Continuous versus intermittent extraoral traction: An experimental study

American Journal of ORTHODONTICS Volume

71,

Number

ORIGINAL

6,

June,

1977

ARTICLES

Continuous versus intermittent extraoral traction: An experimental study Michel

Brousseau,

D.D.S.,

MAD.,

and

Raymond

G.

W.

Kubisch,

D.D.S.,

M.S.D.

Dollar&des-Ormeuux,

Quebec, Cwlada, and Bellevue, Wash.

E

xtraoral traction to the maxilla has proved to be clinically effective in the correction of anteroposterior discrepancies in occlusion. Recently, the effect of such traction on the bones of the craniofacial complex has also been recognized.5y i, 9, I*, 13,l6 In all previous experimental studies, with one exception,16 extraoral traction to the maxillas of monkeys has been achieved with continuously applied force (24 hours per day). However, the intermittent application of ext,raoral traction is a common clinical procedure, and investigation is indicated to compare different force-application schedules. This article will describe the treatment effects and the posttreatment stability of extraoral high-pull traction applied to the maxilla of Macaca nemestrina on an intermittent versus a continuous schedule. Duration of force application is the independent variable of study. Materials

and

methods

The experimental protocol used in this study is described in articles by Elder and Tuenge.5s I3 Modifications were made and are noted in this description. Subjects (Table I). The subjects were eight male Macaca nemestrina monkeys provided by the Regional Primate Research Center at the University of Washington. All subjects had complete deciduous dentitions with the maxillary first perFrom versity

the Department of Washington,

of Orthodontics Seattle, Wash.

and

Regional

Primate

This research was supported by Grants DE 02931 States Public Health Service, by a grant from the dontic Memorial Fund, and by NIH Grant RR00166.

and DE University

This article is hased on research submitted by the authors the requirements for the Master of Science in Dentistry Orthodontics, University of Washington.

Research

Center,

02918 from the of Washington in partial degree,

fulfillment Department

UniUnited Orthoof of

607

608

Brausseau und Kubisch

Table

I. General

data concerning

I

Am.

the experimental

J. Orthod. June 1971

animals

Continuous* I M74039 M74040 M74080 M74050 I-50 c-39 c-40 C-80

Intermittent

M74064 M74206 T74074 Animal No. 1-64 I-06 I-74 Code Age at beginning of active treatment (mo.) 15 I5 I5 I5 14 II 16 Duration of active treatment (days) 87 84 75t 8X 84 96 673 Weight at beginning of active treatment (kg.) 2.10 2.30 1.86 1.95 2.30 2. IO 2.70 Weight at end of active treatment (kg.) 2.4 2.2 1.6 2.2 2.6 2.2 2.6 Weight at end of relapse period, 6 months (kg.) 2.8 2.5 2.0 2.8 3.4 2.4 3.7 “M 74240, the fourth animal of the continuow group, died 6 days into the experimental period. t Treatment stopped because of excessive distal movement of maxilla. :Treatment stopped because of loss of headgear plug and bow resorption. molars unerupted. Two groups of four each were randomly assigned : one group to receive intermittent estraoral traction (12 hours per day) and the other to receive continuous traction (24 hours per day). ma,ncnt

IMPLANTS. Tantalum implants were placed with a modified Bjiirk implant gun. Implant,ation was done in a sterile surgical field, exposing the individual sutures for visual identification. This technique assured proper placement of the implants on each side of the sutures. Twent>--two implants were used in each animal. Implant sites were the facial sutures, the maxilla, the prcmaxilla, the mandible, and the cranial base, as described by Elder and Tuenges and Van Ncss.~.~ IMPLANTED CEI'HALOMETRIC III&U) POSITIONER (FIG. I). To minimize error i?1 positioning of animals in the cephalostat, a custom-fnbricatetl Vitallium implant was attached to the front,al bone of each animal, anterior to the coronal suture, in a sterile surgical procedure in whicdh general ancsthcsia wils cniplo;vcd. A custom coupling device was fabricated for each animal by means of a stereotaxic instrumelit, with the head orientctl so that Frankfort plane was perpendicular to the coupler. In this way, the animal was consistently repositioned in the cephalostat and the central ray entered the three planes of the head at a right angle. The details of this procedure are described by Van Ness and associates.l” SPLINT AND HEADGEAR AI’I’I,IANCES (FIG. 1 ) Rubber-base impressions of each maxillary arch were taken and a cast-Vitallium splint. was constructed to cover the hard palate, the alveolus, and the labial a,nd lingual surfaces of the teeth. The splints were fixed by intcrproximal ligatures. An 0.045 inch (1.143 mm.) round buccal tube was soldered lateral to the terminal molar (maxillary deciduous second molar) to receive an 0.045 inch (1.143 mm.) inner bow of a commercially available Kloehn-style face-bow. The outer bow terminated eren with the tube and was bent 10 degrees a,bo\To the occlusal plant. Extracranial anchorage was obtained by direct. bony attac*hmcnt. An ovoid arca of scalp orcr the lamhdoidal

