- Email: [email protected]
Adaptations in tip posture and pressure following orthognathic surgery
Adaptations in lip posture and pmwure following otihognathic surge~# William R. P&fit,
D.D.S., Ph.D., and c+iePhi
, Ph.D.
Chapel Hill, N.C.
Lip pressures before and after orthogoathii surgery were studied to evaluate the rel@ionship between posttreatment soft-tissue adaptation and incisor stabiBy. Aftsr atI surgical p@cM&m+s, physkitasic adaptation resulted in the~maintenance of pressures during speech and wdioying. When tie maxilla was advanced by LeFort I osteoto@!, a signifkarit d@cr@@ein re&ng presswr8j of *he upper lip was observed inst%ad of the~expeqted incre&Weand inc!sur s~~~-~~ not seef’n rod&e4 to soft-tissue influences. When the mand@ie was advanced by s@g&k%i split M&&my,. r&s&q prrrssure did not increase as etipeeted, but there was a tenr,fency for in&orS to become we upr&@ after fixation release, perhaps as a rebound frorr:labial @ping in fixation, @/hen suft tissues we&relaxed as the mandible rata@d forward fallowing superior repositioning of the maxilla, resting pre~fes decreased and lower incisors tended to be p&Hotied forward as predk%d by equilibrium theory. (AM J ORT~-IOO DENTOFAC ORTHOP19#;93:294-302.)
L
ight pressures of long duration, primarily those from the soft tissues at rest, appear to be major components of the pressure equilibrium that determines tooth position.’ Orthognathic surm has the potential to affect lip position and thereby alter this equilibrium because it produces both lip movement in response to movement of the teeth and jaws, and independent lip movement caused by contraction of soft-fissw5 incisions or a change in muscle tonicity. Studies of lip posture and lip pressures in orthognathic surgery patients are interesting for two reasons: (1) the changes produced by the surgical procedure provide an experimental model in human beings to evaluate lip influences on tooth position and (2) pressure/posture.data should provide additional insight into the reasons for stability or relapse after surgicaI treatment. This report is based on studies of lip pressures and morphologic changes in orthognathic surgery patients treated at the University of North Carolina. Lip pressures are determined by the tautness of the lips and by their anteroposterisr and vertical positions relative to the incisors. The tighter the lips and the more facial the incisor position, the greater the-lip pressure, and vice versa. An increase in vertical facial height often leads to a separation of the lips at rest (lip incompetence). If the incisors continued to e~~pf, they From the Department of Orthodontics. School of Denttstry, University ofF&th Carolina at Chapel Hill. Supported in pat by Grant DE-05215 from the National Institute of Dental Research.
294
would move vertically away from the lips and~outside their control. The expected result would be greaterprominence of the dent&ion. Another possibility, proposed by Wow and Kreibor& and extended iti later works,3.4 is that a_n increase in facial height would stretch and tighten the soft tissues, w~hich~iivould lead to an increasein lip pressure and a more upright positioti of the incisors. Upright incisors often are fuund in lotig face~patients with anterior open bite’ in whom toothlip relationships are maintained. Studies of Hp pressures in orthognathic surgical patients offer a unique opportunity toobserve the ch&g& in pressure~pattems that accompany the changes ii~ vertic@ and horizontal tooth-lip relationships. Superior repositioning of the maxilla usually places previou%ly eiposed =upper incisors at least partially GidE and in greater contact with the upper lip. This type of surgical procedure also produces a rotational advancement 6f the mandible that is accompa&d by relaxation of the lips and cheeks. Advancement of the mandible by ramus osteotomy without simuitaneous maxillary surgery s&e&hes the~soft tissues around the lower jaw and presumably Would ir!crease tension in the lower lip. Advan&me@ of the maxilla would have the same stretching iffect on the upper lip. The objective of the studies reposed here was to document changes in lip position and pressures rel#ed to these orth6gnathic sufgical procedures, and to eval: uate the relatiOnship between incisor stability postsurgically and 3he pauern of lip pressures. We exkted
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Fig. 1. Completed upper carrier with pressure transducers in place on the dental cast before use. The pressure-receiving surface of each transducer is flush with the surface of the carrier. Wires from each transducer are conveyed in the lower border of the carrier to the right posterior area, then brought forward in the buccal vestibule to exit at the corner of the mouth.
different effects on lip pressure and different patterns of postsurgical changes in incisor pattern from different surgical procedures. Our hypotheses were as follows: (1) in patients in whom the soft tissues are stretched at surgery, as in mandibular or maxillary advancement, lip pressures will increase and the incisors will move lingually postsurgically; (2) when incisors are moved within the sphere of influence of the lips after previously being outside of it, as when vertically prominent maxillary incisors are elevated to a new position beneath the lip, lip pressures will increase and the incisors will tend to move lingually postsurgically; and (3) when soft tissues are relaxed by the surgical treatment, as when the mandible rotates upward and forward following maxillary intrusion, lip pressures will decrease and the incisors will move labially. On the basis of current equilibrium theory, we expected that pressures during function (speech and swallowing) would show little, if any, change postsurgically unless normal function was disturbed; any relationship between incisor position and lip pressure would be for resting pressure only. MATERIALS AND METHODS
Subjects for this study were selected from the orthognathic surgical patients of the Dentofacial Program at the University of North Carolina on the basis of their willingness to cooperate with repeated recordings of lip pressure during and after treatment. Lip pressures were studied in a total sample of 60 patients. Seventeen of
these patients were lost to follow-up; eight declined surgical intervention after presurgical orthodontic treatment; and nine moved or refused to return for follow-up. A number of techniques for recording lip pressure have been proposed and data from both hydraulic and electronic devices have been reported recently. In this study lip pressures were evaluated by an array of five small cantilever beam strain gauge transducers contained within a thin plastic carrier that was placed labially and buccally to the upper and lower arches (Fig. 1). Transducers were located bilaterally adjacent to the first molars and canines with a single transducer between the central incisors in the midline. The sensing portion of each transducer was 2 to 3 mm from the tooth surface. The carrier itself also was 2 to 3 mm in thickness over the teeth and slightly thicker where it extended into the labial and buccal vestibules. Special miniature cables were used to reduce the bulk of lead wires, which were conveyed in the lower border of the carrier to the right molar area and then brought forward in the vestibule to the comer of the mouth. Gould and Picton6 studying cheek pressures in patients with a premolar extraction site, found that lip pressures increased only slightly as a pressure transducer was moved out buccally from the surface of a tooth for approximately 2 mm, then increased more rapidly. Therefore, the transducer positions used in this study should have provided pressure readings similar
Table 1. Maxillary/upper
lip landmark changes (mm) in max&ry Change ut surgely
Horizontal (anterior ANS A Maxillary incisor Upper lip prominence Vertical (inferior = ANS A Maxillary incisor Upper lip border
=
advancement patients (n = 10)
Change in fixation
Change presurgerj 2 y
Change postjixation
to
+ change) 3.88 3.52 3.54 7.32
(2.03)* (1.54) (2.48) (4.41)
-- 1.77 -0.84 -0.96 -4.77
(1.44) (1.33) (1.54) (2.21)
-0.42 -0.53 -0.99 - 1.80
(1.39) (1.84) (2.48) (2.57)
1.99 2.32 I .74 1.51
(1.62) 11.70) (2.33) (2.55)
- 3.07 - 2.25 -2.67 -0.20
(3.86) (3.58) (4.15) (2.45)
0.14 -0.49 -0.27 0.81
(1.31) (0.96) (1.09) (0.98)
0.69 0.77 0.03 1.17
(1.11) (1.03) (0.96) (2.03)
- 2.27 - 1.95 -2.81 -- 0.59
(2.97) (33.75) (3.73) (2.16)
t change)
I_*Mean
(standard
deviation).
