Vertical anterior relapse

American Journal of ORTHODONTICS Volume 65, Number

ORIGINAL

6 June,

1974

ARTICLES

Vertical anterior relapse Robert Robert

6. Nemeth, J. Isaacson,

D.D.S., M.S.D., D.D.S., Ph.D.

and

Minneapolis, M&n.

E

very orthodontist is concerned about maintaining treated cases. In this regard, the tendency of anterior teeth to return toward their pretreatment vertical relationship following orthodontic treatment is well recognized. After active orthodontic treatment, some patients who exhibited deep anterior overbite before treatment return toward deep overbite. Similarly, some patients who exhibited anterior open-bite prior to treatment return toward open-bite. For vertical incisor relations to regress toward their former deep-bite or open-bite condition, two theoretic possibilities exist. One possibility is vertical movement of teeth relative to the mandible or maxilla. This can be termed toothto-bone change. The other general category of possible change is vertical movement of one jaw relative to the other, which would carry the teeth to new vertical relations with each other. This can be termed bone-to-bone change. Of course, these two processes are not mutually exclusive, and a third possibility is for both processes to occur. Tooth-to-bone

changes

In the general category of tooth-to-bone change, incisor overbite or open-bite is altered by vertical movement of the incisors through the alveolar bone of either jaw. Such tooth movement can be vertical translation, with no axial inclinational change of the incisor involved. The tooth movement can also be rotational and result in an alteration of the axial inclination of the tooth or teeth involved. In the latter instance, the effective vertical length is altered (and therefore the overbite or open-bite is altered) without moving the tooth apex vertically. 565

566

Nemeth

Bone-to-bone

nd

Isnocso~~~

Am. J. Orthod. Jwne 1974

changes

In the general category of bone-to-bone changes, vertical incisor relations are altered when one jaw is vertically repositioned relative to the other. Such repositioning carries the teeth to new relative positions. If no compensatory vertical movement of anterior teeth occurs, the vertical dental relations may be changed also. The amount of dental change is a function of the amounts of growth and the dental occlusion present. Bone-to-bone changes may occur by proportionately greater amounts of vertical increase in the posterior facial height than in the anterior facial height. This occurs when the mandibular condyle experiences a vertical increment of growth or if the temporal fossa should move vertically. When increases occur in either or both of these areas without a compensatory anterior facial height increase, the mandible rotates in a forward direction. If the most anterior vertical dental contact is posterior to the incisors, forward mandibular rotation tends to deepen the overbite. If the upper and lower incisors are in contact, this will be the center of rotation and the overbite will not clinically increase. Bone-to-bone changes may also occur by proportionately greater amounts of vertical increase in anterior facial height than in the posterior facial height. This occurs when the maxillary sutures experience a vertical increment of growth. When increases occur here without compensatory posterior facial height increases, the mandible rotates in a backward direction, tending to open the bite. The sutural or periodontal areas around the anterior teeth also undergo vertical increases. However, if the buccal teeth experience a vertical increase resulting in a backward rotation, the anterior teeth would have to experience an even greater vertical increase to maintain anterior vertical dental relations due to the rotational nature of the bone-to-bone movement. Such dental compensations frequently do occur. Isaacson and associatesz5 noted that backwardrotating mandibular growth patterns had, on the average, greater vertical incisor growth combined with open-bite. Conversely, forward-rotating mandibular growth patterns showed less vertical incisor development coupled with deep incisor overbite. This article will attempt to show that changes in vertical jaw relation produced by mandibular rotation resulting from vertical growth at the condyle, at the maxillary sutures, or at the alveolar processes after orthodontic treatment can contribute to vertical anterior relapse. Review

of the

literature

Tooth-to-bone changes regarding vertical anterior relapse. A review of the literature reveals diverse opinions concerning the cause of overbite relapse in terms of tooth-to-bone changes. Tooth-to-bone changes causing relapse of deep anterior overbite are depression of elongated posterior teeth, elongation of depressed incisors, uprighting of distally tipped posterior teeth, or distal tipping of upper and/or lower incisors. Porter34 and Hopkinsz4 noted that stability of overbite is questionable with an elevation of posterior teeth. Similarly, Cole,14 Mershon,33 and Wylie4g reported that overbite corrected by elongation of the posterior teeth produces a constant strain on the muscles of mastication. Jn

Volume Number

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Vertical

anterior

rekpse

567

contrast, Hemley,23 Merritt,3Z and Schudy37T 39 stated that eruption of posterior teeth is permanent. Cole,14 Leff ,26 Litowitz,*? and Schudy39 stated that extrusion of depressed lower incisors contributes to return of overbite. StackleF noted that deep overbite return is due to a combination of elongat.ion of mechanically depressed maxillary incisors and mesial tipping of leveled posterior teeth. Thompson*’ found that the upper and lower incisor heights increased during and after retention but remained intruded in all groups except his Class I nonextraction group. He also found that the maxillary and mandibular molar heights increased during and after retention in all groups. Corlett,15 Graber,21 Strang,42 Schudy,“” and Tweed4* suggested that incisor axial inclination and/or interincisal relationships at the end of active treatment may be one factor in overbite return. With increases in the interincisal angle, anterior vertical overbite increases, if other relationships remain unchanged.Z8s 30,39 Little has been written explaining the cause of open-bite relapse in terms of tooth-to-bone changes. With decreases in the interincisal angle and all else remaining unchanged, anterior open-bite increases.28, 30 Garline? and Straub43, 44 stated that tongue or finger habits produce open-bite relapse. On the other hand, Subtelny and Subtelny,4S in an excellent survey of the literature, concluded that the muscular activity of deglutition is dictated principally by form. Bone-to-bone changes regarding vertical anterior relapse. Graber,21 Markus, Riede1,35 and others have stated that the effects of growth may alter the changes accomplished during active treatment. Bj6rk7 found that growth of the condyles can be detected in some persons even after the age of 20 years. Skielle?’ suggested that after the treatment of basal deep overbite (that is, overbite produced by underdevelopment of the lower face) the period of retention should take account of the time for completion of condylar growth in that particular patient. This suggestion considers deep overbite relapse in terms of a bone-tobone change. A careful review of the literature reveals nothing explaining the cause of open-bite relapse in terms of a bone-to-bone relationship change. A few authors have shown that bone-to-bone changes produced by growth cause overbite changes , in untreated persons. Bj6rk1e3 found that overbite diminishes, on the average, but exhibits individual variation in both directions, closing or opening during growth. In a study of growth changes in forty-one pairs of like-sexed twins over a period of 13 years, LundstrSmZ9 noted that the vertical pattern of growth far the chin was accompanied by development of open-bite in the anterior segment. Mandibular growth rotation is a term used to describe the rotational change of the mandible relative to cranial structures resulting from growth. This growth rotation, a bone-to-bone relationship change, takes place as a result of two separate processes. The first involves the differential vertical relationship between mandibular condylar growth and the combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible.4, 5* s, I3916-19,38,33 If the combined vertical growth of the nasal, zygomatic, and frontal sutures of the maxilla and the vertical growth of both the maxillary and mandibular molars

568

Nemeth

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J. Orthod.

