- Email: [email protected]
The borderline patient and tooth removal
The borderline patient and tooth removal Donald
T. Schwab,
Oalcland,
Calif.
O.O.S.
T
he combination of occlusal harmony and facial balance has long been the goal of the dental profession. Since the time that the orthodontist became aware of the possibility that he was more than a bystander in the facial development of his patients, the literature has been replete with studies of the relationship of the denture to the soft-tissue profile. A great many of the patients for whom this combination of ocelusal harmony and facial balance is of particular importance are those classified as borderline extraction patients. When teeth are removed in the treatment of these patients, the goal of occlusal harmony is readily attained but, sadly, often at the expense of a pleasing total facial profile. The term borderline has been used to cover a wide range of arch-length to profile-balance relationships. A sizable portion of this range of interest consists of patients with a good profile balance accompanied by a mild a.rchlength discrepancy. In many instances, extractions are considered necessary for future dental stability. In evaluating the probable soft-tissue response to the removal of teeth, one must bear in mind the possibility of an unfavorable retraction of the lips following treatment. One reason for this occurrence is thka possibility of excessive retraction of incisors when premolars are removed for the correction of arch-length discrepancies in the range of 2.5 t,o 5 mm. Another reason may be skeletal patterns and growth direct.ions that, either singly or in combination, lead to a recessive dentoalveolar arca in relation to the nose and chin following growt,h and mat~urat,ion. The removal of four second premolar% This thesis, which was given as a parCal fulfillment of the requirements for certification by the American Board of Orthodontics, is being published with the consent and the recommendation of the Board, but it should be understood that it does not necessarily represent or express the opinion of the Board.
126
Volume Number
59 2
Borderline
patient
and tooth removal
127
rather than four first premolars, in these borderline cases has been used to minimize the amount of posterior displacement of the incisal segments. Two cases may serve to illustrate the dental and facial types that somewhat typify this group of borderline extraction cases. The first patient, a 12-year-old girl, has a well-balanced face accompanied by a Class I malocclusion with a mandibular arch-length discrepancy of 3.8 mm. (Fig. 1). There has been a mild collapse of the six lower anterior teeth. The cuspal relationship in the buccal segments is excellent. The alveolar bone surrounding the lower incisors and canines is very delicate. The relationship of the lips, nose, and chin is harmonious. The tracing of the lateral head film demonstrates an underlying skeletal pattern which corresponds to the excellent soft-tissue one. If premolars are to be removed to gain alignment, many orthodontists would select the four second premolars for extraction in order to lessen the resistance of the posterior segments to space closure. From a purely esthetic standpoint, the removal of four second premolars is not wit.hout its risks. Even a mild retraction of the incisal segments during space closure may disturb the existing harmonious profile contour following maturation of the soft tissues. The second patient, also a 12-year-old girl, has a Class I malocclusion with 4.6 mm. of arch-length discrepancy (Fig. 2). Her lip musculature is tense and has evidenced itself in the malocclusion by pressing the maxillary incisors in good alignment against the lower incisors. In addition to the discrepancy between tooth size and supporting bone, this muscular pressure has caused the partial blocking-out of the four canines. As a further sign of lip pressure, the mandibular right canine erupted in a distal-axial inclination. The mandibular alveolar bone in the incisor region is thin and fragile, as seen in the lateral head film and intraoral examination of the hard tissue. Although the head film reveals a good skeletal pattern, the soft tissue denotes a disparity in thickness of the lips as related to the tissue anterior to pogonion. The upper lip is in a more relaxed position than in the facial photographs but demonstrates a thinness in comparison to the width of the tissue in the pogonial region. The removal of four first premolars appears to be more plausible for this patient than for the preceding one. This girl, however, shows all the indications for facial growth during treatment. If the maxillary anterior teeth are retracted too far posteriorly while growth is occurring, the upper lip will lose the support of both the maxillary incisors and the premaxillary bone. This loss of support could lead to a recessive and shortened upper lip or give a concave appearance to the subnasal area. The objective of this article is to examine cephalometrically the hard- and soft-tissue changes occurring in borderline cases with facial patterns similar to those of the foregoing examples and to determine the answers to the following questions : 1. Is there a difference in the final positioning of the anterior teeth depending upon whether first or second premolars are removed? 2. What is the general soft-tissue response to the extraction of either first or second premolarsl 3. By what means can we effect a correction of arch-length discrepan-
I28
Schwab
Fig.
1. Pretreatment
records
of borderline
extraction
case
used
as first
example.
Bordedine
Vo2ume Numba
Fig.
2.
Pretreatment
records
of
borderline
tie B with premolar removal sof it-tissue balance? Review
r of
the
extraction
patient
case
and still maintain
used
ad
tooth removal
as second
a harmonious
129
example.
hard- ant
literature
Th .e interrelationship between incisal positioning and premolar removal has been E1 matter of concern for many years. Naneel was among the first to bbring
130
Schwab
this to the attention of the orthodojltist. In 19l’i 1~: stated : “While t*xtJr;tci,i<)li, when supplemented with judicious trcat,ment, can’& t,hc promist~ of stable 1’1’ sults, excessive lingua,1 tipping of Itiandibular inAsol*s is Itr IW tl(:plolWl ;is much as excessive labial tipping of thaw twth [Tvilh c>spansion lllcrapy / .” Jle believed that the proper anteroposterior positioning oi’ the mantlil~nlat~ alltctriol teeth required the correct decision as to which teeth to &rad. As (~;lYI~ :IS 1941, he emphasized the need for cam in pitting anterior segmc~nt: auclroragc? against the posterior segment,s and advocate?tl the l*cmoval of four xccont 1 pr+ molars in the treatment of cases of slight arch-length discrepancy.’ Carey,” in 1952, was the first to use the term ho&~li~. 1Ir describctl a mPtho(l ot measuring arch-length discrepancies and observctl : “Two an(1 fi\-~tcnths millimeters is the borderline. The decision to extract, or not is made 1)~.studying thtl positions of the third molars, width of the mouth, flesibility of the labial tissues. and the facial type of the indi\-itlual. IIf the discrepancy is snore thail 25 mm. but less than 5 mm., consideration will 1~ given to mtraction of the second premolars. Here we must study the c~onclition of the tct:th to be sacrificcL(l ant1 their anatomy. . . . The second premolars arc removctl in the arch with the least discrepancy. . . _ Thus, it is frequently desirabl(1 to IWUOVC 1hfa upper srco~~cl and lower first premolars.‘! In 1954 Dewel’ thoroughly analyzed the diagnosis, appliance p~oced~~c~. and treatment results of a Class I borderline case requiring the remova. of four second premolars. He used cephalometric tracings to demonstrate that the mandibular incisors were neither labially nor lingually displaced by treatjment,. Keedy,” in presenting the treatment results of a Class I borderline case treated with the removal of fous second prcmolars, emphasized the need for anchorage control in the incisal regions in order to place these teeth in harmony with the lip musculature. In 1963 SchoppeG studied the results of cases treated by the removal of four second premolars to determine whether the anchorage values changed significantly from those of cases in which first premolars were extracted. He stated: “There does not a,ppear to be any dominating evidence from which conclusions can be drawn; however, a few generalizations may be permitted. . . . more mesial movement of molars (maintaining good inclinations) may be accomplished through second bicuspid ext ract.ion rather than first bicuspitl extraction.” Steadman, in discussing Schoppe’s article, remarked : “Extraction of any tooth in the buccal segment immediately stops the forward push of the anterior cornponent of force upon those teeth mesial to the site of the extractions. As long as there is any spacing between contact points in the bucacal segment,, the anterior teeth stop moving forward in relation to the orbital plane, while the nose and soft tissue chin point continue to grow forward as if no tooth had been extracted. The result is that the incisors and lips become less and less prominent, while the nose and soft tissue chin point become more and more prominent.” NC suggested that the value of removing four second premolars lies in the facility of a more rapid space closure of the extraction spaces, which allows the denture to keep pace with the growth of the soft-tissue profile.