Tab4 11.Upper lip pressures in maxillary advancement patients (mean peak pressure, g/cm2) Right
canine
Midline
2 yr Pretreatment lml IPI lb/ Swallow Rest *Approached
140.1 123.8 138.5 127.4 13.6 significance
posttreatmeni 121.6 127.6 137.4 175.0 3.8
Pretreatment 43.7 38.1 44.4 73.9 4.9
tef 2 .vr posttreatment 35.1 34.3 34.5 76.X 0.4
Pretreatment 113.5 110.3 96.3 119.3 15.8
canine 2 .vr p@treatment 118.4 118.4 119.8 151.7 4.6*
(P < 0.10).
to, but somewhat greater than, pressures that would have been recorded at the tooth surface. Carriers for the pressure transducers were fabricated for each patient on dental casts made just before each recording session, so that the ~devicefitted quite accurately. Calibrations were carried out each time after the. transducers were mounted in the carrier because sensitivity can be affected by the way transducers are attached. On each experimental occasion, pressures were recorded (1) during ten swallows, (2) during live repetitions of each of the utterances “mama,” “papa,” and “baby” (which were used to record pressures associated with these bilabial consonants), and (3) six times with the lips at rest. Resting pressures were evaluated by holding the lips and cheeks away from the transducers while recording a baseline, and then recording again immediately afterward with the patient reIaxed and the lips and cheeks resting against the transducers. Pressure against the lower teeth was recorded first, and then the recording sequence was repeated for the upper arch. For the recordings patients were~placed in a quiet,
electrically shielded chamber and positioned so that the instrumentation was visible to the operator but not the patient. For each event (such as a word, swallow, or rest), 3 seconds of data were recorded, amplified, computer-processed, and the resulting sealed presStire waves displayed-almost immediately on a graphics terminal whileethe data were held in buffer memory. Data editing functions permitted~ immediate exclusion of extraneous events. For instance, if the patient said “papa” when he should have said “mama,” coughed during a swallow, or moved when he was supposed to-be at rest; such data were disc.arded immediately and another recording was taken. At a later time the data were recalled from computer memory for analysis. For each patient lip pressures were recorded before the beginning of any treatment, immediately before a surgical procedure, and at 6, 12, and 24 months postsurgery. The presence of orthodontic appliances greatly compticates the measurement of lip pressure because the transducers must be placed outside the brackets even if arch- yires are removed. A typical bracket extends 2 to 3 mm-from the tooth surface, so that~with
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Lip posture and pressure after orthognathic
an orthodontic appliance in place, the carriers were 5 to 6 mm out into the lip, increasing the probability of significant artifact. In this article we discuss only data from the pretreatment and 24-months postsurgical appointments, when no orthodontic appliances were present. Cephalometric radiographs taken in natural head position were available for each patient from the same time frame as each lip pressure recording session. Because natural head position changes somewhat following orthognathic surgery,7 x and y coordinates of cephalometric landmarks were analyzed with true horizontal (from natural head position) as the horizontal reference axis and a perpendicular vertical line through sella as the vertical reference axis. Cranial base superimpositions were registered on SN at S, with SN rotated up 6” from true horizontal-that is, landmark position changes were not affected by postsurgical changes in true horizontal. Descriptive statistics for landmark position changes and lip pressure were calculated using SAS.8 Because the distribution of lip pressure changes tended to be skewed, the Wilcoxon matched pairs signed-rank test, a nonparametric analogue of the paired t test, was used to evaluate lip pressure changes.’ The significance level was set at 0.05 for all comparisons. RESULTS 1. Maxillary advancement,
LeFort I osteotomy
Ten patients had horizontal advancement of the maxilla (more than 2-mm surgical change at both ANS and A). Tabulated landmark changes are displayed in Table I and postfixation changes in maxillary tooth-lip positions are shown in Fig. 2. Note that in overall change, the upper lip advanced about the same amount as the skeletal landmarks. Swelling that developed after the surgical procedure and resolved during the next 6 months accounts for the lip changes in fixation and postfixation. In comparison to pressures before treatment, at 2 years postsurgery pressures by the lower lip were unchanged at rest and showed a nonsignificant tendency to increase during swallow and speech. For the upper lip (Table II), pressures during speech were unchanged. There was a tendency for pressures during swallowing to increase, particularly in the canine region, but this was not statistically significant. There was a marked decrease in resting pressures at all locations, which approached statistical significance. The hypothesis that upper lip pressure would increase for these patients therefore was rejected. After fixation release incisor position was relatively stable with as much tendency to tip labially as lingually (Table I).
7
surgery
297
0.1
0.1
M
w \
1.0
1.8
1.2
0.03
Fig. 2. Changes in maxillary incisor and lip positions from release of fixation (6 weeks postsurgery) to 2 years postsurgery for patients who underwent maxillary advancement. Mean millimeter movements relative to the skeletal x-y coordinate system described in the text are shown.
2. Mandibular advancement, split osteotomy
sagittal
Twenty patients underwent a sagittal split osteotomy to bring the mandible forward. There were two subgroups of these patients-one with mandibular ramus surgery alone (n = 1 l), the other with simultaneous repositioning of the maxilla and mandible (n = 9). Mandibular and lower lip landmark changes for the combined subgroups are displayed in Table III. Mean changes in lip/tooth position postfixation are shown for the subgroups in Fig. 3 and pressure data for the lower lip are shown in Table IV The expected increase in lower lip pressures postsurgically in these patients was not observed. After advancement there was a 50% decrease in resting cheek pressures in the lower molar region (P < 0.05) and a tendency for lower lip pressure to decrease (Table IV). Resting pressures of the upper cheek and lip also showed approximately a 50% decrease in the molar and canine regions (P < 0.05), but were unchanged in the midline. When the patients who underwent only mandibular ramus surgery were compared to those who had both maxillary surgery and mandibular surgery, differences in pressure patterns were confined to the upper lip; resting pressure in the upper canine region de-
298
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,4,n. J. Orthcd.
and Phillips
Dent&c.
Whop. April-1988
Fig. 3. Changes in mandibular incisor and #p positions [email protected] patients with mandibulq advanoament &ne (A) and combined tia$lWy intru&n-ma&diibIar advaiient (8). -in b6th gcoups the mqxt&le rotated qwqrd and,&warcf relatkqtu#ikcraniat brain this tirns@iod du+to ramoval of the intarocclusal wafer sptint that was p~~@%t during fiiration. Note #Q&the incisor went forward less than point 8, that is, was rep~rx$t&ed lkngua#y r&We %Hhe mandible in the patients who underwent mandibular advancement alone.
