Reliability of soft-tissue profile in cephalometrics E. Hillesund, D. Fjeld, and B. U. Zachrisson Oslo, Nonvaj
he purpose of the present investigation was to study some problems regarding the reproducibility of the soft-tissue profile in attempts to obtain the most correct recording of lip position and morphology in clinical practice, particularly for patients with large overjets. For this purpose, two groups of children were studied-one with normal incisor relationship and another group with excessive overjet. Registrations on two films exposed within an interval of 3 weeks, as well as double registrations on the same film, were made. In particular, the following problems were taken up: 1, How reliable are the most commonly used soft-tissue landmarks in the relaxed versus closed lip positions? 2. How reproducible are the relaxed and closed lip positions in different patients with malocclusion? 3. What changes in lip thickness take place from a position where the lips are relaxed to one where the lips are in slight contact? 4. What is the relationship of these changes to the degree of overjet? Cephalometric measurements are influenced by several different sources of error, including those related to technical equipment and procedure and to the operator interpreting the radiographs. Previous investigations on the reliability of head film measurements have dealt mainly with the skeletal reference points,2, I4 and only a few authors have investigated problems regarding the reproducibility of soft-tissue measurements.“, r6, 2u Uncertainty prevails regarding the degree of accuracy with which the different softtissue landmarks, especially the lips, can be used for clinical treatment-planning and evaluation purposes. Further, there is some confusion as to which lip position should be used in routine clinical cephalometry, particularly when single cephalograms are taken. This is especially important for children with marked overjet and morphologically incompetent lips:’ Normal1 y , two porttural positions of the lips can be observed-the so-called “relaxed” and “closed” positions.” In the former, the lips are relaxed. apart. and hanging loosely with no effort made at lip contraction. A small vertical space. the interlabial gap, is normally found between the upper and lower lips. In the closed position, the lips are lightly touching to produce an anterior seal. Burstone” showed that a great deal of confusion can arise if one does not differentiate between these positions in the evaluation of malocclusion and facial disharmonies. For instance. attempts to predict and evaluate soft-tissue changes on the basis of the closed lip position are complicated by the fact that From the Department of Orthodontics, University of Oslo 0002.9416/78/110537+
1978 The C.
Am. J. Orthod. November I978
538 Hill~sut~d, Fjeld, and Zuchrisson
prior to orthodontic treatment the lips may be overly stretched and flattened in their effort to effect lip closure. In attempts to answer questions of how far backward the lips will move following orthodontic retraction of incisors, some authors’. r9 have made cephalograms with the lips in light contact both before and after treatment, other?, 12, lx have taken the radiographs with lips relaxed, and still others lo* 13,I7 have not specified whether or not a standardized lip position was used. It is obvious that a relaxed lip position has many advantages and may give valuable information also when it comes to evaluations of lip competence, anterior seal, interlabial gap, and lip line (particularly the relationship between lower lip and upper incisor clinical crown). There is still a question, however, as to how stable and reproducible this position is when the patient’s head is seated in the cephalostat. Burstone’ emphasized that, to obtain the relaxed lip position, simply instructing the child to relax his lips was not entirely reliable because in attempting to achieve a relaxed position the patient may curl the lips away from the teeth. Therefore, he advocated lightly stroking the upper and lower lips with the fingers and/or lightly jiggling the mandible in an opening and closing manner (in attempting to relax the mandible, the patient usually simultaneously relaxes the lips). In so doing, the reproducibility of the relaxed lip position, as expressed by the interlabial gap, may be relatively good, even in patients with malocclusion.6 Subjects TWO groups of children were investigated-one with excessive overjet and one with normal overjet. The first group, to be termed the overjet group, consisted of sixteen boys and nineteen girls 10 to 14 years of age. The criterion for those included in this group was an overjet of at least 8 mm. (average, 9.9 mm.; range, 8 to 13 mm.). The second group, to be termed the normal group, comprised fifteen boys and seventeen girls, also 10 to 14 years of age. The only criterion for inclusion in this group was a “normal incisor relationship” (that is, an overjet and overbite between 1 and 3 mm.). All children were of Norwegian origin and of medium socio-economic status. They were randomly selected among patients at the Oslo University Department of Orthodontics or the Oslo and Baerum School Dental Services. The patients were called in twice at 3-week intervals, and each time two different cephalograms were taken. The first radiograph was taken with the teeth in centric occlusion and the lips in light contact, and the second was taken with the teeth in occlusion and the lips relaxed. Consequently, the material was divided into four test groups, which were termed accordingly: 1. 2. 3. 4.