Volume Number2
59
Borderline
patient
ami tooth removal
131
The relationship between incisor positioning and lip posture has been explored in many studies. Subtelny,g in examining serial head films of normal subjects, noted that the anteroposterior posture of the vermilion border of the lips was closely related to their supporting hard-tissue structures. Similar findings were reported by Bloom*o and Rucleell in separate studies of the relationship between incisor movement and lip changes resulting from treatment. The sample used by Subtelny was composed of thirty untreated subjects with normal occlusions who were followed via serial head films from 3 months to 18 years of age. Subtelny found a general increase in convexity of the soft tissue covering the denture, with the exception of the tissue overlying the symphysis. The increase in convexity of the soft tissue contrasted with the straightening of the ha,rd-tissue profile during growth, and Subtelny12 thought that this indicated a growth differential between the soft tissue and the underlying hard structures. It is of interest that all three investigators reached essentially the same conclusion, namely, that changes in lip posture are generally closely correlated with changes in position of the incisors. Material
Pre- and posttreatment head films of patients with good profile balance and borderline malocclusions were collected. All had Class I or near Class I occlusions with arch-length discrepancies ranging from 3 to 5 mm., treatment involved the removal of four first or four second premolars. The amount and type of arch-length discrepancy were considered very important. Cases in which lower premolars were blocked buccally or lingually to the extent that one half of the space was closed were not selected. Some of the cases were selected from my practice, others from the files of clinicians using the same appliance who graciously searched their records for borderline extraction cases that met the requirements previously mentioned. All patients were treated with the edgewise appliance. It was believed that, with orthodontists of proved clinical ability using essentially the same appliance, the differences in operators would balance out when tallied against growth, cooperation, and the other vagaries of patient response to treatment. Nine pairs of cases were selected for measurement. Each pair was matched as closely as possible with regard to facial pattern and dental relationship (Figs. 3 to 11). All patients were females and were treated in the permanent dentition. In nine eases four first premolars were removed, and in nine cases four second premolars were removed. A comparison of the changes in incisal and soft-tissue positions between the groups might determine whether there are any differences in the hard- and soft-tissue profiles resulting from the removal of either four first or four second premolars. Method
Hard-tissue measurements. Linear changes in the positions of the mandibular and maxillary incisors were recorded in the following manner : 1. MANDIBULAR INICISOR CHANGE. The tracings were registered on the posterior outline of the symphysis, and the change in incisal position was measured
132
Schwab
Fig. 3
Fig. 4
Figs.
3
and 4. A, First
premolar
removal.
8, Second
premolar
removal.
Volume Number
59 2
Borderline
patied
and tooth removal
133
Fig.
Figs.
5 and
6. A,
First
premolar
removal.
B, Second
premolar
removal.
6
134
Fig.
7
Fig.
8
Figs.
Schwab
7 and
8. A, First
premolar
removal.
II, Second
premolar
removal.
Volume Number
Figs.
59 2
9 and
Borderline
10.
A,
First
premolar
removal.
B, Second
patient
premolar
and tooth removal
removal.
135
Fig.
9
Fig.
10
136
Schwub
Fig. 11. A, First premolar
removal.
8, Second
premolar
removal.
either directly or by sliding the symphysis perpendicularly up from the mandibular plane in cases of increased size of the symphysis in the before- and after-treatment tracings (Fig. 12). Changes in the relationship of the lower incisor to pogonion were not recorded because of the alterations that can occur in this area as a result of appositional growth. 2. MAXILLARY INCISOR CHANGE. Two linear measurements were recorded. The first was the change in position of the maxillary incisors in relation to the posterior outline of the pterygomaxillary fissure. The second registration point selected was sella turcica. The pterygomaxillary fissure was used in an attempt to locate an area deep in the maxillofacial complex that might have a reasonable amount of stability. Sella turcica was used as a second reference point to correct any error that might be caused by changes in position of the pterygomaxillarg fissure from growth. The method of using these landmarks for registration was as follows : Pterygomaxillary fissure. The Frankfort plane was drawn on t,he original tracing, and a perpendicular line was dropped from the Frankfort plane through the posterior border of the pterygomaxillary fissure. The final tracing was superimposed upon the sellanasion line and registered upon sella. The Frankfort plane for the second tracing was traced exactly over the original Frankfort plane. A perpendicular line was dropped through the posterior border of the pterygomaxillary fissure, as in the original tracing. These perpendicular lines were then superim-
Volume
Number
59
and tooth removal
2
Fig. 12. Mandibular
incisor change. 1, Mandible registration on posterior border of symphysis and dible demonstrating growth and showing method pendicular pendicular tracing.
line from inferior line tangent to Dotted
lines
depict
border posterior final
to obtain border
of
137
demonstrating minimal growth. Note method of measuring change. 2, Manof sliding symphysis vertically up per-
direct reading symphysis.
of incisor Solid lines
change. represent
Note peroriginal
tracing.
Fig. 13
Fig.
Fig. 13. Maxillary pterygomaxillary change are
incisor change. fissure and the illustrated.
Fig. 14. Maxillary tracings reading
incisor on perpendicular of incisor change.
Method sliding of
change. Note method line from Frankfort
of registration on tracings to obtain of registration plane through
the direct
posterior reading
on sella turcica sella turcica to
border of of incisor and obtain
sliding direct
posed, and, by sliding the second tracing up the perpendicular line, the maxillary incisor change could be measured directly (Fig. 13). Sella turcica. Tracing the two Frankfort planes, as previously mentioned, a perpendicular line from each was projected up through the center point of sella turcica. The tracings were superimposed upon the sella-nasion line, and, by sliding the second tracing up this perpendicular line, the change in incisal position could be measured directly. The perpendicular line through the pterygomaxillary fissure was used as a guide for this (Fig. 14). Soft-tissue measurements. Two methods of recording lip changes were selected :
138
b’chwc/l,
Fig. 15. Method J. Orthodont. inferior labial
of recording lip changes in relation to Frankfort plane. (After Neger: Amer. 45: 738-751, 1959.) Soft-tissue profile angles: S, superior labial angle; I, angle; Pg, pogonial angle; p, philtrum angle (added for present study).
