Treatment Protocol

Pendulum appliances used were as described by Hilgers.8 The TMA springs exerted 230 grams of force, as the springs were activated to 90°. The K-loop was constructed according to the description by Kalra.12 The K-loop was made from 0.017 inch × 0.025 inch TMA wire and located between the upper first molar and the first premolar. The K-loop was activated to produce 200 grams of force (Figure 1).

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After placement of the appliances, patients were monitored every 3 weeks, and the K-loop was activated every 6 weeks. When the molars achieved a Class I occlusion, the appliance was replaced with a Nance button for retention. Patients were instructed to wear high-pull headgear at night to achieve molar uprighting.

In the headgear group, long outer bows were used and these bows were parallel to the occlusal plane, exerting a force of 400 grams. The patients in the headgear group were instructed to wear their appliances 16–20 hours a day and were motivated at each visit to wear the appliance for corporation. Patients in both groups were matched according to the GOGnSN angle and length of treatment.

Cephalometric Measurements

Cephalometric head films were obtained pretreatment (T0) and at the end of distal molar movement (T1). The cephalograms were traced by one investigator in random order. In instances of bilateral structures, a single average tracing was made. Two coordinate systems related to the cranial base and maxilla were established: a CT horizontal reference plane passing through the C point (the most anterior point of the cribriform plate at the junction with the nasal bone) and point T (the most superior point of the anterior wall of the sella turcica at the junction with the tuberculum sella). A vertical reference plane (Vp) was constructed perpendicular to the CT horizontal reference line at the T point as recommended by Viazis.19 The cephalometric profile analysis included 18 landmarks (11 dentoskeletal and 9 soft tissue, Figure 1) and 24 linear and angular variables (Figures 2–4). Descriptions of the measured parameters are given in Table 1.

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Table 1.  Skeletal, Dental, and Soft Tissue Variables Used in This Study

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Statistical Analyses

Descriptive statistics (mean, standard deviation, and ranges) were calculated for each of the cephalometric measurements at T0 and T1. The data were analyzed using SPSS software (Statistical Package for the Social Sciences, version 10.0, SSPS Inc, Chicago, Ill).

Paired t-tests were used to analyze differences between the pretreatment and post distal molar movement cephalometric variables from Groups 1 and 2. To compare differences in soft tissue profiles between Groups 1 and 2, independent t-tests were done. Values of P < .05 were considered statistically significant.

The size of the combined method error (ME) in the changes in the different landmarks was calculated according to Dahlberg's formula. Before and after treatment, cephalograms from 10 randomly chosen subjects were traced and superimposed with measurements recorded on two different occasions. The combined ME did not exceed 0.7 mm for any variable investigated.

Skeletal Changes

The pendulum/K-loop appliance caused insignificant changes in both the maxilla and the mandible. Also, there was no change in the mandibular plane angle. However, in the headgear group, the maxilla moved backward by 1 mm, and the mandible rotated posteriorly causing a decrease in SNB of 0.9 mm and an increase in GoGnSN of 0.9 mm. The overall change in treatment between the two groups in SNA was statistically significant (P < .05).

Dental Changes

There was a decrease in U1-SN angle and Vp-U1 distance in the headgear group, showing a statistically significant retrusion of the upper incisor (P < .05). The pendulum/K-loop appliance seemed to have no significant effect on upper incisor position. Lower incisors were retruded in both the pendulum/K-loop and headgear groups, but there was no significant difference between the groups (P > .05).

Soft Tissue Changes

Skeletal Changes

With regard to skeletal changes of the maxilla, the SNA angle showed no statistical differences in the intraoral distal molar movement group. However, significant differences between the groups were found for changes in the SNA angle, confirming previous findings.925 A significantly greater retraction of A point relative to the anterior cranial base was found in the headgear group. The changes in the vertical plane in the pendulum/K-loop group were insignificant (as has been demonstrated by other studies), but an increase was observed in the headgear group. SNB also was affected in the headgear group due to posterior mandibular rotation, which agrees with previous findings.925

Dental Changes

Surprisingly, the results of the present study demonstrated no upper incisor protrusion and a slight retrusion was statistically insignificant. This finding can be attributed to the reinforced anchorage obtained with the K-loop. Ghosh and Nanda9 found an incisor proclination of 2.4° relative to the SN line. Likewise, a mean of 1.71° of labial tipping was measured by Byloff and Darendeliler,26 and an average of 1.8 mm of anterior movement of the incisor edge and 6° of anterior tipping of the same teeth was measured by Bondemark et al.27 Kalra12 claimed that the K-loop produced bodily distal molar movement relative to the 20° bend. Buccal support seemed to reduce anchorage loss and provide a more effective distal molar movement in this study.

Soft Tissue Changes

Prediction of soft tissue changes is difficult because of the vast number of variables to consider. Differences in soft tissue thickness and tension between individuals produce a complex variation in profiles as demonstrated by hard tissue changes. However, changes in the positions of the incisors do have a direct impact on the supporting soft tissues.22

Most of the previous studies on variations of the pendulum appliance have focused on soft tissue changes relative to the E plane.2829 In one of the earliest studies, Byloff and Darendeliler26 analyzed the effects of the pendulum appliance on distal movement of the maxillary molars. However, they only studied changes in the hard tissues. Ghosh and Nanda9 evaluated the soft tissue changes relative to the E plane and reported a 0.31-mm protrusion in the upper lip and a 0.95-mm protrusion in the lower lip due to upper incisor protrusion. Bussick and McNamara25 evaluated four soft-tissue variables: upper incisor and lower incisor position relative to the E plane, nasolabial angle, and cant of the upper lip. Their results also showed protrusion in both the upper and lower lips and a 2.5° decrease in the nasolabial angle and 2.0° decrease in the cant of the upper lip, reflecting a slight protrusion of upper lip contour.

The only significant change in upper lip position in the pendulum/K-loop group was seen in the upper lip-vertical plane (Vp-Ls) distance. However, in contrast to other published data, this variable showed a decrease.

There exists only one study that showed a 0.4-mm retrusion of the upper lip relative to the E plane, and the results of that study were found insignificant.30 Increased lip prominence after pendulum treatment is related to a loss of anchorage and labial incisor tipping. The dentoskeletal effects of the pendulum/K-loop appliance will be discussed elsewhere in detail, but it may be assumed here that no anchorage loss occurred as reflected by the incisors and soft tissues.31

Sagittal soft tissue position was not affected, except for the lower lip-E plane distance. The decrease in lower lip position relative to the E plane resulted in lower incisor retrusion due to the bite-opening effect of premolar occlusal rests during pendulum therapy. Significant soft tissue differences between the groups were found for changes in the lower lip and soft tissue B point only. A significantly greater retraction of the lower lip and soft tissue B point relative to the vertical plane was observed in the headgear group. Had the duration of cervical headgear treatment been longer (until a Class I classification existed), we expect that changes in the soft tissue profile between the groups would have been greater.