OC OR NC NR
= = = =
Over-jet Overjet Normal Normal
group-closed group-relaxed group-closed group-relaxed
lips. lips. lips. lips.
Methods The cephalograms were taken in a Lumex Type B cephalostat (Pedersen & Schmidt A/S, Denmark), with a focus-to-film distance of 190 cm. and a 10 cm. distance from the midsagittal plane to the film. This gives a linear enlargement of midsagittal structures of 5.6 percent, which was not corrected in the study. Since in a pilot study9 a modified low-kilovoltage technique had been found clearly superior in terms of soft-tissue landmark reproducibility to the conventional technique (70 kv., 16 Ma.S., 0.1 s, and aluminum wedge), all cephalograms in this studv wprp Y;)Z\CC?2: -G ;\v., S ka.S., and 0.1 s without
Reliability of soft-tissue profile
60.0 m m
Fig. 1. Skeletal3 and soft-tissue reference points’, 5. I1 used. Lip thickness was measured over A (TSS) and B points (E&f), labrale superius (US), and labrale inferius (TLI).
any aluminum wedge (Fig. 3). The following precautions were taken to secure optimal recordings: The chair height at the first recording was registered for each patient, and the three recordings to follow were made at the same height. Head position was standardized with a fixed light cross. The patient was oriented with his midsagittal plane paral!el to the film and with the Frankfort plane horizontal.’ Before exposure, the patient was fluoroscoped with low radiation by means of an image intensifier and closed-circuit television was used to check that all radiographs were taken with the teeth in centric occlusion. The first radiograph at each session was taken with the lips in light contact. The following instruction was given: “Sit relaxed, bite lightly together on your posterior teeth, breathe through your nose, and close the lips to light contact.” The second radiograph was taken with lips relaxed in response to the following instruction: “Sit relaxed, bite lightly together on your posterior teeth, breathe through the nose, and relax completely in your lips.” In all cases the lip position was checked and, if necessary, adjusted by the operator after lightly stroking the upper and lower lips with the fingers.” All registrations were made on an electronic digitizer with automatic coordinatelocating equipment. The precision was 0.1 mm. W ith the digitizer it was possible to register any point in an x, y coordinate system at any chosen origin and axis directions; thus, the x and y components of the total variability could be isolated for each landmark. The registrations were made by two operators (D.F. and E.H.) with the same degree of training in locating the reference points. To avoid systematic errors between the operators, the two groups were divided at random so that each operator registered one half of each group. Eight reference points in the soft-tissue profile (Fig. 1) were registered in a coordinate system.
Am. J. Orthod. November 197 8
As in several previous studies ’ a, I”. I”. In, I8 the skeletal facial plane (nasion-pogonion) was chosen as the y axis, and origin was defined by the x axis through incision superius (Fig. I ). This coordinate system is based upon stable and easily recognizable reference points. Baumrind and Frantz ’ showed that the anteroposterior location of nasion and pogonion is reliable and the uncertainties in locating incision super& is small. To get all the registrations in the same quadrant, the coordinate system was moved 50 mm. vertically and 40 mm. horizontally, as shown in Fig. 1. Standard definitions were used for the skeletal” and soft-tissue landmarks.” 3, ‘I The lip thickness was registered at four different locations parallel to the x axis in all cases (Fig. 1). The recordings were automatically transferred to punched paper tape which was read by a computer. To illustrate the reproducibility of the soft-tissue reference points, scattergrams were produced by means of a x-y plotter program. Thus, each point received four scattergrams (for the OC, OR, NC, and NR groups, respectively). The basis for the scattergrams was that the first registration on each patient represented the origin in the scatter diagram. The individual points in the scattergrams therefore represented the difference between the registrations on the first and the second cephalograms of the same patient. All these differences were marked as points in correct linear magnitude and direction around the first registration, making the dispersion of location errors directly visible. The method errors and the variances jk double recordings on the same radiograph were studied on forty-eight randomly selected cephalograms that were registered twice by the same operator with a 7-day interval. The method errors were calculated according to the formula r2 = Zd’l2 n, where d is the difference between the first and second recordings, and n is the number of participants, and ranged from 0.16 to 0.30 and from 0.21 to 0.47 for the x and y coordinates, respectively.” The variance for the differences between the first and second recordings of the x coordinates for the reference points in Fig. 1 generally ranged from 0.05 to 0.13 (except for S with 0.32), and the variance for the y coordinates ranged from 0.08 to 0.14, except for SS (0.45), N (0.36), and PG (0.27).g Both