1. A VARIATION OF NEGER’SSMETHOD OF SOFT-TISSUE EVALUATION. This method, originally designed for facial photographs, was adapted for use with cephalometric tracings. Lines are projected from soft-tissue nasion (the deepest point of the curve joining the tissues covering the frontal and nasal bones) and pass tangent to the upper and lower lips. The intersection of these lines with the Frankfort plane forms an angle that can be used to record lip changrs (Fig. 15). The lines p and Pg were included in t,his study to denote philtrum changes and original soft-tissue pogonion positions as a matter of interest. The means and standard deviations of the original soft-tissue contours of this group would also provide a means of comparison of t,his sample of “good” faces with those selected by Neger for his study. The method of recording changes appeared to lend itself quite well for use in this stntly. ‘L. RICKETTS’ ESTHETIC PLANE. A lint was projected from the soft-tissue pogonion to the tip of the nose. Changes in lip position from this plane were recorded on lines parallel to the Frankfort plane. The maxillary and mandibular incisors were also related to this plane. Previous measureInents recordecl their change relative to structures deep in the face; this measurement would cvalnat,e incisor changes in relation to the anterior limits of the soft-tissue profile. A transparent grid was constructed t.o slide over the tracings and provitltl lines parallel to the Frankfort plane to be used as a guide for the linear measurement (Fig. IS). The tracings were made on acetate paper. A Boley gauge was used to make measurements directly on the tracings, to t,ht: nearest 0.1 mm., for lineal changes. Angular changes were measurect with a prot r&or to thcl nearest 0.5 degree. The t test for significance was us4 to compare the first- and secondpremolar-removal groups. With this test, it is assumed that there is no difference between the incisor and lip position changes when either four first or four
Volume Number
59 2
Borderli?le
Fig. 16. Method of recording shows use of grid to measure shows points measured after
Table
I. Hard-tissue
Lower Upper Upper Upper Lower
incisor incisor: incisor: incisor: incisor:
reference
and tooth removal
139
lip changes in relation to esthetic plane. Original tracing change along line parallel to Frankfort plane. Final tracing registering original and final tracings on esthetic plane.
measurements First
Variable
patie&
points
: Symphysis p.t.m. Sella turcica Esthetic plane Esthetic plane
premolar removals
Second
Mean change (mm.)
S.D.
-2.1 -2.7 -2.6 -4.5 -2.6
0.6 0.7 1.1 0.9 0.7
premolar
removals
change
FIi -0.8 -1.6 -1.6 -3.4 -1.4
) S.D. 1.1 1.1 0.9 1.4 1.3
1
t ratio -3.1149 -2.4168 -2.1735 -2.0842 -2.3769
~
p 0.01 0.05 0.05 0.1 0.05
second premolars are removed. If this assumption is proved false by showing that the difference is so great that it cannot be logically accounted for by chance sampling, the difference is termed significant. Findings
The readings for mandibular and maxillary incisor changes are summarized in Table I. Both upper and lower incisors were found to be retracted less in relation to skeletal landmarks when four second premolars were removed. This difference was significant at the 1 per cent level of confidence for the lower incisors and at the 5 per cent level for the upper incisors. The lower incisors were also moved posteriorly to a lesser degree in relation to the esthetic plane when four second premolars were removed. This difference was significant at the 5 per cent level of confidence. The upper incisors demonstrated a trend toward lesser retraction in relation to the esthetic plane with the removal of four second premolars (10 per cent level of confidence).
Table
II. Soft-tissue
Partible Upper
measurements
reference
lip:
._---.-- --.---_. -- _.-__ -- -,_-__-_.. --_..-_.. / First premolar / / wYnocaEs PecYitld pre?Ylolar rt~rtl0ctrl.s _ j--.---~__-~_~~_~. ___ _~ ._.. _~ ....__ ~~_ I ~ xcan ~ Xul‘tI j 1 change 1 8.1). chanyc / AS.1). 1 t rcitio i’
points
Nasion-Frankfort plane angle
.-2,lO
11.4
-1.Y”
1 .<) ”
-1.lO43
;\‘.s.
Lower
lip : Nasion-Frankfort plane angle
-1.4”
1.0
-l.5o
I .4
0.0948
S.h.
Upper
lip:
Esthetic
plane
-3.1
mm.
1.1
-2.5
mm.
1.”
-0.9660
N.S.
Lower
lip:
Esthetic
plane
-2.8
mm.
1.2
-2.4
rmll.
1 .:I
-0.7716
N.S.
Il.8
-l..j”
I.2
-O.-M34
N.S.
1.1
-2.3
Philtrum
Phi&rum
Table
: Nasion-Frankfort plane angle
- 1.7”
: Esthetic
-3.0
Ill.
plane
Comparison
of sample
First
Variable Upper lip Lower lip Pogonion
mm.
before
treatment
premolar p’On*p __-
Scco?td
mm.
(Neger’s
premolar
0.9
~1.f5110
N.S.
method)
group -.-----~
Hean (degrees)
S.D.
Mean (degrecsj
S.D.
t ratio
95.9 92.4 88.4
2.7 3.2 3.7
96.2 93.3 89.5
3.1 2.6 2.4
-0.2301 - 0.7331 -0.8120
I I
----
I i
--
Segcr’s .-. ----~_
group
p
Mean (degrees)
8.D.
N.S. N.R. N.S.
96.8 92.9 88.1
2.9 3.0 3.0
Changes in lip position are summarized in Table II. No significant difference could be found in lip or philtrum changes between first- and second-premolar removals. Table III compares the first- and second-premol.ar-extraction groups’ softtissue positions prior to treatment. It was noticed that both groups were @te similar in lip and soft-tissue pogonial positions prior to treatment. There is also a striking similarity between the means for each group and Neger’s sample of forty-eight patients with acceptable soft-tissue profiles. Discussion
One objective of this study is to determine whether there are vn.lid reasons for removing four second premolars in borderline extraction cases in order to minimize lip retraction. Previous studies have shown the close correlation between lip posture and the underlying dentSal and alveolar structures.g-ll The finding that both upper and lower incisors were retracted less with secondpremolar removals would tend to lead to the assumption that the lips would behave similarly. Although the average amount of lip retraction was smaller when four second
Volume *Number
59 2
Borderline
patient
and tooth removal
141
premolars were removed, the difference between the means of the groups was not great enough to be termed significant. An explanation for this finding may be that growth changes were occurring in t,he soft tissues covering the denture as well as the underlying hard tissues. It was noticed that all but two pairs (Figs. 4 and 9) demonstrated average or above average a,mounts of hard- and soft-tissue growth during treatment. The soft-tissue growth in the nasal and lip areas of both groups may have compensated for the difference in incisal retraction between the groups. Subtelnyg found a general increase in soft-tissue convexity during growth, due mainly to the lengthening of the nose and thickening of the tissue covering the maxillary region. He also found an increase in thickness at the vermilion border of both lips during growth, although this ceased in girls at the age of 14 to 15 years. If treatment occurs after hard- and soft-tissue growth has ceased, the lips may demonstrate a closer correlation with the behavior of the incisors (Fig. 4). The remoTa1 of four second premolars in these cases might help to reduce lip retraction. It was noted that the mandibular incisors of the groups demonstrated a marked difference in their relation to the esthetic plane following treatment (Table I). The incisors of the second-premolar-extraction group were placed less posteriorly than those of the first-premolar group in relation to the anterior limits of the soft-tissue profile. This finding was significant at the 5 per cent level for the mandibular incisors, although it appeared only as a trend for the maxillary incisors. In relating the lips of both groups to the esthet.ic plane after treatment, it was noticed that again they did not demonstrate a difference great enough to be termed significant (Table II). The foregoing findings may be of clinical importance. It has been observed that the removal of premolars in borderline cases will at times cause the incisors to appear to bc orerly recessive when the lips are parted in normal speech and while smiling. This condition often does not affect lip contours when the lips are closed. A growth differential between the hard and soft tissues in the lip area, accompanied by an overretraction of the incisors in treatment, may be the cause of this phenomenon. The removal of four second prcmolars in these cases may help to reduce this effect. A second objective of this study was to present material that would assist in the treatment of borderline extraction cases with good profiles. The incidence and direction of growth during treatment can often create an undesired response of the incisors to appliance mechanics. This response often is not in harmony with the pattern that the incisors would follow if left untreated. Serial growth studies of normal subjects demonstrate a general downward and forward repositioning of the maxillary incisors during the active growth periodI (Fig. 1’7). The vector of this repositioning can be plotted, and the pattern is almost a straight line progressing downward and anteriorly away from the deeper structures of the face. With normal occlusions, the mandibular incisors will also follow this pattern. When premolars are removed and space-closure mechanics initiated, there is a tendency for the normal downward and forward repositioning of the incisors to be altered from a straight-line path to one of an increased amount of vertical progression (Fig. 18). The result is that the incisors become
142
.‘Ivrr:r.