June1974

exceed the vertical component of condylar growth, the mandible rotates clockwise (as viewed from the patient’s right side). Conversely, if t,he vertical comnonent of condplar growth exceeds the combined vertical growth of the nasal, xpgomatic, and frontal sutures of the maxilla and molar vertical growth of both t,hc maxilla and the mandible, the mandible rotates counterclockwise. Schndy”7s X8wrote that clockwise rotation is a result of more vertical growth at the molar area than at the mandibular condyles, and extremes of this condition cause open-bites. Counterclockwise rotation is a result of more condylar growth than vertical growth at the molars, and extremes of this condition cause closed bites. The second process involved in mandibular growth rotation is the direction in which the mandibular condyle grows. Early studiesllv I2 of facial growth showed that the mandibular border remained constant in its angular relationship to cranial structures during growth. However, more recent studies7, I8 have shown that appositional and resorptive processes take place on the lower border of the mandible to mask the growth rotation and maintain the apparent constant relation with cranial structures. IVith the aid of metallic implants in the mandible, Bjiirk7 found that the direction of condylar growth could be vertical, sagittal (posterior-superior), or any dir&ion in between. When condylar growth took place in a vertical direction, resorption occurred at the mandibular angle and apposition occurred at the symphysis, thus maintaining the constant relation between the mandibular plane and cranial structures. Conversely, when condylar growth took place in a posterior-superior direction, apposition occurred at the mandibular angle and resorption occurred at the symphysis, thus maintaining the constant relation between the mandibular plane and cranial structures. Most recently, Bj6rkg focused on the center of rotation as a critical factor determining mandibular inclination. He stated that the center does not necessarily lie at t,he temporomandibular joints, as is usually imagined, but may be located at the posterior or anterior ends of the mandible or somewhere in between. According to B jiirk,” forward rotation may occur from three separate mechanisms and backward rotation by two separate mechanisms. Methods

and

materials

The material for this study consisted of twenty-six patients chosen from the files of the Division of Orthodontics, School of Dentistry, University of Minnesota, and the private practices of Brs. .John Barton, Lloyd Pearson, and Frank Worms. The patients were selected on the basis of deep overbite or open-bite return following orthodontic treatment as observed directly from dental casts. The criteria for selection were as follows: 1. One set of dental casts taken before orthodontic treatment. 2. A second set of dental casts taken at the beginning of retention. 3. A third set of dental casts taken at a subsequent date sometime after the end of retention, showing return toward the original overbite or open-bit,e relationship. 1 4. The backs of all dental casts were trimmed perpendicular to the occlusal piano.

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Y.

Fig.

1. Cranial

Fig.

2.

and

Constructed

defined

reference

anatomic lines

and

and

bony

planes

landmarks.

used

in this

study.

Two

special

lines

were

as:

Z line-A

line

facial

heights.

PFH

line-Posterior

through

mandibular

perpendicular facial

to height

the

SN line

plane

at

perpendicular

nasion,

used to

the

to SN

measure plane

anterior passing

gonion.

5. Three standardized sagittal roentgen head films corresponding to the dates of the three sets of dental casts. The time period between the beginning of retention (criterion No. 2) and the follow-up records (criterion No. 3) varied from as little as 1 year to as long as 6 years. Patient age and technique of treatment, except the use of Class II and Class III elastics, were not variables important to the selection of these patients. No patients were selected who exhibited anterior or posterior cross-bites. Landmarks. Conventionally defined bony landmarks (Fig. 1) were recorded, including sella, nasion, gnathion, gonion, subspinale (A), supramentale (B) , mention, pogonion, and anterior nasal spine. Other dental landmarks utilized were defined as: The maxillary~and mandibular central incisors (1 and 7). Molar superius (6)-tip of the mesiobuccal c&p of the maxillary first molar. Molar inferius (G)-tip of the distobuccal cusp of the mandibular first molar.

570

Fig.

Nemeth and Isaacson

3. Angular

measurements

based

Am.

on constructed

reference

lines

and

J. Orthod. Jme 1974

planes.

Fig. 4. Linear measurements based on constructed reference lines and planes Ok-Overbite or open-bite is the distance between incison superius and incison inferious on a perpendicular to the occlusal plane. Increases are designated positive (t), whereas decreases are designated negative (-) Oj-Overjet is the distance between incison superius and the labial surface of the mandibular incisor on a line parallel to the occlusal plane. Increases are positive (t); decreases are negative (-) TAFH-Total anterior facial height is the linear distance along the Z line from nasion to menton. UAFH-Upper anterior facial height is the linear distance along the Z line from nasion to the anterior nasal spine. LAFH-Lower anterior facial height is the linear distance along the Z line from anterior nasal spine to menton. PFH-Posterior facial height is the distance along the PFH line from the SN plane to gonion. The posterior facial height represents a combination of the distance from the SN plane to the glenoid fossa and the distance from the glenoid fossa to gonion.

In addition, landmarks proposed by Bj6rk7 were used to superimpose mandibles, including : Anterior midline curvature of the chin between B point and pogonion. Inner cortical structure of the inferior border of the symphysis. Detailed trabecular structures related to the mandibular canal. Superimposition was also done using various conventional cranial landmar&, such as crista galli, ethmoidale, the posterior midline floor of the anterior cranial fossa, the medial border of the orbital roof, sphenoidale, anterior and posterior clinoicl processes, the clivus, and the posterior midline portion of the middle cranial fossa. Lines and planes of reference. Using the above landmarks, the following lines and planes were constructed (Fig. 2) : SN plane, mandibular plane (MP) , occlusal plane (OP), axis of upper incisor, axis of lower incisor, N-A line, and N-B line. Two special lines were defined as : (1) Z line-A line perpendicular

Volume Number

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to the XN plane located at nasion. The menton and the anterior nasal spine were projected on a perpendicular to this line. (2) Posterior facial height (PFH) line-a line perpendicular to the XN plane passing through gonion. Measurements based on constructed lines and planes. From the lines and planes, angular and linear measurements were made to determine tooth-to-bone changes and bone-to-bone changes. The following angular measurements were recorded (Fig. 3). MP-SN-The

internal

angle

formed

by

the

mandibular

plane

and

the

sella-nasion

plane. OP-SN-The internal angle OP-MP-The internal angle SNA -The internal angle SNB -The internal angle l-SN -The internal angle upper incisor. i-MP -The internal angle lower incisor. Tnterincisal angle (IA)-The and the axis of the

