Dentofacial Effects of Asymmetric Headgear and Cervical Headgear with Removable Plate on Unilateral Molar Distalization

Headgears were first used in the early 1800s, and modifications have been made throughout time. Cervical headgear (CHG) therapy has been studied extensively for the last 50 years, but treatment results have varied greatly because of modifications of the appliance. Extraoral traction has been used successfully to correct skeletal or dental Class II malocclusion by restraining the forward growth of the maxilla or by distalizing the maxillary molars. The effects of CHG on the craniofacial complex have been evaluated by numerous experimental and clinical studies.1–8 However, extraoral cervical traction requires considerable patient compliance to obtain successful results.5,9–11 

In recent years, methods have been sought for correcting Class II malocclusions without the need for strict patient compliance. Different treatment modalities have been suggested to distalize maxillary molars including palatal bars,12 repelling magnets,13–16 Nitinol coil springs,17–18 K-loops,19 superelastic wires,20 Wilson arches,21 Jones jig appliances,22,23 pendulum appliances,24 distal jet appliances,25 three-dimensional bimetric maxillary distalizing arches,26 and intraoral bodily molar distalizer.27,28 

In the early 1980s, Cetlin and Ten Hoeve29 introduced a nonextraction treatment method for Class II division 1 malocclusion, which corrected the molar relationship with the use of a distalizing plate combined with extraoral traction. Extraoral traction should be worn 10 to 12 hours a day and produce a force of 150 to 200 g/side, or more, for an orthopedic effect on the maxilla.

Orthodontic treatment often requires an extraoral facebow that will predictably deliver a greater distal force to one side of the dental arch. Facebows providing an asymmetric distal force to their inner-bow terminals are termed unilateral facebows.

Studies describing the dentoskeletal changes associated with the Cetlin method have been rare. The aim of this study was to evaluate and to compare the dentoskeletal changes produced by a CHG used with a removable plate (CHG-RP) with those effects produced by an asymmetric headgear (AHG).

This prospective study consisted of 20 patients (12 girls and eight boys) divided randomly into two groups. Group I (AHG group) comprised 10 children (seven girls and three boys) with a mean age of 14.1 years, and group II (CHG-RP group) comprised 10 children (five girls and five boys) with a mean age of 14.6 years. Cases were selected with inclusion criteria as: (1) skeletal Class I, unilateral dental Class II molar relationship, (2) normal growth pattern and direction, (3) lower midline coincident with the midsagittal plane (MSR), (4) minimal or no dentoalveolar discrepancies in the lower arch, (5) normal overbite, (6) erupted upper second molars, and (7) absence of any shape or size anomalies or congenital missing tooth or teeth.

The study was carried out after the institutional approval for the use of humans was obtained from ethics committee of Gulhane Military Medical Academy. The maxillary first molars were unilaterally distalized using 250 g of force in both groups. Records of all the patients were obtained before treatment (T1) and after molar distalization (T2). Distalization was considered adequate when a super Class I molar relationship was obtained. The appliances were removed at the end of distalization, and a passive transpalatal arch was inserted for retention.

Lateral and basilar radiographs were obtained before and after the distalization period. Molar positions were identified on the radiographs by the use of individual vertically oriented guiding markers (0.41 × 0.56 mm Blue Elgiloy) placed in the rectangular double buccal tubes of molar bands while obtaining the radiographs. Occlusal radiographs were taken for evidence of sutural opening.

One investigator (Dr Altug) traced the radiographs, and the landmarks were verified by the other three investigators. Suspicious structures and landmarks were retraced to the mutual satisfaction of the investigators. A single average tracing was made in instances of bilateral structures. Twenty-three landmarks and 32 parameters were used in the study.

The parameters were measured by one investigator (Dr Altug) once more at another time to evaluate measurement errors. Measurements used in the study are shown in Figures 1–4 and Tables 1 and 2. The frequently used points and measurements are not shown in the figures.

Thirty-two lateral and basilar radiographs were chosen randomly for examination of the measurement error. The reliability of a single measurement was calculated by using Dahlberg's formula of method error. The method error did not exceed 0.395.