Volume

Number

Contiv~u0u.s z’ersus intermittent

71

6

e‘xtraoral

traction

609

MODIFIED CEPHALOSTAT

Fig.

1. Extraoral

traction

and

head-positioning

devices.

suture was surgically exposed, a stainless steel screw was placed in each parietal bone, and two screws were placed in the occipital bone. Cold-cure acrylic was molded over the screw heads and an 0.059 inch (1.49 mm.) round wire was embedded in the acrylic. This wire was adapted to the hea,d so that it coursed superior to the ear. The outer bow was connected to the anchorage wire with a SAW spring (Northwest Orthodontics, Inc., Seattle, Wash.) at 30 degrees to the oeclusal plane to deliver a force of 400 Gm. per side. Nylon bands with perforations connected the springs to the anchorage wire, allowing selective variation of force between 0 and 400 Gm. for the intermittent group. Protocol and records. A complete series of cephalometric radiographs consisting of (1) a lateral view of the head positioner, (2) a lateral view of the ear rods, (3) a posteroanterior (frontal) view of the head positioner, and (4) an inferosuperior (basilar) view of the head positioner, was taken on the following schedule : (1) prior to active treatment, (2) at 3-week intervals during active treatment, (3) at cessation of active treatment (one series with the splint and one series after splint removal), (4) 5 weeks posttreatment, and (5) at irregular intervals until 6 months posttreatment. Dental casts were obtained at the start of active treament, at the end of active treatment, and 6 months posttreatment to supplement the serial cephalometric records. In animals of the intermittent group the traction force was activated normally on a daily basis at 11 P.M. and deactivated at 11 A.M. Animals of the continuous group had 24 hours of active traction per day and needed no additional attention other than the usual care. During the active treatment phase, the animals were kept in restraining chairs which allowed maximal freedom without contact of their heads and hands. The splint and headgear appliances were removed at the end of active treatment and the animals were maintained in cages

610

Am.

Brousseau and Kubisch

1.5-23 Fig. 2. Lateral

head

film

tracing

and

8-month

composite

of

a normal

J. Orthod. June 1977

MONTHS untreated

Macaca

nemestrina.

from this point on. No attempt was made to retain the created malocclusion during the posttreatment observation period. Method of amnaZysis.After confirmation of implant stability, sutural changes were measured radiographically from implants on either side of the sutures. Skeletal change was measured from the postsphenoidal cranial base implants to the maxillary implants. Rotational effects wcrc evaluated from the change in occlusal plane on cranial base superimpositions. Dental change was measured from the maxillary implants to the splint for the active treatment evaluation and from the maxillary implants to the canine for the posttreatment evaluation. The underjet (negative overjet) was measured on lateral head films from the labial surface of the mandibular central incisor to the labial surface of the maxillary central incisor and to the mesial surface of the maxillary canine, respectively. All superimpositions were done from films taken with the implanted head positioner. Over-all lateral superimpositions were registered on the implants in the postsphenoidal portion of the cranial base, the general contour of sella turcica, and anterior and posterior cranial outlines. For superimpositions of the maxilla and mandible, the best fits of stable implants and bony outlines were used. Fig. 2 provides a comparison with a normal untreated McwK~~, nemestri?za. Further data on normal growing macaque monkeys can be found in previous studies.F, 8, lo Time intervals are designated by code as follows : T, = Beginning of active treatment. T, = End of active treatment. T, = 5 weeks posttreatment. T,? = 6 months posttreatment.

Volume

71

Table

II.