The following

formed by the occlusal plane and the sella-nasion plane. formed by the ocelusal plane and the mandibular plane. formed by the sella-nasion plane and the N-A line. formed by the sella-nasion plane and the N-B line. formed by the sella-nasion plane and the axis of the formed

by

the

internal angle lower incisor.

mandibular formed

plane by the

axis

and of

the

axis

the

upper

apex

of

the

the

root

of

the

incisor

linear measurements were recorded (Fig. 4).

a-The perpendicular central incisor. b--The perpendicular mandibular incisor.

distance

from

distance

from

the the

SN

plane

to the

mandibular

plane

root to

maxillary

apex

of

the

The two distances, a and b, would be subject to error in those cases where root tip resorption occurred during orthondontic treatment. Therefore, the original length of the tooth before orthodontic treatment was measured along the axis of the tooth with incisal edges coincident in those cases where tooth length changed during orthodontic treatment. c-The d-The

perpendicular perpendicular

distance distance

from from

the SN plane the mandibular

to the molar superius. plane to the molar

inferius.

Measurements based on structural landmarks. Using anatomic and bony landmarks for superimposition of the roentgenogram taken at the beginning of retention and the follow-up roentgenogram, a second set of measurements were recorded to determine tooth-to-bone changes and bone-to-bone changes. Structural landmarks of the anterior and middle cranial fossae were used for superimposition of the two roentgenograms to determine the upper incisor angular axial inclination change and linear measurements a’ and c’ (Fig. 5). This technique was used to eliminate or reduce the biologic error incurred by an upward or downward displacement of nasion with growth at the frontonasal suture.F Structural landmarks as described by BjorkQ were used to superimpose the two roentgenograms in determining the lower incisor angular axial inclinational change and linear measurements b’ and d’ (Fig. 6). This technique was used to eliminate the biologic error incurred by mandibular lower border compensatory remodeling with growth when the mandibular plane was used as a reference plane for linear measurements.

572

Nemeth

Am.

and Isaacson

The following

angular measurements

J. Orthod. June 1974

were recorded :

Upper

incisor axial inclinational change (I&$A)-The angular difference of the upper incisor axial inclination between the two roentgenograms. The angle was designated positive (+) when the crown moved labially with the center of rotation apical to the in&al edge and negative (-) when the crown moved lingually with similar centers of rotation. Lower incisor axial inclination change (i&A)-The angular difference of the lower incisor axial inclination between the two roentgenograms. The same positive and negative designation for angles was used as with the upper incisor axial inclinational change.

The following a’-The

linear measurements

linear difference in the along a perpendicular beginning of retention. b’-The linear difference in the grams along a perpendicular beginning of rentention. grams at the

were recorded :

upper line

incisor to the

root apex between the two roentgenoSN plane of the roentgenograms taken

lower line

incisor to the

root apex MP of the

between the roentgenogram

two

roentgenotaken at the

Corrections were made in those cases in which tooth length changed during orthodontic treatment : cl--The linear difference in the molar superius between the two roentgenograms along a perpendicular line to the SN plane of the roentgenogram taken at the beginning of retention. d’-The linear difference in the molar inferius between the two roentgenograms along a perpendicular line to the occlusal plane of the roentgenogram taken at the beginning of retention. Posterior facial height increase (PFH inc.)-The distance between the SN plane on the roentgenogram taken at the beginning of retention and the transferred SN plane (transfer technique to be described below) on the follow-up roentgenogram along the PFH line of the follow-up roentgenogram with the mandible superimposed on structural mandibular reference landmarks (Fig. 7). The PFH inc. represents any sutural growth of the temporal bone with presumed lowering of the glenoid fossa and the vertical component of mandibular condylar growth.

A technique described by Skieller*O was used to determine mandibular growth rotation, a bone-to-bone relationship change. The technique involves the transfer of the SN plane from the head film taken at the beginning of retention to the follow-up head film with cranial bony landmarks coincident. The rotation of the mandible is then measured as the angle between the SN planes on the two films when these have been superimposed with natural mandibular reference landmarks coincident (Fig. 8). In this study, SN planes intersecting anterior to S are designated positive (+) , indicating forward mandibular growth rotation, while those intersecting posterior to S are designated negative (-), indicating backward mandibular growth rotation. Linear measurements were made with a modified Boley gauge to the nearest 0.25 mm. and angular measurements were made with a Baum cephalometric protractor to the nearest 0.25 degree. Since these tracings are subject to both tracing and measurement error, a general determination of such error and reliability of the technique was undertaken. The roentgenograms taken at the beginning of retention and the follow-

Volume Number

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573

Fig. 5. Angular and linear measurements based on cranial anatomic landmarks for superimposition. Solid line represents the roentgenogram taken at the beginning of retention. Dashed line represents the follow-up roentgenogram. 14A, Upper incisor axial inclinational change between beginning of retention and follow-up roentgenogram. The angle is positive (+) when the crown moved labially and negative (-) when the crown moved lingually. a’, The linear difference in the upper incisor root apex between the two roentgenograms along a perpendicular line to the SN plane of the roentgenogram taken at the beginning of retention. c’, The linear difference in the molar superius between the two roentgenograms along a perpendicular line to the SN plane of the roentgenogram taken at the beginning of retention. Fig. 6. Angular and linear measurements based on mandibular anatomic landmarks for superimposition. Solid line represents the roentgenogram taken at the beginning of retention. Dashed line represents the follow-up roentgenogram. ldA, Lower incisor axial inclinational change between the two roentgenograms. b’, The linear difference in the lower incisor root apex between the two roentgenograms along a perpendicular line to the MP of the roentgenogram taken at the beginning of retention. d’, The linear difference in the molar inferius between the two roentgenograms along a perpendicular line to the occlusal plane of the roentgenogram taken at the beginning of retention.

up roentgenograms of four patients were used for this purpose. Each roentgenogram was traced and measured at two different times on two different days. The mean error for linear measurements was -0.01 mm. with a standard deviation of 10.25 mm. The mean error for angular measurements was +0.06 degrees with a standard deviation of kO.40 degrees. Results

Only measurements based on structural landmarks are presented. Measurements based on constructed lines and planes using changing landmarks are available for comparison but are not presented because of their inherent biologic error. Theoretically, the tooth-to-bone changes which affect vertical anterior relapse

574

Nemeth

and Isaacson

fig. 7. Posterior facial height increase (PFH inc.), measured as the distance SN plane on the roentgenogram taken at the beginning of retention and SN plane on the follow-up roentgenogram along the PFH line of the follow-up gram with the mandible superimposed on stable mandibular anatomic SN plane of the roentgenogram taken at the beginning of retention. **, follow-up roentgenogram. ***, SN plane of the roentgenogram taken at of retention transferred to the follow-up roentgenogram after superimposition cranial anatomic landmarks. Solid line represents the roentgenogram beginning of retention. Dashed line represents the follow-up roentgenogram.