Statistical analyses were performed with a statistical package (SPSS Inc, Chicago, Ill), and the results are shown as a mean ± standard deviation. After the parametric assumptions were tested and if the variables were suitable for parametric tests, the differences between the T1 and T2 measurements were evaluated with the paired-samples t-test. The differences between the two groups were evaluated using Student's t-test. P values ≤.05 were considered statistically significant.

The T1 to T2 changes of the groups in the cephalometric and basilar radiographs are shown in Tables 3 through 6. The y-axis (P < .01 for AHG and P < .05 for CHG-RP), palatal plane (P < .05 for AHG and P < .01 for CHG-RP), mandibular plane (P < .01 for both groups), and occlusal plane (P < .01 for AHG and P < .05 for CHG-RP) all revealed posterior rotation. Anterior and lower face heights (P < .01 for both groups) and posterior face height (P < 05 for AHG and P < .01 for CHG-RP) were increased.

Upper molars and central incisors were extruded in both groups, and it was denoted by increases in the cephalometric variables Ud6o-FH, Up6o-FH, and U1i-FH (P < .01 for AHG and P < .05 for CHG-RP). Extrusion of the second premolars was observed only in AHG group (U5o-FH was increased by P < .01).

Distopalatal rotation of the first molars and second premolars was determined by increases in basilar variables MBD-DPD/MSR, MBP-DPP/MSR, PVP-PPP/ MSR (P < .01 for both groups), and PVD-PPD/MSR (P < .01 for AHG and P < .05 for CHG-RP), whereas the expansion of these teeth was shown by increases in MDC-MSR, MDC-MPC, PDC-MSR (P < .01 for both groups), and MPC-MSR, PPC-MSR (P < .01 for AHG and P < .05 for CHG-RP).

Distalization of molars and premolars was denoted by increases in basilar variables MDC–Transversal Plane (TP), MPC-TP, PDC-TP (P < .01 for both groups) and PPC-TP (P < .01 for AHG and P < .05 for CHG-RP). Cephalometric findings also revealed distalization and distal tipping of these teeth by decreases in the variables Ud6a/FH, Up6a/FH, U5a/FH, Ud6-Ptv, Up6-Ptv, and U5-Ptv (P < .01 for both groups).

Upper incisors were retruded in both groups (U1i-Ptv was decreased by P < .01 for AHG and P < .05 for CHG-RP), and they were also distally tipped in CHG-RP group (U1a/SN was decreased by P < .05 and I-TP was decreased by P < .01).

Significant increases in the basilar variables MADD-MSR, MAPD-MSR, MADD-MAPD, MADD-TP, and MAPD-Trans (P < .01) showed the displacement of the alveolar bone in both groups.

When the means of the groups were compared, significant changes were found in variables Up6a/FH, Up6-Ptv, and U5-Ptv (P < .05) and U5a/FH (P < .01) showing more distalization and distal tipping of molar at the passive side and of second premolar at the distalization side in AHG group (Table 7).

Alternative intraoral molar distalization modalities have been sought to create noncompliance therapies. Because the most unavoidable effect of intraoral molar distalization is the undesirable alterations in the alveolar bone and the anchor teeth, these appliances were suggested for use before eruption of the second molars.15,16,20,22,24 Several AHG forms have been used for unilateral molar distalization.30–32 An undesirable effect of the AHG is the derangement of the upper molars in the sagittal and transverse planes because of lateral forces.31 In this study, a removable plate with a screw and a CHG combination was used to eliminate these lateral forces.

Studies of distalization were conducted usually on bilateral maxillary molars. Several authors have investigated unilateral molar distalization with intraoral appliances. In the literature, despite the investigations explaining the biomechanics of extraoral unilateral molar distalization, the number of clinical trials is few. The direction of vertical force could be controlled with the angulation of outer arms of the facebow, but in this situation, a decreased amount of molar distalization should be expected. Our first target was to obtain rapid molar distalization, so angular alterations were not performed to the outer arms and 250 g of force was applied in our study.