Schwab
J. 0rthodon.t. PehruarglSil
Fig. 17
8 m3
2-v
years
Superimposition. Sella -Nasion
Fig. 18
i
Fig. 17. Composite years.
[Courtesy
Fig. 18. Solid
lines
of serial tracings of E. 0. Bergersen.) show
change
of
in incisor
a normal vector
subject with
between
extractions.
j; ‘> I” the Dotted
Alteration normal
of path
ages
of
lines
show
2 and
17
normal
pattern.
less prominent in relation to the soft-tissue profile. Blthough the direction of mandibular and maxillary growth plays the prime role in spatial repositioning of the incisors, treatment procedures can either maintain or worsen the inherent vector of repositioning that the incisors would follow. If the objective of treatment is to maintain a normal incisor-to-lip relationship, precautions must hn
Volume Number
59 2
Borderline
patient
and tooth removal
143
Fig. 19
Fig. 20
Fig. 19. Borderline of incisors.
Fig. 20. control
(Courtesy
Borderline of incisors.
case treated of William
by removal C. Crockett.)
case treated by (Courtesy of Sidney
removal Meek.)
of four of
first four
premolars. second
Note premolars.
anchorage Note
control anchorage
t,aken during the treatment period to lessen the amount of deviation of this vector. The finding that the incisors are retracted less in relation to skeletal structures when four second premolars are removed may provide one avenue of approach in treatment. The careful control of anchorage in the anterior regions is another factor to be considered (Figs. 19 and 20). The retraction of canines (or canines and premolars) separately into the extraction space, followed by space closure distal to the lateral incisors, may disturb the anterior segments too severely for these patients. The use of six anterior teeth (or eight, if second premolars are removed) as one anchorage unit will assist in preventing a change in the normal vector of incisal positioning. The newer concept of applying forward traction on the posterior teeth from elastics attached to a chin cup may be indicated for patients with difficult anchorage problems. A final factor, and ulti-
Summary
1. Nine borderline cases trcatctl wit,11 thtb ~.moml of foulfinest p~+c~rnolars were compared wit.11 nine closely matched borderlinc casts trcatcd with the removal of four second premolars. 7’1~~ diffcrencrs in incisal and lip changes were analyzed by means of lateral ccphalometric films. Tests of significance of difference between the treatment result,s of the groups were made. 2. The mandibular incisors demonstrated a lesser amount of posterior repositioning in relation to the s,vmph,vsis when four second premolars were removed (0.01 level). 3. The maxillary incisors were repositioned less posteriorly in relation to deep cranial and facial structures when four secontl prcmolars were removed (0.05 level). 4. There was no significant diffcrcnce in lip retraction between the firstpremolar-removal group and the grol~p in which four sec.ond-premolars were removed. 5. The mandibular incisors were rvpositionccl less posteriorly in relation to the esthetic plane when four second premolars were removed (0.05 level). 6. An analysis of the treat,ment, rcsponsc to premolar removal in borderline cases was discussed, and information was presented to assist in obtaining a harmonious incisor-to-lip relationship following tlcatnrcllt. The author wishes to express his grat,itudc to the following nmn who searched their records for cases for this study and without whose help this thesis would not have been possible: William C. Crockett, R. Morley Davis, Owen 1). Dwight, Ernest N. Kaye, Roscoe L. Keedy, Sidney L. Meek, John W. Merchant, William H. Parker, and Fay C. Van. REFERENCES
1. Nance, SURG.
2. Nance,
H. N.: 33:
The
253-301,
H.
ORTHODONT.
N.: 35:
limitations
of
orthodontic
of
second
treatment.
II,
A.MER.
J. ORTHODONT.
& ORAL
1947.
The
removal
686,
1949.
premolars
in
orthodontic
treatment,
AMI?%
J.
3. Carey, C. W.: Diagnosis and case analysis in orthodontics, AMER. J. ORTHODONT. 38: 149. 161, 1952. 4. Dewel, B. F.: Second premolar extraction in orthodontics, AMER. J. ORTHODONT. 41: 107-120, 1955. 5. Keedy, R. L.: Indications and contra-indications for extraction in orthodontic treatment, Angle Orthodont. 26: 243-249, 1956. 6. Schoppe, R. J.: An analysis of second premolar extraction procedures, Angle Orthodont. 34: 292-302, 1964. 7. Steadman, S. R.: Discussion of “An analysis of second premolar extraction procedures,” Angle Orthodont. 34: 301-302, 1964. 8. Neger, M.: A quantitative method for the evaluation of the soft tissue facial profile, AMER. J. ORTHODONT. 45: 73%751,1959. 9. Subtelny, J. D.: -4 longitudinal study of soft tissue facial structures and their profile characteristics, defined in relation to underlying skeletal structures, AMER. J. ORTHODONT. 45: 481-507, 1959.
VNo$mn;;;;
10. Bloom,
.Borderli?ze patient L. A.:
Perioral
profile
changes
in orthodontic
awl tooth removal
145
AMER. J. ORTHODONT.47:
treatment,
371-379, 1961. 11. Rudee,
D. A.:
Proportional
profile
changes
concurrent
with
orthodontic
therapy,
AMER. J.
ORTHODONT.50: 421-434,1964. 12. Subtelny,
J. D.:
31: 105122, 13.
Broadbent,
The
soft
tissue
profile,
growth
and
treatment
changes,
Angle
Orthodont.
1961. B.
68.80 Mountain
H.:
The
face
of
the
normal
child,
Angle
Orthodont.
7:
183-208,
1937.
Blvd.
The difference between industry as it exists today and a profession is, then, simple and unmistakable. The essence of the former is that its only criterion is the financial return which it offers to its shareholders. The essence of the latter is that, though men enter it for the sake of livelihood, the measure of their success is the service which they perform, not the gains which they amass. They rich; but the meaning of their profession, that they make money but that they government or good law. They depend that any conduct which increases their
in the case of a successful doctor, grow for themselves and for the public, is not make health, or safety, or knowledge, or good on it for their income, but they do not consider income is on that account good, (Tawney, R. H.:
The
Harcourt,
Acquisitive
Society,
New
York,
1920,
may,
as
both
Brace
& Company.]