Am.

J. Orthod.

June

1974

between the transferred roentgenolandmarks. *, SN plane of the beginning on stable taken at the

the

fig. 8. Technique used to determine the mandibular rotation resulting from posterior facial growth. The degrees of rotation are measured as the angle between intersecting SN planes * and *** after superimposition on stable mandibular anatomic landmarks. This figure represents an example of backward mandibular growth rotation as indicated by SN planes intersecting posterior to S. An example of forward mandibular growth rotation may be seen in Fig. 7, where the SN planes intersect anterior to S. *, SN plane of the roentgenogram taken at the beginning of retention. **, SN plane of the follow-up roentgenogram. * * *, SN plane of the roentgenogram taken at the beginning of retention transferred to the follow-up roentgenogram after superimposition on stable cranial anatomic landmarks. Solid line represents the roentgenogram taken at the beginning of retention. Dashed line represents the follow-up roentgenogram.

are the incisor axial inclination changes, the incisor vertical positional changes, and the molar vertical positional changes. However, the molar vertical positional changes in relation to the posterior facial height changes produce bone-to-bone changes. Table I summarizes the incisor axial inclinational changes for both anterior open-bite relapse and deep-overbite relapse patients. The results in both groups are quite variable. Four of the thirteen anterior open-bite relapse patients showed upper incisor axial inclinational changes with the crown moving toward the labial. Six of the thirteen anterior open-bite relapse patients showed upper incisor axial inclinational changes with the crown moving toward the lingual,

Vertical

Table

I. Upper

and

lower

Patient Anterior

open-bite J. N. M. M. J. El. M. D. J.

M. S. A. M. P. R. S. H. Pr.

incisor

OB rclnpse

axial

(mm.)

inclinational 1

anterior

relapse

change

1 qC A (degrees)

1

1 4

A (degrees)

patients - 1.00 - 1.00

-

2.00

-

2.00

- 1.00 -

4.00

- 0.50

n

-

5.00

- 0.50

n

-

2.00

- 0.50

n

-

5.00

-

1.75

- 4.00

-

5.00

-

I.50 2.25

+ 3.00 + 1.00

-

3.00

0

-

2.50

-

1.00

+ 2.00

G. S.

-

1.50

+ 3.50

+ 5.00 + 3.00 - 2.00

S. H.

-

1.75

G. C.

-

1.75

+ 5.00 - 3.00

L. J.

- 1.00

- 3.00

Anterior

deep-overbite J. M. G. M. C. G. D. G. J. J. D. M. J.

A. A. M. B. E. B. E. P. M. R. B. M. L.

575

relapse

n

patients

+ 1.50

+ 2.00

+ 2.00

+ 2.00

+ 2.25

-

+ 1.00

+ 5.00

+ 3.00 + 3.25

-10.50 - 5.50

+ 3.00 - 2.50

+ 1.00

+ll.OO

+ 3.25 + 1.25

-

+ 2.50

3.50

-

6.75

-

1.00

+ 8.00

t

3.75

- 3.00 - 4.00

-

2.00 3.00

+ 3.50 + 3.00

+ 2.00

+ 3.25

+ 1.00

+ 4.00

+ 2.00

+ 4.00

+ 1.00

6.00

0

0

while three remained unchanged. Eight of the anterior deep-overbite relapse patients exhibited upper incisor axial inclinational changes with the crown moving toward the labial as compared to five who showed lingual crown movement. Lower incisor axial inclinational changes for the anterior open-bite relapse patients showed three cases in which the crown moved labially, eight cases in which the crown moved lingually, and two cases that remained unchanged. For the anterior deep-overbite relapse patients, the lower incisor axial inclination changed with the crown moving labially in five cases and lingually in six, and remained unchanged in two cases. Table II summarizes the vertical positional changes of the incisor root apex. Both groups expressed increases in upper incisor apical vertical position between the beginning of retention and the follow-up records. The range for anterior open-bite relapse patients was from +0.25 to +i’.OO mm. The range in anterior deep-overbite relapse patients was from +l.OO to +5.00 mm. The lower incisor apical vertical position in the anterior open-bite relapse patients increased in six cases, remained unchanged in six cases, and decreased

576

Nemeth and

Table

II. Upper Patient

Anterior

open-hits

and

Tsaacson lower

root

OB

I ralnpsa

Am.

apex

(mm.)

vertical I

positional

J. Orthod. June 1914

change

a’ (mm.)

b’ (mm.)

patients -

1.00 1.00 0.50 0.50

+ + + +

J. P.

-

0.50

+ 7.00

8. M. I). J. G. S. G. IA.

R. 8. H. Pe. S. H. C. J.

-

1.75 1.50

-

2.25

+ 0.25 + 0.50

-

2.50

+ 2.00

-

1.50

-

1.75 1.75

+ 1.00 + 0.50

+ 0.50

+ 0.50

-

-

1.00

+ 3.00

+ 1.00

J. M. 0. M.

A. A. M. R.

+ 1.50

+ 3.00

+ 3.50

+ 2.00

+ 2.00

+ 0.50

+ 1.00

+ 2.50

+ 1.50

+ 3.00

+ 5.00

+ 2.00

c. E. G. H.

+ *3 .du5

+ 1.00 + 2.00

+ 1.00

D. E. G. P. J. M.

t

+ 1.25

+ 0.50 + 0.50

+ 2.50

+ 2.00 + 3.00 + 7.00

.T. R.