In bilateral CHG applications, force lines intersect at the posterior of the neck on the MSR at an illusive point. The force vector occurs as the bisector of the angle formed by the force lines passes through the MSR and the midpoint of the distance between the upper molars. When the geometric configurations of the unilateral CHG were evaluated, the angle formed by the force lines is also at the posterior of the neck but is positioned to the side that is to be stable. In this condition, the force component runs in a direction that crosses the MSR and comes close to the upper molar desired to be distalized.

Hershey et al32 determined that increase in the asymmetry of the unilateral headgear leads to an increase in lateral force vector. In our study, short arm of the ACH was at the level of upper bicuspids. The intraoral molar distalization techniques were often introduced in the literature, so the results of our study were compared with these investigations.

The y-axis, SN-PP, SN-MP, SN-Occ, N-Me, ANS-Me, and S-Go variables showed statistically significant increases in both groups. These alterations revealed the changes in the relationship of maxilla and mandible against the cranial base and posterior rotation of the chin because of orthopedic and dentoalveolar effects of extraoral appliances. Therefore, anterior face height/posterior face height ratio changed and the facial height parameters increased. Statistically significant differences were found in the variables MADD-MSR, MAPD-MSR, MADD-MAPD, MADD-TP, and MAPD-TP. According to these findings, we concluded that the alveolar bone moved distally.

When the dentoalveolar effects of the appliances were evaluated, statistically significant differences were found in the amount of distalization of the upper molars. Maxillary molars on the passive side were also distalized in both groups. This finding was in accordance with Hershey et al32 and Baldini.31 The between-group difference for this parameter was statistically significant. The distalization was more in the AHG group. This finding was a result of the plate that facilitates the distalization in one side because of the screw and tightens the contralateral against the distalization force of the headgear.

Significant alteration in the Ud6a/FH and Up6a/FH showed the tipping of the molars. This finding was similar to other investigations evaluating intraoral molar distalization. On the other hand, Keles and Sayinsu27 and Keles et al28 advocated bodily tooth movement. The between-group differences revealed a significant alteration for the variable Up6a/FH and showed less distal tipping of the molar in the passive side of CHG-RP group. The variables describing the extrusion of the molars increased significantly in both groups, and no statistically significance was found between the groups. Extrusion of molars is in accordance with Greenspan6 and Baalack and Poulsen4 but conflicts with Ringenberg and Butts.8 

In the evaluation of the basilar radiographs, it was found that rotation of the molars was statistically significant in both groups. Rotation was more in the AHG group, but the between-group differences were statistically insignificant. Although the acrylic plate reduced the rotation of the molars to a degree, it could not prevent it completely. Contrary to our findings, Carano and Testa25 advocated no rotational alterations. Because of the molar rotations, intermolar width showed statistically significant increases in both groups.

When the alterations in the upper bicuspids were evaluated, a significant distal movement, extrusion, and distopalatal rotation were observed in both groups. When the groups were compared, more distalization and distal tipping were found in AHG group. The ball loop and the acrylic were believed to be the reason for the decreased distal movement in the CHG-RP. Jones and White22 and Ucem et al26 also found distal tipping and distalization in the premolars. Extrusion of the bicuspids was also found in the studies of Ghosh and Nanda33 and Keles and Sayinsu.27 However, mesial tipping of the upper bicuspids was observed in most of the intraoral molar distalization techniques because they were used as anchor teeth.

The variables evaluating the effect of the extraoral distalization force on the incisors showed statistically significant alterations. The incisor retrusion was in accordance with the findings of other investigators who used extraoral forces. The proclination of the anterior teeth was reported by several authors who used intraoral molar distalization methods.22–25 The differences among groups were also statistically significant for these variables. The palatal tipping of the anterior teeth was more in the CHG-RP group. The reason may be the removable plate that transferred the force to the anterior region through the labial arch. Extrusion of the anterior teeth was observed in both groups, which was in accordance with the findings of other investigations.6,21 Soft tissue changes were not significant in both groups.

• The unilateral distalization of the maxillary molars was achieved effectively in both groups.

• In the AHG group, the maxillary first molars on the passive and the second premolars on the distalization side were distalized more than those in the CHG-RP group.

• Incisor retrusion was more significant with CHG-RP combination.

• Palatal, occlusal, and mandibular plane angles and anterior and posterior face height were increased in both groups.