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

ORIGINAL ARTICLE 

Leveling the curve of Spee with a continuous 

archwire technique: A long term 

cephalometric study 

Rael L. Bernstein, a Charles B. Preston, b and Judith Lampasso c 

Buffalo, NY 

Introduction: The orthodontic technique favored by a clinician frequently determines how a deep curve of 

Spee (COS) is leveled. The primary purpose of this investigation was to confirm radiographically the 

long-term effectiveness of a continuous archwire technique—the Alexander discipline—in leveling the COS 

in patients with Class II Division 1 deep-bite malocclusions treated without extractions. Methods: The sample 

for this retrospective cephalometric study consisted of the randomly selected orthodontic records of 31 subjects 

(22 female, 9 male) treated with the continuous archwire technique in the private practice of Dr R.G. “Wick” 

Alexander in Arlington, Texas. Results: The mean pretreatment COS for this sample was 2.47 mm, and the 

corresponding mean posttreatment COS was 0.19 mm. The COS was completely level in 21 patients after 

treatment, and the rest had slight residual COS at the end of this phase. Ten of the 31 subjects remained level 

from 5 to 25 years after orthodontic treatment. Conclusions: The results indicate that most leveling was 

accomplished by the extrusion of the premolars. The continuous archwire technique is effective in leveling the 

COS in patients with Class II Division 1 deep-bite malocclusions treated without extractions when the initial COS 

is 2 to 4 mm. The leveling of the COS with the continuous archwire technique takes place by a combination of 

premolar extrusion and, to a lesser extent, incisor intrusion. (Am J Orthod Dentofacial Orthop 2007;131:363-71) 

The need to correct an accentuated curve of Spee 

(COS) that is commonly encountered in a malocclusion 

characterized by a deep bite presents 

diagnostic and therapeutic challenges for the orthodontist. 

1,2 Unfortunately, the orthodontic technique favored 

by each clinician, rather than the nature of a specific 

malocclusion, will frequently determine how deep bites 

are corrected. There is some disagreement among the 

proponents of the various orthodontic techniques as to 

what mechanical approach is the most suitable to level 

an exaggerated COS. 

3-5 Clinicians who follow a segmented 

wire approach to arch leveling suggest that 

leveling with continuous archwires will extrude the 

posterior teeth, which, in turn, will result in increased 

lower facial height. 

3-7 They also believe that, in patients 

with strong muscles of mastication, the extrusion of the 

buccal segments will tend to relapse after orthodontic 

treatment. Furthermore, these clinicians believe that 

placing a reverse COS in a continuous archwire for arch 

a Private practice, Calif. 

b Professor and chair, School of Dental Medicine, University at Buffalo. 

c Assistant professor, School of Dental Medicine, University at Buffalo. 

Reprint requests to: Charles B. Preston, School of Dental Medicine, State 

University of New York at Buffalo, 140 Squire Hall, 3435 Main St, Buffalo, 

NY 14214; e-mail, cbp@buffalo.edu 

Submitted, February 2005; revised and accepted, May 2005. 

0889-5406/$32.00 

Copyright © 2007 by the American Association of Orthodontists. 

doi:10.1016/j.ajodo.2005.05.056 

leveling will almost always flare the mandibular incisors 

labially. 8,9 On the other hand, proponents of the 

continuous-arch treatment philosophy contend that premolar 

and molar extrusions represent stable occlusal 

changes, whereas mandidular incisor intrusion is an 

unstable movement that will almost certainly relapse in 

time. 6,7,10-16 

Cephalometric studies undertaken to compare the 

sectional and continuous arch leveling methods report 

that both the Ricketts 

4 and the modified Tweed 

5 techniques 

successfully correct deep overbites. At the same 

time, a comparative study of these 2 approaches to 

orthodontic treatment found that they result in similar 

mandibular incisor positions. 