+ 4.00

+ 2.00

D. I3. M. M. J. 12.

+ 1.00

+ 2.00

+ 3.25

+ 2.00

+ 1.00

+ 1.00

+ 1.00

+ 1.00

J. M. iv. P. M. A. M.

Anterior

M.

deep-overbite

relapse

2.00 2.00 2.00 2.00

+ 7.00

+ 1.00 0 + 1.00 0 + 1.00 + 3.00 0 0

1.50

patients

+ 1.00 3.25

0

0 0

+ 1.00

in one case. In the anterior deep-overbite relapse patients, the lower incisor increased vertically in ten patients and remained unchanged in three patients. Presented in Table III are the molar vertical positional changes and the posterior facial height changes between the beginning of retention and the follow-up records. Also included is a ratio expressing the relation between the combined upper and lower molar vertical positional change and the posterior facial height change. Both groups exhibited increases in the upper molar vertical position. The range for the anterior open-bite relapse patients was from +0.50 to +9.00 mm. The range for the anterior deep-overbite relapse patients was from +0.50 to +6.00 mm. The lower molar vertical positional changes (lower alveolar growth changes) for the anterior open-bite relapse patients remained unchanged in three cases and increased in ten cases, with a range from +0.25 to +3.00 mm. In the anterior deep-overbite relapse patients, the lower alveolar growth remained unchanged in three patients and increased in ten, with a range from +0.50 to +4.00 mm. The posterior facial height in twelve of the thirteen anterior open-bite relapse patients increased, with a range from +0.25 to +lO.OO mm. The remaining

Volume65

Vertical

Number

6

Table

III.

change,

and

Upper

and

ratio

lower

between

molar the

verticle

positional

anterior

change,

posterior

facial

Anterior

OB (mm.)

inc.

Ratio

open-bite

relapse

577 height

two PFH

Patient

relapse

d (mm.)

d’ (mm.)

PFH

inc./c’+d

(mm.)

pnticnts

J. M.

-

1.00

+ 3.00

+ 0.50

+ 1.00

0.286

N.

R.

-

1.00

+ 4.00

+ 1.on

+ 2.00

0.40

M.

A.

-

0.50

t

1.75

+ 0.75

+ 1.00

0.40

M. M. J. P.

-

0.50 0.50

+ 1.50 + 9.00

+ 0.50

+ 1.00

0.50

+ 2.00

+lO.OO

0.91

S. R.

-

1.75

+ 8.00

+ 3.00

+lO.OO

0.91

M.

S.

-

1.50

+ 1.50

+ 0.50

D. H. J. Pe.

-

2.25 2.50

+ 2.00 + 1.50

+ 1.50 + 1.00

0.75 0.50

+ 0.75

0.33

G. S.

-

1.50

+ 1.75

S. H. G. C.

-

1.75 1.75

+ 0.50 + 2.00

+ 1.00 + 0.25

0.57 0.50

+ 0.25

L. J.

-

1.00

+ 3.00

+ 0.50

Anterior

deep-overbite

relapse

0 + 0.75 0 0

0

0

+ 1.00

0.286

patients

J. A.

+ 1.50

4- 3.00

+ 4.00

+lO.OO

1.43

M. A. G. M.

+ 2.00 + 1.00

t 2.25 + 3.00

4. 0.50

+ 7.50

+ 1.50

t

2.73 1.83

M. B. C. E.

+ 3.00 + 3.25

+ 6.00 + 0.50

+ 3.00

G. B. D. E.

+ 1.00 + 3.25

+ 2.00 + 0.50

G. P. J. M.

+ 1.25 + 2.50

+ 3.00 + 1.00

J. R.

+ 4.00

+ 3.00

D.

+ 1.00

+ 1.50

+ 3.25 + 1.00

+ 1.00 + 4.00

B.

M. M. J. L.

0 0 0 + 1.50 + 1.00 t 3.00 + 1.50

8.25

+12.00 + 3.00 + 5.00 + 1.00 + 6.50 + 3.00 +12.00

1.33 6.00 2.50 2.00 1.44 1.50 2.00

+ 4.00

1.33

+ 1.00

+ 6.00

3.00

+ 2.00

+ 8.06

1.33

anterior open-bite relapse patient showed no change in posterior facial height. In all anterior deep-overbite relapse patients, the posterior facial height increased, with a range from +l.OO to +12.00 mm. The differential vertical relationship of the posterior facial height increase and the combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible, expressed as a ratio, shows a number less than 1 for the anterior open-bite relapse patients and a number greater than 1 for the anterior deep-overbite relapse patients. Another way to state the foregoing result is that the combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible was larger than the posterior facial height increase in the anterior open-bite relapse patients and smaller in the anterior deep-overbite relapse patients. The degrees of mandibular growth rotation measured as the SN plane change can be found in Table IV. All anterior open-bite relapse patients showed negative angles (that is, angles where the SN planes intersected posterior to S).

578 Table

Nemeth IV.

a&

Change

retention

and

resulting

from

the

Isaacson in the

SN

plane

follow-up

posterior

Ana. J. Orthod. June 1974

facial

open-bite

J. N. M. M. J. S. M. D. J. G. S. G. L. Anterior

J. M. G. M. C. G. D. G. J. J. D. M. J.

A. A. M. B. E. B. E. P. M. R. B. M. L.

the

taken mandibular

at the

beginning

growth

of

rotation

(mm.)

Rotation

SN

(degrees)

patients

M. S. A. M. P. R. S. H. Pe. S. H. C. J.

deep-overbite

roentgenogram

indicating

OB rclupse

the

growth

Patient Anterior

between

roentgenogram

relapse

-1.00 -1.00 -0.50 -0.50 -0.50 -1.75 -1.50 -2.25 -2.50 -1.50 -1.75 -1.75 -1.00

-1.00 -2.00 -2.00 -1.00 -1.00 -2.00 -0.75 -1.00 -1.25 -0.75 -1.00 -2.00 -2.00

+1.50 +2.00 +l.OO +3.00 +3.25 +1 .oo +3.25 +1.25 +2.50 +4.00 +l.OO +3.25 +l.OO

+4.00 +3.00 +6.00 +5.00 +2.25 +5.25 +1.75 +4.00 +1.50 +3.00 +l.OO +3.00 +2.25

patients

All anterior deep-overbite relapse patients exhibited angles where the SN planes intersected anterior to S) .

positive

angles (that

is,

Discussion

Tooth-to-bone changes. One tooth-to-bone change that can contribute to anterior open-bite or deep-overbite relapse is a tooth-to-bone relationship change produced by axial inclinational changes of the upper and/or lower incisors. From Table I it is evident that some patients in each group exhibited axial inclinational changes opposite the change that would potentially contribute to the overbite or open-bite relapse. The second tooth-to-bone change that can contribute to anterior open-bite or deep-overbite relapse is the incisor root apex vertical positional change. Intrusion of one or both incisors would produce an open-bite. No patients exhibited intrusion of the maxillary incisor or intrusion of both incisors. Only