Number

Continuous

6

Changes

that

Active Treatment (initial-final)

Zygomaticotemporal suture (mm.) Zygomaticomaxillary suture (mm.) Zygomaticofrontal suture (mm.) Cranial base-maxillary implants (mm.) Splint-maxillary implants (dental) (mm.) Splint-cranial base implants (over-ail) (mm.) Occlusal plane clockwise rotation splint (degrees) Mandibular plane rotation (degrees) Net underjet l/l after splint removal (mm.) Net underjet 3/l after splint removal (mm.) *Splint unreliable.

occurred

during

cersus intermittent the active

treatment

extraoral

traction

611

phase

c-39

c-40

C-80

1-64

I-06

1-74

I-50

-2.8

-2.3

-2.0

-0.7

-1.0

-1.3

-0.8

-1.8

-2.1

-2.2

-0.8

-1.0

-0.7

-0.6

f0.4

-0.4

-0.4

-4.6

-5.5

-4.4

-1.7

-2.2

-2.4

-1.7

-2.0

-1.5

-1.5

-1.5

-2.0

-1.5

*

-1.9

-6.8

-6.5

-4.0

-4.8

-3.8

*

14.0 4.0

6.5 11.0 Counterclockwise -3.0 0.5

0.0

12.0

1.5

+0.2

0.0

7.0 4.5 Counterclockwise -3.5 -1.0

-0.3

* *

9.0

11.0

9.0

6.0

5.0

4.5

7.0

20.0

19.0

19.0

16.5

15.0

16.0

15.0

Results

One animal of the continuous group died of unknown causes 6 days into the active treatment phase. All other animals experienced general good health, with no apparent discomfort and with weight gain throughout the experimental period (Table I). Active treatment (TO-T,) (Table II). DENTITION. At the end of active treatment (T,) , all three monkeys in the continuous group showed the maxillary canine occluding with the mesial cusp of the mandibular second deciduous molar (Figs. 3 and 5). The four monkeys in the intermittent group showed the maxillary canine oeeludipg with the mandibular first deciduous molar (Figs. 4 and 6). The continuous group exhibited an average of 4 mm. more underjet than the intermittent group. The average incisor underjet of animals subjected to an intermittent force was 5.6 mm. (Table II). The amount of intramaxillary dental change ranged from 1.5 to 2.0 mm. for all seven animals, with no distinction in the amount of dental tipping between the two groups. FACIAL SKELETON. All subjects showed a clockwise rotation of the midfacial complex and especially of the maxilla and premaxilla. The amount of maxillary rotation varied from 4.5 to 14 degrees. A marked clockwise tipping of the premaxilla with an opening at the superior aspect of the pr~maxillomaxillary suture was observed in three monkeys of the intermittent group. The amount of linearly measured skeletal change was significantly greater for animals with continuous

612

Am.

Brousseau avzd Kubisch

FIf$AC ACTIVE

J. Orthod. June 1977

TREATMENT

\-,., ._.._._- -PCJsjTTREATMENT

CHANGES

6 MONT‘NS POSTTREATMENT Fig. 3. Models tinuous group

and during

lateral active

head film treatment

tracings of animal and posttreatment.

C-39,

representative

of

the

con-

force, with an average reduction in the distance between the implants of the cranial base and maxillary bone of 4.8 mm. for the continuous group and 2.0 mm. for the intermittent group; that is, there was 2.4 times more skeletal change in the continuous group (Fig. 7). Over-all superimposition revealed rotation of the mandibular plane in a range

Continuous

versus

intermittent

FlNkL

POSTTREATMENT

Fig. 4. mittent

Models

and

group

during

lateral active

extraoral

ACTiVE

traction

613

TREATMENT

CtfAh’SES

head

film

treatment

tracings and

of

6

MONTHS

animal

I-06,

POSTTR representative

EATMENT of

the

inter-

posttreatment.

of 3.5 degrees counterclockwise to 4 degrees clockwise, and no relationship was seen between subjects receiving intermittent force and those receiving continuous force. A counterclockwise rotation of the mandible was observed when maxillary rotation was less than 10 degrees, and a clockwise rotation when maxillary rotation was more than 10 degrees.

614

Fig. ment

Rrousseau

5.

Occlusion (T,)

(left)

Am.

a?ld Kubisch

tracings and

of

6 months

animals

of

posttreatment

the

continuous (T,)

group

at

the

end

of

J. Orthod. JU?Lt? 1977

active

treot-

(right).

