With the recent trend toward nonextraction
treatment, many appliances have been advocated for maxillary molar distalization.1-20
Although the Pendulum appliance as described by Hilgers10 is
one of the most commonly used for this purpose, its effects on the dentofacial
complex have not been well documented.
The purpose of this study was to determine
the effects of the Pendulum molar distalization appliance on the dentition and
facial form.
Materials and Methods
The sample consisted of 26 patients who
were treated with the Pendulum appliance. The patients, 10 boys and 16 girls,
ranged in age from 7 years, 3 months, to 15 years, 5 months, with a mean age of
11 years, 2 months, at the start of treatment. All patients met the following
criteria:
• End-to-end or greater Class II molar
relationship at the start of treatment.
• Use of the Pendulum appliance for molar
distalization in the first phase of treatment.
• Nonextraction treatment plan.
• Absence of other molar distalization
procedures during the Pendulum appliance period.
The second molars were erupted in 11 patients
and unerupted in 15 patients. The mandibular plane angle ranged from 17.0° to
29.5°, with a mean of 24.1°. All patients were treated in Dr. Chaqués-Asensi's
office.
The basic design of the Pendulum appliance used in
this study is shown in Figure 1. The distalizing arms, made from .032"
TMA* wire, were activated 80° prior to insertion in the mouth. The appliance
was not reactivated during treatment, and the distalizing arms were not
modified at any time. Treatment time ranged from four to nine months, with a
mean of 6.5 months, and patients were seen at monthly intervals.
(Fig. 1 A. Pendulum appliance used in this
study, with palatal acrylic button attached to first premolars by retaining
wires soldered to bands, and .032" TMA distalizing springs activated 80°.
B. Appliance seated in mouth. C. After six months of treatment with Pendulum
appliance.)
Cephalometric Analysis
Lateral cephalograms were taken prior to treatment
(T1) and at the end of molar distalization (T2). Standard cephalometric tracing
and measurement techniques were used, as described by Ghosh and Nanda15
(Fig. 2). Unilateral centroid points were constructed for the maxillary first
and second molars and first premolar, using the midpoint of the crown's
greatest mesiodistal diameter.15-17 The amount of horizontal
movement of the molars, premolar, and central incisor was determined by
superimposing tracings on the pterygoid vertical plane (PTV), and vertical
movement by superimposing on the palatal plane (PP).15
All radiographs were traced and measured by one
author. To determine the error of measurement, 10 cephalograms were retraced
and measured. The combined error was found to be less than .5° and .5mm.
The mean and standard deviation were calculated for each measurement. Student's t-tests were performed to determine the significance of differences between the pretreatment (T1) and post-treatment (T2) measurements (Table 1).
(Dr. Chaqués-Asensi is an
Associate Professor, Department of Orthodontics, School of Dentistry,
University of Seville, Spain, and in the private practice of orthodontics in
Seville. Dr. Kalra is a Clinical Associate Professor, Department of
Orthodontics and Dentofacial Orthopedics, School of Dental Medicine, University
of Pittsburgh, and in the private practice of orthodontics at 20119 Van Aken
Blvd. #204, Shaker Heights, OH 44122.)
Results
The
maxillary first molars moved distally 5.3mm, as measured by the position of the
centroid (p < .001), tipped distally 13.1° (p < .001), and intruded
1.2mm (p < .001).
The maxillary first premolars or deciduous first
molars advanced 2.2mm (p < .001), tipped mesially 4.8° (p < .001), and
extruded 1.2 mm (p < .001). The maxillary central incisors advanced 2.1mm (p
< .001), and their inclination increased by5.1°(p<.001).
Overjet increased by 1.8mm (p < .001), and overbite
decreased by 1.8mm (p < .001).
Lower facial height (ANS-Me) increased by 2.8mm (p
< .001), while the mandibular plane angle increased by 1.3° (p < .01).