the method errors and the variances involved in locating the reference points indicate that the errors introduced by the operator were on an acceptably low level and of the same order as in previous studies. r6, ‘O This indicates that the selected coordinate system introduced only negligible uncertainty in addition to that inherent in locating the landmarks. Statistical analysis. The reproducibility of each landmark was expressed by the difference between the coordinates for the first and second recordings with the same lip position for each patient. The variance of these differences was taken as the measurement for reproducibility. To test statistically significant differences between the reproducibility of points in the different test groups, the following test9 was used: F = ST/S”,,where F is Fischer-distributed with n, and n2 degrees of freedom, and SFand sz are the variances for the two test groups tested against one another. A two-sided Student’s t test was used to determine whether lip thickness or changes in lip thickness were significantly different between the different test groups.” Results Reproducibility of soft-tissue rqference points. The reliability of the selected softtissue landmarks in the four test groups is indicated in Table I. Scattergrams illustrating
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Table I. Reproducibility of eight soft-tissue reference points with closed versus relaxed lips Variance $w differences y coordinates
Variance .fkr differences s coordinates I
Reference point Overjet group N
PRN s SS LS LI SM PG Normal group N
PRN S ss LS LI SM FG
0.66 0.42 0.30 0.38 0.89 1.37 0.91 0.70
0.53 0.24 0.45 0.33 0.64 0.74 0.47 0.42
1.41 0.31 0.19 0.63 0.88 0.79 1.80 3.20
0.53 0.18 0.20 0.38 0.53 2.07 2.73 5.76
0.19 0.15 0.47 0.41 0.78 0.90 0.38 0.35
0.34 0.19 0.40 0.24 0.75 0.68 0.47 0.50
0.85 0.20 0.18 0.38 0.50 0.96 1.02 1.94
1.42 0.16 0.14 0.47 0.35 l.% 1.68 5.15
Figures refer to variance for differencesbetween first and secondregistrations(3-week interval). Note marked difference betweenhorizontal (x coordinates)and vertical (y coordinates)reproducibility in both groups (see scattergramsin Fig. 2).
the reproducibility of six important soft-tissue reference points in the overjet and normal groups with the lips closed or relaxed are given in Fig. 2. CLOSED VERSUS RELAXED LIP POSITION. The differences in reproducibility between closed and relaxed lips in both the overjet and normal groups were not statistically significant in the horizontal plane. neither were the differences in the horizontal and vertical planes for for the upper lip (LS). However, the reproducibility of the lower lip (LI) in the vertical plane was significantly better for exposures with lips in contact than with relaxed lips in the overjet (P < 0.01) and normal groups (P < 0.05). OVERJET VERSUS NORMAL GROUP. There were no significant differences in reproducibility for the upper or lower lip reference points between the two groups, for either closed or relaxed lips. Lip thickness. The average thickness of the upper and lower lips and over soft-tissue A and B points (closed and relaxed lips) is shown for both groups in Table II. Fig. 3 illustrates the typical changes in lip morphology from relaxed to closed position in patients with large overjet. The lower lip thickness (LI) was significantly (P < 0.01) greater in the overjet group than in the normal group for exposures with both relaxed and closed lips. On the other hand, the upper lip thickness (LS) was significantly (P < 0.01) greater in the normal group than in the overjet group for closed lips (but not for relaxed lips). Also, thickness over B point was significantly (P < 0.05) greater in the normal group than in the overjet group. Fig. 4 presents a schematic drawing of these differences in lower lip morphology between the overjet and normal groups. The thickness over soft-tissue A point did not show any significant differences between the groups.
Am. J. Orthod. 1978 November
0% [email protected]
*. . : . . :‘; ‘..*8.* : &.. . .
l . .‘=”
Fig. 2. Scattergram illustrating the reliability of six soft-tissue reference points. Each dot represents one individual and indicates the linear difference (magnitude and direction) in that patient between two registrations with a 3-week interval. Thus, dispersion directly illustrates how reliable each landmark may be for purposes of treatment planning and profile evaluation. For each reference point, the situation is shown with closed versus relaxed lips in children with marked overjet or normal incisor relationship. OC, Overbite, closed lips; OR, overbite, relaxed lips; NC, normal, closed lips; A/R, normal, relaxed lips. Scale is 1 mm. for all reference points; thus, magnification differs. Also note the marked difference between reproducibility in horizontal and vertical planes for some landmarks. CHANGES IN LIP THICKNESS F R O M RELAXED T O CLOSED POSITION. In both the overjet (P < 0.01) and normal groups (P < O.OS), there was a significant reduction in upper lip thickness (over LS) when lip position was changed from relaxed to closed (Fig. 3). The fT,,hle TTl reduction averaged 2.5 mm. (S.D. I .61 and I 0 m m (C n 1 31 wrr,prt;,r~l.r --I . ~
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5 . 6 ./
.* l .