T~IU.~Mandibular/lower
lip landmark changes (mm) in mandibular advancement patients (n = 20) Change at surgery
Horizontal (anterior = + change) B Pg Mandibular incisor Lower lip-prominence Vertical (inferior = + change) B Pg Mandibular incisor bwer lip border
Change jxation
in
Change posrfuration
Change presurgery 2yr
to
5.32 7.91 5.43 7.73
(3.18) (4.68) (3.42) (3.62)
-1.24 - 2.21 -0.56 -4.15
(1.60) (1.90) (1.33) (2.63)
1.05 1.15 0.17 - 0.79
(1.65) (1.85) (1.68) (1.86)
5.23 6.83 4.44 2.85
(2.75) (4.22) (2.49) (2.48)
2.71 1.73 1.92 - 1.49
(6.12) (4.36) (4.08) (4.76)
0.76 0.74 0.43 I .41
(1.86) (1.73) (1.17) (4.74)
- 2.88 -0.97 -2.66 -2.00
(2.07) (1.16) (1.40) (2.17)
0.36 1.14 - 0.39 -2.13
(6.09) (4.01) (4.38) (4.33)
creased in the subgroup receiving mandibular surgery only, but not in the two-jaw surgery subgroup. During the speech sounds, both subgroups showed a tendency toward an increase in lower lip pressure in the canine region, but there was no change in pressure during swallowing in either subgroup (Table IV). There was no evidence to support the hypothesis that resting pressure by the lower lip would increase following mandibular advancement. Despite this, in all but one of these patients, the lower incisors did move slightly lingually relative to the mandible after fixation release (note in Table III that the incisor moved slightly forward in the x-y coordinate system, but less than B and Pg, showing its lingual movement relative to
these points). This effect was greater in the subgroup who underwent~ mandibular advancement alane (compare movement of point B and incisal &ge in Fig. 3, A and-B). As shown inPig. 3, both the incisor and the lip moved upward and slightly forward reIative to the cranial base postfixation after removal of the splint that was presem during fixation. d Seven patients underwent horizontal mandibular advancement without surgery on the mandible itself. in response to superior repositioning~ of the maxillas that allowed the mandible to rotate upward and forward.
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Fig. 4. Changes in maxillary incisor and lip positions at surgery (A) and postsurgery (6) for patients who underwent only superior repositioning of the maxilla, so that the mandible rotated upward and forward.
Table IV. Lower lip pressures in mandibular advancement patients (mean peak pressure, g/cm2) Right canine
Left canine
Pretreatment
2 yr posttreatment
Pretreatment
2 Y’ posttreatment
Pretreatment
2 Yr posttreatment
48.2 50.3 63.5 114.0 2.4
54.6 49.0 58.8 143.4 0.4*
38.5 33.1 49.8 138.8 2.6
28.0 20.8 30.7 97.3 0.5
45.0 48.8 67.2 143.1 3.7
47.2 45.1 51.7 148.6 0.3t
lmi ’ P’ IhI Swallow Rest *Approached
Midline
significance
(P < 0.10).
tP < 0.05.
Changes in upper/lower lips and tooth positions are shown in Figs. 4 and 5, respectively. Changes in lip pressures for these patients are shown in Table V. Although the upper incisors were moved superiorly in these patients, the movement was not great enough to place them beneath the lip when it also shortened and so the expected “capture” of the upper incisors by the lip did not occur. Resting lip pressures decreased rather than increasing, particularly in the midline. No consistent changes in upper incisor position occurred postsurgically. There was a marked decrease in resting lip and cheek pressures against the mandibular teeth. This was statistically significant (P < 0.05) for two channels despite the small sample size. There were no consistent or statistically significant changes in pressures by either lip during swallow or speech. In contrast to the patients who underwent mandibular advancement by ramus osteotomy, there was a tendency for the lower incisors to reposition forward relative to the mandible after fixation release in this
group. The difference in postsurgical movement of the lower incisors between this group and the group whose mandible was advanced by ramus osteotomy was statistically significant (unpaired t test, P < 0.05). This result supports the hypothesis that relaxing the soft tissues will decrease resting lip pressure and allow the incisors to move forward. DISCUSSION
In any studies of lip pressures, the bulk of the recording apparatus is a problem and the possibility of artifact cannot be excluded. Because the measuring device stretches the lip away from the teeth, it is unlikely that actual pressures at the tooth surface were larger than those that were recorded, but they could be smaller. There is also the possibility of error caused by alteration of lip posture by the apparatus. It is difficult to estimate exactly what effect this might produce. The magnitude of lip pressures reported in this study are quite comparable to those reported previously by US~‘*‘~ and by most other investigators. 12-‘4The emphasis
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0
3.6
Fig. 5. Changes in mandibular incisor and lip J.W&&N at surgery (AJ and pqsk~gery who ufxWw& only Superior repcx&nm ofti t&&Ma. I?&ovaiofthe interocelu~ allowed further upward and f&ward rota&m of the mandible.
in this article is on the direction of changes in lip pressure that accompany adaptations fuHowing-orthognathic surgery, rather than on their absolute magnitude. The use of an identical technique before and after treatment imparts a degree of confidence in the accuracy of the change data. Previous work on the relationship between tonguelip pressures and tooth position has shotlrn that resting pressures, but not pressures during function, have an effect.’ This can be explained by the duration of the pressure; resting pressures have a duration of many hours per day, easily exceeding the 4 to 6-hour duration threshold necessary to produce tooth movement, but swallowing and speech produce intermittent pressures with a total duration of a few minutes. As we expected, lip pressures during function were maintained postsurgically in our subjects and were not related to morphologic changes. Changes in the position of skeletal landmarks during and after surgical treatment reflect a combination of two effects: (-1) changes produced by the surgery itself and (2) postsurgical changes related to skeletal relapse and-/or remodeling. Changes in dental landmarks could occur due to both of the- sketetal possibilities. In addition, all these patients underwent orthodontic treatment that included some postsurgical finishing, which means that some orthodontic tooth movement occurred after the surgical~treatment and before removal of the appliances. As one might expect, detailed studies of relatively large groups of patients undergoing orthognathic- surgery show that significant changes-in landmark position are produced by the surgical procedure it&f. Both LeBort I osteotomy and sag&al split osteotomy typ-
@for
patients
ically produce 5 to 1.5mm changes at the time of surgery as was the case with these patients. We have recently reported a study of 61 patients who unde~ent L&x-t I osteotomy for superior repositioning of ~the maxilla.15 In this group only four persons had significant vertical relapse-that is, postsurgical downward movement of the maxilla ,of 2 mm or more --&lit 20% of the subgroups who had their maxilla advanced: had 2 to 4 mm of horizontal relapse. Several investigators have reported stability, .or lack thereof, following mandibular advancement.““9 Mandibular advancement patients who are placed in intermaxillary fixation tend to have the mandible slip posteriorly during the period of initial heding and intermaxillary fixation, after which the great -majority are clinically~ stable. During the period of intermaxilhuy fixation, however, the lower incisors tend to tip forward relative to the mandible. Remodeling of aIveol$r bone around the teeth, that is, inadvertent orthodontic tbdh movement, allows the mandible to move posteriorly while- the mandibular teeth are held.ia their relationshipto the maxillary teeth because of the splint and intqrmaxillary fixation. Therefore, one might expect that patients who had a ramus osteotomy for mandibular advancement would show some pro&nation ~of lower incisors relative to the mandiMe during intermaxiIlary fixation. This would overwhelm any effect produced by lip pressure. Any uprighting- of incisors caused by lip pressure should occur after removal of fixation. It is also pertinent that -the type of fixation may affect stability of incisors. All patients included in .mis report had wiring of max&aq~and mzmdibnlar &twEomy sites, and were @aced in in&m&I&q. &&on for approximately 6 weeks. None had-rigid fixationin
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Table
Lip posture and pressure
after
orthognathic
surged
301
V. Lower lip pressures in mandibular upward rotation patients (mean peak pressure, g/cm*) Right Pretreatment
Upper lml
Midline
2 yr
2 Y’
posttreatment
Left canine
Pretreatment
posttreatment
Pretreatment
2 Y’ posttreatment
lip
IPl lb/ Swallow Rest Lower lip lml ‘P’ lb1 Swallow Rest *Approached tP < 0.05.