T. Schwab,
Oalcland,
Calif.
O.O.S.
T
he combination of occlusal harmony and facial balance has long been the goal of the dental profession. Since the time that the orthodontist became aware of the possibility that he was more than a bystander in the facial development of his patients, the literature has been replete with studies of the relationship of the denture to the soft-tissue profile. A great many of the patients for whom this combination of ocelusal harmony and facial balance is of particular importance are those classified as borderline extraction patients. When teeth are removed in the treatment of these patients, the goal of occlusal harmony is readily attained but, sadly, often at the expense of a pleasing total facial profile. The term borderline has been used to cover a wide range of arch-length to profile-balance relationships. A sizable portion of this range of interest consists of patients with a good profile balance accompanied by a mild a.rchlength discrepancy. In many instances, extractions are considered necessary for future dental stability. In evaluating the probable soft-tissue response to the removal of teeth, one must bear in mind the possibility of an unfavorable retraction of the lips following treatment. One reason for this occurrence is thka possibility of excessive retraction of incisors when premolars are removed for the correction of arch-length discrepancies in the range of 2.5 t,o 5 mm. Another reason may be skeletal patterns and growth direct.ions that, either singly or in combination, lead to a recessive dentoalveolar arca in relation to the nose and chin following growt,h and mat~urat,ion. The removal of four second premolar% This thesis, which was given as a parCal fulfillment of the requirements for certification by the American Board of Orthodontics, is being published with the consent and the recommendation of the Board, but it should be understood that it does not necessarily represent or express the opinion of the Board.
126
Volume Number
59 2
Borderline
patient
and tooth removal
127
rather than four first premolars, in these borderline cases has been used to minimize the amount of posterior displacement of the incisal segments. Two cases may serve to illustrate the dental and facial types that somewhat typify this group of borderline extraction cases. The first patient, a 12-year-old girl, has a well-balanced face accompanied by a Class I malocclusion with a mandibular arch-length discrepancy of 3.8 mm. (Fig. 1). There has been a mild collapse of the six lower anterior teeth. The cuspal relationship in the buccal segments is excellent. The alveolar bone surrounding the lower incisors and canines is very delicate. The relationship of the lips, nose, and chin is harmonious. The tracing of the lateral head film demonstrates an underlying skeletal pattern which corresponds to the excellent soft-tissue one. If premolars are to be removed to gain alignment, many orthodontists would select the four second premolars for extraction in order to lessen the resistance of the posterior segments to space closure. From a purely esthetic standpoint, the removal of four second premolars is not wit.hout its risks. Even a mild retraction of the incisal segments during space closure may disturb the existing harmonious profile contour following maturation of the soft tissues. The second patient, also a 12-year-old girl, has a Class I malocclusion with 4.6 mm. of arch-length discrepancy (Fig. 2). Her lip musculature is tense and has evidenced itself in the malocclusion by pressing the maxillary incisors in good alignment against the lower incisors. In addition to the discrepancy between tooth size and supporting bone, this muscular pressure has caused the partial blocking-out of the four canines. As a further sign of lip pressure, the mandibular right canine erupted in a distal-axial inclination. The mandibular alveolar bone in the incisor region is thin and fragile, as seen in the lateral head film and intraoral examination of the hard tissue. Although the head film reveals a good skeletal pattern, the soft tissue denotes a disparity in thickness of the lips as related to the tissue anterior to pogonion. The upper lip is in a more relaxed position than in the facial photographs but demonstrates a thinness in comparison to the width of the tissue in the pogonial region. The removal of four first premolars appears to be more plausible for this patient than for the preceding one. This girl, however, shows all the indications for facial growth during treatment. If the maxillary anterior teeth are retracted too far posteriorly while growth is occurring, the upper lip will lose the support of both the maxillary incisors and the premaxillary bone. This loss of support could lead to a recessive and shortened upper lip or give a concave appearance to the subnasal area. The objective of this article is to examine cephalometrically the hard- and soft-tissue changes occurring in borderline cases with facial patterns similar to those of the foregoing examples and to determine the answers to the following questions : 1. Is there a difference in the final positioning of the anterior teeth depending upon whether first or second premolars are removed? 2. What is the general soft-tissue response to the extraction of either first or second premolarsl 3. By what means can we effect a correction of arch-length discrepan-
I28
Schwab
Fig.
1. Pretreatment
records
of borderline
extraction
case
used
as first
example.
Bordedine
Vo2ume Numba
Fig.
2.
Pretreatment
records
of
borderline
tie B with premolar removal sof it-tissue balance? Review
r of
the
extraction
patient
case
and still maintain
used
ad
tooth removal
as second
a harmonious
129
example.
hard- ant
literature
Th .e interrelationship between incisal positioning and premolar removal has been E1 matter of concern for many years. Naneel was among the first to bbring
130
Schwab
this to the attention of the orthodojltist. In 19l’i 1~: stated : “While t*xtJr;tci,i<)li, when supplemented with judicious trcat,ment, can’& t,hc promist~ of stable 1’1’ sults, excessive lingua,1 tipping of Itiandibular inAsol*s is Itr IW tl(:plolWl ;is much as excessive labial tipping of thaw twth [Tvilh c>spansion lllcrapy / .” Jle believed that the proper anteroposterior positioning oi’ the mantlil~nlat~ alltctriol teeth required the correct decision as to which teeth to &rad. As (~;lYI~ :IS 1941, he emphasized the need for cam in pitting anterior segmc~nt: auclroragc? against the posterior segment,s and advocate?tl the l*cmoval of four xccont 1 pr+ molars in the treatment of cases of slight arch-length discrepancy.’ Carey,” in 1952, was the first to use the term ho&~li~. 1Ir describctl a mPtho(l ot measuring arch-length discrepancies and observctl : “Two an(1 fi\-~tcnths millimeters is the borderline. The decision to extract, or not is made 1)~.studying thtl positions of the third molars, width of the mouth, flesibility of the labial tissues. and the facial type of the indi\-itlual. IIf the discrepancy is snore thail 25 mm. but less than 5 mm., consideration will 1~ given to mtraction of the second premolars. Here we must study the c~onclition of the tct:th to be sacrificcL(l ant1 their anatomy. . . . The second premolars arc removctl in the arch with the least discrepancy. . . _ Thus, it is frequently desirabl(1 to IWUOVC 1hfa upper srco~~cl and lower first premolars.‘! In 1954 Dewel’ thoroughly analyzed the diagnosis, appliance p~oced~~c~. and treatment results of a Class I borderline case requiring the remova. of four second premolars. He used cephalometric tracings to demonstrate that the mandibular incisors were neither labially nor lingually displaced by treatjment,. Keedy,” in presenting the treatment results of a Class I borderline case treated with the removal of fous second prcmolars, emphasized the need for anchorage control in the incisal regions in order to place these teeth in harmony with the lip musculature. In 1963 SchoppeG studied the results of cases treated by the removal of four second premolars to determine whether the anchorage values changed significantly from those of cases in which first premolars were extracted. He stated: “There does not a,ppear to be any dominating evidence from which conclusions can be drawn; however, a few generalizations may be permitted. . . . more mesial movement of molars (maintaining good inclinations) may be accomplished through second bicuspid ext ract.ion rather than first bicuspitl extraction.” Steadman, in discussing Schoppe’s article, remarked : “Extraction of any tooth in the buccal segment immediately stops the forward push of the anterior cornponent of force upon those teeth mesial to the site of the extractions. As long as there is any spacing between contact points in the bucacal segment,, the anterior teeth stop moving forward in relation to the orbital plane, while the nose and soft tissue chin point continue to grow forward as if no tooth had been extracted. The result is that the incisors and lips become less and less prominent, while the nose and soft tissue chin point become more and more prominent.” NC suggested that the value of removing four second premolars lies in the facility of a more rapid space closure of the extraction spaces, which allows the denture to keep pace with the growth of the soft-tissue profile.