17 

In support of the contention that it is important to 

18 

level an excessive COS, Andrews noted that the 

occlusal planes of nonorthodontically treated normal 

occlusions tend to be level. He associated a COS with 

postorthodontic treatment relapse and concluded that, 

even though not all normal occlusions have flat planes 

of occlusion, this should be an orthodontic treatment 

goal. Because of the tendency for the COS to return 

after orthodontic treatment, other authors in support of 

Andrews’ point of view suggest that it should be an aim 

of orthodontic treatment to establish a level occlusal 

plane. 19,20 

Several authors commented on the amount and 

363

364 Bernstein, Preston, and Lampasso 

Table I. Sample (n 31; 9 male, 22 female) and time 

characteristics 

Characteristic Time 

Mean age at T1 12 y6mo 

Mean age at T2 14 y 11 mo 

Mean age at T3 26 y4mo 

Mean treatment time (T2-T1) 2y5mo 

Mean fixed retention time 3y4mo 

Mean postretention time (T3-T2) 11 y5mo 

type of occlusal relapse after orthodontic treatment. 

3,12,17,21-30 In general, these studies noted - in 

creases in overjet, overbite, and mandibular incisor 

crowding along with decreases in arch length and arch 

width. Although postorthodontic relapse was studied in 

some detail, relatively little is known about the longterm 

stability of leveling the COS and how the different 

methods of arch leveling relate to its subsequent relapse. 

The primary purpose of this investigation was to 

determine radiographically the long-term effectiveness 

of the Alexander discipline (continuous archwire technique) 

in leveling the COS in Class II Division 1 

deep-bite nonextraction patients. We also report on 

some relevant cephalometric changes that take place 

during arch leveling with the continuous archwire 

technique. The cephalometric data obtained were used 

to determine whether a COS that was leveled remains 

stable in the long term. 

MATERIAL AND METHODS 

The sample for this retrospective study consisted of 

the randomly selected orthodontic records of 31 white 

patients treated without extractions in the private practice 

of Dr R.G. “Wick” Alexander in Arlington, Texas 

(Table I). These patients all met the following criteria 

for selection: they had Class II (ANB angle 4°) 

skeletal patterns, at least half-step Class II molar dental 

relationships, incisor overbites of 50% or greater as 

measured on the initial (T1) study models, and angles 

between the mandibular plane (MP) (Go-Gn) and the 

sella-nasion (S-N) line less than 32°. A COS equal to or 

deeper than 2 mm was present on all T1 models. 

Only patients with complete clinical records were 

included in this study. These records consisted of 

radiographs and dental casts taken at T1, posttreatment 

(T2), and postretention (T3). All patients were retained 

with lower fixed canine-to-canine lingual retainers for a 

mean period of 3 years 4 months. The patients were all 

treated with fully preadjusted fixed orthodontic appliances 

according to the continuous archwire technique. 

We selected this technique for this study because of its 

American Journal of Orthodontics and Dentofacial Orthopedics 

March 2007 

Fig 1. Cephalometric landmarks and lines. 

biomechanical principles that aim to provide a level 

occlusal plane (OP) during and at the end of active 

treatment. 31 

Three radiographs (T1, T2, T3) were collected for 

each subject. The 93 radiographs were assigned random 

numbers to enable 1 investigator (R.L.B.) to measure 

each in a random, blind fashion. 

All radiographs were taken on a Quint Sectograph 

machine (Los Angeles, Calif) and were hand traced by 

1 operator (R.L.B.) from the original radiographs. 

Standard cephalometric landmarks (S, N, ANS, PNS, 

A, B, Go, Gn) were used to construct the reference lines 

required to obtain the craniofacial measurements re- 

32 

corded in this study (Fig 1). The functional OP was 

defined by a line intersecting the intercuspation of the 

posterior occlusion (Fig 2). 

33 The following additional 

reference points and planes were used to measure the 

COS; these form the focus of this study (Figs 1 and 2): 