Vertical

anterior

relapse

579

one of the anterior open-bite relapse group exhibited intrusion of the lower incisor. This patient also showed an increase in upper incisor vertical root apex position, tending to reduce the amount of open-bite produced by intrusion of t,he lower incisor. The vertical positional change of the upper and lower incisor root apices tended to deepen the bite in all cases except the one mentioned above. The net effect of the anterior tooth-to-bone changes (that is, incisor axial inclinational change with the centers of rotation within the tooth substance or apical to the tooth and vertical root apex change) can produce varying degrees of anterior open-bite or deep-overbite relapse, Solely on the basis of a tooth-tobone change, some patients of the anterior deep-overbite relapse group might be expected to exhibit opening of the anterior vertical relation during the interval studied. From the data in Tables II and III, some patients of the anterior open-bite relapse group might be expected to show a deepening of the anterior vertical relation during the interval studied. On the basis of anterior tooth-to-bone changes alone, other patients of the anterior open-bite relapse group and two patients of the anterior deep-overbite relapse group should have remained unchanged. Tooth-to-bone changes produce no consistent predictable results in overbite relapse. On the basis of anterior tooth-to-bone changes alone, reversals or amplifications of what might be expected in vertical anterior relation changes after orthodontic treatment become difficult to explain. Bone-to-bone changes (that is, changes in vertical jaw relation to the maxilla and the mandible to each other) could explain these reversals and amplifications. The third tooth-to-bone cha.nge important in the discussion of vertical anterior relapse after orthodontic treatment is the molar vertical positional change. As measured in this study, the upper molar vertical positional change represents the total vertical changes occurring between the cranial base and the mesiobuccal cusp of the maxillary first molar between the beginning of retention and the follow-up records. The lower molar vertical positional change, using anatomic landmarks for superimposition, measures the vertical movement of the distobuecal cusp of the mandibular first molar without introducing the error incurred by mandibular lower border remodeling when measuring from the mandibular plane. Some investigators in the past have observed depression of elongated posterior teeth of anterior deep-overbite relapse patients after orthodontic treatment using the SN plane as a reference plane for linear measurements of the upper molar vertical positional change and the mandibular plane as a reference plane for linear measurements of the lower molar vertical positional change. Patients D. E. and G. P. of the anterior deep-overbite relapse group, according to these planes of reference, showed negative changes for the upper molar vertical position and lower molar vertical position, respectively. This could be interpreted to indicate depression of the upper molar in patient D. E. and depression of the lower molar in Patient G. P. However, when stable anatomic landmarks rather than lines and planes constructed through changing landmarks were used for superimposition, these teeth were actually found to increase in vertical position during the time interval studied.

580

Nemeth

and

Isaacsow

Am. J. Orthod. June 1974

Bone-to-bone chalzges. Upper and lower molar vertical positional changes arc not important in themselves in det,ermining what changes will take place in anterior tooth vertical relations, but only in combination and in relation to posterior facial height increases. If the increase in the combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible (Sut + Av) and in the posterior facial height (PFH inc.) are equal, parallel vertical repositioning of the mandible would occur (Sut + Av = PFH inc.). With differential increases favoring one or the other, forward or backward rotation of the mandible would occur. In Table III, those patients who exhibited anterior open-bite relapse showed greater combined vertical growth (Sut + Av) than posterior facial height increase (PFH inc.), resulting in backward mandibular rotation (Sut + Av > PFH inc.), In contrast, those patients who exhibited anterior deep-overbite relapse showed greater posterior facial height increase (PFH inc.) than combined sutural and alveolar vertical growth (Sut + Av), resulting in forward mandibular rotation within the time interval studied (Sut + Av < PFH inc.). When backward mandibular rotation takes place, opening of the vertical anterior dental relation results, whereas deepening of the dental relation results from forward mandibular rotation. From Table IV, it is evident that all anterior open-bite relapse patients exhibited backward mandibular growth rotation during the time interval studied. All anterior deep-overbite relapse patients exhibited forward mandibular growth rotation during the same time period. Backward mandibular growth rotation resulting from Sut + Av > PFH inc. could account for opening of the vertical anterior relation observed in seven of the open-bite relapse patients rather than the deepening that was expected on the basis of anterior tooth-to-bone changes alone. Backward mandibular growth rotation could also account for opening of the vertical anterior relation in two other patients of the same group where the relation might be expected to remain the same. This type of rotation could further account for greater opening in the remaining four patients when these vertical anterior relations are based on anterior tooth-to-bone changes alone. Forward mandibular growth rotation resulting from PFH inc. > Sut + Av could account for deepening of the overbite rather than the expected opening based on anterior tooth-to-bone changes alone seen in one of the deep-overbite relapse patients. Forward mandibular growth rotation could also account for deepening of the vertical anterior relation in four patients of the same group where the relation was expected to remain unchanged. Again, forward mandibular growth rotation could account for greater deepening of the vertical anterior relation than expected by anterior tooth-to-bone changes alone in the rest of the anterior deep-overbite relapse patients. From this evidence, it would seem that the differential vertical relationship between the posterior facial height increase and the combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible contributed to vertical anterior relapse. After orthodontic treatment, anterior open-bite or deep-overbite relapse is partly due to mandibular growt,h rotation.

Volume Number

65 6

Vertical

anterior

relapse

581

The average age of the twenty-six patients in this study was 13 years 0 months at the beginning of retention and 18 years 2 months at the time of the follow-up records. All patients of both groups showed upper molar vertical positional increases during the time interval studied. Tvventy of the twenty-six showed lower molar vertical positional increases during the same time period. All patients, except G. C. of the anterior open-bite relapse group, exhibited posterior facial height increases during the interval studied. Posterior facial height increases might be expected on the basis of Bjiirk’s” evidence of mantlibular condylar growth even after the age of 20 years. As stated in the review of the literature, mandibular growth rotation takes place as a result of (1) the direction of mandihular condylar growth and (2) the differential vertical relationship between the posterior facial height increase and the combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible. According to Bjork,!’ the direction of mandibular condylar growth and the center of rotation are important in determining mandibular rotation. Specifically, it is the amount of vertical component of the mandibular growth in relation to Sut + Av and the location of the center of rotation along the dentition that determines mandibular growth rotation. Because each patient has a different direction of mandibular condylar growth, each patient will exhibit different amounts of vertical component (PFH inc.). Also, the center of rotation at a point along the dentition can vary with each patient. Quantitative co?&usions. The amount of vertical anterior relapse depends on the age and the growth potential of the patient at the completion of active orthodontic treatment. The amount, direction, and relative proportions of orofacial growth remaining after band removal will determine the amount of vertical anterior relapse. Qualitative conclusiom. Most, but not all, of the open-bite relapse patients in this study exhibited steep mandibular plane angles. However, as stated earlier, all were backward rotators during the time interval between the last two sets of records. Most, but not all, of the deep-overbite relapse patients presented smaller than average mandibular plane angles. All, however, were forward rotators during the posttreatment time interval. CliGcnl implicntioxs. Orthodontists at this time are unable to demonstrate conclusively an ability to affect the direction of mandibular condylar growth and posterior facial height increases. However, they can affect upper and lower molar vertical positions. In essence, then, orthodontists can affect the differential vertical relationship between Sut + Av and PFH inc. and the center of mandibular rotation. Use of a biteplate type of retainer has become common practice for the retention of deep-overbite patients to allow extrusion of both upper and lower mo1ars.2”, 3G,4F The mechanics of this type of retention simulates Bjiirk’ss Type II forward rotation. That is, the center of rotation takes place about the lower incisal edges, allowing normal posterior facial height increases to lower the mandible vertically and permit the eruption of the molars to keep pace with the rotation. The important point is to maintain this type of retention until growth of the jaws is complete.22~ a594’1

Am.