(Fig. 2 A. Cephalometric dental angular measurements: 1. SN-maxillary incisor; 2. SN-maxillary first premolar; 3. SN-maxillary first molar; 4. SN-maxillary second molar. B. Cephalometric dental linear measurements: Vertical, measurements (solid lines) to first molar, second molar, and first premolar centroids and central incisal edge from palatal plane (PP); horizontal measurements (dashed lines) to first molar, second molar, and first premolar centroids and central incisal edge from pterygoid vertical plane (PTV). C. Cephalometric skeletal measurements: 1. Lower anterior facial height (ANS-Me); 2. Mandibular plane angle (FH-MP).
Discussion
Use of the Pendulum appliance resulted in a 5.3mm
distalization of the maxillary first molars in 6.5 months, at a rate of .8mm
per month: Gulati and colleagues reported the same rate of distalization using
a sectional jig assembly.17 Similarly, Bondemark and Kurol,8
using magnets, and Gianelly,19 using a nickel titanium coil spring,
reported a rate of about 1 mm per month of first molar distalization.
The Pendulum appliance also caused substantial distal
molar tipping. Ghosh and Nanda reported that the Pendulum resulted in 3.4 mm of
distalization and 8.4° of distal tipping of the first molar.15
Considering both their results and ours, one would expect the maxillary first
molar to tip distally about 2.5° for every 1mm of distalization. Because
distally tipped molars do not provide effective anchorage for retracting the
teeth anterior to them, anchorage should be vigorously reinforced during
retraction.
In the present study, despite the use of Nance
buttons, the maxillary first premolars or deciduous first molars came forward
2.2 mm, and the overjet increased by 1.8 mm. This mesial movement amounted to
30% of the space created between the first molar and first premolar. Ghosh and
Nanda reported an even greater anchorage loss - about 40%.15 Either
finding emphasizes the need for conservative selection of patients for Pendulum
treatment.
Since the Nance button alone did not prevent anterior
movement of the first premolars, additional methods of reinforcing anchorage
may be necessary, including extraoral traction to the first molars, inclusion
of the canines and incisors in the anchor unit by means of archwires,
uprighting springs on the first premolars, and Class II elastics.5, 10,
15, 19
The amount of first molar distalization and
inclination was about the same in the 15 patients in whom the second molars had
erupted, compared to the 11 patients in whom they had not erupted. Ghosh and
Nanda reported similar results.15 The amount of anchorage loss,
however, as measured by anterior movement of the first premolars and incisors,
was .5mm greater in the patients with erupted second molars (p < .05).
In our measurements of facial form, lower anterior
facial height increased by 2.8mm, the mandibular plane angle increased by 1.3°,
and overbite decreased by 1.8mm during 6.5 months of treatment with the
Pendulum appliance. Similarly, Ghosh and Nanda reported a 2.8mm increase in
lower anterior facial height, a 1.1° increase in the mandibular plane angle,
and a 1.4mm decrease in overbite during six months treatment with the Pendulum.15
The increased lower facial height and mandibular plane angle could have
resulted from driving the molars back into the "wedge".15
These results suggest that the Pendulum may be contraindicated in patients with
excessive lower facial height and/or minimal overbite.
Conclusion
Treatment with the Pendulum molar distalizing
appliance appears to produce the following changes:
• Considerable distal movement of the molars.
• Considerable distal tipping of the molars.
• A substantial amount of anchorage loss, resulting in
anterior movement of the first premolars and incisors.
• Some increase in lower facial height and reduction
in overbite.
The presence of erupted second molars does not seem to
affect distalization of the first molars, but it does slightly increase the
mesial movement (anchorage loss) of the first premolars.
The Pendulum
appliance is effective in distalizing molars. As with other molar distalization
appliances, however, one should be conservative in choosing patients for
treatment with the Pendulum. Long-term studies evaluating the net gain in molar
distalization at the completion of orthodontic treatment are indicated.