I1, the incisal tip of the most extruded mandibular 

incisor; L6, the highest cusp tip of the mandibular 

permanent first molar; L1-MP, tip of the L1 perpendicular 

to Go-Gn; L6-MP, mesial cusp tip of the L6 

perpendicular to Go-Gn; L4-MP, the cusp tip of the L4 

perpendicular to Go-Gn; COS line, the line joining the


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


Table II. Changes in cephalometric measurements from T1 to T3 

Measurement 

T1 T2 T3 

Mean SD Mean SD Mean SD 

L4-COS line (mm) 2.47 0.69 0.19 0.31 0.69 0.64 

L1-MP perp (mm) 38.89 3.02 39.42 2.94 41.08 3.27 

L4-MP perp (mm) 32.50 2.76 35.31 3.01 36.31 3.18 

L6-MP perp (mm) 29.16 2.14 31.47 2.81 32.70 3.20 

L1-MP (°) 94.85 5.43 95.68 6.93 94.50 5.80 

L1 to A-Po (mm) 1.18 1.98 0.34 1.51 0.24 2.04 

L1-NB (°) 22.81 5.16 24.18 4.82 23.15 4.94 

SNA angle (°) 82.03 3.33 79.39 4.08 79.76 4.14 

SNB angle (°) 76.87 3.34 77.21 3.75 77.76 3.91 

ANB angle (°) 5.16 1.60 2.18 1.76 2.00 2.25 

Y-axis (°) 66.21 2.91 67.26 3.36 66.92 3.77 

SN-MP (°) 31.23 4.35 32.21 5.54 31.65 6.30 

SN-OP (°) 17.76 3.31 14.77 2.94 14.58 3.63 

OP-MP (°) 13.47 3.18 17.44 4.58 17.06 4.23 

SN-PP (°) 8.00 2.89 8.95 3.35 8.23 3.04 

U6-PP perp (mm) 20.00 4.15 22.73 2.52 23.97 2.84 

U6-PP (°) 78.89 6.29 81.00 6.24 83.11 6.27 

U1-PP perp 26.29 2.46 26.87 2.84 28.29 3.10 

U1-PP (°) 109.24 9.31 111.23 5.30 111.97 7.87 

U1-NA (°) 19.18 8.27 22.68 4.25 23.68 5.74 

U1-L1 (°) 134.27 13.56 130.53 7.02 131.35 7.98 

L6-MP (°) 84.95 4.10 78.53 5.60 80.40 6.05 

Perp, Perpendicular. 


March 2007 

OP-MP angle was 3.90° (SD, 3.83). Both changes molar (L6), the most infra-occluded premolar (L4), and 

were statistically significant (P .0001). 

the most extruded incisor (L1) were measured with 

According to the literature, angular changes of less reference to the mandibular plane. Since appositional 

than 10° in the long axes of the teeth do not have a bony growth at the inferior border of the mandible can 

significant effect on the perpendicular linear measure- 

38 

ments made from L1, L4, or L6 to the MP. In this 

radiographic study, no patients had angular changes 

greater than 10° for any teeth in question (Table III). 

The mean COS at T1 for the 31 patients treated with 

the continuous archwire technique was 2.47 mm (SD, 

0.69 mm; range, 2.00-4.00 mm). The mean COS at T2 

for this sample was 0.19 mm (SD, 0.31 mm; range, 

0.00-1.00 mm) (P .0001). During treatment, the mean 

reduction in the COS was 2.27 mm (SD, 0.77 mm), 

which corresponds to a 92.16% average reduction in 

this measurement. Twenty-one of the 31 subjects 

(about 67.80%) were completely level at T2, but 10 had 

slight residual COS at the end of this phase. The mean 

COS at T3 was 0.69 mm (SD, 0.64 mm; range, 

0.00-2.00 mm). The mean increase in the COS from T2 

to T3 was 0.49 mm (SD, 0.69 mm) (P .001). The 

overall mean time from T1 to T3 was 14 years 4 

add significant amounts to these measurements, growth 

prediction charts for normal white American youths 

were used to calculate net treatment (T2-T1) and 

posttreatment (T3-T2) changes. 

months, with a range of 7 years to 28 years 8 months. 

Over this period, the overall effect on the COS was an 

average reduction of 1.78 mm, which represents a 

72.97% reduction. 

The perpendicular heights of the mandibular first 

36 No growth data were 

found for mandibular premolar heights (L4-MP); therefore, 

figures midway between those of the molars and 

36 

the incisors were used for comparison. Growth adjustments 

were made by adding the relevant mean 

growth increments from the growth charts to the 

respective measurements made at T2 and T3. Paired 

t tests (with set at 0.01) were calculated for both 

the growth-adjusted and the unadjusted measurements 

(Table IV). 

