistically significant. In group 2, the maxillary incisor was shown to have flared by 1.86°, compared with 0.07° of uprighting in group 1. Although there was no significant difference in IMPA changes between the groups, the lower incisors may have advanced more in group 2, thereby causing the upper incisors to tip forward. Further research is required to investigate changes in the AP position of lower incisors with the use of CMA.

The increase in IMPA was not significantly different between groups 1 and 2 (3.50° and 4.06°, respectively). This may suggest that, as an anchorage unit, an Essix retainer is better than a lower lingual holding arch (4.6°) but worse than fixed appliances (1.2°).¹⁹ 

Overjet is typically observed in Class II malocclusions. From the data, although fixed appliances were not used on the anterior teeth, group 1 showed a mean 1.70 mm of overjet reduction, while group 2 showed a mean 2.03 mm reduction, similar to the 1.87 mm reported previously¹⁹  but less than the 5.8 mm when only Class II elastics were used in combination with fixed appliances.²⁰ 

Both groups showed decreases in overbite (1.55 mm in group 1 and 2.00 mm in group 2), similar to the 1.78 mm reduction previously reported¹⁹  but less than the 3.0 mm shown when only Class II elastics were used in combination with fixed appliances.²⁰  The overbite reduction observed was probably due to the extrusion of lower molars, distal tipping of upper molars, and flaring of the lower incisors with the use of CMA.

Mandibular and occlusal plane angles underwent similar changes between the two groups. Mean mandibular plane changes were –0.54° and –0.47° in groups 1 and 2, respectively. Mean occlusal plane changes were –1.66° and –1.51°, respectively. Clinicians may observe that the mandibular plane angle likely does not change or increases slightly, and occlusal plane angles may increase slightly, with the use of CMA.

The limitations of this research included the following: (1) there was no comparison to a nontreated sample, (2) there were no reports available regarding patient compliance, and (3) overall treatment was not completed at the time of data collection. Additionally, SN-7 was used as a reference line instead of FH plane because some of the CBCT images did not include the external auditory meatus.

• The Class II CMA was effective at correcting Class II malocclusions before fixed appliance treatment in a mean time of 4.6 months.

• The maxillary canine showed distal movement with distal tipping, distal rotation, and extrusion.

• The maxillary first molar showed distal movement with distal tipping and rotation.

• The mandibular first molar showed mesial movement with mesial tipping and extrusion.

• Lower incisor proclination was evident even with the use of an Essix retainer as anchorage in the lower arch.

• When comparing skeletal Class I and Class II patients, mandibular molar mesial movement appeared to be the difference in the added correction observed in skeletal Class II patients.

• Maxillary incisor flaring after CMA was more evident in skeletal Class II patients than in skeletal Class I patients.

The authors wish to acknowledge Dr David Paquette, Dr Becky Schreiner, and Dr Shipley Thomas for providing the sample.