The underjet at, the incisors was reduced by au average of 5.7 mm. for the continuous grciup and by 3.3 mm. for the intermittent group during this S-week posttreatment period. Likewise, the underjet at the canine showed an arerage reduction of 3.0 mm. for the continuous group and 1.5 mm. for t,he intermittent group. The amount of intramasillary dental change measured from the canine was within it range of 0 to 1.5 mm. Car all animals, ant1 no tlistinrtion was noted between the intermittent and continuous groups. FXIAI, SKELETOS. Ihring the T,-T, period, a rcvclrsal in the direction 01 changes was noted. Th(~ mitlfac:iaI ~~mr~~lcs rotatctl in a c.omlterclockmisc~ dircetion, and the cranial vilult ant1 calvnria rotated iI1 iI clockwise tlirection with a clcpression at lamb&~. There was ;I ~bountl of thr premaxilla toward its initial position as displayed by a cuunterclockwisc rotation of’ the premasilla and nasomasillary bones, intlepc~ndent from the maxilla. The amount and rate of skeletal trha,nge were greater clurillg the: T-T, period for the animals that were DESTITIOS.

C’o?ltiwous

z!ersus

\

Fig. 6. Occlusion ment

(T,)

(left)

and

tracings of animals of the 6 months posttreatment

i?lterneittent

extraoral

trnctio?l

I

615

\

intermittent (T,) (right).

group

at the

end

of

active

treat.

Brousseax md

616

mm. (CRANIAL

Fig.

7.

curred

Maxillary at

implants. than

jected

to an skeletal

posttreatment maxilla

facial

During

more more

skeletal

the

per

BASE - MAXILLA)

change

sutures,

active

twice

the

is represented

measured

treatment amount

intermittent

force.

change

for

period

(T,-Ts),

se were

Ant. J. Orthod. June 1977

Kubisch

the

comparable

(TO-T,) of

by

from

the

the

animals

skeletal

The

retraction

immediate

animals apposition for

the

of of both

resorption

cranial

the

to

when

compared

continuous facial

and

and

that

to

maxillary

the

a continuous

response group.

sutures

apposition

implants

subjected

posttreatment the

base

However, forward

with (T,-T,)

force

ocshow

animals shows over

movement

subslightly

a 6-month of

the

groups.

subjected to a continuous force (Fig. 7). The skeletal change for the continuous group represented an average increase in interimplant distance of 2.6 mm. (range, 2.5 to 2.7 mm.) and, for the intermittent group, an average increase of 1.95 mm. (range, I.8 to 2.1 mm.). Xix modhs posttreatment (TI-TQ) Table III. DENTITION. At the end of the 6-month posttreatment period (T,), each of the three animals in the continuous group had a full Class III malocclusion as illustrated in E’igs. 3 and 5, with the maxillary canine and permanent molars used as points of reference. Three monkeys in the intermittent group also presented Class III malocclusion, but to a lesser degree (Figs. 4 and 6). One animal, I-50, of this group had an occlusion that was closer to a Class I. The anteroposterior relationship of the maxillary posterior teeth and mandibular teeth achieved at the end of active treatment (T,) was closely maintained 6 months posttreatment (T,) in three monkeys of the intermittent group (Fig. 6). In animals submitted to a continuous force, the occlusion achieved at the end of active treatment (T,) was not maintained as well after treatment (T,-T,) . These animals showed change in the interocclusal relationship at a decreasing rate for 15 weeks posttreatment, and from that, point on the occlusal relationship was stable. FACIAL SKELETON. Throughout the posttreatment period (T1-TR), a gradual decrease in the rate of change in distance between the maxillary implants and

Continuous III. Changes that occurred

Table

Posttreatment changes (6 months) Maxillary implantMaxillary central (mm.) Cranial baseMaxillary central (mm.) Maxillary implantMaxillary canine (mm.) Cranial baseMaxillary canine (mm.) Cranial base-Maxillary implants (mm.) Occlusal plane counterclockwise rotation (degrees) Mandibular plane counterclockwise rotation (degrees) Reduction of underjet Maxillary central-Mandibular central (mm.) Reduction of underjet Maxillary canine-Mandibular central (mm.)