Analysis of the data, unadjusted for growth, showed 

that there were statistically significant changes associated 

with treatment for premolar (L4-MP) and first 

molar (L6-MP) vertical heights (P .0001). The mean 

treatment changes for the dental heights were 0.53 mm 

(SD, 1.60 mm) for L1-MP, 2.81 mm (SD, 1.69 

mm) for L4-MP, and 2.31 mm (SD, 2.28 mm) for 

L6-MP (Table III). All unadjusted posttreatment (T3- 

T2) t test results for the L1, L4, and L6 perpendiculars



Table III. Cephalometric measurements from T1 to T3 

Measurement 

Treatment changes 

(T1-T2) 

to the mandibular plane (Tables III and IV) were 

statistically significant (P .01). 

After the relevant age- and sex-related mean growth 

increments were added to the data, the following results 

Posttreatment changes 

(T2-T3) 

Total change 

(T1-T3) 

Mean SD Mean SD Mean SD 

L4-COS line (mm) 2.50 0.77 0.49 0.69 1.78 0.74 

L1-MP perp (mm) 0.53 1.60 1.66 2.30 2.19 2.37 

L4-MP perp (mm) 2.81 1.69 1.00 2.00 3.81 2.15 

L6-MP perp (mm) 2.31 2.28 1.23 2.38 3.53 2.24 

L1-MP perp: growth (mm) 0.87 0.66 0.21 



L1-MP (°) 0.82 6.08 1.18 5.21 0.35 3.91 

L1 to A-Po (mm) 1.51 1.57 0.10 1.31 1.41 1.57 

L1-NB (°) 1.37 4.81 1.03 4.21 0.34 4.35 

SNA angle (°) 2.65 2.17 0.37 2.23 2.27 2.51 

SNB angle (°) 0.34 1.29 0.55 1.34 0.89 1.58 

ANB angle (°) 2.98 1.55 0.18 2.06 3.16 2.34 

Wits (mm) 0.52 1.86 0.06 1.45 0.59 1.95 

Y-axis (°) 1.05 1.34 0.34 1.33 0.71 1.73 

SN-MP (°) 0.98 2.43 0.56 2.44 0.42 2.75 

SN-OP (°) 2.98 3.09 0.19 2.56 3.18 3.22 

OP-MP (°) 3.90 3.83 0.32 3.14 3.58 3.18 

SN-PP (°) 0.95 1.91 0.73 1.64 0.23 1.78 

U6-MP perp (mm) 2.73 2.85 1.24 1.59 3.97 2.56 

U6-MP (°) 2.11 5.32 2.11 5.40 4.23 5.67 

U1-PP perp (mm) 0.58 1.99 1.42 1.79 2.00 2.20 

U1-PP (°) 1.98 9.29 0.74 5.22 2.73 9.00 

U1-NA (°) 3.50 8.09 1.00 3.92 4.50 7.24 

U1-L1 (°) 3.70 11.37 0.82 6.55 2.92 10.28 

L6-MP (°) 6.42 3.04 1.87 4.63 4.55 5.37 


Table IV. Paired t tests for cephalometric measurements 

Measurements T1 vs T2 T2 vs T3 

COS P .0001 P .0004 

L1 perp to MP P .0742 P .0004 

L4 perp to MP P .0001 P .0093 

L6 perp to MP P .0001 P .007 

L1 perp to MP, growth P .0052 P .0001 



L1 to MP P .4569 P .2181 

L1 to A-Po line P .0001 P .6829 

L1 to NB P .1227 P .1822 

SN-MP P .0316 P .2072 

Y-axis P .0001 P .1651 

OP-MP P .0001 P .5151 

SN-OP P .0001 P .6769 

SN-PP P .0095 P .0198 

ANB angle P .0001 P .6357 



were recorded. The mean adjusted (T2-T1) changes for 

L1-MP and L4-MP (Tables III and IV) were statistically 

significant (P .0052). The mean treatment 

changes allowing for growth were –0.87 mm for 

L1-MP, 1.26 mm for L4-MP, and 0.61 mm for L6-MP. 