canine
significance
112.8 109.3 113.5 118.2 14.4
138.8 138.2 181.2 207.6 6.1
71.8 83.0 91.3 86.8 5.5
16.6* 12.1* 19.1* 105.2 0.1*
110.4 124.2 93.2 123.8 17.0
103.8 103.0 125.4 173.3 5.3
68.2 75.8 77.8 89.1 5.3
49.8 53.6 71.5 253.3 0.5*
23.2 22.4 36.1 78.7 3.71
30.6 23.2 35.3 169.9 0.3t
37.4 48.1 53.2 117.5 8.9
43.0 42.6 60.0 217.6 0.4t
(P < 0.10).
the form of bone plates or lag screws. Recent reports by our group” and others*’ indicate that when sag&al split advancement is followed by rigid intraosseous fixation with screws and when intermaxillary fixation is not used or is used only briefly, the stability of skeletal mandibular landmarks is improved and the tendency for forward tipping of the incisors is reduced. Bone plates probably also enhance maxillary stability and reduce compensatory tooth movement. In the patients studied here who did not have rigid fixation after mandibular advancement, the expected forward movement of the lower incisors during fixation was observed in almost every instance (note in Table III that during fixation the lower incisor moved slightly back in the x-y coordinate system but much less than point B and Pg-that is, the incisor moved forward relative to these points). It is noteworthy, however, that there was a tendency for uprighting of the incisors after fixation was released even though resting lip pressure did not increase. We believe this was related to a rebound phenomenon from the changes in fixation, rather than to alteration in lip pressure. We did not measure tongue pressure, but it is possible that a decline in resting tongue pressure because of a change in tongue position also contributed to this tooth movement. In contrast, the relaxation of soft tissues that accompanies superior repositioning of the maxilla could be seen clearly in lower resting lip and cheek pressures. Although resting pressures declined, pressures during speech and swallow did not, perhaps indicating that the degree of muscle contraction necessary to obtain an appropriate lip seal is monitored and maintained. When resting lip pressure declined, the incisors tipped forward
postsurgically in a pattern of morphologic change that was clearly different from the patients who had stretching of the soft tissues. These changes were exactly as equilibrium theory predicted. How can one explain the failure of lip pressure to increase when the jaws and teeth are moved in a way that stretches these soft tissues? Tongue pressure usually does not increase when the teeth are moved back into space previously occupied by the tongue** because the tongue also moves and a new postural position is adopted.23 Archer and Vig” used pressure transducers placed labially and lingually to the lower incisors to observe changes in pressures when head posture was altered, and noted that tongue pressure changed more than lip pressure as head posture went from flexion to extension. The posture of the tongue determines resting tongue pressure; the mobility of the tongue gives great potential for change. Repositioning of the lips via an alteration in posture is not accomplished as easily as repositioning of the tongue, but at least, to some extent, this may be involved in lip adaptation. In addition, surgical treatment itself can affect lip posture, particularly when a genioplasty or total maxillary osteotomy is performed through incisions in the labial vestibule. This can be seen clearly in the elevation of the upper lip in our patients who underwent LeFort I osteotomy (Fig. 4). This effect has been recognized for some years and surgical techniques have been altered over the past decade to decrease the amount of shortening of the lip and inward rolling of its vermilion border that accompanies healing of the vestibular incision used for maxillary osteotomy. Even so, the upper lip is noticeably shorter, tighter, and less mobile
302
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and
Phillips
a few weeks following maxillary surgery than it was previously. As healing proceeds, this “tethering” of the upper lip decreases, but is still present at least to some extent.” If lip pressures against the alveolar process above the teeth were measured after maxillary advancement, there well might be an increase, but often the shortening of the lip means that there is little or no pressure against the labial surface of the teeth. In an article of this type, it is natural to focus on the changes that occurred. Sometimes, however, the absence of change that might reasonably have been expected is as important an observation. The degree of lip adaptation displayed by these patients falls into that category. Pressures during lip function were maintained despite large changes in position, which may be o-neof the requirements for a continuation of normal speech. tip adaptation also was evident in the lack of increase in resting pressures. Stated more broadly, the stability of incisor position that usually is seen after orthognathic surgery probably is related to the degree of lip adaptation that occurs.
Siegel S. Nonparametric statistics. New York: McGraw-Hill Book Company, l956:75-83. 10. Pmffit WR. Muscle pressures and tooth position: North American whites and Australian aborigines. Angle Orthod 1975;45: 1-l I. 11. Proffit WR, McGlone RE. Tongue-lip pressures during speech of Australian aborigines. Phonetica 1975;32:200-20. 12. Bardach J, Bakowska J, McDermott-Murray J, Muoney MP. Dusdieker LB. Lip pressure changes following lip repair in mfants with unilateral clefts of the lip and palate. Plast Reconstr Surg 1984;74:476-81. 13. Luffingham JK. Lip and cheek pressure exerted upon teem m three adult groups with different occlusions. Arch Oral Biol 9.
1%9;14:337-50.
Thuer U. Janson T, lngervall B. Application in children of a new method for the measurement of forces from the lips on the teeth. Eur J Ortbod 1985;7:63-78. 15. Proffit WR, Phillips C. Turvey TA. Stability following superior repositioning of the maxilla by Le Fort I osteotomy. AM J &rTHODDEN~OFACORTHOP1987;92: 151-61. 16. Kohn MW. Analysis of relapse after mandibular advancement surgery. J Oral Surg 1978;36:676-81. 17. Ives J, McNeil1 RW, West RA. Mandibular advancement: skeletal and dental changes during fixation. J Oral Surg 1977:35: 14.
881-7.
Lake SL, McNeil] RW, Little RM, West RA. Surgical mandibular advancement: a cephaiometric analysis of treatment response. AM J ORTHOD1981;80:376-94. 19. Schendel SA, Epker BN. Results after mandibular advancement surgery: an analysis of 87 cases. J Oral Surg 1980;38:265-73. 20. Thomas PM, Tucker MR, Prewitt JR, Proffit WR. Earty skeletal and dental changes following mandibular advancement and rigid internal lixation. Int J Adult Otthodon Orihognath Surg 1986; 18.
We thank Larry Moray, Tony Hatcher, Debra Price, and Nancy Arellano for technical assistance.
REFEREWES 1. Proffn WR. Equilibrium theory revisited. Angle Ortbod 1978;
3:171-8.
48: 175-86. 2.
Solow B, Kreiborg S. Soft tissue stretching: a possible control factor in craniofacial morphcgenesis. Stand J Dent Res 1977:
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1986;44:698-702.
85505-7. 3.
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5. 6.
7. 8.