versus

intermittent

during the 6-month

posttreatment

extraoral

traction

617

phase

c-39

c-40

C-80

1-64

I-06

1-74

I-50

5.5

4.8

4.1

3.9

6.2

4.3

6.5

12.7

II.7

I I.3

II.4

12.7

II.7

12.0

2.5

I.4

1.2

I.0

1.3

2.0

3.5

9.6

8.3

8.0

8.4

1.5

9.5

9.0

1.2

6.9

1.2

7.4

6.5

1.5

5.5

16.0

10.0

10.0

II.0

8.0

4.0

22.0

3.0

2.0

2.5

0.0

2.5

0.0

2.0

7.0

9.5

7.0

4.0

4.0

4.0

8.0

4.0

6.0

4.0

I.0

0.0

2.0

5.0

the upper incisors was noted. The average increase in distance (TX-T3) from the maxillary implant to the maxillary central incisors was 5.1 mm., as contrasted to a similar measurement of 1.8 mm. from the maxillary implant to the maxillary canine. The absolute amount of skeletal change seen in the maxilla was not distinguishable between intermittent and continuous groups over a period of 6 months (T,-T,) , All animals exhibited counterclockwise rotation of the maxilla reflected in occlusal plane change over a range of 4 to 22 degrees and the rotation obtained during treatment relapsed during the posttreatment observation period (Tables II and III). The mandibular plane rotated counterclockwise in a range of 0 to 3 degrees. Discussion

At the end of active treatment (T,), the Class III malocclusion created in the animals subjected to a continuous application of force (24 hours per day) was significantly greater than the one created in animals subjected to an intermittent force application (12 hours per day). Since there was no distinction between groups with regard to intramaxillary dental change, the intergroup difference is attributed to skeletal response; animals in the continuous group experienced 2.4 times more sutural resorption than the ones in the intermittent group. Posttreatment (T1-T3), all seven animals responded in a similar pattern : (1) dental tipping and skeletal rotation that occurred during active treatment had reverted, (2) linear measurements between cranial base implants and maxillary implants show that the maxilla had moved forward a comparable linear amount for all animals. Therefore, the net difference at the end of 6 months posttreatment can be

explained only by growth inhibition and sutural resorption that occurred during the active treatment phase. The more nonrotational retraction of the maxilla that was achier-ed during treatment, the more net retract,ion was maintained posttreatment. It is possible to create diff’ercnt occlusal relationships within a given animal l)y rotating the maxilla while interimplant distances measured linearly to a reference point, such as the cranial base, remain the same. A vlockwisc rotation of the maxilla has been reported previously when extraoral traction ~-as applied to tht maxrilla.5, 7. 3, 12 The skeletal rotation that was protl~m~l in the midfacial complex during active treatment rcverscd when traction was discontinued as measured b,v occlusal planr changes. This observation intlicatcs a lack of stability in mechanically produced skclctal rotation. Evaluation of’ the occlusal relationships (Figs. 3 to 6) shows that the continuous group had more maxillary dental retraction and more occlusa I rclapsc than did the intermittent group. Il;ren though the two groups cannot be statistically distinguished on the basis of range of change in the occlusal plant, subjecti\c comparison of mean values for Mach group shows a tendency for the continuous group to have more rotat’ion of the maxilla. (Animal J-50 was not, included because of an instable splint.) Other subjective cvidencc also lends support to this theory. I+‘014c~samplo, t)litJ opcnitlg of the prcmaxillon~axillar~ suture at the superior aspect (T,) in three animals of the intermittent group and none of thosr in the continuous gronp may bc a result of vertical masillary growth, as seen in untreated animals, during inactive traction. Also, the two animals of the intermittent group that showed the least change in occlusal plane (l-06 and I-74)) as SWII ill Tahlc TI, snbsequcntl!- showc~l the least change in tlental occlusion during the course’ of the posttreatment period (Fig. 6). In an evaluation of immediate posttrcatment changes IT,-T,) , the continuous group illust~ratetl a greater rate of skeletal change when compared with the intcrmittent group. Although it is impossibl~~ to differentiate brtwccn growth ant1 1*0lapse, it is likely that the relapse at the sutures was clxprcssctl by a minimal amount, of catch-up growth at the sutures, which occurred early after remora1 of the traction force. Yamamoto’” studied the application of extraoral traction to the maxillas of monkeys for 18 hours per day and confirmed remodeling of facial sutures, both histologically and cephalometric~ally. One of the conclusions he reached was that extraoral traction to the maxilla had less retraction effect as his subjects increased in age. Elder and Tuenge5 found more dental c*ontribution and less skeletal contribution to the over-all treatment change than was observed in the continuous group of the present study. In addition, more midfacial skeletal rotation was produced in the present investigation. It is likely that these disparities arc, in part, attributablc to the inabilit,y to completely distinguish between dental tipping and skeletal rotation, as well as to differcnrcs in suljject age level and appliance drsign. Mandibular plane rotational change during maxillary traction has been c*lockwisc in previous studies,‘, !I, 1~’with one exception.” The present studp confirms earlier investigations and did not demonstrate the counterclockwise rotation during the actirc treatment phase that was reported by Elder and Tueng~.