Volume Number2
59
Borderline
patient
ami tooth removal
131
The relationship between incisor positioning and lip posture has been explored in many studies. Subtelny,g in examining serial head films of normal subjects, noted that the anteroposterior posture of the vermilion border of the lips was closely related to their supporting hard-tissue structures. Similar findings were reported by Bloom*o and Rucleell in separate studies of the relationship between incisor movement and lip changes resulting from treatment. The sample used by Subtelny was composed of thirty untreated subjects with normal occlusions who were followed via serial head films from 3 months to 18 years of age. Subtelny found a general increase in convexity of the soft tissue covering the denture, with the exception of the tissue overlying the symphysis. The increase in convexity of the soft tissue contrasted with the straightening of the ha,rd-tissue profile during growth, and Subtelny12 thought that this indicated a growth differential between the soft tissue and the underlying hard structures. It is of interest that all three investigators reached essentially the same conclusion, namely, that changes in lip posture are generally closely correlated with changes in position of the incisors. Material
Pre- and posttreatment head films of patients with good profile balance and borderline malocclusions were collected. All had Class I or near Class I occlusions with arch-length discrepancies ranging from 3 to 5 mm., treatment involved the removal of four first or four second premolars. The amount and type of arch-length discrepancy were considered very important. Cases in which lower premolars were blocked buccally or lingually to the extent that one half of the space was closed were not selected. Some of the cases were selected from my practice, others from the files of clinicians using the same appliance who graciously searched their records for borderline extraction cases that met the requirements previously mentioned. All patients were treated with the edgewise appliance. It was believed that, with orthodontists of proved clinical ability using essentially the same appliance, the differences in operators would balance out when tallied against growth, cooperation, and the other vagaries of patient response to treatment. Nine pairs of cases were selected for measurement. Each pair was matched as closely as possible with regard to facial pattern and dental relationship (Figs. 3 to 11). All patients were females and were treated in the permanent dentition. In nine eases four first premolars were removed, and in nine cases four second premolars were removed. A comparison of the changes in incisal and soft-tissue positions between the groups might determine whether there are any differences in the hard- and soft-tissue profiles resulting from the removal of either four first or four second premolars. Method
Hard-tissue measurements. Linear changes in the positions of the mandibular and maxillary incisors were recorded in the following manner : 1. MANDIBULAR INICISOR CHANGE. The tracings were registered on the posterior outline of the symphysis, and the change in incisal position was measured
132
Schwab
Fig. 3
Fig. 4
Figs.
3
and 4. A, First
premolar
removal.
8, Second
premolar
removal.
Volume Number
59 2
Borderline
patied
and tooth removal
133
Fig.
Figs.
5 and
6. A,
First
premolar
removal.
B, Second
premolar
removal.
6
134
Fig.
7
Fig.
8
Figs.
Schwab
7 and
8. A, First
premolar
removal.
II, Second
premolar
removal.
Volume Number
Figs.
59 2
9 and
Borderline
10.
A,
First
premolar
removal.
B, Second
patient
premolar
and tooth removal
removal.
135
Fig.
9
Fig.
10
136
Schwub
Fig. 11. A, First premolar
removal.
8, Second
premolar
removal.
either directly or by sliding the symphysis perpendicularly up from the mandibular plane in cases of increased size of the symphysis in the before- and after-treatment tracings (Fig. 12). Changes in the relationship of the lower incisor to pogonion were not recorded because of the alterations that can occur in this area as a result of appositional growth. 2. MAXILLARY INCISOR CHANGE. Two linear measurements were recorded. The first was the change in position of the maxillary incisors in relation to the posterior outline of the pterygomaxillary fissure. The second registration point selected was sella turcica. The pterygomaxillary fissure was used in an attempt to locate an area deep in the maxillofacial complex that might have a reasonable amount of stability. Sella turcica was used as a second reference point to correct any error that might be caused by changes in position of the pterygomaxillarg fissure from growth. The method of using these landmarks for registration was as follows : Pterygomaxillary fissure. The Frankfort plane was drawn on t,he original tracing, and a perpendicular line was dropped from the Frankfort plane through the posterior border of the pterygomaxillary fissure. The final tracing was superimposed upon the sellanasion line and registered upon sella. The Frankfort plane for the second tracing was traced exactly over the original Frankfort plane. A perpendicular line was dropped through the posterior border of the pterygomaxillary fissure, as in the original tracing. These perpendicular lines were then superim-
Volume
Number
59
and tooth removal
2
Fig. 12. Mandibular
incisor change. 1, Mandible registration on posterior border of symphysis and dible demonstrating growth and showing method pendicular pendicular tracing.
line from inferior line tangent to Dotted
lines
depict
border posterior final
to obtain border
of
137
demonstrating minimal growth. Note method of measuring change. 2, Manof sliding symphysis vertically up per-
direct reading symphysis.
of incisor Solid lines
change. represent
Note peroriginal
tracing.
Fig. 13
Fig.
Fig. 13. Maxillary pterygomaxillary change are
incisor change. fissure and the illustrated.
Fig. 14. Maxillary tracings reading
incisor on perpendicular of incisor change.
Method sliding of
change. Note method line from Frankfort
of registration on tracings to obtain of registration plane through
the direct
posterior reading
on sella turcica sella turcica to
border of of incisor and obtain
sliding direct
posed, and, by sliding the second tracing up the perpendicular line, the maxillary incisor change could be measured directly (Fig. 13). Sella turcica. Tracing the two Frankfort planes, as previously mentioned, a perpendicular line from each was projected up through the center point of sella turcica. The tracings were superimposed upon the sella-nasion line, and, by sliding the second tracing up this perpendicular line, the change in incisal position could be measured directly. The perpendicular line through the pterygomaxillary fissure was used as a guide for this (Fig. 14). Soft-tissue measurements. Two methods of recording lip changes were selected :
138
b’chwc/l,
Fig. 15. Method J. Orthodont. inferior labial
of recording lip changes in relation to Frankfort plane. (After Neger: Amer. 45: 738-751, 1959.) Soft-tissue profile angles: S, superior labial angle; I, angle; Pg, pogonial angle; p, philtrum angle (added for present study).