Solow B, Siersb;eck-Nielsen S, Greve E. Airway adequacy, head posture, and craniofacial morphology. AM J ORTHOD 1984; 86214-23. Solow B, Siersbreck-Nielsen S. Growth changes in posture and morphology. AM J ORTHOD1986;89: 132-40. Fields HW, Proffit WR, Nixon WL, Phillips C, Stanek E. Facial pattern differences in long face children and adults. AM J ORTHOO 1984;85:217-23. Gould MS, Picton DC. A study of pressures exerted by the lips and cheeks on the teeth of subjects with Angle’s Ciass II Division 1, CIass II Division 2, and Class-III malocclusions compared with those of subjects with normal occlusions. Arch Oral Biol 1%8;13:527-41. Schellhase DJ. An evaluation of osseous relationships following superior repositioning of the maxilla: immediate and long-term results [M.S. thesis]. University of North Carolina, 1984. SAS user’s guide. Statistics. 5th ed, version 5. Gary, North Carolina: SAS Institute Inc., 1985:433-S%.
van Sickels JE, Larsen AJ, Thrash WJ. Relapse after rigid 6xation of mandibular advancement. J Oral Maxillofac Surg
Wickwire NA, White RP, Proffit WR. The effect of mandibular osteotomy on tongue position. J Oral Surg 1972;30:184-90. 23. Wickwire NA, Proffit WR. Changes in tongue position and activity following mandibular osteotomy. AM J ORTHOI) 1972: 62:94-106. 24. Archer SY. Vig PS. Effects of head position on intraoral pressures in CIass I and Class Badults. AM J ORTHOD1985$7: 22.
311-8. 25.
Phillips C, Devereux JP, Tulloch JFC, Tucker MR. Full face soft tissue response to -surgical maxillary intrusion. Int J Adult Orthodon Orthognatb Surg 198634~299-304.
Reprint
requests
to:
Dr. William R. Proffit Department of Orthodontics School of Dentistry University of North Carolina Chapel Hill, NC27514
D.D.S., Ph.D., and c+iePhi
, Ph.D.
Chapel Hill, N.C.
Lip pressures before and after orthogoathii surgery were studied to evaluate the rel@ionship between posttreatment soft-tissue adaptation and incisor stabiBy. Aftsr atI surgical p@cM&m+s, physkitasic adaptation resulted in the~maintenance of pressures during speech and wdioying. When tie maxilla was advanced by LeFort I osteoto@!, a signifkarit d@cr@@ein re&ng presswr8j of *he upper lip was observed inst%ad of the~expeqted incre&Weand inc!sur s~~~-~~ not seef’n rod&e4 to soft-tissue influences. When the mand@ie was advanced by s@g&k%i split M&&my,. r&s&q prrrssure did not increase as etipeeted, but there was a tenr,fency for in&orS to become we upr&@ after fixation release, perhaps as a rebound frorr:labial @ping in fixation, @/hen suft tissues we&relaxed as the mandible rata@d forward fallowing superior repositioning of the maxilla, resting pre~fes decreased and lower incisors tended to be p&Hotied forward as predk%d by equilibrium theory. (AM J ORT~-IOO DENTOFAC ORTHOP19#;93:294-302.)
L
ight pressures of long duration, primarily those from the soft tissues at rest, appear to be major components of the pressure equilibrium that determines tooth position.’ Orthognathic surm has the potential to affect lip position and thereby alter this equilibrium because it produces both lip movement in response to movement of the teeth and jaws, and independent lip movement caused by contraction of soft-fissw5 incisions or a change in muscle tonicity. Studies of lip posture and lip pressures in orthognathic surgery patients are interesting for two reasons: (1) the changes produced by the surgical procedure provide an experimental model in human beings to evaluate lip influences on tooth position and (2) pressure/posture.data should provide additional insight into the reasons for stability or relapse after surgicaI treatment. This report is based on studies of lip pressures and morphologic changes in orthognathic surgery patients treated at the University of North Carolina. Lip pressures are determined by the tautness of the lips and by their anteroposterisr and vertical positions relative to the incisors. The tighter the lips and the more facial the incisor position, the greater the-lip pressure, and vice versa. An increase in vertical facial height often leads to a separation of the lips at rest (lip incompetence). If the incisors continued to e~~pf, they From the Department of Orthodontics. School of Denttstry, University ofF&th Carolina at Chapel Hill. Supported in pat by Grant DE-05215 from the National Institute of Dental Research.
294
would move vertically away from the lips and~outside their control. The expected result would be greaterprominence of the dent&ion. Another possibility, proposed by Wow and Kreibor& and extended iti later works,3.4 is that a_n increase in facial height would stretch and tighten the soft tissues, w~hich~iivould lead to an increasein lip pressure and a more upright positioti of the incisors. Upright incisors often are fuund in lotig face~patients with anterior open bite’ in whom toothlip relationships are maintained. Studies of Hp pressures in orthognathic surgical patients offer a unique opportunity toobserve the ch&g& in pressure~pattems that accompany the changes ii~ vertic@ and horizontal tooth-lip relationships. Superior repositioning of the maxilla usually places previou%ly eiposed =upper incisors at least partially GidE and in greater contact with the upper lip. This type of surgical procedure also produces a rotational advancement 6f the mandible that is accompa&d by relaxation of the lips and cheeks. Advancement of the mandible by ramus osteotomy without simuitaneous maxillary surgery s&e&hes the~soft tissues around the lower jaw and presumably Would ir!crease tension in the lower lip. Advan&me@ of the maxilla would have the same stretching iffect on the upper lip. The objective of the studies reposed here was to document changes in lip position and pressures rel#ed to these orth6gnathic sufgical procedures, and to eval: uate the relatiOnship between incisor stability postsurgically and 3he pauern of lip pressures. We exkted
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Lip posture and pressure after orthognathic
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295
Fig. 1. Completed upper carrier with pressure transducers in place on the dental cast before use. The pressure-receiving surface of each transducer is flush with the surface of the carrier. Wires from each transducer are conveyed in the lower border of the carrier to the right posterior area, then brought forward in the buccal vestibule to exit at the corner of the mouth.
different effects on lip pressure and different patterns of postsurgical changes in incisor pattern from different surgical procedures. Our hypotheses were as follows: (1) in patients in whom the soft tissues are stretched at surgery, as in mandibular or maxillary advancement, lip pressures will increase and the incisors will move lingually postsurgically; (2) when incisors are moved within the sphere of influence of the lips after previously being outside of it, as when vertically prominent maxillary incisors are elevated to a new position beneath the lip, lip pressures will increase and the incisors will tend to move lingually postsurgically; and (3) when soft tissues are relaxed by the surgical treatment, as when the mandible rotates upward and forward following maxillary intrusion, lip pressures will decrease and the incisors will move labially. On the basis of current equilibrium theory, we expected that pressures during function (speech and swallowing) would show little, if any, change postsurgically unless normal function was disturbed; any relationship between incisor position and lip pressure would be for resting pressure only. MATERIALS AND METHODS
Subjects for this study were selected from the orthognathic surgical patients of the Dentofacial Program at the University of North Carolina on the basis of their willingness to cooperate with repeated recordings of lip pressure during and after treatment. Lip pressures were studied in a total sample of 60 patients. Seventeen of
these patients were lost to follow-up; eight declined surgical intervention after presurgical orthodontic treatment; and nine moved or refused to return for follow-up. A number of techniques for recording lip pressure have been proposed and data from both hydraulic and electronic devices have been reported recently. In this study lip pressures were evaluated by an array of five small cantilever beam strain gauge transducers contained within a thin plastic carrier that was placed labially and buccally to the upper and lower arches (Fig. 1). Transducers were located bilaterally adjacent to the first molars and canines with a single transducer between the central incisors in the midline. The sensing portion of each transducer was 2 to 3 mm from the tooth surface. The carrier itself also was 2 to 3 mm in thickness over the teeth and slightly thicker where it extended into the labial and buccal vestibules. Special miniature cables were used to reduce the bulk of lead wires, which were conveyed in the lower border of the carrier to the right molar area and then brought forward in the vestibule to the comer of the mouth. Gould and Picton6 studying cheek pressures in patients with a premolar extraction site, found that lip pressures increased only slightly as a pressure transducer was moved out buccally from the surface of a tooth for approximately 2 mm, then increased more rapidly. Therefore, the transducer positions used in this study should have provided pressure readings similar
Table 1. Maxillary/upper
lip landmark changes (mm) in max&ry Change ut surgely
Horizontal (anterior ANS A Maxillary incisor Upper lip prominence Vertical (inferior = ANS A Maxillary incisor Upper lip border
=
advancement patients (n = 10)
Change in fixation
Change presurgerj 2 y
Change postjixation
to
+ change) 3.88 3.52 3.54 7.32
(2.03)* (1.54) (2.48) (4.41)
-- 1.77 -0.84 -0.96 -4.77
(1.44) (1.33) (1.54) (2.21)
-0.42 -0.53 -0.99 - 1.80
(1.39) (1.84) (2.48) (2.57)
1.99 2.32 I .74 1.51
(1.62) 11.70) (2.33) (2.55)
- 3.07 - 2.25 -2.67 -0.20
(3.86) (3.58) (4.15) (2.45)
0.14 -0.49 -0.27 0.81
(1.31) (0.96) (1.09) (0.98)
0.69 0.77 0.03 1.17
(1.11) (1.03) (0.96) (2.03)
- 2.27 - 1.95 -2.81 -- 0.59
(2.97) (33.75) (3.73) (2.16)
t change)
I_*Mean
(standard
deviation).