. ’ . .
Fig. 2 (Cont’d).
l . .’ :
For legend, see opposite page.
Am. J. Orthod. I978 Novrmher
Fig. 3. Typical changes in lip morphology from relaxed to closed position in two persons with large overjet. Note the individual variation in lip thickness between these two patients (A and C). Table II. Lip thickness over four reference points with closed versus relaxed lips, and changes in thickness from closed to relaxed position
Relaxed lips X
A-point (TSS) Upper lip (TLS) Lower lip (TLI) B-point (TSM)
14.6 11.4 16.9 10.3
(2.1) (2.1) (1.5)
14.3 13.9 17.2 9.8
-0.3 2.5 0.3 -0.5
(0.7) (1.6) P < 0.01 (1.3) (0.7)
0.2 1.0 1.5 -0.1
(0.7) (1.2) P < 0.05 (1.2) P
Fig. 6. Scattergram illustrating and comparing the reliability of some key soft-tissue reference points for profile evaluation. PRN, Pronasale; S, Steiner’s S point; LS, labrale superius. Each dot represents one person and indicates the linear difference (magnitude and direction) in that patient between two registrations with a 3-week interval. Diagram shows situation for NR (normal incisor relationship and relaxed lips) and for LS, also with closed lips (NC). For dispersion for LS in persons with marked overjet, see Fig. 2.
measurements of the lips that are most relevant, and there should be little reason to recommend any particular method (closed or relaxed lips) on the basis of such divergences. For clinical purposes, the marked differences in lip morphology between patients with excessive and normal overjets (Fig. 4, Table II) and between recordings with the lips relaxed and closed (Figs. 3 and 5, Table II) are more important. It is likely that recordings with lips relaxed give the most correct reproduction of the morphology of the lips and of lip-to-tooth relationships.“, 8 Changes in lip thickness upon closure to light contact from a relaxed position have not been studied in detail before. However, a number of reports have considered changes in lip thickness in relation to orthodontic incisor retraction. Thus, several authors’, I’. I53“7 *I) have found an increased upper lip thickness in such instances. Opinions differ as to how the lips react on changes in anteroposterior position of the upper incisors. Some authors ?* “‘3 ‘li have found a good correlation between retraction of incisors and lip retraction, others ‘3 “j* ‘O indicate that upper lip reaction is proportional to incisor retraction when overjet is relatively small but whenever large (more than 4 mm.) incisor retractions are made there is no clear pattern of lip response, and still others”, lp, I3 have claimed that the soft-tissue response is variable and difficult to predict. Burstone” claimed that the most dramatic facial changes were seen in those cases in which there is a !arge or normal interlabial gap and that if a redundancy of lip tissue exists most likely the lips will not fall back following retraction of the teeth. These differences of opinion may be explained by differences in degree of incisor retraction, sex and age differences in the groups studied, and variations in lip morphology and also by a variation in lip position in cephalograms (see introduction). The flattening of the lips observed in this study upon a change from relaxed to closed position in patients with both excessive and normal overjets is likely to camouflage some of the lip response on orthodontic retraction of incisors, particularly when one is treating children with large overjets. This fact will also partly explain the increase in lip thickness that several authors have observed subsequent to
Am. .I. Orthod. November 1978
upper incisor retractions. If the radiographs both before and after treatment are taken with the lips in light contact, because of the changed incisor position, the posttreatment film will naturally depict the lips in a more relaxed position after treatment. The interlabial gap undoubtedly is influenced by a number of factors in addition to lip posture, including inherent lip length, dental protrusion, and anterior skeletal height.” As expected, the average interlabial gap was increased for persons with marked overjet, but even a few children with normal incisor relationship showed a marked interlabial distance. Although this study confirms Burstone’s statement that the interlabial gap may be more easily reproduced in persons with normal dental and lip relationships, the distance was fairly reproducible also in patients of the overjet group. This emphasizes one important finding documented in the present study, namely, that there are definite risks involved in using any soft-tissue registration on a strict millimeter basis in an individual child, whether it applies to profile evaluation, lip thickness, or interlabial distance in relaxed lip position. Summary and conclusions The reproducibility of the soft-tissue profile in lateral cephalograms was