1. A VARIATION OF NEGER’SSMETHOD OF SOFT-TISSUE EVALUATION. This method, originally designed for facial photographs, was adapted for use with cephalometric tracings. Lines are projected from soft-tissue nasion (the deepest point of the curve joining the tissues covering the frontal and nasal bones) and pass tangent to the upper and lower lips. The intersection of these lines with the Frankfort plane forms an angle that can be used to record lip changrs (Fig. 15). The lines p and Pg were included in t,his study to denote philtrum changes and original soft-tissue pogonion positions as a matter of interest. The means and standard deviations of the original soft-tissue contours of this group would also provide a means of comparison of t,his sample of “good” faces with those selected by Neger for his study. The method of recording changes appeared to lend itself quite well for use in this stntly. ‘L. RICKETTS’ ESTHETIC PLANE. A lint was projected from the soft-tissue pogonion to the tip of the nose. Changes in lip position from this plane were recorded on lines parallel to the Frankfort plane. The maxillary and mandibular incisors were also related to this plane. Previous measureInents recordecl their change relative to structures deep in the face; this measurement would cvalnat,e incisor changes in relation to the anterior limits of the soft-tissue profile. A transparent grid was constructed t.o slide over the tracings and provitltl lines parallel to the Frankfort plane to be used as a guide for the linear measurement (Fig. IS). The tracings were made on acetate paper. A Boley gauge was used to make measurements directly on the tracings, to t,ht: nearest 0.1 mm., for lineal changes. Angular changes were measurect with a prot r&or to thcl nearest 0.5 degree. The t test for significance was us4 to compare the first- and secondpremolar-removal groups. With this test, it is assumed that there is no difference between the incisor and lip position changes when either four first or four
Volume Number
59 2
Borderli?le
Fig. 16. Method of recording shows use of grid to measure shows points measured after
Table
I. Hard-tissue
Lower Upper Upper Upper Lower
incisor incisor: incisor: incisor: incisor:
reference
and tooth removal
139
lip changes in relation to esthetic plane. Original tracing change along line parallel to Frankfort plane. Final tracing registering original and final tracings on esthetic plane.
measurements First
Variable
patie&
points
: Symphysis p.t.m. Sella turcica Esthetic plane Esthetic plane
premolar removals
Second
Mean change (mm.)
S.D.
-2.1 -2.7 -2.6 -4.5 -2.6
0.6 0.7 1.1 0.9 0.7
premolar
removals
change
FIi -0.8 -1.6 -1.6 -3.4 -1.4
) S.D. 1.1 1.1 0.9 1.4 1.3
1
t ratio -3.1149 -2.4168 -2.1735 -2.0842 -2.3769
~
p 0.01 0.05 0.05 0.1 0.05
second premolars are removed. If this assumption is proved false by showing that the difference is so great that it cannot be logically accounted for by chance sampling, the difference is termed significant. Findings
The readings for mandibular and maxillary incisor changes are summarized in Table I. Both upper and lower incisors were found to be retracted less in relation to skeletal landmarks when four second premolars were removed. This difference was significant at the 1 per cent level of confidence for the lower incisors and at the 5 per cent level for the upper incisors. The lower incisors were also moved posteriorly to a lesser degree in relation to the esthetic plane when four second premolars were removed. This difference was significant at the 5 per cent level of confidence. The upper incisors demonstrated a trend toward lesser retraction in relation to the esthetic plane with the removal of four second premolars (10 per cent level of confidence).
Table
II. Soft-tissue
Partible Upper
measurements
reference
lip:
._---.-- --.---_. -- _.-__ -- -,_-__-_.. --_..-_.. / First premolar / / wYnocaEs PecYitld pre?Ylolar rt~rtl0ctrl.s _ j--.---~__-~_~~_~. ___ _~ ._.. _~ ....__ ~~_ I ~ xcan ~ Xul‘tI j 1 change 1 8.1). chanyc / AS.1). 1 t rcitio i’
points
Nasion-Frankfort plane angle
.-2,lO
11.4
-1.Y”
1 .<) ”
-1.lO43
;\‘.s.
Lower
lip : Nasion-Frankfort plane angle
-1.4”
1.0
-l.5o
I .4
0.0948
S.h.
Upper
lip:
Esthetic
plane
-3.1
mm.
1.1
-2.5
mm.
1.”
-0.9660
N.S.
Lower
lip:
Esthetic
plane
-2.8
mm.
1.2
-2.4
rmll.
1 .:I
-0.7716
N.S.
Il.8
-l..j”
I.2
-O.-M34
N.S.
1.1
-2.3
Philtrum
Phi&rum
Table
: Nasion-Frankfort plane angle
- 1.7”
: Esthetic
-3.0
Ill.
plane
Comparison
of sample
First
Variable Upper lip Lower lip Pogonion
mm.
before
treatment
premolar p’On*p __-
Scco?td
mm.
(Neger’s
premolar
0.9
~1.f5110
N.S.
method)
group -.-----~
Hean (degrees)
S.D.
Mean (degrecsj
S.D.
t ratio
95.9 92.4 88.4
2.7 3.2 3.7
96.2 93.3 89.5
3.1 2.6 2.4
-0.2301 - 0.7331 -0.8120
I I
----
I i
--
Segcr’s .-. ----~_
group
p
Mean (degrees)
8.D.
N.S. N.R. N.S.
96.8 92.9 88.1
2.9 3.0 3.0
Changes in lip position are summarized in Table II. No significant difference could be found in lip or philtrum changes between first- and second-premolar removals. Table III compares the first- and second-premol.ar-extraction groups’ softtissue positions prior to treatment. It was noticed that both groups were @te similar in lip and soft-tissue pogonial positions prior to treatment. There is also a striking similarity between the means for each group and Neger’s sample of forty-eight patients with acceptable soft-tissue profiles. Discussion
One objective of this study is to determine whether there are vn.lid reasons for removing four second premolars in borderline extraction cases in order to minimize lip retraction. Previous studies have shown the close correlation between lip posture and the underlying dentSal and alveolar structures.g-ll The finding that both upper and lower incisors were retracted less with secondpremolar removals would tend to lead to the assumption that the lips would behave similarly. Although the average amount of lip retraction was smaller when four second
Volume *Number
59 2
Borderline
patient
and tooth removal
141
premolars were removed, the difference between the means of the groups was not great enough to be termed significant. An explanation for this finding may be that growth changes were occurring in t,he soft tissues covering the denture as well as the underlying hard tissues. It was noticed that all but two pairs (Figs. 4 and 9) demonstrated average or above average a,mounts of hard- and soft-tissue growth during treatment. The soft-tissue growth in the nasal and lip areas of both groups may have compensated for the difference in incisal retraction between the groups. Subtelnyg found a general increase in soft-tissue convexity during growth, due mainly to the lengthening of the nose and thickening of the tissue covering the maxillary region. He also found an increase in thickness at the vermilion border of both lips during growth, although this ceased in girls at the age of 14 to 15 years. If treatment occurs after hard- and soft-tissue growth has ceased, the lips may demonstrate a closer correlation with the behavior of the incisors (Fig. 4). The remoTa1 of four second premolars in these cases might help to reduce lip retraction. It was noted that the mandibular incisors of the groups demonstrated a marked difference in their relation to the esthetic plane following treatment (Table I). The incisors of the second-premolar-extraction group were placed less posteriorly than those of the first-premolar group in relation to the anterior limits of the soft-tissue profile. This finding was significant at the 5 per cent level for the mandibular incisors, although it appeared only as a trend for the maxillary incisors. In relating the lips of both groups to the esthet.ic plane after treatment, it was noticed that again they did not demonstrate a difference great enough to be termed significant (Table II). The foregoing findings may be of clinical importance. It has been observed that the removal of premolars in borderline cases will at times cause the incisors to appear to bc orerly recessive when the lips are parted in normal speech and while smiling. This condition often does not affect lip contours when the lips are closed. A growth differential between the hard and soft tissues in the lip area, accompanied by an overretraction of the incisors in treatment, may be the cause of this phenomenon. The removal of four second prcmolars in these cases may help to reduce this effect. A second objective of this study was to present material that would assist in the treatment of borderline extraction cases with good profiles. The incidence and direction of growth during treatment can often create an undesired response of the incisors to appliance mechanics. This response often is not in harmony with the pattern that the incisors would follow if left untreated. Serial growth studies of normal subjects demonstrate a general downward and forward repositioning of the maxillary incisors during the active growth periodI (Fig. 1’7). The vector of this repositioning can be plotted, and the pattern is almost a straight line progressing downward and anteriorly away from the deeper structures of the face. With normal occlusions, the mandibular incisors will also follow this pattern. When premolars are removed and space-closure mechanics initiated, there is a tendency for the normal downward and forward repositioning of the incisors to be altered from a straight-line path to one of an increased amount of vertical progression (Fig. 18). The result is that the incisors become
142
.‘Ivrr:r.