Tab4 11.Upper lip pressures in maxillary advancement patients (mean peak pressure, g/cm2) Right
canine
Midline
2 yr Pretreatment lml IPI lb/ Swallow Rest *Approached
140.1 123.8 138.5 127.4 13.6 significance
posttreatmeni 121.6 127.6 137.4 175.0 3.8
Pretreatment 43.7 38.1 44.4 73.9 4.9
tef 2 .vr posttreatment 35.1 34.3 34.5 76.X 0.4
Pretreatment 113.5 110.3 96.3 119.3 15.8
canine 2 .vr p@treatment 118.4 118.4 119.8 151.7 4.6*
(P < 0.10).
to, but somewhat greater than, pressures that would have been recorded at the tooth surface. Carriers for the pressure transducers were fabricated for each patient on dental casts made just before each recording session, so that the ~devicefitted quite accurately. Calibrations were carried out each time after the. transducers were mounted in the carrier because sensitivity can be affected by the way transducers are attached. On each experimental occasion, pressures were recorded (1) during ten swallows, (2) during live repetitions of each of the utterances “mama,” “papa,” and “baby” (which were used to record pressures associated with these bilabial consonants), and (3) six times with the lips at rest. Resting pressures were evaluated by holding the lips and cheeks away from the transducers while recording a baseline, and then recording again immediately afterward with the patient reIaxed and the lips and cheeks resting against the transducers. Pressure against the lower teeth was recorded first, and then the recording sequence was repeated for the upper arch. For the recordings patients were~placed in a quiet,
electrically shielded chamber and positioned so that the instrumentation was visible to the operator but not the patient. For each event (such as a word, swallow, or rest), 3 seconds of data were recorded, amplified, computer-processed, and the resulting sealed presStire waves displayed-almost immediately on a graphics terminal whileethe data were held in buffer memory. Data editing functions permitted~ immediate exclusion of extraneous events. For instance, if the patient said “papa” when he should have said “mama,” coughed during a swallow, or moved when he was supposed to-be at rest; such data were disc.arded immediately and another recording was taken. At a later time the data were recalled from computer memory for analysis. For each patient lip pressures were recorded before the beginning of any treatment, immediately before a surgical procedure, and at 6, 12, and 24 months postsurgery. The presence of orthodontic appliances greatly compticates the measurement of lip pressure because the transducers must be placed outside the brackets even if arch- yires are removed. A typical bracket extends 2 to 3 mm-from the tooth surface, so that~with
vdu?re 93 Number 1
Lip posture and pressure after orthognathic
an orthodontic appliance in place, the carriers were 5 to 6 mm out into the lip, increasing the probability of significant artifact. In this article we discuss only data from the pretreatment and 24-months postsurgical appointments, when no orthodontic appliances were present. Cephalometric radiographs taken in natural head position were available for each patient from the same time frame as each lip pressure recording session. Because natural head position changes somewhat following orthognathic surgery,7 x and y coordinates of cephalometric landmarks were analyzed with true horizontal (from natural head position) as the horizontal reference axis and a perpendicular vertical line through sella as the vertical reference axis. Cranial base superimpositions were registered on SN at S, with SN rotated up 6” from true horizontal-that is, landmark position changes were not affected by postsurgical changes in true horizontal. Descriptive statistics for landmark position changes and lip pressure were calculated using SAS.8 Because the distribution of lip pressure changes tended to be skewed, the Wilcoxon matched pairs signed-rank test, a nonparametric analogue of the paired t test, was used to evaluate lip pressure changes.’ The significance level was set at 0.05 for all comparisons. RESULTS 1. Maxillary advancement,
LeFort I osteotomy
Ten patients had horizontal advancement of the maxilla (more than 2-mm surgical change at both ANS and A). Tabulated landmark changes are displayed in Table I and postfixation changes in maxillary tooth-lip positions are shown in Fig. 2. Note that in overall change, the upper lip advanced about the same amount as the skeletal landmarks. Swelling that developed after the surgical procedure and resolved during the next 6 months accounts for the lip changes in fixation and postfixation. In comparison to pressures before treatment, at 2 years postsurgery pressures by the lower lip were unchanged at rest and showed a nonsignificant tendency to increase during swallow and speech. For the upper lip (Table II), pressures during speech were unchanged. There was a tendency for pressures during swallowing to increase, particularly in the canine region, but this was not statistically significant. There was a marked decrease in resting pressures at all locations, which approached statistical significance. The hypothesis that upper lip pressure would increase for these patients therefore was rejected. After fixation release incisor position was relatively stable with as much tendency to tip labially as lingually (Table I).
7
surgery
297
0.1
0.1
M
w \
1.0
1.8
1.2
0.03
Fig. 2. Changes in maxillary incisor and lip positions from release of fixation (6 weeks postsurgery) to 2 years postsurgery for patients who underwent maxillary advancement. Mean millimeter movements relative to the skeletal x-y coordinate system described in the text are shown.
2. Mandibular advancement, split osteotomy
sagittal
Twenty patients underwent a sagittal split osteotomy to bring the mandible forward. There were two subgroups of these patients-one with mandibular ramus surgery alone (n = 1 l), the other with simultaneous repositioning of the maxilla and mandible (n = 9). Mandibular and lower lip landmark changes for the combined subgroups are displayed in Table III. Mean changes in lip/tooth position postfixation are shown for the subgroups in Fig. 3 and pressure data for the lower lip are shown in Table IV The expected increase in lower lip pressures postsurgically in these patients was not observed. After advancement there was a 50% decrease in resting cheek pressures in the lower molar region (P < 0.05) and a tendency for lower lip pressure to decrease (Table IV). Resting pressures of the upper cheek and lip also showed approximately a 50% decrease in the molar and canine regions (P < 0.05), but were unchanged in the midline. When the patients who underwent only mandibular ramus surgery were compared to those who had both maxillary surgery and mandibular surgery, differences in pressure patterns were confined to the upper lip; resting pressure in the upper canine region de-
298
Profit
,4,n. J. Orthcd.
and Phillips
Dent&c.
