Leveling the curve of Spee with a continuous archwire technique: A ...

American Journal of Orthodontics and Dentofacial Orthopedics
Volume 131, Number 3
Fig 2. COS and lower dental height measurements.
highest cusp tip of the L6 to the tip of the most extruded
mandibular incisor (L1) 34 ; and COS, the depth of the
COS measured as the perpendicular distance from the
tooth cusp of the most infra-erupted premolar to the
COS line.
The premolar used in measuring the deepest part of
the COS had to be in occlusal contact with an opposing
tooth in the maxillary dentition. Because no patients
in this study had their second molars fully erupted at
T1, the COS was measured to the first molars only.
Each COS was measured from the radiographic tracings
by using a commercially available 0.5-mm scale
ruler. Because the cephalometric radiographic scans
taken on the Quint Sectograph were adjusted to focus
primarily on the left half of the face, only the depth of
the COS on the left side could be determined accurately.
The arch leveling was measured by the changes
in the measurements of the distances of L1, L4, and L6
to the MP (Go-Gn).
The size of the combined method error in locating,
superimposing, and measuring the changes of the various
landmarks was calculated. Thirty radiographs (10
subjects) were randomly selected from the original
sample and remeasured by the same operator 2 weeks
later, without reference to the previous measurements.
The casual error was calculated according to Dahlberg’s
formula 35 :S 2 d2/2n, where S 2 is the error
variance and d is the difference between the 2 determinations
of the same variable, and the systematic error
was calculated with paired t tests. A significance level
of 1% was used for this part of the study.
The results achieved for the COS measurements
from an earlier study were compared statistically with
Bernstein, Preston, and Lampasso 365
21
paired t tests with those we obtained. These 2 sets of
data were recorded independently at different times and
in a random, blind fashion. The same sample group was
used in both studies, and the respective study models
and radiographs were obtained at the same time.
Because on average all patients in the sample were
still undergoing active skeletal growth during and after
the treatment period, the growth of the mandible
probably had some effect on the observed changes in
the linear measurements. Sex-based growth charts of
untreated normal patients in the same age and time
period showed that, in our sample, the COS measurements
could have been affected by appositional bone
growth in the mandibular incisor, premolar, and molar
regions. To calculate net mean dental movement, the
appropriate mean growth increments were added to the
affected dimensions. 36 The limitations inherent with
using historical data, as was done here, must, however,
be kept in mind.
37
RESULTS
The casual errors determined in this study did not
exceed 0.5 mm or 0.5°, and no variable had
statistically significant (P .01) systematic errors. Indications
of nonnormality of the data at T1 (Dn
0.2336, Lilliefors P .001) and T2 (Dn 0.4182,
Lilliefors P .001) reflect the high number of repeats
in the measurements (eg, 12 twos at T1 and 21 zeros at
T2). Because the sample size was greater than 30, the
results of the t tests can, however, be considered
acceptably accurate.
There were no statistically significant differences
(P .01) between the pairs of COS measurements (radiographic
vs study model
21 ) for any of the 31 patients
studied at T1, T2, and T3. The cephalometric data
measured from the sample of radiographs are given in
Tables II and III. Paired t tests were conducted for these
measurements, and the statistical findings are shown in
Table IV.
The mean reduction in the ANB angle as a result of
treatment (T2-T1) was 2.98° (SD, 1.55°) (P
.0001); this is equivalent to a 57.75% decrease in the
size of this angle. The overall (T3-T1) mean reduction
of the ANB angle was 3.16° (SD, 2.34°).
The mean Y-axis change associated with treatment
was a clockwise rotation of 1.05° (SD, 1.34°)
(P .0001). After treatment, this angle became more
acute by a mean of 0.34° (Table II), producing an
overall (T3-T1) mean opening rotation of the Y-axis
angle of 0.71° (SD, 1.73°).
Associated with treatment (T2-T1), the SN-OP
angle showed a mean reduction of 2.98° (SD,
3.09°), whereas the mean treatment change in the