The negative value calculated for the incisor represents 

relative intrusive movement over this time period. The 

posttreatment (T3-T2) changes for L1-MP and L6-MP 

adjusted for growth were statistically significant (P 

.0001). The mean net posttreatment dental movements, 

taking growth into account, were 0.66 mm for L1-MP, 

0.00 mm for L4-MP, and 0.23 mm for L6-MP. 

At T2, the mean increase in mandibular incisor 

inclination to the mandibular plane was 0.82° (SD, 

6.08°) (Table III). The mean amount of relapse (T3-T2) 

was –1.18° (SD, 5.21°). A negative number represents 

lingual movement (uprighting) of the mandibular 

incisors relative to the MP. The overall effect (T3-T1) 

on the mandibular incisor inclination to the MP was 

–0.35° (SD, 3.91°). 

Associated with orthodontic treatment, the mandibular 

incisors advanced a mean distance of 1.51 mm 

(SD, 1.57 mm) relative to the A-Po line (Table III).


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). 


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 

21




structural method, 49 to measure the treatment-induced 

changes in dental heights. Whereas this technique was 

suitable for measuring changes in the mandibular incisor 

region (L1-MP), it produced method errors that 

were unacceptably large for the other 2 dimensions 

studied (L4-MP and L6-MP). 

Our results indicate that most of the leveling of the 

COS was accomplished by relative extrusion of the 

premolars (mean, 2.81 mm) as measured by the L4-MP 

perpendicular distance (Table III). It is, however, likely 

that some of the mean increase in this dimension could 

be attributed to bone apposition at the inferior border of 

the mandible. Without control growth data for Class II 

subjects, we decided to use the growth charts derived 

from normal white American youths. In support of the 

use of normal growth data, our selection criteria favored 

subjects with normal to shorter-than-average 

lower anterior facial heights as measured by the MP to 

SN angle (32°). The appositional growth in the 

premolar area was taken to be the average of the 

available mean growth increments of the molar and 

incisor regions. 36 In this study, the mean contribution 

of growth to the L4-MP perpendicular distance was 

calculated as 1.55 mm. 

36 If this estimated growth is 

taken into account, then the mean net extrusion of the 

premolar was 1.26 mm. Likewise, taking appositional 

36 

growth (1.7 mm) into account, it can be said that 

during treatment the mean change in the L6-MP dis- 

36 

tance was 0.61 mm. Allowing for growth (1.4 mm) 

from T1 to T2, the perpendicular distance L1-MP 

decreased by a mean of –0.87 mm. The premolar and 

incisor changes were statistically significant (P .01) 

before and after the possible effects of growth were 

taken into account. These findings agree with previous 

studies suggesting that straight-wire techniques level 

the COS by a combination of premolar extrusion and 

incisor intrusion. 4,5,19,46 Those studies did not, how - 

ever, provide data to quantify the suggested tooth 

movements. 

The relapse of the COS (T3-T2), although small, 

was nonetheless statistically significant (P .01). The 

mean observed relapse in the COS could be attributed 

to changes in the relative vertical heights of 2 of the 

dental elements that were used to define the curve. 

Taking posttreatment growth changes into consideration, 

the mandibular incisor (L1-MP) erupted a mean 

distance of 0.66 mm, whereas the molar erupted a mean 

distance of 0.23 mm after treatment. The premolar, 

however, had no additional mean vertical dental height 

change after treatment and thus had no relapse. These 

results confirm previous findings of a slight return of 

the COS after treatment. 

19-21,27 

archwire mechanics. 

Several authors noted the effects of continuous 

3-9 These effects include flaring of 

the mandibular incisors, extrusion of the mandibular 

molars, and clockwise opening rotation of the OP. 

Some features of the continuous arch technique, including 

the –5° of torque in the mandibular incisors and the 

–6° of distal tip in the mandibular molars, are somewhat 

unique to this technique. These features, along 

with heat-treated stainless steel archwires with reverse 

COS in the mandibular arch and omega stops tied back 

to the molar tubes, might play a role in preventing the 

side effects reported with other straight-wire techniques. 