Whop. April-1988
Fig. 3. Changes in mandibular incisor and #p positions [email protected] patients with mandibulq advanoament &ne (A) and combined tia$lWy intru&n-ma&diibIar advaiient (8). -in b6th gcoups the mqxt&le rotated qwqrd and,&warcf relatkqtu#ikcraniat brain this tirns@iod du+to ramoval of the intarocclusal wafer sptint that was p~~@%t during fiiration. Note #Q&the incisor went forward less than point 8, that is, was rep~rx$t&ed lkngua#y r&We %Hhe mandible in the patients who underwent mandibular advancement alone.
T~IU.~Mandibular/lower
lip landmark changes (mm) in mandibular advancement patients (n = 20) Change at surgery
Horizontal (anterior = + change) B Pg Mandibular incisor Lower lip-prominence Vertical (inferior = + change) B Pg Mandibular incisor bwer lip border
Change jxation
in
Change posrfuration
Change presurgery 2yr
to
5.32 7.91 5.43 7.73
(3.18) (4.68) (3.42) (3.62)
-1.24 - 2.21 -0.56 -4.15
(1.60) (1.90) (1.33) (2.63)
1.05 1.15 0.17 - 0.79
(1.65) (1.85) (1.68) (1.86)
5.23 6.83 4.44 2.85
(2.75) (4.22) (2.49) (2.48)
2.71 1.73 1.92 - 1.49
(6.12) (4.36) (4.08) (4.76)
0.76 0.74 0.43 I .41
(1.86) (1.73) (1.17) (4.74)
- 2.88 -0.97 -2.66 -2.00
(2.07) (1.16) (1.40) (2.17)
0.36 1.14 - 0.39 -2.13
(6.09) (4.01) (4.38) (4.33)
creased in the subgroup receiving mandibular surgery only, but not in the two-jaw surgery subgroup. During the speech sounds, both subgroups showed a tendency toward an increase in lower lip pressure in the canine region, but there was no change in pressure during swallowing in either subgroup (Table IV). There was no evidence to support the hypothesis that resting pressure by the lower lip would increase following mandibular advancement. Despite this, in all but one of these patients, the lower incisors did move slightly lingually relative to the mandible after fixation release (note in Table III that the incisor moved slightly forward in the x-y coordinate system, but less than B and Pg, showing its lingual movement relative to
these points). This effect was greater in the subgroup who underwent~ mandibular advancement alane (compare movement of point B and incisal &ge in Fig. 3, A and-B). As shown inPig. 3, both the incisor and the lip moved upward and slightly forward reIative to the cranial base postfixation after removal of the splint that was presem during fixation. d Seven patients underwent horizontal mandibular advancement without surgery on the mandible itself. in response to superior repositioning~ of the maxillas that allowed the mandible to rotate upward and forward.
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5.4
Fig. 4. Changes in maxillary incisor and lip positions at surgery (A) and postsurgery (6) for patients who underwent only superior repositioning of the maxilla, so that the mandible rotated upward and forward.
Table IV. Lower lip pressures in mandibular advancement patients (mean peak pressure, g/cm2) Right canine
Left canine
Pretreatment
2 yr posttreatment
Pretreatment
2 Y’ posttreatment
Pretreatment
2 Yr posttreatment
48.2 50.3 63.5 114.0 2.4
54.6 49.0 58.8 143.4 0.4*
38.5 33.1 49.8 138.8 2.6
28.0 20.8 30.7 97.3 0.5
45.0 48.8 67.2 143.1 3.7
47.2 45.1 51.7 148.6 0.3t
lmi ’ P’ IhI Swallow Rest *Approached
Midline
significance
(P < 0.10).
tP < 0.05.
Changes in upper/lower lips and tooth positions are shown in Figs. 4 and 5, respectively. Changes in lip pressures for these patients are shown in Table V. Although the upper incisors were moved superiorly in these patients, the movement was not great enough to place them beneath the lip when it also shortened and so the expected “capture” of the upper incisors by the lip did not occur. Resting lip pressures decreased rather than increasing, particularly in the midline. No consistent changes in upper incisor position occurred postsurgically. There was a marked decrease in resting lip and cheek pressures against the mandibular teeth. This was statistically significant (P < 0.05) for two channels despite the small sample size. There were no consistent or statistically significant changes in pressures by either lip during swallow or speech. In contrast to the patients who underwent mandibular advancement by ramus osteotomy, there was a tendency for the lower incisors to reposition forward relative to the mandible after fixation release in this
group. The difference in postsurgical movement of the lower incisors between this group and the group whose mandible was advanced by ramus osteotomy was statistically significant (unpaired t test, P < 0.05). This result supports the hypothesis that relaxing the soft tissues will decrease resting lip pressure and allow the incisors to move forward. DISCUSSION
In any studies of lip pressures, the bulk of the recording apparatus is a problem and the possibility of artifact cannot be excluded. Because the measuring device stretches the lip away from the teeth, it is unlikely that actual pressures at the tooth surface were larger than those that were recorded, but they could be smaller. There is also the possibility of error caused by alteration of lip posture by the apparatus. It is difficult to estimate exactly what effect this might produce. The magnitude of lip pressures reported in this study are quite comparable to those reported previously by US~‘*‘~ and by most other investigators. 12-‘4The emphasis
300
ProfJit and Phillips
0
3.6
Fig. 5. Changes in mandibular incisor and lip J.W&&N at surgery (AJ and pqsk~gery who ufxWw& only Superior repcx&nm ofti t&&Ma. I?&ovaiofthe interocelu~ allowed further upward and f&ward rota&m of the mandible.
in this article is on the direction of changes in lip pressure that accompany adaptations fuHowing-orthognathic surgery, rather than on their absolute magnitude. The use of an identical technique before and after treatment imparts a degree of confidence in the accuracy of the change data. Previous work on the relationship between tonguelip pressures and tooth position has shotlrn that resting pressures, but not pressures during function, have an effect.’ This can be explained by the duration of the pressure; resting pressures have a duration of many hours per day, easily exceeding the 4 to 6-hour duration threshold necessary to produce tooth movement, but swallowing and speech produce intermittent pressures with a total duration of a few minutes. As we expected, lip pressures during function were maintained postsurgically in our subjects and were not related to morphologic changes. Changes in the position of skeletal landmarks during and after surgical treatment reflect a combination of two effects: (-1) changes produced by the surgery itself and (2) postsurgical changes related to skeletal relapse and-/or remodeling. Changes in dental landmarks could occur due to both of the- sketetal possibilities. In addition, all these patients underwent orthodontic treatment that included some postsurgical finishing, which means that some orthodontic tooth movement occurred after the surgical~treatment and before removal of the appliances. As one might expect, detailed studies of relatively large groups of patients undergoing orthognathic- surgery show that significant changes-in landmark position are produced by the surgical procedure it&f. Both LeBort I osteotomy and sag&al split osteotomy typ-
@for
patients
ically produce 5 to 1.5mm changes at the time of surgery as was the case with these patients. We have recently reported a study of 61 patients who unde~ent L&x-t I osteotomy for superior repositioning of ~the maxilla.15 In this group only four persons had significant vertical relapse-that is, postsurgical downward movement of the maxilla ,of 2 mm or more --&lit 20% of the subgroups who had their maxilla advanced: had 2 to 4 mm of horizontal relapse. Several investigators have reported stability, .or lack thereof, following mandibular advancement.““9 Mandibular advancement patients who are placed in intermaxillary fixation tend to have the mandible slip posteriorly during the period of initial heding and intermaxillary fixation, after which the great -majority are clinically~ stable. During the period of intermaxilhuy fixation, however, the lower incisors tend to tip forward relative to the mandible. Remodeling of aIveol$r bone around the teeth, that is, inadvertent orthodontic tbdh movement, allows the mandible to move posteriorly while- the mandibular teeth are held.ia their relationshipto the maxillary teeth because of the splint and intqrmaxillary fixation. Therefore, one might expect that patients who had a ramus osteotomy for mandibular advancement would show some pro&nation ~of lower incisors relative to the mandiMe during intermaxiIlary fixation. This would overwhelm any effect produced by lip pressure. Any uprighting- of incisors caused by lip pressure should occur after removal of fixation. It is also pertinent that -the type of fixation may affect stability of incisors. All patients included in .mis report had wiring of max&aq~and mzmdibnlar &twEomy sites, and were @aced in in&m&I&q. &&on for approximately 6 weeks. None had-rigid fixationin
Volume 93 Number 4
Table
Lip posture and pressure
after
orthognathic
surged
301
V. Lower lip pressures in mandibular upward rotation patients (mean peak pressure, g/cm*) Right Pretreatment
Upper lml
Midline
2 yr
2 Y’
posttreatment
Left canine
Pretreatment
posttreatment
Pretreatment
2 Y’ posttreatment
lip
IPl lb/ Swallow Rest Lower lip lml ‘P’ lb1 Swallow Rest *Approached tP < 0.05.