J. Orthod. June 1974

SkielleP and later Bj6rk and Skieller’O recommended the use of a removable biteplate to avoid rclapse of basal deep overbite due to forward rotation of the mandible about a center of rotation somewhere between the posterior or anterior ends of the mandible. This recommendation is based on the fact that growth of the condyles continues some years after c~omplet~ionof the sutural growth of the upper face. The retention of anterior open-bite patients has recently been directed toward intruding the upper posterior teeth or at least maintaining upper molar vertical position. This type of retention attempts to mat,ch only the lower molar vertical increases against the posterior facial height increases. No appliance has yet been developed to prevent, lower molar vertical positional increases after orthodontic treatment. IIowcver, a Milwaukee brace type of appliance has been suggested for use in treatment to maintain or reduce the combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible in an attempt to allow posterior facial height increases to produce Bj6rk’ss Type II or Type III forward mandibular growth rotation. In the maintenance procedure, rotation would occur about the incisal edges of the lower anterior teeth to hold the anterior relation, whereas in closure of the anterior open-bite, rotation might occur about the molars. Depending upon the severity of the original anterior open-bite, occipital-pull or parietal-pull headgear attached to the upper posterior teeth or a Milwaukee brace type of appliance could be worn until growth of the jaws is complete. There is a strong argument for early treatment of anterior deep-overbite patients to take advantage of all possible upper and lower molar vertical increases to correct the deep overbite. Early treatment of anterior open-bite patients can also be argued to reduce upper and lower molar vertical increases in an attempt to close the open-bite. In both conditions, once corrections have been produced, maintenance of the correction through proper retention should be carried out until growth of the jaws is complete. One variable not assessed in this study was the effect of the facial musculature upon tooth-to-bone changes and bone-to-bone changes. The musculature may be the dominant force in ultimately determining molar vertical position and vertical jaw relations. One possible source of error in analyzing vertical anterior relations would be premature occlusal contacts or improper interdigitation of the teeth. Discriminate inspection of the dental casts offered no evidence of unusual wear facets. For improving future studies of this type, a larger group of patients could be divided into male and female subgroups and further divided by age. This may help in pinpointing the average age at which ,growth of the jaws is complete for boys and girls. Summary

1. The purpose of this study was to show that changes in vertical jaw relation produced by mandibular rotation resulting from growth after orthodontic treatment contribute in part to vertical anterior relapse. Twenty-six

Vertical

nnterior

relapse

583

patients were selected on the basis of ret,urn to deep-overbite or open-bite following orthodontic treatment as observed directly from dental casts. Dental casts and corresponding sagittal roentgen head films before orthodontic treatment, at the beginning of retention, and at a subsequent date sometime after the end of retention were analyzed to evaluate the return toward the original overbite or open-bite relationship. 2. Two sets of measurements for each patient were obtained to determine the changes in tooth-to-bone relationship and bone-to-bone relationship occurring during the time interval studied. The first set of measurements was based on constructed lines and planes of reference, the second on structural landmarks. 3. A method was described for superimposition of the head films using structural (anatomic and bony) landmarks to eliminate or reduce the error in measuring from lines and planes constructed through changing landmarks. A method described by Skieller4” was used to determine mandibular growth rotation. 4. Changes in maxillary and mandibular incisor axial inclination and root apex vertical position producing tooth-to-bone relationship changes were analyzed with respect to their contribution to vertical anterior relapse. 5. Changes in maxillary and mandibular molar vertical position in relation to posterior facial height changes producing bone-to-bone relationship changes were also analyzed and discussed with respect to their contribution to vertical anterior relapse. 6. Those patients who exhibited anterior deep-overbite relapse showed greater posterior facial height increase than combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible. In contrast, those patients who exhibited anterior open-bite relapse showed greater combined sutural and alveolar growth of the maxilla and alveolar growth of the mandible than posterior facial height increase. 7. The patients showing deep-overbite relapse exhibited forward mandibular growth rotation, whereas those showing anterior open-bite relapse exhibited backward mandibular growth rotation. 8. Depression of elongated posterior teeth was not found to contribute to anterior deep-overbite relapse. 9. Possible sources of error in this study and the time to begin orthodontic treatment were discussed briefly. Type of retention, based on the original vertical anterior relation and on the type of mandibular growth rotation, was also discussed. Finally, the length of retention based on the age when growth of the jaws is complete was suggested. REFERENCES

1. BjBrk, A.: The face in profile, Sven. Tandlak. Tidskr. 40: 5, 1947. (Translated into English by LundstrGm, A., Lund, 1947, Berlingska Boktrycheriet.) 2. Bjiirk, A. : The significance of growth changes in facial pattern and their relation to changes in occlusion, Dent. Rec. 71: 197, 1951. 3. Bjiirk, A.: Variability and age changes in overjet and overbite AM. J. ORTHOD. 39: 779-801, 1953. 4. Bjiirk, A.: Facial growth in man studied with t,he aid of metallic implants, Acta Odontol. Stand. 13: 9-34, 1955.

584

Nemeth

and

Isaacson

Am.