Clo~tinuous versus intermittent

estr,aaoral trrrctio?a

619

During a posttreatment observation period of 26 days, Henry” noted movement of the affected bones toward their original positions at a rate that was much higher than could be attributed to normal growth over a similar time period. In contrast, Tuenge and Elde? reported that dental changes were seen immediately but that skeletal changes were insignificant during the early posttreatment phase and were consistent with what would be expected during normal growth. Our findings indicate that tipped teeth are inherently unstable, as reported by Tuenge and Elder, and add support to Henry’s” finding regarding early posttreatment skeletal changes. All studies agree that headgear traction accomplished only a temporary redirection of the maxillary growth pattern. Comparisons with untreated subjects (Fig, 2) illustrate that, over a comparable development period, there is possibly less eruption of the maxillary dentition in the animals receiving extraoral high-pull traction, indicating that the traction retarded vertical development of the dentition and alveolus. It is important to differentiate between maxillary and premaxillary response. Macaque monkeys at this stage of development have a patent premaxillomaxillary suture,8 and independent movement of the premaxilla has been shown in normal development as well as in experimental study. I1 This study confirms independent movement of the premaxilla when viewed on maxillary superimpositions. Also, during the posttreatment phase (T1-T3), there was a greater increase in the distance from the maxillary implant to the maxillary central incisor than from the implant to the maxillary canine. Previous studies of extraoral traction hare made no mention of independent premaxillary movement; however, they involved older subjects. The opening at the superior aspect of the premaxillomaxillary suture in combination with loosening of the occipital anchor plugs in the intermittent group but not in the continuous group during active treatment may be due to the intermittent application of force. This phenomenon is visualized as a mechanical “pumping” effect occurring with the activation and deactivation of the traction force. Further investigation of a histologic nature might contribute to the understanding of this observation. With regard to possible clinical implications of this study, it is critical to distinguish morphologically between monkeys and human subjects37 4 and to consider that monkeys are altered from a normal dental and skeletal relationship to a malocclusion, while with human beings the opposite takes place. In order to achieve a maximal skeletal retraction effect, extraoral traction should be used in conjunction with an appliance that splints the teeth together. A recent clinical study1 reported minimal skeletal effect when continuous extraoral traction was applied to only the maxillary first permanent molars. The maxillary molars also demonstrated a. strong tendency to recover to their original position and inclination relative to their base. Another study2 showed a relatively greater effect of extraoral traction on maxillary position when premolars were splinted to the molars, even when the force application was intermittent. Comparison of the present results with previous studies leads to the conclusion that young patients present the most. favorable prognosis for skeletal retraction of the maxilla. In addition, it appears that minimal retention would be required if the patient were subjected to an intermittent traction force that would deliver nonrotational skeletal retraction of the maxilla.

620

Am.

Brousseau and Kubisch

Summary

and

J. Orthod.

June

1977

conclusions

The comparative treatment and posttreatment effects of intermittent and continuous extraoral traction applied to the maxillas of eight Macaca nemestrina monkeys was studied. Two groups of four subjects each were prepared in identical fashion, with one group receiving 12 hours per day of active traction (12 hours inactive) and the other group receiving continuous traction (24 hours per day). The force level was 400 Gm. per side and was applied to face-bows attached to cast maxillary splints and stabilized by bony extraoral anchorage. The traction was applied for an average of 83 days, and then posttreatment observation was carried out for a minimum of 6 months. Both phases were documented by serial cephalometric radiographs. 1. Intermittent application of extraoral traction to the maxilla of Macaca nemestrina produces significant retraction of the midfacial complex. 2. Maca.ca ~aemestrina monkeys subjected to continuously applied extraoral maxillary traction exhibit a greater than proportional maxillary skeletal retraction than the ones on an intermittent application schedule. 3. Whatever clockwise maxillary skeletal rotation and distal dental tipping are achieved with extraoral traction prove to be unstable posttreatment in young growing monkeys. 4. The more nonrotat,ional retraction of the maxilla achieved during treatment, the more net retraction is maintained posttreatment. The authors would help in the preparation assistance.

like to thank R. of this manuscript.