canine
significance
112.8 109.3 113.5 118.2 14.4
138.8 138.2 181.2 207.6 6.1
71.8 83.0 91.3 86.8 5.5
16.6* 12.1* 19.1* 105.2 0.1*
110.4 124.2 93.2 123.8 17.0
103.8 103.0 125.4 173.3 5.3
68.2 75.8 77.8 89.1 5.3
49.8 53.6 71.5 253.3 0.5*
23.2 22.4 36.1 78.7 3.71
30.6 23.2 35.3 169.9 0.3t
37.4 48.1 53.2 117.5 8.9
43.0 42.6 60.0 217.6 0.4t
(P < 0.10).
the form of bone plates or lag screws. Recent reports by our group” and others*’ indicate that when sag&al split advancement is followed by rigid intraosseous fixation with screws and when intermaxillary fixation is not used or is used only briefly, the stability of skeletal mandibular landmarks is improved and the tendency for forward tipping of the incisors is reduced. Bone plates probably also enhance maxillary stability and reduce compensatory tooth movement. In the patients studied here who did not have rigid fixation after mandibular advancement, the expected forward movement of the lower incisors during fixation was observed in almost every instance (note in Table III that during fixation the lower incisor moved slightly back in the x-y coordinate system but much less than point B and Pg-that is, the incisor moved forward relative to these points). It is noteworthy, however, that there was a tendency for uprighting of the incisors after fixation was released even though resting lip pressure did not increase. We believe this was related to a rebound phenomenon from the changes in fixation, rather than to alteration in lip pressure. We did not measure tongue pressure, but it is possible that a decline in resting tongue pressure because of a change in tongue position also contributed to this tooth movement. In contrast, the relaxation of soft tissues that accompanies superior repositioning of the maxilla could be seen clearly in lower resting lip and cheek pressures. Although resting pressures declined, pressures during speech and swallow did not, perhaps indicating that the degree of muscle contraction necessary to obtain an appropriate lip seal is monitored and maintained. When resting lip pressure declined, the incisors tipped forward
postsurgically in a pattern of morphologic change that was clearly different from the patients who had stretching of the soft tissues. These changes were exactly as equilibrium theory predicted. How can one explain the failure of lip pressure to increase when the jaws and teeth are moved in a way that stretches these soft tissues? Tongue pressure usually does not increase when the teeth are moved back into space previously occupied by the tongue** because the tongue also moves and a new postural position is adopted.23 Archer and Vig” used pressure transducers placed labially and lingually to the lower incisors to observe changes in pressures when head posture was altered, and noted that tongue pressure changed more than lip pressure as head posture went from flexion to extension. The posture of the tongue determines resting tongue pressure; the mobility of the tongue gives great potential for change. Repositioning of the lips via an alteration in posture is not accomplished as easily as repositioning of the tongue, but at least, to some extent, this may be involved in lip adaptation. In addition, surgical treatment itself can affect lip posture, particularly when a genioplasty or total maxillary osteotomy is performed through incisions in the labial vestibule. This can be seen clearly in the elevation of the upper lip in our patients who underwent LeFort I osteotomy (Fig. 4). This effect has been recognized for some years and surgical techniques have been altered over the past decade to decrease the amount of shortening of the lip and inward rolling of its vermilion border that accompanies healing of the vestibular incision used for maxillary osteotomy. Even so, the upper lip is noticeably shorter, tighter, and less mobile
302
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and
Phillips
a few weeks following maxillary surgery than it was previously. As healing proceeds, this “tethering” of the upper lip decreases, but is still present at least to some extent.” If lip pressures against the alveolar process above the teeth were measured after maxillary advancement, there well might be an increase, but often the shortening of the lip means that there is little or no pressure against the labial surface of the teeth. In an article of this type, it is natural to focus on the changes that occurred. Sometimes, however, the absence of change that might reasonably have been expected is as important an observation. The degree of lip adaptation displayed by these patients falls into that category. Pressures during lip function were maintained despite large changes in position, which may be o-neof the requirements for a continuation of normal speech. tip adaptation also was evident in the lack of increase in resting pressures. Stated more broadly, the stability of incisor position that usually is seen after orthognathic surgery probably is related to the degree of lip adaptation that occurs.
Siegel S. Nonparametric statistics. New York: McGraw-Hill Book Company, l956:75-83. 10. Pmffit WR. Muscle pressures and tooth position: North American whites and Australian aborigines. Angle Orthod 1975;45: 1-l I. 11. Proffit WR, McGlone RE. Tongue-lip pressures during speech of Australian aborigines. Phonetica 1975;32:200-20. 12. Bardach J, Bakowska J, McDermott-Murray J, Muoney MP. Dusdieker LB. Lip pressure changes following lip repair in mfants with unilateral clefts of the lip and palate. Plast Reconstr Surg 1984;74:476-81. 13. Luffingham JK. Lip and cheek pressure exerted upon teem m three adult groups with different occlusions. Arch Oral Biol 9.
1%9;14:337-50.
Thuer U. Janson T, lngervall B. Application in children of a new method for the measurement of forces from the lips on the teeth. Eur J Ortbod 1985;7:63-78. 15. Proffit WR, Phillips C. Turvey TA. Stability following superior repositioning of the maxilla by Le Fort I osteotomy. AM J &rTHODDEN~OFACORTHOP1987;92: 151-61. 16. Kohn MW. Analysis of relapse after mandibular advancement surgery. J Oral Surg 1978;36:676-81. 17. Ives J, McNeil1 RW, West RA. Mandibular advancement: skeletal and dental changes during fixation. J Oral Surg 1977:35: 14.
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We thank Larry Moray, Tony Hatcher, Debra Price, and Nancy Arellano for technical assistance.
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Wickwire NA, White RP, Proffit WR. The effect of mandibular osteotomy on tongue position. J Oral Surg 1972;30:184-90. 23. Wickwire NA, Proffit WR. Changes in tongue position and activity following mandibular osteotomy. AM J ORTHOI) 1972: 62:94-106. 24. Archer SY. Vig PS. Effects of head position on intraoral pressures in CIass I and Class Badults. AM J ORTHOD1985$7: 22.
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