investigated with particular reference to relaxed and closed lip positions in patients with large overjets. Also, variations in upper and lower lip thickness in patients with different lip positions and degrees of overjet were measured. The material comprised thirty-five children with marked overjet (more than 8 mm.) and a group of thirty-two children with “normal” horizontal and vertical incisor relationships. All patients were recorded twice at 3-week intervals. Both times two cephalograms were taken, one with the lip in light contact and another with the teeth in occlusion but with lips relaxed. A low-kilovolt technique was used to achieve a good reproduction of the soft tissues (Fig. 3). All measurements were made on an electronic digitizer with automatic coordinate-locating equipment, and the registrations were referred to a coordinate system based on the skeletal facial plane. Method errors and variances were calculated, and scattergrams for the individual landmarks were produced to illustrate the dispersion (magnitude and direction) of locating errors for each landmark. Further, lip thickness, changes in lip thickness from relaxed to closed position on the lips, and the interlabial gap were recorded in the two groups. The following findings were made: 1. Differences in facial expressions from one recording to another may introduce considerable uncertainty in the reproduction of some soft-tissue reference points. 2. Reproducibility was not definitely dependent upon whether or not the recordings were made with relaxed or closed lips. 3. The reproducibility of the soft-tissue reference points showed a distribution pattern that varied in extension and direction from point to point. Each point had its own characteristic and usually noncircular distribution pattern (Figs. 2 and 6). Most registrations in the horizontal plane were within ? 1 to 1.5 mm. of the first registration. This provides an idea of the degree of accuracy with which soft-tissue landmarks can be dealt with for clinical diagnostic and treatment evaluation purposes. 4. For profile analysis purposes, the reproducibility of Steiner’s S point was surpris-
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ingly good. The S line and Rickett’s E line were about equally reproducible; both were less variable than Holdaway’s H line (Fig. 6). 5. A considerable reduction in upper lip thickness (average 2.5 mm.) was recorded in the overjet group when the lips were changed from relaxed to closed position. In the normal group both the upper and lower lips showed a reduction in thickness (about 1 and 1.5 mm., respectively) when the lips were pursed together. Flattening of the lips in closed-position head films may tend to camouflage the lip response to retraction of incisors, particularly when one is dealing with large overjets (Fig. 3). 6. The interlabial gap was increased in persons with marked overjet, and the majority had incompetent lips with interlabial gaps of from 3.5 to 9 mm. Also, a few children with normal incisor relationship showed a marked interlabial gap. The reproducibility of the interlabial gap was not significantly different for the two categories of patients. 7. In conclusion, the present study has demonstrated that, both from the standpoint of reliability and from a desire to accurately evaluate profile changes associated with orthodontic treatment, cephalograms of persons with large overjets should be taken with the lips relaxed. Also, head films of patients with normal incisor relationship may be taken with the lips in relaxed position, because the reproducibility of the soft-tissue profile is fully acceptable. Thus, cephalograms taken with the lips relaxed and the teeth in occlusion seem to provide the most correct reproduction of lip position and morphology. REFERENCES I. Anderson, J. P.. Joondeph. D. R.. and Turpin, D. L.: A cephalometric study of profile changes in orthodontically treated cases ten years out of retention, Angle Orthod. 43: 324-336, 1973. 2. Baumrind, S., and Fran&, R. C.: The reliability of head film measurements, AM. J. OORTHOD. 60: 111-127,
3. Bjiirk, A.: In Lundstrom. A. (editor): Ortodonti. Nordisk ICobok, Sverig. Tandfak. fiirb. Forlagsfiir, 1971, chap. III, p. 131. 4. Bloom, L. A.: Perioral profile changes in orthodontic treatment. AM. J. ORTHOD. 47: 371-379, 1961. 5. Burstone, C. J.: The integumental profile, AM. .l. OORTHOD. 44: l-25, 1958. 6. Burstone, C. J.: Lip posture and its significance to treatment planning, AM. J. ORTHOD. 53: 262-284, 1967. 7. Dann, J. J.. and Epker, B. N.: Proplast genioplasty: A retrospective study with treatment recommendations, Angle Orthod. 47: 173-185, 1977. X. Epker, B. N., and Fish, L. C.: Surgical-orthodontic correction of open-bite deformity, AM. J. ORTHOD. 71: 278-299,
9. Field. D., and Hillesund, E.: Reproduaerbarhet av bl