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

368 Bernstein, Preston, and Lampasso
After treatment, the incisors retroclined a mean distance
of –0.10 mm relative to the A-Po line, resulting
in an overall (T3) mean proclination of 1.41 mm
(SD, 1.57 mm). A negative value for the measurement
represents lingual movement of the tip of the tooth.
There was a statistically significant difference between
the T1 and T2 measurements P ( .0001) (Table IV).
American Journal of Orthodontics and Dentofacial Orthopedics
March 2007
leveled completely, whereas 32% had slight residual
COS at T2. For the latter patients, the average amount
of COS at T2 was 0.19 mm; this is probably clinically
insignificant. The T2 models all showed Class I molar
and canine relationships with properly finished buccal
DISCUSSION
It is generally accepted that, with a few notable
exceptions, leveling a deep COS makes an important
contribution to the success of orthodontic treatment.
18-20,34,39-43 In a study that compared sectional
and continuous archwire treatments of adolescent patients
with Class II, deep-bite, low-angle malocclusions,
it was found that both techniques corrected deep
bites. 4,5 Although these studies compared the effective -
ness of overbite correction as measured on cephalometric
x-rays, they did not measure the COS, or the
effectiveness and long-term stability of leveling the
COS. Our study was prompted by a belief that there
was a need for a long-term, comprehensive, radiographic,
and study model analysis of the effectiveness
and stability of leveling the COS.
Before we analyzed the data from the cephalometric
investigation, the radiographic assessment of the COS
performed in this investigation required validation.
Integral to this process were the COS measurements
21
recorded by Carcara et al in their study model
analysis of the COS in the same sample group. The 2
sets of measurements were compared and analyzed to
determine whether the method of recording the COS
from lateral cephalographic x-rays produced the same
results as those recorded from the study models. There
were no statistically significant differences (P .01)
between the radiographic and the study model COS
measurements for any of the 31 patients at T1, T2, and
T3. 21 occlusions and normal overjets and overbites.
Results of the paired t test comparing the COS at T2
with that at T3 indicated a statistically significant
change (P .001) in this metrical character. The COS
increased from a mean of 0.19 mm at T2 to a mean of
0.69 mm at T3. Thus, the COS relapsed on average 0.5
0mm over a mean period of 7 years 5 months after the
fixed lingual canine-to-canine mandibular retainers
were removed (an average of 11 years 5 months
postdebond). Although the relapse in the COS might be
statistically significant, it is a relatively small change,
which, in turn, probably represents a normal physiologic
process.
The correlation percentage between the 2 meth -
ods was approximately 97%. Only 1 patient who was
measured to be level after treatment in the study model
analysis was not considered level in the cephalometric
analysis. Taking into account all factors that could have
influenced the recordings of the COS by the 2 methods
and the closeness of the results, we believe that the
proposed radiographic assessment of the COS is valid.
The cephalometric radiographs were taken on a Quint
Sectograph that was set to focus on the cranial landmarks
on the left side of the face.
From this study, it seems that the continuous
archwire technique is an effective orthodontic approach
for leveling a COS in Class II Division 1 nonextraction
deep-bite patients whose initial COS was 2 to 4 mm.
Sixty-eight percent of the patients studied here were
19-21,27 A previous study, although con -
firming that the leveling of the COS is a stable
treatment outcome, could not show that the amount of
leveling was correlated with the amount of relapse of
this parameter. 44 Unfortunately, those authors did not
specify the treatment technique used to treat their
patients, who had various malocclusion types. In our
study, the COS tended to relapse more in subjects with
the deepest COS at T1. The Pearson correlation coefficient
(initial COS vs posttreatment changes) was
0.380 (P .0349); this was statistically significant with
set at 0.05 but not with set at 0.01. At least 1 other
study confirmed our finding that the more the COS is
leveled during treatment, the more it relapses after
treatment. 45 That study had a relatively short mean
posttreatment time of 2 years 8 months in their patients,
who were treated with various appliances, and who had
different malocclusion types. Although dental heights
were recorded in the study of mixed malocclusions, no
attempt was made to compensate for the affects of
growth on these dimensions.
The overall long-term (T3-T1) effect of orthodontic
treatment with the continuous arch technique was an
average of 72.97% reduction in the pretreatment COS.
Ten of the 31 patients remained 100% level over a time
span of 5 to 25 years after orthodontic treatment. Only
5 patients had residual COS of over 1 mm, and none
was deeper than 2 mm. This study indicates that relapse
in the COS occurred slowly and over an extended
period of time.
Although there are speculations in the literature
about the contributions of various occlusal elements
involved in leveling the COS, these reports do not
quantify the contributions.
3,19,43-47 At the outset of this
study, there was an attempt to use a mandibular
superimposition method, 48 patterned after Björk’s
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