Schwab
J. 0rthodon.t. PehruarglSil
Fig. 17
8 m3
2-v
years
Superimposition. Sella -Nasion
Fig. 18
i
Fig. 17. Composite years.
[Courtesy
Fig. 18. Solid
lines
of serial tracings of E. 0. Bergersen.) show
change
of
in incisor
a normal vector
subject with
between
extractions.
j; ‘> I” the Dotted
Alteration normal
of path
ages
of
lines
show
2 and
17
normal
pattern.
less prominent in relation to the soft-tissue profile. Blthough the direction of mandibular and maxillary growth plays the prime role in spatial repositioning of the incisors, treatment procedures can either maintain or worsen the inherent vector of repositioning that the incisors would follow. If the objective of treatment is to maintain a normal incisor-to-lip relationship, precautions must hn
Volume Number
59 2
Borderline
patient
and tooth removal
143
Fig. 19
Fig. 20
Fig. 19. Borderline of incisors.
Fig. 20. control
(Courtesy
Borderline of incisors.
case treated of William
by removal C. Crockett.)
case treated by (Courtesy of Sidney
removal Meek.)
of four of
first four
premolars. second
Note premolars.
anchorage Note
control anchorage
t,aken during the treatment period to lessen the amount of deviation of this vector. The finding that the incisors are retracted less in relation to skeletal structures when four second premolars are removed may provide one avenue of approach in treatment. The careful control of anchorage in the anterior regions is another factor to be considered (Figs. 19 and 20). The retraction of canines (or canines and premolars) separately into the extraction space, followed by space closure distal to the lateral incisors, may disturb the anterior segments too severely for these patients. The use of six anterior teeth (or eight, if second premolars are removed) as one anchorage unit will assist in preventing a change in the normal vector of incisal positioning. The newer concept of applying forward traction on the posterior teeth from elastics attached to a chin cup may be indicated for patients with difficult anchorage problems. A final factor, and ulti-
Summary
1. Nine borderline cases trcatctl wit,11 thtb ~.moml of foulfinest p~+c~rnolars were compared wit.11 nine closely matched borderlinc casts trcatcd with the removal of four second premolars. 7’1~~ diffcrencrs in incisal and lip changes were analyzed by means of lateral ccphalometric films. Tests of significance of difference between the treatment result,s of the groups were made. 2. The mandibular incisors demonstrated a lesser amount of posterior repositioning in relation to the s,vmph,vsis when four second premolars were removed (0.01 level). 3. The maxillary incisors were repositioned less posteriorly in relation to deep cranial and facial structures when four secontl prcmolars were removed (0.05 level). 4. There was no significant diffcrcnce in lip retraction between the firstpremolar-removal group and the grol~p in which four sec.ond-premolars were removed. 5. The mandibular incisors were rvpositionccl less posteriorly in relation to the esthetic plane when four second premolars were removed (0.05 level). 6. An analysis of the treat,ment, rcsponsc to premolar removal in borderline cases was discussed, and information was presented to assist in obtaining a harmonious incisor-to-lip relationship following tlcatnrcllt. The author wishes to express his grat,itudc to the following nmn who searched their records for cases for this study and without whose help this thesis would not have been possible: William C. Crockett, R. Morley Davis, Owen 1). Dwight, Ernest N. Kaye, Roscoe L. Keedy, Sidney L. Meek, John W. Merchant, William H. Parker, and Fay C. Van. REFERENCES
1. Nance, SURG.
2. Nance,
H. N.: 33:
The
253-301,
H.
ORTHODONT.
N.: 35:
limitations
of
orthodontic
of
second
treatment.
II,
A.MER.
J. ORTHODONT.
& ORAL
1947.
The
removal
686,
1949.
premolars
in
orthodontic
treatment,
AMI?%
J.
3. Carey, C. W.: Diagnosis and case analysis in orthodontics, AMER. J. ORTHODONT. 38: 149. 161, 1952. 4. Dewel, B. F.: Second premolar extraction in orthodontics, AMER. J. ORTHODONT. 41: 107-120, 1955. 5. Keedy, R. L.: Indications and contra-indications for extraction in orthodontic treatment, Angle Orthodont. 26: 243-249, 1956. 6. Schoppe, R. J.: An analysis of second premolar extraction procedures, Angle Orthodont. 34: 292-302, 1964. 7. Steadman, S. R.: Discussion of “An analysis of second premolar extraction procedures,” Angle Orthodont. 34: 301-302, 1964. 8. Neger, M.: A quantitative method for the evaluation of the soft tissue facial profile, AMER. J. ORTHODONT. 45: 73%751,1959. 9. Subtelny, J. D.: -4 longitudinal study of soft tissue facial structures and their profile characteristics, defined in relation to underlying skeletal structures, AMER. J. ORTHODONT. 45: 481-507, 1959.
VNo$mn;;;;
10. Bloom,
.Borderli?ze patient L. A.:
Perioral
profile
changes
in orthodontic
awl tooth removal
145
AMER. J. ORTHODONT.47:
treatment,
371-379, 1961. 11. Rudee,
D. A.:
Proportional
profile
changes
concurrent
with
orthodontic
therapy,
AMER. J.
ORTHODONT.50: 421-434,1964. 12. Subtelny,
J. D.:
31: 105122, 13.
Broadbent,
The
soft
tissue
profile,
growth
and
treatment
changes,
Angle
Orthodont.
1961. B.
68.80 Mountain
H.:
The
face
of
the
normal
child,
Angle
Orthodont.
7:
183-208,
1937.
Blvd.
The difference between industry as it exists today and a profession is, then, simple and unmistakable. The essence of the former is that its only criterion is the financial return which it offers to its shareholders. The essence of the latter is that, though men enter it for the sake of livelihood, the measure of their success is the service which they perform, not the gains which they amass. They rich; but the meaning of their profession, that they make money but that they government or good law. They depend that any conduct which increases their
in the case of a successful doctor, grow for themselves and for the public, is not make health, or safety, or knowledge, or good on it for their income, but they do not consider income is on that account good, (Tawney, R. H.:
The
Harcourt,
Acquisitive
Society,
New
York,
1920,
may,
as
both
Brace
& Company.]