3-9 

All subjects in this study had mild to moderate 

mandibular incisor crowding that, with a straight 

wire and a nonextraction approach to treatment, 

would have been aggravated by the leveling of the 

COS. 39 Despite the incisor crowding in our sample of 

patients, the effects of the orthodontic treatment on the 

position of their mandibular incisors were minimal. The 

angles (L1-NB, L1-MP) were not statistically significantly 

changed as a result of treatment (P .01). The 

mean treatment change of the significantly (P .01) 

altered variable (L1 to A-Po) was 1.51 1.57 mm. 

Because the T1 average position for the L1 to A-Po was 

–1.18 mm, a mean proclination of 1.51 mm placed the 

tip of the L1 ahead of the A-Po line by a mean of 0.33 

mm. It is thus fair to say that, in this sample, orthodontic 

treatment did not result in excessive flaring of the 

mandibular incisors. 

Since there was very little alteration in the measures 

of the mean positions of the mandibular incisors during 

treatment, it was expected that little posttreatment 

change would occur. This was indeed the case; the 

posttreatment changes in the 3 measurements of mandibular 

incisor position studied here were small and not 

statistically significant (P .01). The L1 to A-Po 

distance relapsed an average of –0.10 mm to leave the 

tip of L1 just 0.23 mm ahead of the A-Po line. Both 

the T2 and the T3 recordings for the L1 to A-Po 

distance were close to the stated ideal position of this 

parameter. 46 In this group of patients, it can be - con 

cluded that the treatment-induced average advancement 

of the mandibular incisor was clinically acceptable and 

stable in the long term. 

From the data, it appears that the mean treatment 

change (T2-T1) for the mandibular molar inclination to 

the mandibular plane was –6.42° (SD, 3.04°). This 

finding indicates that the full 6° of tip back built into 

the molar attachments was expressed in most patients. 

The additional 0.42° might have been due to the use of 

reverse curved archwires that would tend to cause the 

posterior teeth to tip back even farther than the tip 

incorporated in the prescription of the appliance. This


second-order movement relapsed an average of 1.87° 

(SD, 4.63°), resulting in a mean long-term uprighting 

of –4.55°. 

A straight-wire approach to Class II orthodontic 

treatment requiring leveling of the COS has been 

associated with increases in the vertical dimensions of 

the face. 3,5-7 An analysis of the data from this study 

shows that in our patients the treatment did not have a 

major effect on 2 measurements of lower facial height. 

Although the Y-axis changed statistically significantly 

from T1 to T2 (P .001), the mean change was only 

1.05°. During treatment, the MP angle (SN-MP) 

changed by less than a mean of 1.0° (SD, 2.43°), 

which was not statistically significant (P .0316). 

There were changes in the mean angular relationships 

of the OP during treatment. During treatment, 

there were a mean reduction of –2.98° in the SN-OP 

angle and a mean increase of 3.90° in the OP-MP angle. 

These changes occurred during the leveling of the COS, 

and they represent counterclockwise rotation in the OP. 

The posttreatment changes in these 2 angles were not 

statistically significant (P .01). 

We studied only patients with Class II Division 1 

malocclusions with specifically defined parameters. 

Our results cannot be arbitrarily extrapolated to the 

success that can be achieved with other categories of 

malocclusions such as those characterized by vertical 

growth patterns. 

CONCLUSIONS 

1. It is feasible to determine the depth of the COS 

from cephalometric radiographs taken with the 

Quint Sectograph cephalometer. 

2. The continuous archwire technique effectively leveled 

the COS in this sample of Class II Division 1 

deep-bite patients treated without extractions. 

3. In this study, the leveling of the COS with the 

continuous archwire technique occurred by a combination 

of mainly premolar extrusion and, to a 

lesser extent, incisor intrusion. 

4. In the subjects studied here, the continuous archwire 

technique effectively controlled the mandibular 

incisor position during the leveling process. 

These results appear to be stable in the long term. 

6. The –6° of tip back in the molar band tipped the 

mandibular first molar back at least that amount 

during treatment. 

7. In this study, the continuous archwire technique did 

not cause excessive opening rotation of the Y-axis 

or the MP angle. 


March 2007 

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