J. Orthod. Jum 1974

5. BjGrk, A. : The relation of the jaws to the cranium. In LundstrGm, A.: Introduction to Orthodontics, New York, 1960, McGraw-Hill Book Company, Inc. 6. BjBrk, A.: Facial growth in bilateral hypoplasia of the mandibular eondyle: A radiographic cephalometric study of a case using metallic implants. In Kraus, R. S., and Riedel, R. A. (editors) : Vistas in Orthodontics, Philadelphia, 1962, Lea & Febiger, pp. 347-358. 7. BjGrk, A.: Variations in the growth pattern of the human mandible: A longitudinal radiographic study by the implant method, J. Dent. Res. 42: 400-411, 1963. 8. Bjork, A.: Sutural growth of the upper face studied by the implant method, Acta Odontol. &and. 24: 109-127, 1966. 9. BjGrk, A.: Prediction of mandibular growth rotation, AM. J. ORTHOD. 55: 585-599, 1969. 16. BjGrk, A., and Skieller, V.: Facial development and tooth eruption, AM. J ORTHOD. 62: 339-383, 1972. 11. Broadbent, B. Holly: The face of the normal child, Angle Orthod. 7: 183-208, 1937. 12. Brodie, A. G.: On growth of the jaws and the eruptions of the teeth, Angle Orthod. 12: 109-123, 1942. 13. Brodie, A. G.: Late growth changes in the human face, Angle Orthod. 23: 146-157, 1953. 14. Cole, H. J.: Certain results of extraction in the treatment of malocclusion, Angle Orthod. 18: 103-113, 1948. 15. Corlett, E. L.: Mandibular incisor position relative to basal bone, AM. J. ORTHOD. ORAL SURG. 33: 21.29, 1947. 16. Creekmore, T. D.: Inhibition or stimulation of the vertical growth of the facial complex; its significance to treatment, Angle Orthod. 37: 285-297, 1967. 17. Enlow, D. H.: A morphogenetio analysis of facial growth, AM. J. ORTHOD. 52: 283, 1966. 18. Enlow, D. H.: The human face, New York, 19681 Harper & Row. 19. Enlow, D. H., and Hunter, W. S.: The growth of the face in relation to the cranial base, Trans. Eur. Orthod. Soe. 44: 321, 1968. 20. Garliner, D. : Myo-functional therapy: An aid in the practice of orthodontics, 225-276, American Sssociation of Orthodontists Slide-Tape Program. 21. Graber, T. M.: Postmortem in posttreatment adjustment, A&X. J. ORTHOD. 52: 331-352, 1966. 22. Graber, T. M. :, Current orthodontic concepts and techniques, Philadelphia, 1969, W. B. Saunders Company. 23. Hemley, S.: Bite plates, their application and action, AM. J. ORTHOD. 24: 721-736, 1938. 24. Hopkins, S. C.: Bite planes, AM. J. ORTHOD. ORAL SURG. 26: 107, 1940. 25. Isaacson, J. R., and others: Extreme variation in vertical facial growth and associated va.riation in skeletal and dental relations, Angle Orthod. 41: 219-229, 1971. 26. Leff, R. L.: Overbite correction and relapse as analyzed by some cephalometric and treatment related variables, Thesis, University of Minnesota, 1969. 27. Litowitz, R.: A study of the movement of certain teeth during and following orthodontic treatment, Angle Orthod. 18: 113-132, 1948. 28. Ludwig, M.: A cephalometric analysis of the relationship between facial pattern, interincisal angulation and anterior overbite changes, Angle Orthod. 37: 194-204, 1967. 29. Lundstrom, A.: Horizontal and vertical growth of the incision superius, incision inferius, and menton, Trans. Eur. Orthod. Sot. 45: 125-136, 1969. 30. Magill, J. M.: Changes in the anterior overbite relation following orthodontic treatment in extraction cases, AM. J. ORTHOD. 46: 755-788, 1960. 31. Markus, M. B.: The review and consideration of the problem of retention, AM. J. ORTHOD. ORAL SURG. 24: 203, 1958. 32. Merritt, J. L., Jr.: A cephalometric study of the treatment and retention of deep overbite cases, Thesis, University of Texas, 1964, as cited by Creekmore. 33. Mershon, J. V.: Possibilities and limitations in the treatment of closed bites, INT. J. ORTHOD. 23: 581.589,1937. 34. Porter, L. J.: Conservatism in orthodontic procedures and appliancfs, AM. J. ORTHOD. ORAL Su~0.33: 109.1947.

Verticnl 35. 36. 37.

33:

69-82,

505

1963.

Schudy, F. F.: The rotation of the orthodontic treatment, Angle Orthod. 39. Schudy, F. F.: The control of vertical 19-39,

Ykieller, Orthod. 41. Stackler, 28:

mandible resulting 35: 36, 1965. overbite in clinical

from

growth:

Its

orthodontics,

implication

in

Orthod.

38:

Angle

1968.

40.

V.: Cephalometric Sot. 43: 147-157, H. M.: Clinical

108-111,

growth 1967. observations

analysis of

in

cases

the

treatment

five

years

of

out

of

overbite,

Trans.

treatment,

Angle

Eur. Orthod.

1958.

Strang, R. H. TV.: Axial inclination of teeth in extraction cases, Angle Orthod. 27: 11-13, 1957. Straub, TV. J.: Malfunction of the tongue. Part I, AM. J. ORTHOD. 46: 404-424, 1960. Strnub, \V. J.: Malfunction of the tongue. Part TI, AM. J. ORTHOD. 47: 596, 1961. Subtelny, J. Daniel, and Subtelny, Joanne D.: Oral habits-Studies in form, function and therapy, Angle Orthod. 43: 347.383, 1973. Sved, A.: Changing the occlusal level and a new method of retention, AM. J. ORTIIOD. ORAL WRG. 30: 527-535, 1944. Thompson, D. J.: A cephalometric evaluation of vertical dimension (Abstr.) AM. J. ORTHOU. 52: 859, 1966. Tweed, C. W.: Indications for the extraction of teeth in orthodontic procedures, AM. J. ORTHOU. ORAL SURG. 30: 405,1944. Wylie, \V.: Overbite and vertical dimension in t.erms of muscle balance, Angle Orthod. 14: 13.17, 1944.

42.

43. 44. 45. 46. 47. 48. 49.

261

Owre

Hall

THE

JOURNAL

June,

1924

Since

the

the

palpation, subjective of

relapse

Riedel, R. A. : A review of the retention problem, Angle Orthod. 30: 179-199, 1960. Salzmann, J. A.: Practice of orthodontics, Philadelphia, 1966, J. B. Lippincott Company. Hchudy, F. F.: Cant of the occlusal plane and axial inclinations of teeth, Angle Orthod.

38.

in

anterior

the

popularity conditions dental

(55455)

50

discovery

field

of

YEARS

of

the

ray of

roentgen

ray,

among make

for

pain its

the

ray,

technic.

response

symptoms

diagnosis.

roentgen

roentgen

percussion,

AGO

to have

thermal

it a very

and definite

diagnosis

old

a great

its

unerring

of and

extent

qualities, place

has

methods

changes,

to

time-saving

laity,

dental The

the

its part,

almost

a

Ford-like

art.

production

in but

lost

only

exclusively

namely:

interpretation

become

diagnosis as a

advanced diagnosis,

long-standing a part,

inspection, of

the

The

various

convenience and

cost,

chronic in the

scheme

its bone of