William We

McNeil1 also thank

and Benjamin C. Moffett for their Andree Brousseau for her technical

REFERENCES

1. Badell, M. C.: An evaluation of extraoral combined high-pull traction and cervical traction to the maxilla, AK J. ORTHOD. 69: 431-446, 1976. 2. Damon, D. H.: A clinical study of extraoral high-pull traction to the maxilla utilizing a heavy force: A cephalometric analysis of dentofacial changes, M.S.D. thesis, University of Washington, 1970. 3. Enlow, D. H.: A comparative study of facial growth in Homo and Macaca, Am. J. Phys. Anthropol. 24: 293-307, 1966. 4. Duterloo, H. S. : A comparative study of cranial growth in Homo and Macaca, Am. J. Anat. 127: 357-368, 1970. 5. Elder, J. R., and Tuenge, R. H.: Cephalometric and histologic changes produced by extraoral high-pull traction to the maxilla of Macncn mu,Zattcc, AM. J. ORTHOD. 66: 599-617, 1974. 6. Erickson, L. C.: Facial growth in the macaque monkey: A longitudinal cephalometric study using metallic implants, M.S.D. thesis, University of Washington, 1958. 7. Fredrick, D. L.: Dentofacial changes by extraoral high-pull traction to the maxilla of Macaccl mulatta, M.S.D. thesis, University of Washington, 1969. 8. Gans, B. J., and Sarnat, B. G.: Sutural facial growth of the dlncaca rhc.sz~s monkey: A gross and serial roentgenographic study by means of met,allic implants, AM. J. ORTHOD. 37: 827841, 1951. 9. Henry, H. L.: Craniofacial changes induced by orthopedic forces in the Xacaca rhesus monkey, M.S.C. thesis, University of Manitoba, 1973. 10. McNamara, J. A., Jr.: Neuromuscular and skeletal adaptations to altered orofacial function, Monograph No. 1, Craniofacial Growth Series, Ann Arbor, 1972, Center for Human Growth and Development, University of Michigan.

Continuous 11. 12. 13. 14. 15.

16.

versus idermittent

extraoral

traction

621

Moore, G. J.: A longitudinal study of thumb-sucking and open-bite in the ~acacn mulatta, M.S.D. thesis, University of Washington, 1970. Sproule, TV. R.: Dentofacial changes produced by extraoral cervical traction to the maxilla of the Xncaca mulatta, M.S.D. thesis, University of Washington, 1968. Tuenge, R. H., and Elder, J. R.: Posttreatment changes following extraoral high-pull traction to the maxilla of .Uucuca mulatla, AM. J. ORTHOD. 66: 618-644, 1974. Van Ness, A. L.: Cranial base implants for nonhuman primates, Personal communication, 1975. Van Ness, A. L., Merrill, 0. M., and Hansel, J. R.: Cephalometric roentgenography for nonhuman primates utilizing a surgically implanted head-positioner, Am. J. Phys. Anthropol. 43: 141-148, 1975. Yamamoto, J.: Effects of extraoral forces in the dentofacial complex of Xucaca irus, orthodontic thesis, Osaka Dental University, Japan, 1975. Dr. Dr.

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THE JOURNAL

60 YEARS

lY4)

AGO

June,1917 The

great

man

who

doing the

compass, that

belongs Dentistry

American

of

the

walk

is hard beaten

overlooked

in

need will

work,

and

highway, by explore to and Journal

dental

through

and the

man

content

the

travelers the

the

trackless pioneer,

Medicine, of

Orthodontics,

the

medical

untrodden

inherently to

wild, and

is a lazy

pick

who

field

here

have make leave

International 3:369,

professions

today

and

a trail.

leave

animal.

Most

and

there

a

passed

on

before,

a new a trail. Journal 1917.)

path, (Martin

berry

the

a

rather

derive Orthodontia,

all

pathmaker;

Original

men or

Dewey: of

is

prefer

to

flower

that

than the

the

thinking

take

pleasure

Editorial-The predecessor

and

loiter

along

has

been

chart

and

and

profit

Pathmaker of

The